hypothalamus to posterior pituitary

Endocrinology Notes

Hormones Produced by the Hypothalamus

• Gonadotrophin-releasing hormone (GnRH)

  • Also known as Luteinizing-hormone releasing hormone (LHRH)

  • Stimulates FSH and LH release from the anterior pituitary

  • Activity controlled by pulse frequency and feedback mechanisms

• Thyrotropin-releasing hormone (TRH)

  • Stimulates thyroid-stimulating hormone and prolactin release

  • Used in diagnostic tests for thyroid disorders

• Dopamine

  • Inhibits prolactin release from the pituitary

  • Functions as a neurotransmitter and neurohormone

• Corticotropin-releasing hormone (CRH)

  • Involved in stress response and metabolic functions

Hormones Produced by the Anterior Pituitary Gland

• Growth Hormone (GH)

  • Stimulates growth, cell reproduction, and regeneration

  • Controlled by GHRH and Somatostatin

  • Impacts metabolism, bone density, muscle mass, and immune function

  • Excesses lead to acromegaly, deficiencies have varied effects

Effects of Growth Hormone

• Stimulators of GH secretion

  • Include various peptide hormones, sex hormones, and stimuli like deep sleep and fasting

• Inhibitors of GH secretion

  • Include somatostatin, hyperglycemia, and glucocorticoids

• Other effects of GH

  • Include calcium retention, muscle mass increase, lipolysis, protein synthesis, and immune system stimulation

Clinical Significance

• Diagnostic and Therapeutic Uses

  • Hormones like GnRH, TRH, and GH have diagnostic and therapeutic applications in various endocrine disorders

• Treatment

  • Replacement therapies with human growth hormones (HGH) are used for growth disorders and adult growth hormone deficiency

Specimen Requirement and Reference Interval

• Specimen Requirement

  • Fasting serum, complete rest before collection

• Reference Interval

  • Below 1 ng/ml (<1g/L)

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Growth Hormone (GH) Deficiency

• Children:

  • Manifestations: growth failure, short stature

  • Causes: genetic conditions, congenital malformations

  • Effects: delayed sexual maturity

• Adults:

  • Rare deficiency

  • Present with truncal obesity, decreased muscle mass, energy, and quality of life

Follicle-Stimulating Hormone (FSH)

• Structure:

  • Glycoprotein similar to LH, TSH, hCG

  • Sugar part composed of various components

• Activity:

  • Regulates development, growth, pubertal maturation, reproductive processes

  • Stimulates maturation of germ cells in males and females

• Disease States:

  • High and low FSH levels impact fertility and menstrual cycle disorders

  • High levels indicate conditions like premature menopause, gonadal dysgenesis

  • Low levels linked to hypogonadism, conditions like Polycystic Ovarian Syndrome

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Luteinizing Hormone (LH)

• Function:

  • Triggers ovulation in females, stimulates testosterone production in males

• Normal Levels:

  • Low in childhood, high after menopause in women

• Conditions:

  • High levels indicate premature menopause, gonadal dysgenesis

  • Low levels linked to hypogonadism, conditions like Kallmann syndrome

Thyroid-Stimulating Hormone (TSH)

• Function:

  • Regulates thyroid gland function by stimulating T4 and T3 hormone release

• Control:

  • TRH from hypothalamus stimulates TSH production

• Diagnostic Use:

  • Tested for hyperthyroidism, hypothyroidism

  • Standard reference range for adults: 0.4-5.0 uIU/mL

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Adrenocorticotropic Hormone (ACTH)

• Function:

  • Stimulates cortisol production from adrenal cortex

• Effects:

  • Increases androgen production

• Associated Conditions:

  • Addison's disease, Cushing's syndrome, etc.

Prolactin

• Function:

  • Associated with lactation

  • Stimulated by infant suckling for milk production

• Inhibition:

  • Dopamine is the main inhibitory factor

• Specimen Requirement:

  • Blood collection 3-4 hours after awakening; fasting sample

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Effects of Prolactin

• Regulates lactation, orgasms, and oligodendrocyte precursor cells

• Stimulates mammary glands for milk production

• Provides sexual gratification post-sexual acts

• High levels linked to impotence and loss of libido

• Other effects include surfactant synthesis in fetal lungs and immune tolerance during pregnancy

Diagnostic Use of Prolactin

• Checked in sex hormone workup for hypogonadism and erectile dysfunction

• Helps distinguish epileptic seizures from non-epileptic seizures

Conditions Associated with Prolactin Levels

• Elevated: Prolactinoma, excess TRH, antipsychotic meds, stress, pregnancy

• Decreased: Bulimia, excess dopamine

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Melanocyte-stimulating Hormone (MSH)

• Produced in pituitary gland

• Stimulates melanin production in skin and hair

• Affects appetite and sexual arousal

• Increases during pregnancy causing pigmentation

• High levels in Cushing's disease lead to abnormal darkening

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Endorphin

• Endogenous opioid compounds

• Produced during exercise, pain, and orgasm

• Acts as natural pain relievers

• Induces feelings of exhilaration

• Released to prevent pain signals

Lipotropin

• Produced from cleavage of POMC

• Stimulates melanin production

Hormones from Posterior Pituitary Gland

• Releases but does not produce hormones

• Synthesized in hypothalamus

• Controlled by CNS

Vasopressin

• Also known as antidiuretic hormone

• Acts on nephron to reabsorb water

• Regulates water retention and blood pressure

• Released in response to osmolality and blood volume

• Affects blood clotting and urine volume

Endocrinology Notes

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• Kidney Effects of Vasopressin

  • Increases water permeability in tubules for water reabsorption

  • Increases urea reabsorption in collecting duct

  • Stimulates sodium reabsorption in loop of Henle

• Cardiovascular System

  • Vasopressin increases vascular resistance and blood pressure

• Central Nervous System

  • Implicated in memory formation and aggression

• Control of Vasopressin Secretion

  • Response to plasma volume reduction, osmolality increase, and cholecystokinin

• Factors Influencing Vasopressin Secretion

  • Ethanol acts as an antagonist

  • Angiotensin II may stimulate secretion

• Role in Disease

  • Decreased release leads to diabetes insipidus

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• Types of Diabetes Insipidus

  • Central: Deficiency of ADH

  • Nephrogenic: Kidney insensitivity to ADH

• Syndrome of Inappropriate Antidiuretic Hormone (SIADH)

  • Occurs in brain diseases and lung conditions

• Analytical Methods

  • Direct measurement of ADH

  • Tests for SIADH and Diabetes Insipidus

• Oxytocin

  • Roles in female reproduction, behaviors, and social bonding

• Synthesis and Actions of Oxytocin

  • Made in hypothalamus, stored in pituitary, released for letdown reflex and uterine contractions

Endocrinology Notes

Uterine Contractions and Oxytocin

• Function of oxytocin: Inducing uterine contractions during lactation

  • Supporting detail: Assists in clotting the placental attachment postpartum

• Effects of oxytocin:

  • Similarity to vasopressin: Reduces urine excretion

  • Stimulation of sodium excretion: Seen in several species, leading to natriuresis

  • Adrenal axis modulation: Can inhibit release of adrenocorticotropic hormone and cortisol

Potential Adverse Reactions of Oxytocin

• Safety at recommended doses

• Side effects:

  • Central nervous system: Subarachnoid hemorrhage, seizures

  • Cardiovascular: Changes in heart rate, blood pressure, venous return, cardiac output, and arrhythmias

  • Genitourinary: Impaired uterine blood flow, tetanic contractions, uterine rupture, postpartum hemorrhage.