21. Integration of CVS responses - Haemorrhage

Question 1

How is central venous pressure measured?

Answer 1

• Central line into vein
• Catheter pushed to the same level as the heart
• Attached to saline solution and manometer
• Measured (low in haemorrhage)

Question 2

Which cation is involved in the SA nodes?

Answer 2

• Ca2+

* Not Na+ influx - very few sodium channels

Question 3

How does the body compensate for the drop in BP during a haemorrhage?

Answer 3

• Less firing of baroreceptors
• Parsympathetic drive decreases
• Sympathetic drive increases
• Heart rate increases

Question 4

How does noradrenaline lead to heart muscle contraction?

Answer 4

• Noradrenaline binds to β1 adrenoreceptor
• Increase in cAMP
• Activates protein kinase A
• Phosphorylation of:
- calcium channel on cell membrane - open for longer
- RyR - open for longer
• Also affect Ca2+ ATPase & phospholamban:
- inhibitory - pump Ca back into SR, more Ca in the SR, force of contraction increases
• Greater stroke volume

Question 5

How does noradrenaline lead to smooth muscle vasoconstriction?

Answer 5

• Noradrenaline binds to α-adrenoreceptor
• Increased production of IP3
• Binds to RyR - calcium influx
• Calcium binds to calmodulin
• Ca2+-CaM complex activates ‘myosin light change kinase’
• Phosporylates myosin light chains allowing them to form cross-bridges with actin
• Contraction => constriction
• Increased total peripheral resistance

Question 6

What happens to ADH secretion if there is a low venous return?

Answer 6

• Decreased left atrial pressure
• Increased ADH secretion
• Increased water & sodium retention
• Preserved blood volume

Question 7

How can lost blood volume be replaced in a clinical environment?

Answer 7

• Crystalloid solution - isotonic sodium chloride (lacks colloid so fluid tends to be pushed out of the blood vessels)
• Colloids - increases oncotic pressure
• Blood products - packed erythrocytes, fresh frozen plasma, whole blood is cross matched

Question 8

What are the the respiratory responses to a loss of blood volume?

Answer 8

• Chemoreceptors are sensitive to less O2, CO2 excess and H+ excess
(• located near carotid bifurcation and on aortic arch)
• Activation => excitation of vasomotor centre
• Increased sympathetic activity
• Increased BP
• Changes gas exchange and preserves the internal environment