lecture 25 Flashcards
What is synaptic communication?
Action potentials in axons and neurotransmitter release at synapse- it is the fastest transmission speed to minimise response delays and good for brief responses
What is endocrine communication?
Hormones released into the blood- relatively slow but long lasting action and is good for widespread and sustained responses
What does the endocrine system consist of?
Endocrine glands cells, that secretes hormones, then carried into the blood stream and the hormones act on the target cells.
What are the major endocrine glands?
Hypothalamus, pineal gland, parathyroid glands, pituitary gland, thyroid gland, adrenal glands and pancreas
What is a paracrine system?
Chemicals released such as paracrine through extracellular fluid, and it is primarily limited to the local area, where paracrine
What is an
autocrine system?
It transmission through extracellular fluid which releases a chemical signal called autocrines and is limited to the cell that secretes the chemical signal
What is a true hormone?
They 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.
What is the endocrine system?
It transmits through the bloodstream and sends chemical signals called hormones that target cells are mainly in other distant tissues and organs and must have appropriate receptors.
Can hormones affect all cells?
No they can only affect cells with that specific receptor
What are the cell receptors made out of?
Proteins
Where can you find the receptors?
In or outside the cell.
What is the most common hormone?
75% of hormones are peptides ( chains of amino acids)
How does a peptide travel around the body?
Travels in the blood by dissolving in
Are peptide hormones stored or released straight away?
Stored and released when required through exocytosis
Are peptide hormones lipid soluble or water soluble?
Water soluble
What are the two most important water-soluble hormones?
Adrenaline and noradrenaline
What hormones are lipid-soluble?
Steroids and thyroid hormones
Can you store steroid and thyroid hormones?
You cannot store steroids as they are released straight away and thyroid hormones are made and stored until required
Where are steroids and thyroid hormones made?
Steroids are made from cholesterol and thyroid hormones are made in the thyroid.
How do lipid soluble hormones travel around?
They travel in the blood, bound to a carrier protein.
Can water soluble hormones cross the cell membrane?
No
If the hormone cannot travel throughout the cell where does the receptor lie?
On the outside of the cell, so in the plasma membrane
Can lipid soluble hormones cross the cell membrane?
Yes
If the hormone can travel through the cell where does the receptor lie?
The receptors are found in the cytoplasm and a nucleus
What does hormone binding allow activation of?
G-protein!
What does G-protein activate/inhibits?
It inhibits/activates adenylyl cyclase or increases intracellular Ca2+
Describe the steps that lipid-soluble hormone has to go through to activate in the cell
- Dissociates from carrier protein
- the hormone then diffuses across the cell membrane
- Hormone must then bind to the 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 mediates cell specific response (SLOW PROCESS)
Where are the receptors found for a water-soluble hormone?
On the cell surface
Where are the receptors for a lipid-soluble hormone found?
Intracellular receptors in cytoplasm or nucleus
What is the mechanism of action in a lipid-soluble hormone?
By altering gene transcription
What is the mechanism of action in a water-soluble hormone?
Through 2nd messengers
What is the speed of response for a lipid-soluble hormone
Hours to days
What is the speed of response for a water-soluble hormone
Milliseconds to minutes
What does the amount of hormone in blood depend on?
Rate of hormone secretion and rate of removal from blood.
How is removal of hormones controlled?
Removal is controlled by enzymes in blood or in target cells
How is secretion controlled?
Secretion is controlled by negative feedback loops USUALLY, NOT ALL THE TIME
How does negative feedback occur?
- It occurs in a System and is detected by a receptor/sensor recognised by a control centre.
- A mechanism is activated to bring the variable back to the set point, the change then occurs in the effectors.
How does positive feedback occur?
When you have an outcome you need to complete such as child birth because you need the baby to come out.
What is the overall goal of hormones?
To maintain homeostasis
What happens if you have too much or too little of hormone? levels
Can lead to endocrine disorders
What is homeostasis?
The presence of a stable internal environment.
What is the feedback loop? describe it
Receptors detect change, control centre compares to set point and signals, effectors are the organs or tissues, they respond with various effects: localised or effects throughout the body then it is restored to homeostasis.
Can the receptor and control centre be the same organ/ tissue?
Yes
Is the pancreas an exocrine or endocrine gland?
It is both
What does the exocrine gland secrete?
Cells of the pancreatic acini secrete digestive enzymes
What does the endocrine gland do?
Endocrine gland has two types of cells: beta and alpha and also has pancreatic islets
What does alpha cells secrete?
They secrete glucagon
What does beta cells secrete?
They secrete insulin
Why must our blood glucose concentration be maintained?
If it gets too high for too long you get diabetes and if it gets too low for too long you get hypoglycaemia.
What is the only fuel source the brain uses?
The brain only uses glucose
What are the two metabolic states?
Fed state and fasting state
What is the fed state?
Cellular uptake of nutrients and anabolic metabolism
What is the fasting state?
Mobilisation of nutrients and catabolic metabolism
How is blood glucose concentration regulated?
Hormonal regulation
What hormones maintain blood glucose?
Glucagon and insulin between 70-100 Dl-1 concentration
What are the target cells when the beta cell releases insulin?
Muscles and adipose cells, they increase their uptake in glucose and in liver cells glucose output stops and the net glucose uptake increases
What occurs when the glucose uptake in liver cells, muscles and adipose cells increases?
The overall blood glucose concentration decreases.
Insulin is the only hormone to decrease blood glucose concentration. True or false?
True
Do the target cells for insulin have membrane or internal receptors?
Membrane receptors
What does glucagon do?
Increases fuel release
Describe the effects of the glucagon hormone
A decrease in glucose concentration causes pancreatic islet alpha cells secrete glucagon, the target cells are liver cells- which increases the breakdown of glycogen, glucose synthesis and ketone synthesis therefore increases blood glucose concentration and blood ketones concentration.
What is it called when the liver cell increases its breakdown of glycogen?
Glycogenolysis
What is it called when the liver increases its glucose synthesis?
Gluconeogenesis
what other hormones can increase blood glucose?
Growth hormone, adrenaline and cortisol.
What type of feedback is glucagon?
Negative feedback
Where is the receptor found for the glucagon hormone?
Membrane receptors
What is hypo-secretion?
too little hormone
What is hypersecretion
Too much hormone
What is hyposensitive?
Little or no response to hormone
What is hypersensitive?
Responds too much to hormone
What can problems with hormone signalling cause?
Autoimmunity- destruction of receptors
genetic mutation
Tumors and many other things
