Respiratory System

System

Respiratory

By: Rahul Malik

January,2016

Respiratory System

consists of: nose pharynx (throat) larynx (voice box) trachea (wind pipe) bronchi lungs Its parts can be classified acc. to either structure or function Structurally, Upper respiratory system include nose, pharynx & associated structures Lower respiratory system include larynx, trachea, bronchi & lungs

Functionally, The Conducting Zone: consists of series of interconnecting cavities & tube both outside & within lungs------ nose, pharynx, larynx, trachea, bronchi, bronchioles & terminal bronchioles------- that filter & moisten air & conduct it into lungs The Respiratory Zone: consists of tissues within lungs where gas exchange occurs------ respiratory bronchioles, alveolar ducts, alveolar sacs & alveoli------- main sites of gas exchange b/w air & blood Nose: divided into: External nose consists of a supporting framework of bone & hyaline cartilage covered with muscle & skin & lined by a mucous membrane The Frontal bone, nasal bones & maxillae form bony framework of external nose

The cartilaginous framework of external nose consists of: septal cartilage which form anterior portion of nasal septum lateral nasal cartilages inferior to nasal bones alar cartilages which form a portion of walls of nostrils On undersurface of external nose are two openings called external nares or nostrils Interior structures of external nose have three functions: warming, moistening & filtering incoming air detecting olfactory stimuli modifying speech vibrations as they pass th’ large, hollow resonating chambers

Internal Nose: large cavity in anterior aspects of skull that lies inferior to nasal bone & superior to mouth; lined with muscle & mucous membrane Anteriorly, internal nose merges with external nose & posteriorly it communicates with pharynx th’ two openings called internal nares or choanae space b/w internal nose called nasal cavity Respiratory functions of nose: warming filtering & cleaning humidification

Pharynx: extends from base of skull to level of 6th cervical vertebra lies behind nose, mouth & larynx can be divided into three anatomical regions: Nasopharynx Oropharynx Laryngopharynx Functions: Passageway for air & food Warming & humidifying Taste Hearing Protection Speech

Larynx: Voice box, short passageway that connects laryngopharynx with trachea lies in midline of neck anterior to esophagus & 4th th’ 6th cervical vertebrae Cartilages: composed of several irregularly shaped cartilages attached to each other by ligaments & membranes main cartilages are: 1 thyroid cartilage ---------------- 1 cricoid cartilage ----------------- Hyaline cartilage 2 arytenoid cartilages ------------ 1 epiglottis ------------- Elastic fibrocartilage Functions: Production of sound speech protection of lower respiratory tract passageway for air humidifying, filtering & warming

Trachea: or windpipe continuation of larynx & extends downwards to about level of 5th thoracic vertebra composed of three layers of tissues: outer layer consists of fibrous & elastic tissue & encloses cartilages middle layer consists of cartilages & bands of smooth muscle that wind round trachea in a helical arrangement inner lining consists of ciliated columnar epithelium containing mucus secreting goblet cells Functions: Support & patency: arrangement of cartilage & elastic tissue prevents kinking & obstruction of airway as head & neck move cartilage prevent collapse of trachea when internal pressure less than intrathoracic pressure

Mucociliary escalator: synchronous & regular beating of cilia of mucous membrane lining that walfts mucus with adherent particles upwards towards larynx where it is either swallowed or coughed up Cough Reflex: nerve endings in larynx, trachea & bronchi sensitive to irritation which generates nerve impulses conducted by vagus nerves to respiratory center in brain stem reflex motor response is deep inspiration followed by closure of glottis i.e. closure of vocal cords abdominal & respiratory muscles then contract & suddenly air released under pressure expelling mucus and/or foreign material from mouth Warming, humidifying & filtering

Bronchi: Two primary bronchi formed when trachea divides: Right primary bronchus Left primary bronchus Functions: control of air entry: Dia. of respiratory passages altered by contraction or relaxation of involuntary muscles in their walls thus regulating vol. of air entering lungs These changes controlled by autonomic nerve supply: parasympathetic stimulation causes constriction & sympathetic stimulation causes dilatation Following functions continue as in upper airways : warming & humidifying support & patency removal of particulate matter cough reflex

Lungs: Paired cone-shaped organs in thoracic cavity Separated from each other by heart & other structures in mediastinum Two layers of serous membranes; collectively called pleura membrane enclaose & protect each lung Superficial layers called parietal layer lines of thoracic cavity; deep layer, visceral pleura covers lung themselves Between visceral & parietal pleura, a small space pleural cavity, which contains small amount of lubricating fluid secreted by membranes Pleural fluid reduces friction between membrane; allowing them to slide easily over one another during breathing Pleural fluid also causes two membranes to adhere to one another

Interior of lungs: Lungs composed of bronchi & smaller air passages, alveoli, connective tissue, blood vessels, lymph vessels & nerves, all embedded in an elastic connective tissue matrix Area between lungs is mediastinum Alveoli: Around circumference of alveolar ducts are numerous alveoli & alveolar sacs Wall of alveoli consists of two types of alveolar epithelial cells Type I alveolar cells simple squamous epithelial cells that form a nearly continous lining of alveolar walls, more in no. Type II alveolar cells also called septal cells, fewer in no. & found between Type I alveolar cells Type I alveolar cells-------- main sites of gas exchange Type II contain microvilli, secrete alveolar fluid which keeps surface between cells & air moist

Respiration: Exchange of gases between body cells & environment Involves two main processes: Breathing (Pulmonary Ventilation): Movement of air into & out of lungs Exchange of gases takes place: In lungs: external respiration In tissues: internal respiration Breathing: supplies O2 to alveoli & eliminates CO2

Cycle of Breathing: Average Respiratory rate is 12 to 15 breaths/min. Each breath consists of 3 phases: Inspiration Expiration Pause

Lung Volumes & Capacities: In normal quiet breathing there are about 15 complete respiratory cycles/min. As exchange of gases takes place only across walls of alveolar ducts & alveoli, remaining capacity of respiratory passages is called Anatomical dead space (about 150 mL) Tidal Volume (TV): amount of air passing into & out of lungs during each cycle of breathing (about 500 mL) at rest Inspiratory Reserve Volume (IRV): extra volume of air that can be inhaled into lungs during maximal inspiration i.e. over & above normal TV Inspiratory Capacity (IC): amount of air that can be inspired with maximum effort, consists of Tidal Volume + IRV Functional Residual Capacity (FRC): amount of air remaining in air passages & alveoli at end of quiet expiration Tidal air mixes with this air, causing relatively small changes in composition of alveolar

Expiratory Reserve Volume (ERV): largest volume of air which can be expelled from lungs during maximal expiration Residual Volume (RV): cannot be directly measured but is volume of air remaining in lungs after forced expiration Vital capacity (VC): maximum volume of air which can be moved into & out of lungs VC= TV+IRV+ERV Alveolar Ventilation: volume of air that moves into & out of alveoli/min. Alveolar Ventilation = (TV-anatomical dead space) X respiratory rate = (500-150)mL X 15/min. = 5.25 l/min.

Exchange of gases: although breathing involves alternating process of inspiration & expiration, gas exchange at respiratory membrane & in tissues is continuous & ongoing process External respiration: exchange of gases by diffusion between alveoli & blood in alveolar capillaries across respiratory membrane Internal respiration: exchange of gases by diffusion between blood in capillaries & body cells Transport of gases in bloodstream: Transport of blood O2 & CO2 essential for internal respiration to occur Oxygen: Carried out in blood in chemical combination with Hb as OxyHb (98.5%)

Carbon dioxide: One of waste products of metabolism Excreted by lungs & transported by 3 mechanisms: As bicarbonate ions (HCO3

-) in plasma (70%) Some carried in erythrocytes, loosely combined with Hb as carbaminoHb (23%) Some dissolved in plasma (7%) Control of Respiration: Normally involuntary Voluntary control exerted during activities such as speaking & singing but overridden if blood CO2 rises (hypercapnia)