Histology of the heart and blood vessels Flashcards
What are the 2 related systems which make up the circulatory system?
The cardiovascular system (blood vascular system) - consisting of the heart, arteries, capillaries and veins
The lymphatic system
What are the roles of the CV system?
Transport of oxygen and nutrients to the tissues.
Transport of CO2 and other metabolic waste from the tissues.
Temperature regulation.
Distribution of hormones and immune cells.
Reproductive function in males: penile erection.
What are the 3 layers of the blood vessels?
Tunica intima - inner layer of single squamous epithelium called endothelial cells supported by the basal lamina and a thin layer of connective tissue
Tunica media - prodominately smooth muscle , the thickness of this layer is very varied
Tunica adventita- outer layer of supporting connective tissue
What separates the tunica intima and tunica media?
a layer of elastic tissue called the internal elastic membrane
What separates the tunica media and the tunica adventitia?
a layer of elastic tissue called the external elastic membrane
What are the largest arteries collectively termed as?
Elastic arteries as they have many sheets of elastic fibres in the tunica medica in order to provide elastic recoil
How does the arterioles structure differ from the general artery structure?
only have one or two layers of smooth muscle in their tunica media and almost no adventitia. Particularly important for controlling blood flow in tissue
What is the structure of the wall of a capilliary?
Essentially a endothelial layer and a basal lamina
What are pericytes?
connective tissues cells with contractile properties which are just outside the basal lamina of capillaries at intervals
3 types of capillary
Continuous - more common in muscle, connective tissue, lung, skin, nerve
Fenestrated capillaries - have 50 nm pores in the wall - in the gut mucosa, endcocrine glands, glomeruli of the kidney
Sinusoidal and discontinuous capillaries - large gaps macromolecules can fit through - basal lamina is either discontinuous or absent - in the liver, spleen and bone marrow
What connects small arterioles to a postcapillary venule?
a network made up of metarterioles, thoroughfare 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?
endothelial cell-lined, with a thin layer of connective tissue and occasional pericytes (important when moving cells into the tissue in inflammation)
What are venules?
Similar to post-capillary venules but have an intermittent smooth muscle layer in the tunica media
What is the structure of veins?
Have a tunica intima, a relatively thin but continuous tunica media with a few layers of smooth muscle - much thinner than in an artery
- largest veins have a tunic adventitia which incorporates bundles of longitudinally orientated smooth muscle
- they have valves - extensions of the tunica intima
3 layers of the heart
endocardium - inner layer
myocardium - middle layer
epicardium - outer layer
What is the structure of the endocardium?
- inner surface including valves
- Endothelium
- Basal lamina
- Thin layer of collagen fibres
- Layer of denser connective tissue
- Also a subendocardium of loose connective tissue in some areas which contains small blood vessels and nerves and the branches of the impulse conducting system.
What is the structure of the myocardium?
- Thick middle layer
- bundles & layers of fibres of contractile cardiac muscle
- individual muscle fibres which are surrounded by delicate, collagenous connective tissue with a rich capillary network
What is the role of the intercalated discs?
Attaches cells but also allows the spread of electrical activity
What is the structure of the epicardium?
outer layer of the heart
- on the heart surface a single layer of flatttened epithelium called mesothelium
- basal lamina
- fibroelastic connective tissue and in some places adipose tissue
What are the 2 parts of the pericardium?
Fibrous pericardium - tough fibrocollagenous sac of connective tissue
Serous pericardium - made up mesotheluim which is backed by a basal lamina and connective tissue
Where is the serous pericardium?
It lines the inner surface of the fibrous pericardium - termed the parietal pericardium an covers the heart surface - where it is termed the visceral serous pericardium
What is found between the 2 mesothelial layers?
They are apposed to each other and sepataed by a small amount of pericardial fluid which provides the heart with lubrication for movement
Describe the heart’s fibrous skeleton
formed by thick bands of fibrous connective tissue around the heart valves, atria and ventricles.
The connective tissue provides support for the valves and an attachment for the cardiac muscle fibres
electrically isolates the atria from the ventricles
Histology of the heart valves
- outer endothelial layer with a basal lamina
- layer of collagen and elastin fibres
- dense core of connective tissue called lamina fibrosa - continuous with the fibrous skeleton
- leaflets of the atrioventricular valves anchored to papillary muscles in the wall of the ventricle by collagenous strands called the chordae tendineae, which merge with the lamina fibrosa (continuous with the fibrous skeleton).
- no blood vessels
What are the 3 types of cardiac muscle cells?
Contractile cells (99%)
Pacemaker cells
Conducting cells
What is the histology of the pacemaker cells?
highly specialised muscle cells - smaller than the cardiac myocytes
embedded in a more extensive connective tissue matrix
few myofibrils and no proper T-tubule system
- appear pale
Where are the conducting cells found?
In the bundle of His and in the purkinje fibres
The purkinje fibres are found in the subendocardial layer just deep to the endocardium
What is the histology of the purkinje conducting fibres?
abundant glycogen
no T-tubules
no intercalated discs
sparse actin and myosin filaments (tend to be found at the cell periphery)
appear pale - often exhibit a very pale/clear centre.
The Purkinje fibres distribute the excitatory activity such that ventricular contraction generally occurs from inferior to superior.
What does the lymphatic vascular system consist of?
relatively thin walled lymphatic vessels that drain interstitual fluid - eventually returning to the veins at the neck base
What is the benefit of interstitual fluid being drained by the lymphatic vasculature?
lymph passes through the lymph nodes which provides immunological surveillance
What is the structure of the lymphatic vessels?
no central pump
smooth muscle in walls
hydrostatic pressure in the tissue and compression of the vessels by voluntary muscle, combined with valves in the vessels, produces flow.
