The digestive system Flashcards
Which enzymes are made in the salivary glands?
Salivary amylase
What do salivary amaylse do?
- They hydrolyse the 1-4 and 1-6 glycosidic bonds in starch
- They hydrolyse starch into shorter chains
- This increases the surface area of the molecule
What is found in saliva?
Enzymes
Buffer
What is a buffer?
It helps maintain the optimum pH
What pH does salivary enzymes work best at?
7
What enzymes are found in the stomach?
Endopeptidases
What does the stomach also produce apart from enzymes?
Hydrochloric acid
What do endopeptidases do?
- They hydrolyse the peptide bonds within the peptide chain
- They hydrolyse protein chains into shorter chain polypeptides
- This increases the number of terminal ends, increasing the surface area
What pH do endopeptidases work best at?
2
What enzymes are found in the pancreas?
Endopeptidases
Exopeptidases
Pancreatic amalyse
Lipase
Where are the enzymes in the pancreas delivered to?
They are delivered by the pancreatic duct to the duodenum
What is the duodenum?
The upper part of the small intestine
What is bile and where is it made?
- Made in the liver and stored in the gall bladder
- Neutralises the acidic food to pH 8/9 so enzymes are at their optimum pH and not denatured
What do exopeptidases do?
- Hydrolyse peptide bonds at the terminal ends of the shorter polypeptide chains
- They hydrolyse shorter chains into di-peptides
What does pancreatic amylase do?
Hydrolyses shorter chain starch into maltose disacharrides
What do lipases do?
- Hydrolyses the ester bond
- Hydrolyses lipids into monoglyceride and 2 fatty acids
What enzymes do enzymes from the pancreas work at?
8/9
Which enzymes are found in the lower part of the small intestine?
Dipeptidase
Maltase
Sucrase
Lactase
What is the lower part of the small intestine known as?
The Ileum
Where are the enzymes located in the ileum?
They are embedded in the wall of the ileum
What do dipeptidases do?
They hydrolyse dipeptides to 2 amino acids
What do maltase do?
Hydrolyse maltase to 2 alpha glucose
What do sucrase do?
Hydrolyse sucrose to fructose and alpha glucose
What do lactase do?
Hydrolyse galactose and alpha glucose
What muscles do the oesphagus have?
It has 2 rings of muscle
- Circular
- Longitudinal
- They are separate
How do the 2 rings of muscle in the oesophagus ineract?
They are an antagonistic pair. When one contracts, the other one relaxes
They cause a wave of muscle contraction known as peristalsis
What is chewing food known as?
Mastication - it increases the surface area of food and allows it to mix with the saliva
What do the salivary glands do?
There are 3 pairs of salivary glands
They produce saliva (which contains enzymes and buffer and antibacterial properties)
What is the epiglotis?
Every time you swallow, it closes the pathway to the trachea
What happens if food gets stuck by the epiglotis?
If food gets stuck there, the trachea is closed and asphyxia (choking) takes place
What is the oesophagus shaped like?
In reality, its more twisted so you cant rely on gravity to pull the food down
So, it has rings of muscle around it that help to propel the food down (peristalsis)
How does bile act as an emulsifier?
- Lipase is water soluble. Lipids are not. Bile has one part hydrophilic and one part hydrophobic
- It keeps the lipids suspended in the place where lipase are
- So we have also increased the surface area so the enzymes have a larger area over which to work
What is the duodenum known as?
The mixing bowl where everything comes together - all the enzymes from the pancreas and also the bile
What is on the outside of the stomach (structurally)?
3 layers of muscle - it helps the stomach contract (peristalsis) and digest the food
What is the lining of the stomach like and why?
It has a thick cell lining to protect the stomach tissue from HCl
What cells are found in the lining of the stomach and what do they do?
- Goblet cells
- These produce mucus
- These are barriers to protect the lining of the stomach
What glands are on the lining of the stomach?
Peptic glands which produce peptic juice
What does peptic juice contain and why is this useful?
- It contains enzymes and HCl
- It moves into the stomach and mixes with the food
What does HCl acid do in the stomach?
It kills pathogens in food and ensures optimum pH for enzymes in the stomach
What cells line the ileum?
Epithelial cells
What is the lining of the ileum like?
It is a single cell lining - one cell thick for short diffusion pathway
What is found on the walls of the ileum?
Enzymes
Goblet cells - produce mucus as don’t want food to be dried out
What are on the individual cells on the ileum?
Microvilli - increases the surface area at which absorption happens so increases the rate of absorption
What are on the cell - surface membrane of epithelial cells?
Protein channels
What do epithelial cells contain a lot of?
Mitochondria - high production of ATP from respiration for active transport
Why is it useful that enzymes are embedded on the wall of the ileum?
- So they are not lost as once the ‘food’ leaves the ileum, the remnants are egested
- Allows the final hydrolysis of disomers to occur next to the ileum wall so the efficiency of absorption increases and less are lost
What is the hepatic portal vein?
Blood from the small intestine(ileum) is carried to the liver to remove excess monosaccharides, vitamins, minerals, lipids etc
What muscles surround the ileum?
Circular and longitudinal muscles - will allow peristalsis so we can propel everything along
What do capillaries that surround the ileum do?
Carry absorbed substances away
How are capillaries adapted for efficient exchange?
- One cell thick meaning there is a short diffusion pathway
- Large network so they have a large surface area so increases rate of diffusion
- Constant flow of blood which maintains concentration gradient
What are lacteal?
Responsible for carrying lipids (monoglycerides + fatty acids) which are reconstructed
What is the lymphatic system and what does it do?
- Absorbs lipids
- Used for removal of lymphatic fluids
- Carries leukocytes(WBC) - part of our immune system
- Used to make milk (more in women)
What passes into the large intestine from the ileum?
Undigested material (e.g. cellulose(fibre)) + water (+ any minerals or dissolved vitamins in water)
What happens in the colon?
- Water is absorbed via osmosis
- Water potential inside colon is higher than outside so water moved into blood via osmosis
What is stored in the rectum?
Faeces
What happens in people who are lactose intolerant?
- They don’t produce sufficient lactase so the lactose is not digested in the ileum
- This passes into the large intestine but it is too large so it is uncomfortable
- Millions of bacteria in the large intestine so produces gas
- Lactose lowers water potential of colon so less water moves out by osmosis and results in diarrhoea
What are smaller lipid droplets known as?
Bile salts
What is a micelle?
- It is what we call the fat droplets after hydrolysis has occurred
- It consists of a mono glyceride, fatty acids and bile salts
How do micelles enter epithelial cells?
They fuse with the membrane and pass through via diffusion (they can pass through the bilayer as they are lipid soluble)
This is known as endocytose
What happens to micelles when they enter the epithelial cells?
These will diffuse into the smooth endoplasmic reticulum where they will be rebuilt
What happens to the reconstructed lipids after they leave the smooth endoplasmic reticulum?
- They are passed though the Golgi
- They have proteins attached to them and form structures called chylomicrons
What happens to the chylomicrons after they leave the Golgi?
They are in transported in vesicles to the basal membrane where they are exocytosed
They diffuse into the lacteal
What happens to chylomicrons in the lacteal?
The lymph in the lacteal transports them away from the intestine
What is also absorbed from the micelles by the intestinal cells?
Fatty acids, fat soluble vitamins and sterols
