Digestive System Functions of the digestive system Ingestion

Digestive System

Functions of the digestive system • Ingestion, the taking in of food into the body. • Mechanical processing of food into smaller pieces and mixing it together.

• Secretion of water, acids, enzymes and buffers to aid in digestion. • Digestion, the chemical breakdown of large food molecules into smaller ones.

• Absorption of nutrients from food into the bloodstream. • The removal of waste products, called excretion.

Mouth • In the mouth, mastication occurs as the teeth physically tear the food into smaller pieces. ▫ This increases the surface area of food, allowing it to dissolve and chemically digest more quickly.

• Three pairs of salivary glands produce salivary amylase an enzyme that breaks down starch (polysaccharide) into maltose (disaccharide). Sublingual Gland Parotid Gland Submandibular Gland

Tooth Anatomy • The outermost layer of the tooth is enamel. ▫ Made of pure calcium phosphate (Ca 3(PO 4)2), the hardest biologicallymade substance. • Under the enamel is dentin, which is less mineralized and yellowish in color. ▫ At the roots, dentin is covered by cementum, which attaches teeth to underlying ligaments.

• The hollow area inside the tooth is called the pulp cavity. ▫ Each tooth has 1 -4 hollow root canals that contain nerves and blood vessels. • Periodontal ligaments attach teeth to the maxilla or mandible.

Crown Enamel Gingiva Dentin Bone Tissue (Mandible) Root Canals Pulp

Types of teeth • Incisors are blade-shaped teeth at the front of the mouth. ▫ Clipping or cutting.

Types of teeth • Canines are cone-shaped with a pointed tip. ▫ Tearing or slashing.

Types of teeth • Premolars and molars have flattened tops. ▫ Crushing, mashing, or grinding.

Types of teeth • Wisdom teeth are an additional set of molars that often develop in locations where they cannot erupt.

Incisors Canine Premolars Palatal Arches Palatine Tonsils Molars Hard Palate Soft Palate Uvula Tongue Frenulum Vestibule (between lower lip and gingiva)

• Cavities occur when bacteria produce waste acids that dissolve the calcium phosphate of the enamel, creating a hole. • https: //www. youtube. com/watch? v=z. G o. BFU 1 q 4 g 0 • A root canal is a procedure that removes the contents of the pulp cavity, replacing it with solid filling. • Extractions: https: //www. youtube. com/watch? v=8 m k 8 I 3 t. Tod 8 • https: //www. youtube. com/watch? v=8 j. F mn 4 Nln. U 4

Pharynx • The tongue produces a ball of chewed, softened food called a bolus, which is swallowed. • The uvula folds back, closing off the nasopharynx and forcing food down the laryngopharynx.

• A flap of tissue called the epiglottis closes of the opening to the larynx and trachea.

• The bolus passes through the pharynx and esophagus through a series of involuntary wavelike contracts of smooth muscle called peristalsis. ▫ These are visible on an X-ray when barium is swallowed.

Stomach • Food enters the stomach through the cardiac sphincter, which prevents it from going back up the esophagus.

• The stomach has internal folds called rugae, that increase surface area. The rugae contain several cell types: ▫ Mucous cells produce mucus needed to protect the stomach from digesting itself. ▫ Parietal cells secrete hydrochloric acid. ▫ Chief cells secrete pepsin, which digests proteins into amino acids. Chief Cells Parietal Cells Rugae Mucus Cells

• The number of each cell type varies by stomach region: ▫ The cardiac and pyloric regions produce mucus. ▫ The fundus and body produces pepsin and HCl.

Fundus Esophagus Cardia Duodenum Body (Rugae) Pyloric Sphincter Pyloric Region

• The inner layer of the stomach contains smooth muscles that allow the stomach to churn and mix food.

• The partially digested food, mucus, and acid mixture is now referred to as chyme. ▫ The pyloric sphincter will open and release small amounts (30 m. L) of chyme into the small intestine.

Small intestines • The duodenum is where most of the digestion in the small intestines occurs. ▫ Receives secretions from the gall bladder and pancreas. ▫ The duodenum also add its own secretions.

Falciform Ligament Liver Gall Bladder Duodenum Pancreas

Organ Enzyme Substrate Product Duodenum Sucrase Lactase Maltase Sucrose Lactose Maltose Monosaccharides (e. g. glucose, fructose) Pancreas Trypsin Lipase Amylase Protein Lipids Starch Amino acids Fatty acids and glycerol Maltose • The pancreas also releases bicarbonate, which neutralizes the stomach acid.

• The liver releases bile salts through the gall bladder. ▫ These emulsify, or break up fat globules into smaller droplets that can be digested more easily. ▫ Similar in action to detergent or soap.

Jejunum-ileum • The jejunum is the middle segment of the small intestine; the ileum is the last segment. • Both segments specialize in the absorption of nutrients. ▫ Villi increase surface area. ▫ The hepatic portal system is a series of blood vessels that deliver nutrients to the liver.

Large Intestine • The first part of the large intestine is a pouch called the cecum. ▫ A dead-end pouch called the appendix is attached here. • The remaining segments of the large intestine are: ▫ Ascending colon → Transverse colon → Descending colon → Sigmoid colon

• In herbivores, the appendix and cecum are larger and contain bacteria that help to digest plant fiber. Rabbit digestive system. Shows the cecum (E) and appendix (F)

• Water is reabsorbed from the large intestines into surrounding tissues through osmosis.

Oral Cavity Sublingual Gland Submandibular Gland Parotid Gland Uvula Tongue Pharynx Trachea Esophagus Diaphragm Liver Pancreas Ascending Colon ileum Appendix Spleen Stomach Transverse Colon Descending Colon Jejunum Sigmoid Colon Rectum Anus

• A complex community of beneficial bacteria called gut flora live in the large intestines. ▫ Ferment undigested carbohydrates, aid in vitamin B and K production, and prevent the growth of harmful bacteria. ▫ Also responsible for the production of intestinal gases like H 2 S.

Defecation Reflex • The rectum stores fecal matter. ▫ The internal anal sphincter is an involuntary muscle that opens when the rectum is full. ▫ The external anal sphincter must be voluntarily relaxed. • The rectus abdominis and transversus abdominis muscles compress the rectum, removing the feces.

Pancreas • The pancreas, in addition to producing digestive enzymes, also controls blood sugar. • Islets of Langerhans contain the cells that actually produce these hormones. ▫ Insulin lowers blood sugar by absorbing glucose into the liver and muscles. ▫ Glucagon has the opposite effect, raising blood sugar.

Connective tissues • The stomach is held in place with the other abdominal organs by the greater omentum. ▫ This is also a major body fat storage area.

• The mesentery holds the intestines together and contains all intestinal veins and arteries.

Digestive System Disorders • The mumps is a viral infection that causes painful swelling of the salivary glands, especially the parotid gland. ▫ Airborne and highly contagious.

• Heartburn is caused by an influx of stomach acid into the esophagus. ▫ Caused by excessive acid production in the stomach, or a faulty cardiac sphincter.

• An ulcer is an erosion of the lining of the digestive tract. ▫ Peptic ulcers occur in the stomach. ▫ Duodenal ulcers occur in the duodenum. • Causes may include bacterial infections, overuse of oral painkillers, and stress.

Vomiting • Vomiting is an involuntary opening of the stomach caused by: ▫ Irritation of the gastrointestinal tract. ▫ Irritation of the pharynx (gag reflex) ▫ Multiple trigger zones in the brain.

1. Salivation protects the teeth from stomach acid. 2. A deep breath is taken to prevent pulmonary aspiration. 3. Retroperistalsis (reverse peristalsis) sweeps the digestive tract from the small intestine towards the esophagus. 4. Abdominal muscles contract.

Diarrhea • Diarrhea is the presence of abnormally loose or liquid feces caused by an excess of water inside the intestines, caused by: ▫ Bacteria (Cholera, E. coli O 157: H 7) produce a toxin that creates an ion imbalance in the intestines, disrupting normal osmosis. ▫ Laxatives often contain an ion (like magnesium) that will intentionally create an osmotic imbalance.

Lactose intolerance • People that are lactose intolerant stop producing the lactase enzyme when breastfeeding ends. ▫ Undigested lactose eventually reaches the large intestine, causing an osmotic imbalance (diarrhea). ▫ Bacteria are able to ferment the lactose, producing excessive amounts of gas.

Diabetes • Type I Diabetes is the result of the immune system destroying the insulin-producing cells of the pancreas. ▫ No insulin is produced. The patient is dependent on insulin injections. • Type II Diabetes occurs because cells in the liver, muscles, and fat do not respond adequately to insulin. ▫ Most common cause is obesity.