digestive system part 2

small intestine is long (provide sufficient time for absorption to take place) inner walls of the small intestine have many transverse folds bearing many finger- like projections called villi. Each villus possesses numerous microvilli (to increase surface area to volume ratio for faster rate of absorption of digested food by diffusion) the epithelium of the villus is one cell thick (to reduce the distance for digested products to diffuse into the capillaries and lacteal) the small intestine consists of a dense network of blood capillaries and lacteal within the villi (the continuous transport of absorbed food substances by capillaries and lacteal away from the small intestine help to maintain a steep concentration gradient for faster absorption of digested products by diffusion)

glucose and amino acids are absorbed by facilitated diffusion into the blood capillaries of the villi. they can also be transported by active transport when the concentration is lower in the intestinal lumen than the blood capillaries fatty acids and glycerol diffuse into the epithelial cells and recombine to form minute fat globules before diffusing into lacteal most water and minerals are absorbed in the small intestine blood capillaries of the small intestine join to form venules which join together to form hepatic portal vein (carry mainly glucose and amino acids to the liver to be processed)

the utilisation of absorbed nutrients and how the body deals with the excess nutrients

glucose is a substrate for respiration to release energy for cellular activities excess glucose is converted into glycogen by liver cells and stored. this is stimulated by insulin produced by pancreas when the blood glucose level in the body is low, glycogen will be converted back into glucose by liver cells stimulated by glucagon produced by pancreas

required to make new cell materials that is used for growth and repair of worn out parts of the body it is also required to make enzymes and hormones excess amino acids are deaminated in the liver. their amino groups are removed and converted into urea

required in the production of cell membranes and steroid hormones fats serve as cushioning to protect vital organs such as the heat and kidneys when there is an inedequate supply of glucose, fats will be oxidised in liver to provide energy excess fats are stored in adipose tissues under the skin in adipose cells, fat droplets can collect in the cytoplasm and their fat droplets increase in size and number to form on large globule in the middle pushing the cytoplasm into a thin layer and nucleus to the side groups of fat cells form adipose tissue

after the absorption of nutrients in small intestine. undigested and unabsorbed food enters the large intestine. the undigested and unabsorbed matter consists of a mixture of water, bile pigments, dead cells from intestinal lining, dead and live bacteria and cellulose from plant cells. the undigested material moves along the large by peristalsis. large intestine absorbs minerals and any remaining water into the blood stream absorption of water from the undigested remain in the large intestine results in the formation of faeces. walls of large intestine secrete mucus which helps to bind the faeces along the large intestine faeces is temporarily stored in the rectum and as it accumulates, pressure in the rectum increases causing desire. when rectum is full, muscles of the rectal wall contract to egest the faeces

• produce bile which is a greenish yellow alkaline stored in the gall bladder. bile emulsifies lipids to increase surface area to volume ratio of the lipids for lipase to act on • regulation of blood glucose when blood glucose concentration increases, insulin stimulates liver cells to convert excess glucose into glycogen for storage when blood glucose concentration is low, glucagon stimulates liver cells to break down glycogen into glucose to be released into the bloodstream

excess amino acids cannot be stored by the body and must be deaminated amino groups of excess amino acids are removed and converted into urea which will be removed by the kidneys carbon residues of the deaminated amino acids are converted into glucose

birth defects slower reflex, poor coordination dementia, brain damage slows down working of brain and nervous system increase risk of gastric ulcers reduced self control

liver cells convert harmful substances into harmless ones alcohol is broken down in the liver and then removed from the body system hydrogen peroxide is a toxic by product of cellular activities and it is broken down into water and oxygen by the enzyme catalase in the liver cells