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