Introduction to endocrinology Flashcards
What do hormones control?
- the rate of enzymatic reactions
- transport of ions or molecules across cell membranes
- gene expression and protein synthesis
How are hormones terminated?
Enzymes that are always present in the plasma can degrade peptide hormones bound to cell membrane receptors
Intracellular enzymes can metabolise hormones in cells
In some cases the receptor hormone complex is brought into the cell by endocytosis
What is endocytosis?
Endocytosis is a cellular process in which substances are brought into the cell. The material to be internalised is surrounded by an area of cell membrane, which then buds off inside the cell to form a vesicle containing the ingested material
Inactive broken down metabolites are then excreted in the bile or urine
What is the half life of a hormone?
Indicates length of activity- amount of time required to reduce a hormone concentration to half
What are the 3 main types of hormone?
Peptide/protein hormones
Steroid hormones
Amine hormones
What are amine hormones derived from?
Derived from amino acids= either tryptophan or tyrosine
What is an example of a amine hormone made of tryptophan?
Melatonin, made in the pineal gland
What hormones are tyrosine amine hormones and how do they differ?
Catecholamines which have a one ring structure and thyroid hormones which have a two ring structure
What are examples of catecholamines?
Adrenalin, noradrenalin and dopamine
Where do catecholamines and thyroid hormones bind to?
- Catecholamines= bind to membrane structures
- Thyroid hormones= bind to intracellular receptors that activate genes
How are catecholamines and thyroid hormones formed?
Where are steroid hormones derived from?
Cholesterol
Where are steroid hormones produced and what are examples?
The adrenal cortex (outer portion of adrenal gland). Aldosterone and cortisol
Gonads= oestrogen, progesterone and androgens
What do cells that produce steroid hormones usually have?
A large amount of smooth ER (endoplasmic reticulum) which is responsible for synthesis of cholesterol
How do steroid cells move in and out of cells?
They are lipophilic and can move via simple diffusion
What is the rate of action for steroid hormones?
Slow- half life can be years
Where do steroid hormones bind to?
They bind to cytoplasmic or nuclear receptors. Control DNA synthesis
In what case can steroid hormones initiate a faster pathway?
- Several steroid hormones, including oestrogen and aldosterone have cell membrane receptors linked to signal transduction pathways (like peptide hormones)
- These allow steroids to initiate rapid non genomic responses in addition to their slower genomic effects
How are steroid hormones transported around the blood?
Steroid hormones are lipophilic and thus, are usually transported in the plasma bound to a serum binding protein, such as albumin- or sex hormone–binding globulin
What do peptide or protein hormones start as?
They start as a preprohormone (large and inactive). Once they undergo post-translational modification they are changed into prohormones and later become peptide hormone
How are peptide hormones formed?
Step 1.5- the pro hormone is contained within a transport vesicle which then fuses to the Golgi complex
What is the half life of a peptide hormone?
Short half life- minutes
Are peptide hormones water soluble?
Yes
What do peptide hormones bind to?
Binds to membrane receptors- unable to diffuse through and enter cells.
Most initiate a response through cyclic AMP messenger systems
What are examples of peptide hormones?
ADH, CCK, oxytocin and leptin
What is the order of hormone reflex pathways?
Stimulus ⇒ Afferent signal ⇒Integration of the signal⇒ Efferent signal (the hormone) ⇒ Physiological action ⇒ Negative feedback
What is the reflex pathway for parathyroid hormone?
What is the hormone reflex pathway for insulin?
What is a neurohormone?
A chemical secretion released into the blood from a neurone
What are two endocrine structures found in the brain?
Pineal gland and pituitary gland, have an influence on emotion hormone secretion and function
What is the anatomy of the pituitary gland?
Connected by a thin stalk (infundibulum) to the hypothalamus
Has an anterior and a posterior part to it
What are alternate names for the anterior and posterior pituitary parts of the gland?
Anterior pituitary = adenohypophysis Posterior pituitary = neurohypophysis
What hormones does the posterior area of the pituitary gland release?
Releases vasopressin (Anti-diruretic hromone, ADH- regulates water balance in the kidneys) and oxytocin (released during uterine contractions for childbirth and released to allow ejection of breast milk)
How do hormones from the brain pass into the bloodstream via posterior pituitary?
What are the 6 major hormones released by the anterior pituitary?
- Prolactin
- Thyrotropin (Thyroid Stimulating hormone) (TSH)
- Adrenocorticotropin (Adrenocorticotropin hormone-ACTH)
- Growth hormone (GH)
- Follicle stimulating hormone (FSH)
- Luteinizing hormone (LH)
What is a topic hormone?
A hormone that controls the secretion of another hormone
How do the anterior and posterior parts of the pituitary differ?
The clusters of cells that produce the six anterior pituitary hormones are under hypothalamic control. Unlike the posterior pituitary which basically stores hormones produced by the hypothalamus, the hypothalamus regulates the anterior pituitary via secreting “releasing or inhibiting hormones” (topic hormones)
What are the 3 levels of stimulation involving the anterior pituitary?
- Hypothalamic stimulation—from CNS
- Pituitary stimulation—from hypothalamic trophic hormones
- Endocrine gland stimulation—from pituitary trophic hormones
What are long loop and short loop feedback pathways related to the hypothalamus- anterior pituitary hormones?
- Long-loop feedback= Hormone released from final target cell feeds back to suppress anterior pituitary and hypothalamic hormones
- Short-loop feedback= Pituitary hormones feed back to suppress hypothalamic hormone
What is the portal system related to the pituitary?
The hypophyseal portal system
What is the advantages of a portal system to the pituitary gland?
- Allows small amount of hypothalamic trophic hormone to elicit given response
- Less dilution of hormone
- Delivered directly to target
- Only a small number of neurosecretory neurons in hypothalamus can effectively control activity of anterior pituitary
What is the hypothalamic pituitary thyroidn axis (HPT)
Thyrotropin releasing hormone is released it stimulates pituitary to release thyroid stimulating hormone. Once it is released goes to thyroid gland
Thyroid hormones impact many different tissues
What is the hypothalamic pituitary adrenal axis? (HPA)
CRH= corticotrophic releasing hormone from hypothalamus releases ACTH= adreno-corticotrophic hormone from the pituitary which acts upon the adrenal cortex to release cortisol
What is the hypothalamic pituitary gonadal axis?
gonadotrophin releasing hormone in hypothalamus causes follicle stimulating hormone and luteinising hormone from pituitary which acts on the gonads to produce androgens, oestrogen and progesterone.
What hypothalamic hormone inhibits and triggers prolactin release from the pituitary?
Dopamine= inhibits
Thyrotropin releasing hormone= stimulates
What is synergism?
When more than one hormone that produces the same function is released, the effects are not additive (the simple sum of the effects of the chemicals acting independently) but potentiated or synergistic (greater than additive).
What does synergism effect?
Hormones as well as pharmacological substances
What is permissiveness?
A hormone cannot fully exert its effects unless a second hormone is present
What are examples of permissiveness of hormones?
- Example= Thyroid hormone is responsible for epinephrine efficacy.
- Example 2= for sexual maturation to occur, thyroid hormone must be present, otherwise just having the reproductive hormones (GnRH, steroid hormones, ect) will not result in sexual development, and neither will just having thyroid hormones.
What is an example of synergism?
Glucagon from pancreas is primarily responsible for elevating blood glucose levels however so does cortiol and epinephrine.
What is hormone antagonism?
Action of one hormone opposes effects of another hormone
What are the different ways antagonism works?
- Hormones with antagonistic actions may:
- Compete for same receptor
- Act through different metabolic pathway- Glucagon and insulin
- Decrease number of receptors for opposing hormone- Growth hormone decreases number of insulin receptors
What are the 3 main endocrine pathologies?
- Hormone excess
- Hormone deficiency
- Abnormal responsiveness of target tissue to hormone
What are the main causes of hyper secretion?
Benign tumours
Cancerous tumours
Non-endocrine tumours
Iatrogenic
What are the issues with providing exogenous cortisol?
May exceed normal amount of hormone
Causes risk of atrophy in tissues such as hypothalamus, anterior pituitary
Cells shrink and lose their ability to produce hormones that lead to cortisol production
What is down regulation in hormones?
if hormone secretion is high for an extended period of time target cells may downregulate or decrease their number of receptors to diminish their reaction
What are causes of abnormal responsiveness of target tissues to hormones?
Transduction abnormalities- when a mutation alters the protein sequence of a receptor, and the cellular response can be changed, absent or non-functional
Can also get mutated receptors passed down genetically
Also down regulation can cause it
What is the archetypal hypothalamus-pituitary feedback circuit?
How do hypothalamic releasing hormones get to the posterior and anterior pitutiary?
Anterior= blood supply from medial eminence (portal system)
Posterior= hypothalamic axons
What hormones does the posterior pituitary release?
Oxytocin and vasopressin which are stored and released in response to neural stimulation
What are the 5 main types of hormone released from the anterior pituitary>
Somatotrophs
Gonadotrophs
Corticotrophs
Thyrotrophs
Lactotrophs
What are different types of gonadotroph?
Follicle stimulating hormone and Luteinizing hormone
What is an example of a corticotrophin hormone?
Adrenocorticotropic hormone
What is an example of a thyrotroph?
Thyroid-stimulating hormone
What is an example of a lactotroph?
Prolactin
What is an example of a somatotroph?
Growth hormone
What are the different types of endocrine tumours?
99% adenomas= A type of non-cancerous or benign tumour that may affect various organs. It is derived from the word “adeno” meaning ‘pertaining to a gland’
1% carcinoma= A type of cancer that starts in cells that make up the skin or the tissue lining organs, such as the liver or kidneys
What are the two types of adenoma?
Functional= making hormone in an uncontrolled fashion. Only one hormone produced
Non-functional tumour= does not produce hormone, larger. It traumatises the tissue around it and stops glands from producing hormones. Can affect glands producing multiple hormones.
What will happen to the levels of hormones if there is a target gland tumour?
If there is a hormone producing tumour, there will be high levels of target gland hormone, which increases feedback on hypothalamus and pituitary. That will lead to low levels of hypothalamic releasing and anterior pituitary hormones, which can be measured
What will happen to the levels of hormones if there is a pituitary tumour?
High levels of pituitary gland hormone
High levels of target gland hormones
Pituitary is unresponsive to the high levels of feedback, although the hypothalamus is- low levels of hypothalamic releasing hormone
What happens to the levels of hormones in primary end organ failure?
Low levels of target hormone, which reduces feedback, causing high levels of hypothalamic and pituitary hormone
How are hormones that have a short half life measured in the plasma?
measured by petrosal sinus sampling
What is dynamic function testing?
If a hormone is in excess, can test to see if it can be suppressed normally
If a hormone is deficient, can test to see if it can be stimulated normally
Which nucelus in the hypothalamus controls the release of oxytocin and which one controls the release of vasopressin?
The supraoptic nucleus makes vasopressin
The paraventricular nucleus makes oxytocin
