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