Gas exchange in humans

What is the structure of the human breathing system

1. Thorax - an airtight compartment that encloses the lungs and respiratory system

2. Pleural membranes - line the thorax and cover each lung. They have a fluid called the pleural fluid which is a lubricant between them to stop the lung friction and chest cavity as the lungs move

3. Diaphragm- the base of the thorax and it is a done shaped sheet of muscle seperating the thorax from the abdomen

4. Ribs - surround thorax - protect lungs and help inspiration

5. Lungs - the tissue is elastic and so they recoil and return to their original shape. This recoil helps push the air out of the lungs

6. Intercostal muscles - between ribs and there is external and internal parts. During inspiration the external contracts and internal relaxes

7. The larynx - top of trachea

8. Trachea - a flexible airway to bring air into the lungs they have semi circles of cartilage to ensure the lungs don’t collapse under negative pressure

9. The two bronchi - branch of trachea

10. Alveoli- air sacs where gas exhange occurs

explain the key terms: breathing, ventilation

Breathing is a physical action performed by the diaphragm and inter coastal muscles for ventilation

Ventilation is the refreshing of the air in the lungs so there is a higher oxygen conc in the lungs than the blood for a faster diffusion and faster respiration

Explain ventilation of the lungs and inspiration steps and expiration steps

Ventilation in mammals like humans is by negative pressure breathing as the air in the lungs needs to be below atmospheric pressure for air to enter

Inspiration - breathing in

1. External intercostal muscles contract

2. Ribs move upwards and outwards pulling on the outer pleural membrane and the pressure in the pleural cavity decreases

3. The inner pleural membrane pulls on the lungs outwards

4. The diaphragm contracts and flattered

5. Volume inside the thorax increases

6. Pressure Decreased in the thorax below atmospheric pressure

7. Air rushes into lungs to maintain conc gradient for efficient gas exchange

For expiration - breathing out - opposite

Explain the layers of the trachea

1. Cilia on the columnar epithelium move unwanted particles back up the airway

2. Ciliated Columnar epithelium

3. Goblet cells - secrete mucus to trap bacteria to prevent lung infections

4. Elastic tissue

5. Blood vessels with blood cells

6. Smooth muscle fibres in bundles

7. Cartilage- chondrocytes - they are c-shaped so the open part can accommodate for tbe movement of the oesophagus to aid digestion - as well as support for lungs in negative pressure breathing

   outside trachea

Explain how the alveoli are adapted for efficient gas exchange

• they have a large surface are to volume ratio due to there numbers and sphere shape

• Surfactant lining enables gases to dissolve easily and diffuse across the alveoli - they are permeable - the surfactant is a soapy substance containing phospholipids and proteins in water to stop the alveoli sticking together during exhaling as it reduces surface tension because the hydrogen bonds don’t fully form in the water and stick the lungs together when pressure is low.

• They have thin walls made of one layer of squamous epithelium cells so diffusion pathway is short

• An extensive capillary network surrounds the alveoli for the maintenance of the conc gradient and to be a short diffusion pathway. Each blood vessel is made of endothelial one cell thick

• Concentration gradient is maintained by haemaglobin carrying away oxygen on red blood cells so low concentration in blood and ventilation by breathing meaning a high conc in lungs so quick rate of diffusion

Explain how o2 enters and co2 exits

Deoxygenated blood enters the capillaries around the alveoli and oxygen diffuses across alveoli from lungs into blood and co2 diffuses out of plasma in blood to alveoli for expiration