1. ANATOMY & PHYSIOLOGY
THE DIGESTIVE SYSTEM

2. Digestive System Ingestion: receiving food
Digestion: breakdown of food particles small enough to pass through cell membranes
Absorption: transfer of food into circulation

3. A. Alimentary Canal – The Tube from beginning to end ~ 9m or 30ft.
Oral Cavity
Pharynx
Esophagus
Stomach
Small Intestine
Large Intestine
Rectum/Anal Canal

4. Walls of Alimentary Canal – 4 layers (inside  outside)
Mucosa – secrete mucus, protects surrounding tissue, absorbs nutrients
Submucosa – nourishes surrounding tissues, carry away absorbed nutrients
Muscular layer – move food to stomach (peristalsis)
Circular: changes diameter of tube
Longitudinal: changes length of tube
Serous layer/serosa – produce serous fluid to prevent friction

5. Tube Movements
Mixing – some sections of the tube contract to mix and breakdown food
Propelling (peristalsis) – wave-like movements push food through the canal

6. B. Mouth/ Oral Cavity Cheeks – muscles for chewing
Lips – sensory and manipulation of food
Tongue – manipulated food; taste buds/receptors
Frenulum connects the tongue to the bottom of the mouth
Palate (roof of mouth) – hard
anterior, soft posterior
Uvula is extension of
soft palate hangs down to
direct food

7. Teeth 20 as a child, 32 as an adult
Incisors and canines: cutting and tearing
Premolars and molars: mastication

8. Salivary Glands
Saliva – mostly water; slightly acidic, some antibodies
Serous cells: secrete serous fluid with digestive enzymes (amylase enzyme of the mouth) to lubricate food and begin digestion
Mucous cells: produce mucous to clump food into a ball/bolus
Three Glands
Parotid – below the ear
Submandibular – under the mandible (jaw)
Sublingual – under the tongue

9. Pharynx – cavity; posterior end of the mouth, leads to the esophagus
Step 1 – chew, breakdown, mix with saliva into bolus
Step 2 – swallowing reflex, once near the pharynx
Soft palate is raised to block the nasal passageway
Hyoid bone – larynx elevated to block trachea epiglottis then covers the opening
Muscle relax, lower pharynx
and open esophagus
Peristaltic wave begins
pushing food down
esophagus

10. Stomach – located on left portion of body, j-shaped
Holds between 50 mL – 4L, folded when empty
Digest proteins
Absorbs very little – only few liquids, drugs, alcohol, and salts
Mechanical and chemical digestion

11. Regions of the Stomach
Cardia –small region at the esophageal-stomach junction
Fundus – formed by the upper curvature of the organ; temporary storage area for food
Body – main, central region; holds max 4 Liters, avg. 0.9L
Pylorus – small region at the stomach-duodenal junction; holds 30 mL only releases 3mL

12. Cells of the Stomach/ Gastric Glands
Mucous cells – secrete mucous for protection
Chief cells – secrete digestive enzymes; pepsinogen
Parietal cells – secrete HCL (hydrochloric acid); pH~ 2
Pepsinogen (an inactive enzyme) is converted to Pepsin when it reacts with HCl/acidic environment
Pepsin breaks down proteins into amino acids

13. 3 Layers of the Stomach Wall
Serosal: outermost; thick connective tissue binds to other organs
Muscularis: thick-middle; three layers of smooth muscle tissue.
Mucosal: innermost; relatively thick and contains numerous tubular glands called gastric pits
Little to no digestion occurs here; alkaline (high pH) to combat HCl
Ulcers- holes in stomach, esophagus, duodenum brought on by stress

14. Control of Gastric Juices
Sight, smell, taste stimulates secretions (parasympathetic)
Distension of the stomach and production of chemicals due to breakdown of food
Gastrin: hormone released with secretion also stimulates increase of secretion
Decrease juices if lots of fat/protein in the duodenum or if the intestine is extended.

15. Digestion and Absorption in Stomach
HCl  + churning action  breaks down food
Smaller particles does what to surface area? What does this have to do with enzyme digestion?
Enzymes able to work better because they can attack a higher surface area
Chyme: mixture of small food particles + acid + mucous
Little absorption occurs through the walls of the stomach; foods high in fat stay in stomach the longest

16. Exiting the Stomach
Chyme: Ingested substances combine with the secretions of the glands of the stomach, producing a viscous, highly acidic soupy mixture of partially digested food

17. Accessory Organs
Liver
Gallbladder
Pancreas

18. Liver: Largest gland/organ of the body; produces bile that is stored in the gallbladder
supplies quick energy
metabolizes alcohol
makes proteins
stores vitamins and minerals
regulates blood clotting
regulates cholesterol production
detoxifies poisons
3lbs.
Requires 25% of cardiac
output

19. Gallbladder: stores and concentrates bile that is not needed immediately for digestion
Bile: yellow-green, alkaline solution containing bile salts, bile pigments (primarily bilirubin), cholesterol, neutral fats, phospholipids, and a variety of electrolytes
Fat emulsification via bile salts
Bile does not usually enter the small intestine until the gallbladder contracts 

20. Pancreas (exocrine)
Digestive enzymes - break down carbs, proteins, and fats.
Base, bicarbonate ion (alkaline).
Neutralizes chyme from the stomach, permitting digestive enzymes to function.
Secretin stimulates production
of bicarbonate ions
Cholecystokinin (CCK) stimulates
production of enzymes
Enzymes include: proteases,
pancreatic lipase, and pancreatic
amylase

21. Small Intestine
Receives chyme, pancreatic and liver secretions to complete digestion of nutrients
Duodenum: 25cm long x 5cm wide; c-shaped, most absorption of nutrients occurs here
Jejunum: middle; thicker more vascular walls, greater in diameter
Ileum: last section; suspended from abdominal wall by mesentery

22. Duodenum Pancreatic enzymes & bile enter, continuing digestion.
Villi: microscopic hair-like structures; absorption of nutrients
Active transport of sugars, amino acids, and fatty acids across membranes.
Pass through the epithelial wall into the bloodstream.
Enzymes: break down carbs, proteins, and fats into sugars, amino acids, & fatty acids
This is where most nutrients are absorbed in the digestive system

23. Large Intestine
Large Intestine: serves to compact the solids remaining after digestion.
Lacks villi: little to no absorption of nutrients
Water and a few ions (e.g. sodium) are absorbed through the walls of intestine; only sig. secretion is mucous
Undigested material then passes into the rectum and is finally eliminated through the anus.

24. Sections of the Large Intestine
Cecum: beginning of the large intestine; receives chyme from the ileum, and connects to the ascending colon; appendix attached
Ascending Colon: begin the process of extracting water and electrolytes; peristalsis required to move up to transverse colon
Transverse Colon: attached to the stomach by a wide band of tissue called the greater omentum; mobile section

25. Descending Colon: store undigested wastes before moving into the rectum; IBS and colon cancer most common here
Sigmoid Colon: s-shaped; walls are muscular and contract to increase pressure inside the colon to move wastes into the rectum
Rectum: final straight portion of the large intestine; acts as a temporary storage site for undigested wastes; stretch receptors located in the walls

27. Ailments & Diseases of the Digestive System
Dysphagia: difficulty swallowing; common in old age or after a stroke/nervous system malfunction
Gastroesophageal Reflux Disease (GERD): stomach contents leak backwards from the stomach into the esophagus irritating the esophagus, causing heartburn

28. Crohn’s Disease: type of inflammatory bowel disease (IBD) that may affect any part of the gastrointestinal tract; primarily causes abdominal pain, diarrhea, vomiting, or weight loss;  caused by interactions between environmental, immunological and bacterial factors in genetically susceptible individuals

29. Ulcers: Peptic ulcers are holes/breaks in the lining of the duodenum or the stomach, areas that come into contact with stomach acids and enzymes. Duodenal ulcers are more common than stomach ulcers; recent theory holds that bacterial infection is the primary cause is the bacterium Helicobacter pylori (H. pylori)
Celiac Disease: a disease that damages the small intestine and interferes with absorption of nutrients from food. Cannot tolerate gluten, a protein in wheat, rye, and barley. Gluten is found mainly in foods but may also be found in everyday products such as medicines, vitamins, and lip balms.

30. Ulcerative colitis: a chronic, long-lasting disease that causes inflammation and sores (ulcers) in the lining of the large intestine, especially the colon and rectum
Irritable Bowel Syndrome (IBS): a common disorder that affects the large intestine (colon); commonly causes cramping, abdominal pain, bloating gas, diarrhea and constipation
Diverticulosis: small pouches may form along the walls of the large intestine called diverticuli; may collect and not be able to empty fecal material which can lead to inflammation

31. Jaundice: “yellow” in french; backup of bile by-products from the blood into body tissues. May result from blockage of the ducts draining bile into the intestines
Gallstones: hard, pebble-like deposits that form inside the gallbladder;  may lead to inflammatory condition characterized by retention of bile in the gallbladder
Cirrhosis: is scarring of the liver and poor liver function. It is the final phase of chronic liver disease;  most commonly caused by alcoholism, hepatitis B and hepatitis C

32. Vaccines are readily available in developed countries
Hepatitis: inflammation of the liver; viruses cause most cases of hepatitis. Drug or alcohol use can also cause hepatitis. In other cases, your body mistakenly attacks healthy cells in the liver.
A -  hepatitis A virus (HAV); usually spread by eating or drinking food or water contaminated with infected feces, undercook shellfish, or close contact with an infectious person. After a single infection a person is immune for the rest of their life.
B - hepatitis B virus (HBV); transmitted by exposure to infectious blood or body fluids; causes liver inflammation, vomiting, jaundice, and, rarely, death. Chronic hepatitis B may eventually cause cirrhosis and liver cancer.
C -  hepatitis C virus (HCV); spread primarily by blood-to-blood contact associated with intravenous drug use, poorly sterilized medical equipment, and transfusions; often asymptomatic, but chronic infection can lead to scarring of the liver and ultimately to cirrhosis, liver failure, or liver cancer.
Vaccines are readily available in developed countries