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