Circulatory System Histology Flashcards
Circulatory systems of the body?
CVS - closed system consisting of the heart, arteries, capillaries, veins
Lymphatic vascular system
Roles of the CVS?
Transport of O2 and nutrients to tissues and CO2 and other metabolic waste away from tissues
Temp regulation
Distribution of hormones and immune cells
Reproductive function in males; penile erection
At any one moment, where is the majority of the blood located?
Peripheral veins (capacitance vessels)
3 layers of the blood vessels?
Tunica intima (inner layer) - single layer of squamous epithelial cells (endothelium) supported by a basal lamina and a thin layer of CT
Tunica media (middle layer) - predominantly muscle (in some areas, there is a lot of elastic tissue); layer varies a lot between blood vessels and, sometimes, can completely disappear (capillaries)
Tunica adventitia (outer layer) - made up of supporting connective tissue
What are the elastic arteries and why?
Very largest arteries, e.g: aorta, as they have many sheets of elastic fibres in their tunica media to provide elastic recoil
Why do some vessels have their own vascular supply?
Called vasa vasorum:
In very large arteries, only the inner half of the wall can obtain nutrients from the lumen, thus these vessels must have their own blood supply
Structure of arterial walls?
Tunica intima extends to an internal elastic membrane
Tunica media
Tunica adventitia…separating media and adventitia is an internal elastic membrane
Structures of arteriolar walls?
Typical diameter - 30-200μm
Have only 1 or 2 layers of smooth muscle in their tunica media and almost no adventitia; there is still an internal elastic membrane
Structure of capillaries?
Composed of endothelial cells and a basal lamina (diameter of 4-8μm) - often form capilarry networks
Often have pericytes at intervals, just outside the basal lamina - they are CT cells that have contractile properties
Types of capillary and where they are found?
Continuous - most common and have a continuous endothelial coat; found in muscle, CT, lung, skin and nerves
Fenestrated - have ~50nm pores in their walls; found in mucosa of gut, endocrine glands, glomeruli of the kidney
Sinusoidal/discontinuous - lack a basal lamina and have large gaps through which macromolecules, and even cells, can pass; found in liver, spleen, and bone marrow (for easy access)
Structure of post-capillary venules?
10-30μm diameter - important sites for exchange, e.g: cells into inflamed tissue
Endothelial cells associated with pericytes or occasional smooth muscle cells
What is microvasculature?
Small arteriole connected to a post-capillary venule, through a network of metarterioles (smallest arterioles), thoroughfare channels and capillaries
Flow in microvasculature?
Precapillary sphincters, at the beginning of the artery help control flow through the network
Structure of veins?
Relatively thin tunica media relative to the size of the lumen (compared to a muscular artery, as blood is at low pressure)
Contain valves - invaginations of tunica intima
Layers of the heart?
Endocardium - inner layer
Myocardium - thick, middle layer
Epicardium (visceral serous pericardium) - outer layer
What is the endocardium?
Inner layer that lines entire inner surface of the heart, inc. valves
Structure of the endocardium?
Endothelium
Basal lamina
Thin later of collagen fibres
Layer of denser CT
In some areas, there is a SUBENDOCARDIUM (between endocardium and myocardium) of loose CT, containing small blood vessels and nerves and branches of the impulse conducting system
Structure of myocardium?
Bundles and layers of contractile cardiac muscle fibres
Individual muscle fibres are surrounded by delicate, collagenous CT with a rich network of capillaries
Differences between cardiac muscle cells and skeletal muscle cells?
Cardiac muscle cells have a single, central nucleus, whereas skeletal muscle cells have a nucleus at the cell periphery
Cardiac muscle cells also have intercalated discs (desmosomes and adherent junctions) passing across the fibres at regular intervals - these act to attach cells and also allow electrical activity (gap junctions)
Structure of epicardium?
On the surface of the heart - a single layer of flattened epithelium, called MESOTHELIUM
Basal lamina
Fibroelastic CT and, in some places, adipose tissue (large branches of coronary vessels are found in epicardium)
Parts of the pericardium?
Fibrous - sac of tough fibrocollagenous CT
Serous pericardium - later of simple squamous epithelium, backed by a basal lamina and CT:
Parietal serous pericardium - lines inner surface of fibrous pericardium
Visceral serous pericardium (epicardium) - covers heart surface
What is the pericardial cavity?
Two mesothelial (serous) layers are apposed to each other and separated by a thin pericardial cavity, containing a small amount of serous fluid (lubrication) for heart movement
Structure of fibrous “skeleton” of heart and location?
Formed by thick bands of fibrous CT around the heart valves, between the atria, and between the ventricles
Functions of fibrous “skeleton” of heart?
CT supports valves
Also provides attachment for cardiac muscle fibres
Electrically isolates atria from ventricles as fibrous skeleton is non-conducting
Heart valve structures?
Outer ENDOTHELIAL layer with basal lamina
Layer of elastic and collagen fibres
Core of dense CT, called the LAMINA FIBROSA (in continuity with the fibrous skeleton)
Leaflets of the valves separating the atria from the ventricles (mitral and tricuspid) are anchored to papillary muscle in the wall of the ventricle by chordae tendinae (collagenous strands that merge with the lamina fibrosa)
Types of cardiac muscle cells?
Contractile cells (99%)
Modified muscle cells:
Pacemaker cells - highly specialised muscle cells (heart does not beat due to innervation)
Conducting cells
Structure of pacemaker cells?
Diameter - 4-8µm (considerably smaller than contractile cardiac myocytes)
Are embedded in a more extensive matrix of CT
Histologically, appear PALE (P cells) due to paucity of organelles within Few myofibrils (which are irregularly arranged), little glycogen and no proper T-tubule system (as their main function is not contraction)
Structure of Purkinje fibres?
Larger than normal cardiac muscle cells (unlike pacemaker cells)
Found in SUBENDOCARDIAL LAYER, deep to endocardium
Have abundant glycogen, no T-tubules, no intercalated discs and sparse actin and myosin filaments (tend to be found at cell periphery); thus, histologically, appear PALE and often have a very pale/clear centre
What is the lymph vascular system?
Consists of lympathic vessels that drain excess tissue fluid (most returns to venules), eventually returning it to veins in the vase of the neck
Structure of lymphatic capillaries?
Begin as BLIND SACS and consist of, essentially, endothelial cells
Functions of lymphatic system?
Drain excess tissue fluid
Vessels pass through lymph nodes, where IMMUNOLOGICAL SURVEILLANCE occurs
How is flow achieved in lymphatic vessels?
No central pump
Flow is achieved by:
Smooth muscle in walls
Hydrostatic pressure in the tissue
Compression of vessels by voluntary muscle
Valves in the vessels ensure unidirectional flow
