The Endocrine System How Hormones Affect the Body

Endocrine System • Second-messenger system of body • Uses chemical messengers (hormones) that are released into the blood • Hormones control several major processes: – Reproduction – Growth and development – Mobilization of body defenses – Maintenance of much homeostasis – Regulation of metabolism

Hormones • Hormones are produced by specialized cells • Cells secrete hormones into extracellular fluids • Blood transfers hormones to target sites • These hormones regulate the activity of other cells

Glands

Hypothalamus • Location-the brain – Hormones released by the posterior pituitary; releasing and inhibiting hormones that regulate the anterior pituitary – Master endocrine organ

Pituitary Gland • Location – Size of a pea – Hangs by a stalk from the hypothalamus in the brain – Has two functional lobes • Anterior • Posterior

Pituitary Gland: Anterior Pituitary Hormones Representative actions Regulated by 1. Growth hormone (GH) Growth bones, muscles and metabolism Hypothalamic releasing and inhibiting hormones 2. Prolactin (PRL) Milk production (male function unknown) Hypothalamic hormones 3. Follicle- stimulating hormone (FSH) Production of ova and sperm Hypothalamic hormones 4. Luteinizing hormone (LH) Stimulates ovaries and testes Hypothalamic hormones 5. Thyroid stimulating hormone (TSH) Stimulates thyroid gland Hypothalamic hormones 6. Andrenocorticotrophic Stimulates adrenal hormone (ACTH) cortex to secrete glucocorticoids Glucocorticoids; hypothalamic hormones

Pituitary Gland: Posterior Pituitary Hormone Representative actions Regulated by 1. Oxytocin Stimulates contraction of uterus and the milk “letdown” reflex Hypothalamus and Nervous system: in response to uterine stretching or suckling of a baby 2. Antidiuretic hormone (ADH) Promotes retention of water by kidneys Hypothalamus in response to water/salt imbalance

Thyroid Gland • Location – Found at the base of the throat – Consists of 2 lobes and connecting isthmus – Produces two hormones

Thyroid Gland Hormones Representative actions Regulated by 1. Thyroxine (T 4) (T 3) Stimulates metabolism TSH 2. Calcitonin Reduces blood calcium level Calcium level in blood

Parathyroid Gland • Location – Tiny masses on the posterior of the thyroid

Parathyroid Gland Hormones Representative Action Regulated by: 1. Parathyroid hormone (PTH) Raises blood calcium level Calcium level in the blood

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Adrenal Glands • Location – Sits on top of kidneys – Two regions • Adrenal cortex (outer region) • Adrenal medulla (inner region)

Adrenal Glands Adrenal Medulla Hormones Representative Action Regulated by: 1. Epinephrine and norepinephrine • Raises blood glucose Sympathetic nervous level, increases system metabolism • Constrict certain blood vessels

Adrenal Glands Adrenal Cortex Hormones Representative Actions Regulated by: 1. Glucocorticoids Increase blood glucose Adrenocorticotrophic hormone (ACTCH) 2. Mineralocorticoids Promotes reabsorption of Na+ and excretion of K+ in kidneys Changes in blood volume or blood pressure; K in blood or Na levels in blood

Pineal Gland • Location – Found on the third ventricle of the brain

Pineal Gland Hormones Representative action Regulated by 1. Melatonin Biological rhythms seasonal and daily cycles Light/dark cycles

Thymus Gland • Location – Located posterior to the sternum – Largest in infants and children

Thymus Gland Hormones Representative Action Regulated by 1. Thymosin Programs T lymphocytes unknown

Pancreas • Location: – Located closest to the stomach in the abdominal cavity – Known as pancreatic islets also the islets of Langerhan’s – Mixed gland that produces both endocrine and exocrine functions

Pancreas Hormones Representative action Regulated by 1. Insulin Reduces blood glucose Glucose levels in blood 2. Glucagon Raises blood glucose Glucose levels in blood

Gonads • Location – Female and male gonads produce sex cells (exocrine)

Gonads Testes Hormones Representative action Regulated by 1. Androgen s Support sperm formation; development and maintenance of male sex characteristics FSH and LH Ovaries Hormones Representative action Regulated by 1. Estrogens Stimulate uterine lining growth, FSH and LH development and maintenance of female sex characteristics 2. Progesterone Promotes growth of uterine lining FSH and LH