Flashcards in packet 4 Deck (37)
These muscular, elastic vessels carry blood under pressure from the heart. They branch many times before they become arterioles
Microscopic, thin-walled but still muscular vessels that regulate blood flow into the capillaries
Single layer of epithelial cells that allow exchange of fluids, gasses, and nutrients in tissues. They then pass on to venuoles
Thin-walled vessels that intersect others to begin returning blood to the heart. Eventually they merge to become larger veins
Similar structure to arteries, but much thinner walls, wider diameter, and less elastic; role?
tunica interna. Very thin inner lining in contact with blood.
three layers of inner layer
squamous cell epithelium
epithelial basement membrane
internal elastic lamina
“endothelium” that lines the entire circulatory system. Cells help in regulation of vessel contraction, protection of cells, mediating capillary permeability and preventing permeability elsewhere.
squamous cell epithelium
Tough acellular layer that anchors endothelium to connective tissues. Additional barrier to diffusion.
epithelial basement membrane
Porous, elastic fibers
internal elastic lamine
*thin, tough, flexible layer to contain blood and mediate exchange with surrounding tissues.
inner layer (tunica internal)
tunica media. Muscular, elastic layer that varies considerably in thickness between the vessel types. Composition: smooth muscle, elastic fibers
encircle vessel to regulate diameter, essential to direct blood flow and modify blood pressure.
smooth muscle cells
provide flexible support within the muscular layer.
essential to direct blood flow and provide structural strength and flexibility.
middle layer (tunica media)
tunica externa. Three primary elements:
elastic and collagen fibers of the external elastic lamina. Again = tough flexibility.
nerves to interact with and regulate smooth muscles of tunica media
vascular system (vasa vasorum) to nourish cells in larger vessels (e.g., aorta, vena cavae, etc.)
connections/anchorage to surrounding tissues.
* Outer protective (rip, stretch, feed) layer.
Vascular smooth muscle is innervated by sympathetic nervous system
increase in stimulation causes muscle contraction or vasoconstriction
decreases diameter of vessel
injury to artery or arteriole causes muscle contraction reducing blood loss (vasospasm)
decrease in stimulation or presence of certain chemicals causes vasodilation
increases diameter of vessel
nitric oxide, K+, H+ and lactic acid cause vasodilation
Structure: thick-walled elastic, muscular vessels that take blood from the heart under pressure.
Two types: elastic, musclular
thick tunica media and both elastic lamina. Ex.: pulmonary, aorta. Stretches, then pushes blood away from the heart.
elastic (connecting) arteries
thick muscle, low elastic, high collagen = regulation of blood pressure & direction, but do not aid in propelling flow.
muscular (distributing) arteries
Small arteries delivering blood to capillaries
tunica media containing few layers of muscle
Metarterioles form branches into capillary bed
to bypass capillary bed, precapillary sphincters close & blood flows out of bed in thoroughfare channel
vasomotion is intermittent contraction & relaxation of sphincters that allow filling of capillary bed 5-10 times/minute
Structure: endothelial cell layer only; no tunica media or externa. Desmosomes, tight jcns, but also intercellular clefts between cells.
Types via basement membrane: continous, fenestrated, sinusoid
complete basement membrane. Most capillaries.
pores in basement membrane. Increase fluid exchange in kidneys, sm. intestine, and choroid plexes.
gaps in basement membrane. Allow cell crossing in bone marrow, liver, spleen.
Essentially the reverse of arterioles, but no bordering muscular sphincter.
Postcapillary venule, muscular venules
larger than capillary but very loose intercellular endothelial connections allow continued exchange of nutrients, gasses, wastes, etc. No sphincter.
muscle fibers surround thickened endothelium; exchange no longer occurs
Like arteries, 3 tunics, but
tunica interna and tunica media are much thinner
elastic layers missing
blood with little pressure
veins in extremities have valves to aid return
more veins than arteries, often with interconnected superficial and deep or paired, connected veins following artery
venous sinuses = no tunica media & externa; bordered by connective tissue.
Twisted, dilated superficial veins
caused by leaky venous valves
congenital or mechanically stressed from prolonged standing or pregnancy
allow backflow and pooling of blood
extra pressure forces fluids into surrounding tissues
nearby tissue is inflamed and tender
Deeper veins not susceptible because of support of surrounding muscles
3 mechanisms of capillary exchange
Filtration and Reabsorption
Movement of materials in and out of a capillary
Oxygen, carbon dioxide, nutrients,
and metabolic wastes diffuse
between the blood and interstitial
fluid along concentration gradients
Oxygen and nutrients pass from
the blood to tissues
Carbon dioxide and metabolic wastes
pass from tissues to the blood
Most important mechanism
Substances move down concentration gradient
through lipid bilayer, fenestrations or intercellular clefts
Lipid soluble substance
O2 and CO2
lipid soluble substance
glucose and electrolytes
must pass through
Passage of material across endothelium in tiny vesicles by endocytosis and exocytosis
large, lipid-insoluble molecules such as insulin or maternal antibodies passing through placental circulation to fetus