hormones chapter 12 endocrine system function major control and communication system controls...
TRANSCRIPT
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Hormones
Chapter 12
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Endocrine System Function
• Major control and communication system
• Controls activities that require long duration– digestion and energy metabolism– osmoregulation, water balance, ion balance and
excretion– growth and development– reproduction
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Endocrine Systems
• Invertebrates– Most hormones arise from neurosecretory
cells in CNS– Hormones typically released directly to
target tissues– Principally involved in regeneration, growth,
development, and reproduction– Little homeostatic function
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Endocrine Systems
• Vertebrates– Much greater prevalence of non-neural
endocrine glands– More complex control pathways
• One hormone stimulates the release of another.
– Greater involvement in homeostasis
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Hormones
• Chemical signals broadcast to other cells
• Endocrine– signals circulated throughout the body
• Paracrine– signals broadcast locally within tissues
• Autocrine– Signals act directly on the cell that releases it
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Hormone Classes
• Amines– hormones derived from tyrosine and tryptophan
– adrenal medulla hormones, thyroid hormones, pineal gland hormones
• Peptide Hormones – made from polypeptide chains
– most hormones (insulin, FSH)
• Steroids– derivatives of cholesterol
– adrenal cortex hormones, gonadal hormones
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Mechanism of Action:Steroids & Thyroid Hormones
• nonpolar – pass directly through the cell
membrane • bind to protein receptor in
cytoplasm or in nucleus • protein binds to gene on DNA in
the nucleus • stimulates expression of that
gene (protein production)
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Mechanism of Action: Peptides and Most Amines
• Polar– cannot pass through hydrophobic lipid bilayer
• bind to receptor proteins on cell surface – activation of membrane-bound enzymes
• production of a second messenger inside the cell – e.g. cAMP, DAG-IP3,
• 2nd messenger activates or deactivates various enzymes
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Hormonal Regulatory Mechanisms
• Regulating hormone levels– e.g. Negative feedback
• Change causes change in opposite direction
• e.g. thyroxine/TSH
• Regulating tissue response– e.g. down regulation
• Decrease # of receptors on target cell with chronically elevated hormone levels
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Vertebrate EndocrinologyHypothalamus-Pituitary Axis
• Hypothalamus (brain region)– controls release of pituitary hormones
• Neural control of endocrine function
• Pituitary gland– Two distinctive lobes (posterior and anterior)
– Linked to hypothalamus by infidiubulum
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Posterior Pituitary (Neurohypophysis)
• Composed of neurosecretory cells• Hormones released when neurons undergo
action potentials
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Posterior Pituitary Hormones
• ADH (Anti-Diuretic Hormone)– Arginine vasopressin (mammals) or arginine vasotocin (other verts)– increases reabsorption of H2O by kidneys – induces vasoconstriction in arterioles - BP– Sexual behavior (amphibians) and oviposition (reptiles and birds)– Skin permeability (amphibians)
• Oxytocin – Uterine contraction during childbirth – milk letdown during breast feeding – male function unclear ( occurs in both sexes during sexual arousal)
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Anterior Pituitary (Adenohypophysis)
• Composed of epithelial cells• Different cell types secrete
various peptide hormones• Secretion controlled by
hormonal release from hypothalamus into hypothalamal-hypophyseal portal system
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Anterior Pituitary Hormones
• TSH (Thyroid Stimulating Hormone, Thyrotropin)– Stimulates thyroid gland
• Release thyroid hormones• Stimulates thyroid growth
• ACTH (Adrenocorticotropin)– Stimulates adrenal cortex to release glucocorticoids
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Anterior Pituitary Hormones• PRL (Prolactin)
– Breast development and milk production during pregnancy
– Development and maintenance of corpus lutea (non-primate mammals)
– Crop milk secretion in pigeons, brood patch development in birds
– Controls sensitivity of testes to LH
– Enhances uptake / inhibits secretion of ions in fish and amphibians
– Lots of other modulatory functions
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Anterior Pituitary Hormones
• MSH (Melanocyte Stimulating Hormone)– Integument pigmentation
• GH (Growth Hormone, Somatotropin)– Stimulates growth, protein synthesis, fat breakdown and
blood glucose levels– Functions indirectly through somatomedins
(e.g., insulin-like growth factors)
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Anterior Pituitary Hormones
• FSH (Follicle Stimulating Hormone, Follitropin)– regulates female sex hormones, egg development – Stimulates Sertoli cells to release local mediators that
induce spermatozoa development
• LH (Luteinizing Hormone, Lutropin)– ovulation, regulation of female sex hormones– induces corpus luteum formation after ovulation – Induces secretion of androgens by Leydig cells of testes
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“Adrenal” Glands• Releases hormones in response to stress
– glucocorticoids (e.g. cortisol)• Elevate blood glucose• Anti-inflammatory and Immunosuppression
– mineralocorticoids (e.g. aldosterone)• Na+/K+ balance, blood pressure regulation
– androgens (e.g., DHEA)• sexual characteristics
– epinephrine (“flight vs. fight”)• ↑ blood glucose, lipolysis• ↑ thermogenesis (shivering and non-)• ↑ cardiovascular / respiratory activity
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Thyroid Gland (Tetrapods)
• Thyroid hormones (TH)– Thyroxine (T4) and triiodothyronine (T3)
• Increase metabolic rate and body heat production (endotherms)
• Metamorphosis in amphibians
• Growth and development
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Pancreas
• Endocrine cells located in Islets of Langerhans
• Contain two cell types cells - secrete glucagon cells - secrete insulin
• Important in regulating glucose levels of the blood
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Insulin
• Induces glucose uptake and utilization by cells (esp. muscle and liver)
• Lowers blood glucose levels– promotes removal of glucose from blood
• Promotes formation of glycogen– polymer of glucose for storage
• Promotes conversion of glucose into fat in adipose tissue
• Stimulates amino acid uptake by cells and protein formation
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Glucagon
• Increase in blood glucose:– Activates liver enzymes to convert
glycogen into glucose
• Stimulates breakdown of stored fat and release of fatty acids into blood – used as secondary energy source
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Gonads (Testes and Ovaries)
• Produce steroid hormones– androgens (e.g., testosterone)
• sperm development
• reproductive tract maturation
• secondary sex characteristics
• sexual behavior (M and F)
– estrogens and progesterone• oocytic development
• reproductive tract development
• secondary sex characteristics
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Comparative Endocrinology:Insect Molting / Metamorphosis
• Development patterns in insects:– Hemimetabolous
• go through nymph stages (instars) and slowly transform into adults
– Homometabolous• Go through prolonged larval stage, then
develop into pupa, then adult
• Development in both occurs through similar endocrine control
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Key Hormones• Prothoracicotropic Hormone (PTTH)
– Peptide hormone secreted by neurosecretory cells brain– Stimulates release of ecdysone
• Ecdysone– steroid hormone produced by prothoracic gland– Stimulates molting and development
• Juvenile hormone (JH)– Terpenoid hormone produced by corpus allatum– Stimulates retention of juvenile characters
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Hormone Function: Molting
• Growth of juvenile stimulates PTTH secretion• Stimulates ecdysis (molting)
– Cuticle detaches from epithelium
– Muscular contractions pull insect away from cuticle
– New cuticle forms
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Hormone Function: Metamorphosis
• Levels of JH initially high– Retains juvenile characters
• Levels begin to fall as larva grows• When JH falls to below a certain level → pupation• Continue to fall to during pupation• At minimum JH production, adult form develops• JH levels rise in adult
– stimulate reproductive development
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Additional Important Hormones
• Eclosion Hormone (EH)– stimulates inka cells to secrete PETH and ETH
• Pre-ecdysis Triggering Hormone (PETH)– Coordinates muscle contractions that pull epidermis away from old
cuticle• Ecdysis Triggering Hormone (ETH)
– Cooordinates contractions that allow final escape from the old cuticle
• Bursicon– tanning/hardening of new cuticle after molting