Blood Vessels II

Question 1

What are the functions of lymphatic vessels?

Answer 1

Lymphatic vessels act as reservoirs for plasma and other substances including cells that have leaked from the vascular system and transport lymph fluid back from the tissues to the circulatory system. They aid in lymphocyte circulation.

Without functioning lymphatic vessels, lymph cannot be effectively drained and edema typically results.

Question 2

What are the three types of capillaries?

Answer 2

1. Continuous capillary
2. Fenestrated capillary
3. Sinusoidal (discontinuous) capillary

Question 3

Continuous capillaries location, structure, and function?

Answer 3

1. Continuous capillary:
   - location: muscle, nervous & connective tissue, exocrine pancreas
   - structure: continuous (complete) basal lamina, very long in skeletal muscle
   - function: most common, tons of vesicles, occluding junctions, complete endothelium

Question 4

Fenestrated capillary location, structure, and function?

Answer 4

2. Fenestrated capillary:
   - location: endocrine pancreas, intestines, and endocrine glands (special kind with no diaphragms in the renal glomerulus)
   - structure: holes, continuous basal lamina
   - function: specialized for rapid exchange of materials

Question 5

Sinusoidal (discontinuous) capillary location, structure, and function?

Answer 5

3. Sinusoidal (discontinuous) capillary:
   - location: sinusoidal capillaries in endocrine glands with large fenestrae. Discontinuous sinusoids in the liver and bone marrow have large gaps. Venous sinusoids in spleen.
   - structure: larger than the others, has large openings, discontinuous basal lamina. Irregular blood channels.
   - function: all allow very rapid exchange of materials with tissue.

Question 6

Small pores (9-11 nm)

Answer 6

are believed to be pores in the occluding junctions

Question 7

Large pores (50-70 nm)

Answer 7

correspond to transcytosis by vesicles

Question 8

PORTAL SYSTEMS

Answer 8

carry blood from one capillary bed to another

Question 9

Define what a capillary is & describe the 3 types of capillaries.

Answer 9

Capillaries are the smallest of a body’s blood vessels and are parts of its microcirculation.

Continuous capillaries, which are continuous in the sense that the endothelial cells provide an uninterrupted lining, and they only allow smaller molecules, such as water and ions to diffuse through tight junctions, leaving gaps of unjoined membrane called intercellular clefts. Those without tight junctions are primarily found in the central nervous system & are a constituent of the blood-brain-barrier.

Fenestrated capillaries (derived from “fenestra,” Latin for “window”) have pores in the endothelial cells that are spanned by a diaphragm of radially oriented fibrils and allow small molecules and limited amounts of protein to diffuse. This type of blood vessel has a continuous basal lamina and is primarily located in the endocrine glands, intestines, pancreas, and glomeruli of kidney.

Sinusoidal capillaries are a special type of fenestrated capillaries that have larger openings in the endothelium. These types of blood vessels allow red and white blood cells and various serum proteins to pass aided by a discontinuous basal lamina. Sinusoid blood vessels are primarily located in the bone marrow, lymph nodes, and adrenal gland. Some sinusoids are special, in that they do not have the tight junctions between cells. They are called discontinuous sinusoidal capillaries, and are present in the liver and spleen where greater movement of cells and materials is necessary.