CV Histology Flashcards by kevin silva

What is the structure of capillary walls

Single layer of simple squamous epithelium (endothelium) surrounded by basement membrane
average diameter is ≈8mm

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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

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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

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How do cells pass through capillaries

Cells (WBC’s, MØ’s) pass endothelium by ameboid migration

movement known as known as diapedesis

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Explain capillary junctions

Junctions between cells
interdigitations of the adjacent cell membranes
joined by tight junctions
Some fluid exchange occurs through this space

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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

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What are support cells of capillaries

Mesenchymal-like cells (pericytes) associated with, and surrounded by, capillary basement membrane
found intermittently
Contractile cells

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What are the capillary types

Continuous
Fenestrated
Sinusoid

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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

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What are some sinusoidal phagocytic cells

Macrophages (bone marrow, spleen) , Kupffer cells (in liver),
some sinusoids lack phagocytic capability

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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

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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

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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

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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

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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)

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Describe the morphology of arterioles

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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

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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

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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

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small nutrient arteries supplying walls of larger arteries

What is a carotid body

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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

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Dilatation of internal carotid artery
contains specialized nerve endings
sensitive to blood pressure change

Describe vein tunics

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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

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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

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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

CV Histology Flashcards

(38 cards)