The Small Intestine and Large Intestine

1. The Small Intestine and Large Intestine

2. Review • Salivary Juice contains: • 1. Water • 2. Salivary amylase • Gastric Juice contains: • 1. Mucous • 2. HCl • 3. Pepsinogen

3. The Small Intestine • Averages about 6 metres in length • Small diameter • Why is the small intestine so long? • Time and surface area for digestion to occur • The first 25 cm is called the duodenum • Ducts from the gallbladder (bile) and pancreas (pancreatic juice) enter the duodenum

4. Bile • Bile: Emulsifies fat into droplets that disperse in water

5. Pancreatic Juice • Water • Sodium bicarbonate • Lipase • Trypsin • Nuclease • Pancreatic Amylase

6. Pancreatic Juice • Source of Enzymes Pancreas • Lipids  Glycerol + fatty acids (fat droplets) Lipase • Nucleic acids  Nucleotides nuclease Source of enzyme – also Sm. Intestine Optimal pH: 8

7. Pancreatic Juice • Source of Enzymes Pancreas • Starch  maltose pancreatic amylase • Protein  shorter polypeptides Trypsin Optimal pH: 8

8. Question • What is the optimal pH of the small intestine and how is it achieved? • Optimal pH is 8 • The bile and pancreatic juice neutralizes the pH of the chyme (stomach pH 2)

9. Question • It has been suggested that the surface area of small intestines is analogous to the surface area of a tennis court. How? A: The wall of the small intestine contains finger-like projections called villi (sing. villus) Villi increase the surface area of the intestinal wall which increases the amount of nutrients that can be absorbed.

10. Villi • A villus has an outer layer of epithelial cells that contain thousands of tiny extensions called microvilli • Forms a brush border where intestinal enzymes are secreted • Greatly increase the surface area available for nutrient absorption

11. Villi • A villus contains blood capillaries and a small lymphatic capillary called a lacteal • Glucose and amino acids enter the blood capillaries of a villus • Hepatic portal vein  liver • Glycerol and fatty acids are packages as lipoproteins and enter the lacteal • Lymphatic system • After absorption, they are carried to the cells by the bloodstream

12. Small Intestine • Absorption occurs across the wall of each villi and continues until the nutrients are absorbed • This occurs actively (with ATP) or passively (without ATP)

13. Anatomy of the Small Intestine

14. Interstitial glands • Walls of the duodenum and small intestine are lined with millions of interstitial glands • Produce Interstitial juice which contains • Peptidases • Maltase • Sucrase • Lactase • Interstitial juice finishes the digestion of protein and starch

15. Interstitial Juice • Source of enzymes – interstitial gland /small intestine Peptides  Amino acid peptidase Maltose  Glucose + Glucose (dissacharide) maltase (monosacharide) Optimal pH: 8

16. Interstitial Juice • Source of enzymes – interstitial gland /small intestine Sucrose  Glucose + Fructose (disaccharide) sucrase (monosaccharide) Lactose  Glucose + Galactose (disaccharide) lactase (monosaccharide) Optimal pH: 8

17. The Large Intestine • Consists of the cecum, the colon, the rectum and the anal canal • Larger in diameter than small intestine • But shorter (1.5 meters) • Does not produce digestive enzymes, but does absorb water, salts and some vitamins • Also stores indigestible waste until defecation

18. The Cecum • Lies below the junction of the small intestine • Has a small projection called the appendix • What is the role of the appendix? A: Plays a role in fighting off infections in humans.

19. The Colon • Includes the • ascending colon (right side), • transverse colon (passes abdominal cavity), • descending colon (left side) • sigmoid colon (enters the rectum) • Does not play a role in nutrient absorption • Absorbs water from waste before it is eliminated

21. The Rectum • The last 20 cm of the large intestine • Opens at the anus, where defecation of indigestible material is expelled • Main function is storage of feces • Components of feces: • 3/4 water • 1/4 solid

22. Question • Why is feces so smelly? A: The rectum contains bacteria that act on indigestible material resulting in an unpleasant odour and also produce gas, which has a foul smell.

23. Intestinal Bacteria • 99% of colon bacteria are obligate anaerobes (poisoned by oxygen) • Break down indigestible material and produce vitamins that our bodies need • Perform services for us!

24. Question • What are two common disorders that are related to the large intestine? A: Diarrhea and constipation

25. Diarrhea • Prolonged diarrhea can lead to dehydration due to water loss and disturb heart contractions due to ion imbalance • 2 major causes of diarrhea: • 1. Infection of the lower intestinal tract • Food poisoning from contaminated food • Irritated intestinal wall • Increase in peristalsis • 2. Nervous stimulation • Stimulation of intestinal wall

26. Constipation • Feces are dry and hard and defecation does not occur regularly • To prevent constipation: • Diet rich in water and fibre • Take laxatives • Prevent water from being absorbed and expel the contents of the colon • Chronic constipation due to hemorrhoids, which are large, inflamed blood vessels of the anus

27. Photo References • http://healthy-diet.maxupdates.tv/the-basics-of-the-human-digestive-system/ • http://www.cancer.umn.edu/cancerinfo/NCI/CDR350260.html • http://cureibszone.com/diarrhea • http://remedynatural-herbs.com/home-remedies-for-constipation • http://www.thenibble.com/reviews/news/2007-01.asp • http://www.nlm.nih.gov/medlineplus/ency/imagepages/1128.htm • http://www.smithinst.ac.uk/Projects/PG2004/CASE-Unilever04/ProjectSummary • http://blog.beliefnet.com/chatteringmind/2006_07_01_chatteringmind_archive.html • http://www.coloniccleansing.org/ • http://www.nlm.nih.gov/medlineplus/ency/imagepages/9390.htm