Chapter 24

The Digestive System

Functions of the Digestive System

• Ingest food

• Digest food

• Absorb nutrients

• Eliminate indigestible waste

Digestive anatomy overview

Organization of the Digestive organs

Alimentary Canal Mouth Pharynx Esophagus Stomach Small intestine Large intestine Anus

Accessory organs Teeth Tongue Salivary glands Gall bladder Liver Pancreas

The Digestive Process

IngestionPropulsionMechanical DigestionChemical DigestionAbsorptionDefecation

Motility vs. MixingThe difference between peristalsis and segmentation:

Peristalsis moves food along the tract. Segmentation is mixing and part of the mechanical digestion

process.

Daddy, what does “retroperitoneal” mean?

This is your basic alimentary tract structure.

The oral cavity and pharynx

Say “ahhh”…

Road map of the tongue

Salivary glands

Human dental formula:Baby teeth

Human dental

formula: Permanent

teeth

Anatomy of a Tooth

The Stomach

Gastroesophageal junctionEsophagus

Stomach

Stratified squamous epitheliumSimple columnar epithelium

Gastric histology

Stimulus and control of gastric activity

HCl secretion

The stately process of gastric emptying

Control mechanisms

of gastric contractions

The duodenum, gall bladder and pancreas

Histology of the small intestine

Adaptation for absorption

Duodenal mucosa

Duodenal glands

VilliGoblet cells

Crypts of Lieberkuhn!

Brunner’s (duodenal) glands

You only find us here,In the duodenum!

Absorption of Nutrients• Nearly all occurs in the small intestine.

– 80% of the electrolytes and virtually all food

• Most nutrients are absorbed by active transport.– Glucose, amino acids, & nucleic acids are absorbed

by secondary active transport with sodium.– Iron and calcium require transport proteins (ferritin) or

cofactors (vitamin D).– Anions follow Na+.

• Vitamins -– Fat soluble (A, D, E & K) vitamins are carried with

micelles. Much of the K is absorbed in the colon.– Water soluble vitamins diffuse with the exception of

B12, which requires intrinsic factor.

Crypts of Lieberkuhn!

Paneth cells

The Liver

Hormonal regulation of bile release

Exocrine tissues of the pancreas

Pancreas: Acinar cells

Activation of pancreatic proteases in the duodenum

Regulatory mechanisms for release of pancreatic juice

Anatomy of the large intestine

The Colon

Look at all those goblet cells!

The rectum and anus

The peritoneum

The Defecation

reflex

Location of mesentary:The lesser omentum

Location of mesentary:The greater omentum

Chemical Digestion Carbohydrates & proteins

Chemical Digestion Lipids & Nucleic acids

Protein digestion in the small intestine

Bile salts emulsify fats

Absorption of lipid

Dietary fats are absorbed into the “lacteals” of the lymphatic system before being transferred to the circulatory system.

Lacteals