CV Histology Flashcards
What is the structure of capillary walls
Single layer of simple squamous epithelium (endothelium) surrounded by basement membrane
average diameter is ≈8mm
Explain interchange between capillary lumen and extravascular space
Occurs via simple diffusion
Rate depends on blood and colloid osmotic pressure
Even capillaries w/o fenestrae (pores) very permeable to water, gases, salts, nutrients
Describe capillary transport using vesicles
Numerous pinocytotic vesicles are present
50-70nm in diameter
transport soluble high MW molecules across Endothelial wall originate as invaginations of cell membrane on both inner and outer surfaces
How do cells pass through capillaries
Cells (WBC’s, MØ’s) pass endothelium by ameboid migration
movement known as known as diapedesis
Explain capillary junctions
Junctions between cells
interdigitations of the adjacent cell membranes
joined by tight junctions
Some fluid exchange occurs through this space
What are fenestrae
In some organs capillary endothelium has thin fenestrae (windows)
e.g. endocrine glands, renal glomerulus, intestinal villi
Pores closed by diaphragm thinner than unit membrane
What are support cells of capillaries
Mesenchymal-like cells (pericytes) associated with, and surrounded by, capillary basement membrane
found intermittently
Contractile cells
What are the capillary types
Continuous
Fenestrated
Sinusoid
Describe sinusoid capillaries
Specialized enlarged capillary-like vascular channels
Sinusoids differ from true capillaries:
Larger than capillaries, with an irregular lumen diameter up to 30mm
Sinusoidal endothelium
-discontinuous in some locations
-possess a discontinuous basement membrane
-allows close association with parenchyma (functional cells) liver, spleen, bone marrow
What are some sinusoidal phagocytic cells
Macrophages (bone marrow, spleen) , Kupffer cells (in liver),
some sinusoids lack phagocytic capability
What is the general vessel organization
Tunica intima (TI) - nearest the lumen Tunica media (TM) - external to the intima Tunica adventitia (TA) - outermost vessel coat aka tunica externa
What is the morphology of the Tunica intima
Endothelium surrounds lumen
Basement membrane underlies endothelium
Subendothelial connective tissue
- fibroblasts and CT fibers some of which run longitudinally
Inner elastic lamina (IEL)
- fenestrated layer composed of accumulated elastic fibers
- outermost component of the tunica intima
visible when vessel is >60mm in size
What is the morphology of the Tunica media
Composed primarily of: smooth muscle and connective tissue fibers
Circumferentially arranged
- numerous CT fibers formed by specialized smooth muscle cells
- fibroblasts may be present or lacking
External elastic lamina (EEL)
- concentration of elastic fibers
- form outermost component of tunica media
What is the morphology of the Tunica adventitia
Composed primarily of moderately dense connective tissue
CT fibers longitudinally arranged
Adventitial CT components formed by fibroblasts
- adventitia merges with loose connective tissue
Describe the tunica media in arteries
Most prominent tunic in all arteries
Inner elastic lamina nearly always present
- may not be discernable in:
- small arterioles (due to lack of fiber mass)
- elastic arteries (due to mass of fibers in media)
External elastic lamina visible in:
- larger muscular arteries
- smaller elastic arteries
(may be present in all vessels, but: insufficient fiber mass to make visible, or volume of fibers makes indiscernable)
Describe the morphology of arterioles
Tunica intima
very thin
little, or no subenodothelial CT
inner elastic lamina not distinct
Tunica media 1-5 layers of smooth muscle* controls blood flow to capillaries, regulates blood pressure no visible external elastic lamina
Tunica adventitia
usually thinner than media
not well developed
Describe the morphology of muscular arteries
Tunica intima
small amounts of subendothelial CT present
prominent, well-developed inner elastic lamina (IEL)
Tunica media
very thick, 5-40 layers of smooth muscle*
smaller arteries have lower elastic fiber content
larger arteries have increasing quantities of elastin
ANS control of smooth muscle regulates blood flow
some collagen present
external elastic lamina well developed (but less visible)
Tunica adventitia
usually thinner than media
some elastic fibers usually present near media
mostly composed of collagen
Describe the morphology of large elastic arteries
Tunica intima
- endothelial cells may be polygonal
- subendothelial CT relatively thick with many fibers
- IEL present, but not as distinct as in muscular arteries
Tunica media
- smooth muscle fibers, much elastic fiber accumulation
elastic lamina – numerous thin tubular elastic “membranes”
- high elastic content retains shape while preventing excessive expansion
receives excess blood during ventricular contraction
diminishes pulsatile delivery to peripheral vessels
- fibroblasts may be present
- external elastic lamina is indistinct due to elastin throughout
Tunica adventitia
- thinner than media, composed of loosely arranged coliagen bundles
- spiral longitudinally around vessel
- overdistention of intima and media prevented by adventitia
What is vasa vasorum
small nutrient arteries supplying walls of larger arteries
What is a carotid body
Mass of epithelioid cells and nerve endings found at bifurcation of common carotid artery
- stimulates respiration in response to lowered blood 02
What is a carotid sinus
Dilatation of internal carotid artery
contains specialized nerve endings
sensitive to blood pressure change
Describe vein tunics
Tunica intima
very thin
smooth muscle, arranged longitudinally
diffuse inner elastic lamina - seen only in large veins
Tunica media variable thickness, lacks definition very thin compared with lumen size contains: more collagen than anything else little smooth muscle or elastic fiber content muscle arranged spirally no distinct external elastic lamina
Tunica adventitia thickest-coat smooth muscle & fibrous CT may be present longitudinally or spirally oriented no circular smooth muscle
Describe valves in veins
Medium-sized veins often have valves
lined by endothelium on either side
paired invaginations of tunica intima
free edges face in direction of blood flow
have intimal core reinforced by collagen and elastic fibers
Describe venule morphology
Tunica intima
composed only of endothelium and basement membrane
Tunica media
very thin
1 to 3 smooth muscle layers
scattered elastic fibers may be present
Tunica adventitia
thickest part of vessel wall
primarily longitudinal collagen bundles
Describe morphology of medium veins
Tunica intima endothelial cells may be polygonal small amount of subendothelial CT longitudinal/spiral smooth muscle fibers IEL diffuse (when present) Tunica media very thin smooth muscle in spiral bundles separated by collagen more smooth muscle in lower extremity Tunica adventitia well developed collagen and elastic fibers predominate longitudinal or spiral smooth muscle may be present near media
Describe morphology of Large veins
Tunica intima
subendothelial CT nearly always present
longitudinal smooth muscle nearly always present
thin, delicate IEM may be observed
Tunica media
very thin
little or no circumferential smooth muscle
Tunica adventitia
very thick (compared to intima and media)
collagen bundles are present
prominent longitudinal or spiral smooth muscle
Compare Arteries and Veins
artery wall is thicker than accompanying vein wall
artery contains:
more smooth muscle
more elastic fibers
all arteries possess an inner elastic lamina
vein wall contains:
more collagen
less smooth muscle
veins may have valves
Describe Cardiac muscle junctions
Intercalated discs rich in junctions - fascia adherens - modified macula adherens - occurs in sheet-like formations also rich in gap junctions for rapid intercellular communication
Describe heart enodocardium
Continuous with tunica intima of great vessels
Consists of:
endothelium & underlying basement membrane
subendothelial CT (may include some sm. muscle)
subendocardial connective tissue
responsible for binding endocardium to Myocardium
loose CT with collagen, elastic fibers, and fat
impulse conducting system of heart within this layer
Describe the morphology of Purkinje fibers
Cardiac muscle specialized for impulse conduction
contain fewer myofibrils
coordinates heart beat
high glycogen content
Describe heart myocardium
Bundled cardiac muscle fibers
Bundles thick in ventricles, thinner in atria
Bundles spiral around heart
Thin CT networks separate muscle bundles
Networks consist of: collagen fiber, elastic fibers, reticular fibers
Capillaries/nerves run in CT
Describe heart epicardium
Visceral layer of the pericardial sac
mesothelium lined
fluid-filled (approximately 50 ml).
thin layer of loose CT (subepicardium)
carries coronary arteries & cardiac veins
also carries nerves & ganglia
connects serous mesothelium to myocardium
Fat found in epicardium (especially around vessels)
distinguish epicardium from endocardium by Fat in epicardium
Describe the fibrous skeleton of the heart
Fibrous ring
dense fibrous connective tissue
surrounds AV, aortic, and pulmonary valves of heart
composed of collagen and elastic fibers
cartilage may be found (may calcify with age)
rings provide attachment for cardiac muscle & valves
Fibrous trigones
thickened areas of dense fibrous CT
lies between right and left AV canals and aortic valve
membranous part of the atrioventricular septum
Describe heart valve morphology
Evaginations of endocardium into AV canals at fibrous rings & at origins of aorta and pulmonary trunk
Each valve is covered on both sides with endothelium and has a reinforcing core of collagen and elastic fibers
How does capillary pressure affect hydrostatics of lymph
At arterial origin of capillary
- hydrostatic pressure of blood exceeds osmotic pressure of interstitium
- H2O, electrolytes pass from blood to extracellular space
At venous terminus of capillary
- osmotic pressure of interstitium exceeds hydrostatic pressure of blood
- some fluid is returned to vascular system but exchange at arterial end exceeds resorption at venous end excess fluid is lymph
Describe lymphatic valve morphology
More numerous than blood capillaries
Characteristic of lymph channels
Structure similar to venous valves, except:
valve core composed exclusively of collagen III
Describe the structure of large lymph vessels
Structurally similar to veins of comparable size, but Not identical
Differences: thinner walls, tunics less distinguishable, many valves, with sinuses (dilations) in vessel walls
Describe thoracic duct and right lymphatic duct structure
Structurally similar in structure to great veins, but Not identical
Differences: thinner walls, muscle layers more prominent, tunica adventitia not well developed
