Water is taken into the body through drinking and eating. Water is absorbed in the large and small intestines, along with other substances. In the small intestine, the high efficiency of water absorption is ensured not only by the huge total surface of the intestinal mucosa, but also by the conjugation of absorption and hydrolysis processes on the enterocyte membrane. In ensuring absorption, the intensity of lymph flow and blood flow in the villi covering the intestinal walls, as well as their reduction, is of some importance. When the villi contract, the lymphatic capillaries inside them contract, which contribute to the outflow of lymph. The suction action, which facilitates suction, is created by spreading the villi. Intestinal peristalsis promotes absorption, as this results in an increase in intracavitary pressure, which contributes to an increase in filtration pressure.
The process of digestion leads to a sharp increase in the blood supply to the intestinal mucosa. So through the mucous membranes outside the meal passes up to two hundred milliliters of blood per minute, and at the height of digestion - five hundred to six hundred milliliters of blood per minute. Increased blood circulation fills the enterocytes with energy, which is used for the active absorption of carbohydrates, ions and other compounds. Also, abundant blood flow maintains the concentration of water and substances between the flowing blood and the intercellular contents of the villi. The mechanisms of diffusion, passive osmosis and active energy-dependent transport provide absorption. Up to ten liters of water pass through the digestive tract per day - six to seven comes with digestive juice, two or three - with food.
Most of the water is absorbed in the small intestine (its upper sections), one hundred to one hundred and fifty milliliters of water is excreted in the feces.
Throughout the intestine, the osmotic pressure of the plasma is almost always equal to the osmotic pressure of the dietary chyme. The absorption of water is facilitated by the simultaneous absorption of mineral salts, amino acids and carbohydrates. Water along the osmotic gradient penetrates quite easily in both directions. Water-soluble vitamins are absorbed along with water. Factors that disrupt the absorption of nutrients lead to the fact that the body's water metabolism is also difficult.
Ions Cl ~ and Na + play a decisive role in the transfer of water through intercellular spaces and membranes. Na + is actively absorbed from the intestinal cavity. It is followed by the flow of HCO3 and C1~ ions along the electrochemical gradient. The exchange diffusion of SG to HCO3 and Na+ to K+ also occurs in the intestine.
Water imbalance in the body occurs as a result of fluid loss due to diarrhea and vomiting. With profuse diarrhea, tens of liters of water can be lost, with simple diarrhea and vomiting - several liters. Therapeutic measures that are aimed at eliminating the disease should be accompanied by the restoration of the electrolyte and water balance of the body.
When chewing food, a person moves it in the oral cavity with the help of the tongue (with the help of receptors of which we feel the taste, mechanical properties and temperature of food). In the oral cavity are the teeth necessary for the mechanical grinding of food in the process of chewing. The finer the food is crushed in the mouth, the better prepared it is for processing by digestive enzymes.
In the mouth, food is moistened with saliva, which is secreted by the salivary glands. Saliva 98-99% consists of water.
- enzymes that break down complex carbohydrates into simple carbohydrates ptyalin breaks down starch into an intermediate product that another enzyme maltase converts to glucose).
- substance mucin, which makes the food bolus slippery;
- lysozyme- a bactericidal substance that partially disinfects food from bacteria that enter the oral cavity and heals damage to the oral mucosa.
Poorly chewed food impedes the work of the digestive glands and contributes to the development of stomach diseases.
From the oral cavity, the food bolus passes into throat and then pushed into the esophagus.
Food moves through the esophagus thanks to peristalsis- wave-like contractions of the muscles of the esophagus wall.
Mucus, which is produced by the glands of the esophagus, facilitates the passage of food.
Digestion in the stomach
Proteins and some fats (for example, milk fat) begin to be digested in the stomach.
For some time, saliva enzymes that digest sugars continue to act in the food bolus, and then the food bolus is saturated with gastric juice and proteins are digested in it under the action of gastric juice.
An important feature and condition for effective digestion in the stomach is acidic environment(because gastric juice enzymes act on proteins only at body temperature and in an acidic environment).
Gastric juice is acidic. Hydrochloric acid, which is part of it, activates the enzyme of gastric juice - pepsin, causes swelling and denaturation (destruction) of proteins and contributes to their subsequent cleavage to amino acids.
In the process of digestion of food, the walls of the stomach contract slowly (peristalsis of the stomach), mixing food with gastric juice.
Depending on the composition and volume of food eaten, its stay in the stomach lasts from 3 to 10 hours. After treatment with enzymes of gastric juice, food masses pass in portions from the stomach to the duodenum (the initial section of the small intestine) through an opening surrounded by sphincters.
Digestion in the small intestine
The most important processes of digestion of food occur in the duodenum. Digestion occurs both in the intestinal cavity (abdominal) and on cell membranes (parietal), which form a huge number of villi lining the small intestine.
In the process of digestion, which begins in the oral cavity and ends in the small intestine, food experiences the action of enzymes and prepares for absorption (absorption is the penetration of substances from the digestive tract into the internal environment of the body - blood and lymph).
Suction device.
In infants, absorption occurs in the stomach and intestines, which have a dense network of blood and lymph vessels. With age, absorption in the stomach decreases, but in 8-10-year-old children it is still well manifested. In adults, only alcohol is well absorbed in the stomach, less water and mineral salts. The main site of absorption of nutrients is the small intestine, which has a special suction apparatus in the form of intestinal villi.
Intestinal villi are microscopic outgrowths of the mucous membrane of the small intestine, the total number of which reaches 4 million. Externally, the villus is covered with a single-layer epithelium, and its cavity is filled with a network of blood and lymphatic vessels. The height of the villi is 0.2-1 mm. There are up to 40 villi per 1 mm 2 of the mucous membrane of the small intestine. Due to this structure, the inner surface of the small intestine reaches 4-5 square meters, that is, approximately twice the surface of the body.
The decay products of nutrients in the intestinal cavity are fenced off from the blood and lymph by a very thin membrane. It consists of a single-layer epithelium of the villi and a layer of cells of the capillary wall. The large surface of the small intestine and the thinness of the membrane through which absorption occurs greatly facilitate and speed up this process.
suction mechanism.
Absorption in the digestive tract is the process of transferring the products of digestion from the cavity of the gastrointestinal tract through the living cells of the villi, the walls of the capillaries and the walls of the lymphatic vessels into the blood and lymph. In this complex physiological process, there are mainly two mechanisms: filtration and diffusion. However, the transition of the breakdown products of nutrients from the intestines into the blood and lymph cannot be explained by the physical laws of filtration and diffusion alone.
Thus, it has been proven that the epithelium of the intestinal villus has one-sided permeability, that is, it allows many substances to pass only in one direction - from the intestines to the blood. The second feature of the villi is their permeability only for some, and not for all substances. Finally, it has been established that glycerol and fatty acids, passing through the wall of the villus, are synthesized and form fats. All this indicates that absorption is a physiological process, which is determined by the active activity of the cells of the intestinal epithelium.
Absorption is also facilitated by the contraction of the villi, in the walls of which there are smooth muscle fibers running from the base of the villus to its top. When these fibers contract, the villus also contracts, squeezing the lymph out of itself into the lymphatic vessels of the intestinal wall. The return of fluid to the villi is prevented by the valves of the lymphatic vessels.
Therefore, when the muscle fibers are relaxed, the pressure of the lymph decreases, and this contributes to the passage of nutrients from the intestinal cavity to the lymphatic vessels of the villi. Periodically repeating, the contraction and relaxation of the muscle fibers of the villi turn it into a constantly acting suction pump. There are many such villus pumps; they create a powerful force that promotes the flow of cleavage products into the lymph.
Absorption of carbohydrates.
Carbohydrates are broken down into monosaccharides during digestion. Of the carbohydrates, only fiber (cellulose) remains undigested. Carbohydrates are absorbed mainly in the form of glucose and partly in the form of other monosaccharides (fructose, galactose). The absorption of carbohydrates is stimulated by vitamins of groups B and C. Having been absorbed, carbohydrates enter the blood of the capillaries of the villus and, together with the blood flowing from the small intestine, enter the portal vein, from which blood enters the liver.
If there is more than 0.12% glucose in this blood, then excess glucose is retained in the liver and converted into a complex carbohydrate - glycogen (animal starch), which is deposited in the liver cells. When blood glucose is less than 0.12%, the glycogen deposited in the liver is converted into glucose and released into the blood. Glycogen can also be stored in muscles.
The conversion of glucose into glycogen is facilitated by insulin, a hormone produced by the pancreas. The reverse process of converting glycogen to glucose occurs under the action of the adrenal hormone - adrenaline. Insulin and adrenaline are products of endocrine glands and enter the liver with blood.
Absorption of proteins.
Proteins in the small intestine are broken down into amino acids, which in a dissolved state are easily absorbed by the villi. Like carbohydrates, amino acids are absorbed into the blood through the walls of the venous capillary network of villi.
Absorption of fats.
Fat is broken down into glycerol and fatty acids by bile and the enzyme lipase. Glycerin is soluble and easily absorbed, while fatty acids are insoluble in water and therefore cannot be absorbed. Bile delivers a large amount of alkali to the small intestine. Fatty acids interact with alkali and form soaps (salts of fatty acids), which dissolve in an acidic environment in the presence of bile acids and are easily absorbed.
But, unlike amino acids and glucose, the products of fat breakdown are not absorbed into the blood, but into the lymph, while glycerin and soaps recombine during the passage of the villus cells and form the so-called neutral fat. Therefore, droplets of newly synthesized fat, and not glycerol and fatty acids, enter the lymphatic vessels of the villi.
Absorption of water and salts.
Water absorption begins in the stomach, but mainly occurs in the small intestine and ends in the large intestine. Some mineral salts dissolved in water are absorbed into the blood unchanged. Calcium salts are absorbed in combination with fatty acids. Salts are absorbed both in the small and in the large intestine.
Protective (barrier) function of the liver.
During digestion, toxic substances are formed in the intestines. Especially a lot of them are formed in the large intestine, where, under the influence of bacteria, undigested proteins rot. The resulting toxic substances (indole, skatole, phenol, etc.) are absorbed by the walls of the colon and enter the bloodstream.
But they do not poison the body, since all the blood that flows from the stomach, intestines, spleen and pancreas is collected in the portal vein and through it to the liver, in which toxic substances are neutralized. In the liver, the portal vein breaks up into a network of capillaries that gather into the hepatic vein. So, the blood, flowing from the abdominal organs, enters the general bloodstream only after passing through the liver.
The human digestive system:
- oral cavity
- pharynx
- esophagus
- stomach
- small intestine (begins in the duodenum)
- large intestine (begins with the caecum, ends with the rectum)
Digestion of nutrients occurs with the help of enzymes:
- amylase(in saliva, pancreatic and intestinal juice) digests starch to glucose
- lipase(in gastric, pancreatic and intestinal juice) digests fats to glycerol and fatty acids
- pepsin- (in gastric juice) digests proteins to amino acids in an acidic environment
- trypsin- (in pancreatic and intestinal juice) digests proteins to amino acids in an alkaline environment
- secretes bile, which does not contain enzymes, but emulsifies fats (breaks them into small droplets), and also stimulates the work of enzymes, intestinal motility and suppresses putrefactive bacteria
- performs a barrier function (purifies the blood of harmful substances obtained during digestion).
In the oral cavity saliva containing amylase is secreted.
in the stomach- gastric juice containing pepsin and lipase.
Into the small intestine secreted intestinal juice, pancreatic juice (both contain amylase, lipase, trypsin), and bile. In the small intestine, digestion is completed (the final digestion of substances occurs due to parietal digestion) and the absorption of digestion products occurs. To increase the suction surface, the small intestine is lined with villi on the inside. Amino acids and glucose are absorbed into the blood, glycerol and fatty acids into the lymph.
In the large intestine water is absorbed, and bacteria (for example, E. coli) live. Bacteria feed on plant fiber (cellulose), supply vitamins E and K to humans, and also prevent other, more dangerous bacteria from multiplying in the intestines.
List the organs of the digestive system in order, starting with the large intestine. Write down the corresponding sequence of numbers.
1) pharynx
2) oral cavity
3) large intestine
4) small intestine
5) stomach
6) esophagus
Answer
1. Choose three options. What features are characteristic of the structure and functions of the human small intestine?
1) provides absorption of nutrients
2) performs a barrier role
3) the mucous membrane does not have outgrowths - villi
4) includes the duodenum
5) secretes bile
6) provides parietal digestion
Answer
2. Choose three correct answers from six and write down the numbers under which they are indicated. What are the characteristics of the human small intestine?
1) the longest part of the digestive tube
2) includes the duodenum
3) absorption of the bulk of nutrients occurs
4) the main absorption of water occurs
5) fiber is broken down
6) fecal masses are formed
Answer
3. Choose three correct answers out of six and write down the numbers under which they are indicated in the table. Processes take place in the human small intestine.
1) production of pancreatic juice
2) water suction
3) glucose absorption
4) fiber breakdown
5) protein breakdown
6) absorption through the villi
Answer
Choose one, the most correct option. In what part of the human intestine does the breakdown of plant fiber occur?
1) duodenum
2) large intestine
3) small intestine
4) caecum
Answer
Choose one, the most correct option. What role does bile play in digestion?
1) breaks down fats into glycerol and fatty acids
2) activates enzymes, emulsifies fats
3) breaks down carbohydrates into carbon dioxide and water
4) Accelerates the process of water absorption
Answer
Choose one, the most correct option. The vestige of the caecum in the human body is located between the small intestine and
1) duodenal
2) thick
3) stomach
4) straight
Answer
Choose one, the most correct option. Bile is produced in
1) gallbladder
2) glands of the stomach
3) liver cells
4) pancreas
Answer
Choose one, the most correct option. The breakdown of fiber with the participation of microorganisms in humans occurs in
1) duodenum
2) caecum
3) large intestine
4) small intestine
Answer
Choose one, the most correct option. In the human body, it facilitates the breakdown of fats, enhances intestinal motility
1) insulin
2) hydrochloric acid
3) bile
4) pancreatic juice
Answer
Choose one, the most correct option. In which part of the human alimentary canal is most of the water absorbed?
1) stomach
2) esophagus
3) small intestine
4) large intestine
Answer
Choose one, the most correct option. B vitamins are synthesized by symbiont bacteria in
1) liver
2) stomach
3) small intestine
4) large intestine
Answer
1. Establish the sequence of processes occurring in the human digestive system during the digestion of food. Write down the corresponding sequence of numbers.
1) intense water absorption
2) swelling and partial breakdown of proteins
3) the beginning of the breakdown of starch
4) absorption of amino acids and glucose into the blood
5) splitting of all food biopolymers to monomers
Answer
2. Establish the sequence of digestion processes
1) absorption of amino acids and glucose
2) mechanical grinding of food
3) bile processing and lipid breakdown
4) absorption of water and mineral salts
5) food processing with hydrochloric acid and protein breakdown
Answer
3. Establish a sequence of changes that occur with food in the human body as it passes through the digestive canal. Write down the corresponding sequence of numbers.
1) processing of the food bolus with bile
2) cleavage of proteins under the action of pepsin
3) breakdown of starch by salivary amylase
4) absorption of water and the formation of feces
5) absorption of cleavage products into the blood
Answer
4. Set the sequence of stages of the process of digestion in the human body. Write down the corresponding sequence of numbers.
1) the entry of monomers into the blood and fats into the lymph
2) the breakdown of starch into simple carbohydrates
3) breakdown of proteins to peptides and amino acids
4) removing undigested food from the body
5) the breakdown of fiber to glucose
Answer
5. Establish the sequence of processes occurring in the human digestive system during the digestion of food. Write down the corresponding sequence of numbers.
1) entry of bile into the duodenum
2) cleavage of proteins under the action of pepsin
3) the beginning of the breakdown of starch
4) absorption of fats into the lymph
5) the flow of feces into the rectum
Answer
6. Set the sequence of processes occurring in the human digestive system. Write down the corresponding sequence of numbers.
1) breakdown of carbohydrates by salivary amylase
2) breakdown of fats by pancreatic lipase
3) active absorption of amino acids, glucose, glycerol and fatty acids
4) emulsification of fats by bile
5) cleavage of proteins by pepsin
6) fiber breakdown
Answer
COLLECTING 7:
1) final water suction
2) digestion of proteins by trypsin
Choose three correct answers from six and write down the numbers under which they are indicated. What are the functions of the digestive system in the human body?
1) protective
2) mechanical processing of food
3) removal of liquid metabolic products
4) transport of nutrients to body cells
5) absorption of nutrients into the blood and lymph
6) chemical breakdown of food organic matter
Answer
Determine the sequence of movement of food that enters the human digestive system. Write down the corresponding sequence of numbers.
1) duodenum
2) throat
3) esophagus
4) rectum
5) stomach
6) large intestine
Answer
Determine the correct sequence of events that occur in the metabolism of carbohydrates in the human body, starting with the entry of food into the oral cavity. Write down the corresponding sequence of numbers.
1) Oxidation of sugars in cells to carbon dioxide and water
2) Entry of sugars into tissues
3) Absorption of sugars in the small intestine and their entry into the blood
4) The beginning of the breakdown of polysaccharides in the oral cavity
5) The final breakdown of carbohydrates into monosaccharides in the duodenum
6) Removal of water and carbon dioxide from the body
Answer
1. Establish the sequence of protein metabolism in the human body, starting with their intake with food. Write down the corresponding sequence of numbers.
1) oxidation with the formation of ATP, carbon dioxide, water, urea
2) formation of peptides under the action of pepsin
3) synthesis of myosin, casein
4) food proteins
5) the formation of amino acids under the action of trypsin
Answer
2. Establish the correct sequence of protein digestion, starting with their entry into the oral cavity with food. Write down the corresponding sequence of numbers.
1) mechanical grinding and wetting
2) the entry of amino acids into the blood
3) cleavage into peptides in an acidic environment
4) cleavage of peptides to amino acids using trypsin
5) entry of the food bolus into the duodenum
Answer
1. Establish a correspondence between the features and sections of the human intestine: 1) thin, 2) thick. Write the numbers 1 and 2 in the correct order.
A) there are bacteria that synthesize vitamins
B) absorption of nutrients
C) all food groups are digested
D) movement of undigested food debris
D) The length is 5-6m
E) the mucous membrane forms villi
Answer
2. Establish a correspondence between the characteristics and sections of the intestine: 1) thin, 2) thick. Write down the numbers 1 and 2 in the order corresponding to the letters.
A) absorption of the bulk of the water
B) intensive absorption of glucose and amino acids
C) the breakdown of fiber by bacteria
D) emulsification of fats with the participation of bile
D) the formation of feces
Answer
Establish a correspondence between the process of digestion in humans and the organ of the digestive system in which it occurs: 1) stomach, 2) small intestine, 3) large intestine. Write down the numbers 1-3 in the order corresponding to the letters.
A) There is a final splitting of fats.
B) Digestion of proteins begins.
C) Digestion of fiber occurs.
D) The food mass is processed by bile and pancreatic juice.
D) There is an intensive absorption of nutrients.
Answer
Establish a correspondence between the functions and organs of the human digestive system: 1) oral cavity, 2) stomach, 3) large intestine. Write down the numbers 1-3 in the order corresponding to the letters.
A) absorption of the bulk of the water
B) the breakdown of fiber
B) protein breakdown
D) the initial breakdown of starch
D) the formation of a food bolus
E) synthesis of B vitamins by symbiont bacteria
Answer
Choose three options. What positive role does the microflora of the large intestine play in the human body?
1) activates enzymes of intestinal juice
2) synthesizes vitamins
3) participates in the digestion of fiber
4) destroys blood cells
5) inhibits the development of putrefactive bacteria
6) enhances the contraction of the intestinal walls
Answer
Choose three correct answers from six and write down the numbers under which they are indicated. The large intestine and its microflora provide
1) activation of pancreatic enzymes
2) synthesis of vitamins E, K and group B and other biologically active substances
3) breakdown of proteins, fats and carbohydrates
4) absorption of amino acids, glucose, glycerol and fatty acids into the blood or lymph
5) maintaining water and mineral balance in the body
6) immune and competitive protection against pathogenic microbes
Answer
Establish a correspondence between the characteristics and organs of the human digestive system: 1) stomach, 2) liver, 3) pancreas. Write down the numbers 1-3 in the order corresponding to the letters.
A) produces mucus, enzymes and hydrochloric acid
B) is the largest gland in the body
B) is a gland of mixed secretion
D) performs a barrier function on the way of blood flow
D) provides the initial cleavage of proteins
Answer
Establish a correspondence between the structural features and the human digestive organs: 1) stomach, 2) pancreas
A) The organ has exocrine and intrasecretory parts.
B) The walls consist of three layers.
C) The hollow organ is lined with glandular epithelium.
D) The mucous membrane has glands that secrete enzymes and acid.
D) The organ has ducts that open into the duodenum.
Answer
Choose three correct answers from six and write down the numbers under which they are indicated. What are the functions of bile in the human body?
1) provides a barrier function
2) activates the enzymes of pancreatic juice
3) crushes fats into small drops, increasing the area of contact with enzymes
4) contains enzymes that break down fats, carbohydrates and proteins
5) stimulates intestinal peristalsis
6) provides water suction
Answer
Read the text below with a number of words missing. For each letter, select a term from the list. “Nutritional absorption occurs in (A), which are located in (B). The surface of each villus is covered (C), under which are located the blood vessels and (D). The cleavage products of starch (D) and proteins (E) enter the blood vessels. The cleavage products of fats are converted in the cells of the epithelium of the villi into fats characteristic of this organism.
1) villi
2) glucose
3) stratified epithelium
4) large intestine
5) amino acids
6) lymphatic vessel
7) single layer epithelium
8) small intestine
Answer
1. Establish a correspondence between the processes and departments of the digestive system: 1) small intestine, 2) stomach. Write down the numbers 1 and 2 in the order corresponding to the letters.
A) cleavage of peptides to amino acids using trypsin
B) the breakdown of carbohydrates to monosaccharides with the help of amylase
C) cleavage of proteins to short peptides using pepsin
D) secretion of juice containing hydrochloric acid
E) emulsification of lipids by bile acids
E) absorption of amino acids, glycerol, fatty acids, glucose
Answer
2. Establish a correspondence between the processes and human organs: 1) stomach, 2) small intestine. Write down the numbers 1 and 2 in the order corresponding to the letters.
A) absorption of most nutrients
B) neutralization of food from bacteria
B) denaturation and swelling of proteins
D) splitting of the bulk of proteins, lipids, carbohydrates
D) parietal digestion
Answer
© D.V. Pozdnyakov, 2009-2019
Absorption of various substances in the small intestine
Absorption of water and mineral salts. Water enters the digestive tract as part of food and drinking liquids (2-2.5 l), secrets of the digestive glands (6-7 l), but 100-150 ml of water is excreted with feces. The rest of the water is absorbed from the digestive tract into the blood, a small amount - into the lymph. Water absorption begins in the stomach, but it occurs most intensively in the small and especially the large intestine (about 8 liters per day).
Some water is absorbed along the osmotic gradient, although water is also absorbed in the absence of a difference in osmotic pressure. The main amount of water is absorbed from isotonic solutions of intestinal chyme, since hyper- and hypotonic solutions are quickly concentrated or diluted in the intestine. The absorption of water from isotonic and hypertonic solutions requires energy. Dissolved substances actively absorbed by epitheliocytes “pull” water along with them. The decisive role in the transfer of water belongs to ions, especially Na +, therefore, all the factors affecting its transport also change the absorption of water.
Due to the energy released in the small intestine during glycolysis and oxidative processes, water absorption is enhanced. The most intensive absorption of sodium and water in the intestine is carried out at pH 6.8 (at pH 3, water absorption stops).
Change the absorption of water diets. An increase in the proportion of protein in it increases the rate of absorption of water, sodium and chlorine.
The rate of water absorption varies depending on the hydration of the body. Anesthesia (with ether and chloroform), as well as vagotomy, slow down the absorption of water. A conditioned reflex change in water absorption has been proven. Its absorption is influenced by many hormones of the endocrine glands and some gastrointestinal hormones (gastrin, secretin, CCK, VIP, bombesin, serotonin reduce the absorption of water).
Sodium enters from the cavity of the small intestine into the blood both through intestinal epitheliocytes and through intercellular channels. The flow of Na + ions into the epitheliocyte occurs along the electrochemical gradient in a passive way. . In the small intestine, the transfers of Na+ and C1- ions are conjugated with each other; in the large intestine, the absorbed Na+ ion is exchanged for the K+ ion. With a decrease in the content of sodium in the body, its absorption by the intestine increases sharply. Potassium absorption occurs mainly in the small intestine through the mechanisms of active and passive transport along an electrochemical gradient. The absorption of chloride ions occurs in the stomach and is most active in the ileum by the type of active and passive transport. Doubly charged ions in the digestive tract are absorbed very slowly. Thus, 35 mmol of calcium enters the human intestine daily, but only half of it is absorbed. It is absorbed 50 times slower than the Na ion, but faster than the doubly charged iron, zinc, and manganese ions. Calcium absorption is carried out with the participation of carriers, activated by bile acids and vitamin D, pancreatic juice, some amino acids, sodium, and some antibiotics.