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50 terms

Circulatory System Histology

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mesothelium
simple squamous epithelium lining both walls of the pericardial sac
endocardium
consists of 2 layers: endothelium and subendocardial CT; wraps around the internal structures of the heart
myocardium
contains layered cardiomyocytes that insert into the cardiac skeleton
endomysium
CT around each cardiac muscle fiber
perimysium
CT between the bundled cardiac layers
epicardium
consists of 2 layers: CT (subepicardium) layer and mesothelium (visceral layer of serious pericardium)
myocardial infarction
death of cardiac muscle cells due to ischemia;
scarring repairs heart wall since cardiac myocytes cannot be replaced; results in cardiac hypertrophy due to the increased size of individual cardiac myocytes (NOT increased # of cells)
chondroid
dense irregular CT with 'cartilage-like' cells
cardiac skeleton
dense irregular CT consisting fibrocollagen and chondroid; (1) attachment site for cardiac muscle, (2) AV separation facilitates conduction, (3) maintains valve patency
annulus fibrosus
CT rings around the openings of each valve; maintains their shape while holding them open
fibrous trigones
(R one is pierced by the AV bundle of HIS)
triangular CT between the valves; supportive structures
septum membranaceum
downward CT extension from trigone into top of IV septum
SA node
at junction of SVC and atria; pacemaker cells fire 70 bpm, (para)sympathetic inn MODIFY rate of depolarization (DONT initiate impulse b/c it's intrinsic)
AV node
found near atrial septum by tricuspid valve; follower cells that pick up the conduction signal
AV bundle of HIS
leave AV node, pierce R. trigone, and enter the IV septum where they divide into L and R branches
L and R bundle branches
travel down IV septum to supply their respective ventricles
subendocardial plexus
impulse from bundle branch runs from apex up toward the base allowing contraction to push blood toward outflow tracts
pacemaker cell
leaky cells (Na+ into cell causes depolarization wave thus initiating contraction); unstable RMP
follower cells
pick up depol. wave via gap junctions
purkinje fibers
modified cardiac muscle cells; start in bundle branches and go into the subendocardial plexus; lots of gap junctions for impulse transfer
tunica intima
simple squamous endothelial lining with a subendothelial CT and a fenestrated internal elastic lamina
tunica media
consists of circularly oriented SM, elastic and collagen fibers, external elastic lamina; prominent in arteries; replaced by pericytes in capillaries and venules; reduces lumen of the vessel
tunica adventita
dense irregular CT with vaso vasorum and longitudinally oriented elastic fibers ; prominent in veins; keeps vessels from distending
atherosclerosis
remodeling of the tunica intima into a thickened structure with fatty streaks (accumulated cholesterol in SM) and plaques; immune condition attracts macrophages which ingest LDL but inability to process LDL creates foam cells
vaso vasorum
blood supply to the larger BVs
elastic artery
large lumen, thin walls, numerous elastic lamellae; has a t. intima characterized by 40-70 layers of elastic sheets; func= maintain BP within vessel during diastole due to passive contraction of elastic lamellae; "conducting"
muscular artery
round lumen, prominent scalloped IEL, thick t.media made of 30-40 layers of SM; "distributing": regulate flow to diff. parts of the body as needed
arteriole
~IEL, no EEL, only 1-3 layers of SM, minimal t.adventitia; feeds the capillary bed to supply metarteriole or AV shunt
microvascular bed
consists of arterioles, true capillaries, central channel, venules, and AV shunts
metarteriole
beginning of the central channel; scattered SMCs; opens into true capillaries (which are smaller)
thoroughfare channel
distal end of the central channel; no SMCs; drains true capillaries into the venule
AV shunt
alternate channel that directly links the arteriole and venule; bypasses capillaries to conserve heat; 2-3 layers of SM
capillary
simple squamous epithelium; tube of endothelial cells; no media (no SM); some pericytes; func= thin-walled for rapid (transport and secretion) exchange with parenchyma
pericyte
myoepithelial cells on capillary and venule walls that form gap junctions for communication; contractile mech. aids in controlling the diameter of the capillary lumen
continuous capillary
found in muscle, CT, gut; connected by tight junctions, continuous basal lamina around the endothelium
fenestrated capillary
found in endocrine/exocrine glands, intestinal villi, pancreas, renal glomeruli; onnected by tight junctions, continuous basal lamina around the endothelium; holes perforating through the cytoplasm
discontinuous capillary
found in spleen, bone marrow, lymph nodes, liver; irregularly shaped with large gaps between endothelial cells; discontinuous basal lamina
endothelial cells
help form basal lamina; secrete collagen type IV; produce signals for extravasation and diapedesis; secrete substances that affect vascular tone; produce clotting factors
von willebrand factor
glycoprotein that promoted coagulation of platelets during clotting; found in weibel-palade (secretory) bodies of endothelial cells
von willebrand's disease
genetic disease that destroys VWF thus slowing down coagulation and causing excessive bleeding
venules
collects blood from capillary beds; companion to arterioles; irregular lumen, thinner but larger than arterioles; no media (no SM); WBCs like to exit here
medium sized veins
companion to muscular arteries; thinner but larger than than muscular arteries; ~IEL, no EEL, thick t.adventitia; only vessels that contains valves
valves
protrusions of the intima into the medium veinlumen of the vein; ensure unidirectional flow of blood; usually in extremities
leaflets
help direct blood flow back to the heart
valve sinus
dilation of the wall behind the leaflet; close and balloon out the leaflets when blood tries to back flow in the wrong direction
varicose veins
large tortuous (usually superficial) veins on surface of legs due to excess venous pressure; causes distention and dilation of vessel walls (leaflets dont meet to prevent backflow)
large veins
large, thin wall (vs. lumen), low P vessels that return blood to heart; no valves, longitudinally-oriented SM in adventitia, no IEL, reduced t.media thickness, thick t. adventitia; vaso vasorum
lymphatic capillary
delicate, have valves to direct fluid back to heart which is taken to nodes for filtering before returning it to the blood vascular system
L thoracic duct
begins as cisterna chyli at level of diaphragm; drains 2/3 body; drains into subclavian vein
R duct
drains upper 1/3 body into R subclavian vein