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