OCR (A) Biology A-Level: Transport in Animals

Circulatory Systems

• Types of Circulatory Systems
  • Open system: Found in insects
  • Closed system: Found in fish and mammals
    • Single circulatory system: Heart with two chambers, blood passes through heart once per circuit.
    • Double circulatory system: Heart with four chambers, blood passes through heart twice per circuit.

Important Blood Vessel Structures and Functions

• Arteries
  • Carry blood away from the heart.
  • Thick walls to withstand high pressure.
  • Contain elastic tissue for stretching and recoiling.
  • Smooth muscle to vary blood flow.
  • Lined with smooth endothelium to reduce friction.
• Arterioles
  • Branch off arteries.
  • Thinner and less muscular walls.
  • Feed blood into capillaries.
• Capillaries
  • Smallest blood vessels.
  • Site of metabolic exchange.
  • One cell thick for fast substance exchange.
• Venules
  • Larger than capillaries but smaller than veins.
• Veins
  • Carry blood to the heart.
  • Wide lumen for increased blood volume.
  • Thin walls since blood is under low pressure.
  • Valves to prevent backflow.
  • Little elastic tissue or smooth muscle due to lack of pulse.

Tissue Fluid and Its Functions

• Contains dissolved oxygen and nutrients.
• Provides tissues with essential solutes and exchanges for waste.
• Formed by hydrostatic pressure forcing blood fluid out of capillaries.
• Osmotic pressure pushes fluid back into capillaries.
• Lymphatic system returns remaining tissue fluid, containing lymph fluid and nodes that filter bacteria.

Mammalian Heart and Cardiac Cycle

• Myogenic Heart: Initiates its own contraction.

  • Sinoatrial Node (SAN): Pacemaker in the right atrium, initiates contraction.
  • Atrioventricular Node (AVN): Conducts excitation to ventricles via the bundle of His and Purkyne fibres.

• Cardiac Cycle Stages

  1. Atrial Systole: Atria contract, AV valves open, blood flows into ventricles.
  2. Ventricular Systole: Ventricles contract, AV valves close, semilunar valves open, blood ejected.
  3. Cardiac Diastole: Atria and ventricles relax, semilunar valves close, blood drawn into heart.

Haemoglobin and Oxygen Transport

• Structure: Water-soluble protein with two alpha and two beta chains, each containing a haem group.

• Function: Binds and carries oxygen, released as needed.

• Oxygen Affinity and Partial Pressure

  • High partial pressure increases haemoglobin's oxygen affinity (loading in lungs).
  • Low partial pressure decreases affinity (unloading in tissues).

• Dissociation Curves

  • Show haemoglobin saturation changes with partial pressure.

• Fetal vs. Adult Haemoglobin

  • Fetal haemoglobin has higher oxygen affinity to compensate for decreased oxygen saturation in placenta.

• Bohr Effect

  • Presence of CO2 decreases oxygen affinity, promoting oxygen release.