Vasculature

Question 1

What is the order of tissues extending from the center of a blood vessel to its exterior?

Answer 1

Lumen, tunica interna, tunica media, tunica adventitia (including vasa vasorum, and nervi vascularis). Vasa vasorum provide O2 and nutrients from the outside in, not from the lumen of the vessel.

Question 2

What is the structure of an elastic artery such as the aorta?

Answer 2

The aorta is the largest elastic vessel. The tunica interna consists of endothelial cells & loose connective tissue (w/ fibroblasts and myoinfamil (?) cells). The tunica media consists of 30-70 layers of elastic laminae with smooth muscle cells interspersed within them (the SM cells actually produce the elastic laminae). The tunica adventitia consists of denser elastic and collagen fibers (containing FB and immune cells) and vasa vasorum.

Question 3

What is the relationship of elastic layers and blood pressure?

Answer 3

Elastic properties of the aorta absorb the spikes in blood pressure produced by the heart. This produces a sinusoidal blood pressure wave, and minimizes damage to the vessels by reducing the maximal pressure.

Question 4

What is the structure of a muscular artery?

Answer 4

First layer is endothelial cells with a basal lamina and small amounts of connective tissue. Second layer is an “inner elastic lamina” containing 4-10 layers of smooth muscle. Third is an outer elastic lamina, and then the tunica adventitia. Vasa vasorum start to disappear as vessel size diminishes and outer layers get nutrients from main lumen. There is also a decrease in the number of elastic layers relative to smooth muscle as the artery size diminishes, and outer elastic lamina is lost first.

Question 5

What is the structure of arterioles?

Answer 5

2-3 endothelial cells can form the tunica intima. 2-3 layers of smooth muscle form the tunica media. Tunica adventitia almost blends into the connective tissue, and may be hard to distinguish. Inner elastic lamina is lost as arteries branch into arterioles.

Question 6

What features do large veins have?

Answer 6

Some elastic fibers, vasa vasorum, and some smooth muscle, but nowhere near the thickness of largest arteries.

Question 7

Where do blood pressure controls function?

Answer 7

Blood pressure control is at the level of the smooth muscle in the arteries and arterioles, and in met-arterioles and pre-capillary sphincters. Angiotensin and aldosterone function in these tissues.

Question 8

What are lymphatic vessels bound by?

Answer 8

Lymphatic vessels, even large lymphatics, are bound by a single layer of simple squamous epithelium. Very large lymphatic vessels may contain more than a single layer of squamous epithelia.

Question 9

Overview of arteriole, venuole, and lymphatic structures.

Answer 9

Arteriole - endothelial layer, 2-3 layers of smooth muscle, possibly no distinguishable adventitia (only CT) Venuole - endothelial layer, maybe 1 layer of smooth muscle, no adventitia. Lymphatic - single squamous epithelium, then basal lamina and CT.

Question 10

What is the structure of the smallest arterioles?

Answer 10

Two endothelial cells and a single layer of smooth muscle. No adventitia.

Question 11

What is the process of diseases of plaque buildup (such as congestive heart disease) in arteries?

Answer 11

The intimal layer grows very thick, to the point is can occlude the vessel. Due to actions of cells like myointimal (?) cells and fibroblasts in the intimal layer excreting fibrous tissue and exacerbated by lipid build up.

Question 12

What are three methods for controlling blood flow to capillaries?

Answer 12

Arteriole-venule shunts, met-arterioles, and pre-capillary sphincters. Arteriole-venule shunts are direct connections between arteries and veins that can direct blood flow away from a capillary bed. They are regulated by muscular contractions controlling blood flow from the arterial side. Met-arterials connect arterioles with cap beds and control the flow of blood into capillaries through muscular contractions. Pre-capillary sphincters can also control blood flow at the start of a capillary.

Question 13

What is the size and structure of a capillary?

Answer 13

RBCs have a distinct diameter of about 7-8 microns, thus capillaries are 5-15 microns in size. They have a single endothelial cell, basal lamina, and pericyte embedded in the basal lamina/CT and wrapped partially around the capillary.

Question 14

What is the structure and function of pericytes?

Answer 14

Pericytes wrap diagonally around capillaries and function in angiogenesis. They assist in building new capillaries after damage to a site.

Question 15

How do endothelial cells exchange material from the lumen to the CT and back?

Answer 15

Bi-directional pinocytosis.

Question 16

What are fenestrated endothelia and where are they found?

Answer 16

Fenestrated endothelia contain holes in the endothelial layer that allow larger volumes of fluids to pass through. These holes are through the endothelial cells themselves, and not in between them. They are found in the kidney and major glands (and possibly elsewhere, not detailed)

Question 17

What are stave cells and how do they function?

Answer 17

Stave cells are endothelial cells arranged like a picket fence that allow the passage of RBCs and WBCs (and plasma) into sinuses. This occurs in the spleen (and elsewhere, not detailed).

Question 18

What is one example of capillaries that are extra-secure to disallow transport of substances other than nutrients?

Answer 18

The blood/thymus barrier, where antigens are specifically excluded from passing from the blood into the thymus.

Question 19

Why may arterioles in dense connective tissue not have muscle tissue surrounding them?

Answer 19

If the CT is very dense, there would be little point in contraction the arteriole because it may tear away from the surrounding CT.

Question 20

What is a major cellular event that occurs in the post-capillary venules?

Answer 20

Leukocytes leave the blood in the post-capillary venules. They interact with selectins (among others) and move through the endothelium (either between or straight through the cells) via diapedesis.

Question 21

What happens in post-capillary venules during an inflammatory response.

Answer 21

In an inflammatory response, the release of histamine results in increased permeability of the endothelium. This causes an increase in plasma in the local CT, and swelling results.

Question 22

What is the structure of the largest veins?

Answer 22

Endothelial layers with basal lamina and some CT leading to sparse but noticeable smooth muscle layers and elastic fibers, and vasa vasorum due to the thickness of the vessels. Valves are also present in many veins.