6. The digestive system

Question 1

What is the digestive system?

Answer 1

In the digestive system we can find: mouth, esophagus, stomach, pancreas, liver, gallbladder, small intestine, large intestine, anus

Question 2

What is involved in the digestion process?

Answer 2

• mixing of food with secretions
• mechanical and chemical breakdown of molecules
• transport

Question 3

Which are the different steps in the digestion?

Answer 3

1. ingestion (800 g/1.2 L of food and drinks)
2. Digestion (mechanical and chemical)
3. Secretion
4. Propulsion/motility
5. absorption
6. Excretion

Question 4

What happens in the mouth?

Answer 4

Mechanical: Chewing/mastication
Chemical: Saliva is produced (water 99%-electrolytes, mucin and enzyme)
mucin is important for lubrication and to keep everything together

Question 5

Which are the function of saliva?

Answer 5

• moistens and lubricates the food
• solubilises dry food
• improves dental health
• initiates starch digestion

Question 6

What happens from mouth to stomach?

Answer 6

Pharynx and esophagus 9 m
Peristalsis help the food to reach stomach: In all parts of digestive tract especially the small intestine
It is not only for moving the food but also for mixing it is important for the uptake of nutrients (disintegration of food matrix and cell walls)

Question 7

Describe what happens in the stomach

Answer 7

The stomach is a muscle surronded by 3 layers of smooth muscle, can contain 1.5- 2 l when we eat.
Glands located in the fundus (upper part) secrete 2-3 l a day of:
water, salt, HCl, mucus and bicarbonate, Pepsinogen, gastric lipase, intrinsic factor
bolus is transformed into chymus
Then the food pass into the duodenum through pyloric sphincter

Question 8

Describe how the consistence of food influence satiety

Answer 8

the larger a meal, the faster stomach empty initially, solid meal are digest after a lag phase not like liquids that start to be digested subito

Question 9

Small intestine, pancreas and liver:

Answer 9

the gut microbiota is mainly in the Ileum, pancreas excrete bicarbonate to neutralize the pH of the chymus otherwise the enzyme will not work
liver excrete the bile
pancreas bicarbonate, proteases, amylases, lipases

Question 10

Describe the funcion of gastrointestinal wall:

Answer 10

Where the nutrient are absorbed:
the laectal contains lipid soluble nutrients and the blood contain the water soluble nutrients

The surface area of the gut mucosa is 30-40 m2

Question 11

Describe digestion of starch:

Answer 11

starch –> (amylases from saliva and pancreas) oligosaccharides –> (anzyme in microvilli) monosaccharides

Question 12

digestion of protein:

Answer 12

In stomach:
protein (HCl) –> denaturated proteins (pepsinogen) –> polypeptides

small intestine:
proteins –> oligopeptides + free aminoacids

Question 13

digestion of fat:

Answer 13

tryglycerides –> (lipases) monoglycerides, glycerol, free fatty acids, phospholipds

Question 14

what are the function of the colon?

Answer 14

• reabsorb water and maintain fluid balance
• Certain vitamin B and K are produced by bacteria
• processes undigested material (fibre)
• store waste before eliminate

1.2 kg of bacteria that produces enzymes and ferment carbohydrates ( CO2, CH4, H2S…)

Question 15

How is the digestive system controlled?

Answer 15

smell,taste (signal) –> stretch receptor are activated –> histamine –> gastrin is stimulated by digestion products –> High acid concentration

Gastrin can be switched off by somatostatin

Question 16

Time in the digestion

Answer 16

2.5-3 hours in stomach, 4-5 hours before the stomach is totally empty- 2.5-3 hours 50 % empty small intestine
30-40 hours through the colon