Intro to the endocrine system Flashcards
What is homeostasis?
The ability or tendency of a living organism, cell, or tissue to maintain a state of internal balance and dynamic equilibrium despite any changes in the conditions around it
Why is homeostasis important? (2)
- Keeps conditions constant for enzyme action and cell functions
- Prevents disease (as a failure in homeostasis may lead to disease)
What are the characteristics of a control system (4)
1) Stimulus (a change in the environment)
2) Receptor (detects stimuli)
3) Control centre
4) Effector (causes change)
Give examples of receptors that detects stimuli (4)
- Chemoreceptors
- Thermoreceptors
- Proprioreceptors (position of body and movement)
- Nocireceptors (pain)
What does the control centre do? (3)
- Determines set point
- Analyses afferent input
- Determines response
Examples of effectors (3)
Sweat glands
Muscle
Kidney
What types of communication systems are there? (2)
Nervous system- action potentials
Endocrine system- hormones
What is the afferent pathway?
Communication pathway that links the receptor to the control centre and so conducts the action potential towards the brain (though communication could be endocrine too)
What is the efferent pathway?
Communication pathway that links the control centre to the effector and so conducts the action potential in this direction (though communication could be endocrine too)
What is a circadian rhythm? (2)
- A natural biological process that regulates physiological functions in living organisms
- It is a 24-hour cycle that is controlled by the internal biological clock in the brain
Where is the biological clock controlling circadian rhythm located?
in small group of neurones in suprachiasmatic nucleus of the hypothalamus
What keeps our biological clock in cycle? (2)
Zeitgebers - cues from environment such as light, temperature, social interaction, exercise, eating/drinking pattern
+ Melatonin
What cues from the environment keep the body on a 24 hour cycle? (5)
- light
- temperature
- social interaction
- exercise
- eating/drinking pattern
What causes jet lag?
Mismatch between environmental cues and body clock when crossing time zones on a flight
What hormone is involved in setting biological clock?
Melatonin
Where is melatonin produced?
Pineal gland
When is cortisol high and low?
High: 8am - morning
Low - Midnight
When is melatonin high/low?
High during sleep
Low during the day
What is negative feedback? (2)
Give 2 examples
- A response to a change in the body that counteracts or opposes the change
- Most common form of feedback,
eg. the control of plasma glucose by insulin/glucagon, the control of water content by ADH
What is positive feedback? (2)
Give 3 examples
- A given action promotes more of the same action until the stimulus is removed.
- Rare, used when rapid change is desirable,
eg. blood clotting, ovulation, contraction of uterus
Examples of positive feedback
Blood clotting
Contraction of uterus
Ovulation
What is the percentage of total body water in males?
50-60%
What is the percentage of total body water in females?
45-50%
What is osmotic pressure of blood plasma monitored by?
Osmoreceptors in hypothalamus
Fluid distribution 70KG man
- 42L of water
- 2/3 intracellular (28L)
- 1/3 extracellular (14L) - 11L interstitial, 3L plasma
How many litres of blood does a 70kg man
5 litres - 2 litres of red cells and 3 litres of blood plasma
Osmolarity vs osmolality
Osmolarity - the number of osmoles per litre of solution (volume)
Osmolality - osmoles per kg of solution (mass)
What is an osmole?
Give an example
(the amount of substance that dissociates in solution to form 1 mole of osmotically active particles) The number of osmotically active particles
eg. a 1mM (1Molar) solution of NaCl corresponds to an osmolarity of 2 as 1 from Na+ ions and one from Cl- ions as you have 2 osmotically active particles
Why is serum osmolality useful?
To investigate hyponatraemia (low Na+ in blood)
reference range is 275-295 mOsmol/kg
Normal blood osmolality/Normal sodium in blood
275-295 mOsmol/KG
Concentration of saline
0.9% NaCl
How does ADH control body fluids (What happens if water is low)?
- High blood osmolality is detected by osmoreceptors in hypothalamus:
1)
- There is increased thirst
- Thus you drink more water, which reduces osmolality
2)
- Posterior pituitary secretes more ADH
- You get increased reabsorption of water from urine into blood in collecting ducts in the kidney
= small volume of concentrated urine
What does ADH do?
Increases reabsorption of water from urine back into blood in kidney collecting ducts
How does ADH control body fluids (if water high)
- Low blood osmolality detected by osmoreceptors in hypothalamus
- Posterior pituitary secretes less ADH
- Descreased reabsorption of water from urine into blood in collecting ducts in kidney
= large volumes of dilute urine
What is the normal plasma glucose level?
5mM (millimolar)
Describe what happens in the fed state (6)
- Eating a meal increases plasma glucose
- Detected by B cells in islets of langerhans in pancreas
- Pancreas secretes insulin
- Insulin stimulates glycogenesis in liver (storage of glucose as glycogen
- It also stimulates glucose uptake into tissues (GLUT 4)
- This will decline plasma glucose levels
What does insulin do?
Stimulates glycogenesis in liver
Stimulates glucose uptake via translocating GLUT4
Describe what happens in the fasted state (5)
- Fasting decreases plasma glucose
- Detected by Alpha cells in islets of langerhans of pancreas
- They releases glucagon
- Glucagon stimulates glycogenolysis (break down of glycogen to release glucose) in the liver
- This increases plasma glucose
What does glucagon do?
Stimulates glycogenolysis
What are hormones? (2)
- Chemical signals produced in endocrine glands or tissues
- They can travel in the blood stream to cause an effect on other tissues
What hormones does the stomach release?
Gastrin and Ghrelin
What hormones does adipose tissue release?
Leptin
Name the 4 mechanisms of communication via hormones
- Autocrine
- Paracrine
- Endocrine
- Neurocrine
Autocrine communication
Hormone signal acts back on cell of origin
Paracrine communication
Hormone signal is carried to adjacent cells over short distance via interstitial fluid
Endocrine communication
Hormone signal is released into blood stream and carried to distant target cells
Neurocrine communication
- Hormone originates in neurone, transported down axon and released into blood stream and carried to distant target cells
Endocrine and nervous system similarities
Both secrete Both can be depolarised Some molecules can be neurotransmitter and hormone Have specific receptors on target cells Control homeostasis
Fill this table in for the endocrine and nervous system
4 different types of hormones
- Glycoproteins
- Amino acid derivatives (amines)
- Peptide/polypeptide
- Steroids
(GAPS)
Describe the solubility of peptide hormones and give 3 examples
- All Water soluble
(insulin, glucagon, growth hormone)
Describe the solubility of amino acid derivatives (amines)
Give 4 examples
- Adrenal medulla hormones = water soluble
- Thyroid hormones = lipid soluble
Examples:
- Adrenaline
- Noradrenaline
- Thyroid hormones
- Melatonin
Describe the solubility of glycoprotein hormones (4)
Give 3 examples
- All water soluble
eg LH, FSH, TSH
Describe the solubility of steroid hormones (3)
Give 3 examples
- All lipid soluble
eg cortisol, aldosterone and testosterone
What are steroid hormones synthesised from?
Cholesterol
How are hormones transported in blood? Give examples
Water soluble hormones can travel freely in blood ie Peptide hormones
Lipid soluble ones have to bind to carrier proteins in order to travel ie thyroid hormone
How are thyroid hormones transported in the blood?
Bound to Thyroxine-binding globulin TBG
What hormones are biologically active?
Free form of hormone (not bound to protein)
Roles of carrier proteins (3)
- Increase solubility of hormone in plasma
- Increase half life
- Readily accessible reserve
3 main factors determining hormone levels
Rate of production
Rate of delivery
Rate of degradation
Describe how the 3 main factors that determine hormone levels in blood work
.
What kind of concentrations do hormones circulate the blood?
- Very low concentrations (pmol/L) picomoles per litre
How do hormones exert their effects?
Bind to specific receptors
What do water soluble hormones bind to in order to exert their effects?
Cell surface receptors as they can’t cross the plasma membrane
What are the 2 main classes of receptors for water soluble hormones? Give an example of each
- G protein coupled receptor ie adrenaline receptor
- Tyrosine kinase receptor ie insulin receptor
What do lipid soluble hormones bind to in order to exert their effects?
Intracellular receptors (they can diffuse across the membrane)
Describe what a Type 1 intracellular receptor does
- Cytoplasmic receptor binds to hormone
- Receptor hormone complex enter nucleus and binds to DNA
Describe what a Type 2 intracellular receptor does
- Hormone enters nucleus and binds to prebound receptor on DNA e.g. thyroid hormone
- Binding relives repression of gene transcription
What does the receptor bind to on DNA?
Hormone response element (HRE)
In promotor region of genes
Which works faster, water soluble hormones or lipid soluble?
Water soluble
Where is appetite control centre located?
Hypothalamus - arcuate nucleus
What do the primary neurones in the arcuate nucleus sense? (3)
Primary neurones sense:
- Neuronal signals
- Nutrient signals
- Hormonal signals
From the blood
Name the Two types of primary neurones in arcuate nucleus
- Stimulatory neurones
- Inhibitory neurones
What do stimulatory neurones contain? What do these do?
Neuropeptide Y (NPY) and agouti-related peptide (AgRP)
These promote hunger
What do inhibitory neurones contain?
What do these promote?
Pro-opiomelanocortin (POMC), which yields several neurotransmitters including alpha-MSH and Beta-endorphin
These promote satiety
What do primary neurones do in order to alter feeding behaviour? (2)
- Primary neurones synapse with secondary neurones
In other regions of the hypothalamus - And the signals are integrated to alter feeding behaviour
What does POMC do?
Yields a-MSH and B-endorphin
These promote satiety
Name 2 Hormone signals from the gut to the hypothalamus
Ghrelin
Peptide tyrosine tyrosine (PYY)
1) What is Ghrelin?
2) When is it released?
3) What does it stimulate?
1) A peptide hormone released from the stomach wall when empty (Ghrelin = Stomach Growling)
3)Stimulates excitatory primary neurones in arcuate nucleus so stimulates HUNGER/APPETITE
What inhibits Ghrelin release?
Filling of the stomach
1) What is PYY?
2) What cells release PYY?
3) What does PYY do?
1) A peptide hormone released in response to feeding
2) by cells in the ileum and colon
2) Inhibits excitatory/stimulatory primary neurones of the arcuate nucleus and and stimulates inhibitory neurones
to SUPPRESSES APPETITE
What does PYY do when injected to mice?
Makes them anorexic
What do obese humans have?
A blunted PYY response following food intake
1) Where is leptin released from and to?
2) What does leptin do?
3) What is the overall effect of leptin?
1) Released from adipocytes into blood stream
2) Stimulates inhibitory (POMC) neurones
Inhibits stimulatory (NPY and AgRP) neurones
3) SUPRESSES APPETITE
What does leptin to do mitochondria?
Induces expression of uncoupling proteins
Energy is the dissipated as heat
What does insulin do?
- Suppresses appetite - similar mechanism to leptin
- Seems to be less important than leptin in this respect
What does amylin do and where does it come from?
From beta cells in pancreas
Suppress appetite
What is Pramlintide
Amylin analogue - used to treat Type 2 diabetes
What do aMSH (from POMC) synapse at?
MC4 receptors - promoting satiety
Leptin mutation discovery
ob/ob mice have loss of function mutation on leptin gene
Treatment loss of leptin gene
Leptin injection
What can’t you use leptin injections for?
Common obesity - leptin resistance instead is the problem
What do inhibitory neurones contain?
What do these promote?
Pro-opiomelanocortin (POMC), which yields several neurotransmitters including alpha-MSH and Beta-endorphin
These promote satiety
What do inhibitory neurones contain?
What do these promote?
Pro-opiomelanocortin (POMC), which yields several neurotransmitters including alpha-MSH and Beta-endorphin
These promote satiety
