Circulatory Systems in Mammals

Cards (100)

  • Mammalian circulatory system

    • Small surface area to volume ratio
    • Necessary to transport materials to and from large volume of metabolically active tissue
  • Double circulatory system
    Blood goes through the heart twice for each complete circuit of the body
  • Pulmonary circulation
    1. Supplies the lungs
    2. Blood pumped at lower pressure
    3. Allows more time for gas exchange
  • Systemic circulation

    1. Supplies the other organs and the rest of the body
    2. Blood pumped at higher pressure
    3. Ensures delivery of metabolites and removal of waste
  • Blood going through pulmonary circulation is pumped by the right side of the heart, blood going through systemic circulation is pumped by the left side of the heart
  • Cardiac muscle in the wall of the left ventricle is much thicker than that of the right ventricle
  • Double circulatory system
    • Very efficient system necessary in meeting the high metabolic needs of mammals
  • In animals with a single circulatory system, such as fish, the blood is pumped through the gas exchange surfaces (gills) and the rest of the body in the same circuit
  • Arteries
    Carry blood away from the heart
  • Veins
    Return blood to the heart
  • Blood flow
    1. Arteries subdivide to form arterioles
    2. Arterioles subdivide to form capillaries
    3. Blood returned to heart via venules that combine to form veins
  • Arteries
    • Thick wall with outer layer of fibrous tissue, middle layer of smooth muscle and elastic tissue, inner layer of endothelium
    • Narrow lumen, tend to retain rounded shape
    • High blood pressure
  • Elasticity of arteries
    Allows arteries to stretch as blood pumped through, helps push blood along
  • Smooth muscle in arteries

    Supports artery, can constrict (vasoconstriction) or dilate (vasodilation) to control blood flow
  • Veins
    • Thin wall, large lumen, valves to prevent backflow
    • Low blood pressure
  • Capillaries
    • One cell thick walls, extensive network providing large surface area for exchange of materials
    • Very thin walls allow easy diffusion of substances
  • Red blood cells can just about squeeze through narrow capillaries
  • Proportion of elastic tissue to muscle is relatively high in arteries close to the heart, but lower in arteries close to organs
  • As blood flows through the circulatory system
    Blood pressure decreases, blood velocity decreases, total cross-sectional area of blood vessels increases
  • Heart
    • Highly specialised muscular organ that pumps blood through the body
    • Two separate pumps, one for pulmonary circulation and one for systemic circulation
  • Atria
    Receive blood and pump it into the ventricles
  • Ventricles
    Pump blood out of the heart, left ventricle has thicker walls to pump blood around the body
  • Valves
    • Prevent backflow of blood, include atrioventricular valves between atria and ventricles, and semilunar valves at base of aorta and pulmonary artery
  • Chordae tendinae
    Tough, flexible 'heart strings' that anchor the atrioventricular valves and prevent them turning 'inside out'
  • Semilunar valves

    Pocket valves on artery walls that only close when blood pressure in arteries exceeds pressure in ventricles
  • Major blood vessels entering/leaving the heart

    • Aorta
    • Pulmonary artery
    • Vena cava
    • Pulmonary vein
  • The heart has a very high metabolic rate and is supplied by the coronary arteries
  • Pulmonary artery
    Carries deoxygenated blood from the right ventricle to the lungs
  • Vena cava

    Brings deoxygenated blood back from the body, returning blood into the right atrium
  • Pulmonary vein
    Transports oxygenated blood from the lungs to the left atrium
  • The heart has a very high metabolic rate, as it continually contracts throughout the life of the individual concerned and consequently has high respiratory demands
  • Coronary arteries
    Branch off the aorta shortly after it leaves the heart and travel over the heart muscle, continually supplying it with its metabolic needs
  • The pulmonary artery and pulmonary vein are unusual in that the artery carries deoxygenated blood and the vein carries oxygenated blood. They are typical in that they carry blood away from and to the heart respectively, and are histologically (structurally) similar to other arteries and veins
  • Cardiac cycle

    1. Diastole
    2. Atrial systole
    3. Ventricular systole
  • During atrial systole

    Walls of the atria contract forcing more blood into the ventricles
  • During ventricular systole
    Walls of ventricles contract, AV valves close as the pressure in the ventricles now exceed the pressure in the atria. The chordae tendinae prevent the AV valves blowing inside out. As ventricle pressure reaches its peak, semilunar valves are forced open, forcing blood into the arteries
  • By the end of ventricular systole, the ventricles will be at their smallest volume
  • Stages of the cardiac cycle

    1. A. Atrial walls contract, increasing atrial pressure. AV valves are open and semilunar valves remain closed
    2. B. Atrial contraction complete, ventricles begin to contract, ventricular pressure > atrial pressure - AV valves close (first heart sound)
    3. C. Continued contraction of ventricles - ventricle pressure > arterial pressure, semilunar valves open
    4. D. Arterial pressure > ventricular pressure - semilunar valves close due to loss of blood from ventricles (second heart sound)
    5. E. Ventricular pressure falls as little blood present and walls begin to relax - atrial pressure > ventricular pressure - AV valves open
    6. F. Atrial pressure > ventricle pressure as blood flowing into atria - AV valves remain open, blood passively flows into the ventricles from the atria
  • The changes in atrial pressure between R and E are caused by the increased pressure of the contracting ventricle causing back pressure of the contracting ventricle on the atria, the subsequent fall in pressure caused by the relaxation (and increase in volume) of the atria, and the increase in pressure between 0.2 seconds and is caused by the atria filling with blood
  • When the heart valves close, the flaps of tissue bang together to make a sound. This occurs twice in each cycle (at B and D in the diagram)