Digestive System

Chapter 17

Functions of Digestive System

•Ingestion•Secretion•Movement•Digestion •Absorption•Excretion

Digestion Types:

Mechanical or Chemical

Mechanical – muscular actions or movement to tear, grind and mix

Chemical – enzymes used to breakdown nutrients.

Tissue Layers

1.Serosa:Visceral Peritoneum

2.Muscularis: smooth muscle, circular and longitudinal layers

3.Submucosa4.Mucosa:epithelial

(strat.simple or simple columnar) and areolar tissue

Specialized Tissues…

• Peritoneum – lines cavity wall (parietal) and covers abdominal organs (visceral). - Retroperitoneal: positional term for behind peritoneum.

• Mesentary – thick peritoneal sheets that suspend digestive tract, stabilizing organs, prevents intestine tangling.

• Greater Omentum “Fatty apron”– Large folded tissue containing adipose and lymph nodes. Protects, insulates and provides energy reserve.

What organs compose theDigestive Tract or

Gastrointestinal Tract?

What is the direction of transport through the tube from start to

finish?What structures are help with

digestion but are not part of the GI Tract?

Which regions do mechanical and/or chemical digestion?

The Oral Cavity

• Sensory analysis of material.

• Mechanical digestion by teeth and tongue.

• Chemical digestion by enzymes.

• Lubrication by mucus and saliva

• Bolus is formed at end.

• 32 adult teeth, 20 deciduous

Halitosis – Bad breath

Salivary Glands• Types: Parotid,

submandibular, and sublignual.

• Function: Releases enzymes to digest carbohydrates (starches) into tri-& disarccharides with Salivary amylase.

• Small amount of Lingual Lipase starts fat breakdown.

• “Mumps”- virus attacks usually parotid glands

Pharynx

• Common passageway for solid food, liquids and air.

• Regions:1. nasopharynx2. oropharynx3. layrngopharynx

• Uvula – blocks food from going into nasophayrnx

Uvula

Epiglottis flap is pushed down by food to cover tracheal opening

Esophageal Cancer

Human esophagus – 10 inches long

Giraffe esophagus – 6 feet long

Esophagus• Muscular tube that

moves bolus to the stomach by PERISTALSIS.

• Mucus secretions keep tube lubed

• “Swallow reflex” controlled by medulla.

• Heartburn and GERD can be problems

Hiatal Hernia

•Part of the stomach moves up through an opening (hiatus) in the diaphragm.

•The presence increases the risk for GERD.

Stomach• J-shaped organ• Muscular rugae to churn food.• Sphincter doors at both ends.• Gastric Glands:

Mucous (Goblet) cells – secrete mucusChief cells – secrete pepsinogenParietal cells – secrete HCl and intrinsic factor (helps small intestine to absorb Vitamin B12)

• Pepsin = Pepsinogen + HCl *This begins digestion of proteins into polypeptides and smaller peptides.

Stomach Continued…• Absorption of nutrients:

NONE! Only certain drugs and alcohol can be absorbed here.

• Hormones regulating stomach:Gastrin – increases gastric secretionCholecystokinin(CCK) and Gastric Inhibitory Peptide (GIP) - slows gastric motility and secretionsSecretin – inhibits gastric secretions

Animation• Bolus is turned into CHYME

before leaving

Carbs pass through quickest and lipids take the longest due to CCK release.

Peptic Ulcers

*Erosion of the digestive tract layers. Can affect any part of tract.

Causes: “Helicobacter pylori” Bacteria (80%), stress, cancers, other disorders

Gastric Bypass Surgery• Restricts appetite • Restricts stomach size

significantly• Limits absorption of

nutrients, fat, and calories.

• Allows patients to achieve rapid loss.

• Side effects: nausea, weakness, sweating, faintness, and, occasionally, diarrhea after eating, anemia, calcium absorption, and gallstones.

Lap Band Procedure

A ‘gastric band’ with a small balloon inside is attached around the top portion of your stomach, forming a smaller ‘gastric pouch’. The placement of the band creates a small pouch at the top of the stomach that holds up to approximately 30 ml, which works out to about 1/8 cup. You are inclined to eat less because the pouch holds less food than the whole stomach. As the upper part of the stomach registers itself as being full, it sends a message to the brain saying that the entire stomach is full.

Small Intestine• Function: digestion and absorption (90%)• 3 sections: duodenum, jejunum, ileum

• Mesentary stabilizes/holds intestine, provides access for blood vessels.

• Intestinal villi – fingerlike projections, absorbs nutrients; increases surface area. (There are microvilli on the villi too!)

• Ileocecal valve – sphincter muscle; door to cecum of large intestine.

• Peristalsis moves chyme through tube.• Bicarbonate ions (from pancreas) increase pH

of chyme released at duodenum.

Small Intestine• Intestinal enzymes:

(peptidase, sucrase, maltase, lactase, lipase, enterokinase)

• Lacteals: structures within villi that take in fat/protein complexes; connects with lymphatic system.

• Chylomicrons: fatty/protein structures formed by intestinal cells.Video Video 2 Video 3

Small Intestine Disorders• Inguinal Hernia: protruding

through a weak point or tear in the thin muscular abdominal wall.

• Can restrict blood supply to the bowel herniated through the defect, creating a medical emergency. Gangrene!

• Causes: for adults - heavy lifting, straining bowel movements, coughing.

Celiac Disease: Autoimmune, body attacks villi of small intestine. Can be environmentally triggered.

Pancreas

• Exocrine function: chemical digestion• Released into the duodenum via pancreatic

duct that connects with common bile duct.• Enzymes: amylase, lipase, nuclease, trypsin,

chymotrypsin, carboxypeptidase.• Trypsin = trypsinogen + enterokinase• Secretes Bicarbonate ions to increase pH of

chyme.• Hormone Regulation: (secreted by small intestine)

1. Secretin- increase pancreatic secretion2. Cholecystokinin (CCK)- slows down stomach release of chyme, stimulates pancreatic secretion

Pancreatitits: inflammation of pancreas; blockage of duct leads to enzymes destroying pancreas.

Nutrients are broken down into basic units for absorption

LIVER

Liver• Bi-lobed, reddish brown

organ• All blood from digestive

organs stops here first.• Functions:

1. Carbohydrate, protein, and lipid metabolism2. Detoxification of blood3. Removes damaged/old blood cells4. Produces bile5. Stores vitamins, minerals and glycogen.6. Participates in formation of vitamin D.

•Falsiform Ligament – holds liver to anterior wall

•Regeneration capabilities

•Hepatocytes – liver cells

• Kupffer cells - phagocytize pathogens and old RBC’s

• Blood from the hepatic artery and hepatic portal vein carry blood into the liver to be serviced.

• Serviced blood leaving the liver exits the hepatic vein which connects with inferior Vena Cava.

• Hepatitis – Inflammation of the liver, causes can be viral or chemical.

Liver

Gall Bladder• Green muscular sac; 10cm• Ventral surface of liver• Stores bile made from liver.• Bile consists of:

cholesterol, salts, bilirubin, & other lipids.

• Bile emulsifies fats (breaks down into smaller droplets), helping digestion & absorption of fat-soluble molecules.

• Released into Cystic duct and travels to bile duct.

Fat droplet

Bile

Fat droplets coated with bile

Micelles formed: fatty acids, monoglycerides and bile

Absorption of lipid material into villus and chylomicrons formed, moving into the lacteal.

Gall StonesFormed from the crystallization of bile salts or cholesterol in the gall bladder.

Blockage of cystic duct…PAINFUL!

Removal of gall bladder or other ways to break up crystals is the treatment.

Diet will have to be careful with fat and cholesterol intake.

Large Intestine• Functions: Reabsorbs water; absorbs certain vitamins

and electrolytes; forms semi-solid feces; stores feces • Suspended inside cavity by peritoneum but rectum is

retroperitoneal.• Sections:

a. Cecum: pouch-like part; appendix is posterior endb. Colon: ascending, transverse, descending, sigmoidc. Rectum: anal canal and anus located at end

• Ecoli bacteria break down cellulose, make vitamin K, vitamin B5, and GAS! Break down bilirubin giving fecal colors.

• No villi but tons of goblet cells for lubrication.• Colon pouches are called “Haustrum” or haustra.

Large Intestine…Defecation!

• Distension of rectal wall triggers defecation reflex.

• Internal anal sphincter (involuntary control)Relaxes on stool entrance

• External anal sphincter (voluntary control)Relaxation results in defecation

• Hemorrhoids: distended, swollen veins in anal canal

Bowel Issues• Diarrhea: not enough water absorbed, food is

hurried through.

Causes: microbes, stress, food intolerances

Problems: dehydration and malnutrition• Constipation: feces remain too long in tract,

drying too much.

Causes: lack of fiber, dehydration, stress, failure to relieve

Problems: Hemorrhoids, hernias, diverticulitis

Colitis – inflammation of the colon

Diverticulosis – formation of colon pouches, weakening of wall

Polyps – bumps on colon wall, precancerous

Colon Cancer• 3rd leading cause of cancer related deaths

• Standard screening: stool checks and colonoscopy

Quizzes and more!

And more!

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Digestion Animation