3.3 Digestion Flashcards
What are the 2 types of digestion
- Mechanical/ physical
- Chemical
What 2 structures in the body are involved in physical digestion
- Teeth and stomach
Why is physical digestion important
-To break larger pieces into smaller ones
- Providing a large surface area for chemical digestion
- Increasing the rate of digestion
What does chemical digestion do
It hydrolyses large, insoluble molecules into smaller soluble ones
Explain why it is necessary for food to be digested, in order to be absorbed into our body
To make it smaller and soluble so that it can be transported across the membrane to be absorbed into the blood plasma
What are the 3 functions of mucus
- Lubricant
- Neutralises acids
- Protects gut wall from acid erosion
Where is amylase secreted from
- Salivary glands
- Pancreas
What does amylase hydrolyse
Starch
What are the products of amylase when starch is hydrolysed
Maltose
Where are the sites of action for amylase
-Mouth (salivary glands)
- Duodenum (pancreatic juices)
Roughly what is the optimum pH of amylase
About 8
What type of bond does amylase hydrolyse
Glycosidic bonds
Where is maltase found
In the ileum
What is the substrate for endopeptidase
Proteins/ polypeptides
What is the product from endopeptidase
Shorter polypeptides
Where are endopeptidases secreted from
- Gastric glands
- Pancreas
Where are the sites of action for endopeptidases
- Stomach
- Duodenum
What are the substrates for exopeptidases
Short polypeptides
What are the products from exopeptidases
- Amino acids
- Dipeptides
Where are exopeptidases secreted from
- Pancreas
- Epithelial cells
Where are the sites of action of exopeptidases
Duodenum
Ileum
What is the substrate for lipase
Lipids
What are the products from lipase
- Monoglycerides
- Fatty acids
Where are lipase secreted from
Pancreas
Where is the site of action for lipase
Duodenum
What is the substrate for disaccharidases
Disaccharides
What is the product from disaccharidases
Monosaccharides
Where are disaccharidases secreted from
Epithelial cells
Where is the site of action for disaccharidases
Ileum
Do endopeptidases or exopeptidases hydrolyse the bonds at the end of the chain
Exopeptidases
Why are endopeptidases secreted inactive
So they don’t digest the gut wall before they reach the stomach or the duodenum
Where is bile produced
Liver
Where is bile stored
Gallbladder
What is the name of tube where bile travels from the gallbladder to the duodenum
Bile duct
What are the 2 components of bile
- Bile salts
- Sodium hydrogen carbonate
What is the name of the process from which lipid droplets become micelles
Emulsification
What does sodium hydrogen carbonate do
Neutralises stomach acid
Micelles make the lipids more _______ so therefore easier to _______
- Soluble
- Transport
What is the pH range in the mouth
6.5-7.5
What types of digestion happen in the mouth
- Physical/ mechanical
- Chemical
What feature in the mouth carries out physical digestion
Teeth - increase the SA for chemical digestion
What is digested by chemical digestion in the mouth
Starch only
What are the 3 components of saliva
- Amylase
- Mucus
- Mineral ions
What is the role of amylase in saliva
To breakdown starch
What is the role of mucus in saliva
Lubricant
What is the role of mineral ions in saliva
Maintain pH
What is the name given to the process where there is co-ordinated contractions
Peristalsis
What is the role of goblet cells
To secrete mucus
What are the general 2 muscles in the digestive system
- Circular muscle
- Longitudinal muscle
What does the contraction of circular muscles do to the gut
Squeeze the gut
What does the contraction of the longitudinal muscles do to the gut
Shorten the gut
What is the name given to the ball of food that travels down the oesophagus
Food bolus
What is the role of mucus in the oesophagus
Lubrication
What is the pH in the stomach
pH 2
What is the name of the soupy consistancy product formed from the stomach churning
Acidic chyme
What biological molecule is chemically digested in the stomach
Proteins only
What does the gastric gland secrete
Gastric juice
What are the 3 components of gastric juice
- Endopeptidase
- Mucus
- HCl
What are the functions of mucus in the stomach
- Lubricant
- Protect the lining from acid erosion
What are the functions of HCl in the stomach
- Maintains pH to activate enzymes
- Kill bacteria
What part of the digestive system is the main site of chemical digestion
Duodenum
What are the 2 external glands to the duodenum
- Liver
- Pancreas
What does the liver secrete
Bile
What are the 4 components of pancreatic juice
- Amylase
- Endo and Exopeptidases
- Lipase
- Hydrogen carbonate ions
What is the name of the gland in the gut wall of the duodenum
Brunner’s gland
What is secreted from the Brunner’s gland, and what is its function
Mucus
- Neutralise stomach acid
- Protect the lining from acidic erosion
Where is the final region of chemical digestion
The ileum
Where are the enzymes in the ileum
In the microvilli, so the wall before the lumen
What is absorbed in the colon
- Water
- Vitamins
Why is water absorbed in the colon
To produce solidified faeces
Why do we need to have solidified faeces
In order to stimulate peristalsis
What synthesises the vitamins in the colon
The bacteria
Why is cellulose needed in the diet if it cannot be digested
It provides bulk since the fibres provide the solidity to the faeces
How do bile salts help the digestion of lipids
They emulsify them which increases the surface area for lipase
Why are hydrogen carbonate ions secreted into the duodenum
To neutralise the stomach acid
What is assimilation
How molecules are used by the cell, used for their relative process
What are amino acids used for by the cell
Protein synthesis
What are fatty acids and monoglycerides used for by the cell
Formation of cell membrane
What type of surface is the ileum
Exchange surface
What are the 4 features of the ileum that increase absorption efficiency
-Villi and microvilli
- Thin gut wall
- Muscle layer
- Blood flow carries the products away
How do villi and microvilli increase absorption efficiency in the ileum
They increase the surface area, so more carrier proteins therefore more molecules can pass through the membrane at one time
How does the ileum having a thin gut wall increase absorption efficiency
Shorter diffusion pathway, so increased rate of absorption
How do the muscle layers in the ileum increase absorption efficiency
They ensures that the molecules are in contact with the villi, so a concentration gradient is maintained
Why does blood flow carrying products away in the ileum increase absorption efficiency
It maintains the concentration gradient
Once molecules are absorbed into the lumen of the ileum, which 2 ‘tubes’ can the be absorbed into
- Capillary
- Lacteal
What product of digestion is absorbed into the lacteal
Products of lipid digestion
What products of digestion are absorbed into capillaries
Products of protein and carbohydrates digestion
Before lipids are absorbed into the epithelial cells of the ileum, what do the fatty acids and monoglycerides leave first
The micelle
Once inside the epithelial cell of the ileum, what happens to the fatty acids and the monoglycerides
The reform as triglycerides
Once triglycerides have been formed in the epithelial cells of the ileum, what happens to them- what are they combined with, what is the new name of them
- The triglycerides are chemically modified in the golgi body
- Triglycerides are combined with proteins
- Forming chlyomicrons
Once the chlyomicrons are formed in the epithelial cells of the ileum, what is the name of the process by which they leave the epithelial cell
Exocytosis
Once chlyomicrons leave the epithelial cell of the ileum, where do they go
Into the lacteal
What is the name of the duct that the chlyomicrons are transported to once in the lacteal
Thoracic duct - then into the blood stream
Why do chlyomicrons have to go through the lacteal and the lymphatic system instead of diffusing directly into the blood stream
Because its too large to fit through the fenestrations of the capillary
What is the name of the pump which starts the absorption process of glucose or amino acids
Sodium, potassium pump
When absorbing glucose/ amino acids, what is the 1st step of the process, bonus points if you can name the type of co-transporter protein it is
Sodium ions are actively out of the ileum into the tissue fluid through a antiporter while potassium ions are actively transported into the ileum
When absorbing glucose/amino acids, what happens after the sodium ions have been pumped out of the ileum
This sets up a concentration gradient for sodium between the lumen of the ileum and the ileum wall
When absorbing glucose/ amino acids, what happens once a sodium concentration gradient has been set up, bonus points for the name of the co-transporter protein
Sodium is transported down it’s concentration gradient through a symport protein, while pulling glucose/ amino acids into the ileum wall too- by indirect active transport
When absorbing glucose/ amino acids, how does the glucose/ amino acids enter the tissue fluid from the ileum wall
A concentration gradient has been set up so glucose/ amino acids can now facilitated diffuse down their own gradient into the tissue fluid
When there is excess glucose/ amino acids what is the name of the vein that takes it away from the ileum, and where does this vein take it
- Hepatic portal vein
- From ileum to liver
What is excess glucose converted into at the liver, and why is it converted to this
Into glycogen so it can be stored in the liver
What is the name of the process that happens to excess amino acids in the liver
Deamination
What is deamination
Where the liver removes the amino group and the hydrogen on the amino acid
Why does deamination occur
Because amino acids in high concentrations are toxic, so removing the ammonia from the amino acid and converting into urea to excrete is beneficial
Explain why it is more efficient for the endopeptidase enzymes to act before the exopeptidases
- Endopeptidases hydrolyse the internal peptide bonds
- Therefore increasing the surface area
- For exopeptidases to act on
- So a faster rate of break down
What is ingestion
The taking in of food
What does the epiglottus do
Blocks the trachea when swallowing food
Describe the processes involved in the absorption and transport of digested lipid molecules from the ileum into lymph vessels (5 marks)
- Micelles contain bile salts and fatty acids/ monoglycerides
- Make fatty acids/ monoglycerides more soluble in water
- Fatty acids/ monoglycerides absorbed by diffusion
- Triglycerides reformed in cells
- Vesicles move to cell membrane
The movement of Na+ ions out of the cell allows the absorption of glucose into the cell lining the ileum. Explain how. (2 marks)
- Generates a concentration gradient for Na+ ions
- Na+ ions moving in by facilitated diffusion, brings glucose with it
Describe the role of micelles in the absorption of fats into the cells lining the ileum. (3 marks)
- Micelles include bile salts and fatty acids
- Make the fatty acids more soluble in water
- Brings fatty acids to the lining of the ileum
- Maintain higher concentration of fatty acids to the lining of the ileum
- Fatty acids absorbed by diffusion
Describe the role of enzymes in the digestion of proteins in a mammal (4 marks)
- Hydrolysis of peptide bonds
- Endopeptidase act in the middle of protein/ polypeptide
- Exopeptidases act at end of protein/ polypeptide
- Dipeptidases acts on dipeptides/ between 2 amino acids
Explain the advantages of lipid droplet and micelle formation (3 marks)
- Droplets increase surface area for lipase action
- So faster hydrolysis of lipids/ triglycerides
- Micelles carry fatty acids and glycerol through membrane to cells
Cell lining the ileum of mammals absorb the monosaccharide glucose by co-transport with sodium ions. Explain how. (3 marks)
- Sodium ions actively transported from ileum cell to blood
- Forms diffusion gradient fro sodium ions to enter cells from guy and with it glucose
- Glucose enters by facilitated diffusion with sodium ions
What are microvilli (1 mark)
Highly folded cell surface membrane
Vitamin A is a fat-soluble substance.
Micelles are involved in the process of Vitamin A absorption.
Describe the process of vitamin A absorption into cells lining the ileum (3 marks)
- Combine with bile salts
- Makes more soluble in water
- Micelles breakdown close to cells
- Diffuses into cells
Describe how the anti-toxin antibody would be digested ( 3 marks)
- Peptide bonds hydrolysed
- Endopeptidases break internal peptide bonds
- Exopeptidases break terminal peptide bonds
- Dipeptidases break dipeptides to amino acids
Describe and explain 2 features you would expect to find in a cell specialised fro absorption (2 marks)
- Folded membrane/microvilli so large surface
area (for absorption); - Large number of
co-transport/carrier/channel proteins so fast
rate (of absorption)
OR
Large number of co-transport/carrier proteins
for active transport
OR
Large number of
co-transport/carrier/channel proteins for
facilitated diffusion; - Large number of mitochondria so make
(more) ATP (by respiration)
OR
Large number of mitochondria for aerobic
respiration
OR
Large number of mitochondria to release
energy for active transport; - Membrane-bound (digestive) enzymes so
maintains concentration gradient (for fast
absorption);
Describe the role of epithelial cell membranes in the ileum in the absorption of amino acids
- Sodium ions are actively transported out of the epithelial cells into the blood via the sodium/potassium pump lowering the sodium ion concentration inside the cell
- Sodium ions diffuse back into the epithelial cell from the lumen via co-transport protein, bringing amino acids with them
- Amino acids are transported out of the epithelial cell into the blood via a specific carrier protein in the membrane
- The epithelial cell membrane contain microvilli, which increase the surface area for amino acid absorption, maximising efficiency
