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Flashcards in Homeostasis part 1 Deck (50):

What is homeostasis ?

Homeostasis is the maintenance of a constant internal environment despite changes in the external environment


What happens if the blood pH is too high?

Enzymes may become denatured. The hydrogen bonds that hold the tertiary structure too can be altered and the enzyme no longer acts as a biological catalyst. This means metabolic reactions are less efficient e-s complexes can no longer form . Substrate doesn’t fit active site as it has changed shape


What happens if the temperature drops too low?

Reduces the rate of enzyme activity
Cells cannot respire fast enough to produce ATP


Why is a high blood glucose concentration potentially dangerous

Water potential in blood is low so water molecules diffuse out of the cell by osmosis and cells may shrivel up and die


Why is Low blood glucose concentration potentially dangerous?

They can’t carry out metabolic processes such as respiration to release energy


What is negative feedback?

Negative feedback is a mechanism that restores a deviation from the norm to the normal level


How does negative feedback work?

Receptors detect the change ie whether it is too high or too low and the information is communicated via the nervous system or hormonal system to effectors.
The effectors respond to counteract the change and initiate corrective mechanisms


What is the problem with negative feedback?

It only works within certain limits if the change is too big then effectors may not be able to counteract it.


What is the advantage of having multiple feedback mechanisms for controlling one factor?( ie increase and decrease temperature)

Gives you more control over changes in your internal environment
You’d only be able to actively change level in one direction so it returns to normal
It’s a much faster response


What are the two main functions of the kidney?

Excretion ie the filtration of blood to remove urea
Osmoregulation ie the kidneys maintain the blood at a constant water potential


What is positive feedback?

A mechanism ( not homeostatic) and it amplifies changes away from the norm. Any change away from the norm creates more change.


How do positive feedback mechanisms work?

Receptors detect the change and there’s communication via the nervous or hormonal system
Effectors respond by amplifying the change.


Why May positive feedback mechanisms be useful? Give an example?

Rapidly activate processes in the body
During injury platelets become activated and release a chemical this triggers more platelets to be activated and easily forms a blood clot
It’s useful when homeostatic mechanisms break down
When body temperature falls brain stops working properly and shivering stops
Positive feedback takes body temperature further away from the normal level and it continues to decrease unless action is taken
( ie negative feedback which brings it to normal level see page 116)


What is glucose?

It’s a respiratory substrate than can be broken down during respiration to release energy?
It’s a type of monomer called a monosaccharide.


What are the 3 ways in which blood glucose concentration increases?

Directly from the diet in the form of glucose absorbed following the hydrolysis of carbohydrates such as starch, maltose and lactose.

Hydrolysis of glycogen stored in the muscle and liver. This is known as GLYCOGENOLYSIS
Breakdown of glycogen( lysis means breakdown)
From gluconeogenesis( production of glucose from amino acids and or glycerol


Why do organs such as the brain need a constant supply of glucose?

Unable to store carbohydrates


What is the pancreas and what does it contain?

It’s an organ containing a tissue called the islets of langerhans. These contain receptors that are sensitive to blood glucose concentrations


What are islet of islet of langerhans?

These are tissues that contain the alpha and beta cells


Describe hormonal action

Hormones( ie insulin and glucagon ) are chemical messengers that travel in the blood to their target cells.
These target cells( ie effectors such as muscle cells ) have specific receptor proteins in the plasma membrane


Why are these receptor proteins specific ?
Note: hormones tend to be proteins

Each has a specific tertiary structure which only a hormone with a complementary shape will bind to as the receptor has a specific binding site


Where are hormones produced?

Endocrine glands( ie glands in endocrine system)


What happens if blood glucose concentration is high?

Once high blood glucose concentration is detected by the receptors on the beta cells in islet of langehans secrete insulin. This is released into the blood and travels to its target cells . These are mainly muscle or liver cells. Insulin binds to specific receptors on the target cell membrane.

Ensure you say this is a positive feedback mechanism and explain why


How does insulin cause a reduction in blood glucose?
Note: Sanna needs insulin as her blood sugars are always high so insulin is reduction in blood sugar levels

Insulin increases the permeability of muscle cell membranes to glucose, so the cells take up more glucose. They do this by increasing the number of channel proteins in the cell membrane

Insulin activates enzymes inside the muscle and liver cells that convert glucose into glycogen( glycogenesis)
The ( muscle or liver) cells store glycogen in their cytoplasm as an energy source
Therefore increased absorption of glucose by these cells via glucose transport proteins in te cell membrane

Insulin activated enzymes which convert glucose into fats for storage in adipose tissue ( adipose tissue is essentially fatty tissue).

Insulin also increases the rate of respiration of glucose, especially in muscle cells.


How does Gluacagon raise blood glucose concentration when it’s too low?
Gone: glucose concentration is ‘gon’ so needs to be increased

Released by alpha cells in the islet of langerhans

It binds to specific receptors in plasma/cell membrane of liver cells and activates enzymes that break down glycogen into glucose ( glycogenolysis)

Glucagon also activates enzymes that are involved in the formation of glucose from glycerol( component of lipids) and amino acids.
This is gluconeogenesis

Glucagon decreases the rate of respiration of glucose in cells

Inhibits release of insulin

Glucose leaves the cells by facilitated diffusion/through channel proteins

Ensure you say this is a negative feedback mechanism and explain why


What happens if blood sugar concentration is low?

Alpha cells release glucagon. Glucagon binds to specific receptor proteins in plasma membrane is target cells


What are glucose transporters? How do they work depending on their conditions?

These are channel proteins which allow glucose to be transported across a cell membrane
Skeletal and cardiac muscles contain a glucose transporter called GLUT4
When insulin levels are low( the glut4) the channel proteins are stored in vesicles in the cytoplasm of the cells, but when insulin binds to receptor proteins on the plasma membrane/ cell surface membrane of the cell it triggers the movement of channel proteins( glut4) to the membrane .Glucose can be transported into the cells by the GLUT4 protein by facilitated diffusion.
-Permeability to glucose is increased.


What is adrenaline? And what is it’s role in controlling blood glucose concentrations?

Adrenaline is a hormone that is secreted from your adrenal glands. Its secreted when there’s a low concentration of glucose in the blood and it binds to the receptors on the cell membranes of the liver cells .
Often responds to the ‘flight or fight’ response when stressed or exercising when blood glucose concentrations are low and serves to increase them.( there’s more muscle contraction in the flight or fight response)


How does adrenaline increase blood glucose concentrations?

It activates glycogenolysis( the breakdown of glycogen to glucose)
It inhibits glycogenesis( the synthesis of glycogen from glucose)

It also activates glucagon secretion and inhibits insulin secretion, which increases glucose concentration

Adrenaline gets the body more ready for action by making more glucose available for muscles to respire


What is the second messenger model and give some examples of hormones that act via the second messenger?

Cyclic AMP is a second messenger (cAMP)
Glucagon and Adrenaline activate glycogenolysis inside a cell even though they bind to receptors outside of a cell. This is done via the second messenger model.

The binding of a hormone activates enzymes inside of the cell membrane which produces the second messenger

The second messenger activates other enzymes in the cell to bring about a response.


How does adrenaline and glucagon act via the second messenger?

The hormones bind to receptor site on the plasma membrane of the liver cell which have a complimentary structure to their respective hormones
This activates the enzyme adenylate cyclase inside the membrane
The activated adenylate Cyclase converts ATPto cyclic AMP which acts as a second messenger that activates an enzyme called protein kinase A.
Protein Kinase A activates a chain of reactions that breaks down glycogen to glucose (glycogenolysis)


What is the function of protein Kinase A?

Phosphorylates other molecules which activates other enzymes


When would blood glucose concentration get too high or too low?

Rises when you eat a meal filled with carbohydrates
Falls during respiration as glucose is used as a respiratory substrate


How does the formation of glycogen result in an increased diffusion of glucose into the liver cells?

Lowers glucose concentration in liver cells
So glucose can diffuse down the concentration gradient out of the blood and into liver/muscle cells

Channel proteins /facilitated diffusion


How do we cool down?

Sweating produced by sweat glands evaporate to cool down as water has a high latent heat of vaporisation
Body temperature is maintained by hypothalamus which contains thermoreceptors info is communicated via nervous system and impulse sent to effectors


What is diabetes?

Diabetes Mellitus is a disease where the body is unable to control the blood glucose concentrations effectively


What is type 1 diabetes?

This is an inability to produce insulin. The body’s own immune system may destroy the beta cells and this is known as an autoimmune response.
Blood glucose concentrations therefore stay high for a long period of time after eating and this hyperglycaemia can be fatal.
The kidneys cannot possibly reabsorb all the glucose so some of it is excreted in the urine
Has genetic links


How is type 1 diabetes controlled?

Blood glucose concentrations need to be monitored regularly and this can be done via a biosensor.
Insulin can be given by injection but this has to match the glucose intake.
Diabetics must also manage their diet and levels of exercise.
Care must be taken to balance diet and insulin to avoid hypoglycaemia ( ie through injecting too much insulin)
Insulin pumps can deliver insulin continuously .


Why can’t insulin be given orally?

It will be hydrolysed by proteases in the digestive system as it is a protein.


What are the risk factors for type 2 diabetes?

This is usually acquired later in life and it is often linked with obesity, unhealthy diets and low levels of physical activity.
Genetically predisposed


How is type 2 diabetes thought to be caused?

The beta cells don’t produce enough insulin or when the body’s cells don’t respond properly to insulin. The body cells don’t respond to insulin properly as the insulin receptors on their membranes don’t work properly so the cells don’t take up enough glucose
The blood glucose concentration is higher than normal


How can type 2 diabetes be treated?

Eating a healthy, balanced diet
Losing weight if necessary and exercising regularly
Glucose lowering medications can be taken if diet and exercise can’t control it
Eventually injections may be needed.


What are the health impacts of diabetes?

People with diabetes are at a greater risk of chronic health condition such as cardiovascular disease, blindness( diabetic retinopathy),amputation, kidney disease and depression than people without diabetes.


What are the diagnostic features of diabetes?

High concentration of blood glucose means that the kidneys is unable to reabsorb all the glucose filtered back into the blood( glucose comes the glomerular filtrate) this results in large amount of glucose in the urine

Frequent urination( blood glucose concentration increased so water enters blood by osmosis not as much can be reabsorbed by kidneys so produce more urine.
Craving sweet foods
Persistent thirst


What can society do and health advisors do to decrease the incidences of type 2 diabetes?

Health advisors recommend that people eat a diet that’s low in fat, sugar and salt
Educate people on healthier lifestyle choices and challenge the food industry to reduce advertising of junk food and to improve nutritional value of products and use clearer labelling so consumers can make a more informed choice


What are the issues relating to food companies contributing towards the diabetes epidemic?

In response to pressure some food companies have made their products more heathy. Using sugar alternatives to sweeten food and drinks and reduce sugar and fat content

However there’s pressure to increase profits so they may be reluctant to develop healthier alternatives if the unhealthy product is still popular and generates lots of profit

They may only respond in long term when public perception about healthy eating changes.


A 55 year old man was newly diagnosed with diabetes? How is his condition similar to type 2 diabetes?

Diabetes developed in an older man.


When testing for diabetes/blood glucose concentration why is it important that patients don’t eat before the test?

Time is needed for restore normal glucose concentration / for insulin to act


Why might someone have a high blood glucose concentration?

They may have had a drink containing High levels of sugar


Why is haemoglobin not effective in accurately determining mean blood glucose concentration after a certain time worked

Haemoglobin has a short lifespan and will break down after a few weeks


Under what circumstances may someone be given glucagon injections?

Dangerously low blood glucose concentration
Can’t produce enough glucagon
Glucagon source can’t be taking orally as it is a protein