Digestive Processes: From Small Intestine to Egestion
Small Intestine: Digestion and Absorption
The small intestine is involved in chemical digestion and absorption of nutrients. It is connected with valves to:
- The stomach through the pylorus.
- The large intestine through the ileocecal valve.
The small intestine has three parts:
- Duodenum: Primarily responsible for the digestion of proteins (using trypsin), carbohydrates (using pancreatic amylase), and fats (using lipase).
- Jejunum: Focuses on food absorption. The inner layer is full of folds called villi, which increase the surface area for absorption. Food absorption refers to the passage of:
- Glucose and amino acids into the bloodstream.
- Fatty acids and glycerol into the lymph.
- Ileum: Continues the process of nutrient absorption and connects to the large intestine.
Assimilation
Assimilation ensures that nutrient levels are balanced in the blood. If there is too much of a nutrient, the liver converts it into a storage or waste form. The liver processes sugars, amino acids, and fats differently:
- Excess amino acids can be:
- Removed as a waste product called urea.
- Converted into proteins.
- Glucose can either be used for energy production or stored as glycogen.
Digestive Process in the Large Intestine
The large intestine is the final section of the alimentary canal. It is responsible for water absorption and the storage of faeces. The large intestine is composed of three main sections:
- The colon absorbs water and some minerals from digested food.
- The rectum stores undigested material. This forms solid faeces after sufficient water has been absorbed.
- The anus is where faeces is removed from the body. This is called egestion.
Key Respiratory Concepts
Respiration: A series of chemical reactions that happen in all living cells, in which food is broken down to release energy, usually by combining it with oxygen.
Gas exchange: The exchange of gases across a respiratory surface.
Breathing: Muscular movements which keep the respiratory surface supplied with oxygen.
Aerobic Respiration: Releases energy from glucose by combining it with oxygen.
Anaerobic Respiration: Releases energy from sugar without using oxygen.
Nose and Mouth
It is better to breathe through the nose because the structure of the nose allows the air to become warm, moist, and filtered before it gets to the lungs. Hairs in the nose trap dust particles.
Other cells have tiny hair-like projections called cilia. The cilia are always moving, and bacteria get trapped in them and in the mucus. Cilia are found all along the trachea and bronchi.
Trachea
At the top of the trachea is the epiglottis. This closes the trachea and prevents food from going down the trachea when you swallow.
Bronchi
The trachea divides into two branches called bronchi. One bronchus goes to each lung and then branches out into smaller tubes called bronchioles.
Alveoli
Alveoli are where gas exchange takes place.
Breathing Movements
Breathing is the process of getting oxygen into the lungs and carbon dioxide out of the lungs.
Intercostal muscles: Located between the ribs. Diaphragm: A large sheet of muscle and elastic tissue that stretches across your body, underneath the lungs and heart.