Patho Hypo-.pdf

Page 5 Hypothalamus and Pituitary Glands: o Hypothalamus function in maintaining homeostasis o The hypothalamus links the nervous and endocrine systems by way of the pituitary gland. The hypothalamus secretes tropic hormones such as releasing hormones and inhibiting hormones that stimulate or inhibi...

Page 5 Hypothalamus and Pituitary Glands: o Hypothalamus function in maintaining homeostasis o The hypothalamus links the nervous and endocrine systems by way of the pituitary gland. The hypothalamus secretes tropic hormones such as releasing hormones and inhibiting hormones that stimulate or inhibit production of hormones in the anterior pituitary o Link between hypothalamus and pituitary gland o Secretion of tropic hormones affecting anterior pituitary gland o Tropic hormones (regulate the secretory action of other endocrine glands) o 1. Hypothalamus releases hormones 2. Hypothalamus hormone stimulates pituitary to release hormones. 3. Anterior Pituitary. Page 6 Relationship between hypothalamic and pituitary hormones o Control through release of regulatory hormones o Direct release of hormones affecting various target tissues o List of hormones released by hypothalamus and their effects on different organs: Corticotropin- releasing hormone (CRH). Thyrotropin- releasing hormone (TRH). Growth hormone- releasing hormone (GH-RH). Growth hormone- inhibiting hormone (GH-IH). Prolactin- releasing factor (PRF). Prolactin- inhibiting hormone (PIH). (Dopamine) Gonadotropin- releasing hormone (GnRH). o ACTH: Adrenal Cortex to Adrenal glands and produces Glucocorticoids (steroid hormones) o TSH goes to thyroid gland and produces thyroid hormones. o GH: goes to the Liver then somatomedins and bone, muscle and other tissues. o PRL: produces mammary glands o FSH: goes to testes of male and produces inhibin, testosterone. o LH: goes to the ovaries of a female and produces estrogen, progesterone, inhibin. o MSH: produces melanocytes which is melanin o In the posterior pituitary only Oxytocin and ADH are produced. o Oxytocin: is responsible for female uterine smooth muscle and mammary glands. As well as in males, smooth muscle in ductus deferens and prostate gland. o ADH: goes to kidneys Page 9 Functions of the Hypothalamus: o Role in homeostasis, water balance, and temperature regulation o Endocrine control via pituitary gland: Growth hormones, stress Reproductive hormones, etc o o Autonomic control: Integration of sensory information, memory and emotion to organize sympathetic and parasympathetic responses Limbic function related to memory and emotion. The limbic system is an aggregation of brain structures that are generally located lateral to the thalamus, underneath the cerebral cortex, and above the brainstem. Page 10 Mechanism of hypothalamic hormones affecting anterior pituitary o Stimulation of releasing or inhibiting hormones by hypothalamic neurons o Pathway of hormone secretion into the general circulation o Hypothalamic neurons synthesize GHRH, GHIH, TRH, CRH, GnRH, PIH, PRF o 1. When appropriately stimulated, hypothalamic neurons secrete releasing or inhibiting hormones into the primary capillary plexus. o 2. Hypothalamic hormones travel through portal veins to the anterior pituitary where they stimulate or inhibit release of hormones made in the anterior pituitary. o 3. In response to releasing hormones, the anterior pituitary secretes hormones into the secondary capillary plexus. This in turn empties into the general circulation o GH, TSH, ACTH, FSH, LH, PRL, Gonadotropins, MSH: Anterior Pituitary o Hypophyseal portal system Primary capillary plexus Hypophyseal portal veins Secondary capillary plexus. A portal system is two capillary plexuses (beds) connected by veins. Page 11 Synthesis and release of oxytocin and ADH by hypothalamic neurons o Storage in axon terminals and release into the blood o Transport of hormones through the hypothalamic-hypophyseal tract to the posterior pituitary. o 1. Hypothalamic neurons synthesize oxytocin or antidiuretic hormone (ADH). o 2. Oxytocin and ADH are transported down the axons of the hypothalamichypophyseal tract to the posterior pituitary. 3. Oxytocin and ADH are stored in axon terminals in the posterior pituitary. o 4. When hypothalamic neurons fire, action potentials arriving at the axon terminals cause oxytocin or ADH to be released into the blood. Page 12 Hormones secreted by the Hypothalamus: o List of hormones including PRH, PIH, TRH, CRH, GHRH, GHIH, GnRH o Anterior Pituitary: Prolactin, TSH, ACTH, GH, LH, FSH. o o Prolactin: Breast. TSH: Thyroid gland. ACTH: Adrenal Cortex produces cortisol. GH: liver it produces insulin like growth factors. GH goes to cells throughout body. LH, FSH: Gonads. In male, it produces androgens. In females it produces estrogens, progesterone. Page 15 Pituitary Gland: o Description of the "Master gland" o Location and composition of anterior and posterior pituitary o Structure of the anterior and posterior pituitary lobes o Posterior pituitary (neurohypophysis) Anterior pituitary (adenohypophysis): originates as an out-pocketing of the oral mucosa o Anterior lobe of pituitary: The anterior pituitary contains abundant hormonesecreting epithelial cells. o The posterior pituitary is composed largely of unmyelinated secretory neurons. Page 16 Posterior Pituitary: o Contains axons of hypothalamic neurons o Stores antidiuretic hormone (ADH aka vasopressin) and oxytocin o ADH and oxytocin are released in response to nerve impulses o ADH and oxytocin are nonapeptide hormones Hormones Released by The Posterior Pituitary (Neurohypophysis) Oxytocin o Stimulates uterine contractions during childbirth o Triggers milk ejection in lactating women o Suckling stimulates oxytocin release: positive feedback loop, with infant completing the loop o Acts as a neurotransmitter in the brain, associated with emotions like love, empathy, trust, and sexual activity. Known as the love hormone. o Levels increase during hugging and orgasm o Used in labor induction and to prevent postpartum hemorrhage o Oxytocin (Pitocin, a synthetic version) is widely employed to induce or augment labor, especially at term, when adequate oxytocin receptors are present. It is also one of the principal uterotonic drug used to prevent post partum hemorrhage. Antidiuretic Hormone (ADH) o o o o o o o o o o o o o Regulates osmotic balance, blood pressure, sodium homeostasis, and kidney function Released in response to changes in plasma osmolarity, blood pressure, and blood volume Binds to receptors to induce vasoconstriction and regulate water reabsorption in the kidneys Antidiuretic Hormone (Vasopressin or Arginine Vasopressin (AVP)) ADH or AVP is a nonapeptide synthesized in the hypothalamus. It plays an essential roles in the control of the body’s osmotic balance, blood pressure regulation, sodium homeostasis, and kidney functioning. ADH is released from the posterior pituitary gland into the systemic circulation in response to: 1) Increase in plasma osmolarity (eg, hypernatremia, which is a common electrolyte problem that is defined as a rise in serum sodium concentration to a value exceeding 145 mmol/L). 2) Reduction in blood pressure 3) Decreased volume of circulating blood (hypovolemia). ADH binds to V1a receptors on vascular smooth muscle cells to induce vasoconstriction. Skin, muscle, and splanchnic arterial beds are highly sensitive to the vasoconstrictor actions of ADH, an effect that may be important for shunting blood to more vital organs. ADH binds to the V-2 receptor in the principal cells of the collecting duct. Splanchnic: relating to the viscera or internal organs, especially those of the abdomen. Binding of ADH (AVP) to the V2R triggers an intracellular cAMP pathway, which causes phosphorylation of the aquaporin-2 (AQP2). This causes AQP2 to move to the apical membrane. After achieving water homeostasis, the ADH levels decrease, and AQP2 is internalized from the plasma membrane, leaving the apical plasma membrane watertight again. Homeostatic Imbalances of ADH ADH Deficiency o Leads to diabetes insipidus (DI) characterized by excessive urine output and thirst o Central DI results from impaired ADH secretion (AVP) could result from traumatic brain injury, surgery, or tumors. Whereas nephrogenic DI is due to kidney failure to respond to AVP is usually inherited. ADH Hypersecretion o Can cause syndrome of inappropriate ADH secretion (SIADH) after neurosurgery, trauma, or by cancer cells Case Study: Central Diabetes Insipidus Patient: Lucia Sanchez, 24-year-old with polyuria and polydipsia Symptoms: Increased urination, intense thirst, craving for ice water Diagnosis: Central diabetes insipidus Treatment: Given ADH resulting in reduced urine output, instructed to take desmopressin acetate Syndrome of Inappropriate ADH (SIADH) Excessive ADH Release o Leads to excess water reabsorption and dilutional hyponatremia o Patients remain euvolemic due to increased salt excretion by the kidneys Hormones Released by Anterior Pituitary Gland Anterior Pituitary Hormones o Include growth hormone, thyroid-stimulating hormone, adrenocorticotropic hormone, follicle-stimulating hormone, luteinizing hormone, and prolactin All are proteins and All except GH activate cyclic AMP second-messenger systems o o TSH, ACTH, FSH, and LH are all Tropic hormones regulate the secretory action of other endocrine glands. FSH and LH are called gonadotropins because they regulate the activities of the gonads. Growth Hormone Functions o Indirect actions on growth promotion and direct metabolic effects o Stimulates most cells, but targets bone and skeletal muscle o Promotes protein synthesis, fat breakdown, and anti-insulin effects Regulation o Inhibits GHRH release, stimulates GHIH release, and inhibits GH synthesis and release o Stimulated by thyrotropin- releasing hormone (TRH) o Inhibited by rising blood levels of thyroid hormones that act on the pituitary and hypothalamus. Effects o Increased cartilage formation, protein synthesis, fat breakdown, and blood glucose levels Main Ideas from the Transcript Page 32 Thyroid Hormones o Produced by the thyroid gland. o Regulated by Thyroid-Stimulating Hormone (TSH) and Thyrotropin-Releasing Hormone (TRH). Regulation of Thyroid-Stimulating Hormone o Stimulated by TRH. o Inhibited by rising blood levels of thyroid hormones. Page 33 Adrenocorticotropic Hormone (ACTH) o Secreted by corticotrophs of the anterior pituitary. o Stimulates the adrenal cortex to release corticosteroids. Regulation of ACTH Release o Triggered by hypothalamic corticotropin-releasing hormone (CRH). o Factors like fever, hypoglycemia, and stressors can alter CRH release. Page 34 Gonadotropins o Follicle-stimulating hormone (FSH) and luteinizing hormone (LH). o Secreted by gonadotrophs of the anterior pituitary. o SH stimulates gamete (egg or sperm) production o LH promotes production of gonadal hormones o Absent from the blood in prepubertal boys and girls Regulation of Gonadotropin Release o Triggered by gonadotropin-releasing hormone (GnRH) during and after puberty. o Suppressed by gonadal hormones through feedback. Page 35 Prolactin (PRL) o Secreted by lactotrophs of the anterior pituitary. o Promotes mammary gland growth and milk production. Regulation of PRL Release o Controlled by prolactin-inhibiting hormone (dopamine) and prolactin-releasing hormone (PRH) as well as Prolactin Releasing Hormone (PRH) o Blood levels rise toward the end of pregnancy o Suckling stimulates PRH release and promotes continued milk production o Prolactin release has an inhibitory effect on the release of gonadotropin-releasing hormone (GnRH) from the hypothalamus. The loss of GnRH results in a lack of pulsatile stimulation of gonadotrophic cells, resulting in the loss of FSH and LH release from the anterior pituitary. FSH and LH are the primary hormones needed to regulate menstruation; thus, females who are lactating will experience a period of transient amenorrhea until the cessation of breastfeeding. This mechanism serves as a natural contraceptive and may play a role in pregnancy spacing. Page 37 Disorders of the Pituitary Gland o Adiposogenital Dystrophy: childhood disorder with obesity and growth issues. o Acromicria: condition with small and delicate bones. o Simmonds Disease: atrophy of various organs leading to emaciation and death. Page 38 Pineal Gland o Secretes melatonin derived from serotonin. o Impacts sexual maturation, day/night cycles, and physiological