The Circulatory System

Functions:

  • transport - shuttles materials to body parts

  • defense

  • regulation

Animals without circulatory system

  • simple organisms with simpler body plans

  • simple diffusion

  • Single-celled protist (paramecium, amoeboid)

    • animals whose surface area is easily exposed to environment; diffusion of nutrients and exchange of materials is easy for

  • Hydra

    • gastrovascular cavity opens to the exterior so both outer and inner layers are bathed in water

  • Cnidarians

    • easy diffusion of nutrients from mouth opening to other parts due to simple body plan

  • Flatworm

    • flat body allows maximum exposure to the surrounding medium

Animals with circulatory system

Two types

  1. Open - blood is pumped out into an open pool of blood; there are vessels still; organs “bathing” in blood; still have blood vessels

  2. Closed - network of blood vessels

The open circulatory system

Plan and Parts

  • chambers consisting of atrium/atria and ventricles

  • blood vessels

  • blood

Simple Pathway:

Atrium → ventricle → artery → arteriole → capillaries → venule → vein → atrium

Vertebrate circulatory system

  • closely intertwined with the respiratory system

  • Fishes

    • one atrium, one ventricle

    • single circuit

  • Frog (amphibian)

    • Double circuit

    • left and right atrium, one ventricle

    • ventricle contains both oxygenated and deoxygenated blood (partially divided)

  • Mammals

    • two atria, two ventricles

    • right atrium and ventricle - deoxygenated blood

    • left atrium and ventricle - oxygenated blood

    • crocodiles, birds, mammals

    • double circuit (one leads to lungs, one leads to systemic)

Human heart

  • valves

    • AV valve - allows unidirectional flow of blood; prevents backflow; tricuspid for right, bicuspid for left

    • Semilunar valve - prevents backflow of blood from artery to ventricle space

  • the cardiac cycle

    • 1. atrial and ventricular diastole - relaxation phase; blood from the veins return to right atrium and ventricle

    • 2. atrial systole and ventricular diastole - forces the blood to be pumped into the ventricle from the atria

    • 3. ventricular systole and atrial diastole - ventricular contraction pumps blood to arteries

    • cardiac output - 5.25L; depends on 2 factors

      • heart rate - beats per seconds

      • stroke volume (75 mL)- amount of blood pumped by the left ventricle in each contraction

  • The structure of blood vessels

    • arteries

      • thick - withstands high pressure

      • endothelium

      • has smooth muscles - allows vasodilation and constriction

      • connective tissue

    • capillaries

      • thin

      • endothelium

      • no smooth layers

    • vein

      • have endothelium

      • have smooth muscles

      • have valves which prevent backflow of blood

    • properties of blood pressure

      • arterial blood pressure - highest, occurs during ventricular systole

      • ventricular diastole - pressure when ventricles are relaxed

      • in the graph, crest is systolic pressure, trough is diastolic pressure

      • at the arterial end of capillaries, blood pressure is higher than osmotic pressure so fluid diffuses out of the capillaries

  • Blood composition

    • platelets

      • responsible for clogging to prevent excessive loss of blood

      • clotting factors are secreted by platelets, damaged cells, and plasma, epithelial cells

      • 13 clotting factors

        • Fibrinogen (Factor 1)

        • Prothrombin (Factor 2)

      • Hemophilia - inability to clot blood

        • hemophilia A - missing clotting factor VIII

        • hemophilia B - deficient clotting factor IX