E6 - Hypothalamus & pituitary Flashcards
(40 cards)
What is the clinical relevance of pituitary tumours?
- Most common cause of pituitary disease (adenomas)
- Mostly benign/slow-growing (years)
- Cause problems as pressure on surrounding structures (due to location); greater intra-cranial pressure, close to optic nerve = headaches/visual disturbances
What problems can pituitary tumours cause?
- Over-production of a pituitary hormone (hypersecretion)
- Inadequate production of other remaining hormones (squeezing/squashing other pituitary cells; hyposecretion)
- Local effects on anatomically-related structures (e.g. visual disturbances, headaches; greater intra-cranial pressure)
What is hypopituitarism?
Inadequate secretion of pituitary gland hormones causing dwarfism in children and premature aging in adults
What is the relationship between the hypothalamus and the anterior pituitary with regards to cell bodies etc?
- Cell bodies located in the hypothalamus: arcuate, ventromedial and preoptic nuclei, give signal for hormone synthesis at anterior pituitary
- Releasing factors pass along portal vessels to reach the capillary bed of the anterior pituitary
What is the relationship between the hypothalamus and the posterior pituitary with regards to cell bodies etc?
- Cell bodies of the paraventricular (PVN) and supraoptic (SON) nuclei located in the hypothalamus - site of hormone synthesis ‘neuro’
- Hormones oxytocin and vasopressin respectively stored in the axon terminus of the posterior pituitary before release
Where is growth hormone synthesised, what does it do (briefly) and where does it act?
- Synthethised in somatotrophs in the anterior pituitary
- Has a major role in growth & development (particularly linear growth; elongation of long bones) + affects metabolism
- Acts via GH receptor on target cells
What does the hormone prolactin do?
- Stimulates mammary glands to produce milk (lactation) and promotes growth & development of breasts
- Inhibits GnRH release
- Synthesised in lactotrophs (/mammo-)
What does ACTH do?
- Adrenocorticotropic hormone
- Stimulates synthesis/release of cortisol
- Synthesised from a very large precursor glycoprotein known as pro-opiomelanocortin (POMC)
What does TSH do?
- Thyroid-stimulating hormone
- Stimulates synthesis and release of thyroid hormones
What is LH (luteinizing hormone)?
- Stimulates steroid hormone synthesis (e.g. testosterone)
- Causes ovulation/formation of corpus luteum
What is FSH?
- Stimulates follicular development (ovaries) and spermatogenesis (testes)
Which anterior pituitary hormones are single-chain polypeptides with disulfide bonds?
- Somatotropes(trophs) e.g. somatotropin (growth hormone, GH)
- Lactotropes(trophs) e.g. prolactin
Which anterior pituitary hormone is a small peptide?
Corticotrope(trophs) e.g. corticotropin (adrenocorticotropic hormone, ACTH)
Which anterior pituitary hormones are glycoproteins with 2 subunits?
- Thyrotropes(trophs) e.g. thyrotropin (thyroid stimulating hormone, TSH)
- Gonadotropes(trophs) e.g. LH, FSH
What is the difference between tropic and trophic?
- Tropic: ‘turning’; affecting activity of an endocrine gland
- Trophic: ‘feed, grow’; promoting growth, tissue integrity
Describe the OG endocrine axis.
- Hypothalamus:
Releasing hormone
+/- Anterior pituitary:
Tropic hormone (short -ve feedback to hypothalamus)
+ Peripheral endocrine glands
Peripheral hormone (long -ve feedback to ant pit. and hypo.)
+ Target cell response (some -ve feedback to hypo.)
What effect does hypothalamic stimulation usually have on the anterior pituitary and which hormone is the exception?
- Hypothalamus usually exerts stimulatory influence on the anterior pituitary (e.g. on LH/FSH, GH, TSH, ACTH)
- Prolactin is the exception; under major inhibitory influence (from dopamine from hypothalamus) unless stimulated by TRH
What are the direct actions of growth hormone (somatotropin)?
On metabolism:
- Increases lipolysis (catabolic; triglycerides broken down to fatty acid + glycerol)
- Increased AA uptake and protein synthesis (anabolic)
- Increased hepatic glucose output (gluconeogenesis) & decreased glucose uptake (fat/adipose, skeletal muscle)
Anti-insulin (diabetogenic; counter-regulatory to insulin)
- NET effect, shift of fuel source from CHOs to fats
- GH elevates blood glucose; secondary cause of diabetes
What are the indirect actions of growth hormone (somatotropin)?
Promotes growth:
- Stimulates release of growth factors such as IGF-I (insulin-like GF) & II (somatomedins) from liver (and other cell types)
How does growth hormone stimulate growth and what are the processes that are stimulated?
Growth is via the action of IGF-I on cells:
- Stimulate protein synthesis, increase cell size (hypertrophy) increasing lean body mass
- Stimulate cell division, increase cell number (hyperplasia) increasing size of individual organs
- Promotes skeletal growth (increasing linear growth = height)
(Not about fat accumulation)
How is GH release controlled?
Hint: re. endocrine axis
- Environmental stimuli: sleep, stress, exercise
- Nutrient stimuli: decrease glucose, decrease [FFA], increased [AA]
HYPOTHALAMUS
+ GHRH/ - SST (somatostatin)
ANTERIOR PITUITARY
+ GH > direct effect on metabolism
> Short feedback loop to hypothalamus
LIVER/OTHER TISSUES
+ Somatomedins (e.g. IGF-I) > indirect effect increasing growth
> Long feedback loop to Liver + Hypothalamus
What is the pattern of GH secretion throughout the day/throughout life?
Day:
- 70% of total daily GH released during sleep (pulsatile release)
Life:
- Mean daily secretions are high during childhood reaching a peak at puberty
- Fall to lower concentrations in adulthood
- Fall in GH in later life partially responsible for some signs of aging
What can occur as a result of GH (growth hormone) deficiency?
- Stunted growth in children (pituitary dwarfism; no long bone development)
- Deficiencies in adulthood:
> psychological changes,
> malaise, excessive tiredness, anxiety, depression
> osteoporosis
> poor muscular tone, decrease in lean body mass
> impaired hair growth
> increase in adipose tissue
Normally signs associated with old age.
How is GH deficiency treated?
Recombinant human growth hormone (anabolic effects abused in sport)
