MECH 430 Lecture Notes - Lecture 6: Posterior Pituitary, Anterior Pituitary, Pituitary Gland
9 Jun 2018
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Lecture 5
➢ The Four Elements
➢ HISTORY: The Hypothalamo-pituitary axis
o Pituitary gland (also called the hypophysis) 2000 years ago Aristotle described the organ as the
major connection between brain and body through which the four essential humours pass from
the brain into the body
o 19th century: Rathke describes the two parts of the pituitary, the anterior pituitary
(adenophyophysis) and posterior pituitary (neurophypophysis
▪ Pierre Marie associates pituitary tumors with acromegaly in 1886
o 1909: Cushing (pioneered modern neurosurgical techniques) removes part of the pituitary in an
acromegaly patient and notices improvement
o Evan and Long (1922) show that injection of crude extracts of the pituitary gland in animals
causes increased growth
▪ Leads to the discovery of growth hormone
o Other functions are discovered:
▪ Lactation → prolactin or PRL
▪ Action on the Thyroid → thyrotrophin or thyroid stimulating hormone (TSH)
▪ Action on the adrenals → adrenocorticotrophin or ACTH
▪ Action on the gonads → luteinizing hormone and follicle stimulating hormone or LJ and
FSH
o Pituitary was considered as the “conductor of the endocrine orchestra”
o However, the pituitary is itself controlled by the nervous system via the hypothalamus
▪ Hence the name “hyopthalamo-pituitary axis”
➢ The Pituitary Gland
o Weight of the pituitary is 0.5-1.0 g (1 cm diameter about
size of a pea)
o Increases in size (>30%) during pregnancy to
accommodate the extra production required for pregnancy
▪ The fetus takes over the womb’s body and
manipulates the endocrine system which includes
increasing the size of the pituitary gland to maintain
pregnancy and prepare for post pregnancy lactation
o There are also constraints as to how large the gland can grow and can cause issues if there isn’t
enough room for the pituitary gland to expand
▪ Ex: May push on the optic nerve and cause vision problems
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➢ Development of the hypothalamus and pituitary
o The Hypothalamo-hypophyseal tract derived from two different ectodermal components:
▪ 1. Rathke’s pouch:
• outgrowth of the buccal cavity detaches itself and becomes the anterior pituitary
▪ 2. The infundibulum:
• develops from an outgrowth of the neuroectoderm from the floor of the 3rd
ventricle
• it gives rise to the pituitary stalk, the median eminence and the posterior pituitary
▪ these 2 tisssues are developed from 2 different types of ectoderm tissues in the
developing embryo
• you have one growing downward and one growing upward → one devaginating
and one invaginating that evening grow closer to each other to combine
o the entire structure will then be encased in a boney matrix
o one of neural original and one of ectodermal tissue that forms the anterior
and posterior components
➢ The Interrelation between the Hypothalamus and the Pituitary
o The hypothalamus is organized into discrete nuclei
o Anterior pituitary is highly
vascularized
▪ the unusual arrangement
→ a blood vessel comes in
forming the capillary bed
that breaks into a local
capillary bed in the
anterior pituitary that
allows hormones from the
hypothalamus to
subsequently be
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transported by the portal hypophysial vessel
▪ this arrangement allows for pituitary function as required
▪ any hormone produced in the pituitary gland can retrospectively travel backwards
towards the hypothalamus as negative feedback to shut off the delivery of signaling
molecules
▪ Note capillary bed in median eminence connected to portal veins, then a 2nd capillary bed
in anterior pituitary
▪ Some retrograde flow of blood to allow hormonal feedback from pituitary to
hypothalamus (short loop)
o If we stimulate these neurons, we directly release the contents
from the posterior pituitary
o The hormones are then released into the general circulation to
travel around the body to find its respective target
➢ Synthesis, transport and release of the hormones of the posterior
pituitary
o Posterior pituitary is an extension of the hypothalamus
▪ Composed of the nerve ending (axons) of neurons
whose cell bodies are located in the hypothalamus
▪ Hormones (oxytocin & vasopressin) are produced in the
cell bodies, packaged into granules which migrate to the
ends of the axons located in the posterior pituitary
• Vasopressin → anti-duiretic hormone and
produced in the supraoptic nucleus
• Oxytoxin is produced in the …. Check
▪ Stimulation of neurons in the neurons in the
hypothalamus triggers the release of the hormones from
the axon tips located in the posterior pituitary
▪ The hormones are taken up by capillaries and enter the
blood stream
➢ Control of the anterior pituitary gland (adenolypophysis) by the hypothalamic hormones
o Axon terminals of hypothalamic neurons release
hypophysiotropic hormones in the area of the median eminence
o Hormones are taken up by capillary blood vessels
o Travel to the anterior pituitary via the portal vein
o Hormones enter the anterior pituitary and trigger the release of a
second wave of hormones
o The pituitary hormones enter the blood stream via the venous
capillaries
o The arrangement between the anterior and posterior pituitary
are differently organized
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find more resources at oneclass.com
Document Summary
Fsh: pituitary was considered as the conductor of the endocrine orchestra , however, the pituitary is itself controlled by the nervous system via the hypothalamus, hence the name hyopthalamo-pituitary axis . Development of the hypothalamus and pituitary: the hypothalamo-hypophyseal tract derived from two different ectodermal components, 1. Rathke"s pouch: outgrowth of the buccal cavity detaches itself and becomes the anterior pituitary, 2. The interrelation between the hypothalamus and the pituitary: the hypothalamus is organized into discrete nuclei, anterior pituitary is highly vascularized the unusual arrangement. Check: stimulation of neurons in the neurons in the hypothalamus triggers the release of the hormones from the axon tips located in the posterior pituitary, the hormones are taken up by capillaries and enter the blood stream. The hypothalamus: halasz knife originally used to selectively destroy areas of the brain to observe function of nuclei, the different regions of the hypothalamus are labelled based on their positions relative to one another.
