Pituitary Gland Flashcards
What hormones does the anterior pituitary secrete?
GH ACTH LH/FSH TSH Prolactin
What is the structural difference between the anterior and posterior pituitary glands?
Anterior:
Primitive gut tissue origin (upgrowth of endodermal Rathke’s pouch)
Endocrine cells
Posterior: Brain tissue origin (ectodermal? downgrowth) Neuroendocrine cells (stimulated by nerves)
What hormones does the posterior pituitary secrete?
ADH
Oxytocin
What functions does GH have?
- skeletal growth (in children)
- gluconeogenesis
- increase in muscle strength
- bone density
- cardiac function
- emotional state (deficiency = depression)
What type of hormone is GH? What stimulates/inhibits GH? How does GH affect cells? What mode of release does GH have?
Peptide hormone
GH-releasing hormone stimulates/somatostatin inhibits
Acts on tissues via producing insulin growth factor-1 (produced by liver)
Pulsatile release (max. during sleep)
What does a deficiency in GH cause? How do you test for this?
Children:
Slow growth, delayed puberty
Adult:
Fatigue, less muscle, more fat, reduced bone density, high LDL cholesterol
Test: Insulin Tolerance Test
What is the Insulin Tolerance Test? What are the contra-indications?
Give insulin to cause hypoglycaemia —> STRESS
See if GH increases in response
Contra-indications: ischaemic heart disease, epilepsy
What does excess GH cause? What is the test for this?
Children (before epiphyseal plates fuse)
Gigantism
Adults: Acromegaly
Test: Glucose Tolerance Test
What is the Glucose Tolerance Test?
Give glucose and then measure glucose (& GH) over time
How is ACTH produced?
POMC produces beta-endorphins, alpha-MSH, and ACTH
What does alpha-MSH do?
Stimulates melanocytes to produce melanin
What does ACTH do? What mode of release does it have? What is it stimulated by?
Stimulates adrenal cortex to produce cortisol
Pulsatile release (max. morning)
Stimulated by Cortisol Releasing Hormone (CRH)
What does a deficiency in ACTH cause? How can you test for this?
Hypoglycaemia, weight loss, etc.
Insulin Tolerance Test
What does an excess in ACTH cause? How can you test for this?
Cushing’s syndrome
Dexamethasone supression test (no reduction at high dose, therefore due to excess ACTH secretion by pituitary - Cushing’s disease)
What do gonadotrophins do? What are they stimulated by?
Men:
LH —> stimulates testosterone secretion (max. morning)
FSH —> sperm production
Women:
LH —> oestrogen release during follicular phase (max. at egg release)
—> progesterone release during luteal phase (max. period)
FSH —> estradiol release (max. endometrial lining at its thickest)
Stimulated by gonadotrophin releasing hormone (GnRH)
What can a gonadotrophin deficiency cause?
Hypogonadism
What does thyroid stimulating hormone do? What is it stimulated by?
Stimulates thyroid to produce T3 & T4
Stimulated by thyroid releasing hormone
What does prolactin do? What is the mode of secretion? What are prolactin’s target tissues? What stimulates/inhibits prolactin release?
Initiates and maintains lactation
Pulsatile (max. night)
Acts on peripheral tissues with no target gland (exception: breast tissue)
TRH & oestrogen have minor positive feedback effect
Dopamine has tonic inhibitory effect
What are the symptoms of hyperprolactinaemia?
Amenorrhoea Galactorrhoea (excessive/spontaneous lactation) Gynaecomastia Hypogonadism Infertility
What are the causes of hyperprolactinaemia?
5 P’s:
- pregnancy
- physiological (stress)
- pharmacological (drugs affecting dopamine e.g. anti-sickness & anti-psychotics)
- pituitary (prolactinoma secreting prolactin/preventing dopamine release)
- polycystic ovaries
What is polycystic ovary syndrome?
Cysts in ovary due to arrested follicular development cause excess androgen production
S&S:
- amenorrhoea
- hirsutism
- acne
- virilisation
- obesity
What does ADH do? What stimulates ADH release?
Inserts aquaporins into collecting duct —> recycles water back into bloodstream
Low water potential in blood (high osmolality)
What is the difference between osmolarity and osmolality?
Osmolarity = no. of particles per litre of solution
Osmolality = no. of particles per kg of solvent
What does ADH deficiency cause?
Diabetes insipidus
What does oxytocin cause?
Stimulates lactation, uterine contraction (birth), maternal behaviour (+ ejaculation/male sexual behaviour)
How do hormones from the hypothalamus reach the pituitary?
Hypophyseal portal vessels (connecting capillary beds of hypothalamus and pituitary)
Therefore quick response & low levels of hormones are concentrated to cause a response
