Digestion Flashcards
What layers does the stomach have?
- mucosa
- submucosa
- muscularis
- serosa
What is the in the mucosa layer of the stomach?
Epithelium, lamina propria and muscularis mucosa
What is the in the submucosa layer of the stomach?
Blood vessels
What is the in the muscular layer of the stomach?
oblique, circular and longitudinal
How do carbohydrates enter the digestive system?
Disaccharides and polysaccharides
How are carbohydrates absorbed?
Monosaccharides
What are polysaccharides?
These are long chains of monosaccharides. Examples are starch and glycogen. Food examples are oats, legumes and beans.
What are disaccharides?
These are two monosaccharides joined. These include maltose, sucrose and lactose. Food examples can be seen in the dairy foods.
Give some examples of monosaccharides
Glucose, Fructose, pentose and galactose
What is the first enzyme involved in carbohydrate digestion?
Salivary amylase and this breaks down alpha-1,4-glycosid bonds. This enzyme will break done polysaccharides into monosaccharide and disaccharides.
What is the function of pancreatic amylase?
This has the same function as salivary amylase.
What is the function of disaccharidases?
These are brush-border enzymes that are responsible for converting disaccharides into monosaccharides.
Examples include
- Maltase: breaks down maltose into glucose
- Sucrase: sucrose into glucose and fructose
- Lactase: lactose into glucose and galactose
What are the three ways in which monosaccharides can be absorbed?
- passive diffusion (high to low with no energy)
- facilitated diffusion (high to low with carrier protien)
- active transport (low to high with ATP and carrier protein)
What are the transporters for glucose?
Sodium dependant and sodium independent
Explain how Sodium dependant transporters of glucose work
Sodium binds to a receptor and causes a shape change, allowing glucose to bind. Sodium and glucose are then transported through. They both go into the proximal cell.
Sodium is then pumped out by ATP via the sodium/potassium pump and glucose will diffuse into the interstitum down its concentration gradient.
Why can glucose not diffuse through the membrane by itself?
It is a polar molecule
Explain how Sodium independent transporters of glucose work
This is facilitated diffusion. Examples include GLUT1, GLUT2, GLUT5.
Where does protien digestion start?
Stomach
What chemical starts off the process of protien digestion?
Pepsin. Pepsinogen is activated by HCL.
What four enzymes are secreted by pancreatic juice and that are involved in protien digestion?
Trypsinogen
Proelastase
Carboxypeptidase
Chymotrypsinogen
How is Trypsinogen activated and what affect does this have on the other enzymes?
This is activated by enterokinase on the border of the duodenum. This will then cause the activation of the other zymogens.
What do the following break down in protien? Trypsinogen Proelastase Carboxypeptidase Chymotrypsinogen
These form small polypeptides and dipeptides.
What enzymes complete protein digestion and what are some examples?
- dipeptidases: hydrolyses dipeptides
- aminopeptidases: hydrolyses at amino end
- tripeptidases: acts on tripeptides
How are amino acids absorbed?
Amino acids are absorbed via a Sodium cotransporter, in a similar mechanism to the monosaccharides. They are then transported across the basolateral membrane via facilitated diffusion. Di and tripeptides are absorbed via separate H+ dependent cotransporters and once inside the cell are hydrolysed to amino acids.
