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Hypothalamus. Older part of the brain (Primitive) –Maintenance of homeostasis Reception of...

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Hypothalamus
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Page 1: Hypothalamus. Older part of the brain (Primitive) –Maintenance of homeostasis Reception of external and internal signals Incorporation of signals to generate.

Hypothalamus

Page 2: Hypothalamus. Older part of the brain (Primitive) –Maintenance of homeostasis Reception of external and internal signals Incorporation of signals to generate.

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

Page 3: Hypothalamus. Older part of the brain (Primitive) –Maintenance of homeostasis Reception of external and internal signals Incorporation of signals to generate.

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

Page 4: Hypothalamus. Older part of the brain (Primitive) –Maintenance of homeostasis Reception of external and internal signals Incorporation of signals to generate.
Page 5: Hypothalamus. Older part of the brain (Primitive) –Maintenance of homeostasis Reception of external and internal signals Incorporation of signals to generate.

• Neural organization of hypothalamus– Clusters of neurons

• Nucleus/nuclei

– Different section of hypothalamus contains different nuclei

Page 6: Hypothalamus. Older part of the brain (Primitive) –Maintenance of homeostasis Reception of external and internal signals Incorporation of signals to generate.

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

Page 7: Hypothalamus. Older part of the brain (Primitive) –Maintenance of homeostasis Reception of external and internal signals Incorporation of signals to generate.

• 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

Page 8: Hypothalamus. Older part of the brain (Primitive) –Maintenance of homeostasis Reception of external and internal signals Incorporation of signals to generate.

• 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

Page 9: Hypothalamus. Older part of the brain (Primitive) –Maintenance of homeostasis Reception of external and internal signals Incorporation of signals to generate.

• Release of hypothalamic peptides– Depolarization of

neural cells– Supporting elements

• Non-neural cells

– Coordinated regulation by interaction of neurons

• Hypothalamic• CNS

Page 10: Hypothalamus. Older part of the brain (Primitive) –Maintenance of homeostasis Reception of external and internal signals Incorporation of signals to generate.

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

Page 11: Hypothalamus. Older part of the brain (Primitive) –Maintenance of homeostasis Reception of external and internal signals Incorporation of signals to generate.
Page 12: Hypothalamus. Older part of the brain (Primitive) –Maintenance of homeostasis Reception of external and internal signals Incorporation of signals to generate.

• 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

Page 13: Hypothalamus. Older part of the brain (Primitive) –Maintenance of homeostasis Reception of external and internal signals Incorporation of signals to generate.
Page 14: Hypothalamus. Older part of the brain (Primitive) –Maintenance of homeostasis Reception of external and internal signals Incorporation of signals to generate.

• 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

Page 15: Hypothalamus. Older part of the brain (Primitive) –Maintenance of homeostasis Reception of external and internal signals Incorporation of signals to generate.
Page 16: Hypothalamus. Older part of the brain (Primitive) –Maintenance of homeostasis Reception of external and internal signals Incorporation of signals to generate.

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

Page 17: Hypothalamus. Older part of the brain (Primitive) –Maintenance of homeostasis Reception of external and internal signals Incorporation of signals to generate.

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

Page 18: Hypothalamus. Older part of the brain (Primitive) –Maintenance of homeostasis Reception of external and internal signals Incorporation of signals to generate.

• 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

Page 19: Hypothalamus. Older part of the brain (Primitive) –Maintenance of homeostasis Reception of external and internal signals Incorporation of signals to generate.

• Types of feedback– Long-loop

• From target organ to hypothalamus, pituitary, or higher brain

Page 20: Hypothalamus. Older part of the brain (Primitive) –Maintenance of homeostasis Reception of external and internal signals Incorporation of signals to generate.

– Short-loop• Between hypothalamus

and pituitary• Retrograde flow of

pituitary hormones to hypothalamus

– Autofeedback (autoinhibition)

• Within the hypothalamus

Page 21: Hypothalamus. Older part of the brain (Primitive) –Maintenance of homeostasis Reception of external and internal signals Incorporation of signals to generate.

• 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

Page 22: Hypothalamus. Older part of the brain (Primitive) –Maintenance of homeostasis Reception of external and internal signals Incorporation of signals to generate.

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

Page 23: Hypothalamus. Older part of the brain (Primitive) –Maintenance of homeostasis Reception of external and internal signals Incorporation of signals to generate.

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


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