digestive system L11

Question 1

what is the Digestion ?

Answer 1

Digestion is the process during which food physicaly changes and particularly enzymaticallybreaks down to its elementary constituents (monomers) and is absorbed.

Question 2

explain the food composition ?

Answer 2

• Food that we consume consists of water, inorganic compounds, vitamins and nutrients. Inorganic substances are microelements (elements of Mendeleyev periodic table) and their compounds,
• There are 3 groups of nutrients (organic compounds):
  1- proteins,
  2-fats (lipid)
  3- carbohydrates.

Question 3

explain the stages for each group of food or compounds ( nutrients )

Answer 3

1- proteins :
- in the polymer :polypeptides
- in the Oligomer : Peptides
- in the  Monomer : Amino acids
2- Fat :
- in the polymer :Triglycerides
- in the Oligomer : - 
- in the  Monomer : Glycerol and fatty acids
3-Carbohydrate :
- in the polymer :Starch, cellulose, etc.
- in the Oligomer : Sucrose, maltose, etc.
- in the  Monomer : Glucose, fructose

Question 4

EXPLAIN the Digestion process and what the types of changes happens to the food ?

Answer 4

• Entering the digestive system, food undergoes physical and chemical changes.
  1- Under physical changes we understand division (particle size reduction), swelling and dissolution of food.
  2- Whereas under breakdown of food we understand only the chemical processing (chemical treatable), the result of which is transition of nutrients from polymer condition to monomer one. Only in the form of monomers food can be absorbed

Question 4

in which form the food can be absorbed ?

Answer 4

• Only in the form of monomers food can be absorbed.

Question 5

what is the enzyme , and explain what they do in the digestion ?

Answer 5

• An enzyme is a biological catalyst, connecting with a molecule of another substance with a view to its rendering into an active state.
• Enzymes are secreted very diverse (not necessarily secretory) cells.
• Enzymes of the digestive system are secreted into the cavity of this system. As the cavity of the digestive system opens into the external environment (by its oral and anal orifices), enzymes are excreted out. Therefore, glands of the digestive system are called exocrine glands. The enzymes of the digestive system are substances causing breaking down food polymers to monomers (which means to such active state that they can be absorbed).

Question 6

what is a catalyst mean ?

Answer 6

-meaning that it speeds up a chemical reaction , without them these reactions would take place very slowly

Question 7

why most of the enzyme there is the prefix - ase -

Answer 7

-“-ase” is. It indicates that this protein breaks down a substrate the name of which stands at the beginning of this enzyme:
protease breaks down protein, lipase breaks down lipid, maltase – maltose.

Question 8

what is the difference between enzymes and hormones ?

Answer 8

• Enzymes are Biological catalysts that increase the speed of biochemical reactions without any changes. Hormones are molecules like steroids (testosterone/estrogen) or peptides (insulin) produced by a part of an organism and send messages to other organs or tissues for cellular reactions.

Question 9

Types of digestion and explain them

Answer 9

• they are 4 :.
• 1-Autolytic digestion. Due to the enzymes present in the food. For example, an infant – breast milk. Milk quickly goes sour because it contains enzymes that break it down.
• 2-Intracellular digestion. It takes place in any cell, in its digestive vacuoles.
• 3-Cavitary digestion. This is digestion that takes place in cavities of the digestive system. For example, in the stomach under the action of gastric juice
• 4-Parietal digestion : Parietal digestion is carried out by enzymes fixed on intestinal microvilli

Question 10

explain the Parietal digestion experiment ?

Answer 10

• First described by Ugolev, Alexander Mikhailovich
• He made the following experiment. In 2 tubes he placed some nutrient, such as meat or dried fibrinogen. In both tubes intestinal juice was added. And to one tube (test-tube) scraping from the intestinal mucosa was added. It turns out that in this test-tube protein breaking down goes much faster.

Question 11

explain the Parietal digestion , ?

Answer 11

• Parietal digestion is carried out by enzymes fixed on intestinal microvilli. The entire surface of the small intestine sent microfibers is lined with microvilli which are covered by glycocalyx – mucopolysaccharide, having sticky properties
• Part of the enzymes, secreted in the intestines, ( such as Protease - peptidase produced in the Wall of ileum ) enters the intestinal cavity and participates in cavitary digestion. Another part of enzymes “sticks” to microvilli and participates in parietal digestion.

Question 12

• what is the Advantages of parietal digestion ?

Answer 12

1- Economy of enzymes.There is no loss of enzymes. Since enzymes are “glued” to the intestines, they do not leave the body with the fecal masses. And an enzyme is a protein, the body has spent a lot of his own energy to synthesize it. So it’s inefficient to loose the enzymes or their integral components.
2-. High intensity of breakdown. : In parietal digestion only microscopic bits of food squeeze through microvilli and they turn out to be surrounded by digestive enzymes.
3- High intensity of absorption: . Since intensity of breakdown is high, the intensity of absorption will be high as well.
4- . Bactericidal property. Non-indigenous micro-organisms could not squeeze between intestinal microvilli because their size is considerably smaller than that of an individual cell
. Even if a small size micro-organism turns out to be between microvilli, it will be surrounded by digestive enzymes and they will break it down (destroy).
Now it can be seen that parietal digestion prevents foreign microorganisms from outside of the digestive system from penetrating to the body’s interior medium.

Question 13

explain intensity of parietal digestion :

Answer 13

• In adult mammals and a human being the intensity of parietal digestion is above 50%. , it is more important than cavitary digestion, which accounts for less than half of nutrients intake.

Question 14

explain the Digestion in the oral cavity :

Answer 14

• Composition of saliva
  -1- Water – more than 99%.
  -2- Dry residue which is divide into :
  1- Inorganic substances : ions, bases (mainly hydrocarbonates)
  2- Organic compounds : mainly enzymes
  —– Key enzymes in saliva :
  1- amylase : Amylase breaks down polymers of sugars to disaccharides – maltose and sucrose.
  2- maltase : Maltase breaks down maltose to glucose.
  —-
• The quantity of saliva is up to 2.0 liters per 24 hours, salivary pH is weakly alkaline which is betwenen 6.2-7.6 PH
  -As food in the mouth stays a few tens of seconds, digestion under the action of salivary enzymes occurs mainly in the stomach.

Question 15

explain the Digestion in the stomach ?

Answer 15

• we have 4 types of cells in the stomach
  1-Mucocytes (mucoid cells). They secrete mucous especially abundant in the pyloric part
  2-Parietal glandulocytes (oxyntic cells). They form HCl and are located everywhere except the pyloric part
  3-(chief) glandulocytes (principal cells). They form pepsin and are mainly located in the fundus of the stomach.
  4-G-cells – endocryne cells. They produce gastrin.
  ———
• Inspite of lipase is secreted in gastric juice its functional activity is very low and must be neglected.
  -Intrinsic factor is not a part of gastric juice , Intrinsic factor is a glycoprotein secreted by parietal (humans) or chief (rodents) cells of the gastric mucosa. In humans, it has an important role in the absorption of vitamin B12 (cobalamin) in the intestine, and failure to produce or utilize intrinsic factor results in the condition called pernicious anemia.
  -Gastrin is not a part of gastric juice too. It’s a hormone

Question 16

explain Composition of gastric juice ?

Answer 16

- The quantity of gastric juice is up to 2,0 liters per 24 hours.
 its composed  of 4 substance 
1- water 
2-HCL
3-Mucus 
4-Enzymes : 
4.1-Pepsin, its inactive form – pepsinogen;
4.2-Gastricsin, a variety of pepsin;
4.3-Chemosin (rennin)
4.4-Gelatinase;
4.5-Lipase

Question 17

explain the Pepsin and gastricsin break down proteins. ?

Answer 17

• Pepsin is active at pH of gastric contents 1.5-2.0, gastricsin – at pH 3.0-4.0. Gastric medium is sour, but gastricsin is produced in greater quantities than pepsins.
• in what way acidity of the gastric medium changes?
  its happened due to Role of HCl in stomach , where Hydrochloric acid is involved in the process of digestion. It creates a medium of gastric juice acidic so that the enzyme pepsin digests the protein and kills the bacteria present in them

Question 18

explain the Chemosin ?

Answer 18

-Chemosin in the same way as pepsins, refers to proteases, but it breaks down milk protein.
–With age, the quantity of rennin reduces and it can even be absent in gastric juice.
In this case milk protein would not brake down, it comes to the large intestine, where it decomposes by putrefactive microorganisms with the formation of hydrogen sulfide, causing flatulence.

Question 19

explain the Gelatinase ?

Answer 19

• Gelatinase is a protease breaking down conjunctive tissue

Question 20

explain the HCl ?

Answer 20

• Gastric juice is the most acidic body medium about 1-2 PH
  – function of HCL :
  1- It denaturates proteins., Denaturation is a protein’s loss of its :
• quaternary
• tertiary
• and secondary structure.
  At this amino acid sequences in a protein do not change. The protein does not lose its polymeric structure, therefore denaturation is not breakdown
  2-. It creates an acidic medium and activates pepsinogen :
  Pepsin is secreted in an inactive form of pepsinogen in order not to break down stomach own mucosa in absence of food
  Activation of pepsinogen occurs under the action of hydrochloric acid. And its quantity sharply increases when food enters the stomach. pH of HCl – 1.0, gastric pH is – 1.5 – 2.0, pH of gastric contents is 2.0 and more.
  3- It has a bactericidal action. : It denaturates receptors proteins of non-indigenous microorganisms that enter abundantly into the stomach with food.
  4-It performs regulatory functions : its creates optimal acidic environment for the help the pepsin work properly

Question 21

explain the mucus ?

Answer 21

• Mucopolysaccharide: . It covers the gastric mucosa as an interlayer separates mucus from gastric juice. As in gastric juice there are no enzymes for carbohydrates, it does not break down mucus, and it does not allow proteases to contact with cells of the stomach wall.
  If secretion of mucus is broken, gastric juice begins to digest the wall of the stomach. Mucosal erosion appear at first, which has a predisposition to transfer to gastritis and then to ulcer which may, in its turn, cancerate.

Question 22

explain the Gastric functions

Answer 22

-. The function of the stomach can be divided into
1- major function:
1.1 Deposition of food.
1.2 Forming a food bolus – chymus.
1.3 Food portioning.
1.4 Primary break downing of nutrients, mainly proteins.
1.5 Regulatory function.

2- minor function:

2. 1 Digestion.
3. 2 Absorption.
4. 3 Hematopoietic.
5. 4 Regulation of blood pH.

Question 23

explain the Major functions ?

Answer 23

1-Deposit of food : temporary storage for food, which passes from the esophagus to the stomach where it is held for 2 hours or longer.
2-Forming a food bolus – chymus : food bolus in the stomach food becomes a chymus. Chymus is a pulpy mass representing a mixture of nutrients in the polymeric state which is partly broken down to oligo- and monomers, mixed with digestive juices
3-Food portioning : . It is the responsibility of a pyloric sphincter. It opens under certain conditions for a short time and passes into the duodenum a portion of food from the stomach
4-Primary processing of nutrients, mainly proteins.
5-Regulatory function.

Question 24

explain the Mainor functions ?

Answer 24

1-Absorption.: It does not practically take place in the stomach. If monomers are not formed, it means there is nothing to be absorbed. In the stomach only water and alcohol are intensely absorbed.
2-On the lesser gastric curvature there are special secretory cells, producing Castle intrinsic factor. It comes into the chymus and is needed for absorbing in the intestines Castle extrinsic factor – vitamin B12. Without vitamin B12 formation of hemoglobin is impossible. Therefore, even in total stomach removal during operations a part of it on the lesser curvature is always left. If the stomach is completely removed, hemoglobin will not be produced.
3-Regulation of blood pH. Gastric juice in the composition of the HCl contains Н+, that is why its secretion reduces Н+ content, the main acidifying factor in the blood.
4-Digestion.: mixing and breakdown of food by contraction and relaxation of the muscle layers in the stomach.

Question 25

why Pepsin is secreted in an inactive form of pepsinogen ?

Answer 25

in order not to break down stomach own mucosa in absence of food.

Question 26

what staminate HCL

Answer 26

• The parasympathetic nervous system, via the vagus nerve, and the hormone gastrin stimulate the parietal cell to produce gastric acid, both directly acting on parietal cells and indirectly, through the stimulation of the secretion of the hormone histamine from enterochromaffine-like cells (ECL).