1) When a person moves from a sitting to a standing position, blood temporarily
accumulates in the leg veins due to the effect of gravity.
a) Identify potential problems with this effect
b) Describe the physiological response to this daily event
You do not need to include intracellular second messenger pathways in this answer. [10
marks]
a) If blood accumulates in the veins, decreases venous return (VR)
VR  decrease end-diastolic volume (EDV)  stroke volume(SV)  cardiac
output (CO)   mean arterial pressure (MAP)
also  venous pressure (Pv) in legs   capillary pressure (Pc)   NFP  more fluid
out legs (edema)
b) Response:
MAP detected by baroreceptors   AP from baroreceptors   SNS activity
 SNS activity:
 heart rate (HR)
 contractility  SV
 vasoconstriction  TPR
 venoconstriction  Psf  VR  SV
Since MAP = HR x SV x TPR (SV = EDV-ESV)
All of these will lead to  MAP, restoring to normal
Standing will lead to muscle activity and muscle pumps will help move blood from
legs help VR
Since SNS more effective at vasoconstriction than venoconstriction, the net effect on
fluid movement is to  Pc and  NFP, therefore less fluid out.
(as MAP returns to normal NFP to normal and excess fluid returned by lymph)
Compare and contrast the function of the parasympathetic and sympathetic nervous
system in regulation of cardiac heart rate and contractility. Include second messenger
pathways where relevant [7 marks]
Contractility
PNS little role since PNS doesn’t innervate ventricle (or could say slight role in
contractility)
SNS enhances contracility – acts through receptor to increase cAMP, increase PKA.
PKA increase L-type Ca channel (DHP or dihyropyridine receptor) activity, increase
rynaodine receptors, and increase calcium pump activity
HR
HR set by number of open funny sodium channels
Number of open channels a function of cAMP
SNS increase heart rate – NorEpinephrine (or Epinephrine) acts on  receptors
activates adenylate cyclase, increases cAMP
PNS decrease heart rate – Acethycholine acts on mAchR (muscarininc type Ach)
receptors, inhibits adenylate cyclase, decreases cAMP
3) During exercise the muscles require increased blood flow to maintain their function,
but SNS activity is greatly increased during physical activity. Explain the mechanism that
ensures increased blood flow to the muscles during exercise. Include second messenger
pathways where relevant [5 marks]
Blood flow a function of resistance
Resistance a function of blood vessel radius (inversely proportional to radius4)
Vessel radius controlled by  and  adrenergic receptors
 causes constriction through DAG/IP3 pathway to increase Ca, leading to smooth
muscle contraction
 causes dilation through cAMP/PKA
most vessels have more  than  so if SNS activity goes up, most vessels contstrict
vessels in the skeletal muscles have more  than  so if SNS is up vessels dilate
also increase SNS, leads to increase epinephrine from adrenal medulla, this further dilates
since vessels in muscle dilate, resistance goes down and flow goes up
4) Answer 2 of the following: [3 marks each=6]
a. The concept of autoregulation implies constant blood flow over a range of
pressure. Explain the vascular changes that are necessary for this to happen.
b. Why would increased parasympathetic nervous system activity decrease
venous return?
c. Determine the direction of fluid flow in a capillary bed if there is a reduction
in plasma protein concentration. Explain why
a) autoregulation indicates flow (Q) is constant.
Q = P/Resistance
If Q=constant and pressure goes up (or changes or goes down)
Then resistance must go the same way (if pressure up, resistance up Q=K) or radius
must go opposite way (if pressure is up, the radius gets smallet Q=K)
Vessels contract myogenically to decrease radius
b)
increase PNS  HR   Cardiac output (CO), since CO=VR, VR
c)
NFP = (PIC-PIF)-(IC-IF)
if plasma protein goes down, IC-IF goes down and NFP goes up. Therefore more fluid
moving out of capillary.