Pituitary Histology and Physiology Flashcards
True or false: The pars distalis of the anterior pituitary has no direct arterial supply.
True
What are the three cell types in the anterior pituitary and their relative proportions?
Acidophils (40-70%)
Chromophobes (50%)
Basophils (10%)
Which two secretory cells of the anterior pituitary are acidophils?
Somatotropes and lactotropes
Which two cell types secrete ACTH in the pituitary?
Corticotropes (pars distills)
Melanotropes (pars intermedia)
What are two major products of melanotropes?
ACTH
Melanocyte-stimulating hormone (MSH)
Basophils produce ____ hormones
Tropic hormones (i.e. hormones that act on other endocrine glands)
What are two histological characteristics of the anterior pituitary?
Lots of rER (b/c produce PEPTIDE hormones)
Fenestrated capillaries
Describe breakdown of POMC
- y-MSH, ACTH, and B-lipotropin
- ACTH -> a-MSH and CLIP
- B-lipotropin -> y-lipotropin and B-endorphin
- y-lipotropin -> b-MSH
Why does Equine Pars Intermedia Dysfunction occur mostly in older horses?
Pars intermedia secretions are inhibited by dopamine, which declines with age
Growth hormone is inhibited by
Somatostatin
Cortisol
Negative feedback (via IGF-1)
Growth hormone is stimulated by
Ghrelin
T4
Androgens/Estrogen
Which hormone controls growth at each life stage?
In utero - thyroid hormone
Postnatal - growth hormone/IGF-1
Puberty - sex hormones
How do GH and IGF-1 affect bone growth differently?
GH - stimulates differentiation of prechondrocytes
IGF-1 - stimulates division of progenitor cells
What are the 4 anti-insulin actions of GH?
- Stimulates lipolysis/FFA in blood
- Increases hepatic gluconeogenesis
- Protects muscle protein
- Enhances FFA oxidation by muscle
What are growth promoting effects of GH?
- Stimulates erythropoiesis
- Enhances muscle maturation
- Enhances skeletal maturation
- Enhances milk production
- Accelerates chondrogenesis
- Increases calcium absorption
Which factors promote prolactin secretion?
- TRH
2. Estrogen/estradiol
Which part of the hypothalamus produces ADH and oxytocin?
The cranial nuclei:
- Paraventricular nucleus
- Supraoptic nucleus
Name three features of the hypothalamohypophyseal tract
- Unmyelinated axons
- End near capillaries (not neurons)
- Neurosecretary vesicles clustered in Herring Bodies (hormones in Herring Bodies are bound to neurophysin)
Glial cells in the pineal gland are called ______ whereas glial cells in the pars nervosa of the pituitary are called _____.
Pineal - astrocytes
Pituitary - pituicytes
How do pituicytes appear in stained slides and EM?
Stained slides - oval/round nucleus, irregular branches, GFAP (+)
ER - big gap (“empty space”) between Herring Bodies (vesicles) and fenestrated capillaries
Why is growth hormone diabetogenic?
It increases (hepatic) gluconeogensis AND inhibits insulin, which would normally promote glucose uptake into muscle
