Lecture 3 CVS: Blood Vessels Flashcards
what are blood vessels
-a delivery system of dynamic structures that begins nad ends at the heart
what system do blood vessels work with
it works with the lymphatic system to circulate fluids
what are arteries
they carry blood away from the heart; oxygenated blood, except for the pulmonary circulation and umbilical vessels of a fetus
what are capillaries
they have direct contact with tissue cells; directly serve cellular needs
-one cell thick good for transfer of oxygen and nutrients and removal of used goods
what are veins
carry blood toward the heart; deoxygenated, except for the pulmonary circulation and umbilical vessels of a fetus
what is the structure of blood vessel walls
all consist of a lumen, central blood-containing space, surrounded by a wall
what are the layers of the walls in all blood vessels except for capillaries
there are three layers or tunica
1. tunica intima/ interna
2. tunica media
3. tunica externa
what are the walls in the capillaries
endothelium with sparse basal lamina
describe the tunica intima
-innermost layer, “intimate”
there are three layers of the tunica intima: endothelium, subendothelial layer, and internal elastic membrane
what is the endothelium of the tunica intima
-simple squamous epithelium lines the lumen of all vessels
-continuous with the endocardium
-slick surface reduces friction (reduces friction between blood & walls)
what is the subendothelial layer of the tunica intima
-connective tissue basement membrane
-found only in vessels > 1mm
what is the internal elastic membrane of the tunica intima
elastic fibers in outer margin of arteries (divides tunica intima and media)
what is the tunica media
the middle layer is composed mostly of smooth muscle and sheets of elastin
-innervated by SYMPATHETIC VASOMOTOR NERVE FIBERS which controls:
vasoconstriction: decreased lumen diameter
vasodilation: increased lumen diameter
-bulkiest layer responsible for maintaining blood flow and BP
has the external elastic membrane
what are the sympathetic vasomotor nerve fibers responsible for
changes size of lumen, adjust diameter of lumen
-vasoconstriction: decreased lumen diameter
-vasodilation: increased lumen diameter
what is the external elastic membrane of the tunica media
it seperates the tunica media from the externa
what is the tunica externa (adventitia)
the outermost layer of the wall
-composed mostly of loose collagen fibers that protect and reinforce wall and anchor it to surrounding structures
-infiltrated with nerve fibers and lymphatic vessels
large veins also contain elastic fibers in this layer
describe vasa vasorum and its function
a system of tiny blood vessels found in larger vessels
-functions to nourish outermost external layer
what are the three types of vessels
arteries, capillaries, and veins
what are the three types of arteries
- elastic artery (conducting artery)
- muscular artery (distributing artery)
- arterioles
explain the elastic/ conducting arteries
thick-walled, low resistence lumen, lots of elastin in all tunics, have pressure resevoirs
explain the muscular/ distributing arteries
account for most arteries, thickest tunica media, less elastic, has a lot more smooth muscles (tunica media)
explain arterioles
smallest of the arteries, vasodilation and constriction-> blood flow into capillary beds resistance arteries
describe capillaries
-smallest vessels (microscopic networks), with thin walls
-single-walled; absence of tunica media and externa
-supply almost every cell, except for cartilage, epithelia, cornea, and lens of the eye
what are the functions of the capillaries
exchange of gases, nutrients, wastes, hormones, etc., between blood nad interstitial fluid
what are pericytes and where are they found
they are stem cells that stabilize capillary walls, control permeability, and vessel repair
they are found on capillaries
why are capillaries single cell walled
due to an abscence of tunica media and externa
what type of junctions do all capillaries have
all capillary endothelial cells are joined by tight junctions wuth gaps called intercellular clefts, which allow for passage of fluids and small solutes
what are the three types of capillaries
continuous, fenestrated, and sinusoid capillaries
describe the continuous capillaries
-the least permeable and most common
-abundant in SKIN, muscles, lungs, and CNS
-pinocytotic vesicles (bulk transport/ endocytosis “cell drinking”) ferry fluid across the endothelial cell
-most continuous capillaries have INTERCELLULAR CLEFTS BETWEEN ENDOTHELIAL CELLS. however brain capillary endothelial cells lack intercellular clefts and have tight junctions around thier entire perimeter
describe fenestrated capillaries
-have large fenestrations (pores) that increase permeability
-occur in active areas of filtration (ex. kidney) or absorption (ex. intestines) and areas of endocrine hormone secrection
-fenestrations are swiss-cheese like holes that tunnel through enodthelial cells
-fenestrations are usually covered by a very thin layer of condensed extracellular glycoproteins. this layer has little effect on solute and fluid movement
-in some digestive tract organs, the number of fenestrations in capillaries increase during active absorption of nutrients
describe sinusoid capillaries
-the most permeable and occur in limited locations
-occur in liver, bone marrow, spleen, and adrenal medulla
-have LARGE INTERCELLULAR CLEFTS as well as fenestrations
-have few gap junctions
-have an incomplete basement membrane
-are irregularly shaped and have larger lumens than other capillaries
-allow large molecules and even cells to pass across thier walls
-blood flows slowly through their walls
-macrophages may extend processes through the clefts to catch “prey” or in liver, form part of the sinusoid wall
describe capillary beds
-interwoven network of capillaries between artioles and venules
-microcirculation: flow of blood through bed from arteriole to venule
-terminal arteriole: branch of atriole that further branches into 10-20 capillaries (exchange vessels) that form capillary beds
-capillaries then drain into postcapillary venule
-flow through bed controlled byy diameter of terminal arteriole and upstream arterioles
what is microcirculation
flow of blood through bed from arteriole to venulea
what is terminal arteriole
branch of arteriole that further branches into 10-20 capillaries (exchange vessels) that form capillary bed
explain capillaries in serous membranes of intestinal mesentaries
they have two additional features that form a special arrangement of capillaries which are the 1. vascular shunt and 2. precapillary sphincter
describe the vascular shunt
capillaries in serous membranes of intestinal mesentaries that channel directly connects arteriole with venule (bypasses true capillaries/ capillary bed)
-consists of metarteriole (micro vessels that link) and thoroughfare channel (connects metarteriole to venule)
describe precapillary sphincters
capillaries in serous membranes of intestinal mesentaries that cuff off smooth muscle surrounding each true capillary that branches off mertarteriole
-acts as valve regulating blood flow into capillary bed
-controlled by local chemical conditions (not innervated)
what are veins
-carry blood toward the heart; formed from convergence of venules
describe venules
-capillaries unite to form postcapillary venules-» veins
-consists of endothelium and a few pericytes
-very porous; allow fluids and white blood cells into tissues
-larger venules have on or two layers of smooth muscle cells
explain the tunica components of veins
-have all 3 tunics but thinner wall and larger lumens
-the tunica media is thin, but tunica externa is thick
-large lumen and thin walls make veins good storage vessels (called capacitance vessels/ blood reservoirs-> contain up to 65% of blood supply
what is the distribution of blood in the cardiovascular system
-pulmonary vessels= 9%
-heart= 7%
-systemic arteries and arterioles= 13%
-systemic capillaries= 7%
-systemic veins and venules (blood reservoirs)= 64%
what are systemic veins
-supply all of the body except the lungs
-are distensible (able to stretch and expand)
-contain a large proportion of blood volume and so are called capacitance vessles or blood reservoirs
explain the three types of veins
- Large vein
- medium-sixed vein
- venule
why are there venous adaptations
since blood pressure is in the veins there has to be adaptations to ensure return of blood to the heart
what are the three types of venous adaptations
- large-diameter lumens
- venous valves
- venous sinuses
describe how large-diameter lumens are a venous adaptation
this offers little resistence
describe how venous valves are a venous adaptation
they are fold of tunica intima
-they prevent backflow of blood
-most abundant in veins of limbs
-compression pushes blood toward heart
describe how venous sinuses are a venous adaptation
they are flattened veins with extremely thin walls
-composed of only endothelium
ex. coronary sinus of the heart and dural sinuses of the brain
what is angiogenesis
formation of new blood vessels from preexisting ones
-promoted by pro-angiogenic factos (proteins)= VEGF, FGF, EGF, PDGF, HGF, TGF
-inhibitied by antiangiogenic factors (proteins)= angiostatin, endostatin, thrombospondins, interferons, vasostatin
-implicated in several conditions: tumorgenesis, diabetic retinopathy, age-related blindness, skin diseasem CVDs, stroke, etc.
what are the proteins that promote angiogenesis
-VEGF= vascular endothelial growth factor
-FGF= fibroblast growth factor
-EGF= epidermal growth factor
-PDGF= platelet derived growth factor
-HGF= hepatocyte growth facotr
-TGF= transformin growth factor
what is angiogenesis- based medicine
used in the prevention of blood vessel formation-> inhibit diseases
what are varicose veins and how do they form
-abnormally twisted and enlarged veins
-due to weakening of valves-> incompetent vein valves
-most significant in limbs rather than upper parts of body (neck, head)
what is arteriosclerosis
arterial walls become thickened
what is atherosclerosis
formation of plaque (fatty deposits) within tunica media
what is focal calcification
deposition of calcium salts
smooth muscle cells within tunica media eroded
