L25 Flashcards
What is homeostasis?
Maintaining internal environments to normal range eg temp, blood glucose levels, pH through feedback loops when it’s out of range
What problems can occur because of individual normal range and population normal range
Misleading results if a person’s test shows they are within normal population range, but out of personal range.
Features of synaptic (neural signalling) in neural control signals
AP along axons release Neurotransmitters at synapse
-Rapid transmission speed
-Need specific ‘wiring’
-good for brief responses
Features of Endocrine (hormonal signalling) in endocrine system
Hormone released into blood
-relatively slow transmission speed however longer lasting action
-good for widespread and sustained responses
Where do hormones travel to after entering the blood stream
Target cells, in distant tissues and organs that must have appropriate receptors
What is secrete travel target pathway?
Endocrine gland cells produce hormones which is secreted by endocrine gland into blood stream, travels to target cells
What are the major endocrine glands
-Hypothalamus
-Pituitary gland
-Parathyroid glands
-Thyroid glands
-Adrenal glands
-Pancreas (pancreatic islets
Function of hypothalamus in conjunction with endocrine system
-links nervous system to endocrine system
-turns neural signals into endocrine signals
-Controls secretion of many endocrine glands
4 physiological variables maintained homeostatically through hormones
-Blood sugar concentration
-Growth and repair
-Basal metabolic rate
-Blood calcium concentration
What are hormones?
Chemical messengers via bloodstream to target location
How do hormones have specific targets?
-specific receptors for specific hormone
Receptors are proteins, where can they be with the cell?
-embedded in cell membrane
-Inside of target cell
Features of water soluble hormones, eg peptides and catecholamines (adrenaline, noradrenaline) (Chemical classification, storage, transport)
-Made and stored until required via exocytosis
-able to move freely dissolved in blood
-unable to diffuse through lipid bilayer
Features of lipid soluble hormones, eg steroid, cortisol and thyroid hormones (Chemical classification, storage, transport)
Steroids are made from cholesterol as required (not stored)
Thyroid hormones, made in thyroid cells and stored until required
Both travel in blood, bound to a carrier protein
Where are hormone receptors located on water soluble hormones (peptides and catecholamines)
As they cannot cross cell membrane, receptors are located in target cell membrane
Location of hormone receptors on lipid soluble hormones, steroid and thyroid
Able to diffuse cell membrane into target cell, so receptors are located in cytoplasm or nucleus
Receptor activation in water-soluble hormones
- Hormone binds to cell surface receptors
- Activates G protein
- G protein activates or inhibits second messenger signalling of production/reduction
- Downstream proteins are activated or deactivated
Lipid soluble hormone receptor activation
- Dissociation between hormone and protein
- Hormone diffuses into the cell
- Binds to intracellular receptor (can be in cytoplasm or nucleus. Complex will move to nucleus)
- Hormone receptor complex acts as transcription factor
- Target gene is activated
- New mRNA is synthesises
- New protein is synthesised through translation
- New protein mediates cell specific response
This process is a slow process takes time
Features of WS hormones (Receptors, mechanism of action, speed)
-Cell surface
-through 2nd messengers
-milliseconds to minutes
Features of LS hormones (Receptors, mechanism of action, speed)
- intracellular receptors in cytoplasm or nucleus
- altering gene transcription
- hours to days (due to synthesis of products)
What is negative feedback (most common)
-Reduce change until stimulus is removed or directly inhibit further release
- Need to maintain hormone levels to maintain effects of hormones
What is positive feedback?
eg birth
-amplification of change until desired outcome is achieved
What does the amount of hormones in blood depends on?
-Rate of hormone secretion
-rate of removal from blood
What is removal or hormones controlled by?
Enzymes in blood or in target cells
What is secretion of hormones usually controlled by?
Mainly negative feedback loop, occasionally positive.
Homeostatic processes: receptor, control centre, change, eqbm
What are endocrine disorders caused by?
Too much or little hormone
What is within the endocrine gland of pancreas
-Pancreatic islets ~1% mass which contain beta and alpha cells
function of beta cells
Secretes insulin
Function of alpha cells
secretes glucagon
What happens if blood glucose is too high or low? Disorders
High: Diabetes
Low: Hypoglycemia
Why does the brain need glucose at all times?
because its the only fuel the brain uses
What are the two metabolic states?
Fed and Fasting
What is the fed state
Cellular uptake of nutrients and anabolic metabolism, from blood ad store away
Synthesis of glycogen, protein, fat
What is fasting state?
Mobilisation of nutrients and catabolic metabolism, glucose from store then put into blood
Breakdown of glycogen, protein and fat
What is the function of insulin and glucagon
Maintains blood glucose concentration between
Increase in blood glucose concentration leads too..
Increase of insulin secretion
Decrease in blood glucose concentration leads too..
Increase in glucagon secretion
Gluconeogenesis
We have mechanisms able to convert fatty acids and amino acids into glucose
Glycogenolysis
Cutting of glycogen into glucose to release stored glucose
which is faster glycogenolysis or gluconeogenesis
glycogenolysis
Can glucose be turned back to glycogen?
yes
