Pituitary Hormones Flashcards
Anterior pituitary gland
-major hormones it secretes (6)
- Prolactin (PRL)
- Growth hormone (GH)
- Adrenocorticotropic hormone (ACTH)
- Luteinizing hormone (LH)
- Follicle-stimulating hormone (FSH)
- Thyroid stimulating hormone (TSH)
Anterior pituitary hormone
- stimulators (6)
- inhibitors (7)
- cytokines, ghrelin, GHRH, TRH, GnRH, estrogen
2. glucocorticoids, somatostatin, IGF-1, dopamine, T3, T4, sex steroids
Prolactin (PRL) (2)
- synthesized in lactotrophs
- lactotroph cell hyperplasia develops during pregnancy and the first few months of lactation
- the predominant control mechanism is inhibitory –> tonic dopamine mediated suppression of PRL release
Prolactin (PRL)
-when do levels rise (8)
- after exercise
- meals
- pregnancy - decline after parturition, but if breast feeding is initiated levels remain elevated
- sexual intercourse
- minor surgical procedures
- general anesthesia
- chest wall injury
- acute MI and other forms of acute stress
Prolactin (PRL)
-acts to induce and (3)
- maintain lactation
- decrease reproductive function –> by suppressing hypothalamic gonadotropin-releasing hormone (GnRH) and pituitary gonadotropin secretion –> impaired gonadal steroidogenesis
- suppress sexual drive
Growth hormone (6)
- GH-releasing hormone (GHRH) stimulates GH synthesis and release
- Somatostatin –> inhibits GH secretion
- IGF-1 –> feeds back to inhibit GH
- GH secretory rates decline markedly with age
- secretion is pulsatile –> highest peak levels occurring at night
- liver and cartilage express the greatest number of GH receptors
Growth hormone
-actions (3)
- GH induces protein synthesis and nitrogen retention and also impairs glucose tolerance by antagonizing insulin action
- GH stimulates lipolysis –> increased circulating fatty acids levels and enhanced lean body mass
- GH promotes sodium, potassium and water retention
Growth hormone
-is a single random measurement enough? (2)
- single random GH measurements do not distinguish patients with adult GH deficiency or excess from normal persons
- secretion is pulsatile –> highest levels at night
Adrenocorticotropic hormone (ACTH) (3)
- secretion is pulsatile and exhibits a characteristic circadian rhythm, peaking about 6AM and reaching the lowest point about midnight
- CRH is the predominant stimulator of ACTH synthesis and release
- the major function of the HPA axis is to maintain metabolic homeostasis and mediate the neuroendocrine stress response
Adrenocorticotropic hormone (ACTH) -increased by...? (4)
- physiological and psychological stress
- exercise
- acute illness
- insulin-induced hypoglycemia
Thyroid stimulating hormone (TSH) (2)
- TRH is a hypothalamic tripeptide that stimulates TSH synthesis and secretion
- it also stimulates the lactotroph cell to secrete PRL
Thyroid stimulating hormone (TSH)
-regulation (2)
- TSH secretion is stimulated by TRH, whereas thyroid hormones, dopamine, somatostatin and glucocorticoids suppress TSH by overriding TRH induction
- Thyrotrope cell proliferation and TSH secretion are both induced when negative feedback inhibition by thyroid hormones is removed (ex: primary hypothyroidism)
Gonadotropins: FSH and LH (4)
- hypothalamic GnRH –> regulates the synthesis and secretion of both LH and FSH
- estrogens –> modulate gonadotropin secretion
- chronic estrogen exposure –> inhibitory
- rising estrogen levels –> positive feedback –> increase gonadotropin pulse frequency and amplitude
Function of FSH and LH
- in women
- in men
- FSH regulates ovarian follicle development and stimulates ovarian estrogen production. LH mediates ovulation and maintenance of the corpus luteum
- LH induces Leydig cell testosterone synthesis and secretion and FSH stimulates seminiferous tubule development and regulates spermatogenesis
Hypopituitarism
-reduction or absolute absence of hormones secretion of anterior, posterior or both parts of pituitary gland
total > panhypopituitarism
partial >2 or more hormones
selective > 1 single hormone
- Primary Hypopituitarism
- Secondary Hypopituitarism
- Acquired Hypopituitarism
- Congenital Hypopituitarism
- disorders of the pituitary gland - loss, damage or dysfunction of cells
- disorders of hypothalamus or pituitary stalk - interruption of the nerve or vascular connections to the pituitary gland
- commonly during adult life - neoplastic, vascular, traumatic, autoimmune, infectious
- disorders present at the birth - rare, usually genetic mutation
Hypopituitarism
-Clinical presentation
- space occupying lesion –> hypopituitarism accompanied by headache, visual impairment, change of personality
- acute onset is rare but life threatening
- most patient –> slow loss of pituitary function with vague and non-specific symptoms
- trophic hormone failure occurs sequentially : GH > FSH > LH > TSH > ACTH
- during childhood –> growth retardation
- in adults –> hypogonadism
Pituitary apoplexy
- bleeding into or impaired blood supply of the pituitary gland.
- usually occurs in the presence of a tumor
hypopituitarism evident within:
- several hours –> diabetes insipidus, posterior involvement
- few days –> adrenal insufficiency, anterior involvement
ACTH deficiency
-Clinical features
Acute: dizziness, nausea, vomiting, hypotension, hypoglycemia
Chronic: fatigue, weakness, tiredness, pallor, anorexia, weight loss
ACTH deficiency
-Lack of adrenal androgens - clinical features
Female: loss of sexual desire, loss of pubic and axillary hair
Male: compensation by testosterone from testicles
Primary adrenal insufficiency (6)
- Addison’s disease
- course of the disease: chronic with acute adrenal crisis
- cortisol deficiency
- hypoandrogenism
- aldosterone deficiency
- hyperpigmentation –> increase ACTH
Secondary adrenal insufficiency (5)
- ACTH deficiency due to hypopituitarism
- course of the disease: chronic with latent onset
- cortisol deficiency
- aldosterone is diminished but not abolished
- hypoandrogenism
TSH deficiency
-clinical features
-hypothyroidism features
- tiredness,
- cold intolerance,
- constipation,
- weight gain,
- hair loss,
- dry skin,
- bradycardia,
- hoarseness,
- impairment of memory,
- growth retardation in children
FSH/LH deficiency - clinical features in:
- Women before menopause
- Women during and after menopausal
- loss of target organs (gonads) function
1. amenorrhea, oligomenorrhea, infertility, loss of libido
2. osteoporosis, premature atherosclerosis
FSH/LH deficiency - clinical features in:
- Men
- Children before puberty
- loss of libido, impaired sexual function, decreased muscle and bone mass, erythropoiesis and hair growth
- delayed or missing onset of puberty
GH deficiency - clinical features:
- in children
- in adults
- short stature
- decreased muscle mass and strength, fatigue, general weakness and reduced vitality, moderate obesity, hyperlipidemia and decreased HDL, osteopenia, increased risk of metabolic syndrome, increased cardiovascular risks
PRL deficiency
-clinical features (2)
- inability to produce milk after childbirth
- isolated hyperprolactinemia is very rare
Congenital hypopituitarism
- Acquired pituitary failure - cause
- Hypothalamic dysfunction
- Imp. transcription factors
- birth trauma, including cranial hemorrhage, asphyxia and breech delivery
- dysgenesis of the septum pellucidum or corpus callosum
- Pit-1 and Pop-1
Autosomal dominant or recessive Pit-1 mutations
cause combined GH, PRL and TSH deficiencies
Familial and sporadic Pop-1 mutations
result in combined GH, PRL, TSH and gonadotropin deficiency
Congenital hypopituitarism - Kallmann syndrome (5)
- defective hypothalamic gonadotropin releasing hormone (GnRH) synthesis
- associated with anosmia or hyposmia due to olfactory bulb agenesis or hypoplasia
- GnRH deficiency prevents progression through puberty
- males –> delayed puberty and pronounced hypogonadal features (micropenis), may result of low testosterone levels during pregnancy
- females –> primary amenorrhea and failure of secondary sexual development
Congenital hypopituitarism - Kallmann syndrome
-hormone levels
- low LH and FSH
- low concentration of sex steroids (testosterone and estradiol)
Hypopituitarism
-diagnosis - lab investigations
-low or inappropriately normal levels of trophic hormones in the setting of low levels of target hormones
Hormone replacement therapy
- ACTH
- TSH
- GH
- Hydrocortisone (1-20mg AM; 5-10 mg PM), Cortisone acetate, Prednisone (5mg AM)
- L-thyroxine
- Somatotropin
Hormone replacement therapy
-FSH/LH
Males
-Testosterone enanthate (200mg IM every 2 weeks) or Testosterone skin patch
Females
- Conjugated estrogen (0.65-1.25 mg for 25 days) and Progesterone (5-10 mg qd) on days 16-25
- Only estrogen –> possible complications: proliferation of mucous membrane of uterus, if there is no progesterone we won’t have menstrual cycle and then there is increased risk of cancer
