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Title: Renal%20Physiology


1
Renal Physiology
PART ONE Renal Physiology Overview PART
TWO Renal Clearance PART THREE Renal Acid-Base
Balance
2
Role of the kidney in maintaining water,
electrolytes, and pH balance
  • Plasma leaks out of the capillaries in the
    glomerulus. The kidneys return the nutrients to
    the plasma, while removing the waste products.
    This also maintains the pH balance, since some of
    the wastes are acids and bases.
  • Under the direction of aldosterone, they keep the
    balance between electrolytes, especially sodium
    and potassium.
  • This keeps the plasma volume constant to maintain
    BP.

3
Role of Kidneys
  • The kidneys can adjust blood volume, blood
    pressure, and blood composition
  • BLOOD VOLUME
  • Adjusts the volume of water lost in urine by
    responding to ADH, aldosterone, and renin
  • BLOOD PRESSURE
  • Releasing renin and adenosine (increases blood
    pressure)
  • BLOOD COMPOSITION
  • Releasing erythropoietin (increases RBC
    production)

4
Sympathetic Nervous System Effect on Kidneys
  • Decreases the rate of blood flow to the
    glomerulus by telling the precapillary sphincters
    to contract. This will raise blood pressure.
  • Sympathetic nervous system is stimulated by
    renin, which is released by the kidney.
  • Causes changes in water and sodium reabsorption
    by the nephron.

5
Hypothalamus
  • The hypothalamus monitors the concentration of
    water in the plasma.
  • If the plasma is too concentrated (high osmotic
    pressure), it means there are many electrolytes
    and not enough water inside the blood vessels
    (the person is dehydrated, and blood pressure
    will drop).
  • Since water goes to the area that has the most
    particles (particles SUCK water!), water will be
    drawn out of the nearby cells, which will cause
    them to shrink.
  • If the plasma is too dilute (low osmotic
    pressure), it means there is too much water and
    too few electrolytes inside the blood vessels
    (the person is over-hydrated, and blood pressure
    will rise).
  • Water will be drawn out of the blood vessels to
    enter the nearby cells (causing them to swell) or
    the space between them (interstitial space,
    causing edema).

6
Video
  • Osmotic Pressure
  • http//www.showme.com/sh/?hP2a0rWi

7
Hypothalamus and Adrenal Gland
  • When a person is dehydrated and has low blood
    pressure, the hypothalamus will sense that the
    osmotic pressure of the plasma is too high (above
    homeostatic levels plasma is too concentrated
    too many electrolytes and not enough water is in
    the plasma), it tells the pituitary gland to
    release ADH (antidiuretic hormone) to cause the
    kidneys to retain additional water to dilute the
    plasma. This will make the low blood pressure go
    back up.
  • The adrenal cortex will also release aldosterone,
    which causes sodium ions to be reabsorbed by the
    kidneys, and water will follow. This will also
    increase the plasma volume (which will dilute
    it), and also help the low blood pressure to go
    back up.
  • If the osmotic pressure is too low (plasma is too
    dilute too much water and not enough
    electrolytes in the plasma), ADH and aldosterone
    are not released, and excess water will pass out
    of the body as urine. This will make the high
    blood pressure go back down.

8
Quiz Yourself
  • What does it mean when the osmotic pressure is
    too high? Too low?
  • What are the causes of each of these situations?
  • How does the body compensate for each of these
    situations?
  • What does it mean when the plasma is too dilute?
    Too concentrated?
  • What are the causes of each of these situations?
  • How does the body compensate for each of these
    situations?

9
pH Imbalances
  • Many things can alter the pH of the blood
  • Beverages we drink
  • Acids produced by metabolism
  • Breathing rate
  • Vomiting (loss of acid)
  • Diarrhea (loss of base)
  • pH imbalances are dangerous because many enzymes
    only function within a narrow pH range.

10
Renal Physiology
Basic Mechanisms of Urine Formation
1) Glomerular filtration 2) Tubular reabsorption
3) Tubular secretion 4) Excretion How do we
determine these rates? Master formula
11
Glomerular Filtration
  • The capillaries in the glomerulus contain many
    holes, called fenestrations. As blood passes
    through the glomerulus, the plasma passes through
    the fenestrations. Proteins and other large
    substances do not cross through they stay in the
    bloodstream.
  • The filtered plasma leaves the bloodstream in
    this way, and enters the glomerular capsule, and
    then enters the proximal convoluted tubule.

12
Glomerular Filtration
  • In a sprinkler hose, the higher the water
    pressure, the faster the water squirts through
    its holes. The same process is also true for the
    glomerulus.
  • The blood pressure inside the glomerulus affects
    how fast the fluid can filter through the
    fenestrations. Therefore, blood pressure affects
    the glomerular filtration rate (GFR). The higher
    the blood pressure, the higher the GFR.
  • The pre-capillary sphincters can also control how
    much pressure is in the glomerulus, much like the
    water faucet controls the pressure in a hose.

13
Glomerular Filtration Rate
  • GFR is used as a measure of kidney function.
  • Normal GFR is 125 ml per minute for both kidneys
    combined.
  • That means 7.5 liters per hour, or 180 liters per
    day.
  • That is 45 gallons of filtrate produced per day!
  • Of course, most of that is reabsorbed.
  • Average urine output is about 1.2 liters per day.
  • That means you need to drink 1.2 liters of fluid
    per day (remember that caffeine and alcohol are
    diuretics, so you need more than that to
    compensate if you drink those beverages). You
    need to drink more (about 2 liters per day) if
    you are getting a cold or flu.

14
Altering GFR
  • Several different mechanisms can change the
    diameter of the afferent and efferent arterioles
    to alter the GFR
  • Hormonal (hormones)
  • Autonomic (nervous system)
  • Autoregulation or local (smooth muscle sphincters
    around the arterioles or capillaries near the
    glomerulus)

15
Remember the route the fluid takes Glomerulus ?
Proximal convoluted tubule (PCT) ? Descending
limb of LOH ? Ascending limb of LOH ? Distal
Convoluted tubule (DCT) ? Collecting duct (CT)
16
Tubular Reabsorption
  • This is the process by which substances in the
    renal tubules are transferred back into the
    bloodstream. Reabsorption is the removal of
    water and solute molecules from filtrate after it
    enters the renal tubules.
  • Fluid goes from the glomerulus to the proximal
    convoluted tubule (PCT), down the loop of Henle
    and back up, then into the distal convoluted
    tubule (DCT), and into the collecting duct.
  • In the PCT, the nutrients are reabsorbed. If
    there are more nutrients than can be reabsorbed
    (such as excess sugar), it will be excreted in
    the urine.
  • When the nutrients are reabsorbed (in the PCT),
    the inside of the tubule will have more water and
    less nutrients. Since water goes to the area that
    has a higher concentration of particles
    (osmosis), water will also leave the tubules
    this occurs mostly in the PCT.
  • By the time the fluid has reached the collecting
    duct, nothing but waste products are left, such
    as urea, ammonia, and bilirubin.

17
Tubular Reabsorption
  • Capillaries follow the renal tubules and wrap
    around them.
  • The straight capillaries that travel
    longitudinally next to the tubules are called
    vasa recta, and the capillaries that wrap around
    the tubule are called peritubular capillaries.
  • There is a space between the capillaries and the
    tube, called the peritubular space.

18
Tubular Reabsorption
Filtrate arriving from Bowmans Capsule
Tubular Cells
Lumen of Tubule
Peritubular Capillaries
  • The peritubular capillaries are nearby, and the
    particle concentration is high inside of them.
    Therefore, the water in the peritubular space
    (lower concentration of particles) will leave
    that space and enter into the peritubular
    capillaries by osmosis.
  • That is how the nutrients are reabsorbed from the
    tubules back into the bloodstream.

19
Tubular Reabsorption
  • The ascending limb of the Loop of Henle and the
    DCT are impermeable to water unless hormones
    cause substances to be moved through their walls.
  • If the blood is low in sodium, (after excessive
    sweating), aldosterone (from the adrenal cortex)
    will cause more sodium to be pumped out of the
    tubule and into the peritubular space. The sodium
    will then enter the capillaries.
  • Since water follows where salt goes, whenever the
    body needs more water (such as dehydration), ADH
    is released (from the neurohypophysis posterior
    pituitary). The synthetic form of ADH is
    vasopressin (a medicine).
  • Aldosterone and ADH will increase blood volume,
    increasing blood pressure.
  • These two hormones begin their action in the
    ascending limb and continue to work in the DCT.

20
Tubular Secretion
  • Some substances are unable to filter through the
    glomerulus, but are not wanted by the body.
  • Examples are pollutants like pesticides, and many
    drugs, such as penicillin and non-steroidal
    anti-inflammatory drugs (NSAIDs).
  • As blood passes through the peritubular
    capillaries, those substances are moved from the
    capillaries directly into the PCT and DCT.
  • This is called tubular secretion.

21
Juxtaglomerular Apparatus
  • The distal end of the renal tubule passes next to
    the glomerulus to form the juxtaglomerular
    apparatus (juxta means next to).

22
Juxtaglomerular ApparatusAlters BP and GFR by
autoregulation
  • Two types of cells
  • 1) Macula densa cells
  • 2) Juxtaglomerular cells

23
Juxtaglomerular Apparatus Macula Densa Cells
  • If blood pressure is too low, the macula densa
    releases adenosine, which causes
    vasoconstriction of the afferent arteriole. This
    will slow the GFR, so less water is lost, and
    blood pressure increases.

24
Juxtaglomerular Apparatus Macula Densa Cells
  • If blood pressure is too high, the macula densa
    stops releasing adenosine, which allows the
    sphincters to relax.
  • This will increase GFR so more water is lost, and
    blood pressure decreases.

25
Juxtaglomerular Apparatus Juxtaglomerular Cells
  • Juxtaglomerular cells secrete renin if the blood
    pressure is still too low after adenosine has
    caused vasoconstriction.
  • Renin causes more sodium to be reabsorbed, and
    water follows, so blood volume increases, so
    blood pressure increases.

26
Summary of Autoregulation
  • The nephron can alter the blood pressure and flow
    into the glomerulus by autoregulation.
  • The JGA senses the blood pressure going into the
    glomerulus and the flow rate of the fluid going
    through the renal tubule. If the GFR is too low,
    the JGA (macula densa) will cause the
    pre-capillary sphincters on the nearby arterioles
    to contract, increasing core blood pressure.
  • If that restores the desired filtration rate and
    flow, no further action is needed. If not, the
    kidneys produce the enzyme renin, which cuts
    angiotensinogen into A1. The lungs produce
    angiotensin converting enzyme (ACE), which turns
    A1 into A2, which constricts blood vessels, and
    also causes the release of aldosterone and ADH,
    raising the blood pressure further.

27
Hormonal Regulation
  • If a person sweats from activity, eats very salty
    food, or has diarrhea, it changes the sodium and
    water content of the plasma.
  • Two hormones that affect the ascending limb of
    the Loop of Henle are aldosterone and
    antidiuretic hormone (ADH).
  • Adosterone is produced by the adrenal cortex and
    causes additional sodium ions to be pumped out of
    the tubule and into the bloodstream. Water comes
    with it by osmosis, and the blood pressure
    increases.
  • ADH is produced by the posterior pituitary gland
    and causes retention of additional water from the
    DCT and collecting ducts. Sodium is not included
    in this process, so the result is to dilute the
    plasma during dehydration from not drinking
    enough water.

28
How Low BP is RaisedThe renin-angiotensin system
  • When baroreceptors detect low blood pressure, the
    kidney releases an enzyme called renin.
  • In the meantime, angiotensinogen is made by the
    liver and released into the blood.
  • Renin cuts angiotensinogen into angiotensin-1
    (A1), which travels through blood to the
    pulmonary capillary bed, where cells have
    angiotensin converting enzyme (ACE) that cuts A1
    into A2 (the active form).
  • Any word that ends in ogen means it is a
    longer, inactive protein, called a zymogen.
  • To become activated, they need to be cut by an
    enzyme into a smaller segment.
  • A2 then causes vasoconstriction of the peripheral
    blood vessels so the bodys blood will pool up to
    the core organs.
  • Also, these high levels of A2 stimulates the
    adrenal cortex to make more aldosterone, and also
    stimulates the posterior pituitary gland to
    release ADH. These events will raise the blood
    pressure.
  • When blood pressure is too high, the patient
    might be given an ACE inhibitor such as
    Captopril, or a renin inhibitor such as
    Aliskiren, or an A2 antagonist, such as
    Azilsartan.

29
ALDOSTERONE
RENIN
ACE
ADH
Renin-Angiotensin Kit
30
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31
Erythropoietin
  • The kidneys also monitor the oxygen content of
    the blood.
  • If O2 levels are low, the JGA releases the
    hormone erythropoietin to stimulate the bone
    marrow to produce more red blood cells.

32
Neural Regulation
  • The kidneys receive about 22 of the blood pumped
    out of the heart, so that is a substantial
    quantity passing through the kidneys at any given
    time.
  • If there is a stressor and the sympathetic
    nervous system causes us to go into fight or
    flight mode, the skeletal muscles need to have a
    maximum amount of blood flow.
  • Neurons from the sympathetic nervous system
    innervate the kidneys will constrict the blood
    vessels entering the kidney to decrease renal
    blood flow during critical situations.

33
Urine
  • Urine contains ions such as sodium, chloride, and
    potassium, as well as suspended solids, known as
    sediments, such as cells, mineral crystals, mucus
    threads, and sometimes bacteria.
  • The pH of urine is normally 4.6-8
  • A urinalysis can identify abnormal processes
    occurring in the body.
  • Because urine is a waste product, its contents
    are influenced by the foods and drinks we ingest.
  • We may lose fluid elsewhere, such as through
    sweating or diarrhea, which causes the urine to
    become more concentrated.
  • Acids produced through metabolism can also change
    the pH of our urine. Even changes in breathing
    rate can change the urine pH as excess acids or
    bases are excreted to maintain normal plasma pH.

34
Abnormal Urinalysis
  • These substances should not be in the urine. When
    they are, it is abnormal.
  • Glucose
  • Blood
  • Protein
  • Pus
  • Bilirubin
  • Ketones

35
Causes of abnormal UA
  • Glucose diabetes mellitus
  • Blood bleeding in urinary tract from infection
    or kidney stone
  • Protein kidney disease, hypertension, excessive
    exercise, pregnancy
  • Pus bacterial infection in urinary tract
  • Bilirubin liver malfunction
  • Ketones excessive breakdown of lipids

36
Micturition
  • Urination is technically known as micturition.
  • Once the volume in the urinary bladder exceeds
    200 ml stretch receptors in its walls send
    impulses to the brain, indicating the need to
    eliminate.
  • When you make the decision to urinate, the
    parasympathetic nervous system stimulates the
    smooth muscle in the urinary bladders internal
    sphincter to relax.
  • Remember, the internal sphincter is smooth muscle
    (involuntary) and the external sphincter is
    skeletal muscle (voluntary). Both must relax for
    urine to exit.

37
Diuretics for hypertension and congestive heart
failure
  • Diuretics decrease plasma volume. One group of
    these drugs are called thiazide diuretics (such
    as Lasix). They inhibit the reabsorption of
    sodium and potassium from the renal tubule,
    causing more water to pass out as urine.
  • Compared to sodium, the homeostatic range of
    potassium is quite narrow. You can lose or gain
    much sodium without causing a problem, but you
    need a fairly exact amount of potassium or all
    your neurons can die.
  • Lasix (Furosemide) inhibits reabsorption of
    potassium more than other diuretics. Low blood
    levels of potassium are called hypokalemia. It is
    important for someone on Lasix to take potassium
    supplements or eat fruits or vegetables that have
    a lot of potassium (such as cantaloupe).
  • However, too much potassium from excessive
    supplements can have fatal side effects.

38
Diuretics
  • Furosemide (Lasix)
  • Mannitol
  • Spironolactone
  • Amiloride
  • Hydrochorothyozide

39
Homeostasis
  • Maintaining the proper concentration of sodium
    and water is critical to keep your blood pressure
    normal.
  • If the plasma is too concentrated with particles,
    nearby cells can shrink and lose their function.
  • If the plasma is too dilute, water can enter the
    nearby cells and cause them to expand, also
    decreasing their function.
  • This is especially dangerous in the brain.
  • Studies have shown a close link between obesity,
    diabetes, and kidney disease. Exercise helps
    maintain normal kidney function by increasing
    blood flow, and it decreases the incidence of
    high blood pressure. People receiving dialysis
    and those who have had kidney transplants
    especially need to exercise.

40
  • The rest of this lecture is not on the test.

41
  • Renal Physiology Video

42
Countercurrent exchange
You Tube Animation 1 https//www.youtube.com/watch
?vXbI8eY-BeXY
Counter heat current exchange Note the gradually
declining differential and that the once hot and
cold streams exit at the reversed temperature
difference the hotter entering stream becomes
the exiting cooler stream and vice versa.
You Tube Animation 2 https//www.youtube.com/watch
?vAOqIlrQhqHQ
You Tube Animation 3 https//www.youtube.com/watch
?v3THZeaMfuSw
43
Countercurrent exchange
  • Countercurrent exchange is a mechanism occurring
    in nature and mimicked in industry and
    engineering, in which there is a crossover of
    some property, usually heat or some component,
    between two flowing bodies flowing in opposite
    directions to each other. The flowing bodies can
    be liquids, gases, or even solid powders, or any
    combination of those.
  • The maximum amount of heat or mass transfer that
    can be obtained is higher with countercurrent
    than co-current (parallel) exchange because
    countercurrent maintains a slowly declining
    concentration difference or gradient.
  • Countercurrent exchange, when set up in a loop
    (such as the Loop of Henle), can be used for
    building up concentrations of solutes. When set
    up in a loop with a buffering liquid between the
    incoming and outgoing fluid, and with active
    transport pumps, the system is called a
    Countercurrent multiplier, enabling a multiplied
    effect of many small pumps to gradually build up
    a large concentration in the buffer liquid.

44
Countercurrent exchange
  • Countercurrent multiplication is where liquid
    moves in a loop followed by a long length of
    movement in opposite directions with an
    intermediate zone. The tube leading to the loop
    passively building up a gradient of solvent
    concentration while the returning tube has a
    constant small pumping action all along it, so
    that a gradual intensification of the heat or
    concentration is created towards the loop.
    Countercurrent multiplication has been found in
    the kidneys as well as in many other biological
    organs.

45
Countercurrent exchange
  • Countercurrent exchange is used extensively in
    biological systems for a wide variety of
    purposes. For example, fish use it in their gills
    to transfer oxygen from the surrounding water
    into their blood, and birds use a countercurrent
    heat exchanger between blood vessels in their
    legs to keep heat concentrated within their
    bodies. Mammalian kidneys use countercurrent
    exchange to remove water from urine so the body
    can retain water used to move the nitrogenous
    waste products.

46
Countercurrent multiplier 
A countercurrent multiplier is a system where
fluid flows in a loop so that the entrance and
exit are at similar low concentration of a
dissolved substance but at the tip of the loop
there is a very high concentration of that
substance. The system allows the buildup of a
high concentration gradually, with the use of
many active transport pumps each pumping only
against a very small gradient.
47
  • The incoming flow starting at a low concentration
    has a semipermeable membrane with water passing
    to the buffer liquid via osmosis at a small
    gradient. There is a gradual buildup of
    concentration inside the loop until the loop tip
    where it reaches its maximum.

48
  • In the example image, water enters at 299 mg/L
    (NaCL / H2O). Water passes because of a small
    osmotic pressure to the buffer liquid in this
    example at 300 mg/L (NaCL / H2O). Further up the
    loop there is a continued flow of water out of
    the tube and into the buffer, gradually raising
    the concentration of NaCL in the tube until it
    reaches 1199 mg/L at the tip. The buffer liquid
    between the two tubes is at a gradually rising
    concentration, always a bit over the incoming
    fluid, in our example reaching 1200 mg/L. This is
    regulated by the pumping action on the returning
    tube as explained immediately.

49
The tip of the loop has the highest concentration
of salt (NaCL) in the incoming tube - in the
example 1199 mg/L, and in the buffer 1200 mg/L.
The returning tube has active transport pumps,
pumping salt out to the buffer liquid at a low
difference of concentrations of up to 200 mg/L
more than in the tube. Thus when opposite the
1000 mg/L in the buffer liquid, the concentration
in the tube is 800 and only 200 mg/L are needed
to be pumped out. But the same is true anywhere
along the line, so that at exit of the loop also
only 200 mg/L need to be pumped. In effect, this
can be seen as a gradually multiplying effect -
hence the name of the phenomena a
'countercurrent multiplier' or the mechanism
Countercurrent multiplication.
50
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51
  • A circuit of fluid in the Loop of Henle - an
    important part of the kidneys allows for gradual
    buildup of the concentration of urine in the
    kidneys, by using active transport on the exiting
    nephrons. The active transport pumps need only to
    overcome a constant and low gradient of
    concentration, because of the countercurrent
    multiplier mechanism.
  • Various substances are passed from the liquid
    entering the Nephrons until exiting the loop.

52
  • The sequence of flow is as follows
  • Renal corpuscle Liquid enters the nephron system
    at the Bowman's capsule.
  • Proximal convoluted tubule It then may reabsorb
    urea in the thick descending limb. Water is
    removed from the nephrons by osmosis (and Glucose
    and other ions are pumped out with active
    transport), gradually raising the concentration
    in the nephrons.
  • Loop of Henle Descending The liquid passes from
    the thin descending limb to the thick ascending
    limb. Water is constantly released via osmosis.
    Gradually, there is a buildup of osmotic
    concentration, until 1200 mOsm is reached at the
    loop tip, but the difference across the membrane
    is kept small and constant.

53
  • For example, the liquid at one section inside the
    thin descending limb is at 400 mOsm while outside
    it's 401. Further down the descending limb, the
    inside concentration is 500 while outside it is
    501, so a constant difference of 1 mOsm is kept
    all across the membrane, although the
    concentration inside and outside are gradually
    increasing.
  • Loop of Henle Ascending after the tip (or
    'bend') of the loop, the liquid flows in the thin
    ascending limb. Salt - Sodium and Chlorine ions
    are pumped out of the liquid, gradually lowering
    the concentration in the exiting liquid, but,
    using the countercurrent multiplier mechanism,
    always pumping against a constant and small
    osmotic difference.

54
  • For example, the pumps at a section close to the
    bend pump out from 1000 mOsm inside the ascending
    limb to 1200 mOsm outside it, with a 200 mOsm
    across. Pumps further up the thin ascending limb,
    pump out from 400 mOsm into liquid at 600 mOsm,
    so again the difference is retained at 200 mOsm
    from the inside to the outside, while the
    concentration both inside and outside are
    gradually decreasing as the liquid flow advances.
  • The liquid finally reaches a low concentration of
    100 mOsm when leaving the thin ascending limb and
    passing through the thick one.
  • Distal convoluted tubule Once leaving the loop
    of Henle the thick ascending limb can optionally
    reabsorb and increase the concentration in the
    nephrons.

55
  • Collecting duct The collecting duct receives
    liquid between 100 mOsm if no re-absorption is
    done, to 300 or above if re-absorption was used.
    The collecting duct may continue raising the
    concentration if required, by gradually pumping
    out the same ions as the Distal convoluted
    tubule, using the same gradient as the ascending
    limbs in the loop of Henle, and reaching the same
    concentration.
  • Ureter The liquid urine leaves to the Ureter.

56
Renal Solutes
  • Amino Acids
  • Ammonia
  • Bicarbonate
  • Calcium
  • CO2
  • Chloride
  • Creatine
  • Creatinine
  • Hydrogen
  • Magnesium
  • Nitrogen
  • Phosphate
  • Potassium
  • Sodium
  • Urea
  • Uric Acid
  • Urea Cycle

57
Amino Acids
  • Amino acid definition and classifications
  • Essential vs. Non-Essential Standard Amino Acids
  • Essential vs. Non-Essential AA List
  • Function of Standard and Non-Standard amino acids
  • Discovery of Amino Acids
  • Branched-chain amino acids
  • Amino Acids in human nutrition
  • Non-protein functions
  • Uses in technology
  • Biodegradable plastics
  • Peptide bond formation
  • Amino Acid Breakdown
  • Deamination
  • Deamination reactions in DNA
  • Catabolism 

58
Amino Acids
  • Amino acid definition and classifications
  • Amino acids are made from an amine group (-NH2)
    and a carboxylic acid group (-COOH), along with a
    side-chain specific to each amino acid. About 500
    amino acids are known and can be classified in
    many ways. They can be classified according to
    the location of their functional groups,
    polarity, pH level, and side chain group type.
    The side-chain can make an amino acid a weak acid
    or a weak base, and hydrophilic if the side-chain
    is polar or hydrophobic if it is nonpolar.

59
Amino Acids
  • Essential vs. Non-Essential Standard Amino Acids
  • There are 20-22 amino acids in humans which form
    proteins, and are known as "standard" amino
    acids. The amino acid Phenylalanine breaks down
    into the amino acid tryptophan, and arginine
    breaks down into ornithine, so some people count
    tryptophan and ornithine as the 21st and 22nd
    standard amino acids, while others just count the
    original 20. Nine of the standard amino acids are
    known as essential because they cannot be
    created from other compounds by the human body,
    and so must be taken in as food on a daily basis
    (we cannot store up any excess amino acids). The
    other 11 standard amino acids are called
    non-essential because the body can make them.
    There are many other amino acids that are
    non-standard because they do not make proteins.
    Many amino acids also play other critical roles
    in the body that are not related to protein
    synthesis. For example in the brain, glutamate
    (glutamic acid) and gamma-amino-butyric acid
    ("GABA") are the main excitatory and inhibitory
    neurotransmitters. Proline is a major component
    of collagen. Glycine makes up red blood cells.

60
Amino Acids
Essential Nonessential
Histidine Alanine
Isoleucine Arginine (breaks down to ornithine)
Leucine Asparagine
Lysine Aspartic acid
Methionine Cysteine
Phenylalanine (breaks down to tyrosine) Glutamic acid (glutamate)
Threonine Glutamine
Tryptophan Glycine
Valine Proline
Serine
Tyrosine
61
Amino Acids
  • Function of Standard amino acids
  • The process of making proteins is called
    translation and involves the step-by-step
    addition of amino acids to a growing protein
    chain. The order in which the amino acids are
    added is read through the genetic code from an
    mRNA template, which is a RNA copy of one of the
    organism's genes.
  •  
  • Function of Non-standard amino acids
  • Non-standard amino acids are those that do not
    make proteins (for example carnitine, GABA), or
    are not produced directly by the cell (for
    example, hydroxyproline and selenomethionine).
    They often function to modify proteins after they
    are made. For example, glutamate allows for
    better binding of calcium ions, and proline is
    critical for maintaining connective tissues.
    Modifications can also determine where proteins
    will bind, such as the addition of long
    hydrophobic groups can cause a protein to bind to
    a phospholipid membrane. Some nonstandard amino
    acids do not modify the function of proteins.
    Examples include the neurotransmitter GABA. They
    also might occur as intermediates in the
    metabolic pathways for standard amino acids for
    example, ornithine and citrulline occur in the
    urea cycle, which is part of amino acid
    catabolism.

62
Amino Acids
  • Discovery of Amino Acids
  • In the 1800s, proteins were found to yield amino
    acids after enzymatic digestion. It was therefore
    realized that proteins are formed when amino
    acids are linked together. A short protein (less
    than 70 amino acids in length) is called a
    peptide. The first amino acid was discovered in
    1806, when two French chemists isolated a
    compound in asparagus that was subsequently named
    asparagine. Glycine and leucine were discovered
    in 1820. Cystine was discovered in 1810, although
    its monomer, cysteine, remained undiscovered
    until 1884. Cystine is produced in the body from
    two cysteine molecules. Despite this, cysteine
    and cystine work differently to maintain health.
    Cysteine helps promote skin protection through
    white blood cell and collagen production and
    assists in the production of an antioxidant known
    as gluthathione, while cystine can aid in surgery
    recovery, hair growth, and treatment of anemia.
  • Amino acids are usually classified by the
    properties of their side-chain into four groups.

63
Amino Acids
  • Branched-chain amino acids
  • The phrase "branched-chain amino acids" or BCAA
    refers to the amino acids having side-chains
    that are non-linear these are leucine,
    isoleucine, and valine. Branched-chain amino
    acids are essential nutrients that the body
    obtains from proteins found in food, especially
    meat, dairy products, and legumes. Branched-chain
    amino acids are used to treat amyotrophic lateral
    sclerosis (ALS, Lou Gehrig's disease), brain
    conditions due to liver disease (chronic hepatic
    encephalopathy, latent hepatic encephalopathy), a
    movement disorder called tardive dyskinesia, a
    genetic disease called McArdle's disease, a
    disease called spinocerebellar degeneration, and
    poor appetite in elderly, kidney failure patients
    and cancer patients. Branched-chain amino acids
    are also used to help slow muscle wasting in
    people who are confined to bed. Some people use
    branched-chain amino acids to help symptoms of
    chronic fatigue syndrome and to improve
    concentration. Athletes use branched-chain amino
    acids to improve exercise performance and reduce
    protein and muscle breakdown during intense
    exercise.

64
Amino Acids
  • In human nutrition
  • When taken up into the human body from the diet,
    the standard amino acids either are used to
    synthesize proteins or are oxidized to urea and
    carbon dioxide as a source of energy. The
    oxidation pathway starts with the removal of the
    amino group by a transaminase, the amino group is
    then fed into the urea cycle. The other product
    of transamination is a keto acid that enters the
    citric acid cycle. Glucogenic amino acids can
    also be converted into glucose, through
    gluconeogenesis.

65
Amino Acids
  • Non-protein functions
  • In humans, non-protein amino acids also have
    important roles as metabolic intermediates, such
    as synthesizing other molecules, for example
  • Tryptophan is a precursor of the neurotransmitter
    serotonin.
  • Tyrosine (and its precursor phenylalanine) are
    precursors of the catecholamine neurotransmitters
    dopamine, epinephrine and norepinephrine.
  • Glycine is a precursor of porphyrins such as heme
  • Arginine is a precursor of nitric oxide.
  • Aspartate, glycine, and glutamine are precursors
    of nucleotides.

66
Amino Acids
  • Uses in technology
  • Amino acids are used for a variety of
    applications in industry, but their main use is
    as additives to animal feed. This is necessary,
    since many of the bulk components of these feeds,
    such as soybeans, lack some of the essential
    amino acids Lysine, methionine, threonine, and
    tryptophan are most important in the production
    of these feeds. The food industry is also a
    major consumer of amino acids, in particular,
    glutamic acid, which is used as a flavor
    enhancer, and Aspartame as a low-calorie
    artificial sweetener. Some amino acids are used
    in the synthesis of drugs and cosmetics.

67
Amino Acids
  • Biodegradable plastics
  • Amino acids are under development as components
    of a range of biodegradable polymers for use as
    environmentally friendly packaging and in
    medicine in drug delivery, the construction of
    prosthetic implants, and use of polyaspartate, a
    water-soluble biodegradable polymer that may have
    applications in disposable diapers and
    agriculture.

68
Amino Acids
  • Peptide bond formation 
  • The condensation of two amino acids to form a
    dipeptide through a peptide bond. This
    polymerization of amino acids is what creates
    proteins. This condensation reaction yields the
    newly formed peptide bond and a molecule of water.

69
Amino Acids
  • Amino Acid Breakdown
  • Degradation of an amino acid often involves
    deamination by moving its amino group to
    alpha-ketoglutarate, forming glutamate. This
    process involves transaminase enzymes. The amino
    group is then removed through the urea cycle and
    is excreted in the form of urea. However, amino
    acid degradation can produce uric acid or ammonia
    instead. For example, serine is converted to
    pyruvate and ammonia. After removal of one or
    more amino groups, the remainder of the molecule
    can sometimes be used to synthesize new amino
    acids, or it can be used for energy by entering
    glycolysis or the citric acid cycle.

70
Amino Acids
  • Deamination is the removal of an amine group from
    a molecule. Enzymes which catalyse this reaction
    are called deaminases. There are 4 types of
    deamination intramolecular, resulting in the
    formation of unsaturated fatty acid restorative,
    with formation of saturated fatty acid
    hydrolytic, with formation of hydroxy carboxylic,
    and oxidative, with formation of a keto acid. In
    the human body, deamination takes place primarily
    in the liver, however glutamate is also
    deaminated in the kidneys. Deamination is the
    process by which amino acids are broken down if
    there is an excess of protein intake. The amino
    group is removed from the amino acid and
    converted to ammonia. The rest of the amino acid
    is made up of mostly carbon and hydrogen, and is
    recycled or oxidized for energy. Ammonia is toxic
    to the human system, and enzymes convert it to
    urea or uric acid by addition of carbon dioxide
    molecules in the urea cycle, which also takes
    place in the liver. Urea and uric acid can safely
    diffuse into the blood and then be excreted in
    urine.

71
Amino Acids
  • Deamination reactions in DNA 
  • Spontaneous deamination of cytosine into uracil,
    releasing ammonia in the process. In DNA, this
    spontaneous deamination is corrected for by the
    removal of uracil (product of cytosine
    deamination and not part of DNA.

Cytosine
Uracil
72
Amino Acids
  • Catabolism 
  • Catabolism of proteinogenic amino acids. Amino
    acids can be classified according to the
    properties of their main products as either of
    the following
  • Glucogenic, with the products having the
    ability to form glucose by gluconeogenesis
  • Ketogenic, with the products not having the
    ability to form glucose. These products may still
    be used for ketogenesis or lipid synthesis.
  • Amino acids catabolized into both glucogenic
    and ketogenic products.

73
Ammonia
  • Ammonia is a compound of nitrogen and hydrogen
    with the formula NH3 , while ammonium is NH4.
    Ammonia is a colorless gas with a characteristic
    pungent smell. Ammonia contributes significantly
    to the nutritional needs of terrestrial organisms
    by serving as a precursor to food and
    fertilizers. Ammonia is also a building-block for
    the synthesis of many pharmaceuticals and is used
    in many commercial cleaning products. Although in
    wide use, ammonia is both caustic and hazardous.
    Household ammonia is a solution of NH3 in water.

74
Ammonia
  • Natural occurrence
  • Ammonia is found in trace quantities in the
    atmosphere, being produced from the putrefaction
    (decay process) of animal and vegetable matter.
    When we consume those foods, the nitrogen is
    taken into our body and used to make amino acids
    and other important substances. When amino acids
    are broken down, NH3 is the toxic waste product,
    and has an alkaline pH. The kidneys excrete or
    reabsorb NH3 to keep the blood plasma at neutral
    pH. Dilute aqueous ammonia can be applied on the
    skin to lessen the effects of acidic animal
    venoms, such as from insects and jellyfish. The
    basic pH of ammonia also is the basis of its
    toxicity and its use as a cleaner. By creating a
    solution with a pH much higher than a neutral
    water solution, proteins (enzymes) will denature,
    leading to cell damage, death of the cell, and
    eventually death of the organism. Dirt often
    consists of fats and oils, which are not very
    soluble in water. Ammonia causes them to dissolve
    in water. This will allow the ammonia and water,
    with its dissolved dirty oils to evaporate
    completely, leaving a clean surface.

75
Ammonia
  • History
  • The Romans called the ammonium chloride deposits
    they collected from near the Temple of Amun in
    ancient Libya 'sal ammoniacus' (salt of Amun).
  •  
  • Toxicity
  • The toxicity of ammonia solutions does not
    usually cause problems for humans and other
    mammals, as a specific mechanism exists to
    prevent its build-up in the bloodstream. Ammonia
    is converted to carbamoyl phosphate by an enzyme,
    and then enters the urea cycle to be either
    incorporated into amino acids or excreted in the
    urine. However, fish and amphibians lack this
    mechanism, as they can usually eliminate ammonia
    from their bodies by direct excretion. Ammonia
    even at dilute concentrations is highly toxic to
    aquatic animals, and for this reason it is
    classified as dangerous for the environment.

76
Ammonia
  • Formation and elimination in the body
  • Ammonia is a metabolic product of amino acid
    deamination catalyzed by enzymes. Ammonia is
    quickly converted to urea, which is much less
    toxic, particularly less basic. This urea is a
    major component of the dry weight of urine. The
    liver converts ammonia to urea through a series
    of reactions known as the urea cycle. Liver
    dysfunction, such as that seen in cirrhosis, may
    lead to elevated amounts of ammonia in the blood
    (hyperammonemia). Likewise, defects in the
    enzymes responsible for the urea cycle, leads to
    this disorder. It causes confusion and coma,
    neurological problems, and aciduria (acid in the
    urine).

77
Ammonia
  • Acid base balance
  • Ammonia is important for normal animal acid/base
    balance. After formation of ammonium from
    glutamine, a-ketoglutarate may be degraded to
    produce two molecules of bicarbonate, which are
    then available as buffers for acids. Ammonium is
    excreted in the urine, resulting in net acid
    loss. Ammonia may itself diffuse across the renal
    tubules, combine with a hydrogen ion, and thus
    allow for further acid excretion.

78
Bicarbonate
  • Bicarbonate has the chemical formula HCO3-.
    Bicarbonate serves a crucial biochemical role in
    the physiological pH buffering system.
  •  
  • Bicarbonate participates in this equilibrium
    reaction.
  • CO2 H2O ? H2CO3 ? HCO3- H
  • Bicarbonate is alkaline, and a vital component of
    the pH buffering system of the human body
    (maintaining acid-base homeostasis). 70-75 of
    CO2 in the body is converted into carbonic acid
    (H2CO3), which can quickly turn into bicarbonate
    (HCO3-). Bicarbonate in conjunction with water,
    hydrogen ions, and carbon dioxide forms a
    buffering system, which provides prompt
    resistance to drastic pH changes in both the
    acidic and basic directions. This is especially
    important for protecting tissues of the central
    nervous system, where pH changes too far outside
    of the normal range in either direction could
    prove disastrous. Bicarbonate also acts to
    regulate pH in the small intestine. It is
    released from the pancreas in response to the
    hormone secretin to neutralize the acidic chyme
    entering the duodenum from the stomach.
  •  
  • The most common salt of the bicarbonate ion is
    sodium bicarbonate, NaHCO3, which is commonly
    known as baking soda. When heated or exposed to
    an acids, such as acetic acid (vinegar), sodium
    bicarbonate releases carbon dioxide. This is used
    as a leavening agent in baking.

79
Calcium
  • Calcium is the fifth-most-abundant element by
    mass in the Earth's crust. Calcium is essential
    for living organisms, where movement of the
    calcium ion Ca2 into and out of the cytoplasm
    functions as a signal for many cellular
    processes. It is the major material used in
    mineralization of bone, and teeth. It is the
    relatively high-atomic-number of calcium that
    causes bone to be radio-opaque (can see bone on
    x-rays). Of the human body's solid components
    after cremation, about a third of the total
    "mineral" mass is the approximately one kilogram
    of calcium that composes the average skeleton
    (the remainder being mostly phosphorus and
    oxygen). Calcium, combined with phosphate forms
    hydroxyapatite, which is the mineral portion of
    human and animal bones and teeth.

80
Calcium
  • Calcium compounds
  • Calcium carbonate (CaCO3) is used in
    manufacturing cement and mortar, lime, limestone, 
    and in toothpastes.
  • Calcium hydroxide solution (Ca(OH)2) (also known
    as limewater) is used to detect the presence of
    carbon dioxide by being bubbled through a
    solution. It turns cloudy where CO2 is present.
  • Calcium arsenate (Ca3(AsO4)2) is used
    in insecticides.
  • Calcium carbide (CaC2) is used to
    make acetylene gas (for torches for welding) and
    in the manufacturing of plastics.
  • Calcium chloride (CaCl2) is used in ice removal
    and dust control on dirt roads, in conditioner
    for concrete, as an additive in canned tomatoes,
    and to provide body for automobile tires.
  • Calcium cyclamate (Ca(C6H11NHSO3)2) is used as a
    sweetening agent in several countries. In the
    United States it is no longer permitted for use
    because of suspected cancer-causing properties.
  • Calcium gluconate (Ca(C6H11O7)2) is used as
    a food additive and in vitamin pills.

81
Calcium
  • Calcium compounds
  • Calcium hypochlorite (Ca(OCl)2) is used as
    a swimming pool disinfectant, as
    a bleaching agent, as an ingredient in deodorant,
    and in algaecide and fungicide.
  • Calcium permanganate (Ca(MnO4)2) is used in
    liquid rocket propellant, and as a water
    sterilizing agent and in dental procedures.
  • Calcium phosphate (Ca3(PO4)2) is used as a
    supplement for animal feed, fertilizer, in
    commercial production for dough and yeast products
    , in the manufacture of glass, and in dental
    products.
  • Calcium phosphide (Ca3P2) is used
    in fireworks, rodenticide, torpedoes and flares.
  • Calcium stearate (Ca(C18H35O2)2) is used in the
    manufacture of wax crayons, cements,
    plastics and cosmetics, as a food additive, and
    in paints.
  • Calcium sulfate (CaSO42H2O) is used as common
    blackboard chalk, and Plaster of Paris.
  • Calcium tungstate (CaWO4) is used in
    luminous paints, fluorescent lights and
    in X-ray studies.
  • Hydroxylapatite (Ca5(PO4)3(OH), makes up seventy
    percent of bone. Also carbonated-calcium
    deficient hydroxylapatite is the main mineral of
    which dental enamel and dentin are comprised.

82
Calcium
  • Calcium is an important component of a healthy
    diet and a mineral necessary for life.
    Approximately 99 percent of the body's calcium is
    stored in the bones and teeth. The rest of the
    calcium in the body has other important uses,
    such as some exocytosis, especially neurotransmitt
    er release, and muscle contraction. In
    the electrical conduction system of the heart,
    calcium replaces sodium as the mineral that
    depolarizes the cell, proliferating the action
    potential. Long-term calcium deficiency can lead
    to rickets and poor blood clotting and in case of
    a menopausal woman, it can lead to osteoporosis,
    in which the bone deteriorates and there is an
    increased risk of fractures. While a lifelong
    deficit can affect bone and tooth formation,
    over-retention can cause hypercalcemia (elevated
    levels of calcium in the blood), impaired kidney
    function and decreased absorption of other
    minerals. Several sources suggest a correlation
    between high calcium intake (2000 mg per day, or
    twice the U.S. recommended daily allowance,
    equivalent to six or more glasses of milk per
    day) and prostate cancer. High calcium intakes or
    high calcium absorption were previously thought
    to contribute to the development of kidney
    stones. However, a high calcium intake has been
    associated with a lower risk for kidney stones in
    more recent research. Vitamin D is needed to
    absorb calcium.

83
Calcium
  • Dairy products, such as milk and cheese, are a
    well-known source of calcium. Some individuals
    are allergic to dairy products and even more
    people, in particular those of non Indo-European
    descent, are lactose-intolerant, leaving them
    unable to consume non-fermented dairy products in
    quantities larger than about half a liter per
    serving. Others, such as vegans, avoid dairy
    products for ethical and health reasons.
  • Many good vegetable sources of calcium exist,
    including seaweeds such as kelp, and nuts and
    seeds like almonds, hazelnuts, sesame, and
    pistachio molasses beans (especially soy
    beans) figs rutabaga broccoli dandelion
    leaves and kale. In addition, some drinks are
    often fortified with calcium (like soy milk or
    orange juice).
  • Numerous vegetables, notably spinach and rhubarb,
    have a high calcium content, but they may also
    contain varying amounts of oxalic acid that binds
    calcium and reduces its absorption. An overlooked
    source of calcium is eggshell, which can be
    ground into a powder and mixed into food or a
    glass of water.

84
Calcium
  • Dietary supplements
  • Most experts recommend that supplements be taken
    with food and that no more than 600 mg should be
    taken at a time because the percent of calcium
    absorbed decreases as the amount of calcium in
    the supplement increases. It is recommended to
    spread doses throughout the day. Recommended
    daily calcium intake for adults ranges from 1000
    to 1500 mg. It is recommended to take supplements
    with food to aid in absorption.
  • Vitamin D is added to some calcium supplements.
    Proper vitamin D status is important because
    vitamin D is converted to a hormone in the body,
    which then induces the synthesis of intestinal
    proteins responsible for calcium absorption.

85
Calcium
  • The absorption of calcium from most food and
    commonly used dietary supplements is very
    similar. This is contrary to what many calcium
    supplement manufacturers claim in their
    promotional materials.
  • Calcium carbonate is the most common and least
    expensive calcium supplement. It should be taken
    with food, and depends on low pH levels (acidic)
    for proper absorption in the intestine.  While
    most people digest calcium carbonate very well,
    some might develop gastrointestinal discomfort or
    gas. Taking magnesium with it can help to avoid
    constipation. Calcium carbonate is 40 elemental
    calcium. 1000 mg will provide 400 mg of calcium.
    However, supplement labels will usually indicate
    how much calcium is present in each serving, not
    how much calcium carbonate is present.
  • Antacids frequently contain calcium carbonate,
    and are a commonly used, inexpensive calcium
    supplement.
  • Coral calcium is a salt of calcium derived from
    fossilized coral reefs. Coral calcium is composed
    of calcium carbonate and trace minerals.
  • Calcium citrate can be taken without food and is
    the supplement of choice for individuals with
    achlorhydria or who are taking histamine-2
    blockers or proton-pump inhibitors due to gastric
    ulcers. Calcium citrate is about 21 elemental
    calcium. 1000 mg will provide 210 mg of calcium.
    It is more expensive than calcium carbonate and
    more of it must be taken to get the same amount
    of calcium.

86
Calcium
  • Calcium phosphate costs more than calcium
    carbonate, but less than calcium
    citrate. Microcrystalline Hydroxyapatite (MH) is
    one of several forms of calcium phosphate used as
    a dietary supplement. Hydroxyapatite is about 40
    calcium.
  • Calcium lactate has similar absorption as calcium
    carbonate, but is more expensive. Calcium lactate
    and calcium gluconate are less concentrated forms
    of calcium and are not practical oral
    supplements.
  • Calcium chelates are synthetic calcium compounds
    in which calcium is bound to an organic molecule,
    such as malate, aspartate, or fumarate. These
    forms of calcium may be better absorbed on an
    empty stomach. However, in general they are
    absorbed similarly to calcium carbonate and other
    common calcium supplements when taken with
    food. The "chelate" mimics the action that
    natural food performs by keeping the calcium
    soluble in the intestine. Thus, on an empty
    stomach, in some individuals, chelates might, in
    theory, be absorbed better.

87
Calcium
  • Hazards and toxicity
  • Excessive consumption of calcium carbonate
    antacids/dietary supplements (such as Tums) over
    a period of weeks or months can cause milk-alkali
    syndrome, with symptoms ranging
    from hypercalcemia to potentially fatal renal
    failure. Persons consuming more than 10 grams/day
    of CaCO3 (4 g Ca) are at risk of developing
    milk-alkali syndrome. Oral calcium supplements
    diminish the absorption of thyroxine when taken
    within four to six hours of each other. Thus,
    people taking both calcium and thyroxine run the
    risk of inadequate thyroid hormone replacement
    and thence hypothyroidism if they take them
    simultaneously or near-simultaneously.

88
Carbon dioxide
  • Carbon dioxide is an important greenhouse gas,
    warming the Earth's surface to a higher
    temperature by reducing outward radiation.
    Atmospheric carbon dioxide is the primary source
    of carbon in life on Earth and its concentration
    in Earth's pre-industrial atmosphere since late
    in the Precambrian eon has been regulated by
    photosynthetic organisms. Burning of carbon-based
    fuels since the industrial revolution has rapidly
    increased concentrations of atmospheric carbon
    dioxide, increasing the rate of global warming
    and causing anthropogenic climate change. It is
    also a major source of ocean acidification since
    it dissolves in water to form carbonic acid,
    which is a weak acid as its ionization in water
    is incomplete.
  • CO2  H2O    H2CO3

89
Carbon dioxide
  • History
  • Carbon dioxide was one of the first gases to be
    described as a substance distinct from air. In
    the seventeenth century, the Flemish chemist Jan
    Baptist van Helmont observed that when he
    burned charcoal in a closed vessel, the mass of
    the resulting ash was much less than that of the
    original charcoal. His interpretation was that
    the rest of the charcoal had been transmuted into
    an invisible substance he termed a "gas" or "wild
    spirit" (spiritus sylvestre). Carbon dioxide is
    used by the food industry, the oil industry, and
    the chemical industry.
  •  

90
Carbon dioxide
  • Foods 
  • A candy called Pop Rocks is pressurized with
    carbon dioxide gas. Leavening agents cause dough
    to rise by producing carbon dioxide. Baker's
    yeast produces carbon dioxide by fermentation of
    sugars within the dough, while chemical leaveners
    such as baking powder and baking soda release
    carbon dioxide when heated or if exposed
    to acids.
  • Beverages 
  • Carbon dioxide is used to produce carbonated soft
    drinks and soda water. Traditionally, the
    carbonation in beer and sparkling wine came about
    through natural fermentation, but many
    manufacturers carbonate these drinks with carbon
    dioxide recovered from the fermentation process.

91
Carbon dioxide
  • Wine making 
  • Carbon dioxide in the form of dry ice is often
    used in the wine making process to cool down
    bunches of grapes quickly after picking to help
    prevent spontaneous fermentation by wild yeast.
    The main advantage of using dry ice over regular
    water ice is that it cools the grapes without
    adding any additional water that may decrease
    the sugar concentration in the grape, and
    therefore also decrease the alcohol concentration
    in the finished wine.
  • Biological applications 
  • In medicine, up to 5 carbon dioxide (130 times
    atmospheric concentration) is added to oxygen for
    stimulation of breathing after apnea and to
    stabilize theO2/CO2 balance in blood.
  • It has been proposed that carbon dioxide from
    power generation be bubbled into ponds to grow
    algae that could then be converted
    into biodiesel fuel.

92
Carbon dioxide
  • Biological role 
  • Carbon dioxide is an end product in organisms
    that obtain energy from breaking down sugars,
    fats and amino acids with oxygen as part of
    their metabolism, in a process known as cellular
    respiration. This includes all plants, animals,
    many fungi and some bacteria. In higher animals,
    the carbon dioxide travels in the blood from the
    body's tissues to the lungs where it is exhaled.
    In plants using photosynthesis, carbon dioxide is
    absorbed from the atmosphere.

93
Carbon dioxide
  • Toxicity
  • Acute carbon dioxide physiological effect is
    hypercapnia or asphyxiation sometimes known by
    the names given to it by miners blackdamp.
    Blackdamp is primarily nitrogen and carbon
    dioxide and kills via suffocation (having
    displaced oxygen). Miners would try to alert
    themselves to dangerous levels of blackdamp and
    other gases in a mine shaft by bringing a caged
    canary with them as they worked. The canary is
    more sensitive to environmental gases than humans
    and as it became unconscious would stop singing
    and fall off its perch. The Davy lamp could also
    detect high levels of blackdamp (which collect
    near the floor) by burning less brightly, while
    methane, another suffocating gas and explosion
    risk would make the lamp burn more brightly).

94
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Carbon dioxide
  • Human physiology
  • The body produces approximately 2.3 pounds (1 kg)
    of carbon dioxide per day per person, containing
    0.63 pounds (290 g) of carbon. In humans, this
    carbon dioxide is carried through the venous
    system and is breathed out through the lungs.
    Therefore, the carbon dioxide content in the body
    is high in the venous system, and decreases in
    the respiratory system, resulting in lower levels
    along any arterial system. Carbon dioxide content
    in this sense is often given as the partial
    pressure, which is the pressure which carbon
    dioxide would have had if it alone occupied the
    volume.

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Carbon dioxide
  • Transport in the blood 
  • CO2 is carried in blood in three different ways.
  • 70 to 80 is converted to bicarbonate ions HCO3-
    by the enzyme carbonic anhydrase in the red blood
    cells, by the reaction
  • CO2  H2O ? H2CO3 ? H  HCO3-5 10
    is dissolved in the plasma
  • 5 10 is bound to hemoglobin 
  • Hemoglobin, the main oxygen-carrying molecule
    in red blood cells, carries both oxygen and
    carbon dioxide. However, the CO2 bound to
    hemoglobin does not bind to the same site as
    oxygen. Instead, it combines with the N-terminal
    groups on the four globin chains. However,
    because of its effects on the hemoglobin
    molecule, the binding of CO2 decreases the amount
    of oxygen that is bound for a given partial
    pressure of oxygen. The decreased binding to
    carbon dioxide in the blood due to increased
    oxygen levels is known as the Haldane Effect, and
    is important in the transport of carbon dioxide
    from the tissues to the lungs. Conversely, a rise
    in the partial pressure of CO2 or a lower pH will
    cause offloading of oxygen from hemoglobin, which
    is known as the Bohr Effect.

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Carbon dioxide
  • Regulation of respiration
  • Carbon dioxide is one of the mediators of local
    autoregulation of blood supply. If its levels are
    high, the capillaries expand to allow a greater
    blood flow to that tissue.
  • Bicarbonate ions are crucial for regulating blood
    pH. A person's breathing rate influences the
    level of CO2 in their blood. Breathing that is
    too slow or shallow causes respiratory acidosis,
    while breathing that is too rapid leads to
    hyperventilation, which can cause respiratory
    alkalosis.

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Carbon dioxide
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