334 Student Notebook for The Human Body: Concepts of Anatomy and Physiology 7. D
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334 Student Notebook for The Human Body: Concepts of Anatomy and Physiology 7. Describe the role of the hepatocytes in deansing the blood that travels through the liver 8. Discuss how the storage of toxins can damage the liv 9. What is the function of the gallbladder? 10. Trace the low of bile from the gallbladder to the small intestine soon after a meal. Small Intestine The small intestine is the body's most important digestive organ. It performs digestion and is the main site of Structure of the Small Intestine The small intestine: . Extends from the Has a diameter of about 2.5 centimeters (2 inch). . Is suspended in the abdominal cavity by the posterior abdominal wall. Is framed by the large intestine laterally and superiorly both chemical and mechanical to the large intestine for about 6 meters (20 feet) which anchors it to the Three Segments of the Small Intestine Duodenum is the first portion. It is approximately 25 centimeters (10 inches) in length. It receives chyme from the stomach through the valve. . Jejunum is the middle region. It extends for 2.5 meters (8 feet) to the third and the last . Ileum is the last segment. It is about 3.6 meters (12 feet) in length. The ileum unites with the segment. at the ileocecal valve. The ileocecal valve regulates the flow of material from the ileum to the large intestine. Modifications of the Layers of the Small Intestine Wall 1. Mucosa has modifications for chemical digestion and the absorption of nutrients Villi are tiny, 1 millimeter projections of the mucosa that come into contact with the contents of the small intestine. What is the function of the villi? Lacteal is a lymphatic vessel that is present within each villus along with a blood capillary. These vessels carry absorbed nutrients. Microvilli are thousands of tiny projections covering each villus. How do the villi and microvilli affect absorption? Intestinal glands are situated between the bases of adjacent villi. They release a colorless secretion of water and mucus with a neutral pH.Explanation / Answer
7. Role of hepatocytes: Hepatocytes are modified epithelial cells which constitute 80% of the liver. Hepatocytes along with Kupffer cells (stellate phagocytic macrophages lining liver sinusoids), which are in direct contact with the hepatic blood flow helps in cleansing the blood by removing pathogens (bacteria, virus), dead liver cells. They also filter the bacteria from portal blood which are picked up from intestines during course of circulation. They remove the toxins (drugs, alcohol and other metabolites like ammonia), detoxify them and get rid of them from the body by turning into non toxic polar substrates that can be easily eliminated by kidney.
Thus, they efficiently cleanse the blood when it passes through the sinuses and play a major role in host defense mechanisms.
8. Liver cells absorb toxic substances like drugs, alcohol, pathogens and detoxify them. In this process excessive inflow of toxins may result in inefficient detoxification and leads to accumulation of toxins in hepatocytes that leads to proliferation and inflammation (as seen in viral hepatitis, cirrhosis) of hepatocytes causing hepatitis.
9. Liver secretes 600-1200 ml bile juice per day which is stored and concentrated in gall bladder (concentrated 12-20 times by active absorption of Sodium ions as gall bladder can hold only 60 ml of bile).
10. Bile is stored in gall bladder. When gall bladder contracts under the influence of Cholecystokinin or relaxation of sphincter of oddi, secretin or vagal stimulation bile flows into the cystic duct and then the common bile duct that empties into the duodenum.
Small intestine:
The small intestine is the body's most important digestive organ. It performs both chemical and mechanical digestion and is the main site of Absorption.
THREE SEGMENTS OF THE SMALL INTESTINE:
Duodenum is the first portion. It is approximately 25 cm in length. It receives the chyme from the stomach through the pyloric valve.
Jejunum
Ileum is the last segment. It is about 3.6 m in length. The ileum unites with the large intestine at the ileocecal valve.
Modifications of the layers of the small intestine wall:
1. Functions of villi:Villi are small fold like projections from the mucosal lining of the circular folds which are made of simple columnar epithelium and contain blood capillaries, lacteals. The main function is that they increase the surface are for absorption of nutrients.
Villi and Microvilli affecting absorption: Microvilli are small finger like extensions of the plasma membranes of the simple columnar epithelium of villi. They further vastly increase the surface area for absorption as they are extremely long and present on the apical surface of the simple columnar cells called as brush border.
In what part of the small intestine are these glands most numerous? They are present on the crypts of lieberkuhn (colonic crypts) which are simple tubular glands. They are simple invaginations of surface epithelium and extend from surface down to muscularis mucosae. They open near base of skill.
What function does this secretion serve?
Intestinal glands or crypts of lieberkuhn are glandular cells which secrete intestinal juice that helps in digestion and nutrient absorption along with pancreatic juice and bile.
Bruners gland are present in the submucosa in the duodenum part of the small intestine.
Bruners gland secretes mucus which is alkaline in nature and neutralises the stomach acid, thus protecting the duodenal lining. Bruners glands also secrete activates trypsinogen to trypsin.
Plicae circulares are one of the three levels of structural modifications of small intestine along with villi and microvilli. They are permanent circular folds of the mucosa and submucosa which are about 1cm tall and visible to the naked eye. They force the chyme to spiral around the lumen and slow down the movement of chyme which allows more time for processing and absorption. In addition, the plicae circulares increase the surface area for absorption by 4 times.
1. Chemical digestion
Pancreatic enzymes from the pancreas break down a wide spectrum of foods.
Intestinal enzymes of the small intestine also break down a wide variety of foods.
Bile from the liver emulsifies fats.
2. Carbohydrate digestion begins in the mouth (by salivary amylase) and is completed in the small intestine.
Once inside the epithelial cells, the monosaccharides are transported by facilitated diffusion.
Protein digestion begins in the stomach by pepsin and is completed in the small intestine by pancreatic and intestinal enzymes.
Lipid digestion is completed by bile salts and enzymes within the small intestine.
Thee lipids are resynthesized into fat droplets called chylomicrons which move to the lacteals
Two thirds of the water entering the small intestine is absorbed into the capillaries by osmosis.
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