Endocrine Pathophysiology I Kyong Soo Park Dept of MMBS & Dept of Internal Medicine, Seoul National University College of Medicine

Introduction The endocrine system assists the nervous system with communication and control of the body Endocrine glands They are ductless They secrete hormones into bloodstream There are also similar glands called paracrine and autocrine glands that are quasi-endocrine Exocrine glands They have ducts They deliver their products directly to a specific site

Hormone: is a chemical messenger secreted by one endocrine gland or cell into the bloodstream and targeted toward cells in another organ

Hormones that bind to cells near the cell that released them mediate paracrine effects

General Characteristics of the Endocrine System The endocrine and nervous systems communicate using chemical signals

Endocrine Gland The endocrine system. Endocrine organs are located throughout the body

Chemistry of Hormones Chemically, hormones are either: Steroid or steroid-like hormones such as: Sex hormones Adrenal cortex hormones Non-steroid hormones such as: Amines Proteins Peptides Glycoproteins

Action of Steroid Hormones Steroid hormone cross the plasma membrane and bind to intracellular receptors. Hormone receptor complex bind to DNA then regulate target gene transcription.

Action of Non-Steroid Hormones While nonsteroid hormones bind to cell surface receptor.. Exception is thyroid hormone which cross plasma membrane and binds to nuclear receptor. Binding to cell surface receptor lead to intracellular signalling cascade such as G-protein coupled receptor -cAMP signalling

Control of Hormonal Secretions Hormones can be short-lived or may last for days Amines (2-3 minutes) polypeptides (4-40 minutes) steroid and proteins (4-170 minutes), thyroid hormones (0.75-6.7 days) Primarily controlled by negative feedback mechanism Hormone secretions are precisely regulated – Hypothalamus – Nervous system – Changing level of substance in plasma – Anterior pituitary gland Peripheral endocrine gland Endocrine gland Endocrine gland Target cells Target cells Target cells Action Action Action (a) (b) (c)

Pituitary Gland Lies at the base of the brain in the sella turcica Optic nerve Sphenoid bone Hypothalamus Optic chiasma Sella turcica Third ventricle T rochlear nerve Basilar artery Anterior cerebral artery Pituitary stalk (Infundibulum) Anterior lobe of pituitary gland Sphenoidal sinus Posterior lobe Oculomotor nerve Lies at the base of the brain in the sella turcica Consists of two distinct portions: Anterior pituitary (adenohypophysis) Posterior pituitary (neurohypophysis)

Anterior Pituitary Hormones Hypothalamic releasing hormones stimulate cells of anterior pituitary to release hormones – Hypothalamus – Third ventricle Releasing hormone (Hormone 1) Optic chiasma Neurosecretory cells that secrete releasing hormones + – Anterior pituitary Hypophyseal portal veins Anterior pituitary hormone (Hormone 2) Secretory cells of anterior pituitary gland Superior hypophyseal artery Capillary bed + Peripheral endocrine gland Capillary bed Hypophyseal veins Anterior lobe of pituitary gland (Hormone 3) Stimulation + Inhibition T arget cells Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Hormones from Hypothalamus Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Hormones from Hypothalamus GHRH Growth hormone- releasing hormone SS Somatostatin PRF Prolactin- releasing factor PIH Prolactin- release inhibiting hormone TRH Thyrotropin- releasing hormone CRH Corticotropin- releasing hormone GnRH Gonadotropin- releasing hormone Hormones from Anterior Pituitary GH Growth hormone PRL Prolactin TSH Thyroid- stimulating hormone ACTH Adrenocorticotropic hormone LH Luteinizing hormone FSH Follicle- stimulating hormone Bone Muscle Adipose tissue Mammary gland Thyroid Adrenal cortex Ovary T estis

Posterior Pituitary Hormones Structurally consists of nerve fibers and neuroglia v. glandular epithelial cells of the anterior pituitary gland The nerve fibers originate in the hypothalamus Two hormones are produced: Antidiuretic hormone (vasopressin) Oxytocin Third ventricle Optic chiasma Neurosecretory cells that secrete posterior pituitary hormones Neurosecretory cells that secrete releasing hormones Hypothalamus Superior hypophyseal artery Capillary bed Inferior hypophyseal artery Hypophyseal veins Sella turcica of sphenoid bone Posterior lobe of pituitary gland

Thyroid Gland The thyroid gland has two lateral lobes and lies just below the larynx It produces three hormones: T4 (thyroxine), T3 (triiodothyronine), Calcitonin Follicular cells Colloid Extrafollicular cells Larynx Isthmus (a) (b) Thyroid gland Follicular cell Extrafollicular cell

Thyroid Hormones OH OH I I I O O I I I I CH2 CH2 NH2CHCOOH NH2CHCOOH Thyroxine (T4) Triiodothyronine (T3)

Parathyroid Glands The parathyroid glands are on the posterior surface of the thyroid gland There are typically four parathyroid glands It secretes one hormone: PTH (parathyroid hormone or parathormone) Posterior view Esophagus Pharynx Thyroid gland Parathyroid glands Trachea Secretory cells Capillaries

– Changing level of substance in plasma Endocrine gland Target cells Action

Adrenal Glands The adrenal glands are closely associated with the kidneys The gland sits like a cap on each kidney Hormones are secreted from two different areas of the gland, the adrenal cortex and the adrenal medulla Numerous hormones are secreted by the adrenal glands Adrenal gland Kidney Adrenal cortex (a) Zona glomerulosa Connective tissue capsule (b) Zona fasciculata Zona reticularis Adrenal medulla Adrenal medulla Surface of adrenal gland

Hormones of the Adrenal Gland

Cushing’s syndrome Addison’s disease

Pancreas The pancreas has two major types of secretory tissue This is why it is a dual functioning organ as both an exocrine gland and endocrine gland Pancreatic islet (Islet of Langerhans) Gallbladder Common bile duct Pancreatic duct Pancreas Duct Capillary Small intestine Digestive enzyme- secreting cells Pancreatic islet (Islet of Langerhans) Hormone-secreting islet cells

Hormones of the Pancreatic Islets

Other Endocrine Glands Pineal Gland Secretes melatonin Regulates circadian rhythms Thymus Gland Secretes thymosins – Promotes development of certain lymphocytes Important in role of immunity after puberty, it starts to shrink and become replaced by fat Reproductive Organs Ovaries produce estrogens and progesterone Testes produce testosterone Placenta produces estrogens, progesterone, and gonadotropin Other organs: digestive glands, heart, and kidney