9.3, 9.4 & 9.5 Absorption, Assimilation & Defaecation PDF

9.3 Absorption (Textbook page 151 - 152)  (Textbook page 151) The Adaptations of Ileum in the Absorption of Digested Food Simple molecules produced from the digested food are absorbed in the ileum of the small intesti...

9.3 Absorption (Textbook page 151 - 152)  (Textbook page 151) The Adaptations of Ileum in the Absorption of Digested Food Simple molecules produced from the digested food are absorbed in the ileum of the small intestine The adaptations of the small Intestine to increase the surface area for absorption of nutrients： The ileum is very long The inner layer of the small intestine is highly folded and covered by tiny projections called villi (singular: villus) There are many microvilli found on the epithelial surface of the villi  (Textbook page 151) The Adaptations of Villus in the Absorption of Digested Food Villus has the following adaptations to absorb nutrients: The epithelial layer of the villus is one cell thick. - This helps accelerate nutrient absorption. Has Goblet cells - to secrete mucus to aid digestion The network of blood capillaries - helps to transport digestive products to then whole body Has Lacteal - to carries droplets of fatty acids and glycerol, fat soluble vitamin (Vitamin A, D, E &K) Has intestinal glands - to secrete intestinal juices that have digestive enzymes On the surface of the villus epithelium, there are many tiny projections called microvillus. - Microvillus provides a large surface area to increase the rate of nutrient absorption  (Textbook page 152) Absorption of Digested Food Nutrients that absorb into the blood capillaries: Water, glucose, amino acids, vitamin B and C Nutrients that absorb into the lacteal (lymph vessel): Fatty acids, glycerol and fat-soluble vitamins (Vitamin A, D, E, K)  Absorption of Digested Food Glucose, galactose, fructose, amino acids, vitamin B and C and water: Are absorbed through the ileum epithelial cells then absorbed into the blood circulatory system through blood capillaries then transported by the hepatic portal vein to the liver Then to the heart via hepatic vein Epithelial cells Blood Hepatic portal vein Liver (ileum) capillaries Hepatic vein All part of body Heart  Absorption of Digested Food Fatty acid, glycerol, Vitamin A, D, E and K Are absorbed through the ileum epithelial cells by simple diffusion - Fatty acids and glycerols recombine through the condensation process to form tiny droplets of lipids in the epithelial cells then absorbed into the lacteals of villi then transported from the lacteal by the lymphatic system into the thoracic duct and finally enters the blood flow through the left subclavian vein Epithelial cells Lacteals Lymphatic system (tiny droplets) Left subclavian Bloodstream Thoracic duct vein  (Textbook page 152) Method Absorption in the Ileum Lumen of small intestine Epithelial cell of villi Fructose Facilitated diffusion Monosaccharides Glucose Active transport Galactose Blood capillaries Amino acids Active transport Amino acids Vitamin B and C Absorb with water Vitamin B and C Water Osmosis Water Fatty acid Tiny droplets of Simple diffusion Glycerol lipids Vitamins A, D, E &K Vitamins A, D, E &K Lacteal Simple diffusion (dissolve in lipid) (dissolve in lipid) Liver 9.4 Assimilation (Textbook page 153 - 154) Small intestine  (Textbook page 153) The Role of the Circulatory System The human circulatory system consists of the blood circulation system and the lymphatic system to help transport nutrients to be assimilated. In the assimilation process that occurs in cells, nutrients are used to form complex compounds or structures of components. The blood capillaries in the small intestine combine to form the hepatic portal vein that transports blood to the liver.  (Textbook page 153) The Role of the Circulatory System Lacteals combine to form bigger lymph vessels in the lymphatic system. Then, the contents of the lymph vessels enter the thoracic duct that flows into the left subclavian vein. This lipid is then transported by blood throughout the body.  (Textbook page 153) Functions of Liver in the Assimilation of Digested Food of the Circulatory System The liver is the regulator that controls the quantity of nutrients that enter the blood circulatory system. The functions of liver: (i) Metabolism of Digested Food (ii) Detoxification (iii) Storage of Nutrients  (Textbook page 153) (i) Metabolism of Digested Food Glucose is used for cellular respiration. Amino acids are used for synthesising plasma proteins and enzymes. Through the deamination process, excess amino acids are turned into urea to be excreted through the urine.  (Textbook page 153) (ii) Detoxification (iii) Storage of Nutrients Liver cells expel toxic substances such as Excess glucose is converted to glycogen drugs, alcohol and other foreign to be stored. substances from the blood. Provides a place to store vitamins and Toxic substances are expelled through mineral salts the urine.  (Textbook page 153) Liver Diseases Liver cirrhosis is a type of liver disease caused by factors such as alcoholic drinks, toxic substances and hepatitis. Liver cells are replaced by scarred cells that can cause failure in the liver functions. Hepatitis is an inflammation of the liver caused by viral infection, toxic substances or autoimmune reaction  (Textbook page 154) Assimilation Process in the Liver Amino acids 1 Amino acids The liver synthesises plasma protein and enzymes from amino acids. Synthesis Conversion Deamination Excess amino acids cannot be stored in the body and are broken down through the deamination process to form urea Plasma protein Glucose Urea which is then expelled. & Enzymes When the glucose supply is insufficient, the liver converts amino acids into glucose. Body cells Kidney  (Textbook page 154) Assimilation Process in the Liver 2 Glucose Glucose in the liver is used for cellular Glycogen (stored in liver) respiration when required by the body and the excess is converted to glycogen and stored in the liver. excess Glucose Fat When the glucose level in the blood Glycogen excess decreases and the body needs energy, Cellular glycogen is converted to glucose. respiration Energy When the glycogen supply reaches a maximum level, the excess glucose is converted to fats.  (Textbook page 154) Assimilation Process in Cells 1 Amino acids Amino acids are used to synthesise new protoplasm and also repair damaged tissues. Amino acids are used to synthesise hormones and enzymes. 2 Glucose Glucose is oxidised through cellular respiration to release energy, water and carbon dioxide. Excess glucose is kept as glycogen in muscles. Energy is used for cell processes such as protein synthesis.  (Textbook page 154) Assimilation Process in Cells 3 Lipids Lipids such as phospholipid and cholesterol are the primary components that build the plasma membrane. Excess fats are kept in adipose tissues found underneath the skin as stored energy. Fat is oxidised to release energy when there is insufficient glucose.  9.5 Defaecation (Textbook page 155)  (Textbook page 155) Functions of the Large Intestine After the absorption of nutrients in the small intestine, the remaining mixture enters the colon. The remainder mixture consists of water, undigested food, bacteria, dead cells and fibre. The undigested food move along the colon to the rectum through peristalsis The large intestine carries out two main functions: i. absorption of water and vitamins Substances absorbed are ✓ water and mineral salts ✓ metabolic byproducts of some bacteria such as vitamin B, vitamin K and folic acid.  (Textbook page 155) Functions of the Large Intestine The large intestine carries out two main functions: ii. Formation of faeces After the water is absorbed, the remaining waste is a semisolid called faeces. ✓ Faeces contains dead cells from the inner layer of the intestine, waste products such as bile pigments, bacteria and toxic substances. The walls of the large intestine secrete mucus to smoothen the movement of faeces until the anus. ✓ The movement of faeces takes about 12 to 24 hours before entering the rectum. The faeces will accumulate in the rectum until the pressure in the rectum increases and triggers the need to expel faeces from the body. The rectum muscles will contract to expel faeces from the anus. This process is called defaecation  (Textbook page 155) Bacteria in the Colon The large intestine has a huge population of bacteria. There are more than 1000 different species of bacteria in the large intestine - E.g. Escherichia coli (E. coli). They decompose the food waste and synthesizes vitamin B12 and K that can be absorbed in the colon A healthy balance between beneficial and less beneficial bacteria is very important for health and a stable environment in the alimentary canal. Consumption of antibiotics can kill and decrease the microbial population in the colon. Vitamin B12 and K cannot be synthesised