Endocrine Flashcards
(41 cards)
1
Q
Name the main endocrine glands?
A
- hypothalamus (brain).
- pituitary (brain).
- thyroid glands (neck).
- parathyroid glands (neck).
- adrenal glands (right and left: sit on upper pole of each kidney).
- pancreas.
- gonads (ovaries and testis).
2
Q
What do we know about pituitary gland (also known as hypophysis)?
A
- it’s known as the master gland.
- it regulates the secretion of many other endocrine glands.
- its located at the base of the brain close to nasal sinuses (surgeons approach this gland through nasal sinuses).
- it has an anterior and posterior lobe: secrete different hormones, they are connected to hypothalamus by the pituitary stalk.
3
Q
How many hormones are secreted by the anterior pituitary, and what are they?
A
- 6 hormones secreted.
- thyroid stimulating hormone (TSH).
- adrenocorticotrophin (ACTH).
- lutenising hormone (LH).
- follicle stimulating hormone (FSH).
- prolactin.
- growth hormone.
4
Q
How many hormones are secreted by the posterior pituitary, and what are they?
A
- 2 hormones secreted.
- both are produced in hypothalamic region of brain and travel down the pituitary stalk for storage and secretion from the posterior pituitary.
- oxytocin (responsible for uterine contractions during labour).
- anti-diuretic hormone (ADH) also known as vasopressin: (regulates water excretion by kidneys by opening or closing pores in renal collecting ducts).
5
Q
How many hormones do thyroid glands secrete, and what are they?
A
- they secrete 2 hormones.
- thyroxine (t4) and tri-iodothyronine (t3) (regulate basal metabolic rate).
6
Q
What are parathyroid glands, and what hormones do these glands secret?
A
- the parathyroid glands are four tiny glands, located in the neck, that control the body’s calcium levels.
- located on the back of the thyroid gland.
- they secrete parathyroid hormone which regulates calcium metabolism.
7
Q
Where are the adrenal glands located and what hormones do they secrete?
A
The adrenal glands sit on the upper pole of each kidney (2).
- they have two distinct regions: adrenal medulla (central) and adrenal cortex (outer).
- adrenal medulla: secretes the catacholamines adrenaline and noradrenaline - these regulate blood pressure. They evoke the “fright, flight and fight” response.
- adrenal cortex: secretes the steroid hormones cortisol, aldosterone and sex hormones.
8
Q
What is interesting about the pancreas and hormones does it excrete?
A
- its both an exocrine and endocrine gland.
- the bulk is an exocrine gland and it secretes digestive hormones via the pancreatic duct into the gastrointestinal tract.
- within body of the pancreas sit islets of cells known as the islets of langerhans, these are endocrine cells which secrete insulin and glucagon which together regulate blood glucose concentration.
9
Q
What are the types of hormones and how are they determined?
A
- the type of hormone is determined by its distinct biochemical structure.
- peptide: (chains of amino acids) include pituitary hormones, insulin, PTH.
- steroid hormones: (4 ringed structure) include cortisol, sex hormones.
- tyrosine derivatives: (derived from this amino acid) include thyroxine, adrenaline.
10
Q
When it comes to endocrine glands/hormonal secretions where are the target organs in comparison to the gland?
A
- distant from gland.
11
Q
Why do endocrine disorders arise?
A
- deficiency syndromes (destruction of gland or inherited defects).
- hormone excess (secretory tumours and inappropriate activation in glandular tissue).
12
Q
Give some examples of destruction of a gland causing a deficiency syndrome.
A
- autoantibodies: cause destruction of islets of langerhans in type 1 diabetes.
- infection: can destroy glands e.g. Destruction of adrenal glands by tuberculosis leading to adrenal insufficiency.
- trauma: patients with head injuries may suffer damage to pituitary gland.
- tumours: pituitary tumours, may be secretary or non secretory but if are secretory tend to secrete just one pituitary hormone and pressure of growing tumour on remainder of pituitary tissue results in deficiency of other pituitary hormones
13
Q
Give some examples of secretory tumours which can lead to hormone excess.
A
- benign; most people with insulin secreting tumours (insulinoma) are benign tumours.
- malignant/cancerous: case with patients with catecholamine secreting tumours (phaeochromocytomas).
- over growth of glandular tissue/hypertrophy: case in patients with high/excess aldosterone (hyperaldosteronism).
14
Q
What are clinical features of hyperthyroidism (thyrotoxicosis)?
A
- weight loss.
- heat intolerance (both this and the above are due to increased metabolism).
- swelling in neck (goitre).
- agitation.
- palpitations.
- diarrhoea.
- eyelid retraction.
- graves ophthalmopathy (eye bulge out of socket).
15
Q
Treatment for hyperthyroidism.
A
- antithyroid drugs - carbimazole and propylthiouracil.
- radioactive iodine - iodine taken up by the thyroid gland for incorporation into thyroid hormones and so radioactive iodine targets the thyroid gland and causes radiation damage and destruction of thyroid gland tissue.
- surgery - partial removal of thyroid gland tissue (probably done if severely enlarged).
16
Q
What are the clinical signs of hypothyroidism (myxodema)?
A
- weight gain.
- lethargy: cold intolerance.
- coarsening of features, dry hair.
- constipated.
- anaemia.
17
Q
What are hormones?
A
- chemical messengers that are secreted directly into the blood, which carries them to organs and tissues of the body to exert their functions.
- they are secreted into the blood stream from ductless glands (endocrine) in contrast to exocrine glands which secrete their hormones to the outside of the body using ducts.
- endocrine glands/hormonal secretions are distant from the target organ.
- hormones are used to communicate between organs and tissues to regulate physiological and behavioural activities such as digestion, metabolism and respiration.
17
Q
The glands that secrete hormones comprise …
A
- the endocrine signalling system.
18
Q
What is the exocrine system?
A
- the exocrine system is in contrast to the endocrine system.
- exocrine glands are glands that produce and secrete substances onto an epithelial surface by way of a duct.
- examples of exocrine glands include: sweat, salivary, mammary, lacrimal and mucous.
19
Q
How does peptide hormone synthesis take place?
A
- peptide hormones or their precursors - encoded by nuclear genes and synthesised within the cells cytosol by ribosomes.
- they are frequently produced as pro-hormones which require further processing often including cleavage/addition of glucose residues or protein folding (all take place in golgi apparatus) in order to produce active hormone.
- secretory granules within the cytosol store the peptide hormone/pro-hormone until it’s released from the cell by exocytosis in response to appropriate stimulus.
20
Q
How do peptide hormones exert their action on their target cells?
A
- they lock onto target cells via specific receptors.
- some receptors coupled to intracellular molecules known as G proteins (these are activated when a hormone molecule binds to its receptor).
- other receptors are able to phosphorylate intracellular proteins due to their intrinsic tyrosine kinase enzymatic activity.
- these actions trigger a cascade of protein activity sometimes known as 2nd messengers which may result in activation of enzymes or opening/closing of ion channels in the cell membrane or activation of transcription factors which induce transcription of genes.
21
Q
How does steroid hormone synthesis take place?
A
- in contrast to peptide hormones steroid hormones are not directly coded by genes.
- they are synthesised within the endocrine cell from precursor molecules e.g. cholesterol.
- this process requires production of synthetic enzymes and it’s these which are encoded in nuclear DNA.
- steroid hormones can pass out of the cell by diffusion and they are bound to transport proteins for transfer to their target tissue.
22
Q
How does steroid and thyroid hormone action differ from that of peptide hormone?
A
- these differ from peptide hormone in that they can diffuse into their target cells and bind to intracellular receptors.
- these in turn can carry hormone into the nucleus and bind directly to DNA where they act as a TF.
23
Q
What is the difference between steroid and thyroid hormones and peptide hormones.
A
- steroid and thyroid hormones: enter cell by diffusion and intracellular receptors transport hormone to nucleus.
- peptide hormones: cell surface receptors and intracellular proteins transduce signal to nucleus.
24
Once the endocrine cell has been stimulated to release the hormone how is secretion regulated?
- feedback!
25
Give examples of direct feedback.
- e.g. increase in blood glucose stimulates insulin release.
- decrease in blood glucose inhibits insulin release.
- decrease in blood calcium triggers the release of parathyroid hormone.
- increase in blood calcium suppresses the release of parathyroid hormone.
26
Many hormones are regulated by the pituitary gland in ...
- a -ve feedback loop.
27
What are the target organs of the 6 hormones secreted by the anterior pituitary gland?
- LH: targets gonads (affect sex hormone secretion and gametogenesis).
- FSH: targets gonads (affect sex hormone secretion and gametogenesis).
- GH: targets multiple organs (effects glucose and protein metabolism and tissue growth).
- TSH (thyroid stimulating hormone): targets thyroid (thyroxine).
- ACTH (adrenocorticotrophin): targets adrenals (cortisol).
- PRL (prolactin): targets breast (during pregnancy and lactation).
28
Each of the anterior pituitary hormones are regulated by releasing hormones secreted by the hypothalamic region of the brain, explain.
- GnRH released from hypothalamus regulates LH.
- GnRH released from hypothalamus regulates FSH.
- GHRH released from hypothalamus regulates GH.
- TRH released from hypothalamus regulates TSH.
- CRH released from the hypothalamus regulates ACTH.
- PRH released from the hypothalamus regulates PRL.
29
In addition to feedback regulation hormone secretion is also controlled by ...
- neuroendocrine reflexes and specifically signals from the cerebral cortex.
- e.g. Stress associated with increase secretion of ACTH and adrenal corticol hormones.
30
Some hormone secretion is also subject to diurnal rhythms, explain.
- cortisol provides one such example, secretion of cortisol is at its lowest around midnight when plasma levels are at trough levels as this time.
- cortisol secretion peaks in the morning between 6-8 am in someone with a normal sleep pattern.
31
Why do endocrine disorders arise?
- deficiency syndromes (inadequate secretion of hormones from particular glands).
- inherited defects which lead to endocrine deficiency.
- hormone excess.
32
Give some examples of how endocrine disorders come about due to deficiency syndromes.
- destruction of a gland (various mechanisms).
- autoantibodies: cause of destruction of islets of langerhans in type 1 diabetes.
- infection: can destroy glands e.g. destruction of adrenal glands by tuberculosis, leading to adrenal insufficiency.
- trauma: patients with head injuries may suffer damage to the pituitary gland.
- tumours: pituitary tumours, may be secretory or non-secretory BUT if are secretory tend to secrete just one of pituitary hormones and pressure of growing tumour on remainder of pituitary tissue results in deficiency of other pituitary hormones.
33
Give some examples of how endocrine disorders come about due to inherited defects.
- inherited defects in:
- gene encoding peptide hormone.
- gene encoding synthetic enzyme.
- hormone receptor.
- congenital absence of glandular tissue.
34
Give some examples of how endocrine disorders come about due to hormone excess.
- secretory tumours: benign, most people with insulin secreting tumours (insulinoma) are benign tumours. Malignant/cancerous, case with patients with catecholamine secreting tumours (phaeochromocytomas).
- overgrowth of glandular tissue/hypertrophy: case in patients with high/excess aldosterone (hyperalsteronism/cons syndrome).
35
Give an example of a cause of hormone excess inappropriate in glandular tissue.
- e.g. TSH receptor antibodies which are present in patients with Graves' disease: these are antibodies caused by an autoimmune disorder.
36
What are common causes of hyperthyroidism?
- Graves' disease: patients produce autoantibodies which bind to TSH receptors on the thyroid gland and activate thyroid hormone secretion BUT are not subject to +ve feedback regulation.
- toxic multinodular goitre: enlarged thyroid glands and multinodular can develop hyperthyroidism when some nodules within gland start secreting thyroid hormones (usually due to benign tumour within thyroid gland).
- toxic nodule: benign tumour, autoactivation of TSH receptor.
37
What do you seen in a thyroid function test of a patient with hyperthyroidism?
- high plasma thyroxine and tri-iodothyronine.
| - suppressed TSH.
38
What treatment would you give someone with hyperthyroidism?
- antithyroid drugs (carbimazole and propylthiouracil).
- radioactive iodine: iodine is taken up by the thyroid gland for incorporation into thyroid hormones and so radioactive iodine targets the thyroid gland and causes radiation damage and destruction of thyroid gland tissue.
- surgery: partial removal of thyroid gland tissue (probably done if severely enlarged).
39
What are the common causes of hypothyroidism?
- autoimmune destruction thyroid gland.
- post ablative hypothyroidism happens in patients who have been treated with radioactive iodine or in patients who have had thyroid surgery (often end up requiring thyroid hormone replacement).
- thyroid hormone secretion driven by TSH secretion from pituitary gland and hypothyroidism can result from pituitary insufficiency BUT uncommon cause of hypothyroidism.
40
In a test on a patient with hypothyroidism what would you expect to see?
- in patients with primary hypothyroidism due to disorders of thyroid gland typically the plasma thyroxine levels are low and the plasma TSH levels are higher due to absence of +ve feedback regulation of pituitary gland.
- raised TSH is a very sensitive indicator of thyroid insufficiency, used in neonatal screening.
