Human Physiology Week 6b

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Questions and Answers

What is the primary factor that allows blood to flow from the veins into the right atrium?

High pressure in the veins

Low pressure in the right atrium (correct)

High resistance in the veins

High viscosity of blood

Which mechanism can lead to an increase in venous return?

Muscle contraction surrounding the veins (correct)

Decrease in systemic blood pressure

Vasodilation of veins

Increase in right atrial pressure

What happens to venous return when there is an increase in right atrial pressure?

Venous return increases significantly

Venous return remains unchanged

Venous return decreases (correct)

Venous return fluctuates rapidly

How does vasoconstriction of veins affect venous return?

It increases pressure in the veins Signup and view all the answers

What is the typical pressure in the right atrium under normal conditions?

Around 0 mmHg or lower Signup and view all the answers

What is the primary difference in pressure between the left and right sides of the heart during systole?

The left side has significantly higher pressure than the right side. Signup and view all the answers

Why does the left side of the heart require more powerful contractions compared to the right side?

Blood from the left side has to travel longer distances. Signup and view all the answers

What is the approximate diastolic pressure in the pulmonary arteries?

7 mmHg Signup and view all the answers

How does the systolic blood pressure of the right ventricle compare to that of the aorta?

The systolic pressure in the right ventricle is significantly lower than in the aorta. Signup and view all the answers

What role do the pulmonary arteries play in the circulatory system?

They carry deoxygenated blood from the heart to the lungs. Signup and view all the answers

What is the main purpose of the Bainbridge reflex?

To increase heart rate in response to elevated right atrial pressure Signup and view all the answers

Which hormone is released when the atria are stretched from chronically elevated right atrial pressure?

Atrial natriuretic peptide (ANP) Signup and view all the answers

When does blood start to accumulate in the right atrium?

When the atrioventricular valve is closed during systole Signup and view all the answers

Which pressure is typically observed in the right atrium during normal conditions?

0 mmHg Signup and view all the answers

What happens to the heart rate when the Bainbridge reflex is activated?

The heart rate increases to help reduce blood accumulation Signup and view all the answers

What is the consequence of an increased end systolic volume in the right ventricle?

More blood left in the right ventricle at the end of systole Signup and view all the answers

How does decreased venous pressure affect venous return?

It decreases venous return due to reduced pressure gradient Signup and view all the answers

What happens to stroke volume if venous return decreases?

Stroke volume decreases due to reduced filling of the heart Signup and view all the answers

Which of the following factors contributes to increased venous pressure?

Increased total blood volume Signup and view all the answers

What physiological reflex helps regulate elevated right atrial pressure?

Bainbridge reflex Signup and view all the answers

Study Notes

Right Atrial Pressure and Venous Return

Right atrial pressure is important for physiological regulation.
Elevated right atrial pressure leads to a smaller pressure gradient between the vena cava and the right atrium, decreasing venous return, which can be problematic.
Bainbridge reflex: Right atrial pressure receptors detect elevated pressure and stimulate the cardiovascular control center in the brain to increase heart rate, which helps remove blood from the atrium.
Atrial natriuretic peptide (ANP): With chronically elevated right atrial pressure, the atrium stretches and releases ANP, which helps the kidneys increase filtration and remove excess water from the body.

Venous Return and its relationship to atrial pressure

Blood flows from high pressure areas to low pressure areas.
Venous blood pressure is around 7 mm Hg, while right atrial pressure is typically around 0 mm Hg.
This pressure gradient facilitates blood flow from the vena cava to the right atrium.
During systole when the atrioventricular valve is closed, blood accumulates in the right atrium, causing a slight increase in right atrial pressure until the valve reopens, allowing blood to flow into the ventricle.
If there is a backup in the right ventricle, or if the valve is unable to open properly, blood will accumulate in the right atrium, further increasing right atrial pressure.
As more blood enters the right atrium, it may flow to the right ventricle, increasing the ventricle's pressure. The pressure increase is important for contracting the ventricle and moving blood to the lungs.
When the valve closes, blood accumulates in the right atrium, increasing its pressure. This is a normal physiological response to the pumping cycle of the heart.

Right Atrial Pressure

If blood cannot leave the right ventricle, pressure will build up in the right atrium.
Factors that could lead to difficulty in blood leaving the right ventricle include weak ventricle contractility and high pulmonary arterial pressure (increased afterload).
Increased pressure in the right atrium can stimulate low-pressure (baroreceptors) receptors.
Stimulation of the low-pressure receptors sends a signal to the cardiovascular control center (cardiovascular center) which triggers an increase in heart rate. This response is known as the Bainbridge reflex.
Atrial natriuretic peptide (ANP or ANF) is released from the right atrium when the atrium is stretched, helping to reduce plasma volume and blood pressure.

Venous Return & Edema

Backflow of blood in the right ventricle leads to increased pressure in the right atrium, eventually causing pressure to increase in the vena cava.
Pressure buildup in the vena cava can lead to increased pressure in veins, venules and capillaries.
Increased pressure in the capillaries on the venous end causes fluid to accumulate in the interstitial space, leading to edema.

Factors that Influence Venous Return

Increased blood volume increases venous pressure, leading to increased venous return.
Dehydration or blood loss decreases venous pressure, leading to decreased venous return.
Venous vasoconstriction increases venous pressure which leads to increased venous return.

Factors that Influence Right Atrial Pressure

Right atrial pressure is influenced by the strength of the right ventricle (contractility) and the resistance to blood flow from the right ventricle into the pulmonary arteries (afterload).
High pulmonary arterial pressure increases the afterload, making it harder for blood to leave the right ventricle.
A weak right ventricle struggles to pump blood effectively, leading to backflow and increased pressure in the right atrium.

Venous Return and Heart Function

Increased venous return leads to a larger end diastolic volume in the right ventricle, contributing to a stronger contraction and increased stroke volume.
The relationship between end diastolic volume and stroke volume is known as the Frank-Starling mechanism.
Venous return is a key factor in regulating cardiac function, contributing to the overall blood flow and the effectiveness of the heart's contractions.

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Human Physiology Week 6b - Transcripts

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