16. Homeostasis Flashcards
Define homeostasis
The maintenance of a constant internal environment
Name 4 things that must be controlled in an organism via homeostasis
- temperature
- pH
- water potential of blood and fluids
- blood glucose and concentration
Why must pH and temperature be controlled in an organism via homeostasis
- enzymes and proteins (eg. protein channels) in the body are sensitive to changes in pH and temperature
- that can cause them to denature
Why must water potential be controlled in an organism via homeostasis
- changes to water potential of blood and tissue may cause cells to shrink or burst (via osmosis)
- cells would not be able to function
What other factor must be maintained to ensure a constant water potential
Blood glucose concentration
What does the ability to maintain a constant internal environment mean
- organisms have a wider geographical range
- which increases the chance of finding food, shelter etc.
- as they are more independent of changes in the external environment
Name the stages in a self-regulating system
- optimum point
- receptor
- coordinator
- effector
- feedback mechanism
What is the optimum point in a self-regulating system
- the point at which the system operates best
- it is monitored by a receptor
What is a receptor in a self-regulating system
- detects any deviation from the optimum point
- informs the coordinator
What is a coordinator in a self-regulating system
- coordinates information from receptors
- sends instructions to an appropriate effector
What is an effector in a self-regulating system
- often a muscle or a gland
- brings about the changes needed to return the system to the optimum point
What is a feedback mechanism in a self-regulating system
-by which a receptor responds to a stimulus created by a change to the system brought about by the effector
What is negative feedback
A series of changes, important in homeostasis that, result in a substance being restored to its normal level
What is positive feedback
Process which results in a substance that departs from its normal level becoming further from its norm.
Give an example of negative feedback
Regulation of blood glucose
Give an example of positive feedback
- in neurones where a stimulus leads to a small influx of sodium ions
- this influx increases the permeability of the neurone membrane to sodium ions, more ions enter, causing further increase in permeability
Describe the one side of the feedback loop with glucagon (control of blood glucose)
- if there is a fall in the conc. of glucose
- this stimulus is detected by receptors on the cell-surface membrane of the alpha cells (coordinator) in the pancreas
- these alpha cells secrete the hormone glucagon
- glucagon causes liver cells (effectors) to convert glycogen into glucose
- which is released into the blood, raising the glucose concentration
- as this blood with a raised glucose concentration circulates back to the pancreas there is reduced stimulation of alpha cells
- which therefore secrete less glucagon
The secretion of glucagon leads to…
A reduction in its own secretion
Describe one side of the feedback loop with insulin
- if there is a rise in the conc. of glucose
- this stimulus is detected by receptors on the cell-surface membrane of the beta cells (coordinator) in the pancreas
- these beta cells secrete the hormone insulin
- insulin increases the uptake of glucose by cells
- its conversion to glycogen and fat
- decreasing the glucose concentration
- as this blood with a lowered glucose concentration circulates back to the pancreas there is reduced stimulation of beta cells
- which therefore secrete less insulin
Where are hormones produced and secreted
- produced in gland
- secreted directly into the blood
What are hormones effective at and what kind of effect do they have
- low concentrations
- widespread and long lasting effect
What is the mechanism of hormone action
Second messenger model
Name two hormones use the second messenger model mechanism
Adrenaline and glucagon
Describe the steps in the second messenger model mechanism involving adrenaline
- adrenaline binds to a transmembrane protein receptor with the cell-surface membrane of a liver cell
- the binding of adrenaline causes the protein to change shape on the inside of the membrane
- this change of protein shape leads to the activation of an enzyme called adenyl cyclase
- the activated adenyl cyclase converts ATP to cAMP
- the cAMP acts as a second messenger that binds to the protein kinase enzyme, changing its shape therefore activating it
- the active protein kinase enzyme catalyses the conversion of glycogen to glucose
- which moves out of the liver cell by facilitated diffusion and into the blood through protein channels
What does adrenaline bind to in the second messenger model mechanism involving adrenaline
-adrenaline binds to a transmembrane protein receptor within the cell-surface membrane of a liver cell
What effect does adrenaline binding to a transmembrane protein have, in the second messenger model mechanism involving adrenaline
-the binding of adrenaline causes the protein to change shape on the inside of the membrane
What does the change in the shape of the transmembrane protein lead to
-the activation of an enzyme called adenyl cyclase
Name two enzymes involved in the second messenger model mechanism
- adenyl cyclase
- protein kinase
What does adenyl cyclase do
-converts ATP to cAMP
What does cAMP act as
-a second messenger
What does cAMP bind to and what effect does it have
-binds to the protein kinase enzyme, changing its shape therefore activating it
What does protein kinase do
-the active protein kinase enzyme catalyses the conversion of glycogen to glucose
What happens to the glucose produced using the second messenger model involving protein
-it moves out of the liver cell by facilitated diffusion and into the blood through protein channels
Where are the hormones insulin and glucagon produced
Pancreas
What are the hormone producing cells called in the pancreas
Islets of Langerhans
What are the two types of Islets of Langerhans
- alpha cells
- beta cells
What are alpha cells
- a type of Islets of Langerhans
- produces glucagon
- slightly larger
What are beta cells
- a type of Islets of Langerhans
- produces insulin
- slightly smaller
Where do the hormones insulin and glucagon take effect
The liver
Define glycogenesis
The conversion of glucose into glycogen
Define glycogenolysis
The breakdown of glycogen to glucose
Define gluconeogenisis
The production of glucose from sources other than carbohydrate
Define two substances that can act as a source of glucose other than a carbohydrate
- glycerol
- amino acid
Why must blood glucose concentration remain constant
- if too low cells are deprived of energy and die
- if too high it lowers the water potential of the blood, causing cells to shrink
Name and describe 3 factors that influence blood glucose concentration
- diet, glucose is absorbed by the hydrolysis of carbohydrates e.g, starch, maltose, lactose and sucrose
- glycolysis (from the hydrolysis of glycogen in the SI), stored in the liver and muscle cells
- from gluconeogeneisis
- glucogenisis
Name 3 hormones that maintain a constant blood glucose
- insulin
- glucagon
- adrenaline
What do insulin molecules bind to
Specific glycoprotein receptors on cell-surface membranes
Describe 4 ways blood glucose concentration is lowered when insulin binds with receptors
- glucose transport carrier proteins allow more glucose through
- number of glucose transport channels is increased
- glycogenesis and fat production (from glucose)
- increasing the respiratory rate of cells so more glucose is used up (increasing the uptake of glucose)
Describe how glucose transport carrier proteins allow more glucose through when insulin binds with receptors, thereby decreasing glucose concentration
- insulin binds with receptors on cell surface membranes
- glucose transport carrier proteins tertiary structure changes
- changes shape to be more open allowing more glucose to move into the cells via facilitated diffusion
Describe how the number of glucose transport channels is increased by the binding of insulin to receptors on the cell surface membrane, thereby decreasing glucose concentration
- at low concentrations of insulin the protein from which the glucose transport channels are made of is contained in vesicles
- a rise in insulin concentration causes vesicles to fuse with the cell-surface membrane when insulin binds to the receptors
- this increases the number of glucose transport channels
Why is the secretion of insulin a negative feedback loop
- the effect of B cells cause the decrease in glucose concentration
- this causes the B cells to reduce their secretion of insulin
Describe 3 ways blood glucose concentration is increased when glucagon binds with receptors
- activating enzymes that convert glycogen into glucose (glycolysis)
- activating enzymes involved in the conversion of amino acids and glycerol into glucose (gluconeogenesis)
How does insulin cause glycogenesis and fat production (from glucose), thereby decreasing glucose concentration
by activating the enzymes that cause glycogenesis and fat production (from glucose)
Why is the secretion of glucagon a negative feedback loop
- the effect of A cells cause the increase in glucose concentration
- this causes the A cells to reduce their secretion of glucagon
How does adrenaline raise blood glucose concentration
- attaching to protein receptors on cell-surface membrane of target cells
- activating enzymes that causes the breakdown of glycogen to glucose in the liver
How are the hormones insulin and glucagon said to work
Antagonistically
What is diabetes
A metabolic disorder caused by the inability to control blood glucose concentration due to to a lack of the hormone insulin or a loss of responsiveness to insulin
Type 1 diabetes is
Insulin dependent
Type 2 diabetes is
Insulin independent
What is type 1 diabetes caused by
- due to the body being unable to produce insulin.
- may be the result of an autoimmune response
- where the body’s immune system attacks its own cells, in this case the B cells of islets of Langerhans.
When does type 1 diabetes usually develop
In childhood
What is type 2 diabetes caused by
- glycoprotein receptors on body cells become lost or lose their responsiveness
- may also be due to an inadequate supply of insulin.
When does type 2 diabetes usually develop
People over the age of 40
In what way does type 1 diabetes develop
- quickly over a few weeks
- signs and symptoms are obvious
In what way does type 2 diabetes develop
- slowly
- symptoms are less severe and may go unnoticed
How is type 1 diabetes controlled
By injections of insulin
Why cannot insulin be taken by the mouth
- insulin is a protein
- would be digested
How is insulin dose decided and why
- must be matched exactly to glucose intake
- if too much insulin was taken she will experience a low blood glucose concentration that could result in unconsciousness
- correct dose is insured by monitoring blood glucose concentration using biosensors
How is type 2 diabetes controlled
- regulating the intake of carbohydrate in the diet and exercise
- sometimes supplementary injections or drugs that stimulate insulin production
