BIOL 142 Study Guide - Midterm Guide: Vasa Vasorum, Tunica Externa, Tunica Media
4 Jul 2018
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The outermost layer of a blood vessel wall that is composed largely of loose woven
collagen fibers that protect and reinforce the vessel, and anchor it to surrounding
structures. The tunica externa is infiltrated with nerve fibers, lymphatic vessels, and, in
larger veins, a network of elastic fibers.
Tunica Externa
...
Vasa Vasorum
In larger vessels, the tunica externa contains a system of tiny blood vessels, the vasa
vasorum - literally "vessel of vessels" - that nourish the more external tissues of the
blood vessel wall. The innermost (luminal) portion of the vessel obtains nutrients directly
from blood in the lumen.
Vasa Vasorum
In the systematic circulation arteries always carry oxygenated blood and veins always
carry oxygen-poor blood. In the pulmonary circulation, arteries carry-poor blood to the
lungs and the veins carry oxygen-rich blood from the lungs to the heart.
Differentiate between Arteries and Veins
1. Elastic Arteries
2. Muscular Arteries
3. Arterioles
Three Types of Arteries
Thick walled arteries near the heart - the aorta and its major branches. These arteries
are the largest in diameter, ranging from 2.5cm to 1 cm, and the most elastic.
Elastic Arteries
Their large lumens make them low-resistance pathways that conduct blood from the
heart to medium-sized arteries
Why are elastic arteries sometimes called conducting arteries?
Elastic arteries contain more elastin than any other vessel type. It is present in all three
tunics, but the tunica media contains the most. Although elastic arteries also contain
substantial amounts of smooth muscle, they are relatively inactive in vasoconstriction.
Thus, in terms of function, they can be visualized as simple elastic tubes.
Composition of Elastic Arteries
Elastic arteries are pressure reservoirs, expanding and recoiling as the heart ejects
blood. Consequently, blood flows fairly continuously rather than starting and stopping
with the pulsating rhythm of the heartbeat. Without the pressure-smoothing effect of the
elastin arteries, the walls of the arteries throughout the body experience higher
pressure.
Why are elastic arteries pressure reservoirs?
Distally the elastic arteries give way to the muscular arteries, which deliver blood to
specific body organs (and are sometimes called distributing arteries).
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Document Summary
The outermost layer of a blood vessel wall that is composed largely of loose woven collagen fibers that protect and reinforce the vessel, and anchor it to surrounding structures. The tunica externa is infiltrated with nerve fibers, lymphatic vessels, and, in larger veins, a network of elastic fibers. In larger vessels, the tunica externa contains a system of tiny blood vessels, the vasa vasorum - literally "vessel of vessels" - that nourish the more external tissues of the blood vessel wall. The innermost (luminal) portion of the vessel obtains nutrients directly from blood in the lumen. In the systematic circulation arteries always carry oxygenated blood and veins always carry oxygen-poor blood. In the pulmonary circulation, arteries carry-poor blood to the lungs and the veins carry oxygen-rich blood from the lungs to the heart. Differentiate between arteries and veins: elastic arteries, muscular arteries, arterioles. Thick walled arteries near the heart - the aorta and its major branches.
