Medic_Summaries (IMS) Topic 6
Endocrinology
Endocrine glands: hypothalamus/pituitary, thyroid, parathyroid, pancreas, adrenal, ovaries/testes
Hypothalamic-pituitary axis: connection between the two; hypothalamus CONTROLS pituitary
Pituitary gland:
- CONTROLS most glands in the body
- Two lobes:
- Anterior pituitary: PRODUCES various hormones
- Posterior pituitary: STORES hormones
Anterior pituitary produces hormones:
- Growth hormone (GH) - for skeletal growth
- Adrenocorticotrophic hormone (ACTH) - stimulates testicles/ovaries to make sex hormone
- Thyroid stimulating hormone/thyrotrophin (TSH) - stimulates thyroid make thyroid hormone
- Prolactin (PRL) - stimulates breast milk production
Posterior pituitary: stores hormones produced in hypothalamus (does NOT produce them)
- Antidiuretic hormone (ADH) - stimulates water reabsorption by the kidneys
- Oxytocin - helps uterine contractions during labour
Pituitary gland is under the control of the hypothalamus:
- Corticotrophin releasing hormone (CRH) - stimulates ACTH secretion - adrenal (steroids)
- Growth hormone releasing hormone (GHRH) - stimulates GH secretion
- Thyrotrophin releasing hormone (TRH) - stimulates TSH secretion - thyroid (T3 and T4)
- Gonadotrophin releasing hormone (GnRH) - stimulates FSH and LH secretion - ovaries/
testes - sex hormones
- Prolactin releasing hormone does not exist as prolactin is under the INHIBITORY effect of
the hypothalamus
Switching pituitary hormones:
- Cortisol: switches off ACTH and CRH
- Growth hormone: switches off GH and GHRH
- Thyroid hormones: switches off TSH and TRH
- Sex hormones: switch off FSH/LH and GnRH
- NEGATIVE FEEDBACK
Glands NOT controlled by the pituitary:
- Adrenal medulla: produce adrenaline and noradrenaline
- Parathyroid: controls calcium levels
- Pancreas: controls sugar levels
- Gut hormones
Thyroid gland: midline isthmus, just below the cricoid cartilage (right lobe and left lobe)
- Thyroid cells are arranged in follicles and produce thyroid hormones
- Thyroid contains C cells that produce calcitonin (calcium metabolism)
- Thyroid hormones interact with their receptors in various organs regulating gene
expression and aspects of organ function
- Hypothalamus - TRH - pituitary - TSH - thyroid - thyroid hormones - negative feedback on
hypothalamus and pituitary
1 Adapted from Lectures at the University of Leeds Medical School
, Medic_Summaries (IMS) Topic 6
Calcium metabolism: controlled by four parathyroid glands sitting behind the thyroid
- Other organs involved in calcium metabolism:
- Kidneys: calcium excretion and production of active vitamin D
- Gut: absorption of calcium
- Bone: storage of calcium
- Thyroid
Adrenal glands: adrenal cortex and medulla
- 90% of the gland is ADRENAL CORTEX and produces:
- Corticosteroids (cortisol)
- Androgens (male hormones)
- Mineralocorticoids (aldosterone)
- Secretion is not controlled by the pituitary (RAAS system - related to BP)
- 10% of the gland is ADRENAL MEDULLA and produces:
- Catecholamines (adrenaline, noradrenaline, dopamine)
- Secretion is not controlled by the pituitary (related to BP)
The reproductive system: ovaries/testes
- Ovaries:
- Situated in the pelvis, either side of the uterus
- Contain follicles, each containing an oocyte at different stages of maturation
- Hypothalamus - GnRH - pituitary - FSH/LH - ovaries - progesterone:
- Switched on = oestradiol
- Switches off = inhibin
- Testes:
- Adults, found in the scrotum, except minority (testicular maldescent)
- Interstitial/leydig cells (produce TESTOSTERONE)
- Seminiferous tubules (germ cells producing SPERM)
- Sertoli cells (help in SPERM production and produce INHIBIN)
- Hypothalamus - GnRH - pituitary - FSH/LH - testis - inhibin: sertoli cells or testosterone -
Leydig cells
Clinical abnormalities:
- Hormonal over-secretion (primary/secondary)
- Hormonal under-secretion (primary/secondary)
- Tumour/nodules in the gland without affecting hormone secretion
Static tests: diagnose abnormalities of thyroid and sex glands
- Primary hyperthyroidism (thyroid hormone overproduction)
- Test for thyroid hormones T3 & T4, and TSH
- T3 and/or T4 increase with suppressed undetectable TSH
Stimulation tests: for suspected hormonal under-secretion, static test not enough
- ACTH to test for adrenal insufficiency (SYNACHTEN TEST)
- Failure to respond leads to gland failure
- Glucagon stimulation/insulin stress test for pituitary failure (test for ACTH/GH response)
Suppression test: for some hormonal over-secretion
- Giving steroids and testing for endogenous steroid production
- External steroids should switch off internal steroid production
- Giving glucose and testing GH secretion (glucose switches off GH secretion normally)
Disease of the endocrine glands:
- Over-secretion: usually benign tumours
- Under-secretion: gland destruction due to:
- Inflammation (autoimmune conditions)
- Infarction
- Other
- Tumour/nodules with normal hormone production
2 Adapted from Lectures at the University of Leeds Medical School
Endocrinology
Endocrine glands: hypothalamus/pituitary, thyroid, parathyroid, pancreas, adrenal, ovaries/testes
Hypothalamic-pituitary axis: connection between the two; hypothalamus CONTROLS pituitary
Pituitary gland:
- CONTROLS most glands in the body
- Two lobes:
- Anterior pituitary: PRODUCES various hormones
- Posterior pituitary: STORES hormones
Anterior pituitary produces hormones:
- Growth hormone (GH) - for skeletal growth
- Adrenocorticotrophic hormone (ACTH) - stimulates testicles/ovaries to make sex hormone
- Thyroid stimulating hormone/thyrotrophin (TSH) - stimulates thyroid make thyroid hormone
- Prolactin (PRL) - stimulates breast milk production
Posterior pituitary: stores hormones produced in hypothalamus (does NOT produce them)
- Antidiuretic hormone (ADH) - stimulates water reabsorption by the kidneys
- Oxytocin - helps uterine contractions during labour
Pituitary gland is under the control of the hypothalamus:
- Corticotrophin releasing hormone (CRH) - stimulates ACTH secretion - adrenal (steroids)
- Growth hormone releasing hormone (GHRH) - stimulates GH secretion
- Thyrotrophin releasing hormone (TRH) - stimulates TSH secretion - thyroid (T3 and T4)
- Gonadotrophin releasing hormone (GnRH) - stimulates FSH and LH secretion - ovaries/
testes - sex hormones
- Prolactin releasing hormone does not exist as prolactin is under the INHIBITORY effect of
the hypothalamus
Switching pituitary hormones:
- Cortisol: switches off ACTH and CRH
- Growth hormone: switches off GH and GHRH
- Thyroid hormones: switches off TSH and TRH
- Sex hormones: switch off FSH/LH and GnRH
- NEGATIVE FEEDBACK
Glands NOT controlled by the pituitary:
- Adrenal medulla: produce adrenaline and noradrenaline
- Parathyroid: controls calcium levels
- Pancreas: controls sugar levels
- Gut hormones
Thyroid gland: midline isthmus, just below the cricoid cartilage (right lobe and left lobe)
- Thyroid cells are arranged in follicles and produce thyroid hormones
- Thyroid contains C cells that produce calcitonin (calcium metabolism)
- Thyroid hormones interact with their receptors in various organs regulating gene
expression and aspects of organ function
- Hypothalamus - TRH - pituitary - TSH - thyroid - thyroid hormones - negative feedback on
hypothalamus and pituitary
1 Adapted from Lectures at the University of Leeds Medical School
, Medic_Summaries (IMS) Topic 6
Calcium metabolism: controlled by four parathyroid glands sitting behind the thyroid
- Other organs involved in calcium metabolism:
- Kidneys: calcium excretion and production of active vitamin D
- Gut: absorption of calcium
- Bone: storage of calcium
- Thyroid
Adrenal glands: adrenal cortex and medulla
- 90% of the gland is ADRENAL CORTEX and produces:
- Corticosteroids (cortisol)
- Androgens (male hormones)
- Mineralocorticoids (aldosterone)
- Secretion is not controlled by the pituitary (RAAS system - related to BP)
- 10% of the gland is ADRENAL MEDULLA and produces:
- Catecholamines (adrenaline, noradrenaline, dopamine)
- Secretion is not controlled by the pituitary (related to BP)
The reproductive system: ovaries/testes
- Ovaries:
- Situated in the pelvis, either side of the uterus
- Contain follicles, each containing an oocyte at different stages of maturation
- Hypothalamus - GnRH - pituitary - FSH/LH - ovaries - progesterone:
- Switched on = oestradiol
- Switches off = inhibin
- Testes:
- Adults, found in the scrotum, except minority (testicular maldescent)
- Interstitial/leydig cells (produce TESTOSTERONE)
- Seminiferous tubules (germ cells producing SPERM)
- Sertoli cells (help in SPERM production and produce INHIBIN)
- Hypothalamus - GnRH - pituitary - FSH/LH - testis - inhibin: sertoli cells or testosterone -
Leydig cells
Clinical abnormalities:
- Hormonal over-secretion (primary/secondary)
- Hormonal under-secretion (primary/secondary)
- Tumour/nodules in the gland without affecting hormone secretion
Static tests: diagnose abnormalities of thyroid and sex glands
- Primary hyperthyroidism (thyroid hormone overproduction)
- Test for thyroid hormones T3 & T4, and TSH
- T3 and/or T4 increase with suppressed undetectable TSH
Stimulation tests: for suspected hormonal under-secretion, static test not enough
- ACTH to test for adrenal insufficiency (SYNACHTEN TEST)
- Failure to respond leads to gland failure
- Glucagon stimulation/insulin stress test for pituitary failure (test for ACTH/GH response)
Suppression test: for some hormonal over-secretion
- Giving steroids and testing for endogenous steroid production
- External steroids should switch off internal steroid production
- Giving glucose and testing GH secretion (glucose switches off GH secretion normally)
Disease of the endocrine glands:
- Over-secretion: usually benign tumours
- Under-secretion: gland destruction due to:
- Inflammation (autoimmune conditions)
- Infarction
- Other
- Tumour/nodules with normal hormone production
2 Adapted from Lectures at the University of Leeds Medical School
