Circulatory System

• Layers of blood vessels:

  • Tunica externa/adventitia: connective tissue, collagen
  • Tunica media: smooth muscle, elastic fibres
  • Tunica interna/intima: endothelium
• Arteries:

  • Narrow lumen
  • Thick muscular walls
  • No pocket valves
  • Elastic walls
  • Can constrict and dilate
  • Do not collapse when empty
  • Carry oxygenated blood except the pulmonary artery which carries deoxygenated blood
  • Carry blood from heart to body
• Veins:

  • Wide lumen
  • Thin muscular walls
  • Pocket valves present
  • Less elastic walls
  • Cannot constrict and dilate
  • Collapse when empty
  • Carry deoxygenated blood except the pulmonary vein which carries oxygenated blood
  • Carry blood from body to heart
• Blood vessels:

  • Arteries break up into arterioles
  • Arterioles lead to capillaries
  • Venules join up to form veins
• Specific blood vessels:

  1. Pulmonary artery: transports deoxygenated blood from right ventricle to lungs for oxygenation

  2. Pulmonary vein: transports oxygenated blood from lungs to left auricle

  3. Renal artery: transports oxygenated but impure blood from dorsal aorta to kidneys for purification

  4. Renal vein: transports deoxygenated but pure blood from kidneys to inferior vena cava

  5. Coronary artery: transports oxygenated blood from left ventricle to heart walls for respiration and energy

  6. Coronary vein: transports deoxygenated blood from heart walls to right auricle/atrium
• 7. Hepatic portal vein: transports blood from gastric vein, splenic vein, and mesenteric vein to liver

  8. Hepatic vein: transports deoxygenated blood from liver to inferior vena cava

  9. Hepatic artery: transports oxygenated blood from dorsal aorta to liver

  10. Anterior/superior vena cava: transports deoxygenated blood from upper body to right auricle

  11. Posterior/inferior vena cava: transports deoxygenated blood from lower body to right auricle

  12. Aorta: transports oxygenated blood from left ventricle to all parts of the body
• Large lymphatic organ:

  • Location: in the abdominal region, behind the stomach above the left kidney
  • Functions:
  • Blood reservoir
  • Produces lymphocytes
  • Produces RBCs in an embryo
  • Destroys old RBCs, sharing the function with the liver
• Blood is contained in the heart and in the blood vessels (arteries, veins, and capillaries) of the circulatory system
• Tissue fluid is present in the spaces between cells in the organs
• Lymph is contained within lymph vessels and lymphatic organs such as the spleen and tonsils
• The 3 principal circulatory fluids in our body are blood, tissue fluid, and lymph
• The two types of vascular/circulatory systems are closed circulatory system (blood circulates in closed blood vessels) and open circulatory system (blood flows from the heart to open spaces without vessels)
• Non-circulating fluids are stationary and do not move around in the body, examples include synovial fluid, vitreous humour, and perilymph
• Properties of blood:

  • Blood is always in motion from the heart to the arteries and back through the veins
  • Color: bright red in arteries and dark red in veins
  • It is a saltish liquid due to the presence of NaCl and NaHCO3
  • Slightly alkaline with a pH of 7.3 to 7.45
  • An adult human has 5-6 liters of blood in the body
• Transport functions of blood include:

  • Transport of digested food from the intestines to the tissues of the body
  • Transport of oxygen from the lungs to the tissues of the body
  • Transport of CO2 from tissues to the lungs
  • Transport of excretory material from tissues to the liver, kidney, or the skin
  • Distribution of hormones from endocrine glands to the target organs or cells
  • Distribution of heat to keep body temperature uniform
• Protective functions of blood:

  • Blood forms a clot to protect against excessive blood loss and entry of germs
  • White blood cells engulf pathogens in a process called phagocytosis
  • Antibodies and antitoxins neutralize poisonous germs and substances
• Blood consists of:

  • Plasma (fluid part of blood) which includes water, proteins (fibrinogen, albumen, globin), inorganic salts (sodium chloride, sodium bicarbonate), and other substances (glucose, amino acids, hormones, urea)
  • Blood corpuscles (cellular part of blood) which include red blood cells (erythrocytes) containing haemoglobin, white blood cells (leucocytes) for immunity, and platelets or thrombocytes for clot formation
• Complete Blood Count (CBC) includes lymph, the fluid surrounding body cells, with the cellular part containing only leucocytes, mostly lymphocytes, and the non-cellular part containing plasma with water, solids (carbohydrates, proteins, fats, enzymes, antibodies, etc.)
• Endothelium


  Innermost layer of a blood vessel, composed of a single layer of epithelial cells, playing a crucial role in regulating blood flow, vascular tone, and coagulation.
• Tunica adventitia (Tunica externa)


  Outermost layer of a blood vessel, located outside the tunica media, primarily composed of connective tissue, specifically collagen and elastin fibers, providing structural support and helping to anchor the vessel to surrounding tissues.