Human Biology - Circulatory / Lymphatic / Respiratory system

• Circulatory system


  The link between cells inside body and environment outside body, comprising of heart and vessels (veins, arteries and blood)
• Heart


  • Pumps blood around the body
  • Located between the two lungs slightly on the left
  • Enclosed by a membrane called pericardium which holds the heart in place but lets it move while it beats
  • Made up of cardiac muscle
• Valves of the heart

  • Ensure that blood only flows in one direction
  • Atrioventricular (between the atria and ventricles)
  • Tricuspid (right) / Mitral (left)
  • Semi-lunar (in arteries leaving the heart)
  • Pulmonary (right) / Aortic (left)
  • The valves work by: 1. The cups pressed flat against the artery wall, 2. When blood tries to flow back into the ventricle, the cups fill out and seal off the artery
• Blood vessels


  • Arteries - carry blood away from the heart
  • Capillaries - tiny vessels that carry blood between cells
  • Veins - carry blood back to the heart
• Arteries


  • Carry blood away from the heart
  • Has a blood pressure that increases as the ventricles contract & decrease as the ventricles relax
  • Has thick, muscular, elastic walls made of smooth muscles and can change diameter but have no valve
  • Arterioles - small arteries that transport blood to the capillaries
• Veins


  • Carries blood towards the heart
  • Has thin walls and valves that direct blood flow to the heart & prevent the backflow of blood
  • Venules - tiny veins that carry blood away from the capillaries
• Capillaries

  • Microscopic blood vessels that form a network and carry blood to nearly every cell of the body
  • Only 2 cell thick which allows for exchange of materials (nutrients + O2) between blood and body cells
• Vasodilation


  An increase in the diameter of blood vessels, allowing increase in blood flow
• Vasoconstriction


  A decrease in diameter of blood vessels restricting flow of blood
• Functions of blood


  • Transport oxygen & nutrients to cells
  • Transport O2 and waste away
  • Transport hormones
  • Maintain pH of bodily fluids
  • Distribute heat - maintain body temperature
  • Maintain water content & ion concentration
  • Protect against disease-causing microorganisms
• Composition of blood


  • 55% plasma: 91% H2O & 8% dissolved substances including nutrients (glucose, amino acids & lipids), ions, gases (CO2 & O2), hormones and waste (e.g. urea)
  • 45% formed elements: ERYTHROCYTES, LEUKOCYTES, PLATELETS (THROMBOCYTES)
• Erythrocytes (Red blood cells)

  • Biconcave in shape
  • Increased surface area for oxygen exchange & thick edges give large volume for more haemoglobin
  • No nucleus - maximised room for haemoglobin (can combine with O2 = oxyhemoglobin)
  • Life span = 120 days
  • Produced in BONE MARROW ; destroyed in liver & spleen
• Leukocytes (White blood cells)

  • Larger but fewer in number than RBC and also produced in the bone marrow
  • Involved in immunity, remove dead or injured cells & invading micro-organisms
  • Live for a few minutes during infection and up to years when infection not present
  • Two types: Granulocytes (granular cytoplasm & lobed nucleus) and Monocytes & lymphocytes (spherical nucleus + agranular cytoplasm)
• Thrombocytes (Platelets)


  • Very small cell fragments with no nucleus (⅓ of erythrocyte)
  • Formed also in bone marrow
  • Lifespan: about 7 days
  • Important in normal blood clotting
• Transport of oxygen


  1. 3% is carried in blood plasma

  2. 97% is carried in combination with haemoglobin molecules to form a compound called oxyhaemoglobin

  3. Oxygen combines with haemoglobin in situations of HIGH OXYGEN concentrations (capillaries in lungs)

  4. Oxyhaemoglobin breaks down to haemoglobin & oxygen in situations where the concentration of OXYGEN IS RELATIVELY LOW. the oxygen then diffuse into the tissue of the surrounding cells

  5. Oxygenated blood contains a high proportion of oxyhaemoglobin & is bright red in colour

  6. Deoxygenated blood contains less oxygen & is dark red / purple in colour
• Transport of carbon dioxide

  1. 8% dissolved in plasma

  2. 22% carried on haemoglobin forming a compound called carbaminohaemoglobin

  3. 70% as bicarbonate ions, CO2 is converted to carbonic acid & further broken down into H+ & HCO3-

  4. When in the capillaries of the lungs: CO2 dissolved in the plasma diffuses out of the capillaries & into the alveoli, Carbaminohaemoglobin breaks down & carbon dioxide released also diffuses into the alveoli, Hydrogen ions & bicarbonate ions recombine to form carbonic acid, which breaks down into CO2 & H2O, the CO2 diffuses into alveolus
• Transport of oxygen and carbon dioxide

  • Oxygen: 3% dissolved in plasma, 97% as oxyhaemoglobin
  • Carbon dioxide: 8% dissolved in plasma, 22% as carbaminohaemoglobin, 70% as bicarbonate ions
• Transport of nutrients and waste

  • Nutrients: Inorganic (ions e.g. Na+, Ca2+, K+, Cl-), Organic (glucose, vitamins, amino acids, fatty acids, glycerol)
  • Metabolic wastes: Urea, creatinine, uric acid
• The heart


  • Function: Pump that pushes blood around the body
  • Size: Clenched fist, 12 cm long, 9 cm wide, 6 cm thick
  • Location: Thoracic cavity (slight left), inside pericardium
  • Muscular type: Cardiac muscle
• The pericardium


  • The membrane around the heart
  • Secretes fluid reducing friction
  • Holds heart in place with allowance for movement while beating
  • Prevents heart from overstretching
• Parts of the cardiovascular system

  • Atrium = receives blood from veins; thin walls
  • Ventricles = take blood to the arteries: thick walls
  • Septum = walls that separate right/left sides of the heart
  • Atrioventricular valves: allow blood to flow from atrium to the ventricle (no backward flow), fibres called the CARDIAC TENDINAE prevent flaps from turning "inside out", right AV valve has 3 flaps, left AV valve have 2 flaps
  • Semi-lunar valves: prevent the backward flow of blood from arteries into heart, has 3 cups
• The cardiac cycle


  1. Systole: pumping phase - when the heart muscle contracts

  2. Diastole: filling phase - heart muscle relaxes

  3. Atrial systole: contraction of atria (moves blood into ventricles)

  4. Ventricular systole: contraction of ventricle (move blood out of heart)

  
• Cardiac output


  Amount of blood leaving ventricle each minute, affected by heart rate and stroke volume

  
• Blood pressure


  • Pressure of blood in arteries as it is pumped around the body by the heart, affected by various factors, can lead to problems if too high (hypertension) or too low (hypotension)
  • Measured by wrapping an inflatable pressure cuff around the upper arm, with a larger number indicating systolic pressure and a lower number indicating diastolic pressure
• Vasoconstriction


  Muscle of the artery wall can contract to reduce the diameter & decrease blood flow
• Vasodilation


  The muscle can relax to increase diameter & allow more blood flow
• Factors affecting blood vessel diameter

  • Hormones (e.g. adrenaline causes vasoconstriction in most arterioles but vasodilation in skeletal muscles & heart)
  • Accumulation of waste products in skeletal muscle stimulating vasodilation
  • Increased oxygen supply and removal of waste causing vasoconstriction
• Blood clotting process


  Vasoconstriction - muscle in capillaries constrict to reduce blood flow/loss

  2. Platelet plug - platelets stick to the site, attracting more, forming a plug

  3. Coagulation/clotting - blood flow restricted, platelets agglutinate, fibrin forms a mesh trapping blood cells, clot forms
• Clotting factors


  • Chemical substances present within the blood plasma that send signals for clotting to occur, proteins that work together to form insoluble fibrin threads

  Clot retraction - the fibrin network contracts, pulling the edges of the damaged blood vessels together, squeezing out a fluid called serum, forming a dried scab
• ABO blood system


  • Antigens on red blood cells: A, B, AB, O

  Antibodies in plasma: Anti-B for type A, Anti-A for type B, None for AB, Both Anti-A and Anti-B for type O
• Rhesus factor


  Antigen on red blood cells, Rh+ have the antigen, Rh- do not have the antigen
• Transfusions of incompatible blood can cause agglutination (clumping) of red blood cells
• Antigen


  Substance that can combine with the antibody that initiated the immune response
• Blood group antigens on RBC

  • A
  • B
  • AB
  • O
• Incompatible blood types mixed

  Causes clumping of red blood cells (agglutination)
• Rhesus factor


  Antigen on surface of RBC, unlike ABO which are sugars, Rh are proteins
• Rhesus factor types


  • Rh positive (have antigen)
  • Rh negative (don't have antigen)
• Transfusion types


  • Whole blood (plasma & cells)
  • Red cell concentrates (cells only)
  • Plasma (liquid part of blood)
• Lymphatic system


  • Collects escaped fluid from blood capillaries and returns it to circulatory system
  • Important part of body's internal defence against disease causing organisms
  • Drains excess fluid from tissue
  • Remove debris from cells of body
  • Transport fats from digestive system
• Lymphatic system structures


  • Lymph capillaries
  • Lymph vessels
  • Lymph nodes