Structure of Gas Exchange.
- All aerobic organisms require oxygen to release ATP.
- Lungs are inside the body as air is not dense enough to support them and they would lose water so dry out.
- They are protected by the rib cage which are moved by muscles.
Trachea - is supported by cartilage and lined with cilia and goblet cells producing mucus to trap dirt.
Bronchi - are the 2 divisions of the trachea leading to lungs and have mucus and cilia.
Bronchioles - are subdivisions of the bronchi and are lined with muscle and epithelial cells. They can constrict to control air flow.
Alveoli - are air sacs that contain collagen and elastic fibres which allow them to stretch and spring back. The membrane is the exchange surface and they are 100-300 micrometres in diameter.
Mechanism of Breathing.
Ventilation - air is constantly moved in and out of the lungs.
Inspiration - when atmospheric pressure is greater than air pressure in lungs air is forced INTO the alveoli.
Expiration - when air pressure in lungs is greater than atmospheric pressure air is forced OUT OF the alveoli.
Pressure changes are due to:
- Diaphragm - this is a sheet of muscle separating the thorax and abdomen.
- Intercostal muscles - the internal contract leading to expiration and the external contract leading to inspiration.
Plural membranes - form an airtight plural cavity.
Inspiration, Expiration and Pulmonary Ventilation.
Inspiration - is active. External contract and internal relax. Ribs move up and out and diaphragm contracts increasing the volume which reduces the pressure so air is forced in.
Expiration - is passive. Internal contract and external relax. Ribs move down and in and diaphragm relaxes decreasing the volume which increases the pressure is air is forced out
- .Pulmonary ventilation - is the total volume of air moved into lungs in 1 minute.
- Tidal volume - is the volume of air taken in at each breath. (0.5 dm3).
- Ventilation rate - is the number of breaths in 1 minute. (12 to 20).
- Vital capacity - is the max volume of air that can be forcibly expired after max intake. (3.5 to 6 dm3).
- Residual volume - is the vol of air left in lungs at end of max expiration. (1.5dm3).
- Anatomic dead space - the vol of airways not invloved in gas exchange (1.5dm3).
- Physiological dead space - is the volume of air taken in that doesn't take part in exchange. (same volume as anatomic, lower if lungs diseased).
- Measured using a spirometer.
Pulmonary ventilation = tidal volume x ventilation rate
Exchange Surfaces - Alveoli.
A good exchange surface has a large surface area to volume ratio, is very thin, is partially permeable and has movement of environmental and internal mediums.
- Lined mostly with epithelial cells. (0.5 to 3 micrometers thick).
- Surrounded by network of capillaries. (7 to 10 micrometers). which are very thin so blood flattened to fit through. Their wall is 1 cell thick.
- Diffusion rate is fast because:
- Red blood cells are slowed so more time available.
- Distance to blood reduced as are flattened.
- Very thin walls mean short distance.
- Large surface area.
- Breathing constantly ventilates and heart circulates so steep concentration gradient maintained.
- Inner surfaces covered in film of water as plasma membranes are permeable to water so diffusion rate is lowered.
- Cell walls secrete surfactant to prevent them sticking together.
- Lungs and chest wall stick together as covered in pleural membrane which creates surface tension. This forces alveoli to open when chest expands.
Caused by 2 species of rod-shaped bacteriawhich leads to a persistent cough, tiredness and lack of appetite and develops into fever and coughing blood.
M. tuberculosis is transmitted by droplets in the air, normally through close contact. M. bovis is transmitted by drinking cows' milk.
- Grows and divides in upper lungs where there's lots of oxygen.
- White blood cells accumulate leading to inflammation of lymph nodes (PRIMARY).
- It is controlled but bacteria remain and re-emerge years later.
- Lung tissue is destroyed leading to cavities and scar tissue being coughed up.
- It then spreads to the rest of the body - post-primary TB.
It is prevented using vaccinations, education, good housing, health facilities and nutrition.
Pulmonary Fibrosis, Asthma and Emphysema.
- Fibrosis is when scars on epithelia thicken so oxygen can't diffuse to blood efficiently.
- Volume of lungs and elasticity are reduced which leads to shortness of breath.
- Chronic, dry cough is caused by obstruction by fibrosis tissue. Chest pain because of pressure, tissue damage and scarring from cough. Fatigue due to reduced oxygen supply. It interferes with exhilation and short diffusion pathway.
- Asthma is an allergic reaction to allergens and is triggered by many factors.
- Causes white blood cells on bronchi lining to release histamine which inflames the air lining, causes more mucus to be released, fluid enters airways and bronchi contract which causes difficulty breathing and keeping diffusion gradient.
- Wheezing, tightness in chest, coughing. It is genetic, treated with antihistamines. It interferes with inhilation.
- Emphysema is caused by smoking, pollution, genetics or infections.
- Elastin permanently streched so can't force air out, surface area decreases and alveloi burst.
- Shortness of breath due to to difficulty exhaling and reduced alveoli. Bluish skin and chronic cough. It interferes with exhilation and large surface area.