Flashcards in L19. Histology of the Heart Deck (23):
What are the three histological layers of the heart?
Epicardium (outer surface), simple squamous epithelium, thick CT, nervous tissue, blood vessels and fat
Myocardium: thickest layer, contains the myocardial (functional) layer
Endocardium (inner layer) of endothelial cells with CT and contains the specialised conduction tissue
What are the histological features of the cardio myocytes?
Small cells with central nuclei
Connected by intercalated discs
What are the functions of gap junctions between cardiac cells?
Coordinate contraction: electrically couple cells and coordinate the action potentials running through the cells
What is meant by the SA node being the pace setters?
The SA node has intrinsic/spontaneous action potentials. These fire at the fastest speed compared to all other pacemaker cells in the heart (ie. the AV node)
This means that all cells of the heart follow the beat set by these cells.
What are the Purkinje Fibres?
What do these cells look like microscopically?
Modified cardiac muscle cells: act as cables for the electrical signals
They are larger
Lost/limited contractile ability
Full of glycogen (stored starch as energy)
Form bundles in the SUB-ENDOCARDIUM
What are the three layers of the blood vessels?
What are the features of the Tunica Intima?
In contact with the blood
Simple squamous epithelium: endothelium - elongated cells in the direction of flow
Lies on a basal lamina
Supported by thin subendothelial connective tissue layer
An ACTIVE LAYER: inhibits clotting and seceretes factors (eg. vWF, NO, endothelin)
What are the features of the tunica media?
Consists mainly of smooth muscle arranged concentrically
Contraction: constricts the lumen: increases BP
SYNTHETIC CELLS: secrete connective tissue components (act like fibroblasts): collagen type III, elastin, ground substance
What are the features of the tunica adventitia?
Binds the vessel to the surrounding tissue
Connective tissue with fibroblasts embedded throughout
What is the vaso vasorum?
In larger vessels where the tunica adventitia layer is very thick, it requires its own blood supply called the vaso vasorum.
How do arteries play a role in regulating pressure?
They regulate the pulsatile pressure of the blood coming out of the heart
What are the elastic arteries and their characteristics?
Closest to the heart: aorta, carotid, bracheocephalic
Very thick and multiple layers of elastin in the t.media which store energy and compress the blood in the lumen. This is important because blood is very pulsatile coming out of the heart and the elastic arteries control this
What are the muscular arteries and their characteristics?
Distribute the blood to the tissues
Little elastin in the media: only has 2 areas: internal and external elastic membrane
Contractions of the smooth muscle: under the influence of the autonomic nervous system
What are the arterioles and their characteristics?
Very small diameter vessels (<0.1mm)
Have only 1-3 layers of smooth muscle
But these CONTRIBUTE THE MOST to blood pressure changes: constriction and dilation
What are the capillaries and their characteristics?
Very small diameter (t have associated SM)
What are fenestrated capillaries?
Found in the pancreas, intestine and endocrine glands and kidney
Inner and outer membranes fuse: single membrane with pores: very rapid exchange
Is the diameter of veins larger or smaller than that of their corresponding arteries? Why?
It is larger because the flow is slower in the veins and so there is a larger blood volume in the veins
What is the pressure in the veins compared to that in the arteries?
The pressure is much much smaller.
The capillaries act as a pressure filter
What characteristics to veins generally have, compared to arteries?
Thicker adventitia: require extra help to withstand hydrostatic pressures
Contain valves: one way flow
Skeletal muscle contractions aid the flow back to the heart
What is special about the venules?
Preferred site of diapedesis (inflammation)
What are the medium and large veins and their characteristics?
Have very well developed subendothelial CT
Sometimes longitudinal smooth muscle bundles run through the adventitia
What is the purpose of the lymphatic system?
Extracellular fluid leaks out into the capillaries and is carried away by the vessels
Carry it the large veins