L7: Control of cardiac output & blood pressure

Question 1

Define bulk flow

Answer 1

The movement of a mass of fluid molecules due to the presence of a pressure or temperature gradient

Question 2

Define flow

Answer 2

Movement of substance by pressure difference

Question 3

Define pressure

Answer 3

Force generated by molecules moving around

Question 4

Equation for MAP

Answer 4

MAP = CO x TPR

Mean Arterial Pressure = Cardiac Output x Total Peripheral Resistance

Question 5

What is the equation for Darcy’s Law ?

Answer 5

P = F x R

Pressure Difference = Flow x Resistance

Question 6

Risk of high pressure of MAP

Answer 6

Stroke, kidney damage, heart failure

Question 7

Risk of low pressure of MAP

Answer 7

Insufficient blood flow, causing fainting

Question 8

2 determinants of CO

Answer 8

1) Changes in stroke volume (inotropy)
2) Changes in heart rate (chronotropy)

Question 9

Define inotropy & chronotropy

Answer 9

Inotropy: Strength of contraction
Chronotropy: Rate of contraction

Question 10

Equation for CO

Answer 10

CO = SV x HR

Product of stroke volume & heart rate

Question 11

What is stroke volume influenced by ?

Answer 11

Venous return

Question 12

What does filling pressure determines?

Answer 12

Degree of stretch of a ventricle immediately before it conctracts

Question 13

How does an increase in venous return affect stroke volume?

Answer 13

1) Increased venous return from lungs
2) Increase ‘filling’ pressure of LA
3) More blood enters ventricle
4) Increased ‘filling’ pressure of LV
5) Increase stroke volume (more blood leaves ventricle)

Question 14

What does the Frank-Stirling mechanism state?

Answer 14

The stroke volume of the left ventricle will increase as the left ventricular volume increase

Question 15

2 changes that can alter venous return

Answer 15

1) Venous capacitance changes

2) A drop in blood volume

Question 16

How does orthostasis alter venous return?

Answer 16

1) Whilst standing, gravity pulls blood into lower body

2) Veins are distended (increased capacitance)

3) Reduced central venous pressure difference

4) Reduced venous return

5) Reduced stroke volume

Question 17

How does dynamic exercise alter venous return?

Answer 17

1) Active constriction of veins

2) Increased central venous pressure difference

3) Increased venous return

4) Increased stroke volume

Question 18

Does myocardial contractility influence the alteration of stroke volume

Answer 18

YES

Question 19

Is control of heart rate autonomic or somatic?

Answer 19

Autonomic

With opposing actions of sympathetic & parasympathetic NS

Question 20

Function of SA node

Answer 20

1) Generates AP
2) Site for regulation of the rate at which the heart contracts & relaxes

Regulated by the ANS

Question 21

What does SNS release to increase HR?

Answer 21

Noradrenaline

Question 22

What does PSNS release to decrease HR?

Answer 22

Acetylcholine

Question 23

Name of unstable membrane potential of SA node

Answer 23

Pacemaker potential

Question 24

What is heart rate set by?

Answer 24

Pacemaker potential in the SA node

Question 25

How does the NS system act on the SA node?

Answer 25

1) The pacemaker potential slowly depolarises 2) When depolarised to the threshold potential, it triggers an AP causing heart to contract ## Footnote Depolarise quickly- HR increased Depolarise slowly- HR decreased

Question 26

How does sympathetic & parasympathetic stimulation affect the slope of pacemaker potential & HR?

Answer 26

Sympathetic: Increase slope, HR increases Parasympathetic: Decrease slope, HR decreases

Question 27

Define total peripheral resistance (TPR)

Answer 27

Amount of force affecting resistance to blood flow throughout circulation

Question 28

How is TPR regulated?

Answer 28

Altering the radius of arterioles ## Footnote Increasing resistance is proportional to pressure - Reducing tube radius, increases resistance

Question 29

Does TPR increase/decrease during vasconstriction & vasodilation?

Answer 29

Vasoconstriction (decrease radius) = increase Vasodilation(increase radius) = decrease

Question 30

How does arterioles actively adjust their radius?

Answer 30

Vasoconstriction or Vasodilation

Question 31

What does baroreceptor use to regulate MAP via adjustments to CO & TPR?

Answer 31

Negative feedback

Question 32

Function of the baroreceptor reflex

Answer 32

Responds rapidly to change in MAP & pulse pressure in short-term

Question 33

Components of the baroreceptor reflex

Answer 33

- Sensors in the carotid sinuses - Integrating centre - Effects: Heart, Veins, Arterioles

Question 34

What system regulates BP in the kidneys?

Answer 34

RAAS (Renin-angiotensin-aldosterone system)

Question 35

2 effect sympathetic nerves have on the kidney

Answer 35

1) Constrict renal afferent arteriole to reduce GPR and restore MAP 2) Stimulate **renal juxtaglomerular cells** to secrete renin- producing more angiotensin II

Question 36

Define angiotensin II

Answer 36

Vasoconstrictor that acts on arterioles, restoring MAP

Question 37

What is extracellular fluid volume coupled with to maintain salt-water balance?

Answer 37

Total extracellular fluid Na+ content

Question 38

Main purpose of RAAS

Answer 38

Regulate plasma volume in the long-term & maintain MAP

Question 39

What group of specialised epithelial cells detects changes in plasma volume? How?

Answer 39

**Macula densa** in the DCT of the kidney indirecly sense changes in the GPR & delivery of NA+ in the filtrate

Question 40

How do macula densa respond when plasma volume, MAP & GFR falls?

Answer 40

Telling nearby **juxtaglomerular cells ** to secrete more RENIN into the blood

Question 41

Function of Renin

Answer 41

Enzyme that divide angiotensinogen in the blood to angiotensin I

Question 42

What enzyme further cleaves angiotensin I to angiotensin II?

Answer 42

Angiotensin-converting enzyme (ACE)

Question 43

Effects of angiotensin II in the body?

Answer 43

Vasoconstriction & stimulation of **aldosterone secretion** from the adrenal cortex

Question 44

What is the main effect of the steroid hormone **aldosterone**?

Answer 44

Increase reabsorption of Na+ in the renal tubule

Question 45

Main way in which blood volume is regulated?

Answer 45

Adjustments to Na+ reabsorption in the kidney performed by the RAAS

Question 46

Explain how RAAS restores MAP from a decreased plasma volume via an increased renal Na+ reabsorption

Answer 46

1) Drop in blood volume sensed by **baroreceptors & macula densa** 2) They respond by secreting **renin** from **juxtaglomerular cells** 3) Renin triggers **increased production of angiotensin II** 4) It stimulates the secretion of **steroid hormone aldosterone** from the adrenal cortex 5) Aldosterone alters gene expressions and** increases expression of channels for rebaosprtion of Na+** 6) Na+ reabsorption increases, H2O reabsorption increases and this restores MAP

Question 47

2 hormones that control plasma voluma

Answer 47

1) RAAS 2) Atrial natriuretic hormone (ANP)

Question 48

Difference between ANP & RAAS

Answer 48

ANP tries to **decrease** plasma volume RAAS tries to **increase** plasma volume

Question 49

Where is ANP secreted from?

Answer 49

Lining of the atria of the heart **in response to stretch **