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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