Regulation of tissue blood flow L9

Question 1

what forms the main resistance to blood flow in systemic circulation
what does this factor control

Answer 1

arterioles
arterioles control total peripheral blood pressure
- it decreases at the levels of the arterioles (in systematic circulation)

Question 2

what do arterioles have a good supply of

Answer 2

vascular smooth muscle

Question 3

describe structure of arteriole

Answer 3

outer layer is smooth muscle
middle layer is basal lamina
inside layer is endothelial cells

Question 4

what is tissue vessel tone and what happens when it is regulated

Answer 4

The smooth muscle cells surrounding arterioles are normally partially contracted
This ‘tone’ can be regulated (increased or decreased) so affecting the radius of the vessel and therefore Resistance, and thus blood flow.

Question 5

what is the major role of arterioles

Answer 5

match local blood flow to metabolic need
- metabolic need increases during exercise, vessle tone decreases as smooth muscle relaxes so the radius increases - the resistance to flow decreases which increases blood flow

Question 6

what is the difference between vasoconstriction and vasodilation

Answer 6

C: smooth muscle contracts
D: smooth muscle relaxes

Question 7

what determines blood flow through an individual vessel

Answer 7

the resistance

Question 8

what happens if blood flow to a particular tissue needs to be increased

Answer 8

other blood vessels will constrict allowing the other to dilate
- Resistance, and therefore flow, is controlled by the vascular smooth muscle surrounding arterioles/sphincters

Question 9

what Three major physiological mechanisms regulate arteriolar radius

Answer 9

1. Local control
2. Hormonal control
3. Neural control
   - regulate arteriolar radius by affecting the contractile state of the surrounding vascular smooth muscle

Question 10

what are the two types of local control

Answer 10

1.autoregulation of tissue blood flow
2. metabolic control of tissue blood flow

Question 11

describe autoregulation of tissue blood flow

Answer 11

known as myogenic response
- involves the intrinsic activity of smooth muscle
- pressure high in artery, increased blood flow casues smooth muscle on arteriole to stretch
- allows more Ca in which causes contraction (myogenic vasoconstriction)
- brings the flow back to original level
Flow stays constant with increasing pressure
Safety mechanism to prevent damage to delicate blood vessels due to high pressure

Question 12

what can overcome autoregulation

Answer 12

high metabolism

Question 13

describe metabolic control of tissue blood flow

Answer 13

at high metabolism levels, there are higher amounts of vasodilators
- CO2, lactate, temp, adenosine from ATP, K+
and less amounts of vaso constrictors
- Oxygen
causes dilation of smooth muscle in arterioles

Question 14

what are the two types of hormones used in hormonal control
- give examples

Answer 14

1. Vasoconstrictors
   - Angiotensin II
   - Vasopressin (ADH)
   - Adrenaline (A1-adrenergic receptors)
2. Vasodilators
   Histamine (allergic response)
   Kinins (e.g. Bradykinin, for sweating)
   Adrenaline (B2- adrenergic receptors)
   - anything that binds to Beta is vasodilator, anything that binds to alpha is constrictor

Question 15

what are the two types of neural control

Answer 15

1. Sympathetic vasoconstrictor fibres – release noradrenaline
2. Parasympathetic vasodilator fibres

Question 16

describe sympathetic vasoconstrictor fibre

Answer 16

the most widespread fribre and most physiologically important
a fibre that releases noradrenaline which binds to A1 adrenergic receptors on smooth muscle of blood vessels
- causes vasoconstriction
Note blood vessels in heart, lungs and liver don’t have many of these fibres, but these vessels do have 2 adrenergic receptors

Question 17

describe parasympathetic vasoconstrictor fibre

Answer 17

these fibres release ACh and cause nitric oxide to be produced in endothelial cells
- NO binfs to guanyly cyclase which causes production of cGMP
- cGMP relaxes smooth muscle

Question 18

what is angina and why is sodium nitroprusside or organic nitrates prescribed to teach it

Answer 18

a symptom of reduced blood flow to the heart
the chemicals are broken down to release ‘NO’, which then relaxes smooth muscle in arterioles, thus reducing resistance and therefore improving coronary blood flow. NO reduces MABP, so reducing the ‘work’ of the heart, further helping to reduce the symptoms of angina