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The Urinary System

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The Urinary System Functions: Excretion of wastes from the blood (kidneys) Elimination of wastes into environment (ureters, bladder, urethra) Regulation of volume and ... – PowerPoint PPT presentation

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Title: The Urinary System


1
The Urinary System
  • Functions
  • Excretion of wastes from the blood (kidneys)
  • Elimination of wastes into environment (ureters,
    bladder, urethra)
  • Regulation of volume and solute concentration of
    blood plasma

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3
Organs of the Urinary Tract
  • Kidneys
  • reddish brown, bean shaped, located just below
    the ribs on posterior wall of abdominal cavity
  • regulate volume, composition, and pH of body
    fluids (remove metabolic wastes in the process)
  • secrete hormone erythropoetin (controls rate of
    RBC formation)
  • secrete enzyme renin (regulates blood pressure)
  • functional unit is the nephron (will discuss
    later)

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Organs cont.
  • Ureters
  • transport urine from kidneys to bladder
  • 25 cm long tubes
  • muscular walls help move urine by peristalsis
  • kidney stones can block this tube

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Organs cont.
  • Urinary bladder
  • temporarily stores urine
  • hollow, muscular organ composed of transitional
    epithelium (stretches)
  • internal urethral sphincter - muscle that
    surrounds the neck of the bladder remains
    contracted to prevent the bladder from emptying
    until pressure increases to a certain level
    autonomic controlled
  • External urethral sphincter voluntarily
    controlled, ring of muscles where urethra exits
    body. How you control when you use the restroom.

8
Female Male
9
Organs cont.
  • Urethra
  • conveys urine out of body
  • about 4 cm long in females
  • about 19 cm long in males

10
Urethral Sphincters
11
Micturition
  • bladder can hold as much as 600 ml of urine
  • urge to urinate occurs when it contains 200 ml
  • the reflex to urinate is inhibited by the
    conscious control of the external urethral
    sphincter
  • Urine leaves the bladder by micturition (a.k.a.
    urination)

12
Micturition Reflex
  • bladder distends as it fills with urine and
    stimulates stretch receptors in bladder wall
  • when stretch receptors are triggered, they
    stimulate muscular bladder wall to contract
  • external urethral sphincter is relaxed
    voluntarily, and the internal urethral sphincter
    relaxes also
  • urination occurs
  • if ext. urethral sphincter does not relax, int.
    urethral sphincter remains closed

13
Micturition Reflex cont.
  • What happens if you hold it too long?
  • Once volume exceeds 500 ml, pressure may force
    open internal sphincter which causes reflexive
    relaxation of external sphincter, and urination
    occurs

14
Urinary Diseases and Disorders
  • UTI - urinary tract infection
  • more common in women than men b/c the urethra is
    shorter in females
  • symptoms burning pain during urination
  • cause bacteria spread from rectum to urethra
  • Kidney Stones (a.k.a. renal calculi)
  • result from chronically concentrated urine which
    causes uric acid to clump and form stones
  • Possible causes oxalate found in green, leafy
    vegetables, coffee, and chocolate
  • Gout uric acid build up in joints

15
Gout Kidney Stones
16
Worlds Largest Kidney Stone 22 oz. 5.5 in across
17
The Nephron
  • each kidney contains 1 million nephrons
  • they filter 7.5 liters of plasma each hour
  • each nephron consists of a renal corpuscle (blood
    vessels) and a renal tubule (tube)
  • the renal corpuscle is divided into 3 parts.
    Renal artery, glomerulus, and peritubular
    capillary.
  • renal artery becomes a cluster of capillaries
    called a glomerulus (surrounded by Bowmans
    capsule)
  • Then goes to a network of capillaries called
    peritubular capillaries which surround the renal
    tubule
  • the renal tubule is divided into 4 parts
    Bowmans capsule, the proximal convoluted tubule,
    loop of Henle, and the distal convoluted tubule

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19
Urine Formation
  • Urine formation occurs in the nephrons
  • Consists of 3 processes
  • 1. glomerular filtration (collects good and bad
    stuff)
  • 2. tubular reabsorption (removes good stuff from
    filtrate and put back into body)
  • 3. tubular secretion (puts in extra bad stuff
    into filtrate which is going to the toilet)

20
1. Glomerular Filtration (collecting good and bad
stuff)
  • Occurs when the renal artery delivers blood to
    the glomerulus
  • blood pressure forces water and small molecules
    from blood plasma into the Bowman's capsule
  • this fluid is now known as filtrate and moves
    into the renal tubule
  • ex. of molecules in filtrate water, glucose,
    amino acids, sodium, urea, uric acid, other
    minerals
  • Filters both good and bad stuff for example
    water and toxic substances

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2. Tubular Reabsorption (removes good stuff from
filtrate)
  • occurs in the proximal convoluted tubule, loop of
    Henle, distal convoluted tubule, and collecting
    duct
  • molecules from the filtrate (in the tubule) are
    returned by diffusion and active transport to the
    blood in the peritubular capillaries
  • ex. of molecules that are reabsorbed glucose,
    amino acids, and almost all of the water and
    sodium that enters the tubule is reabsorbed
  • Make a really salty place so that on the next
    pass by we can remove almost all the water. (good
    stuff)

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3. Tubular Secretion (Puts in extra bad stuff
into filtrate)
  • occurs mainly at the distal convoluted tubule
  • molecules from the peritubular capillaries (blood
    vessels) are actively transported into the renal
    tubule (tubes)
  • ex. of molecules that are secreted uric acid,
    hydrogen ions, ammonia, penicillin (and other
    drugs)

25
Notice hormones in orange and green on right
3
2
1
26
Urine Formation cont.
  • the distal convoluted tubule empties the fluid
    (urine) into a collecting duct which carries it
    away from the nephron
  • Each collecting duct empties many nephrons
  • Many collecting ducts empty the medullas into the
    funnel-shaped central chamber of the kidney
    (renal pelvis)
  • the ureters drain this chamber
  • the peritubular capillaries merge to form venules
    that carry the filtered blood away from the
    nephron and eventually out of the kidney

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29
Urine
  • Physical characteristics
  • The yellow color in urine is due to chemicals
    called urobilins. These are the breakdown
    products of the bile pigment bilirubin. Bilirubin
    is itself a breakdown product of the heme part of
    hemoglobin from worn-out red blood cells. Most
    bilirubin is partly broken down in the liver,
    stored in the gall bladder, broken down some more
    in the intestines, and excreted in the feces (its
    metabolites are what make feces brown), but some
    remains in the bloodstream to be extracted by the
    kidneys where, converted to urobilins, it gives
    urine that familiar yellow tint.
  • pH slightly acidic (6.0)
  • Chemical composition
  • 95 water, 5 solutes

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31
Urine Components
  • Urea is the bodys main waste product - formed
    when amino acids are broken down into energy is
    toxic to cells in high levels
  • Uric acid a by-product of the breakdown of
    nucleic acids (RNA DNA)
  • Creatinine a by-product of muscle metabolism
  • Ammonia waste formed when bacteria break down
    proteins
  • Ketones waste produced when fats are digested
    (diabetes and Atkins diet)

32
Urine
  • Composition affected by lifestyle and diet
  • Volume varies from 0.6 to 2.5 liters/day
  • Diuretics inhibit reabsorption of water so
    increase urine volume ex. coffee, tea,
    alcoholic beverages

33
Hormonal Regulation
  • Aldosterone
  • stimulates both reabsorption of Na and the
    secretion of K
  • Na reabsorption increases water reabsorption,
    leading to a rise in blood volume and therefore a
    rise in blood pressure

34
Hormonal Regulation
  • ADH (antidiuretic hormone) causes increased water
    absorption
  • high solute conc. in blood ? increased ADH
    secretion
  • alcohol and caffeine inhibit ADH secretion
    causing excess excretion of dilute urine and
    dehydration

35
Diuretics in orange
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