Circulatory System

• Four Main Functions:

  1. Transportation of oxygen and carbon dioxide
  2. Distribution of nutrients and wastes
  3. Maintenance of body temperature
  4. Circulation of hormones
• Structural Components of a circulatory system:

  1. A fluid in which material is transported (blood)
  2. A system of blood vessels or spaces through which the fluid moves (veins, arteries, capillaries)
  3. A pump that pushes the fluid through the vessels or space (heart)
• Components of blood

  Blood is made in the bone marrow and stored in the spleen.

  • An average 70 kg person has about 5L of blood circulating through his/her body
  • 55% is made up of plasma liquid (water, proteins, solutes)
  • 45% is made up of the following components

  → red blood cells (erythrocytes)

  → white blood cells (leukocytes)

  → platelets
• Plasma

  • A fluid medium in which solid blood components are transported
  • Contains a number of dissolved proteins and nutrients
• Red Blood Cells (Erythrocytes)

  • Produced in bone marrow
  • Stored in spleen
  • Do not have a nucleus or mitochondria
  • Because specialized to carry oxygen
  • Hemoglobin binds oxygen
  • Iron gives blood its red colour
  • Biconcave shape (flexibility) - to also increase surface area
  • Blood disorders: anemia, sickle cell anemia, thalassemia
• White Blood Cells (leukocytes)

  • Aid in body defense mechanisms
  • Amoeboid-shaped
  • Destroy bacteria and damaged cells
  • Produced in bone marrow
  • Pus forms at a cut: live and dead WBC, bacteria
  • Increase in volume when body is fighting infection (ex. Macrophages destroy foreign invaders by phagocytosis)
  • Five main types that each have a different function 
• Platelets (Thrombocytes)

  • Blood clotting agents
  • Gather at site of damaged blood cells
  • They break open, releasing enzymes and clotting factors which create a plug
  • Fibrin forms a “mesh” to clot the wound
  • Scabs occur when fibrin, platelets and blood clots mesh together
  • Clotting disorders: hemophilia
• Blood Types & Rh System

  • Two systems that classify blood, ABO system and Rh system
  • Group you belong to depends on the presence or absence of proteins and sugars called antigens on the surface of your blood cells, as well as proteins called antibodies in the watery part of your blood
  • Not all blood types are compatible
• Rhesus (Rh) factor is an inherited protein found on the surface of red blood cells. If your blood has the protein, you're Rh positive. If your blood lacks the protein, you're Rh negative. Rh positive is the most common blood type
• Donating Blood

  Basic Eligibility

  • Between 17 and 71 birthday 
  • At least 50 kg (110 lb)
  • Minimum interval between blood donations is 56 days.
  • In general good health and feeling well. You should have had something to eat and adequate sleep. 
  • If you have had ear or body piercing or tattooing you must wait 6 months before donating blood
• Low RBC count

  • Leads to anemia
  • Caused by bleeding (ulcer, external injury etc) or iron deficiency
  • Person will feel tired and run down

  High WBC count

  • Sign the body is fighting an infection
  • One of the symptoms of leukemia (cancer of bone marrow and blood)
• The Blood Vessels 

  • Blood vessels create a continuous pathway to and from heart
  • 3 main types of blood vessels

       arteries

       veins

  •      capillaries
  • All arteries carry blood away from heart
  • All veins carry blood towards the heart
  • Capillaries connect arteries to veins
• Arteries

  • Large, muscular thick-walled vessels with a small inner diameter
  • Carry oxygenated blood under high pressure from heart to body*
  • *Exception – pulmonary arteries deliver deO2 blood from heart to lungs
  • Disorder – aneurysm
• Structure: Arteries

  • Three layers of tissue
  • Contraction of the heart → arteries slightly expand to accommodate the increased pressure
  • Very elastic
  • Expansion = your pulse 
• Veins

  • Large, thin-walled vessels with a large inner diameter and one-way valves
  • Carry deoxygenated blood under low pressure from body to heart*
  • *Exception – pulmonary veins return O2 blood from lungs to heart
  • Skeletal muscle contractions return blood to heart
  • Disorder – varicose veins
• Structure: Veins

  • Middle layer is not as thick as the arteries
  • Walls are not elastic
  • Greater internal diameter → lower pressure 
• Capillaries

  • Microscopic, one-cell thick vessels
  • Inner diameter less than 7 μm
  • Carry blood cells under low pressure in single file for O2CO2 exchange and nutrient-waste exchange
• Vasoconstriction vs Vasodilation


  Vasoconstriction:

  • Nerve impulses cause the smooth muscle in the arterioles to contract
  • Narrows the blood vessel diameter
  • Decreased blood flow
  • Decreased thermal energy loss to the environment
  • Occurs when the body is cold

  Vasodilation:

  • Nerve impulses cause the smooth muscle in the arterioles to relax
  • Increases the blood vessel diameter
  • Increased blood flow
  • Increased thermal energy loss to the environment
  • Occurs when the body is warm → cooling mechanism