42 - Cardiovascular Histology Flashcards
Three layers of heart
1) Epicardium 2) Myocardium 3) Endocardium
Epicardium
Simple squamous epithelium lies on top of a lot of connective tissue. Blood vessels, fat, nervous tissue in this layer.
Myocardium
Cardiac muscle cells and capillaries
Endocardium
Endothelial layer, subendocardial connective tissue, conducting tissue.
Why is conductive tissue needed for synchronised heart contraction?
Gap junctions only provide local sharing of electric charge.
Which cell type is this?
Cardiac muscle
Conducting pathway through heart
How is the contraction of different heart chambers co-ordinated?
Purkinje fibres
Function of Purkinje fibres
Conduct signals from SA/AV nodes to ventricles
Purkinje fibres 1) 2) 3) 4)
1) Modified cardiac myocytes 2) Limited contractile machinery 3) Full of glycogen 4) Form bundles in subendocardium
Layers of all blood vessel walls
1) Tunica intima 2) Tunica media 3) Tunica adventitia
Tunica intima 1) 2) 3)
1) Lined with simple squamous epithelium 2) Epithelium lies on basal lamina 3) Supported by a thin subendothelial layer
What is this?
Tunica intima of a blood vessel. Note how, as the blood vessel is not full of blood, the endothelial cells bulge into lumen. When blood vessel is full, endothelial cells are taught
Roles of the endothelium 1) 2) 3)
1) Actively inhibit clotting by secreting inhibitors (EG: prostacyclin) 2) Prime underlying subendothelial tissue with Von Willebrand factor for clotting 3) Release vasoactive substances to smooth muscle like NO (vasodilatory), endothelin (strongly vasocontrictive)
How is smooth muscle arranged in media?
Concentrically or helically
Where does the connective tissue of the tunica media come from?
Secreted by smooth muscle. Collagen type III, elastin, ground substance.
Variation in thickness of tunica media muscle
From one to 40-50 layers
Tunica adventitia composition
Type I collagen, elastin, ground substance. Fibroblasts,.
Tunica adventita role
Anchor to surrounding connective tissue
Name for blood supply of larger vessels
Vaso vasorum. Supplies tunica adventitia.
Two types of arteries
Elastic and muscular arteries
Location of elastic arteries
Near heart, where the blood pressure fluctuations are highest
Effect of elastic arteries
Ensures continuous, pulsatile blood flow. Means that blood flow doesn’t cease during diastole
Role of muscular arteries
Regulate blood pressure, redirect blood to tissues
Arterioles 1) 2) 3)
1) Very small arteries with diameter less than 0.1mm 2) Between 1-3 layers of smooth muscle 3) Contribute most to blood pressure changes
What gives rise to capillaries?
Arterioles
What characterises meta-arterioles?
Incomplete smooth muscle coat
What controls capillary flow?
Single smooth muscle cells in meta-arterioles act as sphincters
How do capillaries ensure that there is good contact between RBC and capillary endothelium
Diameter is less than RBC width
Distance from a capillary that most cells in the body are
Within 50 micrometers
Thickness of arteriolar media
One cell thick
Capillary media
No smooth muscle associated with media in capillary wall
Structure of a capillary 1) 2) 3)
1) Single epithelial cell rolled into a tube, with tight junctions. 2) Sometimes associated with a pericyte (media) 3) Surrounded by only a few collagen fibres (adventitia)
*Shape of a capillary
Fenestrated capillaries 1) 2) 3) 4)
1) Capillaries with holes (fenestrations) in the walls. 2) Fenestrations are often covered diaphragms. 3) Found in pancreas, intestines, endocrine glands, kidneys. 4) For fast transport of things in blood
Difference in structure of veins and arteries
Media of veins is thinner, adventitia is thicker than arteries. Veins have valves
Why do veins have thicker adventitia than arteries?
Withstand hydrostatic forces
Venules function
Blood form capillaries is collected by venules.
Structure of venules
Media is initially pericytes, but is replaced by smooth muscle
Preferred site of leukocyte diapedesis
Venules
What do lymphatic vessels collect?
Extracellular fluid that leaks from veins
Structure of lymphatic vessels
Have valves. Have gaps in walls to let in extracellular fluid. Have absence of red cells. Some leukocytes are present
Difference in lymph vessel walls as lymph vessels approach heart
Grow more substantial
