Cardiovascular System Histology Flashcards
What are the 3 layers of blood vessels?
Tunica intima, media and adventitia (or serosa)
Outline the general composition of the tunica intima
Endothelium layer, layer of loose CT and internal elastic lamina (separates from tunica media)
Outline the general composition of the tunica media
Circular layer of smooth muscle (contraction regulates blood flow), supporting ECM (collagen and elastic fibres) and external elastic lamina (separates from adventitia)
Outline the general composition of the tunica adventitia
Loose CT, vasa vasorum (nutrient arteries) to supply outer portion of large vessels
What are the 3 layers of the heart wall?
Endocardium, myocardium and epicardium
Describe the composition of the endocardium
Endothelial lining supported by elastic fibrocollagenous tissue (allows stretch)
Describe the composition of the myocardium
Cardiac myocytes (intercalated discs connect) supported by vascularised fibrocollagenous tissue
Describe the composition of the epicardium
Fibrocollagenous tissue with adipose tissue, act to carry coronary arteries and autonomic nerves
What is mesothelium?
Epithelia that lines the pericardium
What are cardiac myoocytes?
Short, branching cells with round central nuclei which are connected by intercalated discs (muscle cells of heart)
What is angina?
Chest pain at times of increased heart demand
What is myocardial infarction?
Heart attack; tissue necrosis due to ischaemia
What is the biggest cause of death in the UK?
IHD
Describe what happens to necrotic cardiac muscle following myocardial infarction (heart attack)
Necrotic cardiac myoocytes are replaced by a fibrous scar tissue to an acute inflammation response where neutrophils invade the site and cause tissue granulation to form cellular and vascularised loose CT
What are the two main types of artery?
Elastic and muscular
How are elastic arteries characterised?
Predominance of elastin and little SM in tunica media
Describe the histology of elastic arteries
Intima: endothelium, loose CT and internal elastic lamina
Media: concentric fenestrated elastic sheets (merge with int/ext lamina) with smooth muscle and collagen between sheets
Adventitia: loose CT with vasa vasorum
How are muscular arteries characterised?
Predominance of smooth muscle in tunica media
Describe the histology of muscular arteries
Intima: smaller CT layer than elastic artery
Media: circular SM layers
Adventitia: Thick for vessel size with collagen and thicker elastic fibres
What is arteriosclerosis?
Thickening and loss of elasticity in arterial walls leading to increased PVR and BP, increasing the risk of rupture
What is atherosclerosis?
Most common pathology of arteriosclerosis and involves formation of yellow, fatty plaques in larger arteries
Outline the pathogenesis of atherosclerosis
Endothelial damage –> altered endothelial permeability –> LDL and cell adhesion factors present –> monocyte and T cell migration –> accumulation of T cells and lipid-laden foam cells (macrophages) and lipid-laden SM from tunica media –> fatty streak formed –> fibrous cap over plaque toped by endothelia
Which cells accumulate lipid in the development of atheromas?
Smooth muscle cells and macrophages
What type of cell cover atheromatous plaques?
Endothelial cells
What is a precapillary sphincter?
Band of SM at start of capillary (from arteriole) where contraction determined the extent of the capillary bed involved in exchange
What are thoroughfare channels?
A-V shunts, connects arterioles and venules and relaxation of SM causes the blood to shunt away from capillary bed to venules
What are pericytes?
Contractile cells which can proliferate to become mesenchymal cells in repair, which can differentiate into new endothelial cells, fibroblasts or myofibroblasts
Describe the histology of capillaries
Single layer of endothelial cells which don’t have tunica media and have little/no adventitia
What are sinusoids?
Large diameter capillaries
What are the 3 types of capillary?
Continuous, fenestrated and discontinuous
Describe the structure of continuous capillaries
Uninterrupted endothelium on continuous basement membrane (form BBB and are relatively impermeable)
Describe the structure of fenestrated capillaries
Found at sites of great molecular exchange; have uninterrupted endothelium with circular pores (fenestrae)
Describe the structure of discontinuous capillaries
Found where blood components interact directly with tissue/organ; endothelium and basement membrane are discontinuous and endothelium is supported by reticulin fibre meshwotk
Describe the general structure of veins
Large lumen and thin walls
What are the two types of venules?
Post-capillary and muscle venules
Describe the structure of post-capillary venules
There are only pericytes surrounding epithelium
Describe the structure of muscular venules
Continuous smooth muscle (media) and fibrocollagenous adventitia present
What is the main role of venules?
Major site of leucocyte migration in tissues and venule endothelium is sensitive to histamine –> leakiness
Describe the histology of veins
Intima: endothelium and CT (elastic fibres)
Media: variable, more circular muscle in legs
Adventitia: thick fibrocollagenous CT with vasa vasorum in larger veins
What are valves?
Semi-lunar projections of tunica intima consisting of fibro-elastic tissue covered by endothelium
What is vasa vasorum?
Network of arteries which supply the tunica adventitia of larger blood vessels
What is the main type of connective tissue present in the heart walls?
Fibrocollageneous connective tissue
What is the main difference between elastic and muscular arteries?
Muscular have much smooth muscle in tunica media, elastic arteries do not
Where are pericytes found?
In tunica intima; form discontinuous layer external to the capillary endothelium
