Flashcards in Metabolism Session 7 - Introduction to the endocrine system and the endocrine pancreas Deck (100):
What are the four main types of communication in the body?
Give four characteristics of control systems
What are the two main types of communication in body? (I know I said there were four before, but these are the biggies)
What is the mechanism of action for nervous communication?
What is the afferent branch?
Signal direction towards the brain
What is autocrine communication?
Variety of agents released by cells have effect on cell itself
What is paracrine communication?
Hormones released locally rather than directly into the blood
What are the three roles of a control center in the body?
Name two control centers, and what they control
Determine set reference point of chemical levels
Analyses signals from afferent branch
Determines appropriate response
Hypothalamus involved in endocrine control.
Medullar involved in cardiovascular and respiratory.
What is a receptor used for?
To detect stimuli, such as changes in environment
Name three examples of receptors
Chemo, pressure and temperature
What is an effector?
An agent that controls change
What is the pathway from control center once response has been decided?
Control --> Efferent nervous pathway --> Effector
What does loss of efferent pathway use do in paraplegic patients?
Sweat glands cannot be controlled, so reduces ability of paraplegic patients to lose heat
What is negative feedback, and how common is it?
Effectors oppose stimulus
Occurs in most homeostatic control systems
What are the two advantages of negative feedback?
Give stability to control systems
Allow a point to be controlled within fine limits
What is hunting behaviour and what is it indicative of?
Occurs in negative feedback when levels overshoot set points several times before rest. Indicative of dynamic equilibrium.
What is positive feedback?
Stimulus produces a response which increases its effect
How fast is the change caused by positive feedback?
Give two examples of positive feedback in the body
Ovulation and blood clotting cascade
Give two examples of negative feedback in body
Hyperglycaemia stimulates insulin release
Body water homeostasis
Where is biological clock situated in body? (think chasm)
Suprachiasmaic nucleus in hypothaamus
Give three examples of biological rhythmns
Cortisol levels vary throughout the day. Peak at 7 am and trough at 7 pm. So, blood cortisol levels should be measured at same time each day.
Menstral cycle varies over month. Womans core body temperature varies during cycle and can be used as a marker of ovulation.
Melatonin released from pineal gland in response to light and dark
What do you have to do when measuring cortisol levels in patients and why?
Take measurement same part of day, varies throughout day (peaking at 7 am, troughing at 7pm)
How many litres of water in normal healthy 70KG male?
How many litres of blood in heathy 70 kg male?
What is an increase in blood osmolarity?
What happens when it is detected?
Increase in conc (not enough water)
Osmoreceptors in hypothalamus detect decrease in water potential (increased osmolarity)
ADH (vasopressin) is released from the posterior pituatry
Causes increase in permeability of collecting ducts to water, increasing reabsorption of water from the urine into the blood
Makes urine more concentrated
Where is ADH released from?
What is ADH released in response to?
Increased blood osmolarity
What does ADH do?
Causes increase in permeability of collecting ducts in kidney to water, increasing reabsorption of water
What is a HORMONE?
Chemical messengers travel via blood stream
Afferent branch Hypothalamus Anterior pituitary gland Endocrine glands
What is missing?
Outline Hypothalamic-Pituitary-Adrenal axis
Hypothalmus Corticotrophin releasing hormone (CRH) Anterior pituitary Adrenocorticotrophic hormone Adrenal cortex Cortisol Inhibits anterior pituitary
What are two factors which control hormone secretion?
•Change in a variable regulated by a hormone
•Concentration of hormone itself or another hormone
Why do hormones bind with proteins in the blood?
Mostly not soluble enough to dissolve
Name two hormones which exhibit specific binding to proteins
Steroid and thyroid hormones
Give three reasons why hormones bind with protein carriers
•Increases solubility of hormone in plasma
•Increases half life of hormone
Serves as readily accessible reserve
Name four main types of hormone
Amino acid derivatives
Why is the largest hormone group?
What do polypeptide hormones consist of?
Short or long single chain(s) of amino acids
Give two types of polypeptide hormone
Insulin and Glucagon
(also GSH and placental lactogen)
What do glycoprotein hormones consist of?
Large two chained protein molecules with carbohydrate sidechains
Name two types of glycoproteins
LH, FSH and TSH
What do amino acid derviatives consist of?
Small molecules synthesised from amino acids
Name two types of amino acid derivatives
Adrenaline and thyroid hormones
What are steroids derived from?
What do different steroid hormones differ in?
The number of carbons
Give three examples of steroid hormones
Cortisol, testosterone, oestrogen, progesterone
Name three hydrophillic hormone types
Polypeptide, Glycoprotein and adrenaline (amino acid derivative)
Name two hydrophobic hormone types
Steroid and thyroid hormones
What is the main variable which determines the effect of hormones on target cell?
Concentration of free or unbound hormone
What two changes in concentration can have clinical consequences?
Defiency and excess
Where are the receptors bound to by lipophillic hormones situated?
Inside cell (cytoplasmic/nuclear)
What do hormones bind to
Specific, high affinity receptor
Give examples of things which hormone binding to receptors may affect
Activity of enzyme or gene expression
How long does a change in gene expression take to take effect?
Give three factors which influence magnitude of hormonal response
• Concentration of active hormone at target tissue
• Receptor number
• Affinity of receptor for hormone
• Degree of signal amplification
How is rate of secretion of hormones affected?
By blood concentration of hormones
What is a trophic hormone?
One that controls the secretion of another hormone by targeting endocrine tissue
Where are trophic hormones secreted?
Name three hormones secreted by the anterior pituitary gland and their role
Thyroid Stimulating Hormone = Thyrotrophin (TSH) – affects thyroid gland
Adrenocorticotrophic Hormone = Corticotrophin (ACTH) – affects adrenal gland
Growth Hormone = Somatotrophin (GH) – affects metabolism
Luteinizing Hormone (LH) = Affects ovary and testis function
Name a regulatory mechanism for trophic hormones
Inhibited by high level of hormone they cause the secretion of in the blood (Wen concentration of thyroid hormone gets too high, less TSH is secreted. Negative feedback)
Where do releasing or inhibiting hormones come from?
Nerve cells in the hypothalamus
How do releasing or inhibiting hormones travel to endocrine glands?
Specialised blood vessels known as hypophseal portal vessels
Name three releasing hormones and what they effect
Thyrotrophin Releasing Hormone (TRH) – stimulates TSH release
Corticotrophin Releasing Hormone (CRH) – stimulates ATCH release
Somatotrophin Releasing Hormones (SRH) – stimulates GH release
Where does inactivation of hormones occur?
Liver, kidney and sometimes in target tissues
How are steroid hormones inactivated?
Relatively small change in chemical structure which increases water solubility enabling them to be excreted from the body in urine or bile
How are protein hormones inactivated?
Undergo extensive chemical change and are degraded to amino acids, which are then reused.
What is the structure of insulin?
Two chains linked covalently by two disulphide bridges. Extra third disulphide bridge in alpha chain
Where is insulin secreted?
B cells of islets of langerhans
How is insulin stored?
In B cells as crystalline-zinc complex storage granules
What is the structure of glucagon?
Single chain polypeptide hormone, lacking disulphide bridge so has flexible 3D structure
How is insulin circulated?
Dissolve in the plasma and circulates as free hormon
When is Glucagon activated?
Upon binding to its receptor on surface of target cells
What are the three main target tissues of insulin?
Liver, Skeletal muscle and adipose tissue
What part of a cell does insulin react with?
Cell surface receptors
What does insulin stimulate to work?
Enzymes and proteins inside target cell
How does glucagon become an active molecule?
Post translational processing to produce biologically active molecule
What type of metabolism does insuline encourage?
What type of metabolism does glycogen encourage?
What three metabolic reactants do insulin and Glucagon influence?
Carbohydrate, lipid and amino acid metabolism
What are the function of insulin in the short term?
Removes absorbed nutrients from blood following a meal
What are the long term functions of insulin?
cell growth/cell division that relate to its ability to stimulate protein synthesis and DNA replication.
What is the name for a glucagon receptor?
G protein coupled receptor (GPCR)
What does binding to the GPCR receptor by glucagon do?
Causes adenylate cyclase to increase, which increases cyclic AMP in the cell
Effect of insulin on glucose transport into adipose tissue?
What affect does insulin have on glycogenolysis?
Decrease in insulin
What effect do insulin and glucagon have on gluconeogenesis?
Increase in glucagon
What effect do insulin and glucagon have on ketogenesis in the liver?
Decrease in insulin
Increase with Glucagon
What effect does insulin have on lipolysis?
Decrease in insulin
Increase in glucagon
What effect does insulin have on amino acid uptake in liver?
What are the major cell types in islets of langerhans, and what quantities do they exist in?
B - 75% - Insulin
A - 20% - Glucagon
Where is glucagon and insulin stored in a cell?
In a storage granule
What are the three main features of a cell specialised for protein synthesis?
More RER, well defined golgi, more mitochondria and system of microtubules and filaments
Where is proinsulin converted to insulin?
Where is preproinsulin converted to proinsulin?
How does glucose move into B cells?
What does increase of glucose in cells cause an increase in?
What channels does increase in ATP inhibit and what effect does this have?
ATP sensitive potassium ion channels
Depolarises cell membrane
What enters through voltage gated channel after membranal depolarisation?
What do calcium ions do in B cells?
Stimulate exocytosis of insulin