Basic Physiology of Pituitary Disease Flashcards
What does the hypothalamus do?
It secretes neurohormones
Where do the trophic hormones from the hypothalamus go? And what is their role?
They are secreted into capillaries travelling to the anterior pituitary to govern release of anterior pituitary hormones
Give examples of trophic hormones released from the hypothalamus (and state what kind of hormone they are)
- Thyrotropin releasing hormone (TRH) (peptide)
- Corticotrophin releasing hormone (CRH) (peptide)
- Growth hormone releasing hormone (GHRH) (peptide)
- Gonadotrophin releasing hormone (GnRH) (peptide)
- Growth hormone inhibiting hormone (GHIH) = somatostatin (peptide)
- Prolactin inhibiting hormone (PIH) (dopamine)
Where do the non-trophic hormones from the hypothalamus go?
They travel to posterior pituitary via neuronal axons in the infundibulum where released into blood
Explain the pathway from the stimulus to the response (without any feedback loops)
Stimulus –> Hypothalamus (Integrating centre 1) –> Trophic hormone (H1) –> Anterior pituitary (IC2) –> Trophic hormone (H2) –> Endocrine gland (IC3) –> Hormone (H3) –> target tissue –> response
Explain the short-loop negative feedback of the stimulus to response pathway
Trophic hormone (H2) when in excess inhibits the Hypothalamus (IC1) so it no longer produces Trophic hormone (H1)
Explain the long-loop negative feedback of the stimulus to response pathway
Hormone (H3) when in excess inhibits both the hypothalamus (IC1) and the anterior pituitary (IC2)
describe the anterior pituitary gland
true endocrine tissue of epithelial origin; releases peptide hormones, all of which are tropic (promote growth) except prolactin
give examples of hormones released from the anterior pituitary gland
o Thyroid stimulating hormone (TSH) = thyrotropin
o Adrenocorticotrophic hormone (ACTH) = corticotropin
o Follicle stimulating hormone (FSH) and luteinizing hormone (LH) = gonadotropins
o Growth hormone (GH) = somatotropin
o Prolactin
describe the posterior pituitary gland
A neuroendocrine tissue of neural origin.
It releases 2 peptide neurohormones
what hormones are released by the posterior pituitary gland?
o Vasopressin = anti-diuretic hormone (ADH)
o Oxytocin
describe the growth feedback loop
- GHRH secreted from hypothalamus in response to stimuli
- Triggers GH secretion from anterior pituitary which triggers insulin-like growth factor-I (IGF-1) secretion by the liver and other cell types
describe what happens when GHRH is secreted from hypothalamus in response to stimuli in growth feedback loop
o Actual or potential decrease in energy to cells
o Increased amounts of amino acid in plasma
o Stressful stimuli
o Delta sleep
o Oestrogen and testosterone
What is the function of the GH in growth feedback loop?
o Stimulates prechrondrocytes in epiphyseal plates differentiate into chondrocytes which begin to secrete and become responsive to IGF-1
o Anti-insulin: increases liver gluconeogenesis, reduces insulin’s ability to stimulate muscle and adipose glucose uptake and makes adipocytes more sensitive to lipolytic stimuli
o BUT increases amino acid uptake and protein synthesis (anabolic as opposed to cortisol which is catabolic)
What is the function of IGF-1?
autocrine or paracrine agent to stimulate differentiating chondrocytes to undergo cell division and produce cartilage for bone growth
Describe the negative feedback lop on the growth feedback loop
IGF-1 exhibits a negative feedback loop on GH and GHRH by inhibiting GHRH and stimulating somatostatin. Somatotrophs in the anterior pituitary also provide negative feedback on GH
In response to what stimuli is Somatostatin secreted from the hypothalamus?
o Glucose
o Free fatty acids
o REM sleep
o Cortisol
What are some other influences on growth?
o Thyroid hormones
o Sex hormones
o Nutrition
o Genetic factors
In what ways do thyroid hormones influence growth?
essential for growth and effects permissive to GH and IGF-1; required for cartilage ossification and teeth maturation (hypothyroid children retain infantile proportions whereas children with GH deficiency are proportionally normal but just small)
In what ways do sex hormones influence growth?
stimulate GHRH at puberty for growth spurt
IN what way does nutrition influence growth?
injury and disease stunt growth due to increased cortisol and increased protein metabolism
in what way do genetic factors influence growth?
determine maximum growth
when is GH mostly released?
GH is mostly released during the first two hours of sleep and secretion rate has rapid spontaneous and stimuli-specific responses
how is an erratic pattern prevented with GH and IGF-1?
GH and IGF-1 are peptide hormones but are bound to carrier proteins in the blood (like thyroid and steroid hormones) which provides a reservoir in the bloodstream and prevents an erratic pattern
