Hypothalamus-Pituitary Axis

Question 1

Number of ventricles in forebrain, midbrain, hindbrain
- Filled with what
- Barrier between fluid and blood

Answer 1

Forebrain- I and II
Midbrain - III
Hindbrain - IV

Cerebral spinal fluid (CSF)
Blood-brain barrier

Question 2

Capillary walls of endothelial cells in blood-brain barrier covered by? (3)
- Fenestrated vs Closed/Continuous capillary
- What’s transported w/ passive diffusion and transported

Answer 2

Basement membrane, pericytes, astrocyte endfeet
- Fenestrated has more tight junctions

Passive: Water, lipophilic (steroids, eicosanoids), drugs (barbiturates), alcohol
Transported: Glucose, neural amino acids (neurotransmitter synthesis), peotides

Question 3

Circumventricular organs:
- Pineal gland
- Subforbical organ
- Organum vasculosum
- Area postrema
- Median eminence
- Neurohypophysis

Answer 3

Melatonin, rhythms

Regulates fluids, osmoreceptor cells

Peptides, osmoregulation, fever

Vomiting centre, osmoregulation

Associated w/ anterior pituitary

Neurosecretion AVP, oxytocin

Question 4

Pituitary gland consists of what 2 main lobes?
- 3 areas?
- Formation of pituitary gland (4 steps)

Answer 4

Anterior (epithelial tissue) and posterior (nervous tissue)
- Anterior pituitary (adenohypophysis)
- Posterior pituitary (neurohypophysis)
- Intermediate lobe (pars intermedia)

1) Adenohypophysis formed w/ epithelial and nervous tissue
2) Neural tissue extends to form neural infundibulum
3) Epithelial tissue extends to form Rakthe’s pouch
4) Tissues come together to form pituitary gland

Question 5

Hormones produced in pituitary gland + state if sent to endocrine or nonendocrine target:
- In adenohypophysis (5 + 1 in fish)
- In neurohypophysis (2 in mammals, 2 in non-mammals)
- In intermediate lobe (1)

Answer 5

• FSH and LH (gonadotrope) - Endocrine targets
• Thyroxine stimulating hormone (TSH) (Thyrotrope) - Endocrine targets
• Adrenocorticotropic hormone (ACTH) (Corticotrope) (Endocrine targets
• Growth hormone (GH) (Somatotrope) - Endocrine and non targets
• Prolactin (Lactotropes) - Nonendocrine targets
• Fish: Somatolactin (Somatolactropes)
  —
  Mammals: Vasopressin and oxytocin - Nonendocrine targets
  Non: Variants of isotocin and vasotocin
  —
  Melanocyte-stimulating hormone (Nonendocrine targets)

Question 6

Median eminence
- What is it?
- Specialized cells that regulate permeability of blood vessels + What they secrete

Answer 6

Circumventricular region of CNS that acts as gatekeeper
- Tanycytes; VEGF

Question 7

Tropic hormones of adenohypophysis:
- Category 1
- Category 2
- Category 3

Answer 7

• LSH, FSH, TSH
• Consists of heterodimer of two pro-peptides
  —
• GH (2 disulfide bonds), PRL (3 disulfide bonds) - Paralogues
• Large, single polypeptides
  —
• Small peptides ACTH, alphaMSH, LPH, endorphins
• Several hormones from same precursor
• Also found in brain and pars intermedia

Question 8

Pituitary glands:
- Aghathan
- Chondrichthyan (Cartlaginous fish)- Elasmobranchii vs Holocephali
- Actinipterygian-Sarcopterygian bifurcation
- Reptiles
- Teleost

Answer 8

• Jawless fishes; most primitive chordate
• Separate adenohypophysis from rest of hypothalamus, unclear portal system
• Hypothalamic releasing factor entering blood is main communication between parts
  —
• Fused neurohypophysis and pars intermedia (together called the neurointermediate lobe)
• Portal system
• Separate ventral lobe (receives info from circulatory system but not connected to brain)
  —
• Similar structure as elasmobranchii but ventral lobe is called buccal lobe
• In roof of mouth separated w/ layer of cartilage
• Hypothalamus communicates to it w/ releasing factors in blood
  —
• Sarcopterygii (lobe-finned fishes) developed more distinct portal system
• Actinopterygii (ray-finned fishes) lost portal system and developed direct neural connections
  —
• Older reptile groups like chelonia (turtles) and rhybchocephalians (tuataras) developed interdigitation of neurohypophysis and pars intermedia
• Crocodulia and squamata (lizards/snakes) not as much
• All had expanded portal system and mix of cell types instead of clusters of similar cells
  —
• Adenohypophysis clustered into nuclei of similar cells
• Interdigitation of neural lobe w/ rest of pituitary
• Direct neural connection between hypothalamus and pars distalis (adenohypophysis)