Digestive System

What is Digestion?

The process by which complex chemicals in food are broken down into simpler chemicals that can be used by the body.

The Digestive System

Has 6 Parts:◦Ingestion◦Mechanical Processing◦Digestion◦Secretion◦Absorption◦Excretion

Mouth/Oral Cavity

Food enters the digestive tractAKA buccal cavityFunctions:

Sensory analysis Mechanical processing Lubrication Limited digestion of carbohydrates and lipids

Oral Cavity

Lined by the oral mucosaTongue and the roof of the mouth have

stronger cells to withstand abrasion from food

Includes: ◦Tongue◦Salivary glands◦Teeth

Oral Cavity (cont.)

Tongue◦Manipulates material in the mouth and assists

in chewing◦Sensory analysis◦ligual lipase-starts lipid digestion

Oral Cavity (Cont.)

Salivary Glands-secrete 0.5-1.5 liters of saliva each day◦Paratoid salivary glands(25%)

Produce salivary amylase-breaks down starches◦Sublingual salivary glands(5%)

Produce mucous that acts as a lubricant◦Submandibular salivary glands(70%)

Produces lubricant, salivary amylase and mucins

Oral Cavity (cont.)

Teeth◦Mastication (chewing)◦Incisors

Front teeth-cutting or clipping (scissors)◦Cuspids

Canines-tearing or slashing◦Bicuspids/molars

Premolars-crush/mash

Pharynx

Passage of solid food, liquid, and airBolus-small oval mass of digestive

contentsPharyngeal constrictor muscles push bolus

alongPalatopharyngeal and Stylopharyngeal

Muscles elevate the larynx

Esophagus

Transport solid and liquid food to the stomach

Passes through the esophageal hiatus-an opening in the diaphragm

Peristalsis: waves of muscle contractions that move the bolus through the digestive tract.

Stomach

Shaped like a J-lesser curvature is on the medial surface, greater curvature is on the lateral surface

4 Regions:◦Cardia◦Fundus◦Body◦Pylorus

4 Regions of the Stomach

Cardia-first 3 cm.◦Contains mucus to coat the connection to the

esophagus and protect the esophagus from stomach acids

Fundus◦Contacts the diaphragm

Regions of the Stomach

Body◦Largest region of the stomach◦Mixes ingested food with acids and enzymes-

most acids and enzymes are produced in the body and fundus by Gastric Glands

Pylorus◦Sharp curve of the J◦Pyloric sphincter regulates the release of

chyme ◦Pyloric canal empties into the duodenum

Functions of the Stomach

Rugae-folds in the stomach-flatten when stomach is full

4 functions:◦Storage◦Mechanical breakdown of food◦Production of acids and enzymes to break down

chemical bonds in food◦Production of intrinsic factor-B12

Small Intestine

Movement◦Gastroenteric reflex-stimulates movement◦Gastroileal reflex-relaxes ileocecal valve

Intestinal villi-fingerlike projections in the inner membrane of the small intestine◦Covered by microvilli◦Increases the surface area for absorption by

600

Small Intestine

90% of nutrient absorption happens in the small intestine

Average length: 6 meters3 sections:

◦Duodenum◦Jejunum◦Illeum

Large Intestine-Colon

Cecum-collects, stores, and begins to compact food

Colon-◦Haustra-pouches that allow for expansion◦Taeniae coli-smooth muscle-runs along outer

surfaces of the colon◦Fatty appendices-teardrop shaped fat along the

outer surface

Function of the Large Intestine

Reabsorption of water1500ml enters the large intestine-200ml is

ejectedAbsorbs bile salts and vitamins

Colon

4 sections:◦Ascending Colon◦Transverse Colon◦Descending Colon◦Sigmoid Colon

Duodenum

Smallest portion-25cmClosest to the stomachReceives chyme and digestive secretions

from pancreas and liverMixing bowl

Jejunum

Middle section-2.5 metersMost chemical digestion and nutrient

absorption happens here

Illeum

Last segment-largest-3.5 metersEnds at the illeocecal valve-controls the

flow of food into the cecum (beginning of the large intestine)

Ascending Colon

Begins at the upper border of the cecumRight side of the peritoneal cavity to the

inferior surface of the liverEnds at the right colic flexure, AKA hepatic

flexure

Transverse Colon

Crosses from right to left along the abdomen

Travels from the right colic flexure to the left colic flexure (splenic)

Descending and Sigmoid Colon

Descending Colon: Travels down the left side from the left colic flexure to the sigmoid flexure

Sigmoid Colon: S shaped◦Empties into the rectum

Rectum

Last 15 cm of the digestive tractTemporary storage of fecesAnal Canal is the last portion of the

rectum

Accessory Organs

LiverPancreasGall Bladder

Liver

Second largest organ in the body (skin is largest)

Left lobe and right lobe are separated by the falciform ligament

Porta Hepatis-convergence of hepatic portal vein, hepatic artery and common bile duct

Function of the Liver

3 main functions:◦Metabolic regulation

Regulates nutrients, glucose levels, cholesterol, and amino acids in the blood. Also removes wastes and breaks down drugs

◦Hematological regulation Phagocytosis, removes hormones, antibodies,

toxins◦Bile production

Gallbladder

Green organSmall, hollow organ that stores and

concentrates bile before it is released into the small intestine

Bile enters from the liver through the cystic duct and is released through the common bile duct when CCK is released (because chyme enters the duodenum)

Gallstones form when bile becomes TOO concentrated in the gallbladder

Pancreas

Posterior to the stomachLong pinkish-grey organHead of the pancreas lies in the loop of

the duodenumBody-extends toward the spleenTail- short and roundedLumpy and lobular and wrapped in a thin

connective tissue

Functions of the Pancreas

Pancreatic alpha-amylase◦Breaks down some starches

Pancreatic lipase◦Breaks down complex lipids

Nucleases◦Break down nucleic acids

Proteolytic enzymes◦Breaks apart proteins

Digestion/Metabolism

Carbohydrate MetabolismLipid MetabolismProtein Metabolism

Carbohydrate Metabolism

Starches (bread, cereal, rice, etc.) and fruit2 part Digestion

◦Carbohydrases are released in the salivary glands and pancreas Salivary amylase continues working for 1-2 hours

after food is swallowed◦Brush border(in the small intestine) enzymes

Maltase-breaks maltose Sucrase-breaks down sucrose Lactase-Breaks down lactose

Lipid Metabolism

Lingual Lipase-from the tongue-begins lipid digestion

Pancreatic Lipase-breaks down triglycerides with the help of bile salts

Protein Metabolism

Complex and time consumingMastication begins the processStrong acids in the stomach break down

connective tissue or cell wallsPepsin-breaks down polypeptidesPeptidase-breaks down peptide chains

into amino acids which can be absorbed

Fat Soluble Vitamins

Vitamin A◦Significance: synthesis of visual pigment,

supports immune system, promotes growth◦Source: leafy green vegetables, yellow

vegetables◦Deficiency: night blindness, retarded growth

Vitamin D◦Sig: normal bone growth, calcium absorption◦Source: sunlight◦Deficiency: rickets, skeletal deterioration

Fat Soluble Vitamins

Vitamin E◦Sig: Prevents breakdown of vitamin A and fatty

acids◦Source: meat, milk, veggies◦def.: anemia

Vitamin K◦Sig: liver synthesis; clotting factors◦Source: vegetables◦Def.: bleeding disorders

Water Soluble Vitamins

B1 (thamine):◦Sig: coenzyme in decarboxylations◦Source: milk, meat, bread◦Def: muscle weakness, cardiovascular problems

B2 (riboflavin):◦Sig: part of FMN and FAD◦Source: milk, meat◦Def: epithelial and mucosal deterioration

Niacin:◦Sig: part of NAD◦Source: Meat, bread, potatoes◦Def: pellagra

Water Soluble Vitamins

B5 (Pantothenic acid):◦ Sig: Part of Acetyl-CoA◦ Source: milk, meat◦ Def: retarded growth

B6 (pyridoxine):◦ Sig: coenzyme in lipid and amino acid metabolism◦ Source: meat◦ Def: retarded growth, anemia

Folacin (folic Acid):◦ Sig: coenzyme in nucleic acid and amino acid metabolism◦ Source: vegetables, cereal, bread◦ Def: anemia, GI disorders, developmental disorders

Water Soluble Vitamins

B12 (cobalamin):◦Sig: coenzyme in nucleic acid metabolism◦Source: milk, meat◦Def: pernicious anemia

Biotin:◦Sig: coenzyme in decarboxylations◦Source: eggs, meat, vegetables◦Def: fatigue, nausea

C (ascorbic acid):◦Sig: coenzyme, antioxidant◦Source: citrus fruits ◦Def: scurvy