Endocrine Flashcards
What are the major endocrine glands of the body?
Pituitary gland, thyroid gland, parathyroid gland, adrenal glands, pancreas, ovaries, testes
What are steroid hormones derived from?
Cholesterol
What is autocrine signalling?
When the cell produces signalling molecules which are released into the ECF and act on themselves to release more signalling molecules
What is paracrine signalling?
Cell produces signalling molecules which act on cells next to it
What is endocrine signalling?
signalling molecule is released into the ECF and enters the blood stream and travels a distance to the target cells
Which hormones act in a complementary way during exercise to prevent hypoglycaemia and hypokalaemia?
Glucagon, cortisol and Adrenaline
What is the role of Insulin?
Lowers plasma glucose levels by inhibiting hepatic glycogenolysis (breakdown of glycogen to glucose) and gluconeogenesis (formation of glucose) and stimulating glucose uptake into muscle and adipose tissue
What is the role of Glucagon?
Increases plasma glucose levels by stimulating hepatic glycogenolysis and gluconeogenesis.
Where does gluconeogenesis and glycogenolysis occur?
Liver
What is glucose stored as in the liver?
Glycogen
What type of hormone is adrenaline and how is it released into the body?
It is an amine hormone and is released into the ECF by a signal from calcium. It then enters the circulation and is hydrophillic in nature.
How does steroid storage differ from amine and polypeptide hormones storage?
Steroids are not stored- they are released right away and only synthesised when required. Amine and polypeptide are pre-made and stored waiting on a signal- this means they are faster at being released
Are steroid hormones hydrophillic or hydrophobic?
Hydrophobic- they must be bound to specialised transport proteins.
What are biologically active steroids?
The small percentage of steroid hormones that are not bound- they can cross capillary walls
Give examples of carrier proteins
Cortisol binding protein: binds cortisol in a selective manner (and some aldosterone)
Thyroxine binding globulin: binds thyroxine (T4) selectively and some T3
Sex steroid binding globulin: binds mainly testosterone and oestradiol
What is the role of Albumin?
It is a carrier protein that binds mainly steroids and thyroxine
Which carrier protein binds to hormones when there is a large surge, increasing plasma concentration?
Globulin
Where does corticotrophin releasing factor act on?
the anterior pituitary
Where does ACTH work on?
The adrenal cortex to secrete cortisol
What is the negative feedback of cortisol?
Cortisol can work on the anterior pituitary to stop producing ACTH and thus cortisol, or working on the hypothalamus to stop the release of corticotrophin releasing factor
What causes a positive effect on the hypothalamus to secrete more cortisol?
Physiological stress
Describe the pattern of production of cortisol
Diurnal variation- it peaks in the morning and steadily decreases until nighttime and then rises again
What is the half-life of Amine, protein/peptide and steroid hormones?
Amines: seconds
Proteins: minutes
Steroids: hours- due to extensive protein binding
How do amine hormones signal?
They act via G-protein coupled receptors
What hormones does the anterior pituitary produce?
ACTH, GH, FSH, LH, Prolactin, TSH
What hormones does the posterior pituitary produce?
ADH, Oxytocin
What hormone does the intermediate pituitary gland produce?
Melanotropic stimulating hormone
What hormones does the Parathyroid hormones produce?
Calcitonin and PTH
What hormones does the adrenal cortex produce?
Cortisol (glucocorticoids) and aldosterone
What hormones does the adrenal medulla produce?
Adrenaline and noradrenaline
Describe the processes leading to the secretion of T3 and T4
Thryotrophin releasing hormone is secreted in the hypothalamus and travels via the portal system to the anterior pituitary where it stimulates the thyroid stimulating hormone. TSH stimulates increased thyroidal iodine uptake by the thyroid and release of T3 and T4. T4 is converted to the biologically active T3 by TSH. T3 and T4 then enter cells and bind to nuclear receptors and promote increased metabolic and cellular activity.
What is the negative feedback of thyroid hormones?
The anterior pituitary and hypothalamus sense high levels of T3 and suppress TRH and TSH leading to reduced T3 and T4. If these levels get too low then TRH and TSH are secreted stimulating the thyroid to produce more T3 and T4.
What is primary hormone deficiency?
Due to a disease process in the endocrine end-organ which will lead to a loss of negative feedback and subsequent elevation in the corresponding anterior pituitary hormone
What is secondary gland failure?
There are low or inappropriately normal levels of the pituitary hormone in the face of a low end-organ hormone level e.g. Low T3 and T4 in the levels of a low TSH- pituitary disease should be suspected.
What does oversecretion and undersecretion of ADH cause?
Over: water retention and swelling
Under: dehydration
What does an oversecretion and undersecretion of growth hormone cause in children and adults?
Over: children- gigantism, adults- acromegaly
Under:dwarfism
What cells in the testes produce testosterone?
Leydig cells (in the presence of LH)
What is the role of LH in females?
it stimulates the release of the oocyte from the Graafian follicle and then develops it into the corpus luteum
What is the role of FSH in females?
stimulates the development of the follicle for ovulation
What is the role of FSH in men?
Spermatogenesis
What is the function of thyroxine?
regulates the basal metabolic rate of the cells in the body. it affects growth and functioning of the heart and nervous system, it stimulates growth and differentiation of tissue in a foetus and in children and it regulates body temperature
What is the role of aldosterone?
helps the uptake of sodium ions in the loop of henle in the kidneys and maintains salt balance
What does undersecretion of aldosterone cause?
Addisons disease
What does the beta, alpha and gamma cells secrete in the pancreas?
alpha- glucagon
Beta- insulin
Gamma- somatostatin
What happens in the sertoli cells?
Differentiation from germ cells into spermatazoa (caused by testosterone)
What is the role of progesterone?
prepares the endometrium for implantation once fertilisation of the egg cell has occurred. it is necessary for the production of the mucous plug to prevent sperm or other substances from entering the uterus during pregnancy.
What is the colloid?
it is a viscous fluid in the centre of the thyroid gland which contains thyroglobulin. When iodine binds to thyroglobulin, hormones are produced
What is T3 and T4 usually bound to?
Thyroxine binding globulus (TBG) or to albumin
Why type of thyroid hormone is biologically active?
T3
What causes a goitre?
When the T3 and T4 cannot be produced (may be due to iodine deficiency) then TSH is produced in increasing amounts. As a result of the hyperstimulation, thyroglobulin accumulates in the thyroid gland follicles increasing their deposits in the colloid which causes a goitre.
Why is iodine deficiency so important?
it is the primary cause of preventable mental retardation
What is neonatal hypothyroidism?
cognitive deficits, short stature, deafness and muteness in children and adults born to mothers who were iodine deficient during pregnancy
What is Calcitonin?
peptide hormone produced and secreted by the parafollicular cells of the thyroid gland that functions to decrease blood calcium levels. It is released in response to increased calcium levels.
How does Calcitonin function?
it decreases Calcium by:
inhibiting the activity of osteoclasts, increasing the activity of osteoblasts, decreasing Ca absorption in the intestines, increasing Ca loss in the urine
What are the 6 steps involved in the synthesis of iodine?
- Active transport: of iodide into follicular cells
- Thyroglobulin: large protein rich in tyrosine is placed in secretory vesicles
- Exocytosis: of thryoglobulin into follicular lumen where it is stored as colloid.
- Iodination: of thryoglobulin to form DIT and MIT.
- Coupling: of DIT with MIT to form T3 and DIT x2 to form T4
- Exocytosis: of iodinated thryoglobulin back into the follicular cell.
What is the treatment of hyperthyroidism?
Carbimazole
What is the treatment of hypothyroidism?
Thyroxine (T4)- it has a longer half life than T3
What is the infundibulum?
The stem that suspends the pituitary gland
What is the function of melanocyte stimulating hormone\?
Stimulates melanin formation in melanocytes
Does the posterior pituitary gland produce hormones?
No- it stores hormones that are made in the hypothalamus
Where is oxytocin produced?
The paraventricular nulcei in the hypothalamus
Where is ADH produced?
the supraoptic nucleus in the hypothalamus
What is the function of oxytocin?
When fetal development is complete, oxytocin stimulates uterine contractions and dilation of the cervix.
When is oxytocin released?
It is at high levels throughout pregnancy and increases during childbirth where it is continually released through a positive feedback system. It is also necessary for milk ejection.
How does oxytocin help with childbirth?
It promotes uterine contractions that push the foetal head to the cervix and in response, cervical stretching stimulates additional oxytocin to be stimulated by the hypothalamus which increases the intensity of the contractions and prompts additional dilation of the cervix.
What is the mechanism of action of ADH?
ADH causes reabsorption of water. in response to high blood osmolarity (which can be due to dehydration), the osmoreceptors signal the posterior pituitary to release ADH. Its effect is to increase epithelial permeability to water allowing increased water reabsorption
Explain negative feedback with ADH
As blood osmolarity decreases, the osmoreceptors sense the change and prompt a corresponding decrease in the secretion of ADH. As a result, less water is reabsorbed from the filtrate.
What is diabetes insipidus?
chronic underproduction of ADH that causes chronic dehydration. Symptoms are usually polydipsia and dysuria
What controls the release of growth hormone from the pituitary gland?
Somatostatin (GHIH) and GHRH
What is the glucose sparing effect?
It occurs when GH stimulates lipolysis or the breakdown of adipose tissue releasing fatty acids into the blood and so fatty acids is the main source of energy.
What is the Diabetogenic effect?
GH stimulates the liver to break down glycogen to glucose which is then deposited into the blood leading to a rise in blood glucose
How does growth hormone cause growth?
it triggers the liver and other tissues to produce IGF’s which enhance cellular proliferation and inhibit apoptosis or programmed cell death.
What acts on the anterior pituitary to produce growth hormone?
growth hormone releasing hormone
Explain the negative feedback of growth hormone
Growth hormone stimulates tissues to produce IGF’s but when there is too much, this is recognised by the hypothalamus which produces somatostatin (GHIH) to stop the production of GH.
What is the action of ACTH?
It stimulates the adrenal cortex to secrete corticosteroid and hormones such as cortisol
What regulates ACTH?
corticotrophin releasing hormone from the hypothalamus
What controls the secretion of ACTH?
hypothalamic-pituitary-adrenal axis
What happens when ACTH levels are low?
The hypothalamus releases CRH which acts on the anterior pituitary to release ACTH
How is Cortisol produced?
ACTH acts on the adrenal glands which stimulates the release of cortisol
What effect does increased cortisol have on ACTH?
Negative- increased cortisol it is noticed and the hypothalamus stops producing CRH which stops ACTH being released from the pituitary.
Which hormone initiates puberty?
gonadotrophin releasing hormone
GnRH stimulates the anterior pituitary to release which hormones?
FSH and LH
What is the function of FSH?
stimulates the production and maturation of sex cells including ova in women and sperm in men.
What is the function of LH?
triggers ovulation in women as well as the production of oestrogen and progesterone by the ovaries. LH stimulates the production of testosterone by the male testes.
What condition can cause too much ACTH?
Cushings disease- the most common cause of increased ACTH
How does FSH and LH contribute to the menstrual cycle?
At the end of the cycle, the hormones have both decreased and so the hypothalamus stimulates release of more FSH and LH which is released into the bloodstream. FSH will cause growth of the follicle in the ovary which produces oestradiol and inhibin. These are sensed by the hypothalamus and pituitary so less GnRH is released, and thus FSH and LH decrease
How does oestrogen manipulate the levels of LH and FSH
As the follicle in the ovary grows, more and more oestrogen is produced from the follicles, it stimulates a surge in LH and FSH which stimulates the release of an egg from a mature follicle e.g. ovulation
What happens after ovulation?
the ruptured follicle forms a corpus luteum that produces high levels of progesterone which inhibits FSH from being released. Towards the end of the cycle, the corpus luteum breaks down and progesterone stops and the next cycle begins as FSH starts to be produced again
What is hypergonadotropic hypogonadism?
When the gonads fail to create enough oestrogen, testosterone and/or inhibin which messes with FSH production and so FSH and LH rise
What are the effects of low FSH in women
leads to incomplete development at puberty and poor ovarian failure. in this situation, ovarian follicles do not form properly and do not release an egg causing infertility
What is Kallmann’s syndrome?
Delayed/absent puberty due to low FSH and impaired sense of smell
What is the role of LH in men?
stimulates leydig cells in the testes to produce testosterone
What is the role of LH in women?
in week 1-2 of mestruation, LH is required to stimulate oestradiol. Around day 14, there is a surge in LH levels which causes the ovarian follicle to tear and release a mature oocyte from the ovary e.g. ovulation. LH also stimulates the corpus luteum to produce progesterone (which supports fertilisation).
What hormone is responsible for ovulation?
LH (from oestradiol)
What can too much LH mean?
infertility (due to low levels of sex steroids)
What are the characteristics of PCOS?
high LH and reduced fertility
What is Klinefelters syndrome?
It is a male only disease when they have an extra X chromosome (XXY). They have small testes and so not secrete adequate levels of testosterone to support sperm production.
What is Turners syndrome?
It is a female only disorder caused by a partial or full deletion of an X chromosome. Ovarian function is impaired and LH may be high.
Where is Prolactin released from?
Lactroph cells in the pituitary gland
How does Dopamine influence prolactin release?
Dopamine restrains prolactin production so the more dopamine there is, the less prolactin is released
What is hyperprolactinaemia?
too much prolactin in the blood
Where does prolactin act on?
The mammary glands
What are the causes of hyperprolactinaemia?
Pregnancy, medications that reduce dopamine, thyroid underactivity and prolactinomas.
How are prolactinomas treated?
Most can be treated successfully with drugs that mimic the action of dopamine such as cabergoline
What is the primary cause of acromegaly?
too much growth hormone from a pituitary adenoma
What are the key diagnostic features of acromegaly?
coarsening of facial features, soft tissue and skin changes, carpal tunnel syndrome, joint pain and dysfunction, sleep apnoea and alterations in sexual functioning.
What is the diagnostic test for acromegaly?
OGTT (GH levels are measured after drinking sugar water. Normally, the pituitary would stop producing GH but a GH producing tumour won’t stop so levels will be unchanged)
A value of what confirms acromegaly?
If the lowest GH value during OGTT is above 1 microgram/L then acromegaly is confirmed.
Why can you not rely on GH levels for acromegaly?
because secretion of GH is pulsatile
What inhibits GH?
Glucose inhibits GH usually but not in acromegaly
What is the treatment of acromegaly?
Removal of the pituitary adenoma trans-sphenoidally
Is follow-up required for patients with acromegaly?
Yes- yearly GH, IGF-1, OGTT, visual fields and vascular assessment
What is Cushing’s syndrome?
When the body produces too much cortisol. it is usually caused by corticosteroid use
What is Cushing’s disease?
It is when there is too much ACTH producing too much cortisol from a pituitary adenoma
What are the features of cushings disease?
Abdominal/axillae striae, rapid and unexplained weight gain, skin changes such as bruising, acne, hair growth and red cheeks, memory loss, depression, mood and behaviour disorders, fatigue, muscle weakness, mensural cycle disorders, osteoporosis, high blood pressure, etc
What investigation is done in suspected Cushings disease?
a low dose dexamethasone test leads to no change in plasma cortisol
What is the treatment of Cushing’s Disease?
Selective removal of pituitary adenoma trans-sphenoidally
What does the Zona reticularis secrete?
Androgens
What does the Zona glomerulosa secrete?
Mineralcorticoids, mostly aldosterone
What does the Zona fasiculata secrete?
Glucocorticoids such as cortisol
What are the ACTH dependent causes of cushing syndrome?
Cushing’s disease and Ectopic ACTH production especially small cell lung cancer and carcinoid tumours
What are the ACTH independent causes of Cushing syndrome?
Adrenal adenoma/cancer, adrenal nodular hyperplasia, iatrogenic (steroids), McCune-Albright syndrome (rare)
What is diabetes inspidius?
metabolic disorder characterised by defective ability to concentrate urine in the kidneys result in the production of large quantities of urine.
What volume of urine would suggest diabetes insipidus?
> 3L/day
What is the cause of diabetes insipidus?
Usually due to low levels of ADH or resistance to its action in the collecting ducts
What are the clinical symptoms of Diabetes insipidus?
Polydipsia, polyuria and hypotonic urine
What investigations are carried out in diabetes insipidus?
Desmopressin test, urine osmolarity, serum osmolarity, water deprivation test
What is the treatment of diabetes insipidus?
1st line: desmopressin
2nd line: IV fluid management
What are the 4 types of diabetes insipidus?
Central- most common
nephrogenic
dipsogenic
pregnancy related
What is Desmopressin?
Synthetic ADH
What is the cause of central diabetes insipidus?
Damage to the pituitary gland or hypothalamus from head injury
What is nephorgenic diabetes insipidus?
the pituitary releases enough ADH into the body but the kidneys cannot respond to it. Can be caused by lithium, sickle cell disease or genetics.
What is the treatment for central diabetes insipidus?
desmopressin
What is the treatment for nephrogenic diabetes insipidus?
Anti-inflammatory medication such as indomethacin and bendorflumathiazide
What is dipsogenic diabetes insipidus?
excess fluid intake caused by a problem with the thirst mechanism or deliberately drinking too many fluids
How does hyperprolactinaemia present?
In women- missed periods
in men- erectile dysfunction