Homeostasis Flashcards
What is homeostasis?
The optimal conditions for a species which is maintained however there are levels within which can fluctuate
What is synaptic intracellular communication?
Action potentials in axons and neurotransmitter release at synapse
- Targeting achieved by specific wiring
- Fastest transmission speed, to minimise response delays
What is endocrine intracellular communication?
Hormones are released into the blood
- Targeting by presence of specific receptors on target cells
- Relatively slow, but long lasting action
- Good for widespread and sustained responses
What does the endocrine system consist of?
Endocrine gland cells that secrete hormones which are carried in the bloodstream to the target cells upon which they act
What are the major endocrine glands?
Hypothalamus, pituitary gland, thyroid gland, adrenal glands, pancreas, parathyroid glands
What links the endocrine and nervous system
The hypothalamus links the endocrine system to the nervous system and controls the secretion of any endocrine glands
What are hormones?
Messengers produced in one location and transported via the bloodstream to a second location where they cause a response in those cells
What is a specific receptor?
A hormone that 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
Chemical classification of water soluble hormones
Mostly peptides (75% of hormones)
Chemical classification of lipid soluble hormones
Steroids and thyroid hormones
Storage of water soluble hormones
Made and stored until required, released by exocytosis
Storage of lipid soluble hormones
Steroids are made from cholesterol as required (not stored)
Thyroid hormones are made in thyroid cells and stored until required (this storage is unusual for lipid-soluble hormones)
Transport of water soluble hormones
Travel dissolved in the blood
Transport of lipid soluble hormones
Travel in the blood bound to a carrier protein
Where are the hormone receptors located?
Water soluble hormones: cannot cross cell membrane, receptors are located on the target cell/plasma membrane
Lipid soluble hormones: can diffuse across the cell membrane into the target cell, receptors are located in cytoplasm or nucleus
Cellular response to receptor activation: water soluble hormones
Water soluble hormone binds to cell surface receptor
Hormone binding allows activation of associated of G-protein
G-protein activates/inhibits second messenger production/reduction
Downstream proteins/pathways are activated or deactivated
Lipid soluble hormones: steroid and thyroid hormones through a membrane
Lipid soluble hormone dissociates from carrier protein -> hormone diffuses across membrane and binds to intracellular receptor which acts as a specific transcription factor -> target gene is activated and new mRNA is generated -> new protein is generated by translation of mRNA
Water soluble hormone receptors
Cell surface
Where are water soluble hormones mechanisms of action
Through 2nd messengers
How long is water soluble hormones speed of response?
Milliseconds to minutes
Where are lipid soluble hormones mechanisms of action?
Intracellular receptors in cytoplasm or nucleus
How long is the speed of response for lipid soluble hormones?
Hours to days
What is negative feedback?
Process of reducing a change until stimulus is removed or directly inhibiting further release of a hormone
What is positive feedback?
Amplification of change until a desire outcome is achieved
What does the amount of hormone in blood depend on?
Amount of hormone in blood depends on rate of hormone secretion and rate of removal from blood
Why does blood - glucose concentration need to be controlled?
If too high for too long diabetes develops, if too low hypoglycaemia occurs.
The brain must be supplied with glucose at all times as glucose is the only fuel that the brain uses
What is the fed state when referring to metabolic states?
Cellular uptake of nutrients and anabolic metabolism (synthesis of glycogen, protein and fat)
What is the fasting state when referring to metabolic states?
Mobilisation of nutrients and catabolic metabolism (breakdown of glycogen, protein and fat)
What does insulin and glucagon do?
Increases fuel storage
Peptide hormone that has membrane receptors in or on target cells
An increase in blood glucose concentration stimulates what…
Pancreatic islet beta cells to secrete insulin
Insulin stimulates what?
Muscle and adipose cells: increase in glucose uptake
Liver cells: glucose output stops increases net glucose uptake, glycogen’s and fat synthesis
Muscle, adipose and liver cells decrease what?
Blood glucose concentration which inhibits for increases blood glucose concentration
Muscle and adipose cells increase what?
Amino acid uptake, glycogen and protein synthesis
Fat synthesis
A decrease in blood glucose concentration results in what
Stimulation of pancreatic islet alpha cells secrete glucagon
Glucagon stimulates what in liver cells?
Increase in breakdown of glycogen
Increase in glucose synthesis
Increase ketone synthesis
