Digestive system

Why a
Digestive System ?

Kingdom Animalia

Heterotrophism

Digestive System
General Function

The digestive system is responsible for the

Intake and breakdown of complex foods into two categories:

Useable materials (nutrients)

Non-useable materials (wastes)

Six Major Digestive Processes

INGESTION

PROPULSION

MECHANICAL DIGESTION

CHEMICAL DIGESTION

ABSORPTION (of nutrients)

DEFECATION (of wastes)

GI Accessory
TractOrgans

Oral Cavity

Esophagus

Stomach

Small Intestine

Large Intestine

Anus

Teeth

Tongue

Gall Bladder

Glands

Liver

Pancreas

Salivary

GI Tract and
Accessory Organs

Appendicitis

Functional Anatomy
of the Digestive System

Part I

Oral Cavity

Pharynx

Esophagus

Digestive Processes of the Oral Cavity

INGESTION

MECHANICAL DIGESTION

CHEMICAL DIGESTION

Oral Cavity

Borders:

Anterior Lips Lateral Cheeks Superior Palate (Hard/soft) Inferior Tongue Tongue:

Accessory Organ for: mixing, taste buds

***

Oral Cavity contd

Salivary glands secrete saliva!

Saliva components:

water, amylase, mucin, lysozyme

Salivation controlled by

PNS

3 pairs of Salivary Glands

Parotid

Submandibular

Sublingual

Saliva functions:LubricationCleansingChemical digestion

Oral Cavity cont.

Palate:

Hard Palate bony anterior region

Soft Palate muscular posterior region

Uvula

Oral Cavity cont

Teeth

Function in MASTICATION

Work with tongue, saliva, and palate to form BOLUS.

Bolus is swallowed at pharynx, prevented from entering trachea by epiglottis and passed to esophagus

Automatic Propulsion of food (PERISTALSIS) begins!

Deglutition (Swallowing)

THE ESOPHAGUS

carries bolus from oral cavity to stomach.

PERISTALSIS

the automatic, involuntary, continuous propulsion of food through the GI tract.

P E R I S T A L S I S

Functional Anatomy cont

PART II

The STOMACH

Digestive Processes of the Stomach

Storage tank

Chemical digestion of proteins

Mechanical digestion

Bolus Chyme

Volume 50 ml 4 liters

Rugae allow for expansion

Enervated by ANS

Divided into four regions cardiac region

fundus

body

pyloric region

Lesser curvature--lesser omentumGreater curvature--greater omentum

Gastric Sphincters

Cardiac Sphincter

Pyloric Sphincter

Functions:

Regulates/controls propulsion of food into/out of the stomach

Cardiac sphincterPyloric sphincter

Peristaltic Waves in the Stomach!

What is Gastric Juice?

A collection of chemicals produced by a variety of cells lining the gastric pits!

Examples:

CELL TYPESECRETIONMucus Neck Cellsmucus

Parietal CellsHCl

Chief Cells Pepsinogen Pepsin

Enteroendocrine CellsHormones

So Hows It All Related?

Bolus enters stomach through cardiac sphincter

Stomach distends (stretches)

Receptors detect stretch stimulus

Gastrin secreted

Gastrin stimulates secretion of HCl by Parietal Cells

HCl stimulates conversion of pepsinogen (produced by chief cells) to pepsin!

The Effect of It All?

Stomach Distension/Muscle Contraction:Completion of Mechanical Digestion

Acidic Environment:Bolus Chyme

Pepsinogen Pepsin:Initiates Chemical Digestion of Proteins

Stomach Disorders/Conditions

Gastroesophageal Reflux Disease

Gastritis

Gastric Ulcer

Emesis

PART IIISMALL INTESTINE

ACCESSORY STRUCTURES

LIVER

GALL BLADDER

PANCREAS

Small Intestine

Three Regions:Duodenum

~1 ft

Jejunum~8 ft

Ileum~12 ft

Digestive Processes
of the Small Intestine

CHEMICAL DIGESTION OF

CARBOHYDRATES

PROTEINS

LIPIDS

NUTRIENT ABSORPTION!!

Microscopic Anatomy of the Small Intestine

Mucosa

Circular folds (plicae circulares)

Slow propulsion of chyme

Villi

Finger-like projections w/ capillaries in center

Microvilli

Small projections of cells that absorb nutrients (aka absorptive cells)

(Location of duodenal glands)

Before Nutrient Absorption occurs

CHEMICAL DIGESTION MUST BE COMPLETED IN THE SMALL INTESTINE

THROUGH ENZYMATIC ACTIVITY!

But Theres a Problem

THE SMALL INTESTINE LACKS CELLS THAT PRODUCE/SECRETE DIGESTIVE ENZYMES!

Accessory Structures to the Rescue

LIVER

Largest internal organ of the body

Over 500 metabolic functions

Digestive Function:

Produces BILE for chemical digestion of LIPIDS

GALL BLADDER

Small sac embedded in liver

Stores bile produced by liver

Bile Pathway

Produced in Liver

Travels from Liver to Gall Bladder

Released from Gall bladder via cystic duct

Cystic duct fuses with bile duct

Bile duct drains bile into duodenum of small intestine

PANCREAS

Embedded within outer duodenum

Produces PANCREATIC JUICE containing:

Secretes PJ into duodenum via common bile duct

amylases

proteases

Lipases

nucleases

PART IV

THE LARGE INTESTINE (aka COLON)

Digestive Processes of the Large Intestine

ABSORPTION OF:

WATER

VITAMINS

PRODUCTION OF VITAMIN K

E. coli; bacterial flora

PROPULSION OF FECES FOR DEFECATION

Regions of the Colon

Cecum

appendix

Ascending colon

Transverse colon

Descending colon

Sigmoid colonrectum

anus

Microscopic Anatomy

Mucosa

Goblet cells!

thick mucus

Lubrication/movement of feces

Protection against bacterial flora

Muscularis

Tight band arrangement (Taniae coli)

Haustra formation

Vermiform appendixcecumileumHaustra of ascending colon

Taniae coliColonoscopy of a Healthy Colon

FUNCTIONS OF THE LIVER

Destruction of RBCs

Old, worn out RBCs removed daily

~120 days:

RBCs collect in spleen

Macrophages in spleen break down RBCs

Fe in heme gets recycled

Remainder of heme broken down to bilirubin

Bilirubin binds to plasma albumin, sent to liver

Liver sends bilirubin to intestine

Leaves body in feces

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Digestive system