MEH: Endocrine System Intro Flashcards
Define haemostasis.
A dynamic equilibrium that the body maintains in order to keep the internal conditions stable and relatively constant.
Describe the main processes involved in control systems of the body.
- Stimulus: brings parameter outside of desired limit
- Receptor: detects stimuli
- Afferent communication pathway
- Control centre
- Efferent pathway
- Effector: brings it back to desired level
What is meant by a circadian (diurnal) rhythm?
A rhythm isn’t constant and therefore the set point can vary.
What controls a persons biological clock?
A small group of neurones in the brain found in suprachiasmiatic nuclei.
It gets ques from the environment to keep the body on a 24 hour cycle. (E.g. Light, temp, exercise, eating/drinking pattern)
Which hormone is involved in setting a persons biological clock?
Melatonin
Where is melatonin released from?
Pineal gland
What is negative feedback?
Response in a way to reverse the direction of change.
What is positive feedback?
Response in a way so as to change the variable even more in the direction of the change.
Give some examples of positive feedback.
- Blood clotting
- Ovulation
What receptors maintain body water homeostasis?
Osmoreceptors
What is osmolarity?
The number of osmoles per litre of solution.
What is osmolality?
The number of osmoles per Kg of solution.
What is the reference range for serum osmolality?
275-295 mOsmol/kg
Describe the processes that take place when a patient has high blood osmolality. (Is hypertonic)
The body needs to conserve water in this state. The lack of water is therefore detected by osmoreceptors in the hypothalamus.
This stimulates the posterior pituitary to secrete more ADH.
This increases water abortions from urine into collecting ducts of the kidneys.
This result in a small volume of concentrated urine and the body to return to its normal state.
Describe the processes that take place when a patient has low blood osmolality. (Is hypotonic)
The body needs to excrete water. The high osmolality is detected by osmoreceptors in the hypothalamus.
The posterior pituitary secretes less ADH which results in decreased absorption of water into the collecting ducts of the kidney so more is excreted as urine.
This therefore returns the body to its normal state.
How does the body maintain glucose homeostasis when a patient eats a meal?
When a patient eats a meal there is an increase in blood glucose concentration.
In response to this the pancreas released insulin which can stimulate two actions.
- Stimulates glucose uptake into tissues via GLUT4
- Stimulates glycogenesis in the liver so that the glucose is stored as glycogen
Both of these actions decrease the plasma glucose.
How does the body maintain glucose homeostasis when a patient is in a fasted state?
The plasma glucose decreases stimulating the pancreas to released glucagon.
This stimulates glycogenolysis in the liver which relates more glucose into the blood restoring normal plasma levels.
What is a hormone?
A chemical signal produced in endocrine glands or tissues that travel in the blood stream to cause an effect on other tissues.
Name the 4 classifications of hormones.
- Peptide/polypeptide
- Amines (amino acid derivatives)
- Glycoproteins
- Steroids
What amino acid is adrenaline, noradrenaline and thyroid hormone derived from?
Tyrosine
What are steroid hormone derived from?
Cholesterol
How are hormones transported in the blood?
- Some hormones such as peptide and adrenaline can simply travel in the blood
- Most hormones are bound to proteins
Which is biologically active: Bound hormone or free form hormone?
Free form only
Describe three ones of carrier proteins.
- Increase solubility in plasma
- Increase half life
- Act as a reserve of the hormone
TRUE OR FALSE: hormones circulate in the blood at very high concentrations.
False (normally pm)
Describe 3 ways in which hormone levels in the blood are determined.
- Rate of production
- Rate of delivery
- Rate of degradation
What effect does the binding of a water soluble hormone to a G-protein receptor have on a cell?
- Dissociation of alpha subunit
- Activation of effector protein
- Formation of secondary messenger
- Activation of protein kinase
- Phosphorylation of target proteins
- Cellular response
What effect does the binding of a water soluble hormone to a tyrosine kinase receptor have on a cell?
- Dismerisation
- Autophospholyation
- Recruitment of adapter proteins and signalling complex
- Activation of protein kinase
- Phosphorylation of target proteins
- Cellular response
Where do lipid soluble proteins bind?
Intracellular receptors
Where is the satiety centre (appetite control centre located?
Hypothalamus
What is the name of the cluster of neurones that play a central role in controlling appetite?
Arcuate nucleus
Name and describe the 2 types of primary neurones in the arcuate nucleus where neuronal, nutrient and hormonal signals are processed.
- Stimulatory neurones: these contain neuropeptide Y (NPY) and Agouti-related peptide (AgRP). These promote hunger.
- Inhibitory neurones: these contain pro-opoimelanocortin (POMC) which yields several neurotransmitters including alpha-MSH and beta-endorphin. These promote satiety.
Name 2 substances that promote hunger.
- NPY
- AgRP
Name 2 neurotransmitter that promote satiety.
- Alpha-MSH
2. Beta-endorphin
What peptide hormone is released from the stomach wall when its empty to stimulate appetite.
Ghrelin
What inhibits ghrelin release?
Filling of the stomach.
What peptide hormone is released in response to feeding?
PYY
Where is PYY released from?
Cells in the ileum and colon
What is leptin?
A peptide hormone released into the blood by fat cells.
What affects does leptin/insulin have in arcuate nucleus.
- Stimulates inhibitory (POMC) neurones
- Inhibits excitatory (AgRP/NPY) neurones
Hence the overall effect is a suppressed appetite.
What is amylin?
A peptide hormone also secreted by beta cells in the pancreas.
Does amylin suppress or increase appetite?
Suppress
