Flashcards in Blood Vessels II Deck (15)
What are pericytes?
stellate cells that surround capillaries and some post-capillary venules. They share the basal lamina of endothelial cell and can serve as stem cells for endothelial and smooth muscle cells after injury.
Where are continuous capillaries found?
They are the most common of the three types of capillaries. Found in muscle, nervous and connective tissues, and the exocrine pancreas.
Describe the structure and function of continuous capillaries.
The endothelial lining and basal lamina are complete. [The cells are sealed by occluding (tight) junctions that permit passage of small molecules]. The cytoplasm has many vesicles that transport large molecules.
Where are fenestrated capillaries located?
Pancreas, intestines and endocrine glands. A special type with no diaphragms is found only in the renal glomerulus.
Describe the structure and function of fenestrated capillaries.
They have a continuous but thin endothelium and basal lamina. The cells have small pores (fenestrae) in their walls covered by a diaphragm (except renal glomerulus). They are special for rapid interchange of substances between blood and tissue
Where are sinusoidal capillaries located?
There are three types: sinusoidal capillaries found in endocrine glands, discontinuous sinusoids found in the liver and bone marrow and venous sinusoids in the spleen.
Describe the structure and function of sinusoids.`
They are irregular blood channels that conform to the shape of the structure they line. They have a continuous basal lamina and fenestrae with diaphragms that are much larger than in fenestrated capillaries. Discontinuous sinusoids have a discontinuous or absent basal lamina and have large gaps between endothelial cells that permits enhanced exchange between blood and tissue.
When comparing veins to arteries what are some of the differences?
Veins show greater variation in size and structure than arteries. Veins are larger caliber and more numerous. Veins have a more extensive vasa vasorum and lymphatics. Veins contain more collagen and less elastic substance and smooth muscle. Veins owe most of their thickness to adventitia. Small and medium veins have valves.
The following describes?
Intima - contains a continuous endothelium and basal lamina, but no internal elastic connective tissue core.
Media - is frequently incomplete or absent
Adventitia - is the largest, best developed tunic and forms 95% of thickness. Well-developed vasa vasorum and lymphatics
Large veins. Ex. SVC and IVC and portal vein.
The following describes?
Intima - has a continuous endothelium and basal lamina. Complete internal elastic laminae are usually only found in veins of the leg. Some valves.
Media - is poorly developed except in the limbs. Smooth muscle is circumferential.
Adventitia - is the thickest tuni and usually has no smooth muscle. It does contain collagen and elastic fibers, fibroblasts, lymphatics, and vasa vasorum
Small and medium veins.
What are the functions of both pericytic and muscular venues?
To continue the exchange of materials that was started in the capillaries. They are the preferred location for leukocyte emigration. They become leaky in response to histamine and serotonin.
What are pericytic venules?
They are the post-capillary venules that resemble large capillaries in that they have a pericyte.
What are muscular venules?
They receive the blood from the pericytic venules and accompany arterioles. They media has 1 or 2 circular layers of smooth muscle cells. They have a thin adventitia of loose connective tissue.
What are characteristics of lymphatic vessels?
Large lumens, thin walls, irregular shape, extensive branching that runs parallel to blood capillaries and veins.