1. Digestive system Csaba Bödör, bodor@korb1.sote.hu
Chapter 45, (page 875- )

2. Food processing and nutrition
ingestion: taking of food into the digestive cavity
digestion: process of breaking down food mechanically and chemically
absorption: nutrients pass through the lining of the digestive tract and into the blood
egestion (or elimination): food that is not digested and absorbed is discharged from the body

3. Digestive system
in most invertebrates and in all vertebrates digestive tract is a complete tube with openings to each ends
digestion takes place as food passes through the tube

4. Digestive system
some parts of the tract are specialized to perform specific functions
Food passes through: mouth, pharynx, esophagus, stomach, small intestine, large intestine and anus
salivary glands, pancreas, liver

5. Digestive system
In the wall of the digestive tract: 4 layers (Fig. 45-5)
mucosa: a layer of epithelial tissue and underlying connective tissue lines the lumen of the digestive tract highly folded in stomach and intestine > incr. surface
submucosa: connective tissue layer rich in blood vessels, lymph vessels and nerves
muscle layer: 2 sublayers of smooth muscle fibers inner circular fibers, outer longitudinal fibers
peritoneum: under the diaphragm, the outer connective tissue coat of the dig. tract > visceral peritoneum
it is connected to the parietal peritoneum that lines abdominal and pelvic cavities > peritoneal cavity

7. Digestive system
some parts of the tract are specialized to perform specific functions
Food passes through: mouth, pharynx, esophagus, stomach, small intestine, large intestine and anus
salivary glands, pancreas, liver

8. Digestive system Food processing begins in the mouth
Mechanical and enzymatic digestion of carbohydrates begins in the mouth
teeth and salivary glands (3 pairs)

9. Digestive system Types of teeth Type Shape Function Incisors chisel
biting
Canines
long, pointed
tearing
Premolars
flattened surface
crushing grinding
Molars
( ) x 4 = 32

10. Digestive system Structure of teeth
the hardest substance in the body !!!
Resembles the hardness of bones

11. Digestive system Food processing begins in the mouth
Mechanical and enzymatic digestion of carbohydrates begins in the mouth
teeth and salivary glands (3 pairs)
They produce saliva (1 liter each day)
enzyme: salivary amilase (carbohydrates (starch) > sugars)

12. Digestive system After chewing bolus (lump) is formed …
A bite of food is swallowed and moved through
the pharynx and esophagus to the stomach
Role of the epiglottis (see respiratory system!)
Food is moved by the propulsive activity if the digestive tract
It is peristalsis; waves of muscular contractions > that push the food in one direction
The mixing and propulsive movements of the digestive tract are known as motility

14. Digestive system Stomach: mechanical and enzymatic digestion
Large, muscular organ
The entrance is normally closed by the sphincter
Folds of the wall: rugae, wrinkled appearance
lined with columnar epith. large amounts of mucus
gastric glands > deep in the stomach wall
parietal cells: HCl,
chief cells: pepsinogen

16. Digestive system Stomach: mechanical and enzymatic digestion
food is mechanically digested by vigorous churning
gastric glands; parietal cells > HCl, intrinsic factor chief cells > pepsinogen
pepsinogen: inactive enzyme precursor comes in contact with gastric juice converted into pepsin the active enzyme
pepsin: the main digestive enzyme of the stomach proteins > short polypeptides
the wall of the stomach is protected from acidic gastric juice > alkaline mucus, epithelial cells fit tightly together

17. Digestive system After several hours in the stomach…
partially digested food: chyme („thick soap”)
salivary amilase inactivated by acidic pH
chyme is released through the pylorus (exit) into the small intestine
Digestion is completed in the small intestine
Small intestine (5-6 meters long): 3 regions
duodenum: most chemical digestion takes place here bile (emulsifies fats) from liver and enzymes from pancreas are released here, they act on the chyme
jejunum and ileum
Surface area is increased by folds in the wall, intestinal villi and intestinal microvilli

18. Digestive system

19. To increase the surface
Digestive system
Villi and microvilli
To increase the surface
Digestion, absorption

20. Digestive system Liver, the largest internal organ
secretes bile: important in mechanic digestion fats
adding or removing nutrients to and from the blood (homeost.)
converts glucose to glycogen and stores it
converts excess amino acids into fatty acids
stores iron and vitamins
detoxifies alcohol and other drugs and poisons
a single liver cell: more than 500 metabolic activities
bile (water, bile salts, bile pigments, cholesterol), released by the gall bladder, no digestive enzymes !!!

21. Digestive system Pancreas secretes digestive enzymes
The pancreas releases enzymes that digest protein, lipid, and carbohydrates, as well as RNA and DNA
trypsin, chymotripsin: polypeptides > dipeptides
pancreatic lipase: digests fats
pancreatic amilase: almost all types of carbohydrates > disacch (except cellulose)
ribonucleases, deoxyribonucleases: RNA and DNA > nucleotides
they act on the chyme in the duodenum!
nutrients are digested as they move through the digestive tract

22. a cells: glucagon
b cells: insulin

23. Digestive system
Summary of the digestion

24. Digestive system
Polysaccarides are digested to the disaccharide maltose
by salivary and pancreatic amylases
Maltase splits maltose into glucose
Proteins are split by pepsin, trypsin, chymotripsin into small peptides, dipeptides
Small peptides, dipeptides > proteolytic enzymes (dipeptidases) into the final product of amino acids
Lipids are emulsified by bile salts and then hydrolyzed by pancreatic lipase into fatty acids and monoacidglycerols

25. Digestive system Regulation by nervous system and hormones
Extensive network of neurons: enteric nervous system
Polypeptides secreted by endocrine cells of the mucosa of the digestive tract.

26. Digestive system Absorption
Takes place mainly through the villi of the small intestine
Water, simple sugars, alcohol, salts … are small enough for absorption
2 single epithelial linings
Absorption occurs by: Diffusion
Facilitated diffusion
Active transport
Amino acids, glucose: directly transported to the liver (by hepatic portal vein)
Free fatty acids and monoacylglycerols > reassembled in epithelial cell > triacylglycerols > +cholesterol > chylomicrons > lymph vessel > circulation (90% of fats)

27. Digestive system Large intestine eliminates waste
Undigested material, unabsorbed chyme passed into large intestine
Shorter but larger in diameter, water and sodium absorbed
Incubates bacteria that produce Vitamin K and certain B vitamins
the small intestine joins it few cm-s from its end: cecum (blind pouch)
vermiform appendix: projects from the end of the cecum
regions of the large intestine: cecum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum, anus
Elimination of wastes (defecation)

28. Digestive system

29. Digestive system Minerals Vitamins
Organic compounds required in small amounts for many biochemical processes
Many serve as components of coenzymes
Fat soluble vitamins: D, E, K, A
Water soluble vitamins: C and B complex
Minerals
Minerals are inorganic nutrients ingested as salts dissolved in food and water
Trace elements are minerals required in amounts less than 100 mg per day

30. Vitamins

31. Some important minerals and their functions

32. How the body uses protein
How the body uses fat

33. Most carbohydrates are ingested in the form of complex carbohydrates
Fiber is a mixture of cellulose and other indigestible carbohydrates
Carbohydrates are used mainly as an energy source
Lipids are used as an energy source, Components of cell membranes
To synthesize steroid hormones and other lipid substances
Most lipids are ingested in the form of triacyglycerols
Proteins serve as enzymes, Are essential structural components of cells
The best distribution of essential amino acids is found in the complex proteins of animal foods

34. Under-nutrition > protein deficiency > kwashiorkor > edema