Bio 12 - Chapter 10 ( review)

• Arteries


  • Carry blood away from the heart
  • Thickest walls
  • Aorta is the largest
  • Lead to arterioles
  • Blood flow kept moving by the pumping of the heart
• Capillaries


  • Permit exchange of material with the tissues
  • Walls are one cell thick
  • Drain blood to venules
  • Extremely narrow
  • Contain shunts
• Veins


  • Carry blood toward the heart
  • Largest holding capacity
  • Vena cava are the largest
  • Contain valves
  • Contain approximately 70% of blood
  • Act as a blood reservoir
• All three blood vessel types have an inner endothelium, a simple squamous epithelium attached to a connective tissue basement membrane that has elastic fibres
• Arterioles


  • Inner layer: endothelium
  • Middle layer: some elastic tissue but mostly smooth muscle
  • Outer layer: fibrous connective tissue
• Smooth muscle in arterioles contracts

  Blood vessel constricts, resulting in higher blood pressure
• Smooth muscle in arterioles relaxes

  Blood vessel relaxes, resulting in lower blood pressure
• Capillaries


  • Composed of a single layer of epithelium with a basement membrane
  • Form vast networks (capillary beds) throughout the body
• Exchange of substances across capillary walls

  1. Oxygen and nutrients diffuse out of the capillary and into the tissue fluid

  2. Wastes (carbon dioxide) diffuse into the capillary

  3. Some water leaves the capillaries, and excess is picked up by lymphatic vessels
• Veins and venules


  • Have the same three layers as arteries, but there is less smooth muscle and connective tissue
  • Veins have valves, which allow blood to flow toward the heart when open and prevent blood from flowing backward when closed
  • Veins act as a blood reservoir
• The cornea of the eye is nearly free of capillaries
• How the cornea obtains nutrients

  By diffusion from the tears on the outside surface, and from the fluids on the inside surface
• Capillaries play an important role in homeostasis by regulating the body systems by exchanging water, wastes, and nutrients across their membranes between the blood and the tissues
• How capillary beds open and close


  1. Only certain capillary beds are open at any given time

  2. After eating, capillary beds that serve the digestive system are open, and those that serve the muscles are mostly closed

  3. Sphincter muscles relax to open the bed and allow blood flow

  4. Sphincter muscles contract to close the bed and prevent blood flow

  5. When the bed is closed, blood flows through anastomoses (arteriovenous shunts) directly from arterioles to venules, bypassing the bed
• Capillary beds need to open and close to divert blood to the areas that are working and require more oxygen and nutrients and waste removal at any one time
• Recent evidence suggests that the blood supply to the brain is maintained under most physiological conditions, including ingesting a heavy meal, and that hormones released by the digestive tract may instead be the cause of "postprandial somnolence" (being sleepy after eating)
• Blood


  A liquid connective tissue that has many different functions: transports nutrients, wastes, and hormones; regulates body temperature; regulates blood pressure; protects the body against invasion by disease-causing pathogens; clotting mechanisms protect the body against loss of blood
• Composition of blood in a test tube

  • Upper layer: plasma (liquid portion of blood)
  • Lower layers: formed elements (white blood cells, platelets, red blood cells)
• Plasma


  The liquid portion of blood that contains a variety of inorganic and organic substances dissolved or suspended in water
• Components of plasma


  • Water
  • Proteins
  • Glucose
  • Lipids
  • Electrolytes
  • Hormones
  • Waste products
• 1. Sinoatrial Node: The SA node (the pacemaker located in the upper dorsal wall of the atrium) initiates the heartbeat. It sends out a stimulus (an excitation electrical impules, every 0.85s), which causes the atria to contract. It also stimulates the AV node b) Atrioventricular node Th SA stimulus reaches the AV node in the base of the right atrium near the septum. The AV node signals the ventricles to contract. Impulses pass down the two branches of the atrioventricular bundle to the Purkinje fibres, and thereafter the ventricles