Blood Flow and Vascular Distensibility Chapter 15

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the primary mechanism by which smooth muscles in blood vessels resist excessive stretching?

By increasing the diameter of the vessel

By relaxation of the smooth muscle

By decreasing the blood pressure

By constriction of the smooth muscle (correct)

What is the result of a decrease in vascular resistance in response to low blood pressure?

An increase in smooth muscle relaxation

An increase in blood flow (correct)

A decrease in smooth muscle contraction

A decrease in blood flow

What is the name of the mechanism that regulates blood flow in the kidneys?

Autoregulation

Humoral control

Tubuloglomerular feedback (correct)

Myogenic theory

What is the primary function of vascular distensibility in arteries?

To average out pressure pulsations and provide smooth, continuous flow of blood Signup and view all the answers

Which of the following vessels is more distensible in the pulmonary circulation?

Arteries Signup and view all the answers

Where is the macula densa located?

At the juxtaglomerular apparatus Signup and view all the answers

What is the relationship between vascular compliance and distensibility?

Compliance is directly proportional to distensibility Signup and view all the answers

What is the result of constriction of the afferent arterioles in the kidney?

A decrease in renal blood flow Signup and view all the answers

What plays a prominent role in local blood flow control in the brain?

Concentration of carbon dioxide and hydrogen Signup and view all the answers

How does sympathetic stimulation affect vascular capacitance?

It decreases vascular capacitance Signup and view all the answers

What is the general mechanism for local blood flow control present in most tissues of the body?

Autoregulation Signup and view all the answers

What is the ratio of distensibility of veins to arteries in the systemic circulation?

8:1 Signup and view all the answers

What is the formula for vascular distensibility?

Increase in volume / (Increase in pressure × Original volume) Signup and view all the answers

What is still debated by physiologists regarding autoregulation of blood flow?

The relative importance of the myogenic and metabolic mechanisms Signup and view all the answers

What is the ratio of compliance of a vein to its corresponding artery in the systemic circulation?

24:1 Signup and view all the answers

Why do local autoregulatory mechanisms override the effects of vasoconstrictors?

To provide a blood flow that is appropriate for the needs of the tissue Signup and view all the answers

What is the primary factor that increases pulse pressure when the arteries 'harden' with aging?

Decreased arterial compliance Signup and view all the answers

What is the effect of aortic valve stenosis on the aortic pulse pressure?

It decreases the aortic pulse pressure Signup and view all the answers

What is the result of patent ductus arteriosus on the pulse pressure?

It increases the pulse pressure Signup and view all the answers

What is the effect of arteriosclerosis on the arteries?

It decreases the arterial compliance Signup and view all the answers

What is the result of aortic regurgitation on the aortic valve?

The aortic valve becomes less competent Signup and view all the answers

What is the relationship between stroke volume and pulse pressure?

Increased stroke volume increases pulse pressure Signup and view all the answers

What is the effect of patent ductus arteriosus on the diastolic pressure?

It decreases the diastolic pressure Signup and view all the answers

What is the result of decreased arterial compliance on the pulse pressure?

It increases the pulse pressure Signup and view all the answers

What is the hydrostatic value of venous pressure when a person stands perfectly still?

90 mm Hg Signup and view all the answers

What happens to the valves of the venous system when they become incompetent or are destroyed?

Their effectiveness is decreased Signup and view all the answers

What is the result of varicose veins developing and the venous and capillary pressures increasing to high levels?

Leakage of fluid from the capillaries and edema in the legs Signup and view all the answers

What percentage of the blood in the circulatory system is usually contained in the veins?

60 percent Signup and view all the answers

What is the function of the venous system as a blood reservoir?

To provide a reserve of blood for the circulation Signup and view all the answers

Which of the following is NOT a part of the circulatory system that serves as a blood reservoir?

The kidneys Signup and view all the answers

How much blood can the spleen release into the circulation when it decreases in size?

100 milliliters Signup and view all the answers

What is the total amount of blood that can be contributed by the venous plexus underneath the skin and the large abdominal veins?

500 milliliters Signup and view all the answers

Which of the following vessels are not innervated by sympathetic nerve fibers?

Capillaries Signup and view all the answers

What is the effect of sympathetic stimulation on the small arteries and arterioles?

Increases vascular resistance and decreases blood flow Signup and view all the answers

What is the main role of the parasympathetic system in controlling the circulation?

To decrease heart rate and slightly decrease heart muscle contractility Signup and view all the answers

What is the distribution of vasoconstrictor fibers in the sympathetic nerves?

In almost all segments of the circulation Signup and view all the answers

Where is the vasomotor center located in the brain?

In the reticular substance of the medulla and the lower third of the pons Signup and view all the answers

What is the effect of sympathetic stimulation on the heart?

Increases the rate and strength of pumping Signup and view all the answers

Through which nerves do the sympathetic impulses transmit to the blood vessels?

Peripheral sympathetic nerves Signup and view all the answers

Which of the following is a result of sympathetic stimulation of large vessels?

Decreases the volume of the vessels Signup and view all the answers

Study Notes

Vascular Distensibility and Functions of the Arterial and Venous Systems

Vascular distensibility allows arteries to accommodate the pulsatile output of the heart and average out pressure pulsations, providing smooth, continuous flow of blood through small blood vessels of tissues.
Veins are more distensible than arteries, allowing them to store large quantities of blood that can be called into use when needed.
Vascular distensibility is normally expressed as Increase in volume / (Increase in pressure × Original volume).
Vascular compliance (capacitance) is the total quantity of blood that can be stored in a given part of the circulation for each millimeter of mercury of pressure.

Factors Affecting Vascular Distensibility and Compliance

The compliance of a vein in the systemic circulation is about 24 times as great as its corresponding artery because it is about eight times as distensible and has a volume that is three times as great.
Sympathetic stimulation decreases vascular capacitance.
The two most important factors that can increase pulse pressure are increased stroke volume and decreased arterial compliance.
Decreased arterial compliance can result when the arteries "harden" with aging (arteriosclerosis).

Abnormal Pressure Pulse Contours

With aortic valve stenosis, the aortic pulse pressure is greatly decreased because of diminished blood flow through the stenotic aortic valve.
With patent ductus arteriosus, some of the blood pumped into the aorta flows immediately through the open ductus arteriosus into the pulmonary artery, allowing the diastolic pressure to fall very low before the next heartbeat, thereby increasing pulse pressure.
With aortic regurgitation, the aortic valve is absent or functions poorly.

The Veins Function as Blood Reservoirs

More than 60 percent of the blood in the circulatory system is usually contained in the veins.
The venous system can serve as a blood reservoir for the circulation.
When blood is lost from the body, activation of the sympathetic nervous system causes the veins to constrict, which takes up much of the "slack" of the circulatory system caused by the lost blood.

Mechanisms for Blood Flow Control in Specific Tissues

The myogenic theory of autoregulation suggests that sudden stretch of small blood vessels causes the smooth muscles in the vessel walls to contract automatically.
In the kidneys, blood flow is regulated, in part, via a mechanism called tubuloglomerular feedback.
In the brain, the concentrations of carbon dioxide and hydrogen play prominent roles in local blood flow control.

Autonomic Control of the Circulation

Sympathetic stimulation of the small arteries and arterioles increases the vascular resistance and decreases the rate of blood flow through the tissues.
Innervation of large vessels, especially the veins, makes it possible for sympathetic stimulation to decrease the volume of the vessels.
Parasympathetic stimulation decreases heart rate markedly and slightly decreases heart muscle contractility.

Control of the Sympathetic Vasoconstrictor System

The sympathetic nerves carry large numbers of vasoconstrictor nerve fibers and only a few vasodilator fibers.
The vasoconstrictor fibers are distributed to almost all segments of the circulation.
Vasomotor centers of the brain control the sympathetic vasoconstrictor system.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Learn about the regulation of blood flow and vascular distensibility, including the role of vasoconstrictors and local autoregulatory mechanisms. Understand the functions of arterial and venous systems.