HE 21 Cardiovascular System

Question 1

What is endothelium?

Answer 1

It is the simple squamous epithelium that lines all blood and lymphatic vessels.

Question 2

What are the general functions of the endothelium?

Answer 2

Paracellular and transcellular transport
Blood coagulation and thrombus
Lets fluid and white blood cells out when needed
Angiogenesis

Question 3

What is von Willebrand Factor, where is it made, where is it stored, and what does it do?

Answer 3

Synthesized by endothelial cells and some is stored in the subendothelial layer and some stored in endothelial cells in vesicles called Weibel-Palade Bodies. It is used to help platelets adhere to a site of injury.

Question 4

What happens to the endothelial cells when there is an injury nearby and an inflammatory response is triggered?

Answer 4

Mast cells release histamine and cytokines which relax tight junctions in the endothelial cells and release fluid and WBCs into the surrounding connective tissue.

Question 5

What is diapedisis?

Answer 5

WBCs passing through the leaky endothelium into the surrounding tissue in response to an injury.

Question 6

How do Weibel-Palade Bodies (WP) play a role in attracting WBCs to the site of injury?

Answer 6

They have in their vesicles P-Selectins which are surface adhesion molecules. The vesicles secrete these to the surface of the endothelial cells in response to histamine and cytokines and WBCs bind to these molecules.

Question 7

How are endothelial cells replaced after injury?

Answer 7

In vessels besides the smallest ones, endothelial cells act as their own stem cells for regrowth.
In capillaries and postcapillary venules, Pericytes (rouget cells) in the basal lamina of the endothelium act as stem cells and communicate with endothelial cells through gap junctions to repair injuries. Pericytes can make smooth muscle or endothelial cells during angiogenesis.

Question 8

What is intimal thickening?

Answer 8

In response to injury, the endothelial cells will replicate to recover the site, smooth muscle will migrate into the tunica intima from the TM, the smooth muscle will proliferate and secrete ECM. The TI will be thicker forever more at that spot.

Question 9

How are veins and arteries different in regard to lumen, walls, lamina, and valves?

Answer 9

Veins: wider irregular lumen, less thick walls, less developed TM, more developed TA, no Internal elastic lamina, valves present

Arteries: smaller regular shaped lumen, thick walls with well developed TM but less TA, has IEL, no valves

Question 10

What is the general path of blood through the whole body to make a complete circuit?

Answer 10

Heart–>Elastic (conducting) arteries–>Muscular (distributing arteries–>Arterioles (smallest have precapillary sphincter)–>Capillaries–>Venules (smallest: postcapillary venule)–>Medium veins–>Large veins–>Heart

Question 11

What does the TM look like for elastic conducting arteries?

Answer 11

Has 40 to 70 layers of fenestrated elastic lamina synthesized by smooth muscle cells. This allows the walls to stretch and perform their function.

Question 12

What do the walls of large veins look like?

Answer 12

They have well-developed TA with linear smooth muscle cells. The TI and TM are hard to distinguish from each other and they are thin. Vasa vasorum are present in the TA.

Question 13

What are examples of large veins?

Answer 13

Vena cava, brachiocephalic, subclavian, iliac

Question 14

What do muscular (distributing) arteries do and what is their structural makeup?

Answer 14

Function is to distribute blood and control the flow to these areas. Examples include coronary arteries, axillary arteries, intercostal arteries.
Have 5-40 layers of smooth muscle in the TM arranged in spiral fashion. Have prominent IEL and EEL.
Innervation from nerves in the TA and excitation spread through gap junctions. Vasa Vasorum in TA.

Question 15

Describe the structure of medium veins.

Answer 15

No IEL.
TA is thickest part of vessel.
Less smooth muscle in TM than in similar sized arteries.
Prominent vasa vasorum because the blood in the lumen is not oxygenated and can’t supply the cells in the walls.

Question 16

What are valves and where are they found?

Answer 16

They are extensions of the tunica intima.
Found in the heart, larger venules, small and medium veins.
Not found in arteries or large veins.

Question 17

What is a major cause of varicose veins?

Answer 17

Incompetent valves.

Question 18

Describe arterioles and their major functions.

Answer 18

Last vessels before the capillary beds.
Have thin TI and TA.
1-4 layers of smooth muscle
May have IEL, no EEL
Function is to dilate and contract in order to control blood flow to tissues. This is the primary place where blood pressure is controlled.

Question 19

What is a precapillary sphincter?

Answer 19

It is the smallest arteriole just before the capillary beds. It has one layer of smooth muscle and controls blood into capillaries.

Question 20

What are postcapillary venules?

Answer 20

First venules after the capillary beds.
Have endothelial cells, basal lamina, pericytes, but no smooth muscle.
Site of leukocyte extravasation and fluid movement because walls are thin here.

Question 21

Describe venules.

Answer 21

Accompany arterioles
Have 1 or more layers of smooth muscle
Irregular lumen and thin wall

Question 22

What is the function of capillaries and what types are there?

Answer 22

Purpose is to allow exchange.
Continuous: has no or small holes, is the smallest, has tightest tight junctions, prominent pinocytotic vesicles, continuous basal lamina, most common type, found in skin, bone, muscle, heart, lungs, CNS

Fenestrated: middle sized lumen, has small holes in plasma membrane, continuous basal lamina, found in endocrine organs, GI tract, kidney

Sinusoidal: has larger holes and even gaps between cells, largest and irregular lumen, discontinuous or absent basal lamina, least common type, found in bone marrow, liver, spleen (tissues of fluid movement and cell migration)