Human Digestive system HDS Digestion and Organs

Human Digestive system (HDS) – Digestion and Organs of digestive system

NUTRIENTS and THE DIGESTIVE SYSTEM • The energy that food provides is necessary for the continuity of life on earth. • Food can be divided into six groups: • - carbohydrates • - lipids • - proteins • - vitamins • - minerals • - water

Digestion • Digestion is the process by which food is ingested (проглатывать) from the environment, hydrolyzed into its subunits and absorbed from the gut (пищеварительный канал) into the blood.

Digestion (hydrolysis) • The process of hydrolysis is carried out by the digestive system. • Molecules are split into their component parts with water. • During digestion, large molecules are broken into smaller portions that can cross the plasma membrane easily.

Steps in Digestion • • Ingestion of food Mechanical digestion Chemical digestion Absorption

Ingestion of food • Food is ingested into the digestive tract through the mouth, aided by the lips, teeth and tongue.

Mechanical digestion • Food is physically ground or chewed into smaller pieces in the mouth by the teeth. • A bolus is formed and is swallowed. • Peristaltic contractions of smooth muscle in the esophagus (пищевод), assisted by gravity, transport the food to the stomach.

Chemical digestion • Chemical digestion is a series of reactions in which food are hydrolyzed, aided by water and enzymes.

Absorption • After the degradation of food in the digestive tract into its monomeric units, the products are absorbed into the blood through the microvilli (микроворсинки) of the small intestine (тонкая кишка).

Digestive system • The digestive tract is comprised of the mouth, pharynx esophagus stomach small and large intestine. • The major glands which secrete substances are the salivary glands, alveolar glands of the stomach, glands in the intestine wall, the pancreas and the liver.

MOUTH • The structures found in the mouth are the teeth, salivary glands and the tongue. • Function of teeth is to grind food into small particles and to mix it with digestive secretions.

Tongue regions • Sweet foods are tasted at the tip of the tongue, whereas bitter foods are tasted at the rear. • Sour and salty foods are simultaneously tasted on both sides of the tongue. Bitter Salt and sour Sweet

Pharynx • The pharynx is a cavity located directly behind the mouth, in front of the esophagus and trachea.

Esophagus (25 cm) • The esophagus a pipe • It passes from the pharynx to the stomach. • A rhythmic contraction of the digestive tract is called peristalsis, pushes the food along. • Peristalsis begins in the esophagus

Stomach • The largest portion • Cardiac sphincter, a valve through which food enters the stomach. • Pyloric sphincter - it regulates the movement of chyme (a soupy liquid) into the duodenum.

Stomach • The stomach is composed of three layers of smooth muscle: circular, longitudinal and oblique. • They regulate the movement of stomach • Stomach has a mucosal layer (слизистая оболочка). • Mucosal layer has glands

Stomach • Gastric glands have 2 cells: chief cells and parietal cells • Chief cells secrete pepsinogen (enzyme) into the gastric juice, where it is converted to pepsin. • Parietal cells secrete hydrochloric acid (HCl) and intrinsic factors which function in absorption of vitamin B.

Small Intestine (6 m) • • • It has 3 segments: - duodenum (25 cm) - jejunum Villi – 4 millions - ileum Function of the jejunum is the absorption of nutrients into the blood, because this part of small intestine has villi

Large Intestine (1. 5 to 2 meters in length) It has 3 segments: - caecum - colon - rectum The appendix, a projection of the caecum • This organ may become inflamed causing severe pain. • In such cases, it must be surgically removed. • • •

Pancreas • Mixed gland • It’s secretions have basic characteristics – neutralizes acidic (HCl) condition • It opens into small intestine • Hormone – glugacon and insulin

Liver • The liver is the largest organ of the body and gland • It contains the gall bladder. • Bile duct leading from the gall bladder transmits bile salts, which break down fats in the duodenum.

Functions of the liver • Formation and secretion of bile. • Regulation of blood sugar level. • Formation of fibrinogen and thrombogen, which are active during blood clotting. • Detoxification of substances.