Science 3rd Quarter Overview of the Endocrine System PDF

**Overview of the Endocrine System** **The Endocrine System**- a collection of ductless glands scattered around the body. It controls various activities of different organs, such as growth and response to stress. - - - **The Endocrine Glands** - - +----------------------------------...

**Overview of the Endocrine System** **The Endocrine System**- a collection of ductless glands scattered around the body. It controls various activities of different organs, such as growth and response to stress. - - - **The Endocrine Glands** - - +-----------------------------------+-----------------------------------+ | EXOCRINE GLANDS | ENDOCRINE GLANDS | +===================================+===================================+ | - - | - - | +-----------------------------------+-----------------------------------+ - - **Functions of the Endocrine System:** 1. 2. 3. +-----------------------+-----------------------+-----------------------+ | Epinephrine | Similarities | Norepinephrine | +=======================+=======================+=======================+ | \- May be prescribed | \- both produced by | \- May be prescribed | | to treat | the adrenal medulla | to raise dangerously | | life-threatening | | low blood pressure | | conditions like | \- increase heart | after a heart attack, | | anaphylaxis, severe | rate, blood pressure, | septic shock, or | | asthma attacks, and | and blood sugar | critical hypotension. | | cardiac arrest. | levels. | | +-----------------------+-----------------------+-----------------------+ 4. +-----------------------------------+-----------------------------------+ | Estrogen | Progesterone | +===================================+===================================+ | \- produced in the ovaries. | \- prepares the uterus for a | | | possible pregnancy. | | \- stimulates the development of | | | follicles | | +-----------------------------------+-----------------------------------+ 5. 6. +-----------------------------------------------------------------------+ | KEY POINTS: | | | | \- The endocrine system, similar to the nervous system, functions for | | coordination. However, unlike that of the nervous system, | | coordination is accomplished through the chemical messengers called | | hormones. | | | | \- Endocrine glands are ductless organs of the endocrine system. Some | | of them are devoted solely to their endocrine function. Other | | endocrine organs also serve non-endocrine functions, and are thus | | called mixed-function organs. | +-----------------------------------------------------------------------+ **Pituitary and Hypothalamus: The Body's Control Center** \- The pituitary gland was thought to be the "master" endocrine gland because its hormones control other glands. But, the pituitary gland is controlled by the hypothalamus, making it the true "master" gland. \- Pituitary gland, about 1.5 cm in diameter, is a pea-shaped organ. It has 2 anatomical portions: anterior and posterior pituitary glands The pituitary gland secretes a total of seven hormones: Anterior Pituitary Posterior Pituitary --------------------------------------------------------------------- -------------------------------------------------- Somatotropin, thyrotropin, gonadotropin, lactotropin, corticotropin Vasopressin/antidiuretic hormone (ADH), Oxytocin **Anterior Pituitary Hormones** Somatotropins secrete human growth hormone (hGH): \- The hGH stimulates the release of growth factors from the liver, skeletal muscles, cartilage, and bones which cause cells to grow & multiply by increasing the rate of gene expression. \- Somatotropins also release bursts of hGH every few hours, especially during sleep. They also enhance the breakdown of fats in adipose tissues. Thyrotrophs are the master regulators of the thyroid gland hormones. \- They control the body's metabolic rate, heat generation, neuromuscular function, and heart rate. Gonadotrophs secrete 2 gonadotropins: follicle-stimulating hormone (FSH) and luteinizing hormone (LH). These hormones act on the male and female gonads. \- FSH initiates follicular development for menstrual cycle. It stimulates the production of estrogen in females and sperm production in the testes of males. \- LH triggers female ovulation, which is the release of the secondary oocyte in an ovary. It also triggers progesterone production which prepares the uterus for a possible pregnancy. In males, LH stimulates the production of testosterone. Lactotrophs are anterior pituitary cells responsible for secreting prolactin (PRL). \- It initiates and maintains milk production in the mammary glands of females. Corticotrophs secrete adrenocorticotropic hormone (ACTH) or corticotropin. \- This hormone stimulates the adrenal to secret cortisol as response to stress. \- Some corticotrophs secrete melanocyte-stimulating hormone (MSH), which stimulates the dispersion of the pigment, melanin. **Posterior Pituitary Hormones** \- does not synthesize its own hormone. It only stores and releases 2 hormones (oxytocin and vasopressin) that are synthesized in the hypothalamus. Oxytocin is important during and after the delivery of a baby. \- It stimulates uterine contractions during labor and milk ejection from the mammary glands for suckling by the infant after delivery. Vasopressin or antidiuretic hormone (ADH) stimulates the kidneys to reabsorb more water. \- It allows the kidneys to return more water to the blood to decrease the amount of urine. \- Without ADH, urine output may reach from normal of 1-2 liters per day to up to 20 liters a day. This hormone is usually secreted in response to dehydration. \- It also targets the sweat glands to reduce water loss by perspiration from the skin. **The Hypothalamic Hormones** \- The hormones of the hypothalamus serve as major controls to the secretions of the anterior pituitary gland. They are called releasing hormones or inhibiting hormones which are all peptide hormones. \- Example of pathways for releasing hormones: The gonadotropin-releasing hormone (GnRH) stimulates the release of the FSH and LH, which will then activate their corresponding functions. Other examples of inhibiting and releasing hormones: **Hormones** **Functions** ----------------------------------------- ------------------------------------------------------------ Thyrotropin-releasing hormone (TRH) Stimulates the release of TSH from the anterior pituitary. Prolactin-inhibiting hormone (PIH) Inhibits the release of prolactin. growth hormone-releasing hormone (GHRH) Stimulates the release of the growth hormone. Corticotropin-releasing hormone (CRH) Stimulates the release of ACTH. **Related Disorders** \- Hypothalamic dysfunction is the general interruption in the functioning of the hypothalamus. Because the hypothalamus is the "master" endocrine gland, it greatly affects the pituitary glands. \- Pituitary dwarfism results in the hyposecretion of the hGH during growth years, which slows down bone growth. \- Gigantism is caused by the hypersecretion of GH which can cause the femur to grow very long. \- Acromegaly is a condition in adults where the bones of the face and hands thicken. This is caused by hypersecretion or overproduction of GH. \- Neurogenic diabetes insipidus is brought about by the inability to secrete the ADH. Its common symptom is the release of large volumes of urine, with accompanying dehydration and thirst. This disorder can be caused by brain tumor, head trauma, or brain surgery that damages the posterior pituitary gland. +-----------------------------------------------------------------------+ | KEY POINTS: | | | | \- The hypothalamus serves as the "master" endocrine organ by | | producing tropic hormones that control the secretion of the hormones | | of the anterior pituitary gland. Hypothalamic hormones may either be | | releasing or inhibiting hormones. | | | | \- The anterior pituitary gland releases different hormones, namely, | | adrenocorticotropic hormone (ACTH), follicle-stimulating hormone | | (FSH), luteinizing hormone (LH), prolactin (PRL), human growth | | hormone (hGH), and thyroid-stimulating hormone (TSH) | | | | \- The posterior pituitary gland secretes 2 hormones: oxytocin and | | vasopressin. Both of these hormones are produced by neurosecretory | | cells of the hypothalamus. | | | | \- Disorders that primarily involve these endocrine centers include | | hypothalamic dysfunction, pituitary dwarfism, gigantism, acromegaly, | | and neurogenic diabetes insipidus. | +-----------------------------------------------------------------------+ **The Major Peripheral Endocrine Glands** \- Hypothalamus and pituitary gland are central endocrine glands since they control other glands. 4 major peripheral endocrine glands: thyroid gland, parathyroid gland, adrenal gland, pancreas **Thyroid Gland** \- are two-lobed endocrine structure that's located just below the larynx. The narrow middle portion gives it a butterfly or bow-tie shape. Its main hormone is the thyroxine. \- The major secretory cells of the thyroid are called the follicular cells. They are arranged into hollow spheres called follicles. These are filled with colloid substance which are storage sites for thyroid hormones. \- The follicular cells contain 2 iodine-containing hormones: tetraiodothyronine & triiodothyronine \- Thyroid hormones increase basal metabolic rate (BMR). It is the rate at which oxygen is consumed under standard conditions (awake, at rest, and fasting). The increase in BMR increases metabolism of macronutrients. \- Thyroid hormones maintain normal body temperature by stimulating ATP and heat production through sodium-potassium pumps. They also hasten protein synthesis and glucose &fatty acid breakdown to produce ATP. **Parathyroid Glands** \- are endocrine structures that are partially embedded in the thyroid gland. Majority of their cells are called chief cells or principal cells (these produce parathyroid hormone aka PTH or parathormone). \- PTH is a major regulator of the levels of calcium, magnesium, and phosphate ions in the blood. PTH increases the number and activity of osteoclasts (These are bone cells that degrade bone to initiate remodeling) **Adrenal Glands**- are paired and pyramidal endocrine structures located above each kidney. They have 2 functional regions: Adrenal cortex (outer region) & Adrenal medulla (inner) Adrenal cortex produces three sets of hormones: Mineralocorticoids (important for mineral homeostasis) Glucocorticoids (important for glucose homeostasis) Weak androgens - - Adrenal medulla is a modified ganglion of the autonomic nervous system. It synthesizes 2 hormones: epinephrine (adrenaline) & norepinephrine (noradrenaline) \- During stressful situations, the adrenal medulla receives impulses from the hypothalamus to secrete epinephrine and norepinephrine. - **Pancreas** Pancreatic islets consist of different types of hormone-producing cells: \- The alpha cells produce glucagon. \- The beta cells secrete insulin. \- The delta cells produce somatostatin, which is a hormone identical to the GH inhibiting hormone of the hypothalamus. - - **Related Endocrine Disorders** \- Congenital hypothyroidism, aka cretinism, refers to the hyposecretion of thyroid hormones from birth. Affected individuals are characterized by severe mental retardation and stunted bone growth. \- Grave's disease is due to hypersecretion of the thyroid hormone. Affected individuals produce antibodies that mimic the effects of TSH, which stimulates the enlargement of the thyroid gland and greater thyroid production. A person with Grave's disease exhibits exophthalmos, the protrusion of the eyeballs. \- Hypoparathyroidism is characterized by low levels of PTH which results in calcium ion deficiency. This causes neurons and muscle fibers to spontaneously contract, a state called tetany for skeletal muscles. \- Hyperparathyroidism, or the increased secretion of PTH, results in high bone resorption to increase the calcium and phosphate ions in the blood, making the bones soft and fragile. \- Cushing\'s syndrome is caused by the hypersecretion in the adrenal cortex. It's caused by hgh levels of cortisol in the blood due to an adrenal gland tumor. Common symptoms of Cushing's syndrome ---------------------------------------------------------------------------------------------------------------------------------- Buffalo hump (neck), moon face, excessive hairiness, acne in all parts of the skin, irregular menstruation, slow healing of cuts \- Addison's disease results in the hyposecretion of glucocorticoids and aldosterone. Affected individuals experience lethargy, anorexia, weight loss, hypoglycemia, muscular weakness, and increased skin pigmentation. \- Diabetes mellitus results from the inability of an individual to produce or utilize insulin. It's characterized by an above normal blood glucose level causing it to be present in the urine (glycosuria). +-----------------------------------------------------------------------+ | Symptoms | +=======================================================================+ | Polyuria (excessive urination) | | | | Polydipsia (excessive thirst) | | | | Polyphagia (excessive eating) | +-----------------------------------------------------------------------+ Diabetes mellitus can be classified into 2 types: - - +-----------------------------------------------------------------------+ | KEY POINTS | +=======================================================================+ | \- The thyroid gland secretes the hormones thyroxine and | | triiodothyronine. These hormones primarily act on various cells of | | the body to promote an increased rate of metabolism, particularly the | | use of more glucose and fats. This gland also secretes calcitonin, | | which functions to decrease the levels of calcium in the blood. | | | | \- The parathyroid glands secrete the parathyroid hormone or | | parathormone. This hormone primarily acts on bone osteoclasts and | | functions to regulate the concentration of calcium, phosphate, and | | magnesium ions in the blood. | | | | \- The adrenal cortex secretes mineralocorticoids, glucocorticoids, | | and weak androgens. Aldosterone, a mineralocorticoid, maintains | | salt-water balance. The glucocorticoid cortisol is important during | | the stress response. | +-----------------------------------------------------------------------+