GastroIntestinal System

By. Christina Sanzari, Erin Hines, and Nicole Nunez

Anatomy/Physiology

Responsible for the intake, digestion of food, absorption of nutrients, and elimination of solid waste.

Alimentary canal, or the gastrointestinal (GI) tract, is the continuous muscular digestive tube that winds through the body; its organs include: the mouth, pharynx, esophagus, stomach, small intestine, and large intestine.

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter26/animation__organs_of_digestion.html

Digestion Digestion- The Mechanical and chemical breakdown of foods

and the absorption of the resulting nutrients by cells.

Mechanical Digestion- Breaks large pieces into smaller ones without altering their chemical composition.

Chemical Digestion- breaks down food into simpler chemicals.

Gastrointestinal System carries out these processes.

GI tract

Oral Cavity

• mouth

Oral Cavity: Salivary Glands• 2 types of secretory cells:

o serous cells: produce a watery fluid that is rich in proteins and glycoproteins as well as amylase (split starch and glycogen molecules into disaccharides)

o mucous cells: secrete a thick mucus which lubricates the food before it is swallowed

• Salivation: occurs when one prepares to eat, and nerve signals activate salivary glands to moisten the mouth

• The amount of saliva secreted depends on how appealing the particular food is to the individual

Oral Cavity: Salivary Glands (cont...)• There are three types of salivary glands, each

split up into lobeso partoids

large secrete 25% of saliva (watery) front of ears extending to jaw bone (1 on

each side) drains into mouth near upper teeth

o submandibular secrete 70% of saliva (mucus) drains into mouth from under tongue

Oral Cavity: Salivary Glands (cont... 2)

o sublingual smallest secrete 5% of saliva (mucus) drains into floor of mouth

Oral Cavity: Cheeks and Lips• Buccal

• stratified squamous epithelium

• inside of cheek is lined by mucous membrane

• lips contain sensory receptors and provide information about food before its in the mouth

• few differences between lips and skin on bodyo no sebaceous glands- keep moisturized with

salivao no hair follicles

Oral Cavity: Tongue

• guides and molds food in the mouth

• composed of skeletal muscle fibers (willingly controlled)

• mucous membrane protects it from microbes and pathogens

• lingual frenulum connects tongue to floor of mouth

• perceives taste and texture

• over 10,000 taste buds (change with age)

Oral Cavity: Palate

• forms the roof of the oral cavity and consists of a bony anterior part and a muscular posterior part

• palatine tonsils- two lymphatic tissue masses, located on either side of the pharynxo help protect the body against infection

(respiratory)

Pharynx and Esophagus

• the pharynx connects the nasal and oral cavities with the larynx and esophagus

• the esophagus is a food passageway from the pharynx to the stomach o both do not digest food, but act only as

passageways to the stomach

• there are 3 parts to the pharynx:o nasopharynxo oropharynxo laryngopharynx

Pharynx and Esophagus (cont...)• nasopharynx

o provides a passageway for air when breathing

• oropharynxo passageway for food to move from the mouth,

and for air to move to and from the nasal cavity

• laryngopharynxo provides a passageway to the esophagus

Endoscopy

• when looking into the throat, doctors may use an endoscope, which may be guided through the mouth or the nose

Peristalsis

• the series of muscle contractions through which the esophagus delivers food to your stomach

• contractions are wave-like, beginning in the esophagus

• smooth muscle carries food to stomach

• food is turned into chymeo chyme: a liquid mixture

StomachThe stomach is divided into the fundus(upper, rounded part), body

(main portion), and antrum(lower part).

Rugae- the folds in the mucosa lining the stomach.

Gastric Secretions: Thick mucus membrane forms the inner lining of stomach , studded with small openings (gastric pits) that are at the ends of gastric glands

-Gastric glands have 3 types of secretory cells; mucous, chief, and parietal cells

-Chief secrete digestive enzymes

-Parietal release hydrochloric acid

-The digestive enzymes and the hydrochloric acid forms gastric juice

Stomach (cont.)-When pepsinogen from chief cells comes in contact with hydrochloric

acid from the parietal cells, it breaks down forming pepsin

Gastric Absorption Gastric enzymes break down proteins-The stomach only absorbs small volumes of water and certain salts

Emptying -The rate that your stomach empties depends on fluidity of chyme and

the type of food-Carbohydrates pass through the fastest, followed by foods high in

protein and fatty foods stay in the stomach the longest

PancreasPancreatic Juice- Contains enzymes that digest

carbohydrates, fats, nucleic acids, and proteins

-Pancreatic amylase -splits molecules of starch or glycogen into double sugars

-Pancreatic lipase- breaks triglyceride molecules to fatty acids and glycerol

-Two nucleases, which are enzymes, break down nucleic acid molecules into nucleotides

-Trypsin, chymotrypsin, and carboxypeptidase (protein splitting enzymes) split the bonds between certain amino acids in proteins

Pancreas (Cont.)

Regulation of Pancreatic Secretion

-Nervous and endocrine systems regulate release of pancreatic juice

-Duodenal mucous membrane releases peptide hormone secretin into the bloodstream

-Stimulates secretion of pancreatic juice

Liver

Liver functions -Carbohydrate metabolism- helps maintain concentration

of blood glucose

-lipid metabolism-oxidizes fatty acids at a high rate, synthesizing lipoproteins, phospholipids, and cholesterol, and converting portions of carbohydrate and protein molecules into fat molecules

-Protein metabolism-deaminated amino acids, synthesizing plasma proteins, and converting certain amino acids to other amino acids

Jaundice Jaundice is the yellowing of the skinCaused by hyperbulirubinemia (increased levels of

bilirubin in the blood)Jaundice is often a side effect of liver disease such as

hepatitis or liver cancer.

Gallbladder -Stores bile between meals, reabsorbs water to

concentrate bile, and contracts to release bile into small intestine

Functions of Bile Salts -Aid digestive enzymes

-Break down fat globules into smaller droplets (emulsification)

-Then they mix with water so the fat molecules can be digested more effectively

Small Intestine

�Digestion in Small Intestine Produces:

1) disaccharides

2) fatty acids

3) peptidesmonoglycerides

Portions of the Small Intestine:

1) duodenum

2) jejunum

3) ileum

Small Intestine Wall

• Appears velvety due to intestinal villi

• Villi: tiny projections of mucous membrane

• Villi aid in the absorption of digestive products by increasing the surface area of the intestinal lining

• Consist of a layer of simple columnar epithelium and a core of connective tissue that contain blood capillaries, lacteal, and nerve fibers

• Blood capillaries and lacteals carry away absorbed nutrients, and nerve fibers transmit impulses to stimulate/inhibit villus activities.

Secretion of the Small Intestine

• Intestinal glands secrete large amounts of a watery fluid which carries digestive products into the villi

• The digestive enzymes break down food molecules before absorption takes place.

• Peptidases split peptides into amino acids.

• The amino acids then split the double sugars into simple sugars.

• Then the intestinal lipase splits fats into fatty acids and glycerol.

Small Intestine: Regulation and

Movement Regulation• Distension of the intestinal wall activates the networks of nerves

within the wall and stimulates specific reflexes that trigger the release of secretions

Movement • Segmentation: small, ring-like contractions occurring

periodically, cutting chyme into segments and moving it back and forth.

• Chyme: semifluid mass of partially digested food that passes from the stomach to the small intestine.

• Chyme moves slowly through the small intestine, taking three to ten hours to travel its length.

• At the distal end of the small intestine the ileocecal sphincter joins the small intestines ileum to the large intestine's cecum. After a meal a gastroileal reflex increases peristalsis in the ileum and relaxes the sphincter which forces some of the contents of the small intestine into the cecum

Ileocecal sphincter

Large Intestine

Components

• Cecum, colon (4 parts), rectum, and anal canal.

Structure

• Large Intestine wall does not have villi like the small intestine. The fibers of the wall form three distinct bands that extend the entire length of the colon which creates a series of pouches.

Function

• Mucus secretion is the only significant function. It protects the wall against the tough materials passing through. Chyme that enters the large intestine contains materials that the small intestine didn't digest or absorb, water, electrolytes, mucus, and bacteria. The substances that remain become feces and are stored in the distal portion of the large intestine

Large IntestineMovement

• Slower than in the small intestine. Peristaltic waves happen 2-3 times a day. Intestinal wall constricts vigorously and forces the intestinal contents toward the rectum.

• Defecation reflex: holding a deep breath and contracting the abdominal wall muscles increases internal abdominal pressure and forces feces into the rectum.

Feces

• Materials that were not absorbed or digested, and water (75%), electrolytes, mucus, and bacteria.

• Odor is from a variety of compounds that bacteria produces.

• Color is from pigments now altered by bacterial action.

Activity http://kitses.com/animation/digestion.html