THE ENDOCRINE SYSTEM GROUP 1 By:Janine Kristel M. de Leon
Endocrine Glands and Hormones• Endocrine glands • Ductless • Secrete hormones into the blood• Hormones are regulatory molecules secreted into the body by endocrine glands• Hormones affect the metabolism of their target organs and, by this means, help to regulate total body metabolism, growth and reproduction
Endocrine Gland Major Hormones Primary Target Organs Primary EffectsAdipose tissue Leptin Hypothalamus Suppresses AppetiteAdrenal cortex Glucocorticoids Liver and Muscle Glucocorticoids Influence glucose metabolism; Aldosterone Kidneys aldosterone promotes Na+ retention, K+ excretionAdrenal Medulla Epinephrine Heart, Brochioles, and Causes adrenergic blood vessels stimulationHeart Atrial natriuretic Kidneys Promotes excretion of hormone Na+ in the urineHypothalamus Releasing and inhibiting Anterior pituitary Regulates secretion of hormones anterior pituitary hormonesSmall intestine Secretin and Stomach, liver and Inhibits gastric motility cholecystokinin pancreas and stimulates bile and pancreatic juice secretion
Islets of Langerhans Insulin Many organs Insulin promotes cellular(pancreas) uptake of glucose and Glucagon Liver and adipose tissue formation of glycogen and fat; glucagon stimulates hydrolysis of glycogen and fatKidneys Erythropoietin Bone marrow Stimulates red blood cell productionLiver Somatomedins Cartilage Stimulates cell division and growthOvaries Estradiol-17β and Female reproductive tract Maintains structure of progesterone and mammary gland reproductive tract and promotes secondary sex characteristicsParathyroid glands Parathyroid hormones Bone, small intestine and Increases Ca2+ kidneys concentration in bloodPineal gland Melatonin Hypothalamus and Affects secretion of anterior pituitary gonadotrophic hormones
Pituitary, anterior Trophic hormones Endocrine glands and Stimulates growth and other organs development of target organs; stimulates secretion of other hormonesPituitary, posterior Antidiuretic hormone Kidneys and blood vessels Antidiuretic hormone Uterus and mammary promotes water retention Oxytocin glands and vasoconstriction; oxytocin stimulates contraction of uterus and mammary secretory unitsSkin 1,25-Dihydroxyvitamin D3 Small intestine Stimulates absorption of Ca2+Stomach Gastrin Stomach Stimulates acid secretionTestes Testosterone Prostate, seminal vesicles Stimulates secondary and other organs sexual developmentThymus Thymopoietin Lymph nodes Stimulates WBC
Throid Gland Throxine (T4) and Most organs Throxine and triiodothyronine (T3); triiodothyronine calcitonin promotes growth and development and stimulates basal rate of cell respiration (basal metabolic rate or BMR); calcitonin may participate in the regulation in the blood Ca2+ levels
COMPARISON OFNERVOUS SYSTEM ANDENDOCRINE SYSTEM
CHARACTERISTIC NERVOUS SYSTEM ENDOCRINE SYSTEMMediator molecules Neurotransmitter released Hormones delivered to locally in response to nerve tissues throughout the body response by the bloodSite of mediator action Close to site of release, at a Far from site of release synapse; binds to receptor in (usually) binds to receptors postsynaptic membrane on or in target cellsTypes of target cells Muscle (smooth, cardiac and Cells throughout the body skeletal) cells, gland cells, other neuronsTime to onset of action Typically within millisecond Seconds to hours or days (thousandths of a second)Duration of action Generally briefer Generally longer (seconds to (milliseconds) days)
The Role of Hormone ReceptorsHormones like Neurotransmitter, influence their target cells by chemically binding to specific protein receptors. Only the target cells for a given hormone have receptors that bind and recognize that hormone.Receptors, like other cellular proteins, are constantly beingsynthesized and broken down. Generally, a target cell has 2000to 100,000 receptors for a particular hormone.
If a hormone is present in excess, the number of target-cell receptors maydecrease—an effect called down-regulation. Down- regulation makes a target cell less sensitive to a hormone.In contrast, when a hormone is deficient, the number of receptors may increase. This phenomenon, known as upregulation, makes a target cell more sensitive to a hormone.
Circulating and Local HormonesCirculating hormones—they pass from the secretory cells that make them into interstitial fluid and then into the blood.Local hormones, act locally on neighboring cells or on the samecell that secreted them without first entering the bloodstream.• Paracrines (para- beside or near) - Local hormones that act on neighboring cells• Autocrines - act on the same cell that secreted them (auto- self ).One example of a local hormone is interleukin 2 (IL-2), which is released by helper T cells (a type of white blood cell) during immune responses. IL-2 helps activate other nearby immune cells, a paracrine effect. But it also acts as an autocrine by stimulating the same cell that released it to proliferate.
• Local hormones usually are inactivated quickly; circulating hormones may linger in the blood and exert their effects for a few minutes or occasionally for a few hours. In time, circulating hormones are inactivated by the liver and excreted by the kidneys.
1. Amines• Hormones derived from amino acids tyrosine and tryptophan• Include the hormones secreted by the adrenal medulla, thyroid and pineal glands2. Polypeptides and proteins• Polypeptide hormones contain less than 100 amino acids (ex. Antidiuretic hormone)• Protein hormones are polypeptides with more than 100 amino acids (ex. Growth hormones
3. Glycoproteins• Consist of a long polypeptide (more than 100 amino acids) bound to one or more carbohydrate groups (ex. FSH and LH)4. Steroids• Lipids derived from cholesterol (ex. Testosterone, estradiol, progesterone and cortisol)
Hormone Structure Gland Primary EffectsAntidiuretic hormone 8 amino acids Posterior pituitary Water retention and vasoconstrictionOxytocin 8 amino acids Posterior pituitary Uterine and mammary contractionInsulin 21 and 30 amino acids Beta cells in islets of Cellular glucose uptake, (double chain) Langerhans lipogenesis and glycogenesisGlucagon 29 amino acids Alpha cells in islets of Hydrolysis of stored Langerhans glycogen and fatACTH 39 amino acids Anterior pituitary Stimulation of adrenal cortexParathyroid hormone 84 amino acids Parathyroid Increase in blood Ca2+ concentrationFSH, LH, TSH Glycoproteins Anterior pituitary Stimulation of growth, development and secretory activity of target glands
Hormone molecules can be divided into those that are polar, and therefore water soluble, and those that are nonpolar, and thus insoluble in water. (in terms of their actions in target cells) • Lipophilic hormones – nonpolar hormones soluble in lipids. They can gain entry into their target cells. These include the steroid hormones and thyroid hormones.Steroid hormones are secreted only by 2 endocrine glands: • Adrenal Cortex – secrete corticosteroids (cortisol and aldosterone) and small amounts of sex steroid • Gonads – secrete sex steroids
The major thyroid hormones are composed of two derivatives of the amino acid tyrosine bonded together.• Tetraiodothyronine (T4) or throxine – contains 4 iodine atoms• Triiodothyronine (T3) – contains 3 iodine atoms
The pineal gland secretes melatonin, hormone derived from the amino acid tryptophanThe adrenal medulla secretes the catecholamines epinephrine and norepinephrine which are derived from the amino acid tyrosine.
Endocrine Gland Prehormone Active Products CommentsSkin Vitamin D3 1,25-Dihydroxyvitamin D3 Hydroxylation reactions occur in the liver and kidneysTestes Testosterone Dihydrotestosterone DHT and other 5α- (DHT) reduced androgens are formed in most androgen- dependent tissue E2 is formed in the brain Estradiol-17β (E2) from testosterone, where it si beleived to affect both endocrine function and behavior; small amounts of E2 are also produced in the testesThyroid Thyroxine (T4) Triiodothronine (T3) Conversion of T4 to T3 occurs in almost all tissues
Hormone molecules that affect the metabolism of target cells are often derived from less active ―parent‖ or precursor, molecules.Insulin for example is derived from proinsulin within the beta cells of islets of Langerhans of the pancreas.In some cases, the prohormone itself is derived from an even larger precursor molecule; in the case of insulin, this molecule is calle preproinsulin.Prehormone is used to indicate such precursors of prohormone.The term prehormone designate those molecules secreted by endocrine glands that are inactive until changed by their target cells.
Common Aspects ofNeural and EndocrineRegulation
Regardless of whether a particular chemical is acting as a neurotransmitter or as a hormone, in order for it to function in physiologic condition: (1) target cells must have specific receptor proteins that combine with the regulatory molecule; (2) the regulation of the regulatory molecule with the receptor proteins must cause a specific sequence of changes in the target cells; and (3) there must be a mechanism to quickly turn off the action of the regulator. This mechanism which involves rapid removal and/or chemical inactivation of the regulatory molecules, is essential because without an ―off-switch‖ physiological control would be impossible.
Synergistic and Permissive EffectsWhen two or more hormones work together to produce a particular result, their effects are said to be synergistic. These effects may be additive or complementary.• Additive – action of the epinephrine and norepinephrine on the heart• Complementary – action of FSH and testosterone
A hormone is said to have a permissive effect on the action of a second hormone when it enhances the responsiveness of a target organ to the second hormone or when it increases the activity of the second hormone -Estrogen has a permissive effect on the responsiveness of the uterus to progesterone -Glucocorticoids exert permissive effects on the actions of catecholamins -Parathyroid hormones has a permissive effect on the actions of Vitamin D3
Antagonistic EffectThe action of one hormone antagonize the effects of another. -Lactation during pregnancy (estrogen and prolactin) -Antagonism in the action of insulin and glucagon on adipose tissue
Effects of HormoneConcentrations on TissueResponse
The half-life of a hormone – the time required for the plasma concentration of a given amount of the hormone to be reduced to half its reference level – ranges from minutes to hours for most hormones (thyroid hormone however is for several days)Normal tissue responses are produced only when the hormones are present within their normal, or physiological, range of concentrations.When some hormones are taken in abnormally high, or pharmacological, concentrations, their effects may be different from those produced by lower, more physiologic, concentrations.
Priming EffectsVariations in hormone concentration within the normal, physiological range can affect the responsiveness of target cells. This is due in part to the effects of the polypeptide and glycoprotein hormones on the number of their receptor proteins in target cells. More receptors may be formed in the target cells in response to particular hormones.Sometimes also called upregulationExample: GnRH
Desensitization and DownregulationSubsequent exposure to the same concentration of the same hormone produces less of a target tissue response. This desensitization may be due to the fact that high concentrations of these hormones cause a decrease in the number of receptor proteins in their target cells – a phenomenon called DOWN REGULATION. (ex. Adipose cells and testicular cells)
In order to prevent desensitization from occuring under normal conditions, many polypeptide and glycoprotein hormones are secreted in spurts rather than continuously. This pulsatile secretion is an important aspect in the hormonal control in the reproductive system.Pulsatile secretion of GnRH and LH is needed to prevent desensitization (in gonadal function).