histology Flashcards
describe the tunica intima
single layer of squamous endothelial cells supported by basal lamina and a thin layer of connective tissue called sub-endothelial layer
what is the sub-endothelial layer?
it’s the thin layer of connective tissue that has elastic fibres and an internal elastic lamina
describe tunica media
made of predominantly smooth muscle but also has elastic fibres (it alternates smooth muscle and elastic fibres)
-> the thickness of tunica media varies tremendously
describe tunica adventitia
made of supporting connective tissue and elastic fibres that provide strength
-has collagen fibres & fibroblast
what is fibroblast?
type of cell that contributes to formation of connnective tissue
what type of vasculature is it hard to distinguish between internal elastic lamina, external elastic lamina and tunica media?
in elastic arteries
what is tunica intima and tunica media seperated by?
internal elastic lamina
what is tunica media and tunica adventitia seperated by?
external elastic lamina
what is appearance of layers in elastic arteries?
=thicker tunica media than tunica adventitia
=tunica intima thicker than tunica adventitia
=they have sheets of elastic fibres in their tunica media to provide recoil
what are some examples of elastic arteries?
aorta, aortas branches and pulmonary arteries
how do you stain elastic fibres?
not stained using common stains (including H&E) but can be visualised with special stains like ones that stain fibres black
whats the vasa vasorum?
vessels have own vascular supply called vaso vasorum because in large arteries, only inner part of wall can obtain nutrients from lumen
what are the 2 types of arteriole?
meta arteriole and terminal arteriole
describe appearance of arterioles
-smallest division of arteries
-they lose smooth muscle from tunica media and start to lose layer so only 1 or 2 layers
what is typical diameter of arterioles?
30-200 micrometre
what are arterioles important for?
controlling blood flow in a tissue
describe terminal arteriole appearance
no internal elastic lamina & covered by smooth muscle
describe meta arteriole appearance
part right before capillaries so no smooth muscle, it’s replaced by non-contractile cells, still has endothelial cells
describe capillary appearance
only composed of endothelial cells
what is diameter of capillaries?
4-8 micrometres
what are the 3 types of capillaries?
- continuous
- fenestrated
- discontinous
describe continuous capillaries
endothelial cells have no gaps in between them hence the name
examples = muscle, nerve, lung, skin
describe fenestrated capilllaries
has parasites & small gaps in between endothelial cells. there is a continuous basal lamina so not clear opening. have small pores about 50nm
examples = gut mucosa, endocrine glands, kidney
describe discontinuous capillaries
endothelial cells have very clear gap and basal membrane also discontinuous so obvious gaps
examples = liver, spleen, bone marrow
describe microvasculature from arterioles to veins?
terminal arteriole -> meta arteriole -> thoroughfare channels (some routes skip) ->capillaries -> precapillary sphincters -> post capillary venules -> veins
what are precapillary sphincters?
they’re composed of smooth muscle at the beginning of capillary bed to control flow through the network
what are post capillary venules appearance
endothelial cell lined and contain a thin layer of connective tissue
why are capillary networks important?
they are important sites for exchange e.g. cells moving into tissue in inflammation
what is the diameter of venules?
10-30 micrometres
when do vessels start being referred to as venules?
when they begin to aquire intermittent (not continuous) smooth muscle in tunica media layer
describe appearance of veins
they have tunica intima, thin but continuous tunica media typically consisting of a few layers of smooth muscle and an obvious tunica adventitia
what has valves to prevent backflow?
some smaller veins. varicose veins formed as a result of incompetent valves
what produces flow in lymphatic system?
-smooth muscle in walls
-hydrostatic pressure in tissue
-compression of vessels by voluntary muscles
- valves in vessels
what is lymphatic system?
system of relatively thin walled vessels that drain excess tissue fluid (lymph) into blood vessels and transports lymph to lymph nodes for immunological surveillance
what are the components of blood?
plasma & formed elements (red blood cells, white blood cells and platelets)
what are the 2 branch terms of white blood cells?
granulocytes and agranulocytes
what types of white blood cells are granulocytes?
-eosinophils
-neutrophils
-basophils
what types of white blood cells are agranulocytes?
-lymphocytes
-monocytes
what is plasma made up of?
-water (55%)
-proteins (coloids)
-nutrients
-salts
-crystaloids (calcium, magnesium etc)
when seperating bloods, after spinning what layers are there?
-red blood cells at bottom as densest
-white blood cells next densest
-plasma found at top
what is serum part of blood?
blood with clotting factors are removed
how do you usually obtain serum?
by allowing the blood to clot and then removing clot before spinning
what are erythrocytes?
red blood cells
what diameter are red blood cells?
7 micrometre
what is structure of red blood cells?
they are biconcave discs
-not true cells as have no nucleus or organelles
-basically they are deformable bags with about 1/3 of volume taken up by iron containing protein haemoglobin
what property of rbc’s allow them to deform and slip through small spaces?
their network of flexible cytoskeleton
how long do erythrocytes last in circulation? how are they removed when aged?
they last about 4 months and are removed by spleen and liver
what is hematocrit?
proportion of blood that is red blood cells
what is the avergae hematocrit of:
a) men
b) women
a) 42
b) 38
- means 42/38% of blood volume is red blood cells
what are the proportions of each type of white blood cells?
neutrophils = 40-75%
eusinophils = 5%
basophils = 0.5%
lymphocytes = 20-50%
monocytes = 1-5%
what are some appearances of neutrophils?
-cytoplasm contains many granules but these stain poorly with acidic/basic dyes (hence neutro)
-prominent, multi-lobed nucleus
what are some functions of neutrophils?
they circulate in inactive state but if stimulated by e.g. bacteria or inflammation, they enter tissue where they act as highly motile phagocytes
what are some features of eosinophils?
-bilobed nucleus
-prominent granules in cytoplasm have high affinity for red acidic dye eosin (so look red)
-they’re slightly larger than neutrophils
where are neutrophils production?
bone marrow - as they’re highly abundant and short lived, a large proportion of bone marrow is devoted to them
what are some functions of eosinophils?
-granules contain a variety of hydrolytic enzymes and they’re important in inducing and maintaining inflammation (particularly in allergic reactions&asthma)
-important in fighting paristic infection
how long do eosinophils circulate? and then what happens?
8 - 12 hours and then they move into tissue (particularly spleen, lymph nodes & GI tract) where they live
what is some features of basophils?
-prominent granules have high affinity for basic dyes like methylene blue so stains intensely blue-purple
-cells have bilobed nucleus but it’s often obscured by granules
what is function of basophils?
acts as effector cell in allergic reactions.
high affinity IgE receptors in their cell membrane are directed against a particular allergen and when they bind their antigen to cell its stimulated to release granules (termed degranulation).
= this leads to hayfever, allergic asthma, allergic dermmitus etc
what do granules in basophils contain?
-histamine
-heparin
-other inflammatory mediators
what is appearance of monocytes?
- numerous small lysosomal granules in cytoplasm (not normal granules)
-they’re the largest cells circulating in the blood and have a non-lobulated nucleus which often appears kidney bean shaped
what are the functions of monocytes?
-serve as precursor of tissue macrophages & together they form what is termed mononuclear phagocyte system
what are macrophages?
monocytes that have migrated into blood stream
(Monocytes typically circulate through the blood for 1–3 days before migrating into tissues, where they become macrophages or dendritic cells)
where abouts in body are macrophages?
they’re widely distributed but are particularly found in loose connnective tissue
what is appearance of lymphocytes?
-they have round nucleus by a thin to moderate rim of cytoplasm that doesn’t have granules
what are the 2 types of lymphocytes and can you distinguish between them?
B lymphocyte and T lymphocyte
= can’t be distinguished in routine stained sections
where are the lymphocytes produced?
- both arise in bone marrow
-but T cells differentiate in the thymus
what are functions of lymphocytes?
-both cell types participate in specific immune response
-B cells give rise to antibody secreting plasma cells
-T cells form a complex set of cells that perform many defuse functions (aiding other immune cells, killing defective cells etc)
what are platelets?
-part of formed element of blood
-small cell fragments about 2 micrometres in diameter found in large numbers in blood
what is composition of platelets?
-they have well developed cytoskeleton, which participates in extrusion of granules and in clot retraction
-platelets have some organelles but no nucleus
-they have conspicuous granules that include, among other things some coagulation factors
what are coagulation factors?
proteins in your blood that help to form blood clots to stop bleeding when you have an injury
what is platelets main function?
they play a key role in hemostasis (prevention of blood loss)
what is hematopoeisis?
formation of blood cellular components
where is development of blood cells in embryology?
earliest site of erythrocyte formation is outside embryo in yolk sac (beginning at about 3 weeks gestation)
-later the liver, and to some extent the spleen is colonized by hemapoetic stem cells so in 2nd trimester, liver principal site of blood formation
by birth, where is development of blood cells?
bone marrow, essentially all bones participate
by maturity, where is development of blood cells?
only vertebrae, ribs, skull, pelvis and proximal femurs retain hematopoeisis
-marrow in other bones is largely adipose tissue although in emergency they can revert to blood formation
what are megakaryocytes?
large cells of bone marrow that produces plateletes by undergoing multiple duplications of nuclear material but it doesn’t undergo cell division so nucleus is very large
-the platelets are formed as extensions at outer margin of cell which fragment from cell
