CVS Physiology Quiz

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Questions and Answers

What is the primary role of autorhythmic cells in cardiac function?

To regulate the pH levels in blood

To deliver oxygen and nutrients to cardiac myocytes

To control blood pressure through vasodilation

To initiate and propagate electrical impulses for heartbeats (correct)

Which of the following best explains how the nervous system regulates heart rate?

It increases the volume of blood ejected with each heartbeat

It modulates the frequency of electrical impulses generated by autorhythmic cells (correct)

It directly influences the contraction strength of cardiac muscle

It alters the diameter of blood vessels to reduce resistance

Which of the following statements about ECG waveforms is incorrect?

The T wave represents ventricular repolarization

The ECG can illustrate electrical activities during the cardiac cycle

The P wave corresponds to atrial depolarization

The QRS complex indicates atrial contraction (correct)

What is the significance of maintaining homeostasis in relation to cardiac myocytes?

It allows for proper nutrient and waste exchange necessary for myocardial function Signup and view all the answers

Homeostatic regulation requires which of the following steps?

Detection of deviations from the norm Signup and view all the answers

What does the P wave represent in an ECG?

Depolarization of the atria Signup and view all the answers

Which leads provide information about the inferior wall of the heart?

Leads II, III, and aVF Signup and view all the answers

Why is the P wave smaller than the QRS complex?

Atria have a smaller muscle mass than ventricles Signup and view all the answers

What occurs during the PR interval in an ECG?

AV node delay Signup and view all the answers

What does the ST segment represent in an ECG?

Plateau phase of ventricular contraction Signup and view all the answers

In which situation is there no electrical activity recorded on an ECG?

While the heart muscle is at rest, ventricles filling Signup and view all the answers

What is the significance of the differential recording in an ECG?

It reflects potential differences between two electrodes Signup and view all the answers

What is the normal rate at which the ECG strip is run?

25 mm/s Signup and view all the answers

What physiological mechanism primarily acts to counteract the effects of gravity on venous return?

One-way valves in veins Signup and view all the answers

What is the primary function of the baroreceptor reflex in the context of blood pressure?

To restore blood pressure to normal levels after a decrease Signup and view all the answers

What is one consequence of incompetent venous valves?

Development of varicose veins Signup and view all the answers

How does ventricular contraction contribute to venous return?

It creates a negative pressure in the atria Signup and view all the answers

What role do respiratory activities play in venous return?

They create an external pressure gradient between lower and upper veins Signup and view all the answers

What long-term regulatory mechanism helps control blood pressure?

Reabsorption of fluid by the kidney Signup and view all the answers

What is a common cause of secondary hypertension?

Known medical conditions or diseases Signup and view all the answers

What happens to baroreceptors during chronic hypertension?

They adapt to function at a higher blood pressure level Signup and view all the answers

What occurs during isovolumetric ventricular contraction?

Ventricular volume decreases without a change in muscle length. Signup and view all the answers

Which of the following best describes end diastolic volume (EDV)?

Volume of blood in the ventricles at the end of filling. Signup and view all the answers

What electrical event corresponds with ventricular excitation in the heart cycle?

QRS complex Signup and view all the answers

What happens when ventricular pressure exceeds aortic pressure?

The aortic valve opens and blood is ejected. Signup and view all the answers

Which heart sound occurs due to the closure of the AV valves?

1st heart sound Signup and view all the answers

At what stage of the cardiac cycle does ventricular repolarization occur?

T wave Signup and view all the answers

What physiological event corresponds with the dicrotic notch in the aortic pressure curve?

Closure of the aortic valve Signup and view all the answers

During which phase does the left ventricular pressure drop significantly?

Ventricular relaxation Signup and view all the answers

During which phase is the ventricular pressure less than the atrial pressure, leading to the opening of the AV valves?

Ventricular filling Signup and view all the answers

What happens to the left atrial pressure during the rapid filling phase?

Increases due to blood rush from veins Signup and view all the answers

Which phase involves no change in volume but an increase in pressure?

Isovolumetric contraction Signup and view all the answers

What is the primary function of the aortic pressure during systole?

To assist in the ejection of blood into the aorta. Signup and view all the answers

What is the primary purpose of the isovolumetric relaxation phase?

To reset ventricular pressure for the next contraction Signup and view all the answers

What occurs when the SA node fires and the impulse spreads through the atria?

Atrial contraction (P wave) Signup and view all the answers

What happens during the ejection phase of the cardiac cycle?

Blood is actively pumped from the ventricles into the aorta. Signup and view all the answers

Which of the following statements describes end systolic volume (ESV)?

It represents the amount of blood remaining in the ventricles after contraction. Signup and view all the answers

What occurs during the rapid filling phase of the ventricles?

Blood rapidly fills the ventricles Signup and view all the answers

When is the first heart sound typically heard?

At the end of isovolumetric contraction Signup and view all the answers

What describes the condition when ventricular and aortic pressures are equal?

Ejection phase end Signup and view all the answers

Which event signifies the transition from systole to diastole?

Closure of the aortic valve Signup and view all the answers

Which statement accurately describes the left ventricular pressure during the diastolic phase?

It remains constant and falls steadily Signup and view all the answers

What is the consequence of ventricular pressure being less than aortic pressure immediately after blood ejection?

The heart enters a state of diastole. Signup and view all the answers

What occurs to the left ventricular chamber volume during the end-systolic phase?

It remains constant Signup and view all the answers

What physiological change primarily causes an increase in atrial pressure during ventricular relaxation?

Increased blood return from systemic circulation Signup and view all the answers

What occurs at the closure of the aortic valve during the cardiac cycle?

Isovolumetric contraction begins Signup and view all the answers

During the ejection phase, what ensures the unidirectional flow of blood from the ventricles?

High pressure in the ventricles Signup and view all the answers

What vital role does the T wave represent in the electrocardiogram?

Ventricular repolarization Signup and view all the answers

What primarily contributes to the plateau phase of the action potential in cardiac contractile cells?

Slow inward diffusion of calcium ions Signup and view all the answers

What effect does the slow removal of calcium ions have on cardiac muscle contraction?

It prolongs the contraction duration Signup and view all the answers

During one cardiac cycle, which interval represents the time taken for one complete heartbeat?

RR interval Signup and view all the answers

How does calcium entry from the extracellular fluid impact cardiac muscle cells?

It induces a larger release of calcium from the sarcoplasmic reticulum Signup and view all the answers

What is the main physiological consequence of prolonged influx of calcium during cardiac action potentials?

Enhanced force of contraction Signup and view all the answers

Which structure has the highest rate of action potential generation in the heart?

SA node Signup and view all the answers

What is the main purpose of the slight delay at the AV node during cardiac excitation?

To ensure ventricles are fully filled before contraction Signup and view all the answers

Which of the following factors does NOT directly influence the heart rate through the autonomic nervous system?

Oxygen saturation levels Signup and view all the answers

When cardiac muscle fibers are excited, what is the primary outcome?

Contraction of the myocardium occurs. Signup and view all the answers

How do the sympathetic and parasympathetic systems affect heart rate at rest?

Parasympathetic activity prevails, decreasing heart rate. Signup and view all the answers

Which factor contributes to the consistent rhythm of the heart under resting conditions?

Constant depolarization of the SA node Signup and view all the answers

What does an electrocardiogram (ECG) primarily record?

Electrical events in the heart from the body surface Signup and view all the answers

Which layer of the heart is primarily responsible for its contraction?

Myocardium Signup and view all the answers

Which event corresponds to the first heart sound being heard?

Closure of the AV valves Signup and view all the answers

What characterization of isovolumetric ventricular contraction is correct?

Volume remains constant while pressure increases Signup and view all the answers

What physiological change occurs during the ejection phase of the cardiac cycle?

Ventricular pressure becomes greater than aortic pressure Signup and view all the answers

In which phase of the cardiac cycle does left atrial pressure play a crucial role in opening the AV valves?

Rapid filling phase Signup and view all the answers

What event marks the transition from systole to diastole in the cardiac cycle?

Ventricular pressure dropping below atrial pressure Signup and view all the answers

Which of the following occurs at the peak of the ventricular pressure curve?

Blood ejection into the aorta begins Signup and view all the answers

Which wave on the electrocardiogram corresponds to ventricular repolarization?

T wave Signup and view all the answers

What is the primary characteristic of end systolic volume (ESV)?

Volume of blood remaining after ejection Signup and view all the answers

During which phase does isovolumetric relaxation occur?

Immediately following the ejection phase Signup and view all the answers

What condition exists when ventricular and aortic pressures are equal?

Aortic valve closure Signup and view all the answers

What physiological change primarily causes a rise in atrial pressure during ventricular relaxation?

Passive filling from the vena cava Signup and view all the answers

Which of the following events occurs at point 9 on the cardiac cycle diagram?

Ventricular contraction begins Signup and view all the answers

What leads to the creation of the dicrotic notch in the aortic pressure curve?

Closure of the semilunar valves Signup and view all the answers

During which phase does the left atrial pressure increase due to the continuous influx of blood from the veins?

Ventricular diastole Signup and view all the answers

What occurs regarding ventricular volume at point 14 during the cardiac cycle?

Volume significantly decreases Signup and view all the answers

What triggers the closing of the aortic valves during the cardiac cycle?

Ventricular pressure dropping below aortic pressure Signup and view all the answers

What occurs immediately after the SA node fires and the impulse spreads through the atria?

Contraction of atrial muscles Signup and view all the answers

Which event corresponds with the closure of the AV valves in the cardiac cycle?

Beginning of isovolumetric contraction Signup and view all the answers

What is primarily responsible for the constant volume of the left ventricular chamber during isovolumetric contraction?

All valves remain closed Signup and view all the answers

What happens to the left atrial pressure during the rapid filling phase?

It increases dramatically Signup and view all the answers

Which pressure phase indicates that ventricular pressure has exceeded atrial pressure, causing the AV valves to close?

Early systolic phase Signup and view all the answers

What phase is characterized by no change in volume but a notable rise in pressure within the ventricles?

Isovolumetric contraction phase Signup and view all the answers

What effect does ventricular contraction have on the flow of blood into the aorta?

Promotes ejection of blood into the aorta Signup and view all the answers

What is the principal action occurring during the isovolumetric relaxation phase?

All valves are closed Signup and view all the answers

During which phase does the ventricular volume begin to decrease as blood is ejected into the aorta?

Ejection phase Signup and view all the answers

What physiological condition is signified by the equalization of ventricular and aortic pressures?

Ejection phase transition Signup and view all the answers

What marks the beginning of the rapid filling phase of the ventricles?

Opening of the AV valves Signup and view all the answers

What is observed during the end-systolic phase of the cardiac cycle?

Minimum ventricular volume attained Signup and view all the answers

Which factor contributes to the slow down of filling during late diastole?

Decreased atrial pressure Signup and view all the answers

What primarily determines the fraction of total cardiac output delivered to each organ?

Local metabolic demands Signup and view all the answers

How do pre-capillary sphincters respond to increased metabolic activity in tissues?

They relax to allow more blood flow. Signup and view all the answers

What is the role of sympathetic innervation in regulating venous return?

Causes vasoconstriction to increase venous pressure Signup and view all the answers

What effect does increased skeletal muscle activity have on venous return?

Increases vein compression during contraction Signup and view all the answers

What mechanism ensures that blood flow remains the same throughout the circulatory system despite the varying diameters of blood vessels?

Constant total flow rate Signup and view all the answers

Which factor contributes to the drop in blood pressure as blood moves from arteries to veins?

Increased resistance in capillaries Signup and view all the answers

During exercise, what is the main effect on blood flow distribution?

More blood to skeletal muscles and the heart Signup and view all the answers

Which of the following hormones is known to produce generalized vasoconstriction?

Vasopression Signup and view all the answers

What happens to pre-capillary sphincters during a state of rest in metabolic inactive tissues?

Many capillaries remain closed. Signup and view all the answers

How does the body compensate for the effects of gravity on venous return when standing up?

Triggers sympathetic vasoconstriction. Signup and view all the answers

What is the primary physiological purpose of local control mechanisms over arteriolar radius?

To ensure organs receive blood based on their metabolic needs. Signup and view all the answers

What causes blood velocity to decrease significantly in capillaries?

Greater surface area due to branching Signup and view all the answers

What is the effect of vascular tone on arterioles?

It establishes a baseline of arteriolar resistance. Signup and view all the answers

What defines total peripheral resistance (TPR)?

The combined resistance offered by all peripheral blood vessels Signup and view all the answers

Study Notes

Homeostasis

The internal environment of the body is the fluid that surrounds cells, allowing for life-sustaining exchanges. This fluid is also known as extracellular fluid, and the fluid inside cells is termed intracellular fluid
Homeostasis maintains a relatively stable internal environment.
The body must detect deviations from the norm, integrate this information with other information, and execute a response
Body temperature is maintained at a set point of 37.2°C. Deviation from this point is corrected by mechanisms within the body

ECG

The Electrocardiogram (ECG) is not a direct recording of the electrical activity of the heart
This is the overall spread of electrical activity through the heart during depolarization and repolarization
It is a sum of the electrical activity going through the heart
It is a differential recording calculated by measuring the potential difference between two electrodes

12 Lead ECG

Electrodes placed on specific locations on the chest, limbs and back
Each lead forms an axis in the vertical or horizontal plane.
Each lead provides electrical information about the heart from a unique “vantage point” (spatial location)
Lead II is located directly at the apex of the left ventricle.
Leads V2, V3 and V4 are horizontal and look at the anterior part of the left ventricle.
The 12-lead ECG can help localize an infraction in the heart.
Each of the 12 leads can monitor a specific part of the heart, and therefore a specific coronary artery
Anatomical relationships of leads to specific areas of the heart:
- Inferior wall – Leads II, III and aVF
- Anterior wall – Leads V1 to V4
- Lateral wall – Leads I, aVL, V5 and V6

Typical Lead II ECG Waveform

Represents millivolts over time
Higher muscle mass depolarization means higher voltage
Normal rate at which an ECG strip is run is 25mm/s
The p- wave is the first wave to be sensed as it is when the impulse spreads through the atria. The SA node firing does not generate sufficient electrical activity to be recorded.
Atrial depolarization is masked by ventricular depolarization, which is why atrial repolarization is not observed on the ECG
The P wave is smaller because the atria have smaller muscle mass.
There are three occasions where there’s no electrical activity, and therefore no signal on the ECG
- AV node delay (PR segment)
- Ventricles completely depolarised, and cardiac cells undergoing plateau phase (ventricles contracting) (ST segment)
- Heart muscle at rest, ventricles filling
The PR interval (0.12s-0.20s) represents the time it takes for the signal to travel from the SA node to the AV node, the time it takes for the AV node delay, and then the time it takes for the signal to travel to the bundle of His.

Ventricular Contraction

An impulse passes through the AV node.
Ventricular excitation is represented by the QRS complex on an electrocardiogram.
A sharp increase in ventricular pressure occurs.
The first heart sound occurs when the AV valves close.
The isovolumetric ventricular contraction phase begins when all valves are closed, there is no change in volume or muscle length, but pressure continues to increase.
Ventricular pressure exceeds aortic pressure causing the aortic valve to open and blood to be ejected.
Aortic pressure increases.
Ventricular volume decreases as blood is pumped into the aorta.
Ventricular volume decreases as blood is pumped into the aorta faster than blood can drain off from smaller vessels at the other end.

Ventricular Repolarization and Diastole

End systolic volume (ESV) is reached with some blood not pumped out.
Ventricular repolarisation is represented by the T wave on an electrocardiogram.
Ventricles relax and pressure drops.
The pressure drops to a point where aortic pressure now exceeds ventricular pressure and the aortic valve closes. This is represented by the second heart sound.
The ventricles are now in the isovolumetric relaxation phase.
Left atrial pressure begins to rise while ventricular pressure continues to drop.
The AV valve opens and rapid filling of the ventricle begins (ventricular filling).
The cycle repeats.

Heart Sounds

First heart sound is generated during ventricular contraction when the AV valves close
Second heart sound is generated when the semilunar valves close at the end of ventricular ejection

Ventricular Filling

Ventricular filling occurs during diastole
Ventricular filling occurs in three phases: rapid filling, reduced filling, and diastasis

Rapid Filling

Occurs when the AV valves open
Driven by the pressure gradient between atria and ventricles
Occurs immediately after the semilunar valves close
Leads to a sharp increase in ventricular volume

Reduced Filling

Occurs when the pressure gradient between atria and ventricles decreases
Ventricular filling slows down

Diastasis

Occurs towards the end of diastole
Minimal change in ventricular volume
Driven by passive flow of blood from veins

Ventricular Contraction

Occurs during systole
Begins with isovolumetric contraction
Isovolumetric contraction occurs when the AV and semilunar valves are closed and ventricular pressure increases
Ventricular pressure eventually exceeds aortic pressure, causing the semilunar valves to open
Ejection begins when the semilunar valves open, and ventricular pressure decreases

Ventricular Relaxation

Occurs during diastole
Begins with isovolumetric relaxation
Isovolumetric relaxation occurs when the semilunar valves close, but the AV valves remain closed
This causes the pressure in the ventricles to decrease, and the AV valves open

Valves

Valves are one-way and spaced 2-4 cm apart
Their function is to prevent backflow and aid in the process of moving blood against gravity
Incompetent venous valves are a common cause of varicose veins

Effect of Gravity

Gravity can cause a decrease in blood pressure, especially when standing for long periods
Prolonged standing can lead to venous pooling, which can further decrease blood pressure and cause fainting

Other Factors Affecting Venous Return

Respiratory activity aids in venous return by creating a pressure gradient between the lower veins and the chest veins
Cardiac suction aids venous return by creating a vacuum effect during ventricular contraction and relaxation

Short-Term Regulation of Blood Pressure

Baroreceptor reflex is a key component of short-term blood pressure regulation
Baroreceptors are pressure sensors located in the carotid sinus and aortic arch
They detect changes in blood pressure and send signals to the cardiovascular center in the brainstem
Cardiovascular center adjusts sympathetic and parasympathetic nervous system activity to regulate heart rate, stroke volume, and peripheral vascular resistance

Long-Term Regulation of Blood Pressure

Long-term blood pressure regulation is primarily achieved by regulating blood volume
The kidneys play a key role in regulating blood volume by adjusting fluid reabsorption
Renin-angiotensin system is a key hormonal system involved in long-term blood pressure regulation

Hypertension

Hypertension is a major public health problem with unknown causes
There are two main types: primary and secondary
Baroreceptors adapt to maintain blood pressure at a higher level in individuals with hypertension.

Learning Outcomes

Students will be able to describe the events of the cardiac cycle
Students will be able to explain the changes in pressure and volume in the heart chambers
Students will learn to explain the ECG in the context of the cardiac cycle

Heart Sounds and Stages of the Cardiac Cycle

The heart sounds are generated by the closing of the valves in the heart.
The first heart sound occurs during ventricular contraction when the atrioventricular (AV) valves close.
The second heart sound is heard at the end of ventricular contraction, when the aortic and pulmonary valves close, initiating ventricular relaxation.
The volume of blood left in the ventricle at the end of diastole is known as the end diastolic volume (EDV).
The volume of blood remaining in the ventricle at the end of systole is known as the end systolic volume (ESV).

Ventricular Contraction

The QRS complex on an electrocardiogram (ECG) corresponds to the electrical stimulation of the ventricles, which triggers ventricular contraction.
The QRS complex also corresponds to the first heart sound (1st heart sound), and marks the onset of ventricular contraction.
Ventricular pressure increases at the start of ventricular contraction (marked as "9" in the image).
At this point, the AV valves close to prevent backflow into the atria.
This period is known as isovolumetric ventricular contraction as volume remains unchanged despite the increase in pressure.
Aortic valve opens (marked as "12", at the point where ventricular pressure exceeds aortic pressure) with blood ejected into the aorta.
This leads to an increase in aortic pressure as the blood is pumped into the aorta faster than it exits into the smaller vessels.
Ventricular volume decreases as blood is ejected during ventricular contraction and ejection (marked as "14").

Ventricular Repolarisation and Diastole

The T wave on an ECG represents the electrical repolarisation of the ventricles, marking the relaxation of the muscle.
Repolarisation of the ventricles initiates ventricular relaxation.
End systolic volume (ESV) is the volume left in the ventricle after the blood ejection phase is complete.
As ventricular pressure drops (marked as "17") below aortic pressure, the aortic valve closes (marked as "18"), generating the second heart sound (2nd heart sound).
This creates a period of isovolumetric ventricular relaxation, during which the ventricles relax, but there is no change in volume.
Pressure continues to drop as ventricular relaxation progresses.
As ventricular pressure drops below atrial pressure, the AV valves open (marked as "21"), initiating the rapid filling phase of the heart cycle.

Cardiac Cycle: Ventricular Filling

Isovolumetric Relaxation: Ventricular pressure decreases rapidly, all valves closed, ventricle volume remains constant.
Passive Filling: Ventricular pressure < atrial pressure, AV valves open, rapid flow of blood into ventricles due to pressure gradient.
Slow Filling: Filling slows down as ventricles are nearly full.
Atrial Contraction: Atrial pressure increases due to constant blood flow from veins, AV valves open allowing remaining blood into ventricles.
End Diastolic Volume: Ventricle is filled with maximum volume of blood, SA node fires triggering atrial contraction.

Cardiac Cycle: Ventricular Ejection

Isovolumetric Contraction: All valves closed, ventricle volume remains constant and pressure increases.
Ejection Phase: Ventricular pressure exceeds aortic pressure, aortic valve opens and blood flows into aorta.
End Systolic Volume: Minimal volume of blood remaining in ventricle, aortic valve closes.

Cardiac Cycle: Sounds & Electrocardiogram

Heart Sounds:
- 1st Heart Sound: AV valves closing at the start of isovolumetric contraction.
- 2nd Heart Sound: Aortic valve closing at the end of ejection.
Electrocardiogram:
- P wave: Atrial depolarization, leading to atrial contraction.
- QRS Complex: Ventricular depolarization leading to ventricular contraction.
- T wave: Ventricular repolarization, as ventricles relax.

Blood Pressure

Blood pressure is affected by cardiac output and total peripheral resistance.
Blood pressure needs to be closely regulated:
- High enough to maintain blood flow and tissue perfusion.
- Not too high to overwork the heart and cause vascular damage or rupture of small vessels.
Cardiac output, heart rate, stroke volume, arteriolar radius and blood viscosity all have an effect on blood pressure.

Arteries

Arterial blood pressure is relatively constant throughout the arterial system.
Pressure drops from arteries to veins as blood flow becomes less pulsatile.

Capillaries

Thin walls facilitate exchange of substances.
Extensive branching ensures proximity to every cell.
Red blood cells pass through in a single file.
Blood velocity is very slow compared to arteries.
Total flow rate (5L/min) remains constant throughout the system due to increased surface area.

Pre-capillary Sphincters

Tissues with high metabolic activity require more capillaries.
Many capillaries remain closed during resting conditions.
Capillaries lack smooth muscle, therefore pre-capillary sphincters control blood flow.
Sphincters are sensitive to local metabolic activity changes.
Increased metabolic activity relaxes the sphincter, opening more capillaries and increasing blood flow to active tissues.

Regulation of Blood Flow and Distribution

Local control of arteriolar radius is important in determining the distribution of cardiac output.
The fraction of total cardiac output delivered to each organ varies depending on blood demand.
The differences in flow to organs are determined by variations in vascularization and resistance offered by arterioles supplying each organ.

Vasoregulation of Arterioles

Vasoconstriction refers to narrowing of the arteriole.
Vasodilation refers to widening of the arteriole.
Vascular tone refers to the state of partial constriction of the arteriolar smooth muscle.
Vascular tone establishes a baseline for arteriolar resistance.

Extrinsic Control of Arteriolar Radius

Plays a crucial role in regulating blood pressure.
Sympathetic fibers supply arteriolar smooth muscle everywhere except in the brain.
Increased sympathetic activity causes generalized vasoconstriction.
Decreased sympathetic activity causes generalized vasodilation.
Local controls can override sympathetic vasoconstriction.
There is no parasympathetic innervation to arterioles except in the penis and clitoris.

Cardiovascular Control Center

Controls sympathetic output.

Adrenal Hormones

Norepinephrine leads to generalized vasoconstriction.
Epinephrine reinforces local vasodilatory mechanisms, particularly in skeletal muscles and the heart.

Vasopressin and Angiotensin II

Potent vasoconstrictors.
Vasopressin regulates water balance.
Angiotensin II regulates salt balance.

During Exercise

Cardiac output increases.
Vasodilation occurs in skeletal muscle and heart.
More blood is diverted to these organs.
Body heat increases.
Vasodilation of the skin also occurs, resulting in flushed skin.

Venous Return

Blood returning to the heart.
Veins act as a blood reservoir due to their low resistance, less elastic recoil, and less smooth muscle.
Slow transit time through veins allows them to store blood.
Venous capacity (amount of blood veins can hold) depends on vessel wall distensibility and external pressures like skeletal muscle squeezing.
During exercise, stored blood is needed, increasing venous return.

Regulation of Venous Return

Sympathetic innervation of veins causes vasoconstriction, increasing venous pressure.
Skeletal muscle activity compresses veins, decreasing venous capacity and increasing venous pressure. This is known as the skeletal muscle pump.
Gravity affects venous return, particularly when standing up, as hydrostatic pressure causes blood to pool in the veins below the heart.

Effect of Gravity

Compensatory mechanisms when shifting from lying down to standing up include:
- Sympathetic venous vasoconstriction.
- The skeletal muscle pump.
- Sympathetic venous vasoconstriction is insufficient without the skeletal muscle pump.
- Blood pooling occurs in extended veins, decreasing venous return and cardiac output.

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Description

This quiz covers the essential concepts of homeostasis, including the internal environment of the body and its mechanisms to maintain stability. Additionally, it explores the Electrocardiogram (ECG), detailing how it captures the heart's electrical activity and the significance of a 12 Lead ECG setup.