David Sadava H Craig Heller Gordon H Orians

David Sadava H. Craig Heller Gordon H. Orians William K. Purves David M. Hillis Biologia. blu C – Il corpo umano Endocrine System

Endocrine System • What are hormones and how do they work? • How do the nervous and endocrine systems interact? • What are the major mammalian endocrine glands and hormones? • What happens when a gland malfunctions?

Endocrine System - What are hormones and how do they work? Hormones are chemical signals secreted by cells of the endocrine system. Endocrine cells: cells that secrete hormones. Target cells: cells that have receptors for the hormones.

Endocrine System - What are hormones and how do they work? Circulating hormones diffuse into the blood and can activate target cells far from the site of release. • Paracrine hormones: affect only target cells near the site of release. • Autocrine hormones: affect the cells that released the hormones.

Endocrine System - What are hormones and how do they work? Chemical signaling systems (part 1)

Endocrine System - What are hormones and how do they work? Chemical signaling systems (part 2)

Endocrine System - What are hormones and how do they work? Some endocrine cells are single cells (e. g. , in the digestive tract). • Endocrine glands: aggregations of secretory cells; hormones are secreted to the extracellular space. • Exocrine glands: ducts carry products to the outside of the body.

Endocrine System - What are hormones and how do they work? Three types of hormones: • peptides or polypeptides - water-soluble, transported in blood but not across membranes; • steroid hormones - lipid-soluble, must be bound to carrier proteins to be carried in blood; • amine hormones - derivatives of tyrosine.

Endocrine System - What are hormones and how do they work? Hormone receptors: • lipid soluble hormones - receptors are inside the cell; • water-soluble hormones cannot readily pass cell membrane - receptors are on the outside.

Endocrine System - What are hormones and how do they work? The endocrine system (part 1)

Endocrine System - What are hormones and how do they work? The endocrine system (part 2)

Endocrine System - What are hormones and how do they work? Multiple feedback loops control hormone secretion

Endocrine System - What are hormones and how do they work? Epinephrine (adrenalin) stimulates “Fight or Flight” responses

Endocrine System - How do the nervous and endocrine systems interact? The pituitary gland is attached to the hypothalamus of the brain. Posterior pituitary secretes neurohormones (synthesized by neurons in the hypothalmus): oxytocin and ADH.

Endocrine System - How do the nervous and endocrine systems interact? The posterior pituitary releases neurohormones

Endocrine System - How do the nervous and endocrine systems interact? The anterior pituitary secretes: • tropic hormones - control other endocrine glands; • growth hormone - promotes growth; • prolactin - breast development and milk production; • enkephalins and endorphins - natural opiates.

Endocrine System - How do the nervous and endocrine systems interact? The anterior pituitary produces hormones

Endocrine System - How do the nervous and endocrine systems interact? Hormones from the hypothalamus control the anterior pituitary. The hypothalamus produces releasing hormones—carried to the anterior pituitary by portal blood vessels. Negative feedback loops control hormone secretion from the anterior pituitary.

Endocrine System - How do the nervous and endocrine systems interact? The thyroid gland consists of many follicles (A) Thyroxine is produced by the follicles

Endocrine System - How do the nervous and endocrine systems interact? The thyroid gland consists of many follicles (B)

Endocrine System - What are the major mammalian endocrine glands and hormones? Thyroxine regulates cell metabolism. Anterior pituitary secretes thyrotropin (TSH), which activates the follicles to produce thyroxine. The thyroid gland also produces calcitonin. Regulation of calcium levels in the blood is controlled by calcitonin, parathyroid hormone, and vitamin D.

Endocrine System - What are the major mammalian endocrine glands and hormones? The thyroid gland produces thyroxine (T 4) and triiodothyronine (T 3).

Endocrine System - What are the major mammalian endocrine glands and hormones? Hormonal regulation of calcium (part 1)

Endocrine System - What are the major mammalian endocrine glands and hormones? Hormonal regulation of calcium (part 2)

Endocrine System - What are the major mammalian endocrine glands and hormones? The parathyroid glands secrete parathyroid hormone (PTH). PTH raises blood calcium levels: • stimulates osteoclasts; • stimulates kidneys to reabsorb calcium; • activates vitamin D, which stimulates digestive tract to absorb calcium. Vitamin D (calciferol) is produced by skin cells from cholesterol, by UV light.

Endocrine System - What are the major mammalian endocrine glands and hormones? Insulin binds to receptors on target cells and allows uptake of glucose. • Lack of insulin: type I diabetes. • Lack of insulin receptors on target cells: type II diabetes.

Endocrine System - What are the major mammalian endocrine glands and hormones? Islets of Langerhans: clusters of endocrine cells in the pancreas. • b cells produce insulin. • a cells produce glucagon: stimulates liver to convert glycogen back to glucose. • d cells produce somatostatin: inhibits release of both (also released by the hypothalamus).

Endocrine System - What are the major mammalian endocrine glands and hormones? Adrenal gland: two glands, on top of the kidneys. Adrenal medulla: epinephrine and norepinephrine. On target cells: a-adrenergic and badrenergic receptors. b-blockers block b-adrenergic receptors.

Endocrine System - What are the major mammalian endocrine glands and hormones? The adrenal gland has an outer and an inner portion

Endocrine System - What are the major mammalian endocrine glands and hormones? Adrenal cortex produces corticosteroids from cholesterol: • glucocorticoids - cortisol; • mineralocorticoids - aldosterone; • sex steroids.

Endocrine System - What are the major mammalian endocrine glands and hormones? The corticosteroid hormones are built from cholesterol

Endocrine System - What are the major mammalian endocrine glands and hormones? Aldosterone stimulates kidneys to retain sodium and excrete potassium. Cortisol mediates reaction to stress; cells not critical for action decrease use of blood glucose; blocks immune system reactions. Cortisol release is controlled by corticotropin from the anterior pituitary, in turn controlled by corticotropin -releasing hormone from the hypothalamus. Stress response is turned off by negative feedback of cortisol to brain.

Endocrine System - What are the major mammalian endocrine glands and hormones? Gonads produce sex steroids: • androgens - testosterone; • estrogens - (estradiol) and progesterone. In development, sex hormones determine whether fetus will become male or female.

Endocrine System - What are the major mammalian endocrine glands and hormones? At puberty, production of sex hormones increases. Controlled by gonadotropins from the anterior pituitary: • luteinizing hormone (LH); • follicle-stimulating hormone (FSH).

Endocrine System - What are the major mammalian endocrine glands and hormones? The pineal gland produces melatonin from tryptophan. Melatonin is released in the dark; light inhibits release. Involved in photoperiodicity: seasonal changes in light trigger physiological changes.

Endocrine System - What happens when a gland malfunctions? Goiter is an enlarged thyroid gland. It can result from either hyperthyroidism (thyroxine excess) or hypothyroidism (thyroxine deficiency). Epithelial cells produce excess thyroglobulin and the follicles enlarge.