homeostasis Flashcards
homeostasis
the presence of a relatively stable internal environment
normal range is?
an individual’s normal range within which their levels of a given variable fluctuate
reference range is?
the populations reference range based on the breadth of individual normal ranges within a population. the population reference range tends to be wider than normal fluctuations within an individual:
features of neural (aka synaptic) control system (4 features)
- action potentials in axons and neurotransmitter release at synapse
- targeting achieved by specific ‘wiring’
- fastest transmission speed (compared to endocrine), to minimise response delays
- good for brief responses
features of endocrine control system (3 features)
- hormones released into the blood
targeting by presence of specific receptors on target cells - relatively slow, but long lasting action
endocrine system (secrete-travel-target) consists of (4 facts)
- endocrine gland cells that secrete hormones
- these are carried in the bloodstream to the target cells upon which they act
- target cells are mainly in other distant tissues and organs
- target cells must have appropriate receptors
major endocrine glands
7 glands
hypothalamus pituitary gland thyroid gland adrenal gland pancreas (pancreatic islets) pineal gland parathyroid glands
hypothalamus does?
links the nervous system to the endocrine system and controls the secretion of many endocrine glands
organs with secondary endocrine functions
5 organs
heart thymus digestive tract kidneys gonads - testis, ovary
hormones
true hormones are chemical messengers produced in one location and transported via the bloodstream to a second location (target cells) where they cause a response in those cells
specificity of hormone action
what is the only thing a hormone can affect?
a hormone can only affect cells with specific receptors for that hormone. each receptor is a protein. it can be in the target cell membrane or inside the target cell
water soluble hormones
chemical classification
mostly peptides (75% of hormones), some catecholamines include adrenaline and noradrenaline
water soluble hormones
storage classification
made and stored until required (released by exocytosis)
water soluble hormones
transport classification
travel dissolved in the blood
water soluble hormones
receptors classification
cell surface
water soluble hormones
mechanism of action classification
through 2nd messengers
water soluble hormones
speed of response classification
milliseconds to minutes
Lipid (fat) soluble hormones
chemical classification
steroids
thyroid hormones including both T3 and T4
Lipid (fat) soluble hormones
storage classification
steroids are made from cholesterol as required
thyroid hormones are made in thyroid cells and stored until required
Lipid (fat) soluble hormones
transport classification
travel in blood bound to a carrier protein
Lipid (fat) soluble hormones
receptors classification
intracellular receptors in cytoplasm or nucleus
Lipid (fat) soluble hormones
mechanism of action classification
by altering gene transcription
Lipid (fat) soluble hormones
speed of response classification
hours to days
where are the water soluble hormone receptors located?
cannot cross the cell membrane, therefore receptors are located in target cell/plasma membrane
where are the lipid soluble hormone receptors located?
can diffuse across the cell membrane into the target cell, therefore receptors are located in the cytoplasm or nucleus
cellular response to receptor activation
water soluble hormones (4 steps)
- water soluble hormone binds to cell surface receptor
- hormone binding allows activation of associated G-protein
- G-protein activates/inhibits second messenger production/reduction
- downstream proteins/pathways are activated or deactivated
cellular response to receptor activation
lipid soluble hormones (8 steps)
- lipid soluble hormone dissociates from carrier protein
- hormone diffuses across cell membrane
- hormone binds to intracellular receptor
- hormone-receptor complex acts as a specific transcription factor
- target gene is generated
- new mRNA is generated
- new protein is generated by translation of mRNA
- new protein mediates cell specific response (slow process)
maintenance of hormone levels for?
need to maintain hormone levels to maintain effects of hormones
maintenance of hormone levels
negative feedback
most common
reduce change until stimulus is removed or directly inhibit further release
maintenance of hormone levels
positive feedback
occasionally
amplification of change until a desired outcome is achieved
control of hormone secretion is?
amount of hormone depends on rate of hormone secretion, rate of removal from blood
control of hormone secretion
what is secretion usually controlled by?
negative feedback loops, most use negative feedback control
control of hormone secretion
what does deviation do?
occurs in a system and is detected by a ‘receptor’ and recognised by a control centre (sometimes the same organ is the ‘receptor’ and control centre, sometimes they are different).
control of hormone secretion
a mechanism is activated to?
bring the variable back to the set point (or reference range), change occurs in effectors
control of hormone secretion
in the long term, the secretion rates of many hormones?
are maintained at a fairly constant level by negative feedback
control of hormone secretion
a few hormones use?
positive feedback (at specific times)
control of hormone secretion
the goal of hormones is to?
maintain homeostasis
too much or too little hormone can lead to endocrine disorders
pancreas
an exocrine gland and an endocrine gland
pancreatic islets
~1% of mass
beta cells secrete insulin
alpha cells secrete glucagon
energy utilisation and storage
blood glucose concentration must be?
maintained within a narrow range at all times for normal functioning (homeostasis)
energy utilisation and storage
diabetes develops if?
blood glucose concentration is too high for too long
energy utilisation and storage
hypoglycemia occurs if?
blood glucose concentration is too low
energy utilisation and storage
what must the brain be supplied with at all times and why?
glucose as glucose is the only fuel that the brain uses
energy utilisation and storage
why do blood glucose levels fluctuate throughout the day?
because we use fuel continuously but eat intermittently
energy utilisation and storage
two metabolic states
fed state
fasting state
energy utilisation and storage
fed state
cellular uptake of nutrients and anabolic metabolism
synthesis of glycogen, protein and fat
energy utilisation and storage
fasting state
mobilisation of nutrients and catabolic metabolism
breakdown of glycogen, protein and fat
hormone regulation
insulin and glucagon maintain blood glucose concentration between 70-110 dL-1
pituitary gland
location
base of the brain and attached to the hypothalamus
pituitary gland
controls the?
secretion of pituitary hormones (when activated by neural input, the hypothalamus stimulates the pituitary gland to secrete hormones)
pituitary gland
what do pituitary hormones do?
(2 jobs)
some stimulate target cells
some stimulate the secretion of hormones by other endocrine glands
pituitary gland
two part of the pituitary gland are?
anterior lobe
posterior lobe
pituitary gland
posterior lobe
connected to the hypothalamus by?
neurons - cell bodies in the hypothalamus
axons terminate in the posterior lobe
pituitary gland
posterior pituitary hormones
3 facts
made in hypothalamus (cell body of the neuron)
travel down the axon
stored at the axon endings until required (peptide hormones)
pituitary gland
posterior lobe
communication
hypothalamus uses neural communication with the posterior lobe to release hormones into the blood: increased (or decreased) frequency of action potentials leads to corresponding change in hormone release
pituitary gland
posterior lobe
what two hormones can be released into the blood by means of the posterior lobe?
antidiuretic hormone (ADH
or
oxytocin
pituitary gland
posterior lobe
antidiuretic hormone
stimulates kidneys to reabsorb water (the kidneys conserve water when the body dehydrates)
pituitary gland
posterior lobe
oxytocin
stimulates the contraction of uterine muscles during childbirth (an example of positive feedback)
stimulates milk release in breastfeeding (milk ejection reflex)
pituitary gland
posterior lobe hormones
made and stored where?
both hormones are made in the hypothalamus and stored in the posterior pituitary until required
pituitary gland
anterior lobe
connected to the hypothalamus by?
blood vessels
hypothalamic hormones stimulate or inhibit release of stored hormones from specific anterior pituitary cells
pituitary gland
anterior lobe
communication
3 steps
stimulus - neural input within hypothalamus
hypothalamus signals the anterior pituitary to release hormones by hormonal stimulation, secreting stored releasing hormone (or inhibiting hormone)
hormone binds to receptor on membrane of a specific cell type and a specific anterior pituitary hormone is secreted e.g. prolactin, growth hormone
pituitary gland
anterior lobe
feedback regulation of the anterior pituitary gland
4 steps
hypothalamus releasing hormone —>
anterior pituitary gland releasing the pituitary hormone —>
target organ to release another hormone —>
hormone has an effect
pituitary gland
anterior lobe
8 hormones
GH-RH GH-IH (SS) TRH PIH PRH PRL GnRH CRH
pituitary gland
anterior lobe
GH-RH function, target gland, secretes?
stimulates release of growth hormone
liver
IGF-1
pituitary gland
anterior lobe
GH-IH (SS) function
inhibits the release of growth hormone and TSH
pituitary gland
anterior lobe
TRH function, target gland, secretes?
stimulates the release of TSH
thyroid
T3 and T4
pituitary gland
anterior lobe
PIH function
inhibits the release of TSH and PRL
pituitary gland
anterior lobe
PRH function, target gland, secretes?
stimulates the release of PRL
mammary
breast milk
pituitary gland
anterior lobe
PRL function
inhibits the release of GnRH
pituitary gland
anterior lobe
GnRH function, target gland, secretes?
stimulates the release of FHS and LH
gonads
estrogen and testosterone
pituitary gland
anterior lobe
CRH function, target gland, secretes?
stimulates the release of ACTH
adrenal cortex
cortisol
pituitary gland
anterior lobe
growth hormone
activity in the hypothalamus
one set of neurons will release the growth hormone releasing hormone and one set of neurons will release the growth hormone
pituitary gland
anterior lobe
growth hormone
travels to?
the anterior pituitary gland where the growth hormone is released
then travels to the liver and causes it to release somatomedin C (IGF-1) which will cause effects in the body
pituitary gland
anterior lobe
growth hormone
once the growth hormone has been released what feedback to we get and why?
negative feedback to the hypothalamus to limit GH-RH release
and negative feedback to anterior pituitary via stimulation of hypothalamus to release GH-IH
pituitary gland
anterior lobe
growth hormone
direct effects - muscle
stimulates protein synthesis (long term) and inhibits cellular uptake of glucose (short term)
pituitary gland
anterior lobe
growth hormone
direct effects - liver
stimulates glucose synthesis (short term)
pituitary gland
anterior lobe
growth hormone
direct effects - fat
increases triglyceride breakdown in adipose tissue (short term)
pituitary gland
anterior lobe
growth hormone
indirect effects (2)
promotes the growth of bones, muscle and other tissues by causing release of somatomedin C which promotes cell division (long term)
GH has a long term effect on growth and short-term effects on metabolism
