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Cardiac Output (CO) Amount ejected by ventricle in 1 minute

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Presentation on theme: "Cardiac Output (CO) Amount ejected by ventricle in 1 minute"— Presentation transcript:

1 Cardiac Output (CO) 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 Heart Rate 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 Chronotropic Effects 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 Sympathetic Nervous System
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 Parasympathetic Nervous System
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 Inputs to Cardiac Center
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 Inputs to Cardiac Center
Chemoreceptors sensitive to blood pH, CO2 and oxygen aortic arch, carotid arteries and medulla oblongata primarily respiratory control, may influence HR  CO2 (hypercapnia) causes  H+ levels, may create acidosis (pH < 7.35) Hypercapnia and acidosis stimulates cardiac center to  HR

8 Chronotropic Chemicals
Affect heart rate Neurotransmitters - cAMP 2nd 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 Chronotropic Chemicals
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 Stroke Volume (SV) Governed by three factors: Example preload
contractility afterload Example  preload or contractility causes  SV  afterload causes  SV

11 Preload 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 Contractility 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 Afterload 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

14 Blood vessels and circulation

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 Circulatory Routes Most common route Portal system
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 Anastomoses 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 Principles of Blood Flow
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 Blood Pressure 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 BP Changes With Distance

22 Blood Pressure 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 Abnormalities of Blood Pressure
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 Peripheral Resistance
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 Regulation of BP and Flow (ml/min)
Local control Neural control Hormonal control

26 Regulation of BP and Flow (ml/min)
Local control Autoregulation – the ability of tissues to regulate their own blood supply. Metabolic wastes stimulate vasodilation Neural control Hormonal control

27 Neural Control of BP and Flow
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 Neural Control: Baroreflex
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 

29 Baroreflex Negative Feedback Response

30 That’s it for today

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