Le Grice: Cardiovascular Homestasis Flashcards
Homeostasis is?
Constancy of the internal environment and is a characteristic property of living organisms.
This is all dependent on feedback, which senses the output and compares it to a set point. If different, it changes the feedback to bring it back!
**Positive feedback is different, when it amplifies endlessly!
Although the body has feedback mechanisms, how is it different?
We do not have one single ‘set point’ as the body has multiple, overlapping points that are all trying to maintain their own control points or an appropriate constancy!
What is equilibrium in a closed system?
2 or more processes whose outputs are maintained by a common parameter, can operate at a stable equilibrium.
eg; MRAP: inc CO and decr Venous return.
This system works only when CO = VR (can only be mismatched for a few beats), where the 2 lines cross.
Whats happening here?
If you increase venous return (via venous constriction or blood transfusion), but not CO: will only increase to a certain point. limited @10L/min
If we increase CO (inotropic rate, decreased AL etc) but not the VR it will do the same with a max of about 8L/min
but if BOTH VR and CO are increased together you will get a huge increase in overall output (eg; exercise) and it will not work alone
How does the distribution of CO change during exercise, and why?
The organs supplied by the systemic circulation compete for blood flow and the proportion of the CO. The amount they receive is determined by the resistance to blood flow presented by its associated capillary network
@ Rest: CO distributed relatively uniformly, (lots to gut, kidney)
w exercise: blood directed preferential to exercising skeletal/cardiac muscle and skin. (although the liver, kidney and brain have a constant amount, this decreases as a proportion of the absolute CO)
The intrinsic and extrinsic mechanisms of cardiovascular control?
Intrinsic: local where acidotic or hypoxic tissues secrete components that dilate blood vessels to attract blood in the area.
Extrinsic:
Neural: PNS and SNS
Endocrine: Adr, RAAS, ADH and NP
There are lots of receptors and lots of ways to get messages around.
The Autonomic Nervous System innervation of the heart
S: top three ganglia of the sympathetic chain.
Superior cervical, middle cervical and stellate cervical
PS: Vagus Nerve (X)
Plexus Nerve: plexus of PS and S nerves on the surface of the heart
** heart issues are thought to be due to an imbalance of PS/S and sometimes ablation therapy will target these nerves!!
Parasympathetic Nerves?
Preganglionic fibres that originate in the brainstem carrying CN III, VII, IX and X. Synapse at ganglia located in or near the walls of the viscera that the supply and give rise to short postganglionicc viscera
Sympathetic Nerves?
preganglionic sympathetic axons originate in the thoracic lumbar region of the spinal cord T1-T12, L1-L3 and synapse in the paravertebral chain which innervates the viscera via relatively long postganglionic nerves
postganglionic sympathetic axons originate in the superior cervical, middle cervical and stellate ganglia (3 upper ganglia in the Paravertabral ganglion chain)
THe endocrine system: RAAS and NP, what do they do and how do they oppose each other?
RAAS: very important in regulating blood pressure, a big territory for drug input into controlling and increasing BP. Angiotensin II acts to:
- Increase sympathetic action
- Increase tubular H20, Na and Cl reabsorption and K excretion
- Increase aldosterone from adrenal g. = increase H20 reab
- Inc arteriolar vasoconstriction to inc Bf and BP
- Inc ADH from post pituitary = Inc H20
- Inc ANP secretion
Natriuretic Peptides: synthesized by the heart, brain and other organs. ANP (atrial) and BNP (brain but work in ventricles).Release by the heart is stimulated by atrial and ventricular distention, sympathetic stimulation, angiotensin II and endothelin usually in response to heart failure to help decrease BP and fluid retention.
- inhibit renin, so increase natriuresis and dec.blood volume
- Cause direct vasodilation
- BOTH lead to decreased blood pressure
Summarise the Cardiovascular and renal actions of Natriuretic peptides? what do these lead to?
