12. Intro To Endocrine System And Appetite Flashcards
What are the characteristics of a control system?
Stimulus
Receptor
Communication via afferent pathway to control centre
Communication via efferent pathway to effector (causes change)
Via negative feedback to stimulus
What curs from the environment keep body on a 24 hour cycle?
Light Temperature Social interaction Exercise Eating/drinking pattern
Which hormone is involved in setting biological clock?
Melatonin from pineal gland
What is the body’s natural body clock called?
Circadian rhythmic
Where is the ‘biological clock’?
In brain in small group of neurones in suprachiasmatic nucleus
What is negative feedback?
Response in a way to reverse direction of change
Most common form of feedback in physiological systems
What is positive feedback?
Response in a way also as to change the variable even more in the direction of the change
Used when rapid change is desirable
E.g. blood clotting, in childbirth
How does negative feedback work?
Hypothalamus detects change and releases hormone 1
Anterior pituitary receives hormone 1 and releases hormone 2
Target gland receives hormone 2 and releases hormone 3 to cause change
What is osmolarity?
Number of osmoles per litre of solution
What is osmolality?
Number of osmoles per Kg of solution
What is an osmole?
Amount of substance that dissociates in solution to form one mole of osmotically active particles
What is autocrine communication?
Hormone signal acts back on cell of origin
What is paracrine communication?
Hormone signal carried to adjacent cells over a short distance via interstitial fluid
What is endocrine communication?
Hormone signal released into bloodstream and carried to distant target cells
What is neurocrine communication?
Hormone originates in neurone and after transport down axon released into bloodstream and carried to distant target cells
What are the similarities between endocrine and nervous systems?
Both neurons and endocrine cels are capable of secreting
Both neurons and endocrine cells can be depolarised
Some molecules act as both neurotransmitter and hormone
Mechanism of action requires interaction with specific receptors in target cells
Both work in parallel to control homeostasis
What are the 4 classes of hormones?
Peptide/polypeptide
Amino acid derivatives
Glycoproteins
Steroids
Describe peptide/polypeptide hormones
Short chains of amino acids
E.g. insulin, glucagon, growth hormones
All water soluble
Describe amino acid derivatives hormones
Synthesised from aromatic amino acids
E.g. adrenaline, noradrenaline, thyroid hormones, melatonin
Adrenal medulla hormones water soluble
Thyroid hormones lipid soluble
Describe glycoprotein hormones
Often made up of subunits
Carbohydrates size chain
E.g. luteinizing hormone, follicle stimulating hormone, thyroid stimulating hormone
All water soluble
Describe steroid hormones
All derived from cholesterol
Steroidogenic tissues convert cholesterol to different hormones
E.g. cortisol, aldosterone, testosterone
All lipid soluble
How are hormones transported?
Some travel in blood in simple solution (peptides, adrenaline)
Most hormones must bind to proteins
Dynamic equilibrium between bound and free forms of hormone in plasma
Only free form is biologically active
What are the roles of carrier proteins?
Increase solubility of hormone in plasma
Increase half-life
Readily accessible reserve
What are the 3 main factors that determine hormone levels in blood?
Rate of production: synthesis and secretion
Rate of delivery: higher blood flow will deliver more hormone
Rate of degradation: hormones are metabolised and excreted from the body
How do water soluble hormones bind to GPCRs on cell surface?
Dissociation of G protein to alpha subunit
Activation of effector protein (e.g. adenylyl cyclase)
Formation of second messenger (e.g. cAMP)
Activation of protein kinase
Phosphorylation of target proteins
Cellular response
How do water soluble hormones bind to tyrosine kinase on cell surface?
Dimerisation
Autophosphorylation of specific tyrosines
Recruitment of adapter proteins and signalling complex
Activation of protein kinase
Phosphorylation of target proteins
Cellular response
How do type 1 lipid soluble hormones bind to intracellular receptors?
Cytoplasmic receptor binds hormone and receptor hormone complex enters nucleus and bind to DNA
Receptor bind to specific DNA sequence called a hormone response element (HRE) in promoter region of specific genes
Expression of new protein mediates effects of hormone
How do type 2 lipid soluble hormones bind to intracellular receptors?
Hormone enters nucleus and binds to pre-bound receptor on DNA
Binding relieves repression of gene transcription
Receptor binds to specific DNA sequence called a hormone response element (HRE) in promotor region of specific genes
Expression of new protein mediates effects of hormone
Where is the satiety centre (appetite control centre)?
Hypothalamus
Contains servers clusters of neurones referred to as nuclei
Arcuate nucleus plays central role in controlling appetite
Where are neuronal, nutrient and hormonal signals processed?
By primary neurones in the arcuate nucleus
What are the 2 types of primary neurone?
Stimulatory - contain neuropeptide Y (NPY) and Agouti-related peptide (AgRP), promote hunger
Inhibitory - contain pro-opiomelanocortin (POMC) which yields several neurotransmitters including alpha-MSH and beta-endorphin, promote satiety
What is ghrelin?
Peptide hormone released from stomach wall when empty
Stimulates excitatory primary neurones in arcuate nucleus and stimulates appetite
Filling of stomach inhibits ghrelin release
What is PYY (peptide tyrosine tyrosine)?
Short peptide hormone released by cells in ileum and colon in response to feeding
Inhibits excitatory primary neurons of arcuate nucleus and stimulates inhibitory neurones, suppress appetite
What is leptin?
Peptide hormone released into blood by fat cells
Has 2 effects in arcuate nucleus:
- stimulates inhibitory (POMC) neurones
- inhibits excitatory neurones in arcuate nucleus
Suppresses appetite
Induces expression of uncoupling proteins in mitochondria
How does insulin work?
Suppresses appetite by similar mechanism as leptin
What is amylin?
Peptide hormone also secreted by beta cells in pancreas
Suppress appetite, decrease glucagon secretion ad slow gastric emptying
