Histology Flashcards
what are the 3 layers of the blood vessels?
tunica intima
tunica media
tunica adventitia
describe the tunica intima
inner layer
single layer of squamous epithelial cells termed endothelial cells supported by a basal lamina and a thin layer of connective tissue
describe the tunica media
middle layer
made up predominantly of smooth muscle
thickness can vary
describe the tunica adventitia
outer layer
made up of supporting connective tissue
what is the internal elastic membrane?
a layer of elastic tissue which operates the tunica intima from the tunica media
what is the external elastic membrane?
a layer of elastic tissue which separates the tunica media from the tunica adventitia
why are the largest arteries termed elastic arteries?
because they have many sheets of elastic fibres in their tunica media to provide elastic recoil
what is the vasa vasorum?
the vascular supply for large vessels as only the inner part of the wall can obtain nutrients from the lumen
describe the structure of arterioles
only one or two layers of smooth muscle in their tunica media and almost no adventitia
describe the structure of capillaries
essentially composed of endothelial cells and a basal lamina
sometimes have pericytes at intervals just outside the basal lamina
what are pericytes?
connective tissue cells that have contractile properties
what are the 3 types of capillaries?
continuous
fenestrated
sinusoidal or discontinuous
where are continuous capillaries found?
muscle connective tissue lung skin nerve
describe fenestrated capillaries
have small pores in walls
where are fenestrated capillaries found?
mucosa of the gut
endocrine glands
glomeruli of the kidney
describe sinusoidal or discontinuous capillaries
lack a basal lamina and have large gaps through which macromolecules can in some cases, even cells, can pass
where are sinusoidal or discontinuous capillaries found?
liver
spleen
bone marrow
describe the microvasculature
small arterioles connect to a post capillary venule through a network made up of metarterioles, channels and capillaries
precapillary sphincters, composed of smooth muscle, at the beginning of the capillary help control flow through the network
describe post capillary venules
endothelial cell lined and contain a thin layer of connective tissue and occasional pericytes
what is the role of post capillary venules?
important sites for exchange eg cells moving into the tissue in inflammation
describe veins
have a tunica intima and a tunica media consisting of a few layers of smooth muscle
the tunica media is thinner than what would be found in an artery
large veins have a thick tunica adventitia which incorporates bundles of longitudinally orientated smooth muscle
flexible and can accommodate expansion
what are valves in veins?
inward extensions of the tunica intima in most small to medium veins
what are the 3 layers of the heart?
endocardium
myocardium
epicardium
what is the endocardium?
inner layer
lines the entire surface of the heart, including the valves
describe the structure of the endocardium
endothelium
basal lamina
thin layer of collagen fibres
layer of denser connective tissue
what is the subendocardium?
in some areas of the endocardium, it is a loose connective tissue containing small blood vessels and nerves and the branches of the impulse conducting system
what is the myocardium?
thick middle layer of the heart
describe the structure of the myocardium
bundles and layers of contractile cardiac muscle fibres
individual muscle fibres are surrounded by delicate, collagenous connective tissue with a network of capillaries
describe cardiac muscle cells
a single central nucleus (sometimes 2)
have intercalated discs passing across the fibres at irregular intervals
what is the role of the intercalated discs in cardiac muscle cells?
act to attach cells and allows spread of electrical activity
what is the epicardium?
outer layer of the heart
describe the structure of the epicardium
on the surface of the heart: a single layer of flattened epithelium called mesothelium
basal lamina
fibroelastic connective tissue and, in some places, adipose tissue
what are the two layers of the pericardium?
fibrous pericardium
serous pericardium
describe the fibrous pericardium
a sac of tough fibrocollagenous connective tissue
what does the serous pericardium do?
lines the inner surface of the fibrous pericardium (where it is termed the parietal serous pericardium) and covers the surface of the heart (where it is termed the visceral serous pericardium?
describe the serous pericardium
made up of a layer of simple squamous epithelium (termed mesothelium), backed by a basal lamina and connective tissue
describe the pericardial cavity
separates the two layers of the pericardium and contains a small amount of pericardial fluid which provides lubrication for heart movement
what is the role of the fibrous skeleton of the heart?
supports the valves and provides the attachment for the cardiac muscle fibres
describe the fibrous skeleton of the heart
formed by thick bands of fibrous connective tissue around the heart valves, between the atria, and between the ventricles
describe the structure of the heart valves
outer endothelial layer with basal lamina
a layer of collagen and elastin fibres
lamina fibrosa
the leaflets of the valves separating the atria from the ventricles (mitral and tricuspid) are anchored to papillary muscles in the wall of the ventricle by collagenous strands called the chord tendinea, which merges with the lamina fibrosa
describe the lamina fibrosa
a core of dense connective tissue, that is in continuity with the fibrous skeleton
what are the 3 types of cardiac muscle cells?
contractile cells
pacemaker cells
conducting cells
describe pacemaker cells
highly specialised muscle cells
smaller than contractile cardiac myocytes and embedded in a more extensive matrix of connective tissue
they appear pale because of the paucity of organelles within them
few myofibrils, little glycogen and no proper T-tubule system
describe purkinje fibres
larger than normal cardiac muscle cells
abundant glycogen
no T-tubules
no intercalated discs sparse actin and myosin filaments
appear pale and have a very pale/clear centre
where can purkinje fibres be found?
in the subendocardial layer just deep to the endocardium
describe the lymph vascular system
a system of relatively thin walled vessels that drain excess fluid (lymph) into the blood stream
along the way the lymph passes through lymph nodes, providing for immunological surveillance
describe the interstitial fluid of the lymph vascular system
it contains ions, lipids, proteins and occasional cells
most returns to capillaries and venous vessels but some returns to the circulatory system by entering the lymphatic vessels
describe lymphatic vessels
they have no central pump but smooth muscle in the walls, hydrostatic pressure in the tissue and compression of the vessels by voluntary muscle, combined with valves in the vessels;s produces flow
