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Hypothalamus-Pituitary Axis

Hypothalamus-Pituitary Axis

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Hypothalamus-Pituitary Axis

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  1. Hypothalamus-Pituitary Axis A major endocrine control component in vertebrates

  2. Major Concepts: — organization and embryonic development of the hypothalamus & pituitary structures — importance of this axis — different components of the pituitary and pituitary hormone release regulation — feedback systems and levels of feedback

  3. Hypothalamus-pituitary-target axis: — Consists of 1) Hypothalamus (part of forebrain) 2) Pituitary gland (also called the hypophysis) 3) Endocrine glands or cells that are target of pituitary hormones — Pituitary hormones and their target endocrine organs control a large number of physiological functions E.g., reproduction, body growth, intermediary metabolism, metamorphosis, behaviour, ionic and osmotic balance, stress responses, blood pressure, inflammation and immune responses — Hypothalamus not only controls pituitary gland hormone secretion, but hypothalamic neuronal terminals also form part of the pituitary

  4. External & Internal Stimuli Central Nervous System Hypothalamic Neurosecretory Cells Releasing & Release-inhibitory Neurohormones Pituitary Pars Pars Pars Intermedia Nervosa distalis Pituitary hormone release Control of many physiological functions Schematic of hypothalamus-pituitary axis organization Pars tuberalis

  5. Anatomical Relationship Between the Hypothalamus and Pituitary Gland in Mammals Optic tectum Hippocampus Cerebral cortex Thalamus Cerebellum Olfactory Bulb oc Hypothalamus MB Medulla Pituitary Mid-brain Tuber Cinereum MB = mammillary body (part the posterior diencephalon) (Modified from Norris: “Vertebrate Endocrinology”)

  6. General Scheme of Developing Brain of Vertebrate Embryo developing mid-brain developing hind-brain developing forebrain (Prosencephalon) telencephalon notochord diencephalon developing gut developing mouth oral plate

  7. — part of the lateral wall and floor of the diencephalon lining the 3rd brain ventricle will develop into the hypothalamus — the floor of the developing hypothalamus grows downwards in a protrusion called the infundibulum — the roof of the embryonic oral cavity in front of the oral plate grows upwards towards the brain in an evagination called the Rathke’s pouch.

  8. Parts of the pituitary or hypophysis: Adenohypophysis (Pars Tuberalis, Pars Distalis, Pars Intermedia) Anterior Lobe (PT and PD) Intermediate Lobe (PI) Neurohypophysis = Post. Lobe/Neural Lobe = Pars Nervosa Neurointermediate Lobe = PI + PN, interdigitated

  9. Connections between hypothalamic neurons and the different parts of the pituitary gland (Modified from: Norris “Vertebrate Endocrinology”) Median eminence Pituitary stalk (infundibulum) Optic chiasm Inferior hypophyseal artery Superior hypophyseal artery Hypothalamo- hypophyseal portal vessel Pituitary (hypophysis) POA – Preoptic area SCN – Suprachiasmatic nucleus SON – Supraoptic nucleus ARC – Arcuate nucleus PVN – Paraventricular nucleus

  10. other feedback Other responses Pars tuberalis