Regulation of blood pressure cont.

Question 1

blood flow to any given organ depends on:

Answer 1

1. MAP (the driving pressure head)
2. resistance of local arterioles (which overrides sympathe4c effect)
3. vascularisation/open capillaries

Question 2

Several factors can detect and/or influence MAP:

Answer 2

• Baroreceptors in the aortic arch & carotid sinus sensitive to pressure > short-term
• Left atrial volume receptors & hypothalamic osmoreceptors > long-term
• Chemoreceptors in carotid & aortic arteries sensitive to low O2 & high H+ > short-term
• Cerebral cortex-hypothalamic pathway sensitive to behaviour & emotion, which influence MAP
• Hypothalamus sensitive to body temperature, which affects cutaneous arterioles & overrides regulation of MAP

Question 3

Resistance in arterioles 1 & 2 increase while CO is unchanged:

Answer 3

1. what happens to flow through vessels 1 & 2? - decrease
2. what happens to MAP? - increase
3. what happens to flow through vessels 3 & 4? - decrease

Question 4

Resistance in arterioles 1 & 2 increase while CO is unchanged:
2

Answer 4

4. Baroreceptor reflex compensates within seconds – what steps are involved in this response? - describe the reflex arc (look at previous lecture)
   - increase in arterial pressure
5. What happens to the hydrostatic/ultrafiltration pressure in the capillaries downstream of arterioles 1 & 2? - decreases

Question 5

L arterial volume receptors & hypothalamic osmoreceptors

Answer 5

regulate long-term responses in MAP

• long term changes have much volume in body
• regulating ECF volume = regulating blood plasma volume
• constricting arterioles increases TPR

Question 6

The cardiovascular system under stress: exercise

Answer 6

Marked changes occur in anticipation & at the onset of exercise:
• CO increases 2.5-fold with moderate exercise. And CO is re- distributed compared to rest:
- skeletal muscle, cardiac muscle & skin receive a greater proportion
- other organs receive less blood flow, but brain is maintained
• TPR reduced due to widespread vasodila4on in skeletal muscle
• MAP modestly increases
* wide spread vasodilation in running > net reduction in TPR

Question 7

The cardiovascular system under stress: hypertension

Answer 7

• Hypertension > 140/90 mmHg
• Two broad types:
- Secondary: known cause & accounts for 10% of cases, e.g. kidney disease
- Primary/Essential: unknown cause, accounts for 90% of cases, e.g. genetic, exacerbated by environmental factors
• Vicious cycle: damages vessel walls, atherosclerosis > increased TPR > further elevates BP

Question 8

The cardiovascular system under stress: hypertension

2

Answer 8

• Baroreceptors do not return blood pressure back to normal levels >new set-point?
• Increased workload on heart as it is now pumping against an increased TPR.

 Complicatons:
-  L ventricular hypertrophy > systolic heart
failure
-  Stroke (rupture of cerebral vessels)
-  Myocardial infarction (rupture of coronary
vessels)
-  Kidney failure
-  Vision loss

Question 9

The cardiovascular system under stress: hypotension

Answer 9

• Low blood volume for given vascular capacity or weakened heart
• Orthostatic (postural )hypotension:transient inadequacy in sympathetic activity
– Lying to standing > blood pools in lower leg veins > reduced venous return >reduced SV, CO & MAP > reduced baroreceptor response > dizziness or fainting
• Circulatory shock:extremely low blood pressure such that blood flow to tissues is compromised.
Causes: hypovolemic shock, cardiogenic shock, vasogenic shock, & neurogenic shock