Digestion Definition And Human Digestive System

Digestion Definition : Food is essential for all living organisms. Food contains carbohydrates, proteins and fats. Some amount of vitamins and minerals are also needed by the body. Food gives us energy and organic materials needed for the growth and repair of tissues. All metabolic processes require water, and water also keeps our body hydrated.

Diffusion Means Of Transport

Digestion Definition

Human Digestive System

Mouth

• Mouth is a slit-like aperture surrounded by upper and lower lips. Lips are a muscular structure that makes them movable. They are made up of muscles known as orbicularis oris muscles.
• Mouth leads into the buccal cavity. Buccal cavity consists of buccal vestibule and oral cavity.
• Oral cavity contains teeth, muscular tongue and palate. The roof of the buccal cavity is the palate. The tongue is attached to the floor of the buccal cavity via a freely movable muscular organ known as the frenulum.
• Tongue contains transverse ridges known as palatine rugae. These rugae help in the mastication of food.

Teeth

• Teeth are ecto mesodermal in origin.
• Human dentition is of 3 types- Thecodont, diphyodont and heterodont.
• Most mammals, including humans, contain two sets of teeth during their life- milk teeth/deciduous teeth and permanent teeth. Permanent teeth replace milk teeth; this is known as diphyodont.
• Adult humans contain four types of teeth- incisors, canine, premolar and molars. This type of arrangement of teeth is known as heterodont.
• Human teeth are also embedded in the sockets of the jaw bone; it is known as the codont.
• Arrangement of teeth in each half of the lower and upper jaw is known as a dental formula. The human dental formula is 2123/2123.
• The hard chewing surface of teeth is made up of enamel. It helps in the mastication of food.

Oesophagus

• Oesophagus is a tube-like structure that extends posteriorly from the neck, thorax and diaphragm and opens into the stomach.
• At the junction of the oesophagus, a sphincter is located, known as the gastroesophageal sphincter.
• Oesophagus hiatus is the opening in the diaphragm via which the vagus nerve and oesophagus pass.
• No digestive glands are found in the oesophagus.

Digestion In Ruminants

Stomach

• Oesophagus opens into a J-shaped structure known as the stomach.
• Stomach is divided into four parts- cardiac, fundus, body, and pylorus. The oesophagus opens into the cardiac portion, a fundus region, the body is the main central region, and the pyloric opens into the duodenum.
• The layer that covers the stomach is known as the peritoneum. The peritoneum contains lymph and fat tissues, and such peritoneum is known as momentum.
• Stomach also contains longitudinal folds known as rugae.
• Epithelium in the stomach gets invaginated and forms simple, branched tubular glands known as gastric glands.
• Gastric glands contain 4 types of cells-

Intestine

• Intestine includes the small intestine and large intestine.
• Small intestine is divided into the duodenum, jejunum and ileum.
• Small intestine contains finger-like projections known as villi which increase the absorptive surface area at the time of digestion of food.
• Ileum opens into the large intestine, comprising the caecum, colon and rectum.
• Illeum opens into the caecum and is guarded by an ileocaecal valve.
• Caecum is a blind sac that hosts symbiotic microorganisms. Caecum also contains a worm-like structure known as a vermiform appendix. It is a vestigial organ. Inflammation of the vermiform appendix is known as appendicitis.
• Colon opens into the rectum. Rectum opens into the anal canal, which finally leads into the anus.

Different Types of Ecological Pyramids

Digestive Glands

• Liver is made up of two lobes, and each lobe comprises hepatic lobules.
• Hepatic lobules are the structural and functional unit of the liver and contain hepatic cells.
• Each lobule is covered by a sheath known as Glisson’s capsule.
• Liver secretes bile. Bile is a yellowish-green, alkaline fluid that contains bile pigments (bilirubin and biliverdin), bile salts (sodium taurocholate and sodium glycolate), and cholesterol, but no enzymes are present.

Digestive Enzymes

Pancreas

• Pancreas is endodermal.
• It is a heterodyne/mixed/composite/dual gland. It functions as both endocrine and endocrine.
• Exocrine part secretes pancreatic juice. It contains enzymes and salts.
• Pancreatic juice contains trypsin, chymotrypsin, procarboxypeptidase, etc.