vascular regulation

Question 1

describe the fluid compartments

Answer 1

60% of body weight = fluid

• intracellular (2/3)
• extracellular (1/3)
  - interstitial fluid
  - intravascular fluid

Question 2

water movement between ISF and plasma

Answer 2

• dependent on the pressure within the vascular system

net fluid movement dependent on:

• K = capillary permeability
• capillary hydrostatic pressure
• tissue pressure
• osmotic pressure

Question 3

water between cells and interstitial spae

Answer 3

• driven by osmotic gradients
• cell volume is determined by Na+ and water balance in the extracellular compartment
• osmosis

Question 4

how and why is ADH released

Answer 4

hypothalamic nuclei (supraoptic & paraventricular) sense changes in plasma osmolality by altering their volume. This causes synthesis and release of ADH from the posterior pituitary gland

increased osmolality also stimulates thirst centres in the hypothalamus

Question 5

flow effect of blood volume loss

Answer 5

if BV is reduced the cardiac filling is decreased. This decreases the activity of cardiac receptors.
- if >10% loss of BV, arterial pressure falls which causes a reduced firing in arterial baroreceptors

Question 6

what are the neuro-humoral effects of decreased cardiovascular receptors (baroreceptor firing)

Answer 6

reduced afferent input into the central nervous system:

immediate response is to increase HR and contractile state, increase SNS

• increase ADH quick response
• sympathetic tone (vasoconstriction) - increase renin etc
• increased thirst

Question 7

restoration of red cells and other blood constituents

Answer 7

• albumin transferred into circulation quickly
• most plasma proteins replaced (hepatic synthesis) in 3-4 days
• red cell synthesis complete after 4-8 weeks

Question 8

define non-hypotensive haemorrhage

Answer 8

with a blood loss of <10% MAP is maintained although pulse pressure is reduced
- not a huge change in baroreceptor firing

Question 9

define hypotensive haemorrhage

Answer 9

with blood loss of >10% there is a graded fall in systemic arterial pressure
- both cardiac and arterial baroreceptors sense

Question 10

define hemorrhagic shock

Answer 10

where blood loss is extreme and remains uncompensated for long periods, replacement of volume deficit may not restore CVS homeostasis

Question 11

systemic arterial baroreceptors

Answer 11

• firing increases w/ increased MAP
• baroreceptor firing curve shifts (resets) w/ high maintained MAP
• also effected my neural and paracrine inputs