What are the small muscular arteries with 1,2 or 3 layers of smooth muscle?
What is the function of an arteriole?
Arterioles are the last small branches of the arterial system and act as control valves through which the flow of blood is regulated into the terminal vascular bed.
True of False: In arterioles the internal elastic lamina is absent?
In arterioles a small internal elastic lamina (tunica intima level) may be present but the external elastic lamina (tunica media level) is absent.
Describe a venule
Characterized by a relatively indistinct tunica media and adventitia. Often have a bigger lumen compared to their wall thickness and are irregularly shaped
True or False: Venules collect blood from the terminal vascular bed and gradually coalesce into progressively larger veins?
True or False: Arterioles are small muscular arteries that most often are found by themselves?
Like other larger vessels, you will often see arterioles and venules together side by side or in very close proximity.
What is responsible for shunting blood from arterioles to venules without passing through a capillary bed?
Arteriovenous (A-V) anastomoses
What are the main characteristics of arteriovenous anastomoses?
1. Smooth muscle adjacent to the tunica intima which is oriented longitudinally and has an epithelioid appearance
2. Remainder of the tunica media is comprised of circularly arranged smooth muscle
3. Can open or close to regulate blood flow to certain capillary beds
List three locations where arteriovenous anastomoses are found and three functions they might perform.
Skin, Digestive tract, and erectile tissue of male reproductive tract
Function in regulation of blood pressure, thermoregulation, and erection
What is a pericyte and where is it found?
Pericytes are pluripotent cells capable of differentiating into fibroblasts, smooth muscle cells and mast cells. They are associated with vessels of the terminal vascular bed and located within the vessel's basement membrane.
What is the term for the last little artery comprised of a single layer of smooth muscle?
In a terminal arteriole a ____ is present while the ____ is absent.
tunica media is present (composed of a single layer of smooth muscle) but the tunica adventitia is absent.
What are the simplest members of the vascular system that provide the means by which metabolites gain access to and waste products leave the connective tissue.
Capillaries are usually big enough to let ____ red blood cells pass.
Only 1 red blood cell at a time can pass through a capillary
What are the 4 types of capillaries?
1. Continuous (non-fenestrated)
What type of capillary matches each description:
1. Pores scattered throughout the walls of the endothelium
2. Resemble blood capillaries but carry lymph
3. Wall is fenestrated and the basal lamina is discontinuous or missing
4. No interruptions in the continuity of their endothelial cells
1. Fenestrated capillary
2. Lymph capillary
3. Discontinuous capillary-sinusoids
4. Continuous capillary
In a continuous capillary the wall is _____ and _____ juntions are present. In muscle _____ vessicles are present and aid in transport of materials across the wall.
uniform in thickness
A type of continuous capillary that forms the blood brain barrier and lacks pinocytotic vesicles
In a fenestrated capillary the wall is _____ where _____ is absent and _____ are present for movement of materials.
Wall is attenuated where cytoplasm is absent and pores or fenestrae are present for moving materials.
What type of tissues are fenestrated capillaries associated with?
Metabolically active tissues such as kidney and intestine.
What common characteristic do continuous and fenestrated capillaries share?
Intact basement membrane
True or False: A discontinuous capillary will have a small lumen (only one RBC at a time can pass) and thick walls?
False-the lumens are large enough to allow passage of several RBCs at a time and the vessels are thin walled
Where would you find discontinuous capillaries?
Endocrine glands and organs that have phagocytic cells associated with the endothelium, such as the liver.
What are two primary differences between lymph capillaries and blood capillaries?
1. Lymph capillaries lack a basal lamina and pericytes
2. Lymph capillaries end blindly whereas blood capillaries have an arteriole and venous end
Where would lymph capillaries predominate and what function to they have?
Prominent in the gut where they collect fatty acids and glycerol for transport to the blood.
What is the most permeable part of the terminal vascular bed and the site of an inflammatory response?
True or False: Postcapillary venules can have associated pericytes?
What is the main difference between a capillary and a postcapillary venule?
The structure is similar but the lumen of a postcapillary venule can accomodate 2 to 3 red blood cells.
What are blood sinuses and where are they located?
Blood sinuses are large, round to irregularly shaped vessels that usually lack smooth muscle. They occur in erectile tissue and are for pooling of blood.
What is the venous portal system and give an example of one?
The venous portal system is a capillary bed situated between two veins. The portal vein is the venous drainage for the GI tract which supplies the hepatic capillary bed and sinusoids. These empty into the hepatic veins.
What is the arterial portal system and give an example?
The arterial portal system is a capillary bed situated between two arterioles. In the kidney the afferent arteriole supplies the renal capillary bed which empties into the efferent arteriole.
Arrange from largest to smallest:
Artery is largest
Arteriole is a small artery