1. The Digestive System

2. objective
SC.912.L Describe the physiology of the digestive system, including mechanical digestion, chemical digestion, absorption and the neural and hormonal mechanisms of control.

4. 6 functions Ingestion Mechanical Processing Digestion Secretion
Absorption
Excretion

5. ingestion
Materials enter via the mouth

6. mechanical processing
Crushing and shearing of materials
makes it easier to propel along digestive tract

7. digestion
Chemical breakdown of foods

8. secretion
Release of water, acids, enzymes, buffers, and salts

9. absorption
Movement of organic substrates, electrolytes, vitamins, and water

10. excretion
Removal of waste products from body fluids

12. Alimentary canal Muscular tube Extends from mouth to anus 1-way tract
pharynx
esophagus
stomach
small intestine
large intestine
anus

14. Oral cavity Sensory analysis Mechanical processing Lubrication
of material before swallowing
Mechanical processing
teeth, tongue, palatal surfaces
Lubrication
saliva, mucus
Digestion
carbohydrates, lipids

15. pharynx
A common passageway for solid foods, liquid, and air

16. esophagus A hollow, muscular tube
~25 cm long, 2 cm wide
Conveys solid foods and liquids to the stomach

17. peristalsis
Wave-like contractions that move food along the digestive tract

18. stomach 4 functions: store ingested food
mechanical breakdown of ingested food
acids/enzymes disrupt chemical bonds in food
production of intrinsic factor
glycoprotein required for absorption of B12

19. regions of stomach
Cardia
Fundus
Body
Pylorus

20. Digestion in the stomach
Pepsin
aids in preliminary digestion of proteins
Salivary amylase
digests carbohydrates
Lingual lipase
digests lipids
pH ~2.0

21. small intestine Where 90% of absorption occurs 3 segments:
microvilli increase surface area
3 segments:
duodenum
jejunum
Ileum

22. Duodenum ~25 cm long “Mixing bowl” receives: chyme from stomach
digestive secretions from pancreas and liver

23. jejunum Middle segment ~2.5 m long Location of most:
chemical digestion
nutrient absorption

24. ileum
Final segment
~3.5 m long

25. large intestine Has a larger diameter than the small intestine
4 main segments:
ascending colon
transverse colon
descending colon
sigmoid colon

26. large intestine Functions: reabsorbs water
compaction of intestinal contents into feces
loaded with bacteria
feed on indigestible carbohydrates
produce flatus

27. rectum Last 15 cm of digestive tract
An expandable organ for temporary storage of feces
Anal canal
last portion of rectum
ends in the anus

28. accessory organs Pancreas Liver Gall Bladder
secrete insulin & glucagon into the bloodstream
secrete digestive enzymes
Liver
secretes bile
aids in the
digestion of lipids
Gall Bladder
stores bile

29. aging Smooth muscle tone decreases
peristalsis contractions becomes weaker
Cumulative damage from toxins are transported to liver for processing
alcohol, other chemicals
Rates of stomach/colon cancer rise
Decline in olfactory/gustatory senses
dietary changes that affect entire body