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Endocrine System. Endocrine System. Works together with nervous system to maintain homeostasis Primary function: produces hormones Hormones act on specific target cells to produce specific effects No ducts. Exocrine/Endocrine Glands. Gland Exocrine Endocrine
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Endocrine System • Works together with nervous system to maintain homeostasis • Primary function: produces hormones • Hormones act on specific target cells to produce specific effects • No ducts
Exocrine/Endocrine Glands GlandExocrineEndocrine Pancreas digestive enzymes insulin, glucagon Ovary egg estrogen, progesterone Testes sperm testosterone Kidney urine erythropoietin
Endocrine System vs. Nervous System Characteristic Endocrine System Nervous System General Function Maintain homeostasis Maintain homeostasis Reaction to stimuli slow rapid Duration of effect long short Target tissue entire body muscles and glands Chemical messenger hormone neurotransmitter Messenger producing cell endocrine gland neurons Distance to target cells long (via bloodstream) short (across synaptic space)
Hormones • Chemical messengers produced by endocrine glands • Secreted into interstitial fluid and absorbed into blood vessels • Contact all cells in body • Produce effects only on cells containing specific receptors • Target cell • ‘Lock and key’ arrangement causes a change in activity of target cell • Growth hormone—all cells • Prolactin—mammary tissue
Control of Hormone Secretion Negative feedback systems (like a thermostat) • If hormone level is low: • Appropriate endocrine gland is stimulated to produce more hormone • Once adequate hormone concentration is attained in the bloodstream: • Stimulation of endocrine gland is reduced and production of the hormone is stopped/reduced
Control of Hormone Secretion • Direct stimulation from the nervous system • Secretion of some hormones is stimulated by sympathetic nerve impulses when an animal feels threatened. • “Fight or flight" response
Hypothalamus (controls pituitary gland) • Part of diencephalon section of brain • Controls activities of pituitary gland • Portal system of blood vessels links hypothalamus with anterior portion of pituitary gland • Modified neurons in hypothalamus secrete releasing and inhibiting hormones into portal blood vessels • Specific for a particular anterior pituitary hormone
GHRH, GHIH (Don’t memorize) Thyrotropin releasing hormone (TRH) Gonadaotropin releasing hormone (GnRH) PRH, PIH Corticotropin releasing hormone (CRH) Hypophyseal Portal System Growth hormone Thyroid stim hormone (TSH) Follicle stim hormone (FSH) Luteinizing hormone (LH) Prolactin Posterior pituitary Oxytocin Antidiuretic hormone (ADH) Adrenocorticotropic hormone (ACTH) Melanocyte stim hormone (MSH)
Hypothalamus Modified neurons in hypothalamus also secrete antidiuretic hormone (ADH) and oxytocin Transported to posterior pituitary (along neurons) for storage Released into the bloodstream by nerve impulses from hypothalamus
Pituitary Gland (Hypophysis) Rostral • Two separate glands with different structures, functions, and embryological origins • Anterior pituitary - adenohypophysis; rostral portion • Stimulated by hypothalamus (portal system) and direct (neg) feedback from target tissues to produce hormones • Posterior pituitary - neurohypophysis; caudal portion • Stores and releases hormones produced in hypothalamus (oxytocin, ADH) Caudal
Growth Hormone (GH) • a.k.a. somatotropin and somatotropic hormone • Promotes body growth in young animals • Helps regulate metabolism of proteins, carbohydrates, and lipids in all body cells • The effect of GH on protein metabolism is to encourage anabolism (synthesis of proteins by body cells) • The effects of GH on carb and lipid metabolism are linked. • While lipids are broken down via catabolism for energy production, the use of carbs (especially glucose) as energy sources is discouraged. • Less glucose is removed from the blood and hyperglycemia occurs (hyperglycemic effect). • Important for the body to maintain a balance between GH and insulin to control blood glucose levels.
Prolactin 1. Baby sucks/stimulates 2. ↓PIH, ↑PRH 3-4. Stimulates milk glands • Helps trigger and maintain lactation in females • Secretion of milk by mammary glands • Prolactin production continues as long as teat/nipples are stimulated by nursing or milking • When prolactin stimulation stops: • Milk production stops • Mammary gland shrinks to original/nonlactating size
Thyroid-Stimulating Hormone (TSH) • a.k.a. Thyrotropin/Thyropropic Hormone • Stimulates growth/development of thyroid gland and Causes thyroid to produce its hormones. • Secretion regulated by: • Feedback (neg) from thyroid gland hormone • Thyroid hormone levels too low- TSH production increases • Thyroid hormone levels too high- TSH production diminishes
Adrenocorticotropic Hormone (ACTH) • Stimulates growth/development of adrenal cortex and the release of some of its hormones • Regulated by: • Release of CRF from hypothalamus to anterior pituitary through portal system • Neg feedback from adrenal hormones and administered cortisones • During sudden stress, ACTH can quickly be released after the hypothalamus is stimulated to send out ACTH- releasing factor to the anterior pituitary via the portal system
Follicle-Stimulating Hormone (FSH) Males- stimulates spermatogenesis in the testes Females—stimulates growth/development of ovarian follicles – where oogenesis occurs Also stimulates the cells lining the follicles to produce/secrete estrogens Used to superovulate
Luteinizing Hormone (LH) • Completes follicle development in ovary • Increasing amounts of estrogens feedback to the anterior pituitary and cause reduced production of FSH and increased production of LH • LH levels reach a peak when follicle is fully mature • Usually causes ovulation • After ovulation, LH stimulates cells in empty follicle to multiply and develop into corpus luteum (CL) • CL produces progesterone necessary for maintenance of pregnancy
Luteinizing Hormone (LH) In males, LH stimulates interstitial cells to produce testosterone
Melanocyte-Stimulating Hormone (MSH) • Controls color changes in pigment cells (melanocytes) of reptiles, fish, and amphibians • Administration of artificially large amounts of MSH to higher mammals can cause darkening of skin from melanocyte stimulation (↑ melanin) • Effect at normal levels in mammals unknown
Posterior Pituitary Posterior pituitary Oxytocin ADH • Stores (does NOT produce) two hormones produced in hypothalamus • Antidiuretic hormone (ADH) and oxytocin • Transported from hypothalmus to post pituitary along axons and stored in nerve endings • Periodically released into bloodstream in response to nerve impulses from hypothalamus
Antidiuretic Hormone (ADH) • Helps prevent diuresis • Receptors in hypothalamus detect changes in osmotic pressure (concentration) of blood (due to dehydration - hemoconcentration) • Generates nerve impulses from hypothalamus- causes release of ADH • ADH causes kidneys to reabsorb more water from urine and return it to bloodstream • Urine then more concentrated • ADH deficiency causes Diabetes Insipidus(PU/PD occurs)
Oxytocin • Effects on uterus - causes contraction of myometrium at breeding and at parturition • Induces uterine contractions that aid transport of spermatozoa to oviducts • Stimulates uterine contractions that aid in delivery of fetus and placenta • Effect on active mammary glands - causes milk let down to lower parts of gland • Stimulation of teat/nipple by nursing or milking causes oxytocin release into bloodstream • Causes contraction of musclelikemyoepithelial cells around mammary gland alveoli and small ducts • Forces milk into lower parts of gland, making it accessible for nursing/milking (milk letdown)
