Digestive System

Role of Digestive System A. Prepare food for absorption and utilization by all the body cellsB. Excess food material (not absorbed) becomes feces to be eliminatedC. Ingestion vs. Digestion

1. Ingestion – process of taking food into the GI tract2. Digestion –

a. food and fluid is broken down so the body can use them to build and nourish cells, along with providing energyb. absorption – movement of nutrients into internal environment

A. Gastrointestinal (GI) Tract [aka alimentary canal] (listed in order of food pathway)

1. mouth2. oropharynx3. pharynx

4. esophagus5. stomach6. small intestine

a. duodenumb. jejunumc. ileum

7. large intestinea. cecumb. colon

1. ascending colon2. transverse colon3. descending colon4. sigmoid colon

8. rectum9. anus

B. Accessory Organs1. salivary glands2. tongue3. teeth4. liver5. gallbladder6. pancreas7. vermiform appendix

Layers of the walls of the gastrointestinal (GI) tract1. (deepest) mucosasubmucosamuscularisserosa (most superficial)2. Tissue layers have variation in different organs

Mouth and Pharynx• Buccal Cavity

– Lips – external is skin; internal is mucous membranes– Cheeks – lined by mucous membranes; contain

mucous secreting glands– Hard and Soft Palates

• Hard palate – four bones• Soft palate – muscle; forms partition between

mouth and nasopharynx; uvula extend from soft palate

– Tongue – muscle covered by mucous membrane• mastication (chewing) and deglutition

(swallowing)• papillae – surface of tongue; some contain taste

buds• lingual frenulum – mucous membrane fold that

anchors tong to bottom of mouth

Mouth and Pharynx• Salivary Glands

– Secrete about 1L of saliva/day

• Salivary amylase – enzyme in saliva that converts starch to sugar

– Three pairs of glands (parotid, submandibular, sublingual)

Mouth and Pharynx• Teeth

– Anatomy • crown - covered in enamel• neck – connects crown to root• root – fits into socket in the gum

– Types • Deciduous teeth (20 baby teeth)

– Incisors– Canines– first molars– second molars– third molars – wisdom teeth

• Permanent Teeth (32 adult teeth)– incisors– canine– premolars– Molars

• Pharynx – tube through which bolus (chewed ball of food) passes when moved from mouth to esophagus (deglutition)

Esophagus and Stomach

• Esophagus– Extends from pharynx

to stomach– Resides in both

abdominal and thoracic cavities

– Peristalsis begins

Esophagus and Stomach

• Stomach– Functions

• reservoir for food• secretes gastric juice • breaks food into small particles and mixes them with

gastric juice• limited absorption• helps protect body from bacteria swallowed with food• produces gastrin – (hormone that causes the stomach

to produce acid)

Esophagus and Stomach• Stomach

– Sphincter Muscles• lower esophageal sphinter (LES)/cardiac sphincter -

controls opening of esophagus into stomach • pyloric sphincter - controls opening of stomach into

small intestine (duodenum)– gastric reflux – sphincter working improperly causing

heartburn

– Stomach wall• Gastric mucosa

– Rugae – folds in lining of the stomach• gastric glands – below rugae; secrete most of gastric

juice– chief cells – secrete the enzymes of gastric juice– parietal cells - secrete HCl

» Zantac – reduces HCl formation in stomach– endocrine cells – secrete gastrin

• Gastric muscularis – thick layer of muscle that allows stomach to contract

• Helicobacter pylori – bacteria that causes peptic ulcers• Stomach lining replaces itself every 3 days• Chyme – liquefied food; form that food leaves the stomach• Gastroenteritis – stomach inflammation• Emesis – vomiting• 35 million digestive glands in the stomach

Gastroesophageal Reflux

Gastric Ulcer

Small Intestine

• Proximal to stomachduodenumjejunumileum• Microvilli (villus) allow for

absorption (increase surface area by hundreds)

• Where majority of substances are absorbed

• 22 feet long• Food can stay here for up to 4

hours

Large Intestine

Large Intestine

• Proximal to small intestinececum ascending colontraverse colondescending

colonsigmoid colon rectum• Haustra – pouchlike structures• Constipation – movement of lower colon and rectum

contents at a rate slower than normal• Diverticulosis – outpouchings of intestinal wall• Colitis – inflammation of large intestine• 5 feet long• Waste stays 10-12 hours• Main function is water absorption in order to eliminate

feces

Appendix and Peritoneum

• Vermiform Appendix– function not fully known; but thought to provide safe

place for good bacteria – appendicitis

• inflammation of appendix• not common in elderly• appendectomy – surgical removal of appendix

• Peritoneum– large, continuous sheet of serous membrane– parietal and visceral portions– mesentery – extension of parietal peritoneum that

anchors GI tract to abdominal wall.

Liver• Anatomical units – lobes and lobules

– left lobe– right lobe – biggest section of liver– hepatic lobules – branch of hepatic vein extends through each lobule (main anat unit)

• Blood flows to hepatic lobules via branches of the hepatic artery and hepatic portal vein

• Common bile duct – merger of the hepatic duct and cystic duct• Produces bile

– Bile salts – aid in the absorption of fats; most essential part of bile– No enzymes

• Functions of liver– Detox – Bile secretion – secrete 1 pint/day– Metabolizes proteins, fats, and carbohydrates

• Misc. Info– Hepatic refers to liver– Largest gland in the body– Hepatitis – inflammation of the liver– Cirrhosis – degenerative liver condition– Removes harmful substances from the blood– Stores vitamins and sugars until your body needs them

• Gallbladder

– Stores bile (holds 30-50 ml bile)

– Cholecystokinin (CCK) – hormone that stimulates gallbladder to release bile into duodenum (small intestine)

– Secretin – stimulates release of bile

– Cholelithiasis - gallstones

– Cholecystectomy – surgical removal of gallbladder

– Below liver

– Pear shaped

Cholelithiasis - Gallbladder with yellow cholesterol gallstones

CholecystectomyGallbladder before removal

• Pancreas

– Both endocrine and exocrine gland

– Pancreatic juice secreted by exocrine acinar cells

– Pancreatic cancer – form of adenocarcinoma

– Breaks down sugar

– Beta cells secrete insulin

Digestive Physiology

Mechanical Digestion •Mastication •DeglutitionOral stage – mouth to oropharynx- voluntary control- bolus formed- soft palate acts as valve to prevent

food from enetering nasopharynx

Pharyngeal stage – oropharynx to esophagus

- involuntary control- epiglottis prevents bolus from

entering larynx to trachea Esophageal stage – esophagus to

stomach- involuntary control

Peristalsis

•wavelike ripple of smooth muscle•ring of contraction occurs where GI wall is stretched, pushing bolus forward•stimulated by CCK – secreted by endocrine cells in presence of chyme

Segmentation

•mixing movement•forward and backward movement that mechanically breaks down food and mixes it with digestive juices

Organ Mechanical Process

Mouth (teeth and tongue) MasticationDeglutition

Pharynx Deglutition

Esophagus DeglutitionPeristalsis

Stomach ChurningPeristalsis

Small Intestine SegmentationPeristalsis

Ascending and Transverse Colon

SegmentationPeristalsis

Descending Colon Mass peristalsis

Rectum Defecation

Chemical Digestion

Digestive enzymesa. extracellular, organic (protein) catalystsb. enzyme action

1. specificity2. optimal pH

Stomach Jejunum Ileum Colon

pH 3.0 6.0-7.0 7.5 6.8-7.3

3. catalyst4. continually destroyed or eliminated, so constantly being made

Digestive Enzyme Action

•proenzyme altered by kinase to form active enzyme 1. kinase removes prosthetic group to expose active

site 2. substrate (food) binds to active site of active

enzyme 3. enzyme splits substrate into components and

releases them 4. enzyme can now digest new substance

Carbohydrate digestion (bread, potato, rice, pasta, fruit, vegetables)

•Starch and sugar are broken down by saliva, pancreatic and small intestinal juices

salivary amylase, small intestine pancreatic juices enzymes

* starch maltose glucose (monosac)

absorbed into blood liver (stored or used)

small intestine enzymes

* sugar (sucrose) glucose + fructose absorbed into blood

* fiber – undigestible

•Cellulose cannot be broken down; eliminated in feces

Pepsin

Trypsin

Lipid Digestion

•emulsification – bile breaks down fat into small droplets within the small intestine

•Steatorrhea - impaired fat absorption producing large, greasy, foul-smelling stool

•Fat-soluble vitamins – A, D, E, K (stored in liver and fatty tissue)

•Pancreatic lipase – main fat-digesting enzyme

Digestive Juice Enzyme Substance Digested

End Product

Saliva Salivary amylase

Starch (polysacc)

Maltose (monosacc)

Gastric Juice Protease (pepsin)

Protein Partially digested protein

Pancreatic Juice Protease (trypsin)

Proteins Peptides and a.a.

Lipase Fats Fatty acids, glycerol

PancreaticAmylase

Starch

(polysacc)

Maltose (monosacc)

Intestinal Peptidases Peptides a.a.

Sucrase Sucrose Glucose, fructose

Lactase Lactose Glucose, galactose

Maltase Maltose Glucose

Disorders• Mumps• Tooth Decay• Malocclusion• GERD (gastroesophageal reflux disease)• Ulcers• Pyloric stenosis• Appendicitis• Hemorrhoids• Proctitis• Diabetes• Gastroenteritis• Anorexia• Nausea• Emesis• Diarrhea• Constipation• Malabsorption• Diverticulitis• Colitis• Irritable Bowl Syndrome• Colorectal Cancer• Hepatitis• Cirrohsis• Pancreatitis• Pancreatic cancer