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19-1  Amount ejected by ventricle in 1 minute  Cardiac Output = Heart Rate x Stroke Volume  about 4 to 6L/min at rest  vigorous exercise  CO to 21.

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Presentation on theme: "19-1  Amount ejected by ventricle in 1 minute  Cardiac Output = Heart Rate x Stroke Volume  about 4 to 6L/min at rest  vigorous exercise  CO to 21."— Presentation transcript:

1 19-1  Amount ejected by ventricle in 1 minute  Cardiac Output = Heart Rate x Stroke Volume  about 4 to 6L/min at rest  vigorous exercise  CO to 21 L/min for fit person and up to 35 L/min for world class athlete  Cardiac reserve: difference between a persons maximum and resting CO   with fitness,  with disease

2 19-2  Pulse = surge of pressure in artery  infants have HR of 120 bpm or more  young adult females avg bpm  young adult males avg. 64 to 72 bpm  HR rises again in the elderly  Tachycardia: resting adult HR above 100  stress, anxiety, drugs, heart disease or  body temp.  Bradycardia: resting adult HR < 60  in sleep and endurance trained athletes

3 19-3  Positive chronotropic agents  HR  Negative chronotropic agents  HR  Cardiac center of medulla oblongata  an autonomic control center with two neuronal pools: a cardioacceleratory center (sympathetic), and a cardioinhibitory center (parasympathetic)

4 19-4  Cardioacceleratory center  stimulates sympathetic cardiac nerves to SA node, AV node and myocardium  these nerves secrete norepinephrine, which binds to  - adrenergic receptors in the heart (positive chronotropic effect)  CO peaks at HR of 160 to 180 bpm  Sympathetic n.s. can  HR up to 230 bpm, (limited by refractory period of SA node), but SV and CO  (less filling time)

5 19-5  Cardioinhibitory center stimulates vagus nerves  right vagus nerve - SA node  left vagus nerve - AV node  secretes ACH (acetylcholine) which binds to muscarinic receptors  nodal cells hyperpolarized, HR slows  vagal tone: background firing rate holds HR to sinus rhythm of 70 to 80 bpm  severed vagus nerves (intrinsic rate-100bpm)  maximum vagal stimulation  HR as low as 20 bpm

6 19-6  Higher brain centers affect HR  cerebral cortex, limbic system, hypothalamus  sensory or emotional stimuli (rollercoaster, IRS audit)  Proprioceptors  inform cardiac center about changes in activity, HR  before metabolic demands arise  Baroreceptors signal cardiac center  aorta and internal carotid arteries  pressure , signal rate drops, cardiac center  HR  if pressure , signal rate rises, cardiac center  HR

7 19-7  Chemoreceptors  sensitive to blood pH, CO 2 and oxygen  aortic arch, carotid arteries and medulla oblongata  primarily respiratory control, may influence HR   CO 2 (hypercapnia) causes  H + levels, may create acidosis (pH < 7.35)  Hypercapnia and acidosis stimulates cardiac center to  HR

8 19-8  Affect heart rate  Neurotransmitters - cAMP 2 nd messenger  catecholamines (NE and epinephrine)  potent cardiac stimulants  Drugs  caffeine inhibits cAMP breakdown  nicotine stimulates catecholamine secretion  Hormones  TH  adrenergic receptors in heart,  sensitivity to sympathetic stimulation,  HR

9 19-9  Electrolytes  K + has greatest effect  hyperkalemia  myocardium less excitable, HR slow and irregular  hypokalemia  cells hyperpolarized, requires increased stimulation  Calcium  hypercalcemia  decreases HR  hypocalcemia  increases HR

10 19-10  Governed by three factors: 1. preload 2. contractility 3. afterload  Example   preload or contractility causes  SV   afterload causes  SV

11 19-11  Amount of tension in ventricular myocardium before it contracts   preload causes  force of contraction  exercise  venous return, stretches myocardium (  preload), myocytes generate more tension during contraction,  CO matches  venous return  Frank-Starling law of heart - SV  EDV  ventricles eject as much blood as they receive  more they are stretched (  preload) the harder they contract

12 19-12  Contraction force for a given preload  Positive inotropic agents  factors that  contractility  hypercalcemia, catecholamines, glucagon, digitalis  Negative inotropic agents  factors that  contractility are  hyperkalemia, hypocalcemia

13 19-13  Pressure in arteries above semilunar valves opposes opening of valves   afterload  SV  any impedance in arterial circulation  afterload  Continuous  in afterload (lung disease, atherosclerosis, etc.) causes hypertrophy of myocardium, may lead it to weaken and fail

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15  What’s the difference between arteries and veins?  It’s NOT oxygen saturation!

16  If the heart is the body’s “pump,” then the “plumbing” is the system of arteries, veins, and capillaries.  Arteries carry blood away from the heart.  Veins carry blood toward the heart.  Capillaries allow for exchange between the bloodstream and tissue cells.

17 20-17  Most common route  heart  arteries  arterioles  capillaries  venules  veins  Portal system  blood flows through two consecutive capillary networks before returning to heart  hypothalamus - anterior pituitary  found in kidneys  between intestines - liver

18 20-18  Point where 2 blood vessels merge  Arteriovenous shunt  artery flows directly into vein  Venous anastomosis  most common, blockage less serious  alternate drainage of organs  Arterial anastomosis  collateral circulation (coronary)

19 20-19  Blood flow: amount of blood flowing through a tissue in a given time (ml/min)  Perfusion: rate of blood flow per given mass of tissue (ml/min/g)  Important for delivery of nutrients and oxygen, and removal of metabolic wastes  Hemodynamics  physical principles of blood flow based on pressure and resistance

20 20-20  Force that blood exerts against a vessel wall  Measured at brachial artery of arm  Systolic pressure: BP during ventricular systole  Diastolic pressure: BP during ventricular diastole  Normal value, young adult: 120/75 mm Hg  Pulse pressure: systolic - diastolic  important measure of stress exerted on small arteries  Mean arterial pressure (MAP) is an estimate of tissue perfusion:  Formula is: MAP ≈ DP + ⅓(DP-SP)  Less than 60 mmHg leads to tissue damage

21 20-21

22 20-22  Importance of arterial elasticity  expansion and recoil maintains steady flow of blood throughout cardiac cycle, smoothes out pressure fluctuations and  stress on small arteries  BP rises with age: arteries less distensible  BP determined by cardiac output, blood volume and peripheral resistance

23 20-23  Hypertension  chronic resting BP > 140/90  consequences  can weaken small arteries and cause aneurysms  Hypotension  chronic low resting BP  caused by blood loss, dehydration, anemia An aneurysm (or aneurism) is a localized, blood-filled dilation (balloon-like bulge) of a blood vessel caused by disease or weakening of the vessel wall. Most common in the aorta and the arteries at the base of the brain.

24 20-24  Blood viscosity - by RBC’s and albumin   viscosity with anemia, hypoproteinemia   viscosity with polycythemia, dehydration  Vessel length  pressure and flow  with distance (friction)  Vessel radius - very powerful influence over flow (ml/min)  most adjustable variable, controls resistance quickly  vasoconstriction and vasodilation  arterioles can constrict to 1/3 of fully relaxed radius Know these 3 factors

25 20-25  Local control  Neural control  Hormonal control

26 20-26  Local control  Autoregulation – the ability of tissues to regulate their own blood supply.  Metabolic wastes stimulate vasodilation  Neural control  Hormonal control

27 20-27  Vasomotor center of medulla oblongata:  sympathetic control stimulates most vessels to constrict, but dilates vessels in skeletal and cardiac muscle  integrates three autonomic reflexes  baroreflexes (pressure)  chemoreflexes (esp. pH)  medullary ischemic reflex (brain perfusion)  stress, pain, anger

28 20-28  Changes in BP detected by stretch receptors (baroreceptors), in large arteries above heart  aortic arch  aortic sinuses (behind aortic valve cusps)  carotid sinus (base of each internal carotid artery)  Autonomic negative feedback response  baroreceptors send constant signals to brainstem   BP causes rate of signals to rise, inhibits vasomotor center,  sympathetic tone, vasodilation causes BP    BP causes rate of signals to drop, excites vasomotor center,  sympathetic tone, vasoconstriction and BP 

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