Chemical digestion Flashcards
Where does the digestion of carbs begin and what is the pH?
- mouth: salivary amylase
- 6.75 - 7
What happens to salivary amylase in the stomach?
inactivates because of stomach acid
Where is most starch reduced to maltose?
in small intestine by pancreatic amylase
Which enzymes in the small intestine complete carbohydrate digestion?
- dextranase
- glucoamylase
- maltase
- sucrase
- lactase
What are the main sources of protein in the diet?
- dietary proteins (125g/day)
- enzymes proteins (15-25 g/ day)
- protein (15-25 g/day)
What do these proteolytic enzymes break protein down into?
free amino acids and some di- and tripeptides
What does pepsin break down in protein digestion?
pepsin cleaves peptide bonds
- tyrosine and phenylalanine
What proteolytic enzymes are involved in protein digestion in the small intestine?
- pancreatic trypsin
- chymotrypsin
- carboxypeptidase
- aminopeptidase
- dipeptidase
What enzymes from the pancreas digest nucleic acids?
RNAase and DNAase
Where does significant lipid digestion occur and what emulsifies it?
the small intestine
What enzymes break down triglycerides in lipids?
pancreatic lipase
What enters the large intestine at the end of the ileum?
some water, indigestible food materials (cellulose) and million of bacteria enter via the ileocecal valve
What are the products of triglyceride digestion?
fatty acids and glycerol/ 2 mono glycerides
How much food, drink and GI secretion enter the GI tract daily?
10L, but only 0.5 - 1 L reaches large intestine
What are the final products of nucleic acid digestion?
free bases, pentose sugars and phosphate ions
What do pancreatic nucleases break RNA and DNA into?
nucleotides
What enzymes in the small intestine further break down nucleotides?
nucleosidases and phosphatases
What are the final products of nucleic acid digestion absorbed?
absorbed through villi into the blood
What does it imply that mast digestion and absorption are complete by the time chyme reaches the ileum?
to recycle bile salts via portal circulation to the liver
How are glucose and galactose absorbed?
through common protein carriers using active transport linked to Na+
How does fructose and monosaccharides move into cells
by facilitated diffusion (no ATP required)
How are amino acids absorbed?
using several types of amino acids carriers, with secondary active transport linked to Na+
How are di- and tripeptides absorbed?
actively transported into epithelial cells, then digested into single amino acids in the cytoplasm
Why can infants sometime absorb whole proteins?
their intestinal mucosa is immature, lacking certain cellular structures
- can contribute to allergies
What role do bile salts play in lipid absorption?
emulsify lipid and form micelles
What are micelles?
small droplets formed from monoglycerides, glycerol and FFA, mixed with bile salts and lecithin
How are lipids absorbed into cells?
micelle diffuse across the lipid bilayer of epithelial cells
What are the implications in terms of absorption of most nutrients?
nutrients must go through the cells
What happens to chylomicrons after formation?
extruded by exocytosis and enter lacteal/lymphatic system
Where is lipid absorption usually complete?
the ileum
What happens if bile secretion is disturbed?
lipid digestion and absorption are impaired
How are fat soluble vitamins (A, D, E, K) absorbed?
as part of micelles
Why should fat-soluble vitamins be ingested with some fat?
to aid in absorption as part of micelles
How are water soluble vitamins (B, C) absorbed?
easily. like mono and amino acids
What is an exception in the absorption of water-soluble vitamins?
V B12, which requires intrinsic factor for absorption
How is sodium absorbed?
is coupled with glucose and amino acid absorption
How are anions absorbed?
follow the electrical gradient established by sodium
How is cholride absorbed?
actively transported
How is bicarbonate (HCO3-) transported?
Actively secreted into the lumen in exchange for chloride
How is potassium absorbed?
simple diffusion in response to osmotic gradient (water absorption)
What happens if water absorption is impaired?
potassium absorption is affects, leading to imbalances
How is iron absorbed and transported?
actively though mucosal cells and binds to ferritin
How is calcium and iron absorption regulated?
based on body’s needs, mostly through duodenum
How much water enters and is absorbed the small intestine daily?
~9 L of water, mostly from GI tract secretions, enters the small intestine each day.
- 95%
What type of digestion occurs in the large intestine?
only small amount, primarily resident bacteria
How does water move in the small intestine?
freely in both directions, with active uptake of solutes directing water from chyme into enterocytes and blood
How long does it take material to move through the large intestine?
12-24 hours
What is the primary function of the large intestine?
defecation; the large intestine is not essential for life
How many species of bacteria are found in the large intestine?
700
What are some functions of the bacteria flora in the large intestine?
- fermentation of cellulose
- producing acids and gases
- synthesizing Vit B and K
What happens to most bacteria entering the large intestine?
killed by HCL, lysozymes and proteases
What does stool in the rectum consist of?
- food residues
- mucus
- epi tissue
- bacteria
- water
How does fiber in the diet affect colon motility?
increases the strength of colon contractions and softens stool
How much food residue enters the cecum daily?
500 ml and 150 ml become feces
