Physiology 1 Flashcards
Individual set point
Each individual will have a normal range within which their levels of a given variable fluctua
Population reference range
The population has a reference range based on the breadth of individual normal ranges within population
The population reference range tends to be wider than normal fluctuations within an individual
Most individuals will have a set point that is within the population reference range
Synaptic (aka Neural) control systems
APs in axons and neurotransmitter release at synapse
- targeting achieved by specific ‘wiring’
- fastest transmission speed, to minimise response delays
- good for brief responses
Endocrine (hormonal) control systems
- hormones relased into blood
- targeting by presence of specific receptors on target cells
- relatively slow, but long lasting action
- good for widespread and sustained responses
Mechanisms of intracellular communication
The endocrine secrete travel target
Consists of - endocrine gland cells that secrete hormones which are carried to the blood steam to the target cells upon which they act
purpose of the hypothalamus
- a major endocrine gland??
- the hypothalamus links the nervous system to the endocrine system and controls the secretion of many endocrine glands
Major endocrine glands
Physiological variables that are maintained homeostatically through hormones
- blood sugar concentration
- growth and repair
- basal metabolic rate
- blood calcium concentration
Often multiple hormones are involves in homeostasis of one variable
What is a hormone?
- true hormones are chemical messengers produces in one location and transported via to blood stream to a second location (target cells) where they cause a response in those cells
Specificity of hormone action
- a hormone can only effect cells with specific receptors for that hormone
- each receptor is a protein
- it can be in the target cell membrane or inside the cell target
Classification of hormones
Water soluble:
- mostly peptides (75% of hormones) - adrenaline and noradrenaline
- made and stored until required (released by exocytosis)
- travel dissolved in the blood
Lipid (fat) soluble:
- steroids and thyroid
- steroids are made from cholesterol as required
- thyroid hormones are made in thyroid cells and stored until required (unusual for lipid soluble hormones)
- travel in blood bound to carrier
Where are the hormone receptors located?
Water-soluble hormones (peptides and catecholamines)
- cannot cross the cell membrane
- therefore receptors are located in the target cell/ plasma membrane
Lipid-soluble hormones (steroid and thyroid hormones)
- 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
- water-soluble hormone binds to cell surface receptor
- hormone binding allows activation of associated G-protein
- G-protein activates/inhibits second messenger production/reduction (e.g cyclic AMP/cAMP or Ca2+)
- downstream proteins/ pathways are activated or deactivated
Receptor activation: Lipid-soluble hormones: steroid and thyroid
- Lipid-soluble hormones dissociated 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 activated
- New mRNA is generated
- New protein is generated by translation of mRNA
- New protein mediated cell spicifc response (SLOW)
Composition of water soluble and lipid soluble hormones
Maintenance of hormone levels
- negative feed back (most common):
- reduce change until stimulus is removed or directly inhibit further release
- need to maintain hormone levels to maintain effects of hormones
- positive feedback (occasionally)
- amplification of change until a desired outcome is achieves
Amount of hormone in blood depends on:
- Rate of hormone secretion
- Rate of removal from blood
Removal is controlled by enzymes in blood or in target cells
Secretion usually controlled by negative feedback loops
Deviation occurs in a system and is detected by a ‘receptor’ and is recognised by a control centre (sometimes the same organ is the receptor and control centre, sometimes they are different)
A machanism is activated to bring the variable back to the set point (or preference range), change occurs in effectors
In the long term, the secretion rates of many hormones are maintained at fairly constant level by negative feedback
A few hormones use positive feed back
The goal of hormones
To maintain homeostasis
What happens if there is too much or too little hormone
Endocrine disorders
The pancreas
Is an exocrine and endocrine gland
Exocrine gland: cells of pancreatic acini secrete digestive enzymes
Endocrine gland: pancreatic islets (less then 1% of mass)
- beta cells secrete insulin
- alpha cells secrete glucagon
Energy utilisation and storage - blood glucaose concentration
Blood glucose concentration must be maintained within a narrow range at all times for normal functioning
But blood glucose concentration changes throughout the day as we use fuel continuously but eat intermittently
What happens if blood glucose concentration is too low
Hypoglycaemia
What happens if blood glucose is too high for too long
Diabeties develops
The two metabolic states we move bertween throughout the day:
Fed state: cellular uptake of nutrients and anabolic metabolism (synthesis of glycogen, protein and fat)
Fasting state: mobilisation of nuterins and catabolic metabolism (breakdown of glycogen, protein and fat)
How blood glucose concentration is regulated
Hormonal regulation:
Insulin and glucagon maintain blood concentration
Gluconeogenisis
Fatty acids and amino acids ——-> glucose
Insulin: increases fuel storage INCREASE IN BLOOD GLUCOSE CONCENTRATION
Increase in blood glucose concentration
Detected by pancreatic islet beta cells (the sensor and the control centre)
Secrete insulin
In the target cells :
- muscle and adipose cells increase glucose uptake (
- Muscle - increase in amino acid uptake, glycogen and protein synthesis
- adipose - fat synthesis
- liver cells glucose output stops (increase in net glucose uptake)
- in liver will make glycogen and fat
Therefore blood glucose concentration will go down
Insulin is the only hormone that can decrease the blood glucose concentration - peptide hormone so can sit there waiting to be released - water soluble so has cell surface receptor
Negative feedback control - response reduced the stimulus
Glucagon: increase fuel release DECRESE IN BLOOD GLUCOSE CONCENTRATION
decrease in blood glucose concentration
Pancreatic islet alpha cells detect it and secrete glucagon
Target cell: liver cells:
- increased breakdown of glycogen (glycogenolysis)
- increase in glucose synthesis (gluconeogenesis)
- increase in ketone synthesis
Increase in blood glucose concentration
Increase in blood ketones concentration
Negative feed back removes stimulus
(Growth hormone adrenaline and cortisol can also increase blood concentration)
Glycogen
Stored form of glucose
(insulin is a peptide hormone - target cells have membrane receptors)
Glucagon
Hormone
What is glucagon
Glucagon is a peptide hormone and target cells have membrane receptors
What is homeostasis
Homeostasis is the maintenance of a relatively stable internal environment
Hormones cause a cellular response through a signalling cascade that can be:
- stimulated through a plasma membrane receptor and a second messenger
- stimulated through an intracellular receptor a;tearing gene transcription
