Blood Pressure- Physiology and Pathology

Question 1

formula for mean BP

Answer 1

(SBP+2xDBP)/3

Question 2

the difference in flow between the arteries and veins

Answer 2

in arteries and the aorta, the flow is pulsatile and in the capillaries and veins, the flow is laminar

Question 3

what are the effects of too high or low systemic arterial blood pressure

Answer 3

too low: faint (vaso-vagal attack), shock (tissue acidosis pH<7.35)
too high: tissue damage
therefore, pressure regulated to maintain adequate tissue perfusion

Question 4

list the determinants of blood pressure

Answer 4

1. cardiac output
2. vascular resistance
3. physical factors (gravity, arterial compliance, blood viscosity)

Question 5

vascular resistance

Answer 5

predominantly determined by level of constriction of arterioles which is under hormonal and neurological control.

Question 6

how does arterial compliance contribute to BP?

Answer 6

• arteries stretch and stores elastic potential energy in systole
• releases this energy to maintain flow in diastole
• stiff arteries, e.g., due to old age, reduces compliance and increases systolic BP

Question 7

how does blood viscosity contribute to BP?

Answer 7

• contributes to resistance to flow
• high protein/hypercellular blood has high viscosity
• therefore, higher pressure to maintain flow

Question 8

what effect does prostacyclin and NO have on the vascular system?

Answer 8

• vasodilators

- produced by the endothelium that controls the local vascular tone

Question 9

what effect does endothelin have on the vascular system?

Answer 9

• vasoconstrictor

- produced by the endothelium that controls the local vascular tone

Question 10

what determines venous return that further affects preload?

Answer 10

1. circulating blood volume- can be affected by dehydration-major bleeding, kidney failure-over transfusion
2. venous tone- autonomic nervous system, circulating vasoconstrictors (e..g, adrenaline), local vasoactive substances (e.g, NO, prostacyclin, endothelin)

Question 11

how does aldosterone affect blood volume?

Answer 11

aldosterone produced by the adrenal cortex causes an increase in salt and water absorption in the distal convoluted tubule that increases blood volume and restores BP

Question 12

how does ADH affect blood volume?

Answer 12

ADH, produced by the posterior pituitary gland, increases water reabosorption in the distal convoluted tubules and collecting ducts by the insertion of aquaporins that transport water through the tubular cells and back into blood, leading to a decrease in plasma osmolarity

Question 13

what are the different ways the autonomic system controls the heart rate

Answer 13

1. sympathetic NS via b1 receptors- increases heart rate

2. Parasympathetic NS via M receptors (i.e., vagus nerve)- increases HR

Question 14

different factors that affect HR

Answer 14

intrinsic HR (sinus node in right atrium), autonomic controls (SNS, PNS), circulating substances- Adrenaline increases HR via b1 receptors

Question 15

what factors can cause vasodilation

Answer 15

-low O2/high CO2 -acidosis -NO -prostacyclin

Question 16

what factors can cause vasoconstriction

Answer 16

-endothelin

Question 17

what are the causes of high blood pressure

Answer 17

-CKD -Structural causes -Endocrine causes -Preganancy/pre-eclampsia -Essential hypertension

Question 18

what are the structural causes of high BP

Answer 18

• renal artery stenosis

- aortic coarctation

Question 19

what are the endocrine causes of high BP

Answer 19

-high aldosterone (Conn’s syndrome) -High catecholamines (phacochromocytoma) -High Cortisol (Cushing’s syndrome) -High growth hormone levels (acromegaly)

Question 20

What are the essential hypertension causes of high BP

Answer 20

-polygenetic -obesity -high salt intake -high alcohol intake -ethinicity

Question 21

effects of chronic hypertension

Answer 21

• heart muscle damage
• large vessel damage
• microvascular damage

Question 22

examples of large vessel damage in hypertension

Answer 22

• aortic aneurysm (and rupture)
• cerebrovascular disease (stroke)
• CAD (angina, MI)
• peripheral vascular disease (claudication, amputation)

Question 23

examples of microvasculature damage

Answer 23

• CKD
• Brain dysfunction (multi-infarct dementia)
• Exacerbates vascular effects of diabetes (kidneys, eyes and peripheral nerves)

Question 24

acute effects of severe hypertension

Answer 24

• aortic dissection
• acute heart failure (high afterload)
• confusion (‘encephalopathy’)
• cerebral hemorrhage
• retinal haemmorrhage

Question 25

explain the pathophysiology of faints

Answer 25

• vaso-vagal episodes
• neurally mediated syncope
• typically occurs as a reaction to a stressful epidoe
• disporportionate PNS activation causes arteriolar dilation and slowing of heart rate which causes a drop in BP
• reduced cerebral perfusion
• tl.c= transient loss of consciousness

Question 26

explain the pathophysiology of shock

Answer 26

• persistently low blood pressure (<90) which could be due to a range of causes: -cardiogenic (large MI-low CO) -sepsis (e.g. meningitis-low SVR), anaphylaxis (e.g, penicillin or nuts-low SVR), low blood volume (eg., bleeding, burns, diarrhoea- low CO)
• SNS activation- blood flow redistributed to heart, heart, muscle
• poor tissue perfusion can cause organ malfunction, esp in the kidneys and acidosis (lactase)

Question 27

special circulation in the coronary arteries

Answer 27

• flow occurs mainly in diastole because
• it occurs when there is a pressure difference between the aorta and the small vessels
• during systole, the small (intramyocardial vessels) are ‘squeezed’
• therefore, this pressure difference if highest in diastole.

Question 28

special circulatin in the pulmonary system

Answer 28

• contains c.20% of the blood volume
• starling’s law ensures the same volume of blood flows through the systemic and pulmonary circulation
• pulmonary arteries respond differently to systemic e..g, pul arteries constrict if there is a high level of CO2 or low levels of O2 to minimise perfusion of non-functional lung tissue
• different sensitivity to vasoactive stimuli, e.g., very sensitive to prostacyclin and endothelin
• pulmonary hypertension is entirely different to systemic hypertension