Unit IV- Blood Vessels I

Question 1

Functions of blood vessels

Answer 1

• allow exchange of gases
• carry nutrients to tissue
• carry metabolic wastes away
• carry hormones and signaling substances
• maintain quality and quantity of tissue fluid

Question 2

Histophysiology

Answer 2

• the large or conducting arteries allow rapid blood flow and their elastic laminae help to smooth out pressure differences with distance from the heart
• the medium or distributing arteries have a slower bloo9d flow and the flow can be controlled by regulatory factors such as chemical or neural input to regulate flow to various organs

Question 3

Tunica intima

Answer 3

• consists of the endothelium, basal lamina, and a subendothelial layer of loose connective tissue that may contain an occasional smooth muscle cell
• in arteries an internal elastic lamina (sometimes considered part of the media) borders the media
• this is a fenestrated layer of elastin

Question 4

Tunica media

Answer 4

• the media is composed of smooth muscle and variable amounts of elastic fibers and lamellae, reticular fibers, and proteoglycans
• the extracellular matrix is synthesized by smooth muscle cells
• larger vessels have an external elastic lamina
• pericytes replace the media in capillaries and postcapillary venules

Question 5

Tunica adventitia

Answer 5

• the outermost layer is composed of fibroblasts and longitudinally oriented type I collagen and elastic fibers
• larger blood vessels have a vasa vasorum (vessels of the vessel) in the adventitia and a portion of the media that provides nutrients via small vessels to the vessel wall
• veins have a more extensive vasa vasorum because of the low nutrient and oxygen content of venous blood

Question 6

Functions of structures of blood vessels

Answer 6

• the intima forms a permeable or semipermeable barrier
• the media controls diameter and blood pressure and movement
• the adventitia provides physical support, attaches vessels to tissue, and carries vessels and nerves

Question 7

Endocardium

Answer 7

• homologous to the intima of blood vessels
• the endocardium lines the atria and ventricles
• it is composed of an endothelium and a subendothelial layer of connective tissue

Question 8

Myocardium

Answer 8

• homologous to the media of blood vessels
• it is the thickest layer of the heart wall and composed of cardiac muscle that is thicker in the ventricles than in the atria

Question 9

Epicardium

Answer 9

• homologous to the adventitia of blood vessels
• it forms the surface of the heart and is anatomically defined as the visceral layer of the pericardium
• the epicardium is composed of a mesothelium and the subepicardial layer of loose connective tissue that contains nerves, adipose tissue, and the coronary blood vessels

Question 10

Location and Function of Large, Elastic, Conducting Arteries

Answer 10

• the aorta and its main branches, common carotid, brachiocephalic, subclavian, and pulmonary arteries are elastic arteries
• systole distends the elastic arteries and they recoil and contract during diastole. This produces a more uniform flow and pressure

Question 11

Intima of Large Elastic Artery

Answer 11

• 150 microns thick in adults (1/6th of wall thickness)
• there are scattered smooth muscles in the subendothelial layer
• the endothelial cells contain Weibel-Palade bodies that are membrane-bound inclusions (0.1 by 3 microns) that have a dense matrix containing von Willebrand factor
• the endothelial cells are slightly elongate polygons with their long axes oriented with the blood flow and the cells are connected by occluding junctions

Question 12

Media of Large Elastic Artery

Answer 12

• is about 2 millimeters thick and is made of 40-70 layers of fenestrated elastic lamellae with smooth muscle cells interspersed between
• there is a thin external elastic lamina and the vasa vasorum of the adventitia penetrates the outer third to half of the media

Question 13

Adventitia of Large Elastic Artery

Answer 13

-relatively thin with nerve fibers, lymphatics and vasa vasorum in loose connective tissue

Question 14

Mixed, Musculo-Elastic Arteries Location and Functions

Answer 14

• forms part of terminal abdominal aorta, the iliac arteries, external carotids, axillary arteries and others
• these are transitional segments between large and medium arteries

Question 15

Histology of Mixed, Musculo-Elastic Arteries

Answer 15

• intermediate characteristcs
• the tunica media and adventitia are about the same thickness. The media has fewer elastic lamellae and there is a more obvious internal elastic membrane

Question 16

Medium, Muscular, Distributing Arteries Location and Functions

Answer 16

• most named arteries are of this type such as coronary, renal, mesenteric, brachial femoral and others
• the muscular arteries distribute blood to tissues and organs regulated by autonomic nervous system control of the media

Question 17

Histology of Medium Muscular Distributing Arteries

Answer 17

• intima-relatively thin and includes a prominent internal elastic lamina that undulates
• media- relatively thick and is composed of many concentric layers of smooth muscle cells bounded in large muscular arteries by an external elastic lamina (EEL) that gets thinner and disappears in smaller diameter specimens
• adventitia may be as thick as the media. The vasa vasorum and lymphatics are poorly developed

Question 18

Arterioles Features and Functions

Answer 18

• 100 microns or less in diameter
• invisible to the naked eye
• function to maintain normal blood pressure in the arterial system and to reduce the pressure of the blood entering the capillaries

Question 19

Histology of Arterioles

Answer 19

• Intima- only a thin subendothelial layer of reticular fibers and the internal elastic membrane is absent in the smallest arterioles
• media- composed of one to fiver layers of smooth muscle
• adventitia is moderate to scant
• the terminal segment before a capillary bed forms a metarteriole or precapillary sphincher that regulates blood flow into capillaries

Question 20

Structural changes in arteries with age

Answer 20

• the three tunics are complete during the fourth month in utero
• the largest arteries continue to grow until about age 25
• the aging process involves the intima and media
• after age 30, the media becomes stiffer due to the increase in elastic lamellae and deposition of collagen and proteoglycans

Question 21

Pathophysiological changes in arteries with age

Answer 21

• large elastic arteries show greater change than muscular arteries
• in the media, elastic tissue can develop irregular thickenings and elastic fibers can fragment
• atherosclerotic plaques form in the intima as a consequence of noncellular lipid material accumulation in the subendothelial layer
• muscular arteries undergo calcification of the media. Large muscular arteries like the coronaries develop atherosclerotic plaques in their intima that can reduce the luminal diameter appreciably even by age 25