STRUCTURE AND FUNCTION Lecture—1 Dr.Zahoor Ali Shaikh 1

 Nasal passages (Nose)  Pharynx (Throat )  Larynx (Voice box)  Trachea –Divides into Right main bronchus and Left main bronchus  Bronchi  Bronchioles—large and small  Terminal Bronchioles  Respiratory Bronchioles  Alveolar Duct  Alveoli 2

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 Trachea divides into Right and Left Bronchi which enter Right and Left Lungs  Within each lung, bronchi continue to branch into narrow (small diameter),shorter and more numerous airways like branching of a tree.  Small braches are known as Bronchioles- lastly Terminal bronchioles 5

 At the end of Terminal Bronchioles, are Respiratory Bronchioles, Alveolar duct, Alveoli.  Tiny sacs(Alveoli) where gas exchange takes place between alveolar air and blood capillaries 6

 Trachea and large bronchi have cartilaginous rings that prevent these from compressing  Very small bronchioles have no cartilage to hold them open. Their wall has smooth muscle  This smooth muscle is innervated by Autonomic Nervous System, and is also sensitive to some hormones and local chemicals, which affect the air flow in small bronchioles 7

 1- Breathing Oxygen in, and breathing out Carbon dioxide  Helps in regulation of pH of blood (Acid –base balance), by adjusting the rate of removal of CO2. 8

 -- Cellular Respiration ( Internal Respiration)  --External Respiration  Cellular Respiration  It refers to intracellular metabolic process in the Mitochondria, which uses O 2 and produces CO 2 and energy ATP from food. 9

10 CELLULAR RESPIRATION

 On a mixed diet ( Carbohydrate, Fat, Protein ) O 2 used is 250 ml/min and CO 2 produced is 200 ml/min.  We use the Term Respiratory Quotient (RQ) CO 2 produced = 200 RQ= O 2 used = On a mixed diet RQ = O.8 -- RQ depends on the type of food used -- when Carbohydrate is used RQ= 1 -- when Fat is used RQ= when Protein used RQ=0.8 11

 Exchange of O 2 and CO 2 between External environment and cells of body. It has 4 steps.  1 – Gas exchange between the atmosphere and alveoli.  2- Exchange of O 2 and CO 2 between air in the alveoli and blood in pulmonary capillaries.  Transport of O 2 and CO 2 by the blood to the tissues.  4 – Exchange of O 2 and CO 2 between system capillaries and tissue cells 12

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 Helps in regulation of pH of blood (Acid –base balance), by adjusting the rate of removal of CO 2.  It is route for water loss and heat elimination.  Inspired air is humidified and warmed by the respiratory airways.  Respiratory pump – helps in venous return.  It enables speech, singing. 14

 It defends against inhaled foreign material.  Prostaglandins are inactivated in the lungs.  Conversion of angiotensinI to angiotensinII hormone, by ACE ( angiotensin converting enzyme ).  Nose– part of respiratory system, organ of smell. 15

 O 2 and CO 2 diffuse through alveoli.  Rate of diffusion depends on thickness of alveolar membrane, surface area and partial pressure of O 2 and CO 2.  Alveolar wall consists of single layer of alveolar epithelial cells [type 1]. 16

 Each alveolus is surrounded by a network of pulmonary capillaries, which is also single layer.  The interstitial space between an alveolus and capillary is very thin 0.5 µm which facilitates gas exchange.  Respiratory Membrane [Alveolar wall and Capillary wall]. 17

 Lungs contain about 500 million alveoli, each about 300 µm in diameter [surface area exposed between alveolar air and pulmonary capillary blood is about 75 m 2, size of tennis court].  In alveoli, there are Type II alveolar epithelial cells. They secrete Pulmonary Surfactant.  Pulmonary Surfactant is a phospholipoprotein complex that helps in lung expansion. 18

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 Also in alveolar lumen, present are alveolar macrophages which help in defense [Phagocytosis].  Pore of Kohn – are present between adjacent alveoli. Their presence permits air flow between adjacent alveoli. This process is called Collateral Ventilation. 21

 Two lungs - Right lung is divided into 3 lobes [upper, middle, lower] by oblique and transverse fissure. - Left lung is divided into 2 lobes [upper, lower and has lingula] by oblique fissure.  Lung – has alveoli, blood vessels and large quantities of elastic connective tissues.  Changes in lung volume and alveolar volume are brought about through changes in dimensions of thoracic cavity. 22

 The outer chest [Thorax] is formed by 12 pairs of curved ribs, which join the sternum anteriorly and thoracic vertebrae posteriorly.  Diaphragm – forms floor of thoracic cavity. Diaphragm is sheet of skeletal muscle that separates thoracic cavity from abdominal cavity. It is penetrated by esophagus and blood vessels.  In the lung and chest wall, there is considerable amount of elastic connective tissue. 23

 Pleura – separates each lung from the thoracic wall.  Pleura which surround each lung has two layers – Visceral Pleura [inner layer] which surrounds the lung and Parietal Pleura [outer layer] which is under thorax.  Interior of pleural sac(space between parietal and visceral pleura) is known as Pleural Cavity.  Surfaces of pleura secrete intrapleural fluid which lubricates surfaces as they slide on each other during respiratory movements.  Clinical application – pleurisy – [inflammation of pleura]. It causes pain during inspiration and expiration, and friction rub. 24

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 Ventilation - air flow into and out of lungs.  We will consider 1. Atmospheric [barometric] pressure 2. Intra-alveolar pressure or Intra-pulmonary pressure 3. Intra-pleural pressure 26

 It is pressure exerted by weight of air in the atmosphere on objects on Earth, as Earth surface.  At sea level, atmospheric pressure is 760mmHg.  Atmospheric [Barometric] pressure decreases at high altitude as layers of air decrease in thickness. 27

 It is pressure within alveoli. It is 760mmHg. It decreases slightly during inspiration and increases during expiration.  Intra-Pleural Pressure or Intra-thoracic Pressure  It is pressure within pleural sac.  It is pressure exerted from outside the lungs within thoracic cavity.  Intra-pleural pressure is -4 mmHg [756mmHg which is 4mmHg less than atmospheric pressure of 760mmHg] 28

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 Flow of air into and out off lung occurs due to cyclic changes in intra-alveolar pressure.  Intra-alveolar pressure is less than atmospheric pressure during inspiration.  Intra-alveolar pressure is greater than atmospheric pressure during expiration. 30

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 When thorax expands, the lungs also expand that is lungs follow the movements of chest wall. Transmural or Transpulmonary Pressure Gradient  It is the pressure difference between alveolar pressure and intra-pleural pressure in the lungs.  Intra-alveolar pressure equals to atmospheric pressure of 760mmHg.  Intra-pleural pressure is 756mmHg.  So there is greater pressure in the lungs as compared to pleura.  This Transmural pressure of +4mmHg causes stretching or opening of alveoli,therefore lungs are always forced to expand. 32

 Pneumothorax – air in the pleural cavity.  If there is chest injury, air rushes into the pleural cavity from high atmospheric pressure when chest is punctured e.g. broken rib or stab wound.  In Pneumothorax, pressure in the pleural cavity increases and causes the collapse of the lung.  Pleural Effusion – Abnormal collection fluid in the pleural cavity e.g. Tuberculosis 33

 Functional Anatomy of Respiratory System  Functions of Respiratory System  External and Cellular Respiration  Non-respiratory functions of respiratory system  Gas Exchange between alveoli and pulmonary capillaries  Respiratory membrane (Alveolar wall & capillary wall)  Lungs and Thoracic Cavity  Visceral, Parietal Pleura and Pleura Cavity  Atmospheric pressure, Intra-alveolar pressure and Intra- pleural pressure  Transmural or Transpulmonary Pressure and its importance  Applied Aspects – Pleurisy, Pneumothorax, pleural- effusion 34

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