Histology Flashcards
Layers of the heart
- Epicardium
- Myocardium
- Endocardium
Epicardium
Simple squamous epithelium (mesothelium)
Thin layer of (fibroelastic) CT and fat
Myocardium
Cardiac muscle fibres (striated) in different planes to close down lumen chamber
- Central rounded nuclei
- Intercalated discs
- Rich capillary bed
Endocardium
Simple squamous epithelium that lines the atria, ventricles and valves
- Underlying basement membrane
- Small layer of loose CT and adipose tissue
Elastic aorta examples
Aorta
Pulmonary trunk
Elastic artery function
Large conducting vessels that act as pressure reservoirs by stretching during systole
- Pressure falls during diastole and the artery recoils maintaining pressure on the blood
Elastic artery histology
Vasa vasorum in T. adventitia
Elastic fibre laminae (elastin secreted by smooth muscle cells) in T. media
Single layer of endothelial cells with elastin rich collagen supporting layer in T. intima
- Fibroblasts and myointimal cells
- Accumulate lipid with ageing
Muscular artery function
Distributing vessels
Muscular artery histology
T. adventitia contains collagen and elastin.
- External elastic layer
Thick T. media primarily smooth muscle (no elastic laminae), elastin and collagen
- Internal elastic layer
T. intima is flattened endothelial cells
Arteriole function
Terminal branches which supply blood to capillary bed (local) and control blood pressure (systemic)
Arteriole histology
T. adventitia merges with surrounding tissue
- No EEL
Only 1-2 layers of smooth muscle for T. media
- No IEL
T. intima is simple squamous epithelium
Rich sympathetic innervation
Diameter: 100-300 um
Capillary function
Main site of exchange for nutrients and gases
- Low blood pressure
- Very thin-walled
Capillary histology
T. Intima only
Diameter 3-4 um
- Endothelium on BM
Pericytes
Incomplete layer of cells surrounding BM have contractile properties to control blood flow
Continuous capillaries
Materials must pass through cell or between cell
Selective transport mechanisms
- E.g. muscle
Fenestrated capillaries
Have fenestrations/pores (up to 100 um)
- With or without protein diaphragms (filter by MW and/or charge)
- e.g. endocrine glands, renal corpuscle
Discontinuous
Gaps between endothelial cells (and BM) which allows free movement of fluid and cells
- e.g. liver, spleen, bone marrow
Sinusoids
Large diameter discontinuous capillaries. Found where large amount of exchange occurs (e.g. liver)
- T. Intima contains phagocytic cells
Venule histology
T. adventitia fuses with surrounding tissue
1 or 2 layers of smooth muscle in the T. media
Clear T. intima without elastic fibres
- Diameter: 8-100 um
Veins
- Superficial
- Deep
Superficial: thick walled, no surrounding support
Deep: thin walled, surrounding support from deep fascia and muscles
Vein histology
T. adventitia is the broadest layer containing longitudinal collagen fibres and vasa vasorum.
T. media contains 2-3 layers of muscle cells
T. intima is thin and folds produce valves
IEL and OEL thin or absent
Muscular vein histology
T. adventitia contain vasa vasorum
T. media: thick muscular wall
T. intima: simple squamous endothelial cells
IEL and OEL absent
Lymphatic system function and histology
Drains tissue fluid lost from blood capillaries and returns to systemic circulation
- Nodes present alongside major veins
- Valves direct flow
Lymph capillary histology
Endothelium very thin.
No fenestrations
Absent or rudimentary basal lamina
Anchoring filaments (collagen link endothelial cell to surrounding tissue)
No RBCs
- Lumen maintained at negative hydrostatic pressure
