Histology of the CVS Flashcards
What are the layers of the cardiovascular system?
The heart and blood vessels have 3 layers of tunicas:
Tunica intima - innermost
Tunica media - middle
Tunica externa/adventitia - outer
What are the layers in the heart?
Endocardium (tunica intima) - the epithelia lining the heart, in contact with blood.
Myocardium (tunica media) - cardiac muscle.
Epicardium (tunica adventitia) - inner layer of pericardium, outer layer of heart.
What do the layers of the heart look like?
see picture
What are the layers of the heart and pericardium?
Endocardium
Myocardium
Epicardium
Pericardial space
Parietal pericardium
Fibrous pericardium
What is the pericardial space?
Pericardial space has fluid in it which acts as a lubricant, so heart doesn’t rub against fibrous pericardium when it contracts.
What is the endocardium?
Endothelium and subepithelial connective tissue
Endothelium is the simple squamous epithelium that lines the blood vessels and the heart.
What does the endocardium look like?
Endothelial layer
Underneath is dense irregular connective tissue
Then subendothelial layer, which connects it to myocardium.
See picture.
What is the myocardium?
Striated - myofibrils
Involuntary, under influence of ANS.
Central nuclei
Elongated and branched cells
Tightly connected by intercalated discs.
What are the intercalated discs?
Contain gap junctions, desmosomes, and adhering junctions.
Allows electrical and physical connecting of myocardial cells.
Rapid spread of contractile stimuli, and physical anchorage, allows cardiomyocytes to form functional syncytium.
What does the myocardium look like?
See picture
What is the epicardium?
Collection of connective tissue - adipose and collagen, and lymphatic vessels.
On the outside is the mesothelium, simple squamous epithelium, lines the pericardial cavity.
see picture
What are the valves?
Formed by thin folds of endocardium.
Covered with endothelium.
At the core is dense connective tissue - fibroelastic.
Prevent backflow of blood.
What is the pathology of heart valves?
Endocarditis infection can cause faulty valves and damages them, causes clots, which can cause strokes.
Oral microbes can cause infective endocarditis.
What is the fibrous cardiac skeleton?
Four fibrous rings of dense irregular tissue make up the fibrous core of the heart.
Insulates electrically atria above from the ventricles below.
Attachment site for the myocardium and heart valves.
What is the conductive system of the heart?
Impulses start at the SA node, then travel to AV node, then to interventricular septum via bundle of his.
Separates and forms Purkinje fibres, which spread across the ventricles.
Go into the capillary bodies, specialised to carry cardiac impulses for contraction.
What do the Purkinje fibres look like?
Specialised for conduction:
In subendocardial layer.
Bigger than fibres of cardiomyocytes, of myocardium.
Paler as fewer myofibrils are present, and mainly at cell periphery.
More glycogen.
No intercalated discs.
See picture.
What are the layers of the blood vessels?
Tunica intima - inner, continuous with endocardium.
Tunica media - middle, continuous with myocardium.
Tunica externa/adventitia - outer, continuous with pericardium.
What is the tunica intima?
Endothelium, sat on a basement membrane.
Has connective tissue - subendothelial layer.
Sometimes has internal elastic lamina - continuous layer of elastic tissue.
What is the tunica media?
Mainly concentric layers of smooth muscles and elastin.
Sometimes has external elastic lamina.
Some collagen present.
What is the tunica externa?
Collagen rich connective tissue - strength and anchor to structures.
Simple squamous epithelium - mesothelium on outer surface.
Larger vessels have lymphatics, nerves and vasa vasorum - own blood supply to the vessel walls.
How are the arteries different from veins?
More defined and broader tunica media than veins, and it has different contents depending on the specific function - muscular or elastic.
What are the elastic arteries?
The major arteries immediately off the heart -aorta, carotid and pulmonary arteries.
Very broad tunic media, with lots of elastic fibres and collagen and some smooth muscle cells.
Elastic arranged in layers.
What is the function of the elastic arteries?
Elastin allows vessels to expand to accept large volume of blood.
Elastin allows recoil, which helps maintain arteriole pressure during diastole.
What are the distinguishable features of the elastic arteries?
Many elastic lamina.
Fenestrations of elastic tissue.
Broad tunica media.
What is the pathology of the elastic arteries?
Age causes arteries to lose elastic tissue.
Increases arterial resistance.
Increases arterial blood pressure.
What do the elastic arteries look like?
See pictures
Stained with H&E
Stain with elastin von gieson
What are the muscular arteries?
Medium in size
Femoral arteries and coronary arteries.
Have lots of smooth muscle present - up to 40 layers.
What is the specialised function of the muscular arteries?
Smooth muscle changes the vessel diameter to control blood flow to organs.
What are the distinguishable features of the muscular arteries?
Large amount of smooth muscle seen.
Not many layers of elastic lamina, only internal and external elastic lamina.
See picture
What are arterioles?
Small arteries with a small lumen.
Contain 1-3 layers of smooth muscle in the tunica media.
Internal elastic lamina present in large arterioles, no external.
Ill-defined adventitia, only thin layer of collagen.
See picture.
What is the function of the arterioles?
Control blood flow into capillaries by vasoconstriction of smooth muscle in tunica media.
Control blood resistance/pressure at the periphery.
What are the capillaries?
Single thin layer of endothelial cells - intima.
No media or adventitia layer.
One cell thick.
Supportive pericytes surround capillary to repair the vessels.
What is the function of the capillaries?
Connect arterioles to venules.
Exchange materials across its thin barrier.
What are the types of capillaries?
Continuous
Fenestrated
Sinusoid (discontinuous)
What are continuous capillaries?
No pores in endothelial cells.
Tightly adhere to each other by tight junctions.
Sat on a complete basement membrane.
Pinocytic vesicles - exchange of macromolecules in both directions.
What are fenestrated capillaries?
Large pores (fenestrae) in walls.
Basement membrane is complete and continuous.
What are sinusoid capillaries?
Large diameter
Large fenestrations.
Discontinuous basement membranes.
Permeable to larger macromolecules.
Larger gaps between cells.
Found in liver, spleen and bone marrow.
What do the continuous capillaries look like?
Tight junctions connecting endothelial cells together.
Basement membrane.
See picture
What do fenestrated capillaries look like?
Fenestrated - gaps between cells.
See picture
What do sinusoid capillaries look like?
Large gaps allow blood to be in direct contact with the underneath cell.
See picture
What are collecting venules?
After the capillaries, blood is collected into collecting venules.
Site where white blood cells leave the blood stream.
Wall is composed of an endothelial cell, 1 or 2 layers of smooth muscle cell, and very thin adventitia, which increases in size as lumen increases.
What are the small veins?
From collecting venules are muscular venules then small veins.
Small veins have valves, fibroelastic tissue lined with endothelium to prevent backflow.
Muscular and elastic components of veins are less prominent.
What do the veins look like?
See picture
What is the appearance of large veins?
Internal elastic lamina
Large adventitia
Modest tunica media.
Small muscular artery of vasa vasorum, large adventitia protects the vena cava.
see picture
What are the lymphatic vessels?
Carry lymph to the blood vessels.
Thin, close ended vessels
Holes in endothelium - fenestrated
Similar appearance to veins, but smaller tunica media and less distinct layers.
More valves but more delicate
Less developed adventitia.
What is loss of elastic tissue?
Aging - arteries lose elastic tissue.
Elastic fibres can be replaced with collagen in disease - atherosclerosis, MFS, Ehlers Danlos syndrome.
Increased arterial resistance and blood pressure.
Increased risk of wall weakening - aneurysm.
What does a loss of elastic tissue look like?
See picture
What is arteriosclerosis?
Hardening of arteries.
Tunica intima increases in size, by an immune response to an infection.
Connective tissue fibroblasts and smooth muscle of vasculature wall can proliferate and increase in size.
Some by natural aging.
Start of atherosclerotic plaque formation.
What is blood?
Blood is specialised connective tissue
Cells in plasma
Plasma - aqueous solution of proteins and small molecules and ions
Cells are RBCs, white blood cells and platelets.
What is a haematocrit?
An estimate of the erythrocytes (RBCs) per volume of blood.
Normally 40-50% in men, 35-45% in women.
What does blood look like?
Blood can be visualised via a blood smear.
Concave red discs - RBCs.
White blood cells are white blood, fewer than RBCs.
What are blood cells?
Mostly derived from bone marrow.
Erythrocytes - RBCs, a-nuclear, disc shape, small.
Transport gases using haemoglobin.
Platelets, small, for clotting.
White blood cells.
What are white blood cells?
Leukocytes
Neutrophils - phagocytic, for inflammation, have lobular nuclei.
Monocytes - inflammatory response, precursor to macrophages, convoluted lobe with notch.
Basophil - red, two lobed, for parasitic infections.
Eosinophil - contain histamine for parasitic infections.
Lymphocytes
What are lymphocytes?
Lymphocytes, big round nucleus, small cytoplasm.
B - antibody production.
T - kill virus infected cells.
Where are white blood cells?
Some can leave the bloodstream into nearby tissues, sometimes found residing in connecting tissue.
What is the correct histological classicfication of endothelium found in the tunica intima of the heart and blood vessels?
Simple squamous epithelia
Which of the following is cardiac muscle?
it has striations, uninuclear, central nucleus, and intercalated discs - increased staining.
see picture
What muscle has true syncytium?
Skeletal muscle is syncytium but is not functional because they do not have together.
cardiac muscle is functional because the individual cells act as one to uniformly beat the heart, because of intercalated discs.
What is A and B in the picture?
A is tunica media - smooth muscle.
B is tunica adventitia - collagen and elastic fibres.
What is D?
external elastic lamina
How do large vessels recieve nutrients and oxygen?
large vessels have vasa vasorium in the tunica adventitia which supply them.
the middle layers still recieve nutrients by diffusion from the blood stream.
How does atherosclerosis happen?
The tunica intima is thickened because of smoking, and high blood pressure, which causes an inflammatory reaction.
Macrophages enter the tissue and take up cholesterol, become foam cells
More fibroblasts in tunica media, distribute fibres and create fibrosis - hardening of the walls.
What are the consequences of atherosclerosis?
Plaque can become unstable and form a clot.
The plaque can weaken the vessel wall and it can rupture.
there is severe stenosis (narrowing), and decrease in force so oxygen delivery is reduced.
