Digestive System

P & A

I. Intro to Digestive System

• A. Function: to process food into forms that can be absorbed by the cell membranes

• B. Includes:– Alimentary Canal

• Tube from mouth to anus– Accessory Organs

• Structures which secrete into A.C.– Salivary glands, liver, pancreas, gall bladder

II. Alimentary Canal

• A. Structure– 9 m. long– Includes: mouth, pharynx, esophagus,

stomach, small intestine, large intestine

– 1. wall of canal (inside out)• A. mucosa – functions to absorb and secrete

– S:» Inner layer of wall» Made up of: epithelial tissue, connective tissue, and

smooth muscle» Has projections which extend into canal to increase

surface area» Has glands to secrete mucous and enzymes

– F:» Absorb & secrete

• B. submucosa– Outside mucosa– S:

» Loose connective tissue, blood vessels, lymph vessels, nerves

– F: » Blood nourishes surrounding tissue & carries away

absorbed nutrients by mucosa

• Muscular layer– S:

» Outside submucosa» Includes circular & long muscles» Made up of muscle tissue

– F:» To constrict/elongate to move food down tube

• Serosa– S:

» Outer covering» Visceral peritoneum: moist, slimy tissue

– F:» To secrete fluid so that canal stays lubricated to slide

by other organs in the DS

– 2. Movement• A. mixing by smooth muscles contracting in small

segments of canal• B. peristalsis

– Wavelike contractions of tract that moves food downward

III. Types of Digestion

• A. chemical– Involves enzymes breaking down food into

usable substances for cells– Chemicals enter blood for body to use

• B. mechanical– Chewing food into smaller pieces for the

system to break down further

• C. physical– Peristalsic mixing– Stomach churning

IV. Mouth/Oral Cavity

• Center of mechanical digestion• Reduces food size• Mixes food with saliva

• A. cheeks and lips – Cheeks used for chewing– Lips judge temp & texture of food

• B. tongue– 1. frenulum

• Membranous fold which connects floor of mouth to tongue

– 2. very muscular – moves food to pharynx– 3. has papillae - tastebuds

• C. lingual tonsils– Rounded masses of lymphatic tissue at base

of tongue– ** NOT the ones you get removed

• D. Palate– A. hard palate top/front portion of mouth– B. soft palate top/back portion of mouth– C. uvula – sac of tissue extending off the soft

palate which closes the nasal cavity while swallowing

– D. palantine tonsils:• Back of mouth on either side of tongue• Lymphatic tissue that fights disease• ** GET THESE OUT

• E. teeth– A. primary: 20 teeth

• Come b/n 6 months & 2 yrs– B. secondary: 32 teeth

• Come b/n 6 yrs & 23 yrs

– C. teeth types• Incisors: 8 (4 front top and bottom)

– Cut food into smaller pieces• Cuspid: 4

– Canines that cut and tear food• Bicuspids: 8

– Premolars• Molars: 12

– Crush and grind food• Wisdom teeth: 4 (don’t always get)

• F. Salivary glands– Function: secrete saliva to moisten food, bind

food together, and digest carbs– A. secretions:

• Amylase– Enzyme that breaks down carbs

– B. parotid glands• - largest salivary gland• - lies in front of and below each ear

– C. submandibular glands• On floor of mouth

– D. sublingual glands• Smallest salivary glands under the tongue

– E. psychological stimulus• Think about food and salivate

– F. mechanical stimulus• Action of chewing stimulates salivation

V. Pharynx• A. pharynx

– Connects nasal and oral cavities• Very short• 1. nasopharynx

– Provides passageway for air for breathing• 2. oropharynx

– Passageway for food• 3. laryngopharynx

– Opens into larynx & esophagus

• B. swallowing process– 1. soft palate/uvula is raised closing nasal

cavity so food cannot enter– 2. hyoid bone (front of larynx) & larynx are

raised so food doesn’t enter trachea– 3. EPIGLOTTIS is pressed down by the tonue

closing the trachea

– 4. muscles in pharynx relax, opening esophagus

– 5. peristalsic motion of esophagus begins forcing food down to stomach• ** during this process breathing is stopped

VI. Esophagus

• A. Structure– Straight, collapsible tube– 25 cm long– Located behind trachea– Connects pharynx to stomach

– Inner layer (mucosa) has much mucous to keep food lubricated to keep traveling smoothly

– Strong muscles at base to keep stomach contents from coming up

• B. Function– Move food to stomach– Keep food moist & lubricated

VII. Stomach

• A. structure– J-shaped– Under diaphragm– Inner lining: RUGAE

• Thick folds which increase surface area for absorption

• B. function– Mixing food w/ gastric juice rich in enzymes– Begins protein digestion– Absorbs smalls amounts of nutrients

• C. special parts– 1. cardiac region

• Small area right off espophagus– 2. fundic region

• “puffy” part – greater curve

– 3. pyloric region• Narrow – lesser curve• Leads to small intestine

– 4. pyloric sphinctor• Thick muscle at end of pyloric region which

prevents contents of sm. Intestine from going back into stomach

– 5. cardioesophageal sphinctor• Prevents food from going back into esophagus

– 6. serosa• Protective inner lining• Secretes mucous to protect stomach inner lining

from gastric acids

• D. secretions– 1. digestive enzymes

• Pepsin & pepsinogen – split proteins• Sucrase, maltase, lactase – split sugars• Lipase – split fat

– 2. hydrochloric acid• Enzymes need acid environment to work on

proteins– 3. intrinsic factor

• Lets vitamin B12 be absorbed by small intestine– *****These 3 make up gastric juice

• E. stomach contents– 1. as stomach mixes food with gastric juice =

CHYME is produced• Food + gastric juice in pasty form

– 2. liquids pass through stomach quickly– 3. foods high in carbs pass fastest

– 4. foods high in proteins pass next fastest– 5. fatty foods remain 4-6 hrs

VII. Pancreas

• A. Structure– C-shaped organ– Pancreatic duct runs through it

• B. Function– Production of pancreatic juice which flows

pancreatic duct to sm. intestine

• C. pancreatic juice– Enzymes which break down: work when they

get to small intestine• Carbs – pancreatic amylase• Proteins – trypsin, chymostrypsin,

carboxypeptidase• Fats – pancreatic lipase• Nucleic acids - nucleases

VIII. Liver

• A. intro– Located below diaphragm– Mostly covered by ribs– Reddish- brown– Many blood vessels– 2 lobes

• B. functions– 1. regulation of blood glucose level

• Can change glycogen to glucose, glucose to glycogen, or non-carbs to glucose

– 2. synthesis of fats

– 4. stores glycogen, vit A, D, B12– 5. destroys damaged RBCs– 6. detoxifies blood of toxins– 7. secretes bile

• D. Bile– Bile salts – does the actual digestion of fats– F: EMULSIFICATION

• BREAKING DOWN OF FATS

IX. Gall bladder

• A. s:– Pear shaped sac attached to the liver

• B. F:– Bile is stored here

X. Small intestine

• A. s:– Extends from stomach to L. intestine– Fills most of abdominal cavity

– Divided into 3 main parts:• A. duodenum: 12 in – biggest diameter• B. jejunum: 2 m – thickest wall• C. ileam: 3-4 m

– Mesentery• Thin issue which holds sm. Intestine to body wall

– Intestinal villi• In duodenum and jejunum• Fingerlike projections which increase SA for

absorption

XI. Large Intestine• A. s:

– 1.5 m long– Parts of LI:

• Cecum – beginning pouchlike structure of LI• Vermiform appendix

– Hangs off cecum– No digestive function– Contains lymphatic tissue for immune system

• Colon: 4 parts– Ascending – travels up to liver– Transverse – long, straight mobile part of LI– Descending – downward portion– Sigmoid – S-shaped curve which ends with rectum

• Rectum – Attached to bottom of spine or tailbone– Muscular end of colon

• Anal canal– 2.5 – 4 cm long– Muscular tube at end of DT– Contains internal and external sphinctors which are

under voluntary control to rid of waste