Hypothalamus and Pituitary Gland

Question 1

Anatomy of the Pituitary

Answer 1

• Sella Turcica: where pituitary gland is located
• Infundibular Stalk: Nerve fibers and blood vessels
• Optic Chiasm: region where nerve fibers from each eye cross to opposite half of the brain
• Hypothalamic Hypophysial Portal System: provides local delivery of substances at high concentration
• Adenohypophysis: glandular tissue- anterior pituitary
• Neurohypophysis: neural tissue- posterior pituitary

Question 2

Anterior Pituitary

Answer 2

• Mosaic tissue with cells of similar type aggregating in certain regions, but are interspersed among each other
• All AP hormones are peptides/proteins
• 39-211 amino acids
• Some are glycosylated
• 3 families based on structure

Question 3

AP Cell Types and Hormones

Answer 3

1. Thryotrophs: TSH
2. Gonadotrophs: LH and FSH
3. Corticotrophs: ACTH
4. Somatotroph: GH
5. Lactotroph: Prolactin

Question 4

Glycoprotein Family

Answer 4

• Glycoprotein hormones with glycosylated α and β polypeptide chains
• All α chains are identical while β chains are unique and convey specificity
• Includes
  
  • TSH
  • FSH
  • LH

Question 5

Somatomammotropin Family

Answer 5

• Single polypeptide chain with several disulfide bonds
• Includes
  
  • GH- highly species-specific
  • Prolactin

Question 6

POMC Family

Answer 6

• Members of hormone family derived from same precursor molecules
• Same precursor can produce different products depending on enzyme expressed by cell
• Precursor is Pro-opiomelanocortin
• ACTH is the main POMC-derived hormone secreted by the anterior pituitary

Question 7

Biosynthesis and Secretion of Pituitary hormones

Answer 7

• Synthesized on endoplasmic reticulum
• Modified in the Golgi apparatus
• Stored in vesicles until needed
• Contents are release from vesicles when cell is stimulated

Question 8

Tropic Hormones

Answer 8

• Hormone whose primary function is the regulation of a hormone secreted by another gland
• Tropic hormones:
  
  • TSH
  • FSH
  • LH
  • ACTH
  • *GH
    
    • stimulates liver to release IGFs
    • designation as a tropic hormone is controversial

Question 9

Regulation of AP hormone synthesis and secretion

Answer 9

• Hypothalamus integrate input from the brain and sends signals to Anterior Pituitary
• Hypothalamic hormones are both releasing and inhibiting hormones
• Neurosecretory neurons
  
  • Cell bodies in hypothalamus organized into nuclei
  • Axons terminate in Median Eminence
• Hypothalmic-hypophysial potal system
  
  • Vessels originate in the Median Eminence and profuse to anterior pituitary

Question 10

Releasing and Inhibiting Hormones

Answer 10

• Releasing hormones
  
  • TRH
  • GnRH
  • CRH
  • GHRH

*all are peptides

• Inhibiting hormones
  
  • GHIH- peptide
  • PIH (dopamine)- catecholamine

Question 11

Biosynthesis and Secretion of Hypothalamic Hormones

Answer 11

• Biosynthesis of hypothalamic releasing and inhibiting hormones via parvocellular neurons
• Anatomical separation of synthesis and secretion of hypothalamic hormones

1. Synthesized in ER in cell body
2. Modified in golgi of cell body
3. Stored in vesicles in cell body
4. Vesicles travel down the axon to the axon terminal
5. Vesicles release contents into portal vessels

Question 12

Ordinary and Neurosecretory Hormones

Answer 12

• Both
  
  • Dendrites and axons
  • Polarized membranes
  • Relay messages
  • Regulated by other neurons
• Ordinary neuron
  
  • Products released into synaptic cleft- neurotransmitter
  • Acts over short distances
• Neurosecretory neuron
  
  • Product transported by blood- neurohormone
  • Can act over longer distances

Question 13

Hypothalamic Nuclei

Answer 13

• Region of hypothalamus containing cell bodies of neurons secreting a neurohormone
• Paraventricular nucleus:
  
  • TRH, CRH, ADH, OT
• Suproptic nucleus:
  
  • ADH, OT
• Arcuate Nucleus:
  
  • GHRH, GnRH, GHIH, PIH
• Ventromedial Nucleus:
  
  • GHRH, GHIH

Question 14

Parvocellular Neurons

Answer 14

• Located in multiple nuclei
• Neurons are small in size
• Releasing and inhibiting hormones
• Parvocellular neuron à axonal transport à Median Eminence à APà systemic circulation
• Median eminence hormones:
  
  • CRH, TRH, GHRH, DA
• AP hormones:
  
  • ACTH, TSH, LH, FSH, GH, Prolactin

Question 15

Magnocellular Neurons

Answer 15

• Predominantly located in paraventricular and supraoptic nuclei
• Neurons are large in size
• Magnocellular neuron à axonal transport à Posterior Pituitary à systemic circulation
• Posterior Pituitary Hormones
  
  • OT, ADH

Question 16

GPCR and Hormones

Question 17

Feeback Loops

Answer 17

• Long Loop: Hormone produced by target tissue feeds back on hypothalamus OR Anterior Pituitary
• Short Loop: Hormone produced by Anterior Pituitary feeds back on itself
• Ultrashort Loop: Hormone produced by Anterior Pituitary feeds back on Anterior Pituitary

Question 18

Posterior Pituitary

Answer 18

• Received input from Paraventricular Nucleus and Suproptic Nucleus
• Neurosecretory Neurons
  
  • Magnocellular Neurons
  • Cell bodies in hypothalamus
  • Axon travels through median eminence travel through Neurohypophysis, and terminate in posterior pituitary
• Hormones stored in Posterior Pituitary are released into blood

Question 19

ADH

Answer 19

• Stimulus for release: baroreceptors and osmoreceptors
• Site of synthesis: PVN and SON
• Size: 9 amino acids
• Receptor:
  
  • G_s (V₂ receptor in kidney collecting ducts)
  • G_q (V₁ receptor in vascular smooth muscle)
• Stimulates:
  
  • Kidney water retention: increase blood volume
  • Vascular smooth muscle contraction: Increase BP
• Diuresis- increased urinary output (decreases water loss)

*Alcohol suppressed ADH secretion and can lead to dehydration

Question 20

Oxytocin

Answer 20

• Stimulus for release: lactation, parturition
• Site of Synthesis: PVN and SON
• Size: 9 amino acids
• Receptor: G_q
• Stimulates:
  
  • mammary gland milk ejection
  • uterine myometrium contraction
• Some overlap in biological activity between OT and ADH due to similar amino acid sequence