Ch-1 Respiratory System

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RESPIRATORY

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SYSTEM

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Chapter 1

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Objective :-

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Anatomy

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Physiology

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Overview

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Respiratory Diseases

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Respiration is the process of making energy available to organisms and their living cells through enzyme controlled catabolic breakdown of organic molecules, especially hexose sugars.

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Types of Respiration

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The classification depends upon the availability of oxygen and thus it has been divided into two categories. (a) Aerobic Respiration: It takes place in presence of oxygen and the stored food (respiratory substrata) gets completely oxidised into carbon dioxide and water as end products. (b) Anaerobic-respiration: It takes place in absence of oxygen and stored food is incompletely oxidised and instead of carbon dioxide and water certain other compounds are also formed. This type of respiration is of rare occurrence but common among micro organisms like yeasts.

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Humans perform Aerobic Respiration

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Respiratory System - 1

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Human Respiratory System

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It consists of a respiratory tract, a pair of lungs and structures involved in ventillation. Respiratory tract consists of external nares, nasal cavity, internal nares, nasopharynx, larynx, trachea, bronchi and bronchioles.

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External Nares (Nostrils): They are a pair of slit-like openings present on the lower end of nose. Nasal Cavity: It is situated between palate and cranium. Nasal cavity is divisible into two nasal chambers by a nasal septum. Each nasal chamber has three parts. Vestibule: It is lower small part just above the external nares which is lined by skin and bears hair as well as oil glands. Hair help in filtering out dust particles from incoming air.

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Lung: A pair of conical spongy elastic lungs of pinkish to salty grey colour occur inside air tight thoracic cavity. Left lung is slightly narrower and longer than the right one. Right lung has three lobes, left lung has two lobes. Each lobe is divided internally into segments and segments into lobules. A lobule receives a terminal bronchiole. Terminal bronchiole produces a few respiratory bronchioles. A respiratory bronchiole give rise to 2-11 alveolar ducts, each of which ends in an alveolar sac. The latter has a number of small pouches named alveoli or air sac. Blood capillaries occur on the surface of alveoli for gaseous exchange. Diaphragm: It is a membranouus musculo-tendinous partition between thorax and abdomen. Phrenic muscles attach diaphragm to ribs and vertebral column. Contraction of muscles straighten the diaphragm to increase thoracic cavity. There are two sets of Intercostal Muscles: (i) external intercostal for normal inspiration and expiration (ii) internal intercostal for forceful expiration.

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THE MECHANISM OF BREATHING

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INSPIRATION: Inspiration is the active part of the breathing process, which is initiated by the respiratory control centre in medulla oblongata (Brain stem). Activation of medulla causes a contraction of the diaphragm and intercostal muscles leading to an expansion of thoracic cavity and a decrease in the pleural space pressure. The diaphragm is a dome-shaped structure that separates the thoracic and abdominal cavities and is the most important muscle of inspiration. When it contracts, it moves downward and because it is attached to the lower ribs it also rotates the ribs toward the horizontal plane, and thereby further expands the chest cavity. In normal quite breathing the diaphragm moves downward about 1 cm but on forced inspiration/expiration total movement could be up to 10 cm. When it is paralysed it moves to the opposite direction (upwards) with inspiration, paradoxical movement.

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The external intercostal muscles connect adjacent ribs. When they contract the ribs are pulled upward and forward causing further increase in the volume of the thoracic cavity. As a result fresh air flows along the branching airways into the alveoli until the alveolar pressure equals to the pressure at the airway opening.

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The external intercostal muscles connect adjacent ribs. When they contract the ribs are pulled upward and forward causing further increase in the volume of the thoracic cavity. As a result fresh air flows along the branching airways into the alveoli until the alveolar pressure equals to the pressure at the airway opening.

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Expiration

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Expiration is a passive event due to elastic recoil of the lungs. However, when a great deal of air has to be removed quickly, as in exercise, or when the airways narrow excessively during expiration, as in asthma, the internal intercoastal muscles and the anterior abdominal muscles contract and accelerate expiration by raising pleural pressure.

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COUPLING OF THE LUNGS AND THE CHEST WALL

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The lungs are not directly attached to the chest wall but they change their volume and shape according to the changes in shape and volume of the thoracic cavity. Pleura covering the surfaces of the lungs (visceral) or the thoracic cavity (parietal) together with a thin (20 μm) layer of liquid between them create a liquid coupling.

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OVERVIEW

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GAS EXCHANGE

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Regulation of Breathing

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1. Breathing is so important that your body will not let you have complete control of it. 2. Breathing is controlled by the medulla oblongata in the lower part of the brain, though, obviously, you can temporarily suppress this reflex. The diving reflex (not breathing when your face is submerged – particularly in cold water) is found even in babies, and allows them to be bathed and swim (under supervision) with complete security. 3. Although you can hold your breath for a while, you cannot die this way. You can only hold your breath until you lose consciousness - then the brain takes control and normal breathing resumes. 4. The concentration of oxygen in the blood has little effect on breathing rate and you can suffocate in a low oxygen environment (e.g. on a mountain or in a plane when the pressurisation fails.) 5. Breathing is controlled by the levels of CO2 and H+ ions in the blood. These are measured in two places in the neck (carotid arteries) and just outside the heart (aorta). These regions have swollen areas known as sinuses which also measure blood pressure. Nerves lead from these regions to the hypothalamus (hind-brain), which controls most aspects of homeostasis.

Tidal volume (TV) The tidal volume Is the amount of air moved In 500 ml a normal breath (Inspired or expired) at rest

lnsplratory reserve The lnsplratory reserve volume ls the 3,000 ml volume (IRV) amount of air that can be forcefully Inspired

beyond the amount Inspired In a normal breath at rest.

Expiratory reserve The expiratory reserve volume Is the 1,100 ml volume (ERV) amount of air that can be forcefully expired

beyond the amount expired In a normal breath at rest.

Residual volume The residua I volume Is the amount of air In 1,200 ml (RV) the lungs that cannot be moved.

Functional residual The functional residual capacity Is the 2,300 ml ca paclty (FRC) amount of air remaining In the lungs after

the expiration of a normal breath at rest. FRC = ERV + RV.

lnsplratory capacity The lnsplratory capacity ls the maximum 3,500 ml (IC) amount of air that can be Inspired after

the expiration of a normal breath at rest. IC =TV+ IRV.

Vital capacity (VC) Vltal capacity ls the maximum amount of air 4,600 ml that can be moved. VC =IC+ FRC.

Total lung capacity The total lung capacity ls the maximum 5,800 ml (TLC) amount of air the lung can hold.

TLC= VC + RV.

iTyP.ical valu~ I Volume or capacit~ Definition

TABLE 12.1 Lung volumes and capacities

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Lung Volumes

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Ch-1 Respiratory System

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