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 Secrete Digestive Enzymes Parietal Cells Secrete Hydrochloric 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 Factor Produced by parietal cells. Essential for absorption of vitamin B 12 in the intestine.

Control of Gastric Secretions 1.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 the duodenum 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, chemically digested nutrients must move through the wall of the intestine and enter the blood circulation or the lymph (lacteal). Mesentery has blood and lymph supply The inner wall of the intestinal lumen is folded to form villi. Each villus has blood capillaries and lymph 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 microvilli and goblet cells

Absorption of Lipids 1. In the duodenum, lipids mix with Bile, become emulsified and forms “micelles.” 2. Micelles are taken up by endocytosis and moved through the mucosal cell. 3. While in the mucosal cell proteins are added to the micelle to make them more soluble. 4. The new mixture of bile, lipids and protein is called a chylomicron. 5. The chylomicron enters the lymph and is carried away.

6. Chylomicra pass through lymph nodes and are carried up the torso to the lymph duct. 7. Lymph vessels empty into the blood circulation at the subclavian vein. 8. Chlymycra are carried in the blood to the liver where the liver converts them into HDL’s and LDL’s that 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 move these nutrients through the mucosal cells and into the blood.

Sugars, amino acids and nucleotides move into the mesentery and are carried to the liver via the hepatic portal vessel. Liver may store nutrients. Liver may remove toxins. Amino Acids nucleotides sugars

The Amazing Liver Stores and Releases Glucose Produces bile Stores Lipids and Converts Chylomicra to HDL’s and LDL’s Removes toxins from blood Produces 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 the cecum, and hanging from that is the appendix. The appendix is believed to be a vestigial 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 essential for 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