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Tuesday, April 16, 2019

The Endocrine System

          The Endocrine System 


                                      (Hormones, chemical messengers of the body)





The Endocrine System





Our body secretes and circulates around 50 different hormones. These substances produce very different types of chemicals from endocrine cells, generally grouped into glands. They then borrow the system to reach the whole body and activate the target cells. Closely related to the nervous system, the endocrine system controls many functions of the body: metabolism, homeostasis, growth, sexual activity or contraction of the smooth and cardiac muscles



 Endocrine glands




The Endocrine System



The endocrine system consists of a dozen specialized glands (the pituitary gland, the thyroid gland, the four parathyroid glands, the adrenal glands and the thymus), as well as various organs capable of producing hormones (pancreas, heart, kidneys, ovaries, testes , intestine ... ). The hypothalamus, which is not a gland, but a nerve center, also have an important role in the synthesis and secretion of some hormones. Unlike the substances created by the exocrine glands, which flow into the channels, hormones are released directly into the space surrounding the secretory cells. The very strong vascularization of the endocrine glands allows the hormones to spread in the bloodstream through the capillaries. Some of them circulate freely in the blood, while others must carry proteins in the target cells


Generally considered the major endocrine glands, the pituitary gland secretes a dozen different hormones. Some of these substances act to activate other endocrine glands. Located above each kidney, the adrenal glands are made up of two distinct parts. Barking (or adrenal cortex) secretes corticosteroid hormones such as aldosterone and cortisol, as well as male and female sex hormones (androgens and estrogens). For its part, the marrow (or adrenal medulla) mainly produces adrenaline and norepinephrine, hormones that participate in the body's response to stress


Features of the endocrine epithelium

• Formed by a glandular epithelium resting on highly vascularized connective tissue

• Synthesis of hormones secreted directly into the bloodstream

• Concept of regulation of hormonal synthesis

• Action of hormones on target cells or organs



Organization of endocrine epithelia:


• Endocrine glands (thyroid, pituitary ...)

• Endocrine cell groups (Leydig cells, Langerhans islands)

• The prevalent of endocrine system or APUD system:



Hormones


A hormone is a type of chemical signal. They are a means of communication between cells. The endocrine system produces hormones essential for maintaining homeostasis and regulating reproduction and development. A hormone is a chemical messenger produced by a cell that causes a specific change in the cellular activity of other cells (target cells). The difference between the exocrine  and endocrine glands is that the exocrine glands produce substances such as saliva, milk, stomach acid and digestive enzymes, the opposite of the endocrine glands which do not secrete substances into the conduits, test tubes. Instead, the endocrine glands secrete their hormones directly into the surrounding extra cellular space. The hormones then spread to nearby capillaries and are transported throughout the body in the blood

Endocrine and nervous system often work for the same goal. Both affect other cells with chemicals (hormones and neurotransmitters). However, they achieve their goals differently. Neurotransmitters act directly (in milliseconds) on muscles, glands or other approaching  nerve cells and their effect is short-lived. Rather, hormones take longer to produce the desired effect (from seconds to days), they can affect any cell, near or far and produce effects that last as long as they remain in the blood, which can last up to several hours. The following table lists the main hormones, their target and their function once in the target cell

• Hypothalamus gland

Hormone release: hypothalamic release and inhibition of hormones
Chemical class: peptide
Target organ / tissue: anterior pituitary
Main hormone function: regulate the anterior pituitary hormone

• Posterior pituitary gland

Hormone release: antidiuretic (ADH)
Chemical class: peptide
Target tissue / organ: kidneys
Main function of the hormone: stimulates the reabsorption of water by the kidneys

Hormone release: oxytocin
Chemical class: peptide
Target tissue / organ: uterus, mammary glands
Main function of the hormone: stimulates uterine muscle contractions and milk release by the mammary glands


• Anterior pituitary gland

Hormone release: thyroid stimulant (TSH)
Chemical class: glycoprotein
Target organ / tissue: thyroid
Main function of the hormone: stimulates the thyroid

Hormone release: adrenocorticotropic (ACTH)
Chemical class: peptide
Target tissue / organ: adrenal cortex
Main function of the hormone: stimulates the adrenal cortex

Hormone release: gonadotropic (FSH, LH)
Chemical class: glycoprotein
Target tissue / organ: gonads
 Main function of the hormone: production of eggs and sperm, production of sex hormones

Hormone release: prolactin (PRL)
Chemical class: proteins
Target tissue / organ: mammary glands
Main function of the hormone: milk production

Hormone release: growth (GH)
Chemical class: proteins
Target tissue / organ: soft tissues, bones
Main function of the hormone: cell division, protein synthesis and bone growth


• Thyroid gland

Hormone release: thyroxine (T4) and triiodothyrony (T3)
Chemical class: iodized amino acid
Target tissue / organ: all tissue
Main function of the hormone: increases the metabolic rate, regulates growth and development

Hormone release: calcitonin
Chemical class: peptide
Target organ / tissue: bones, kidneys and intestines
Main function of the hormone: lowers the level of calcium in the blood


• Parathyroid gland

Hormone release: parathyroid (PTH)
Chemical class: peptide
Target organ / tissue: bones, kidneys and intestines
Main function of the hormone: increases the level of calcium in the blood


• Adrenal Cortex gland

Hormone release: glucocorticoids (cortisol)
Chemical class: steroids
Target tissue / organ: all tissue
The main function of the hormone: to increase blood-glucose levels  by triggering the breakdown of proteins

Hormone release: mineralocorticoids (aldosterone)
Chemical class: steroids
Target tissue / organ: kidneys
Main function of the hormone: reabsorb sodium and expel potassium

Hormones release: sex hormones
Chemical class: steroids
Target tissue / organ: gonads, skin, skeletal muscle
Main function of the hormone: stimulates the reproductive organs and gives sexual features

• Adrenal Medulla Gland

Hormone release: epinephrine and norepinephrine
Chemical class: modified amino acid
Target tissue / organ: heart muscles and other muscles
Primary hormonal function: released in an emergency, increases blood glucose level, "fight or flight" response


• Pancreas gland

Hormone release: insulin
Chemical class: proteins
Target tissue / organ: liver, muscle, fatty tissue
Main function of the hormone: lowers blood glucose levels, stimulates glycogenesis, inhibits glycogenolysis

Hormone release: glucagon
Chemical class: proteins
Target tissue / organ: liver, muscle, fatty tissue
Main function of the hormone: stimulates glycogenolysis and gluconeogenesis, causing an increase in blood glucose levels


• Testicle gland

Hormone release: androgens (testosterone)
Chemical class: steroids
Target tissue/organ: gonads, skin, bones and muscle
Main function of the hormone: stimulates the development and is  responsible for the secondary sexual characteristics of males and spermatogenesis


• Ovary gland

Hormone release: estrogen and progesterone
Chemical class: steroids
Target tissue/organ: gonads, skin, bones and muscle
Main function of the hormone: stimulates the development of female secondary sex characteristics and ovulation... .


• Thymus gland

Hormone release: thymosines
Chemical class: peptide
Target organ / tissue: T lymphocytes
Main function of the hormone: stimulates the production and maturation of T lymphocytes


• Pineal gland

Hormone release: melatonin
Chemical class: modified amino acid
Target tissue / organ: brain
Main function of the hormone: controls the circadian and circanual rhythms, possibly involved in the maturation of the sexual organs



Hormones can be chemically classified into:

● Hydrophilic compounds

Biogenic proteins, peptides or amines, hormones that are chains of amino acids less than or greater than about 100 amino acids, respectively. Some protein hormones are actually glycoproteins, which contain glucose or other groups of carbohydrates, hormones that are modified amino acids

● Hydrophobic compounds

  • Steroids: lipid hormones synthesized by cholesterol. Steroids are characterized by four interlocking carbohydrate rings
  • Membrane receiver
  • Prevalent through the plasma membrane: eicosanoids: they are the lipids incorporated by the fatty acid chains of the phospholipids
  • Intracytoplasmic receptor link
  • Activation of the ligand receptor

Action of most endocrine cells under the control of the HPA system


The hormones diffuse in the blood and are transferred to various organs of the body, which are secreted into the surrounding interstitial fluid. Cells with specific hormone receptors respond with appropriate action for the cell. Due to the specificity of the hormone and target cell, the effects produced by a single hormone can vary between different types of target cells. Hormones activate target cells with one of two processes, based on the chemical nature of the hormone

• Fat-soluble hormones such as steroid and thyroid hormones, are  activating a particular segment of the cell's DNA and also activates particular genes by binding to a receptor protein. Which spreads through the target  cell membranes. Proteins produced as a result of gene transcription and subsequent translation of mRNA act as enzymes that regulate specific physiological cellular activity

• Water-soluble hormones (polypeptides, proteins and most amino acid hormones) bind to a receptor protein on the plasma membrane of the cell. The receptor protein stimulates the production of one of the following second messengers:

Cyclic AMP (cAMP) is released when the receptor protein activates another membrane-bound protein named G protein. G protein activates adenylate cyclase, the enzyme that catalyzes the production of cAMP by ATP. Cyclic AMP then releases an enzyme that generates certain cellular changes. Inositol triphosphate (IP3) is produced from membrane phospholipids. IP3, in turn, triggers the release of CA2 + from the endoplasmic reticulum, which then activates the enzymes that cause cellular changes. The endocrine glands produce hormones in response to one or more of the following triggers:

  • Hormones of other endocrine glands
  • Chemical characteristics of the blood (other than hormones)
  • Neural stimulation. Most of the hormone production is managed through a negative feedback system. The nervous system and some endocrine tissues control various internal conditions of the body. If effect is required to preserve homeostasis, hormones are triggered, directly from an endocrine gland or indirectly by the brain's hypothalamus, which stimulates other endocrine glands to produce hormones

Hormones activate target cells, which initiate physiological changes that regulate the body's conditions. When conditions return to normal, corrective action, hormone production is stopped. Therefore, in negative feedback, when the original (abnormal) condition has been repaired or negated, corrective actions are diminished or stopped. For example, the amount of glucose in the blood controls the secretion of insulin and glucagon through negative response

The stimulate of some hormones is controlled by the positive response. In such a system, hormones generate a condition to intensify rather than decrease. As the condition intensifies, hormone production increases. Such positive feedback is rare, but occurs during labor, where hormone levels accumulate with increasingly intense contractions of labor. Even during breastfeeding, hormone levels increase in response to breastfeeding, causing an increase in milk production. The hormone produced by the hypothalamus that causes milk to fall and uterine contraction is oxytocin

Five main functions of hormones

• Regulate metabolic processes (for example, thyroid hormones)

• Control the rate of chemical reactions, for example, growth hormone

• It permits the transport of substances through the cell membrane of the target cells, for example, insulin and glucagon

• Adjust the water and electrolyte balance (for example, antidiuretic hormone, calcitonin and aldosterone)

• It plays a vital role in reproduction, growth and development, example, estrogen, progesterone and testosterone


Major Endocrine glands and Hormones


The pituitary gland: attached to the hypothalamus by the infundibulum Divided into the anterior lobe (adenohypophysis) and the posterior lobe (neurohypophysis). The anterior lobe is approximately 3 times larger than the posterior lobe

• The anterior pituitary is under hormonal control of the hypothalamus, in which the blood vessels carry "releasing hormones" into the anterior lobe. The anterior pituitary contains 5 types of glandular cells

  • Somatotrophies produce GH
  • Lactotrophs produce PRL
  • Corticotrophies produce ACTH and MSH
  • Tirotrophies produce TSH
  • Gonadotropes produce FSH and LH
• The posterior pituitary is under nervous control from the hypothalamus, where nerve fibers innervate the posterior lobe to release hormones (the posterior pituitary does not produce hormones; it only releases hormones produced by the hypothalamus)



Endocrine glands



The hypothalamus and the pituitary

                  (The control centers of the endocrine system)




The Endocrine System




Since it controls the activity of several other glands, the pituitary gland is often considered the primary gland of the endocrine system. However, it is controlled by the hypothalamus, a nerve center involved in the regulation of many vital functions. Among these, the hypothalamus and the pituitary gland produce one third of all body hormones and act both in lactation and in urinary retention, as well as in pigmentation of the skin or in bone growth


The hypothalamus

The hypothalamus is consist of several nuclei that located under the thalamus, which plays a role that regulate the autonomic nervous system and regulate body temperature and sleep, hunger and thirst. The hypothalamus also affects sexual behavior and begets reactions of anger and fear. Intimately related to the pituitary gland, it plays a coordinating role between the nervous system and the endocrine system


Pituitary gland


The Endocrine System



Small mass of about 1.3 cm in diameter, the pituitary gland is housed in a bone cavity sphenoids, Turkish saddle. This gland, also called the pituitary gland, consists of two very different structures: the neurohypophysis, which contains axonal projections of the secretory neurons of the hypothalamus, and the adenohypophysis, which consists only of endocrine cells


Anterior pituitary:

The anterior lobe is derived from the oral ectoderm known as Rathke's pouch and is composed of glandular epithelium. The link between the hypothalamus and anterior pituitary occurs through secretion of hormones, which serves the release of hormones and the inhibition of hormones by the hypothalamus and transported to the anterior pituitary through a portal network of capillaries. The hormones that secrete and inhibit are generated by specialized neurons of the hypothalamus known as neurosecretory cells

Hormones are released into a primary capillary network or plexus and are transported through the veins or veins of the pituitary portal to a second capillary or secondary plexus network that feeds the anterior pituitary gland. The hormones then spread from the secondary plexus to the anterior pituitary, where the production of specific hormones by the anterior pituitary begins. The anterior pituitary produced hormones, known as tropical hormones or tropins, which are hormones that stimulate other endocrine glands to secrete their hormones


Posterior pituitary:

Post pituitary or neurohypophysis Contains the median eminence, the infundibulum and the posterior lobe of the pituitary gland

Through neurosecretory cells, the communication between the hypothalamus and the posterior pituitary occurs, these cells covers the short distance between them. The hormones excreted by the cell bodies of neurosecretory cells are packed into vesicles and transferred through the axon and stocked in the axon terminals located in the posterior pituitary. When stimulation of neurosecretory cells, occurs the production and  the formation of stored hormones from the axon terminals to a capillary network within the posterior pituitary. In this way two hormones are produced and released, oxytocin and antidiuretic hormone (ADH). Decreased ADH release or decreased kidney sensitivity to ADH produces a condition known as diabetes insipidus. Insipid diabetes is characterized by polyuria (excessive production of urine), hypernatremia (increased sodium content in the blood) and polydipsia (thirst)

The posterior lobe is formed of neural tissue, known as neural ectodermand is derived from the hypothalamus. Its function is to conserve oxytocin and antidiuretic hormone. When hypothalamic neurons are activated, these hormones are released into the capillaries of the posterior lobe. The posterior pituitary is a directly projection of the hypothalamus. It does not make its own hormones, but stores and stimuli only oxytocin and antidiuretic hormone. ADH is also known as arginine vasopressin, or simply vasopressin

• Oxytocin acts on the uterus in pregnancy and stimulates the contraction of the uterine myometrium

• The goals of vasopressin are the kidney collection tubes in which it causes a greater reabsorption of water


Thyroid gland


Thyroid gland arranged in two lobes on both sides of the larynx, the thyroid gland is activated by the thyroid stimulating hormone secreted by the pituitary gland. Thyroid hormones, commonly called T3 and T4, develop in small pockets, the thyroid follicles, from iodide in the blood. They serve in particular to regulate growth and metabolism


Parathyroid gland


The Endocrine System




There are four parathyroid glands. They are small, light-colored cusp that emerge from  the thyroid gland surface's.  All four glands are located in the thyroid. They are butterfly shaped and are located inside the neck, particularly on both sides of the trachea. One of the most important functions of the parathyroid glands is to regulate calcium and phosphorus levels in the body. Another function of the parathyroid glands is to secrete the parathyroid hormone, which causes the release of calcium present in the bone into the extracellular fluid. PTH does this by depressing the production of osteoblasts, special body cells involved in bone production and activating osteoclasts, other specialized cells involved in bone extraction

There are two main types of cells that make up the parathyroid tissue:

• One of the main cells is called oxyphilic cells. Its function is essentially unknown

• The second type is called main cells. The main cells produce parathyroid hormone

There are differences in the structure of a parathyroid gland from that of a thyroid gland. The main cells that release the parathyroid hormone are ordered in tight nests around small blood vessels, unlike the thyroid hormone-releasing cells, which are arranged in spheres known as  thyroid follicles. PTH or parathyroid hormone is secreted by these four glands. It is released directly into the bloodstream and transports to its target cells. Then it binds to a structure called a receptor, which is located on or on the surface of the target cells

• The receptors bind to a specific hormone and the result is a specific physiological response, which means a normal response from the body

• PTH perceives its main target cells in the bones, kidneys and gastrointestinal system

• Calcitonin, a hormone secreted by the thyroid gland, that regulates the levels of calcium in the ECF and provides to counteract the influence of the PTH that released calcium

• The adult body contains up to 1 kg of calcium. Most of this calcium is found in the bones and teeth

All four parathyroid glands secrete parathyroid hormone (PTH). It opposes the effect of tirocalcitonin. It does this by removing calcium from its bone storage sites, releasing it into the bloodstream. It also tells the kidneys to reabsorb more of this mineral, transporting it into the blood. It also indicates to the small intestine to absorb more of this mineral, transporting it from the diet to the blood

Calcium is important for the body's metabolism stages. Blood cannot clot without enough calcium. Skeletal muscles require this mineral to contract. A deficiency of PTH can lead to tetany, muscle weakness due to the lack of calcium available in the blood

The parathyroid glands have long been thought to be part or functionally associated with the thyroid. We now know that their proximity to the thyroid is misleading: both evolutionarily and functionally, they are completely different from the thyroid

The parathyroid hormone, called parathyroid hormone, regulates the calcium-phosphate balance between blood and other tissues. The secretion of this hormone is immediately controlled by the calcium rate of the extracellular fluid which rinsing the cells in these glands. Parathormne has at least the following five effects:
(1) Increases the gastrointestinal absorption of calcium by activating the transport system and carrying calcium from the intestinal lumen into the blood
(2) Increases the movement of calcium and phosphate from the bone to the extracellular fluid. This is accomplished by stimulating osteoclasts to break the bone structure, thereby releasing calcium phosphate into the blood. In this way the reserve of calcium contained in the bone is used
(3) Increases the reabsorption of calcium by the renal tubules, thereby decreasing the urinary excretion of calcium
(4) Reduces the reabsorption of phosphate by the renal tubules
(5) Stimulates the synthesis of 1,25-diidrixicolecalciferol by the kidney

The first three impacts lead to an increase of  concentration of extracellular calcium. The fourth of adaptive value is to inhibit the formation of kidney stones

When the parathyroid glands are accidentally removed through thyroid surgery procedure, the concentration of phosphate in the blood would raise. There would also be a drop in calcium concentration as the kidneys and intestines expel more calcium and incorporate more calcium into the bone. This can lead to serious ailments, particularly in the muscles and nerves, which use calcium ions for normal functioning. The excessive activity of the parathyroid glands, which can be the result of a tumor in the glands, causes weakening of the bones. This is a condition that makes them much more vulnerable to fractures due to the excessive extraction of calcium from the bones



Adrenal glands

The Endocrine System




The adrenal glands are a pair of ductless endocrine glands, which that their secretions are released directly into the blood, not to any tubes or ducts. Situated directly on upper of each kidney. During hormones secretions, the adrenal glands facilate to control basis functions in the body: including the biochemical balances that impact sports exercise and the general response to stress. They produce hormones such as estrogen, progesterone, steroids, cortisol and cortisone and chemicals: including,  adrenaline, norepinephrine and dopamine. Glucocorticoids include corticosterone, cortisone and hydrocortisone or cortisol. These hormones allow to stimulate the conversion of amino acids into carbohydrates, which is a process known as gluconeogenesis and the production of glycogen by the liver. They also stimulate the formation of reserve glycogen in the tissues, as in the muscles. Glucocorticoids are also involved in lipid and protein metabolism. The cortex of the adrenal gland is known to produce more than 20 hormones and are classified into three categories: glucocorticoids, mineralocorticoids and sex hormones. When the glands produce more or less hormones than those required by the body, diseases can occur

The adrenal cortex secretes at least two families of hormones, glucocorticoids and mineralocorticoids. The adrenal medulla secretes the hormones epinephrine (adrenaline) and norepinephrine (norepinephrine)

The two adrenal glands are very close to the kidneys. Each adrenal gland is actually a double gland, consisting of an internal core such as the medulla and an external cortex. Each of these is not functionally related. The adrenal medulla secretes two hormones, adrenaline or adrenaline and noradrenaline or norepinephrine, whose functions are very similar but not identical. The adrenal medulla is embryogenetically derived from neural tissue. It has been compared to an excessively large sympathetic ganglion whose cell bodies do not send nerve fibers, but release their active ingredients directly into the blood, thus meeting the criteria for an endocrine gland. By controlling epinephrine secretion, the adrenal medulla behaves like any sympathetic ganglion and is dependent on stimulation by the sympathetic preganglionic fibers

Epinephrine promotes several responses, all useful for dealing with emergencies: increases in blood pressure, increases in heart rate, increase in blood glucose content due to the breakdown of glycogen, the spleen contracts and compresses an escort. Blood supply, the clotting time lowering, the pupils stretch, the blood flow to the skeletal muscles increases, the blood flow to the intestinal smooth muscle decreases and the hair becomes erect. These adrenal functions, which crowd the body's resources in a requirement, known as the fight or flight response. Norepinephrine triggers feedbacks similar to those made by epinephrine, but is less effective in transforming glycogen into glucose

The importance of the adrenal medulla may seem questionable since complete removal of the gland causes few noticeable changes; humans can still show the answer to flight or struggle. This occurs because the sympathetic nervous system completes the adrenal medulla by stimulating the fight or flight reply and the absence of hormonal control will be recompense for by the nervous system


 Adrenal cortex:

The hormones secreted by the adrenal cortex give long-term responses to stress. The two types hormones produced are mineral corticosteroids and glucocorticoids. Mineral corticosteroids serves to regulate the equilibrium of salt and water and mineral metabolism, this major feature leading to an increase in blood volume and pressure. Glucocorticoids monitor ACTH, in turn by regulating the metabolism of carbohydrates, proteins and fats. This causes an increase in blood sugar. Glucocorticoids also reduce the body's inflammatory response. Hormonal production in the adrenal cortex is directly controlled by the anterior pituitary hormone known as adrenocorticotropic hormone (ACTH)

Cortisol is one of the most active glucocorticoids. It typically reduces the effects of inflammation or swelling throughout the body. It also stimulates the production of glucose from fats and proteins, which is a process known as gluconeogenesis

Aldosterone is an example of a mineral corticosteroid. Tells tubules in kidney nephrons to reabsorb sodium while secreting or eliminating potassium. If the sodium levels are low in the blood, the kidney secretes more renin, which is an enzyme that stimulates angiotensin formation from a molecule produced by the liver. Angiotensin stimulates aldosterone secretion. As a result, more sodium is reabsorbed when it enters the blood

Aldosterone, the main mineral corticosteroid, stimulates the cells of the distal convoluted tubules of the kidneys to reduce the reabsorption of potassium and increase the reabsorption of sodium. This in turn leads to a greater reabsorption of chloride and water. These hormones, simultaneously with hormones such as insulin and glucagon, are leading controller of the ionic environment of the internal fluid. The renin-angiotensin-aldosterone mechanism can increase blood pressure if it tends to decrease. It does this in two ways. Angiotensin is a vasoconstrictor, which decreases the diameter of the blood vessels. As the vessels narrow, blood pressure rises. Also, when sodium is reabsorbed, the blood that passes through the kidney becomes more hypertonic. Water follows sodium in hypertonic blood by osmosis. This increases the amount of volume in the blood and also raises the blood pressure


• Adrenal cortex: external portion of the adrenal gland which is attached to the upper surface of the kidney
• Divided into 3 regions, from the outside in: glomerulose zone, fasciculated zone and reticular zone
• It secretes more than 30 steroid-based substances and various steroid hormones, all of which are essential for normal homeostasis
• The glomerulose zone secretes mineralocorticoids which help regulate the levels of minerals such as sodium, potassium and magnesium. Aldosterone is the most important hormone in this group, in which it increases the blood levels of sodium and water and decreases the level of potassium in the blood
• The fascicular area secretes glucocorticoids which influence glucose or carbohydrate metabolism. Cortisol is the major important hormone in this set, where it serves in  carbohydrates metabolism's, lipids and proteins and also promotes fight stress and inflammation. Hyposecretion causes Addison's disease and hypersecretion causes Cushing's syndrome
 • The reticular area secretes the gonadocorticoids which complement the sex hormones of the testes and ovaries and stimulate the early development of the reproductive organs. These hormones are male (adrenal androgens), ie testosterone, but can be converted into female types, such as estrogens, from the skin, liver and adipose tissues. Hyposecretion leads to congenital adrenal hyperplasia, and hypersecretion leads to gynecomastia in the male


Adrenal medulla:

The hypothalamus initiates nerve impulses that proceed the path from the bloodstream, the spinal cord and the sympathetic nerve fibers to the adrenal medulla, which then releases hormones. The influences of these hormones provide a short-term response to stress. Excessive glucocorticoid secretion causes Cushing's syndrome, which is characterized by muscle wasting or degeneration and hypertension. The secretion of these substances produces Addison's disease, identified by low blood pressure and stress

Epinephrine and norepinephrine produce the "fight or flight" response, similar to the effect of the sympathetic nervous system. Therefore, heart rate, respiratory rate, blood flow to most skeletal muscles and blood glucose concentration increase. They reduce blood flow to the digestive organs and decrease most of the digestive processes

Adrenal sex hormones are made up primarily of male sex hormones (androgens) and smaller amounts of female sex hormones (estrogen and progesterone). Normally, the sex hormones released by the adrenal cortex are negligible due to the low concentration of secretion. However, in the condition of immoderate secretion, male or female effects appear. The most common syndrome of this type is the "virilism" of women

If the supply of cortical hormones were insufficient, a condition known as Addison's disease would occur. This disease is characterized by an excessive excretion of sodium ions and, therefore, water, due to the lack of corticoid minerals. This is accompanied by a decrease in the level of glucose in the blood due to a deficiency of glucocorticoids. Adrenal cortical hormone injections quickly relieve these symptoms


• Adrenal medulla: the inside portion of the adrenal gland
• Made of modified nervous tissue which is under the direct regulation of the sympathetic nerves of the autonomic nervous system
• It contains glandular cells known as chromaffin cells that secrete two closely related hormones: epinephrine (or adrenaline) and norepinephrine (or norepinephrine)
• The effects of these hormones resemble sympathetic stimulation, where body activities such as heart actions, blood pressure and respiratory rate increase, while digestive processes decrease. Hypersecretion can cause hypertension, increased blood sugar and elevated heart rate



Pancreas

The Endocrine System



The pancreas, which plays an important role in digestion by producing enzymes, also participates in the endocrine system. Groups of cells called "islands of Langerhans" secrete four different hormones, the most important of which are glucagon and insulin, which regulate blood sugar levels in the body

The pancreas is a very important organ in the digestive and circulatory system because it helps maintain blood sugar levels. The pancreas is part of the gastrointestinal system. It produces digestive enzymes that are released into the small intestine to help reduce food particles into basic elements that can be absorbed by the intestine and used by the body. It has a very different role, in that it forms insulin, glucagon and other hormones that are sent into the bloodstream to regulate blood sugar levels and other activities throughout the body

It is pear-shaped and about 6 inches long. It is located in the middle and rear of the abdomen. The pancreas is connected to the first part of the small intestine, the duodenum, and is located behind the stomach. The pancreas is composed from glandular tissue: any substance secreted by the cells of the pancreas will be produced outside the organ

The pancreas excreted the pancreatic juice, which contains digestive enzymes and are releasing it through a Y-shaped duct into the duodenum (at the point just before entering the duodenum, where the combined bile duct from the liver and the pancreatic duct join)


• The Pancreas is the only exocrine and endocrine gland in physiology
• In its exocrine aspect, 99% of its mass is made up of cells called acini which secrete enzymes and digestive fluids into the small intestine through the pancreatic ducts
• In its endocrine aspect, 1% of its mass is made up of small groups of cells called islets of langerhans (or pancreatic islets) which secrete hormones to regulate the level of glucose in the blood
• In each pancreatic islet, alpha cells (α cells) secrete glucagon to increase blood glucose levels
• Beta cells (beta cells) secrete insulin to lower the blood glucose level. Hyposecretion causes diabetes mellitus in which there is an excess of glucose in the urine and hypersecretion causes hyperinsulinism



Sexual organs

The sexual organs (gonads) are the testicles in men and the ovaries in women. Both organs produce and secrete hormones balanced by the hypothalamus and pituitary glands. The main hormones of the reproductive organs are:

Testosterone is most important in men. It belongs to the family of androgens, which are steroid hormones that produce male effects. Testosterone stimulates the development and function of the primary sexual organs. It also triggers the development and keeping of secondary male characteristics, such as hair growth on the face and the deep tone of the voice

Estrogen In women, this hormone stimulates the development of the uterus and vagina. It is also responsible for the development and keeping of secondary female features, such as the distribution of fat throughout the body and the display of the pelvis


Female

Ovary:

The female sexual organ which serves as an endocrine gland. It contains follicular cells in mature and secondary follicles, where they produce estrogen to maintain female sexual features, regulate ovarian and menstrual cycles, preserve pregnancy and develop secondary sexual features. Both hyposecretion and hypersecretion will have large influences on female reproductive functions. It also contains degenerative scar tissue called the corpus luteum which contains progesterone-secreting lutein cells to help maintain ovarian and menstrual cycles and pregnancy. The ailments are similar to those of estrogen

Estrogen is also responsible for secondary sexual features, including female body hair and fat distribution in the body. Estrogen and progesterone are important for breast and uterine cycle development. During the second half of the menstrual cycle, progesterone is a main female hormone secreted by the corpus luteum after ovulation and  It prepares the lining of the uterus for the implantation of a fertilized egg, which permits the complete detachment of the endometrium at the time of menstruation. In case of pregnancy, the progesterone level remains stable for about a week after conception


Male

Testicles

The male sexual organ which also plays a role as an endocrine gland. It contains interstitial cells (or Leydig cells) that secrete testosterone to develop secondary sexual characteristics. Both hyposecretion and hypersecretion will have large effects on male reproduction

Testosterone is labeled as a steroid and is important for many of men's physical features, such as:

• Broad shoulders

• Muscular body

• Capillary testosterone increases protein production. The hormones that structure proteins, known as anabolic steroids. Anabolic steroids are commercially available and athletes use them because they help improve their physical capacity, however they have important side effects such as:

• Liver and kidney diseases

Hypertension (high blood pressure)

• Decreased sperm count and impotence

• Aggressive behavior ("roid mania)

• Baldness

• Acne


Pineal gland


The pineal gland also determined as the pineal body or epiphysis, is a small gland located precisely between the two hemispheres, near the center of the brain, concealed in a crack where the two rounded thalamic bodies meet

The pineal gland is a reddish-gray body (8 mm) found just in dorsal side of forebrain with respect to the superior colliculus and behind and below the medullary streak, between the thalamus bodies positioned laterally. It is part of the epithelium. The pineal gland is a structure of the midline and is often marked on simple x-rays of the skull, as it is often calcified. Melatonin is the main hormone, which that secreted by the pineal gland. The discharge is higher at night


Relationship of the pituitary gland and hypothalamus



The Endocrine System


The hypothalamus forms the lower region of the diencephalon and is located just above the brain stem. The pituitary (pituitary) gland is attached to the bottom of the hypothalamus by a thin stem called the infundibulum. The pituitary gland divided into two main regions, the anterior pituitary gland, anterior lobe or adenohypophysis and the posterior pituitary gland, posterior lobe or neurohypophysis. The hypothalamus also controls glandular secretion from the pituitary gland.

The hypothalamus monitors many internal conditions of the body. It receives nerve stimuli from receptors throughout the body, meanwhile,  controls the chemical and physical blood characteristics's, such as temperature, blood pressure and the content of nutrients, hormones and water. The hypothalamus triggers cellular activity when deviations from homeostasis happen or if certain developmental changes are required. The process occurs in different parts of the body by managing the secretion of hormones from the anterior and posterior pituitary glands

The hypothalamus transfers directives to these glands: The pituitary is located in the lower part of the brain and is connected by the pituitary stem. It can be called the master gland because it is the main place of everything that happens within the endocrine system. It is divided into two portions: the anterior lobe , adenohypophysis and the posterior lobe, neurohypophysis. The anterior pituitary gland is involved in sending hormones that control all the other hormones in the body


1. Thymus gland: a diminishing gland over time, it is found between the lungs. secretes a group of hormones, such as thymosin, to influence the production and maturation of lymphocytes in the body's defenses



The Endocrine System



2. Heart: the organ for pumping blood into the cardiovascular system. It contains two small chambers called the atrium which secrete the atrial natriuretic factor (ANF) which helps regulate blood pressure

3. Digestive organs: the stomach secretes hormones such as gastrin to stimulate stomach activities. The small intestine secretes hormones such as cholecystokinin (CCK) to stimulate the activities of the gallbladder and intestinal gastrin to regulate the activities of the stomach

4. kidneys:


  • organs for filtering and cleaning blood and tissue fluids
  • secretes a hormone called erythropoietin to stimulate the production of red blood cells in the red bone marrow


5. Placenta:

  • Protective bag around the fetus during pregnancy
  • Secretes estrogen and progesterone to maintain a normal pregnancy


Thyroid Disorders


• Grave's disease: autoantibodies (against themselves) bind to TSH receptors on the membranes of thyroid cells, mimicking the action of TSH on the stimulating gland (hyperthyroidism); This is an exothermic goiter

• Hyperthyroidism: including, hyperactivity, weight loss, high metabolic rate, goiter, sensitivity to heat, restlessness,bulging eyes

• Hashimoto's disease: automatic antibodies (against themselves) attack thyroid cells and cause hypothyroidism

• Hypothyroidism (infantile): cretinism: deviant growth, abnormal bone formation, mental retardation, low body temperature, slowness

• Hypothyroidism (adult): myxedema: low metabolic rate, sensitivity to cols, slowness, lack of appetite, inflamed tissue, mental opacity

• Simple goiter: iodine deficiency causes no thyroid hormone, which inhibits the pituitary release of TSH. The thyroid gland is overstimulated and enlarged, but works below normal (hypothyroidism)

Thyroid Nodules



Disorders of the parathyroid glands


• Hyperparathyroidism: fatigue, muscle weakness, painful joints, impaired mental functions, depression, weight loss, bone weakness, increased secretion of PTH on stimulates osteoclasts

  • Cause: tumor
  • Treatment: remove the tumor, correct bone deformities
• Hypoparathyroidism: muscle cramps and convulsions. The reduced secretion of PTH reduces the activity of osteoclasts, reducing the concentration of calcium ions in the blood

  • Cause: involuntary surgical removal, injury
  • Treatment: taking heavy doses of vitamin D, and calcium salt injections 


Important events in general stress syndrome


• When stress, nerve impulses are transferred to the hypothalamus

• Sympathetic impulses deriving from the hypothalamus increase the glucose concentration, concentrated glycerol in the blood, concentration of fatty acids in the blood, heart rate, blood pressure and respiratory rate. They dilate the air passages, divert blood into the skeletal muscles and increase the secretion of adrenaline from the adrenal medulla

• Epinephrine intensifies and prolongs sympathetic actions

• The hypothalamus secretes CRH, which stimulates the secretion of ACTH by the anterior pituitary gland

•  ACTH activates the secretion of cortisol hormone from the adrenal cortex

•  Cortisol increases the conc. of amino acids in the blood, releases fatty acids and forms glucose from non-carbohydrate sources

• Secretion of glucagon from the pancreas and growth hormone by the increase in the anterior pituitary gland

• Glucagon and growth hormone help to mobilize energy sources and stimulate the absorption of amino acids by cells

• ADH secretion by mail. Increase the pituitary gland

• ADH promotes kidney retention of H2O by increasing blood volume

• Renin increases the blood level of angiotnsin II, which acts as a vasoconstrictor and also stimulates the secretion of aldosterone by the adrenal cortex. Aldosteron increases the retention of Na + by the kidneys


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