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The Endocrine System

The endocrine system utilizes hormones as chemical messengers that regulate various bodily functions through slower and long-lasting communication with target organs. This chapter explores hormonal secretions and their origins—either from endocrine glands, exocrine glands, or individual cells. It details the effects of hormone hypo- and hypersecretion, the roles of the pituitary gland, thyroid, adrenal glands, and the interplay of negative and positive feedback mechanisms in homeostasis. Additionally, it covers the functions of sex hormones and the impact of diseases, offering a comprehensive understanding of this complex system.

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The Endocrine System

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  1. The Endocrine System Chapter 9

  2. Communication and Control – slower and long lasting through hormones – chemical messages – that effect a target organ • Diseases (tumors) influence by: • Hyposecretion – too little secretion • Hypersecretion –two much secretion • All organs are glands: • Exocrine – secrete products into ducts • Endocrine – ductless glands • Heterocrine Gland - Both (pancreas)

  3. Origin Of Hormones • Hormones affects target cells • Secreted by endocrine glands • Secreted by neurons (neuro-hormones) - neurosecretory cells • Secreted by individual cells or tissues (Growth Factors, prostaglandins, histamine)

  4. Chemical Nature of Hormones • Derived from cholesterol • Derived from amino acids • Derived from fatty acids

  5. Second Messenger Hypotheses Cause specific affects on target organs only Hormone binds to specialized receptor – “first messenger” Second Messenger is Cyclic Adenosine MonoPhosphate (cAMP) The bonding of the hormone activates activates a G4 protein, which in turn activates adenylate cyclase (enzyme) to react with ATP to produce cAMP Protein Hormones

  6. Steroid Hormones • Small – lipid soluble Hormones • Pass directly through the cell membrane of target organs • Go to nucleus, interact with DNA to allow transcription of certain proteins

  7. Prostaglandins • PG’s - tissue hormone – produced on a tissue and acts on nearby cells • Three groups PGA, PGE, PGF • Might have a role in asthma, blood pressure disorders, and ulcers

  8. Negative Feedback • Reverses a change in a body condition • Insulin – high blood-sugar content after a meal, pancreas secretes insulin to move blood-sugar into cells, thus decreasing levels

  9. Other types of Negative Feedback

  10. Positive Feedback • More Uncommon than negative feedback • Amplify changes rather than reverse them • Labor – the contractions are amplified through hormone control

  11. Pituitary Gland • Gland in hind brain about the size of a pea • Anterior (adrenohypophysis)- gland / Posterior (neurohypophysis) - nervous

  12. Anterior (adrenohypophysis)- gland - hypothalamin releasing hormones get anterior to release hormonesPosterior (neurohypophysis) - nervous- nerve endings from hypothalamus cause hormones to be released

  13. Hormones of Anterior Pituitary • Tropic Hormones – Stimulates another endocrine gland to grow and secrete its hormone

  14. ANTERIOR GLAND - TROPIC • TSH - (thyroid-stimulating) Growth and secretion of the thyroid • ACTH - (adenocorticotropic) Growth of Adrenal cortex and secretions • FSH - (follicle stimulating) Growth and development of Ovarian Follicles - providers of ova (eggs), release of estrogen/progesterone • LH - (Luteinizing) Control ovulation - maturation and bursting of follicle - males - interstitial cells • ICSH - (Interstitial cell)Testosterone secretion of testes

  15. MSH - (melanin stimulating hormone) - synthesizes and spreads melanin - pigment • GH - (Growth Hormone) -stimulates growth by protein anabolism (building) - fat and glucose catabolism - enhances the movement of Amino acids across cell membrane • Insufficient GH - dwarfism • Oversecretion - giagntism • Prolactin - (lactogenic) - stimulates milk production, in males excess may decrease sex hormones

  16. Posterior Pituitary Hormones • ADH- retention of water by kidneys (diuretic - loss of water by kidneys)- maintained by osmoreceptors in the brain • Oxytocin - stimulates uterine contraction - positive feedback

  17. Located in the neck, below the larynx Thyroxin (T4 - four atoms of iodine - accelerates metabolism Calcitonin - decreases blood calcium, puts calcium into bones Triiodothyronine (T3 three atoms of iodine) -energy for metabolism - five times as potent as thyroxin Small (usually 4) found on the back of the thyroid Increases Blood Calcium - breaks down bone Thyroid Gland ---Parathyroid Gland

  18. Adrenal Glands • Adrenal Glands - Lie on top of the kidneys • Two separate endocrine glands the adrenal cortex and the adrenal medulla

  19. CORTEX Glucocorticoids - maintain blood pressure, sugar, stress - cortisol Mineralocorticoids - increase blood sodium, decrease blood potassium sex hormones - small amount secreted, female converted to estrigens Medulla Produces epinephrine and norepinephrine for stress response - sympathetic inervation The effects include increase heart rate, breathing rate, and all assoisiated sympahtetic responses ADRENAL GLANDS

  20. Pancreatic Islets/ Islets of Langerhans • Alpha cells = glucagon, Beta cells = insulin

  21. Female and Male Sex Hormones • Ovaries – female, Testis - male • Female characteristics and fertility - release of estrogen and progesterone • Male - secretes testosterone - interstitial cells - controls male sexual development

  22. PLACENTA • Temporary endocrine gland • secretes choriongonadotropin hormone - maintains corpus luteum - high in urine = pregnancy • PINEAL • Small pine-coned shaped gland at the roof of the third ventricle of the brain • Also called third eye – responds to senses • Produces melatonin • inhibits ovarian activity • influences menstrual cycle • biorhythms

  23. HEART • Atrial Natriuretic Hormone – secreted by the walls of the atria – regulates fluid and electrolytes • THYMUS • Located in mediastinum. Has cortex and medulla • Houses lymphocytes • secretes thymosin - immune regulator

  24. Digestive Glands - stomach and small intestines secrete hormones to aid digestion - gastrin, secretin

  25. Endocrine Development • Endocrine tissue develops from the ectoderm, epithelial tissue

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