The Small Intestine and Large Intestine

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

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

Bile Bile: Emulsifies fat into droplets that disperse in water

Pancreatic Juice Water Sodium bicarbonate Lipase Trypsin Nuclease Pancreatic Amylase

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

Pancreatic Juice Source of Enzymes  Pancreas Starch  maltose pancreatic amylase Protein  shorter polypeptides Trypsin Optimal pH: 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)

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.

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

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

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)

Anatomy of the Small Intestine

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

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

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

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

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.

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

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

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.

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!

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

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

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

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