Unit 6.1 - Digestion and Absorption Flashcards
Name all parts of the human digestive system
Mouth (ingestion/chewing)
Oesophagus (swallowing)
Gall bladder (stores bile)
Stomach (killing pathogens in food and protein digestion)
Liver (secretes Bile)
Pancreas (secretes digestive enzymes)
Small intestine (digestion and absorption)
Large intestine (Absorption of Water)
Anus (egestion of feces)
Outline Peristalsis and the types of muscle involved
Muscle contraction (peristalsis) pass along the intestine. Contraction of circular muscle behind the food constricts gut to prevent food being pushed back. Longitudinal Muscle contracts where food is located to move along the gut.
Outline the role of enzymes in the small intestine
digest most macromolecules in food into monomers. Macromolecules include proteins, starch, glycogen, lipids and nucleic acids.
What remains undigested throughout the digestive system
Cellulose
What enzymes are secreted by the pancreas
Lipase - breaks down lipids into fatty acids and glycerol
Endopeptidase - breaks down polypeptides into shorter peptides
amylase - breaks down starch into maltose
Structure of the small intestine
Mucosa
Submucosa
Longitudinal muscle
Circular Muscle
Villi
Outline the Digestion of Starch
two types of molecule in starch- amylose and amylopectin. Both polymers of alpha glucose molecules but amylopectin branched molecule. Amylase breaks down 1,4 bonds in chains of four of more glucose = amylose into maltose. cannot breakdown 1,6 bonds - fragments containing branches that amylase cannot digest = dextrins.
Outline the role of Dextrinase
Digestion of starch completed by enzymes in the membrane of microvilli on villus epithelium cells - maltose and dextrinase digest maltose and dextrins into glucose. Also in the membranes of the microvilli are protein pumps that cause the absorption of glucose by digesting starch.
Where does excess glucose go in the bloodstream
Blood flows through the villus capillaries to venules in the submucosa of the small intestine. The blood in these venules is carried via the hepatic portal vein in the liver, where excess glucose can be absorbed by liver cells and converted to glycogen for storage
What occurs in the Intestinal Villi
Absoprtion = taking up substances into cells. Nutrients are absorbed by the epithelium, which is a single layer of cells forming the inner lining of the mucosa. Rate of absorption depends on the surface area of epithelium.
Where does absorption occur?
Occurs primarily in the small intestine. The small intestine in adults is about seven meters long and 25-30 millimeters wide (folding of surface = large surface area).
How is the surface area of the intestine increased?
Due to the presence of villi which are small finger like projections of the mucosa on the inside of the mucosa on intestinal wall. 0.5-1,, long - as many as 40 per square millimeter. Villi absorb mineral ions and vitamins as well as monomers eg glucose.
Structure of a Villus
epithelium
layer of microvilli
blood capillary
lacteal
goblet cells (secrete mucus)
Methods of absorption
Simple diffusion : down concentration gradient between phospholipids in the membrane = fatty acids and monoglycerides
Facilitated Diffusion: down the concentration gradient through channel proteins in membrane = fructose
Active Transport : pumped through membrane against gradient through pump proteins = sodium /calcium ions
Endocytosis : small droplets of fluid are passed through the membrane by means of vesicles = triglycerides and cholesterol
How is glucose absorbed
glucose is absorbed by sodium co-transporter proteins which move a molecule of glucose together with a sodium ion across the membrane together into the epithelium cells. Glucose can be moved against its gradient because the sodium ion is moving down its concentration gradient - sodium gradient generated by active transport of sodium out of epithelium cell by a pump protein.
