Human Respiratory System

1. Nostrils: There are two nostrils that converge to form a nasal passage. The inner lining of the nostrils is lined by hair and remains wet due to mucus secretion. The mucus and the hair help in filtering the dust particles out of inhaled air. Further, the air is warmed up when it enters the nasal passage.
2. Pharynx: A tube-like structure that continues after the nasal passage. The pharynx is where the food pipe and windpipe start. The windpipe is in front of the food pipe and has a lid that closes when we swallow food to stop it from entering the windpipe. When not eating, the windpipe stays open so air can pass through.
3. Larynx: This part comes after the pharynx. This is also called a voice box. It is located in the throat. It helps us produce sound and also ensures that air passes safely to the lungs.
4. Trachea: This is composed of rings of cartilage. Cartilaginous rings prevent the collapse of the trachea in the absence of air.
5. Lungs: Each lung is located on either side of the heart in the thoracic cavity. The lungs occupy most of the thoracic cavity and partially cover the heart. The pleura is a double-layered membrane that encloses each lung. Lungs are elastic and spongy, made up of many small compartments called alveoli. A dense network of capillaries surrounds each alveolus. The thin walls of alveoli and capillaries allow for easy gas exchange. The numerous alveoli provide a large surface area for efficient gas exchange.
6. Bronchi: A pair of bronchi emerges from the trachea, with one bronchus going to each lung. They ensure air is distributed evenly throughout both lungs. 
7. Bronchioles: A bronchus divides into branches and sub-branches inside the lung. Bronchioles are small branches that come from the bronchi inside the lungs. They carry air to the alveoli, where gas exchange occurs. Bronchioles help control airflow within the lungs.
8. Alveoli: These are air sacs at the end of bronchioles. The alveolus is composed of a very thin membrane and is where blood capillaries open. This is the alveolus, where the oxygen mixes with the blood and carbon dioxide exits from the blood. The exchange of gases in alveoli takes place due to the pressure differential in the body for release into the alveoli, and the oxygen in the alveolar air is taken up by the alveolar blood vessels to be transported to all the cells in the body.
9. Diaphragm: The diaphragm is a muscular partition at the base of the thoracic cavity, separating it from the abdominal cavity. When the ribs rise and the diaphragm lowers, lung pressure decreases, and air flows into the lungs. When the ribs return to their position and the diaphragm rises, lung pressure increases, pushing air out. The diaphragm's continuous movement up and down is essential for breathing.

Respiratory System

Alveoli

Human Respiratory System and Alveoli

• Gaseous exchange occurs continuously as blood flows around the alveoli.
• Haemoglobin in red blood cells absorbs oxygen from the air in the alveoli.
• At the same time, carbon dioxide and water vapours move from the blood into the alveoli.
• Oxygen is absorbed into the blood, while carbon dioxide and water vapour are removed. These waste gases are expelled from the body during exhalation.

• All the important functions of our body need energy, and this energy comes from respiration. The energy from respiration helps our body grow, repair itself, and make new cells.
• Respiration, along with photosynthesis, helps keep the balance of oxygen and carbon dioxide in the air.
• Anaerobic respiration, which happens without oxygen, is useful in making products like alcohol, vitamins, and antibiotics. It is also used in industries like bakeries and distilleries to produce various items.

1. In plants, exchange of gases (O₂ and CO₂) occurs through stomata by diffusion, depending on day or night.
2. Aquatic animals like fish breathe faster because water has less oxygen; they absorb oxygen through gills.
3. In terrestrial animals, oxygen is taken from the air using special respiratory organs like lungs.
4. In humans, air enters through nostrils, passes through the trachea and bronchi, and reaches the lungs, where gas exchange happens in tiny sacs called alveoli.
5. Oxygen is carried by haemoglobin in red blood cells, and carbon dioxide is mostly transported in dissolved form in blood.