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THE ENDOCRINE SYSTEM

THE ENDOCRINE SYSTEM. Explain how the endocrine system differs from the nervous system in its function and control of the body. DIFFERENCES IN FUNCTION BETWEEN THE NERVOUS SYSTEM & THE ENDOCRINE SYSTEM. Both systems have a key role in homeostasis.

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THE ENDOCRINE SYSTEM

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  1. THE ENDOCRINE SYSTEM Explain how the endocrine system differs from the nervous system in its function and control of the body.

  2. DIFFERENCES IN FUNCTION BETWEEN THE NERVOUS SYSTEM & THE ENDOCRINE SYSTEM • Both systems have a key role in homeostasis. • Endocrine glands are ductless glands which secrete a range of different hormones into the bloodstream. These hormones are chemical signals delivered to target organs/parts of the body, usually through the circulatory system. • Hormonal messengers tend to have relatively slower, longer lasting effects than the very speedy, short term effects sent out by action potentials of the nervous system. See example later.

  3. ENDOCRINE SYSTEM • The endocrine system is composed of ductless glands that secrete hormones into the interstitial fluid (the fluid that bathes the cells & tissues) and from there into the circulatory system. Endocrine glands have a very rich blood supply which enables this function. • See p277 & 278 for names, locations & functions of individual glands.

  4. ENDOCRINE SYSTEM FUNCTIONS • Water balance – by controlling the solute concentration of the blood. • Ion regulation – regulates Sodium, potassium, and calcium concentrations in the blood. • Growth, rate of metabolism & tissue maturation. • Heart rate & BP regulation, helping to prepare the body for action. Example later.

  5. ENDOCRINE SYSTEM FUNCTIONS • Blood glucose control • Immune system regulation – the production & functions of the immune cells. • Reproductive functions control. • Uterine contractions & milk release

  6. ENDOCRINE SYSTEM FUNCTIONS The example below shows the initial, short term nervous systemfunction & effect, followed by the more long lasting endocrine system function & effect. • Someone gets a fright. Initial reaction from: • Sympathetic nerves which send the neurotransmitter, noradrenaline, to the heart. • As a result, the pacemaker speeds up the heartbeat. • After approx. 1 min the hormone, adrenaline, is released from the adrenal glands & takes over from the nervous stimuli to maintain this, if necessary over a longer period of time.

  7. Hypothalamus • The hypothalamus is part of the autonomic nervous system & is the brain’s control centre for all endocrine gland functions. Chemical secretions- inhibiting or releasing factors- cause the endocrine organ to secrete or cease secretion of their hormones.

  8. THE PITUITARY GLAND • . • The pituitary gland is about the size of a pea. It is situated close to the hypothalamus, near the base of the brain. It secretes hormones that influence other glands. It is divided into 2 - anterior & posterior parts.

  9. ANTERIOR PITUITARY • Growth hormone (Somatotrophin) • Thyroid stimulating hormone (TSH) • Adrenocorticotropic hormone (ACTH) • Melanocyte stimulating hormone (MSH) • Follicle stimulating hormone (FSH) • Leuteinising hormone (LH) or interstitial cell stimulating hormone (ICSH) • Prolactin See p277 for table of target tissues.

  10. POSTERIOR PITUITARY • Antidiuretic hormone (ADH)- When released in large amounts it causes blood vessels to constrict. In this context it is called vasopressin. • Oxytocin – secreted in labour & in release of milk in breast feeding See p277 for table of target tissues.

  11. THYROID GLAND • Thyroxin – regulates metabolic rate & important in growth & development. • Triiodothyronine – ditto • Calcitonin – helps to prevent elevated blood calcium levels. See p278 for table of all endocrine target tissues.

  12. PARATHYROID GLANDS • Parathyroid hormone – more important role than the thyroid gland in the regulation of blood calcium levels.

  13. ADRENAL MEDULLA & ADRENAL CORTEX Adrenal Medulla: • Adrenaline (epinephrine) • Noradrenaline (norepinephrine) – much less of this is secreted Adrenal cortex: • Mineralocorticoids (aldosterone) – regulates potassium & sodium balance (controls reabsorption in the kidneys). • Glucocorticoids (cortisol) – increases breakdown of proteins & fat into forms that can be used to provide energy. • Adrenal androgens – male hormones, small amounts

  14. PANCREAS An exocrine (non-endocrine) part of pancreas produces digestive enzymes carried by system of ducts to small intestine) Endocrine portion of pancreas produces: • Insulin – metabolism & reduction of blood sugar levels • Glucagon – conversion of glycogen to glucose, raising blood sugar levels.

  15. THYMUS GLAND & PINEAL BODY • Thymus gland secretes thymosin – aids formation of T-cells (white blood cells). • Pineal body secretes melatonin – inhibits functions of the reproductive system. May have a role in onset of puberty.

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