Introducción a la endocrinologÍa - Guyton capitulo 75

Introduction to Endocrinology

In this section, we will begin studying the physiology of endocrinology. We will explore the basic concepts of hormones, receptors, and the glands where hormones are released.

Hormones and their Functions

• Hormones are substances synthesized in specialized cells and secreted into circulation.

• They act as messengers that travel through the bloodstream to target cells or tissues.

• Hormones exert their functions by binding to specific receptors on target cells.

• Different hormones can have different chemical structures, such as proteins, polypeptides, or steroids.

Communication between Cells

• Cells can communicate with each other using chemical messengers.

• Neurotransmitters are chemical messengers released by neurons at synapses to control nervous functions locally.

• Neurons release neurotransmitters from axon terminals that bind to receptors on target neurons.

• Endocrine hormones are produced by glands and secreted into the bloodstream to influence distant target cells located throughout the body.

• These hormones travel through circulation to reach their target cells.

Types of Hormones

Endocrine Hormones

• Endocrine hormones are produced by specialized glands or cells and released into the bloodstream.

• They influence the function of target cells located in various parts of the body.

Neuroendocrine Hormones

• Neuroendocrine hormones are secreted by neurons directly into the blood.

• They affect target cells in different areas of the body.

Paracrine Hormones

• Paracrine hormones are secreted by cells into extracellular fluid to act on nearby neighboring cells.

Summary

In this introductory section on endocrinology, we learned about hormones as substances synthesized in specialized cells and secreted into circulation. We explored how they communicate with target cells through specific receptors. Additionally, we discussed different types of hormone communication including endocrine, neuroendocrine, and paracrine hormones.

Hormone Communication

This section discusses the communication of hormones between cells and the interstitial space.

Hormone Communication

• Cells release hormones to communicate with neighboring cells.

• The space between cells is called the interstitial space.

• Hormones can act on the same cell that released them, known as autocrine communication.

• Cytokines are peptides secreted by cells into the extracellular fluid and can function as hormones.

Types of Hormones

This section explains different types of hormones and their functions.

Types of Hormones

• Autocrine hormones act on the same cell that releases them.

• Cytokines are peptides secreted by cells into the extracellular fluid and can function as hormones.

• Various glands in the human body secrete hormones, including the hypothalamus, pituitary gland, thyroid gland, pancreas, adrenal glands, ovaries (in women), testicles (in men), kidneys, heart, stomach, and adipose tissue.

Chemical Structure of Hormones

This section describes the chemical structure of hormones.

Chemical Structure of Hormones

• Hormones can have a protein or polypeptide structure. Examples include those secreted by the pituitary gland and pancreas.

• Steroid hormones are derived from cholesterol. Examples include cortisol and aldosterone secreted by the adrenal cortex.

• Thyroid hormones (such as thyroxine) and catecholamines (such as adrenaline) are derived from tyrosine amino acid.

Synthesis of Peptide/Protein Hormones

This section explains how peptide/protein hormones are synthesized.

Synthesis of Peptide/Protein Hormones

• Peptide/protein hormones are synthesized as proteins through transcription and translation processes.

• The DNA is transcribed into mRNA, which then leaves the nucleus and enters the cytoplasm.

• In the cytoplasm, the mRNA is translated to form proteins in a process called translation.

• Pre-prohormones are formed in the rough endoplasmic reticulum and further processed into prohormones.

• Prohormones are packaged into vesicles in the Golgi apparatus before being released into the cytoplasm.

Storage and Release of Peptide/Protein Hormones

This section discusses how peptide/protein hormones are stored and released.

Storage and Release of Peptide/Protein Hormones

• Peptide/protein hormones are stored in secretory vesicles until they are needed.

• When required, these hormones are released from secretory vesicles into the extracellular fluid.

Hormone Synthesis and Release

This section discusses the synthesis and release of hormones, focusing on protein-based hormones, steroid hormones, and amine hormones derived from tyrosine.

Protein-Based Hormones

• Protein-based hormones are synthesized in the rough endoplasmic reticulum as preprohormones.

• Preprohormones are then modified into prohormones in the Golgi apparatus.

• Prohormones are packaged into secretory vesicles where they undergo further modifications.

• Upon stimulation, these vesicles fuse with the plasma membrane to release active hormone molecules.

Steroid Hormones

• Steroid hormones are synthesized from cholesterol.

• They are not stored but can easily diffuse out of cells due to their liposolubility.

• Once released, they travel through the bloodstream primarily bound to proteins.

Amine Hormones Derived from Tyrosine

• Amine hormones derived from tyrosine include thyroid hormones (T4 and T3) and catecholamines (adrenaline and noradrenaline).

• Thyroid hormones are produced in the thyroid gland, while catecholamines are produced in the adrenal medulla.

• Catecholamines are stored in preformed vesicles until secretion is triggered.

Secretion, Transport, and Clearance of Hormones

This section covers the secretion, transport, and clearance of hormones in the bloodstream.

Secretion of Hormones

• Hormonal secretion is stimulated by various factors depending on the hormone.

• Some hormones have a short duration of action (seconds or minutes), while others have a long duration (days, weeks, or months).

Concentrations and Rhythms of Hormonal Secretion

• Hormone concentrations in the bloodstream vary depending on the time of day and other factors.

• Some hormones exhibit diurnal rhythms, with higher levels during certain periods.

• The concentration of a hormone in the blood is regulated by its secretion rate and clearance rate.

Transport of Hormones

• Liposoluble hormones, such as steroid hormones, travel through the bloodstream bound to proteins.

• Hydrophilic protein-based hormones can freely circulate in the bloodstream.

Clearance of Hormones

• Hormones are cleared from the bloodstream through various mechanisms, including metabolism by enzymes and excretion by organs like the liver and kidneys.

Timestamps have been associated with relevant bullet points.

New Section

This section discusses the regulation of hormones through feedback mechanisms and the different types of feedback, including negative and positive feedback.

Regulation of Hormones

• Hormone concentrations in the blood are reduced when their secretion is decreased.

• Secretion of hormones is regulated by feedback mechanisms.

• Feedback can be either negative or positive.

Negative Feedback

• Negative feedback is a type of feedback where the initial stimulus leads to an opposite effect.

• Example: In the hypothalamus, a hormone called TRH stimulates the release of TSH. When T3 and T4 levels increase, they inhibit TRH and TSH release, reducing further hormone production.

Positive Feedback

• Positive feedback is a type of feedback where the initial stimulus leads to similar reactions.

• Example: LH (luteinizing hormone) released from the pituitary gland stimulates estrogen production in ovaries. Increased estrogen levels further stimulate LH release.

New Section

This section explains how hormones are transported in the blood and distinguishes between hydrophilic and lipophilic hormones.

Transport of Hormones

• Hydrophilic hormones, such as peptides and catecholamines, are soluble in water and can freely circulate in plasma.

• Lipophilic hormones, such as thyroid hormones and steroids, require binding to plasma proteins for transport in plasma.

New Section

This section discusses how hormones bound to plasma proteins lack biological activity until they dissociate from these proteins.

Binding to Plasma Proteins

• Hormones bound to plasma proteins do not have biological activity.

• Hormones need to dissociate from plasma proteins to exert their effects.

New Section

This section introduces the concept of hormone clearance and factors that can affect hormone concentrations in the blood.

Hormone Clearance

• Hormone clearance refers to the elimination of hormones from the blood.

• Two factors can affect hormone concentrations: factors that increase or decrease hormone production and factors that affect hormone clearance.

The transcript does not provide further details on these factors.

Metabolic Clearance Rate

In this section, the speaker discusses the concept of metabolic clearance rate and how it is calculated. They also mention different ways in which hormones can be eliminated from the plasma.

Calculation of Metabolic Clearance Rate

• The metabolic clearance rate is calculated using a formula: metabolic clearance rate = hormone disappearance rate in plasma / hormone concentration in each milliliter of plasma.

Elimination of Hormones from Plasma

• Hormones can be eliminated from the plasma through various mechanisms, including metabolic destruction by tissues, binding to tissues, hepatic excretion via bile, and renal excretion via urine.

Introduction to Receptors

In this section, the speaker introduces the topic of receptors and mentions that they will discuss different hormones and their general functions in the next class.

Introduction to Receptors

• The next class will cover receptors and provide an overview of different hormones.

• The speaker shares an image with abbreviations for various hormones and mentions that they will use these abbreviations throughout the course.

Hypothalamus and Pituitary Gland

In this section, the speaker highlights the importance of two organs - hypothalamus and pituitary gland - in hormone regulation. They explain how hormones released by the hypothalamus stimulate the pituitary gland to release its own hormones, which then travel to different glands in the body.

Role of Hypothalamus and Pituitary Gland

• The hypothalamus releases a series of hormones or releasing factors that travel to the pituitary gland.

• These releasing factors stimulate the pituitary gland to release its own hormones.

• The pituitary gland's hormones travel to different glands in the body, such as the thyroid, adrenal glands, ovaries (in women), and testicles (in men).

Hormones of the Hypothalamus

In this section, the speaker discusses specific hormones released by the hypothalamus and their functions.

Hormones of the Hypothalamus

• The first hormone discussed is Thyrotropin-Releasing Hormone (TRH), which stimulates the release of thyrotropin and prolactin.

• Corticotropin-Releasing Hormone (CRH) induces the release of corticotropin or adrenocorticotropic hormone (ACTH).

• Growth Hormone-Releasing Hormone (GHRH) stimulates the release of growth hormone.

• Somatostatin inhibits the release of growth hormone.

• Gonadotropin-Releasing Hormone (GnRH) induces the release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH).

• Dopamine inhibits prolactin release.

Other Hypothalamic Hormones

In this section, the speaker mentions other hormones released by the hypothalamus.

Other Hypothalamic Hormones

• The speaker mentions two additional hormones: Vasopressin and Oxytocin.

• These hormones are synthesized by the hypothalamus but stored in and released from the posterior pituitary gland.

Hormones and their Functions

In this section, we will explore different hormones and their functions in the body.

Growth Hormone (GH)

• GH stimulates protein synthesis and overall growth of cells and tissues.

• It is a peptide hormone.

Thyroid Stimulating Hormone (TSH)

• TSH stimulates the synthesis and secretion of thyroid hormones (T3 and T4).

• It is a peptide hormone.

Adrenocorticotropic Hormone (ACTH)

• ACTH stimulates the synthesis and secretion of corticosteroid hormones by the adrenal cortex.

• It travels to the adrenal glands to stimulate the production of cortisol, androgens, and aldosterone.

• ACTH is a peptide hormone.

Prolactin

• Prolactin promotes breast development in females and milk secretion.

• It is a peptide hormone.

Follicle Stimulating Hormone (FSH)

• FSH induces follicle growth in the ovaries for egg maturation, as well as sperm production in testicular cells.

• FSH is a peptide hormone.

Luteinizing Hormone (LH)

• LH stimulates testosterone synthesis in Leydig cells of the testes.

• In females, it triggers ovulation, formation of corpus luteum, and synthesis of estrogen and progesterone.

• LH is a peptide hormone.

Neurohypophyseal Hormones

Vasopressin or Antidiuretic Hormone (ADH)

• ADH increases water reabsorption by the kidneys, leading to vasoconstriction and increased blood pressure.

• It is a peptide hormone.

Oxytocin

• Oxytocin stimulates milk ejection during breastfeeding and uterine contractions during labor.

• It also plays a role in bonding and social behavior.

• Oxytocin is a peptide hormone.

Thyroid Hormones

• T3 (triiodothyronine) and T4 (thyroxine) are the main hormones produced by the thyroid gland.

• They regulate metabolism and have various functions in almost all cells of the body.

• These hormones are amino acid derivatives.

Adrenal Cortex Hormones

Cortisol

• Cortisol plays a crucial role in metabolic processes, protein, carbohydrate, and fat metabolism.

• It also has anti-inflammatory effects.

• Cortisol is a steroid hormone.

Aldosterone

• Aldosterone increases sodium reabsorption in the kidneys while promoting potassium and hydrogen ion excretion.

• It helps regulate electrolyte balance and blood pressure.

• Aldosterone is a steroid hormone.

Calcitonin

• Calcitonin, secreted by the thyroid gland, promotes calcium deposition in bones, reducing extracellular calcium levels.

• It is a peptide hormone.

Adrenal Medulla Hormones

Epinephrine (Adrenaline) and Norepinephrine (Noradrenaline)

• Epinephrine and norepinephrine are involved in sympathetic stimulation, fight-or-flight response, and stress reactions.

• They are catecholamines.

Summary

This section provides an overview of the different types of hormones discussed earlier.

Thyroid Gland Hormones

• The thyroid gland produces T3 and T4 hormones that regulate metabolism throughout the body. These hormones have numerous functions in various cells.

Adrenal Cortex Hormones

• The adrenal cortex produces cortisol, which controls protein, carbohydrate, and fat metabolism. It also possesses anti-inflammatory properties. Aldosterone regulates electrolyte balance by increasing sodium reabsorption in the kidneys.

Calcitonin

• Calcitonin, secreted by the thyroid gland, promotes calcium deposition in bones and reduces extracellular calcium levels.

Adrenal Medulla Hormones

• The adrenal medulla produces epinephrine (adrenaline) and norepinephrine (noradrenaline), which play a role in sympathetic stimulation, fight-or-flight response, and stress reactions.

Neurohypophyseal Hormones

• Vasopressin (ADH) increases water reabsorption by the kidneys and induces vasoconstriction. Oxytocin stimulates milk ejection during breastfeeding and uterine contractions during labor.

These hormones have diverse functions in the body and are essential for maintaining homeostasis.

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This section focuses on the hormones released by different organs in the body and their functions.

Hormones and Their Functions

• The pancreas releases insulin, which plays a role in carbohydrate metabolism, specifically in glucose transport into cells. Insulin is a peptide hormone. [[timestamp]]

• The pancreas also secretes glucagon, which has opposite functions to insulin. It increases the synthesis and release of glucose from the liver into the bloodstream. Glucagon is an antagonist hormone to insulin. [[timestamp]]

• The parathyroid glands, located behind the thyroid gland, release parathyroid hormone (PTH). PTH controls calcium ion concentration in the blood and has important functions in bone regulation. PTH is a peptide hormone. [[timestamp]]

• Testes secrete testosterone, an important male hormone derived from cholesterol. Testosterone belongs to the steroid group of hormones. [[timestamp]]

• Ovaries secrete estrogen and progesterone, which are primarily responsible for female reproductive system development and secondary sexual characteristics. These hormones also belong to the steroid group of hormones derived from cholesterol. [[timestamp]]

• Placenta releases various hormones during pregnancy, including human chorionic gonadotropin (hCG), which supports the growth of corpus luteum and secretion of estrogen and progesterone. hCG is a peptide hormone.

• Kidneys produce renin, which converts angiotensinogen to angiotensin I, regulating blood pressure. Renin is a peptide hormone.

• Kidneys also produce calcitriol (active form of vitamin D), erythropoietin (stimulates red blood cell production), and prostaglandins (involved in various physiological processes). [[timestamp]]

• Heart releases atrial natriuretic peptide (ANP), which increases sodium excretion by the kidneys and reduces blood pressure. ANP is a peptide hormone. [[timestamp]]

• Stomach secretes gastrin, which stimulates the secretion of hydrochloric acid by parietal cells. Gastrin is a peptide hormone.

• Small intestine secretes secretin, which stimulates the release of bicarbonate and water from pancreatic duct cells. Secretin is a peptide hormone.

• Adipose tissue releases leptin, an important hormone involved in appetite regulation and energy balance. Leptin inhibits appetite and promotes energy expenditure. Leptin is a peptide hormone.

New Section

This section discusses additional hormones released by the placenta, as well as their functions.

Placental Hormones

• Human chorionic gonadotropin (hCG) supports the growth of corpus luteum and secretion of estrogen and progesterone during pregnancy. hCG is a peptide hormone.

• Human placental lactogen (hPL) promotes mammary gland development and regulates maternal metabolism during pregnancy. hPL is a protein hormone.

• Estrogen and progesterone produced by the placenta have various functions related to fetal development, including stimulating uterine gland secretion, mammary gland development, and maintaining pregnancy.

New Section

This section focuses on hormones released by the kidney.

Kidney Hormones

• Renin converts angiotensinogen to angiotensin I, regulating blood pressure. Renin is a peptide hormone.

• Calcitriol (active form of vitamin D) promotes intestinal calcium absorption and bone mineralization. Calcitriol is a steroid hormone.

• Erythropoietin stimulates the production of red blood cells in the bone marrow. Erythropoietin is a peptide hormone.

New Section

This section discusses hormones released by adipose tissue and their role in obesity.

Adipose Tissue Hormones

• Leptin, released by adipose tissue, inhibits appetite and increases energy expenditure. Leptin is a peptide hormone.

These are some of the key hormones released by different organs in the body and their functions. Each hormone plays a crucial role in maintaining various physiological processes within the body.

Hormones of the Hypothalamus and Pituitary Gland

This section discusses the hormones released by the hypothalamus and pituitary gland, their functions, and how they stimulate other glands in the body.

Hormones Released by the Hypothalamus and Pituitary Gland

• The hypothalamus releases hormones that stimulate the pituitary gland.

• The pituitary gland consists of two parts: the anterior pituitary (adenohypophysis) and the posterior pituitary (neurohypophysis).

• Hormones such as vasopressin and oxytocin are released by the posterior pituitary in response to stimulation from the hypothalamus.

• The hormones released by the anterior pituitary travel to different glands in the body, such as the thyroid gland, adrenal glands, ovaries (in women), and testes (in men).

• These hormones stimulate these glands to release their own specific hormones.

Examples of Hormone Release

Thyroid Gland

• The hormone TSH (thyroid-stimulating hormone) is released by the anterior pituitary to stimulate the thyroid gland.

• This leads to the release of thyroid hormones from the thyroid gland.

Adrenal Glands

• The hormone ACTH (adrenocorticotropic hormone) travels to the adrenal glands.

• This stimulates these glands to release cortisol or aldosterone.

Ovaries/Testes

• Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) travel to ovaries in women and testes in men.

• These hormones stimulate these organs to produce their respective sex hormones.

It is important to understand that each hormone has its own specific target organ or gland for regulation.