digestion and absorption Flashcards
digestion
getting food (fuel) so that respiration (combustion) can take to release energy (ATP+heat)
autotrophs
self feeding = make their own food - mainly using light energy (photosynthesis)
- algae, plants
heterotrophs
depend on autotrophs directly or indirectly
- they get large molecules / polymers - too large to cross membrane and enter cells
- therefore are digested (hydrolysed) into monomers, which are absorbed
structure of digestion system
mouth - enzymes
oesophagus
stomach
liver - bile duct - duodenum pancreatic duct - pancreas
ideum (small intestine)
colon (large intestine)
rectum
anus
mouth
mechanical digestion to increase surface area of food so enzyme have a larger area to work on
reaction
starch to maltose via hydrolysis of glycosidic bond
amylase
neutral pH
stomach
mechanical digestion to increase surface area of food so enzyme have a larger area to work on
proteins - smaller polypeptide via hydrolysis of peptide bond
pepsin - endopeptidase
~2 pH - HCl
duodenum
absorption of organic molecules
starch - maltose (amylase)
large - smaller peptides (trypsin is an endopeptidase)
triglycerides - monoglycerides and fatty acids (ester bond hydrolysed by lipase)
7 to 8 pH
HCl - neutralised with NaHCo3 from liver, pancreas and duodenum
liver
secretes bile salts for lipid emulsification
ileum
disaccharides - monosaccharides (maltase, sucrase, lactase)
short peptides - dipeptides - exopeptidases
dipeptides - amino acids - dipeptidases
neutral pH
colon
large intestin
lots of bacteria - could secrete vitamins
rectum
absorption of water and vitamins only
process of digestion
ingestion - digestion and egestion
digestion leads to absorption - assimilation (using the molecule/breaking it down)
egestion (faeces)
The hydrolysis of larger molecules into smaller molecules.
To produce molecules small enough to be absorbed across the gut wall
carbohydrate digestion
in the mouth - salivary amylase hydrolyses starch to maltose - released in solution in saliva from salivary glands (optimal pH 7 neutral)
from pancreas - released down pancreatic duct - acting in the small intestine - pancreatic amylase hydrolyses starch to maltose - pH 7
attached to the wall of the small intestine - maltase hydrolyses maltose to glucose (and other disaccharides) - pH7
lipid digestion
pancreatic lipase - triglycerides to diglycerides and fatty acids to monoglycerides and fatty acids to glycerol and fatty acids
bile salts - made in the liver - stored in gall bladder - released down the bile duct - emulsify facts - this creates a larger surface area for lipase action
protein digestion
pepsin (a type of protease) - stomach - polypeptides hydrolysed to shorter polypeptides
also called an endopeptidase as breaks peptide bonds in the middle of the polypeptide chain
released in solution in gastric juice from the wall of the stomach - released in an inactive form as pepsinogen
pepsinogen (inactive) -> HCl -> pepsin (active)
trypsin - pancreatic duct - hydrolyses polypeptides to shorter polypeptides
also called an endopeptidase as hydrolyses the peptide bonds in the middle of a polypeptide chain
released in solution in pancreatic juice - travels down the pancreatic duct - acts in the small intestine - released in an inactive form as trypsinogen
trypsinogen (inactive) -> trypsin (active)
exopeptidases - some break off one amino acid at a time, some break off two - all bound onto wall of small intestine
hydrolyse peptide bonds at end of the polypeptide chain
dipeptidases - hydrolyse the peptide bond in dipeptides to form amino acids
absorption
occurs in the small intestine - ileum
The ileum is lined with finger-like processes called villi. Increases the SA for absorption.
Villi filled with capillaries, so there’s a short diffusion distance from the LUMEN of the gut (space inside the gut) into the blood.
Has a structure called a LACTEAL running up the centre into which fats are absorbed. This a branch of the LYMPH SYSTEM, which is a system of tubes that fills your body.
ileum is lined with columnar epithelial cells - villi - increase surface area
carbohydrate digestion - shanti
polymers - starch (long and branches)
starch - amylase (salivary and pancreatic) - maltose (ileum) - glucose (monosaccharides)
lactose - lactase (ileum) glucose and galactose
sucrose - sucrase (ileum) - glucose and fructose
hydrolysis reactions in which the glycosidic bond is broken using water
protein digestion - shanti
proteins - endopeptidases - smaller polypeptides - exopeptidases - dipeptides + AA - dipeptidases - AA
hydrolysis of peptide bond using water
endopeptidases - pepsin, trypsin - hydrolyse the peptide bond in the middle of the chain to make more ends available
exopeptidases - aminopeptidases and carboxypeptidases
- hydrolyse the peptide bond at the ends of the chain to release amino acid and dipeptides in the duodenum and ileum
dipeptidase hydrolyse the dipeptides to amino acids - ileum
transport in small intestine
villi and microvilli to increase surface area of the lumen of the small intestine - intestinal epithelial cell
membrane bound enzymes which allow for a short diffusion distance for glucose and amino acids
capillary - circulation of blood maintains the concentration gradient
the intestinal epithelial cells complete the hydrolysis reaction using membrane-bound enzymes and absorb the monomers and pass them into the capillary
water soluble monomers into the capillary
co-transport of glucose / amino acids with Na+
- There is a higher concentration of glucose inside the epithelial cell than in the lumen.
- There is a lower concentration of Na+ inside the epithelial cell than in the lumen.
- The co-transport / carrier protein has two binding sites, one for glucose and one for Na+.
- When both glucose and Na+ bind to the carrier protein, the protein changes its tertiary structure to transport them into the cell. (Na+ move down the concentration gradient, while glucose is transported against the concentration gradient.)
- Glucose enters the capillary from the epithelial cell by facilitated diffusion through a carrier protein.
- The low concentration of Na+ within the ep cell is maintained by the Na+/K+ pump, which actively transports 3 Na+ out of the cell and 2 K+ into the cell using energy from ATP hydrolysis.
- For aa, there are several different co-transport proteins (for aa with different types of side chains).
lipid digestion - shanti
- are not polymers
- insoluble in water to form droplets
in the duodenum - liver secretes bile salts, which emulsify the large lipid droplets into smaller droplets increasing surface area
lipase - from the pancreas - attaches to the small droplets - hydrolysis of ester bond
TG + 2H2O = monoglyceride + 2FA
triglycerides + 3H2O = glycerol + 3 FA
micelle formation
- phospholipids also combine with the digested droplets to form a micelle
- forms a phospholipid monolayer on the outside with monoglyceride, fatty acid ect inside
- micelles transport the monoglyceride, fatty acid to the epithelial cell
- monoglyceride and fatty acids enter the epithelial cell via simple diffusion through the phospholipid biplayer
triglycerides are re-synthesised in the epithelial cell in the smooth endoplasmic reticulum
proteins get added to the triglyceride in the golgi apparatus to form chylomicrons
chylomicrons enter the lymph vessel or lacteal
lipid digestion - summary
- emulsification by bile
- enzymatic digestion by pancreatic lipase
- absorption of products of fat digestion depend on size
short and medium chain fatty acids and glycerol absorb into blood via capillary
long chain fatty acids and monoglycerides form into triglycerides by fatty acid linking and are transported in chylomicrons into lymph vessels
villi
villus - folding of intestine
epithelial cells line the villi
microvilli - folding of the cell membrane
intestinal villi - lumen
lacteal and blood capillar
water soluble monomers - glucose and amino acids enter the blood capillaries
these capillaries join into the hepatic portal vein - carries monomers to the liver, where they are used / stored
lipids (water insoluble) enter the lymph - a slow moving fluid in the lymph vessels containing white blood cells
the lymph joins the blood circulation at the carotid duct
define digestion
the hydrolysis of large, insoluble molecules into smaller molecules that can be absorbed across cell membranes
which molecules require co-transport
amino acids and monosaccharides
explain how sodium ions are involved in co-transport
sodium ions are actively transported out of the cell into the lumen, creating a diffusion gradient
nutrients are then taken up into the cells along with the Na+ ions
why do fatty acids and monoglycerides not require co-transport
the molecules are nonpolar, meaning they can easily diffuse across the membrane of the epithelial cells
