Hormones are chemical information substances synthesized by highly differentiated endocrine cells and directly secreted into the blood. It affects the physiological activities of the human body by regulating the metabolic activities of various tissue cells. Efficient bioactive substances secreted by endocrine glands or endocrine cells serve as messengers in the body to transmit information and substances that regulate the body's physiological processes are called hormones. It is an important substance in our lives.
Physiological significance of hormones
Hormones are a class of chemicals that are efficiently transmitted by endocrine cells. By transmitting information, they play an important role in coordinating physiological processes such as metabolism, growth and development. . There are three main ways of hormonal transmission: most hormones are secreted directly into the blood, and reach certain tissue cells through the blood circulation. Such cells are called target cells. The target cell contains a three-dimensional structure of a special substance and the corresponding hormone, and recognizes the information carried by the hormone, and converts it into a series of complex chemical reactions in the cell, thereby producing specific physiological effects. According to the chemical properties of hormones, hormones can be divided into nitrogen-containing protein hormones (and steroid hormones. Their physiological functions can be divided into three categories: one is to regulate the body's metabolism and maintain a relatively stable internal environment, such as insulin, gastrointestinal hormones, And parathyroid hormone, etc. The first is to promote cell proliferation and differentiation, control the growth and development of the human body and reproductive functions, and affect its aging process, such as growth hormones and sex hormones. There is a group of close cooperation with the nervous system to enhance the body's environmental impact adaptability, such as adrenocortical hormones and pituitary hormones.
Examples of Hormones
Estradiol is a steroidal estrogen. There are two types of α and β, which have strong physiological effects. Wintersteiner et al. (1935) have been extracted from pregnant horse urine, and can also be obtained from maternal urine, human placenta, and pig ovaries. The horse's testis or urine is also present. Because it has a strong sex hormone effect, it is considered that it or its ester is actually the most important sex hormone secreted by the ovaries.
Figure 1. Chemical structure of Estradiol.
2. Arachidonic acid
Arachidonic acid plays an important role as a phospholipid-bound structural lipid in the blood, liver, muscle, and other organ systems. In addition, AA is a biologically active substance of many circulating eicosanoid derivatives, such as prostaglandin E2 (PGE2), prostacyclin (PGI2), thromboxane A2 (TXA2), and Precursor. These bioactive substances have important regulatory effects on lipid protein metabolism, hemorheology, vascular elasticity, leukocyte function, and platelet activation.
Figure 2. Chemical structure of arachidonic acid.
Testosterone is the main male sex hormone and anabolic steroid. In men, testosterone plays a key role in the development of male reproductive tissues, such as testes and prostate, and plays a key role in promoting secondary characteristics such as increasing muscle and bone mass, and promoting hair growth. In addition, testosterone is also involved in health and well-being, and prevents osteoporosis. Insufficient testosterone levels in men can cause abnormalities, including weakness and bone loss.
Figure 3. Chemical structure of Testosterone.
Examples of Hormones Proteins
Insulin is a protein hormone secreted by pancreatic islet beta cells in the pancreas stimulated by endogenous or exogenous substances such as glucose, lactose, ribose, arginine, glucagon and the like. Insulin is the only hormone in the body that lowers blood sugar and promotes glycogen, fat, and protein synthesis. Exogenous insulin is mainly used for the treatment of diabetes.
Figure 4. Insulin is a peptide hormone containing two chains crosslinked by disulfide bonds.
2. G Protein-Coupled Receptors (GPCRs)
G Protein-Coupled Receptors (GPCRs) is a collective term for a large class of membrane protein receptors. The common feature of these receptors is that they have 7 transmembrane α-helixes in the three-dimensional structure, and the C-terminus of the peptide chain and the intracellular loop connecting the 5th and 6th transmembrane helix have G protein (bird Binding site). Studies have shown that G protein-coupled receptors are only found in eukaryotes and are involved in many cellular signal transduction processes. In these processes, G protein-coupled receptors can bind to chemicals in the environment surrounding the cell and activate a series of signaling pathways within the cell, eventually causing changes in the state of the cell. Known ligands that bind to G protein-coupled receptors include odors, pheromones, hormones, neurotransmitters, chemokines, and the like. These ligands can be small molecules such as sugars, lipids, peptides, or biological macromolecules such as proteins. Some special G protein-coupled receptors can also be activated by non-chemical stimuli. For example, rhodopsin in photoreceptor cells can be activated by light. There are numerous diseases associated with G protein-coupled receptors, and about 40% of modern drugs target G protein-coupled receptors.
Figure 5. Protein structure of G Protein-Coupled Receptors (GPCRs).
3. Nuclear receptors
Nuclear receptors are one of the most abundant transcriptional regulators in metabolites. They play important roles in metabolism, sex determination and differentiation, reproductive development, and maintenance of homeostasis.
Figure 6. Protein structure of Nuclear receptors.
TSH receptors are mainly distributed in thyroid follicular cells. Receptor stimulation increases the production and secretion of T 3 and T 4. TSH receptor-stimulating antibodies mimic TSH and cause Graves disease. In addition, hCG and TSH receptors show some cross-reactivity, so they can stimulate the production of thyroid hormones. During pregnancy, high levels of hCG for a long period of time can produce a transient condition called hyperthyroidism in pregnancy. This is also the mechanism by which trophoblast tumors increase thyroid hormone production.
Figure 7. Protein structure of TSH receptor.
1. Heyland A. Hormone signaling in evolution and development: a non-model system approach. BioEssays. 1980, 27 (1): 64-75.