Norm Eizenberg; Week 10 MED1011; Anatomy
CV system is a closed system and a double system, systemic arteries transport oxygenated blood and pulmonary arteries deoxygenated blood. Arterial blood is oxygenated except for pulmonary arteries to the lungs and umbilical arteries to the placenta. Lumen has intima (lined by endothelium), media and adventitia. Elastic arteries are closer to heart, and have abundant elastic tissue in media. Muscular has predominantly smooth muscle in media and is branching. When arteries divide, the larger branch tends to be more in line with the main trunk, the smaller is at a greater angle. Arterial branches in limbs are cutaneous, muscular, nutrient, articular and arteriae nervorum.
Arterioles have largest ratio of wall thickness to lumen. Smooth muscle tone comes from sympathetics, and they regulate flow and pressure. They are the small branches prior to a capillary bed. Capillaries are thinnest and smallest vessels. Permeability varies according to sites. Sinusoids are specialised capillaries in haemopoietic organs with wide lumen (sluggish flow), modified endothelium (with phagocytes), absent basement membrane (gaps between cells) and increased permeability. Arteries are derived from mesoderm, commence as networks, preferred channel develops into main branch, axial artery runs along the centre of a limb rather than the periphery, and arteries do not run superficially for long distances. Surface epithelia and articular cartilage are avascular.
Systolic pressure is from ventricular contraction, diastolic due to recoid of elastic arteries. Pulse pressure is the difference between the two. There is pulsatile flow in elastic and muscular vessels, continuous flow in capillaries and veins. First aid for bleeding is RICE. Anastomoses allow collateral supply/alternate. True anastomoses connect large calibre artery branches and potential anastomoses are small calibre connections. Skeletal muscles recieve the most arterial branches and have the most anastomoses. Anastomoses occur around joints but are only significant within muscle bellies that cross the joint.
Anatomical end arteries have no anastomoses. Functional end arteries only have potential anastomoses via arterioles. An end organ is usually supplied by an end artery. Can also be to visceral segments, emboli can lodge distal to a branch point where the main artery narrows.
Nerve supply is by vasomotor nerves, sympathetic fibres are to all arterioles, parasympathetic nerve fibres are supplied to erectile tissue.
Azygos venous system drains the vertebral venous system. Portal system links two capillary beds. Venous valves direct flow and are mediated by valve cusps. A valve is typically located at the termination of a vein. Venae comitantes allow arteries to warm venous blood and push flow around the body. Venous flow is pushed by a vascular venous pump, muscular venous pump and thoracic venous pump.
Vena caval, vertebral and azygos systems of veins are valveless. Venous sinuses exist in muscles as large plexuses that collect blood. Emissary veins are communicating CSF to veins. Portal/systemic anastomoses exist. Pooling in venous sinuses can occur eg DVT.