Module 4: Endocrine Flashcards
How is homeostasis restored after being disturbed by the increase decrease of a variable?
Receptor (sensor), detects the change, control center compares it to the set point and signals effectors.
Set point
The ideal, healthy point for a variable
Differs between individuals
Normal range
The range in which a variable is normal
Differs person to person
Population reference range - how does it compare to an individual’s normal range?
The population reference range tends to be wider than normal fluctuations within an individual
How do the neural and endocrine control systems differ?
Neural transmits information quickly across synapses with neurotransmitter
Endocrine releases hormones into the bloodstream for slow but long lasting action
What must the target cells of a hormone have?
Appropriate receptors
Where do hormones come from?
Endocrine gland cells
Hormone
A chemical messenger which travels through the bloodstream from one organ to the next, where they cause a response in the cells
What links the nervous system to the endocrine system?
What else does it do?
Hypothalamus
Controls the secretion of many endocrine glands
What are four variables that hormones maintain?
Blood sugar concentration
Growth and repair of tissues
Basal metabolic rate
Blood calcium concentration
Two classifications of hormones
Water-soluble and lipid-soluble
Two types of water-soluble hormones
Peptides- short chain of amino acids
Catecholamines- including adrenaline and noradrenaline
Two types of lipid-soluble hormones
Steroids (base of cholesterol)
Thyroid hormones (modified amino acids)
What about thyroid hormones is unusual for their classification?
They are made in thyroid cells and stored until required
Unlike other lipid-soluble hormones, which are made as required
Are water-soluble hormones stored or made when required?
Stored- released by exocytosis when required
Which classification of hormone travels dissolved in the blood?
Water-soluble hormones
How do lipid-soluble hormones travel in the blood?
Bound to a carrier protein
Where are the receptors for water-soluble hormones located? Why?
Within the target cell or it’s plasma membrane
Because water-soluble hormones cannot cross the cell membrane
Where are the receptors for lipid-soluble hormones located? Why?
In the cytoplasm or nucleus of the target cell
Because lipid-soluble hormones can diffuse across the cell membrane
What does the binding of a water-soluble hormone to a receptor allow?
The activation of an associated G-protein
What does the G-protein do?
Activates/ inhibits adenylyl cyclase
Or increases intracellular calcium ions
(ACTIVATES A SECOND PATHWAY)
What does a lipid-soluble hormone need to do before diffusing across the cell membrane?
Dissociate from its carrier protein
What does the hormone-receptor complex do once the hormone is bound?
It binds to DNA and the target gene is activated
New mRNA is generated, and so is a new protein
What does the new protein produced due to the binding of a lipid-soluble hormone do?
Mediates target cells response
A slow process
Difference between the mechanisms of water-soluble and lipid-soluble hormones?
Through second messengers (water-soluble)
And by altering gene transcription (lipid-soluble)
Difference in speed of response between water-soluble and lipid-soluble hormones
Water- milliseconds to minutes
Lipid- hours to days
How are hormone levels maintained?
Most commonly through negative feedback:
- by reducing change until stimulus is removed
- or by directly inhibiting further hormone release
What two factors determine the amount of hormone in the blood?
- rate of hormone secretion
- rate of removal
What controls the removal of hormones from the bloodstream?
Enzymes in the blood or in target cells
What controls hormone secretion?
Negative feedback loops
What is the goal of hormones? And what happens if they fail?
To maintain homeostasis
Can lead to endocrine disorders
Is the pancreas an exocrine or endocrine gland?
Both
Three cells of the pancreas
Pancreatic islets (make up 1% mass)
Beta cells
Alpha cells
If blood glucose concentration gets too high, or too low, what happens?
Too high- diabetes
Too low- hypoglycaemia
Which organ must be supplied with glucose at all times and why?
The brain, because it’s its only fuel
Two metabolic states
Fed and fasting states
Fed state
Cellular uptake of nutrients and anabolic metabolism
Synthesis of glycogen protein and fat
Fasting state
Mobilisation of nutrients and catabolic metabolism
Breakdown of glycogen protein and fat
Reference range of blood glucose concentration
70-110 mg dL^-1
How is blood glucose lowered if too high?
Pancreatic islet beta cells secrete insulin into bloodstream
Target cells of insulin and effects
Muscle and adipose- increase glucose uptake
Liver cells- stop glucose output
Which materials are synthesised due to insulin secretion? Which materials uptake is increased?
Glycogen and fat
Amino acid uptake is increased in muscle and adipose cells
Which is the only hormone that can lower blood glucose concentration?
Insulin
How is blood glucose concentration increase when too low?
Pancreatic islet alpha cells secrete glucagon
Target cells of glucagon and effects (3)
Liver cells
Breakdown of glycogen, glucose and ketone synthesis all increase
Which other hormones can increase blood glucose? (3)
Growth hormone
Adrenaline
Cortisol
Difference between glycogen and glucagon
Glycogen is a stored form of glucose
Glucagon is a hormone which lowers blood glucose concentration
Which part of the body can be considered ‘outside’ the body?
Inside of gastrointestinal system
Function of kidneys
Regulate water loss in urine
Two parts of the pituitary gland
Posterior lobe/ pituitary
Anterior lobe/ pituitary
Where is the pituitary gland?
The base of the brain, connected to the hypothalamus
Function of hypothalamus
Controls secretion of pituitary hormones by stimulating the pituitary gland
What do pituitary hormones stimulate? (2)
Target cells
Secretion of hormones by other endocrine glands
How is the posterior pituitary connected to the hypothalamus?
By neurons
Cell bodies in the hypothalamus, axon terminals in posterior pituitary
Where are posterior pituitary hormones made and stored?
Made in the cell body of the neuron in hypothalamus, stored at axon endings until required (in posterior pituitary)
Hormones released by posterior pituitary (2) and their functions
Antidiuretic hormone- stimulates kidneys to reabsorb water
Oxytocin- stimulates the contraction of uterine muscles during childbirth (positive feedback), and stimulates milk release in breastfeeding
Both are peptides
How is the anterior pituitary connected to the hypothalamus?
By blood vessels
How does the hypothalamus communicate with the anterior pituitary?
Stimulus arrives at cell body of neurons in hypothalamus,
releasing hormone is made and travels down blood vessel to anterior pituitary
What do the hormones released by the hypothalamus do?
They are releasing/ inhibiting hormones
So they move down the portal system to the anterior pituitary, bind to receptor on membrane of the cell
There, a specific peptide hormone is secreted
Describe feedback regulation of the anterior pituitary gland
Level of hormone secreted by target organ controls (feeds back) secretion of both releasing and pituitary hormone
GH-RH and what it’s secreted by
Growth hormone releasing hormone
GHRH neurons
GH-RH and what secreted it
Growth hormone inhibitory hormone/ somatostatin
Somatostatin neurons
Which cells does growth hormone target?
Liver, muscle and fat cells
IGF-1
Insulin-like growth factor-1 / somatomedin C
A hormonal growth factor secreted by the liver
Direct effects of growth hormone on muscle, liver and fat cells
Muscle: stimulates protein synthesis (long term), inhibits cellular uptake of glucose (short term)
Liver: stimulates glucose synthesis (short term)
Fat: increases triglyceride breakdown in adipose tissue (short term)
Indirect effects of growth hormone/ effects of somatomedin C
Promotes cell division
What is growth hormone’s long-term and short-term effect in general?
Long term effect on growth
Short term effect on metabolism
Term for gluconeosynthesis
Glucose synthesis
When is growth hormone concentration the highest? (2)
During sleep
During puberty
Where is the thyroid?
Just below the larynx, on the anterior and lateral surfaces of the trachea
Which main hormone is made and secreted from the thyroid gland?
Function
Thyroid hormone- essential for optimal metabolic activity
Describe three cellular components of the thyroid gland
Follicles- small fluid filled sacs
Follicular cells surrounding follicles- site of thyroid hormone synthesis
Follicular space- in between follicles and follicular cells
TGB protein- where’s it made?
Thyroglobulin protein is made in thyroid follicles
What has to happen before thyroid hormones can detach from TGB?
Iodine enters follicle cell from the blood and reacts with tyrosine
Two types of thyroid hormones
T3- the active form
T4- the more plentiful form
Number shows how many tyrosines are attached
T4 can be turned into T3
How do T3 and T4 travel to target cells and why?
They’re lipid-soluble hormones so they travel through the blood bound to a carrier protein called thyroid-binding globulin (TBG)
Why is iodine a necessary part of our diet?
Because it is required for the production of thyroid hormone
Where is the receptor for T3? Why?
In the nucleus, bound to a specific DNA site
So gene transcription can occur straight away, as soon as T3 bonds to the receptor
Response time of thyroid hormone
45 minutes- days
Is thyroid hormone secretion stimulates by internal or external stimuli?
Both- which lead to CNS input at the hypothalamus
What two hormones are secreted before thyroid hormones and where?
TRH thyrotropin-releasing hormone (hypothalamus)
TSH thyrotropin-stimulating hormone (anterior pituitary)
Effects of increased thyroid hormones
Increased basal metabolic rate
Stimulates growth and effects alertness and reflexes
BMR and basal conditions
Basal metabolic rate
The body’s rate of energy expenditure under basal conditions
- awake
- physical and mental rest
- lying down
- no muscle movement
- comfortable temperature
- fasted
What happens to a persons BMR throughout their lifetime?
Decreases
Specific effects of thyroid hormone on metabolism (5)
Increases body heat production
Stimulates fatty acid oxidation (stored fat usage)
Increases proteolysis (breakdown of proteins)
Stimulates carbohydrate metabolism (stored glucose usage)
Increase gluconeogenesis and glycogenolysis (formation of glucose)
Why does thyroid hormone not cause significant increase in blood glucose?
There’s a balance between glucose breakdown and formation
How is calcium normally gained and lost in the body?
Gained through diet (1000mg/day)
Lost through faeces and urine (1000mg/day)
Where is calcium stored in the body?
Absorbed by digestive tract and stored in blood plasma and bone
Two functions calcium is essential for
Contraction of muscles
Release of neurotransmitters
Name a hormone involved in calcium regulation
PTH parathyroid hormone
Where is PTH produced?
In thyroid follicles in the parathyroid glands
What stimulates the parathyroid gland?
A decrease in blood calcium concentration
What effect does PTH have on the kidneys?
Increases calcium reabsorption- which decreases urinary excretion of calcium
Converts vitamin D to calcitriol- which increases absorption of calcium from food (reducing loss in faeces)
What effect does PTH have on bone?
Increase bone breakdown- which increases the release of calcium into the blood
Which hormonal release pathway is not controlled by the hypothalamus?
PTH (parathyroid hormone)
Two separate glands of the adrenal gland
Adrenal cortex (outer)- secretes steroid hormones Adrenal medulla- secretes adrenaline
Where are the adrenal glands located?
Superior to each kidney
Which hormone does the adrenal cortex secrete?
Cortisol
Adrenal medulla is part of the _______ ________ system
Sympathetic nervous
In times of stress, how does the adrenal medulla respond?
Secretes noradrenaline (20%) and adrenaline (80%)
Explain the two pathways of adrenaline + noradrenaline secretion
Pre and post-ganglionic fibres synapse in the adrenal medulla secretory cells, where post fibre secretes adrenaline and noradrenaline (travels through bloodstream to target cell)
- Pre and post ganglion of fibres synapse in adrenal medulla secretory cell- BUT axons of post fibres extend to target cell, where noradrenaline is secreted
What is adrenaline?
A catacholamine
Water soluble hormone
Uses a second messenger system- which amplifies the cellular response- and is fast
Pathway of adrenaline secretion
Stress stimulates hypothalamus to send neural signal to sympathetic preganglionic fibres
These stimulate the adrenal medulla to secrete adrenaline- which travels in the blood to target cells
Effects of adrenaline (3)
Increases breakdown of glycogen to glucose in muscle in liver
Increases breakdown of fat to fatty acids in fat cells
(Make fuel more readily available to cells)
Systems not crucial for short term survival are shut down
What kind of hormone is cortisol?
Lipid-soluble steroid hormone
How does cortisol travel in the blood?
Bound to a carrier protein
Where is the cortisol receptor?
In the cytoplasm of the target cell
Is the effect of cortisol fast or slow?
Slow (hours to days)
Which two hormones lead to the release of cortisol and where are they released?
CRH (corticotropin releasing hormone) in the hypothalamus
ACTH (adrenocorticotropic hormone) in the anterior pituitary
Is cortisol stored, or produced when needed? Why?
Produced when needed, because it is a steroid hormone
If not undergoing stress response, the cortisol secretion of the body is mainly controlled by ______ _______
Negative feedback
Metabolic effects of cortisol (3)
Increase in protein and fat breakdown (in muscles and fat respectively)
Decreases in glucose uptake (in muscles and fat)
Increase in glucose synthesis (gluconeogenesis) in the liver
Other effects (non-metabolic) of cortisol (3)
Helps to cope with stress
Suppresses immune system (long term)
Maintains blood pressure
When in the day is cortisol secretion the highest?
Upon waking
What can affect daily pattern of cortisol secretion?
Disturbance to normal sleep schedule e.g. sleeping in, jet lag
Overall functions of cortisol in the body (6)
Increased blood glucose
Increased metabolism to maintain blood glucose
Anti-inflammatory actions
Increased blood pressure
Increased heart and blood vessel contraction
Activation of CNS
Hyposecretion
Too little or zero level of hormone in the blood
Hypersecretion
Too much hormone in the blood
Hyposensitive
Little or no response from a hormone receptor
Hypersensitive
Too large of a response from a hormone receptor
Autoimmunity
Destruction of hormone receptors
What can cause problems with hormone signalling? (3)
Autoimmunity
Genetic mutation: cause gain or loss of function
Tumours: excess tissue can lead to too much or not enough hormone release
Low cortisol concentration leads to _________ secretion
What does this cause? (2) (Addisons disease)
Increase in ACTH
Low blood pressure
Weakness (due to lack of fuel)
What three symptoms can too much cortisol cause? (Cushings disease)
High blood pressure
Weakness (muscle being broken down)
Too much fat is broken down and deposited in different places
How does the body respond to different kinds of stresses?
The same way
By activating the hypothalamus
Which activates the adrenal glands, sympathetic nervous systems and posterior pituitary
Which three hormones are secreted in response to stress, and where? What is their common effect?
ADH (antidiuretic hormone) in the posterior pituitary
Adrenaline in the adrenal medulla
ACTH (adrenocorticotropin hormone) in the adrenal cortex
Increase in blood pressure
What causes gigantism?
Hypersecretion of growth hormone
What can cause dwarfism?
Hyposecretion of growth hormone
What is infantile hypothyroidism caused by? What are the effects? (4)
Hyposecretion of thyroid hormone (usually due to lack of iodine in mothers diet)
Low metabolic rate
Cold intolerance
Retarded growth
Inhibited brain development
What cause iodine deficiency disorder? What is the other name for it? What are its effects?
Hyposecretion of thyroid hormone due to lack of iodine in the diet
Simple goitre
TRH and TSH secretion increases to try and secrete more thyroid hormone
- there is no negative feedback so instead the thyroid gland grows
How have we added more iodine to our diets in NZ and why?
Low levels of iodine in our soil so we don’t get enough through produce
Added iodine into table salt and now into commercially prepared bread
What is Graves’ disease caused by? What are two symptoms?
Hypersecretion of thyroid hormone due to an autoimmune disorder
- where antibodies act like TSH
High metabolic rate Weight loss Thyroid swelling Heat intolerant Hair loss Increased heart rate
What is hyperparathyroidism, what causes it, and what are its effects?
Hypersecretion of parathyroid hormone, caused by a parathyroid tumour (usually), so the cells are no longer under control (negative feedback doesn’t work)
Raises blood calcium and phosphate
Bones become soft and deformed
Promotes kidney stone formation
Hypercalcaemia and it’s effects
Blood calcium is too high
Nerve and muscle cells are less responsive/ excitable (because they’re far away from threshold)
Muscle weakness
Sluggish reflexes
Can potentially lead to cardiac arrest
Hypocalcaemia and its effects
What is it caused by?
Blood calcium is too low
Increased excitability of the nervous system (always at threshold)
Spontaneous nerve firing
Muscle cramps
Laryngospasm (larynx muscles contract)
Caused by excess loss of calcium through faeces
- vitamin D deficiency (gut doesn’t absorb)
- diarrhoea
Diabetes mellitus- two types
Type 1- hyposecretion of insulin
Type 2- insulin receptors are hyposensitive to insulin
What is type 1 diabetes caused by, and what are its effects?
How is it treated?
Can be caused by destruction of the pancreatic beta cells by the immune system
Glucosuria (excess glucose in urine)
Thirst
Heart problems
Insulin injections/ infusion
What is type 2 diabetes caused by, and what are its effects?
How is it treated?
Desensitisation of insulin receptor causes ‘insulin resistance’ (usually due to a high sugar diet/ obesity)
Same effects as type 1- glucosuria, thirst, heart problems
Changes in diet and exercise
What happens if we have a hyper or hyposecretion of glucagon?
Other hormones will increase blood glucose
When might you need a change in set point for a hormone? (3)
Change in altitude (blood count)
Change in climate (BMR)
Fever (temporary)
