Histology Flashcards
What are the 3 layers of every macroscopic vessel?
tunica adventitia
tunica media
tunica intima
What’s tunica adventitia?
Collagenous connective tissue, loose to dense
Role of tunica adventitia?
Anchorage, support (transgenic mice deficient in type I collagen gene prematurely die with ruptured arteries), elasticity
Carries nerve + blood supply to vessel (vasa vasorum in larger vessels)
What’s tunica media?
smooth muscle
Role of tunica media?
Support, elasticity, contractility (tone).
Physical regulation of blood flow.
Smoothing of blood flow of elastic arteries
What’s tunica intima?
Endothelium, over a little dense connective tissue
Role of tunica intima?
Selectively permeable barrier to blood.
Regulated adhesion of platelets + leukocytes
Makes mediators controlling vessel tone (maintained by tunica media), eg NO, endothelins
Makes mediators of inflammation
Diff between 3 layers in artery vs vein?
Artery: thick T.media>T.adventitia, round, wall>internal diameter
Vein: thin T.media, oval, internal diameter>wall
Diff types of arteries?
elastic (conducting arteries)
muscular
arterioles
eg of elastic (conducting arteries)?
aorta, pul arteries + their largest branches: brachiocephalic, common iliac
Features of elastic (conducting arteries)?
Thick T.media with many elastic laminae (sheets of elastin/lamellae)
Role of elastic (conducting arteries)?
Absorb systolic flow by stretching + continue blood flow in diastole by elastic recoil
How do elastic arteries look with H/E stain?
Smooth muscle cells: purple nuclei, pink cytoplasm
Elastic laminae: darker pink
How do elastic arteries look with EVG (elastic-Van Gieson) stain?
collagen: red
cytoplasm: yellow
elastin: brown/black
elastic laminae: brown
What damage happens in AAA?
Partial rupture of arterial wall, with blood entering T.media, fatal if T.adventitia also ruptures.
Features of muscular (distributing) arteries?
0.3mm diameter (40 🔴 wide)
Contractile - regulate blood flow + BP
How diff types of arteries merge into another?
Elastic -> muscular -> arterioles
How do muscular (distributing) arteries look with EVG (elastic-Van Gieson) stain?
collagen: red
cytoplasm: yellow
elastin: brown/black
Prominent internal elastic lamina, single, between intima and media
Thick T.media with some elastic fibres but no elastic laminae
External elastic lamina, several thin, discontinuous laminae, in adventitia at inner edge
Adventitia: red collagen
Main diff between elastic vs muscular arteries?
ELASTIC: many elastic laminae in T.media
MUSCULAR: single internal + external elastic laminae at edges of T. media.
Where are atheromas?
in T.media
Role of muscular (distributing) arteries?
Contractile to regulate BP + flow
Features of arterioles?
Microscopic, < 0.3 mm wide.
Difference from small arteries is arbitrary, there’s a continuum of sizes.
Role of arterioles?
Regulating BP + flow, globally + locally
How do arterioles look with H/E stain?
More T.media , for contractility against high BP
Smooth muscle of T.media runs circularly
Smallest arterioles have 1-2 layers of smooth muscle
Features of capillaries?
Endothelium only, with scattered pericytes
What are pericytes?
spindly cells, suggested to be stem cells for repair and/or contractile
Diameter of capillaries?
3-(20-40) µm
Diameter of 🔴?
7-8 µm
What’s the capillary diameter made of?
thin cytoplasm of 1-2 endothelial cells
Role of layer of endothelial cytoplasm?
limits exchange + allows regulation
Features of continuous capillaries?
no holes in walls
Features of fenestrated capillaries?
many tiny pores in wall (right through cytoplasm)
Role of fenestrated capillaries?
permeable, although limited by molecular diaphragm.
What are sinusoids?
subgroup of fenestrated capillaries
Features of sinusoids?
wider fenestrated capillaries (20-40 µm)
Where are sinusoids located + why?
liver, spleen, allowing slow blood flow + highest rates of exchange
How do typical capillaries in loose connective tissue look with H/E stain?
endothelial cell + pericyte (purple flat)
How to see fenestrations?
SEM
How big are fenestrations?
~70 nm pores
Features of veins + venules?
Thin, flexible wall
Adventitia: prominent
Media: thin, but still controls BP + flow
No Media in smallest
Major veins have longitudinal smooth muscle in wall to assist flow against gravity
Valves
Role of veins + venules?
return low-pressure blood to heart
Why does the saphenous vein have valves?
help with the flow against gravity
Diff between venule vs arteriole?
larger diameter
thinner wall
less smooth muscle
less rounded
Role of heart?
Pumping blood
Regulation of BP: atria secretes atrial natriuretic peptide (ANP)
What would you see in a TEM of part of atrial cardiac muscle cell?
dense (secretory) granules of ANP
myofibril
What happens when the atria fills with blood?
- atria stretches after being filled with blood
- release atrial natriuretic peptide (ANP)
- increases secretion of water + Na into urine
- reduction of BP
What are the 3 layers of the heart?
epicardium (visceral pericardium)
myocardium
ENDOcardium
Features of epicardium?
Outer layer
Smooth lubricated epithelial covering = mesothelium
Fatty (adipose) loose connective tissue with nerves, blood vessels (coronary arteries)
sparse collagen
Features of myocardium?
Middle layer
bundles of cardiac muscle running in diff directions, with septa of dense connective tissue
Role of myocardium?
Contracts to give heartbeat
Features of endocardium?
Thin layer of connective tissue
Some collagen
Endothelial lining
Rich in Purkinje fibres
What’s mesothelium made of?
simple cuboidal epithelium
Role of Purkinje fibres?
impulse-conducting system
How does the aortic valve look with EVG (elastic-Van Gieson) stain?
elastic fibres along aortic face
collagen fibrous supporting tissue (underneath elastic fibres)
How does an infected valve look with H/E stain?
thrombus
bacteria: purple
