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Yr2 - Advanced Concepts > Cardio Respiratory - Week 4 Circulatory Physiology Mean Arterial > Flashcards

Cardio Respiratory - Week 4 Circulatory Physiology Mean Arterial Flashcards

1
Q

What is the fundamental equation in Cardiovascular Physiology (2)

A

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2
Q

What is the main role of the cardiovascular centre? (2)

A

The primary objective of cardiovascular regulation is to maintain a stable MAP, and therefore ensure adequate blood flow to the vital organs, especially the brain

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3
Q

Describe arterial baroreceptors (4)

A

Sprays of non-encapsulated nerve endings in the adventitial layer of the arterial walls in the carotid sinus and the aortic arch

They are mechanoreceptors, sensitive to stretch

A rise in arterial pressure increases the distending pressure on the arterial wall, resulting in increased stretch, which excites the baroreceptors

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4
Q

Describe the effect of baroreceptor stimulation on heart rate and blood pressure (1)

A

Electrical stimulation of the carotid sinus nerve elicited a reflex hypotension and bradycardia

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5
Q

Baroreflex is an example of what type of mechanism? (1)

A

An example of a homeostatic mechanism driven by negative feedback

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6
Q

Acute regulation of mean arterial pressure is around a ‘set point’ of of what? (1)

A

Acute regulation of mean arterial pressure around a ‘set point’ of about 95 mmHg (in young adults)

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7
Q

Describe the responses (7)

A

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8
Q

What are arterial baroreceptors responsible for? (2)

A

Acute buffering of blood pressure

Arterial baroreceptor inputs are not vital in the long-term regulation of MAP

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9
Q

What do the stretch receptors (also known as cardiopulmonary stretch receptors) respond to and what is their role? (3)

A

Respond to lower pressures than the arterial baroreceptors

The primary role of these receptors is to regulate blood volume.

This parameter is a primary determinant of cardiac output, which (along with total peripheral resistance) determines arterial pressure

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10
Q

What happens if venous blood pressure falls (2)

A

Reflected by a fall in atrial pressure and a decreased stimulation of the cardiopulmonary stretch receptors

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10
Q

Decreased stimulation of the cardiopulmonary stretch receptors initiates what? (2)

A

A reflex release of antidiuretic hormone (ADH; vasopressin) from the hypothalamus. ADH increases the reabsorption of fluid from the renal tubules

A neural reflex which constricts the afferent renal arterioles, so reducing the rate of glomerular filtration

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11
Q

What does a reflex release of antidiuretic hormone and a neural reflex cause? (1)

A

Both these effects reduce fluid losses to urine and act to increase blood volume
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12
Q

What are chemoreceptors responsible for and where are they located? (2)

A

Chemoreceptors monitoring the chemical composition of arterial blood are located close to the arterial baroreceptors in small structures called carotid and aortic bodies

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13
Q

What is the most important determinant of arterial pressure in the long-term (1)

A

The most important determinant of arterial pressure in the long-term is blood volume

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14
Q

Blood volume regulation is ultimately achieved by which organ? (1)

A

Kidneys

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15
Q

What is the renin-Angiotensin-Aldosterone System stimulated by (1)

A

Stimulated by a fall in blood volume or in renal blood flow

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16
Q

Describe the major effect of adrenaline (2)

A

The major effect of adrenaline is to increase cardiac output (as a result of increases in both heart rate and stroke volume). This effect is mediated by beta-adrenoceptors

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17
Q

Describe the major effect of noradrenaline (2)

A

Noradrenaline causes vasoconstriction via alpha-adrenoceptors, raising TPR (total peripheral resistance)

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18
Q

What are the other hormones affecting MAP (3)

A

Antidiurectic hormone (ADH)

Atrial Natiuretic Peptide (ANP)

Nitric Oxide

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19
Q

Describe the distribution of blood flow at rest (3)

A

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20
Q

Where are right and left coronary arteries? (1)

A

Arise from the base of the aorta, just above the aortic valve

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21
Q

How does venous blood drain into the right atrium? (1)

A

Via the coronary sinus

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22
Q

What do the left and right coronary blood vessels supply? (1)

A

Supply walls of the myocardium

23
Q

Describe the structural adaptation of coronary circulation (4)

A

The coronary circulation must deliver O2 at a high rate to meet cardiac demand

Myocardial capillary density is very high

Combined with the relatively small diameter of myocytes, this ensures a very small maximum diffusion distance (~9 micrometer)

O2 transport is further enhanced by the presence of myoglobin in both cardiac myocytes and slow skeletal muscle (red colour)

24
Q

Describe the functional adaptations (3)

A

Cardiac muscle extracts 65-75% of the O2 from the arterial blood

Metabolic hyperaemia:- the high O2 demand during exercise is met by increased blood flow

Stimulation of sympathetic nerves also causes an increase in coronary flow

25
Q

Describe what happens to coronary arteries during systole (3)

A

The coronary arteries are compressed during systole, particularly during the isovolumetric phase when the pressure within the ventricle wall falls markedly

A modest flow is restored during the ejection phase of systole, but it only returns to maximum during diastole

26
Q

What does obstruction of coronary arteries cause? (3)

A

Sudden obstruction of a coronary artery or one of its branches causes ischemia of the tissue downstream, leading to myocardial infarction (heart attack)

27
Q

What does gradual obstruction of vessels lead to? (3)

A

Gradual obstruction allows the development of collateral vessels, reducing the extent of the ischemia, however, at times of increased demand (exercise, stress), local ischemia develops, producing the pain of angina pectoris

28
Q

Describe what pulmonary arteries contain (1)

A

The pulmonary arteries contain deoxygenated blood

29
Q

Describe what pulmonary veins contain (1)

A

The pulmonary veins carry oxygenated blood

30
Q

What does pulmonary circulation receive? (1)

A

The pulmonary circulation receives the entire right ventricular output (i.e. cardiac output).

31
Q

Why does the pulmonary circulation have many structural and functional adaptations? (1)

A

Lungs must handle such a high rate of blood flow

32
Q

Describe capillary density in vascular beds (1)

A

The capillary density in the alveolar vascular beds is very high, resulting in a huge capillary surface area (up to 100 m2)

33
Q

Describe the pulmonary capillaries (3)

A

The densely packed capillaries form a ‘sheet’ of blood covering the surface of the alveoli

This coupled with the small diffusion distance from the alveolar surface to the plasma, results in a very high O2 diffusion capacity

As a consequence, gas exchange in the lung is normally ‘flow limited

34
Q

Describe pressure difference between pulmonary circulation and systemic circulation (1)

A

Pressures in the pulmonary circulation are lower than in the systemic circulation

35
Q

Why is there a pressure difference between pulmonary circulation and systemic circulation (2)

A

Pulmonary circulation only supplies one organ, which is effectively at, or close to, heart level, so high arterial pressures are not needed

Pulmonary capillaries are not surrounded by supporting tissue and are more susceptible to stress failure (rupture) than are systemic capillaries

36
Q

Describe vertical distribution of blood flow (4)

A

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37
Q

How does blood flow distribution change during exercise (3)

A

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38
Q

At rest, skeletal muscle accounts for how much of cardiac output? (1)

A

For about ~20% of cardiac output

39
Q

During extreme physical exertion, skeletal muscle accounts for how much of cardiac output? (1)

A

> 70% of cardiac output can be directed to contracting muscles

40
Q

What becomes the primary determinant of systemic vascular resistance during exercise? (1)

A

Skeletal muscle resistance becomes the primary determinant of systemic vascular resistance during exercise

41
Q

Compare skeletal muscle capillary density (2)

A

Skeletal muscle capillary density is greater in slow twitch (red) than fast twitch (white) muscles

42
Q

During skeletal muscle activity, what leads to an increase in blood flow? (1)

A

During skeletal muscle activity, active hyperaemia leads to an increase in blood flow

43
Q

What is active hyperaemia? (1)

A

Increase in blood flow associated with an increase in metabolic activity

44
Q

Increased skeletal muscle metabolism leads to which local changes? (3)

A

Increased skeletal muscle metabolism leads to local changes, which induce vasodilation (e.g. reduced O2 level, increased levels of adenosine, K+, CO2, H+, and NO)

45
Q

During exercise why are the local metabolic factors important? (2)

A

During exercise, these local metabolic factors primarily underlie vasodilation and overcome basal sympathetic vasoconstrictor influences

46
Q

During exercise, what does sympathetic neural activity result in? (2)

A

During exercise, sympathetic neural activity results in vasoconstriction in other areas of the body (e.g. digestive viscera), which facilitates the increase in skeletal muscle blood flow

47
Q

The brain receives how much of the resting cardiac output? (1)

A

The brain receives around 13% of the resting cardiac output, most of which supplies the grey matter

48
Q

Describe the circle of Willis and its importance (2)

A

The arteries that enter the cerebral circulation (the basilar and carotid arteries) anastomose to form the circle of Willis, an arrangement, that helps to preserve cerebral perfusion even if one artery is occluded

49
Q

Describe the anaerobic capacity of CNS cells (1)

A

CNS cells have a low anaerobic capacity

50
Q

Describe how cerebral blood flow is regulated (4)

A

Grey matter has a very high capillary density

Grey matter has a high basal blood flow and extracts a high level of O2 from the arterial blood

The brain is in the unique position of being able to regulate its own blood supply by controlling systemic cardiovascular parameters via the autonomic nervous system

Cerebral autoregulation is highly developed

51
Q

Describe how cerebral blood vessels respond to arterial CO2 levels (2)

A

Hypercapnia causes vasodilation and hypocapnia results in vasoconstriction

52
Q

What does local hypoxia initiate? (1)

A

Local hypoxia initiates a local vasodilation

53
Q

What are the 3 main functions of skin blood flow? (3)

A

Heat exchanger for thermoregulation

Supply of nutrients to cells

Blood reservoir

54
Q

Why is there an extensive ‘venous plexus’ just under skin surface? (1)

A

Reflects neural adjustments of blood flow through arterioles and coiled arterio-venous (AV) anastomoses

55
Q

Describe heat and cold effect (5)

A

Check notes week 4

Yr2 - Advanced Concepts (16 decks)

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