Pituitary function and failure Flashcards
Describe the two components of the pituitary?
Include their origins and link to hypothalamus.
Posterior pituitary (neurohypophysis): derived from outgrowth of brain, neural tissue, neural link to hypothalamus
Anterior pituitary (adenohypophysis): derived from glanualr epithelial tissue, ectodermal cells, vascular link to hypothalamus
Describe the location of the pituitary gland?
Deep in base of brain
Sitting in sella turcica (sphenoid bone)
Describe the synthesis, storage and release of posterior pituitary hormones?
Hormone synthesised and packaged in cell body of neuron in hypothalamus > vesicles transported down neuron > vesicles stored in posterior pituitary > hormones released into blood
Where are posterior pituitary hormones synthesised and stored?
Synthesised in hypothalamus
Stored in posterior pituitary
List the major posterior pituitary hormones and their functions?
Vasopressin/ADH: increase collecting duct permeability and decrease urine volume
Oxytocin: milk ejection from breasts and uterine contraction
Describe the synthesis, strorage and release of anterior pituitary hormones?
Neurons synthesising trophic hormones release them into capillaries of portal system > portal vessels carry trophic hormones directly to anterior pituitary > endocrine cells release hormones into second set of capillaries > released to body
List the major anterior pituitary hormones, and the tissues they act on?
Prolactin > mammary glands
GH > musculoskeletal system
TSH > thyroid gland
ACTH > adrenal cortex
Gonadotropins (LH and FSH) > gonads
How is the hypothalamus connected to the anterior pituitary?
Portal vascular system / hypothalamic-hypophyseal portal system
Not connected to wider circulation
What type of hormones are hypothalmic hormones?
Most are releasing hormones
Describe the cell types in the anterior pituitary which are target cells for the hypothalamic hormones?
CRH > corticotroph
TRH > thyrotroph
GnRH > gonadotroph
GHRH > somatotroph
somatostatin (GHIH) > somatotroph
PRF > mammotroph
PIH > mammotroph
Why are there two levels of feedback present in the hypothalamic-pituitary axis?
i.e. final hormone feeds back to anterior pituitary and hypothalamus
Allows for fine control and regulation of hormone levels
Describe the two types of feedback present in the hypothalmic-pituitary axis?
Long loop feedback: final peripheral hormone feeds back to anterior pituitary and hypothalmus
Short loop feedback: pituitary hormone feeds back to hypothalamus
Describe the pathway for the release of GH?
What are somatomedins?
IGFs produced by the liver
Describe the possible causes of decreased hormone activity?
How is this treated?
Hyposecretion: primary (gland abnormal) or secondary (gland normal)
Increased removal from blood
Abnormal tissue response: lack of receptors or enzymes
Treatment: hormone administration
Describe the possible causes of increased hormone activity?
How is this treated?
Hypersecretion: primary (gland abnormal) or secondary (gland normal)
Decreased plasma protein binding
Decreased removal from blood
Treatment: tumour removal, inhibiting drugs
Define growth?
Net synthesis of proteins
Lengthening of long bones
Increased size and number of cells in soft tissues
Describe the requirements for growth?
Growth hormone/somatotropin
Genetic determination
Adequate diet
No chronic disease or stressful environment
Normal mix of growth-influencing hormones
What determines size at birth?
Genetics
Environmental factors
Maternal nutrition
Maternal health in general
How does birth weight relate to disease later in life?
Small birth weight = adult disease
Describe the growth that occurs after birth?
Postnatal growth spurt: first 2 years
2yo to adolescence: linear gorwth rate declines
Pubertal growth spurt
Describe the effect of illness on child growth?
Can this be reversed?
Illness stunts child growth
If normal health is restored, can get period of catch up growth
Describe what happens during the pubertal growth spurt?
Lengthening of long bones > height increase
Testosterone and oestorgen > sexual characteristics
Describe the effects of growth hormone?
Metabolic effects: increase blood fatty acids and glucose
Soft tissues and skeleton: hyperplasia and hypertrophy, increase protein synthesis
Increase IGF production from liver
Describe the half life of GH?
Short: 18 minutes
Describe the factors affecting GH release?
Circadian rhythm of tonic release
Influenced by circulating nutrients, stress and other hormones
What is somatomedin synthesis stimulated by?
Where are somatomedins produced?
GH
(GH does not act directly on target tissues)
Produced in liver
What is somatostatin?
Growth hormone inhibitng hormone
Describe the hormones and paracrines required for tissue and bone growth?
GH and IGFs > protein and cell division
TH (permissive role)
Insulin > supports tissue growth
Oestrogen > closes epiphyseal plates
Calcium > bone growth
Describe the effects of GH deficiency?
How can this be treated?
Dwarfism: decreased GH as child
Laron Dwarfism: GH receptors unresponsive
Adult onset: few effects
If GH deficient, can treat with genetically engineered GH
Desribe the GH indepedent causes of short stature?
Cretinism
Precocious/early puberty
Gonadal dysgenesis
Constitutional delayed/stunted growth
Psychosocial dwarfism
Achondroplasia
Describe the effects of excess GH?
Gigantism: excess GH in childhood
Acromegaly: excess GH in adults
