Pituitary Function and Failure Flashcards Preview

Gabe's Endocrinology > Pituitary Function and Failure > Flashcards

Flashcards in Pituitary Function and Failure Deck (66):

What does the posterior pituitary release?

Vasopressin and oxytocin.


What does vasopressin do?

Increases collecting duct permeability, reducing urine volume.


What does oxytocin do?

Stimulates milk ejection from the breast and contraction of the uterus.


Where are posterior pituitary hormones synthesised?

In the hypothalamus and packaged in the cell body of the neuron.


Where are neurohormones synthesised and packaged?

In the cell body of the neuron.


What happens to neurohormones after synthesis?

  1. They are transported down to the posterior pituitary.
  2. The vesicles are stored in the posterior pituitary.
  3. Hormones are released into general circulation where they travel in tissues to where the receptors are.


Which neurons produce and control the posterior anterior pituitary?

Supraoptic and paraventricular nuclei.


Which neurons are concerned with the anterior pituitary?

Arcuate and other nuclei.


What is the hypothalamic-hypophyseal portal system?

The connection of the hypothalamus to the anterior pituitary.

  1. Neurons synthesising trophic hormones release them into capillaries of the portal system.
  2. Portal vessels carry the trophic hormones directly to the anterior pituitary.
  3. Endocrine cells release their hormones into the second set of capillaries for distribution to the rest of the body


Which hormones are in the hypothalamus?

  • PRFs
  • Dopamine
  • TRH
  • CRH
  • GHRH
  • GnRH
  • Somatostatin.


Which hormones are in the anterior pituitary?

  • Prolactin
  • TSH
  • ACTH
  • GH
  • FSH
  • LH


What is the pathway for IGF release?

Hypothalamus releases GHRH into the hypothalamic-hypophyseal portal system to the anterior pituitary, which release GH. GH travels via circulation to liver, inducing it to synthesise and release IGF.


How is thyroid hormone released?

TSH from anterior pituitary is released into circulation, it acts at the thyroid gland to release T3 and T4 thyroid hormones.


How is cortisol released?

ACTH is released from anterior pituitary and stimulates the adrenal cortex to release cortisol, which then modulates metabolic actions and stress responses.


What is the action of prolactin?

Stimulates mammary glands to increase breast growth and milk secretion.


How is the hypothalamus linked to the posterior pituitary gland?

Via a neural link


How is the hypothalamus linked to the anterior pituitary gland?

Via a vascular link - hypothalamic-hypophyseal system.


How does the final organ producing the hormone act on the structures stimulating it?

  • It often feeds back onto the anterior pituitary and hypothalamus, via negative feedback.
  • This allows for 2 layers of control.


What effect does somatotropin (GH) have on the liver?

Stimulates release of somatomedins, which stimulate bone and soft tissue growth, e.g. IGF-1.


Where are LH and FSH released from?

Anterior pituitary


Where do LH and FSH act?

At the gonads (ovaries or testes)


What are the effects of LH stimulation of the gonads?

Sex hormone secretion (oestrogen and progesterone in females; testosterone in males).


What are the effects of FSH stimulation of the gonads?

Gamete production (ova in females; sperm in males)


What factors can influence hypothalamic regulation of the pituitary?

Neighbouring structures, such as the optic chiasm, pre-optic areas, areas for smell, etc.


What are the afferents for regulation of thyroid stimulating hormone (TSH) via TRH?

Temperature receptors in infants, perhaps others.


What is the integrating centre for regulation of thyroid stimulating hormone (TSH) via TRH?

Paraventricular nuclei and neighbouring areas


Where do ACTH and beta-lipotropin via CRH receive afferents from?

  • Limbic system (emotional stimuli)
  • Reticular formation (systemic stimuli)
  • Hypothalamic and anterior pituitary cells sensitive to circulating blood cortisol level
  • Suprachiasmatic nuclei (diurnal rhythm)


What is the integrating centre for afferents affecting ACTH and beta-lipotropin levels via CRH?

Paraventricular nuclei


What are the afferents affecting FSH and LH via GnRH?

Hypothalamic nuclei sensitive to oestrogen, eyes, touch receptors and genitalia of reflex ovulating species.


What are the integrating centres for afferents affecting FSH and LH?

Pre-optic areas; other areas


What are the afferents affecting Prolactin release via PIH and PRH?

Touch receptors in breasts


What are the integrating receptors for afferents affecting FSH and LH release?

Arcuate nucleus; other areas (hypothalamus inhibits secretion)


What are the integrating centres for afferents affecting GH release via somatostatin and GRH?

Periventricular nucleus; arcuate nucleus


What is Kallmann syndrome?

  • Embryologically GnRH neurons failed to migrate via olfactory pathway
  • Hypogonadotropic hypogonadism
  • Hyposmiaoranosmia (loss of smell)


What are the requirements for growth?

  • Growth hormone (somatotropin) is essential
  • Other important factors:
    • Genetic determination
    • Adequate diet
    • No chronic disease or stressful environment
    • Normal mix of growth‐influencing hormones
      • Thyroid hormone, insulin, sex hormones


What is size at birth determined by?

  • Genetics
  • Environmental (e.g. drug exposure)
  • Nutritional (under‐nourished mother)
  • Research: Small birth weight = adult disease


When are the 2 major growth spurts?

Postnatal and pubertal.


What happens during the post-natal growth spurt?

70% of brain growth.


What happens during the pubertal growth spurt?

  • Adolescence
  • Lengthening of long bones increases growth
  • Genetic and hormonal factors
  • Testosterone and oestrogen
  • Full adult height at end of adolescence


What happens between the two major growth spurts?

  • Little sex difference in height & weight
  • Rate of linear growth declines


What are the metabolic effects of growth hormone?

  • Increased blood fatty acid and glucose – anti insulin
  • During prolonged fasting or when body’s energy needs exceeded


What are the soft tissue and skeletal effects of growth hormone?

  • Hyperplasia and hypertrophy on soft tissues & skeleton
  • Increased protein synthesis


What is the half-life of GH?

18 minutes


How is GH transported in the circulation?

Half is dissolved in plasma, half is bound to a binding protein whose structure is identical to that of the GH receptor.


What factors affect the release of GH?

Circadian rhythm of tonic secretion; influenced by circulating nutrients, stress and other hormones in a complex fashion.


What are the target cells or tissues of GH?

  • Trophic on liver for IGF-1 production
  • Also acts directly on many cells.


What is the control pathway for GH?

GHRH, somatostatin (hypothalamus) → growth hormone (anterior pituitary)


What is the target receptor for GH?

Membrane receptor with tyrosine kinase activity.


What is the whole body or tissue action for GH with IGFs?

  • Bone and cartilage growth
  • Soft tissue growth
  • Increased plasma glucose.


What is the action of GH at the cellular level?

Receptor linked to kinases that phosphorylate proteins to initiate transcription.


What are some somatomedins?

  • Insulin‐like growth factors (IGF‐I and IGF‐II)
  • Polypeptide growth factor


What are somatomedins stimulated by?

Growth hormone


What are the actions of GH via IGF-1?

  • Insulin-like activity
  • Antilipolytic activity
  • Protein synthesis
  • Epiphyseal growth


What are the actions of GH that don't act via IGF-1?

  • Na+ retention
  • Decreased insulin sensitivity
  • Lipolysis
  • Protein synthesis
  • Epiphyseal growth


What is the growth hormone control pathway?

  • Somatostatin = Growth hormone inhibiting hormone (GHIH)
  • Somatotropin = Growth hormone
  • Somatomedin = insulin‐like growth factors (IGF‐I and IGF‐II)
  • See image


What does tissue and bone growth require?

Hormones and paracrines:

  • GH and IGFs required for protein and cell division
  • Thyroid hormone plays permissive role
  • Insulin supports tissue growth
  • Oestrogen close epiphyseal plates of long bones
  • Bone growth requires calcium


Which hormone determines height?

Oestrogen, because it closes epiphyseal plates of long bones.


What is dwarfism a result of?

Decreased GH as a child.


What is Laron dwarfism?

Growth hormone insensitivity, GH receptors are unresponsive to normal GH.


What is the result of adult onset GH deficiency?

Very little effects


What is the treatment for GH deficiency?

Genetically engineered human GH


What are GH-independent causes of short stature?

  • Cretinism: childhood hypothyroidism
  • Precocious/early puberty
  • Gonadal dysgenesis: XO chromosomes
  • Constitutional delayed / stunted growth
  • Psychosocial dwarfism: chronic abuse or neglect
  • Achondroplasia
    • Most common form of dwarfism in humans
    • Fibroblast growth factor receptor 3 mutation (cartilage & brain)
    • FGF receptor III mutation


What are two disorders due to growth hormone excess?

Gigantism and acromegaly


What is gigantism due to?

Overproduction of GH as a child before puberty


What is acromegaly?

  • Overproduction GH in adult; bone and soft tissue deformities
  • Increased viscera size & protein content
  • Progression of acromegaly in one woman


What is the relative importance of hormones in human growth at various stages?

See image.