The document summarizes key aspects of the respiratory system, including: 1. The trachea divides into the right and left bronchi, which further divide into smaller bronchioles before terminating in alveoli where gas exchange occurs. 2. The lungs are enclosed in the pleural cavity and surrounded by pleura. Contraction of the diaphragm and intercostal muscles increases the thoracic cavity volume during inspiration. 3. Expiration is a passive process involving relaxation of the respiratory muscles, while inspiration requires active contraction of muscles like the diaphragm and intercostals to decrease thoracic pressure and draw in air.

1. The Respiratory System
Lumamba . L
BScN , BSc HB

2. The Bronchi
• The trachea divides into right and left bronchi at 5th thoracic
vertabrae
• Right Bronchus.
• It is wider and shorter and more vertical than the left bronchus and is
2.5cm long.
• Lined with ciliated columnar epithelium.
• After entering the hilum of the right lung, It divides into three
branches one to each lobes and then later into smaller bronchioles.
• More prone to obstruction by an inhaled foreign body due to the
position it attains.

3. The Bronchi
• Left Bronchus.
• It is about 5cm long. It is narrower than the right bronchus.
• After entering the hilum of the left lung it divides into two, one each
to lobe and then to into smaller tubes (bronchioles)
• At the point where the LT and RT bronchus divides is called the
carina.
• The mucus membrane of the carina is sensitive and triggers a cough
reflex.

4. Structure of the Bronchi
• This is applied to bronchi and bronchioles.
• Tissue – it is composed of the same tissues like that of trachea.
• They are lined by ciliated columnar epithelium.
• Towards ends of bronchi the cartilage become irregular in shape and
are absent at bronchiolar level.
• Thus bronchioles walls are formed by smooth muscles.
• Ciliated columnar mucous membrane changes gradually to non-
ciliated cuboidal shaped cells.

5. Blood and Nerve Supply
• Arterial – branches of the left and right bronchial artery
• Venous return- it is via bronchial vein.
Nerve supply
• Parasympathetic- necessary for smooth muscle contraction.
• Sympathetic- necessary for smooth muscle vasodilation.
Lymphatic vessels and lymph nodes.
• Lymph is drained from the walls of the air passages via network of
lymph vessels through lymph nodes situated around the trachea and
bronchial tree

6. Function of air passages not involved in gaseous
exchange
• Control of air entering- This is by contraction and relaxation of
involuntary muscles in the walls.
• Other upper respiratory function are;
• Warming and humidifying,
• Support and maintenance of patency
• Removal of particulate matters
• Cough reflex.

7. Respiratory bronchioles and alveoli
• These are considered to be the structures/passages involved in the
process of gas exchange.
• They include respiratory bronchioles, alveoli ducts and alveoli (tiny air
sacs)
• Their walls gradually become thinner until muscles and connective
tissue fade out leaving a single layer of epithelial cells.
• This is where gaseous exchange takes place
• These distal respiratory passages are supported by a loose network of
elastic connective tissue in which macrophages, fibroblasts, nerves
and blood and lymph vessels are embedded.

8. Respiratory Bronchioles and Alveoli
• The alveoli are surrounded by a network of capillaries.
• Their layers are made up of single layers of simple squamous epithelial
cells.
• Alveoli are surrounded by a network of capillaries and within squamous
cells lining the capillaries there are cells that secrete surfactant
(phospholipids fluid) which prevents alveoli from drying out.
• Surfactant also reduces surface tension and prevents alveoli walls from
collapsing during expiration.
• The secretion of surfactant begins about 35th week of fetal life.
• It facilitates lungs expansion in newborn.
• It is not sufficient in immature lungs of premature babies, causing
difficulties in establishing respiration

9. Function of respiratory bronchioles and alveoli
1. External respiration (exchange of gases between blood and alveoli)
2. Defense against microbes because of presence of lymphocytes and
plasma cells. These produce antibiotic and macrophages.
3. Warming and humidifying of air.

11. The Lungs
• There are two lungs each lies on each side of the midline in the
thoracic cavity.
• They are cone shaped.
• Each has 4 parts as follows;
• Apex, Base, Costal surface, and Medial surface
• Apex- It is the rounded part of about 25mm.
• It raises into the root of the neck above the level of the clavicle.

12. The Lung
• Base- It is concave and semilunar
in shape. It is closely associated
with the thoracic surface of the
diaphragm.
• The costal surface- It is convex
closely associated with costal
cartilages, the ribs and intercostals
muscles.
• The medial surface- It is concave
and with roughly triangular shaped
area called Hilium which is at the
level of 5th, 6th, and 7th vertebra.
• Structures which form the root of
the lung enter and leave at the
hilum

13. The Lungs
• Helium- It is a place where structures which form the root of the lungs
enter and leave the lungs.
• The structures include bronchus, pulmonary artery, pulmonary veins,
bronchial artery and vein and the lymphatic and nerve supply.
• The area between two (2) lungs is called Mediastinum which is occupied by
the heart, great vessels, trachea, right and left bronchi, oesophagus, lymph
nodes, lymph vessels and nerves.
• Right lung-It is divided into 3 distinct lobes; superior, middle and inferior
lobe.
• Left lung-It is smaller than the right lung because the heart is situated to
the left of the midline. It is divided into 2 lobes; the superior and inferior
lobes.
• Each lung is composed of bronchi and smaller air passages, sacs (alveoli),
connective tissues, blood vessels, lymph vessels and nerves.

14. The lungs
• Each lobe is made up of lobules and lobules make up collection of
terminal bronchioles and alveoli.
• There are about 300 million alveoli in each lung.
• The alveoli cells are lined with pneumocytes.
• Alveolus is a place where exchange of gases takes place.

15. The Pleura and Pleural Cavity
• The lungs are enclosed in a sac called pleura.
• Pleura consists of a closed sac of serous membrane which contains a
small amount of serous fluid in which the lungs are invaginated into.
• Pleura is made up of two (2) membranes;
• 1. Visceral pleura- This lines the lungs, covering each lobe and
passing into tissues which separate them.
• 2. Parietal – this lines the inside of the chest walls and the thoracic
surface of the diaphragm.
• Pleural cavity – this is the only potential space found between
visceral pleura and parietal.
• The serous fluid in the potential space prevents friction during
breathing secreted by the epithelial cells of the membrane.

16. Pleura and pleural Cavity

17. Muscles of Respiration
• Expansion of the chest during inspiration occurs as a result of
muscular activity, partly voluntary and partly involuntary.
• The main muscles of respiration in normal quiet breathing are the
intercostal muscles and the diaphragm.
• Accessory muscles of respiration are used during difficult or deep
breathing by the muscles of the neck, shoulders and abdomen.
1. Intercostal muscles- There are 11 pairs of muscles occupying the
spaces between the 12 pairs of ribs arranged in two layers – external
and internal layer intercostal muscles.

18. Muscles of Respiration
2. The external intercostal muscle fibres. Extend in a downwards and
forwards direction from the lower border of the rib above to the upper
border of the rib below.
3.The internal intercostal muscle fibres. Extend in a downwards and
backwards direction from the lower border of the rib above to the
upper border of the rib below,
• crossing the external intercostal muscle fibres at right angles.

19. Muscles of Respiration
• First rib is fixed when intercostal muscles contract.
• When intercostals muscles contract they pull toward the first rib.
• This causes upward and outward movement of the chest.
• Diaphragm – It is a dome shape separating the thoracic and abdomen
cavity.
• Diaphragm forms floor of the thoracic and roof of abdominal cavity.
• It consists of central tendon from which muscles radiate to be
attached to the lower ribs and sternum and the vertebral column.

20. Muscles of Respiration
• Contraction of the diaphragm decreases pressure in the thoracic
cavity .
• Intercostal muscles and diaphragm contract simultaneously in order
to ensure enlargement of the thoracic cavity in all directions; front
and back and side to side
• Respiration is defined as the process of constant exchange of oxygen
and carbon dioxide between the living organism and its environment.
• This involves gaseous exchange between tissue cells and the
atmosphere,characterized by inflation and deflation of the lung with
each breath for regular exchange of gases.

21. • Breathing (pulmonary ventilation) – It is a simple term used to
describe the movement of air into lungs (inspiration) and moving of
air out of the lungs (expiration)
• Respiration
• Complete expansion and relaxation of chest occurs in phases known
as cycle of respiration. This is what is counted as respiration rate per
minute.
• The mechanical process of inspiration and expiration is termed as
mechanism of breathing

22. Cycle of Respiration
• It occurs 12 to 15 times per
minute.
• It consists of three phases;
• Inspiration.
• Expiration.
• Pause.

24. Physiology Variables affecting Respiration
• These include;
• Elasticity – the ability of lung to return to its normal shape after
each breath.
• Compliance – the distensibility of lung (i.e. effort required to
inflate the alveoli).

25. Inspiration
• A process in which oxygen is taking into the body.
• It is an active process because energy is required for proper
contraction of respiratory muscles.
• Air (oxygen) from the atmosphere is taken in as the result of
decreased pressure in thoracic cavity less than that of
atmospheric pressure following contraction of respiratory
muscles; intercostals muscles and the diaphragm.
• Intercostals muscles contraction raises ribs and elevates the
sternum and enlarging thoracic cavity the more.
• Intercostals muscles contraction moves thoracic wall upward
and outward.

26. Inspiration
• When the diaphragm contracts, it moves downward and the thoracic
cavity enlarges, pressure falls to about 2mmHg below atmospheric
pressure
• Parietal pleura moves with the walls of the thorax and the diaphragm
while visceral pleura follows the pleura pulling the lung with it.

27. Expiration
• It is a passive process.
• It involves relaxation of the intercostals muscles and the diaphragm
leading to downward and inward movement of the rib cage
accompanied with elastic recoil of the lungs.
• This process causes increased pressure inside the lungs more than
that in the atmosphere.
• This results to expiration or expelling of air from respiratory tract into
atmosphere.
PAUSE
• This is a period after expiration and before the next cycle begins.

28. Lung Volumes and Capacities
• Anatomical dead space – is the
capacity of air (about 150 ml)
that remains in the air passeges
that is not involved in gaseous
exchange.
• Tidal volume (TV) – is the
amount of air which passes into
and out of the lungs during each
cycle of quiet breathing (500 ml).
• Inspiratory reserve volume
(IRV) – is the extra volume of air
that can be inhaled into the
lungs during maximal
inspiration.

29. Lung Volumes and Capacities
• Inspiratory capacity (IC) - Is the
amount of air that can be
inspired with maximum effort.
• Expiratory reserve volume (ERV)
– is the largest volume of air
which can be expelled from the
lungs during maximal expiration
• Residual volume (RV) – is the
volume of air remaining in the
lungs after expiration

30. Lung Volumes and Capacity
• Functional reserve Capacity
(FRC) – Volume of air in the
lungs after a normal expiration
• Vital capacity (VC) – is the
maximum volume of air which
can be moved into and out of
the lungs.
• VC = Tidal volume + IRV + ERV

31. Composition of air
GAS INSPIRED % EXPIRED %
OXYGEN 21 16
CARBON DIOXIDE 0.04 4
NITROGEN 78 78
WATER VAPOUR VARIABLE SATURATED

32. External Respiration
• This is a type of respiration in which exchange of gases by diffusion
take place between the alveoli and the blood.
• The alveoli wall is made up of one cell (single layer) surrounded by
network of tiny capillaries.
• This facilitates diffusion as it allows easy movement of substances
• Because venous blood via pulmonary artery contains high level of
carbon dioxide and low level of oxygen,
• carbon dioxide diffuses from venous blood down its concentration
into alveoli until equilibrium is achieved.
• At the same time oxygen diffuses from alveoli into blood.
• This leads to proper exchange of gases.
• The slow flow of blood through the capillaries increases the time
available for diffusion to occur.

33. External Respiration

34. Internal Respiration
• This involves exchange of gases by diffusion between blood in the
capillary and the body cells.
• Blood is concentrated with oxygen and lower concentration of carbon
dioxide.
• Oxygen concentration in blood is more than that of body tissues/cells.
• The difference in oxygen concentration between blood and the
tissues enhances diffusion from blood stream through the capillary
into tissues and
• carbon dioxide diffuses from cells into the blood stream towards the
venous ends of capillaries

35. Internal Respiration

36. Control of Respiration
• The respiratory centre- These are found in medulla oblongata and
pons.
• Groups of nerves found in these areas control rate and depth of
respiration.
• Medulla oblongata has two (2) neurons which play good roles in
regulation of respiration.
• The neurons are inspiratory neurons for inspiration and expiratory
neurons for expiration.
• These two two neurons are in the pneumotaxic and apneutic centres
in the pons.

37. Control of Respiration
• Chemoreceptors – These are receptors that respond to
changes in the partial pressures of oxygen and carbon dioxide
in the blood and cerebrospinal fluid. They are classified into
two as follows;
1. Central chemoreceptors- Found on the surface of medulla
oblongata and found bathed in cerebrospinal fluid (csf) .
They are stimulated when PCo2 rises (hypercapnia).
• This leads to stimulation of respiratory centre to increase
ventilation of lungs to reduce arterial PCO2.

38. Control of Respiration
• Peripheral chemoreceptors – Found in the aorta and in the carotid
bodies.
• They are sensitive to small rise in arterial PCO2.
• Their impulses are conveyed by glossopharyngeal and vagus nerves
to the medulla oblongata which then stimulates the respiratory
centre leading to increase in rate and depth of respiration.