Lecture 21- Endocrine 1 Flashcards
What is a hormone?
-Chemical messengers secreted into blood or extracellular fluid by one cell that affect functioning of other cells -Specific hormones usually affect only a limited number of cells -i.e. they bind to specific receptors on or in target cells to elicit a response -chemical in blood stream that have an effect on tissues further away from where they are made =usually hormone secretion is at a distance from the target cells
What is an agonist and antagonist?
-An agonist is a chemical that binds to some receptor of a cell and triggers a response by that cell. Agonists often mimic the action of a naturally occurring substance. Whereas an agonist causes an action, an antagonist blocks the action of the agonist agonist=chemicals competing for the target cells antagonist=block or prevent the action of the hormone
What is a paracrine?
-secreting cells and target cells close together, goes into interstitial fluid and finds target cell
What is an autocrine?
-group of cells when stimulated release a chemical that stimulates the neighbouring cells or the same cells
What is a neurohormone?
-can have the neurons send a signal, release neurohormone that goes to distant target cell (noradrenalin)
What are the endocrine glands?
-
What are the hormone categories based on?
-chemical classification 1. Peptides and proteins=small proteins= peptides produced in cells in the normal production of proteins 2.Steroids=chemically and biochemically linked, one can be converted to other -fat soluble -gives them access to the cell easily by diffusion 3.Amino acid derivates=(amino acids can be used as neurotransmitters as well) 4.(Fatty acid derivatives and Eicosanoids) - Eg prostaglandins(=prostaglandins= also effect on bleeding and blood pressure) - Major precursor is Arachadonic acid)
How are peptide hormones synthesised?
- Pre-hormone (RER) 2.Prohormone (RER+ Golgi) 3. Hormone (Golgi) 4 storage vesicles 5. exocytosis
What is an advantage of the peptide hormones?
-major advantage: can be produced in such a package so a snot to be active (eg. trypsin) so first produced as pre prohormone -also can be active right away=once secreted by exocytosis (insulin) is active whereas other hormones are delivered to their target sites before changing to the active form
What are the two groups of hormones derived from the amino acid tyrosine?
- Thyroid hormones=basically a “double” tyrosine with the critical incorporation of 3 or 4 iodine atoms & half-life of a few days -one form more active than the other depending on the structure and the number of iodine atoms also varies in how long are they active for -typically thyroid hormones are active for a long time (days) 2.Catecholamines=include epinephrine and norepinephrine, which are used as both hormones and neurotransmitters= half-life a few minutes(active only for a few minutes)
How are steroids synthesised and secreted?
-Lipid-soluble: diffuse out of cell as they are secreted -structure based on cholesterol but changes to the structure vary a lot aldesterone= important in regulation of body fluids cortisol= stress response also important (fairly linked with aldesterone= some agonist response) -aldesterone and cortisol= similar sort of function just opposite -cortisol also have effect on water balance -only look at aldosterone and cortisol
How are hormones transported (general picture only)?
-have to be secreted from a cell, enter the circulation and then have to get into the target cell/s
Which of the classes have long term and which have short term action?
-short term action= peptides and catecholamines -long term action= thyroid hormones and steroids
How are peptide hormones transported?
-Water soluble, circulate in free form -Some exceptions eg Insulin-like Growth Factor 1 -once created they can just be secereted into the plasma as they are except for Growth Factor 1= needs binding for it to work
How are amine derivates transported?
–the amine der. can be in much higher levels as they can be bound to plasma proteins than if they were in water (as only a bit soluble) -CATECHOLAMINES=Water soluble, 50% circulate in free form, 50% loosely bound to plasma proteins -plasma proteins= albumin and globulins= needed to transport these -buffering effect as 50/50 in different condition when goes through kidney, not all cleared as some bound= gives dynamic as to how long the hormone stays in the circulation -THYROID HORMONE=Lipid soluble, mostly bound to plasma proteins -not water soluble -long term effects (days, weeks) thanks to being bound to the plasma proteins
How are steroid hormones transported in the body?
-Lipid soluble, 1% circulate in free form, 99% bound to plasma proteins -Only the free form is biologically active -1% are water soluble and active 99% like a reservoir (like cortisol= measuring have to look at bound and unbound)
How is endocrine activity controlled?
-endocrine gland produces the hormone (in one of the two forms) and is in the plasma, then activation occuring: (fluid balance) then going to the target cells doing what it’s supposed to -have negative feedback to the gland so it stops producing more -can have excretion in the kidney= inactivation -many hormones=excretion in kidney= inactivation of many hormones -epinephrine
What is desensitization (in control of endocrine activity)?
-Down regulation of receptors -hormone produced, then a number of receptors -the number can change= down regulation of receptors, continuous stimulation of receptors= like eating lot of glucose= lot of insulin= the receptors will be desenthysised
How do hormonal interactions control endocrine activity?
-permissivness:can trigger responses in the target cells, some cells may cause stimulation in tissues = more responsivness = permissiveness -synergism= when different hormones act even on different tissues but have similar effects -antagonistisc=when one hormone is balancing the activity of another
How do diurnal rhythms control endocrine activity?
-Light/dark -Sleep/awake -cortisol= have different level in the morning and evening = nocturnal will have it the opposite -connection with metabolism= when awake have to get it going! (cortisol= stress hormone, but also important in day to day life getting the metabolism going)
How does it happen that abnormal endocrine activity: Too low?
-hyposecretion -increase in clearance from blood -decrease in tissue responsivness =for example:Lack of receptors -thyroid is important for regulating metabolism expecially long-term regulation hypo= less being produces or higher clearance from blood -or decrease in tissue responsiveness due to lack of receptors dog: not as active, lethargic, different distribution of fat and skin problems= also connected to the lack of the thyroid hormone, and decrease in tissue responsiveness
How does it happen that abnormal endocrine activity: Too high?
-Hypersecretion (too much produced) -decerase in clearance from blood(slowing down of clearance in blood (kidney related issues possibly) -increase in free (biologically active hormone) =for example=Lack of plasma binding proteins -or not enough plasma proteins= liver makes them so maybe liver problem -we can be loosing them = can be parasite= worms -bleeding problem= loosing the plasma proteins that way
What is Cushing’s syndrome (hyperadrenocorticism)?
-higher than normal secretion of cortisol -become sensitive to high levels of starch (can’t cope with starch in diet= have to be low glycemic so it’s released slowly= the glucose)=disturbance to metabolism -disturbance to the reproductive system -skin can change due to the cortisol -long hair as it hasn’t molted(loss of hair in spring) =HORSE
How can endocrine activity be affected by genetic modification?
-abnormal activity can be due to genetic issues= can be naturally occuring but also transgenics -eg. extra growth hormone
How do water soluble hormones change their target cells?
- some=Alters channel permeability of pre-existing channel-forming proteins 2.Acts via second-messenger system to alter activity of pre-existing proteins
How do lipid soluble hormones change their target cells?
-Activates specific genes to cause formation of new proteins
What is cyclic AMP?
-used for intracellular signal transduction -messenger important in many biological processe
What hormones act via the cyclic AMP?
-when bind to the surface of the target cell=cyclic AMP is produced -Epinephrine and norepinephrine, glucagon, thyroid-stimulating hormone, calcitonin, antidiuretic hormone
What is protein kinase?
- kinase enzyme that modifies other proteins by chemically adding phosphate groups to them (phosphorylation). Phosphorylation usually results in a functional change of the target protein (substrate) by changing enzyme activity, cellular location, or association with other proteins.
Which hormones act via protein kinase?
-Insulin, growth hormone, oxytocin, erythropoietin
Which hormones act via calcium and/or phosphoinositides?
-Epinephrine and norepinephrine, angiotensin II, antidiuretic hormone, thyroid-releasing hormone
What is cyclic GMP?
-acts as a second messenger much like cyclic AMP. Its most likely mechanism of action is activation of intracellular protein kinases in response to the binding of membrane-impermeable peptide hormones to the external cell surface
What hormones act via cyclic GMP?
-Atrial naturetic hormone, nitric oxide -saw before NO= often in the circulatory regulation
How will the activation pathway of a fat soluble hormone look like?
-the lipid soluble hormone will not be looking for a receptor on the surface of the membrane but inside the cell
