CHAPTER 7(a) - GASEOUS EXCHANGE

RESPIRATORY SURFACE-ALVEOLUS

1. LARGE SURFACE AREA-human lungs consists of million of alveolus.
2. THIN-wall of alveolus consists of one layer of thin squamous epithelial cells to facilitate diffusion of gaseous such as o2 and co2.
3. MOIST-inner surface of alveolus is lined with fluid and its surface tension is lowered by secretion of surfactant from special septal cells in the alveolus . This fluid dissolve respiratory gaseous for diffusion and speed up gas exchange.
4. Each alveolus is covered by a dense of network capillaries which carries away the oxygen and keep the partial pressure low.

THE RESPIRATORY PIGMENT- HAEMOGLOBIN

-The haemoglobin in red blood cells is responsible in transporting oxygen and carbon dioxide.
-Breathing allows the inspired air to come in contact with the blood vessel that cover the alveoli.

HAEMOGLOBIN

HAEMOGLOBIN

-Haemoglobin is  a complex conjugated protein
-Quaternary in nature
-Protein consists of four polypeptide chains , two alpha and two beta
-These polypeptide chains are globular in nature and called globin
-Each haem group can associate with one molecule of oxygen that gives blood its bright red colour
-Process of associating oxygen with the haem group is called oxygenation
-Its a loose combination which allows dissociation occurs easily

TRANSPORT OF OXYGEN AND CARBON DIOXIDE IN BLOOD

-RBC are round disc , concave on each side(biconcave) and do not contain nucleus. Gives it an extremely high surface area to volume ratio for more efficient gaseous exchange.
-In the blood , only small portion of oxygen can dissolve in plasma as the solubility of o2 to plasma is  very low.
-Haemoglobin in RBC increase the ability of blood to transport o2 by about 65 to 70 times.
-The main function of haemoglobin is to carry oxygen but it can help to transport c02.
-It can do so efficiently because it can bind with oxygen at very low partial pressure of oxygen.
-COOPERATIVITY@When the first o2 bind with the first haem group, the haemoglobin molecule  changes shape slightly. This facilitates the binding of the next oxygen.
-When there is a drop in partial pressure of oxygen, haemoglobin will release oxygen.
-In the tissue, the partial pressure of oxygen is lower that at the alveoli , the tissues are continuously  supplied with oxygen.
-CARBON DIOXIDE is more soluble in blood than oxygen.

SIMPLE ILLUSTRATION

TRANSPORTATION OF CO2 BY BLOOD TO LUNGS

-Either in RBC or BLOOD PLASMA

-Can be done in three different ways

1. Transport by RBC in the form of HYDROGEN CARBONATE IONS(HCO3) 85%

-About 85% of the CO2 produced during respiration diffuse into RBC and combine with water to form carbonic  acid (H2CO3) catalysed by carbonic anhydrase.

H20 + CO2 = H2CO3

-The carbonic acid the dissociate to HCO3 and H+ with the presence of same enzyme carbonic anhydrase

H2CO3 = HCO3 + H+

-Then , the HCO3 diffuse out from the RBC into the plasma. 

-This occur because RBC is very permeable to HCO3 

-Later on, CL(CHLORIDE IONS) diffuse into the RBC to maintain electrical neutrality. This process  is called chloride shift.  

-The hydrogen carbonate ions are then carried to lungs and converted to CO2.

-Dont forget that the H+ is still in the RBC , 

-The presence of H+ ions in the RBC decrease the pH of the blood. 

-This proton are quickly mopped by free haemoglobin to form HAEMOGLOBINIC ACID (HHb)

-The free haemogloobin which acts as a pH buffer is made available from the forced dissociation of  oxyhaemoglobin.

-And oxygen is released to the cell , this phenomenon is called BOHR SHIFT. 

-When blood reaches the lungs , the whole process is repeated.

2. CO2 combines with haemoglobin in the RBC to form CARBAMINO COMPOUND 10%

R as Hb(haemoglobin)

-CO2 produced combine in a reversible reaction with the amino group of haemoglobin and form  carbaminohaemoglobin.
-The carbaminohaemoglobin then transported to the lung where it dissociates to CO2.
-The binding of CO2 to haemoglobin lowers the affinity of haemoglobin  for oxygen.
-Which forces to haemoglobin to release its oxygen load. 

3. CO2 dissolve in blood plasma 5%

-About 5% of CO2  dissolve in blood plasma to form carbonic acid ( H2CO3)
-But at a slower rate compared to  in RBC due to lack of enzyme.
-The carbonic acid the ionises to H+ and hydrogen carbonate(HCO3)
-The presence of H+ ions causes in increase in its acidity
-Quickly buffered by plama proteins to form proteinic acid.

PICTURE REFERENCE 

FIRST- CO2  WITH WATER IN RED BLOOD CELLS
SECOND-CO2 WITH HAEMOGLOBIN
THIRD-CO2 WITH WATER AT BLOOD PLASMA

CO2 AND O2

OXYGENATED AND DEOXYGENATED

OXYGEN DISSOCIATION

CHAPTER 7(b) - DISSOCIATION CURVE

OXYGEN DISSOCIATION CURVE OF HAEMOGLOBIN

-Gaseous diffuse  from high partial pressure to low partial pressure
-In inhaled air, the partial pressure of o2 is high but the partial pressure of co2 is low
-oxygen diffuse into the alveolar blood capillaries and co2 diffuse out into the alveolus

LOADING AND UNLOADING OF GASEOUS

-When haemoglobin associates with o2, it undergoes change in shape
-Helps a faster intake of the next oxygen molecule
-The last one is 700 times faster than the first (cooperativity)
-Reverse happens when oxygen dissociates with haemoglobin at a site where the partial pressure of oxygen is low.
-At first, small decrease of Po2 will lead to a big drop of oxygen saturation of haemoglobin
-It then gets harder and harder to remove the oxygen from haemoglobin

DISSOCIATION CURVE

-The haemoglobin can be 95% saturated with oxygen even at a very low Po2(10kPa)
-This is known as oxygen loading
-The partial pressure of oxygen in the lung is 13kPa
-The affinity of haemoglobin for oxygen also lowered by
 (a)2-3-DIPHOSPHOGLYCERATE-product of RBC
 (b)high temperature
-In the respiring cells, the partial pressure of oxygen is very low and oxygen will dissociate from haemoglobin supplying oxygen to the cells

CHANGES BY Pco2

-when the partial pressure of co2 increase or pH decrease will shift the dissociation curve to the right.
-lowering the affinity of haemoglobin for oxygen
-causes oxygen to dissociate from oxyhaemoglobin
-phenomenon is known as BOHR SHIFT

CHANGES BY HIGH TEMPERATURE

-Same goes when the temperature of body increase
-curve shift to the right
-this result in release of more oxygen particularly in vigorous activity

OXYGEN DISSOCIATION CURVE OF MYOGLOBIN

MYOGLOBIN

-Myoglobin is made up of one polypetide chain with a signle iron containing prosthetic group  attached to it
-each myoglobin binf with single oxygen molecule to form oxymyglobin
-the myoglobin dissociation curve is hyperbolic in shape
-this shows that myglobin has higher affinity for oxygen and combines more readily
-but releases it only when the partial pressure of oxygen is low
-myglobin is an oxygen store in muscle

OXYGEN DISSOCIATION CURVE OF FOETAL HAEMOGLOBIN (HbF) AND ADULT HAEMOGLOBIN (HbA)

-During the foetal development , the foetus in the mother's womb is able to obtain the oxygen
-from the mother through increased maternal blood supply to the placenta
-HbF has higher affinity for oxygen than the HbA

HbF VS HbA

-HbF has higher affinity than HbA
-Means hat HbF can easily saturated with oxygen even at low partial pressure
-ensures a sufficient and efficient oxygen supply to the foetus

DOUBLE BOHR EFFECT

-In the maternal blood, there is a high Pco2 which helps to release oxygen
-in the foetal blood , the partial pressure of co2 is low
-so in the foetal ,increase the binding of haemoglobin to oxygen
-taking up more oxygen easily
-this phenomenon is known as double bohr effect
-this causes the curve shifted in the opposite direction
-HbA to the right
-HbF to the left

CHAPTER 7(c) - BREATHING CYCLE

BREATHING MECHANISM

-Events that bring inhaled air to the alveoli and removes exhaled air in a process called ventilation
-ventilation helps to maintain gaseous exchange and blood pH levels
-inspiratory (inhalation) and expiratory (exhalation)
-lungs rely on the diaphragm and the rib cage during breathing

INHALATION AND EXHALATION

-Lungs are not attached to the rib cage by tissues but are separated from it by a thin film of pleural fluid which holds the pleural membrane

-and lubricates it when the lungs expand during inspiration

-medulla oblongata and pons in the hindbrain control this automatic action

RECEPTORS OF BREATHING MECHANISM

1. CENTRAL CHEMORECEPTOR

-In the medulla region of the hind-brain

-sensitive to the pH of the cerebrospinal fluid (indicator of blood Co2)

-the higher the blood CO2 concentration, the lower the pH of cerebrospinal fluid

2. PERIPHERAL CHEMORECEPTOR 

-located in carotid and the aortic bodies

-both bodies are also sensitive to blood pH

-indicates the changes in arterial CO2 concentration

3. MECHANORECEPTOR (STRETCH RECEPTOR)

-In the bronchial tree 

-help maintain any expansion in the lungs and size of airways

-they send impulses to the expiratory centres to shorten inspiration

**respiratory muscles will react to increase or decrease alveolar ventilation as required by regulating amplitude and depth of each breath**

BREATHING RECEPTORS

DURING VIGOROUS EXERCISE

1.Increase in the partial pressure of co2 in the body

2.Drop in the pH of blood

3.Rise in the carbon dioxide partial pressure is detected by chemoreceptors in the carotid artery

4.Impulse are send to stimulate the inspiratory and the cardiovascular center in the brain

5.Inspiratory cente then sends out impulse through

6.Intercostal nerve to stimulate the contraction of the external intercostal muscle of the rib cage

7.Phrenic nerve to stimulate the contraction of the radial muscle of the diaphragm

8.Both contractions bring the rib cage outwards and upwards

9.Air inhaled to the lungs

10.Inhalation and Exhalation are carried out more frequently to increase the rate of alveolar ventilation for faster gaseous exchange in the body.

11.Too much oxygen can cause an increase in the metabolic rate of carbohydrate, fats and protein which will result in accumulation of co2 causing an increase in the rate of ventilation as well as cardiac frequency

CHAPTER 7(d) - GASEOUS EXCHANGE IN PLANTS

THE STRUCTURE AND FUNCTION OF STOMATA

-Stoma is an opening on the epidermis of leaves
-Stoma is actually an opening of two specialised photosynthetic epidermal cells, called guard cells
-the guard cells plays an important role in the opening and closing of stomata
-the guard cell is bean -shaped and its unique as its inner cellulose wall thicker than outer

OPENING AND CLOSING OF STOMATA

-Stoma plays an important role in the exchange of respiratory gaseous
-absorption of co2 for photosynthesis and regulation of water in plants

-Oxygen produced diffuse out through the stomatal pores
-carbon dioxide diffuse in from the atmosphere into the leaves
-under severe water deficit , stomata close automatically
-this is due to the release of ABSCISIC ACID by plant during the water stress condition
-the closure of stomata helps to prevent water loss
-opening and closing of stomata is a response of increse or decrease in water potential

POTASSIUM ION ACCUMULATION HYPOTHESIS

-Opening of the stomata is associated with the influx of potassium ions into the guard cells from the epidermal cells

OPENING

1. During the day, blue light increase the activity of the proton pumps found in the membrane of             guard cells
2. The proton pumps use ATP produced during photosynthesis light reaction to transport H+ ions out
3. When H+ ions are pumped out , K+ ions diffuse into the guard cells through channel protein to           maintain the electrical potential
4. Accumulation of K+ ions in the sap of the guard cells causes its water potential to decrease
5. Water moves into the guard cells by osmosis
6. Guard cells becomes turgid and curve inwards more and causes stomata to open

CLOSING

1. In the dark or night, when the proton pumps are inactive , K+ ions diffuse out of the guard cells
2. Increase the water potential and water moves out of guard cells by osmosis
3. The guard cells lose turgidity and the stomatal aperture closes

WATER STRESS

-During peak transpiration, the tissues of roots, stem and leaves may come under some degree of water shortage
-plant may release abscisic acid
-will trigger the closure of stomatal aperture
-by activating the metabolic ion pump mechanism on the membrane
-K+ will moves out of the guard cells
-resulting in decrease of K+ concentration
-water potential inside the guard cell increase, water flows out
-lose turgidity and stomatal aperture closes

FACTORS AFFECTING THE OPENING AND CLOSING OF STOMATA


1.Water balance@shortage of water, stomata will close
2.Concentration of CO2@low concentration of co2 in the atmosphere will cause stomata open
3.Light@hight light intensity but not very high will cause the stomata to open, guard cells are more sensitive to blue light than red light
4.Circadian rhythm@some plants havea biological clock whereby stomata will open during the day and close at night. In the case of CAM, plants like cactus , the stomata open during the night, and close during the day to avoid excessive loss of water