Cardiovascular System

• The cardiovascular system consists of the heart, blood vessels, and blood.
• Blood is a fluid connective tissue composed of plasma, extracellular matrix, and formed elements, the cells of the tissue.
• The function of blood:

  • Helps to maintain homeostasis in the body
• Homeostasis refers to a state of balance or equilibrium in the body.
• How does blood help to maintain homeostasis?

  • Transport of gases, nutrients and waste products
  • Transport of processed molecules
  • Transport of regulatory molecules
  • Regulation of pH and osmosis
  • Maintenance of body temperature
  • Protection against foreign substances
  • Clot formation
• Blood composition:

  • Plasma- liquid matrix- 55% of blood
  • Formed elements- 45%
  • Red Blood Cells (Erythrocytes)
  • White Blood Cells
  • Platelets
• Total blood volume:

  Males: 5-6 litres and Females: 4-5 litres
• Red Blood Cells:

  • Disc-like biconcave cells
  • 1/3 of the RBC is made of hemoglobin
  • RBCs are approx. 700 times more numerous than WBCs
  • Males: 4.7-6.1 million RBCs per microliter
  • Females: 4.2-5.4 million RBCs per microliter
• Haemoglobin:

  • has a complex protein
  • It has 4 subunits
  • Each subunit has one polypeptide chain called globin
  • It is bound to one haeme group
  • Haeme is a red-pigment molecule that contains one iron atom
• Red blood cells:

  • Approx. 2.5 million RBCs are destroyed every second(hemolysis)

  • Approx 25 trillion RBCs in the adult circulation

  • Approx. 1% of RBCs are replaced daily

  • It takes about 4 days to produce a new RBC
• Life span of RBCs:

  • Males: 120 days

  • Females 110 days
• White blood cells:

  Granulocytes

  • Neutrophils

  • Eosinophils

  • Basophils

  Agranulocytes

  • Lymphocytes

  • Monocytes
• Platelets:

  • Are minute fragments of cells
  • Roughly disc-shaped
  • Glycoproteins and proteins on the surface allow them to attach to other molecules
  • Life span: 5-9 days
  • They prevent blood loss
  • Forming platelet plugs & promoting the formation and contraction of clots
• Hemostasis:

  The stopping of excessive bleeding is necessary

  • Vascular spasm • Platelet plug formation • Coagulation
• White blood cells:

  Spherical cells with a nucleus. They form part of the immune system and defend the body against infection and disease.
• Neutrophil: Phagocytizes microorganisms and other foreign substances.
• Eosinophil:

  Attacks certain worms, and parasites, releases chemicals that modulate inflammation. They negatively impact the airways during asthma attacks.
• Basophil:

  Releases histamine, which promotes inflammation and heparin which prevents blood clots.
• Lymphocytes:

  Produces antibodies and other chemicals responsible for destroying microorganisms, contributes to allergic reactions, graft rejection, tumor control, and regulation of the immune system.
• Monocyte:

  Phagocytic cell in blood, when it leaves blood it becomes a macrophage, which phagocytizes bacteria, dead cells, cell fragments and other debris within the tissues.
• Vascular spasm: The immediate but temporary constriction of a blood vessel. It occurs when the smooth muscle within the wall of the vessel contract. This constriction can close small vessels completely and stop the flow of blood>
• Platelet plug formation: This is the accumulation of platelets that can seal small breaks in blood vessels. It is not a blood clot but it is an important step in blood clot formation
• Coagulation: the process of blood clotting. A network of thread-like fibers called fibrin traps blood cells, platelets and fluids causing a blood clot.
• There are 4 main blood groups: A, B, AB, O
• Group A: Has A antigens on the red blood cells with anti B antibodies in the plasma.
• Group B: Has B antigens on the red blood cells with anti A antibodies in the plasma.
• Group O: has no antigens on the red blood cells but both anti A and anti B in plasma.
• Group AB: Has both A and B antigens on the red blood cells and no antibodies in he plasma.
• Antibodies are proteins found in the plasma and antigens are protein molecules found on red blood cells.
• The Rh system:

  Red blood cells sometimes have another protein called RhD antigen. You can be either RhD negative if you have the antigen or RhD negative if you don't have the antigen.
• Rhesus Disease: A condition where antibodies of a pregnant woman's blood destroy the baby's blood cells.
• The heart is located in the mediastinum, the cavity between the lungs. The heart is tilted so that its pointed end, the apex, points downward toward the left hip, while the broad end, the base, faces upward toward the right shoulder.
• The wall of the heart consists of three layers:

  • The epicardium is the visceral layer of the serous pericardium.
  • The myocardium is the muscular part of the heart that consists of contracting cardiac muscle and noncontracting Purkinje fibers that conduct nerve impulses. Cardiac cells (cardiomyocytes) are in this layer.
  • The endocardium is the thin, smooth, endothelial, inner lining of the heart, which is continuous with the inner lining of the blood vessels.
• The pathway of blood through the heart:

  Deoxygenated blood from the systemic circulation enters the right atrium through three veins: the superior vena cava, the inferior vena cava, and the coronary sinus. During the interval when the ventricles are not contracting, blood passes down through the right atrioventricular (AV) valve into the next chamber, the right ventricle. The AV valve is also called the tricuspid valve because it consists of three flexible cusps (flaps).
• The pathway of blood through the heart:

  The right ventricle, contracts and pumps deoxygenated blood through the three‐cusped pulmonary semilunar valve and into the pulmonary trunk. The pulmonary trunk immediately divides into two pulmonary arteries, which lead to the left and right lungs, respectively.
• The pathway of blood through the heart:

  The left atrium receives oxygenated blood from the lungs through four pulmonary veins (two from each lung). When the ventricles relax, blood leaves the left atrium and passes through the left AV valve into the left ventricle. The left AV valve is also called the mitral or bicuspid valve, the only heart valve with two cusps.
• The pathway of blood through the heart:

  When the left ventricle contracts, the left mitral valve closes and prevents blood from moving back into the left atrium. The blood is then pushed through the aortic semilunar valve and creates high pressure in the aorta. This pressure causes the aortic semilunar valve to close and oxygenated blood moves from the aorta to the body.
• Blood travels away from the heart via arteries, arterioles, capillaries. Blood returns to the heart via capillaries, venules, veins.
• • The sinoatrial (SA) node, located in the upper wall of the right atrium, initiates the cardiac cycle by generating an action potential that spreads through both atria through the gap junctions of the cardiac muscle fibers.
• • The atrioventricular (AV) node, located near the lower region of the interatrial septum, receives the action potential generated by the SA node. A slight delay of the electrical transmission occurs here, allowing the atria to fully contract before the action potential is passed on to the ventricles.