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 body 2) 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

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)

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 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

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 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