CV Histology

Question 1

What is the structure of capillary walls

Answer 1

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

Question 2

Explain interchange between capillary lumen and extravascular space

Answer 2

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

Question 3

Describe capillary transport using vesicles

Answer 3

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

Question 4

How do cells pass through capillaries

Answer 4

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

movement known as known as diapedesis

Question 5

Explain capillary junctions

Answer 5

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

Question 6

What are fenestrae

Answer 6

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

Question 7

What are support cells of capillaries

Answer 7

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

Question 8

What are the capillary types

Answer 8

Continuous
Fenestrated
Sinusoid

Question 9

Describe sinusoid capillaries

Answer 9

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

Question 10

What are some sinusoidal phagocytic cells

Answer 10

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

Question 11

What is the general vessel organization

Answer 11

Tunica intima (TI) - nearest the lumen
Tunica media (TM) - external to the intima
Tunica adventitia (TA) - outermost vessel coat			aka tunica externa

Question 12

What is the morphology of the Tunica intima

Answer 12

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

Question 13

What is the morphology of the Tunica media

Answer 13

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

Question 14

What is the morphology of the Tunica adventitia

Answer 14

Composed primarily of moderately dense connective tissue
CT fibers longitudinally arranged
Adventitial CT components formed by fibroblasts
- adventitia merges with loose connective tissue

Question 15

Describe the tunica media in arteries

Answer 15

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)

Question 16

Describe the morphology of arterioles

Answer 16

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

Question 17

Describe the morphology of muscular arteries

Answer 17

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

Question 18

Describe the morphology of large elastic arteries

Answer 18

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

Question 19

What is vasa vasorum

Answer 19

small nutrient arteries supplying walls of larger arteries

Question 20

What is a carotid body

Answer 20

Mass of epithelioid cells and nerve endings found at bifurcation of common carotid artery
- stimulates respiration in response to lowered blood 02

Question 21

What is a carotid sinus

Answer 21

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

Question 22

Describe vein tunics

Answer 22

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

Question 23

Describe valves in veins

Answer 23

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

Question 24

Describe venule morphology

Answer 24

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

Question 25

Describe morphology of medium veins

Answer 25

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

Question 26

Describe morphology of Large veins

Answer 26

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

Question 27

Compare Arteries and Veins

Answer 27

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

Question 28

Describe Cardiac muscle junctions

Answer 28

Intercalated discs rich in junctions
  - fascia adherens
  - modified macula adherens 
  - occurs in sheet-like formations
also rich in gap junctions for rapid intercellular communication

Question 29

Describe heart enodocardium

Answer 29

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

Question 30

Describe the morphology of Purkinje fibers

Answer 30

Cardiac muscle specialized for impulse conduction
contain fewer myofibrils
coordinates heart beat
high glycogen content

Question 31

Describe heart myocardium

Answer 31

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

Question 32

Describe heart epicardium

Answer 32

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

Question 33

Describe the fibrous skeleton of the heart

Answer 33

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

Question 34

Describe heart valve morphology

Answer 34

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

Question 35

How does capillary pressure affect hydrostatics of lymph

Answer 35

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

Question 36

Describe lymphatic valve morphology

Answer 36

More numerous than blood capillaries
Characteristic of lymph channels
Structure similar to venous valves, except:
valve core composed exclusively of collagen III

Question 37

Describe the structure of large lymph vessels

Answer 37

Structurally similar to veins of comparable size, but Not identical
Differences: thinner walls, tunics less distinguishable, many valves, with sinuses (dilations) in vessel walls

Question 38

Describe thoracic duct and right lymphatic duct structure

Answer 38

Structurally similar in structure to great veins, but Not identical
Differences: thinner walls, muscle layers more prominent, tunica adventitia not well developed