University of Babylon Dr. Ghafil Seyhood Hassan Al-Shujairi 2009.
Collage of medicine
Cardiovascular Physiology
1-Introduction and functional anatomy of blood vessels and lymph.
Blood vessels:
The blood vessels are a closed system, which carry blood from the heart to the tissue, and back to the heart.
The wall of blood vessels is made of:-
A- Inner endothelial and sub endothelial connective tissue (Intima).
B- Middle layer of smooth muscles (Media).
C- Outer layer of connective tissue (Adventitia).
Functions of CVS:
1- Convection of substrates and oxygen to all the body cells.
2-Collection of waste products and carbon dioxide for excretion.
3-Control of blood flow to the skin and extremities to enhance or retard heat
loss.
4-Distribution of hormones.
5-Delivery of antibodies, platelets and leukocytes to aid body defense.
Types of blood vessels:
1- Arteries: The arteries are thick-walled structures with extensive development of elastic tissue. They are stretched during systole and recoil during diastole, such property prevents an excessive rise in blood pressure (during systole) and excessive fall (during diastole). They carry blood from the heart mostly oxygenated (except pulmonary artery), under the highest pressure to tissues. The volume of blood in the arteries is called the stressed volume. The muscles of arteries are innervated by noradrenergic nerve fibers, in some instances by cholinergic fibers. The elasticity of arteries is decreased by aging process due to atherosclerosis.
2-Arterioles: They are the smallest branches of the arteries. Their walls have less elastic tissue but much more innervated by noradrenergic nerve fibers and some time by cholinergic nerve fibers, which constrict or dilate the vessels. They are the site of highest resistance to blood flow. They can alter blood flow to tissue because of their ability of changing their diameter.
3-Capillaries: The capillaries are thin-walled structures lined with a single layer of endothelial cells. They are the site where nutrients, gases, water and solutes exchange between the blood and the tissues. They are about 5mm in diameter at the arterial end and 9 mm at venous end. The diameter of capillaries is just sufficient to permit red blood cells in single file; the total area of all capillary walls in the body exceeds 6300 m² in the adult.
4- Venules and Veins: The venules collect blood from the capillaries and coalesce into larger veins. The veins have thin wall in comparism to the arteries. The veins have a very large capacitance (capacity to hold blood). They contain the largest percentage of blood in the cardiovascular system (65-75% of circulating blood volume). The volume of blood in the veins is called the unstressed volume. The smooth muscle in the walls of the veins is innervated by sympathetic nerve fibers. The blood in veins is under lower pressure. The viens contain valves prevent retrograde flow. Veins carry blood from tissue to right atrium and collect blood from lung to the left atrium.
Arteriovenous anastomosis: In the finger tips, palms of hand and ear lobes, there are short channels that connect arterioles to venules (arterio-venous shunt). These permit the passage of large molecules such as WBCs.
Lymphatic system:
Formation of lymph: As fluid pressure increase in the interstitial space, this will open the valve at the terminal lymphatic capillary, so protein and fluid move to lymphatic vessel. Normal lymph flow is 2 – 3 L / day. The rate of lymph flow varies in different organs, highest in the GIT and the liver. Normally filtration of fluid out the capillaries is slightly greater than absorption of fluid into the capillaries. The excess filtered fluid is return to circulation via lymph which also returns filtered protein (25 – 50%) of the total circulating plasma protein in one day) to circulation
Lymph comes back to the circulation by these mechanisms:
1- Intrinsic rhythmic contraction of collecting lymphatic vessels at rate 10 – 15 per minutes.
2- Contractile filaments and valves in wall of lymphatic capillaries.
3- Contraction of surrounding skeletal muscles.
4- Movement of organs of the body.
5- Pulsation of arteries adjacent to the lymphatic vessels.
6- Interstitial fluid pressure.
7- One way flap valves which permit interstitial fluid to enter lymph vessels but not leave it.
Structure of lymphatic system:
A- Lymphatic capillaries, their diameter 10 – 50 µm, very thin wall, highly permeable to plasma proteins. The junction of Endothelial cells run very obliquely and may function like flap valves allowing fluid to enter but closing to prevent back flow when lymph pressure rise above interstitial pressure.
B- Collecting vessels and afferent lymph trunk.
C- Lymph nodes.
D- Major lymphatic ducts.
All the lymph of body flow to the thoracic duct and right lymph duct which empties into venous system.
Function of lymph:
1- Preservation of fluid and protein.
2- Nutritional function: The transport of absorbed long chain fatty acid and
cholesterol from intestine.
3- Defense function: The foreign material and bacteria are phagocyted in the
lymph node by stimulate lymphocyte and plasma cell.
Edema: It is occur when the volume of interstitial fluid exceeds the capacity of lymphatic to return it to the circulation. Edema can be caused either by excess filtration or blocked lymphatic.
In cirrhosis of liver oncotic pressure is low because synthesis of plasma protein is depressed beside that blockage of portal venous outflow raises, further increase filtration of fluid out of plasma into intra-abdominal area (ascitis). In nephrotic syndrome oncotic pressure is low because large amount of proteins are lost in urine.
Causes of edema:
1- Increased capillary (filtration) pressure. It is secondary to chronic increase of venous pressure which caused by ventricular failure, acute glomerulonephritis, deep venous thrombosis, venous valve incompetence.
2- Reduced plasma colloid osmotic pressure due to hypoproteinaemia.
3- Change in capillary permeability due to inflammation in which protein permeability increase.
4- Inadequate lymph flow. Other cause of edema chronic inflammation of lymph node, removal of lymph node as follow radical mastectomy or obstruction of lymphatic drainage by parasite. The edema caused by lymphatic obstruction is called lymphedema.