Endocrinology Flashcards
Define endocrinology
The study of hormones (and their gland of origin), their receptors, the intracellular signalling pathways, and their associated diseases
Describe functions of endocrine system
Rapid adaptive changes
Integration of whole body physiology
Chronic maintenance of metabolic environment
Communication for multi-cellular organisms
Define endocrine gland
These glands release secretions directly into the blood stream, without ducts
Give example of endocrine glands
Thyroid
Adrenal cells
Beta cells of pancreas
Define exocrine gland
These glands ‘pour’ secretions through a duct to site of action
Give example of exocrine glands
Submandibular
Parotid
Pancreas
(Amylase and lipase)
Where do endocrine hormones act?
Blood-borne, acting at distant sites
Where do paracrine hormones act?
Acting on nearby adjacent cells
Where do autocrine hormones acts?
Feedback on same cell that secreted hormone (acts on itself)
Describe differences between water-soluble and fat-soluble hormones
Water-soluble: Transported unbound Bind to surface receptor on cells Have a short half-life Are cleared fast
Fat-soluble: Transported bound to protein Diffuse into cells Have a long half-life Are cleared slowly
Give example of water soluble hormone
Peptides and monoamines - both stored in vesicles before secretion
Give example of fat soluble hormone
Thyroid hormones
Steroids
*Synthesised on demand
Give examples of hormone classes
Peptides e.g. insulin
Amines e.g. dopamine, adrenaline, noradrenaline
Iodothyronines
Cholesterol derivatives and steroids
Describe how insulin works on insulin receptors
Binds to insulin receptors. Results in the phosphorylation of the receptor and activation of secondary messenger - TYROSINE KINASE. Phosphorylation of signal molecules. Cascade of effect. Glucose uptake.
Give example of a peptide hormone
Insulin
Describe features of peptide hormones
Hydrophilic
Water soluble
Released in pulses or bursts
Cleared by tissue or circulating enzymes
Give product and reactant in synthesis, packaging of peptide hormones. Also give form in storage and secretion
Synthesis: Preprohormone -> Prohormone
Packaging: Prohormone -> Hormone
Storage: Hormone
Secretion: Hormone
Give example of amines
Dopamine
Adrenaline
Noradrenaline
Give order of chemicals that lead to formation of adrenaline
Phenylalanine L-Tyrosine L-Dopa Dopamine Noradrenaline Adrenaline
What breaks Noradrenaline down into Normetanephrine?
Catechol-O-methyl transferase (COMT)
What also breaks down Adrenaline into Metanephrine?
COMT
Catechol-O-methyl transferase
What can measurements of Normetanephrine and Metanephrine in serum be used for?
Act as indicators of noradrenaline or adrenaline activity
What is result of Adrenaline/Noradrenaline binding to alpha receptors?
Vasoconstriction
Bowel muscle contraction
Sweating
Anxiety
What is result of Adrenaline/Noradrenaline binding to beta receptors?
Vasodilation
Increased Heart Rate
Increased force of contractility
Relaxation of bronchial smooth muscles
What do iodothyronines bind to in blood?
Most is bound to THYROID-BINDING GLOBULIN (TBG)
Not soluble in water
What is T3 also known as?
Triiodothyronine
What is T4 also known as?
Thyroxine (less active than T3 but more produced)
What makes up iodothyrosines?
Incorporation of iodine on tyrosine molecule on thyroglobulin
What is made from conjugation of iodotyrosines and where are these products stored?
Gives rise to T3 and T4
Stored in Colloid bound to thryoglobulin
What is effect of TSH on thyroid?
Stimulates the movement of colloid into secretory cell
T3 and T4 cleaved from thyroglobulin
True or False:
Most T3 is made from breakdown of T4 to T3, which is converted OUTSIDE the thyroid gland
True
T4 can be thought of as a Reservoir for additional T3
How is Vitamin D transported and where on the cell does it act
Transported by vitamin D binding protein
Fat soluble and enters cell directly to bind to nucleus and stimulate mRNA production
Give example of steroid hormones/cholesterol derivates
Vitamin D Adrenocortical and Gonadal steroids e.g. Cortisol Aldosterone Testosterone Oestrogen Progesterone
What % of adrenocortical and gonadal steroids are protein bound?
95%
How does steroid hormone bind to cell receptor and what is effect?
Diffuses through plasma membrane and binds to cytoplasm receptor.
Receptor-hormone complex then enters nucleus, where it binds to Glucocoticoid Response Element (GRE).
Binding initiates transcription of gene to mRNA.
mRNA directs protein synthesis.
What hormone receptors are found on cell surface?
Peptides e.g. insulin
What hormone receptors are found in cytoplasm
Steroids, e.g.: Glucocorticoids e.g. cortisol Mineralocorticoids e.g. aldosterone Androgens e.g. testosterone Progesterone
What hormone receptors are found at nucleus?
Thyroid hormones
Oestrogen
Vitamin
**What are different hormone secretion patterns?
Continuous release e.g. prolactin (inhibited by dopamine)
Pulsatile (multiple pulses throughout the day) e.g. insulin
Circadian rhythm e.g. ACTH, prolactin, GH, TSH and cortisol
Give example of continuous hormone secretion
Prolactin (inhibited by dopamine)
Give example of pulsatile hormone secretion
Insulin
What is effect of Somatostatin on growth hormone
Inhibits growth hormone, along with GHRH
What hormone helps regulate circadian rhythms
Melatonin
Where is melatonin secreted from?
Pineal gland
What parts of brain regulates your Circadian Rhythm?
Hypothalamus
What is your Circadian Rhythm
24-hour internal clock that is running in the background of your brain and cycles between sleepiness and alertness at regular intervals
What is meant by hormone receptor down regulation?
Hormone secreted in large quantities causes down regulation of its target receptor
(Down regulation = decrease in cellular component)
Up regulation is opposite
What is synergism?
Give example
Combined effects of two hormone amplified
e.g. glucagon with adrenaline - both released when hypoglycaemic to increase sugar levels
What is antagonism?
Give example
One hormone opposes other hormone
e.g. glucagon (raises glucose levels) antagonises insulin (reduces glucose levels)
Pituitary Anatomy: What is found lateral and next to the pituitary gland
Cavernous sinuses
Pituitary Anatomy: What is found in the cavernous sinus
(Intracavernous) Carotid artery Cranial nerves: Oculomotor III Trochlear IV Abducent VI Ophthalmic V1 Maxillary V2
Pituitary Anatomy: What sinus is found directly inferior to pituitary gland?
Sphenoid sinus
Pituitary Anatomy: What part of optic pathway is found directly superior to pituitary gland?
Optic chiasm
Pituitary Anatomy: Describe the location of pituitary gland
Lies in a pocket of sphenoid bone called the pituitary fossa at the base of the brain, just below the hypothalamus and inferior to the optic chiasm
Why can a pituitary tumour (e.g. acromegaly) lead to vision problems?
Causes pressure on optic chiasm
Can result in a hemianopia
What visual field defect can result from a pituitary tumour
Bitemporal Hemianopsia
pressure on optic chiasm
What visual fields are defective in bitemporal hemianopsia?
Both outer halves of the visual field
Medial halves of retina are defective so outer halves of visual field are not seen
Pituitary Anatomy: What connects the hypothalamus to the pituitary gland?
Infundibulum (or pituitary stalk)
What are the 2 pituitary glands?
Anterior pituitary gland (aka Adenophysis)
Posterior pituitary gland (aka Neurohypophysis)
What is contained in the infundibulum?
Axons from neurones in hypothalamus
Small blood vessels
What type of hormones are secreted by hypothalamus to act on anterior pituitary gland?
Hypophysiotropic hormones
**What nuclei in the hypothalamus send axons to the posterior pituitary gland?
Supraoptic
Paraventricular (more posterior)
How do hypophysiotropic hormones from the hypothalamus reach the anterior pituitary gland?
Hypothalamo-Hypophyseal Portal Vessels/Veins
Name hypophysiotropic hormones released from the hypothalamus that act on the anterior pituitary gland
Corticotropin-Releasing Hormone CRH Growth Hormone Releasing Hormone GHRH Thyrotropin-Releasing Hormone TRH Gonadatropin-Releasing Hormone GnRH Dopamine DA
What hormones are released by the anterior pituitary
Adrenocorticotropic hormone ACTH (aka corticotrophin)
Growth hormone GH (aka somatotropin)
Thyroid Stimulating Hormone TSH (aka thyrotropin)
Luteinising hormone LH
Follicle Stimulating Hormone FSH
Prolactin
What is effect of Corticotropin-releasing hormone (CRH) on anterior pituitary?
Stimulates the release of Adrenocorticotropic hormone (ACTH)
What is effect of Growth Hormone Releasing Hormone (GHRH) on anterior pituitary?
Stimulates the release of growth hormone (GH)
What is effect of Thyrotropin-releasing hormone (TRH) on anterior pituitary?
Stimulates the release of thyroid stimulating hormone (TSH)
What is effect of Gonadatropin-releasing hormone (GnRH) on anterior pituitary?
Stimulates the release of Luteinising hormone (LH) and Follicle-stimulating hormone (FSH)
What is effect of Dopamine (DA) on anterior pituitary?
INHIBITS the release of prolactin
What would be the effect on prolactin levels if the infundibulum was damaged or destroyed?
Prolactin is under negative control by dopamine thus if the pituitary connecting stalk/infundibulum was destroyed then that would result in an
increase in the secretion of prolactin as its negative
pressure (dopamine) would not be able to reach it
True or False:
The anterior pituitary gland has an arterial blood supply
False
Anterior pituitary gland has no arterial blood supply
Where does the anterior pituitary gland receive its blood supply?
Through a portal venous circulation from the hypothalamus:
Hypothalamo-hypophyseal portal vessels/veins
What is a benefit of the Hypothalamo-hypophyseal portal vessels/veins supplying blood from the hypothalamus to anterior pituitary gland?
This local blood system provides a mechanism for hormones of the hypothalamus to directly alter the activity of the cells of the anterior pituitary
gland -
*Bypassing the general circulation and thus efficiently regulating hormone release from that gland
How many types of hormone producing cells are there in anterior pituitary?
5 types (produces 6 hormones in total)
What type of hormones are produced by anterior pituitary?
Peptide hormones
Name the 5 types of hormone producing cells of anterior pituitary
Gonadotrophs Corticotrophs Thyrotrophs Lactotrophs Somatotrophs
What cells of the pituitary gland produce Growth Hormone?
Somatotrophs
of anterior pituitary
What cells of the pituitary gland produce Prolactin?
Lactotrophs
of anterior pituitary
What cells of the pituitary gland produce Thyroid-stimulating hormone (TSH)?
Thyrotrophs
of anterior pituitary
What hormone is produced by Corticotrophs of anterior pituitary gland?
Adrenocorticotropic hormone (ACTH)
What hormones are produced by Gonadotrophs of anterior pituitary gland?
Follicle-stimulating hormone (FSH) Lutenizing hormone (LH)
What is effect of FSH and LH in female?
Targets the gonads and stimulates gonad cell development (females = ovum; males = sperm)
FSH stimulates oestrogen release
Oestorgen also causes a positive feedback effect to stimulate release of more FSH and LH
LH stimulates the release of the egg which in turn stimulates progesterone release
Progesterone release results in increased thickening of uterine wall
What is effect of FSH and LH in male?
LH stimulates testosterone production from Leydig cells (interstitial cells of testes)
FSH stimulates testicular growth and enhances the production of an androgen-binding protein by the Sertoli cells, which are a component of the testicular tubule necessary for sustaining the maturing sperm cell.
What can be measured to reflect levels of GH in the body?
IGF-1