What prevents food being pushed back toward the mouth?
Constructions of circular muscles behind the food constricts the gut to prevent it from being pushed back towards the mouth
What controls the contraction along the small intestine?
The enteric nervous system
What is the main function of peristalsis ?
Is churning up of of the semi- digested food to mix it with enzymes and thus speed up the process of digestion
What does the pancreas secrets?
enzymes into the lumen of the small intestine
Pancreas contains 2 types of gland tissues- what’s the first?
1) small groups of cells secret the hormones insulin and glucagon into the blood
Pancreas contains 2 types of gland tissues- what’s the second?
Secrets digestive enzymes into the gut in response to eating a meal
Where are digestive enzymes synthesized?
In pancreatic gland cells on ribosomes on the rough endoplasmic reticulum- they are then processed in the Golgi apparatus and secreted by exocytosis
Pancreatic juice contains enzymes that digest all 3 main types of macromolecules found in food what are they?
1) amylase to digest stArch
2) lipases to digest triglyceride, phospholipids
3) protease to digest proteins and prep tides
What do enzymes do in digestion?
Enzymes digest most macromolecules in food into monomers in the small intestine
What 4 reaction do enzymes carry out by the pancreas ?
By hydrolysis reactions:
1) starch is digested to maltose by amylase
2) phospholipids are digested to fatty acids and glycerol and phosphates by phospholipase
3) triglycerides are digested to fatty acids and glycerol or fatty acids and monoglycerides by lipase
4) proteins and polypeptides are digested to shorter peptides by protease
What do villi do?
Increase the surface area of epithelium over which absorption is carried out
What do villi absorb? (Overview)
Absorb monomers formed by digestion as well as mineral ions and vitamins
What do villi absorb ? (6)
Absorb products of digestion of macromolecules in food
1) glucose, fructose, galactose- other monosaccharides
2) any of the twenty amino acids used to make proteins
3) fatty acids, monoglycerides and glycerol
4) bases from digestion of nucleotides
5) mineral ions such as calcium, potassium and sodium
6) vitamins such as ascorbic acids (vitamin c)
How do nutrients get absorbed in the body?
Nutrients must pass from lumen of the small intestine to the capillaries of lacteals in the villi
How do triglycerides get absorbed by simple diffusion? Step 1
1) must be digested before they can be absorbed- products of digestion are fatty acids and monoglycerides which can by absorbed into villus epithelium cells by simple diffusion
How are fatty acids absorbed by facilitated transport? Step 2
2) fatty acids are also absorbed by facilitated diffusion as there are fatty acid transporters which are proteins in the membrane
3) once inside epithelium cells, fatty acids combine with monoglycerides to produce triglycerides which can’t diffuse back to lumen
How are triglycerides get to exocytosis ? Step 3
1) triglycerides coalesce with cholesterol to form droplets which become coated in phospholipids and protein
2) these lipoprotein particles are released by exocytosis through the plasma membrane on the inner side of the villus epithelium cells- either enter lacteals and are carried away by lymph or enter the blood capillaries in the villi
How does glucose pass through plasma membrane? Step 1
1) glucose cannot pass through plasma membrane by simple diffusion because it is polar and therefore hydrophilic
2) sodium-potassium pumps are used- they pump sodium ions by active transport from cytoplasm to villus and potassium ions in opposite direction
3) sodium glucose co transporter proteins in the micro villi transfer a sodium ion and a glucose molecule together from lumen to cytoplasm - this is facilitated diffusion and its passive
4) glucose channels allow glucose to move my facilitated diffusion from cytoplasm to villus
What is peristalsis?
The contraction of circular and longitudinal muscle layers of the small intestine mixes the food with enzymes and moves it along the gut