Transport of Oxygen by Haemoglobin

Blood is a tissue which also consists of plasma where red blood cells, white blood cells and platelets are located. Platelets are small parts of cells which are part of clotting wounds, they also contain no nucleus. Red blood Cells contain haemoglobin which also for oxygen loading in the lungs to transport around the body at respiring tissues - only live for about 120 days.

Structure of a red blood cell :

• Very small - short diffusion pathway and a large surface area to volume ratio

• Biconcave disc shape - increases surface area to volume ratio and provides a short diffusion pathway

• No nucleus - allows for carrying the most amount of oxygen as it can in the haemoglobin.

Haemoglobin is a blood pigment which has a high affinity for oxygen and readily loads oxygen in a high partial pressure of oxygen and dissociates at a low partial pressure of oxygen (respiring tissues)

High Affinity = load oxygen more easily and unload less easily

Low Affinity = load oxygen less easily and unload more easily

Haemoglobin is a quaternary protein - 4 polypeptide chains all associated with a haem group which also contains a Fe2+ ion which allows a total of 4 oxygens to bind to one haemoglobin

As oxygen binds to haemoglobin → oxyhaemoglobin

The max amount of oxygen carried by haemoglobin at one time is referred to as the percentage saturation

The oxygen dissociation curve is a sigmoidal shape due to the struggle of haem groups binding with the first oxygen.

After the first oxygen binds, the tertiary group changes shape to increase the affinity of oxygen binding to the other 3 haem groups and as the gradient of the curve reduces the graph flattens off.

In each species there are different types of haemoglobin which forms a different oxygen dissociation curve.

The further to the left the curve, the greater is the affinity of haemoglobin for oxygen (so it loads oxygen more readily)

The Bohr Shift

Haemoglobin has a reduced affinity for oxygen in the presence of carbon dioxide so the greater the partial pressure of carbon dioxide, the more readily the haemoglobin releases oxygen(the Bohr effect)

Respiring Tissues have a low partial pressure of oxygen and a high partial pressure of carbon dioxide.

High Affinity :

• Organisms that live in low oxygen environments

• Haemoglobin loads oxygen more readily

• Curve shifts left

• Haemoglobin is more saturated at any partial pressure of oxygen

Low Affinity :

• Organisms that have a high metabolic rate

• Haemoglobin unloads oxygen more readily

• Curves shifts right

• Haemoglobin is less saturated at any partial pressure of oxygen

The Circulatory System

Mammals have a double circulatory system - blood is confined to vessels and passes through the heart twice to complete the circuit. Blood pressure is reduced when passed through the lungs which decreases circulation for the rest of the tissues.

The Human Heart

The heart is made up of cardiac muscle which acts as 2 pumps on both sides of the heart.

Right - Pulmonary Circulation - Deoxygenated Blood - Body to the lungs

Left - Systemic Circulation - Oxygenated Blood - Lungs to the rest of the body

Each pump has 2 chambers

• Atrium - thin-walled and elastic which stretches as it collects blood

• Ventricle - thicker muscular wall for contraction to pump blood a far distance to the lungs/ rest of the body

Flow of Blood :

• Blood from vena cava flows into the right atrium whilst blood from pulmonary veins flows into the left atrium

• Atria contract and passes blood through the atrioventricular valves into the ventricles and when ventricles contract blood passes up the semi-lunar valves into major arteries

• Blood from the right side passes into the pulmonary artery - deoxygenated blood into lungs

• Blood from the left side passes into the aorta - oxygenated blood to the rest of the body

  Both atria contract together and then both ventricles contract together - pump the same vol of blood

Heart Valves

Heart Valves only open one way to prevent backflow - only open when the pressure behind is higher than the pressure in front

Increases pressure in the chambers is cause by either chambers contracting or blood filling the chamber

Only one set of valves are open at one time

The heart needs its own blood supply which flows using the coronary arteries branched off from the aorta to supply the heart with oxygen and glucose and remove its waste products - when the artery is blocked it starts a myocardial infarction(heart attack) - area of the heart is deprived of oxygen and the heart muscle cannot respire aerobically

The Cardiac Cycle

One complete sequence of contraction and relaxation is called a cardiac cycle

Contraction of the atrial muscle = atrial systole

Contraction of the ventricular muscle = ventricular systole

1) Atrial Systole

• Atria contract and Ventricles relax

• Decrease Vol in atria

• Increase in pressure

• AV valves open

• Slight increase in pressure in the ventricles

2) Ventricular Systole

• Atria relax and ventricles contract

• Ventricular Vol decreases

• Pressure increases

• Pressure in ventricles is higher than the aorta

• SL valves open

• Blood moves out into arteries

3) Cardiac Diastole

• Ventricles and Atria both relax

• Pressure is higher in pulmonary artery and aorta

• SL valves shut

• Atria fill with blood due to higher pressure so it slightly increases

• Pressure in atria is higher than in ventricles

• AV Valves open allowing blood to flow through passively

Cardiac Output

When ventricles of the heart contract the blood flow into the aorta and pulmonary arteries is under pressure which stretched the arteries due to elastic tissue

The stretch and subsequent recoil of the arteries = pulse - identical to the heart rate ( beats per minute)

Stroke Volume = vol of blood pumped out from one ventricle during each contraction

Cardiac Output = total vol of blood pumped out from one ventricle per minute

Cardiac Output = Stroke Volume x Heart Rate

Heart Disease

Heart disease kills more people in the UK than any other disease - half from coronary heart disease (CHD)

• Build up of fatty material inside the coronary arteries and narrows them reducing the flow of blood which results in the lack of oxygen for the heart muscle and can lead to an aneurysm, thrombosis or myocardial infarction

Risk Factors :

• Inheritance

• Gender

• Increasing Age

• Smoking

• Diet

• High blood pressure

The Blood Vessels

• Arteries - blood away from the heart and into arterioles

• Arterioles - smaller arteries that control blood flow from arteries into the capillaries

• Capillaries - tiny vessels that carry blood from capillaries back to the heart

• Small veins = venules

The heart - vena cava and pulmonary vein enter the heart and aorta and the pulmonary vein leave the heart

The Lungs - The pulmonary artery enters the lung and pulmonary vein leaves the lung

The Kidneys - the renal artery enters the kidneys and the renal vein leaves the kidneys

Arteries

• Carry Blood at high pressure

• Thick muscle Layer - smaller arteries can be constricted and dilated to control vol of blood

• Thick Elastic Layer - Stretched at every beat of the heart to recoil when the heart relaxed to maintain high pressure and smooth pressure surges made by contraction of the ventricles

• Large thickness of the wall - withstands high pressure and prevents bursting

• No valves - blood is under constant pressure

• Narrow Lumen - maintains high pressure

• Inner endothelium folded - allows artery to stretch to maintain high pressure

Arterioles

Control blood flow to the capillaries

• Thicker muscle layer - allows constriction of the lumen of the arteriole to control its movement into the capillaries to supply tissues with blood

• Thinner elastic layer - blood pressure is low

Veins

• Low pressure

• Thinner muscle layer - veins carry blood away from tissues and constriction and dilation cannot control flow of blood to the tissues

• Tinner Elastic Layer - low blood pressure so no risk of bursting or recoil needed

• Smaller thickness - no risk of bursting

• Valves - prevent backflow

Capillaries

To exchange metabolic materials

• One cell thick - short diffusion pathway

• Large number - short diffusion pathway

• Highly Branched - large surface area for exchange

• Lumen is narrow - reducing diffusion distance and time available for diffusion

Tissue Fluid

• High hydrostatic pressure to create contraction of ventricles at the end of capillaries at the arteriole

• Water and small solutes are forced out of blood into the pores of capillaries endothelium walls

• Large plasma proteins and red blood cells do not leave as they are too large

• Tissue fluid contains a high concentration of oxygen, glucose and mineral ions needed for cells so they diffuse into cells and waste products diffuse out

• Blood moves to the venous end of the capillary and leads to a decrease in hydrostatic pressure - WP decreases

• Water is drawn back into capillaries by osmosis down the water potential gradient at the venule end

• More fluid leaves the capillaries is then reabsorbed and excess tissue fluid drains into the lymphatic vessels to be returned to the blood.