1. The Digestive System

2. I. Introduction
Digestion is the process of altering the physical state and chemical composition of food, so that it can be absorbed.
The digestive tract is also called the gastrointestinal tract or alimentary canal.

4. II. Digestive Organs Oral cavity (mouth)
hard palate and soft palate form roof
Uvula – cone-shaped projection that keeps food out of nasal cavity during swallowing
Tongue –mixes food particles with saliva and moves food toward pharynx; also aides in speech
Papillae – rough projections on surface of tongue that help handle food and contain taste buds (tip-salty/sweet; sides-sour; back-bitter)
Salivary glands – secrete saliva and are located near the ears and tongue; saliva helps moisten food particles and begins the chemical digestion of carbohydrates

6. II. Digestive Organs (cont)
Teeth
break food into smaller pieces creating more surface area for digestion
32 total; covered with enamel, the hardest substance in the body
Begin physical digestion
Pharynx (throat)
connects oral cavity to esophagus
Esophagus
long tube (~25 cm) dorsal to trachea that delivers food to stomach
made of smooth muscle
transports food by peristalsis (rippling contractions) and secretes mucus

8. II. Digestive Organs (cont)
Stomach
J-shaped organ with a capacity of 1 liter or more
the stomach wall has folds called rugae
Main site of physical digestion, which is almost completed in the stomach by the peristalsis waves which churn the food
chemical digestion of proteins begins in the stomach and is completed in the small intestines
gastric juice – combination of pepsin, pepsinogen, hydrochloric acid, and mucus; pepsin begins the digestion of protein; pepsinogen reacts with hydrochloric acid and changes into pepsin
Little to no fat digestion takes place in the stomach.
Food leaves the stomach as a liquid called CHYME

9. II. Digestive Organs (cont)
Stomach
very limited amount of absorption occurs here; water, some drugs (ex. Aspirin), and alcohol
The cardiac sphincter (lower esophageal sphincter)– is located where the esophagus connects to the stomach. It is a muscular valve which prevents food and gastric enzymes from being pushed back into the esophagus.
The pyloric sphincter – is located where the stomach connects to the small intestine. It prevents backwash from the Small intestine into the stomach.

11. II. Digestive Organs (cont)
Liver
weighs ~3lbs. and is located in the upper right of abdominal cavity
reddish-brown in color because it filters the blood,
and is divided into right and left lobes
functions in protein, carbohydrate, and lipid metabolism
storage area for glycogen, iron, vitamins A, D, and B12
filters blood, destroying damaged RBCs and foreign antigens
removes toxic substances such as alcohol from blood

12. II. Digestive Organs (cont)
Bile – is a yellowish-green enzyme that helps the body digest fats by breaking the fats down physically.
Fats and oils stick together and move away from water this makes them difficult to digest because the enzymes can not get around the fats.
Bile causes EMULSIFICATION to happen – which means it separates the fats into tiny droplets which can now be chemically digested.
Bile is made in the liver, stored in the gall bladder (which is why it is green), and transported to the pancreas and then the duodenum by the bile duct.

14. II. Digestive Organs (cont)
Pancreas
lies posterior to greater curvature of stomach
secretes pancreatic juice into small intestine
pancreatic juice contains enzymes that digest carbs, fats, nucleic acids, and proteins

16. II. Digestive Organs (cont)
Small intestine
between stomach and large intestine
many loops and coils
inner wall lined with villi – projections that increase the surface area for absorption
secretes enzymes that break down food and receives secretions from the pancreas and liver
completes digestion of nutrients in chyme
absorbs 90% of products of digestion
transports wastes into large intestine

17. II. Digestive Organs (cont)
Small intestine - Main site of chemical digestion.
There are 3 sections to the small intestines:
Duodenum which is the first section and is 25 cm long. Pancreatic enzymes and bile are released into the small intestine in this section.
Jejunum is the second section and is about 2.5m (8 ft) long and passes imperceptibly into the
Ileum, which is the final section and is about 4m (12 ft).

19. II. Digestive Organs (cont)
large intestine
also called colon
reabsorbs water, vitamins and electrolytes
last stages of chemical digestion occur here through bacterial, rather than enzymatic action
forms and stores feces (FYI - feces is ~75%water and the odor results from bacteria products; feces is composed of water, salts, bacteria (such as E. coli), and undigested food)
feces formation/defecation: peristaltic waves occur only 2-3 times a day in the large intestine; the waves produce mass movements, usually after a meal

20. II. Digestive Organs (cont)
Large intestine is made up of 3 sections as well –
The first is the ascending colon which connects to the small intestine and has the appendix coming off of it.
The second is the transverse colon.
The third is the descending colon.
Rectum – expandable organ for temporary storage of feces
Anus – final exit lined with keratinized epidermal tissue

22. Enzymes of the digestive system
SOURCE
DIGESTIVE ACTION
Amylase
Salivary glands, pancreas
Begins digestion of carbs; polysacc to disacc
pepsin
stomach
Begins digestion of protein
lipase
Small intestine and pancreas
digestion of lipids; triglycerides to fatty acids and glycerol
chemical

23. Enzymes of the digestive system
bile
Liver
Physical digestion of fats
proteolytic enzymes: ex. trypsin
Pancreas
Breaks down proteins into peptides
peptidases
Small intestine
Breaks down peptides into amino acids
sucrase, maltase, lactase
Breaks down disacc into monosacc

24. Digestive System Key Terms
Peristalsis: waves of rhythmic contractions that aid in digestive processes
Rugae: folds in the stomach
Chyme: partially digested food mixed with stomach acid (stomach to intestines)
Sphincter: ring-like muscles that maintain constriction ( like valves)
Villi: projections of a membrane that increases surface area

25. Digestive System Key Terms
Bolus: chewed up food
Mastication: the act of chewing
Enzymes: proteins that act as catalysts in the body
Amylase: enzyme that breaks down carbohydrates
Pepsin: enzyme that breaks down protein
Lipase: enzyme that breaks down fats
Gallbladder: small organ that stores bile

26. Nutrition
Nutrition is the process by which the body takes in and utilizes necessary food sources (nutrients).

27. Metabolism Cellular Metabolism:
The chemical and physical reactions that take place in the cell.
Normally involves an enzyme to synthesize or break down molecules (CHO, Lipid, PRO) for cell use.
Example: Mitochondria making energy for the body.

28. Nutrients Carbohydrates: Organic Supply energy for cellular processes
Sources: starch from grains, veggies; glycogen from meat; disaccharides from cane sugar; monosaccharides from honey and fruits
Cellulose- sugar that cannot be digested, provides bulk (called fiber) which assists movement thru digestive system
RDI (Recommended Daily Intake) grams

30. Nutrients Lipids: Organic
Supply energy for cellular processes and building cellular structures
Fats, oils
Sources: Meats, eggs, milk, lard, seeds, nuts, plant oils
Saturated fats should account for no more than 10% of diet

32. Nutrients Proteins: Organic Made of amino acids
Imp. Components of enzymes, clotting factors, keratin in skin and hair, collagen in connective tissue, muscle components (actin/myosin) hormones, antibodies
Sources: Meat, fish, poultry, cheese, nuts, milk, eggs, cereals, legumes
RDI is about 0.8 g per kilogram of body weight

34. Nutrients Vitamins Organic
Essential nutrients that must come from foods
RDI varies for each vitamin
See table 25-4, 25-5 in the Anatomy book
Examples: A, B, C, K, Folic Acid

35. Nutrients Minerals: Inorganic Essential for human metabolism
Plants extract minerals from soil, we eat the plants, therefore we get the minerals.
Most concentrated in teeth and bones
Play vital role in nerve impulse conduction, muscle fiber contraction, blood coagulation (CA, NA, K, etc)
Table 25-3 in Anatomy book for more info
Examples: Zinc, Iron, Sodium, Potassium, Calcium, Phosphorus

36. Metabolism
Metabolism - the series of processes by which food is converted into the energy and products needed to sustain life
On the cellular level, metabolism is the process of making ATP.
Why is ATP so important?

37. Metabolism ATP- Adenosine triphosphate:
The version of energy useful to cells
ATP  ADP (triphosphate to diphosphate)- loss of the phosphate releases energy
Lost phos. recharges (like a battery) and bonds with an ADP to make an ATP: Energy must be available in the cells for this to occur
Cellular Respiration provides the energy to regenerate ATP, ATP provides the E for cellular activities.

39. Metabolism Carbohydrate Pathways
Carbohydrates are many sugars hooked together. These pathways break them into individual glucose molecules
CHO used as energy or converted to glycogen or fat
Glucose molecules absorbed from sm. Intestine into blood stream and delivered to body cells
Insulin helps transfer glucose across the cell membrane
3 Steps of Cellular Respiration = 1 Glycolysis, 2 Kreb’s Cycle, and 3 Electron Transport Chain (ETC) combined

40. Metabolism Glycolysis:
Process that breaks down the glucose into pyruvic acid
Occurs in the cytoplasm (all cells)
Product is pyruvic acid which is moved to the mitochondria
Net Yield 2 ATP

42. Metabolism Kreb’s Cycle (Citric Acid Cycle):
Occurs in membrane of the mitochondria, involves the pyruvic acid made in glycolysis
High E compounds made (8 NADH and 2 FADH2) which donate electrons to the electron transport system (ETS)
Net Yield 2 ATP

44. Metabolism Electron Transport System:
ATP produced when NADH and FADH2 release hydrogen atoms generating energy
Net Yield around 32 ATP
**Note: A total of 36 ATP are generated from the energy in 1 molecule of Glucose.**
2 from glycolysis + 2 from Kreb’s cycle + 32 from ETS

46. Digestive System Disorders

47. Digestive System Disorders
Crohn’s Disease - is an autoimmune disease where the immune system attacks the gastrointestinal tract, producing inflammation.

48. Heartburn (acid reflux) – when stomach juices regurgitate back into the esophagus through the cardiac sphincter. This causes a burning sensation that has nothing to do with your heart.

49. Gallstones - form when bile stored in the gallbladder hardens into pieces of stone-like material. The largest gallstone on record was removed from an 80-year old woman in 1952 and weighed 6.29 kg (13.84 pounds).

50. Digestive System Disorders
Ulcers (peptic) – an erosion of the mucous or wall of the stomach or small intestine. Extremely painful because of the acidic wearing down of the walls of your GI tract.
Hernia - is a protrusion of
a tissue or part of an organ
through the muscle tissue
or the membrane by which
it is normally contained.

51. Irritable bowel syndrome (IBS) - is a blanket term for a variety of diseases causing discomfort in the gastro-intestinal tract. It is also called spastic colon, characterized by chronic abdominal pain, discomfort, bloating, and alteration of bowel habits in the absence of any organic cause.

52. Digestive System Disorders
Cirrhosis – liver disease where the liver tissue is replaced by scar tissue. Typically caused by alcoholism or hepatitis.
Jaundice - is a yellowish discoloration of the skin typically caused by excess bilirubin or the breakdown of red blood cells.

53. Colon polyps - A colon polyp is a growth on the surface of the colon
Colon polyps - A colon polyp is a growth on the surface of the colon. Some colon polyps are benign (not cancerous), but some are cancerous. Globally, cancer of the colon and rectum is the third leading cause of cancer in males and the fourth leading cause of cancer in females.

54. Digestive System Disorders
Lactose intolerance - the inability to digest significant amounts of lactose, the major sugar found in milk. Lactose intolerance is caused by a shortage of the enzyme lactase.
Cystic Fibrosis – causes the blockage of the pancreatic duct due to the build up of hardened mucous.
Hemorrhoids - are abnormally swollen veins in the rectum and anus.