The Digestive System

The Digestive SystemFood, Glorious Food!FunctionsTake in food ingestionPhysical & chemical break down of food digestionAbsorption of nutrientsExcretes waste defecatesTwo Main Groups Alimentary Canal (AKA GI tract)Coiled, hollow muscular tube food travels through in bodyPerforms all 4 digestive functionsOpen on both ends outside of body2) Accessory organs help digest, but dont digest directly (never touch food)

"The GI tract extends from the mouth to the anus, is a continuous tube about 30ft long."Van De Graaf, Kent. Human Anatomy. McGraw-Hill. 2000.MouthFood 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 muscleInner 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 peritoneumStomachC-shaped; has 3 muscular layers to move & mix foodHas sphincters (cardioesophageal & pyloric) to prevent unregulated movement of food and gastric juices out of stomach

StomachExpands 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)

rugaeLesser omentum- Connects liver to inside curve of stomach

Greater omentum- Connects large curve of stomach to the intestines

Both areExtensions of visceral peritoneumRiddled 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 StomachMucosa produces alkaline mucus that coats the stomach why?Mucosa has lots of deep gastric pits Where gastric juices are produced

Gastric Pit ExcretionsChief cells (in gastric pit) make enzymes the break down proteinspepsinogen before its activated, pepsin when activated) breakdown of proteins begins hereParietal cells (in gastric pit) produce:HCl- makes stomach acidic activates enzymesIntrinsic factor allows absorption of vitamin B12 in small intestine

Gastric Pit ExcretionsMost digestion in stomach occurs in pyloric region After being processed and churned in the stomach food = chymeTo leave stomach chyme passes through the pyloric sphincterhttps://www.youtube.com/watch?v=YJ34Qx6hzJk

Peptic UlcersHole in the wall of the: StomachEsophagusSmall intestine (upper section)NOT caused by stress & spicy foods a bacteriaSymptoms:Pain navel-chestBlood in vomit or stoolTemp. relief w/ antacids Pain comes & goes

Small IntestineMajor digestive organalmost all food absorption occurs hereGoes from pyloric sphincter (in stomach) to small intestineLongest part of GI tract8 - 20 feet long

Parts of the Small IntestineDuodenum (~5% length)LOTS of enzyme activityPlace where pancreatic and bile ducts empty their chemicals; like a car washJejunum (~40% length)Ileum (~60% length)Both absorb nutrients

Structure of the Small IntestineVilli 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 IntestineMajor functions:Dry out indigestible foodEliminate waste as fecesProduce alkaline mucus Absorb nutrients produced by bacteria in colonNo villiLarge Intestine