A&P II chapter 20

true capillaries

branch fro m the metarteriole and make up the bulk of the capillary bed. there is a pre capillary sphincter at the origin of each true capillary which controls blood flow.

veins

drains blood from capillaries and transports it back to the heart. Have a thicker tunica external, a larger lumen, and less elastic and collagen fibers.

filtration

a process that occurs on the arterial end of a capillary, is the movement of of fluid by bulk flow out of the blood through the openings in the capillaries. build and small solutes flow through easily while large solutes are generally blocked.

capillary beds

aa group of capillaries (10-100) functioning together. they are fed by a metarteriole, which is a vessel branch of an arteriole. at one time only one quarter of the beds are open.

perfusion

amount of blood entering capillaries per unit time per gram of tissue.

companion vessels

arteries and veins that supply the same body region and tend to lie next to one another.

end arteries

arteries that provide only one pathway through which blood can reach an organ .

local short term regulation

blod flow varies in different organs according to need; regulated by changing vessel diameter. vasodilator and vasoconstrictors.

portal system (an artery, capillary bed, portal vein, capillary bed, and a vein)

blood flows between two capillary beds with the two capillary bed separated by a portal vein ( delivers blood to another organ first before blood is sent back to the heart.

fenestrated capillaries

composed of a complete continuous lining of endothelial cells and a complete basement membrane. fenestrations are small regions of the endothelial cells that re small enough to prevent formed elements from passing through , but are big enough to let smaller plasma proteins through. these are found where absorption or filtration occurs like the small intestine, ciliary process, choroid plexus, and most endocrine glands.

tunica intima

composed of endothelium layer lining the lumen and a thin subendothelial layer made up of areolar connective tissue.

vasoconstrictors

constrict arterioles and cause contraction of pre-capillary sphincters; decrease blood flow into capillary beds

precapillary sphincter

controls blood flow into he true capillaries. relaxation permits blood flow into the true capilaries while contraction causes blood to flow directly from the metatriole and the thoroughfare channel into the postcapillary venule with blood by passing through the capillary bed. goes through cycles of contracting and relaxing at a rate of 5 to 10 cycles per minute in a cycling process called vasomotor.

vasodilators

dilate arterioles and relax per capillary sphincters; increase flow into capillary beds

capillaries

exchange substances between the blood and tissues. contain only the tunica intimate composed of an endothelium and its underlying basement membrane, which allows for rapid gas and nutrient exchange. they connect articles to venues. the walls consist of a thin tunica intima, one endothelial cell and a think basement membrane.

systolic pressure

exerted on arterial walls during ventricular systole- 120nmHg

blood pressue

force exerted on the vessel wall per unit area by the contained blood; blood moves from high to lower pressure; blood pressure depends on cardiac output, peripheral resistance, and blood volume

sinusoids

has an incomplete lining of endothelial cells with large openings or gaps and the basement membrane is either discontinuous or absent. the openings allow for transport of large substances as well as plasma between the tissue and the blood. found in the bone marrow, liver, spleen, and some endocrine glands.

muscular arteries

have a diameter of 1 centimeter to 0.3 millimeters. they deliver blood to organs . they have a thicker tunica media with multiply layers of smooth muscle cells. active in vasoconstriction.

alternative pathway

include several anastamoses and partial system. three types

angeogenesis

is the formation of new blood vessels in the tissue that require more perfusion through long-tern anatomical changes,

diastolic pressure

lowest level of arterial pressure during ventricular diastole 80nmHg

arteries

microscopic porous blood vessels that convey blood from the heart to the capillaries. arteries have a thick tunica media, a narrower lumen, and more elastic and collagen fibers. which makes that more resilient and residence to change in blood pressure.

vesicular transport

occurs when the endothelial cells use pinocytosis to fuse fluid-filled vesicles with the plasma membrane and transport their contents either from the blood to the interstitial fluid or from the interstitial fluid into the blood. examples: certain hormones, fatty acids,

simple pathway (one artery, one capillary bed, and vein)

one major artery delivers blood to the organ or body region and then branches into smaller and smaller arteries to become arteriole, which feds into a single capillary bed. a venules drains blood from the capillaries and merges with other venules to form one major veins hat draws blood from the organ or body region. example: transport to and from the spleen

resistance

opposition to flow (the friction of blood) encounters as it passes through BV depending on vessel diameter.

diffusion (capillary exchange)

oxygen, hormones, nutrients are moved from their relatively high concentrations in the blood into the interstitial fluid and then into the tissue cells, where the concentration of those materials is lower. carbon dioxide and waste products diffuse from the higher concentration in the tissue cells to the lower concentration in the blood.

aneurysm

part of the arterial wall thins and balloons out making the wall more prone to rupture which can cause massive internal bleeding and death. the risk is increased with age and the is is most common in the aorta or arteries at the bas of the brain.

mean arterial pressure (MAP)

pressure that propels the blood to the tissues diastolic pressure + 1/3 pulse pressure

atherosclerosis

progressive disease of the elastic and muscular arteries. characterized by the presence of atheroma, a thickening of the tunica intima. increased cholesterol, hypercholesterol are risk factors. males are more likely to be affected. treatment is either a angioplasty to expand narrow region of artery or coronary bypass surgery

blood distribution at rest

pulmonary circulaiton 18% heart 12% systemic circulation 70% -systemic veins 55%

capillary blood pressure

ranges around 40 at the arterial end and about 20 nm Hg at the venous end

bulk flow

refers to the movement of larger amounts of fluids and their dissolved substances in one direction down a pressure gradient.

aldosterone

released from the adrenal cortex in response to angiotensin II; increase absorption of sodium ion and water in the kidney

antidiuretic hormone

released from the posterior pituitary and stimulated by increased angiotensin II; increased absorption water in the kidney.

baroreceptor

respond to stretch in blood vessel walls

local blood flow

the blood delivered locally to the capillaries of specific tissue and is measured in milliliters per minute. the ultimate goal of the vascular system is for adequate perfusion of all tissues.

pulse pressure

the difference between systolic and diastolic pressure 120-80nmHg

how does filtration and resorption occur?

the direction of movement is dependent on the net pressure of two opposing forces at the capillary level- hydrostatic pressure and collide osmotic pressure

degree of vascularization

the extent of blood vessel distribution within a tissue, determines the potential ability of blood delivery.

blood hydrostatic pressure

the force exerted per unit area by the blood as it presses against the vessel wall. promotes filtration from the capillary.

blood osmotic pressure

the force that draws fluid back into the blood due to the proteins in the blood, such as albumin. promotes resorption.

systemic pressure

the highest in the aorta; declines throughout the length of the pathway

elastic arteries

the largest arteries with a diameter of 1 cm- 2.5 cm. they have a larger quantity of elastic which allows them to stretch and recoil. and the can withstand large blood pressure fluctuations .an example is the aorta and the pulmonary trunk. pressure reservoirs

tunica media

the middle layer of the vessel wall that is composed predominately of circularly arranged layers of smooth muscles cells that are supported by elastic fibers.

continuous capillaries

the most common type of capillaries. the endothelial cells form a continuos lining around th lumen that rest on the complete basement membrane. tight junctions secure endothelial cells to one another , but do not form a complete seal. the gaps are called intercellular clefts., which allows material to move into or out of the blood via diffusion or bulk flow.

resorption

the movement of fluid by bulk flow in to the blood , which occurs on the venous end of the capillary.

tunica externa

the outermost layer of the blood vessel wall that is composed of areolar connective tissue that contains elastic and collagen fibers.

metarteriole (thoroughfare)

the proximal part is encircled by the by scattered smooth muscle cells , while the distal part has no smooth muscle. this connects to the post capillary venule, which drains the capillary bed..

arterioles

the smallest arteries at a diameter ranging form 0.3 milimeters to 10 micrometers. have fewer than 6 layers of smooth muscles in their tunica media.the smooth muscle is slightly constricted which is called vasomotor tone and is regulated by the vasomotor center in the brainstem.

venules

the smallest veins at 8 to 20 micrometers in diameter. formed when capillaries unite . postcapillary venuules are the smallest venules that drain capillaries.

venous anastomosis

tow or more veins draining the same body region. example: basilic, cephalic veins draining the upper limb. veins tend to form more anastomoses than arteries do.

arteriovenous shunts

transports blood from an artery directly to a vein, bypassing the capillary bed. present in fingers, toes, palms, ears and they allow these areas to be bypassed if the body is hypothermic.

arterial anastomosis

two or more arteries converging to supply the same body region. example: superior and inferior mesenteric arteries supply intestines

blood reservoirs

veins act as these that contain about 55% of the blood.

veins (structure and function)

venules join to form veins blood pressure in veins is too low to overcome the force of gravity. most veins contain numerous valves (prevent back flow) which are formed primarily of tunic intima and strengthened by elastic and collagen fibers.

total blood flow

volume of blood flowing through the entire vascular system in ml/min is cardiac output.