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Understanding Chemical Signals in Animal Regulatory Systems: Hormones and Their Functions

This lecture explores the complex world of chemical signals in animals, particularly focusing on hormones and the endocrine system. Hormones are vital chemical signals secreted into body fluids, facilitating communication between various body cells known as target cells. The lecture covers key components like endocrine and exocrine glands, neurosecretory cells, feedback mechanisms, growth factors, and various hormones produced by the hypothalamus, pituitary gland, and other endocrine organs. It also discusses hormone functions and actions, including the effects of steroid hormones, tropic hormones, and the roles of specific hormones in bodily processes.

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Understanding Chemical Signals in Animal Regulatory Systems: Hormones and Their Functions

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  1. Lecture #20 Date _______ • Chapter 45 ~ Chemical Signals in Animals

  2. Regulatory systems • Hormone~ chemical signal secreted into body fluids (blood) communicating regulatory messages • Target cells~ body cells that respond to hormones • Endocrine system/glands~ hormone secreting system/glands (ductless); exocrine glands secrete chemicals (sweat, mucus, enzymes) through ducts • Neurosecretory cells~ actual cells that secrete hormones • Feedback mechanisms ~ negative and positive

  3. Local regulators: cells adjacent to or near point of secretion • Growth factors ~ proteins for cell proliferation • Nitric oxide (NO) ~ neurotransmitter; cell destruction; vessel dilation • Prostaglandins ~ modified fatty acids secreted by placenta and immune system; also found in semen

  4. Mode of Action: Chemical Signaling • 1- Plasma membrane reception • signal-transduction pathways (neurotransmitters, growth factors, most hormones) • 2- Cell nucleus reception • steroid hormones, thyroid hormones, some local regulators

  5. Vertebrate Endocrine System • Tropic hormones ~ a hormone that has another endocrine gland as a target • Hypothalamus~pituitary • Pituitary gland • Pineal gland • Thyroid gland • Parathyroid glands • Thymus • Adrenal glands • Pancreas • Gonads (ovary, testis)

  6. The hypothalamus & pituitary, I • Releasing and inhibiting hormones • Anterior pituitary: • Growth (GH)~bones √gigantism/dwarfism √acromegaly • Prolactin (PRL)~mammary glands; milk production • Follicle-stimulating (FSH) & • Luteinizing (LH)~ovaries/testes • Thyroid-stimulating (TSH)~ thyroid • Adrenocorticotropic (ACTH)~ adrenal cortex • Melanocyte-stimulating (MSH) • Endorphins~natural ‘opiates’; brain pain receptors

  7. The pituitary, II • The posterior pituitary: • Oxytocin~ uterine and mammary gland cell contraction • Antidiuretic (ADH)~ retention of water by kidneys

  8. The pineal, thyroid, & parathyroid • Melatonin~ pineal gland; biological rhythms • Thyroid hormones: Calcitonin~ lowers blood calcium Thyroxine~ metabolic processes • Parathyroid (PTH)~raises blood calcium

  9. The pancreas • Islets of Langerhans • Alpha cells: •glucagon~ raises blood glucose levels • Beta cells: •insulin~ lowers blood glucose levels • Type I diabetes mellitus (insulin-dependent; autoimmune disorder) • Type II diabetes mellitus (non-insulin-dependent; reduced responsiveness in insulin targets)

  10. The adrenal glands • Adrenal medulla (catecholamines): •epinephrine & norepinephrine~increase basal metabolic rate (blood glucose and pressure) • Adrenal cortex (corticosteroids): •glucocorticoids(cortisol)~raise blood glucose•mineralocorticoids (aldosterone)~reabsorption of Na+ and K+

  11. The gonads • Steroid hormones: precursor is cholesterol • androgens (testosterone)~ sperm formation; male secondary sex characteristics; gonadotropin • estrogens (estradiol)~uterine lining growth; female secondary sex characteristics; gonadotropin • progestins (progesterone)~uterine lining growth

  12. Steroid Hormone Action

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