RESPIRATORY SYSTEM(STRUCTURE AND FUNCTION)

Dr. Mohammed Sharique Ahmed Quadri Assistant Prof. physiology

Al maarefa college

بسم الله الرحمن الرحيم

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Anatomy Of Respiratory System

• 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

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Important Points

• 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

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Important Points [Cont]

• 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

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Important Points [Cont]• 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

Important Points [Cont]

• Sympathetic stimulation causes bronchodialation by acting on β2(adrenergic) receptors.

• Parasympathetic stimulation causes bronchoconstriction by acting on muscarinic receptors

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FUNCTIONS OF RESPIRATORY SYSTEM

• 1- Breathing Oxygen in, and breathing out Carbon dioxide

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RESPIRATION TYPES

• Cellular Respiration ( Internal Respiration) • External Respiration

• Cellular Respiration – It refers to intracellular metabolic process in the

Mitochondria, which uses O2 and produces CO2 and energy ATP from food.

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CELLULAR RESPIRATION

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CELLULAR RESPIRATION (CONT)

• On a mixed diet ( Carbohydrate, Fat, Protein ) O2 used is 250 ml/min and CO2 produced is 200 ml/min.

• We use the Term Respiratory Quotient (RQ) CO2 produced = 200

RQ = O2 used = 250

- 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= 0.7-- when Protein used RQ=0.8

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EXTERNAL RESPIRATION

• Exchange of O2and CO2 between External environment and cells of body. It has 4 steps.

• 1 – Gas exchange between the atmosphere and alveoli.

• 2- Exchange of O2 and CO2 between air in the alveoli and blood in pulmonary capillaries.

• Transport of O2 and CO2 by the blood to the tissues.

• 4 – Exchange of O2 and CO2 between system capillaries and tissue cells

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Non Respiratory Functions of Respiratory System

• Helps in regulation of pH of blood (Acid –base balance) , by adjusting the rate of removal of CO2.

• 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 .

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Non Respiratory Functions of Respiratory System [cont]

• 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.

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Gas Exchange Between Alveoli & Pulmonary Capillaries

• O2 and CO2 diffuse through alveoli.

• Rate of diffusion depends on thickness of alveolar membrane, surface area and partial pressure of O2 and CO2.

• Alveolar wall consists of single layer of alveolar cells [type I].

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Gas Exchange Between Alveoli & Pulmonary Capillaries [cont]

• 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].

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Gas Exchange Between Alveoli & Pulmonary Capillaries [cont]

• 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 m2, size of tennis court].

• In alveoli, there are Type II alveolar cells . They secrete Pulmonary Surfactant.

• Pulmonary Surfactant is a phospholipoprotein complex that helps in lung expansion.

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Gas Exchange Between Alveoli & Pulmonary Capillaries [cont]

• 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.

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Lungs & Thoracic Cavity

• 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. • Lungs – 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.

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Lungs & Thoracic Cavity [cont]

• 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.

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Lungs & Thoracic Cavity [cont]

• 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.

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References

• Human physiology by Lauralee Sherwood, seventh edition

• Text book physiology by Guyton &Hall,11th edition

• Text book of physiology by Linda .s contanzo,third edition

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