Homeostasis Flashcards
Define homeostasis.
Th maintenance of an internal environment within restricted limits in organisms.
Homeostasis is the ability to return to the optimum point and so maintains organisms in a balanced equilibrium.
What does homeostasis ensure?
That the cells of the body are in an environment that meets their requirements and allows them to function normally, despite external changes.
Outline homeostasis and enzymes?
The enzymes that control biochemical reactions within cells are sensitive to changes in pH and temperature. Any change to these factors reduces the rate of reaction of enzymes eg denaturing them.
Maintaining a fairly constant internal environment means that reactions take place at a suitable rate.
Outline homeostasis and water potential.
Changes to water potential of blood and tissue fluids may cause cells to shrink and expand (even to bursting point) due to water entering or leaving by osmosis. Meaning the cell cannot operate normally.
The maintenance of constant blood glucose concentration is essential in ensuring a constant water potential.
The optimum point is monitored by…
A receptor
The receptor detects any deviation from the optimum point (ie a stimulus) and informs the…
Coordinator.
The coordinator coordinates information from receptors and sends instructions to an appropriate…?
Effector.
An effector (muscle or gland) brings about the changes needed to return the system to the optimum point. This return to normality creates a…?
Feedback mechanism.
What is a positive system?
Occurs when a deviation from the optimum causes changes that result in an even greater deviation from the normal.
When does negative feedback not work?
Negative feedback only works within certain limits - if the change is too big then the effectors may not be able to counteract it (eg huge drop in temp from prolonged exposure to cold weather may be too large to counteract).
Why does homeostasis involve multiple negative feedback mechanisms?
Because more than one mechanism gives more control over changes in your internal environment, and gives a quicker response too.
In homeostasis, when does positive feedback occur?
When a homeostatic system breaks down.
Why aren’t positive feedback systems involved in homeostasis?
Because positive systems don’t keep your internal environment stable.
Where are hormones produced?
Produced in glands, which secrete the hormone directly into the blood (endocrine glands).
What type of cells do hormones act upon?
Target cells - these have specific receptors on their cell-surface membranes that are complementary to a specific hormone.
Hormones are very effective in ______ concentrations, but often have _________ and _______________ effects.
Effective in low concentrations
But have widespread and long lasting effects
What is the second messenger model?
A mechanism used by two hormones involved in the regulation of blood glucose concentration (adrenaline and glucagon)
Outline the second messenger model.
- Adrenaline binds to a transmembrane protein receptor within the cell-surface membrane of a liver cell.
- This changes the shape of the protein on the inside of the membrane.
- This change of protein shape leads to the activation of adenyl cyclase (enzyme). Which converts ATP into cAMP.
- The cAMP acts as a second messenger that binds to protein kinase, changing its shape - activating it.
- This active protein kinase catalysed the conversion to glycogen to glucose (glycogenolysis) which moves out of the cell by facilitated diffusion and into the blood.
Outline the pancreas.
A large gland situated in the upper abdomen. It produces enzymes (protease, amylase, lipase) for digestion and hormones (insulin and glucagon) for regulating blood glucose concentration.
Outline the ‘islets of langerhans’.
The islets of langerhans are hormone producing cells.
The cells of IoL include:
- alpha cells (larger, produce glucagon).
- beta cells (smaller, produce insulin).
Associated with regulating blood sugar levels in the liver, outline what glycogenesis is.
Glycogenesis is the conversion of glucose to glycogen.
When blood glucose conc is higher than normal, the liver removed glucose from the blood and converts it to glycogen.
Associated with regulating blood sugar levels in the liver, outline what glycogenolysis is.
Glycogenlysis is the breakdown of glycogen to glucose.
When blood glucose conc is lower than normal, the liver can convert stored glycogen back into glucose, which diffuses into the blood to restore the normal blood glucose conc.
Associated with regulating blood sugar in the liver, outline what is gluconeogenesis is.
Gluconeogenesis is the prodicerion of glucose from source either than carbs.
This occurs when it’s supply of glycogen is exhausted, so the liver produces glucose from non-carb sources eg glycerol and amino acids.
Why is homeostatic control of blood glucose so important?
Because if the conc falls too low, cells will be deprived of energy and die - brain cells are especially sensitive (as they can only respire glucose).
Also, the the conc rises too high, it lowers water potential of the blood and creates osmotic problems that can cause dehydration.
What are the 3 sources of blood glucose?
- diet, glucose is absorbed following hydrolysis of other carbs eg starch, maltose
- glycogenolysis in small intestine, hydrolysis of glycogen to glucose
- gluconeogenesis, the production of glucose from sources other this carbs
What are the main hormones involved in maintaining a constant blood glucose concentration?
Insulin, glucagon and adrenaline.
What do B cells in the islet of langerhans detect?
They have receptors to detect the stimulus of a rise in blood glucose conc. And they respond by secreting insulin directly into blood plasma.
Outline how insulin lowers blood glucose conc when it’s too high.
- Insulin binds to glycoproteins.
- This increases the permeability of muscle-cell membranes to glucose, so the cells take up more glucose. This involves increasing the no of channel proteins in the cell membrane.
- Insulin also activates enzymes in liver and muscle cells that convert glucose into glycogen (glycogenesis).
- The cells are able to store glycogen in their cytoplasm, as an energy source.
Outline how glucagon increases blood conc when it’s too low.
- A cells of the islets of langerhans detect a fall in blood glucose conc.
- Glucagon attached to specific protein receptors on the cell-surface membrane of liver cells.
- This activates the enzymes that convert glycogen to glucose (glycogenolysis)
- Glucagon also activates enzymes involved in the conversion of amino acids and glycerol into glucose (gluconeogenesis).
Why are hormones slower than responses produced by nerve impulses?
Because hormones travel in the blood.
Why do hormones have longer lasting effects than neurotransmitters?
Because hormones are not broken down as quickly as neurotransmitters.
Define homeostasis.
The maintenance of an internal environment within the restricted limits in organisms.
It is the ability to return to the optimum point (negative feedback) and so maintains organisms in a balanced equilibrium.
Why is homeostasis important?
To maintain the right body core temperature and blood pH. This is because these affect enzyme activity, and enzymes control the rate of metabolic activity.
Why is homeostasis important for pH?
Because if blood pH is too high or low, enzymes become denatured as the hydrogen bonds that hold the, in their 3D shape are broken, so the shape of the active site is changed and no longer works as a catalyst and forms E-S complexes, so metabolic reactions are less efficient.
