Circulatory system

CIRCULATORY SYSTEM

BLOOD

  • An average-sized human has approximately five litres of blood.

  • Blood is composed of:

    • Red blood cells (erythrocytes)

    • White blood cells (leukocytes)

    • Platelets

    • Plasma

RED BLOOD CELLS

  • Function: Responsible for carrying oxygen throughout the body.

  • Components:

    • Contains haemoglobin, an iron-containing pigment responsible for the red color of the cells.

    • Oxygen reacts with haemoglobin to form oxyhaemoglobin, resulting in a brighter red color.

  • Physiological Characteristics:

    • The small size of red blood cells allows them to fit through one-cell-diameter capillaries.

    • Mature red blood cells lack a nucleus, allowing more space for haemoglobin and oxygen.

    • Their biconcave shape increases surface area, enhancing oxygen transport.

WHITE BLOOD CELLS

  • Characteristics: Larger but fewer in number compared to red blood cells.

  • Function: Involved in immune response and disease fighting.

    • Some white blood cells produce antibodies.

    • Others engulf bacteria or foreign materials through a process known as phagocytosis.

  • Response to Infection: The number of white blood cells increases when a person is ill or fighting an infection.

PLATELETS

  • Function: Responsible for forming blood clots to seal damaged blood vessels after bleeding.

  • Mechanism: When a blood vessel is damaged, platelets aggregate to form a plug that prevents further bleeding and acts as a barrier to germs entering the body.

BLOOD TYPES

  • Inheritance: Blood type is inherited from parents.

  • Classification Systems:

    • The ABO and Rhesus systems define eight blood types based on the presence or absence of specific antigens on red blood cells.

    • The Rhesus factor determines whether an individual's blood type is positive or negative.

  • Compatibility: Not all blood types can be mixed; mixing incompatible types can lead to catastrophic consequences such as fatal blockages due to clumping of cells.

VESSELS

  • Arteries:

    • Function: Transport blood away from the heart.

    • Characteristics: Thick, muscular walls enabling transport of blood under high pressure.

  • Veins:

    • Function: Transport blood back to the heart.

    • Characteristics: Thinner walls with valves that prevent backflow of blood.

  • Capillaries:

    • Function: Sites of exchange between blood and body cells, facilitating the transfer of oxygen and nutrients with waste products.

    • Penetrate almost every tissue in the body.

THE HEART

  • Size and Composition: Roughly the same size as a fist and made from cardiac muscle, which never tires.

  • Pumping Mechanism:

    • The heart operates as a double pump: one side handles oxygenated blood (systemic circuit) while the other side handles deoxygenated blood (pulmonary circuit).

  • Chambers of the Heart:

    • The human heart consists of four chambers:

    • Upper chambers (atria):

      • Right atrium

      • Left atrium

    • Lower chambers (ventricles):

      • Right ventricle

      • Left ventricle

    • The left ventricle has thicker, more muscular walls to effectively pump blood around the body.

    • Valves prevent the backflow of blood, ensuring unidirectional flow.

THE SOUND OF THE HEART

  • The sound of a heartbeat is produced by the opening and closing of heart valves, commonly described as “Lub dub.”

    • “Lub”: Sound of the atrioventricular valves (bicuspid and tricuspid) closing.

    • “Dub”: Sound of the semilunar valves (aortic and pulmonary) closing.

PULMONARY CIRCUIT

  • Process:

    • The vena cava brings deoxygenated blood from the body into the right atrium.

    • Blood is pumped into the right ventricle.

    • Upon contraction of the right ventricle, blood is pushed into the pulmonary arteries leading to the lungs.

    • In the lungs, blood releases carbon dioxide and picks up oxygen.

SYSTEMIC CIRCUIT

  • Process:

    • Pulmonary veins transport oxygenated blood from the lungs to the left atrium.

    • Blood is pumped into the left ventricle.

    • The left ventricle contracts and pushes blood into the aorta, initiating systemic circulation.

    • The blood delivers oxygen to body cells and collects waste such as carbon dioxide.

BLOOD PRESSURE

  • Definition: The force with which blood flows through the arteries.

  • Characteristics:

    • Influenced by emotional states and physical activity.

  • Pressure Measurements:

    • Systolic pressure: Represents the highest pressure during heart contraction.

    • Diastolic pressure: Represents the lowest pressure during heart relaxation.

    • Blood pressure is expressed as a fraction, e.g., 120/80 (systolic/diastolic).

HEART RATE

  • Normal Rate: A typical human heart beats approximately 60-100 times per minute.

  • Influence of Activity: Heart rate increases during physical activity or stress.

  • Mechanism of Pulse: Each heartbeat corresponds to a contraction and produces a pressure wave felt as a pulse in areas like the wrist and neck.

  • Heartbeat Regulation: Maintained by electrical impulses originating from the heart’s pacemaker located in the wall of the right atrium.

COURSEWORK

  • Worksheets:

    • Blood and Blood Highways

ASSIGNMENTS

  • Exercises:

    • Understanding and inquiring problems for practice: 3, 4, 6, 8, 12, 17, 19, 24 from Jacaranda Science Quest 8 textbook, p. 190.

LOOKING AHEAD

  • Next Topic: Read section '4.8 Respiratory system – breathe in, breathe out' from Jacaranda Science Quest 8 textbook, p. 199.