Respiratory system

By

Dr Shamshad Begum .Loni

Lecture notes

15-2

15.1 The respiratory tract

• Overview– Inspiration- breathing in– Expiration- breathing out– Ventilation-encompasses inspiration and expiration– Functions

• External respiration

– Exchange of gases between air and blood

• Internal respiration

– Exchange of gases between blood and tissue fluid

• Transport of gases

The respiratory tract

The respiratory tract cont’d.

• The nose– Part of upper respiratory tract– Contains 2 nasal cavities

• Communicate with sinuses

• Lined by mucous membrane

– Bony ridges increase surface area

• Functions

– Warms air- heat from vessels

– Cleanses air-coarse hairs and mucus

– Humidifies air-wet surfaces of membrane

• Olfactory receptors-on cilia high up in cavities

• Lacrimal glands drain into nasal cavity

The respiratory tract cont’d.

• The pharynx– Connects nasal and oral cavities to larynx– 3 divisions

• Nasopharynx– Nasal cavities open posterior to soft palate

• Oropharynx– Where oral cavity opens– Uvula projects into oropharynx

• Laryngopharynx– Opens into larynx

– Tonsils form a protective ring– Larynx and trachea are normally open– Esophagus is normally closed

The path of air

The respiratory tract cont’d.

• The larynx– Passageway for air between pharynx and trachea– Vocal folds found here

• Folds of mucosa

– Glottis-opening between folds

• Supported by elastic ligaments

• Vibrate during exhalation

– Pitch controlled by tension

» Higher tension-higher pitch

– Loudness controlled by amplitude of vibration

• Epiglottis

– Prevents food from entering during swallowing

Placement of the vocal chord

The respiratory tract cont’d.

• The trachea– Connects larynx with primary bronchi– Supported by C-shaped cartilage rings

• Keeps trachea patent yet flexible

– Lined with pseudostratified columnar epithelium• Ciliated

• Goblet cells-produce mucus

• Combined action-mucociliary apparatus

– Mucus traps debris

– Cilia sweeps mucus and debris upward

• Smoking paralyzes the mucociliary apparatus and destroys the cilia in the trachea.

– Tracheostomy-artificial opening to open airway

The respiratory tract cont’d.

• The bronchial tree– Right and left primary bronchi

• Resemble trachea in structure

– Branch to secondary bronchi• Eventually lead to bronchioles

– as airways become smaller, walls become thinner• Lack cartilage rings

– Each bronchiole leads into terminal (respiratory) bronchioles• Respiratory bronchioles surrounded by alveoli-air sacs

Gas exchange in the lungs

The respiratory tract cont’d.

• The lungs– Divided into lobes

• Right lung has 3

• Left lung has 2

– Each lobe is divided into lobules• Lobule has a bronchiole serving many alveoli

– Lungs are covered by serous pleural membrane• Double-layered

• Visceral pleura-on lung surfaces

• Parietal pleura-on walls of thoracic cavity

• Surface tension holds the 2 pleural layers together

The respiratory tract cont’d.

• The alveoli, tiny air sacs of the lung– Simple squamous epithelium– Surrounded by blood capillaries– Gas exchange occurs across alveolar wall and capillary wall

• Oxygen diffuses into blood• Carbon dioxide diffuses into alveoli

– Alveoli must stay open to receive air• Surface tension has tendency to make them collapse• Surfactant-soapy-like lipoprotein

– Produced in lungs– Lowers surface tension– Prevents collapse

• Infant respiratory distress syndrome-premature babies– Lack surfactant; alveoli prone to collapse

15.2 Mechanism of breathing

• Respiratory volumes– Tidal volume

• Amount of air normally moving in and out with each breath during relaxed breathing.

• Average is 500 ml

– Vital capacity• Maximum volume of air that can be moved in and out in deep

breathing.

• Illness can affect vital capacity

– Inspiratory reserve volume• Forced inhalation, maximum amount of air forcibly inspired above

tidal volume

• Normally about 2,900 ml

Mechanism of breathing cont’d.

• Respiratory volumes cont’d.– Expiratory reserve volume

• Forced expiration, maximum amount of air forcibly expired above tidal volume

Normally about 1,400 ml

– Residual volume• Amount of air always remaining in lungs

• Normally about 1,000 ml

• Not useful for gas exchange

– Oxygen depleted

– The vital capacity is tidal volume + inspiratory reserve volume + expiratory reserve volume

Vital capacity

Mechanism of breathing cont’d.

• Respiratory volumes cont’d.– 30% of inspired air never reaches alveoli

• Fills respiratory tree

– Nasal cavities, trachea, bronchi, bronchioles

• Dead space air

– To increase respiratory efficiency• Increase depth and not rate of breathing

• Slow, deep breaths

• Maximizes air reaching alveoli

Mechanism of breathing cont’d.

• Inspiration and expiration– To understand ventilation it is important to remember the

following• Continuous column of air from pharynx to alveoli

• Lungs lie in the sealed-off thoracic cavity

– Rib cage forms top and sides

» Intercostal muscles are between ribs

– Diaphragm forms the floor

• Lungs adhere to the thoracic wall due to surface tension between pleural membranes

Mechanism of breathing cont’d.

• Inspiration– ACTIVE phase– Diaphragm and external intercostal muscles contract

• Rib cage elevates

• Increases volume of thoracic cavity

• Lungs expand

• Creates partial vacuum

– Intraalveolar pressure drops below atmospheric pressure– Air flow into lungs down pressure gradient

Inspiration versus expiration

Mechanism of breathing cont’d.

• Expiration– PASSIVE phase

• Diaphragm and external intercostal muscles relax

• Rib cage drops

• Elastic recoil of lungs and thoracic wall

• Decreases volume of thoracic cavity

• Intraalveolar pressure rises above atmospheric pressure

• Air rushes out

– Forced breathing• Abdominal muscles contract

• Pushes viscera upward against diaphragm

• Pushes air out

Mechanism of breathing cont’d.

• Control of ventilation– Normal rate- 12-20 breaths per minute– Controlled by respiratory center

• In medulla oblongata of brain

• Inspiration

– Sends out impulses to diaphragm and external intercostals

– Causes contraction

• Expiration

– Stops sending impulses to those muscles

– Muscles relax

– Input to the respiratory center• Influenced by chemical and neural input

Mechanism of breathing cont’d.

• Chemical input to respiratory center– Directly sensitive to CO2 and H+

• When levels rise respiratory center increases rate and depth of breathing

– Indirectly responsive to O2

• Chemoreceptors in the carotid and aortic bodies

– Sensitive to oxygen levels in blood

– When oxygen levels in blood decrease, impulses are sent to respiratory center

» Respiratory center then increases rate and depth of breathing

Nervous control of breathing

Gas exchanges in the body

• External respiration– Exchange of gas between air in alveoli and blood– Gases exert pressure

• Partial pressure-amount of pressure each gas in a mixture exerts

– Symbolized by Pco2 and Po2

– Blood in pulmonary capillaries has a higher Pco2 than atmospheric air

• CO2 diffuses from blood into alveoli

Gas exchanges in the body cont’d.

• External respiration cont’d.– Carbon dioxide generated in tissue is transported in blood

• Most transported in the form of bicarbonate ions

• Small amount is transported as dissolved molecular CO2

– Molecular CO2 diffuses into alveoli• This drives the following reaction to the right:

H+ + HCO- H2CO3 H2O + CO2

• Carbonic anhydrase is present in RBC’s

– Increases rate of carbonic acid breakdown

• CO2 then diffuses into alveoli

carbonic anhydrase

Gas exchanges in the body cont’d.

• External respiration cont’d.– Hyperventilation

• Pushes preceding reaction even farther to right

• Decreases hydrogen ions- alkalosis –increased pH

• Compensation-decrease respiratory rate

– Allows hydrogen ions to build up and return pH to normal

– Hypoventilation• Hydrogen ions build up-acidosis-decreased pH

• Compensation-increase respiratory rate to blow off CO2

– Helps return pH to normal along with other mechanisms

Gas exchanges in the body cont’d.

• External respiration cont’d.– Pressure gradient for oxygen is the reverse of carbon dioxide

– Po2 is low in pulmonary capillaries and high in alveoli

– Oxygen diffuses into blood– Hemoglobin in RBC’s picks up oxygen

• oxyhemoglobin

Gas exchanges in the body cont’d.

• Internal respiration– Exchange of gas between systemic capillaries and tissues– Oxygen

• Partial pressure of oxygen is greater in capillaries than tissues

• Oxyhemoglobin gives up oxygen

– Diffuses out of blood into tissues

• Gradient always remains high

– Oxygen is constantly used for cell respiration

Gas exchanges in the body cont’d.

• Internal respiration cont’d.– Carbon dioxide-higher in tissues than blood

– Most diffuses into RBC’s

• Increased carbon dioxide from tissues drives reaction to right

CO2 + H2O H2CO3 H+ + HCO3-

• Bicarbonate ions diffuse out of RBC’s into plasma• Hydrogen ions bind to hemoglobin- buffers• Small amount of carbon dioxide binds to hemoglobin

– carbaminohemoglobin

carbonic anhydrase

External and internal respiration

15.4 Respiration and health

• Upper respiratory tract infections– Nasal cavities, larynx, pharynx– Infections can spread to sinuses, middle ear– Viral infections can lead to secondary bacterial infections– “strep throat”

• Streptococcus pyogenes

• Sore throat, high fever, white patches

– Sinusitis• Nasal congestion blocks sinus openings

• Postnasal discharge, facial pain

• Spray decongestants-help drainage

Respiration and health cont’d.

• Upper respiratory tract infections cont’d.– Otitis media

• Middle ear infection

• Spreads from nasal cavity through eustachian tubes

• Pain is primary symptom

• Antibiotics, typanostomoy tubes for recurrent

– Tonsillitis– Inflammation of tonsils

– Tonsillectomy

» Fewer done today

» Importance of tonsils recognized

Respiration and health cont’d.

• Upper respiratory tract infections cont’d.– Laryngitis

• Infection of larynx

• Hoarseness

• Persistant hoarseness without upper respiratory infection

– Could indicate cancer

Respiration and health cont’d.

• Lower respiratory infections– Acute bronchitis

• Infection of primary and secondary bronchi

• Usually secondary infection

• Deep cough

• Expectoration of mucus, pus

– Pneumonia• Infection of lungs

• Viral or bacterial

• Alveoli and bronchioles fill with fluid

• High fever, chills, chest pain

• Can be generalized or isolated to specific lobes

• Pneumocytis carinii pneumonia- AIDS patients

Respiration and health cont’d.

• Lower respiratory infections cont’d.– Pulmonary tuberculosis

• Tubercle bacillis- bacterium

• Infected tissue encapsulates bacteria-tubercle

• State of immune system determines course

– If competent, infection generally walled off

– If compromised, infection spreads

• Treated by antibiotics

– Individuals are quarantined

– Tine test

Respiration and health cont’d.

• Lower respiratory infections cont’d.– Restrictive pulmonary disorders

• Vital capacity is reduced

• Lungs lose elasticity

• Pulmonary fibrosis

– Inhalation of particles

» Silica, asbestos, coal dust

– Lungs cannot inflate normally

Respiration and health cont’d.

• Obstructive pulmonary disorders– Decreased air flow– Chronic bronchitis

• Airways inflammed• Productive cough• Degenerative changes in bronchi

– Loss of mucociliary apparatus• Smoking, pollutants can predispose

– Emphysema• Alveoli distended• Loss of surface area for gas exchange• Air trapped in lungs due to alveoli damage• Increased workload on heart• Supplemental oxygen, drug therapy, exercise may help

Respiration and health cont’d.

• Obstructive pulmonary disorders– Asthma

• Lower airway sensitivity• Smooth muscle constriction in bronchioles• Produces “musical” wheezing• Chemical mediators in bronchioles cause bronchospasm• Inhalant medications, bronchodilators

• Lung cancer• Progressive steps• Thickening and callusing of airway cells of mucosa of bronchi• Loss of cilia• Cancerous changes occur producing cells with atypical nuclei• Tumor Development and then finally Metastasis.• Can be caused by Active smoking and/or Passive smoking.

Normal lung versus cancerous lung