Estrogen reaches its target cell it moves through the cell membrane. Attaching either to a receptor in the cytoplasm or a receptor in the nucleus. The majority of receptors are found in the nucleus. There are two types of receptors; Estrogen Receptor alpha (ERα) and Estrogen Receptor Beta (ERβ.) These receptors hold chaperones, large clusters of proteins, in the ligand binding domain. Once the estrogen is ready to bind to the receptor the chaperone detaches.
All hormone and receptor complexes act as regulators of mRNA transcription. This means that the amount of protein created from the RNA changes. This is known as altering gene expression. This protein either changes the structure of the cell, it produces enzymes that create chemical reactions. Scientists have yet to finish learning about how estrogen affects gene expression. Baylor college conducted a study in 2017 that then showed once estrogen binds to the receptor coactivators are triggered. These coactivators respond in a certain order and bind to the estrogen receptor. These include SRC-3a, SRC-3b, and p300. From here a change in the gene is created by the hormone. This change is an altering to the amount a part of the DNA is transcribed, which in turn changes the amount of protein created from the RNA. As mentioned above this is called altering gene expression.
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To begin RNA transcription the DNA a RNA polymerase attaches to the DNA at the promoter(end of the gene.) Then the DNA with the polymerase unwinds, and straightens. From here the polymerase slides along the gene, and complementary base pairs match up. Once the polymerase reaches the terminator(opposite end of the gene) the DNA, RNA, mRNA, and polymerase detach. The mRNA has exons, which code for a protein, and introns. The introns are removed from mRNA through intron splicing. The exon strand then leaves the nucleus through a pore into the cytoplasm.
In the cytoplasm translation occurs. The nitrogenous bases in the mRNA are in groups of three called codons. The genetic code includes 64 codons. Codons are the code for specific amino acids to be created in the body. The first codon in the mRNA binds to the ribosomal subunit. Amino Acids which are bound to a RNA transfer molecule bind to the start of the mRNA. Then the large ribosomal binds to the start of the mRNA molecule. This creates the translation complex. The complex holds three codons. This complex can be divided into three sections. The left most we will call E, the center P, and the rightmost A. An amino acid transfer RNA binds to the codon in the A group. Then the ribosome moves over a codon, which moves the amino acid transfer unit to P. A new amino acid RNA transfer molecule binds to A. Again the ribosomal subunit moves over one space. DNA stands for Deoxyribonucleic acid. This is a polymer, made from monomers called nucleotides. 4 nucleotides make up a DNA molecule. Nucleotides have one phosphate(the acidic part of DNA) surrounded by 4 oxygen atoms. These are connected to a ring shaped sugar(the deoxyribose part of DNA). As well as a double or single ring of carbon and nitrogen atoms that is the base. The last part of the name, nucleic, comes from the DNA being found in the nucleus.
DNA strands are in the shape of a double helix. The strands vary from one hundred to millions of nucleotides. These strands are created from the covalent bonding of sugar to phosphate in the DNA molecules. Inside the double helix are rungs, each rung is created by bases of acid. The outer portion of the double helix is created by sugar and phosphate. One acid only pairs with a specific other acid. There are only 4 of these acids; adenine, thymine, guanine, and cytosine. Adenine only binds to thymine, and thymine only binds to adenine. Guanine only bonds to cytosine, and cytosine only bonds to guanine. The human genome has 6 billion base pairs throughout 46 chromosomes. Chromosomes are a part of the DNA...... (Define chromosomes) The human body has 46 chromosomes. Each chromosome has a chromosome similar in size and shape. One of these is from each parent. These pairs are called homologous pairs and there are 26 pairs. The 23rd of these pairs determines a person's sex. An X and Y chromosome pair is male, and two X chromosomes are female. Diploids are cells that contain the complete number of chromosomes. Most human cells are diploid except sex cells(sperm and eggs.) Sperm and eggs contain a single set of chromosomes. In fertilization the chromosomes in the egg pairs with the chromosomes in the sperm. The Pineal gland is located near the center of the brain and is shaped like a pine cone, hence the name. It is a reddish grey color and is 1/3 of an inch long. It is comprised of neuroglial cells, and pineal cells.
Originally the french philosopher, Rene Descartes said that the pineal gland was the principal seat of the soul, and is the place our thoughts are formed. This theory was later rejected by modern scientists. Researchers are still learning about the pineal gland. Currently it is know to release melatonin. This is a hormone that changes with light and affects our circadian rhythm. More light stops melatonin production, and less light creates more melatonin production. Melatonin also blocks the the release of gonadotropins (Luteinizing, and follicle stimulating hormones). The pancreas discharges digestive enzymes to the small intestine. These include insulin and glucagon. Additionally, it works with metabolism, and carbohydrates. The pancreas is located in the upper abdomen. It's function is to secrete enzymes from acinar cells. Between clusters of acinar cells are secretory tissue patches called Islets of Langerhans. In the pancreas there is approximately one million of these, these make up roughly 2% of the pancreas. The islets are made up from endodermal and neuroectodermal precursor cells. These cells contain many autonomic nerve endings, as the autonomic nervous system controls them.
There are four types of these cells. These include alpha, beta, delta, and C cells. Alpha cells produce glucagon. Glucagon breaks down glycogen into glucose, a carbohydrate to a sugar. Beta cells produce insulin. Insulin plays a major role in the regulation of carbs, fats, and protein metabolism. It does the reverse of glucagon, glucose to glycogen. Both of these are peptide hormones. This means they are proteins and therefore are water based. The cells which receive these hormones have receptors on the outside. Delta cells produce somatostatin, which is also produced by the hypothalamus and pituitary glands. This hormone stops the production of other hormones. The function of C cells is unknown. Insulin and glucagon both help to maintain blood glucose. As insulin turns glucose in to glycogen, and glucagon turns glycogen into glucose. When blood glucose is high the islets of Langerhans receive this through the bloodstream. A(alpha) cells receive this and take it as negative feedback to decrease glucagon production. B(beta) cells receive this as positive feedback and increase insulin. This results in the bloods glucose levels returning to normal. The reverse is true for low blood glucose. The A cells increase production of glucagon, as they receive positive feedback. B cells decrease production of insulin as they receive negative feedback from this. Diabetes is a disease that is in relation to the blood glucose. There are two types of diabetes. Type 1 occurs in 10% of diabetes patients. This is from too little insulin production. This often occurs after an autoimmune attack on B cells, resulting in too few of them. Many of these patients recieve insulin injections The pituitary gland is located at the base of the brain, and is essential for almost all hormone signaling. The hypothalamus receives signals from the peripheral nervous system and takes these signals to the pituitary gland through the hypophyseal portal system, a capillary of blood vessels. The pituitary gland then releases signals in the form of hormones to other parts of the endocrine system. The pituitary gland is also a part of feedback loops. By receiving hormones in the bloodstream from other parts of the body, it either continues releasing the hormone that cascades into that hormone, or stops releasing it. For example, the hypothalamus releases corticotropin releasing hormone to the pituitary gland. The pituitary gland then releases adrenalcorticotropic hormone (ACTH) to the adrenal cortex. The adrenal cortex then releases glucocorticoids into the bloodstream. This then moves through the bloodstream, and when there is too much the hypothalamus stops releasing Corticotropin releasing hormone. Then the pituitary stops releasing ACTH.
The hypothalamus releases hormones through the hypophyseal to the anterior pituitary gland.\, this is a form of paracrine signaling. The pituitary gland then releases hormones in response to these some which stimulate parts of the body directly and others that stimulate parts of the body to release other hormones. The tropical hormones it releases, or hormones which stimulate other glands include FSH, LH, ACTH, and TSH. The direct hormones it releases, those that stimulate a part of the body directly include PIF, endorphins, and growth hormones. The pituitary gland has a second part, the posterior pituitary, Hormones in this part of the glsand are created in the hypothalamus and then stored in the posterior pituitary. These include ADH, or antidiuretic hormone, which stimulates the kidneys retention of water. Oxytocin is also stored her which is involved in uterine contractions. All of these hormones are peptide hormones. This means they are water based, and made from proteins. Rather than lipids. Therefore the receptors for these hormones are on the outside of the cell membrane. The thyroid gland regulates the body's metabolism, growth, maturation, heart rate, and more. It is located at the base of the throat and is shaped like a butterfly, . It consists of two lobes, right and left. These are connected by the isthmus between them. The thyroid uses iodine from the food people consume to create Triiodothyronine (T3) and Thyroxine (T4).
The hypothalamus releases TRH(Thyroid Releasing Hormone) to the pituitary gland. The pituitary gland then releases TSH(Thyroid Stimulating Hormone) to the thyroid. The thyroid then releases T3 and T4. These are both hydrophobic, meaning they are lipid soluble. Lipid soluble hormones move through the cell membrane to receptors inside the cell. Once inside the cell T4 is converted to T3. Then once in the nucleus the hormone alters the genes within the cell. The Hypothalamus regulates the amount of T3 and T4 that is released through a feedback loop like all the other hormones in the body. An overactive thyroid gland is called hyperthyroidism. This results in anxiety, sensitivity to high temperatures, light or no menstrual periods, hair loss, and shaking hands. An underactive thyroid is called hypothyroidism, and it results in trouble sleeping, fatigue, difficulty concentrating, depression, sensitivity to cold temperatures, frequent or heavy periods, and joint and muscle pains. The Thymus is a gland behind the sternum and between the lungs. It is often considered to be more a part of the immune system than the endocrine system, since it plays a key role in the development of T-lymphocytes, or T-cells.
White blood cells (lymphocytes) are created in bones. They then travel through the bloodstream to the thymus. In the thymus they mature into T-lymphocytes, through the stimulation of Thymosin. T-cells are in the cortex of the thymus to start. From here they come in contact with epithelial and other cells, which present various antigens. The cells which respond correctly to this move to the medulla, the innermost portion of the cell, and the others are removed through apoptosis. This is positive feedback. Apoptosis is programmed cell death. When a cell is no longer need, is cancerous, or has another issue that will harm the body apoptosis occurs. The cell shrink and develops bubble like protrusions on the exterior called blebs. Then the DNA and other parts of the cell are broken down into smaller pieces surrounded by a membrane. Thus then releases signals to phagocytic (debris eating) immune cells, such as macrophages. These also have a phosphatidylserine (lipid molecule) on the exterior. This is usually on the inside of the cell and is what tells the immune cells to remove the debris. Negative Feedback occurs after positive feedback. In the medulla the cells are then presented with more of the body's own antigens. Autoimmune cells are those that attack the body's own cells. These are eliminated here through apoptosis as well. Around 2% of t-cells make it through this process, and the rest are reabsorbed into the body. Adrenals can be broken down into ad, meaning rear, and renal, meaning kidney. The adrenal glands are just above the kidneys, and have two parts. The Adrenal Medulla is the inner part of the gland, and the Adrenal Cortex is the outer part of the gland. The adrenal medulla produces non essential hormones such as epinephrine, better known as adrenaline. The adrenal cortex produces cortisol, and aldosterone. Cortisol regulates metabolism, blood pressure, and cardiovascular functions. All three of these hormones help with the body's reaction to stress.
Corticosteroids are any hormones released by the adrenal complex. There are two classes of Corticosteroids, glucocorticoids, and mineralocorticoids. First, we'll talk about glucocorticoids. The hypothalamus releases corticotropin releasing hormone (CRH). Then the pituitary gland receives this and releases adrenal corticotropin hormone (ACTH). The adrenals receive this and the adrenal cortex releases corticosteroid hormones, these include Hydrocortisone, better known as cortisol. As well as corticosterone which works with hydrocortisone to regulate immune responses and suppress inflammatory responses. The mineralocorticoid hormones are aldosterone which maintains the salt and water balance in the blood stream, this helps to control blood pressure. This is also released by the adrenal cortex. The Adrenals also plays a role in the fight or flight response, or stress response in the body. The sympathetic nervous system stimulates the adrenals. The adrenal medulla then releases norepinephrine and epinephrine into the bloodstream. Norepinephrine restricts blood flow to certain parts of the body. In this case the sympathetic nervous system is the part of the nervous system that amps up the body in response to stress. The epinephrine speeds up things like the heartbeat to get blood to you muscles so that you can move. It also restricts blood flow to parts of the body where it's not immediately needed, like digestive system. The gonads are the testes in males, and the ovaries in females. The testes release testosterone, which is considered the male sex hormone. The ovaries release estrogen, the female sex hormone. Both of these hormones are found in males and females, however one sex has more of one than the other. Past the age of puberty men have 7-8x as much testosterone than women.
Testosterone is created in the testes in the leydig cells. In women these cells are found in the ovaries. Testosterone is lipid soluble, therefore it's target cell receptors are inside the cell. It passes through the cell membrane to reach the receptor. Once inside the cell it binds with a carrier protein, and moves to the nucleus of the cell. From here it moves to the DNA. Releasing from the protein it binds to the genes, and alters the gene function. In some cells when testosterone enters the cell it changes into another hormone, estrogen or dihydrotesterone(DHT). Testosterone creates muscle mass, male sex characteristics (fat pattern, facial hair, etc), and sperm production. In the womb it creates the male reproductive organs. In excess testosterone creates male pattern baldness, and has been linked to pancreas cancer. Estrogen is the female sex hormone. Like testosterone both sexs have it, but females produce more of it which determines certain characteristics. Estrogen is primarily created in the ovaries but every fat cell in the body creates at least a small of estrogen. As do the adrenals. The anterior pituitary gland releases follicle stimulating hormone (FSH), which then creates the growth of follicles in the ovaries. These then create theca and granulosa cells. These cells produce estrogen. As the bloodstream carries the estrogen throughout the body the hypothalamus and pituitary gland regulate these levels throughout the month. Once the estrogen reaches a cell because it is lipid based it moves through the cell membrane to bind with a carrier protein. The carrier protein brings the estrogen to the nucleus. Then it binds to the genes to change the cells function. The roles estrogen plays in the body are similar to testosterone in that it creates the female sex characteristics. These include breasts, fat patterning around the hips, and growth of external genitalia. In the male body it plays a role in the maturation of sperm. In both sexes it reduces low density cholesterol(LDL) and increases high density cholesterol (HDL). Additionally it slows down bone breakdown and delays osteoporosis. |