Pituitary notes.doc

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Health Sciences
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Cale Zavitz

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Pituitary (Hypophysis) • Made of two distinct areas: o Anterior  Arises from an outgrowth of the ectoderm of the roof of the mouth- in embryological development, begins as a pocket on the roof of the mouth- migrates toward the brain  Sometimes called adenohypophysis because it is a gland that makes and releases own hormones o Posterior  Arises from outgrowth of ectoderm (outer layer of neurological tissue) at base of hypothalamus- starts off in brain and works its way downwards  Sometimes called the neurohypophysis because it arises from neurological tissue Embryological Development • Two layers of ectoderm which will fold in and make the brain as well as the mouth • Mesenchyme is between the two layers of ectoderm- made of a middle layer called mesoderm- will give muscle, bone, and other connective tissue- because it has not developed, we call it mesenchyme (mesoderm that hasn’t grown up yet, or baby mesoderm) • To make pituitary- neurohypophyseal bud from brain begins to grow downward toward mouth cavity- in the mouth endoderm, Rathke’s pouch (hypophyseal pouch) forms- neurohypophyseal bud makes a long “stick”- infundibulum- most fun word in all of anatomy- an extension of the brain- both infundibulum and Rathke’s pouch elongate until they meet, forming Pars Intermedia- where posterior and anterior pituitary meet- Rathke’s pouch seals itself off from roof of mouth- Infundibulum extends down from brain- end up with anterior (from the mouth) and posterior (from the brain) pituitary- sometimes this does not seal properly, leaving a hole from the mouth into the brain • Turk’s Saddle or Sella Turcica- pituitary “rides” in Turk’s saddle o When anterior pituitary came upwards, bone formed underneath it- sits on sphenoid (“wedge-shaped”) bone- sits in Hypophyseal fossa, a little depression in the bone o Tuberculum sellae- “bumpy part of the saddle” o Dorsal sellae- “back part of the saddle” Midsaggital Section • Hypophyseal Fossa- delicate piece of bone in which pituitary sits • Sphenoid sinus- below Hypophyseal fossa- usually filled with air, otherwise filled with mucus • Optic Chiasm- right above Pituitary Pituitary Tumour • Pituitary is a very common place to get a tumour • Tumours grow upwards into the brain- have a mass effect- patients have vision problems- optic chiasm is being compressed- most people die and didn’t even know that they had one • To remove tumour- go through nose Pituitary Blood Supply • Strange blood supply due to dual origins- have a portal system • Superior hypophyseal artery comes in- has a capillary bed- then has Hypophyseal portal veins- normally have arterial capillary vein- except in pituitary we have a portal system- artery- hypophyseal portal vein- and then another capillary bed- very low pressure at end of hypophyseal portain veins- terrible circulation to most important organ for endocrine regulation- has worst blood supply of whole body • Hypophyseal veins then drain into sinuses- blood leaves, usually containing hormones • Inferior hypophyseal artery- mainly goes to posterior pituitary • Portal veins have low blood pressure and are very susceptible to damage after hemorrahage (car accident, having a baby) blood pressure decreases- arterioles constrict in response- if tiny arterioles of Pituitary constrict blood supply, pituitary will die- this is why the there is often damage to the pituitary gland after a massive hemorrhage- because of its crappy blood supply- from then on, nothing sits in Sella Turcica- empty Sella Hormones of the Posterior Pituitary • Oxytocin- released from posterior pituitary- octapeptide o Made by neurosecretory cells in the paraventricular nucleus of the hypothalamus o Incoming neurological stimulus (e.g. suckling, pressure on uterine cervix) stimulates the neurosecretory cells in the hypothalamus to release OT in the posterior pituitary o OT leaves pituitary in the bloodstream and causes uterine contractions as well as milk ejaculation o Post partum, OT helps stop bleeding by contracting uterus- breastfeeding will stimulate this • Antidiuretic Hormone (ADH) o AKA vasopressin- pharmacological doses increase blood pressure o AKA arginine vasopressin o Released from supraoptic (called so because it sits on top of optic chiasm) nucleus of the hypothalamus o Produced in the brain- follows axons down to posterior pituitary o Release is stimulated by:  Increased osmolarity of the blood  Low blood pressure and low blood volume  Pain and certain drugs o Inhibited by:  Adequate or over hydration of the body o Very similar to oxytocin o Alcohol causes inappropriate dehydration- it inhibits ADH release- alcohol also inhibits release of oxytocin- women were given alcohol to delay labour o ADH acts to put water permeable pores in the collecting duct of the kidney- puts water-sized holes in the kidney so you make less urine Hormones of the Anterior Pituitary • hGH- human growth hor
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