Endo 1 janine
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Transcript of Endo 1 janine
THE ENDOCRINE SYSTEM
GROUP 1By:Janine Kristel M. de Leon
• 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 Glands and Hormones
Endocrine Gland
Major Hormones
Primary Target Organs
Primary Effects
Adipose tissue Leptin Hypothalamus Suppresses Appetite
Adrenal cortex Glucocorticoids
Aldosterone
Liver and Muscle
Kidneys
Glucocorticoids Influence glucose metabolism; aldosterone promotes Na+ retention, K+
excretion
Adrenal Medulla Epinephrine Heart, Brochioles, and blood vessels
Causes adrenergic stimulation
Heart Atrial natriuretic hormone
Kidneys Promotes excretion of Na+ in the urine
Hypothalamus Releasing and inhibiting hormones
Anterior pituitary
Regulates secretion of anterior pituitary hormones
Small intestine Secretin and cholecystokinin
Stomach, liver and pancreas
Inhibits gastric motility and stimulates bile and pancreatic juice secretion
Islets of Langerhans (pancreas)
Insulin
Glucagon
Many organs
Liver and adipose tissue
Insulin promotes cellular uptake of glucose and formation of glycogen and fat; glucagon stimulates hydrolysis of glycogen and fat
Kidneys Erythropoietin Bone marrow Stimulates red blood cell production
Liver Somatomedins Cartilage Stimulates cell division and growth
Ovaries Estradiol-17β and progesterone
Female reproductive tract and mammary gland
Maintains structure of reproductive tract and promotes secondary sex characteristics
Parathyroid glands
Parathyroid hormones
Bone, small intestine and kidneys
Increases Ca2+ concentration in blood
Pineal gland Melatonin Hypothalamus and anterior pituitary
Affects secretion of gonadotrophic hormones
Pituitary, anterior
Trophic hormones
Endocrine glands and other organs
Stimulates growth and development of target organs; stimulates secretion of other hormones
Pituitary, posterior
Antidiuretic hormone
Oxytocin
Kidneys and blood vesselsUterus and mammary glands
Antidiuretic hormone promotes water retention and vasoconstriction; oxytocin stimulates contraction of uterus and mammary secretory units
Skin 1,25-Dihydroxyvitamin D3
Small intestine Stimulates absorption of Ca2+
Stomach Gastrin Stomach Stimulates acid secretion
Testes Testosterone Prostate, seminal vesicles and other organs
Stimulates secondary sexual development
Thymus Thymopoietin Lymph nodes Stimulates WBC production
Throid Gland Throxine (T4) and triiodothyronine (T3); calcitonin
Most organs Throxine and triiodothyronine 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 OF NERVOUS SYSTEM AND ENDOCRINE SYSTEM
CHARACTERISTIC
NERVOUS SYSTEM
ENDOCRINE SYSTEM
Mediator molecules
Neurotransmitter released locally in response to nerve response
Hormones delivered to tissues throughout the body by the blood
Site of mediator action
Close to site of release, at a synapse; binds to receptor in postsynaptic membrane
Far from site of release (usually) binds to receptors on or in target cells
Types of target cells
Muscle (smooth, cardiac and skeletal) cells, gland cells, other neurons
Cells throughout the body
Time to onset of action
Typically within millisecond (thousandths of a second)
Seconds to hours or days
Duration of action Generally briefer (milliseconds)
Generally longer (seconds to days)
HORMONE ACTIVITY
Hormones 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 being
synthesized and broken down. Generally, a target cell has 2000
to 100,000 receptors for a particular hormone.
The Role of Hormone Receptors
If a hormone is present in excess, the number of target-cell receptors may
decrease—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 HORMONES
Circulating 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 same
cell 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.
Circulating and Local Hormones
• 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.
CHEMICAL CLASSIFICATION OF HORMONES
1. Amines• Hormones derived from amino acids tyrosine
and tryptophan• Include the hormones secreted by the adrenal
medulla, thyroid and pineal glands
2. 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 Effects
Antidiuretic hormone
8 amino acids Posterior pituitary
Water retention and vasoconstriction
Oxytocin 8 amino acids Posterior pituitary
Uterine and mammary contraction
Insulin 21 and 30 amino acids (double chain)
Beta cells in islets of Langerhans
Cellular glucose uptake, lipogenesis and glycogenesis
Glucagon 29 amino acids Alpha cells in islets of Langerhans
Hydrolysis of stored glycogen and fat
ACTH 39 amino acids Anterior pituitary
Stimulation of adrenal cortex
Parathyroid hormone
84 amino acids Parathyroid Increase in blood Ca2+
concentration
FSH, 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 tryptophan
The adrenal medulla secretes the catecholamines epinephrine and norepinephrine which are derived from the amino acid tyrosine.
Endocrine Gland
Prehormone Active Products
Comments
Skin Vitamin D3 1,25-Dihydroxyvitamin D3
Hydroxylation reactions occur in the liver and kidneys
Testes Testosterone Dihydrotestosterone (DHT)
Estradiol-17β (E2)
DHT and other 5α-reduced androgens are formed in most androgen-dependent tissue
E2 is formed in the brain from testosterone, where it si beleived to affect both endocrine function and behavior; small amounts of E2 are also produced in the testes
Thyroid Thyroxine (T4) Triiodothronine (T3)
Conversion of T4 to T3 occurs in almost all tissues
Prohormones and Prehormones
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 of Neural and Endocrine Regulation
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.
Hormone Interaction
When 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
Synergistic and Permissive Effects
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
The 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
Antagonistic Effect
Effects of Hormone Concentrations on Tissue Response
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.
Variations 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
Priming Effects
Subsequent 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)
Desensitization and Downregulation
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).
THE END BOW.