Iron is an organ of the human body that produces a biologically active substance of a certain type. All glands in the body support humoral immunity and are combined into 3 large groups: glands of internal and external secretion and mixed glands. The humoral system as a whole provides all the vital functions of the body - growth and development, regulation of emotional and mental health, reproductive function, metabolic processes, etc.
Gland difference
The endocrine glands, or internal secretions, without excretory ducts secrete their products directly into the blood. These glands include: the hypothalamus, pituitary gland, thyroid gland, adrenal glands, parathyroid glands. The glands of internal, external and mixed secretion make up the humoral status of the body.
Glands of external secretion, or exocrine, have their own excretory ducts on the surface of the skin or in the body cavity. These include sweat, lacrimal, sebaceous, salivary glands, gall bladder, glands of the intestine and stomach. To the question of which secretion the liver belongs to, according to many sources, the answer is: external.
Glands of mixed secretion have the ability to excrete their products both in the body cavity and in the blood. According to the classical distribution, they include the pancreas and gonads.
Mixed secretion
If we talk about mixed secretion, then by many indicators the liver can be attributed to the representatives of this group. So, according to many researchers, the liver is an iron of mixed secretion. Why? Because in addition to participating in digestion, etc., it is capable of synthesizing certain hormones, i.e., it becomes endocrine for a while.
Hormone-synthesizing liver function
The liver produces the following hormones:
- IGF-1;
- angiotensin;
- thrombopoietin;
- hepsidin.
Another remark: although the liver performs some endocrine functions, it also does not apply to the endocrine system. Here is such a complex organ.
Although the liver is a gland of mixed secretion and exocrine secretion, its range of functioning and significance is much greater than that of all other glands. It refers to vital organs.
The liver as an organ
In humans, it is 2% of its weight, in children - about 5%. It weighs about 1.5 kg. The liver is the largest gland of vertebrates. Its topography is the right upper quadrant of the abdomen, normally its lower edge reaches the 12th rib on the right. It is attached to the anterior abdominal wall and diaphragm with special strong ligaments. It is completely covered with a peritoneum. It consists of 2 halves - left and right, between them there is a falsiform ligament. The whole liver is divided into 4 lobes: left, right, square and tail. Blood flows to them through the portal vein and artery of the liver. The bile produced by the body is collected in the right and left hepatic ducts.
The liver is covered with a thin dense connective tissue membrane - Glisson's capsule. The inner framework of the organ (corset) is also made up of the same dense tissue, which divides its parenchyma into many lobules with vessels and nerves.
Blood supply
The flow of blood into the liver is carried out through several vessels, other organs receive nutrition from only 1 vessel. The inflow binary system is made up of vessels coming from the gastrointestinal tract, therefore in such blood there are a lot of nutrients.
On the other hand, oxygen-rich blood enters the liver through the hepatic artery. After the return of all useful substances, the venous blood that has become collected is collected in 2 portal veins - the right and left (outflow system).
The portal vein brings 75% of all blood circulating in the body. Artery and vein enter the liver together, into the so-called gate of the liver. Then they branch into smaller vessels directly in the parenchyma. Lymphatic vessels also pass near blood vessels.
Liver microanatomy
The histological structure of the liver divides it into lobules - structural units. The hepatic lobule has a 6-sided shape, hepatocytes are radially located in it. They are separated by sinusoidal vessels - hemocapillaries flowing into the central wreath located in the center of the prism. Lobules are divided among themselves by connective tissue partitions.
The main components of the lobules are the radially arranged rows of hepatocytes (liver plates, PP or cords). Biliary capillaries pass between the rows of hepatocytes. They do not have their own wall, their walls are composed of 2 rows of hepatocytes.
Each lobule has its own triad of vessels - a vein, artery and bile duct. Between the hepatocytes and the wall of the hemocapillaries there is a perisinusoidal space, or Disse space (PD), which is almost completely filled with hepatocyte microvilli. All central veins of the lobules collect and flow into the interlobular hepatic and inferior vena cava.
The main types of cells
The liver is a gland of mixed secretion, therefore its cells are heterogeneous. Each has its own function. 60% of the liver mass is hepatocytes (G) - large polygonal cells reaching 15-30 microns.
About 25% of hepatocytes have 2 nuclei. Of mononuclear hepatocytes, 70% have a 4-fold set of chromosomes, and 2% - 8-fold. In the cytoplasm of hepatocytes there are, as in any cell, mitochondria - energy stations of cells. Their number can reach from 800 to 2000.
Hepatocyte has 2 types of surface, or 2 poles. One of them (sinusoidal) is directed to the hepatic sinusoidal capillaries (SC) and is covered with microvilli (MV), it is directed to the Disse space. The villi are involved in the transport of substances from the blood to cells and vice versa. Other bile surfaces form half the wall of the bile duct (LC). Here, too, there are microvilli, but they are few. They help excretion of bile components.
Cholangiocytes (bile duct epithelial cells in the liver parenchyma) make up 2-3% of the total population of liver cells. Actively involved in the transport of proteins and secrete electrolytes.
Sinusoidal liver cells occupy 7% and consist of 4 species: endothelial cells, Kupffer stellate macrophages (neutralize old blood cells, bacteria, etc.), ITO cells and pit cells (cytotoxic to tumor cells).
Liver function
The functioning of the liver (glands of mixed secretion) is vital for the existence of the body. Without this organ, life is impossible. Among its functions are not insignificant.
What functions does the human liver perform?
- Excretory or excretory function - the quality of hepatitis is determined by its quality. Among its indicators - the content in the blood of bilirubin and bile acids.
- Synthetic function - the liver is involved in the exchange of BZHU. It synthesizes the most important blood proteins (albumin, globulins, fibrinogen, transport proteins for vitamins and enzymes, etc.), as well as compounds of the blood coagulation system.
- Energy function. Why does a person need a liver? It combines and regulates the entire metabolism, energy balance. At the right time, it provides energy to those cells that currently need nutrition. In other words, it is a constant battery. The liver is the main source and warehouse of energy reserves, which are stored here in the form of various chemical compounds. For example, with severe hypoglycemia, it is the liver that produces glucose from glycogen stores.
Summary: the liver is a vital gland because it performs a number of important processes:
- Synthesizes proteins.
- He takes part in hematopoiesis.
- Vitamins accumulate here (especially a lot of fat-soluble ones - A, D, E, K, water-soluble B12).
- She is involved in the chemical reactions of these and other vitamins.
- The liver is a depot of cations: iron, calcium, copper and cobalt.
- Produces bile and bilirubin.
- It detoxifies metabolic products.
The liver is the main laboratory for the neutralization of toxic substances in the body. About 500 reactions take place in it per minute. It destroys and neutralizes all foreign substances (xenobiotics). Among them can be noted poisons, allergens, toxins - they all turn it into neutral or less toxic.
In the liver, various biologically active substances unnecessary at the moment are destroyed, excess sex steroids, vitamins, mediators. This also includes the neutralization of toxic metabolic products - ammonia, phenol, ethanol, acetone and ketone bodies.
What other functions does the liver perform?
In addition to the above, the liver:
- Provides protective reactions of the body.
- Active participant in carbohydrate metabolism - creates and maintains reserves of glycogen (the main source of glucose).
- Engaged in gluconeogenesis - converts into glucose those compounds from which energy can be produced: lactic acid, amino acids, free fatty acids, glycerin, etc.
- Participates in lipid metabolism - synthesizes lipids, phospholipids, lipoproteins, cholesterol, from which sex hormones are created.
- The liver is a blood depot (there is always about 0.5 l of blood in it), which, if necessary, for example, with blood loss or shock, can be thrown into the general channel.
- Synthesizes hormones.
Fetal liver
What organ system does the fetal liver belong to? For the fetus in its prenatal development, the liver becomes a hematopoietic organ, i.e., an organ of hematopoiesis. It produces red blood cells and synthesizes many plasma proteins, converts toxic indirect bilirubin into harmless direct bilirubin.
The placenta performs a detoxifying function in the fetus during this period. But it is only with the fetus. In addition, the liver in the embryonic period synthesizes hormones for the fetus, which affect its development and growth in the future.
What organ system does the liver in an adult belong to?
According to the textbooks of anatomy, the liver is an auxiliary gland of digestion, without its bile, proteins and fats simply could not be digested. The glands of the digestive system include the gallbladder and pancreas. They are engaged in the production of enzymes necessary for normal digestion, neutralize toxins, etc.
Synthesis of liver hormones
There are several unique hormones produced by the liver. All of them are actively involved in the biochemical processes of the body, that is, they are not secondary.
- IGF-1 (an insulin-like growth factor, or somatomedin C) is an alkaline protein that is similar in structure and function to insulin. It is produced by hepatocytes upon irritation of somatotropin receptors. Its functions are regulation of tissue growth, formation of bones and muscles, effects on the hypothalamus and adenohypophysis, control of STH production, participation in cell differentiation, and control of apoptosis (aging). If it is reduced in a child, growth stops, and the result is dwarfism, and, conversely, with excess there is gigantism. With its prolonged increase, oncological diseases develop. Insulin and sex hormones contribute to the production of IGF, and glucocorticoids reduce it.
- Angiotensin is an oligopeptide hormone that increases blood pressure. Acts on salt metabolism by reabsorption of sodium. It also stimulates the production of vasopressin in the hypothalamus, which accelerates fluid excretion and causes thirst. The production of this hormone increases when exposed to estrogens and corticosteroids, as well as thyroid hormones.
- Hepcidin is a small peptide, has antimicrobial properties, it always increases with any infections. It blocks the absorption of iron in the small intestine and can cause anemia.
- Thrombopoietin, or TPO. It is produced less in the liver than in the kidneys. He is responsible for the growth and maturation of platelets. If its synthesis is insufficient, thrombocytosis occurs, thrombosis of small vessels (capillaries burst and bruises form), blood circulation is disturbed. With an excess, platelets decrease, and any trauma causes blood loss, cirrhosis, diabetes, heart failure and arthritis can occur.
In addition to all of the above, in the liver inactivation of excess sex hormones (estrogen and testosterone) occurs. On the other hand, the liver creates cholesterol - the basis for steroids. Also, excess of insulin, corticosteroids, thyroxine, antidiuretic hormone, glucagon are destroyed in it.