A&PII Circulatory - Exam 2
*Capillaries are absent in...
Avascular substances such as cornea, lens of eye, cartilage (meniscus)
Change in arteriole diameter causes changes to ___ ___ overall.
Blood pressure
tunica interna (intima)
Direct contact with blood as it flows through the lumen; consists of multiple layers: internal elastic lamina layer (arterial), basement membrane layer (arterial, venous), endothelial cell layer (arterial, venous)
Veins are ___ enough to adapt to variations in volume and pressure of blood passing through them but not designed to withstand ___ pressure.
Distensible, high
*Muscular arteries are also called
Distributing arteries
Venules
Drain capillary beds, thin walls and less smooth muscle, blood reservoir, postcapillary venules have very porous endothelium, microcirculation & emigration of WBCs, lead to muscular venules
*resistance vessels
Due to blood rubbing against vessel wall, when diameter is smaller, friction is higher causing greater resistance; alt name for arterioles
*Capillary beds
10-100 capillaries that arise from single metarteriole, feed tissue; form extensive branching networks that increase the surface area available for rapid exchange of materials; in tissues at rest, only small portion of capillary network receives blood because need for metabolic exchange is low, in tissue that is active, whole capillary beds open to blood flow in order to increase efficiency in metabolic exchange
hepatic portal system
Allows the liver to filter blood from stomach, spleen, pancreas, gallbladder and mesenteric systems without sending that to rest of body
Capillary are found in...
Almost every cell in the body, tissues with higher metabolic demands have extensive capillary networks including muscles, brain, liver, kidneys, nervous system
Microcirculation
Flow of blood from metarteriole through capillaries and into postcapillary venules
Deep veins
Form connections with superficial veins and travel between skeletal muscles
*Continuous capillaries
Most capillaries are continuous, plasma membranes of endothelial cells form a continuous tube interrupted only by intercellular clefts (gaps between neighboring endothelial cells); *found in CNS, lungs, skin, muscle tissue
Lower limb veins are
Much larger than superficial veins, serve as principle return pathway to heart, one-way valves in small anastomosing vessels allow blood to pass from superficial to deep veins that prevent reverse flow (help counteract gravity)
Venous walls (including venules) are...
Much thinner than arteries (average thickness is ~1/10 of vessel diameter; ranges from 0.5mm in small venules to 30mm in venae cava
*external elastic lamina
Only found in arteries, not veins, separates the tunica media from tunica externa, thin sheets of elastic fibers, has variable number of window-like openings that facilitate diffusion of material through tunica externa to tunica media
Internal elastic lamina
Only found in arteries, not veins, separates tunica interna from tunica media, thin sheet of elastic fibers, has variable number of window-like opening (Swiss cheese-like); these facilitate diffusion of materials through the tunica to tunica media
Vessel occlusion with collateral circulation
Open, functioning coronary artery; partial coronary artery closure with collateral circulation being established; total coronary artery occlusion with collateral circulation bypassing the occlusion to supply the myocardium
3 layers of arteries and veins
tunica intima, tunica media, tunica externa
types of blood vessels
arteries, arterioles, capillaries, venules, veins
Blood volume increase of ____ % have been measured in the postcapillary/muscular venules.
360
*Elastic arteries are
Aorta, pulmonary trunk, brachiocephalic, right subclavian, right common carotid, left common carotid, left subclavian, common iliac arteries
elastic arteries
Aorta, pulmonary trunk, brachiocephalic, subclavian, common carotids, common iliacs; largest diameter lumen among the arteries; vessel walls relatively thin (1/10th total diameter)
*Back pressure created by constricting ___ helps to stretch the walls of ___ during heart contractions (keeps pressure in the system and lumen decrease).
Arterioles, arterioles
Muscular venules
As postcapillary venules move away from capillaries, they gain 1-2 layers of smooth muscle, become thicker walled (50-200um diameter) preventing metabolic exchange with interstitial fluid; thin wall of both postcapillary and muscular venules are most distensible elements of entire vascular system, serve as reservoirs for large amounts of blood if needed
*pressure reservoir
Blood expelled into aorta, walls expand accounting for momentary storage of mechanical energy
Superficial veins appear as
Blue colored lines passing under the skin, venous blood is deep-dark red but their thin walls and the tissue of skin absorbs red-light wavelengths allowing blue light to pass through the surface to our eyes and are seen as blue
muscular arteries examples
Brachial, femoral, axillary arteries
*tunica externa (adventitia)
Composed of elastic and collagen fibers (connective tissue); contains nerves of vessels, vasa vasorum, helps anchor vessels to surrounding tissue
Types of capillaries
Continuous, fenestrated, sinusoids
*Vasomotion
Contraction and relaxation of pre-capillary sphincters (5-10 times per min); regulates blood flow through capillary beds; insures all capillary beds receive blood flow *during rest to prevent ischemia; mostly due to chemicals released by endothelial cells such as nitric oxide
vasoconstriction
Contraction of smooth muscle in arterioles causes smaller diameter, causes greater resistance which causes decreased blood blow into capillaries
Vasodilation of arterioles causes ___ BP.
Decreased
What are the two major types of arteries?
Elastic and muscular
Arteries that do not anastomoses are called ____.
End arteries
Function of capillaries
Exchange of substance between blood and interstitial fluid; know as "exchange vessels"
*tunica media
External elastic lamina, smooth muscle (some elastic fibers) layer
Examples of capillary portal systems
Hepatic (liver), hypophyseal (pituitary)
Vasoconstriction of arterioles causes ___ BP.
Increased
Veins lack ___ and ___ found in arteries.
Internal, external laminae
*Sympathetic tone
Keeps most blood vessels partially constricted and maintains blood pressure; influences blood flow through higher rate of firing (vasoconstrict) or lower rate of firing (vasodilate)
Blood pressure in veins is considerably ___ than that of arteries.
Less
*Endothelium
Lining of the lumen of the vessel, continuous with the endocardium lining of the heart, helps to inhibit platelet aggregation, reduces blood cell damage (smooth), facilitates efficient blood flow by reducing friction, secretes chemical mediators that influence contractile smooth muscle in tunica media, assists with capillary permeability
*Thoroughfare channel
Metarteriole that has constricted sphincters to all capillaries except one; provides direct route from arteriole to venule, bypassing majority of capillary bed with very little chance for nutrient exchange; occurs when blood is moving fast throughout systemic system via hemorrhage or increased stroke volume (exercise)
Arterioles are
Microscopic vessels (approx 400 mil); diameter from 15um-300um, rich in smooth muscle, wall thickness is 1/2 of total vessel diameter (7.5um to 150um wall thickness)
End-arteries
Obstruction of end-arteries interrupt the blood supply to segment of organ causing tissue necrosis; end-organ/artery damage (diabetics)
Portal system
Parts of body blood pass from one capillary network into another instead of traditional path of blood flow; transports products of one region into another in high concentrations, bypasses heart and therefore systemic circulation
muscular arteries are
Pencil sized femorals and axillaries to string-sized arteries entering organs (as small as 0.5mm in diameter); also known as distributing arteries, they continue to branch and distribute blood to each of the organs
Liver sinusoids have ___ cells that remove bacteria and other debris.
Phagocytes
*Fenestrated capillaries
Plasma membranes have many fenestrations allowing for easier diffusion, found in kidneys, villi of small intestine, choroid plexuses of ventricles of brain, ciliary processes of eyes, most endocrine glands
Elastic arteries purpose
Propel blood onward while ventricules are in diastole, as blood is expelled into aorta, the walls expand accounting for surge, the expansion causes a momentary storage of mechanical energy called a pressure reservoir, elastic fibers recoil and convert stored (potential) energy into kinetic energy propelling blood forward; also known as conducting arteries, conduct blood from heart to medium sized muscular arteries
*basement membrane (subendothelial layer)
Provides physical support for epithelial layer, network of collagen fibers (provides significant tensile strength, also allows for some stretching and recoil), anchors the endothelium to underlying tunica media, helps regulate molecular movement, guides cell movement during tissue repair of blood vessels
muscular arteries function
Reduced amount of elastic fibers causes reduction in ability to propel blood, muscular tunica media performs the majority of work in these arteries, this muscle contracts and maintains a state of partial contraction, this is called vascular/vasomotor tone which stiffens the vessel wall and helps maintain vessel pressure and efficient blood flow
*Smooth muscle of tunica media
Regulates diameter of vessel lumen, is innervated by sympathetic nerve fibers, smooth muscle contracts and relaxes for blood flow regulation as needed, vasoconstriction and vasodilation, contracts when vessel is damaged to limit blood loss
Vasodilation
Relaxation of smooth muscle in arterioles cause larger diameter, causes less resistance which increases blood flow into capillaries
*Metarterioles
Short vessels that connect arterioles to capillary networks, do not have true tunica media, instead at the metarteriole-capillary junction, a single smooth cell forms a ring; each encircling muscle cell acts as a precapillary sphincter, regulating flow of blood into capillaries that branch from metarteriole; in response to stimuli, muscle cell encircling the metarteriole contracts, reducing the size of lumen or closing it completely
Capillary layers
Single endothelial cell layer and basement membrane only, very thin walls allow for nutrient, gas, and waste diffusion to and from tissue interstitial fluid/tissue cells, lack tunica media and externa
*New formed blood cells pass from marrow into blood stream through what?
Sinusoid capillaries
Spleen, anterior pituitary, parathyroids, bone marrow, and adrenal glands contain ___.
Sinusoids
*Postcapillary venules
Small veins that receive blood flow directly from capillary beds, 10-50um diameter, walls of smallest venules are very porous allowing phagocytic WBCs to pass through to inflamed or infected tissue (site of immune response), functions as significant sites of exchange of nutrients and wastes as well - last site of metabolic exchange (only other site other than capillaries)
vasa vasorum
Small vessels that transport O2 and nutrients to cells of blood vessel walls; easily seen on large vessels like aorta
Capillaries characteristics
Smallest of blood vessels, 5-10um in diameter, blood cells are often 8um, causing them to fold over and pass single file through the capillaries, buys time for nutrient exchange; extensive network throughout the body, approx 20 billion, forms enormous surface area to make contact with cells of the body; forms union between arterial and venous blood
Blood exits a lacerated artery in ___.
Spurts with the pressure of the heart beat
Blood exits a lacerated vein by ___.
Steady oozing flow
Upper limb veins are
Superficial and much larger than the deep veins, serve as pathways from capillaries of upper limbs back to heart
Largest anastomotic vein is the ___.
Superior anastomotic vein in the brain
*Arterioles are regulators of blood flow to ____ ____ ____.
Systemic capillary beds
*Many veins contain valves that are...
Thin folds of tunica interna (intima) that form cusps; cusps project into the lumen with the cup portion aiming toward the heart; low blood pressure in veins allows blood to back up and the valves aid in venous return by helping prevent backflow
Arteries
Transport blood (mostly oxygenated) from heart to tissues throughout the body; much thicker tunica media layer than veins; plentiful elastic fibers lending to high compliance, walls stretch and expand easily without tearing in response to pressure increases/decreases
Elastic arteries layers
Tunica externa (adventitia) later has fibroblasts, nerve fibers and vasa vasorum (blood vessel network); tunica media has more elastic fibers called elastic lamellae than other vessels, more collagen fibers than other arteries, minimal smooth muscle; tunica intima has endothelial and myointimal cells with supporting layer of elastin rich collagen (starting place of atherosclerosis)
*Arterioles layers
Tunica externa consists of areolar connective tissue containing abundant unmyelinated sympathetic nerves along with local chemical mediators, these nerves can alter diameter of arterioles varying blood rate and resistance through these vessels; tunica media, thin with only 1-2 layers of muscle cells, controls BP; tunica intima, thin layer
Vein layers
Tunica externa is thickest layer consisting of collagen and elastic fibers, tunica media is much thinner, much less smooth muscle and elastic fibers than arteries, tunica interna (intima) is much thinner than arteries
Muscular artery layers
Tunica externa layer is thicker in these when compared to elastic arteries, contains fibroblasts, nerve fibers, some collagen and elastin; tunica media layer contains much more smooth muscle but less elastic fibers (when compared to elastic arteries), makes these arteries capable of greater vasoconstriction and vasodilation which helps adjust to rate of blood flow; tunica intima layer contains endothelial cells
Anastomoses
Union of branches of two or more arteries supplying blood to same region of body, provide alternate routes or collateral circulation for blood to reach an organ
Vascular sinus
Vein with thin endothelial wall, no smooth muscle, surrounding dense connective tissue replaces tunica media and tunica externa in providing support, e.g. dural venous sinuses, coronary sinus
Anastomotic veins
Veins that are paired and accompany medium-to-small sized muscular arteries; paired veins escort arteries and connect with one another (veins) via these anastomotic veins, greatest number in limbs
Superficial veins
Veins that lie within subcutaneous layer of skin and are unaccompanied by arteries
Anastomoses may occur between ___, between ___, and between ___.
Veins, arterioles, venules
*Sinusoid capillaries
Wider and more winding than others, incomplete or absent basement membranes, may have unusually large fenestrations, very large intercellular clefts allowing some proteins and even blood cells to pass from tissue into blood; contain specialized lining cells adapted to function of tissue
*Elastic arteries are also known as
conducting arteries
*Vascular tone
the state of partial constriction that stiffens the vessel wall and helps maintain vessel pressure and efficient blood flow; in muscular arteries
