hypothalamus. older part of the brain (primitive) –maintenance of homeostasis reception of...
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Hypothalamus
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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
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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
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• Neural organization of hypothalamus– Clusters of neurons
• Nucleus/nuclei
– Different section of hypothalamus contains different nuclei
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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
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• 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
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• 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
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• Release of hypothalamic peptides– Depolarization of
neural cells– Supporting elements
• Non-neural cells
– Coordinated regulation by interaction of neurons
• Hypothalamic• CNS
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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
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• 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
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• 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
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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
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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
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• 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
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• Types of feedback– Long-loop
• From target organ to hypothalamus, pituitary, or higher brain
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– Short-loop• Between hypothalamus
and pituitary• Retrograde flow of
pituitary hormones to hypothalamus
– Autofeedback (autoinhibition)
• Within the hypothalamus
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• 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
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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
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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