The digestive system

Question 1

How many parts does the digestive system consit of?

Answer 1

8 different parts

Question 2

What is involved in digestion?

Answer 2

mixing of food with secretions, mechanical and chemical breakdown of molecules, transport.

Question 3

Name the processes in the digestive systems?

Answer 3

Ingestion – intake of food and beverages (~800 g solid food/1.2llq food )

Digestion: mechanical (chewing, muscle seqeezing) and chemical (enzymes)

Secretion (~7liters/day)

Propulsion/mobility – transport

Absorption

Excretion

Question 4

What happens in the mouth?

Answer 4

Mechanical treatment : chewing/mastication/oral processing.

Chemical treatment: saliva

Question 5

Describe salivary glands and saliva production.

Answer 5

Clusters of cells secrete a fluid(saliva) that contains water (99%) electrolytes, mucin and enzymes(alfa-amylase and lipase.

Saliva is produced and secreted from salivary glands.

Acidic fruit juices increases saliva production.

Higher saliva production connected with larger blood flow.

Question 6

Name some important functions of saliva.

Answer 6

Moistens and lubricates the food. Solubilisaes dry food, important for the taste. Improves dental health. Initiates starch digestion.

Question 7

How is the food transported from the mouth to the stomach?

Answer 7

Pharynx (sv: svalj) and esophagus (sv: matstrupe).

Peristaltic waves (movement of muscles in the walls of the esophagus) ~9s for a wave to reach the stomach.

Question 8

Describe peristalsis and what it does in the GI-tract.

Answer 8

Segmentation contraction - in all part of the GI-tract, especially in the small intestine.

Alternating contraction and relaxation of the longitudinal muscles in the walls of the stomach also provides effective mixing of its contents.

Is important for the disintegration of food matrix and cell walls - for an efficient uptake of nutrients by the epithelial cells the enzymes need to be adequately mixed with the food.

Question 9

What is sphicters and where can they be found?

Answer 9

Basically doors located in the opening and exit of the stomach. This to allow nothing to go up and small volume to go forward in the system instead of all at ones.

Question 10

Describe the stomach.

Answer 10

stomach or ventriculus is a muscular sac surrounded by three layers of smooth muscle. Relaxation - mediated by parasympathetic nerves.

Question 11

Why are the glands in the stomach?

Answer 11

The glands located in the wall of the fundus (top of the stomach) and body, secrete 2-3 l/day of: water, salt mucus(sv: slem) and bicarbonate, hydrochloric acid (~2 l/day), pepsinogen (chief/zymogenic cells), gastric lipase, “intristic factor” (oxyntic cells- important for uptake of B12).

Question 12

What happens in the body of the stomach?

Answer 12

The stomach starts peristalic waves in respons to food. This starts mixing of food, liquid and enzymes in the antrum (bottom of the stomach).

Persistalic waves passing over the stomach force a small amount of luminal material into the duidenum (emptying through the pyloric sphincter, a few ml each time). Distension of the stomach increase the contractions.

Question 13

How does the food form effect the digestion and satiety?

Answer 13

The physical form, volume and properties of food influences gastric emptying, intestinal transit time and nutrient uptake.

Ex: orange juice - least satiety effect, hungry faster

Ex: bread - comes next, starch easily digested

Ex: oatmeal porridge - viscous product can differ between ppl if it satiety

Ex: Stew: protein takes more time to digest so will take the longest

Question 14

What is the effect of solid vs liquid food on gastric emptying?

Answer 14

The larger a meal, the faster stomach emptying initially. - Depends on the total volume.

Liquid emptying begins instantly in an exponential fashion, whereas the linear solid emptying begins after lag phase.

Question 15

What are the parts of the small intestine and there lengths?

Answer 15

Duodenum 25cm
Jejunum 1~(2)m
Ileum 2~(4)m

Question 16

What is secreted in the liver and what does the gallbladder due?

Answer 16

bile (sv galla): bicarbonate - neutralize acid, cholesterol, phospholipids. bile salt - solubilize fat.

gallbladder - concentrates the bile

Question 17

What is secreted in the pancreas (sv: bukspottskörteln)?

Answer 17

bicarbonate - neutralize the chymus

proteases, amylase and lipases

Question 18

What is the main job of the small intenstine?

Answer 18

To absorbed and transport nutrients.

Question 19

What is the structure of the gastrointestinal wall?

Answer 19

The intestine wall consist of folds called villi. On the villi there is multiple microville and inside the villi there are blood vessels.

The microvilli has a brush border cells with capillaries inside.

The entire epithelium of the small intestine is replace approx every 5 days.

Question 20

How many villis and microvillis can be found?

Answer 20

~20-40 villis/mm2

~2000-4000 cells/microvilli

Question 21

Where does the vitamin end up?

Answer 21

the lactela (branch of lymphatic system) contains lipid-soluble nutrients

Blood leaving the capillaries contains water-soluble nutrients

Question 22

How is starch digested in the stomach?

Answer 22

Starch is digested by alfa-amylase from saliva and pancreas to oligosaccharides, tri- and disaccharide. This is by enzymes (intestinal brush border enzymes, e.g. lactose, glucoamylase). Degraded to monosaccharides.

Question 23

How is protein digested in the stomach?

Answer 23

Protein is degraded by HCl to denatureted protein. With pepsinogen -> pepsin degrade to polypeptides.

Question 24

How is protein digested in the small intestine?

Answer 24

Trypsinogene is degraded by enteropeptidas to trypsin. Trypsin is used to degrade chymotrypsinogen to chymotrypsin, procarbicypeptidase to carbocypeptidase, proelastase to elastase.

All these are used to degrade protein to either free amino acids and/or oligopeptides that is degraded by peptidaaes (brush border enzymes) to tri and dipeptides and free amino acids. A number of amino acids (but not all) are co-transported into the luminal side of the epithelial cells with sodium via secondary active transport - there are a number of different amino acid transporters.

Question 25

How is fat digested?

Answer 25

Triglycerides, cholesterolsesters, phospholipids is degraded to lipases to monoglycerides, glycerol, FFA, phospholipids.

Most lipids digestion occurs in the duodenum.

Question 26

What does the large intestine consist of?

Answer 26

Cecum (sv: blindtarmen), the appendix (thing on the cecum), colon.

Question 27

Describe the colon.

Answer 27

The colon - the ascending, the transverse and the descending. Think about the colon as a square without bottom.

Certain B-vitamin complex and vitamin K are produced by bacteria (and absorbed in the large intestine).

Processes undigested material (fiber), stores waste before its eliminated.

Question 28

What does the large intestine do?

Answer 28

The large intestine has no villi but approx 1-3 kg bacteria that: produces enzymes, ferment carbohydrates and produce volatil compounds (CO2, CH4, H2, H2S, acetate, butyrate and propionate)

Question 29

How is the digestive process controlled?

Answer 29

Sight, smell, taste or thought of food initiate a salivary respons.(peptides AA)

Question 30

Describe the control of the gastric acid secretion.

Answer 30

Regulation of acid: when food enters, strech receptors are activated. Histamine released in respons to food in the stomach. Gastrin production is stimulated by digestion products peptides a.a. caffeine) High acid conc

Question 31

How long does food stay in my stomach?

Answer 31

Estimates of average transit times, there is a high variability among individuals and after different meals.

50% of stomach contents emptied 2.5 to 3 hours
Total emptying of the stomach 4 to 5 hours

50% emptying of the small intestine 2.5 to 3 hours

Transit through the colon 30 to 40 hours.