Blood Vessels

Question 1

What is the increase in number of vessels and cross-sectional diameter going from the aorta to the capilaries

Answer 1

2-3 bilion-fold increase in number of vessels

500-fold increase in overall cross-sectional diameter

Question 2

Where is blood flow slowest?

Answer 2

capillaries and venules

Question 3

What are the layers, from innermost to outermost, in blood vessels?

Answer 3

tunica intima -> tunica media -> tunica adventitia

Question 4

What is the tunica intima?

Answer 4

Innermost layer of blood vessels, comprised of a layer of endothelial cells in intimate contact with blood.

Question 5

What is the tunica media?

Answer 5

A layer in the middle of a blood vessel, may be comprised of multiple layers of elastic laminae, smooth muscle cells, or collagen.

Question 6

What is the tunica adventitia?

Answer 6

The supporting outer layer of a blood vessel, comprised of collagenous tissue.

Question 7

What does the tunica adventitia of larger vessels contain?

Answer 7

vasa vasorum (“vessels of vessels”), blood vessels that actually supply oxygen and nutrients to the adventitia and outer part of the media (diffusion insufficient)

Question 8

Compare wall thickness of arteries and veins

Answer 8

Arteries are quite thick-walled compared to veins, and have approximately the same wall thickness as the lumen of the vessel itself.

Question 9

What does smooth muscle in arterioles allow for?

Answer 9

Permits control of blood flow to capillary beds.

Question 10

What are the elastic arteries?

Answer 10

The aorta and large arteries branching from it.

Question 11

What do myointimal cells do?

Answer 11

Similar structural features to smooth muscle cells

Question 12

Describe arteriole structure

Answer 12

Arterioles contain an inner lining of endothelial cells on a thin basement membrane, surrounded by 1-2 layers of smooth muscle cells and outer collagenous tissue which blends in with surrounding connective tissue.

Question 13

Describe arteriole function

Answer 13

Gatekeepers to local capillary beds, can greatly restrict flow of blood through them.

Question 14

What do a metarterioles and arteriole-venule shunts accomplish?

Answer 14

Can connect larger arterioles and venules, can direct flow through or permit bypass of capillary beds

Question 15

What is the diameter of capillaries?

Answer 15

5-15 um

Question 16

What surrounds capillaries?

Answer 16

No muscular layer, but often surrounded by cells called pericytes

Question 17

What are pericytes?

Answer 17

Relatively unspecialized cells that can give rise to smooth muscle cells during vessel growth and wound healing, can be contractile in nature.

Question 18

Describe capillary structure

Answer 18

1-2 endothelial cells surrounding the lumen, no smooth muscle, possibly pericytes

Question 19

What two main types of capillaries are recognized?

Answer 19

Continuous and fenestrated

Question 20

Describe continuous capillaries

Answer 20

Endothelial cells form an uninterrupted lining, although transfer across the lining can occur via pinocytotic vesicles

Question 21

Describe fenestrated capillaries

Answer 21

Fenestrated capillaries have pores (fenestrations, windows) in the endothelial cells, sometimes covered by a thin diaphragm

Question 22

Where might you find fenestrated capillaries?

Answer 22

Glomerulus of the kidney In the sinusoidal capillaries of liver and spleen larger fenestrations called pores let red blood cells through

Question 23

What do fenestrated capillaries permit?

Answer 23

Bulk flow of plasma past the endothelial boundary

Question 24

Describe post-capillary venules

Answer 24

Initially similar to pre-capillary arterioles, but slightly larger diameter. Surrounded by pericytes. Leukocytes primarily diapedese through vessel walls. Endothelium responsive to vasoregulatory substances such as serotonin and histamine (controlled permeability). Larger venules get 1-2 layers of smooth muscle with thin layers of connective adventitia (muscular venules).

Question 25

What do small veins lack compared to small arteries?

Answer 25

No inner elastic lamina in the tunica media

Question 26

How does blood circulate through veins?

Answer 26

Hydrostatic pressure, aided by contraction of smooth muscle and the compression of surrounding skeletal muscles. Often aided by one-way valves to prevent back-flow (valve failure = varicose veins)

Question 27

At what pressure do pulmonary arteries function?

Answer 27

15-25 mmHg, lower than systemic arteries

Question 28

What direction do lymphatics flow?

Answer 28

One way, from tissues to empty into the blood on the right and left side near the junction of the internal jugular and subclavian veins.

Question 29

Describe lymphatic vessels

Answer 29

Actually begin as nothing more than small spaces in connective tissues. These small spaces connect to larger spaces lined by a very thin layer of squamus endothelium.

Question 30

How are lymphatic vessels discernible?

Answer 30

Size of small veins, have only a single, very thin endothelial layer and little discernible outer layers. Lymphocytes are often visible, but red cells are absent (unless injury is present). Lymph stains a light color, while blood plasma does not.
Larger lymphatic vessels show loosely-defined connective tissue structure, and have many flap-like valves. Also have inline filters, called lymph nodes.

Question 31

What is an anastomoses?

Answer 31

Defined as connections between arteries and veins that permit collateral circulation to occur within tissues.

Question 32

What are End Arteries?

Answer 32

Arteries that supply a section of a tissue that cannot have an alternate arterial supply (i.e., no anastomoses)

Question 33

What are portal systems?

Answer 33

Portal systems begin in a capillary bed and end in a capillary bed

Question 34

Where would you find a portal system?

Answer 34

hypothalamic-anterior pituitary portal system, hepatic portal system

Question 35

What is a pampiniform plexus?

Answer 35

A countercurrent arrangement between an artery and venous network.

Question 36

Where might you find a pampiniform plexus?

Answer 36

Found in the spermatic cord, probably for optimal heat exchange.