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Hypothalamus

Hypothalamus

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Hypothalamus

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  1. Hypothalamus

  2. Hypothalamus • “Older” part of the brain (Primitive) • Maintenance of homeostasis • Reception of external and internal signals • Incorporation of signals to generate appropriate responses • Endocrine • Autonomic • Behavioral • Reception of feedback • Hormones

  3. Anatomy of hypothalamus • Landmarks • Anterior (front) • Optic chiasm (crossing of optic nerve fibers) • Posterior (dorsal/back) • Mamillary body • Superior (cranial) • Third ventricle • Inferior • Pituitary stalk/infundiblum

  4. Neural organization of hypothalamus • Clusters of neurons • Nucleus/nuclei • Different section of hypothalamus contains different nuclei

  5. Median eminence • The center of the tuber cinereum (floor of the third ventricle) • Blood vessels • Nerve endings • Functional link between hypothalamus and pituitary gland • Site where the pituitary portal vessels arise • Extensive network of “arterialized” venus capillaries • Microcirculation between hypothalamus and anterior pituitary

  6. Three zones • Ependymal layer • Cells with microvilli • Tanycytes • Forms barrier between CSF and blood • Prevention of diffusion of hypothalamic factors • Internal zone • Axons of hypothalamic neurons (supraoptic and paraventricular) • Extended to the posterior pituitary

  7. Three zones • External zone • Peptinergic neurons • Thyrotropin-releasing hormone (TRH) • Corticotropin-releasing hormone (CRH/CRF) • Gonadotropin-releasing hormone (GnRH/LHRH) • Neurons that release monoamines • Serotonin and dopamine • Portal vessels

  8. Release of hypothalamic peptides • Depolarization of neural cells • Supporting elements • Non-neural cells • Coordinated regulation by interaction of neurons • Hypothalamic • CNS

  9. Types of neurosecretory system • Magnocellular neurons • Neural cells located within hypothalamus • Paraventricular hypothalamic nuclei • Supraoptic nuclei • Axon extend through median eminence and enter the posterior pituitary gland • Hormones produced by the neural cells in hypothalamus and transported to the posterior pituitary gland to be released • Oxytocin • Vasopressin

  10. Parvicellular hypophyseotropic neurons • Nuerons within Paraventricular hypothalamic nuclei and arcuate nuclei • Axons terminate in median eminence • Portal plexus • Factors released in portal circulation • Triggers secretion of anterior pituitary hormones

  11. Hypothalamic projection neurons • Communication between neurons • Hypothalamic neurons • Paraventricular hypothalamus • Lateral hypothalamic area • Arcuate nuclei • Target neurons • Preganglionic neurons in spinal cord • Use of hormones as neural signals

  12. Regulation of hypothalamic hormone secretion • Role of neurons within the brain • Intrinsic and extrinsic cues • Sensory neurons • Neurotransmitters • Excitatory • Inhibitory • Neurotransmitters • Monoamines • Dopamine, Nor, Epi, Serotonin, Histamine, and acetulcholine • Amino acids • Gamma-aminobutyric acid (GABA), glycine, and glutamate

  13. Regulation of hypothalamic hormone secretion • Role of neurons within the brain • Neurotransmitters • Excitation or inhibition depend on the type of receptor present on the peptinergic neurons

  14. Feedback system • Production of hormones by target tissue • Release of TSH from hypothalamus results in release of TRH from pituitary gland and subsequently production of T3 and T4 by thyroid gland • Hypothalamus and pituitary gland • Target tissue to steroid and thyroid hormones

  15. Types of feedback • Long-loop • From target organ to hypothalamus, pituitary, or higher brain

  16. Short-loop • Between hypothalamus and pituitary • Retrograde flow of pituitary hormones to hypothalamus • Autofeedback (autoinhibition) • Within the hypothalamus

  17. Result of feedback • Inhibition of pituitary hormone release • Prevent action of hypothalamic hormones • Inhibitor production • Alteration of cell population • Alteration of cellular sensitivity to hypothalamic hormones • GnRH receptor concentrations increase in response to estradiol • TRH receptor concentrations decrease in response to thyroxin

  18. Regulation of secretory rhythm/pattern • Biological clock • Circadian rhythm • Diurnal activity • Light-dark cycle (Day/night) • Changes in external environment • Regulated by supraoptic nuclei • Pituitary hormones • Episotic/pulsatile secretion • Critical for normal function

  19. Action of hypothalamic hormones • Anterior pituitary gland • Heterogeneous population of cells • Several secretory cells • Hypothalamic hormones • Elicit/inhibit action potential • Ca-dependent • Induce/inhibit cAMP production • Activity of adenylcyclase