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1. RESPIRATORY SYSTEM
LECTURER: SUMAIRA GEORGE
KMU-INS

2. Objectives
 Describe respiratory system.
 Describe the structure and the function of following
 Upper respiratory tract (Nose, Pharynx, Larynx)
 The lower respiratory tract (Trachea, Bronchial tree, lungs)
 Discuss the physiology of respiration by explaining the
mechanism of:
 Pulmonary Ventilation
 External Respiration
 Internal Respiration
 Briefly discuss the lung volumes & capacities

3. RespiratorySystem
A system consisting of lungs and air passages specialized for the
intake of oxygen and exchange of gases with the blood.
Respiration: The exchange of oxygen and carbon dioxide between
the atmosphere and the cells of the body.
Respiration includes three things:
1) Ventilation of lungs (inspiration and expiration),
2) External respiration (the exchange of gases between lungs and
blood) and Internal respiration (between blood and tissues), and
3) The use of oxygen in cellular metabolism.

5. TYPES OF RESPIRATION
The process of exchange of gases between the atmosphere and
lungs is called PULMONARY VENTILATION.
The process of exchange of gases between the lungs alveoli and
the blood is called EXTERNAL RESPIRATION.
The process of exchange of gases between the blood and the
tissues is called INTERNAL RESPIRATION.

6. Phases of Respiration
Inspiration
Air enters the lugs from atmosphere. It is an active process.
Expiration
Air leaves the lungs into atmosphere. It is an passive process.

7. FunctionsofRespiration
❖ Gas exchanger
❖ Filters, warms, and humidifies air
❖ Influences speech
❖ Allows for sense of smell
Four Major Functions are:
• Pulmonary ventilation
• Diffusion of O2 and CO2 b/w alveoli and blood
• Transport of O2 and CO2 to and from tissues
• Regulation of O2 and CO2 in blood and tissues

8. Respiratory Division
Respiratory tract is divided into two:
Upper Respiratory Tract (URT): consists of nose, pharynx, and
larynx.
Lower Respiratory Tract (LRT): consists of Trachea, Bronchi,
bronchioles and lungs.

10. NOSE
External Nose:
The external nose consists
of a supporting framework
of bone and hyaline
cartilage. The cartilages
framework of external
nose consists of:
✓ Septal cartilages
✓ Lateral nasal cartilages
✓ Alar cartilages
Internal Nose:
Internal nose is a large cavity
in the anterior aspects of the
skull and It lies interior to
nasal bone and superior to
mouth.
• It is lined with muscle and
mucous membrane.
• The space between internal
nose is called nasal cavity.
• Mucous secreted by the
goblet cells moistens the air
and traps the air particles.

12. Nose:
Apart from olfaction the nose has several functions:
• it warms, cleanses, and humidifies the inhaled air.
• It serves as a resonating chamber that amplifies the voice.
❖ Palantine bone separates nasal cavity from mouth.
• Cleft palate - Palantine bone does not form correctly, difficulty in
swallowing and speaking.
❖ Septum - separates right and left nostrils
• rich blood supply = nose bleeds.
❖ Sinuses - 4 air containing spaces – open or drain into nose -
• (lowers weight of skull).
• mucous membrane
– mucus
– hair
– olfactory receptors

13. Pharynx
• Is a muscular tube extending about 13 cm (5 inch).
• It is divided into three regions:
• Nasopharynx
• Lies dorsal to the soft palate.
• Receives the Eustachian (auditory) tubes.
• Houses pharyngeal tonsils.
• Oropharynx
• The space between the soft palate and root of the tongue
which extends inferiorly to the hyoid bone.
• Means it extends from the Uvula to the level of the hyoid
bone.
• It contains palatine and lingual tonsils

15. Contii..
▪ Laryngopharynx
• It extends from the hyoid bone to the cricoid cartilage.
• Oropharynx and laryngopharynx serve as a common
passageway for both food and air.

16. Larynx
• The larynx ( voice box) is located in the neck between the
pharynx (throat) and trachea (windpipe). It is made of
cartilage, muscles and ligaments.
• Main parts:
• Thyroid cartilage: largest; forms the ‘Adams apple’
• Cricoid cartilage : ring shaped, below the thyroid cartilage
• Arytenoid cartilage: control vocal cord movement
• Epiglottis : flap that covers the airway during swallowing to
prevent choking.

18. Contii..
• Vocal cords
• True vocal cords: produce sound
• False vocal cords: protect the true cords and help close the
airway
• Glottis : opening between the true vocal cords
• Muscles: control tension and position of the vocal cords for
speech and breathing

20. Physiology of the larynx
Three main functions :
1. Airway protection
• During swallowing the epiglottis closes over glottis to keep food or liquid from
entering the lungs .
2. Voice production
Air from the lungs passes through the vocal cords, causing them to vibrate and
produce sound
3. Breathing
The larynx keeps the airway open to allow free movement of air to and from the
lungs.

21. LowerRespiratoryTract
Trachea (windpipe) is a tube that connects the larynx
to bronchi of the lungs.
• Location: starts at the lower end of larynx (around
the C6 vertebra) and ends at the level of the T5 vertebra,
where it splits into right and left bronchi.
• Structure : length: 10-12cm , Diameter: 2cm
• Layers
Mucosa: inner lining with cilia and mucus producing cells.
Sub mucosa: supports glands that help trap and move debris
Cartilage: 16-20 C-shaped rings of hyaline cartilage that keeps the trachea
open
Muscle: Trachealis muscle at the back helps to adjust airway size during
coughing and heavy breathing.

22. Physiology of Trachea :
• Airway passage: provides a clear pathway for air to travel
between the larynx and the lungs
• Air filtration and cleaning: Cilia move mucus and trapped dust
or microbes upward towards the throat to be swallowed or
coughed out.
• Air Humidification and temperature control: The mucosa
helps humidify and warm air before it reaches the lungs.
• Cough reflex: if particles irritate the trachea, it triggers a cough
to clear the airway.

23. Bronchi and Bronchial Tree
• At the superior border of the 5th thoracic vertebrae, trachea
divides into right primary bronchi and left primary bronchi
which goes into lungs.
• The right bronchi is more vertical, shorter, wider than left
primary bronchi.
• The primary bronchi divides into secondary bronchi (Lobar
bronchi.
• The secondary bronchi divides into 9 or 10 tertiary bronchi
(Segmental bronchi)
• Tertiary bronchi divides into bronchioles.
• Bronchioles divides into terminal bronchioles.
• The terminal bronchioles divides into respiratory bronchioles.
• This extensive branching is known as bronchial tree

24. Branches of Bronchial Tree
Trachea
• ↓
• Primary bronchi
• ↓
• Secondary bronchi
• ↓
• Tertiary bronchi
• ↓
• Bronchioles
• ↓
• Terminal bronchioles

25. Alveolar Ducts
The alveolar duct is the small airway in the lungs that connects
the respiratory bronchioles to the alveolar sacs. It is the final
pathway for air before it enters the alveoli where gas exchange
happens.
Structure:
lined with alveoli on all sides giving it a grape like
appearance. Surrounded by elastic fibers and capillaries to assist
with gas exchange and recoil during breathing.
Function :
 Air passage: carries air from the bronchioles to the alveoli
 Gas distribution: helps spread air evenly to multiple alveoli for
efficient oxygen and carbon dioxide exchange.

29. Lungs
The lungs are two spongy, cone shape organs in the thoracic (chest)
cavityprotected by the rib cage. They it on the diaghragm and are
separated by the mediastinum (where the heart, trachea and major
vessels are located).The Hilum is the entry / exit point where bronchi,
pulmonary arteries and veins and lympahtic vessels and nerves passes in
and out.
• Lobes of lungs : Right lung have 3 lobes (upper , middle, lower) where
as left lung have 2 lobes ( upper and lower). It is smaller due to space
taken by the heart)
• The left lung has two lobes as superior and inferior lobe with a deep
fissure between them called oblique fissure.
• The right lung has three lobes as superior, middle,
and inferior lobe. Superior lobe is separated from
the middle lobe by horizontal fissure and the inferior lobe from the
middle one by oblique fissure.

30. Lungs
• Surface of lungs: Apex (top portion), base ( bottom surface
resting on diaphragm, costal surface ( faces the ribes ),
mediastinal surface ( faces the heart and other central
structures)
• Each lung is enclosed in pleural membrane
• Visceral pleura: covers the lung surface
• Parietal pleura: lines the chest cavity
• Pleural cavity: space between these layers containing fluid to
reduce friction during breathing
• Alveoli: Tiny air sacs (millions in each lung) where gas
exchange occurs. Its blood supply is through pulmonary
arteries ( carries deoxygenated blood from heart to lungs) and
pulmonary veins ( carries oxygenated blood back to heart).

32. RESPIRATORY
AIRFLOW PATHWAY
Trachea
Primary Bronchi
Secondary Bronchi
Tertiary Bronchi
Bronchioles
Terminal Bronchioles
Respiratory Bronchioles
Alveolar Ducts
Alveolar Sacs
Alveoli

33. Respiratory zones
• The Conducting airways consist of the nasal passages, mouth,
pharynx, larynx, trachea, bronchi, and bronchioles.
• While the Respiratory zone consist of respiratory bronchioles,
alveolar duct, and alveolar sac.

34. RESPIRATORY MUSCLES
Muscles of Inspiration
• Diaphragm (primary/main muscle)
• Sternocleidomastoid (elevates sternum)
• Scalenes (elevates first two ribs)
• External intercostal (move ribs upward and outward)
Muscles of Expiration
• Rectus abdominis (main muscle)
• Internal intercostal (pull ribs downward and inward)
These Abdominal muscles are used when expiration is active
• External oblique
• Internal oblique
• Transverse abdominis

35. NERVOUS CONTROL OF
RESPIRATION
• The nervous control of respiration involves the coordination of multiple brain regions,
nerves, and receptors to regulate breathing.
Brain Regions:
• Medulla Oblongata: Primary center for respiratory control, responsible for generating
rhythmic breathing patterns.
• Pons: Regulates breathing rate and depth, also involved in the transition from
inhalation to exhalation.
• Cerebral Cortex: Influences breathing voluntarily, such as during speech, singing, or
voluntary breath-holding.
Nerves:
• Phrenic Nerve: Originates in the cervical spine (C3-C5) and innervates the diaphragm,
controlling contraction and relaxation.
• Intercostal Nerves: Arise from the thoracic spine (T1-T12) and innervate intercostal
muscles, regulating rib cage movement.
• Vagus Nerve: Provides sensory input from lungs, airways, and chest wall, influencing
breathing patterns

36. NERVOUS CONTROL OF
RESPIRATION
Receptors:
• Central Chemoreceptors: Located in the medulla, sensitive to
changes in CO2 and H+ levels, stimulating breathing in
response to increased CO2.
• Peripheral Chemoreceptors: Found in the carotid and aortic
bodies, detect
• changes in O2, CO2, and pH levels, influencing breathing.
• Mechanoreceptors: Present in lungs, airways, and chest wall,
respond to changes in lung volume, pressure, and stretch.
• Baroreceptors: Located in the carotid sinus and aortic arch,
detect changes in blood pressure, influencing breathing.

37. NERVOUS CONTROL OF
RESPIRATION: How it works?
• Sensors detect changes: CO2, O2, and pH levels in the blood
are monitored by central and peripheral chemoreceptors.
• Signals sent to medulla: Sensors send signals to the medulla
oblongata, the primary respiratory control center.
• Medulla responds: Medulla adjusts breathing rate and depth
based on the signals received.
• Phrenic nerve stimulates diaphragm: Medulla sends signals to
the phrenic nerve, which contracts or relaxes the diaphragm.
• Intercostal nerves regulate rib cage: Medulla also sends signals
to intercostal nerves, which control rib cage movement.
• Breathing occurs: Diaphragm and rib cage movement result in
inhalation or exhalation.

38. Dual blood supply of the lungs
Pulmonary circulation ( Gas exchange)
• Involving pulmonary arteries which carry deoxygenated from left
ventricle of the heart to lungs. Blood flows through the capillaries
around the alveoli fro oxygen and carbon dioxide exchange.
• Pulmonary veins: carry oxygenated blood back to the left atrium of
the heart
Bronchial circulation ( Nourishment of the lung
tissue)
• Bronchial arteries: branches of the aorta that supply oxygenated
blood to the lung tissue ( bronchi, connective tissue, pleura)
• Bronchial veins: drains deoxygenated blood from the lung tissue
into the azygos vein and partially into pulmonary veins.

39. Respiratory Volumes
• Tidal Volume (TV): The amount of air that moves into the
lungs with each inspiration or moves out with each expiration is
called the tidal volume. 500ml
• Inspiratory Reserve Volume (IRV): The air inspired with a
maximal inspiratory effort in excess of the tidal volume is the
inspiratory reserve volume. 3000 ml
• Expiratory Reserve Volume (ERV): The volume expelled by an
active expiratory effort after passive expiration is the expiratory
reserve volume. 1200 ml
• Residual Volume (RV): and the air left in the lungs after a
maximal expiratory effort is the residual volume 1200 ml

40. Contii..
• Tidal Volume(TV): The amount of air normally inhaled or
exhaled with one breath. (500 ml)
• Inspiratory Reserve Volume(IRV): The amount of air forcefully
inhaled after a normal tidal volume inhalation. (3000 ml)
• Expiratory Reserve Volume(ERV): The amount of air forcefully
exhaled after a normal tidal volume exhalation (1200 ml)
• Residual Volume(RV): The amount of air remaining in the
lungs after maximum expiration (1300 ml)

41. Respiratory Capacities
• Vital Capacity(VC): Maximum amount of air expired after a
maximum inspiratory effort (4700 ml) .
VC= TV+IRV+ERV
• Inspiratory Capacity(IC): Maximum amount of air inspired
after a normal tidal expiration. (3500 ml)
IC= TV+IRV
• Functional Residual Capacity(FRC): Volume of air remaining in
the lungs after a normal tidal volume expiration. (2400 ml)
FRC= TV+ERV
• Total Lung Capacity(TLC): The amount of air after a maximum
inspiratory effort. (4900 ml)
TLC= TV+IRV+ERV+ RV

42. Clinical Conditions
• Inflammation of the pleural membrane is called pleurisy or
pleuritis and as a result the accumulation of excess fluid in the
pleural cavity is called pleural effusion.
• The introduction of air into the plural cavity (either by surgical
opening or gunshot) is called pneumothorax while blood or pus
in it is called hemothorax. The collapse of lungs is known as
atelectasis (ateles = incomplete; ectasis = expansion).

43. Clinical terminology of
ventilation
• Apnea: Temporary cessation of breathing.
• Dyspnea: Difficulty in breathing. Eg. SOB
• Eupnea: Normal breathing. 12 to 15 b/m
• Hyperpnea: Increased rate and depth of breathing.
• Hyperventilation: Increased pulmonary ventilation leading to
low blood level of CO2
• Hypoventilation: Decreased pulmonary ventilation leading to
increased blood level of CO2
• Orthopnea: Dyspnea that occurs when a person is lying down.
• Tachypnea: Abnormal quick shallow breathing
• Bradypnea: Abnormal slow breathing.
• Hypoxia: Low oxygen level

44. REFERENCES
▪ Ross & Wilson: Anatomy and Physiology in Health and Illness,
12th edition.
▪ Tortora, Gerad J. (2010). Principles of Human Anatomy and
Physiology (12th ed). New York: Happer & Row.