The document discusses the human gas exchange system and its two main parts: the conducting system and interface. The conducting system includes the nasal passage and leads to the lungs. The interface is where gas exchange occurs between air and blood in tiny sacs called alveoli found inside the lungs. The document also describes the different types of epithelial cells that line the alveoli and their roles in gas exchange and preventing collapse of the alveoli during breathing.

1. Gas Exchange

2. The gas exchange system in humans and other mammals are made up of 2 major parts. Conducting System For the conduction of inspired and expired gases. Which parts make up the conducting system? The conducting system begins with the nasal passage. Interface This is for the exchange of gases between the air and blood.

3. The inside of the thoracic cavity is lined with a Pleural membrane. Each lung is also surrounded by a separate pleural membrane. The space between the two pleural membrane is filled with a thin of fluid known as Pleural fluid. What is the function of the pleural fluid? i. The fluid prevents friction between the lungs during breathing. ii. It causes the outer surface of the lungs to adhere closely to the inside of the thoracic cavity during inspiration.

4. Alveoli They are the sites of gas exchange. The site of gas exchange. Pocket shaped structure. 100 – 300 microns in diameter. Open on one side. Lined with extremely flattened epithelial cells. Why? Each alveolus consists of epithelium and connective tissues including elastic fibres and collagen. Why? The lungs have a number of defence mechanisms against microorganisms and small particles such as carbon in smoke. Explain.

5. There are 2 types of epithelium cell. i. Type I Pneumocytes ii. Type II Pneumocytes Type I are relatively large, extremely flattened cells and make up most of the alveolar wall. Type II pneumocytes secrete Surfactant, a mixture of lipids and proteins, which helps to prevent the alveolus from collapsing completely and ‘sticking shut’ as air moves out of the lungs during expiration. The capillaries surrounding the alveoli are refered to as the Pulmonary capillaries

6. Epithelial tissues are found on the internal and external surfaces of animal organs and may have several roles, depending on their location. Many epithelia protect underlying tissues against water loss, damage (by rubbing), pressure or infection Epithelial cells may be involved in processes such as respiratory gas exchange, the uptake or release of nutrients and excretion. A simple epithelium consists of cells arranged in a singe layer. A compound or stratified epithelia are composed of several layers of cells

7. The main features of simple epithelial tissues are i. They form continuous layers on internal and external surfaces. ii. The cells are held together by a thin layer of intercellular substances containing hyaluronic acid which sticks them together. iii. The cells rest on a basement membrane made up largely of collagen fibre. iv. There are no blood cells present. v. The free surfaces of the cells may be highly specialised. vi. Damaged cells are rapidly replaced by cell division.

8. Types of Simple epithelia Cubodial epithelium – This is the simplest type of epithelium and consists of cubes-shaped cells, each with a centrally situated spherical nucleus. The cells are closely packed together and appear pentagonal or hexagonal in outline. This type of epithelium occurs in the nephrons of the kidney and lines the salivary and pancreatic ducts. It is also present in many glands (mucus, salivary, sweat and thyroid) where it has a secretory function.

9. Squamous epithelium Consist of thin, flattened cells with little cytoplasm. The nucleus of each cell is disc shaped and centrally situated. This type of epithelium is found in the Bowman’s capsule of the kidney, the alveoli of the lungs and lining the blood vessels and the chambers of the heart.

10. Columnar Epithelium It is made up of tall, narrow cells. There is a large spherical nucleus near the base of each cells and the free surface often possess microvilli Mucus secreting goblet cells are often found amongst the columnar cells. This tissue lines the stomach and intestine, and is alos present in some ducts of the kidney.

12. Can you name the following epithelial cells

13. Ventilation in humans Define Ventilation. How does air move in and out of the lungs. Use key words like pressure, pressure gradient. What happens during inspiration – link to the volume of the thorax, movement of the ribs, diaphragm (contraction or relaxation), shape of the diaphragm, intercostal muscles, pressure within the lungs. Also explain into details Expiration. Get pictures showing inspiration and expiration.