The Respiratory System Dr. Suroor Mohamed Lecture one respiratory physiology
Objectives Function of the respiratory tract. Non respiratory function of the lung The passages of air through which passes from exterior to the alveoli Factors that affect bronchial tone. Define partial pressure and calculate the partial pressure of each of the important gases in the atmosphere at sea level.
Why do we respire?Living organisms need a constant supply of energy (continuous use of energy by the body)Oxidation (O2 ) of food substances →Energy + CO2 + H2OThe body can store only 1500 mL of O2 at a timeMaintain life only for 5 minutesMyocardium and brain are very much dependent on O2 for their functioning Cessation of blood flow to cerebral cortex loss of function within 5 seconds loss of consciousness in 10-20 seconds Irreversible changes in 3-5 minutes. The normal adult human lung weighs about 1000g and consists of about 50% blood and 50% tissue by weight. About 10% of the total lung volume is composed of various types of conducting airways and some connective tissue. The remaining 90% is the respiratory or gas exchange portion of the lung, composed of alveoli and supporting capillaries
Respiration is the collective process of absorption of O2 from the environment and oxidation of food materials in the cells with the release of water, CO2 , and energy and elimination of CO2 into the environment. External respiration Internal respiration
Properties of gases: (partial pressure) Air is a mixture of gases Dry atmospheric air ( N2=79%, O2=21%, CO2=O.O4%) Atmospheric pressure (at sea level) =760mmHg Dalton's law of partial pressures :The pressure exerted by any one gas in a mixture of gases (its partial pressure) is equal to the total pressure times the fraction of the total amount of gas it represent
Partial pressure = Total pr Fractional Gas Conc. PO2 (0.21 760) =160 mmHg PN2 (0.79 760) = 600 mmHg PCO2 (0.0004 760) = 0.3mmHgThe water vapor in the air percentages partial pressure of gases Inspired air (PH20 = 5.7 mmHg)PO2 = 158 mmHgPN2 = 596 mmHg PCO2 = 0.3mmHg
Air equilibrated with water is saturated with water vapor, and inspired air is saturated by time it reaches the lungs. The PH2O at body temp is 47mmHg. Gas diffuse from area of high pr to area of low pr
Respiratory parts Upper tract (Nasal cavity, Pharynx and Larynx) •Lower tract (Trachea, Bronchi, and Bronchioles) The gas exchange airway is the functional unit of the lung.It consists of the respiratory bronchioles, alveolar ducts, and alveolar sacs, which collectively comprise the terminal respiratory unit
FUNCTIONS OF THE RESPIRATORY TRACTNasal CavityAir conditionings function of nose (warming, humidification, and filtration of inhaled air): pollutants > 5 μm size are filtered by the hair and cilia present in the nasal cavity and are expelled out by sneezing reflex. Olfactory functionParanasal sinuses modify speech sounds
Pharynx Nasopharynx carries air from nose to pharynx. Oropharynx is the common passage for food & air. Opening of the eustachian tube into nasopharynx. Pharynx houses the tonsils (immunity). Provides a resonating chamber for speech sounds. Larynx Voicebox (vocal cords) Closure of glottis (swallowing, vomiting) help to prevent entry of food into trachea.
Non respiratory functions of lungs1) Protective function: Particles <5 μm in size enter the lung and adhere to the lining mucus → expelled out by cough reflex and also by the escalator action of ciliaKartagener's syndrome (congenital disease) the motility of the cilia is defective → collection of secretions in the lung → infection → bronchiectasisSame condition produced by cigarette smoking (ciliotoxins)The neutrophils, lymphocytes and alveolar macrophages present in the alveoli defend against bacteria and virusesLungs synthesize immunoglobulins like IgA for its own defense and are present in bronchial mucus
2) Acid-base balanceLungs play an important role in maintaining the body pH by regulating the CO2 content of blood3) Anticoagulant function and filtration of bloodLungs contain mast cells → heparin (anticoagulant)Small emboli present in blood are removed from the circulation4) Regulation of blood pressureACE (angiotensin converting enzyme )secreted by the endothelial cells of the pulmonary capillaries5) Regulation of blood volumeLungs act as a storage organ for blood (pulmonary circulation is a low-pressure system and the vessels are highly distensible). About 300 mL of blood can be diverted to the systemic circulation in times of need.
6) Temperature regulation Some amount of heat is lost from the body during expiration 7) Endocrine function Lungs synthesize hormones like PG prostoglandin , serotonin, histamine etc. PGE2 helps to constrict the patent ductus arteriosus in the postnatal period In asthma or anaphylaxis, lungs release substances like histamine, bradykinin, prostaglandin, slow reacting substance etc., into circulation, which are responsible for the reactions of anaphylaxis 8) Degradation of substances Bradykinin, norepinephrine, serotonin, PG are degraded by the lungs
FUNCTIONAL ANATOMY OF THE RESPIRATORY SYSTEMLungs (gas exchanging organs)Pump that ventilates the lungsThe chest wallThe respiratory muscles (↑& ↓thoracic cavity size )Areas in the brain than control the musclesTracts and nerves (brain →muscles)
Trachea-bronchial tree: Trachea:Inner diameter ≈1.5cmLength ≈ 11cmLined by respiratory epithelium15-20 incomplete C-shaped cartilageThe trachealis muscle contracts during coughing →↓size of the lumen of the trachea →↑ rate of air flow The esophagus lies posteriorly to the trachea. The cartilaginous rings are incomplete to allow the trachea to collapse slightly so that food can pass down the esophagusTrachea splits into two primary (main) bronchi
Trachea 2 Primary (main) bronchi (3) (2) Secondary (lobar) bronchi (10) (8)Tertiary (segmental) bronchi Primary bronchioles (< 1mm ) Terminal bronchioles several Respiratory bronchioles 2 to 11 Alveolar ducts 5 or 6 Alveolar sacs alveoli Right primary bronchus is shorter, wider, and more vertically oriented than the left primary bronchus. •Foreign particles are more likely to lodge in the right primary bronchus The left lung has two & the right lung has three Branches into tertiary bronchi
Cartilage
GlandsCilia
Smooth muscle
Trachea
Ring
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1◦ Bronchi Ring
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2◦ Bronchi Plate
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3◦ Bronchi Plate
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Bronchioles
No
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Terminal bronchioles
No
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Respiratory bronchioles
No
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Lined by 2 types of epithelial cellsType I pneumocytes (flat cells) → gas exchange Type II pneumocytes (granular cells) → secrete surfactantOther cells Pul. alveolar macrophages Mast cells Alveoli 300 million alveoli in both lungs Diameter of a single alveolus =0.3mm Total surface area of alveoli of both lungs (70 m2)
Between the trachea & the alveolar sacs, the airways divide 23timesIncreases the total cross sectional area of the airways, from 2.5 cm2 in the trachea to 11800 cm2 in the alveoli →↓the velocity of air flow in the small airways Conducting zone: The 1st 16 generations of passages Made up of bronchi, bronchioles, terminal bronchiolesTransport gas from and to the exteriorRespiratory zone: The remaining 7 generations of passagesGas exchange occursRespiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli
Pleura Pleural cavity Pleural fluid is a serous fluid is produced mostly by the parietal pleura and reabsorbed by pulmonary capillaries the lymphatic system. Few millilitres of pleural fluid is always present in the pleural cavity
Rate of production > rate of reabsorption → accumulation of fluid (pleural effusion)Functions of pleural Fluid1) Pleural fluid keeps the two pleural layers together2) Acts as a lubricant and helps in the sliding movements between the two layers.
Bronchial tone1) Nervous control: bronchi & bronchioles innervated byAutonomic nervous system:Parasympathetic NS → Ach → muscurinic receptors →bronchoconstriction and ↑ secretionSympathetic NS → Nad → β2 → bronchodilation and ↑ secretion: 1 (↓ secretion) Substance P: secreted by some nerve ending to lung → bronchoconstriction and mucus secretion.2) Homurol control:Histamine and slow reacting substance of anaphylaxis released from mast cells →↑bronchiolar tone.Leukotrienes → bronchoconstriction (Leukotrienes receptors blocker useful in bronchial asthma)
3) Circadian rhythm: maximum constriction at about 6:00AM and maximum dilation at about 6:00PM. 4) Irritants and chemicals e.g. sulfur dioxide produces reflex bronchoconstriction that is mediated via cholinergic pathways by stimulation of sensory receptors in the airways. 5) Cool air causes bronchoconstriction, exercise also causes bronchoconstriction (increased respiration cools the airways).