Sapolsky Chapter 3

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Sapolsky Chapter 3

• Stroke, Heart Attack, and Voodoo Death

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Heart has 4 chambers

• Blood enters the right atrium from body and is
  squeezed into the right ventricle.
• From there it goes to the lungs to be oxygenated.
• It then goes to left atrium, which squeezes it
  into left ventricle.
• From there the oxygenated blood is pumped to the
  body.

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Contractions

• The 2 atria contract simultaneously, sending
  blood to the ventricles.
• The 2 ventricles then contract together, sending
  blood to the lungs or body.

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• What are the 2 numbers that designate blood
  pressure?
• What is the difference between systolic and
  diastolic blood pressure?

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• The ventricular contraction is systole.
• The time between ventricular contractions is
  diastole.
• The heart is supplied with blood only during
  diastole.

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• The average human heart beats about 72
  times/minute at rest.
• Hearts of well-conditioned athletes beat more
  slowly at rest.
• Why is this an advantage?
• How do they manage to pump more slowly and still
  send enough blood to the body?

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How does it work?

• The sino-atrial (SA) node (back of right atrium)
  generates an impulse ? atria contract.
• This is carried to atrio-ventricular (AV) node,
  which delays the impulse before sending it to AV
  bundle.
• Why is the delay important?

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How does it work?

• The delay allows the atria to empty before the
  ventricles contract.
• The AV bundle fibers are very fast-conducting and
  innervate the bottom of the heart first.
• Therefore, the contraction begins at the bottom
  of the ventricles and squirts the blood up
  through the appropriate arteries.

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How does it work?

• The heart fibers are all interconnected (called a
  syncytium).
• When one fiber is excited, the action potential
  spreads to all of them.
• Muscle is like neurons inflow of sodium (Na)
  and calcium (Ca) depolarizes it.

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How does it work?

• Heart tissue is self-excitatory.
• Na and Ca slowly leak in.
• The SA node has the fastest rate of
  self-excitation.
• It excites the rest of the heart, and before the
  rest of the heart can re-excite itself, the SA
  node strikes again!
• If SA is blocked, rest of heart contracts 15-40
  times/minute.

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The Cardiovascular Stress Response

• Get the heart to beat faster Increase SNS tone,
  decrease PNS tone
• Norepinephrine (NE) and epinephrine (Epi)
  increase slow inflow of Na and Ca ? increase
  rate of re-excitation in SA node.
• This Ca also increases contractility.
• SNS terminals also excite AV node and whole
  myocardium enhances contractility everywhere.

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PNS

• Vagus nerve (via acetylcholine, ACh) decreases
  rate by decreasing the slow inflow of Na and
  Ca and by increasing the subsequent outflow of
  potassium (K).
• Acts at SA and AV nodes.
• May treat SNS-driven heart attack by gagging or
  massage of carotid arteries ? activate vagal
  reflexes ? PNS counteracts SNS.

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Increase blood pressure

• Sapolskys hose analogy
• To squirt wateror blooda long way
• Small diameter, relatively rigid hose.
• Not 3 ft in diameter with consistency of a
  marshmallow.

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Cardiovascular system

• Arteries arterioles
• Carry blood from heart to body
• Wrapped with circular muscle
• SNS causes muscle to tighten ? increase pressure
• Veins venules return blood to the heart
• Capillaries fine meshwork of vessels connecting
  arterial venous systems.

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Arteries and veins
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Capillaries
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Capillaries

• All exchanges of fluid, nutrients, and wastes
  between blood and tissue occur across capillary
  walls.
• Capillary walls usually only 1 cell thick.
• Only 1 blood cell at a time can pass through.

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Lymphatic system

• Fluid that passes from capillaries into tissue
  interstitial fluid
• Some interstitial fluid is returned to blood in
  the venous side of the capillary system.
• The rest accumulates in lymph vessels.
• Lymph nodes along these vessels cleanse the lymph
  before returning it to veins.

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What
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What causes the fluid to return to the venules?

• Increased pressure from fluid in tissue, compared
  to decreased pressure in the venous system.
• Due to loss of so much fluid from capillaries.

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Functions of the circulatory system

• Transport oxygen and nutrients to tissues.
• Remove wastes from tissues.

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Why do we need adequate blood pressure?

• Extrude plasma from leaky capillaries so it can
  deliver oxygen and nutrients and pick up wastes.
• Pump blood against gravity to upper parts of
  body.

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How does SNS direct blood to active muscles,
heart brain?

• Relative distribution of alpha and beta
  adrenergic receptors.
• NE ? alpha ? constricts blood vessels in
  nonactive muscles and relaxes intestines.
• Epi ? beta ? increase heart rate, dilates vessels
  in active muscle.
• Also, metabolites in active muscle dilate walls

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Final trick Conserve fluid

• How?
• Kidney conserves water.
• Vasopressin from posterior pituitary
• Aldosterone from adrenal cortex

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Kidney
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Kidney actively retains water.

• Blood pressure in glomerulus ? plasma to leave,
  carrying salt, glucose, amino acids other small
  molecules into Bowmans capsule collecting
  tubule.
• This fluid is, for practical purposes, now
  outside the body ? urine
• 180 liters/day!!!

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How do we conserve the water?

• Pump Na back into body.
• Cl- follows passively electrical attraction
• H2O follows passively osmotic pressure
• Aldosterone (from adrenal cortex) increases Na
  pumping.
• Vasopressin (ADH) inserts aquaporins into wall of
  tubule, which let H20 pass through.
• When open, an aquaporin channel allows 3 billion
  molecules of water to pass through each second!!

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What is diabetes insipidus?

• Passing through insipidly
• Lack of vasopressin (ADH) not enough aquaporins
  inserted ? pass 25 liters of urine/day!
• Normally, only 1-2 liters/day

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Chronic stress and cardiovascular disease

• Repeated overuse ? damage to heart blood
  vessels (hose you buy from Sears)
• Branching (bifurcation) of vessels ? turbulence
  at branch points ? damage to lining.
• Fatty acids glucose work into lining,
  thickening it.
• Fatty foam cells join the fray ? plaques

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Chronic stress and cardiovascular disease

• Epi from adrenal medulla ? platelets stickier
• Potentially adaptive decrease bleeding
• But also ? clots that stick to injured area
• All of above ? atherosclerosis

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Atherosclerosis
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Atherosclerosis

• Purely social stress ? atherosclerosis in mice
  and monkeys.
• Jay Kaplan subordinate monkeys got
  atherosclerosis.
• So did dominant males in unstable social groups
• Even with low fat diet
• Hot reactors were worst
• Risk decreased with beta-blocker drugs

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Definitions

• Claudication blockage of blood flow to lower
  part of body.
• Coronary artery disease decreased blood supply
  to heart.
• Stroke blockage of blood supply to brain.

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Sudden Cardiac Death

• Ventricular arrhythmia ventricles contract too
  early or too late.
• Ventricular fibrillation interconnected muscle
  fibers contract randomly, rather than all working
  together ? no blood pumped out of ventricles ?
  ischemia of heart.
• Diseased muscle more excitable, may not wait for
  SA and AV nodes.

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Fatal Pleasures

• Even very good news can ? SNS ? heart attack.
• Rage and ecstasy, grief and triumph all
  represent challenges to allostatic equilibrium.
• Elie Wiesel The opposite of love is not hate.
  The opposite of love is indifference.

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Voodoo Death

• Psychophysiological death occurs when one gives
  up hope.
• Disagreement whether due to massive PNS or
  massive SNS activity.

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Personality cardiac disease

• Individual differences in vulnerability to
  cardiac disease
• Genetic factors
• Life styles
• Personality factors

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Summary

• Path of blood
• Rt. Atrium ? Rt. Ventricle ? lungs ?
• Left atrium ? left ventricle ? body
• Timing of heart beats
• Pacemaker Sinoatrial (SA) node
• Delay Atrioventricular (AV) node
• Fast AV bundle to bottom of ventricles

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Summary

• Stress
• Epi NE ? Na Ca ? heart rate
  contractility
• Plasma nutrients leak out of capillaries
  return either to venules or lymph system.
• Kidney conserves H2O by pumping Na back into
  body Cl- H2O follow passively.
• Aldosterone ? Na pumping
• Vasopressin (ADH) aquaporins ? H2O flow

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Summary

• Chronic stress
• High BP ? damage to vessels ? plaques ?
  atherosclerosis
• Epi ? sticky platelets ? clotting
• Major acute stress ? SNS ? ventricular
  fibrillation, especially if heart was previously
  damaged.