THE RESPIRATORY SYSTEMLesson 04

Overview of the Respiratory System

Primary Functions• Gas exchange, carries oxygen into body and

excels carbon dioxide• Provides oxygen to body which is required for

ENERGY producing process called aerobic respiration

• Eliminates the potentially toxic waste of this reaction, carbon dioxide, from the body

• Controls and regulates the temperature and humidity of the inhaled air

Need for gas-exchange surfaces

• All living cells in an organism’s body respire to produce their own energy. They need O2 !

• They also need to get rid of CO2.

• Not all of them are in direct contact with the outside medium.

• In all such cases, there has been evolved specialized surfaces on which gaseous exchange occurs.

• Delivery of O2 to and collection of CO2 from various parts of the body shall be dealt with in the next lecture.

Types of gas-exchange systems

Tracheal Gas Exchange System in InsectsAtmospheric O2 is made directly available to all parts of the body through an extensively branched system of tubes. Main tubes open to the outside of the body through a row of pores called spiracles on either side of the body. The spiracles are easily seen in larval stage as a row of prominent pores on either side along the length of the body.

Tracheal Tubes

Gas enters through spiracles, the openings on the surface of the body, into tracheal tubes.

Tracheal tubes end in fluid-filled tracheoles Diffusion of air across the moist tracheoles

and body cells.

Gills

Gills are formed by evagination or out-pocketing of body lining. During evolution, gills have become increasingly complex and efficient.

GillsOutfolds of the body surface.Gills usually have a greater surface area than the rest of the body surface.

GillsComposed of many filaments containing

capillaries.Water passes across gills in the opposite

direction than blood flow in capillaries. (Counter-current exchange)

Gases in the water are diffused into blood and transported to where it is needed

Ventilation increases flow of water across gills.

Structure of fish gills – Water flows uni-directionally over the exchange surface

Counter-Current flow of water and blood

LungsTrue lungs of tetrapods are formed by in-pocketing of the hind part of mouth cavity or pharynx. Note the increase in convolutions of the respiratory surface to increase the surface area.

The respiratory system of birds consists of a number of anterior and posterior air sacs connected to a pair of lungs placed in the middle.

Respiration in Humans

The air passages in mammalian lungs are much more branched than other groups of animals. Trachea (the wind pipe) leads to two main bronchi each of which leads to many bronchioles each of which, in turn, leads to numerous alveolar ducts each of which numerous blind-ended alveoli.

Upper Respiratory Tract Organs• Nasal cavity: located behind the nose and is covered

by mucous membrane, blood vessels and tiny hairs.• Functions: Filtration, Moisturizing and

Temperature Control of the air• Pharynx: located in-between nasal cavities and

larynx• Function: Passes air to larynx and coordinates

inspiration and swallowing when eating• Larynx: situated at the opening of the trachea and is

the location of the vocal cords• Functions: Protects and ensures breathing pathway to

trachea is open. Also allows vocal cords to vibrate producing sounds

Upper Respiratory Tract Organs

Lower Respiratory Tract OrgansTrachea: tube that joins larynx to lungs,

it is composed of C-shaped hyaline cartilage rings• Functions: airway in which air travels and

cartilage rings ensures it remains openLungs: biggest structure of respiratory

system that is filled with alveoli, 2 lungs in human; 3 lobes in right lung and 2 in other• Function: produces inspiration and expiration

when it is expanded and compressed

Lower Respiratory Tract Organs

Lower Respiratory Tract OrgansBronchial Tubes: divisions of the trachea

in each lung, also called bronchiBronchioles: small branches of the

bronchi that terminates into the alveoliAlveoli: tiny sac-like structures grouped

at the end of the bronchioles, are in very large number in lungs and their large total surface area is covered by a capillary network• Functions: location of gas exchange with

blood

Lower Respiratory Tract Organs

Complementary tissues• Capillary Network and other blood vessels:

capillary network covers alveoli• Functions: pulmonary artery brings blood rich in carbon

dioxide to the capillary network, where CO2 is taken out and replaced by oxygen. Then the oxygen-rich blood is carried by the pulmonary vein to the heart.

• Diaphragm: muscle located below the lungs• Function: Is responsible for the action of breathing.

Inhalation is when it contracts, the thoracic cavity enlarge causing the lungs to do the same. During exhalation, the diaphragm relaxes and the lungs regain their prior size

• Intercostal Muscles: responsible for rib cage enlargement

Breathing Movement

Breathing Control• The respiratory control center is located at

the base of the brain and sends ongoing signals to the muscles.

• Mostly involuntary to ensure it is regular and continuous although it can be modified voluntarily

• Changes in oxygen level in blood, activity level as well as the presence of irritants in the airways or liquid in the lungs can alter respiration rate

Atmospheric air fills the interior space of the alveolar sacs. Blood capillaries lie close to the inner lining of the alveoli and gas exchange occurs through the capillary wall and the alveolar lining.

Gas exchange surface

Alveolar interior and lining and closely situated capillaries with red blood cells

Concurrent Flow VS Countercurrent flow of water & blood