Small intestine location

• begins at the pyloric sphincter of the stomach
• coils through the abdominal cavity
• opens into large intestine
• 10 ft long

Where does most digestion and absorption of nutrients occur

Small intestine

Regions of small intestine

• Duodenum (10 in)
• Jejunum (3 ft)
• Ileum (6 ft)

Layers of small intestine

• Mucosa
• Submucosa
• Muscularis
• Serosa-visceral

Mucosa - Sm Intestine

• Absorptive and mucous-secreting goblet cells
• Intestinal glands (secrete intestinal juice)
• endocrine cells
• Lymph tissue

Submucosa - Sm Intestine

Duodenal glands

• secrete mucus
• neutralizes gastric acids

Muscularis - Sm Intestine

Two layers of smooth muscle

Serosa - Sm Intestine

Visceral peritoneum

Plicae Circulares

Permanent ridges of the small intestines mucosa and submucosa

• encourages turbulent flow of chyme
• increases the surface area for absorption

Villi

Finger like projections of the small intestines mucosa that increase the surface area for absorption

• Each villus contains a capillary network where nutrients are absorbed and can enter the blood or lymphatic system

Microvilli

• Projections of the apical membrane of the absorptive cells
• Appear in microscope as a fuzzy line called the brush border
• contributes to increase surface area

What contributes to the surface area of the small intestine allowing for maximum reabsorption of nutrients

• plicae circulares
• villi
• microvilli

What are the end products of protein digestion

• Amino acids
• Dipeptides
• Tripeptides

(Brush Border enzymes)

Mechanical digestion - Sm Intestine

Two types of movement:

• Segmentations
• Migrating motility complexes

Segmentations

A type of movement during mechanical digestion used to mix chime and bring it in contact with the mucosa for absorption

Migrating motility complexes

A type of movement during mechanical digestion that occur after absorption and pushes chime toward the large intestine

Chemical digestion - Sm Intestine

Begins with Cyme entering the small intestine to begin the process of digesting materials

Chyme

Substance that passes from stomach to small intestine that contains partially digested carbs, proteins and lipids

Digestion in the small intestine is dependent on which materials being digested

• Carbs
• proteins
• lipids
• nucleic acids

How are carbs broken down in the small intestine

Brush border enzymes break them down into monosaccharides

How are proteins broken down in the small intestine

They are broken down along the brush border by two peptidases:

• Aminopeptidase
• Dipeptidase

How are lipids broken down in the small intestine

• They are digested by enzymes called lipases
• Undergo emulsification by bile salts

How are nucleic acids broken down in the small intestine

They are digested by pancreatic juices and brush border enzymes

What is absorbed in the small intestine

• 90% of all intestinal absorption
• Proteins, amino acids, nucleic acids and sugars
• Dietary lipids
• Water
• Fats

How are proteins, amino acids, nucleic acids and sugars absorbed in the small intestine

Absorbed into the blood capillaries by facilitated diffusion or active transport

How are dietary lipids absorbed in the small intestine

Absorbed via simple diffusion

How is water absorbed in the small intestine

Absorbed via osmosis

How are fats absorbed in the small intestine

Aggregate into globules called chylomicrons

Chylomicrons

Too large for diffusion into blood capillaries, enter specialized lymphatic vessels called lacteals and eventually mix with blood