Digestive SystemDigestive SystemDigestive SystemDigestive System
Anatomy & PhysiologyAnatomy & Physiology
Function & Organization
Function• The breakdown of food into small enough particles to be absorbed
Organization• Alimentary Canal aka GI tract• Accessory Organs
Digestive Processes• Ingestion: bringing food into the
system• Mechanical Digestion: the
mechanical breakdown of food (chewing, mixing, churning)
• Propulsion: movement of food through system
Digestive Processes• Chemical Digestion: breakdown of
large food molecules by enzymes• Absorption: transport of digested
food materials to the blood or lymph• Defecation: elimination of
indigestible material from the body
Peritoneum• The largest serous membrane of the
body lining all organs of the abdominal cavity and the cavity wall– Parietal peritoneum: lines walls– Visceral peritoneum: lines organs– Peritoneal cavity: potential space
between membranes; produces serous fluid
Extensions of the Peritoneum
• Falciform ligament: connects liver to anterior abdominal wall and diaphragm
• Lesser omentum: attaches to medial stomach, attaching it to anterior wall
Extensions of the Peritoneum
• Greater Omentum: extends off stomach; contains lymph nodes and holds fatty deposits
• Mesentary: suspends coils of small intestine and attaches it to posterior abdominal wall
Wall Structure of Alimentary Canal
• 4 layers– Mucosa/mucus membrane– Submucosa– Muscularis– Serosa
Wall Structure of Alimentary Canal
1. Mucosa: lines lumen of alimentary canal– Protects from microorganisms– Absorbs digested food materials– Secretes mucous & digestive
enzymes
Wall Structure of Alimentary Canal
2. Submucosa-Rich in blood vessels, lymphatic
vessels and nerve endings-Provides nourishment for tissues and
carries away absorbed materials
Wall Structure of Alimentary Canal
3. Muscularis- smooth muscular layer (has 2 parts)
• inner layer runs longitudinally• outer layer (constrictor layer) runs
circularly• induces a propelling action called
peristalsis
Wall Structure of Alimentary Canal
4. Serosa- visceral peritoneum-outermost covering of
alimentary canal
Alimentary Canal: Mouth
o Function: receives food and starts digestion and prepares it for swallowing
- Teeth: performs mastication (chewing)- Uvula: fingerlike extension from archway; works with soft palate to close opening to nasal cavity upon swallowing
Mouth continuedo Salivary Glands: accessory organs
around mouth; secretes saliva- saliva: 99.5% water, 0.5% solutes
- Lysozome: destroys bacteria- Salivary amylase: begins chemical
digestion of carbohydrates- Mucus: lubricates and binds food
particles to form a bolus
Alimentary Canal: Pharynx
o Function: transports food from oral cavity to esophagus
-uvula and epiglottis assist pharynx in transporting bolus
to the esophagus ONLY
Alimentary Canal: Esophagus
Function: 10 inch muscular tube that transports bolus to stomach from pharynx
- Peristalsis: alternate waves of muscle contraction & relaxation; moves bolus along alimentary canal
Esophagus continued- Mucosa: made of stratified
squamos epithelium to resist abrasion
- Cardio-esophageal sphincter: found at distal end; acts as a valve to prevent stomach contents from entering esophagus
Alimentary Canal: Stomach
o Function: c-shaped organ acting as a temporary storage site for food; performs mechanical and chemical digestion
-Rugae: deep folds formed by inner lining of stomach when empty
-Full stomach: can hold up to 1 gallon of food
- Pyloric sphincter: valve that controls movement of food from stomach into
small intestine
Stomach Wall• 4 basic layers: mucosa, submucosa,
muscularis and serosa• Mucosa & muscularis is functionally
and structurally different– Mucosa: gastric pits work to produce
and secrete gastric juices• HCL, digestive enzymes and mucus
Stomach Wall– Muscularis
• Stomach has an additional layer of muscle fibers
• Allows stomach to churn and mix stomach contents
Stomach Functions• Mechanical Digestion: churning
and mixing of stomach contents to aid digestion
• Chemical Digestion: pepsin: breaks down proteins (works only in acidic environments)
Stomach Functions• Absorption: limited absorptive abilities
(water, salts, glucose, alcohol, aspirin and some lipid-soluble drugs)
• Propulsion: propels food into small intestine in the form of CHYME (mixture of food particles & gastric juice)– Chyme presses against pyloric sphincter
causing it to relax and allowing chyme to pass
Alimentary Canal: Small Intestine
• Completes mechanical and chemical digestion & is the main site of nutrient absorption
• Propels food through with peristaltic waves• 20 feet long, highly coiled• Takes ~ 3-10 hours to move chyme
through• Suspended to posterior abdominal wall via
mesentary
Small Intestine continued
3 Segments:1. Duodenum: receives chyme
from stomach & digestive enzymes from accessory organs; about 10 inches long
2. Jejunum: site of absorption; about 8 feet long
Small Intestine continued
3. Ileum: about 12 feet long; the end of digestion and absorption of nutrients
Ileocecal valve: the junction at which the small & large intestine join; sphincter muscle controlling the flow of material between organs
Wall of Small Intestine• Highly convoluted mucosa for
better absorption through increased surface area– Intestinal villi: tiny projections of
mucosa– Microvilli: even smaller projections
on the intestinal villi
Wall of Small Intestine• Within each villi is:
– Blood capillaries– Lacteals (lymphatic vessels)- Act to carry absorbed nutrients away
Alimentary Canal: Large Intestine
• Final segment of alimentary canal• ~5 feet long but larger in diameter
than small intestine• Function: to dry out indigestible
material by absorbing water; eliminate unwanted materials
Large Intestine continued
• 5 main segments of large intestine– Cecum: sac-like pouch receiving material
from ileum– Vermiform appendix: worm-like extension
holding lymphatic tissue– Colon: ascending, transverse, descending,
sigmoid– Rectum– Anus
Large Intestine continued
Anus: has 2 sphincters1. Internal: involuntary; told to relax
when fecal matter stimulates the defecation reflex in the rectum
2. External: voluntary; if relaxed, elimination occurs
Fecal Formation• Fecal matter: 75% water, 25%
indigestible material, mucus and bacteria
• Color: produced by bile• Gas: produced by the metabolism of
bacteria or from swallowing air• Movement of matter is very slow ~ 18-
24 hours
Carbohydrate Digestion• Carbohydrate: nutrient; main
source of energy in the body• Glucose: a simple sugar; the end
product of carbohydrate digestion• Takes place in the mouth & small
intestine
Protein Digestion• Protein: basic nutrient; used in
anabolism (tissue building)• Amino Acid: the building blocks of
proteins; the end product of protein digestion
• Takes place in the stomach & small intestine
Fat Digestion• Fat: basic food type; used for energy• Fatty acids and glycerol: end products
of fat digestion• Takes place in the small intestine• Enzymes:
– Bile in duodenum: fat droplets into smaller fat droplets
Time to Digest• Carbohydrate-rich meal: moves
through the stomach rapidly• Fat-rich meals: may take up to 6
hours to pass through the stomach
Digestion Mishaps• Heartburn: the damage to esophageal
mucosa due to presence of stomach acids because of a weak cardio-esophageal sphincter
• Gastric ulcer: when the mucus layer of the stomach is not strong enough to withstand gastric acids; burns a hole in stomach wall
Digestion Mishaps• Diarrhea: the decreased absorption of
water and electrolytes in the small & large intestine leading to watery stool
• Constipation: the increased absorption of water and electrolytes in the large intestine; leads to hard, impacted stool