BY : DR FARIHA RIZWAN

Oxygen Transport The transport of oxygen between the lungs and the cells of the body is a function of the blood and the heart. Oxygen is carried in the blood in two forms: - as dissolved oxygen in the blood plasma - chemically bound to the hemoglobin(Hb) that is encased in the erythrocytes or RBC’s 2

O2 Dissolved in Plasma As O2 diffuses from the alveoli into the pulmonary capillary blood, it dissolves in the plasma of the blood. At normal body temperature about ml of O2 will dissolve in 100 ml of blood for every 1 mm Hg of Po2 In terms of total oxygen transport, a relatively small percentage of O2 is transported in the form of dissolved O2. 3

O2 Bound with Hemoglobin Most of the O2 that diffuses into the pulmonary capillary blood rapidly moves into the RBC’s and chemically attaches to the hemoglobin. Each RBC contains about 280 million Hb molecules, which are highly specialized to transport O2 and CO2. The normal hemoglobin value for the adult male -14 to 16 g% female -12 to 15 g%. 4

VALUE OF OXYGEN & HEMOGLOBIN COMBINATIONS Normal amount of oxygen carried by 1 gram of Hb – 1.34 ml of O2 Maximum amount of O2 that can be carried by 100 ml of blood – 20 ml of O2

OXYGEN-HEMOGLOBIN DISSOCIATION CURVE When the PO2 is high as in lungs, O2 binds with the Hb, but when the PO2 is low as in the tissues,O2 is released from the Hb. This relationship b/w PO2 and amount of oxygenation or deoxygenation of Hb is termed as “oxygen Hemoglobin dissociation curve” The percentage of Hb bound with O2 is known as “ percent saturation of Hb”.

AMOUNT OF O2 RELEASED BY Hb During normal conditions : 5ml of O2 / each ml of blood

AMOUNT OF O2 RELEASED BY Hb DURING EXERCISE It increaes upto three times 15 ml of O2 / 100 ml of blood

UTILIZATION COEFFICIENT The percentage of blood that gives up its 02 as it passes through the tissue capillaries is called the “UTILIZATION COEFFICIENT” DURING REST : 25% of blood gives up its O2 DURING EXERCISE : % or all the blood can give off its O2 to the tissues

Oxygen Dissociation Curve The O2 dissociation curve graphically illustrates the percentage of Hb that is chemically bound to O2 at each PO2 pressure. The curve is SIGMOID,(S-shaped) The flat and steep portions of the curve each have a distinct clinical signi ficance. 10

Factors that effect the 02 Dissociation pH- Change in the blood pH Temperature-temp increases the curve moves to the right 2,3 Diphosphoglycerate-Increases 2,3 DPG results in decreased affinity Carbon monoxide 11

Hb-O2 dissociation curve Right shift = 1. Hb has less affinity for O 2, 2. releases O 2, 3. saturation will be less for a given P O 2 Left shift = 1. Hb has higher affinity for O 2, 2. binds O 2, 3. saturation will be higher for a given P O 2

CAUSES OF RIGHT SHIFT (less affinity for O 2 ) increasedCO2 increased temperature increased metabolism Muscle increase [H + ] – acidosis, lactic acid production. Increased 2,3- diphosphoglycerate Increased thyroid hormones CAUSES OF LEFT SHIFT Increased PCO2 ( decreased pH ) decreased H+ ions decreased temperature decreased 2,3 DPG

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Bohr effect increased 2,3 DPG – generated by glycolysis during anaerobic metabolism,CO2 binds to Hb and decreases affinity for O2 15

INTRODUCTION TO PHSYIOLOGY OF CO2 TRANSPORT 1. CO2 is the end-product of aerobic metabolism. 2. Produced almost entirely in the mitochondria where the PCO2 is the highest 3. Elimination of CO2 – 4. one of major requirement of body. 5. Under normal resting conditions : 4ml of CO2 / 100 ml of blood

 CO2 in blood present in 3 forms: Dissolved : 7% Bound as bicarbonate 70% Bound as carbamino-Hb and combine with plasma proteins : 70% For diffusion across membrane barriers, gaseous form more appropriate while for transport within intra- or extracellular compartments.

CO2 DIFFUSION At each point in gas transport chain, CO2 diffuses in exactly the opp direction to O2 diffusion. CO2 diffuses 20 times as rapidly as O2. Pressure differences required for CO2 diffusion far less than those required to cause O2 diffusion

CO2 TRANSPORT IN BLOOD Under N resting conditions av 4 ml CO2 transported from tissues to lungs/ 100 mL of blood CO2 diffuses out of tissue cells in gaseous form but does not leave cells to any significant extent in form of HCO3 since cell membrane almost impermeable to HCO3

RESPIRATION CHEMICAL CONTROL

The ultimate goal of respiration is to maintain proper concentrations of oxygen, carbon dioxide, and hydrogen ions in the tissues Excess carbon dioxide or excess hydrogen ions in the blood mainly act directly on the respiratory center itself, causing greatly increased strength of both the inspiratory and the expiratory motor signals to the respiratory muscles Oxygen, in contrast, does not have a significant direct effect on the respiratory center of the brain in controlling respiration

Changes in Oxygen Have Little Direct Effect on Control of the Respiratory Center Changes in oxygen concentration have virtually no direct effect on the respiratory center although oxygen changes do have an indirect effect, acting through the peripheral chemoreceptors The body has a special mechanism for respiratory control located in the peripheral chemoreceptors, outside the brain respiratory center; this mechanism responds when the blood oxygen falls too low, mainly below a P O 2 of 70 mm Hg These chemoreceptors are carotid bodies & aortic bodies

Chemosensitive Area of the Respiratory Center

RESPIRATION : NERVOUS CONTROL

Respiratory Center The respiratory center is composed of several groups of neurons located bilaterally in the medulla oblongata and pons of the brain stem Three major collections of neurons 1. a dorsal respiratory group 2. a ventral respiratory group 3. pneumotaxic center

A dorsal respiratory group Dorsal portion of the medulla, which mainly causes inspiration extends most of the length of the medulla Most of its neurons are located within the nucleus of the tractus solitarius (NTS) The NTS is the sensory termination of both the vagal and the glossopharyngeal nerves, which transmit sensory signals into the respiratory center from (1) peripheral chemoreceptors, (2) baroreceptors, and (3) several types of receptors in the lungs.

Inspiratory "Ramp" Signal The nervous signal that is transmitted to the inspiratory muscles, mainly the diaphragm, is not an instantaneous burst of action potentials Begins weakly and increases steadily in a ramp manner for about 2 seconds in normal respiration It ceases abruptly for approximately the next 3 seconds This turns off the excitation of the diaphragm and allows elastic recoil of the lungs and the chest wall to cause expiration

A ventral respiratory group The neurons of the ventral respiratory group remain almost totally inactive during normal quiet respiration Do not appear to participate in the basic rhythmical oscillation Works when pulmonary ventilation becomes greater than normal These neurons contribute to both inspiration and expiration Powerful expiratory signals to the abdominal muscles during very heavy expiration

Pneumotaxic center Located in the superior portion of the pons, which mainly controls rate and depth of breathing. nucleus parabrachialis Control the duration of the filling phase of the lung cycle by providing the "switch-off" point of the inspiratory ramp During strong signals the ramp may be as low as 0.5 sec to 5-6 sec in case of week signals

The Hering-Breuer Inflation Reflex Sensory nerve signals from the lungs also help control respiration Located in the muscular portions of the walls of the bronchi and bronchioles throughout the lungs are stretch receptors When the lungs become overly inflated, the stretch receptors activate an appropriate feedback response that "switches off" the inspiratory ramp and thus stops further inspiration