Physiology of the Cardiovascular System

Question 1

What are the components of the cardiovascular system?

Answer 1

The components of the cardiovascular system include:

Cardiopulmonary unit
Left side and right side
Pulmonary artery and vein
Arteries, arterioles, capillaries, venules, and veins
Portal systems (such as the hepatic portal system, hypothalamus and anterior pituitary)
Intra-renal circulation
Intra-cranial circulation
Intra-coronary circulation

Question 2

What are the functions of the cardiovascular system?

Answer 2

The functions of the cardiovascular system are:

Rapid convective transport of oxygen, glucose, amino acids and fatty acids, vitamins, water, and waste products of metabolism (such as carbon dioxide, urea, and creatine)
Homeostatic control, including the transportation of hormones and regulation of body temperature

Question 3

What is stroke volume?

Answer 3

Stroke volume refers to the volume of blood pumped by the left ventricle per beat. It is denoted by SV.

Question 4

How is cardiac output defined?

Answer 4

Cardiac output is the volume of blood pumped by the heart per unit time. It is measured in liters per minute and is denoted by Q.

Question 5

What is meant by preload?

Answer 5

Preload is the degree to which the ventricles are filled at the end of diastole, just prior to systolic contraction. It is measured as end-diastolic volume (EDV) in milliliters.

Question 6

Define afterload.

Answer 6

Afterload is the resistance against which the left ventricle must eject the stroke volume from the heart. It is measured as the aortic pressure during systole divided by cardiac output.

Question 7

How is compliance defined in the context of blood vessels?

Answer 7

Compliance refers to the ability of a blood vessel to expand and contract with changes in pressure. It is measured as the unit of volume change per unit of pressure change and is denoted by C.

Question 8

What factors influence heart rate?

Answer 8

Heart rate is influenced by factors such as autonomic innervation and hormones. It is initiated in the atria through the atrial reflex, and electric signals travel down the conduction system to regulate the heart rate.

Question 9

What factors affect stroke volume?

Answer 9

Stroke volume is influenced by several factors, including:

Venous return: The filling volume or how full the circulation is, which is determined by preload and end-diastolic volume.
Filling time: The speed at which blood is returning, which is influenced by preload and end-systolic volume.
Autonomic innervation: The contractility or tone of the heart, which affects the force of contraction and end-systolic volume.
Hormones: Certain hormones can increase stroke volume by affecting the speed and force of contraction, as well as end-systolic volume.
Vasodilation or vasoconstriction: Changes in afterload, such as higher resistance or workload on the heart, can impact end-systolic volume.

Question 10

How is stroke volume calculated?

Answer 10

Stroke volume (SV) is calculated by subtracting the end-systolic volume (ESV) from the end-diastolic volume (EDV), using the equation: Stroke volume = EDV - ESV.

Remember, cardiac output is the product of heart rate and stroke volume: Cardiac output = Heart rate x Stroke volume.

Question 11

What is the Frank-Starling mechanism?

Answer 11

The Frank-Starling mechanism describes how the heart’s stroke volume increases in response to an increase in blood volume in the ventricles before contraction, assuming all other factors remain constant.

Question 12

What is a pressure-volume diagram?

Answer 12

A pressure-volume diagram is a graphical representation that shows the relationship between pressure and volume within the heart during the cardiac cycle. It helps visualize changes in pressure and volume during various phases of the cardiac cycle.

Question 13

What is the autonomic nervous system’s role in controlling the cardiovascular system?

Answer 13

The autonomic nervous system exerts control over the cardiovascular system through various mechanisms:

Autonomic vasomotor nerves: These nerves regulate the constriction or dilation of blood vessels.
Sympathetic vasoconstriction: Sympathetic activation can cause vasoconstriction, narrowing the blood vessels.
Parasympathetic vasodilation: Parasympathetic activation can induce vasodilation, widening the blood vessels.
Sympathetic vasodilation: Under certain conditions, sympathetic activation can also result in vasodilation.
Renin-Angiotensin-Aldosterone System: This hormonal system regulates blood pressure and fluid balance.
Epinephrine (Adrenaline): Released from the adrenal glands, epinephrine can affect heart rate and blood vessel constriction.
Antidiuretic hormone/arginine vasopressin: This hormone promotes water retention and vasoconstriction.
Natriuretic peptides: These hormones promote vasodilation and increase urine production.
Other hormonal control: Various other hormones can also influence cardiovascular function.
Sensory nerve vasodilation: Sensory nerves can induce vasodilation in response to certain stimuli.

Question 14

What are the components of the autonomic nervous system?

Answer 14

The autonomic nervous system consists of:

Brainstem: Controls autonomic functions and receives sensory input.
Cranial nerves and sacral outflow: Carry autonomic signals to various organs.
End organ ganglia: Ganglia located near target organs where pre- and postganglionic fibers synapse.
Postganglionic fibers: Release neurotransmitters, such as acetylcholine (ACh) and non-adrenergic, non-cholinergic (NANC) transmitters.

Question 15

How is the autonomic nervous system involved in cardiovascular control?

Answer 15

The autonomic nervous system plays a crucial role in cardiovascular control, including the regulation of heart rate. Here are some key points:

In the absence of extrinsic control, the heart beats at approximately 100 beats per minute (bpm).
Parasympathetic stimulation decreases heart rate to a resting rate of 60-75 bpm.
Parasympathetic system predominates during rest and sleep, counteracting the sympathetic system.
Sympathetic system prepares the body for energy expenditure, emergencies, or stressful situations.
Sympathetic stimulation increases heart rate and myocardial contractility.
Most organs receive innervation from both sympathetic and parasympathetic systems, which usually have opposing actions.
Blood vessels are primarily regulated by sympathetic input, maintaining a constant state of sympathetic tone.
Vasodilation occurs when sympathetic stimulation or tone decreases.
The effect of the autonomic nervous system on the heart is the net balance between the actions of the sympathetic and parasympathetic systems.

Question 16

What are the functions of sympathetic and parasympathetic receptors in the heart and blood vessels?

Answer 16

Sympathetic and parasympathetic receptors play distinct roles in the heart and blood vessels. Here are their functions:

Sympathetic receptors in the heart (β1-adrenoceptors) increase heart rate and contractility when stimulated.
Parasympathetic receptors in the heart (M2 muscarinic receptors) decrease heart rate when activated.
Sympathetic receptors in blood vessels (α-adrenoceptors) cause vasoconstriction when stimulated.
Parasympathetic receptors do not innervate blood vessels significantly.

Question 17

What is the Renin-Angiotensin-Aldosterone System (RAAS)?

Answer 17

The Renin-Angiotensin-Aldosterone System (RAAS) is a hormonal system involved in regulating blood pressure and fluid balance. Here is a brief overview:

Renin, mainly released from juxtaglomerular cells in the afferent arteriole of the renal glomerulus, plays a central role in the RAAS.
Renin release is stimulated by various factors, including sympathetic nerve activation through β1-adrenoceptors, renal artery hypotension (caused by systemic hypotension or renal artery stenosis), and decreased sodium delivery to the distal tubules sensed by cells in the Macula Densa.
Renin cleaves angiotensinogen to form angiotensin I, which is further converted to angiotensin II by the action of angiotensin-converting enzyme (ACE).

Question 18

What is the role of angiotensin I and II and ACE in the Renin-Angiotensin-Aldosterone System (RAAS)?

Answer 18

In the RAAS, angiotensin I (Ang-I) is cleaved to form angiotensin II (Ang-II) by the action of Angiotensin Converting Enzyme (ACE). Here are some key points:

Vascular endothelium, particularly in the lungs, contains ACE, but ACE is also found in many other tissues.
Ang-II is the most active peptide in the RAAS and has two identified receptors: Type 1 and Type 2 receptors.
Type 1 receptors, when activated by Ang-II, cause vasoconstriction, cell proliferation, inflammatory responses, blood coagulation, and extracellular matrix remodeling.
Type 2 receptors counteract the effects of Type 1 receptors.
It is worth noting that the SARS-CoV-2 virus enters cells via the Type 2 receptors.

Question 19

What are the effects of angiotensin II on the cardiovascular system?

Answer 19

Angiotensin II has several effects on the cardiovascular system. Here are some key points:

Angiotensin II constricts resistance vessels, increasing systemic vascular resistance (SVR) and arterial pressure.
It stimulates sodium reabsorption at several renal tubular sites, leading to increased sodium and water retention by the body.
Angiotensin II acts on the adrenal cortex to release aldosterone, which promotes sodium and water retention.
It stimulates the release of vasopressin (antidiuretic hormone or ADH) from the posterior pituitary.
Angiotensin II stimulates thirst and can induce fluid intake.
It facilitates the release of norepinephrine from sympathetic nerve endings and inhibits its reuptake.
Angiotensin II can also stimulate cardiac hypertrophy and vascular hypertrophy.

Question 20

What is the role of the kidney in plasma volume control and hormone production?

Answer 20

The kidney plays a vital role in plasma volume control and hormone production. Here is an explanation of one hormone involved:

Aldosterone:

Angiotensin II, produced in the Renin-Angiotensin-Aldosterone System (RAAS), stimulates the release of aldosterone from the adrenal gland.
Aldosterone acts on the distal tubule and collecting duct of the kidney nephron.
It increases the reabsorption of sodium from the distal tubule, leading to increased water reabsorption as well.
This mechanism fine-tunes the absorption of sodium and water, impacting about 3% of total water absorption.
Aldosterone works synergistically with antidiuretic hormone (ADH) to increase water reabsorption through the nephron, consequently increasing blood pressure.

Question 21

What is the role of epinephrine in the body?

Answer 21

Epinephrine plays a significant role in the body and has effects on various adrenergic receptors. Here are some key points:

Sympathetic preganglionic fibers supply the adrenal medulla and terminate on chromaffin cells.
These chromaffin cells release both norepinephrine and epinephrine (adrenaline) into the bloodstream.
Epinephrine stimulates all major adrenergic receptors, including alpha 1, alpha 2, beta 1, and beta 2 receptors.
At low concentrations, epinephrine is selective for beta 2 receptors, causing vasodilation.
At higher concentrations, it stimulates other adrenergic receptors, leading to vasoconstriction, increased heart rate, and increased contractility.
Epinephrine also causes vasoconstriction in renal arterioles, reducing blood flow to the glomeruli and nephrons.

Question 22

What is the role of ADH (arginine vasopressin) in the body?

Answer 22

ADH, also known as arginine vasopressin, serves important functions in the body. Here are some key points:

ADH is synthesized in the hypothalamus and released from the posterior pituitary gland.
It is released in response to a reduction in plasma volume or an increase in plasma osmolarity, such as during hypovolemic shock.
In the cardiovascular system, ADH acts via V1 receptors to cause arteriolar vasoconstriction.
In the kidney, it acts via V2 receptors to increase the reabsorption of water from the renal tubules.

Question 23

What are the natriuretic peptides released by the heart?

Answer 23

The heart releases two natriuretic peptides:

Atrial Natriuretic Peptide (ANP)
Brain Natriuretic Peptide (BNP)

Question 24

How are natriuretic peptides produced and released?

Answer 24

Natriuretic peptides are primarily produced, stored, and released by atrial myocytes in response to atrial distention. When the atria are stretched due to increased atrial blood volume, natriuretic peptides are released.

Question 25

What is the function of natriuretic peptides?

Answer 25

Natriuretic peptides act to increase renal sodium excretion. They promote the excretion of sodium by the kidneys, helping to regulate salt and water balance in response to increased atrial blood volume and atrial distention.