transport in animals

• Large animals

  • Higher metabolic rates
  • Lower surface area to volume ratios
• Transport systems are essential for the delivery of nutrients and the removal of waste from cells in large animals
• Circulatory system

  • Adapted to meet the needs of each animal
  • Transports gases and nutrients around an organism in a transport liquid (e.g. blood)
  • Has a pump to move the liquid (e.g. heart)
• Invertebrate circulatory systems (e.g. insects)

  • Open circulatory system
  • Transport medium (haemolymph) is pumped directly to the open body cavity (haemocoel)
  • Very few transport vessels
  • Transport medium is pumped at low pressure
  • Transports food and nitrogenous waste, but not gases (transported via tracheal system)
  • Transport medium returns to the heart through an open-ended vessel
• Vertebrate circulatory systems (e.g. fish, mammals) and some invertebrate circulatory systems (e.g. annelid worms)

  • Closed circulatory system
  • Transport medium (blood) remains inside of the vessels (blood vessels)
  • Gases and small molecules can leave the blood by diffusion or due to high hydrostatic pressure
  • Transports oxygen and carbon dioxide, with oxygen usually transported by a pigmented protein (e.g. haemoglobin)
• This single circulatory system would not enable efficient gas exchange for mammals, but it works for fish due to the counter-current flow mechanism in gas exchange
• Blood vessels

  • Most blood vessels contain collagen, smooth muscle and elastic tissues
• arteries:

  • smooth muscle layer thicker than veins so that constriction and dilation can occur to control the volume of blood.

  • elastic layer thicker than veins to help maintain blood pressure. The walls can stretch and recoil in response to the heart beat.

  • Collagen outer layer to provide structural support.

  • Thicker than veins to help maintain blood pressure.
• arterioles:

  • smooth muscle layer thicker than in arteries to help restrict blood flow into the capillaries

  • elastic layer thinner than in arteries as the pressure is lower

  • thinner collagen layer

  • thinner wall as pressure is lower
• capllaries:

  • no smooth muscular layer

  • no elastic layer

  • no collagen layer

  • one cell thick- short diffusion distance
• veins:

  • A thin layer of smooth muscle

  • no elastic layer

  • no collagen layer

  • very thin wall- several venules join to form one vein
• veins:

  • smooth muscle layer relatively thin so it cannot control the blood flow

  • elastic layer relatively thinner as the pressure is much lower.

  • contains lots of collagen

  • Thin wall as the pressure is much lower so there is low risk of the vessel bursting. The thinness means the vessels are easily flattened, which helps the flow of blood up to the heart.
• Capillaries

  • Form capillary beds (many branched capillaries) at exchange surfaces
  • Have a narrow diameter to slow blood flow
  • Red blood cells can only just fit through and are squashed against the walls - this maximises diffusion
• Capillary walls

  Have small gaps so that liquid and small molecules can be forced out - this forms tissue fluid
• Oncotic pressure

  The tendency of water to move into the blood via osmosis
• As blood enters the capillaries from the arterioles

  1. Smaller diameter results in high hydrostatic pressure

  2. This pressure forces water, glucose, amino acids, fatty acids, ions and oxygen out of the capillaries

  3. The solution that has been forced out is called tissue fluid and it bathes the cells in substances they need

  4. The hydrostatic pressure is higher than the oncotic pressure at the arterial end of the capillaries, so the net movement of liquid is out of the blood in the capillaries
• Plasma proteins

  Large molecules that remain in the capillaries
• Large molecules remain in the capillaries

  Lowers the water potential of the blood remaining in the capillary
• Lower water potential in the capillary

  Results in a higher oncotic pressure
• Towards the venule end of the capillaries

  Hydrostatic pressure is low due to the loss of liquid, but the water potential is very low
• Low hydrostatic pressure and water potential towards venule end

  Net movement of liquid is back into the capillary by osmosis
• Once equilibrium of the water potential of the blood is reached, no more water from the tissue fluid can be reabsorbed back into the blood in the capillaries</b>
• Remaining liquid absorption

  1. Absorbed into the lymphatic system

  2. Drains back into the bloodstream near the heart
• Lymph

  Liquid in the lymphatic system, similar composition to plasma but without large plasma proteins and less oxygen and nutrients
• Heart

  Organ made of cardiac muscle, responsible for pumping the blood around the blood vessels
• Cardiac muscle

  • Myogenic (automatically contracts and relaxes)
  • Never fatigues
• Cardiac muscle function

  1. Coronary arteries supply oxygenated blood

  2. Provides ATP for contraction and relaxation
• Left ventricle

  • Thicker muscular wall
  • Can contract with more force
  • Pump blood at higher pressure
• Atria

  • Very thin muscular walls
  • Blood only needs to be pumped from atria into ventricles
  • Minimal pressure and force is required
• Valves open

  When there is a higher pressure behind them
• Atrial systole

  1. Atria contract

  2. Increases pressure in atria

  3. Opens atrioventricular valves

  4. Forces blood to flow into ventricles
• Ventricular systole

  1. Ventricles contract

  2. Atria relax

  3. Increases pressure in ventricles

  4. Causes atrioventricular valves to shut

  5. Causes semilunar valves to open
• Increased pressure in ventricles

  Blood flows out of ventricles and into pulmonary artery and aorta
• Heart rate is a measure of how many time the heart beats per minute.

  Stroke volume is the volume of blood pumped by the heart in one beat.

  Cardiac muscle is myogenic, but the rate of contraction is controlled by waves of electrical activity. The sinoatrial node (SAN) is in the right atrium and is known as the pacemaker. The SAN will release a

  wave of depolarisation across the atria, causing the cardiac muscle to contract.

  The atrioventricular node (AVN) is located near the border of the right and left ventricle within the atria.
• AVN releases another wave of depolarisation

  1. First wave reaches AVN

  2. Non-conductive layer between atria and ventricles prevents wave from travelling down

  3. Bundle of His runs through septum and conducts/transmits wave released by AVN down septum and Purkyne fibres in ventricle walls

  4. Muscles in apex contract first, then walls of ventricles contract
• Atria contracting

  Short delay before ventricles contract
• Delay between atria and ventricles contracting

  Allows time for atria to pump blood into ventricles before they contract
• Cardiac muscle

  1. Cells repolarise

  2. Muscle relaxes
• Electrocardiogram (ECG)

  Measures waves of depolarisation (electrical activity) to diagnose irregularities in heart rhythms
• ECG doesn't directly measure electrical activity of heart, but differences in electrical activity in skin caused by heart's electrical activity