Histology of the Cardiovascular System Flashcards
What is the overall structure and function of the cardiovascular system?
Carries blood and lymph to and from tissues of the body
o Completely closed system of endothelial tubes
o Includes heart, blood vessels and lymphatic vessels
Heart <> Blood vessels <> Capillaries / Lymphatics
Two circuits distribute blood in the body:
o Pulmonary circulation: conveys blood from the heart to the lungs and back
o Systemic circulation: conveys blood from the heart to the other tissues in body and back
What structures are present in the heart and what are their functions?
Cardiac muscle: responsible for contraction
Fibrous skeleton: four fibrous rings surrounding the valves, 2 fibrous triangular structures connecting the rings and membranous parts of the two septa
Conducting system: formed by modified muscle cells (Purkinje fibres). Responsible for initiation and propagation of rhythmic contractions.
Coronary vasculature: two coronary arteries and coronary veins
What tissues are present in the heart and what are their functions?
Epicardium: visceral layer of the serous pericardium. Single layer of mesothelial cells and underlying layer of connective and adipose tissue. Blood vessels and nerves supplying the heart are located in that layer.
Myocardium: Consist of the cardiac muscle of the heart. Myocardium of the ventricles is thicker.
Endocardium: Consist of an inner layer of endothelium, with subendothelial connective tissue (DCT). Middle layer of CT and SMCs. Deeper layer of CT, collagen & elastic fibres (subendocardial layer)
What does the endocardium consist of?
o An inner layer of endothelium
o Subendothelial connective tissue (DCT)
o Middle layer of connective tissue and smooth muscle cells.
o Deeper layer of connective tissue (subendocardial layer)
What does the myocardium look like?
o Myocardium of the ventricles is thicker.
o Layer of interconnected myocytes with associated vessels
Intercalated discs as dense eosinophilic lines
Myocyte fascicles oriented in varying directions
What are the components of the cardiac connective tissue?
o Fibrosa: forms the core of the valve-DIC.
o Spongiosa: LCT on atrial side (loose collagen/elastic fibres), as shock absorber.
o Ventricularis: Adjacent to ventricular surface of the valve. DCT with elastic fibres. Forms the chordae tendineae (fibrous cords covered with endothelium).
What is the cardiac conducting system and what are its components?
Contraction is synchronized by specialized conducting cells.
Purkinje Fibres convey signals 4X faster than muscle fibres across the fibrous skeleton (larger size and lighter cytoplasmic staining).
SA and AV node modified myocytes.
What are the three layers of the arteries/veins?
o Tunica Intima: the innermost layer of the vessel. Consists of the following:
• Endothelium
• Basal lamina
• Subendothelial layer-loose connective tissue
o Tunica Media: Middle layer, consists of circular arrangements of smooth muscle cells layers
o Tunica Adventitia: Outermost connective tissue layers. Contains collagen and few elastic fibres
NOTE: there are morphological variations and differentiations depending on the type (artery/vein) and size of blood vessel
What type of cells feature in the vascular endothelium?
Simple squamous epithelial cells
What are the functions of the endothelium?
o Maintenance of a selective permeability barrier, and of non-thrombogenic, barrier-antigoagulants.
o Modulate blood flow
o Regulation of the immune system
o Hormonal synthesis and modification of lipoproteins
What are the three categories of arteries and how can they be distinguished from one another?
Large arteries or elastic arteries - aorta and pulmonary arteries.
Medium arteries or muscular arteries - sometimes difficult to distinguish from elastic arteries.
Small arteries and arterioles - Can be distinguished from the layers of smooth muscle cells in the tunica media.
What are each of the tunica like in the large/elastic arteries?
Tunica intima is thick and consists of endothelium, subendothelial CT and an internal elastic membrane.
Tunica media is the thickest with multiple layers of smooth muscle cells (SMC) separated by elastic lamellae. Fibroblasts are not present. SMCs synthesize ECM.
Tunica adventitia is relatively thin, with collagen and elastic fibres, fibroblasts, macrophages, blood vessels and nerves.
What are each of the tunica like in the medium/muscular arteries?
Tunica intima is thinner with a prominent internal elastic membrane (thickness varies with age).
Tunica media composed entirely of SMC with little elastic material.
Tunica adventitia is relatively thick and often separated from the tunica media by a recognizable external elastic membrane.
What are the tunica like in the small arteries/arterioles?
Can be distinguished by the number of SMCs layers in their tunica media. Arterioles have one to two.
Arterioles control the blood flow to the capillaries by contraction of SMCs.
What are characteristics of the capillaries and how do they relate to their function?
Smallest diameter BV, a single layer of endothelial cells and their basal lamina (pericytes: multifunctional cells surrounding the capillary)
Allow gas and metabolites exchange between cells and blood stream.
