BIOL 336 Lecture Notes - Lecture 8: Posterior Pituitary, Neurohormone, Median Eminence
Biology 336
Lecture 8: Hypothalamus and the Pituitary Gland
9/19/18
• the hypothalamus us the most important control area for homeostatic regulation of the
internal environment
o hypothalamus lies under the thalamus on the underside of the brain
• the hypothalamus and pituitary gland function to regulate every body system
o ex. preservation of species- reproduction, preservation of self- eating and drinking
• the pituitary is actually two glands with different embryological origins that fused during
development
• pituitary made up of anterior (endocrine gland of epithelial origin, there are glands that
produce and secrete endocrine hormones) and posterior (not a gland but an extension of
neural components of the hypothalamus, no endocrine cells in the posterior)
• Question 1: Answer: D, the infundibulum is the stalk that connects the hypothalamus to
the pituitary gland
• The posterior pituitary is an extension of the brain that secretes neurohormones made in
the hypothalamus
o Neurohormones: hormones produced by specialized nerve cells and secrete them
into circulation
o Supraoptic nuclei extend axons down the infundibulum to the posterior pituitary
and synthesize the neurohormone vasopressin
▪ Also called antidiuretic hormone, acts on kidneys to regulate water
balance in the body
o Paraventricular nuclei: extend axons to the posterior pituitary and synthesize
oxytocin
▪ Oxytocin is involved in the ejection of milk made during nursing
▪ Also released during labor to stimulate contraction of uterine smooth
muscle cells until birth
• The 2 posterior pituitary neurohormone are composed of 9 amino acids each
• Posterior pituitary is NOT a true endocrine gland, and not actually found in posterior
pituitary- those cells are found in hypothalamus
o Neurohormone is made and packaged in cell body of neuron
o Vesicles are transported down axons
o Vesicles containing neurohormone are stored in axon terminals awaiting release
signal
o Neurohormones are released into the blood when a signal is passed down the
neuron
• Question 2: Answer: D, neurosecretoray cells in the hypothalamus
• Neurons in hypothalamus send axons to median eminence
o Signals are hypophysiotropic hormones: regulate anterior pituitary gland function,
they can also release and/or inhibit hormones
• Neurohormones from the hypothalamus reach the anterior pituitary through a specialized
circulatory region called the hypothalamic-hypophyseal portal system
o Neurons-> synthesize trophic hormones
o portal vessels-> carry trophic hormones directly into anterior pituitary
