SECTION II – Structures and functions in living organisms Gaseous exchange

Syllabus understand the role of diffusion in gas exchange describe the structure of the thorax, including the ribs, intercostal muscles, diaphragm, trachea, bronchi, bronchioles, alveoli and pleural membranes understand the role of the intercostal muscles and the diaphragm, in ventilation

Syllabus explain how alveoli are adapted for gas exchange by diffusion between air in the lungs and blood in capillaries understand the biological consequences of smoking in relation to the lungs and the circulatory system describe a simple experiment to investigate the effect of exercise on breathing in humans.

Terminology Gaseous exchange –The exchange of gas (by diffusion) across a respiratory surface. Breathing (ventilation) –the bodily process of inhalation and exhalation –Muscular movements which keep the gaseous exchange surfaces supplied with oxygen Respiration –A series of chemical reactions which happen in all living cells. –Food is broken down to release energy, usually by combining it with oxygen. Respiratory system –The organs, muscle and bones involved in the inhalation and exhalation process.

Structures Lungs –two organs –extract oxygen from inhaled air and expel carbon dioxide in exhaled air. Trachea –Tube through which air passes from the nose to the lungs (also known as the windpipe). –Has rings of cartilage to keep it open. –The rings are in a u shape to allow for the expansion of the trachea during ventilation.

Structures Trachea –Lined with two specialised cells Ciliated cells –Cells that have fine ‘hairs’ on the surface of the cell. –Their beating action carries the mucus (containing microbes & dust) away from the lung surfaces. Goblet cells –Produce mucus, that helps to trap the microbes and dust that is breathed in. Ciliated cells Goblet cells

Structures Larynx –Voice box Location of vocal cords Bronchi –The two main air passages into the lungs. Bronchioles –A small tube carrying air to and from the alveoli in the lungs. Alveoli –Tiny air sacs –The main site of gaseous exchange

Structures Nose and mouth –Cavities where the air passes in and out of the body –Air becomes warm, filtered and moist if it flows through the nasal cavity.

Structures Intercostal muscles –Internal (go from the front of the rib cage to the back) & external (go from the back to the front) –Thin sheets of muscle between each rib that expand and contract. –Involved in breathing

Structures Diaphragm –The main muscle used for breathing; separates the chest cavity from the abdominal cavity. Ribs –Bones attached to the spine and central portion of the breastbone, which support the chest wall and protect the heart, lungs, and other organs in the chest.

Structures Pleural membrane –Covering the lung and lining the chest cavity, this membrane has 2 thin layers. Pleural fluid –The fluid inside the membranes lining the lungs and chest cavity.

Features of gaseous exchange surface Gas exchange surface –The part of the organism through which gases are exchanged. Properties of surfaces: –Thin Allows gases to diffuse quickly –Close to a transport system Takes gases to and from the cells which need them.

Features of gaseous exchange surface Properties of surfaces: –Moist Stops the cells on the surface from drying out and dying –Large surface area Allows a lot of gas to diffuse across a surface at the same time –Supply of oxygen Is needed by the surface

Alveoli Is where gas exchange occurs. Contains all the features of a respiratory surface: –Close to a transport system –Thin –Large SA –Good supply of O 2

Ventilation Also known as breathing Movement of air into and out of the lungs. Air flows because of pressure differences between the atmosphere and the gases inside the lungs. This pressure difference occurs because of breathing movements we undertake. Source: cited 16/11/06http://

Inhalation Also known as inspiration It is the process of taking air into the lungs. It is the active phase of ventilation because the muscles are contracting. During inspiration: –the diaphragm & intercostal muscles contract –This increases the volume of the thoracic cavity. –This decreases the intraalveolar pressure so that air flows into the lungs.

Exhalation Expiration (exhalation) is the process of letting air out of the lungs during the breathing cycle. During expiration: – the diaphragm and intercostal muscles relax –This decreases the thoracic volume and; –increases the intraalveolar pressure –Air is pushed out of the lungs.

Inspired vs expired air Inspired (inhaled) Expired (exhaled) Oxygen21 %18 % Carbon dioxide 0.04 %3 % Nitrogen78 % WaterVariablesaturated TemperatureVariable 37 °C

Carbon dioxide test To determine whether CO 2 is being released in exhalation, the limewater test is used. Limewater –(saturated calcium hydroxide solution) –Turns from clear to cloudy when CO 2 is present.

Physical activity and breathing Aims for investigations: –The longer you exercise, the longer it takes for your breathing rate to return to normal. –The more vigorously you exercise, the longer it takes for your breathing rate to return to normal.

Physical activity and breathing Rate and depth of breathing changes when exercising. –Oxygen is needed by cells, CO 2 is produced as a waste = cellular (aerobic) respiration Rate of breathing increases (more O 2 in, more CO 2 out) Depth of breath changes, so that volume of thoracic cavity is maximised (gets as large as possible) –Tidal volume Volume of air breathed in and out during a normal, resting breath.

Physical activity and breathing More exercise = increased CO 2 concentration = lowering of pH Blood & tissue pH becomes lower, as CO 2 mixes with water in body resulting in carbonic acid (H 2 CO 3 ) being made.

Smoking and the respiratory system In your teenage years your lungs are still growing, and their ability to function is supposed to increase. The smoke inhaled is: –Hot –has a drying effect –Contains many harmful chemicals. Smoking damages your cilia, alveoli, and bronchioles. These are part of the body’s defense mechanism.

Smoking and the respiratory system The lungs are one of the most vulnerable parts of the body, as they have more contact with the outside world than most internal organs do. Anything that's in the air -- including dirt, germs, and smoke -- can find its way into your respiratory system.

Smoking and the respiratory system To protect against these contaminants, your body produces mucus, which helps to trap and carry away irritating substances from the air. The mucus-contaminant mixture is moved through the respiratory system by tiny hairs called cilia that move rapidly back and forth.

Smoking and the respiratory system Smoking decreases the rate of lung growth and therefore decreases the level of maximum lung function reached in the late teens. This happens in both boys and girls, but girls seem to be particularly susceptible to smoking's effects on lung growth and function.

Smoking and the respiratory system Tar –Sticks to cilia, thus they cannot remove the contaminated mucus and causes extra mucus to be produced. This travels down to the lungs with contaminants within (eg. Bacteria) causing infections & smokers cough, as the body tries to get rid of the mucus. –Irritates the lining of the lungs, making them inflamed, causing bronchitis. –Causes cells in respiratory system to multiply uncontrollably, leading to lung cancer.

Smoking and the respiratory system Carbon monoxide –Displaces oxygen from haemoglobin, thus reduces oxygen supply to cells. Nicotine –Causes addiction –Stimulant, causing blood pressure to increase, resulting in more demand more oxygen = increased breathing rate.

Stop Smoking - timeline This is what happens to you when you stop smoking: 20 minutes Blood pressure and pulse rate return to normal. 8 hours Nicotine and carbon monoxide levels in the blood reduce by half, oxygen levels return to normal. 24 hours Carbon monoxide will be eliminated from the body. Lungs start to clear out mucus and other smoking debris. 48 hours There is no nicotine left in the body. Ability to taste and smell is greatly improved. 72 hours Breathing becomes easier. Bronchial tubes begin to relax and energy levels increase weeks Circulation improves. 3-9 months Coughs, wheezing and breathing problems improve as lung function is increased by up to 10%. 1 year Risk of a heart attack falls to about half that of a smoker. 10 years Risk of lung cancer falls to about half that of a smoker.

References wordnet.princeton.edu/perl/webwn, cited 6 th Nov, 2006wordnet.princeton.edu/perl/webwn Jones, M & Jones, G 2002 Biology, Cambridge University Press, Cambridge. cited 16 Nov., e.php, cited 16 Nov., 2006http://thescooponsmoking.org/xhtml/effectsHom e.php Clegg, J, Price, G & Smith, M Cambridge IGCSE Biology, Collins Education, London.