Human Anatomy Chapter 17 Part The Endocrine System PDF

Human Anatomy Chapter 17 Part The Endocrine System Dr. Kim The Endocrine System Interacts closely with the nervous system Organs of the endocrine system Are a disperse group of ductless glands Secrete messenger molecules called hormones Endocrinology Stud...

Human Anatomy Chapter 17 Part The Endocrine System Dr. Kim The Endocrine System Interacts closely with the nervous system Organs of the endocrine system Are a disperse group of ductless glands Secrete messenger molecules called hormones Endocrinology Study of hormones and endocrine glands Endocrine Organs Pure endocrine organs Pituitary Pineal gland Thyroid and parathyroid glands Adrenal glands o Adrenal cortex and adrenal medulla Endocrine Organs Organs containing large proportion of endocrine cells Pancreas Thymus Gonads Hypothalamus—a neuroendocrine organ Endocrine Organs Organs containing some endocrine cells Heart Digestive tract Kidneys Skin Endocrine cells are of epithelial origin Location of the Major Endocrine Organs Hormones Classes of hormones Amino acid–based hormones Steroids—derived from cholesterol Basic hormone action Circulate throughout the body in blood vessels o Influence only specific tissue cells—target cells o A hormone can have different effects on different target cells Control of Hormones Secretion Secretion triggered by one of three major types of stimuli 1. Humoral—simplest of endocrine control mechanisms Secretion in direct response to changing ion or nutrient levels in the blood Parathyroid monitors calcium o Responds to a decline in calcium by secreting a hormone to reverse its decline Control of Hormones Secretion 2. Neural Sympathetic nerve fibers stimulate cells in the adrenal medulla Induces release of epinephrine and norepinephrine 3. Hormonal Stimuli received from other glands Certain hormones signal secretion of other hormones o Hypothalamus secretes hormones → stimulates pituitary → stimulates other glands Three Types of Endocrine Gland Stimuli Feedback Loops Control of hormones secretion Blood concentration declines below a minimum o More hormone is secreted Blood concentration exceeds maximum o Hormone production is halted The Pituitary Gland Secretes nine major hormones Attached to the hypothalamus by the infundibulum Two basic divisions of the pituitary gland Anterior lobe (adenohypophysis) Posterior lobe (neurohypophysis) The Pituitary Gland The anterior lobe Has three major divisions o Pars distalis, pars intermedia, and pars tuberalis The posterior lobe Has two major divisions o Pars nervosa and infundibulum The Pituitary Gland (Hypophysis) The Anterior Lobe The pars distalis—largest division of the anterior lobe Contains five different endocrine cells Makes and secretes seven different hormones Tropic hormones regulate hormone secretion by other glands o Include TSH, ACTH, FSH, LH The Anterior Lobe GH, PRL, and MSH Act directly on nonendocrine target tissues The Anterior Lobe Thyroid-stimulating hormone (TSH) Produced by thyrotropic cells Signals thyroid gland to secrete thyroid hormone Adrenocorticotropic hormone (ACTH) Stimulates the adrenal cortex to secrete hormones that help cope with stress Gonadotropins Are produced by gonadotropic cells o FSH and LH The Anterior Lobe Melanocyte-stimulating hormone (MSH) In humans, MSH functions in appetite suppression Prolactin Produced by prolactin cells Targets milk-producing glands in the breast—stimulates milk production The Anterior Lobe Growth hormone (somatotropic hormone) Produced by somatotropic cells Stimulates body growth by stimulating increased protein production and growth of epiphyseal plates Stimulates growth directly and indirectly by the liver’s secretion of insulin-like growth factor-1 Pituitary Hormones: Summary of Target Organs and Effects Pituitary Hormones: Summary of Target Organs and Effects Pituitary Hormones: Summary of Target Organs and Effects Hypothalamic Control of Hormone Secretion from the Anterior Lobe The hypothalamus Controls secretion of anterior lobe hormones Exerts control by secreting o Releasing hormones—prompt anterior lobe to release hormones o Inhibiting hormones—turn off secretion of anterior lobe hormones Hypothalamic Control of Hormone Secretion from the Anterior Lobe Releasing hormones Are secreted like neurotransmitters Enter a primary capillary plexus Travel in hypophyseal portal veins to a secondary capillary plexus o From the secondary capillary plexus, hormones secreted by the anterior lobe enter general circulation and travel to target organs The Hypothalamus Controls Release of Hormones from the Pituitary Gland in Two Different Ways The Posterior Lobe Is structurally part of the brain Its axons make up the hypothalamohypophyseal tract Arises from neuronal cell bodies in the hypothalamus o Supraoptic nucleus o Paraventricular nucleus The Posterior Lobe Does not make hormones Stores and releases hormones made in the hypothalamus Releases two peptide hormones Antidiuretic hormone (ADH) Oxytocin The Hypothalamus Controls Release of Hormones from the Pituitary Gland in Two Different Ways The Posterior Lobe ADH (vasopressin) Made in supraoptic nucleus Targets kidneys to resorb water Oxytocin Produced in the paraventricular nucleus Induces smooth muscle contraction of reproductive organs, ejects milk during breast- feeding, and signals contraction of the uterus during childbirth Pituitary Hormones: Summary of Target Organs and Effects The Thyroid Gland Located in the anterior neck Largest purely endocrine gland Composed of follicles and areolar connective tissue Produces two hormones Thyroid hormone (TH) Calcitonin The Thyroid Gland The Parathyroid Glands Lie on the posterior surface of the thyroid gland Contain two types of endocrine cells Parathyroid cells o Produce parathyroid hormone (P T H) o Increases blood concentration of C a2+ Oxyphil cells o Function unknown The Parathyroid Glands The Adrenal (Suprarenal) Glands Pyramid-shaped glands located on the superior surface of each kidney Supplied by about 60 suprarenal arteries Nerve supply is almost exclusively sympathetic fibers The Adrenal (Suprarenal) Glands Two endocrine glands in one Adrenal medulla—a cluster of neurons o Derived from neural crest o Part of the sympathetic nervous system Adrenal cortex—forms the bulk of the gland o Derived from somatic mesoderm All adrenal hormones help the body cope with danger, terror, or stress The Adrenal Medulla Medullary chromaffin cells Are modified postganglionic sympathetic neurons o Secrete amine hormones epinephrine and norepinephrine ▪ Enhance “fight-or-flight” response ▪ Hormones are stored in secretory vesicles Are arranged in spherical clusters and some branching cords The Adrenal Cortex Secretes lipid-based steroid hormones Cortex is composed of three layers (zones) Zona glomerulosa—cells arranged in spherical clusters Zona fasciculata—cells arranged in parallel cords; contains lipid droplets Zona reticularis—cells arranged in a branching network The Adrenal Cortex Hormones are corticosteroids Adrenal corticosteroids are of two main classes Mineralocorticoids Glucocorticoids Mineralocorticoids Aldosterone—secreted by the zona glomerulosa Secreted in response to decline in blood volume or blood pressure Is the terminal hormone of the renin- angiotensin mechanism Glucocorticoids Cortisol is the main type Secreted by zona fasciculata and zona reticularis Helps the body deal with stressful situations The Adrenal Gland, Gross and Microscopic Structure Stress and the Adrenal Gland The Pancreas Located in the posterior abdominal wall Contains endocrine and exocrine cells Exocrine cells o Acinar cells—secrete digestive enzymes Endocrine cells o Pancreatic islets o About 1 million islets—scattered throughout the pancreas The Pancreas Main endocrine cell types Alpha cells (α cells)—secrete glucagon o Signal liver to release glucose from glycogen o Raise blood sugar Beta cells (β cells)—secrete insulin o Signal most body cells to take up glucose from the blood o Promote storage of glucose as glycogen in liver o Lower blood sugar The Pancreas Pancreatic islets contain two rare cell types Delta () cells o Secrete somatostatin ▪ Inhibit secretion of insulin and glucagon PP cells o Secrete pancreatic polypeptide ▪ May inhibit exocrine activity of the pancreas The Thymus Located in the lower neck and anterior thorax Important immune organ Site at which T lymphocytes arise from precursor cells Transformation of lymphocytes stimulated by thymic hormones Thymic hormones—peptide molecules Thymopoietin Thymosin The Gonads Main sources of sex hormones Testes and ovaries Male Interstitial cells secrete androgens o Primarily testosterone ▪ Promotes the formation of sperm ▪ Maintains secondary sex characteristics The Gonads Female Ovaries o Estrogen ▪ Maintains secondary sex characteristics o Progesterone ▪ Prepares the uterus for pregnancy Other Endocrine Structures Endocrine cells occur within The heart o Atria contain atrial natriuretic peptide (A N P) The G I tract o Enteroendocrine cells The placenta o Sustains the fetus and secretes several steroid protein hormones Other Endocrine Structures The kidneys Cells of the juxtaglomerular complex (J G A) secrete renin Endothelial cells and interstitial connective tissue—secrete erythropoietin The skin Modified cholesterol molecules convert to a precursor of vitamin D