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Fundamentals of Physiology > L7: Control of cardiac output & blood pressure > Flashcards

L7: Control of cardiac output & blood pressure Flashcards

1
Q

Define bulk flow

A

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

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2
Q

Define flow

A

Movement of substance by pressure difference

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3
Q

Define pressure

A

Force generated by molecules moving around

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4
Q

Equation for MAP

A

MAP = CO x TPR

Mean Arterial Pressure = Cardiac Output x Total Peripheral Resistance

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5
Q

What is the equation for Darcy’s Law ?

A

P = F x R

Pressure Difference = Flow x Resistance

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6
Q

Risk of high pressure of MAP

A

Stroke, kidney damage, heart failure

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7
Q

Risk of low pressure of MAP

A

Insufficient blood flow, causing fainting

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8
Q

2 determinants of CO

A

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

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9
Q

Define inotropy & chronotropy

A

Inotropy: Strength of contraction
Chronotropy: Rate of contraction

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10
Q

Equation for CO

A

CO = SV x HR

Product of stroke volume & heart rate

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11
Q

What is stroke volume influenced by ?

A

Venous return

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12
Q

What does filling pressure determines?

A

Degree of stretch of a ventricle immediately before it conctracts

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13
Q

How does an increase in venous return affect stroke volume?

A

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)

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14
Q

What does the Frank-Stirling mechanism state?

A

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

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15
Q

2 changes that can alter venous return

A

1) Venous capacitance changes

2) A drop in blood volume

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16
Q

How does orthostasis alter venous return?

A

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

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17
Q

How does dynamic exercise alter venous return?

A

1) Active constriction of veins

2) Increased central venous pressure difference

3) Increased venous return

4) Increased stroke volume

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18
Q

Does myocardial contractility influence the alteration of stroke volume

A

YES

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19
Q

Is control of heart rate autonomic or somatic?

A

Autonomic

With opposing actions of sympathetic & parasympathetic NS

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20
Q

Function of SA node

A

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

Regulated by the ANS

21
Q

What does SNS release to increase HR?

A

Noradrenaline

22
Q

What does PSNS release to decrease HR?

A

Acetylcholine

23
Q

Name of unstable membrane potential of SA node

A

Pacemaker potential

24
Q

How does the NS system act on the SA node?

A

1) The pacemaker potential slowly depolarises
2) When depolarised to the threshold potential, it triggers an AP causing heart to contract

Depolarise quickly- HR increased
Depolarise slowly- HR decreased

25
Q

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

A

Sympathetic: Increase slope, HR increases

Parasympathetic: Decrease slope, HR decreases

26
Q

How is TPR regulated?

A

Altering the radius of arterioles

Increasing resistance is proportional to pressure

  • Reducing tube radius, increases resistance
27
Q

How does arterioles actively adjust their radius?

A

Vasoconstriction or Vasodilation

28
Q

Mechanism of vasodilation of arterioles

A

Smooth muscle relaxaction that increases radius & reduce resistance

29
Q

Mechanism of vasoconstriction of arterioles

A

More constriction reduces radius & increase resistance

30
Q

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

A

Negative feedback

31
Q

Function of the baroreceptor reflex

A

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

32
Q

Features of the baroreceptor reflex

A
  • Sensors in the carotid sinuses
  • Integrating centre
  • Multipl effectors communicating via SNS/PSNS
33
Q

What system regulates BP in the kidneys?

A

RAAS (Renin-angiotensin-aldosterone system)

34
Q

2 effect sympathetic nerves have on the kidney

A

1) Constrict renal afferent arteriole to reduce GPR and restore MAP

2) Stimulate renal juxtaglomerular cells to secrete more hormone renin, producing more angiotension II in the blood

35
Q

Define angiotensin II

A

Vasoconstrictor that acts on arterioles, restoring MAP

36
Q

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

A

Total extracellular fluid Na+ content

37
Q

Main purpose of RAAS

A

Regulate plasma volume in the long-term & maintain MAP

38
Q

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

A

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

39
Q

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

A

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

40
Q

Function of Renin

A

Enzyme that divide angiotensinogen in the blood to angiotensin I

41
Q

What enzyme further cleaves angiotensin I to angiotensin II?

A

Angiotensin-converting enzyme (ACE)

42
Q

Effects of angiotensin II in the body?

A

Vasoconstriction & stimulation of aldosterone secretion from the adrenal cortex

43
Q

What is the main effect of the steroid hormone aldosterone?

A

Increase reabsorption of Na+ in the renal tubule

44
Q

Main way in which blood volume is regulated?

A

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

45
Q

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

A

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

46
Q

2 hormones that control plasma voluma

A

1) RAAS
2) Atrial natriuretic hormone (ANP)

47
Q

Difference between ANP & RAAS

A

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

48
Q

Where is ANP secreted from?

A

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

49
Q
A

Fundamentals of Physiology (11 decks)

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