Cardiovascular Physiology: Microcirculation

Questions and Answers

What is the primary function of interstitial fluid hydrostatic pressure (Pif)?

To promote filtration

To increase capillary oncotic pressure

To regulate blood pressure

To drive fluid out of the interstitial space into the capillaries (correct)

What type of pressure is responsible for pushing fluid out of the capillaries?

Interstitial fluid hydrostatic pressure

Hydrostatic pressure (correct)

Capillary oncotic pressure

Blood pressure

What is the approximate pressure of the capillary venous end?

20 mmHg

17 mmHg (correct)

10 mmHg

25 mmHg

What is the primary function of albumin molecules in capillary fluid exchange?

To carry charged particles and attract Na ions Signup and view all the answers

What is the result of the interaction between albumin and Na ions?

A strong attraction of Na ions Signup and view all the answers

What is the primary force opposing filtration in capillary fluid exchange?

Interstitial fluid hydrostatic pressure Signup and view all the answers

What is the typical value of interstitial fluid hydrostatic pressure (Pif)?

Near zero or slightly negative Signup and view all the answers

What is the function of capillary oncotic pressure (πp)?

To pull fluid back into the capillaries Signup and view all the answers

What is the relationship between albumin and capillary oncotic pressure?

Albumin increases capillary oncotic pressure Signup and view all the answers

What is the primary plasma protein responsible for colloid osmotic pressure in the intravascular space?

Albumin Signup and view all the answers

Which pressure favors filtration at the arterial side of the capillaries?

Capillary hydrostatic pressure Signup and view all the answers

What is the net filtration pressure (NFP) when arterial hydrostatic pressure is 35 mmHg and interstitial fluid oncotic pressure is 0 mmHg?

10 mmHg Signup and view all the answers

What is the consequence if the net filtration pressure (NFP) is negative?

Fluid is reabsorbed into the capillaries Signup and view all the answers

What condition can increase the permeability of capillary walls?

Capillary injury Signup and view all the answers

How much fluid is typically reabsorbed back into the circulation each day from the capillaries?

17 liters Signup and view all the answers

What is the role of the lymphatic system in fluid exchange?

It carries proteins and large particles away from tissues Signup and view all the answers

What does the term 'hydraulic conductance' (Kf) refer to?

The water permeability of the capillary wall Signup and view all the answers

What proportion of colloid osmotic pressure is typically exerted by albumin?

80% Signup and view all the answers

What is the primary function of lymphatic capillaries in relation to interstitial fluid?

Drain excess interstitial fluid and proteins. Signup and view all the answers

What mechanism prevents interstitial fluid and proteins from leaving the lymphatic capillaries?

The presence of one-way flap valves. Signup and view all the answers

How does the lymphatic system contribute to fluid balance in the body?

By draining excess interstitial fluid and proteins. Signup and view all the answers

What is the primary role of the lymphatic system in fat transport?

Absorbing fats from the intestines and transporting them to the blood. Signup and view all the answers

How does the lymphatic system contribute to the immune system?

Transporting foreign material to lymph nodes for immune response. Signup and view all the answers

What is the main factor responsible for the flow of lymph through the lymphatic vessels?

The contraction of smooth muscle in the lymph vessels and surrounding skeletal muscle. Signup and view all the answers

Which of the following is NOT a function of the lymphatic system?

Transporting oxygen to the tissues. Signup and view all the answers

What is the primary characteristic of edema?

An increase in interstitial fluid volume. Signup and view all the answers

Which of the following is a potential cause of edema?

All of the above. Signup and view all the answers

What is the primary function of terminal arterioles in the microcirculation?

To supply blood to capillaries Signup and view all the answers

Which statement about metarterioles is true?

They lack a continuous muscular coat. Signup and view all the answers

What regulates the entrance of blood into capillaries?

Precapillary sphincters Signup and view all the answers

How do the pressures in venules compare to those in arterioles?

Venules have lower pressure than arterioles. Signup and view all the answers

What type of blood vessel has a wall composed of a single layer of endothelial cells?

Capillaries Signup and view all the answers

What feature distinguishes the capillaries in the brain from those in the liver?

Capillaries in the brain have tight junctions limiting passage. Signup and view all the answers

Which type of capillaries allows almost all dissolved substances of plasma to pass?

Sinusoidal capillaries Signup and view all the answers

Which layer primarily constitutes the capillary walls?

Endothelial layer Signup and view all the answers

What is the role of smooth muscle fibers at the origin of capillaries from metarterioles?

To regulate capillary entrance Signup and view all the answers

What is a characteristic of an effusion?

It is an abnormal collection of fluid in a hollow space or between tissues. Signup and view all the answers

What is the main reason for fluid accumulation in congestive heart failure?

Increased blood pressure in the veins. Signup and view all the answers

Which of the following is NOT a type of edema or effusion mentioned in the text?

Lymphedema Signup and view all the answers

What is the primary force that drives fluid movement out of the capillaries in congestive heart failure?

Increased capillary hydrostatic pressure Signup and view all the answers

What is the clinical application of the information regarding edema and effusion?

Diagnosing and managing congestive heart failure Signup and view all the answers

What is the term for the fluid buildup in the abdomen that is mentioned in the text?

Ascites Signup and view all the answers

What is the mechanism by which fluid accumulates in the tissues in congestive heart failure?

The heart pumps blood too slowly, causing blood to back up and increase pressure in the capillaries. Signup and view all the answers

What is the key difference between edema and effusion?

Edema is a buildup of fluid in the tissues, while effusion is a buildup of fluid in a hollow space. Signup and view all the answers

What is the main factor contributing to the increased capillary hydrostatic pressure in congestive heart failure?

Increased blood volume in the capillaries. Signup and view all the answers

Study Notes

Microcirculation Structure

The microcirculation of each organ is organized to serve the organ's specific needs
Each artery entering an organ branches 6-8 times before becoming small enough to be called arterioles
Arterioles branch 2-5 times until they become terminal arterioles that supply blood to capillaries
Terminal arterioles are called metarterioles
Metarterioles do not have a continuous muscular coat, but smooth muscle fibers encircle the vessel at intermittent points

Precapillary Sphincter

The point where each true capillary originates from a metarteriole has a smooth muscle fiber that usually encircles the capillary, called a precapillary sphincter
The precapillary sphincter can open or close the entrance of the capillary

Capillaries

Not all capillaries are always perfused with blood, it depends on metabolic needs
The capillary wall is composed of a single layer of endothelial cells and a thin basement membrane
Special types of pores occur in the capillaries of certain organs, such as the brain, liver, and kidney

Venous Structure

Venules are larger than arterioles and have a much weaker muscular coat
The pressure is lower and allows constriction despite the weak muscle

Capillary Fluid Exchange

Capillary arterial pressure = 35 mmHg, capillary venous pressure = 17 mmHg
Interstitial fluid hydrostatic pressure (Pif) drives fluid out of the interstitial space into the capillaries
Capillary oncotic pressure (πp) is also called colloid osmotic pressure, and is exerted by plasma proteins (80% by albumin), favoring reabsorption
Interstitial fluid oncotic pressure (πif) is determined by the interstitial fluid protein concentration and favors filtration
Net filtration pressure = hydrostatic pressure - oncotic pressure

Forces Involved in Fluid Exchange

Hydrostatic pressure pushes fluid out of the capillaries
Osmotic pressure pulls fluid inside of the capillaries
If the result of these forces is positive, there will be a net fluid filtration across the capillaries
If the result is negative, there will be a net fluid reabsorption from the interstitial fluid into the capillaries

Permeability of the Capillary Wall

Permeability is increased in capillary injury (e.g. toxins, burns, inflammation), which increases permeability to water
Hydraulic conductance (Kf) is the water permeability of the capillary wall and varies among different types of tissues

Lymphatic System

The lymphatic system is an accessory route through which fluid can flow from the interstitial spaces into the blood
Lymphatics carry proteins and large particle matter away from the tissue spaces
Lymphatic capillaries possess one-way flap valves that permit interstitial fluid and protein to enter but not to leave
Lymphatic capillaries merge into larger lymphatic vessels/thoracic duct, and lymph flow depends on contraction of the smooth muscle in the lymph vessels and compression of the lymph vessels by activity of the surrounding skeletal muscle
The lymphatic system plays a key role in controlling interstitial fluid protein concentration, volume, and pressure

Clinical Application: Edema and Effusion

Changes in Starling forces can influence the direction and magnitude of fluid movement
Edema is an increase in interstitial fluid volume (swelling)
Effusion is an abnormal collection of fluid in a hollow space or between tissues (e.g. pleural effusion)
Congestive heart failure can lead to edema or effusion due to an increase in capillary hydrostatic pressure

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Description

This quiz covers the structure and function of microcirculation in cardiovascular physiology, including terminal arterioles and related concepts.