Regulation of blood pressure

Question 1

Definition of systolic

Answer 1

BP in aorta and large arteries that increases rapidly during L ventricular contraction

Question 2

Definition of diastolic

Answer 2

BP when cardiac ejection stops due to the aortic valve closure
Minimum pressure reached before next systole

Question 3

Definition of total peripheral resistance

Answer 3

Made up of resistance arteries and arterioles in the system

Question 4

Definition of mean arterial blood pressure

Answer 4

Pressure in aorta

Question 5

Definition of central venous pressure

Answer 5

Pressure in vena cava, normally near 0

Question 6

Definition of afterload

Answer 6

Heart pumps against blood already in the blood vessels

Question 7

Definition of capacitance

Answer 7

Ability to accommodate a greater blood volume

Question 8

Definition of mechanoreceptors

Answer 8

Stretch sensitive, found in baroreceptors

Question 9

Definition of pressure natriuresis

Answer 9

Mechanism within the kidneys by which increased renal perfusion due to increased BP leads to increased Na excretion

Question 10

What does BP consist of
Where is it measured
How does BP vary in the body

Answer 10

Refers to the pressure in large arteries and oscillates with cardiac cycle

Systolic and diastolic, normally 120/80, mean = 93mmHg

Measured in the brachial artery at the height of the heart
BP is lower in the head and higher in the lower limbs

Question 11

How does pressure change in there arteries

Answer 11

Blood ejected => P and F rapidly propagated
P wave increases down arterial tree due to greater stiffness
Enters arterioles and capillaries, P falls due to increased elasticity

Question 12

How does pressure change in low resistance vascular beds

Answer 12

Low resistance vascular beds = kidney, brain, heart

P wave smoothed out less, high pulsatility can damage structures

Question 13

How does flow in the aorta change

Answer 13

Pulsatile but smoothed out as blood => arterioles and capillaries
Elastic vessels take up energy from pressure and pulsatility

Question 14

What happens to arterial BP and flow in systole

Answer 14

75% of SV transiently stored in aorta and large arteries as vessels are compliant

25% SV pushed into smaller arteries

Pressure energy stored in elastic walls

Question 15

What happens to arterial BP and flow in diastole

Answer 15

Still distended but rebound

Arterial recoil pushes blood into smaller arteries

Stored energy keeps flow in diastole

Question 16

How does the speed of the pressure waves compare to the rate of blood flow

Answer 16

Pressure wave propagates faster than blood flow

Question 17

What is mean arterial blood pressure

Answer 17

95mmHg

Question 18

What is the central venous pressure

Answer 18

0-5mmHg, v little resistance

Question 19

Which arteries have the most R resistance and why?

How does this affect P

Answer 19

Resistance arteries, arterioles due to friction

P falls steeply

Question 20

What is the relationship between Pressure difference, MABP and CVP

Answer 20

P difference = MABP - CVP

Question 21

What is the relationship between ABP, F and R

Answer 21

ABP = F x R

Question 22

What is the relationship between ABP, CO, TPR

Answer 22

ABP = CO x TPR

Question 23

What are the short term factors that affect BP

Answer 23

Sleep
Posture
Exercise
Stress

Question 24

How does pressure change over a day

Answer 24

Oscillates in small range

Average does not change much

Question 25

Why is the baroreceptor reflex important

Answer 25

In carotid sinus and aortic arch Maintains BP in upper body, preserving flow to brain Allows body to change F to some organs without affecting F to others -Due to parallel circulation Can alter BP set point, allow body to cope with stress/exercise

Question 26

What does arterial tone affect

Answer 26

Total peripheral resistance

Question 27

What does the total peripheral resistance affect

Answer 27

Afterload

Question 28

What can affect CVP preload/Starling forces

Answer 28

Venous capacitance | BV

Question 29

What can affect stroke volume

Answer 29

Afterload can decrease SV Cardiac contractility CVP preload/Starling forces

Question 30

What can affect venous capacitance

Answer 30

Venous tone

Question 31

What can affect BV

Answer 31

Na excretion/retention

Question 32

What does the ANS affect as a result of the baroreceptor reflex

Answer 32

Arterial and venous tone Cardiac contractility HR and SV All of these stabilize MABP Can also modulate RAAS

Question 33

What determines MABP in the long term | What does it act on

Answer 33

RAAS system Receives input from BP Acts on Na+ excretion/retention Arterial and venous tone

Question 34

What are the effects of increased Na retention

Answer 34

Increased Na Increased H2O Increased BP Increased MABP And vice versa

Question 35

Describe how afferents of the baroreceptor loop reach the brain

Answer 35

Aortic nerve from aortic arch => 4th cranial nerve/vagus Carotid sinus nerve from external carotid => 9th cranial nerve/glossopharyngeal nerve Both reach nucleus solitairius tractus and are compared to the set point

Question 36

What happens in the efferents of the baroreceptor loop when the BP is too low

Answer 36

Increased sympathetic drive => b1 => HR and force increase Increased sympathetic drive => a1 => increased veno and arterial constriction, CVP, TPR Decreased parasympathetic drive => M2 => HR increase All of these contribute to an increased CO

Question 37

How do the baroreceptors function

Answer 37

Mechanoreceptors sensitive to stretch Thin carotid sinus wall => small P changes detected Increased P => increased firing => NST which mediates response

Question 38

When are the baroreceptors most sensitive

Answer 38

When mean BP = 80-150mmHg but sensitivity increased by large pulse pressure

Question 39

What happens in the baroreceptor reflex when there is a new sustained pressure

Answer 39

Can adapt to new sustained pressure but not for long terms

Question 40

When is adrenaline secreted and what adrenergic receptors does it stimulate?

Answer 40

Adrenal secretions during - Exercise - Hypotension - Hypoglycaemia a1, VC most vascular beds b1, +ve chronotrope, inotrope b2, VD in skeletal muscle

Question 41

When is noradrenaline secreted and what adrenergic receptors does it stimulate?

Answer 41

Sympathetic secretion -Mediates SNS efferents More often used, more important a1, VC most vascular beds b1, +ve chronotrope, inotrope b2, has a low affinity

Question 42

Describe mechanisms for the long term regulation of MABP

Answer 42

Due to maintenance of constant ECF via [Na] in ECF/plasma

Question 43

What happens if the amount of Na consumed is too low

Answer 43

``` Less Na consumed Decreased plasma [Na] Decreased Posm Decreased ADH secreted Decreased water consumption/Increased water excretion ``` Decreased BV and preload Decreased BP Decreased diuresis and natriuresis Overall, mean BV and BP lowered and then stabilised

Question 44

How is the RAAS system activated when BV, plasma [Na] and BP are too low

Answer 44

Decreased CVP => decreased atrial stretch => decreased ANP released Decreased atrial stretch => decreased activation of cardiopulmonary receptors => increased SNS outflow to kidney => Renin released from juxtaglomerular cells

Question 45

How does the RAAS system function in the kidney

Answer 45

Renin release => Angiotensinogen converted to Ang1 Ang1 =ACE=> Ang2 Ang => Increased VC, ADH, renal Na reabsoprtion, aldosterone secretions

Question 46

How does increased VC, ADH, renal Na reabsorption and aldosterone secretion increase BV, BP and plasma [Na]?

Answer 46

Increased VC => increased R so P increases to maintain flow Increased ADH secretion => more water retained => increases BV and BP Increased renal Na reabsorption and aldosterone => increased plasma [Na] => increased water reabsorbed => increased BV and BP

Question 47

How does ANP affect the RAAS system

Answer 47

If less ANP released => increase in renal Na reabsorption

Question 48

Describe the process of renal regulation of Na excretion by pressure natriuresis

Answer 48

Increased renal perfusion due to increased BP => increased Na excretion Only small changes in MABP needed to cause large response Increased renal perfusion P Increased in BF in vasa recta Increased in intrarenal release of NO => VD Greater outward P from VR, favours secretion => Decrease in renal Na reabsorption

Question 49

Describe other mechanisms to maintain BP in the long term other than RAAS

Answer 49

SNS activation => increased BP when kidneys denervated, can contribute to long term control Changes in BP don't always affect Na excretion Na excretion can occur without BP changes Baroreceptor reflex does not turn off completely after a short time