Digestion Flashcards
What is the digestive system
A tube extending from the mouth throughout the body to the anus
With glands that produce enzymes
Consists of organs with specialised functions to perform in the breakdown and absorption of food molecules and water
Digestion
Process of hydrolysing large, insoluble polymers into small soluble molecules with enzymes
That can then be assimilated into biological molecules once absorbed into the blood
5 steps to digestion
Ingestion; Eating, mechanical breakdown Digestion; Hydrolysis, smaller molecules Absorption; Small intestine into blood Assimilation; Integrating into body for function Egestion; Removal of waste
4 glands and their enzymes
Salivary; salivary amylase
Stomach; Endopeptidases and exopeptidases
Pancreas; Pancreatic amylase, lipase, exopeptidases
Ileum; Membrane bound dipeptidases and disaccharidases
Salivary gland function
Secretes saliva containing amylase
Hydrolyses starch into amylase
Ileum function
Chemical digestion of carbs, fats, proteins by enzymes
Absorption of most digested food
Maltase embedded in epithelium cell membrane to hydrolyse maltose into glucose for rapid absorption
Oesophagus function
Carriage of food to stomach by peristalsis of the walls
contraction and relaxation of muscle cells and tissues to push food along
Pancreas function
Secretes pancreatic juices (amylase, carbohydrase’s, endopeptidases, exopeptidases, lipases)
buccal purpose
Mechanical digestion of food due to crushing of food by teeth
Chemical digestion by salivary amylase
Rectum function
Stores faeces
Function of stomach
Muscular sac
Contraction of wall muscles churn up food (mechanical)
Secretion of hydrochloric acid to kill microorganisms and maintain optimum pH for enzymes
Chemical digestion of proteins by proteases
Function of colon
Absorption of water from food
Function of anus
Site of egestion
Explain the digestion of starch
Food is ingested
Undergoes mechanical digestion by teeth in the mouth
Then mixed with salivary amylase in saliva
Which hydrolyses the glycosidic bonds to produce maltose (chemical digestion)
Salivary amylase denatured in the stomach due to the acidic pH
In small intestine the pancreatic amylase continues to hydrolyse starch into maltose
Maltose hydrolysed into glucose by maltase enzymes embedded in epithelial cell membrane
Glucose can then be absorbed
Describe the role of digestive enzymes in the complete breakdown of starch
Amylase:
Synthesised and secreted from salivary gland and pancreas
Hydrolyses glycosidic bonds in starch into maltose
Maltose:
Embedded in membrane of epithelial cells of ileum
Hydrolyses glycosidic bonds in maltose into glucose
Co transport of glucose/AA across the epithelial cell membrane structure for easy recall
- Sodium potassium pump
- Concentration gradient
- Theory of co transport
- Facilitated diffusion
- Sodium gradient
- Glucose gradient
- Facilitated diffusion into blood
Co transport of glucose across the epithelial cell membrane
Na+ actively transported out of epithelial cell into blood by Na+/K+ pump
Creating a concentration gradient of sodium between lumen of ileum and epithelial cell
Co-transporter protein has 2 binding sites complementary to Na+ and glucose. Moved across when both bind
Both enter by facilitated diffusion
Na+ diffuses in down its concentration gradient
Glucose actively transported in against its concentration gradient
Glucose moves from the epithelial cell into the blood by facilitated diffusion
Advantage of stomach wall muscle churning up food
Mechanical digestion
Increases the rate of digestion by increases the number of successful collisions per second between enzymes and substrates
Purpose of the sodium potassium pump
Maintains a concentration gradient of sodium between the lumen of the ileum and the epithelial cell
So both Na+ and glucose can enter by facilitated diffusion
Keeps Na+ low inside the cell
3Na+ out and 2K+ in creates an electrochemical gradient
Why does the hydrolysis of triglycerides make solutions acidic
Hydrolysed into glycerol and fatty acids
Fatty acids are acidic so lowers pH
Lipid digestion
Only occurs in lumen of ileum
In the stomach, lipids are churned up into fat droplets
Bile produced in the liver, stored in the gall bladder and released into the small intestine with food
Bile salts in bile emulsify fat droplets
Not digestion but increases the surface area for faster rate of digestion
Increased surface area for lipase to hydrolyse lipids for efficient digestion
Into glycerol, fatty acids, monoglycerides
Bile salts activate lipase
How do chlomicrojs leave the epithelial cell and why
Exocytosis
Bulk transport because very large
Too big to leave otherwise
Explain the tole of the golgi body in lipid absorption
Modifies triglycerides
Combines triglycerides with proteins to form lipoproteins
Packages chylomicrons for exocytosis
Give examples of endopeptidases
Trypsin
Pepsin
Chymotrypsin
Examples of exopeptidases
Dipeptidases
Carboxypeptidases
Aminopeptidases
Why must chylomicrons be water soluble
Chylomicrons transport triglycerides into a lymph vessel by exocytosis
They then enter the blood so must be water soluble to be carried in the blood
What are all disaccharided and what does this mean
Soluble so they lower water potential
Bile salts
Produced in the liver
Stored in the gall bladder
Explain protein digestion
Polypeptides hydrolysed in the stomach by proteases (enzymes)
Endopeptidases hydrolyse the peptide bonds within the polypeptide
Producing smaller shorter polypeptide chains
That increase the surface area for next enzyme to make digestion faster and more efficient
Exopeptidases hydrolyse the peptide bonds at the terminal ends of protein, removing 1 or 2 AA at a time
Specific, one group complementary to N terminal and the other C terminal
AA and dipeptides produced
Dipeptidases embedded in the cell surface membrane of epithelial cells
Which hydrolyse dipeptides into AA so they can be absorbed by co-transport
Co-transport of amino acids across the epithelial cell membrane into blood
Na+ actively transported out of epithelial cell into blood by Na+/K+ pump
Creating a concentration gradient of sodium between lumen of ileum and epithelial cell
Co-transporter protein has 2 binding sites complementary to Na+ and amino acids. Moved across when both bind
Both enter by facilitated diffusion
Na+ diffuses in down its concentration gradient
Amino acids actively transported in against its concentration gradient
Amino acids move from the epithelial cell into the blood by facilitated diffusion
Lipid absorption
Lipid droplets mixed with bile salts and emulsified to form smaller droplets
Which increases the surface area for the action of lipase
Triglycerides hydrolysed into glycerol, fatty acids and monoglycerides
Glycerol and fatty acids form micelles
Micelles enter epithelial cell by simple diffusion
At the S.E.R fatty acids and glycerol recombine to form triglycerides
At the Golgi apparatus triglycerides are modified and proteins added to form the lipoproteins chylomicrons and packaged into vesicles
Chylomicrons are water soluble so can be carried in the blood
Chylomicrons are transported into a lymph vessel by exocytosis then enter the blood
Define absorption
Moving of products of digestion from the small intestine into the blood
Why can’t humans digest cellulose
Do not produce cellulase
Unable to hydrolyse the glycosidic bonds
Adaptation of the epithelial cell
Large surface area for the absorption of products of digestion from microvilli (finger like projections)
Enzymes embedded in membrane so products available for absorption rapidly once hydrolysed
Lots of mitochondria to produce the large amount of ATP needed for active transport
Advantage of endopeptidases and exopeptidases hydrolysing at the same time
The endopeptidases produce many short polypeptide chains
More ends for action of exopeptidases
To produce amino acids
For faster absorption
