Digestive System PDF

The Digestive System Partha Guha Lecturer Dept. of Biochemistry and Biotechnology  Small Intestine The small intestine is around 22ft long, tube-like organ in the digestive system that connects the stomach to the large intestine. The small intestine...

The Digestive System Partha Guha Lecturer Dept. of Biochemistry and Biotechnology  Small Intestine The small intestine is around 22ft long, tube-like organ in the digestive system that connects the stomach to the large intestine. The small intestine's main functions are to digest food, absorb nutrients and water, and move food along the gastrointestinal (GI) tract.  Small Intestine The small intestine consists of three parts: 1. the duodenum, 2. the jejunum, and 3. the ileum Two major accessory glands, the liver and the pancreas, are associated with the duodenum of the small intestine. The small intestine is where the greatest amount of digestion and absorption occurs. The mucosa of the small intestine produces secretions that contain primarily mucus, electrolytes, and water. Intestinal secretions lubricate and protect the intestinal wall from the acidic chyme and the action of digestive enzymes. They also keep the chyme in the small intestine in a liquid form to facilitate the digestive process. Lining of intestine walls has finger-like projections called villi, to increase surface area. The villi are covered in microvilli which further increases surface area for absorption.  Small Intestine Villi structure of small intestine  Large Intestine & Anus The large intestine is the last part of the digestive system—the final stage of the alimentary canal—in vertebrate animals. The large intestine is about 1.5 meters (4.9 ft) long. Its function is to absorb water from the remaining indigestible food matter, and then to pass this useless waste material from the body. The large intestine consists of the cecum and colon. The human anus is the external is opening of the rectum. Its closure controlled by sphincter muscles. Feces are expelled from the body through the anus during the act of defecation.  Liver The liver is the largest gland in the body, weighing between 1 and 2.3 kg. It is situated in the upper part of the abdominal cavity. The liver performs over 500 functions, including breaking down food, producing bile, storing vitamins and minerals, and regulating blood clotting. The liver can regenerate itself. If part of the liver is removed, the remaining cells will divide and regrow the lost tissue within days Anatomy of the Liver  Anatomy of the Liver The liver consists of two major lobes, the right lobe and left lobe, which are separated by a connective tissue septum, the falciform ligament. Two minor lobes, the caudate lobe and the quadrate lobe, can be seen from an inferior view, along with the porta. The porta (gate) is on the inferior surface of the liver, where the various vessels, ducts, and nerves enter and exit the liver. The hepatic portal vein, the hepatic artery, and a small hepatic nerve plexus enter the liver through the porta. The liver is enclosed in a thin inelastic capsule and incompletely covered by a layer of peritoneum. Folds of peritoneum form supporting ligaments attaching the liver to the inferior surface of the diaphragm.  Microscopic Anatomy of the Liver The interior of the liver is filled with innumerable tiny cylinders called hepatic lobules. A lobule consists of a central vein passing down its core, surrounded by radiating sheets of cuboidal cells called hepatocytes. These lobules are hexagonal in outline and are formed by cubical-shaped cells, the hepatocytes, arranged in pairs of columns Microscopic Anatomy of the Liver  Microscopic Anatomy of the Liver The lobes of the liver are made up of tiny lobules just visible to the naked eye. These lobules are hexagonal in outline and are formed by- Hepatocytes: They are the main cells in the liver. Sinusoids: Liver sinusoids are enlarged capillaries that carry blood through the liver and are the primary site for exchanging blood with the perisinusoidal space Bile canaliculus: They are microscopic spaces in the liver that collect bile produced by hepatocytes and carry it to larger bile ducts. Kupffer cells: Kupffer cells are macrophages that are found in the liver and play a critical role in protecting the liver and managing inflammation. Microscopic Anatomy of the Liver