Endocrine System Study Guide PDF

The Endocrine System Overview of the Endocrine System The nervous system and endocrine system work together to monitor the body's activities The nervous system produces short-term, specific responses, while the endocrine system produces long-term, general responses The endocrine...

The Endocrine System Overview of the Endocrine System The nervous system and endocrine system work together to monitor the body's activities The nervous system produces short-term, specific responses, while the endocrine system produces long-term, general responses The endocrine system releases chemicals called hormones Hormones are produced by endocrine cells located in glands or gland-like structures, enter the bloodstream, travel to target organs/tissues, and bind to specific receptors to elicit a response The main endocrine organs: the pituitary gland, hypothalamus, thyroid gland, adrenal glands, pineal gland, parathyroid glands, and pancreas Organs with secondary endocrine functions: include the heart, thymus, adipose tissue, digestive tract, kidneys, and gonads Classification of Hormones Hormones are organized into three main classes based on chemical structure: ○ Amino acid derivatives (e.g., thyroid hormones, catecholamines) ○ Peptide hormones (e.g., pituitary hormones) ○ Lipid derivatives Steroid hormones (e.g., reproductive hormones, adrenal cortex hormones) Eicosanoids (e.g., associated with blood clotting) (Overview of the Endocrine System) Hypothalamus and Pituitary Gland The hypothalamus integrates neural and endocrine activities through three mechanisms: ○ Acts as an endocrine organ, releasing ADH and oxytocin ○ Secretes regulatory hormones that control the anterior pituitary ○ Contains autonomic nervous system centers that control the adrenal medulla ○ The pituitary gland (hypophysis) is attached to the hypothalamus via the infundibulum and consists of two lobes: Adenohypophysis (anterior lobe) releases seven peptide hormones Neurohypophysis (posterior lobe) releases two peptide hormones The Hypophyseal Portal System distributes hypothalamic secretions to the adenohypophysis via a network of capillaries Anterior Pituitary Hormones The anterior pituitary (adenohypophysis) consists of three regions: ○ Pars distalis: Secretes the majority of pituitary hormones ○ Pars intermedia: Secretes melanocyte-stimulating hormone (MSH) ○ Pars tuberalis: Wraps around the infundibulum The five cell types of the anterior pituitary and their hormones are: ○ Thyrotropes: Thyroid-stimulating hormone (TSH) ○ Corticotropes: Adrenocorticotropic hormone (ACTH), MSH ○ Gonadotropes: Follicle-stimulating hormone (FSH), Luteinizing hormone (LH) ○ Lactotropes: Prolactin (PRL) ○ Somatotropes: Growth hormone (GH) Posterior Pituitary Hormones The posterior pituitary (neurohypophysis) releases two hormones produced by the hypothalamus: ○ Antidiuretic hormone (ADH): Targets the kidneys to promote water reabsorption and increase blood pressure ○ Oxytocin (OXT): Targets the uterus and mammary glands to stimulate contractions and milk ejection (Hypothalamus and the Pituitary Gland) Thyroid Gland The thyroid gland is located on the anterior surface of the trachea and is highly vascularized The thyroid gland consists of two lobes connected by an isthmus and contains thyroid follicles lined with thyrocytes Thyrocytes secrete thyroglobulin, which contains the thyroid hormones thyroxine (T4) and triiodothyronine (T3) Thyroid hormone secretion is regulated by a negative feedback loop involving the hypothalamus, pituitary, and thyroid gland The C thyrocytes of the thyroid gland produce calcitonin, which lowers blood calcium levels by inhibiting osteoclast activity and promoting calcium excretion Parathyroid Glands The parathyroid glands are located on the posterior surface of the thyroid gland and contain two main cell types: ○ Parathyroid cells: Produce parathyroid hormone (PTH)  ○ Oxyphil cells: Function unknown ○ PTH increases blood calcium levels by stimulating osteoclasts to release calcium from bone, reducing calcium excretion by the kidneys, and promoting the kidneys to produce calcitriol, which increases intestinal calcium absorption Thymus Gland The thymus gland is located in the mediastinal region posterior to the sternum The thymus produces thymosin, a mixture of hormones that target lymphocytes and promote their development into T cells, supporting the immune system Adrenal Glands The adrenal glands are located superior to the kidneys and consist of two regions: ○ Adrenal cortex: Produces corticosteroids (mineralocorticoids, glucocorticoids, and androgens) ○ Adrenal medulla: Produces catecholamines (epinephrine and norepinephrine) The adrenal cortex has three zones: ○ Zona glomerulosa: Produces mineralocorticoids like aldosterone ○ Zona fasciculata: Produces glucocorticoids like cortisol ○ Zona reticularis: Produces small amounts of androgens ‘ Catecholamines from the adrenal medulla are part of the sympathetic nervous system response, increasing heart rate, blood pressure, glycogen breakdown, and muscle strength/endurance (The Adrenal Glands) Endocrine Functions of the Kidneys and Heart The kidneys produce: ○ Renin: Enzyme that initiates the renin-angiotensin-aldosterone system to regulate blood pressure ○ Erythropoietin (EPO): Hormone that stimulates red blood cell production ○ Calcitriol: Active form of vitamin D that increases intestinal calcium absorption The heart produces: ○ Atrial natriuretic peptide (ANP): Hormone that inhibits ADH and aldosterone, promoting water and sodium excretion to lower blood pressure and volume Pancreas and Other Digestive Endocrine Tissues The pancreas has both exocrine (digestive enzymes) and endocrine functions (pancreatic islets) The pancreatic islets contain four major cell types that produce hormones: ○ Alpha cells: Glucagon, which increases blood glucose levels  ○ Beta cells: Insulin, which decreases blood glucose levels ○ Delta cells: Somatostatin, which inhibits glucagon and insulin secretion ○ F cells: Pancreatic polypeptide, which regulates some pancreatic enzyme production (The Pancreas and Other Endocrine Tissues) Reproductive Endocrine Tissues Testes: ○ Interstitial cells produce testosterone, which promotes sperm production, secondary sex characteristics, and muscle growth ○ Nurse cells produce inhibin, which regulates FSH secretion Ovaries: ○ Follicular cells produce estrogens, which prepare the uterus for implantation ○ Corpus luteum produces progesterone, which further prepares the uterus and stimulates mammary gland development ○ Corpus luteum also produces relaxin, which loosens the pubic symphysis and cervical muscles Pineal Gland The pineal gland (pineal body) is part of the epithalamus and contains pinealocytes that synthesize melatonin Melatonin slows the maturation of sperm, oocytes, and reproductive organs, and its production increases at night and decreases during the day Hormones and Aging Relatively few changes in hormone levels occur with advancing age, except for the decline in reproductive hormones at puberty and menopause Age-related issues in many tissues can result in reduced responsiveness to normal hormone levels Table: Adrenal Hormones Hormone Source Target Effect Aldosteron Zona Kidneys Increases Na+ and water reabsorption, e glomerulosa decreases K+ excretion Cortisol Zona Liver Increases glucose synthesis and glycogen fasciculata storage Androgens Zona reticularis General Contributes to development of pubic hair cells The Cardiovascular System: Blood Introduction The cardiovascular system functions to transport various substances throughout the body, including: ○ Nutrients ○ Oxygen and carbon dioxide ○ Enzymes and hormones ○ Ions ○ Metabolic wastes to the kidneys ○ Leukocytes to aid in fighting infections (Section: Introduction) Other functions of the cardiovascular system include: ○ Stabilizing body temperature ○ Preventing the loss of body fluids via the clotting process ○ Stabilizing pH and electrolyte balance (Section: Introduction) Functions and Composition of the Blood Blood consists of two main components: ○ Plasma Liquid matrix of blood ○ Formed elements Blood cells and cell fragments suspended in the plasma, including: Erythrocytes (red blood cells): transport oxygen and carbon dioxide Leukocytes (white blood cells): function in the immune system Platelets: involved in blood clotting Whole blood consists of: ○ Plasma, erythrocytes, leukocytes, platelets ○ The components contribute to the viscosity of blood  ○ Whole blood can be fractionated into plasma, packed cells, and platelets Whole blood makes up approximately 7% of body weight: ○ Males: 4-6 liters ○ Females: 4-5 liters ○ Can be hypovolemic (low), normovolemic (normal), or hypervolemic (excessive) ○ pH: 7.35-7.45 Plasma Makes up about 55% of the volume of whole blood Consists of: ○ 92% water ○ 7% proteins (albumins, globulins, fibrinogen, regulatory proteins) ○ 1% other solutes (electrolytes, organic nutrients, organic wastes) Differences between plasma and interstitial fluid: ○ Dissolved oxygen concentration is higher in plasma ○ Carbon dioxide concentration is lower in plasma ○ Dissolved protein concentration is higher in plasma Plasma Proteins Produced mainly by the liver Make up about 7% of the plasma Consists of three major classes: ○ Albumins (60%): contribute to osmotic pressure, transport lipids and hormones ○ Globulins (35%): transport ions and hormones, immune function ○ Fibrinogen (4%): essential component of clotting system, can be converted to insoluble fibrin Formed Elements Makes up about 45% of whole blood Consists of: ○ Erythrocytes (99.9% of whole blood) ○ Platelets (