19 1-8 Flashcards
C+C Arteries and Veins
- LUMEN DIAMETER small large
- WALL THICKNESS Thick Thin
- CROSS SECTION SHAPE Cylindrical Elongated
- Blood flow Away fr heart To heart
- BP RANGE 93-35 mmHg 20-0 mmHg
- Valves No Yes
Tunica intima
Innermost layer
STRUCTURE: composed of endothelium and a subendothelial layer (areolar ct), continuous with the endocardium
FUNCTION: provides smooth surface to reduce friction between the vessel wall and the blood, releases local chemicals (Endothelins - vasoconstrictors and NO/vasodilator), blood clotting
Tunica media
Middle layer
STUCTURE: composed of smooth muscle and elastic fibers, innervated by ANS
FUNCTION: controls vasoconstriction/dilation of vessels, blood flow to tissues
Tunica Externa
(adventitia)
STUCTURE: Areolar ct, elastic and collagen fibers. Has vasa vasorum in very large vessels.
FUNCTION: Protects, reinforces, anchors the vessel to surrounding structures.
Vasa Vasorum
Network of small arteries in the tunica externa of very large blood vessels (nourish external tissue)
Vasodilation
Lumen diameter increases as smooth muscle relaxes
Vasoconstriction
Lumen diameter decreases as smooth muscle contracts
Elastic/conducting arteries
STRUCTURE: Contain large amounts of elastin
FUNCTION: Pressure reservoirs, Conduct blood away from the heart, Stretch and recoil
Ex. Aorta
Expand and recoil as the heart ejects blood - has a pressure smoothing effect blood flows continuously instead of stopping or starting with the heartbeat. Must have low compliance.
Muscular/distributing arteries
STRUCTURE: More smooth muscle and less elastic than Elastic arteries.
Greatest proportion of tunica media
Elastic membrane on each face of the tunica media.
FUNCTION: Distributing arteries, Deliver blood to specific body organs/tissues, Active in vasoconstriction, less distensible.
I.e. Brachial artery
Arterioles/resistance vessels
STRUCTURE: Smallest of the arteries, highly innervated by ANS
FUNCTION: Resistance vessels - vasoconstriction/vasodilation - shunting. Regulate blood flow into capillary beds through vasodilation/constriction.
Level of resistance can be regulated neurally/hormonally/by local influence.
Usually slightly constricted, a phenomena called vasomotor tone or arteriolar tone (partially contracted in the absence of any external factors).
Aneurysm
Thinning and ballooning out of an arterial wall often seen in elastic and muscular arteries.
aortic dissection
A tear in the inner wall of the aorta that causes blood flow between the layers of the wall.
Capillaries
GENERAL STRUCTURE: Thin tunica intima, lumen diameter just large enough for RBCs to pass.
GENERAL FUNCTION: Allow for the exchange of substances between the blood and interstitial fluid. All cells in the body must be within 1mm of a capillary for adequate diffusion. Exchange vessels
Continuous capillaries
Most common.
LOCATION: skin, muscles, lungs, CNS.
STUCTURE: Tight junctions, with some gaps (intercellular clefts). Exception is BBB which is continuous.
FUNCTION: Least permeable of capillaries, Intercellular clefts allow for transport processes of diffusion/pinocytosis/bulk flow.
Permeable to water-soluble substances having small molecular size and lipid soluble substances.
Fenestrated capillaries
LOCATION: small intestine, ciliary processes of eye, chorois plexus, endocrine glands, kidneys.
STRUCTURE: Have oval pores/fenestrations
FUNCTION: Active absorption and filtration. More permeable than continuous caps, allow small intestine to absorb food, filtration in kidneys, hormones to enter blood.
Sinusoid capillaries
LOCATION: liver, bone marrow, spleen, some endocrine glands.
STRUCTURE: Highly modified, leaky capillaries. Large usually fenestrated lumens, basement membrane with large gaps.
FUNCTION: Allow large molecules and even blood cells to pass between blood and surrounding tissues.
Blood flows sluggishly through the tortuous channels allowing time for it to be modified.
Pericytes
Smooth muscle like cells that stabilize capillaries.
Capillary bed
Interweaving network of capillaries consisting of a metarteriole thoroughfare channel and true capillaries.
A terminal arteriole feeding the bed leads into a metarteriole which connects with the postcapillary venule that drains the bed.
True caps branch off at the proximal end of the metarteriole and rejoin at the distal end.
Precapillary sphincters surround the roots of the true caps and act as valves to regulate blood flow into the capillary.
Metarteriole thoroughfare channel
A short vessel that directly connects the arteriole and venule at opposite ends of a capillary bed.
True capillaries
Branch off the metarteriole and are the true exchange vessels.
Perfusion
The amount of blood entering capillaries per time unit/per gram of tissue.
Venules
STRUCTURE: small ones are all endothelium, larger sized have one or two layers of smooth muscle cells and a thin tunica externa. Postcapillary venules are extremely porous.
FUNCTION: carry blood away from cap beds. Allow fluid and WBCs to move easily btw blood/tissue
Veins
STRUCTURE: Large diameter. Have valves. Have three distinct tunics. Little smooth muscle and elastin in the tunica media which is thin. Tunica externa is the heaviest layer with thick collagen and elastic networks.
FUNCTION: Carry blood to the heart. Capacitance vessels/Blood reservoirs.
Venous valves
Formed from folds of the tunica media. Prevent blood from pooling. Abundant in limbs, absent from thoracic/abdominal/CNS.
How are veins blood reservoirs?
Veins can hold 55-65% of the body’s blood at one time.
Large lumens and thin walls give veins high compliance so that a small amount of pressure can cause a large degree of expansion.
Storage in important because blood may be shunted from one area to another to meet the body’s needs.
Venous system adaptations
Structural: 1. large diameter 2. valves.
Functional: 1. Skeletal muscle pump (skel musc contraction milks blood toward heart)
2. Respiratory pump (shifting pressure between ab cavity and thoracic cavity)
Simple pathways vs. Alternative pathways
Simple pathway: artery → arteriole → capillary bed → venule → vein Alternatives…..
Anastomoses: Joining of vessels. Arterial - arteries supplying the same area often merge providing alternate pathways (collateral channels). Arteriovenous - metarteriole channel shunts. Veins - connect freely and often (blocked vein rarely causes tissue death.)
Portal system: two capillary beds connected by a vein.
- Explain the distinguishing features of the tunics found in arteries, capillaries and veins.
Caps: only endothelium.
Veins: thicker tunica externa. fibrous tissue is more than smooth muscle, very little elasticity
Arteries: thicker tunica media. significant amount of elastic fibers so they can stretch and recoil, but also significant smooth muscle.
C+C Pressure reservoir vs. Blood reservoir
Vessel type: Arteries Veins
Structure: Elastic Large lumen/thin walls
Compliance: low High
Mechanism: By clamping down/recoiling, arteries maintain pressure.
By expanding, veins can hold a large amount of blood.
Compliance
How easy it is to inflate something. Low compliance = hard to stretch, High compliance = easy to stretch
Vasomotor tone
Most arterioles are under vasomotor tone - they are slightly constricted by the ANS.
Usually slightly constricted, a phenomena called vasomotor tone or arteriolar tone (partially contracted in the absence of any external factors).
Two ways to regulate flow in cap beds?
Arterioles/sympANS, precapillary sphincters
Vasomotion
Precapillary sphincter responding to local conditions
Types of capillaries
Continuous, fenestrated, sinusoidal
Types of arteries
Elastic/conducting
Muscular/distributing
Arteriole/resistance
Arteriole resistance can be controlled by?
Level of resistance can be regulated neurally/hormonally/by local influence.
