Blood Vessels Flashcards
Blood vesels
Blood Vessel
The Vascular System •Transport blood to the tissues and back •3 major types of blood vessels are •Arteries •Capillaries •Veins •Carry blood away from the heart •Arteries •Arterioles – the smallest arteries •Exchange between tissues and blood •Capillaries •Return blood toward the heart •Venules – the smallest veins •Veins
Structure of blood vessel
Composed of three layers (tunics) 1. Tunica intima •Endothelium 2. Tunica media •Smooth muscle •Contraction - vasoconstriction •Relaxation - vasodilation 3. Tunica externa (adventitia) •Mostly fibrous connective tissue •Lumen •Central blood-filled space of a vessel
Structure of
blood vessel: Tunica intima
The endothelium forms a smooth surface that minimize the friction of blood moving across them.
•In vessels larger than 1 mm in diameter, a thin layer of loose CT. called the subendothelial layer,
lies just external to the endothelium.
Structure of blood vessels: tunica media
Tunica media: the middle tunic consists of circularly arranged sheets of smooth muscle fibers that sandwich sheets of elastin and collagen fibrils.
•Contraction of the smooth muscle cells decreases the diameter of the vessel … a process called vasoconstriction, whereas their relaxation increases the vessel’s diameter … a process called vasodilation.
Structure of blood vessel Tunica Externa
Tunica externa: the outermost layer of the vessel wall; composed of connective tissue (elastic and collagen fibers)
•Protect the vessel, further strengthen its wall, and anchors the vessel to surrounding structures.
Types of arteries
Elastic arteries – recoil when stretched, which prevents blood pressure from
falling rapidly.
•Large amount of elastic tissue; smaller amount of smooth muscle
•Muscular arteries: regulate blood flow to different regions of the body
•Thicker layer of smooth muscle in the tunica media
Elastic Arteries
Elastic arteries – the greatest arteries •Diameters range : 2.5 cm – 1 cm •Includes the aorta and its major branches •Sometimes called conducting arteries •Greater proportion of the wall is elastic tissue. •Smaller proportion is smooth muscle, compared to other arteries. •High elastin content reduces surge of blood pressure.
Muscular arteries
Muscular arteries – distributing arteries •Lie distal to elastic arteries •Diameters range : 1 cm – 0.3 cm •Includes most named arteries •Tunica media is thick •Unique features •Internal and external elastic laminae •Vasoconstriction •Vasodilation
Arterioles
Arterioles •Smallest arteries •Diameters range : 0.3 mm – 10 𝜇m •Transport blood from small arteries to capillaries. •Three tunics are identified. •Diameter of arterioles controlled by •Local factors in the tissues •Sympathetic nervous system
Capillaries
Smallest blood vessels
•Endothelium surrounded by a loose connective tissue
•Diameters range : 8 – 10 𝜇m
•Red blood cells pass through single file
•Site-specific functions of capillaries
•Lungs – O2, CO2exchange
•Small intestines – receive digested nutrients
•Endocrine glands – deliver hormone
•Kidneys – get rid of nitrogenous wastes
capillaries
Capillaries are composed of only a single layer of endothelial cells surrounded by a basement
membrane.
•Pericytes: spider-shaped cells who form a network around the periphery of the capillary and serve
to strengthen and stabilize the capillary.
•Function: Renew and refresh interstitial fluid with O2nutrients cells need and removes CO2and
nitrogenous wastes that cells deposit into the fluid.
Types of Capillaries
. Continuous Capillaries
- Fenestrated Capillaries
- Sinusoids
continous capillaries
Most common type of capillary •Occur in most organs •Tight junctions and desmosomes join epithelial cells •Intercellular clefts •Gaps of unjoined membranes •Allow small molecules across capillaries •Pericytes •Spider-shaped contractile stem cells •Generate new vessels
low permeability capillaries
Blood Brain Barrier (BBB) •Capillaries have complete tight junctions •No intercellular clefts are present •Vital molecules pass through •Highly selective transport mechanisms •Not a barrier against: •O2,CO2,some anesthetic
Fenestrated Capillaries
Joined by tight junctions and intercellular clefts
•Have poresin their endothelium
•Occur where high rates of exchange occur
•Intestines
•Glomeruli of kidneys
•Endocrine glands
