Chapter 14 – Part 2The Digestive System

Stomach AnatomyStomach Anatomy

Located on the left side of the abdominal cavity

C-shaped

Nearly hidden by the liver and diaphragm

Stomach AnatomyStomach Anatomy Regions of the

stomach Cardiac region –

near the heart

Fundus – expanded part lateral to the cardiac region

Body - midportion

Pylorus – funnel-shaped terminal end

Stomach AnatomyStomach Anatomy

Food enters the stomach at the cardioesophageal sphincter

Food empties into the small intestine at the pyloric sphincter

Stomach AnatomyStomach Anatomy

The stomach is about 10 inches long

Its diameter depends on how much food it contains

When it is full it can hold about 1 gallon of food

When it is empty it collapses inward on itself

Stomach AnatomyStomach Anatomy

Rugae – internal folds of the mucosa (seen especially when the stomach is empty)

External regions

Lesser curvature – the convex lateral surface of the stomach (smaller curve)

Greater curvature – the concave medial surface of the stomach (larger curve)

Stomach AnatomyStomach Anatomy

There are two layers of peritoneum that are attached to the stomach:

Lesser omentum – attaches the liver to the lesser curvature

Greater omentum – attaches the greater curvature to the posterior body wall

Drapes downward and covers the abdominal organs like a lacy apron

Contains fat which helps to insulate, cushion, and protect abdominal organs

Greater and Lesser Omentum

PeritonitisPeritonitis

Peritonitis – occurs when the peritoneum is infected

The peritoneal membranes tend to stick together around the infection site

Helps to seal off and localize many intraperitoneal infections

Provides time for macrophages to mount an attack

Stomach AnatomyStomach Anatomy

Stomach FunctionsStomach Functions

1. Acts as a storage tank for food

2. Site of food breakdown

3. Chemical breakdown of protein begins

4. After food has been processed in the stomach, it delivers chyme (processed food) to the small intestine

Structure of the Stomach MucosaeStructure of the Stomach Mucosae

Besides the usual longitudinal and circular muscle layers, the stomach contains a third obliquely arranged layer in the muscularis externa.

Does more than just move food along the tract

Allows it to churn, mix and pummel the food, physically breaking it down to smaller fragments

Stomach AnatomyStomach Anatomy

Specialized Mucosa of the StomachSpecialized Mucosa of the Stomach

The mucosae of the stomach is a simple columnar epithelium that produces large amounts of mucus.

It dotted with deep gastric pits (formed by folded mucosa)

Glands and specialized cells are in the gastric gland region

Specialized Mucosa of the StomachSpecialized Mucosa of the Stomach

Mucous neck cells – produce a sticky alkaline mucus

Clings to the stomach mucosa and protects the stomach wall itself from being damaged by the acid and digested by the enzymes

Gastric glands – secrete gastric juice

Specialized Mucosa of the StomachSpecialized Mucosa of the Stomach

Chief cells – produce protein-digesting enzymes (pepsinogens)

Parietal cells – produce hydrochloric acid, which makes the stomach acidic and activates the enzymes

Endocrine cells – produce gastrin (important for digestion)

Structure of the Stomach MucosaStructure of the Stomach Mucosa

Small IntestineSmall Intestine The body’s major digestive

organ

Site of nutrient absorption into the blood

Muscular tube extending from the pyloric sphincter to the ileocecal valve

Longest section of the alimentary canal (6-13 feet in a living person)

Is encircled and framed by the large intestine

Small Intestine: Three SubdivisionsSmall Intestine: Three Subdivisions1. Duodenum

Attached to the stomach Curves around the head

of the pancreas About 10 inches long

2. Jejunum Extends from the duodenum to the ileum About 8 feet long

3. Ileum Terminal part of the small intestines About 12 feet long

Chemical Digestion in the Small Chemical Digestion in the Small IntestineIntestine The small intestine is

able to process only a small amount of food at one time

The pyloric sphincter (literally, “gatekeeper”):

Controls food movement into the small intestine from the stomach

Prevents the small intestine from being overwhelmed

Chemical Digestion in the Small Chemical Digestion in the Small IntestineIntestine Enzymes complete the

chemical breakdown of food in the small intestine

Source of enzymes that are mixed with chyme

Produced by the intestinal cells

Produced by the pancreas and ducted into the duodenum of the small intestine via the pancreatic duct

Chemical Digestion in the Small Chemical Digestion in the Small IntestineIntestine Bile enters the duodenum from the gall

bladder via the bile duct

Bile is formed by the liver

Bile helps to break down fats

Chemical Digestion in the Small Chemical Digestion in the Small IntestineIntestine

Figure 14.6

Main Function of the Small IntestineMain Function of the Small Intestine

Nearly all food absorption occurs in the small intestine Its wall has three structures that increase the

absorptive surface tremondously

1. Microvilli

2. Villi

3. Circular Folds

Well suited for absorption These structural modifications decrease in

number toward the end of the small intestine

Villi of the Small IntestineVilli of the Small Intestine

Villi - Fingerlike structures of the mucosa

Give the small intestine more surface area

Gives it a velvety appearance

Microvilli of the Small IntestineMicrovilli of the Small Intestine

Microvilli - small projections of the plasma membrane

Gives the cell surface a fuzzy appearance

Sometimes referred to as brush border

Found on absorptive cells

Microvilli and Villi of the Small IntestineMicrovilli and Villi of the Small Intestine

Structures Involved in Absorption of Structures Involved in Absorption of NutrientsNutrients

Digested foodstuffs are absorbed through the villus of mucosa cells via:

1. Rich capillary bed

2. A modified (specialized) lymphatic capillary called a lacteal

Folds of the Small IntestineFolds of the Small Intestine

Circular folds, called plicae circulares, are deep folds of both the mucosa and submucosa layers

Do not disappear when filled with food (unlike the rugae)

Folds of the Small IntestineFolds of the Small Intestine

The submucosa has Peyer’s patches (collections of lymphatic tissue)

More are found towards the end of the small intestine

The undigested food residue in the intestine contains huge numbers of bacteria, which must be prevented from entering the bloodstream