Chapter 23: Digestive System

Extrensic

organs, nerves, or tissues outside of the gastrointestinal tract that support digestive processes

Intrinsic

internal network of nerves, muscles, and cellular components located inside of the walls of the gastrointestinal tract

Peritoneum

lining of abdominopelvic cavity

Visceral Peritoneum

covers the outside surface of most organs

Parietal Peritoneum

lines the peritoneum wall

Mesentery

a double thickness of the peritoneum that works to hold the digestive organs in place

Retroperitoneal

behind the peritoneum

Hepatic Portal System

blood leaving digestive organs flows through the liver before entering the vena cava

Bolus

food + saliva

Chyme

bolus + gastric secretions

Rugae

ridges or folds made by wrinkling organ wall

Plical Circularis

crescent shaped folds of mucosa & submucosa lining inner wall of submucosa

Portal Triad

crucial microscopic arrangement in the liver

Bile

digestive fluid made by liver & stored in the gallbladder

Villi

small fingerlike projections that line the mucous membrane of the small intestine

Microvilli

microscopic fingerlike projections on the sirface of certain cells

Peyer’s Patches

organized & oval shaped groupings of lymphoid follicles found in the mucosal lining of the small intestine

6 Digestive Processes

Ingestion, Propulsion, Mechanical Digestion, Chemical Digestion, Absorption, Defecation

Ingestion

taking food in the digestive tract

Propulsion

movement forward

Peristalsis

involuntary movement of food through the digestive tract from the esophagus to the anal canal

Mechanical Digestion

cops up food into smaller pieces and mixes food with digestive secretions; chewing and churning in the stomach

Chemical Digestion

enzymes break down molecules into smaller particles and absorb

Absorption

nutrients, vitamins, minerals, and water are absorbed from the lumen into the body; absorption happens mainly in small intestines

Defecation

elimination of indigestible substances from the body

How many main groups is the digestive system divided into?

2

Gastrointestinal (GI) Tract

actual digestion and absorption happens here

Accessory Digestive Organs

mechanically or chemically contribute to food breakdown

Gastrointestinal Tract Organs

mouth, pharynx, esophagus, stomach, small intestines, large intestines, & anal canal

Accessory Digestive Organs Include

teeth, tongue, salivary glands, gallbladder, liver, & pancreas

Extrinsic Control of Digestive System

controlled by central nervous system

Intrinsic Control of Digestive System

controlled by local enteric reflexes “gut brain”

Layers of the Gut

mucosa, submucosa, muscularis externa, & serosa

Mucosa

innermost layer; contains 3 layers → simple columnar epithelium, lamina propia, & muscularis mucosae

Submucosa

connective tissue → contains blood & lymphatic vessels, lymphoid follicles, & nerve fibers

Muscularis Externa

contains the muscle the propels & mixes food → 2 layers of muscle: inner circular layer & outer longitudinal layer

Serosa

outermost layer & contains peritoneum of abdominopelvic organs

Where is stratified squamous epithelium found in the gastrointestinal fact & why is it important?

mouth, pharynx, & esophagus → protects from abrasion

Mouth (Buccal Cavity)

bordered by lips, cheeks, palate, & tongue

Function of Lips & Cheeks

keep food in mouth during chewing

Lips

formed by orbicularis oris muscle & connective tissue

Cheeks

formed by buccinator muscle & buccal fat pads

Hard Palate

formed by maxilla & palatine bones → provides surface for tongue to work against

Soft Palate

formed mostly by skeletal muscle → closes off nasopharynx when we swallow & contains uvula

Structure of Tongue

mostly skeletal muscle, attaches to floor of mouth by lingual frenulum, & contains 4 types of papille

Function of Tongue

moves food around in mouth, mixes it with saliva, allows it to be repositioned for chewing, also initiates swallowing, & is used for formation of speech

4 Types of Taste Buds

filiform papille, fungiform papille, circumvallate papille, & foliate papille

Filiform Papille

small, keratinized, & conical projects that give the tongue its roughness

Fungiform Papille, Circumvallate Papille, & Foliate Papille

house the tastebuds

Salivary Glands

parotid glands, submandibular gland, & sublingual gland

Parotid Glands

anterior to the ear

Submandibular Gland

posterior & lateral to the chin

Sublingual Gland

under the tongue

Functions of Saliva

cleanse mouth, dissolve food chemicals for taste, moistens food, & contains enzymes to begin breakdown of starch & fats

Composition of Saliva

mostly water, slightly acidic, salivary amylase, mucin, lingual lipase, lyzozyme, definsins, & antibodies

Salivary Amylase

breakdown starch

Mucin

changes to mucous when dissolved in water

Lingual Lipase

fat digesting enzyme

Lyzozome

inhibits bacterial growth & a defense against infection

Definsins

inhibit bacteria, activate immune system, & defend against infection

Antibodies & Cyanide Compound

a defense against infection

Control of Salivation

production increase when food is in the mouth → sight, smell, or thought of food may increase saliva production

Chemoreceptor

respond mostly to acidic food

Mechanoreceptors

respond to the presence of something in the mouth

Parasympathetic Stimulation

increases saliva production

Sympathetic Stimulation

decreases saliva production

Teeth

different shapes of teeth relate to their different jobs in chewing

4 Types of Teeth

incisors, canines, molars, & premolars

Incisors

cut food

Canines

tear and pierce food

Premolars & Molars

grind & crush food

Structure of the Tooth

crown, neck, & root

Crown

above the gum

Neck

surrounded by the gingiva (gum)

Root

embedded in the socket of the jaw

Layers of the Tooth

enamel, cementum, dentin, root canal, & periodontal ligament

Enamel

outer layer above the gum & hardest substance in the body

Cementum

outer layer of tooth below the gum & connective tissue

Dentin

bone-like material & forms the bulk of the tooth

Root Canal

deepest part of the tooth & contains nerves & blood supply

Periodontal Ligament

holds the tooth in the socket

Structure of Esophagus

extends between the pharynx and the stomach, passes through the diaphragm through the esophageal hiatus, between esophagus & stomach is gastroesophageal (cardiac) sphincter

Function of Esophagus

prevents food & acid from flowing back out of the stomach

Layers of the Stomach

mucosa, submucosa, muscularis externa, & serosa

Cells Found in Gastric Pits

mucous neck cells, parietal cells, chief cells, & enterendocrine cells

Mucous Neck Cells

make thin acidic mucous

Parietal Cells

secrete HCI and intrinsic factor

Chief Cells

produce pepsinogen & small amount of lipases

Enterendocrine Cells

release histamine, serotonin, somatostatin, gastrin, & endorphins

Histamine

activates parietal cells to release HCI

Serotonin

causes stomach muscle contraction

Somatostatin

inhibits gastric secretion & motility

Gastrin

regulates stomach movement & secretion

Endorphins

suppress appetite

Cells in the Pancreas

acinar cells & Islets of Langerhans