Physiology 2130 Lecture Notes - Lecture 56: Hypophyseal Portal System, Anterior Pituitary, Posterior Pituitary
1 May 2018
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Lecture 056: Neuroendocrinology
Pituitary and Hypothalamus
● Hypothalamus
○ Sensor
○ Relays information to the pituitary to deal with the information
Functional Anatomy
● Anterior Pituitary
○ Receives signals via the parvocellular neurons from the hypothalamus
○ parvocellular neurons have short axons that don’t reach the hypothalamus
■ Instead they release hormones into the hypophyseal-portal system to
target a cell in the anterior pituitary
○ Anterior pituitary produces a hormone into the bloodstream to target another
organ/gland in the body
● Posterior Pituitary
○ Receives signals via the magnocellular cells
○ Magnocellular cells have long axons so they do not require the hypophyseal-
portal system
■ Directly secretes hormones into the pituitary
○ Also cause the posterior pituitary to produce a hormone to be released into the
bloodstream to target another organ/gland in the body
Hypothalamic Neurons and Factors
● Hypothalamic Projection Neuron
○ Neuronal targets
● Parvocellular Hypophysiotropic Neuron (Anterior Pituitary)
○ Produce trophic hormones (ACTH, TSH, GH, LH, FSH, Prolactin)
■ Most hormones are from the anterior pituitary
○ Targets adrenal, thyroid, liver, ovary
● Magnocellular Neuron (Posterior Pituitary)
○ Release vasopressin, oxytocin
■ Target mammary gland, kidney and uterus
Episodic Endocrine Secretion
● Circadin (around) or Diurnal (exactly)
○ Secretion of hormone once every 24 hr
○ CHRH, RCH, cortisol
○ Terms are often used interchangeably
● Ultradian
○ Secretion of hormone on a minute to minute basis
● Most hormones display more than 1 pattern of secretion
● There are also differences in hormone pattern secretion in male and females
○ Growth hormone is one
find more resources at oneclass.com
find more resources at oneclass.com
○ Must treat male and female patients differently
Endocrine Rhythms
● Suprachiasmatic Nucleus (SCN) of the Hypothalamus
○ Detects light during the day
■ Direct input from the retina (non-visual)
○ Increase in light leads to increase in the activity of SCN leads to an increase in
“clock” genes (Cryptochromes and Period genes)
■ Clock gene leads to hormone release from the hypothalamus and
pituitary
○ Responsible for the intrinsic circadian pattern of secretion and neuronal activity
■ Light resets the pattern corresponding to the day/night cycle
● Pineal Gland
○ SCN relays signals (via the spinal cord) to the pineal gland
■ Decrease signals leads to activation of the pineal gland
○ Leads to secretion of the hormone melatonin
■ During the night (dark)
○ Melatonin
■ Decrease body temperature
■ Drowsiness
■ More importantly acts on and it resets the SCN
● Stops the production of clock genes
● Shuts down the hormone production
Hypothalamus-Adrenal Axis (HPA Axis)
● Acticed in response to stress (cold, hypoglycemia, fear)
● Hypothalamus
○ Parvocellular produces CRH (peptide hormone) in response to stress
■ CRH travels to the anterior pituitary via the hypophyseal-portal
● Anterior Pituitary
○ Secretes ACTH (peptide hormone) into the bloodstream
■ ACTH travels and target the adrenal cortex
○ ACTH is produced as a pro-hormone (POMC)
■ Cleaved to produce active ACTH in the pituitary cell
○ ACTH can also be cleaved into ɑ-MSP if it is not metabolized
■ ɑ-MSP increases skin pigmentation
● Adrenal cortex
○ Produce cortisol (steroid hormone)
■ Increase blood glucose concentration via
● Gluconeogenesis
● Muscle catabolism
○ Breakdown of amino acids for energy
● Inhibition of GLUT4 activity
○ Stops the transport of glucose into the tissues
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Relays information to the pituitary to deal with the information. Receives signals via the parvocellular neurons from the hypothalamus. Parvocellular neurons have short axons that don"t reach the hypothalamus. Instead they release hormones into the hypophyseal-portal system to target a cell in the anterior pituitary. Anterior pituitary produces a hormone into the bloodstream to target another organ/gland in the body. Magnocellular cells have long axons so they do not require the hypophyseal- portal system. Also cause the posterior pituitary to produce a hormone to be released into the bloodstream to target another organ/gland in the body. Produce trophic hormones (acth, tsh, gh, lh, fsh, prolactin) Most hormones are from the anterior pituitary. Secretion of hormone once every 24 hr. Secretion of hormone on a minute to minute basis. Most hormones display more than 1 pattern of secretion. There are also differences in hormone pattern secretion in male and females. Must treat male and female patients differently.
