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
Fat digested -> absorbed as fatty acid and glycerol -> recombined into fat molecules in epithelial cells of villus. Fats then move into the lymphatic system

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