Circulatory System

• Arteries

  • carries blood away from the heart at high pressure
  • thick walls and small lumen
  • collagen: to withstand high pressure
  • smooth muscle: to control blood flow
  • elastic tissue: stretches and recoils to maintain smooth blood flow
  • endothelium: smooth surface to reduce friction as blood flows through
• Arterioles:

  • carry blood to capillaries
  • smooth muscle layer contracts and relaxes to control the amount of blood passing through capillaries
  • thinner layer of elastic tissue and collagen
• Veins:

  • carry blood to heart at low pressure
  • thin walls, large lumen, thinner layer of elastic and muscle tissue
  • contractions of muscles surrounding veins help blood flow
  • valves: prevent backflow of blood
• Capillaries:

  • where gas exchange takes place
  • one cell thick wall: short diffusion pathway
  • highly branched: increases surface area for exchange
  • very small lumen: forces blood to travel slowly so more diffusion
• Formation of tissue fluid:

  • at arteriole end: hydrostatic pressure inside capillaries is larger than that in the tissue fluid -> fluid moves out of capillaries
  • plasma proteins remain inside capillaries, reducing water potential of blood
  • at venule end: water potential inside capillaries is lower than that in the tissue fluid -> water re-enters capillaries by osmosis
  • remaining tissue fluid is transported back to the circulatory system by the lymphatic system
• Capillary bed: a network of capillaries in tissues
• Tissue fluid: fluid that surrounds cells in tissues. It brings oxygen and nutrients to cells and removes waste products from them.
• A circulatory system is needed in large organisms as they have a smaller surface area to volume ratio, so not enough for diffusion alone to supply organs with substances.
• Humans have a closed double circulatory system: blood flows through the heart twice in one complete circuit - once to the lungs, once through the whole body.
• The coronary arteries supply the heart with oxygenated blood.
• The pulmonary artery carries deoxygenated blood from the heart to the lungs.
• The pulmonary veins carry oxygenated blood from the lung to the heart.
• The renal artery carries oxygenated blood from the heart to the kidneys.
• The renal vein carries deoxygenated blood from the kidneys to the heart.
• The aorta carries oxygenated blood away from the heart to the body.
• The vena cava carries deoxygenated blood from the body to the heart.
• Label the blood vessels and chambers of the heart.

  A) Superior Vena Cava

  B) Right Atrium

  C) Right Ventricle

  D) Pulmonary Artery

  E) Pulmonary Vein

  F) Left Atrium

  G) Left Ventricle

  H) Aorta

  
• Label the valves of the heart.

  A) Aortic Valve

  B) Pulmonary Valve

  C) Bicuspid Valve

  D) Tricuspid valve

  
• The left ventricle has a thicker and more muscular wall than the right ventricle: it pumps blood around the whole body, so a high pressure needs to be generated.
• The septum separates the left and right side of the heart, making sure that oxygenated blood and deoxygenated blood don't mix.
• The tendinous cords stop valves from being turned inside out.
• The atrioventricular valves link the atria to the ventricles. They stop blood from flowing back into the atria when the ventricles contract.
• The semilunar valves link the ventricles to the arteries. They stop blood from flowing back into the heart when both atria and ventricle relax.
• The cardiac cycle is a sequence of contraction (systole) and relaxation (diastole) of the atria and ventricles, that keeps blood continuously circulating around the body.
• Pressure changes created in the cardiac cycle opens and closes heart valves, ensuring that blood moves in one direction.
• Cardiac Diastole: both atria and ventricle relax

  • blood flows into the atria, increasing the pressure
  • AV valves open, blood flows passively into the ventricle
  • SL valves close, as pressure is higher in the arteries
• Atrial Systole: atria contract, ventricles relax

  • atria: volume decreases, pressure increases
  • AL valves forced open: remaining blood pushed into ventricles
  • ventricle: slight increase in volume and pressure
  • SL valves remain closed
• Ventricle Systole: atria relax, ventricles contract

  • ventricle: volume decreases, pressure increases
  • AL valves forced shut: prevents backflow of blood to atria
  • SL valves forced open: blood flows into arteries and out of heart
  • atria: volume increases, pressure decreases