Transcript The Digestive System

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
"The GI tract extends from the mouth to the
body anus, is a continuous tube about 30 ft long."
2) Accessory organs – help digest, but
don’t digest directly (never touch food)
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. Submucosaconnective 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
**Structure of the small intestine is key to absorption –
increase surface area to increase rate of absorption**
• Villi – fingerlike
projections (each
has microvilli on
it)
• Microvilli – tiny
projections of
mucosa cells;
make the Brush
border
• Lacteal –
lymphatic
capillary in each
villus
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