digestion and absorption Flashcards
measures taken to help the public with a balanced diet
traffic light system
break down into diagrams
carbohydrate function
energy source
carbohydrate source
bread, pasta, rice, cereals, potatoes
protein function
growth and repair
protein source
meat, fish, dairy, lentils, nuts, seeds, tofu
fat/ lipid function
long term energy store; insulation
protein source
meat, cheese, cream, fish, nuts, avocado, coconut
vitamins function
vitamin specific
A - vision
C - antioxidant
D - Ca absorption
vitamin source
examples are also vitamin specific
A - liver, sweet potato
B - vegetables
C - citrus
D - only fish/ sun
mineral function
mineral-specific
Ca - bone mineralisation
Fe - oxygen transport
mineral source
mineral specific
Ca - milk
Fe - red meat
K - bananas
fibre function
effective bowel function
fibre source
plants (fruit, vegetables, nuts, cereals)
water function
hydration
what are the different types of dietary fats
fatty acids
phospholipids
cholesterol
fatty acids info
saturated/ unsaturated
saturated source: animal foods (meat, dairy)
unsaturated: mainly from plants (rape seed, nuts..)
phospholipids info
sex hormones
bilayer
bile salts
cholesterol info
2 fatty acid chains, glycerol, phosphate group
plants + animals (dairy, palm)
what does eating too many fats lead to
atherosclerosis (MI, stroke)
obesity - risk factor for many other conditions
what are the 9 essential amino acids
phenylalanine
valine
tryptophan
threonine
isoleucine
methionine
histidine
leucine
lysine
carbohydrates - monosaccharides
glucose, fructose, galactose
carbohydrates - disaccharides
sucrose = glucose + fructose
maltose = glucose + glucose
lactose = glucose + galactose
joined by glycosidic bond
carbohydrates - polysaccharides
more tan 10 monomers typically
starch: amylose linear
amylopectin branched
A 1 -> 4 glycosidic bond
A 1 -> 6 beta 1,4 linkage in branched
carbohydrates - fibre
plant cell walls -> cellulose
beta 1,4 linkage
large straight chains
cannot be digested
digestion definition
the process by which food is broken down into components simple enough to be absorbed in the intestine
where are enzymes for digestion secreted
glandular cells in mouth
chief cells in stomach
exocrine cells in pancreas
enzymes bound to the apical membrane of enterocytes
salivary secretions
where: parotid, submandibular and sublingual salivary glands
- moistens food
- starts the digestion of carbohydrates (a-amylase)
starts the digestion of lipids (minor: lingual lipase)
stomach structure in digestion
start of protein digestion
chief cells: secrete pepsinogen
parietal cells: HCl secretion
- denatures proteins
- activates pepsin (=endopeptase)
these cells are present in the pits in the epithelium of the stomach lining
what is a zymogen
zymogens are inactive precursors that are subsequently activated by cleavage of one/ a few specific peptide bonds
- the inactive precursor is called a zymogen (or a proenzyme)
- e.g. pepsinogen (inactive) -> pepsin (active)
- prothrombin -> thrombin
role of pancreas in digestion
exocrine: pancreatic juice (enzymes and alkali secretions
endocrine: secretion of insulin + glucagon
examples of zymogens
trypsin -> proteins ( + other proteases)
chymotrypsin (proteins)
carboxypeptidase (proteins)
elastase (proteins (elastin))
phospholipase (phospholipids)
examples of non-proteolytic enzymes
a-amylase (starch)
lipase (triglycerides)
ribonuclease (RNA)
deoxyribonuclease (DNA)
role of the liver in digestion
produces and secretes bile
- emulsification
stored in gallbladder (released into duodenum)
micelles
what are bile salts
synthesised from cholesterol ->cholic acid, chenodeoxycholic acid
conjugated to amino acid (glycine or taurine) -> secreted
amphipathic (contain both hydrophobic (cholesterol)/ hydrophilic faces (amino acid conjugate)
detergent action on dietary fat -> ^ SA for digestion
what are the functions of fat salts
emulsification of lipid aggregates
solubilisation and transport of lipids in aqueous environment
what are the three sections of the small intestine
duodenum, jejunum, ileum
what is the function of the duodenum
mixing secretion from pancreas, liver and duodenum with food
neutralisation of stomach acid (HCl)
pepsin inactivation
further digestion
absorption
what is the function if the jejunum
completing breakdown
nutrient absorption
what is the function of the ileum
nutrient absorption
what are brush border enzymes
integral part of the membrane (not free in lumen)
peptidases
lactases
sucrase
maltase
what do chief cells secrete
secrete pepsinogen
what do parietal cells secrete
HCl
- denatures proteins
activates pepsin (= endopeptase)
what is mastication
mechanical digestions, moistens food
what is a bolus
broken down and moistened food
digestion in the mouth
carbohydrates - primary digestion
- starch broken down by a-amylase to maltotriose, maltose and a-limit dextrin
proteins - nothing
lipids - lingual lipase present but minor contribution
what is chyme
food that is being churned in the stomach with gastric juice
digestion in the stomach
carbohydrates - nothing
proteins - primary digestion
- HCl denatures proteins + activates pepsin
- endopeptidase that cleaves proteins to smaller peptides
lipids - gastric lipase present but minor contribution
digestion in the duodenum
CARBOHYDRATES
a-amylase further digests starch
brush border disaccharides (maltase, sucrase, lactase)
= monosaccharides
PROTEINS
cleaves by trypsin (activates other enzymes), chymotrypsin, elastase, carboxypeptidases
produces increasingly smaller peptides/ dipeptides
brus border peptides produce dipeptides/ amino acids
LIPIDS
pancreatic juice digests lipids into monoglycerides and fatty acids
phospholipase digests phospholipids to lysolecithin + fatty acids
explain passive absorption
slow
needs conc. gradient or charge gradient
explain facilitated transport
slightly faster
involved membrane carrier
controllable
explain active transport
uses energy
fast
uses membrane carrier
controllable
explain formation of micelles
formed in the lumen with the aid of bile salts
water soluble
explain absorption of lipids
micelles formed
diffuse to the apical brush border epithelial cells
- contents released and diffuse down their conc. gradient into the cell
if the fatty acid chains are short they diffuse directly into the bloodstream
everything else in chylomicrons
- move to basolateral membrane and exit via exocytosis
- too large to enter vascular capillaries so are secreted into lymphatics
carried to thoracic duct
empties into the bloodstream`
explain the activation of pancreatic zymogens
enterokinase -> trypsinogen -> trypsin -> all others
explain the process of absorption of monosaccharides
glucose + galactose
- Na/ glucose transporter -> SGLT1
- Na+/K+ pumps on basolateral membrane shovel out Na+ molecules to create a conc. gradient (maintaining)
GLUT5 facilitated transport protein for fructose
GLUT2 out of the cell
explain the absorption of amino acids
similar to monosaccharides
Na+ dependent amino acid transporters
Na+/ K+ pump maintains the Na+ gradient in the cell
dipeptides/ tripeptides
- cotransport with H+
- further digested inside the cell
facilitated diffusion basolateral membrane
