Chapter 19 lecture notes.docx

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Biological Sciences
BIO 121
Jason Ramsay

Chapter 19: The Endocrine System  The nervous system and the endocrine system work together to monitor the body’s activities.  The nervous system: produces short-term very specific responses.  The endocrine system: produces long-term general responses. The endocrine system releases chemicals called hormones o Hormones leave a gland or gland-like structure o The hormone enters the bloodstream o The hormone travels to its target organ or tissue o The hormone causes the target organ to respond Hormones (which means to “excite”) are organized into four groups  Amino acid derivatives  Structurally similar to amino acids  Examples: thyroid hormones and suprarenal medulla hormones are derivatives of tyrosine. Melatonin is a derivative of tryptophan  Peptide hormones  These hormones are chains of amino acids  Examples: all hormones from the pituitary gland are peptide hormones.  Steroid hormones  These are derived from cholesterol  Examples: reproductive hormones and suprarenal cortex hormones.  Elicosanoids  Derived from arachidonic acid, which is a fatty acid of call membranes  Examples: prostaglandin, leukotrienes, and thromboxane Hypothalamus Functions via three mechanisms 1. Secretes regulatory hormones: secretes releasing hormones(RH) , secretes inhibiting hormones(IH) 2. Acts are an endocrine organ: releases antidiuretic hormones and oxytocin to the pituitary gland 3. Contains autonomic nervous system centers: exerts control over the suprarenal medulla Consists of two lobes  Adenohypophysis: anterior lobe releases seven peptide hormones  Neurohypophysis: posterior lobe releases two peptide hormones The Pituitary Gland  The Neurohypophysis o Innervated by nerves form the hypothalamus o Releases ADH (antidiuretic hormone) - Targets the nephrons of the kidneys - Causes the kidneys to retain water (prevents dehydration) - Constricts peripheral blood vessels (elevates blood pressure) o Releases OT (oxytocin) - Targets the smooth muscles of the uterus - Targets the contractile cells of the mammary glands - Causes the myoepithelial cells of the mammary glands to release milk from the nipple - In males: OT causes smooth muscle contractions in the prostate gland  The Adenohypophysis o Controlled by secretions of the regulatory hormones from the hypothalamus o Made of three different regions: - Pars tuberalis: wraps around a portion of the infundibulum - Pars distalis: secretes the majority of the hormones - Pars intermedia: secretes melanocyte-stimulating hormone o Consists of five different cell types: - Thyrotropes: release thyroid-stimulating hormone (TSH) - Corticotropes: release adrenocorticotropic hormone (ACTH) and melanocyte-stimulating hormone (MSH) - Gonadotropes: release follicle-stimulating hormone (FSH) and luteinizing hormone (LH) - Lactotropes: release prolactin (PRL) - Somatotropes: release growth hormone (GH; also called somatotropin) Hormones of the Adenohypophysis  Hormones releases by the pars distalis: - Thyroid-stimulating hormone (TSH) - Adrenocorticotropic hormone (ACTH) - Follicle-stimulating hormone (FSH) - Luteinizing hormone (LH) - Prolactin (PRL) - Growth hormone (GH); also called somatotropin  Hormone released by the pars intermedia: - Melanocyte-stimulating hormone (MSH)  Thyroid-stimulating hormone - Targets the thyroid gland - Causes the thyroid gland to release thyroid hormones (calcitonin, thyroxine, and triiodothyronine)  Adrenocorticotropic - Targets the suprarenal cortex - Causes the suprarenal cortex to release glucocorticoids  Follicle-stimulating hormone - Targets the ovaries of females - Causes maturation of oocytes - Causes the release of estrogen - Targets the seminiferous tubules of males - Causes sperm production  Luteinizing hormone - Targets the ovaries in females - Causes ovulation - Causes the release of progestin (progesterone) - Targets the interstitial cells in males - Causes the release of androgens (testosterone) - Causes the release of estrogen  FSH and LH are also called gonadotropins  Prolactin - Targets the mammary glands - Causes the production of milk  Growth hormone - Also called somatotropin - Targets general cells and skeletal muscles - Causes protein synthesis resulting in growth - Targets liver cells - Causes the release of somatomedins, which stimulate protein synthesis in muscles and cartilage cells.  Melanocyte-stimulating hormone - Targets the melanocyte cells of the skin - Causes the production of melanin The Thyroid Gland  The thyroid gland is on the anterior surface of the trachea o Highly vascularized - Supplied by the superior thyroid artery (from the external carotid artery) - Supplied by the inferior thyroid artery (from the thyrocervical trunk) o Made of two lobes connected via an isthmus o Consists of thyroid follicles o This is the only gland that stores its hormone products Thyroid follicles manufacture thyroid hormones 1. Follicles are lined with simple cuboidal epithelium and T thyrocytes (follicular cells) 2. Follicular cells secrete thyroglobulin into the follicle 3. Follicular cells transport iodine into the follicle 4. The combination of iodine and the colloidal material within the follicle results in the formation of the thyroid hormones Hormones of the thyroid gland  Calcitonin (CT) o Targets osteoclasts of bones o Causes a decrease in blood calcium ion concentration by: 1. Stimulating calcium ion excretion at the kidneys 2. Inhibiting osteoclast activity (therefore calcium ions do not leave the bones to enter the blood)  Thyroxine (T4)  Triiodothyronine (T3) o Target general cells o Cause an increase in metabolism The parathyroid glands are located on the poster
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