The Transport System

1
The Transport System

• Topic 6.2 and H5

2
Circulatory System- Overview

• System of internal transport that transport
  oxygen and carbon dioxide, distributes nutrients
  to body cells, and conveys the waste products of
  metabolism to specific sites for disposal.
• Necessary in any animal whose body is too large
  or too complex for vital chemicals to reach all
  its parts by diffusion alone.
• Provides an efficient long-distance internal
  transport system that brings resources close
  enough to cells for diffusion to occur.

3
Circulatory System- Overview

• Circulatory system must have an intimate
  connection with body tissues
• For example
• capillaries form a system of microscopic blood
  vessels that the heart pumps blood through once
  it has been oxygenated in the lungs.
• Capillaries form an intricate network among the
  cells of a tissue, such that no substance has to
  diffuse far to enter or leave a cell.
• Figure 23.1 A

4
Circulatory System- Overview

• Materials do no exchange directly between blood
  and body cells
• Each body cell is immersed in a water
  interstitial fluid
• Molecules such as oxygen and nutrients diffuse
  first out of a capillary into the interstitial
  fluid and then from the interstitial fluid into a
  tissue cell.
• Figure 23.1 B

5
Circulatory System- Overview

• Circulatory System is also responsible for
  conveying metabolic wastes to waste disposal
  organs
• Carbon Dioxide to lungs
• variety of metabolic wastes to the kidneys.

6
Circulatory System- Overview

• Circulatory System plays a key role in
  maintaining homeostasis (a constant internal
  environment)
• By exchanging molecules with the interstitial
  fluid, the circulatory system helps control the
  makeup of the blood by continuously moving it
  through organs, such as the liver and kidneys,
  that regulate the bloods contents.

7
Circulatory System-Overview

• Animals with thick, multiple layers of cells
  require a true circulatory system containing a
  specialized circulatory fluid, blood.
• Closed circulatory system
• Also called the cardiovascular system
• Blood is confined to the vessels, which keep it
  distinct from the interstitial fluid.

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Circulatory System-Overview

• Three kinds of vessels in a closed circulatory
  system
• Arteries
• Carry blood away from the heart to organs and
  tissues throughout the body
• Most arteries convey oxygen-rich blood, although
  there are some exceptions
• Two arteries called the pulmonary arteries carry
  oxygen-poor blood from our heart to our lungs.
• Veins
• Return blood to the heart
• Most veins transport blood depleted of oxygen,
  with a few exceptions
• Four pulmonary veins that carry freshly
  oxygenated blood from the lungs to the heart.
• Capillaries
• Convey blood between arteries and veins within
  each tissue.

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Circulatory System-Overview

• Other vessels
• Arterioles
• Branch from large arteries
• small vessels that give rise to capillaries
• Capillary beds
• Network of capillaries that infiltrate every
  organ and tissue in the body.
• Thin wall allow chemical exchange between the
  blood and interstitial fluid
• Venules
• Form from capillaries
• Converge into veins that return blood to the
  heart.

10
Circulatory System-Overview

• Structure of blood vessels fits their functions
• Capillaries
• Form fine branching networks where materials are
  exchanged between the blood and the intersitital
  fluid that bathes the cells.
• Have very thin walls formed of a single layer of
  epithelial cells, which is wrapped in a basement
  membrane.
• The inner surface of the capillary is smooth and
  keeps the blood ells from being abraded as they
  tumble along.
• Arteries, arterioles, veins, and venules have
  thicker walls than those of capillaries

11
Circulatory System-Overview

• Structure of blood vessels fits their function,
  contd.
• All blood vessels have same epithelium as
  capillaries, but they are reinforced by two other
  tissue layers
• An outer layer of connective tissue with elastic
  fibers enables the vessels to stretch and recoil
• The middle layer consists mainly of smooth
  muscle.
• Both layers are thick and sturdier in arteries,
  providing the strength and elasticity to
  accommodate the rapid flow and high pressure of
  blood pumped by the heart.
• Arteries can also regulate blood flow by
  constricting or relaxing their smooth muscle
  layer.
• Thinner-walled veins convey blood back to the
  heart at low velocity and pressure.
• Within large veins, flaps of tissues act as
  one-way valves.

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Arteries, Arterioles, Capillaries
13
Veins
14
Circulatory System-Overview

• Double circulation
• Blood is pumped a second time after it slows down
  in the capillary beds of the lungs
• Pulmonary circuit
• Carries blood between the heart and the gas
  exchange tissues in the lungs
• System circuit
• Carries blood between the heart and the rest of
  the body
• http//www.icyou.com/topics/diseases-conditions/sy
  stemic-and-pulmonary-circulation

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Circulatory System-Overview

• Four chambers to the heart
• Two atria (on top)
• Two ventricles (on bottom)
• Right side
• Handles only oxygen-poor blood
• Left side
• Receives and pumps only oxygen-rich blood
• evolution of a powerful four-chambered heart
  was an essential adaptation to support the high
  metabolic rate characteristic of birds and
  mammals, which are endothermic and require lots
  of energy.need to deliver lots of fuel and
  oxygen to body tissues

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Circulatory System-Overview
17
Human Heart- General Characteristics

• About the size of a clenched fist
• Enclose in a sac just under the breastbone
• Thin-walled atria collect blood returning to the
  heart, most of which then flows into the
  thicker-walled ventricles.
• Ventricles pump blood to the lungs and to all
  other body tissues.
• Flap-like valves regulate the direction of blood
  flow

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Circulatory System- Blood Flow

1. Beginning with the pulmonary (lung) circuit, the
   right ventricle pumps blood to the lungs via two
   pulmonary arteries.
2. As blood flows through capillaries in the lungs,
   it takes up oxygen and unloads carbon dioxide.
3. Oxygen-rich blood then flows back through the
   pulmonary veins to the left atrium.
4. The oxygen-blood flows from the left atrium into
   the left ventricle.
5. Powerful muscles in the left ventricle pump blood
   to all body tissues through the systemic circuit.
6. Oxygen-rich blood leaves the left ventricle
   through the aorta. The aorta is the largest blood
   vessel, with a diameter of roughly 2.5 cm, about
   the same diameter as a quarter.
7. First branches from the aorta are the coronary
   arteries, which supply blood to the heart muscle
   itself.
8. Several large arteries branch from the aorta,
   leading to the head, chests, and arms, and to the
   abdominal region and legs.
9. Within each organ, arteries lead to arterioles
   that branch to capillaries. Capillaries rejoin as
   venules, which convey the blood back to veins.
10. Oxygen-poor blood from the upper body is
    channeled into a large vein called the superior
    vena cava, and the inferior vena cava drains
    blood from the lower body.
11. Both vena cavas empty their blood into the right
    atrium.

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Circulatory System- Blood Flow Summary

• The path of any single blood cell is always heart
  to lung capillaries to heart to body tissue
  capillaries and back to heart.
• In one systemic circuit, a blood cell may travel
  to the brain in the next (after a pulmonary
  circuit) it may travel to the legs.
• It never travels from the brain to the legs
  without first returning to the heart and being
  pumped to the lungs to be recharged with oxygen.
• http//www.smm.org/heart/heart/pumping.htm

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Cardiac Cycle

• Cardiac Cycle
• The heart is the hub of the circulatory system
• In a continuous cycle, it passively fills with
  blood and then actively contracts
• The complete sequence of filling and pumping is
  called the cardiac cycle.

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Cardiac Cycle

• Cardiac Cycle, Figure 23.6
• Shows a cardiac cycle that takes about 0.8
  seconds, corresponding to a heart rate of 75
  beats per minute.
• 3 phases
• Diastole
• When the entire heart is relaxed, in the phase
  called diastole, blood flows into all four of its
  chambers. Blood enters the right atrium from the
  venae cavae and the left atrium from the
  pulmonary veins. The AV valves are open. Diastole
  lasts about 0.4 seconds, during which the
  ventricles nearly fill with blood

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Cardiac Cycle

• Cardiac Cycle, Figure 23.6
• 2. Systole
• Systole begins with a very brief (0.1-second)
  contraction of the atria that completely fills
  the ventricles with blood (atrial systole).
• Then the ventricles contract for about 0.3
  seconds (ventricular systole)
• The force of their contraction closes the AV
  valves, opens the semilunar valves located at the
  exit from each ventricle, and pumps blood into
  the large arteries.

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Cardiac Cycle

• Cardiac output
• The volume of blood per minute that the left
  ventricle pumps into the systemic circuit.
• This volume is equal to the amount of blood
  pumped by the left ventricle each time it
  contracts (about 75mL per beat for the average
  person) times the heart rate (about 70 beats per
  minute). 5,250mL/min
• Influenced by many factors age, fitness, etc.
  Increases during heavy exercise.

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Cardiac Cycle

• Heart valves
• Made of flaps of connective tissue, prevent
  backflow and keep moving in the correct
  direction.
• Closing of the AV valves when the ventricles
  contract keeps blood from flowing back into the
  atria.
• When the ventricles relax in diastole, blood in
  the arteries starts to flow back toward the
  heart, causing the flaps of the semilunar valves
  to close and preventing blood from flowing back
  into the ventricles.
• The heart sound we can hear lub-dup lub-dup
  are caused by the closing of the heart valves.
• Lub comes from the recoil of blood against the
  closed AV valves
• Dup comes as the semilunar valves snap shut.

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Cardiac Cycle

• Heart valves
• Murmurs
• Causes a hissing sound, caused by a defect in one
  or more of the heart valves
• Occurs when a stream of blood squirts backward
  through a valve
• May be born with it, or can be caused by
  infection (rheumatic fever)
• Usually do not reduce efficiency of blood flow
  enough to warrant surgery, however, can be
  corrected by replacing damaged valves with
  artificial valves or by a donor.

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Pacemaker

• PaCeMaKeR!!!, or SA (sinoatrial) node
• Specialized region of cardiac muscle
• Maintains the hearts pumping rhythm by setting
  the rate at which all the muscle cells of the
  heart contract.
• Located in the wall of the right atrium

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Pacemaker

• Function of pacemaker (figure 23.7)
• The pacemaker (SA node) generates electrical
  signals
• a. Cardiac muscle cells are electrically
  connected by specialized junctions between cells,
  allowing signals to spread quickly through both
  atria, making them contract in unison.
• b. Signals pass to a relay point called the AV
  node, in the wall between the right atrium and
  right ventricle. Here the signals are delayed
  about 0.1 second. The delay ensures that the
  atria contract and empty before the ventricles
  contract.
• Specialized cardiac muscle fibers then relay the
  signals to the apex of the heart and
• Up through the walls of the ventricles,
  triggering the strong contractions that drive the
  blood out of the heart.

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Pacemaker

• Although the AV node sets the basic rhythm of the
  heart, the rate and strength of heart beat is
  modified by two centers within the medulla
  oblongata in the brain
• One sends nerve impulses down accelerans nerves.
• Associated with noradrenaline speeds up heart
  rate and strength
• Increase in blood pressure
• The other sends nerve impulses down a pair of
  vagus nerves
• Slows the heart beat
• Decrease in blood pressure

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Pacemaker

• Physiological and emotional cues can influence
  heart rate.
• Hormones also influence heart rate
• Epinephrine (also known as adrenaline)
• fight or flight hormone released at times of
  stress

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Pacemaker

• Certain heart diseases prevent the hearts
  self-pacing system from functioning properly to
  maintain a normal heart rhythm
• Artificial pacemaker
• Tiny electronic device surgically implanted near
  the AV node.
• Emit electrical signals that trigger normal heart
  beats

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Pacemaker

• Electrocardiogram
• ECG or EKG
• Electrical signals in the heart generate
  electrical changes in the skin, which can be
  detected by electrodes and recorded as an EKG.

35
Electrocardiogram
36
Heart Attack

• If one or more coronary arteries become blocked,
  heart muscle cells will die quickly causing the
  heart to not function properly is a heart attack
  (myocardial infarction).
• Approximately 1/3 of heart attack victims die
  almost immediately.
• For those who survive, the ability of the damaged
  heart to pump blood may be seriously impaired
• Heart attacks rank first in causes of death in
  the US
• Strokes, death of brain tissue resulting from
  blockage of arteries in the head, are third.

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Heart Attack

• Diseases of the heart and blood vessels are known
  as cardiovascular disease.
• Accounts for almost 50 of all deaths in the US,
  killing over 1 million people each year- about
  one every 30 seconds

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Heart Attack

• Atherosclerosis
• Chronic cardiovascular disease
• Growths called plaques develop in the inner walls
  of arteries, narrowing the passages through which
  blood can flow
• Smooth muscle layer of an artery becomes
  thickened and infiltrated with cholesterol and
  fibrous connective tissue
• A blood clot is more likely to become trapped in
  a vessel that has been narrowed by plaques.
• Therefore, plaques are common sites of blood clot
  formation.

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Heart Attack

• Causes of cardiovascular disease
• Inheritance
• Smoking doubles the risk of heart attack and
  harms the circulatory system in several other
  ways.
• Lack of exercise
• Exercise can cut the risk of heart disease in
  half
• Diet
• Eating a healthy diet, low in cholesterol and
  saturated fat, can reduce the risk of
  atherosclerosis.

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Heart Attack

• Treatment
• Heart attack victims are treated with
  clot-dissolving drugs, which stop many heart
  attacks and help prevent damage.
• Cholesterol and B.P. measurements, CT and MRI
  help identify risks
• Drugs can lower cholesterol and blood pressure
• Angioplasty
• Inserting a tiny catheter with a balloon that is
  inflated to compress plaques and widen clogged
  arteries.
• Stents
• Small wire mesh tubes that prop arteries open

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Heart Attack

• Treatment (continued)
• Heart transplant
• Severe shortage of donor hearts, various
  artificial pumping devices are under development.
• Bypass surgery
• Blood vessels removed from a patients legs are
  sewn into the heart to shunt blood around clogged
  arteries.

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Heart Attack

• Good news!
• US death rates from cardiovascular disease have
  been cut in half over the past 50 years
• Reduction in risk factors has contributed to
  this.
• Availability of automatic external defribillators
  (AEDs) has saved thousands of lives.
• Devices deliver electric shocks that can reverse
  a short circuit of the hearts pacemaker and
  reestablish normal electrical rhythms in the
  heart.
• Designed to be used anyone
• http//www.pbs.org/wgbh/takeonestep/heart/video-ch
  _01_vid.html?tosvidfiletypemovbandwidth_hi

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Blood Pressure

• Blood pressure
• The force that blood exerts against the walls of
  our blood vessels
• Created by the pumping of the heart
• Drives blood from the heart through arteries and
  arterioles to capillary beds.

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Blood pressure

• Pulse
• Rhythmic stretching of arteries
• When the ventricles contract, blood is forced
  into the arteries faster than it can flow in the
  arterioles.
• This stretches the elastic walls of the arteries.

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Blood pressure

• B.P. depends on cardiac output (volume of blood
  pumped into the aorta) and resistance to blood
  flow imposed by the narrow openings, controlled
  by smooth muscles, of arterioles.
• When muscles relax, arterioles dilate, and blood
  flows through them more readily causing a
  decrease in b.p.
• Physical and emotional stress can increase b.p.
  via nervous and hormonal signals that constrict
  blood vessels

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Blood Pressure

• Regulatory mechanisms coordinate cardiac output
  and changes in the arteriole resistance to
  maintain adequate b.p. as demands on the
  circulatory system change.

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Blood pressure

• Aorta and arteries
• High blood pressure and blood velocity
• Arterioles
• Abrupt decline in b.p. and b.v mainly due to
  resistance to blood flow cuased by friction
  between the blood and large surface area it
  contacts in the wall of numerous tiny arterioles.
• Capillaries
• B.p. and b.v. is slowest
• Enhances the exchange of substances between the
  blood and interstitial fluid.

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Blood pressure

• Veins
• B.p. is nearly at zero due to resistance passing
  through all other blood vessels
• Blood is able to move up legs against gravity due
  to veins sandwiched between skeletal muscles
• Whenever the body moves , the muscles pinch the
  veins and squeeze the blood along toward the
  heart
• Valves allow blood to flow only toward the heart.
• Breathing also helps return blood to the heart
• When we inhale, the change in pressure within our
  chest cavity causes the large veins near our
  heart to expand and fill.

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Measuring blood pressure

• Figure 23.10
• Typical blood pressure for a healthy young adult
  is 110/70. First number is systolic, second
  number is diastolic.
• Once sphygamomanometer, or blood pressure cuff,
  is wrapped around the upper arm, where large
  arteries are accessible, the cuff is inflated
  until the pressure is strong enough to close the
  artery and cut off blood flow to the lower arm.

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Measuring blood pressure

• 3. A stethoscope is used to listen for sounds of
  blood flow below the cuff, and systolic blood
  pressure is the first measurement taken as the
  cuff is gradually deflated.
• The first sound of blood spurting through the
  constricted artery indicates that the blood
  pressure is stronger than the pressure exerted by
  the cuff.
• The pressure at this point is the systolic
  pressure.

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Measuring blood pressure

• 4. The sound of blood flowing unevenly through
  the artery continues until the pressure of the
  cuff falls below the pressure of the artery
  during diastole.
• Blood now flows continuously through the artery,
  and the sound of blood flow ceases.
• The reading on the pressure gauge at this point
  is the diastolic pressure.

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Blood pressure

• Optimal blood pressure for adults is below 120 mm
  Hg for systolic pressure and below 80 mm Hg for
  diastolic pressure
• Lower values are generally considered better,
  except in rare cases where low blood pressure may
  indicate a serious underlying condition (such as
  endocrine disorders, malnutrition, or internal
  bleeding)

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Hypertension

• High blood pressure, or hypertension
• Persistent systolic b.p. at or higher than 140 mm
  Hg and/or diastolic b.p. at or higher than 90 mm
  Hg.
• Silent Killer often displays no outward
  symptoms for years
• Affects almost one-third of the US adult
  population
• Elevated b.p. requires the heart to work harder
  to pump blodo throughout the body, and overtime
  the left ventricle may enlarge
• When the coronary blood supply does not keep up
  with the demands of this increase in muscle mass,
  the heart muscle weakens
• In addition, the increases force on arterial
  walls causes tiny ruptures that promote plaque
  formation, aggravating atherosclerosis, and
  increasing the risk of blood clot formation.

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Hypertension

• Prolonged hypertension is the major cause of
  heart attack, heart disease, stroke, and kidney
  failure.
• Causes
• Some predispositions cannot be avoided, such as
  gender, ethnicity, age, and heredity.
• Males have a greater risk up to age 55, but
  females have a greater risk over 85
• Blood pressure generally increases with age
• Children of parents with hypertension are twice
  as likely to develop the condition.

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Hypertension

• Prevention
• Eating a heart-healthy diet
• Not smoking
• Avoiding excess alcohol (more than two drinks per
  day)
• Exercising regularly (30 minutes of moderate
  activity on most days)
• Maintaining a healthy weight
• Antihypertensive medications
• Although salt is typically associate with high
  b.p, its only a contributing factor for a small
  percentage

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Blood distribution

• Smooth muscles can influence b.p. by changing the
  resistance to flow out of the arteries and
  arterioles.
• Smooth muscle also regulates blood distribution
  to the capillaries of the various organs.
• At any given time, only about 5-10 of the bodys
  capillaries have blood flowing through them.
  However, each tissue has many capillaries, so
  every part of the body is supplied with blood at
  all times.

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Blood distribution

• Capillaries in a few organs, such as the brain,
  heart, kidneys, and liver, usually carry a full
  load of blood, but in many other sites, the blood
  supply varies as blood is diverted from one
  destination to another, depending on need.

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Blood distribution

• Figure 23.11 Smooth muscle regulates the
  distribution of blood
• Thoroughfare channel
• Capillary through which blood streams directly
  from arteriole to venule
• This channel is always open
• Capillaries branch off from thoroughfare channels
  for the bulk of the capillary bed
• Precapillary sphincters,
• rings of smooth muscle located at the entrance of
  the capillary beds
• regulate the passage of blood

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Blood distribution

• Figure 23.11 Smooth muscle regulates the
  distribution of blood
• Precapillary sphincters relaxed blood flows
  though a capillary bed when its.
• Precapillary sphincters contracted blood
  bypasses the capillary bed and goes to venule.

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Blood distribution

• After a meal, p.sphincters in the wall of
  digestive tract let a larger quanity of blood
  pass through capillary beds than when food is not
  being digested.
• During strenuous exercise, many of the
  capillaries in the digestive tract are closed
  off, and blood is supplied more generously to
  skeletal muscles.
• Nerves and hormones influence the contraction of
  the smooth muscles in both these mechanisms that
  regulate the flow of blood to capillary beds.

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Capillaries

• Capillaries are the only blood vessels with walls
  thin enough for substances to cross between the
  blood and the interstitial fluid that bathes the
  cells.
• Most important function of the circulatory system

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Capillaries

• Figure 23.12A Capillary cross section
• Capillary walls consists of adjoining epithelial
  cells that enclose a lumen, or space, that is
  just large for red blood cells to tumble through
  in single file.
• Each epithelial cell contains a nucleus
• Capillary is surrounded by interstitial fluid

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Capillaries

• Exchange of substances between blood and
  interstitial fluid
• Passive transport Some substances, such as
  oxygen and carbon dioxide, simply diffuse through
  the epithelial cells of the capillary wall.
• Active transport Some larger molecules may be
  carried across an epithelial cell in vesicles
  that form by endocytosis on one side of the cell
  and then release their contents by exocytosis on
  the other side

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Capillaries

• Exchange of substances between blood and
  interstitial fluid (continued)
• Due to leaky structure of capillary wall, there
  are narrow clefts between the epithelial cells
  making up the capillary
• Water and small solutes, such as sugars and
  salts, move freely through these clefts
• Blood cells and dissolved proteins remain inside
  the capillary because they are too large to pass
  through these passageways.
• Much of the exchange btw blood and interstitial
  fluid is the result of the pressure driven flow
  of fluid (consisting of water and dissolved
  solutes) through these clefts.

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Capillary
66
Capillaries

• Active forces that drive fluid into or out of the
  capillary
• Blood pressure, which tends to push fluids
  outward
• Osmotic pressure, a force that tends to draw
  fluid into the capillary because the blood has a
  higher concentration of solutes than the
  interstitial fluid.
• Proteins dissolved in the blood account for much
  of this high solute concentration.

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Capillaries

• Direction of fluid movement into or out of the
  capillary
• Depends on the difference btw blood pressure and
  osmotic pressure.
• Net movement of fluid out of the capillary
• Blood pressure exceeds the osmotic pressure
• Upstream (arterial) end of capillary
• Net movement of fluid into the capillary
• Blood pressure drops, osmotic pressure increases
• Downstream (venous) end of capillary

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Capillaries

• Direction of fluid movement into or out of the
  capillary (continued)
• Most of the fluid that leaves the blood at the
  arterial end of a capillary bed reeenters the
  capillaries at venous end.
• Remaining fluid is returned to the blood by the
  vessels of the lymphatic system.

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Capillary
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Blood
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Blood

• Blood consists of several types of cells
  suspended in a liquid called plasma.
• When a blood sample is taken, the cells can be
  separated from the plasma by spinning the sample
  in a centrifuge
• A chemical must be added to prevent the blood
  from clotting
• The cellular elements which make up about 45 of
  the volume of blood, settle to the bottom of the
  centrifuge tube, underneath the transparent,
  straw-colored plasma.

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Blood

• Plasma is about 90 water
• Among its many solutes are inorganic salts in the
  form of dissolved ions.
• These ions have several functions, such as
• maintaining osmotic balance
• keeping the pH of blood at about 7.4
• contributing to the proper environment needed
  for nerve and muscle function
• Also contains proteins
• Help maintain the osmotic balance between blood
  and interstitial fluid
• Some act as buffers
• Some function in blood clotting (fibrinogen)
• Immunity (immunoglobulins)
• Also contains a wide variety of substances in
  transit from one part of the body to another,
  such as nutrients, waste products, O2, CO2, and
  hormones.

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Blood

• Blood plasma contains two classes of cells
• Red blood cells (erythrocytes)
• White blood cells (leukocytes)
• 3rd cellular element platelets, are cell
  fragments involved in clotting

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Blood

• Red blood cells
• Also called erythrocytes
• About 25 trillion rbcs in the average persons
  5K of blood
• Structure of rbc suits its main function to
  carry oxygen
• Small biconcave disks, thinner in the center than
  at the sides
• Small size and shape create a large surface area
  across which oxygen can diffuse
• Each tiny rbc contains about 250 million
  molecules of hemoglobin and can transport about a
  billion oxygen molecules
• It lacks a a nucleus, which allows more room to
  pack in hemoglobin

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Blood
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Blood

• White blood cells
• Also called leukocytes
• Five major types
• Monocytes, neutrophils, basophils, eosinophils,
  and lymphocytes
• Collective function is to fight infections and
  cancer.
• Some are phagocytes, which engulf and digest
  bacteria and debris from out own dead cells
  (monocytes and neutrophills)
• Wbcs actually spend much of their time moving
  through interstitial fluid, where most infections
  are fought

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Blood cell formation

• The red marrow of bones such as the ribs,
  vertebrae, breast-bone, and pelvis all contain a
  spongy tissue in which stem cells differentiate
  into blood cells.
• One type of stem cell may give rise to
  lymphocytes
• A second type of stem cell can produce
  erythrocytes, other wbcs, and cell that produce
  platelets
• After forming in the early embryo, these stem
  cells continually produce all the blood cells
  needed throughout life.

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Red blood cell production

• Adequate numbers of rbcs are essential for body
  function.
• After circulating in the blood for 3 or 4 months,
  rbcs are broken down and their molecules are
  recycled
• Much of the iron removed from the hemoglobin is
  returned to the bone marrow, where new rbcs are
  formed at the amazing rate of 2 million per
  second
• Production of rbcs is controlled by a
  negative-feedback mechanism sensitive to the
  amount of oxygen reaching tissues via the blood.
• If tissues are not receiving enough oxygen, the
  kidneys produce a hormone called erythropoietin
  (EPO) that stimulates the bone marrow to produce
  more rbcs
• Patients on kidney dialysis do not produce enough
  EPO, and therefore have low rbc counts.
• Genetically engineered EPO has significantly
  helped these patients

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Anemia

• Anemia
• Caused by an abnormally low amount of hemoglobin
  or a low number of rbcs
• Person feels constantly tired and is often
  susceptible to infections because the body cells
  do not get enough oxygen.
• Can result from excessive blood loss, vitamin or
  mineral deficiencies, or certain cancers
• Iron deficiency is the most common cause
• Most common in women because of blood loss during
  menstruation.

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Increasing RBCs

• Individuals who live at high altitudes, where
  oxygen levels are low, produce more rbcs
• Many athletes train at high altitudes to benefit
  from this effect
• Other athletes take more drastic and illegal
  measure to increase the oxygen-carrying capacity
  of their blood and improve their performance.
• Injecting synthetic EPO
• Increases normal rbc volume from 45 to 65
• Athletic commissions test for EPO-like chemicals
• Blood doping
• Withdrawing and storing their rbcs and then
  reinjecting them before a competition.
• Athletic commissions test for cheaters by
  measuring the of rbcs in the blood volume
• Can be harmful? a combination of dehydration and
  blood already thickened by increasing rbcs can
  cause stroke, heart failure, and even death

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Leukemia

• Cancer of the wbcs, or leukocytes
• Cause a person to have an unusually high number
  of leukocytes, most of which do not function
  normally
• Overabundance of wbcs can crowd out rbcs and
  platelets, causing severe anemia and impaired
  clotting.
• Usually fatal unless treated

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Leukemia

• Treatment
• Not all cases respond to radiation and
  chemotherapy
• Alternative treatment is transplanting a healthy
  bone marrow tissue from a suitable donor into a
  patient whose own cancerous marrow has been
  destroyed.
• Such a patient requires lifelong treatment with
  drugs that suppress the tendency of some of the
  transplanted marrow cells to reject the cells
  of the recipient.
• To avoid the rejection problem, patients may be
  treated with their own bone marrow
• Marrow from the patient is removed, processed to
  remove as many cancerous cells as possible, and
  then reinjected.

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Leukemia

• Treatment (continued)
• Stem Cells
• Stems cells can be obtained from a donor or from
  the patient in three methods
• 1. Oldest method- whole bone marrow is harvested
  by inserting a large-bore needle into the pelvic
  bone.
• 2. More recent method- drugs are used to draw
  stem cells out of the marrow and into the blood.
• Donor is connected to a refrigerated centrifuge
  that separates blood components, removes the ones
  need for transplantation, and returns the rest.
• 3. newest method- gathers stem cells from
  umbilical cord blood.
• Cells can be stored for possible later use by the
  child or donated to a compatible recipient in
  need of a stem cell transplant.
• Injection of a few as 30 stem cells can
  repopulate the blood and immune system.

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• We will cover blood clotting when we discuss
  the Immune System ?