UNBC Mechanisms of Hormonal Regulation PDF

# Mechanisms of Hormonal Regulation ## Nursing 302 ## Understanding the Endocrine System - Consists of glands which create and release chemical transmitters (AKA hormones) in response to stimulation. - Together with the CNS and immune system, the endocrine system regulates and integrates the body...

# Mechanisms of Hormonal Regulation ## Nursing 302 ## Understanding the Endocrine System - Consists of glands which create and release chemical transmitters (AKA hormones) in response to stimulation. - Together with the CNS and immune system, the endocrine system regulates and integrates the body's metabolic activities and maintains homeostasis. - Stimulation of growth and development. - Maintenance of internal environment. - Adaptation to emergency demands of the body. A diagram of the endocrine system shows the following glands: - Pineal gland - Pituitary gland - Thyroid gland - Parathyroid gland - Thymus - Pancreas - Testis - Adrenal gland - Ovary ## Hormones Endocrine glands respond to specific signals by creating and releasing hormones into the circulation; this triggers intracellular responses. ### General characteristics of hormones: - **Specific rates and rhythms of secretion** - Diurnal, pulsatile, and cyclic and patterns that depend on circulating substances (e.g. electrolytes or the hormones themselves). - **Operate within feedback systems** - Positive or negative; support the best internal environment. - **Affect only target cells with appropriate receptors.** - **Excreted by kidneys or metabolized by liver; inactivating the hormones.** Hormones are classified according to structure, gland of origin, effects, and chemical makeup. ## Regulation of Hormone Release Hormones are released: - In response to an alteration in the cellular environment. - To maintain a regulated level of certain substances or other hormones. A diagram of the regulation of hormone release shows the following: - **Central Nervous System** - **Hypothalamus** - Releasing hormones and factors - Release-inhibiting hormones and factors - **Anterior Pituitary** - Tropic hormones - **Target Organ** - Hormone - Physiologic effect - **Negative feedback loop** - Changing response to the stimulus decreases secretion of the hormone. - **Positive feedback loop** - Changing response to the stimulus encourages more secretion of the hormone. A diagram of the positive feedback loop shows the following: - Baby pushes against cervix, causing it to stretch. - Stretching of cervix causes nerve impulses to be sent to brain. - Brain stimulates posterior pituitary to release oxytocin. - Oxytocin causes smooth muscle lining the uterus to contract. ## Hormone Transport & Action Hormones are released into the circulatory system by endocrine glands. - **Target cell** - **Upregulation or Downregulation** - The cell can adjust its sensitivity. - Decrease in insulin receptor sensitivity resulting in hyperglycemia occurs in which disease process? A diagram of upregulation and downregulation shows the following: - **Hormone** - **Hormone receptor** - **Target cell** ## Endocrine Glands ### Hypothalamic-Pituitary Axis (HPA): Hypothalamus & Pituitary Gland - Forms the structural and functional basis for the integration of the neurological and endocrine systems. - HPA produces several hormones which affect many body functions. A diagram of the Hypothalamic-Pituitary Axis shows the following: - **Hypothalamus** - Fornix of hippocampus - Hypothalamus - Optic chiasm - Anterior pituitary - Posterior pituitary - **Thalamus** - **Pons** ### Pituitary Gland #### Anterior Pituitary - Adrenocorticotropic hormone (ACTH) - Follicle-stimulating hormone - Luteinizing hormone - Thyroid-stimulating hormone - Growth hormone; triggers growth - Prolactin; stimulates milk secretion in lactating women #### Posterior Pituitary - Antidiuretic hormone (ADH); alters permeability of the kidneys to retain water. - Oxytocin; stimulates uterine contractions during labour & milk let-down in lactating women. ### Pineal Gland - Located near centre of brain. - Secretes melatonin. - Regulates circadian rhythms and reproductive systems (onset of puberty). - Exposure to dark stimulates the release of melatonin; exposure to light inhibits. A diagram of the pineal gland shows the following: - **Hypothalamus** - **Thalamus** - **Pineal gland** ### Thyroid Gland - Two lobes lie on either side of the trachea. - C cells → secrete calcitonin - Lowers serum calcium levels by promoting calcium deposits into the bone. - Regulation of thyroid hormone secretion: - A negative feedback loop involving the hypothalamus, anterior pituitary, and thyroid gland. - Regulates the secretion of thyroid hormone (TH). - Thyroid Hormone: - TRH created within the hypothalamus; stimulates release of TSH from anterior pituitary, and then TH is secreted. - 90% T4 and 10% T3 (Most T4 then converted to T3). - Affects growth and maturation of tissues, cell metabolism, heat production, and oxygen consumption. A diagram of the thyroid system and hormones shows the following: - **Thyroid system** - **Hypothalamus** - Thyrotropin-releasing hormone (TRH) - **Anterior pituitary gland** - Thyroid-stimulating hormone (TSH) - **Thyroid gland** - Thyroid hormones (T3 and T4) - Increased metabolism - Growth and development - Increased catecholamine effect - **Thyroid Hormones** - **Hypothalamus** - **Thyroid gland** - Feedback loop - **Pituitary gland** - TRH - TSH - T3 - T4 - **Calcitonin** ### Parathyroid Gland - Small glands located behind the thyroid gland. - Produce parathyroid hormone (PTH) - Single most important factor in the regulation of serum calcium concentration. - Decreased calcium level stimulates PTH secretion. - Increases serum calcium and decreases serum phosphate. - Antagonist of calcitonin (thus acts directly on the bone to release calcium, and kidney to increase calcium reabsorption). - Vitamin D (cofactor) needed for PTH function (calcium reabsorption in intestines!). A diagram of the parathyroid glands shows the following: - **Parathyroid hormone (PTH)** - **Bones** - Release calcium - **Kidneys** - Reduce Calcium clearance - Vitamin D activation - **Intestines** - Activated vitamin D helps absorb calcium in gut A diagram of the thyroid and parathyroid glands shows the following: - **Hyoid bone** - **Thyroid cartilage** - **Cricoid cartilage** - **Isthmus** - **Right lobe of thyroid gland** - **Left lobe of thyroid gland** - **Trachea** - **Inferior pharyngeal constrictor muscle** - **Superior parathyroid gland** - **Inferior parathyroid gland** - **Esophagus** ### Pancreas - Pancreas is both an endocrine and an exocrine gland. - Houses the islets of Langerhans. - Secretion of glucagon (alpha cells) and insulin (beta cells). - These hormones regulate carbohydrate, fat, and protein metabolism. A diagram of the pancreas shows the following: - **Accessory pancreatic duct** - **Body of pancreas** - **Common bile duct** - **Tail of pancreas** - **Duodenum** - Minor duodenal papilla - Hepatopancreatic ampulla - Major duodenal papilla - Plicae circulares - **Pancreatic duct** - **Jejunum** - **Head of pancreas** - **Alpha cells (secrete glucagon)** - **Beta cells (secrete insulin)** - **Pancreatic islet** - **Vein** - **Pancreatic duct (to duodenum)** - **Acinar cells (secrete enzymes)** #### Insulin - Secretion is promoted by increased blood levels of glucose, amino acids, GI hormones; facilitates the rate of glucose uptake into the cells of the body. - Age, weight, abdominal fat, and physical activity affect insulin sensitivity. - Insulin resistance is related to many diseases including HTN, heart disease, DM 2. A diagram of how insulin works shows the following: - **Glucose** - **Insulin receptor** - **Glucose channel** - **Insulin unlocks the glucose channel** - **Cells** #### Glucagon - Acts primarily in the liver; increases blood glucose concentration by stimulating glycogenolysis & gluconeogenesis. - Secretion is promoted by decreased blood glucose levels. A diagram of how glucagon works shows: - **Exercise** - **Decreasing blood sugar** - **Adipose cells take up glucose** - **Insulin** - **Pancreatic alpha cells release glucagon** - **Glucagon** - **Pancreatic beta cells release insulin** - **Increasing blood sugar** - **Liver breaks down glycogen to glucose** - **Eating** #### Gastrin - Stimulates the secretion of gastric acid. #### Ghrelin - Stimulates GH secretion, controls appetite, and plays a role in obesity and the regulation of insulin sensitivity. ### Adrenal Glands - Paired, pyramid-shaped organs close to the top of each kidney. - Consists of an outer cortex & inner medulla. A diagram of the adrenal gland shows the following: - **Adrenal gland** - **Adrenal medulla** - **Adrenal cortex** <h4>Adrenal Cortex - Adrenocorticotropic Hormone (ACTH) from the pituitary gland stimulates the cells of the adrenal cortex → main regulator of cortisol secretion. - Glucocorticoids (steroid hormones) - Direct effects on carbohydrate metabolism; increase blood glucose concentration. - Immunosuppressive, anti-inflammatory and growth-suppressing effects. - Use of glucocorticoids for treatment of disease leads to suppression of innate & adaptive immunity. - Most potent naturally occurring glucocorticoid is cortisol. - Goal is to support life and protect the body from stress. - Aldosterone (mineralocorticoid hormone) - Increase the activity of the sodium pump of the epithelial cells. - Cause sodium retention & potassium and hydrogen loss. - Most potent naturally occurring mineralocorticoid is aldosterone, regulated by the RAS. - Adrenal estrogens and androgens - Estrogen secretion by the adrenal cortex is minimal. - Adrenal cortex secretes weak androgens, which are then converted by peripheral tissue to testosterone. A diagram of the effects of glucocorticoids on the body shows the following: - **Brain/CNS:** - Depression ­­ - Psychosis - **Endocrine system:** - LH, FSH release - TSH release - ↓GH secretion - **Eye:** - Glaucoma - **Cardiovascular/renal:** - Salt and water retention - Hypertension - **Carbohydrate/lipid metabolism:** - ↑Hepatic glycogen deposition - ↑Peripheral insulin resistance - ↑Gluconeogenesis - ↑Free fatty acid production - Overall diabetogenic effect - **Gl tract:** - Peptic ulcerations - **Adipose tissue distribution:** - Promotes visceral obesity - **Bone and calcium metabolism:** - Bone formation - ↓Bone mass and osteoporosis - **Growth and development:** - Linear growth - **Skin/muscle/connective tissue:** - Protein catabolism/ collagen breakdown - Skin thinning - Muscular atrophy - **Immune system:** - Anti-inflammatory action - Immunosuppression #### Adrenal Medulla - Innervated by the sympathetic nervous systems. - Physiological stress to the body triggers the release. - Secrete the catecholamines epinephrine (adrenaline) and norepinephrine. - Release of catecholamines has been characterized as a "fight or flight" response. - Catecholamines promote hyperglycemia. A diagram of the adrenal hormones shows the following: - **SEX HORMONES** - Testosterone - Estrogens - **GLUCOCORTICOIDS** - Cortisone - Cortisol - **MINERALOCORTICOIDS** - Corticosterone - Aldosterone - **Zona reticularis** - **Zona glomerulosa** - **Zona fasciculata** - **Medulla** - **STRESS HORMONES** - Norepinephrine - Epinephrine - **PEPTIDES** - Vasoactive intestinal peptide - Substance P - Somatostatin ## Aging and the Endocrine System - Organ atrophy and weight loss with vascular changes. - Decreased secretion and clearance of hormones. - Variable change in receptor binding and intracellular responses.