Learning Objectives By the end of this lesson, you should know: • Features of effective transport systems; examples of transport systems in multicellular organisms. • Nature of waste products and toxic substances; excretory mechanisms and systems. • Features of effective surfaces of gaseous exchange; mechanisms and systems of gaseous exchange in multicellular organisms; process of diffusion.
Excretory Organs – Lungs Respiration • _________ (the breakdown of glucose) produces ______ ______, which is carried away from the cells by the _____, and removed in the _____. • The loss of water vapour from the lungs is unavoidable. carbon dioxide blood lungs
Structure of the Thorax The thorax is the chest region where the lungs are enclosed and protected. Label the diagrams of the respiratory system with the following: Left lung and right lung Nasal cavity Ribs (add an arrow) Mouth Epiglottis Trachea Bronchus Bronchioles Alveoli Pleural membranes Pharynx (throat) Thyroid cartilage
Functions • Draw a table to show the structure and functions of each part in the respiratory system.
The Lungs • Each lung contains: • A system of branching tubes called bronchioles. • Millions of alveoli at the end of the finest bronchioles. • A large number of capillaries around each alveolus. • No muscle fibres.
The large number of alveoli and capillaries: • Give a large surface area for gas exchange • Make the lungs very efficient at obtaining oxygen and eliminating carbon dioxide. • The linings of the bronchioles contain: • Cells which secrete mucus to trap dust and bacteria • Cells with cilia to ‘waft’ foreign particles towards the pharynx to be expelled from the body by coughing.
Diaphragm • A muscular sheet that divides the lungs from the digestive organs in the abdomen – it extends across the bottom of the ribcage. • When relaxed, it is domed slightly upwards.
Intercostal Muscles • Muscles attached to the ribs. • They are used to move the ribcage: • Upwards and outwards – external intercostals • Downwards and inwards – internal intercostals.
Ventilation • Ventilation is the movement of air into and out of the lungs (breathing). • Lungs are made to expand and contract by movements of the ribs and diaphragm. • Works based on volume and pressure changes in the thorax during inhalation and exhalation. • When volume increases, pressure will drop. • When volume decreases, pressure will increase. • Air will move from an area of high pressure to an area of low pressure.
Alveoli and Gas Exchange • The exchange of gases between the air and blood takes place in the alveoli. • Gas exchange relies on diffusion; therefore concentration gradients need to be maintained. • Oxygen diffuses from air in the alveoli into the blood stream because it moves from an area of high concentration to low concentration.
Oxygen combines with the haemoglobin protein molecule in the red blood cells to form oxyhaemoglobin. • RBC continuously carry oxygen away from the alveoli, so a concentration gradient is maintained. • Carbon dioxide moves from the blood to the air in the alveoli due to diffusion also. • CO2 is transported in the plasma.
The Efficiency of Gas Exchange • Gas exchange in the alveoli is very efficient because: • Each alveolus is surrounded by a dense network of capillaries. • There are many alveoli creating a very large surface area in contact with the capillaries. • The walls of the alveoli are very thin (one cell thick) so gases can pass easily through them. • The wall of the alveoli are moist to help gases dissolve.
Excretory Organs – Gills ADVANTAGES: • No drying out of respiratory surface. • Carbon dioxide easily diffuses into surrounding water. • Countercurrent flow of blood increases rate of gaseous exchange = gills are extremely efficient. DISADVANTAGES: • More energy is required to ventilate gills than lungs. • There is less oxygen in water.
Questions • List the features of an efficient respiratory surface. Explain the importance of each feature. • What is the function of surfactant in mammalian lungs? • Explain what happens to the rib and the diaphragm during inhalation and exhalation. • Why does this cause air to move into and out of the lungs?