Mass transport in animals

Specification

The haemoglobins are a group of chemically similar molecules found in many different organisms. Haemoglobin is a protein with a quaternary structure.

The role of haemoglobin and red blood cells in the transport of oxygen. The loading, transport and unloading of oxygen in relation to the oxyhaemoglobin dissociation curve. The cooperative nature of oxygen binding to show that the change in shape of haemoglobin caused by binding of the first oxygens makes the binding of further oxygens easier. The effects of carbon dioxide concentration on the dissociation ofoxyhaemoglobin (the Bohr effect).

Many animals are adapted to their environment by possessing different types of haemoglobin with different oxygen transport properties.

The general pattern of blood circulation in a mammal. Names are required only of the coronary arteries and of the blood vessels entering and leaving the heart, lungs and kidneys.

The gross structure of the human heart. Pressure and volume changes and associated valve movements during the cardiac cycle that maintain a unidirectional flow of blood.

The structure of arteries, arterioles and veins in relation to their function.

The structure of capillaries and the importance of capillary beds as exchange surfaces. The formation of tissue fluid and its return to the circulatory system.

Haemoglobin

haemoglobin is a quaternary protein - globular (=soluble)

haem group binds to oxygen - each haemoglobin can carry 4 oxygen molecules

haemoglobins affinity to oxygen varies depending on the partial pressure of oxygen (oxygen concentration) - greater concentration of oxygen = higher partial pressure - as pp increases, affinity increases (oxygen binds more tightly to haemoglobin) - this process is called loading (occurs in the lungs). During respiration oxygen is used up = partial pressure decreases = decrease affinity = oxygen released (disassociates) in respiring tissues where it is needed. haemoglobin returns to lungs and process repeats

Dissociation curves illustrate change in haemoglobin saturation as partial pressure changes - saturation of haemoglobin affected by affinity for oxygen - in high pp = high affinity = highly saturated.

After binding to first oxygen molecule the affinity of haemoglobin to oxygen increases (due to a change in shape) = makes oxygen molecules easier to bind

Fetal haemoglobin has a higher affinity to oxygen compared to adult haemoglobin as it needs to be better at absorbing oxygen because by the time oxygen reaches placenta the oxygen saturation of blood has decreased

In presence of carbon dioxide the affinity for oxygen decreases = oxygen disassociates - known as Bohr effect

Circulatory system

Features of circulatory system:

  • suitable medium - e.g. blood - water based so substances can easily dissolve into it

  • means of moving the medium - heart = maintains pressure differences

  • mechanism to control flow around body - valves in veins prevent backflow of blood

  • close system of vessels

Mammals have a double circulatory system - heart pumps to lungs to be oxygenated and body to supply organs and tissues

Deoxygenated blood returns from body and enters right side of heart through vena cava. It enters right atrium and is forced into right ventricle when atrium contracts. Atrioventricular tricuspid valve closes to stop blood flowing backwards. Right ventricle contracts forcing blood out of heart via pulmonary artery to the lungs where it picks up oxygen. Semi lunar valves close to prevent backflow of blood.

Oxygenated blood leaves lungs and through pulmonary vein into left atrium. Left atrium contracts and forces blood into left ventricle. Bicuspid valve closes. Ventricle contracts and forces blood out aorta. Semi lunar valve closes

Cardiac cycle:

  • atrial systole (contraction)

    • contraction of both atria

    • av valves open

    • blood flows into ventricles

    • ventricles remain relaxed throughout

  • ventricular systole (contraction)

    • atria relax

    • ventricles contract simultaneously

    • increase in pressure in ventricles compared to atria

    • av valves close

    • once pressure exceeds that in arteries, blood forced into arteries

    • semi lunar valves open

    • blood flows from ventricle into artery

  • diastole (relaxation)

    • atria and ventricle walls relaxed

    • pressure in arteries higher than ventricles = semi lunar valves shut

    • elastic wall of artery recoils which maintains higher pressure in arteries

    • blood returns the atria at low pressure

cardiac output = heart rate x stroke volume

stroke volume = volume of blood heart pumps out in each beat. increases during exercise

Arteries:

  • thick muscle layer - contracts to constrict and dilate lumen to control volume of blood passing thought

  • thick elastic layer - maintain blood pressure in order to reach extremities - stretching and recoiling maintains high and smooth pressure

  • overall wall thickness = stops vessel bursting and withstands pressure

  • no valves = blood under constant high pressure

Arteriole:

  • thicker muscle layer - allows constriction of lumen = restricts and controls flow of blood to capillaries

  • thinner elastic layer - blood pressure lower

Veins:

  • thinner muscle layer - constriction and dilation doesn’t control flow of blood so not necessary

  • thinner elastic layer - blood pressure low

  • valves - prevent backflow of blood

Capillaries:

  • endothelial layer wall - short diffusion pathway

  • flattened cells - short diffusion pathway

  • numerous and highly branched - large surface area for exchange

  • narrow lumen and diameter - short diffusion pathway

  • fenestrations between endothelial cells - allow large molecules to escape

Tissue fluid:

  • higher hydrostatic pressure (blood pressure) at arteriole end of capillary

  • water and smaller molecules forced out capillary through fenestrations

  • larger molecules (e.g. RBC, proteins) remain in capillary

  • hydrostatic pressure decreases along the capillary as water moves out

  • solute potential increases along length of capillary - decreasing water potential

  • water moves back into venous end of capillary by osmosis down conc grad

  • fluid not reabsorbed by capillary is returned by lymphatic system

Lymphatic system:

  • series of vessels that begin in tissues and drain excess fluid into larger vessels

  • lymph nodes found along these vessels and filter bacteria and foreign material from fluid

  • lymphatic vessels rejoin circulatory system in chest cavity