Capillaries

Question 0

Composition of a capillary

Answer 0

Single layer of endothelial cells and basal lamina

Question 1

What are the smallest blood vessels?

Answer 1

Capillaries

Question 2

What occurs in the capillaries?

Answer 2

Exchange of gasses, nutrients, and waste products between blood and tissues

Question 3

Describe the volume of flow in the capillaries

Answer 3

3x the combined diameter of the aorta

Leads to low pressure and low flow rate (allows diffusion)

Question 4

What agents are vasodilating?

Answer 4

Endothelium derived relaxing factors (EDRF), NO, low O2 tension

Question 5

Vasodilation in capillaries results in?

Answer 5

Smooth muscles of the arterioles relaxes and increases blood flow in the capillaries (can lead to peripheral edema)

Question 6

What causes vasorestriction? Results?

Answer 6

Systemic signals from the autonomic nervous system and release of norephinephrine by adrenal gland to cause smooth muscles in arterioles to contract resulting in decreased blood flow through the capillary bed

Question 7

What maintains blood pressure? What regulates distribution?

Answer 7

Muscular arteries - blood pressure

Small arteries and arterioles - regulates distribution

Question 8

What is the function of metarterioles?

Answer 8

Possess individual smooth muscle cells to act as precapillary sphincters

Question 9

What is the final step before reaching the capillaries?

Answer 9

Arterioles to metarterioles then capillaries

Question 10

Describe blood flow through capillaries

Answer 10

Single blood cell at a time

Question 11

Metarteroles control flow to capillary via?

Answer 11

Smooth muscle cells acting as precapillary sphincters

Question 12

Describe structure of capillary wall

Answer 12

Single layer of squamous endothelial cells
Connected by tight junctions
Basement membrane

Question 13

What layers are present in capillary walls?

Answer 13

Tunica intima and basement membrane

Question 14

Where are pericytes located?

Answer 14

Periphery around capillaries but not technically part of the capillary wall

Question 15

What is the function of pericytes?

Answer 15

Stem cells able to form collagen fibers, endothelial cells, smooth muscle cells, and new pericytes. Functions to repair and support the capillaries

Question 16

Three types of capillaries? Description?

Answer 16

Continuous - no pores inn the walls
Fenestrated - pores (fenestrae) in walls
Sinusoidal - discontinuous endothelial cells, many large fenestrae, and enlarged diameter (30-40 um)

Question 17

T or F: Fenestrae can be open or covered by thin membranes

Answer 17

T

Question 18

Describe continuous capillaries. Location?

Answer 18

Possess a continuous endothelial lining of about equal thickness throughout. Found where movement of molecules fro blood to tissue or the reverse is highly regulated like in the CNS, cardiac, and striated muscle, lung, thymus (cortex), skin

Question 19

Lateral processes in endothelial cells of continuous capillaries are connected by?

Answer 19

Junctional complexes

Question 20

Large number of pinocytotic vesicles in the plasmalemma is characteristic of?

Answer 20

Continuous capillaries

Question 21

Where are fenestrated capillaries found?

Answer 21

GI tract, kidneys, endocrine gland

E.g. pancreas, intestines, renal tubules and glomeruli, cilary body of the eye

Question 22

Describe walls of fenestrated capillaries

Answer 22

Endothelium has constant thickness except at fenestrae

Question 23

Describe fenestrae in fenestrated capillaries

Answer 23

Present and may be covered by thin membranes or diaphragms that are thinner than a plasmalemma.

Question 24

Describe the diaphragm in fenestrae of fenestrated capillaries

Answer 24

2-3 nm thick and allows for bulk movement of ions, hormones, and nutrients

Question 25

Function of fenestrated capillaries

Answer 25

Allow for less impeded movement of molecules across endothelial barrier

Question 26

T or F: Fenestrated capillaries contain both microvesicles and fenestrae

Answer 26

T

Question 27

Describe organization of fenestrae in endothelial cells

Answer 27

Are located in groups and each has a diameter of 60-80 nm. Often circular and well organized

Question 28

Where are sinusoidal (discontinuous) capillaries found?

Answer 28

Liver, bone marrow, and lymphoid organs (e.g. spleen)

Question 29

Function of sinusoidal capillaries

Answer 29

Large molecules or whole cells can move between the tissue and the circulating blood

Question 30

Describe the walls of sinusoidal capillaries

Answer 30

lumens of 20-40 um which is greater than the other two types Gaps separate endothelial cells (in liver and spleen) Basal lamina is discontinous at the gaps

Question 31

What is the space of disse?

Answer 31

Perisinusodial space that exists in the liver between the hepatocytes and the capillaries (called sinusoids) It is filled with plasma into which the microvilli of the hepatocyte extend to absorb molecules

Question 32

Describe the small pore system in capillaries

Answer 32

Small pores up to 9-11 nm in diameter | Discontinuities between endothelial cell junctions (intercellular junctions)

Question 33

Describe the large pore system in capillaries

Answer 33

Large pores up to 50-70 nm. | Represented by fenestrae and microvesicle transport