Control Of Arterial Blood Pressure

Question 1

Blood pressure definition:

Answer 1

The outwards (hydrostatic) pressure exerted by the blood on blood vessel walls

Question 2

What is systolic and diastolic arterial blood pressure?

Answer 2

Systolic BP: Pressure exerted by blood on aorta walls and systematic arteries when heart contracts (normal 120 mmHg, should not exceed 140mmHg)

Diastolic BP: Pressure exerted on aorta walls and systemic arteries when heart relaxes (usually 80mmHg)

Question 3

What is pulse pressure?

Answer 3

The difference between systolic and diastolic BP

Usually 30-50mmHg

Question 4

How to estimate MAP:

Answer 4

MAP = [(2 x diastolic) + systolic]/3

MAP = DPB + 1/3pulse pressure

Normal range 70-105mmHg

Question 5

What are features of normal resting systolic, diastolic, and MAP:

Question 6

Measuring of indirect BP using cuff sphygmomanometer and stethoscope:

Answer 6

Cuff pressure kept between systolic and diastolic pressure to allow flow to be audible through a stethoscope

1st sound - Peak systolic pressure
2nd and 3rd sound - Intermittent sounds due to turbulent spurts of blood
4th sound - Minimum diastolic pressure

Question 7

Why do we need to regulate MAP?

Answer 7

Pressure too low - Inadequate perfusion of tissue (minimum 60mmHg)

Pressure too high - Damage to blood vessels and strain

Question 8

What are the main resistance vessels?

Answer 8

Arterioles

Question 9

Baroreceptor reflex and its role in short term MAP regulation:

Answer 9

Baroreceptors locate changes in BP in aortic arch and carotid sinus

Cannot regulate long term since firing decreases if high BP sustained

Response to Increased BP:
1. Baroreceptors triggered
2. Baroreceptors feedback to ANS
3. ANS lowers HR and cardiac contractility via vagus nerve and decreases sympathetic constrictor tone
4. BP decreased

Response to Decreased BP:
1. Detected by baroreceptors triggering sympathetic response
2. Increases HR, contractility and sympathetic constrictor tone
3. BP increased

Question 10

Postural (orthostatic) hypotension and its risk factors:

Answer 10

Failure of baroreceptor responses to gravitational shifts in blood

Risk factors:
- Age
- Medications
- Disease
- Bed rest

Question 11

Long term regulation of MAP and role of hormones in regulating plasma volume:

Answer 11

Extracellular Fluid Volume:
ECFV = plasma volume + interstitial fluid

Hormones act as effectors to regulate ECFV by regulating water and salt balance in out bodies

Control of ECFV = control of MAP

Question 12

Role of the Renin-Angiotensin-Aldosterone System (RAAS) in regulation of plasma volume and MAP

Answer 12

1. Renin released from kidneys, facilitates conversion of angiotensinogen to angiotensin I
2. Angiotensin I converted into angiotensin II (potent vasoconstrictor) by ACE
3. Angiotensin II increases SVR
4. Angiotensin II stimulates release of aldosterone from adrenal cortex
5. Aldosterone increases renal absorption of sodium and water - INCREASING PLASMA VOLUME

Question 13

Role of the Natriuretic Peptides (NPs) in regulation of plasma volume and MAP

Answer 13

Released in response to cardiac distension or neurohormonal stimuli, causing excretion of salt and water by kidneys - DECREASING BLOOD VOLUME AND BP

Atrial natriuretic peptide (ANP)
- Stored in atrial myocytes
- Released in response to atrial distension

Brain-type natriuretic peptide (BNP)
- Synthesised by ventricles and brain
- BNP and NT-pro-BNP can be measured in suspected heart failure

Question 14

Role of the Antidiuretic Hormones (ADHs) in regulation of plasma volume and MAP

Answer 14

Synthesised by hypothalamus, stored in posterior pituitary

Secretion stimulated by reduced ECFV or increased extracellular fluid osmolarity

Acts in kidney tubules to increase re-absorption of water - INCREASES PLASMA VOLUME, BP AND CO

Causes vasoconstriction - can contribute to hypovolemic shock