Blood flow and volume

Question 1

In what 2 ways can blood flow to an area be varied?

Answer 1

• Altering the vascular resistance

- Altering the perfusion pressure

Question 2

What make up the ‘essential’ organs?

Answer 2

The brain
Coronary circulation
Working skeletal muscle

Question 3

What is active hyperaemia?

Answer 3

An increase in metabolic rate brings about an increased blood flow

Question 4

Increased metabolic rate in the cells of the tissue results in …, … and … ?

Answer 4

Increased oxygen consumption
Increased production of waste products including carbon dioxide and lactic acid
Increased potassium outflow from cells

Question 5

Is oxygen a vasodilator of vasoconstrictor?

Answer 5

Vasoconstrictor

Question 6

Describe metabolic autoregulation

Answer 6

• intrinsic control of blood flow
• An increase in blood pressure leads to increased perfusion of tissue
• This delivers more oxygen and removes waste products more rapidly which causes vasoconstriction thereby decreasing the perfusion

Question 7

What is reactive hyperaemia?

Answer 7

• blood flow to an area is completely interrupted
• depletion of oxygen and build up of waste products
• when blood flow is re-established it increased above normal to re-pay the oxygen debt

Question 8

Give the names of the following:

1. reduced blood flow to tissues
2. cell damage
3. cell death

Answer 8

1 = ischaemia
2 = infarction
3 = necrosis

Question 9

What are the 3 ways the body tries to limit ischaemia?

Answer 9

• causes pain
• a reflex increase in arterial blood pressure which increases perfusion pressure to the muscle
• reduces the strength of the muscular contraction so the ischaemic exercise cannot be performed

Question 10

What is paracrine control of blood flow?

Answer 10

Locally acting chemicals which affect the local blood flow in response to the local environment

Question 11

Increase in blood flow velocity in an area causes endothelial cells to release … ? What is the function of this substance?

Answer 11

Nitric oxide which is a vasodilator

Question 12

Which systems are able to cope with being compromised for a period of time?

Answer 12

Renal, splanchnic and resting skeletal muscle circulations, and the circulation to bone and skin

Question 13

What is the role of the medulla oblongata in extrinsic control?

Answer 13

Contains the cardiovascular centre which coordinates the blood flow of the non-essential organs

Question 14

What does the cardiovascular centre maintain?

Answer 14

Cardiac output and vascular resistance

Question 15

What is the first system to act in response to changes in blood pressure?

Answer 15

Baroreflex

Question 16

Describe how the baroreflex works

Answer 16

• Blood pressure is detected by stretch receptors
• These baroreceptors deliver action potentials to the CV centre in response to stretch
• The CV centre compares the information received to its reference value and makes changes as necessary – this response is known as the baroreflex

Question 17

Where are stretch receptors located?

Answer 17

In the aortic arch and carotid sinuses

Question 18

In response to a decrease in blood pressure, the response of the baroreflex is … ?

Answer 18

1. decreased stretch detected by baroreceptors
2. decreased frequency of AP sent to the brain
3. CV centre causes increased sympathetic activity
4. Increased contractility, heart rate and faster conduction speed
5. Vasoconstriction of peripheral blood vessels and dilation of vessels supplying essential organs
6. These changes cause increased TPR and CO which raises the arterial blood pressure

Question 19

What is blood volume detected by?

Answer 19

Stretch receptors in the left and right atrial walls and the large thoracic veins. These are called atrial volume receptors

Question 20

Which hormone is released in response to the increase in sympathetic activity caused by the baroreflex?

Answer 20

Renin

Question 21

Where is renin released from?

Answer 21

Cells known as the juxtaglomerular apparatus (JGA)

Question 22

What is the function of renin?

Answer 22

Renin causes a substance called angiotensinogen to be converted to angiotensin I in the liver

Question 23

What is the function of angiotensin II?

Answer 23

Angiotensin II causes vasoconstriction, and causes release of aldosterone from the adrenal gland.

Question 24

What is the function of aldosterone?

Answer 24

Causes the kidney to conserve sodium and water which increases the blood volume

Question 25

What effect does angiotensin II have on the pituitary gland?

Answer 25

Causes it to release ADH which causes the kidney to conserve water, increasing blood volume, causing further vasoconstriction

Question 26

What effect does vasoconstriction have on the hydrostatic pressure in capillaries?

Answer 26

Reduces it which favours reabsorption of water from the ISF back into circulation

Question 27

Long term blood pressure is mediated by which organ?

Answer 27

Kidney