Week 3 topic 1 capillaries

Question 1

What are capillary walls constructed of?

Answer 1

A single layer of highly permeable endothelial cells surrounded by a thin basement membrane.

Question 2

What type of capillaries are found in skin, skeletal muscle, fat, and the blood-brain barrier?

Answer 2

Continuous capillaries.

Question 3

What do fenestrated capillaries allow to pass through?

Answer 3

Lipophobic molecules such as ions, water, and limited amounts of proteins.

Question 4

Where are sinusoidal capillaries primarily found?

Answer 4

Liver, spleen, and bone marrow.

Question 5

What is the function of precapillary sphincters?

Answer 5

To control blood flow into the capillary.

Question 6

What are metarterioles?

Answer 6

Direct channels between arterioles and venules.

Question 7

What is the primary site of gas and nutrient exchange?

Answer 7

Capillaries.

Question 8

What are the transport mechanisms across capillary walls?

Answer 8

• Free diffusion
• Channel based diffusion
• Active transport

Question 9

What two types of pressure drive water exchange across the capillary wall?

Answer 9

• Hydrostatic pressure
• Oncotic pressure

Question 10

What does Fick’s law relate to?

Answer 10

The rate of diffusion across a semi-permeable membrane.

Question 11

What is the capillary hydrostatic pressure (CHP) at the proximal end?

Answer 11

30 mmHg.

Question 12

What is the interstitial fluid hydrostatic pressure (Pi) when it is negative?

Answer 12

-3 mmHg.

Question 13

What does plasma oncotic pressure (POC) depend on?

Answer 13

Concentration of proteins in the capillary.

Question 14

What is the formula for net filtration at the arteriole end?

Answer 14

(Pc – Pi) – (πc - πi) = 13 mmHg.

Question 15

What happens if the net filtration pressure is negative?

Answer 15

There will be a net fluid absorption from interstitial spaces into the capillaries.

Question 16

What causes edema in the case of minor capillary damage?

Answer 16

Inflammatory response leading to leaky capillaries and decreased plasma oncotic pressure.

Question 17

What are the major functions of the lymphatic system?

Answer 17

• Production of lymphatic fluid
• Absorption of fat and nutrients from GIT
• Humoral and cell-mediated immune response
• Fluid drainage

Question 18

What is the normal rate of lymph flow through the thoracic duct?

Answer 18

100 ml/hr.

Question 19

What factors increase lymph flow?

Answer 19

• Elevated capillary hydrostatic pressure at the venule end
• Decreased plasma colloid osmotic pressure
• Increased interstitial fluid colloid osmotic pressure
• Increased permeability of the capillaries
• Lymphatic obstruction

Question 20

Fill in the blank: The concentration of proteins in the capillary exerts _______.

Answer 20

osmotic pressure.

Question 21

True or False: Venous capillaries are less numerous and permeable than arterial capillaries.

Answer 21

False.

Question 22

Describe the capillary structure

Answer 22

Capillaries have a thin, highly permeable single layer of endothelial cells surrounded by a thin basement membrane on the outer surface. They an be continuous, fenestrated or sinusoidal (discontinuous)

Question 23

Describe osmosis

Answer 23

Osmosis is the movement of water across a semi permeable membrane from an area of high water concentration/low solute concentration to an area of low water concentration/high solute concentration.
Water moves down the pressure gradient to balance concentration. This is important for fluid balance

Question 24

Describe the forces acting at the capillary wall

Answer 24

1. Hydrostatic pressure - water moves down the pressure gradient
2. Oncotic pressure - water moves from an area of low solute concentration to high solute concentration

Question 25

List the 4 forces acting at the capillary wall

Answer 25

1. Capillary hydrostatic pressure (Pc) 2. Interstital fluid hydrostatic pressure (Pi) 3. Plasma colloid osmotic (oncotic) pressure 4. Interstitial fluid colloid osmotic (oncotic) pressure

Question 26

What happens when net filtration pressure is positive

Answer 26

Favours filtration out of the capillary into the venule

Question 27

What happens when net filtration pressure is negative?

Answer 27

Favours reabsorption into the capillary

Question 28

What is the role of capillaries

Answer 28

Capillaries are the site of exchange of nutrients and waste products in the tissues, as well as the site of fluid exchange between the vascular and interstitial compartments

Question 29

What substances cause vasoconstriction

Answer 29

SNS at α1 angiotensin II ADH Endothelin Adenosine ATP

Question 30

What substances cause vasodilation

Answer 30

SNS at β2 PNS at M3 Sweat glands M3 Histamine ANP NO Bradykinin

Question 31

The exchange of solutes and gases across the capillary wall occurs via .....

Answer 31

simple diffusion Some solutes can diffuse through the EC and others must diffuse between the EC

Question 32

What gases are highly lipid soluble?

Answer 32

Oxygen and carbon dioxide

Question 33

How do water soluble substances cross the capillary?

Answer 33

Water soluble substances (water, ions, glucose, amino acids) are not lipid soluble and cross between EC at aqueous clefts.

Question 34

Osmosis is driven by....

Answer 34

the pressure gradient across a semi permeable membrane

Question 35

What determines Pc?

Answer 35

Pc is determined by both arterial and venous pressure. Although the value for Pc is closer to arterial pressure but affected more by changes in venous pressure.

Question 36

What is Kf

Answer 36

Kf = hydraulic conductance or water permeability of the capillary wall

Question 37

What happens to Kf in injury?

Answer 37

Kf increases so capillary wall permeablility increases leading to a loss of protein from the capillary

Question 38

What does Pi favour?

Answer 38

Pi opposes filtration and is usually zero or slightly negative

Question 39

What determines the plasma oncotic pressure?

Answer 39

Plasma protein concentration of capillary blood

Question 40

What determines interstitial fluid oncotic pressure?

Answer 40

interstitial fluid protein concentration This is normally low as proteins can't cross the membrane

Question 41

What does Pc > πc favour?

Answer 41

filtration

Question 42

what happens if πc decreases?

Answer 42

Increased filtration

Question 43

What is the role of the lymphatic system?

Answer 43

The lymphatic system is responsible for returning interstitial fluid and proteins to the vasculature

Question 44

What factors increase lymph flow?

Answer 44

1. Increased Pc 2. Decreased π c 3. Increased Kf (capillary permeability) 4. Impaired lymphatic drainage - standing, destruction of lymph nodes