Cardiovascular Haemostasis

Question 1

How can an equilibrium in a closed system be achieved?

Answer 1

Closed systems containing two or more processes who’s outputs are determined by a common parameter can operate at a stable equilibrium. e.g. the equilibrium between venous return and cardiac output

Question 2

The equilibrium between cardiac and vascular function

Answer 2

MRAP reflects extent of right heart filling
Inc. MRAP increases cardiac output
systemic venous return to heart inversely proportional to MRAP.
Venous return stops if MRAP= pressure driving blood back to heart, reductions in MRAP result in proportionate increase in venous return till MRAP = extravascular pressure. Then veins in thoracic cavity collapse limiting further venous return

Question 3

How do vascular and cardiac function change during exercise?

Answer 3

At rest in typical adult human CO = 5-6L/min but with vigorous exercise this could increase 5x
Venous: marked reduction in total peripheral resistance with increase in smooth muscle activity in veins. Together this increases pressure in the peripheral veins driving blood back to the heart, therefore increasing MRAP. so through increased cardiac filling can drive cardiac output to around 13 L/min. if the cardiac function regulation is not altered.
Changes in the cardiac function alone produce more vigorous cardiac function and a reduction in MRAP, max cardiac output that can be achieved here is 8L/min.
Conclusion: very large increases in cardiac output as seen in exercise can only be achieved if cardiac function is enhanced sustainably. additionally vascular function must also be enhanced to ensure venous return and cardiac output are matched. In exercise this occurs in an integrated fashion so that an increase in CO can be achieved without a change in MRAP.

Question 4

Changes in distribution of cardiac output during exercise

Answer 4

Proportion of cardiac output that each organ receives is determined by resistance to blood flow. At rest distribution relatively uniform.
With vigorous exercise blood is preferentially distributed to exercising skeletal and cardiac muscle (have immediate requirement for metabolic support). Blood flow to brain, constant. But flow to the liver, spleen, GI tract and kidneys (during short term can tolerate reduction in BF), decreases as a proportion of cardiac output and absolutely.

Question 5

What are the principal extrinsic mechanisms employed that integrate and optimise homeostatic responses?

Answer 5

autonomic and endocrine systems

Question 6

Parasympathetic pre-ganglionic fibers, origin, travel, terminate?

Answer 6

originate in the brainstem and travel in cranial nerves III, VII, IX, X, and also originate in segments S2-S4.
Synapse at ganglia located near the walls of the viscera they supply and give rise to short post ganglionic axons

Question 7

Pre-ganaglionic sympathetic axons

Answer 7

originate in thoracolumbar region of spinal cord, and most synapse in the paravertebral ganglion chain which innervates the viscera via long post ganglionic nerves.
Some pass through the paravertebral ganglion chain and synapse at collateral ganglia close to the organs and glands they supply

Question 8

Post ganglionic sympathetic nerves to the head, neck, lungs, heart

Answer 8

originate in the superior cervical, middle cervical and stellate ganglia, these are the three upper ganglia in the paravertebral ganglion chain

Question 9

The adrenal medulla

Answer 9

synthesises and stores endogenous catecholamines adrenaline and noradrenaline. Recipes pre ganglionic sympathetic innervation and activation causes adrenaline and to a lesser extent noradrenaline release into blood stream.

Question 10

The juxtaglomerular apparatus contains..? and is released in response to?

Answer 10

granules of the enzyme renin and this is released into the blood stream in response to?

1. sympathetic stimulation via B1 receptors
2. Decreased pressure in the afferent arterioles
3. Decreased sodium load at the macula dense

Question 11

Effects of angiotensin II on the cardiovascular system

Answer 11

• Penetrates the blood brain barrier, in hypothalamus activates descending pathways which modulate sympathetic outflow to the cardio system and adrenal medulla, facilitates ADH synthesis and stimulates thirst.
• Potentiates ganglionic transmission which facilitates neurotransmission at the paravertebral ganglia.
• Increases synthesis and release of NA from sympathetic nerve terminals and inhibits its reuptake. Therefore sympathetic transmission is facilitated in the heart and the vessels.
• promotes increased formation and release of aldosterone from the adrenal cortex with a resultant increase in reabsorption of sodium by the renal tubules.

Question 12

ADH

Answer 12

regulates renal water handling, a vasoconstrictor at physiological concentrations

Question 13

ANP, stored? released in response to?

- Elevated levels are found in?

Answer 13

synthesised, stored and released by atrial myocytes in response to: 
- atrial distension 
- Angiotensin II stimulation 
- endothelin 
- sympathetic stimulation 
hypervolemic states and CHF

Question 14

BNP

Answer 14

synthesised in ventricles

Marker for heart failure

Question 15

Natriuretic peptide actions and neutral endopeptidase

Answer 15

NEP is a circulating enzyme that degrades natriuretic peptides. Inhibition of NEP increases circulating levels of NP and potentiates their effects. 
CV and Renal actions of NP 
- Natriuresis (sodium excretion in the urine)
- Diuresis 
- Improve GFR and filtration fraction 
- Inhibit renin release, therefore decrease circulating AII, and aldosterone. 
- Systemic vasodilatation 
- Arterial hypotension 
- Reduced venous pressure 
Together these action lead to: 
- Dec BV 
- DEC arterial pressure 
- Dec, central venous pressure 
- Dec CO 

Is a counter regulatory system for RAAS