Digestive System Of Frog 2f5d4n

DIGESTIVE SYSTEM

Components of the Digestive System Digestive Tract  Gastrointestinal (GI) tract or alimentary canal  muscular tube  extends from oral cavity to anus Digestive Glands

6 Functions of the Digestive System 1.Ingestion:  occurs when materials enter digestive tract via the mouth

2.Mechanical processing:  crushing and shearing  makes materials easier to propel along digestive tract

3. Digestion:  is the chemical breakdown of food into smaller molecules  for absorption by digestive epithelium

4.Secretion:  is the release of water, acids, enzymes, buffers, and salts into tube where digestion occurs  by epithelium of digestive tract

5. Absorption:  organic substrates, electrolytes, vitamins and water  digestive epithelium

6.Excretion  elimination of wastes and residues

Two Types of Digestive System • Incomplete digestive system – One-way, saclike digestive cavity

• Complete digestive system – A tube with an opening at each end

Swallowing • Complex reflex

• Tongue forces bolus into pharynx • Epiglottis and vocal cords close off trachea; breathing temporarily ceases • Bolus moves from the esophagus through the esophageal sphincter into stomach

Parts of Alimentary Tract Mouth  anterior end of the gastrointestinal tract

Pharynx Esophagus  gullet  connects the mouth with stomach

Structure of the Stomach  J-shaped organ lies below the diaphragm  temporary storage of food  protein is partially digested  water is partially absorbed  sphincter at both ends  outer serosa covers smooth muscle layers  Mesogaster - suspends the stomach to the dorsal wall of the abdomen

muscle

Stomach Secretions  Hydrochloric acid (HCl) - produced by parietal cells  Gastric acid - produced by the chief cells  Pepsinogen (inactive form of a proteindigesting enzyme) - produced by chief cells  Mucin - produced by mucous cells

Mixing of Chyme • A thick mixture of

bolus and gastric fluid (chyme)

• Mixed and moved by waves of stomach

contractions (peristalsis)

Small intestine

 longest and most coiled tube of digestive tract  final digestion and absorption of digested food materials a. duodenum – anterior part b. ileum – posterior part c. jejenum – middle part (absent in some species of frog)  mesenterium/ mesentery proper

• movement into duodenum controlled by pyloric sphincter

• duodenum receives secretions from pancreas, liver, and gallbladder; continues process of digestion

Intestinal Secretions  Wall of the duodenum secretes  Disaccharidases - digest disaccharides to monosaccharides

 Peptidases - break protein fragments down to amino acids  Nucleases - digest nucleotides down to nucleic acids and monosaccharides

Large intestine  Shorter and larger than small intestine  Mesorectum  storage of undigested food

 Anus - excretion of undigested food

Digestive Glands

Liver  largest gland  metabolism of fats(fat digestion)  secretes bile • Bile is stored in gallbladder, then secreted into duodenum • Bile emulsifies fats; breaks them into small droplets

Functions of the liver  Inactivation of toxins  Storage of fat soluble vitamins  Storage of iron  Storage of glycogen and lipid  Organ of immune system

Pancreas  adjacent to the duodenum  produce enzymes secreted into duodenum a.Pancreatic amylase b.Trypsin and chymotrypsin c. Carboxypeptidase d. Lipase e. Pancreatic nucleases

Histology (Digestive System)

Stomach  Tunica mucosa - mucous membrane - single layer of columnar epithelial cells  Tunica submucosa - internal layer of c. tissue - blood vessels and nerves  Tunica muscularis - layer of smooth muscle cells arranged in 2 concentric layers  Tunica serosa - single layer of squamous cells

• Rugae (folds)

Structure of Small Intestine submucosa

gut lumen

serosa

circular muscle

longitudinal muscle

blood vessels

mesh of nerves (plexus)

• Villi (folds)

• Different layers of the small intestine

Liver  Hepatocytes/liver cells - secrete bile - metabolism of carbohydrates, fats and amino acid  Sinusoids - Spaces separating group of hepatic cells  Kupffer cells - macrophages found in the sinusoids - destroy bacteria that enter blood through the large intestine

Pancreas - consist of 2 types of glands: 1. Exocrine gland (tubulo-acinous gland) - produce digestive enzymes (pancreatic juices) 2. Endocrine gland (Islet of Langerhans) - produce insulin (controls carbohydrate and sugar metabolism)