Histology Flashcards
describe the inner layer (tunica intima) of blood vessels?
- single layer of squamous epithelial cells termed endothelial cells
- supported by a basal lamina and a thin layer of connective tissue
describe the middle layer (tunica media) of blood vessels?
- made up of smooth muscle
- thickness of this layer varies
describe the outer layer (tunica adventitia) of blood vessels?
- made of supporting connective tissue
what separates the tunica intima from the media?
- by a layer of elastic tissue called the internal elastic membrane
what separates the tunica media from the tunica adventitia?
- a layer of elastic tissue called the external elastic membrane
what are elastic arteries?
- eg aorta
- they have many sheets of elastic fibres in their tunica media to provide elastic recoil
why do elastic arteries require their own vascular supply? (vasa vasorum)
- in large vessels, only the inner part of the wall can obtain nutrients from the lumen
what is the histology of arterioles?
- 1 or 2 smooth muscle layers in their tunica media
- almost no adventitia
what is the histology of a capillary?
- endothelial cells and a basal lamina
- they often have pericytes (P) at intervals outside the basal lamina, these are connective tissue cells which have contractile properties
what are the 3 types of capillaries?
- continuous
- fenestrated
- sinusoidal or discontinuous
what are continuous capillaries?
- common
- found in muscle, connective tissues, lung, skin, nerve
what are fenestrated capillaries?
- 50nm pores in their walls
- found in mucosa of gut, endocrine glands, glomeruli of kidney
what are sinusoidal or discontinuous capillaries?
- lack a basal lamina and have large gaps in their walls
- found in liver, spleen and bone marrow
what is a microvascular network?
- small arterioles connect to a post capillary venuele though a network made up of metarterioles, throughfare channels and capillaries
- precapillary sphincters, composed of smooth muscle, at the beginning of the capillary help control flow through the network
what is a postcapillary venule?
- where capillary networks drain into
- they are endothelial cell-lined and contain a thin layer of connective tissue and occasional pericytes
- import sites for exchange eg cells moving into the tissue during inflammation
- once the vessels has intermittent smooth muscle in the tunica media layer they are termed venules
what is the histology of veins?
- tunica intima and media (thin)
- largest veins (vena cava) have a thick tunica adventitia which incorporates bundles of longitudinally orientated smooth muscle
- veins are flexible
what is the endocardium?
- lines entire inner surface of the heart including valves
- made of endothelium, basal lamina, thin layer of collagen fibres, layer of dense connective tissue
what is the subendocardium?
- loose connective tissue containing small blood vessels and nerves and the branches of the impulse conducting system
- has purkinje fibres
what is the myocardium?
- thick middle layer
- bundles and layers of contractile cardia muscle fibres
- individual muscle fibres are surrounded by delicate, collagenous connective tissue with a rich network of capillaries
- cardiac muscle cells have a single central nucleus
- have intercalated discs passing across the fibers at irregular intervals
what is the epicardium?
- outer layer of the heart
- 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 is the fibrous pericardium?
- a sac of tough fibrocollagenous connective tissue
what is the serous pericardium?
- made up of a layer of simple squamous epithelium (mesothelioma) and backed by a basal lamina and connective tissue
- the serous pricaridum lines the inner surface of the fibrous pericardium (parietal serous pericardium) and covers the surface of the heart (visceral serous pericardium)
what is the fibrous skeleton of the heart?
- formed by thick bands of fibrous connective tissues around the heart valves, between the atria and between the ventricles
- the connective tissue supports the valves but also provides the attachment for the cardiac muslce fibres
what is the histology of the heart valves?
- have an outer endothelial layer with basal lamina
- layer of collagen and elastin fibres
- a core of dense irreglar connective tissue (lamina fibrosa)
- the leaflets of the valves separating the atria from the ventricles (mitral and tricuspid) and anchored to papillary muslces in the wall of the ventricles by collagenous strands called the chordae tendineae, which merge with the lamina fibrosa
- there are no blood vessels in the valves
