Pharmacology Flashcards
Describe the basic structure, synthesis,release and transport in Peptide hormones
Peptide hormones are formed from amino acid chains as long as 3 amini acids to complex hormones of 180 amino acids long.
They start with a gene which is transcribed into mRNAand translated into a protein in the ribosome. These are then attatched to a tubbular network that forms the Rough endoplasmic reticulum
The first structure formed is a preprohormone, this has a presignal that tells the molecule that it needs further processing. From here the signal peptide is cleaved and there is additional protein folding and disulfide bond formation.
This is then imported into the Golgi complex where furtherther processed as a prohormone to its final state. Bu the time it reaches the end of the Golgi complex, it is. packaged into secretory granules where it is stored until the arrival of an appropriate stimulus where they may leave via exocytosis.
Peptide hormones are hydrophilic, and because of this they simply dissolve in the aqueous environment so they do not need to be bound to the plasma proteins, but because of this they have a very short half-life of a few minutes as it is broken down by proteases
Describe and distinguish the basic structure, synthesis,release and transport, mechamism of hormone action in Steroid hormones
This is the formation of lipophilic substances. Cholesterol is taken as a basis and converted into a steroid hormone by a series of enzymatic reactions to give us a steroid. The hormone is lipophilic so it cannor be stored in an excretory granule as it would simply diffuse through the membrane.
As soon as it is synthesised, as it is lipophilic it will pass through the cell membrane via simple diffusion. In the blood it is not transported very well and so binds to carrier proteins. This is because the steroid hormones are highly lipophilic and the blood is an aqueous environment
The carrier proteins, protect the hormones from degradation and hence have a longer half-life of a few hours-days. We also need to bare in mind only the unbound or free hormone is biologically active
Explain the Physiological mechanisms involved in the regulation of hormone release including feedback control, the endocrine axis, neuroendocrine reflexes and diurnal rythms
Homeostasis is the maintenance of a constant internal environment and so is used as a mechanism to keep conditions in the body relatively constant.
One way this may occur is via feedback regulation
Another is via the endocrine axis where the Hypothalamus, peripheral endocrine glands are involved in the feedback regulation of hormone secretion.
Too high levels of peripheral hormone(The one that acts on targer cells) will have a direct and indirect inhibition via a negative feedback loop. The Hypothalamus is the indirect, the anterior pituitary is the direct inhibition
If levels are too low there is simply no inhibition on he anterior pituotary or hypothalamus
The diurnal ryhthm involces cortisol, Which is highest in the morning, supposedly after we wake up to make us alert for the day, so when this rhythm is disrupted
Describe the mechanisms by which endocrine disorders develop(Including autoimmune)
Endocrine disorders can be caused by Hypersecretion which can be as a result of a tumour or immunological factor such as Grave’s disease
Another reason for endocrine disorders is due to genetics,immunological attacks, destruction by disease or surgical removal.
Autoimmunity is where the body starts to attack itself which means we start to have the activation of the innate and adaptive immune systems. This OFTEN results in cellular damage, but not always like in the case of grave’s disease
There may also be a decrease in target-cell responsiveness at the level of receptor or even the downstreaming of the enzyme
The primary defect is release to the endocrine cell that makes the hormone, whereas the secondary defect could refer o the endocrine axis which regulates the endocrine gland
For example a defect at the Adrenal cortex would be primary but at the anterior pituitary would be regarded as a secondary defect.
Outline the types and ourposes of endocrine tests used in the invesigation of endocrine disorders
In order to investigate endocrine disorders there are a few methods we can use:
Single point baseline tests
Dynamic or provocative tests to check the integrity of the feedback control
Stumulation tests are used if we suspect hyposecretion. A failure to secrete indicates hormone insufficiency
Supression tests are used if we suspect Hypersecretion. Failure to supress indicates autonomous secretion, indicative of a tumour
Imaging is done as many endocrine disorders are due to the presence of a tumour
Summarise the principles of treatment of endocrine disorders
In the case of hormone defficiency, hormone reolacement is the general treatment method
In excess hormone producion, drugs which block production are used
If decreased target-cell responivesness - treat with drugs to enhance cellular respons to hormone.
If tumour - radoitherapy or surgery.
Desccribe the Mechanism of Hormone action in Peptide hormones
There are 2 receptors available for peptide hormones:
- G protein coupled receptors for hormones like glucagon
- Tyrosine Kinase receptors like insulin
These receptors are needed for proteins as they are hydrophillic syubstabces so they are required for the hormone to illicit Signal transduction which causes a physological response for example:
- Altered activity of enzymes or ion channels
- Alters expression of specific proteins
Desccribe the Mechanism of Hormone action in Steroid hormones
As steroid hormones are lipophilic when free, they can freely cross the lipid bilayer of the plasma membrane, as a result the majority of their action is via intracelluar receptors.
These nuclear receptors or cytosolic receptors act as hormone-regulated transcription factors
This allows them to either increase or decrease gene expression which increases the protein which the DNA codes for and hence proportionally efefcts the biological action of that protein
Describe the composition of cells types wihin pancreatic islet and state their hormone products
In the pancreatic islets, the cells are:
Alpha cells(30-40%) - which make glucagon
Beta cells(50-60%) - which make insulin
Delta cells(5-10%) - Which make somatostatin
PP cells(1-5%) - which make pancreatic polypeptide
Epsilon cells(Less than 1%) - which make Ghrelin
Briefly describe the steps involved in the biosynthesis of insulin
Insulin is initially made as Prepro-insulin which has 86 amino acis and contains a signalling molecule which indicates that more processing needs to be done. It then goes to the RER for the cleavage of this signalling unit to produce proinsulin in microvesicles. This goes into the Golgi clomplex where the C peptide is produced to produce mature insulin
The cleavage renders insulin less water soluble, so it can precipitate out of with zinc ions to form a dense crystalloid core within the secretory granule in order to pack alot of insulin into a small space.
Outline the control of insulin and glucagon secretion - including effects of nutrients, autonomic innervation and intrapancreatic and paracrine effects
The main regulator of insulin release is glucose, though there are a number of nutrient stimuli like amino acids and fatty acids in addition which can lead to insulin secretion
Gut hormones known as incretins which are secreted from cells in the small intestine after eating can engance the nutrient-stimulated insulin release, it secretes insulin almost in anticipation from the raised blood glucose from eating
Another potential cause for insulin secretion is islet glucagon which is secreted by A cells, so we have paracrine communicationwhere it travels through interstitial fluid to influence neighbouring cells
Somatostatin secreted from the Delta islet cells inhibits both glucose and insulin secretion from their cells
The islets are also innervated by both branches of the nervous system
Describe the steps involved in glucose-indued insulin secretion
At low plasma glucose levels, There is low level of glucose metabolism, hense a low level of basal insulin sedretion due to low levels of calcium ions entering the cell through voltage gated calcium ion channels which would cause depolarisation of the membrane allowing for release of insulin via exocytosis
When levels go up by 5mM there is an increase in glucose metabolism which leads to an increased production of ATP from the phosphorylation of ADP. This increase in the ATP can cause the closing of ATP sensitive potassium ion channels, meaning more Potassium ions will stay in the cell, this reults in membrane depolarisation and so the opening of voltage gated Calcium channels which leads to exytosis of insulin
State the effects of insuslin on glucose uptake and glucose utilisation in key target tissues - state the anabolic effects of insulin
Insulin has effects in 3 differnt areas, The liver, adipose tissue and muscle. In the mucle, It promotes glucose uptake via GLUT-4 and protein synthesis, however decreases proetin breakdown
In the Adipose it promotes glucose uptake and lipogenesis, however decreases lipolysis
In the liiver it promotes Glycogen synthesis, and causes a decrease in glucose glycogen breakdown anf gluconeogenesis.
It has an overall effect of reducing blood glucose levels.
Briefly describe insulin receptor signalling - basic steps, five examples of adapter. proteins and signals
The binding of a hormone to the tyrosine receptor causes intrinsic Tyrosine phosphorylation in the inside of the cell which has a greater affinity for adaptor proteins that produce a number of signals including changes in gene expression
- The adaptor proteins in the insulin receptor are IRS and Shc.
- When IRS drawns near to the receptor it becomes phosphorylated which draws the enzyme PI-3 kinase towards which phosphorylates PIP 2 in the membrane to PIP 3 which activates a kinase PDK1/2 which activates protein kinase B which elicits a number of responses
- When Shc draws near to the phosphorylated receptor it interacts with Grb2 and SOS which causes the beginning of a growth signal
Describe The roles plated by insulin and the counter regulatory hormones in glucose homeostasis
Glucagon is a peptide hormone released in response to Low blood glucose Its release is inhibited by high blood glucose, insulin and somatostatin. They work by stimulating hepatic gluconeogenesis aswell as lipolysis to gibe free gatty acids and glycerol to be used in glucose prduction.
The two insulin and glucose have complementary action. When the level of blood glucose is altered the cells in the islets will stimulate or inhibit appropriate hormone secretion in response to bring blood glucose levels back to normal
Define Diabetes Mellitus and distinguish between T1DM and T2DM he causes, prevalence and key features
Diabetes melitus is a chronic metabolic disorder characterised by hyperglycaemia, the most comon forms are T1DM and T2DM
Type one Diebetes is characterised by a total insulin deficiency whereas Type 2 there is impaired B-islet functions and/or a loss of insulin sensitivity or insulin resistance. In this diabetes, at the start to compensate for insulin resistance in the body, there may be an increased secretion of Insulin which will ultimately offset the insulin resisance, and so overtime when the okasma insulin level may fall with decreased beta cell function to to the earlier proliferation, there may will be a fall in insulin with high plasma glucose levels aswell.
They accounf for 90% of diabetes cases
