Respiration - Human 1

At the end of the lectures on respiration you should be able to, 1. Describe events in the respiratory processes 2. Discuss the mechanism of lung ventilation in human 3. Discuss the factors that control the respiration. 2

Three basic processes in respiration 1. Pulmonary ventilation 2. External respiration 3. Internal respiration 3

1. Pulmonary ventilation The process by which gases are exchanged between the atmosphere and the lung alveoli (breathing) 4

2. External respiration Exchange of O 2 & CO 2 between the alveoli of lungs & pulmonary blood capillaries 5

3. Internal respiration Exchange of O 2 & CO 2 between tissue capillaries & tissue cells 6

Why do we need continuous supply of oxygen to the tissues? Why do we need to get rid of carbondioxide frequently from the body? 7

Pulmonary ventilation Air flows between the atmosphere & lung alveoli through a pressure gradient Breath in when the pressure inside the lung is less than the atmospheric pressure Breath out when the pressure inside the lungs is greater than the atmospheric pressure 8

Muscles involved in pulmonary ventilation - Inspiration Normal inspiration External intercostals & diaphragm (contraction) Deep inspiration External intercostals & diaphragm (contraction) Sternocleidomastoid & scalenus (Contraction elevates sternum & superior ribs)) 9

Muscles involved in pulmonary ventilation - expiration Normal expiration External intercostals & diaphragm (relaxation) Deep expiration External intercostals & diaphragm (relaxation) Internal intercostals & abdominal muscles (Contraction) 10

Clavicle 11

Events in normal inspiration 1. Contraction of the diaphragm (become flat, lowering the dome) Increase the vertical diameter of the thoracic cavity At the same time, External intercostals contract ( ribs pulled upward, sternum pushed forward)- Increase anterior-posterior diameter of the thoracic cavity 13

2. Increase in the thoracic cavity causes drop in intrapleural pressure from 756 to 754 mm Hg (far below the alveolar pressure) 3. The walls of the lung are sucked outward by the partial vacuum 4. Lung volume increases, alveolar pressure drop from 760 to 758 mm Hg 5. Air moves from atmosphere to lungs due to pressure gradient until pressure equals 14

Deep inspiration (active process) Contraction of sternocleidomastoid (elevates the sternum), contraction of scalenus ( elevates superior ribs) Further increase in volume of thoracic cavity, further decrease in alveolar pressure More air comes in from atmosphere to the lungs 16

Events in normal expiration 1. External intercostals relax, the ribs move downwards & sternum lowers(decrease anterior-posterior volume of the thoracic cavity) At the same time diaphragm relaxes (Decrease vertical diameter) Volume of thoracic cavity returns to resting stage 17

2. Intrapleural pressure increases to 758 mm Hg) 3. The walls of the lungs are not sucked out 4. Lung volume decrease 5. Alveolar pressure increases to 762 mm Hg 6. Air moves from the lungs to the atmosphere until pressure become equal 18

Deep expiration (active process) Contraction of internal intercostals (ribs move downward) Contraction of abdominal muscles (compress the abdominal organs, forcing the diaphragm upward) Further decrease in volume of thoracic cavity, further increase in alveolar pressure More air moves out from lungs to atmosphere 20

Factors that prevent collapse of alveoli following expiration 1. Intrapleural pressure is always lower than the alveolar pressure (keeps alveoli slightly inflated, otherwise, elastic alveoli may recoil inward and collapse at the end of expiration.) 2. Thin layer of Surfactant on alveolar walls reduce surface tension, prevent them from sticking together after the expiration (Phopholipid complexed with a protein produced by alveolar walls) 22

Pulmonary air volumes & capacities Respiratory rate of healthy adult 12-15 respirations/min Tidal volume (500 ml) Minute volume of respiration tidal volume X normal breathing rate 500 ml X 12 /min = 6000ml/min 23

Inspiratory reserve volume (IRV) 3100ml Expiratory reserve volume (ERV) 1200 ml Residual volume (RV) 1200 ml Inspiratory capacity =Tidal volume + IRV Functional residual capacity = ERV + RV Vital capacity (VC) IRV + tidal volume +ERV = 4800 ml Total lung capacity VC + residual volume = 6000 ml 24

Respiratory capacities depends on sex, age, health etc. Lung functioning assessed by measurement of respiratory volumes & capacities using spirometer 26

External respiration 1. During inspiration, atmospheric air enters alveoli po 2 = 105 mm Hg, pco 2 = 40 mm Hg 2. Deoxygenated blood is pumped from pulmonary arteries, to pulmonary capillaries overlying the alveoli po 2 = 40 mm Hg, pco 2 = 45 mm Hg 3. Diffusion of O 2 from alveoli to blood & CO 2 from blood to alveoli until they come to equilibrium, po 2 = 100 mm Hg, pco 2 = 40 mm Hg 27

CO 2 that diffuse into the alveoli is eliminated from the lungs through expiration 28

Effects of altitude on external respiration As a person goes up in altitude, the atmospheric p O 2 drops, alveolar p O 2 drops accordingly, & less O 2 diffuse into blood Sea level p O 2 = 160 mm Hg 20,000 feet = 73 mm Hg 50,000 feet = 18 mm Hg Low O 2 conc in blood, short breath, dizziness 29

Internal respiration 1. p O 2 & p CO 2 of oxygenated blood in tissue capillaries entering the tissues po 2 = 100 mm Hg, pco 2 = 40 mm Hg 2. p O 2 & p CO 2 within cells, po 2 = 40 mm Hg, pco 2 = 45 mm Hg 3. Diffusion of O 2 from blood to cells & CO 2 from cells to capillary blood through intercellular fluid until they come to equilibrium 30

Transport of respiratory gases in the blood 31

Oxygen transport Under normal resting conditions each 100 ml of oxygenated blood contains 20 ml of oxygen 3% dissolved in plasma 97% combination with hemoglobin (4 molecules of oxygen / Hb molecule, 4 Fe 2+ ) 32

Factors that determine how much O 2 combines with Hemoglobin Partial pressure of O 2 (p O 2 ) ph, p CO 2 Temperature Pollutants diphosphogycerate 33

Hb and Oxygen Fully saturated Hb = all Hb is in HbO 2 (oxyhemoglobin) Partially saturated Hb= Hb + HbO 2 When po 2 is high (pulmonary capillaries) Hb binds with large amounts of O 2 = almost fully saturated (98%) When po 2 is low (tissue capillaries) Hb does not hold as much as O 2 (partially saturated, 75%), O 2 is released for diffusion into cells 34

P O 2 mm Hg % Hb saturation 10 20 (deoxy. blood when active) 30 40 (deoxygenated blood at rest) 50 60 70 80 90 100 (oxygenated blood) 14 35 57 75 85 90 93 95 97 98 35

O 2 / Hb dissociation curve 36

Effects of ph and p CO2 At low ph, O 2 splits more readily from Hb, when H + binds to Hb, they alter the structure of Hb, decrease its O 2 carrying capacity, more O 2 available to tissues Low blood ph may be due to lactic acid accumulation, high CO 2 levels in the blood When p CO 2 in the blood is high, affinity of Hb for O 2 becomes low, more O 2 available to tissues 38

Effects of temperature Within limits as temperature increases, amount of O 2 released from HbO 2 increases 40

Active cells need more O 2, active cells liberate more heat and acid, in turn, stimulate oxyhemoglobin to release its O 2 42

CO and Hb CO can combine with Hb more strongly, p CO 0.5 mm Hg (0.1%)will combine with half the Hb molecules The oxygen carrying capacity of blood is reduced Hypoxia, CO poisoning 43

NO 2- and Hb Reduce oxygen carrying capacity of blood Fe2+ Fe3+ hypoxia 44

Diphosphoglycerate Metabolite of glycolysis, found in RBCs Decrease affinity of O 2 for Hb, help to release O 2 from Hb. DPG higher in persons living in high altitudes 45

Transport of CO 2 in blood Under normal resting conditions, each 100 ml of deoxygenated blood contains 55 ml of CO 2 7 % dissolved in plasma 23% carbaminohemoglobin Hb + CO 2 Hb.CO 2 70% bicarbonate ions CO 2 + H 2 O H 2 CO 3 H+ + HCO 3-46

Summary Pulmonary ventilation, external respiration, internal respiration Lung volumes and capacities Transport of O 2 & CO 2 in blood 47