EXAM #1: PITUITARY PHYSIOLOGY Flashcards
What is short-loop feedback? Give an example.
Hypothalamus acting on anterior pituitary and vice versa
What is ultra short-loop feedback? Give an example.
Hypothalamus releases a hormone that acts on the hypothalamus
What is long-loop feedback? Give an example.
Target organ exerting negative feedback on the:
- Anterior pituitary
- Hypothalamus
What releasing/inhibiting hormones are made and released by the hypothalamus?
1) CRH= Corticotroptin-releasing hormone
2) TRH= Thyrotropin releasing hormone
3) GnRH= Gonadotropin-releasing hormone
4) GHRH= Growth hormone releasing hormone
5) GHIH/Somatostatin= Growth hormone inhibiting hormone
6) PIH= Prolactin-inhibiting hormone
What is the action of Corticotroptin-Releasing Hormone (CRH) on the anterior pituitary?
Release of ACTH
What is the action of Thyrotropin Releasing Hormone (TRH) on the anterior pituitary?
- Release of Thyroid Stimulating Hormone (TSH)
- Secretion of Prolactin
What is the action of Gonadotropin-Releasing Hormone (GRH) on the anterior pituitary?
Release of LH and FSH
What is the action of Growth Hormone Releasing Hormone (GHRH) on the anterior pituitary?
Release of Growth Hormone
What is the action of Growth Hormone Inhibitory Hormone (GHIH) on the anterior pituitary?
Inhibition of GH release
*Note that this is also called Somatostatin
What is the action of Prolactin-Inhibiting Hormone on the anterior pituitary?
Causes the release of dopamine
Which hormones are made by hypothalamic cells and released by the posterior pituitary?
1) Vasopressin
2) Oxytocin
Where are posterior pituitary hormones made? (Know names of the two hypothalamic nuclei)
1) Supraoptic nucleus
2) Paraventricular nucleus (PVN)
List the anterior pituitary hormones.
1) ACTH
2) TSH
3) FSH
4) LH
5) GH
6) Prolactin
List the posterior pituitary hormones and give their functions.
1) Vasopressin
2) Oxytocin
Which three pituitary hormones have a common α subunit but different β subunits which determine hormone specificity?
1) TSH
2) LH
3) FSH
What is the effect of increased prolactin release on the release of GnRH?
Prolactin inhibits GnRH
How does increased prolactin release affect fertility?
Inhibiting GnRH causes infertility
Describe the effect of pregnancy on lactotropes.
Pregnancy results in hypertrophy and hyperplasia of the prolactin-secreting lactotrophs
Why does the effect of pregnancy on lactotropes make the pituitary more likely to suffer ischemia from postpartum hemorrhage?
- Hypertrophy/hyperplasia causes enlargement of the anterior pituitary
- Enlargement makes the pituitary more likely to suffer ischemia if there is HYPOTENSION s/p post-partum hemorrhage
What is Sheehan syndrome?
Ischemic necrosis of the pituitary associated with post-partum hemorrhage/hypotension
Describe the different types of diabetes insipidus.
1) Neurogenic diabetes insipidus= problem in hypothalamus/posterior pituitary
2) Nephrogenic diabetes insipidus= problem in kidney
3) Acquired diabetes insipidus= lithium induced
4) Psychogenic diabetes insipidus= excessive water intake
How could you distinguish the different types from each other and from polyuria caused by excessive water ingestion?
- Water restrict the patient and measure urine osmolality*
- Give the patient ADH**
*IF psychogenic, the urine should be MORE concentrated with water restriction
Describe the action of oxytocin and the stimulus for the milk let down reflex.
- Infant suckles and stimulates the nipple
- Oxytocin is released
- Milk let-down reflex initiated
What is the role of oxytocin in childbirth.
- Increased number of oxytocin receptors on uterus during pregnancy
- Distension of cervix and contraction of uterus causes release of oxytocin
*Positive feedback increases contraction of the uterus
Describe the metabolic functions of growth hormone. What is the effect of growth hormone on bone growth?
Metabolic
1) Increased protein synthesis
2) Increased release of FA and use of fats for energy
3) Decreased use of glucose/ insulin resistance
Bone= growth at the epiphyseal plates
Describe the relationship between growth hormone and the insulin like growth factors. Where is each produced?
- GH= anterior pituitary
- IGF= hepatocytes
*GH requires IGF-1 to exert its action
What is the other name for the insulin-like growth factors?
Somatomedins C
Define term panhypopituitarism.
Inadequate or absent production of the anterior pituitary hormones
Describe the effect of too much growth hormone.
Giantism vs. acromegaly
Describe the effect of too little growth hormone.
Dwarfism
How do the effects of too much GH differ if the problem is present from birth or occurs in adulthood.
Birth= giantism
Adult= acromegaly
Describe the symptoms seen in patients with acromegaly.
After the epiphyseal plates close, excess GH causes:
- Enlargement of the hands/feet
- Protruding brow/jaw
- Soft tissue swelling
- Growth of internal organs
Describe what is meant by primary hypothyroidism.
Problem is in the thyroid
Describe what is meant by secondary hypothyroidism.
Problem in the pituitary i.e. deficient release of TSH
Describe what is meant by tertiary hypothyroidism.
Problem in the hypothalamus i.e. deficient TRH
Explain how primary hypothyroidism can cause hyperprolactinemia.
- If T3/4 are low, body will compensate with increases TRH and TSH
- TRH increases BOTH TSH and prolactin
*Thus, primary hypothyroid can lead to hyperprolactinemia
What is the Median eminence?
Location in the hypothalamus where the portal vessels arise
Describe the parts of the portal circulation between the hypothalamus and anterior pituitary.
Primary plexus= first part of circulation between hypothalamus and anterior pituitary
Secondary plexus
What is the Hypothalamohypophysial tract?
Axons of the supraoptic and PVN that connect the hypothalamus to posterior pituitary
What function is the associated with the VMN?
Satiety center
What function is the associated with the lateral hypothalamus?
Hunger center
What function is the associated with the anterior hypothalamus?
1) Thermoregulation–cooling
2) Thirst
What function is the associated with the posterior hypothalamus?
Thermoregulation–heating
What are the functions of ACTH?
1) Stimulation of cortisol synthesis and secretion
2) Increased melanin synthesis
*Also increases androgens and aldosterone
What are the functions of TSH?
1) Increased synthesis and secretion of thyroid hormones (T3 and T4)
2) Growth of the thyroid
3) Stimulation the release of Prolactin
What are the functions of FSH in males and females?
Females= growth of follicles in ovaries
Males= sperm maturation
What are the functions of LH in males and females?
Males= stimulation of testosterone synthesis
Females=
1) Stimulation of ovulation
2) Formation of Corpus Luteum
3) Estrogen and progesterone synthesis
What are the functions of Growth Hormone?
1) Stimulation of protein synthesis and overall growth
2) Production of Insulin-like Growth Factors
What are the functions of Prolactin?
1) Breast development and milk production
2) Inhibits ovulation/ spermatogenesis
