Circulatory System

The Need for a Transport System

Problem

For a complex multicelluar organism, many cells are not in direct contact with the environment.

• Diffusion distance increases → cells are unable to receive necessary materials / remove waste products sufficiently

Solution

Multicelluar organisms developed specialised organs in which materials can be exchanged between organism and environment Form these specialised organs, materials can be transported to other parts of the body via circulatory system

Human Circulatory System

• Made up of:
  • Circulating fluid (blood) that transports substances
  • A vascular system in which the fluid flows
  • A central pump that generates pressure required for fluid movement

Blood

• Is a specialised connective tissues
• Made up of red blood cells, white blood cells and platelets, suspended in plasma
• Red blood cells at the bottom of centrifugation, meaning its heaviest
• PLATELETS ARE NOT CELLS, ONLY CELL FRAGMENTS

Plasma

• Amber-coloured liquid
• Components:
  • 90% water
  • 10% dissolved substances
    • proteins
    • food substances
    • excretory products
    • hormones
    • ions
• Blood cells are suspended in plasma

Function

Plasma transports dissolved substances and blood cells around the body.

Red Blood Cells / Erythrocytes

• Constitute 99% cells in blood
• Produced in the bone marrow
• Destroyed at the spleen and liver
• Limited lifespan of 120 days
  • Without nucleus, any damage it acquires cannot be repaired
  • Must be destroyed to create new one

Function

Red blood cells transport oxygen from the lungs to the rest of the body.

Structural Adaptations of RBC for Function

Cytoplasm contains haemoglobin

• Haemoglobin is made up of 4 polypeptide chains, each forming a heme group with a that binds reversibily to O2
• Deoxyhaemoglobin (haemoglobin with no oxygen) is purple-blue and oxyhaemoglobin (haemoglobin with oxygen) is red
• More than 99% of oxygen is bound to haemoglobin in RBC
• Remaining oxygen is dissolved in plasma / RBC cyroplasam

Absence of nucleus in RBC

• Allows for more haemoglobin to be packed into RBC, more oxygen transported per RBC

Biconcave shape of RBC

• Increases surface area to volume ratio → increased rate of diffusion of oxygen into RC
• Optimises flow of RBC in blood vessels

Flexible and deformable cell membrane

• Allows red blood cell to turn bell-shaped to squeeze through narrow blood vessels (e.g. capillaries)

Transport of CO2

• In 3 ways:
  • Dissolved in solution (minor)
  • Bound to haemoglobin to form carbaminohaemoglobin (minor)
  • As bicarbonate ions (major)

White Blood Cells / Keukocytes

• 2 main types: Phagocyte / Lymphocyte
• Fewer in numbers, larger than RBC
• Irregular shape
• Flexible and mobile, can squeeze out of capillary to reach site of infection
• Colourless
• Mostly produced in the bone marrow
• Limited lifespan of a few days even with nucleus

Function

Help to defend against infectious diseases and foreign particles

Phagocyte

• Lobed nucleus
• Granular cytoplasm
• Engulfs and ingests foreign particles, bacteria, dead cells by phagocytosis for digestion
• Pus produced at a wound is an accumulation of dead bacteria and white blood cells

Lymphocytes

• Large rounded nucleus, non-granular cytoplasm

T-Cells

• Directly destroys infected or cancerous cells (Cytotoxic T-cells)
• Gives off signals to activate B-cells to produce antibodies (Helper T-cells)

B-Cells

• Produce antibodies to bind to antigens present on surfaces of bacteria and viruses
• Antibodies function by binding antigens on the same pathogens

Tissue Rejection

• Certain diseased organs can be replaced via a transplant
• Antigens present on transplanted tissue may be recognised as foreign by the immune system, which will destroy the foreign tissue

Prevent Tissue rejection

• Donor of close relation
• Take immunosuppressant drugs
• Bone marrow transplant

Platelets

• Not true cells
• Tiny fragments of cytoplasm pinched off

Blood Clotting

• Clotting occurs when endothelium of a blood vessel is damaged
• Triggers a biochemical pathway that catalyses the conversion of soluble plasma fibrinogen into insoluble fibrin threads
  • Fibrinogen is usually dissolved in plasma
  • Platelets trigger reaction
• Fibrin threads form a network that entangles blood cells to form a clot that prevents excessive loss of blood and entry of foreign pathogens.

ABO Blood Group

• 4 groups:
  • A
    • Has A antigens and anti-B antibodies
  • B
    • Has B antigens and anti-A antibodies
  • AB
    • Has both A and B antigens and no antibodies
  • O
    • Has no antigens and anti-A and anti-B antibodies

Blood Transfusion

• ONLY TRANSFER RBCs!!!
• Antibodies in blood plasma of recipient may bind to antigens on donor’s RBC, causing agglutination.