Intro To The Endocrine System & Endocrine Control Of Appetite Flashcards
Is homeostasis a steady state ?
NO , it is a dynamic equilibrium. Failure in homeostasis leads to disease
Describe the characteristics of the control system in homeostasis
- Stimulus
- Receptor which detects stimuli. Eg chemoreceptors, thermoreceptors , noceptors ( sense pain ) proprioreceptors ( allows self aware)
- Communicate this information from receptor to control centre. This determines the set point and determines response. This communication pathway is called the afferent pathway. Communication can be either via nervous system or endocrine system. HYPOTHALAMUS is the main control centre.
- The control centre then communicates this information again either via the nervous system or endocrine system via the efferent pathway to the effector. Eg sweat glands , muscle , kidney.
Why is it important to consider the time we take a blood sample for cortisol levels ?
Because circadian rhythms of cortisol change throughout the day. They are at their highest in the morning and lowest at midnight. So whenever we take a blood sample , we need to state the time we take it to measure cortisol levels.
Circadian rhythms of body temperature are lowest when and highest when ?
Lowest core body temperature during sleep. And highest when we are awake - midday.
Where isthe biological clock located in the brain ?
In small group of neurones in the suprachiasmatic nucleus
What are examples of cues that feed into the biological clock of the brain ?
Light
Temperature
Social interaction
Exercise
Eating / drinking pattern
Why do we experience jet lag ?
There is a mismatch between environmental cues and body clock.
Define negative feedback
Response in a way to reverse the direction of change
Define positive feedback
Response in a way to amplify the initial change
Used when rapid change is desirable
What does short and long loop refer to in terms of negative feedback ?
Long loop- this is where products from the peripheral target glands feed back to the anterior pituitary gland and hypothalamus often inhibiting production and secretion of hormones from the hypothalamus or anterior P gland.
Short loop often refers to hormones produced by the Pituitary gland are fed back to the hypothalamus to inhibit release and synthesis of hormones from the hypothalamus.
How many litres of water is there in a typical 70kg man ?
42 litres of water
Define osmolality
The number of osmoles of a solute in a kg of solvent
MASS
mOsm/kg
Define osmolarity
The number of osmoles of a solute in a litRe of solvent
R in osmolaRity for litRe
VOLUME
mOsm / L
If there is an increase in osmolality in the blood , what does this suggest to water potential ?
This means there are more particles of solute, so the water potential in the blood is very low.
Outline the process by which the body responds to an increase in osmolality?
- This is detected by osmoreceptors in the hypothalamus.
- Hypothalamus signals this information to the posterior pituitary gland to secrete MORE ADH.
- This results in an increase reabsorption of water from urine into the blood in collecting ducts in the kidney.
- Small concentrated volume of urine produced.
Outline the process of how the body responds when blood glucose levels rise above 5mM
- Pancreas releases insulin.
- Insulin stimulates glycogenesis
- Insulin stimulates glucose uptake into tissues through GLUT4 channels.
- This results in plasma glucose levels declining
Outline the way the body responds to plasma glucose levels decreasing below 5mM
- Pancreas releases glucagon
- This stimulates glycogenolysis in the liver. Glucose is released into blood. And gluconeogensis.
- This causes glucose levels to rise.
Give examples of tissues and organs that secrete hormones even though they are not endocrine glands
- Heart - ANP/BNP
- Liver : insulin like growth factor 1
- Stomach : gastrin , ghrelin
- Placenta : inhibin , placental lactogen
- Adipose : leptin
- Kidney : EPO, renin , calcitriol
State the 4 mechanisms of communication via hormones
- Autocrine signalling
2, paracrine signalling
- Neurocrine signalling
- Endocrine signalling
What is Autocrine signalling
Cell releases a hormone which acts on autocrine receptors on the same cell that secreted that hormone.
What is paracrine signalling
Hormone signal carried to adjacent cells over a short distance via interstitial fluids
An example of this would be synapses.
What is neurocrine signalling
Hormone originates in neurone and after transport down axon , it is released into blood stream where it is carried to distant target cells.
What are the two major communication systems in the body
Nervous system
Endocrine system
What are similarities between the endocrine system and nervous system
- Both neurones and endocrine cells are capable of secreting
- Both neurones and endocrine cells can be depolarised.
- Mechanism of action requires interaction with specific receptors in the target cells.
- Both system work in parallel to control homeostasis
Hat are differences between the endocrine and nervous system ?
E - slow speed of response vs fast speed of response in the nervous system
- Endocrine signal is hormones whereas in nervous system it is NT and action potentials
- Endocrine signals travels through blood stream vs sysnapses and axons.
4,
What are the two ways we classify hormones ?
- Either by their solubility in water or lipids
2. Chemical structure
What are the 4 types of hormones - classifying based on their chemical structure
1) peptide hormones
2. Glycoproteins
3. Steroids
4. Amino acid derivatives
Where are steroid hormones derived from ?
Cholesterol
Steroid hormones examples and whether they are lipid / water soluble
- cortisol
- aldosterone
- testosterone
ALL lipid soluble
Amino acid derivatives hormone examples
All synthesised from aromatic amino acids
Adrenaline ( tyrosine )
Noradrenaline ( tyrosine )
Thyroid hormones ( tyrosine )
Melatonin ( tryptophan )
Adrenal medulla hormones are water soluble.
Thyroid hormones are lipid soluble.
Peptide hormones
Insulin
Glucagon
Growth hormone
ALL water soluble
Glyocproteins
Large protein molecules
Luteinizing hormone
Follicle stimulating hormone
Thyroid stimulating hormone
ALL water soluble
What are the three main factors that determines hormone levels in the blood ?
- Rate of production
- Rate of delivery : higher blood flow to a particular organ will deliver more hormone
- Rate of degradation
Do hormones circulate in blood at high or low concentrations ?
Very LOW.
Picomoles
Hormones which are not water soluble , how do they get transported around the body ?
- they must bind to proteins to help with the transport of hormones in blood.
For example thyroid hormones bind the the protein thyroxine binding globulin.
ONLY the free form is biologically active
What is the role of these carrier proteins that bind to hormones ?
- Increase solubility of hormones in plasma
- Increase half life
- Readily accessible reserve
Do water soluble hormones bind to cell surface receptors or intracellular receptors ?
Cell surface receptors
Do lipid soluble hormones bind to cell surface receptors or intracellular ?
Intracellular
Outline the process by which adrenaline would bind to a receptor
- Adrenaline binds to cell surface G protein (s) coupled receptors
- This activates GTP which binds to the s subunit causing the alpha sub unit to dissosciate from the beta/gamma sub unit.
- Alpha sub unit then activated the effector protein Adenylyl cyclase which catayses the formation of cAMP from ATP.
- cAMP then goes off to activate protein kinase A
- Protein kinase A the phosphorylates target proteins
Outline the process by which insulin binds to their tyrosine kinase cell surface receptors
- Binding of hormones to receptor.
- This causes dimerisation of monomers ( except insulin receptor which is already dimerised )
- Autophosphorylation of specific tyrosine domains on the monomers.
4.
What are the two ways lipid soluble hormones can bind to intracellular receptors
- Type 1 : cytoplasmic receptor binds hormone and receptor-hormone complex then enters nucleus and binds to DNA.
- Type 11 : hormone enters nucleus and binds to pre bound receptor on DNA eg thyroid hormone. Binding relieves repression of gene transcription
- Receptor - hormone complex binds to specific DNA sequence called hormone response element ( HRE) In promoter region of certain genes.
- Expression of new protein mediates effects of hormone.
What has a faster mechanism of action : water soluble hormones or lipid soluble hormones ?
Water soluble hormones because the components are already in place.
Where is the appetite control centre located and what is it called ?
- located in the hypothalamus
- it is called the arcuate nucleus.
What neurones are found in the arcuate nucleus?
Primary neurones and secondary neurones
Role of primary neurones
Neuronal , nutrient and hormonal signals are processed by the primary neurones. Which are located in the arcuate nucleus.
What are the two types of primary neurone
- Stimulatory
2. Inhibitory
Role of stimulatory primary neurones
Contain the neuropeptide Y ( NPY) and agouti related peptide ( AgRP). These promote hunger.
Role of inhibitory primary neurones
Contain pro-opiomelanocorti. (POMC) which yields a-MSH and b-endorphin. These promote satiety ( the feeling that we feel when we are full )
Role of secondary neurones
Primary neurons synapse with secondary neurones in other regions of hypothalamus and the signals integrated to alter feeding behaviour
What are the two hormonal signals primary neurones receive from the gut
- Ghrelin
2. PYY ( peptide tyrosine tyrosine )
Role of ghrelin
Peptide hormone released from the stomach wall when stomach is empty.
Stimulates the excitatory primary neurones
in arcuate nucleus and therefore stimulates appetite
Role of PYY ( peptide tyrosine tyrosine)
Short peptide hormone released by cells in the ilium and colon in response to feeding.
Inhibits the excitatory primary neurones of the acrcuate nucleus and stimulates the inhibitory neurones.
Therefore suppresses appetite
Name examples of hormones that are released by the body that are involved in control of appetite
Leptin
Insulin
Amylin
Function of leptin
- peptide hormone released into blood by adipocytes
- stimulates the inhibitory neurones. And inhibits the excitatory neurones in the arcuate nucleus.
- overall effect is therefore to suppress appetite
- leptin induces expression of uncoupling proteins in mitochondrion therefore energy dissipated as heat
Function of amylin
Peptide hormone secreted by B cells in pancreas
Suppressed appetite , decrease glucagon secretion and slow gastric emptying.
