Digestion

•Mechanical Digestion (mouth, stomach)

•Chemical Digestion (mouth, stomach, intestines)

•Absorption (intestines)

•Assimilation (at each cell in the body)

Sphincters divide the alimentary canal Into separate compartments.

Cardiac sphincter

Pyloric sphincter

Ileocecal sphincter

Anal sphinters

MOTILITY

PERISTALSIS

MIXING WAVES

Mouth

1. Saliva: Mucous - lubricates food, easier to swallow.

Amylase – initiates hydrolysis of starch

Lysozyme – bacteriostatic enzyme

2. Mastication:

3. Epiglottis: cartilage flap that covers the top of the larynx (glottis)

Esophagus

Muscular tube that propels food to stomach using peristalsis

B – Esophagus

D – Cardiac Sphincter (esophageal reflux)

F – Stomach Muscular, mechanical digestion, also produces bacteriostatic acid, and digestive enzymes

H – Pyloric Sphincter (controls flow of food into duodenum)

Internal Structure of Stomach

Rugae

Chief Cells SecreteDigestive Enzymes

Parietal Cells SecreteHydrochloric Acid

Pepsinogen – Most Important of the Stomach Enzymes

When first secreted, pepsinogen is inactive.

When pepsinogen is exposed to HCl, it reacts and converts to Pepsin.

Pepsin is the active form of the enzyme. It is a protease.

Intrinsic FactorProduced by parietal cells. Essential for absorption of vitamin B12 in theintestine.

Control of Gastric Secretions1. Smell, sight or taste of

food stimulates the vagus nerve to stimulate the stomach.

2. Increased motility and increased gastric secretions.

3. Increased release of a hormone called gastrin.

4. Gastrin stimulates the stomach to produce even more secretions.

Peptic Ulcer: a sore in the mucosal lining of the stomach.90% caused by a bacterial infection.

Liver, Gall Bladder and Exocrine Pancreas

Liver produces bile. The bile is stored in the gall bladder, and is delivered to theduodenum by the bile duct.

Exocrine portion of the pancreas produces digestive enzymes that are carried to the duodenum by the pancreatic duct.

Pancreatic Enzymes

• Amylase: hydrolyzes starch to maltose• Protease: hydrolyzes proteins to peptides and

amino acids• Lipase: hydrolyzes triglycerides (fats and oils)

to fatty acids and glycerol• Nucleotidases: hydrolyzes DNA and RNA to

form nucleotides

Digestion at Duodenum

• Role of gastric motility• Role of Bile• Role of pancreatic enzymes• Chemical changes in duodenum

(decreased pH)

Control of Pancreas and Gall Bladder

Cholescystokinin

For Absorption to occur, chemicallydigested nutrients mustmove through the wallof the intestine and enter the blood circulationor the lymph (lacteal).

Mesentery has blood andlymph supply

The inner wall of theintestinal lumen is foldedto form villi. Each villus has blood capillaries andlymph vessels.

villi

Lymph vessel (lacteal)

Blood capillaries

Serosa (serous membrane) - outermost layer

Muscularis (smooth muscle layer)

Submucosa(blood vessels, lymph and nerves)

Mucosa(mucous membrane)Cells with microvilliand goblet cells

Absorption of Lipids1. In the duodenum, lipids mix withBile, become emulsified and forms “micelles.”

2. Micelles are taken up by endocytosis andmoved through themucosal cell.

3. While in the mucosalcell proteins are addedto the micelle to makethem more soluble.

4. The new mixture of bile,lipids and protein is called achylomicron.

5. The chylomicron entersthe lymph and is carried away.

6. Chylomicra pass throughlymph nodes and arecarried up the torso to thelymph duct.

7. Lymph vessels empty intothe blood circulation at thesubclavian vein.

8. Chlymycra arecarried in the blood to the liver where theliver converts theminto HDL’s and LDL’sthat are returned to the blood.

HDL’s and LDL’s• Lipoproteins

- formed by the liver from chylomicra- contain both lipids and proteins

• High Density Lipoproteins - “Good Cholesterol”- contain more protein- more soluble in water- tend to remove fatty deposits from blood vessels.

• Low Density Lipoproteins – “Bad Cholesterol”- contain less protein, more lipid- tend to add fatty deposits to walls of blood vessels

Sugar, Nucleotide and Amino Acid Absorption

blood

Active transport processes movethese nutrientsthrough the mucosal cells and into the blood.

Sugars, amino acids andnucleotides move into the mesentery and are carriedto the liver via the hepaticportal vessel.

Liver may store nutrients.Liver may remove toxins.

Amin

o Ac

ids nucleotidessu

gars

The Amazing Liver

Stores and Releases GlucoseProduces bileStores Lipids and Converts Chylomicra to HDL’s and LDL’s

Removes toxins from bloodProduces blood proteins

The Large Intestine

The ileum is the last segment of the small intestine. It joins the large intestine at the ileocecal sphincter (valve). Below the junction is a small pouch called thececum, and hanging from that is the appendix. The appendix is believed to be avestigial organ because some animals have a very large, functional cecum.

Digestive Tract of the Pig

In the pig the cecum houses micro-organisms that are essentialfor the digestion of cellulose (plant fibers). Humans can not digest plant fiber.

Large Intestine Function• Each day a typical person swallows about two

liters of liquid.• The salivary glands, stomach, pancreas, gall

bladder, and intestines add another 6-7 liters of liquid per day.

• The large intestines reabsorb that liquid, form a more compact feces, and reabsorb salt.

• In diarrhea, bacteria have infected the large intestine and it is no longer able to reabsorb fluids - risk of dehydration.

• Rectum: stores feces

• Anal Sphincters: control defecation