11/24/2014 Microscopic Anatomy Blood Vessels I Thomas Poole Flashcards
The cardiovascular system consists of __ & __
The heart and blood vessels
The blood is pumped in two circuits:
Pulmonary circuit (to and from the lung)
Systemic circuit (to and from the organs and tissues)
Describe the lymphatic vascular system
- parallels the blood capillaries
- carries the lymph (excess tissue fluid, cellular debris and lymphocytes) in one direction only towards the large veins of the neck
The functions of blood vessels are to:
- Allow exchange of gases
- Carry nutrients to tissue
- Carry metabolic wastes away
- Carry hormones and signaling substances
- Maintain quality and quantity of tissue fluid
What is the function of large or conducting arteries?
Allowing rapid blood flow and their elastic laminae help to smooth out pressure differences with distance from the heart
What is the function of the medium or distributing arteries?
Have a slower blood flow and the flow can be controlled by regulatory factors such as chemical or neural input to regulate flow to various organs
Describe the general structure of blood vessels
Blood vessels above precapillaries have three concentric layers or tunics surrounding their lumens:
- intima
- media
- adventitia
Describe the tunica intima
Consists of:
- the endothelium
- basal lamina
- subendothelial layer of loose connective tissue that may contain an occasional smooth muscle cell
What is the internal elastic lamina (sometimes considered part of the media) that borders the media in arteries?
A fenestrated layer of elastin
Describe the tunica media
Composed of:
- smooth muscle
- elastic fibers
- lamellae
- reticular fibers
- proteoglycans
- the extracellular matrix is synthesized by the smooth muscle cells
What do larger vessels have in terms of tunica media
an external elastic lamina
Who replaces the media in capillaries and post-capillary venules?
pericytes
Describe the tunica adventitia
Composed of:
- fibroblasts
- longitudinally oriented type I collagen and elastic fibers
Larger blood vessels have a ___ in the adventitia and a portion of the media that provides nutrients via small vessels to the vessel wall
vasa vasorum (“vessels of the vessel”)
Why do veins have a more extensive vasa vasorum?
Because of the low nutrient and oxygen content of venous blood
What is the function of the intima?
To form a permeable or semipermeable barrier
What is the function of the media?
To control diameter and blood pressure and movement
What is the function of the adventitia?
To provide physical support, attach vessels to tissue, and carry vessels and nerves
Endocardium is homologous to the ___ of blood vessels
intima
What does the endocardium do?
lines the atria and ventricles
What is endocardium composed of?
An endothelium and a subendothelial layer of connective tissue
Myocardium is homologous to the ___ of blood vessels
media
Describe the myocardium
Thickest layer of the heart wall and composed of cardiac muscle that is thicker in the ventricles than in the atria
Epicardium is homologous to the ___ of blood vessels
adventitia
The epicardium forms the ___ of the heart and is anatomically defined as the ___ layer of the pericardium
surface; visceral
What is the epicardium composed of?
Mesothelium and the subepicardial layer of loose connective tissue that contains nerves, adipose tissue, and the coronary blood vessels
Since artery size continually ___, the morphological characteristics change ___ over a length of a vessel
An abrupt change does occur, however, from ___ to ___
decreases; gradually
arteriole; capillary
The aorta and its main branches, common carotid, brachiocephalic,
subclavian, and pulmonary arteries ___
elastic arteries
Systole ___ the elastic arteries and they recoil and contract during ___
distends; diastole
*this produces a more uniform flow and pressure
What are Weibel-Palade bodies?
Membrane-bound inclusions contained by endothelial cells at the intima of elastic arteries that have a dense matrix containing von Willebrand factor
There are scattered smooth muscles in the ___ layer in the intima of elastic arteries
subendothelial
Describe the media of Large, Elastic, Conducting Arteries
- 2 millimeters thick
- 40-70 layers of fenestrated elastic lamellae w/smooth muscle cells interspersed between
- thin external elastic lamina
- vasa vasorum of the adventitia penetrates the outer third to half of the media
Describe the adventitia of Large, Elastic, Conducting Arteries
Relatively thin w/nerve fibers, lymphatics, and vasa vasorum in the loose connective tissue
Describe the location and functions of Mixed, Musculo-Elastic Arteries
- Forms parts of terminal abdominal aorta, the iliac arteries, external
carotids, axillary arteries and others - These are transitional segments between large and medium arteries
Describe the histology of Mixed, Musculo-Elastic Arteries
- Intermediate characteristics
- 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
Describe the location and functions of Medium, Muscular, Distributing Arteries
- 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
Describe the histology of Medium, Muscular, Distributing Arteries
- Intima is relatively thin and includes a prominent internal elastic lamina (IEL) that undulates
- Media is relatively thick and is composed of many concentric layers of smooth muscle cells bounded in larger 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.
Describe the location and functions of Arterioles
- 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
Describe the histology of Arterioles
- Intima has only a thin subendothelial layer of reticular fibers and the internal elastic membrane is absent in the smallest arterioles
- Media is composed of one to five layers of smooth muscle
- Adventitia is moderate to scant
- The terminal segment before a capillary bed forms a metarteriole or precapillary sphincter that regulates blood flow into capillaries
Describe the structural changes of arteries with age
- 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 an increase in elastic lamellae and deposition of collagen and proteoglycans
Describe some of the pathophysiology associated with large elastic arteries
- 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
Describe some of the pathophysiology associated with muscular arteries
- 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
