Biology XI: 22 Chem Cord & Integra(1 Human Endocrine System)

Human Endocrine System & Hypothalamus, Pineal, Thyroid, Parathyroid Hormones Chemicals which act as intercellular messengers; produced in trace amounts Human Endocrine System Pituitary, pineal, thyroid, adrenal, pancreas, parathyroid, thymus, and gonads are the organised endocrine glands in our body. In addition, GI tract, liver, kidney, heart also produce hormones. Hypothalamus Basal part of diencephalon in forebrain It has several groups of neurosecretory cells (known as nuclei) that produce hormones. The synthesis and secretion of pituitary hormones is regulated by these hormones. Hormones originate from hypothalamic neurons, pass through axons, and are released from their nerve endings. Reach pituitary gland through a portal circulatory system and regulate the functioning of anterior pituitary Hormones from hypothalamus are of two types: Releasing Hormones Inhibiting Hormones Stimulate secretion of pituitary hormones Example − Gonadotropin Releasing Hormone (GnRH) Inhibit secretion of pituitary hormones Example − Somatostatin Pineal Gland Location − Dorsal side of forebrain Secretes melatonin that regulates 24-hour (diurnal) rhythm of the body such as sleep-wake cycle, body temperature, etc. Melatonin also regulates metabolism, pigmentation, and menstrual cycle. Thyroid Gland Location − Two lobes of thyroid gland are located on either side of trachea. Isthmus − Thin flap of connective tissue interconnecting the thyroid glands Composition − Follicles + Stromal tissues Follicular cells synthesize two hormones: Tetraiodothyronine or thyroxine (T4) Triiodothyronine (T3) Deficiency of iodine in diet leads to hypothyroidism goitre (enlargement of thyroid gland) Excessive secretion of thyroid hormone leads to hyperthyroidism. This may occur due to cancer of thyroid gland or development of nodules of thyroid glands. Importance: Regulates BMR (Basal Metabolism Rate) Supports the process of RBC synthesis Maintains water-electrolyte balance Secretes thyrocalcitonin which regulates blood calcium levels Symptoms of Hypothyroidism: In children In adults Cretinism (stunted growth), mental retardation, low IQ, deaf-mutism Irregular menstrual cycle Parathyroid Gland Location − Four parathyroid glands are present on back side of thyroid glands. Secretes − Parathyroid hormone (PTH) Secretion of PTH is regulated by circulating level of calcium ions. PTH is a hypercalcemic hormone. It increases blood calcium levels by dissolution/demineralization from bones reabsorption of Ca2+ by renal tubules Ca2+ absorption from digested food