| Question | Answer |
| What hormones does the pituitary release | Anterior - TSH, ACTH, LH, FSH, GH, prolactin
Posterior - Oxytocin and vasopressin (ADH) |
| Diurnal rhythm of plasma ACTH and cortisol | Released in pulses - increase in ACTH followed by increase in cortisol
Peaks at 7am to prepare the body for waking
Disruption of this leads to increased risk of CVD, T2 diabetes and depression
Best health outcomes when hormones given by this rhythm |
| Anterior pituitary vasculature | Prominent vessels in the pituitary stalk
Gonadotrophs directly adjacent to capillaries - allows rapid diffusion into bloodstream
Pituitary can adapt to demands e.g. during pregnancy, lactation, menopause, stress, seasons, fetal stress and puberty |
| Pituitary fossa | The pituitary gland sits at the base of the skull in a recess of the sphenoid bone called the sella turcica
This is a bony cavity in which the pituitary sits
Relatively protected from trauma except the stalk
Tumours cannot expand within the fossa |
| Pathology of oxytocin | Deficit may cause prolonged labour
Knockout mice labour normally but no milk ejection and impaired social recognition |
| Action of ADH | Increases water reabsorption in collecting ducts of kidney
Triggered by increased osmolarity or volume of blood |
| ACTH | A polypeptide hormone from POMC precursor - secreted by corticotroph cells
GPCR coupled to cAMP
Stimulates secretion of cortisol from adrenal cortex in stress
Stimulates growth of adrenal cortex |
| Hypothalamo-pituitary-adrenal axis | Stress e.g. infection, pain etc stimulates hypothalamus to secrete corticotrophin releasing hormone
Anterior pituitary corticotroph cells release ACTH
Adrenal cortex secretes cortisol
Long feedback loop |
| Actions of oxytocin | Contraction of uterine muscle in childbirth
Milk ejection by contraction of breast myoepithelium
Role in social behaviours and parental behaviours due to release in brain
Trust hormone |
| Differences in prolactin release | Only pituitary hormone whose principle control is inhibitory
PRL production is stimulated by estrogen during pregnancy
Dopamine agonists e.g. bromocryptine suppress lactation
Pathology - prolactinomas hyper secrete PRL - cause infertility |
| Hypothalamo-pituitary-gonadal axis | Hypothalamus secretes gonadotrophin releasing hormone
Anterior pituitary gonadotroph cells release LH and FSH
Ovary - oestrogen and progesterone
Testes - testosterone
Released in pulses every 90 mins
Cyclical release in menstrual cycle |
| Posterior pituitary histology | Formed by axons and terminals of hypothalamic neurosecretory neurons
Secretes peptide hormones ADH (vasopressin) and oxytocin
Nuclei present are of glia cells - control nutrient environment |
| Gonadotrophins - LH and FSH | Used for reproduction
Women - act in ovary via GPCR - FSH for follicle development and LH for ovulation and progesterone production
Male - act in testes - LH for testosterone production and FSH for sperm production |
| Control of prolactin release | Suckling inhibits dopamine release from hypothalamus
Dopamine usually inhibits prolactin release, so this allows anterior pituitary lactotroph cells to release prolactin
This triggers breast growth and milk production as well as causing infertility |
| Acromegaly | Due to excess GH secretion after epiphyseal plates have fused
Enlargement of hands and feet
Coarsening of facial features - largening of nose
Weight gain |
| Diabetes insipidus | Disorder of insufficient ADH production
Hypothalamic - lack of ADH production by posterior pituitary
Renal - Kidney fails to respond to ADH
Characterised by production of large amounts of very dilute urine resulting in dehydration and polydipsia |
| Anterior pituitary tumours | Hormonal effects - hormone secreting tumours effects depend on cell type - present as over excretion of the hormone
Mechanical effects - affect vision as tumour presses on optic chiasm - affects peripheral vision field leading to tunnel vision |
| Endocrine disrupting chemicals | Several reports of altered hypothalamic and pituitary hormone secretion, clinical disruption of circadian secretion and delayed puberty
Molecules in the environment can disrupt pituitary function |
| Control of growth hormone | Metabolites, sleep, stress and exercise trigger hypothalamus to secrete growth hormone releasing hormone
Anterior pituitary somatotroph cells release growth hormone
Short feedback loop
GH acts directly + via liver IGFs to induce bone and muscle growth |
| Location of the pituitary | Hypothalamus is superior
Optic chiasma is directly in front (where optic nerves cross)
At the base of the brain behind the nasal cavity |
| Anterior pituitary histology | Five endocrine cell types each secrete different trophic hormones
Cell types can be differentiated by antibody labelling and cell structure of tumours
Non-secretory supporting call types = Folliculo-stellates
These support the cells |
| Function of the pituitary | To produce and secrete eight peptide/glycoprotein hormones and in turn these hormones exert many functions important for health
E.g. PRL, ACTH, TSH, GH, LH, FSH, ADH and Oxytocin |
| Anterior pituitary | No neural innervation - controlled by hormones from the posterior
Capillaries are fenestrated to allow each diffusion of hormones into blood - enters jugular vein
Rabbits perfused with ink allows view of blood vessels - shows hormonal control |
| Control of oxytocin release | Stretch of cervix/vagina at parturition
Sucking - nipple stimulation causes milk ejection reflex |
| Development of the pituitary | Downgrowth from developing hypothalamus - neural ectoderm - posterior pituitary
Upgrowth of oral ectoderm from roof of mouth - anterior pituitary
Development directed by different transcription factors for each section |
| Ultrastructure of anterior pituitary | Lots of mitochondria
Euchromatin - high transcription rate
Hormones stored in secretory granules
RER
Majority of exocytosis occurs at boundary with capillaries - directed |
| Posterior pituitary | Axons and nerve endings - direct extension of the brain
Neurons originate in the brain
Hormones are stored and released from nerve endings
Responsible for neurosecretion |
| Pathology of Gonadotrophins | Deficit - infertility in adult life - lack of sexual maturation
Excess - precocious puberty at age 4/5 |
| ACTH pathology | Excess ACTH from adenoma and in turn excess cortisol - Cushing's syndrome
Deficiency of ACTH in turn cortisol deficient - adrenal insufficiency - treat with replacement cortisol |
| GH pathology | Inactivating mutation in GHRH receptor - dwarfism
No response to GHRH due to a single AA change in the GPCR
Gigantism due to excess GH secretion
Short stature if lack GH
Only if occurs before epiphyseal plate fusion |
| Stimulation of posterior pituitary hormone release | Neural stimulus depolarises neuron
AP down axon
Ca influx
Exocytosis
E.g. osmoreceptor cells outside BBB sense increased osmolarity and depolarise ADH neurons |
| Feedback loops | Short feed back loop - anterior pituitary inhibits hypothalamus e.g. GH and PRL
Long feedback loop - endocrine gland inhibits both anterior pituitary and hypothalamus e.g. cortisol, IGF and testosterone |
| Hypothalamic-pituitary-thyroid axis | Stimulus e.g. cold triggers hypothalamus to produce thyrotrophin releasing hormone
Anterior pituitary thyrotroph cells then secrete thyroid stimulating hormone
Thyroid then secretes T3 and T4
Long feedback loop
Pathology of TSH secretion is rare |
