1. CARDIOVASCULAR - 4
CARDIAC OUTPUT

2. CARDIAC OUTPUT

3. cardiac output = stroke volume X heart rate
Cardiac output – the volume of blood pumped each minute by each ventricle:
cardiac output = stroke volume X heart rate
(ml/minute) (ml/beat) (beats/min)
Average heart rate = 70 bpm
Average stroke volume = 70−80 ml/beat
Average cardiac output = 5,500 ml/minute

4. Spontaneous depolarization occurs at SA node when HCN channels open, allowing Na+ in.
Open due to hyperpolarization at the end of the preceding action potential
Sympathetic norepinephrine and adrenal epinephrine keep HCN channels open, increasing heart rate.
Parasympathetic acetylcholine opens K+ channels, slowing heart rate.
Controlled by cardiac center of medulla oblongata

6. Regulation of Stroke Volume
Regulated by three variables:
End diastolic volume (EDV): volume of blood in the ventricles at the end of diastole
Sometimes called preload
Stroke volume increases with increased EDV.
Total peripheral resistance: Frictional resistance in the arteries
Inversely related to stroke volume
Called afterload
Contractility: strength of ventricular contraction
Stroke volume increases with contractility

7. Frank-Starling Law of the Heart
OTTO FRANK
ERNEST STARLING
Increased EDV results in increased contractility and thus increased stroke volume.

8. Frank-Starling Law of the Heart

9. Extrinsic Control of Contractility
Contractility – strength of contraction at any given fiber length
Sympathetic norepi/adrenal epi can increase contractility by making more Ca2+ available to sarcomeres. Positive inotropic effect. (also increases rate)
Parasympathetic acetylcholine will decrease heart rate which increases EDV  increases contraction strength  increases stroke volume, but not enough to compensate for slower rate, so cardiac output decreases.
Inotrope – an agent that alters strength of muscle contraction.
Chronotrope – agent the alters contraction rate.

10. Regulation of Cardiac Output

11. EDV is controlled by factors that affect venous return:
Total blood volume
Venous pressure (driving force for blood return)
Veins have high compliance - stretch more at a given pressure than arteries (veins have thinner walls).
Veins are capacitance vessels – 2/3 of the total blood volume is in veins
They hold more blood than arteries but maintain lower pressure.

12. Factors in Venous Return
Pressure difference b/w vena cava (0 mmHg) and venules (10 mmHg)
Sympathetic nerve activity to stimulate smooth muscle contraction in venous walls
Skeletal muscle pumps
Pressure difference between abdominal and thoracic cavities (respiration)
Blood volume

13. BLOOD VOLUME

14. Body Water Distribution

15. Net Filtration Pressure
Net filtration pressure is the hydrostatic pressure of the blood in the capillaries minus the hydrostatic pressure of the fluid outside the capillaries
Hydrostatic pressure at arteriole end is 37 mmHg and at the venule end is 17 mmHg
Hydrostatic pressure of interstitial fluid is 1 mmHg
Net filtration pressure is 36 mmHg at arteriole end and 16 mmHg at venule end

16. Colloid osmotic pressure
Due to proteins dissolved in fluid
Blood plasma has higher colloid osmotic pressure than interstitial fluid. This difference is called oncotic pressure.
Osmotic pressure of plasma = 25 mmHg;
Osmotic pressure of interstitial fluid = negligible
This favors the movement of fluid into the capillaries.

17. Starling Forces are opposing forces that affect the distribution of fluid across the capillary
Fluid movement is proportional to: (pc + πi) - (pi + πp) fluid out fluid in pc = Hydrostatic pressure in capillary πi = Colloid osmotic pressure of interstitial fluid pi = Hydrostatic pressure of interstitial fluid πp = Colloid osmotic pressure of blood plasma

19. --Excessive accumulation of interstitial fluids
Edema
--Excessive accumulation of interstitial fluids
--May be the result of:
High arterial blood pressure
Venous obstruction
Leakage of plasma proteins into interstitial space
Myxedema (excessive production of mucin in extracellular spaces caused by hypothyroidism)
Decreased plasma protein concentration
Obstruction of lymphatic drainage
Severe Edema of Elephantiasis

20. Regulation of blood volume by the kidney
The glomerulus filters out 180 L/day of water
Urine volume is about 1.5 L of water
The kidney excretes more or less water depending on the needs of the body, and this is under the control of hormones

21. Negative Feedback Control of Blood Volume by ADH

22. Renin-Angiotensin-Aldosterone System

23. Angiotensin converting enzyme inhibitors (ACE inhibitors)
ACE inhibitors lower blood pressure. Examples: captopril, enalapril, Lisinopril help to treat hypertension, heart failure, stroke Likewise, losartan and valsartan are angiotensin receptor blockers, which have the same effect to lower blood pressure

24. Negative feedback correction of increased venous return
Atrial natriuretic peptide:
Natrium = sodium
Uresis = making water natriuresis = excreting water with salt