Download Hypothalamus

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