Physiology 8 - Control of Blood Volume

Question 1

See diagrams at end of physiology 7 lecture

Answer 1

And at start of 8

Question 2

Which organ is largely involved in blood volume and hence long term blood pressure control?

Answer 2

Kidneys

Question 3

Is kidney function modifiable?

Answer 3

Yes

Question 4

Where is angiotensin released from?

Answer 4

The liver

Question 5

What is the enzyme to angiotensin’s substrate?

Answer 5

Renin

Question 6

What is the action of angiotensin II?

Answer 6

Constricts renal arteries (vasoconstriction), decreasing blood flow through kidneys and also is involved in renal retention of salt & water

Question 7

Angiotensin I?

Answer 7

Converted to angiotensin II by an enzyme in the lungs

Question 8

Study some of the diagrams

Answer 8

On this lecture

Question 9

In order to change long term MABP, one of what two factors must be changed?

Answer 9

Renal output

Salt and water intake

Question 10

What is the equilibrium point on an MABP vs input/output graph?

Answer 10

The MABP at which intake of salt and water = renal output of salt and water

Question 11

What causes decreased osmolarity?

Answer 11

Decreased water or increased salt intake

Question 12

What does decreased osmolarity do to the oncotic pressure?

Answer 12

Decrease it

Question 13

Decreased oncotic pressure is detected by the hypothalamus. What changes does the hypothalamus initiate in order to correct this decrease?

Answer 13

Stimulation of hypothalamic thirst centre

Increased antidiuretic hormone (ADH) output –> decreased water loss at kidneys

Question 14

What 3 factors lead to ADH release?

Answer 14

Increased oncotic pressure
Hypovolaemia (>10%)
Angiotensin II

Question 15

How does hypovolemia stimulate ADH release?

Answer 15

Atrial baroreceptors normally inhibit/restrict ADH release
Decreased BV in atria –> decreased atrial pressure –> decreased atrial baroreceptor firing –> increased release of ADH

Question 16

Briefly summarise the mechanism and location of action of ADH.

Answer 16

It increases blood volume by increasing water permeability in the renal collecting ducts. It therefore reduces urine production.

Question 17

What type of cells is renin released from?

Answer 17

Kidney juxtoglomerular cells

Question 18

What type of receptors regulate renal activity?

Answer 18

Beta receptors

Question 19

What conversion does renin perform?

Answer 19

Angiotensinogen –> Angiotensin I

Question 20

Which enzyme converts angiotensin I to angiotensin II?

Answer 20

ACE (angiotensin converting enzyme)

Question 21

Where is ACE found?

Answer 21

The lungs

Question 22

Briefly describe the three mechanisms of action of angiotensin II.

Answer 22

Constricts renal arteries thereby reducing blood flow via the kidneys.
Also causes release of aldosterone from the adrenal glands, which increase Na+ and H20 reabsorption.
Stimulates release of ADH from the pituitary

Question 23

What is the overall effect angiotensin has on the circulatory system?

Answer 23

Increase in blood volume

Question 24

What is the atrial natriuretic hormone, when is it released and what effect does it have?

Answer 24

A 28-amino acid peptide synthesised and stored in muscle cells of the atria. It is released in response to stretch of the atria. It helps oppose the effects of the RAAS system, therefore counteracting volume overload.

Question 25

What is a major cause of whole blood loss?

Answer 25

Haemorrhage

Question 26

What is a major cause of plasma loss?

Answer 26

Burns

Question 27

What is a major cause of sodium loss?

Answer 27

Vomiting

Question 28

List the percentages of blood loss that enable the classification shock into 4 classes.

Answer 28

Class 1: 10-15% loss
Class 2: 15-30% loss
Class 3: 30-40% loss
Class 4: >40% loss

Question 29

Which classes of shock will require blood transfusion?

Answer 29

Classes 3&4

Question 30

What is the immediate response/reflex to hypovolaemia?

Answer 30

Baroreceptor reflex

Question 31

Describe the intermediate response to hypovolaemia.

Answer 31

Arteriolar constriction (–> increased TPR) –> decreased capillary hydrostatic pressure –> net movement of fluid from interstitium to capillaries –> increase in BV

Question 32

Why is the intermediate response only a temporary solution to decreased BV?

Answer 32

Because net movement of fluid is out of the interstitium, tissues become dehydrated

Question 33

What is a common consequence of severe hypovolaemia?

Answer 33

Heart failure

Question 34

What type of resuscitation fluids are used in fluid replacement therapy?

Answer 34

Colloid or Hartman’s

Blood

Question 35

List 3 other factors affecting BP.

Answer 35

Cortex and emotions
Time of day
Respiration

Question 36

How is long term control of BP achieved?

Answer 36

Control of BV