Endocrine glands are ductless Exocrine glands have ducts Chapter 13 Endocrine System 1 Endocrine System composed of cells, tissues and organs that secrete substances into the internal environment Hormones - chemicals secreted by the endocrine system that diffuses from the interstitial fluid into the bloodstream and eventually act on target cells Endocrine glands and their hormones help regulate metabolic processes; control the rate of certain chemical reactions; aid in transporting substances through membranes; help regulate water balance, electrolye balance and blood pressure; play vital roles in reproduction, development and growth 2 Endocrine Glands Endocrine glands Paracrine secretions release hormones act locally hormones travel affect only neighboring cells through blood to target cells Autocrine secretions affect only the secreting cell Comparison of Nervous System and Endocrine System Neurons release neurotransmitters into a synapse, affecting postsynaptic cells Glands release hormones into the bloodstream Only target cells of hormone responds 3 4 1
Comparison of Nervous System and Endocrine System Chemistry of Hormones Steroid or Steroid-Like Hormones lipids that include complex rings of C and H atoms derived from cholesterol sex hormones adrenal cortex hormones Nonsteroid Hormones amines proteins peptides glycoproteins most hormones 5 6 Actions of Steroid Hormones hormone crosses membranes hormone combines with receptor in nucleus synthesis of mrna activated mrna enters cytoplasm to direct synthesis of protein Actions of Non-steroid Hormones hormone binds to receptor on cell membrane adenylate cyclase activated ATP converted to camp camp promotes a series of reactions leading to cellular changes 7 8 2
Prostaglandins paracrine substances act locally very potent in small amounts Control of Hormonal Secretions primarily controlled by negative feedback mechanism Tropic hormones Nervous system humoral regulate cellular responses to hormones can activate or inhibit adenylate cyclase controls camp production alters cell s response to hormones 9 10 wide variety of functions Major Endocrine Glands 11 12 3
Pituitary Gland Attached to the hypothalamus by the infundibulum Two distinct portions anterior pituitary (adenohypophysis) posterior pituitary (neurohypophysis) Pituitary Gland Control Hypothalamic releasing hormones stimulate cells of anterior pituitary to release hormones Nerve impulses from hypothalamus stimulate nerve endings in the posterior pituitary gland to release hormones 13 14 Hypothalamic Hormones Hormones of the Pituitary Gland 15 16 4
Thyroid Gland Thyroid Gland Hormones Made up of two lobes connected by an isthmus stucture Connective tissue capsule covers gland secretory parts are called follicles Extra follicular cells are cells outside the follicle that also secrete hormones 17 18 Disorders of the Thyroid Gland Disorders of the Thyroid Gland Graves Disease Hyperthyroidism Cretinism Infantile hypothyroidism 19 20 5
Parathyroid Glands Parathyroid Hormone Located on the posterior side of the thyroid gland secrete parathyroid hormone (PTH) or parathormone increases blood calcium concentration and decreases blood potassium concentration through action in the bones, kidneys and intestines 21 22 Disorders of the Parathyroid Glands Adrenal Glands 23 24 6
Hormones of the Adrenal Medulla Hormones of the Adrenal Cortex 25 26 Pancreas Hormones of the Pancreatic Islets 27 28 7
Other Endocrine Glands Other Endocrine Glands Pineal Gland located deep between the cerebral hemispheres secretes melatonin regulates circadian rhythms Thymus Gland located above the heart Shinks with age secretes thymosins promotes development of certain lymphocytes important in role of immunity 29 Reproductive ovaries produce estrogens and progesterone testes produce testosterone placenta produces estrogens, progesterone, and gonadotropins 30 Life-Span Changes endocrine glands decrease in size muscular strength decreases as GH levels decrease ADH levels increase due to slower break down in liver and kidneys calcitonin levels decrease; increase risk of osteoporosis Clinical Application Growth Hormone Ups and Downs Gigantism - hypersecretion of GH in children Acromegaly hypersecretion of GH in adults Dwarfism hyposecretion of GH in children Figure shows oversecretion of GH in adulthood as changes occur in the same person at ages (a) nine, (b) sixteen, (c) thirty-three, and (4) fifty-two PTH level changes contribute to risk of osteoporosis insulin resistance may develop changes in melatonin secretion affect the body clock thymosin production declines increasing risk of infections 31 32 8