Circulatory System Flashcards
Layers of blood vessels
Tunica intima, media, and adventitia
Vasa vasorum
smaller vessels running through large blood vessels (adventitia and outer part of the media) ; veins have more ;
Nervi vascularis
nerves in large blood vessels
Tunica intima
endothelium + underlying subendothelial CT; includes internal elastic lamina in larger vessels
Tunica media
primarily smooth muscle cells & also external elastic lamina (when it’s there LOL)
Tunica adventitia
fibroelastic connective tissue (dense irregular CT w small amounts of elastic fibers)
Types of arteries
large (elastic), medium (muscular), small (arterioles)
Elastic (conducting) arteries
conduct blood to muscular arteries; aorta, pulmonary, brachiocephalic, common carotid, subclavian, & common iliac arteries
Intima of elastic arteries
elastic fibers; subendothelial layer of loose CT contains collagen & elastic fibers & fibroblasts
Muscular (distributing) arteries
deliver blood to organs (.5mm- 1cm)
Intima of muscular arteries
thinner than that of elastic arteries; well developed internal elastic lamina; subendothelial CT lacks smooth muscle cells
Muscular artery media
up to 40 circular layers of smooth muscle interspersed with elastic fibers; thick external elastic lamina at edge
Muscular artery adventitia
MAY BE as thick as media; collagen and elastic fibers
Media of elastic arteries
thick (approx 500 um…(doesn’t seem very thick to me)) of 40-70 concentric elastic sheets
Adventitia of elastic arteries
thin; elastic & collagen fiber; no distinct external elastic lamina
Arterioles
diameter less than .5 mm; very sparse sub-endothelial CT; internal elastic lamina may or may not be present- consists of a network of fibers that may not be visible at the LM level (can see with PAS)
Arteriole media
1-3 layers of smooth muscles cells with occasional elastic fibers
arteriole adventitia
layer of loose CT w longitudinally arranged collagenous and elastic fibers
Capillaries
single layer of endothelial cells; 7-10 um diameter; surrounded by thin sheath of reticular and collagenous fibers and some pericytes
Pericytes
mesenchymal- like stem cells; can differentiate into fibroblasts or smooth muscle cells
Continuous (somatic) capillary
continuous endothelium and basal lamina - no fenestrae; numerous pinocytotic vesicles (for transcytosis)
Location of continuous capillaries
muscle, CT, CNS, exocrine pancreas, gonads; have tight junction (occluding junction) that contributes to blood-brain barrier in CNS
Fenestrated (visceral) capillary
attenuated endothelium with large 60-80 nm fenestrae- closed by thin (4-6 nm) diaphragms; continuous basal lamina
Location of fenestrated capillaries
mucosa of GI tract, endocrine glands, renal, kidney (glomerular & peritubular capillaries) choroid plexus, & ciliary body
Fenestrated endothelium in the glomerular capillaries have no ____.
diaphragms
Location of discontinuous (sinusoidal) capillary
liver and hemopoietic organs (bone marrow, spleen)
Discontinuous capillary
large (30-50 um); irregular, tortuous walls; wide gaps between cells = incomplete basal lamina
Veins and their layers!!! yayy!!!
start as venules (12 um- 1mm)
intima = endothelial cells
media= 1-2 layers of smooth m. cells
adventitia = several layers of collagen fibers
Postcapillary venules
receive blood from capillaries; important site of activity in inflammation; 12-50 um
Vasoactive compounds of postcapillary venules
Histamine and serotonin affect fluid extravasation and migration of white blood cells
Muscular venules
1-2 layers of smooth muscle and thin t. adventitia; no pericytes
Vein layers (for small to medium size veins = 1-9 mm)
intima may have a thin subendothelial CT layer
media= thin; some reticular and elastic fibers interspersed with smooth m. cells
adventitia = well developed; multiple layers of collagenous fibers with a few smooth m. cells and elastic fibers
Large veins and layers!
superior and inferior vena cava and portal trunk; intima is similar to small veins; thin media; thick adventitia w colalgenous fibers and longitudinal arranged smooth m. cells
venous valves
in small to medium size veins; prevent retrograde blood flow (primarily in lower limbs); paired, semilunar folds of the intima
arteriovenous anastomoses
connections primarily between arterioles & venules; specialized tunica media with a sphincter
function of open shunt in anastomoses
blood bypasses the capillary bed & flows into a vein
function of closed shunt in anastomose
arterial blood flows into the capillary bed
precapillary sphincter
in some microvascular beds which control the amount of blood flowing into the capillary
Lymphatic substances
plasma proteins, fluid, enzymes, lipids, antibodies, hormones, and other macromolecules that leak from blood vessels and bathe tissues and interstitial spaces
Lymph system
scavenges fluid that is then filtered by lymph nodes and recycled back into the venous circulation at the base of the neck
Lacteals
important route of fat absorption in the intestine
Lymph vessels
endothelial lined; lymph flows only in the direction toward the base of the neck; originate in CT as closed-end anastomosing capillaries; 10-50 um in diameter; paired cusp valves present to prevent back flow of lymph
Lymphatic capillaries
HAVE NO BASAL LAMINA
No lymphatic system in…
CNS and bone marrow
Mechanism for holding smaller vessels open
fine anchoring filaments attached to perivascular collagen
Larger vessel layers
may have intima, media, and adventitia like blood vessels but may be difficult to discern at the light microscopic level
Main thoracic duct and right lymphatic duct structure (smooth muscle or nah?)
structurally similar to veins, with smooth muscle present (contractile); up to 5 mm in diameter
skeletal m. lymphatics are only in ___.
perimysium
Atherosclerosis
foam cell (lipid laden macrophage) formation & fatty deposits in intima- may block vessel
Restenosis
smooth m. cell proliferation that follows angioplasty procedure- may occlude vessel
Aneurysm
ballooning out of artery- weakness in arterial wall (Ehlers-Danos syndrome, Marfan’s syndrome)
Varicose veins
tortuous, dilated veins, primarily in legs of older persons; caused by decrease in muscle tone and failure of venous valves
Prostacyclin
produced from arachidonic acid by endothelial cells; inhibit platelet adhesion & clot formation
Endothelial cell secretions
nitric oxide = causes smooth m. in the t. media to relax = vasodilation and en
endothelin-1 = vasoconstrictor
Cytokines
macrophages in surrounding connective tissue secrete them to induce expression of E-selectin by endothelial cells; neutrophils bind to selectins and then extravasate by migration through the endothelium= inflammatory cell regulation
Maternal- fetal circulation
no maternal blood is exchanged w a fetus, only materials carried in blood; exchange occurs at the interface where the umbilical cord fuses with the uterine walls (placenta)
Fetal side of circulator exchange wall
Syntrophoblast, consists of an outer layer of multinucleated syncytiotrophoblasts (underlined) :)
Heart Tunics (layers) equivalents to blood vessel layers
- endocardium = inner layer / intima
- myocardium = media
- epicardium = adventitia (outer coat)
Endocardium
lined by endothelium; continuous with blood vessels that enter and leave the heart
subendothelial layer- fine collagenous fibers, thin layer of dense fibroelastic connective tissue and then a subendocardial layer of loose CT connected to the myocardium
Subendocardial CT
contains blood vessels, nerves, portions of the impulse-conducting system (Purkinje fibers)
Myocardium
Cardiac m. tissue!
arranged into deep and superficial layers in the ventricles
Superficial layer
spiral course around the ventricle
Deep layer
circular course around ventricle
Epicardium outer coat
formed by mesothelial cells; * the visceral layer of the serous pericardium = epicardial mesothelium
underneath the mesothelium …
subepicardial layer of loose CT and adipose tissue - contains the coronary blood vessels and nerves!
Fibrous skeleton
composed of dense irregular connective tissue
septum membranaceum
fibrous portion of the interventricular septum
annuli fibrosi
fibrous rings around the origins of the pulmonary artery, aorta, and atrioventricular canals
Trigona fibrosa
fibrous tissue between the arterial foramina and the atrioventricular canals
Annuli around atrioventricular orifices results in ___.
electrical discontinuity between myocardial cells of atria and ventricles; controls communication between them via specialized conduction tissue (AV bundle)
atrioventricular valves
tricuspid and mitral (doesn’t it feel good to know things?!); connected to papillary m. of the ventricles by fibrous cords (chordae tendinae)
semilunar valves
between ventricles, aorta, pulmonary artery
CT of valves
both dense and loose CT layers surrounded by endothelium
SA nodes
pacemaker of the heart; contains modified cardiac m. cells concentrically arranged around a nodal artery; impulse spreads form this node via specialized conduction fibers to the AV node
AV node
lies beneath the endocardium of the septal wall of the right atrium; cells similar to SA node; continues to form AV bundle of His (H-I-S)…not piss
Bundle of His (H-I-S)
formed by Purkinje fibers- penetrate skeleton of heart then branch to form right and left bundle branches
Purkinje Fibers
modified m. cells filled w glycogen; travel in the subendocardial layer to the heart apex- then reverse direction and branch to make contact and form gap junctions w cardia m. cells
Parasympathetic nerves to heart
from vagus nerve (ugh, amateur hour); slow heart
sympathetic nerves
ACCELERATE HEART BEAT!!!!!!!!
Polypeptide hormones
from atrial cardiac m. cells & some cells in the interventricular septum (cardiac endocrine cells): ANP gene makes 4 different hormones
4 Hormones of cardiac endocrine cells
1) long acting natriuretic (sodium) peptide
2) vessel dilator
3) kaliuretic (potassium) peptide
4) ANP
ANP
atrial natriuretic peptide; released from modified atrial m. cells in response to high blood pressure. primary effect is to increase sodium and H20 secretion from kidney
Postcapillary venules have an incomplete layer of ___.
Pericytes; becomes more complete as vessel gets larger (this was in blue so that might mean it’s relatively important… but only relatively);
What are muscular arteries innervated by?
innervated by postganglionic sympathetic nerve fibers
Fenestrae
small pores in endothelial cells that allow for rapid exchange of molecules between fenestrated blood vessels
