Homeostasis And Hormones Flashcards
What is homeostasis
The tendency towards a relatively stable equilibrium between independent elements
Outline the general path/response to an increase in homeostatic stimulus
Increase in stimulus
Receptors detect change
Control centre compares change to set pint and signals effectors
Effectors - organs and/or tissues respond (localised or throughout the body)
Homeostasis restored by decreasing variable
Outline the general path/response to an decrease in homeostatic stimulus
Decrease in stimulus
Receptors detect change
Control centre compares change to set pint and signals effectors
Effectors - organs and/or tissues respond (localised or throughout the body)
Homeostasis restored by increasing variable
Does homeostasis remain perfectly constant
No. Homeostasis in dynamic. It is generally maintained within “normal” levels, with various bodily responses to return non normal levels to normal
Outline the normal range within individuals
each individual will have a normal range within which their levels of a given variable fluctuate
Outline the population reference range
The population has a reference range based on the breadth of individual normal ranges within the population
How do the population reference and individual ranges compare
The population reference tends to be wider than normal fluctuations within an individual
Each individuals normal range in more narrow than the population range
What happens when moving outside the normal range of an individual
Moving outside an individuals normal range may lead to symptoms of a disorder, even when hormone levels are within the population reference range
Where do most individuals have a set point
Most individuals have a set pint that is within the population reference range
Summarise synaptic transmission
Action potentials in axons and neurotransmitter release at synapse
Targeting achieved using specific wiring
Fastest transmission speed, minimising delays
Good for brief responses
Summarise the endocrine system
Hormones released into blood
Targeting by presence of specific receptors on target cells
Relatively slow, long lasting action
Good for widespread and sustained responses
Compare the transmission, chemical signals and distribution effects of the endocrine system vs synaptic communication
Endocrine system - transmission through blood stream, chemical signals hormones, distribution effects target cells in distant tissues and organs (must have appropriate receptors
Synaptic communication - transmission across synapses, chemical signals neurotransmitters, distribution effects limited to specific areas, target cells must have appropriate receptors
What are the major endocrine glads (covered in hubs 191)
HPTAPP
Hypothalamus
Pituitary gland
Thyroid gland
Adrenal glands
Pancreas
Parathyroid glands
What is the function of the hypothalamus
Links the nervous system to the endocrine system and controls the secretions of many endocrine glands
Which physiological variables are maintain homeostatically through hormones (in hubs 191)
BGBB
Blood sugar concentration
Growth and repair
Basal metabolic rate
Blood calcium concentration
What are hormones
Chemical messengers produced in one location and transported via the bloodstream to a second location (target cells) where they cause response in those cells
What is required on/in the cell for the hormon to be able to have an effect
Receptors - proteins that are in the target cell membrane or inside the cell itself
Outline the chemical classification, storage, and transport of water soluble hormones
Chemical classification - mostly peptides (75% hormones). Some catecholamines
Storage - made and stored until required (released by exocytosis)
Transport - Travel dissolved in blood
Outline the chemical classification, storage, and transport of lipid soluble hormones
Chemical classification - steroids, thyroid hormones
Storage - steroids are made from cholesterol as required (not stored). Thyroid hormones are made in thyroid cells and stored until required
Transport - travel in the blood bound to a carrier protein
Where are hormone receptors located for water soluble hormones
Water soluble hormones (peptides, catecholamines) cannot cross cell membrane (lipid bilayer is hydrophobic)
Receptors are located in the target cell plasma membrane
Where are the hormone receptors for lipid soluble hormones located
Lipid soluble hormones can diffuse across the cell membrane and into the target cell
Receptors are located in the cytoplasm or nucleus
Outline cellular response to water soluble hormone receptor activation
Water soluble hormone binds receptor on cell surface
Hormone binds allowing activation of associated G protein (inside cell)
G protein activates/inhibits second messenger production/reduction
Downstream proteins/pathways are activated or deactivated
Outline cellular response to lipid soluble hormone receptor activation
Lipid soluble hormone dissociates form carrier protein
Hormone diffuses across cell membrane
Hormone binds to intracellular receptor
Hormone receptor complex act as a specific transcription factor
Target gene is activated
New mRNA is generated
New protein is generated by translation of mRNA
New protein mediates cell specific responses (slow process)
Outline the receptors, mechanism of action, and speed of response for water soluble hormones
Receptors - cell surface
Mechanism of action - through 2nd messengers
Speed of response - milliseconds to minutes
Outline the receptors, mechanism of action, and speed of response for lipid soluble hormones
Receptors - intracellular receptors in cytoplasm
Mechanism of action - by altering gene transcription
Speed of response - hours to days
Outline positive and negative feed back loops
Negative feedback - reduce change until stimulus is removed or directly inhibit further release
Positive feedback - amplification of change until a desired outcome is achieved
What controls amount of hormone in blood
Rate of hormone secretion
Rate of hormone removal from blood
Removal controlled by enzymes in blood or in target cells
Outline a negative feedback loop
Deviation occurs, detected by receptor, recognised by control centre
Mechanism is activated to bring variable back to set point
In long term, secretion rates of many hormones are maintain at a fairly constant level by negative feedback
