Objectives By the end of the lesson you will be able to:- Identify the gross structures of the respiratory system; Describe the function of 4 of the gross structures; Produce a model to demonstrate the respiratory system.

The purpose of the respiratory system is to… The Respiratory System “bring the air we breathe into close contact with the blood so that oxygen can be absorbed and carbon dioxide removed.” Basically it consists of: A pair of lungs connected to the mouth via the trachea and bronchi. The ribs and intercostal muscles of the chest which protect the lungs, trachea and bronchi.

This chest X-ray shows the organs within the thoracic cavity. Air-filled lung Ribs Position of the diaphragm Position of the heart The Thoracic Cavity

The lungs are in the thoracic cavity and are also protected by 12 pairs of ribs that articulate with the vertebrae towards the back of the body. The sternum (breastbone) is at the front of the rib cage. The portions of the ribs that articulate with the breastbone are made of cartilage rather than bone. Cartilage Cartilage is softer and more pliable than bone and this helps the movement of the rib cage during breathing. Sets of antagonistic muscles are found between the ribs - the intercostal muscles. Sternum

Trachea (wind pipe) Bronchus Bronchioles Alveoli Lung Intercostal muscles Ribs Diaphragm The Respiratory System

The trachea or windpipe is about 10 cm long and is supported by C-shaped rings of cartilage to prevent the tube from collapsing during breathing. The trachea subdivides into the left and right bronchus. The bronchi are also strengthened by cartilage. The two bronchi subdivide to form an extensive network of Bronchioles that deliver air to the gas exchange surfaces – the alveoli. Air enters the body through the nasal passages and mouth, and passes via the pharynx and larynx to the trachea. Air is delivered to the alveoli as the trachea branches into bronchi and bronchioles.

A photomicrograph of a cross-section through the trachea showing the C-shaped ring of cartilage. C-shaped cartilage ring

The Exchange of Gases within the Lungs Single alveolus The 2 bronchi, which lead to each lung divide into many bronchioles. These are less than 1mm in diameter and terminate in grape-like clusters of tiny sacs called alveoli. Section of lung Thorax

Alveolar Tissue A photomicrograph of a section of alveolar tissue showing the delicate nature of the lungs and the 'one cell thick' walls of the alveoli. A photomicrograph of a section of alveolar tissue showing the delicate nature of the lungs and the 'one cell thick' walls of the alveoli.

The Mechanics of Breathing Breathing in (inspiration) and breathing out (expiration) are mechanical processes involving the ribs, intercostal muscles and the diaphragm. Two sets of antagonistic muscles are located between the ribs - these are the external and internal intercostal muscles. External intercostal muscles Internal intercostal muscles The intercostal muscles are antagonistic - the contraction of the external muscles raises the rib cage, whereas contraction of the internal muscles lowers the rib cage. The diaphragm is a powerful sheet of muscle that separates the thorax from the abdomen; it is dome- shaped when relaxed and flattens on contraction. Diaphragm Ribs

The external and internal intercostal muscles are responsible for the movements of the rib cage during breathing. Rib Internal intercostal muscles Contraction of the external intercostal muscles moves the ribs upwards and outwards during inspiration. Relaxation of the external intercostal muscles causes the ribs to move downwards and inwards during expiration at rest. Expiration at rest is a passive process. However, expiration during periods of exercise is an active process - it involves contraction of the internal intercostal muscles and abdominal muscles to produce more forceful expirations. External intercostal muscles The Mechanics of Breathing

During periods of increased activity such as exercise, the rate and depth of breathing increases. The more forceful, downward and inward movements of the rib cage during expiration of exercise are achieved through the contraction of the internal intercostal muscles. At the same time, contraction of the abdominal muscles just below the thorax, pushes the diaphragm into a more domed position. As the diaphragm pushes further into the thorax, the volume of the chest cavity decreases more significantly and the increased thoracic pressure helps expiration. During periods of exercise, expiration is forced - it is now an active process.

How we Breathe Breathing is achieved by making the chest larger or smaller, which results in a change in pressure within the lungs. This forces air either in or out.

Inspiration - Breathing In When inhaling… The intercostal muscles contract and pull the rib cage up and out. The diaphragm contracts causing it to flatten. The chest cavity gets larger causing pressure in the lungs to fall. Air moves into the lungs from the higher outside pressure. Air flowing in

The chest cavity gets smaller and so pressure in the lungs increases. When exhaling… Expiration - Breathing Out The intercostal muscles relax and so the rib cage returns to normal. The diaphragm relaxes pushing it up. Air flows out of the lungs. During periods of exercise, expiration becomes an active process, involving the forced expulsion of air. Air flowing out

Alveoli Alveoli are extremely tiny structures in the lungs where the exchange of oxygen and carbon dioxide takes place. Their walls are very thin and moist to help oxygen and carbon dioxide pass through. This process is called diffusion. The bunches of alveoli are surrounded by a dense network of capillaries. The capillaries also have very thin walls, which again help the diffusion of oxygen and carbon dioxide into and from the blood. A Single Alveolus Capillaries Red Blood Cells Thin wall, one cell thick

How the Alveoli and Capillaries Work How the Alveoli and Capillaries Work 1.Air containing oxygen enters the lungs and passes into each alveolus from outside. 2. Deoxygenated blood containing carbon dioxide comes from the rest of the body. Oxygen is diffused into the blood from the alveoli. Carbon dioxide is diffused from the blood into the alveoli. The blood becomes oxygenated.

3.Air containing more carbon dioxide leaves the lungs. 4.The oxygenated blood leaves the lungs and is transported by the circulatory system for use throughout the body. How the Alveoli and Capillaries Work How the Alveoli and Capillaries Work

Inside Capillary Diffusion of Carbon Dioxide into the Alveoli Inside Alveolus Carbon dioxide Oxygen Capillary Wall Alveolus Wall concentration gradient concentration gradient concentration gradient Decreasing concentration

Capillary Wall concentration gradient concentration gradient concentration gradient Decreasing concentration Carbon dioxide Oxygen Inside Capillary Inside Alveolus Alveolus Wall Diffusion of Carbon Dioxide into the Alveoli

Capillary Wall concentration gradient Decreasing concentration Diffusion of Oxygen into the Capillaries Carbon dioxide Oxygen Inside Capillary Inside Alveolus Alveolus Wall

Capillary Wall concentration gradient Decreasing concentration Carbon dioxide Oxygen Inside Capillary Inside Alveolus Alveolus Wall Diffusion of Oxygen into the Capillaries

Capillary Wall concentration gradient Decreasing concentration Carbon dioxide Oxygen Inside Capillary Inside Alveolus Alveolus Wall Diffusion of Oxygen into the Capillaries

The Difference between Inhaled and Exhaled Air Inhale air into the lungs (%) Exhale air out of the lungs (%) Nitrogen 79%Carbon Dioxide 0.04%Water vapour 0.01%Oxygen 16%Carbon Dioxide 4.0%Nitrogen 79%Water vapour 1%Oxygen %

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