The Digestive System

Food, Glorious Food!

Functions• Take in food ingestion• Physical & chemical break down of

food digestion• Absorption of nutrients• Excretes waste defecates

Two Main Groups 1) Alimentary Canal (AKA GI tract)

Coiled, hollow muscular tube food travels through in body

Performs all 4 digestive functions Open on both ends outside of

body2) Accessory organs – help digest, but

don’t digest directly (never touch food)

"The GI tract extends from the mouth to the anus, is a continuous tube about 30 ft long." Van De Graaf, Kent. Human

Anatomy. McGraw-Hill. 2000.

Mouth• Food enters the mouth (oral cavity)• Enzymes in your saliva (salivary amylase) begin

digestion of starches•Tongue- muscle on floor of mouth, helps mix food and saliva; taste

•Lingual frenulum – holds tongue to floor

•Uvula – tissue at posterior soft palate; gag reflex

•Masticate- chew

Pharynx (pg 473 Fig 14.3)

• Walls contain 2 layers of skeletal muscle– Inner muscle layer

longitudinal – Outer muscle layer

run circularly • Layers alternate

contractions to move food in a wave-like fashion (peristalsis)

https://www.youtube.com/watch?v=-LJVTBuiPgQ

Esophagus (pg 473 Fig 14.3) • Connects pharynx –

stomach (passes through the diaphragm)

• Has 4 tissue layers

Has 4 tissue layers:

1. Mucosa- moist, inner-most, around lumen

2. Submucosa- connective tissue, bl vessels, nerves, etc.

3. Muscularis- (2 layers) inner circular and outer longitudinal

4. Serosa- visceral and parietal peritoneum

Stomach

• C-shaped; has 3 muscular layers to move & mix food

• Has sphincters (cardioesophageal & pyloric) to prevent unregulated movement of food and gastric juices out of stomach

Stomach• Expands and collapses based on food content – Can hold about 1 gallon of food full, 50 mL when empty

• When collapsed mucosa layer make large folds (rugae)

rugae

• Lesser omentum- – Connects liver to

“inside” curve of stomach

• Greater omentum- – Connects large

curve of stomach to the intestines

Both are…• Extensions of visceral

peritoneum• Riddled with fat to

insulate, & protect internal organs– Have many lymph

nodes https://www.youtube.com/watch?v=SKP1q-xpooo start at 26 sec

Digestion Continues in the Stomach

• Mucosa produces alkaline mucus that coats the stomach why?

• Mucosa has lots of deep gastric pits –Where gastric juices are produced

Gastric Pit Excretions• Chief cells (in gastric pit)

make enzymes the break down proteins– pepsinogen before it’s

activated, pepsin when activated) breakdown of proteins begins here

• Parietal cells (in gastric pit) produce:– HCl- makes stomach acidic

activates enzymes– Intrinsic factor – allows

absorption of vitamin B12 in small intestine

Gastric Pit Excretions

• Most digestion in stomach occurs in pyloric region • After being processed and churned in the stomach

food = chyme• To leave stomach chyme passes through the

pyloric sphincter

https://www.youtube.com/watch?v=YJ34Qx6hzJk

Peptic Ulcers• Hole in the wall of the:– Stomach– Esophagus– Small intestine (upper section)

• NOT caused by stress & spicy foods a bacteria• Symptoms:– Pain navel-chest– Blood in vomit or stool– Temp. relief w/ antacids – Pain comes & goes

Small Intestine• Major digestive organ– almost all food absorption occurs here

• Goes from pyloric sphincter (in stomach) to small intestine

• Longest part of GI tract• 8 - 20 feet long

Parts of the Small Intestine• Duodenum (~5% length)

– LOTS of enzyme activity– Place where pancreatic and

bile ducts empty their chemicals; like a “car wash”

• Jejunum (~40% length)• Ileum (~60% length)

– Both absorb nutrients

Structure of the Small Intestine

• Villi – fingerlike projections (each has microvilli on it)

• Microvilli – tiny projections of mucosa cells; make the Brush border

• Lacteal – lymphatic capillary in each villus

**Structure of the small intestine is key to absorption – increase surface area to increase rate of absorption**

Large Intestine• Major functions:–Dry out indigestible

food– Eliminate waste as feces– Produce alkaline mucus –Absorb nutrients

produced by bacteria in colon

• No villi

Large Intestine