Blood Gas transport power point pr.pptx

Blood gas

1. Blood Gas Transport , Tissue Respiration & Regulation . PRESENTOR ; DR. BUKENYA MODULATOR MR.MUGISA

2. Goals For Learning To explore how O2 is transported in the blood . To explore how Co2 is transported in the blood . This will include understanding the oxygen dissociation curve. Respiratory regulation ,

3. Introduction

4. Cont ’ T he amount of both gases transported to and from the tissues would be grossly inadequate if it were not that ; about 99% of the O 2 that dissolves in the blood combines with the O 2 -carrying protein hemoglobin about 94.5% of the CO 2 that dissolves enters into a series of reversible chemical reactions that convert it into other compounds. THUS, the presence of hemoglobin increases the O 2 -carrying capacity of the blood 70-fold & the reactions of CO 2 increase the blood CO 2 content 17-fold .

5. Oxygen transport O 2 delivery to a particular tissue depends on ; the amount of O 2 entering the lungs the adequacy of pulmonary gas exchange the blood flow to the tissue which in turn depends on; degree of constriction in the vascular bed cardiac output the capacity of the blood to carry O

6. Cont ’ O2 is transported by the blood either, – Combined with haemoglobin ( Hb ) in the red blood cells (>98%) or, – Dissolved in the blood plasma (<2%).

7. Hemoglobin structure

8. Haemoglobin molecules can transport up to four O2’s When 4 O2’s are bound to haemoglobin , it is 100% saturated, with fewer O2’s it is partially saturated. Oxygen binding occurs in response to the high PO2 in the lungs. Co-operative binding: haemoglobin’s affinity for O2 increases as its saturation increases . Ie combination of the 1 st heme in the Hb molecule with O2 increases the affinity of the 2 nd heme for o2 and oxygenation of the 2 nd increases the affinity of the 3 rd etc so that the affinity of Hb for the 4 th is many times that for the 1 st

9. T ense (T) configuration ; deoxyhemoglobin , the globin units are tightly bound this reduces the affinity of the molecule for O 2 . R elaxed (R) configuration ; When O 2 is first bound, the bonds holding the globin units are released,expos ing more O 2 binding sites . The net result is a 500-fold increase in O 2 affinity. In the tissues, these reactions are reversed, releasing O 2 . Hence the O2-Hb dissociation curve has a Sigmoid shape due to this T-R interconversion . The Oxygen Disassociation Curve

10. The Oxygen Disassociation Curve

11. The binding of O2 to haemoglobin depends on the PO2 in the blood and the bonding strength, or affinity, between haemoglobin and oxygen . In the lungs the PO2 is 104mmHg, hence Hb has a high affinity for O2 and is 98% saturated. In the tissues of other organs the PO2 is 40mmHg here the Hb has a lower affinity for O2 and it releases some but not all of the it’s O2 to the tissues. Hence when the Hb leaves the tissues it is still 75% saturated

12. Note ; Another 2 percent of the blood has passed from the aorta through the bronchial circulation, which supplies mainly the deep tissues of the lungs and is not exposed to lung air. This blood flow is called "shunt flow," meaning that blood is shunted past the gas exchange areas. On leaving the lungs, the P o 2 of the shunt blood is about that of normal systemic venous blood, about 40 mm Hg. When this blood combines in the pulmonary veins with the oxygenated blood from the alveolar capillaries, this so-called venous admixture of blood causes the P o 2 of the blood entering the left heart and pumped into the aorta to fall to about 95 mm Hg .

13. Factors Affecting the Affinity of Hemoglobin for Oxygen Three important conditions affect the oxygen–hemoglobin dissociation curve ; PH Temperature 2,3- biphosphoglycerate A rise in temperature or a fall in pH shifts the curve to the right. When the curve is shifted in this direction, a higher PO 2 is required for hemoglobin to bind a given amount of O 2

14. Right shift

15. PH A convenient index of such shifts is the P 50 , the PO 2 at which hemoglobin is half saturated with O 2 . The higher the P 50 , the lower the affinity of hemoglobin for O 2 . The decrease in O 2 affinity of hemoglobin when the pH of blood falls is called the Bohr effect It is closely related to the fact that deoxygenated hemoglobin (deoxyhemoglobin) binds H + more actively than does oxyhemoglobin . The pH of blood falls as its CO 2 content increases (see below), so that when the PCO 2 rises, the curve shifts to the right and the P 50 rises 2,3 BPG

16. Conti… 2,3-BPG is very plentiful in red cells. It is a highly charged anion that binds to beta chains of deoxyhemoglobin . One mole of deoxyhemoglobin binds 1 mol of 2,3-BPG Exercise has been reported to produce an increase in 2,3-BPG within 60 minutes Ascent to high altitude triggers a substantial rise in 2,3-BPG concentration in red cells, with a consequent increase in P 50 and increase in the availability of O 2 to tissues. Red cell 2,3-BPG concentration is increased in anemia and in a variety of diseases in which there is chronic hypoxia.

17. Factors affecting Disassociation BLOOD TEMPERATURE • increased blood temperature • reduces haemoglobin affinity for O2 • hence more O2 is delivered to warmed-up tissue BLOOD Ph • lowering of blood pH (making blood more acidic) • caused by presence of H+ ions from lactic acid or carbonic acid • reduces affinity of Hb for O2 • and more O2 is delivered to acidic sites which are working harder CARBON DIOXIDE CONCENTRATION • the higher CO2 concentration in tissue • the less the affinity of Hb for O2 • so the harder the tissue is working, the more O2 is released

18. CARBONMONOXIDE Carbon monoxide combines with hemoglobin at the same point on the hemoglobin molecule as does oxygen; it can therefore displace oxygen from the hemoglobin, thereby decreasing the oxygen-carrying capacity of blood . Further, it binds with about 250 times as much tenacity as oxygen Therefore, a carbon monoxide pressure of only 0.6 mm Hg (a volume concentration of less than one part per thousand in air) can be lethal . Key point Increased temperature and hydrogen ion (H+) (pH) concentration in exercising muscle affect the oxygen dissociation curve, allowing more oxygen to be uploaded to supply the active muscles .

19. Carbon dioxide transport Carbon dioxide also relies on the blood for transportation. Once carbon dioxide is released from the cells, it is carried in the blood primarily in three ways… • Dissolved in plasma, • As bicarbonate ions resulting from the dissociation of carbonic acid, • Bound to haemoglobin CO2 is carried in three forms . Dissolved As bicarbonate As carbamino compouds

20. Dissolved CO2 Part of the carbon dioxide released from the tissues is dissolved in plasma. But only a small amount , typically just 7 – 10%, is transported this way. • This dissolved carbon dioxide comes out of solution where the PCO2 is low, such as in the lungs . • There it diffuses out of the capillaries into the alveoli to be exhaled . Note ’ The solubility of CO 2 in blood is about 20 times that of O 2 ; therefore considerably more CO 2 than O 2 is present in simple solution at equal partial pressures . Formation of bicarbonate The CO 2 that diffuses into red blood cells is rapidly hydrated to H 2 CO 3 because of the presence of carbonic anhydrase. The H 2 CO 3 dissociates to H + and HCO 3 – , and the H + is buffered, primarily by hemoglobin, while the HCO 3 – enters the plasma. The H 2 CO 3 dissociates to H + and HCO 3 – , and the H + is buffered, primarily by hemoglobin, while the HCO 3 – enters the plasma .

21. HALDANE EFFECT Since deoxygenated hemoglobin binds more H + than oxyhemoglobin does and forms carbamino compounds more readily, binding of O 2 to hemoglobin reduces its affinity for CO 2 (Haldane effect ) Haldane effect results from the fact that combination of O2 with Hb causes Hb to be a stronger acid. Thus displaces CO2 . CHLORIDE SHIFT Also know as the Hamburger's shift or Hamburger's phenomenon , named after Hartog Jakob Hamburger ) Since the rise in the HCO 3 – content of red cells is much greater than that in plasma as the blood passes through the capillaries, about 70% of the HCO 3 – formed in the red cells enters the plasma. The excess HCO 3 – leaves the red cells in exchange for Cl –

22. Regulation of Respiration Respiratory centers Central centers ; Dorsal respiratory group (inspiration) Ventral respiratory group (expiration and inspiration) Peripheral centres Baroreceptors peripheral chemoreceptors(carotid and aortic bodies) receptors in the lungs(J recptors )

23. Central respiratory center

24. Central respiratory center

25. Chemical Control of Respiration maintain proper concentrations of oxygen, carbon dioxide, and hydrogen ions in the tissues. CO2 or excess hydrogen ions in the blood mainly act directly on the respiratory center of the brain 02 acts almost entirely on peripheral chemoreceptors(carotid and aortic bodies) with PO2 of 60 down to 30 mm Hg Decreased Stimulatory Effect of Carbon Dioxide After the First 1 to 2 Days(

26. Nervous connections of respiratory centers Afferent pathway : Respiratory center receive afferent impulses from different parts of the body according to movements of thoracic cage and lungs. • From peripheral chemoreceptor and baroreceptor impulses are carried by glossopharyngeal and vagus nerves to respiratory center . Efferent pathway Nerve fiber from respiratory center leaves the brain and descend in anterior part of lateral column of spinal cord. • These nerve fibers terminate in the motor neurons in the anterior horn cells of the cervical and thoracic segments of spinal cord. • From motor neurons two sets of nerve fiber arise which supplies particular muscle: 1. Phrenic nerve fibers: supplies diaphragm 2. The intercostal nerve fibers: supplies intercostal muscles.

27. Factors affecting respiratory centers 1) Impulses from higher centers: impulses from higher center can stimulate or inhibit respiratory centers directly. 2) Impulses from ‘J’ receptors of lungs: • ‘J’ receptors are juxtacapillary receptors which are present in wall of the alveoli and have close contact with the pulmonary capillaries. • These receptors get stimulated during conditions like pulmonary edema, pulmonary congestion, pneumonia as well as due to exposure of exogenous and endogenous chemicals like histamine,serotonin . • Stimulation of ‘J’ receptor produces a reflex response called apnea . 4) Impulses from irritant receptors of lungs: • Irritant receptors are situated on the wall of bronchi and bronchioles of lungs. • They got stimulated by harmful chemicals like ammonia and sulfur dioxide. • Stimulation of irritant receptors produces reflex hyperventilation along with bronchospasm which prevents entry of harmful chemicals into the alveoli.

28. 4) Impulses from stretch receptors of lung

29. 5) Impulses from Proprioceptors: • Proprioceptors are the receptors which give response to the change in the position of different parts of the body. • This receptors are situated in joints, muscles and tendons. They get stimulated during exercise and sends impulses to the cerebral cortex. • Cerebral cortex in turn by activating medullary respiratory centres causes hyperventilation . 6) Impulses from Thermoreceptors : Thermoreceptors give response to change in the body temperature. • They are cutaneous receptors namely cold and warmth, When this receptors get stimulated they send signals to cerebral cortex • Cerebral cortex in turn stimulates respiratory centres and causes hyperventilation.

30. 7) Impulses from pain receptors: • Pain receptors give response to pain stimulus. • Like other receptors this receptors also send impulses to the cerebral cortex. • Cerebral cortex in turn stimulates the respiratory centers and causes hyperventilation . Peripheral chemoreceptors: The receptors are present in peripheral portions of the body They are very sensitive to reduction in partial pressure of oxygen. • Whenever, the partial pressure of oxygen decreases these chemoreceptors become activated and send impulses to inspiratory center and stimulate them. • Thereby increases rate and force of respiration and rectifies the lack of oxygen.