3.6- Chapter 16- Homeostasis Flashcards
(111 cards)
1
Q
In what situation is homeostasis important?
A
- Control of internal environment- important for complex organisms.
- Homeostasis and hormonal coordination are important for an organism’s physiological control.
- Organisms- maintain relatively constant internal environment for their cells- limit external changes.
2
Q
What is homeostasis?
A
- Maintenance of a constant internal environment (within restricted limits) in organisms.
- In mammals involves using physiological control systems to maintain the internal environment within restricted limits.
3
Q
Describe the internal environment in complex organisms, how it is maintained and why this is important.
A
- Internal environment- made of blood and tissue fluid- surround each cell- supply nutrients and remove wastes.
- Chemical make-up, volume and features of blood and tissue fluid are kept within restricted limits by homeostasis.
- Maintaining components of the tissue fluid at optimum levels protects cells from changes in the external environment.
- Ensures cells are in an environment that meets their requirements and enables them to function normally and avoid damage despite external changes.
4
Q
Describe how homeostasis works in terms of levels.
A
- Homeostasis creates dynamic equilibrium- continuous fluctuations brought about by variations in internal and external conditions but occur around an optimum point/ normal level e.g. temperature, pH, water potential.
- Homeostasis- creates ability to return to optimum point and maintain balanced equilibrium
5
Q
Why is homeostasis important to organisms.
A
Organisms more able to manage changes in external environment- able to survive in more habitats- wider geographical range- more likely to find food/ shelter- gives organisms more independence and means it is more likely to outcompete other organisms.
6
Q
Give two example factors of homeostasis and the importance of controlling them.
A
- Important to maintain stable core body temperature and blood pH- affect enzyme activity- enzymes control the rate of metabolic reactions. Even small fluctuations reduce rate of reaction of enzymes and may denature of them. Constant environment- ensures reactions take place at a suitable rate. Other proteins e.g. channel proteins- also sensitive to changes in pH/ temperature.
- Changes to water potential of blood/ tissue fluid- cause cells to shrink/ expand due to water leaving/ entering osmosis- can’t operate normally. Water potential may also affect concentrations of substrates and enzymes and therefore rate of reaction. Constant blood glucose concentration- important to ensure constant water potential and reliable source of glucose for respiration to provide energy.
7
Q
Describe why homeostasis with regards to temperature is important.
A
- Rate of metabolic reactions increases as temperature increases. More heat means more kinetic energy- molecules move faster- makes the substrate more likely to collide with the enzymes active site. Energy of collisions also increases- each collision is more likely to result in a reaction.
- If temperature gets too high- breaks hydrogen bonds that hold enzymes tertiary structure- active site changes shape- enzyme and substrate no longer fit together- enzyme is denatured and no longer functions as a catalyst.
- Body temperature too low- enzyme activity is reduced- slows rate of metabolic reactions. Highest rate of enzyme activity happens at optimum- 37℃.
8
Q
Describe why homeostasis with regards to pH is important.
A
- Too high or too low- enzymes become denatured- ionic and hydrogen bonds broken changing the tertiary structure- shape of active site changed- no longer works as a catalyst.
- Highest rate of enzyme activity- happens at optimum pH- when metabolic reactions are fastest.
- Optimum- around pH7 but some have different optimums e.g. in the stomach.
9
Q
Describe how pH is calculated.
A
- pH- concentration of hydrogen ions- greater= lower pH.
- pH=-log10(H+)- pH is expressed on a logarithmic scale due to large variations- each value on a logarithmic scale using log10 is ten times larger than the value before. A solution of pH 3 contains ten times more H+ ions than a solution of pH 4. Makes it easier to plot very small and very large values on the same graph.
- (H+) is the concentration of hydrogen ions in a solution- usually measured in mol dm-3. Once you know the hydrogen ion concentration you can calculate the pH using the formula.
10
Q
Describe why homeostasis is important with regards to blood glucose concentration.
A
- Important to maintain stable blood glucose concentration.
- Too high- water potential of blood reduced so water molecules diffuse out of cells into the blood by osmosis. Causes the cell to shrivel and die.
- Blood glucose concentration too low- cells unable to carry out normal activities- isn’t enough glucose for respiration- respiratory substrate- to provide energy. (High water potential may also cause cells the burst).
11
Q
Describe the key features of control mechanisms.
Hint: 5 points
A
- Optimum point- point the system works best at- desired level or norm where the system operates.
- Receptor- detects any deviation from the optimum point (too high or too low)- acts as a stimulus - monitors the system.
- Coordinator- coordinates information from various receptors and sends information to the appropriate effector. May be the hormonal or nervous system.
- Effector- muscle/ gland- brings corrective measures needed to return the system to the optimum/ normal- counteract the change.
- Feedback mechanism- receptor responds to stimulus created by the change in the system brought about by the effector and the effector has the appropriate response.
12
Q
Describe the seperate mechanisms of control systems and why they are important. (Give an e.g.)
A
- Control systems- many receptors and effectors- allows them to have separate mechanisms- produce positive movement towards an optimum- allows more control of the factor being regulated.
- Separate mechanisms- control levels in different directions from the original state- feature of homeostasis.
- Important to ensure information provided by receptors is analysed by the coordinator before action happens.
- Control centre coordinates the action of effectors so operate harmoniously- so e.g. sweating is accompanies by vasodilation.
- E.g. Temperature receptors in the skin- signal that the skin is cold and that the body temperature should be raised- information from the hypothalamus may indicate blood temperature is above normal and decides not to raise temperature further- analysing the information from all detectors- brain can decide best course of action.
13
Q
Describe positive feedback.
Hint: 6 points
A
- Not involved in homeostasis- doesn’t keep internal environment stable.
- Small stimulus creates a large and rapid response. Useful to rapidly activate processes.
- Feedback causes corrective measures to remain turned on and effectors cause a response that deviates more from the original level. Amplifies the change away from the normal.
- Hormones will cause more release of the hormone.
- The mechanism will always cause more of a cell/ protein to form, and then sometimes it may involve the production of more of another protein/cell (one stimulates the other).
14
Q
Give examples of positive feedback.
Hint: 2 examples
A
- E.g. blood clot- platelet release chemicals that trigger more platelets- quickly form a blood clot at the injury sight.
- E.g. in neurones- depolarisation- stimulus leads to a small influx of sodium ions- increases the permeability- resulting in increase in sodium ions entering and further increased permeability creating an action potential to allow a rapid response to stimulus.
15
Q
Draw a summary diagram/ process of positive feedback.
A
Normal level –> Normal level changes –> receptors detect change –> Communication via nervous or hormonal system –> effectors respond –> Change amplified (more produced) –> normal level changes.
16
Q
When does positive feedback often occur and give examples.
A
- Occurs more often when there is a breakdown in homeostatic control systems.
- E.g. when infected with a virus- body temperature may rise very high- hyperthermia.
- E.g. When body gets too cold- hypothermia- heat lost faster than produced- brain doesn’t work properly- shivering stops so body temperature falls even more- temperature control breaks and body drops temperature even lower unless action is taken.
17
Q
What is negative feedback?
A
- When the corrective measures produced by the control system leads to a change in the stimulus detected by a receptor and turns the corrective measures off.
- Returns the system to its original normal optimum level- prevents overshoot.
18
Q
Why is negative feedback important?
A
- When an effector has corrected any deviation and returned the system to the optimum point the information is fed back to the receptor.
- If this doesn’t occur the receptor will continue to stimulate the effector leading to an over-correction and causing a deviation in the opposite direction meaning the optimum level is not reached.
19
Q
Why is having multiple negative feedback mechanisms important?
A
- Multiple negative feedback mechanisms are involved in homeostasis for each aspect being controlled. Having more than one mechanism gives more control over changes in internal environment than just having one negative feedback mechanism.
- Multiple negative feedback mechanisms- actively increase or decrease a level so it returns to normal
- Only one negative feedback mechanism- can only be able to turn it on or turn it off- only be able to actively change a level in one direction so it returns to normal- slower response and less control.
- Separate negative feedback mechanisms regulate changes from the normal in each direction.
20
Q
When may negative feedback not work?
A
- Only works within certain limits- if the change is too big effectors may not be able to counteract it e.g. large drops in body temperature.
- This may lead to a positive feedback response as seen with hypothermia.
21
Q
Draw a summary diagram/ process of negative feedback.
A
Normal level –> level changes from normal –> receptors detect change –> communication via nervous or hormonal system –> effectors respond –> level brought back to normal
22
Q
What does negative feedback mean in terms of hormones?
A
Secretion of a hormone leads to a reduction in the secretion of that hormone.
23
Q
Describe how the regulation of blood glucose concentration is negative feedback (with both glucagon and insulin).
A
- Blood glucose concentration falls in the blood- detected by receptors on the cell-surface membrane of alpha cells- coordinator- in the pancreas- secrete hormone glucagon- causes liver cells (effectors) to convert glycogen to glucose- released into the blood raising blood glucose concentration. Blood with raised glucose concentration circulates back to the pancreas- reduced stimulation of alpha cells which secrete less glucagon. Secretion of glucagon- leads to a reduction in secretion- negative feedback.
- If blood glucose concentration rises- insulin is produced from beta cells- increases uptake of glucose by cells- conversion to glycogen and fate. Fall in blood glucose concentration- reduces insulin production once blood glucose concentrations return to optimum.
24
Q
Describe the importance of seperate mechanisms of negative feedback and give an example.
A
- Separate mechanisms involving negative feedback controls departures from the norm in both directions from the original state, giving a greater degree of homeostatic control- positive actions in both directions.
- E.g. glucagon raised blood sugar concentration above optimum- takes time for it to fall if the only way of lowering was through metabolic activity. Second hormone- insulin- lowers blood sugar concentration- secretion brings more rapid return to optimum blood sugar concentration.
25
Describe negative feedback in temperature control.
* If temperature of the blood increases- thermoreceptors in the hypothalamus send more nerve impulses to the heat loss centre- sends impulses to the skin- effector.
* Vasodilation, sweating and lowering of body hairs- reduce blood temperature until it returns to normal.
* Once blood at normal temperature returns to the hypothalmus- thermoreceptors send fewer impulses to the heat loss centre- blood turns off the effector- negative feedback- stops sending impulses to the skin- effectors stop- blood temperature remains at normal level rather than still falling.
26
What are ectotherms and how do they regulate body temperature?
* Obtain heat from sources outside their bodies e.g. lizards/ other reptiles.
* Body temperature fluctuates with their environment- control body temperature by adapting behaviour to changes in external temperature.
27
Give examples of how ectotherms manage their temperature.
* Expose themselves to the sun- orientate so that the maximum surface area of their body is exposed to warming rays of the Sun.
* Taking shelter- shelter in the shade to prevent over-heating when the sun is too hot. Retreat into burrows at night to reduce heat loss when external temperature is low.
* Gaining warmth from the ground- press their bodies against areas of hot ground to warm up. Raise themselves off the ground on their legs when reach temperature so don’t overheat.
28
What are endotherms and how do they regulate body temperature.
* Endotherms- derive heat from metabolic activities inside their bodies e.g. birds and mammals.
* Body temperature remains relatively constant despite fluctuations in the external temperature.
* Use behaviour to maintain constant body temperature but also have a range of physiological mechanisms to regulate their temperature.
29
Where do vasoconstriction/ vasodilation mainly occur?
In arterioles- where muscle layer is.
30
How are endotherms adapted to survive in cold environments (which may reduce their blood temperature).
| Hint: 8 points
* Small SA:V- volume is required to produce heat, SA- where lost- larger size organisms, smaller features such as ears.
* Thick feathers/ fat for insulation.
* Hairs stand- hair erector muscles- contract- raise hairs- thicker layer of still air- insulation.
* Vasoconstriction- diameter of arterioles ear skin smaller- reduces blood reaching the skin- passes below insulation- don’t loose too much energy from blood- heat remains within the body.
* Shivering- muscles contract to produce metabolic heat.
* Increased metabolic rate- e.g. of respiration- more heat generated.
* Decrease in sweating.
* Behaviour- shelter from wind, bask in sun, huddling.
31
How are endotherms adapted to survive in hot environments (which may increase their blood temperature).
| Hint: 7 points
* Larger SA:V, lighter coloured fur to reflect heat.
* Vasodilation- diameter of arterioles- larger- warm blood to surface of skin- heat of blood away from the body.
* Hairs flat
* Increased sweating- evaporate water- removes energy- high latent heat of vaporisation.
* Increased panting to evaporate water.
* Lowering of body hair- erector muscles relax- reduces thickness of insulating layer- allows more heat to be lost.
* Behaviour- hiding from heat- shade/ burrows.
32
What systems maintain homeostasis.
Hormonal and nervous system- interact with each other to maintain the constant internal environment by responding to changes in the external environment.
33
Describe the features of hormones.
* All differ chemically.
* Produced in glands- secrete hormones directly into blood- endocrine glands.
* Carried in the blood plasma to target cells- have specific receptors on their cell-surface membranes complementary to specific hormone.
* Effective in low concentrations- widespread and long-lasting effects.
* Always a time lag between hormone being produced and response- takes time to produce, transport in blood and for it to affect the enzyme/ transport protein on the target cell.
34
How do hormones work?
**Bind to receptor proteins and change the tertiary structure of them and this usually activates/ switches on an enzyme (e.g. ATP hydrolase for phosphorylation of a molecule).**
35
Compare hormones and nerves
* Hormones- slower than nerves which are more rapid.
* Both use chemical messengers- hormones and nerves- neurotransmitters in chemical synapses.
* Hormones- not broken down as quickly as neurotransmitters- effects last for longer.
* Hormones- travel in the blood to target cells- responses slower than nervous impulses but can occur all over the body if their target cells are widespread unlike nerves which are localised.
36
Why is homeostatic control of glucose important?
* Glucose- respiratory substrate- provides a constant source of energy for almost all organisms cells- essential the blood of mammals contains constant concentration for respiration. If concentration falls too low- cells unable to carry out normal activities- isn’t enough glucose for respiration- respiratory substrate- to provide energy- cells deprived of energy and die. (High water potential may also cause cells the burst).
* Too high- water potential of blood reduced so water molecules diffuse out of cells into the blood by osmosis. Causes the cell to shrivel and die.
37
Where does blood glucose concentration regulation occur.
* Pancreas- gland behind the stomach- produces enzymes for digestion (protease, amylase, lipase) and hormones (insulin and glucagon) for regulating blood glucose concentration.
* Microscopically- pancreas is made largely of cells that produce digestive enzymes. However, clusters of cells- islets of Langerhans- secrete hormones.
* Cells in islets of Langerhans:
α-cells- larger- produce glucagon.
β-cells- smaller- produce insulin.
* These cells in the pancreas monitor blood glucose concentration and are stimulated by changes in blood glucose concentration levels.
* Liver- made up of cells called hepatocytes- regulates blood glucose concentration. Where insulin and glucagon have their effects.
38
What three processes regulating blood sugar concentration take place in the liver?
* Glycogenesis- conversion of glucose into glycogen- when blood glucose concentration is higher than normal- glucose removed from the blood and converted to glycogen.
* Glycogenolysis- breakdown of glycogen to glucose- blood glucose concentration is lower than normal- liver can convert stored glycogen back into glucose which diffuses into the blood to restore the normal blood glucose concentration.
* Gluconeogenesis- production of glucose from sources that aren’t carbohydrates such as glycerol (from lipids) and amino acids when glycogen is exhausted.
39
What factors influence blood glucose concentration.
| Hint: 6 points
* Blood glucose comes from:
* Diet- glucose absorbed following hydrolysis of food containing carbohydrates such as starch, maltose, lactose and sucrose.
* Glycogenolysis of glycogen in the small intestine, liver and muscle cells.
* Gluconeogenesis- production of glucose from sources other than carbohydrate.
* Respiration- uses glucose to release energy so blood glucose concentration falls for example after exercise.
* Respiration occurs at different rates glucose is also supplied through diet at different rates- changes in supply and demand mean that insulin, glucagon, and adrenaline operate to maintain constant blood glucose concentration
40
What system controls blood glucose concentration regulation and how does it work.
Hormonal system- controls blood glucose concentration using hormones insulin and glucagon- chemical messengers that travel in the blood to their target cells. Act on effectors- respond to restore the blood glucose concentration back to normal.
41
Give an overview of what happens if there is a rise of blood glucose concentration- too high.
* Islets of Langerhans- β-cells have receptors that are stimulated by a rise in blood glucose concentration- respond by secreting insulin into the blood plasma.
* Insulin- globular protein. Lowers blood glucose concentration. Especially binds to receptors on cell membranes of muscle cells and liver cells- hepatocytes.
* Almost all body cells- have glycoprotein receptors on cell-surface membrane- specific to insulin molecules- bind to target cells receptors and this causes various effects that make them absorb glucose from the blood- removes glucose from the blood and returns it to the optimum.
* This causes β-cells to reduce their secretion of insulin- negative feedback. Less effectors stimulated so less absorbtion occurs- returns to normal.
42
How does insulin reduce blood glucose concentration.
| Hint: 4 points
* **Insulin binds to receptors on target cells** and this causes various effects.
* **Stimulates uptake of glucose by channel/ transport proteins-** leads to a change in the tertiary structure of the glucose transport carrier proteins- causing them to change shape and open- allows more glucose into the cells by facilitated diffusion- increases rate of absorbtion of glucose into cells especially in muscle cells.
* Insulin controls the uptake of glucose by regulating the inclusion of carrier proteins in the surface membranes of target cells. Glucose transporters- carrier proteins that allow glucose to be transported across a cell membrane. Low insulin concentrations- transporters stored as part of vesicles in the cytoplasm of cells. Insulin binds to receptors on the cell-surface membrane- triggers enzymes that cause the fusion of vesicles to the cell-surface membrane- more glucose carrier increases the permeability- cells can take up more glucose. Glucose can then be transported into the cell through the transporter protein by facilitated diffusion more rapidly.
* Increases the rate of respiration of glucose especially in muscle cells. Use more glucose so this increases uptake of glucose from the blood. **More carrier proteins for glucose so more glucose enters the cell so this increases the rate of respiration-**
* **Activates enzymes** in muscle and liver cells that **convert glucose into glycogen** (glycogenesis)- increases the rate of conversion of glucose into glycogen and glucose into fat. Cells store these in cytoplasm as an energy source.
43
What would happen if insulin did not function properly.
* **Enzymes not activated.
* Fewer vesicles move to the membrane, fewer channel proteins in the membrane.
* Less/ no glucose diffuses into the cell.**
44
What is the effect of a decrease in blood glucose concentration (too low).
| Hint: 6 points
* α-cells of the islets of Langerhans- detect fall in blood glucose concentration- secrete glucagon into the blood plasma.
* Glucagon- raises blood glucose concentration when it’s too low.
* Glucagon attaches to specific receptor proteins on the cell-surface membrane of target liver cells and act**ivates enzymes** that convert glycogen to glucose- glycogenolysis- and enzymes that **convert amino acids and glycerol into glucose-** gluconeogenesis.
* Glucagon also decreases the rate of respiration of glucose in cells.
* Increases the concentration of glucose in the blood and return it to its optimum concentration.
* Raising of the blood glucose concentration causes the α-cells to reduce the secretion of glucagon- negative hormone.
45
Describe the effects of adrenaline and how it is produced.
* Increases blood glucose concentration in times of excitement or stress- when there is low concentration of glucose in your blood and glucose is required for a higher rate of respiration.
* Gets body ready for action by making more glucose available for muscles to respire.
* Produced by adrenal glands above the kidneys.
46
How does adrenaline raise blood glucose concentration?
* Attaching to protein receptors on the cell-surface membrane of target cells.
* Binds to receptors on the cell membrane of liver cells- activating enzymes that causes glycogenolysis (the breakdown of glycogen to glucose) and inhibits glycogenesis (the synthesis of glycogen from glucose.
* Activates glucagon secretion and inhibits insulin secretion- increases glucose concentration.
47
Describe the second messenger model and what it is used by.
* Used by adrenaline and glucagon:
* Both activate glycogenolysis inside a cell despite binding to receptors on the outside of the cell.
* Binding of the hormone to cell receptors activates an enzyme on the inside of the cell membrane- produces a chemical which is the second messenger- activates other enzymes in the cell to bring about a response.
* This may apply to other hormones as well- **binding of hormone changes shape/ tertiary structure of the receptor activating/ switching on an enzyme.**
48
Describe how both glucagon and adrenaline increase blood glucose concentration using the second messenger model.
| Hint: 8 points
* Have specific tertiary structures- complementary shape to transmembrane protein receptor within the cell-surface membrane of a liver cell- binds to them.
* Causes the protein to change shape on the inside of the membrane.
* Leads to activation of adenylate cyclase.
* Activated adenylate cyclase **converts ATP to cyclic AMP (cAMP)**
* cAMP- second messenger that binds to **protein kinase enzyme**- changing its shape and **activates it.**
* Active protein kinase enzyme- activates a cascade- chain of reactions- **converts glycogen into glucose- glycogenolysis.**
* Glucose- moves out of the liver cells by facilitated diffusion into the blood through channel proteins.
* Think about impact of one of the enzymes not working- remember to use key term **less**.
49
What word describes the interaction of insulin and glucagon.
| Hint: 3 points
Insulin and glucagon- antagonistic- insulin lowers blood glucose concentration and glucagon increases it.
50
Describe how blood glucose concentration represents the key features of negative feedback.
* System- self-regulating through negative feedback- concentration of glucose in the blood determines the quantity of insulin and glucagon- interaction of the two hormones allows highly sensitive control of blood glucose concentration.
* Concentration of glucose- not constant- fluctuates around an optimum point due to negative feedback mechanisms. Only when blood glucose concentration falls below the set point is insulin secretion reduced leading to a rise in blood concentration. Only when concentration exceeds a set point is glucagon secretion reduced causing a fall in blood glucose concentration.
51
Describe the negative feedback mechanisms keeping blood glucose concentration normal.
* Rise in blood glucose concentration- too high- β-cells secrete insulin and α-cells stop secreting glucagon. Insulin then bind to receptors on liver and muscle cells- respond to decrease blood glucose concentration e.g. glycogenesis is activated. So blood concentration returns to normal.
* Fall in blood glucose concentration- pancreas detects this- β-cells stop secreting insulin and α-cells secrete glucagon- glucagon binds to receptors on liver cells- effectors- respond and increase the blood glucose concentration e.g. by activating glycogenolysis. Blood glucose concentration returns to normal.
52
Fill out the table of the process, conversion, activation, and inhibition of each of the processes that occur in the liver.
Answer on revision card.
53
What is diabetes?
* Diabetes- disease where a person is unable metabolise carbohydrates, especially glucose properly. Metabolic disorder caused by inability to control blood glucose concentration due to a lack of insulin or loss of responsiveness to insulin.
* Sugar diabetes- diabetes mellitus- blood glucose concentration can’t be controlled properly.
* Two types- Type I and Type II
54
Describe the causes and features of Type I diabetes.
| Hint: 4 points
* Insulin dependent- body unable to produce insulin.
* Begins in childhood and due to an autoimmune response to β-cells in the islets of Langerhans so that they can’t produce insulin. May be due to genetics or viral infection.
* Develops quickly and obvious symptoms. After eating, blood glucose level rises and stays high- hyperglycaemia- can result in death.
* Kidneys can’t reabsorb all the glucose so some of its excreted in the urine.
55
Describe the causes and features of Type II diabetes.
| Hint: 5 points
* Insulin independent- glycoprotein receptors lost or lose their responsiveness to insulin or β-cells don’t produce enough insulin.
* **Produce insulin but receptors less responsive.**
* Results in cells not responding properly to insulin and taking up enough glucose so blood glucose concentration is higher than normal.
* Develops in older people and adolescents with obesity, low exercise, genetic disposition, and poor diet.
* Develops slowly, symptoms normally less severe and may go unnoticed. Most common.
* Causes additional problems- visual impairment kidney failures, heart problems and other issues.
56
What may also sometimes be a cause of diabetes.
**Changes in the tertiary structure of insulin so no longer complementary to receptor.**
57
What are the signs and symptoms of diabetes.
* Signs of diabetes are high blood glucose concentration, presence of glucose in urine, need to urinate excessively, weight loss, blurred vision.
* Symptoms of diabetes- tiredness, increased thirst/ hunger.
58
How can blood glucose concentration be controlled in people with diabetes.
* Blood glucose concentration can be controlled by changing the uptake of glucose from the gut (diet) and the rate at which glucose is removed from the blood- exercise and insulin.
* Diabetes can be treated or controlled by using insulin and/or manipulation of the diet depending on the type of diabetes.
59
How is Type I diabetes treated?
| Hint: 4 points
* **Treated by injections of insulin**- dosage must match glucose intake. If take too much insulin- could result in low blood concentration- hypoglycaemia- unconsciousness.
* Monitor blood glucose concentration using biosensors and sometimes use insulin pump to deliver insulin continuously.
* Managing carbohydrate intake and exercise helps treat the condition- **controlling sugar intake/ diet.**
* Eating regularly avoids a sudden rise in glucose.
60
How is Type II diabetes treated?
| Hint: 5 points
* Can’t be controlled the same as Type I as **produce insulin but receptors less responsive.**
* Treated by regulating intake of carbohydrate and matching to exercise.
* Helped by eating a healthy, balanced **diet**, losing weight and regular **exercise**.
* Glucose-lowering drugs can be taken. Drugs can also slow the rate the body absorbs glucose from the intestine.
* Supplemented by injections of insulin or use of drugs that stimulate insulin production.
61
Describe potential responses to Type II diabetes.
| Hint: 7 points
* Should be able to evaluate the positions of health advisers and the food industry in relation to the increased incidence of type II diabetes.
* Linked to increasing levels of obesity, unhealthy diets and low levels of physical activity.
* Health advisors keen to educate people about the risk and encourage the food industry to tackle to problem to reduce the amount of people with disease.
* Healthy diet, regular exercise and losing weight are advised by health advisors- campaigns aim to educate people on healthier diet and lifestyle.
* Health advisors- aimed to reduce promotion/ availability of unhealthy foods, increase nutrition in food and use clearer labelling so people are informed about healthy food choices.
* Food companies- attempted to make products more healthy e.g. using sweeteners and reducing salt, sugar, and fat companies.
* Companies- reluctant to promote healthy products if unhealthy products are more profitable and popular.
62
Describe required practical 11 which is used to test for diabetes, give an overview of the process and how diabetes would be identified.
* Production of a dilution series of a glucose solution and use of colorimetric techniques to produce a calibration curve with which to identify the concentration of glucose in an unknown ‘urine’ sample.
* Normally low concentration- high conc= diabetes but blood tests needed to confirm.
* Determine concentration of glucose using colorimetry- use quantitative Benedict’s test- measure light absorbance- higher conc. of glucose= more blue colour loss- decreased absorbance of red light.
63
Describe how you would make a serial dilution of known glucose concentrations.
* Add 10cm3 of initial glucose solution to first test tube and 5cm3 distilled water to the other tubes.
* Take 5cm3 from the first test tube and add to the 2nd- mix and should have a solution that’s half the concentration of the first.
* Repeat to continue to get half the concentration.
* Could also use a 1:9 ratio to give a factor of 10 each time.
64
Describe how to measure the absorbance of glucose.
* Add equal volumes of solution and set up control of pure water.
* Add quantitative Benedict’s to each test tube and mix.
* Heat the test tubes to over 70 degrees= same amount of time.
* The solution should now be reduced- ready to use colorimeter.
* If using quantitative Benedict’s reagent- no red precipitate forms but if red precipitate does form filter it out.
65
Describe how to use the colorimeter to measure the concentration of glucose.
* Set up with red filter.
* Calibrate the colorimeter to zero using a cuvette. Use a pipette to transfer a sample into a clean cuvette to measure the absorbance.
* Make sure to zero the colorimeter each time and use a clean pipette and cuvette.
66
Describe how you would plot a calibration curve for glucose concentration.
* Absorbance on the y axis against glucose on the x axis.
* Draw line/ curve of best fit.
* Test the unknown solution in the same way as the known and heat the solution for the same amount of time.
* Measuring absorption- compare to calibration curve to find concentration.
* When evaluating data remember to state more/ less effective and look for significant difference due to overlap of standard deviations etc.
67
Describe what osmoregulation is and where it occurs.
* Osmoregulation- homeostatic control of water potential of the blood.
* Quantity of mineral ions taken in and lost varies over days but the optimum concentration of water and salts is maintained in the blood to ensure constant water potential of blood plasma and tissue fluid.
* Osmoregulation occurs in nephrons in the kidneys.
* Kidneys- maintain water potential of plasma and hence tissue fluid- osmoregulation.
68
What is the structure of the mammalian kidney.
| Hint: 8 points
* We have two kidneys in the back of the abdominal cavity on each side of the spinal cord.
* Fibrous capsule- outer membrane that protects the kidney.
* Cortex- lighter coloured outer region made up of renal capsules, convoluted tubules and blood vessels.
* Medulla- darker coloured inner region- loops of Henle, collecting ducts and blood vessels.
* Renal pelvis- funnel shaped cavity that collects urine into the ureter.
* Ureter- tube that carries urine to the bladder.
* Renal artery- supplies the kidney with blood from the heart via the aorta.
* Renal vein- returns blood to the heart via the vena cava.
69
Label a diagram of a kidney.
Answer on revision card.
70
What are nephrons.
* Kidneys contain millions of tiny tubular structures called nephrons- they are the basic structural and functional units of the kidney.
* Nephrons- long narrow tubules and bundles of capillaries which are closed at one end with two twisted regions separated by a long hairpin loop. Where blood is filtered.
71
Describe the structure of the nephron.
| Hint: 6 points
* Renal- bowman’s capsule- closed end at the start of the nephron- cup-shaped, surrounds a mass of blood capillaries- glomerulus. Inner layer of the renal capsule- made of specialised podocytes.
* Proximal convoluted tubule (PCT)- series of loops surrounded by blood capillaries- walls made of epithelial cells with microvilli.
* Loop of Henle- long hairpin loop- extends from the cortex into the medulla and back again, surrounded by blood capillaries.
* Distal convoluted tubule (DCT)- loops surrounded by blood capillaries. Walls made of epithelial cells but surrounded by fewer capillaries than the proximal tubule.
* Collecting duct- distal convoluted tubules from a number of nephrons empty into this tube. Lined by epithelial cells. Increasingly wide as empties into pelvis of the kidneys.
* Mustn't say DCT/ PCT unless put them in brackets after the full word first.
72
Describe the blood vessels associated with a nephron.
* Afferent arteriole- tiny vessel from the renal artery- supplies the nephron with blood. Enters the renal capsule of the nephron and forms the glomerulus.
* Glomerulus- branched knot of capillaries where fluid is forced out of the blood.
* Efferent arteriole- glomerular capillaries recombine and form a tiny vessel- leaves the renal capsule. Smaller diameter than the afferent arteriole- causes increase in blood pressure within the glomerulus. Carries blood away from the renal capsule.
* Blood capillaries- branched from efferent arteriole- concentrated network of capillaries that surround the proximal convoluted tubule, the loop of Henle and the distal convoluted tubule so they can reabsorb mineral salts, glucose and water. Capillaries merge together into venules which then merge together to form the renal vein.
73
Label a diagram of a nephron.
Answer on revision card.
74
Give an overview of how the kidneys perform osmoregulation.
* Blood enters the kidneys through the renal artery and passes through the capillaries into the cortex of the kidneys.
* As blood passes through the capillaries in the cortex, substances are filtered out of the blood into long tubules surrounding the capillaries- ultrafiltration.
* Useful substances- glucose, and the optimal level of water are reabsorbed back into the blood- selective reabsorption. Unwanted substances pass along the bladder and are excreted as urine.
75
Describe the stages of osmoregulation.
* Ultrafiltration- the formation of glomerular filtrate by ultrafiltration.
* Selective reabsorption:
* The reabsorption of glucose and water by the proximal convoluted tubule.
* Maintenance of a gradient of sodium ions in the medulla by the loop of Henle.
* Reabsorption of water by the distal convoluted tubule and collecting ducts.
76
Describe how ultrafiltration works.
| Hint: 11 points
* Blood enters the kidney through the renal artery- branches out into afferent arterioles.
* Each afferent arteriole enters the Bowman’s capsule of a nephron and splits into a glomerulus- a bundle of capillaries inside the Bowman’s capsule (hollow ball)- where ultrafiltration occurs.
* Walls of the glomerular capillaries- made of endothelial cells- pores between them to allow filtrate through.
* Glomerular capillaries- merge at the end to form the efferent arteriole- takes the filtered blood away from the glomerulus.
* Efferent arteriole- smaller in diameter than the afferent arteriole- makes blood in glomerulus under high hydrostatic pressure
* **High hydrostatic pressure forces water and small substances (urea, glucose and ions- must name at lease one)** in the blood **out** of the capillary **through fenestrations- pores in the endothelium and through the basement membrane** and into the Bowman’s capsule, forming the glomerular filtrate.
* Liquid and small molecules pass through 3 layers to get into the Bowmans’ capsule and enter the nephron tubules- the capillary endothelium, a basement membrane and the epithelium of the Bowman’s capsule.
* Substances that enter the Bowman’s capsule- known as the glomerular filtrate- enters the nephron tubules- passes along the rest of the nephron.
* Efferent arteriole- sub-divides into capillaries- wind their way around various tubules of the nephron to reabsorb substances before combining to form the renal vein.
* Most of the substances in the filtrate are useful to the body and are reabsorbed, apart from urea as it is a waste product.
* The filtrate flows through the proximal convoluted tubule, loop of Henle collecting duct and distal convoluted tubule, where substances are reabsorbed and passes out of the kidney along the ureter.
77
Describe how molecules are filtered in ultrafiltration.
* Ultrafiltration- based on the size of the molecule- small molecules removed.
* Blood cells and large proteins- can’t pass through layers into the Bowman’s capsule- too large.
* **Damages to basement membrane** (e.g. due to a disease) may mean that **proteins can pass into the glomerular filtrate** and then into the urine.
78
What is the movement of filtrate out of the glomerulus resisted by?
* Capillary endothelial cells.
* Connective tissue and endothelial cells of the blood capillary.
* Epithelial cells of the renal capsule.
* Hydrostatic pressure of the fluid in the renal capsule space.
* Low water potential of the blood in the glomerulus.
* Total resistance- enough to prevent the filtrate leaving the glomerular capillaries but there are modifications to reduce this barrier to the flow of filtrate:
79
What modifications do glomerular capillaries have to reduce the barrier to the flow of filtrate.
* Podocytes- highly specialised cells the inner layer of the renal capsule is made of. Have spaces between them that allow filtrate to pass beneath them and through gaps between their branches, rather than through the cells.
* Endothelium has spaces between its cells- fenestrations- pores so fluid can pass between rather than through cells.
* Hydrostatic pressure of the blood in the glomerulus is sufficient to overcome the resistance and the filtrate passes from the blood into the renal capsule.
80
Give an overview of selective reabsorbtion.
| Hint: 6 points
* Selective reabsorption of useful substances- occurs when glomerular filtrate flows along the proximal convoluted tubule (PCT), through the loop of Henle and along the distal convoluted tubule (DCT).
* Reabsorption of useful materials from the glomerular filtrate in the tubules of the nephrons into the blood in the capillary network wrapped around the tubules.
* **Glucose is reabsorbed by facilitated diffusion and active transport and water is reabsorbed down a water potential gradient by osmosis.**
* 85% of the filtrate is reabsorbed back into the blood.
* **Concentration of filtrate remains constant as water is also reabsorbed at a similar rate to biological molecules.**
* Water is reabsorbed from the proximal convoluted tubule, loop of Henle, distal convoluted tubule and the collecting duct. The remaining filtrate is urine which passes from the collecting duct along the ureter to the bladder.
81
Describe the composition of urine.
* Urine is usually made up of water, dissolved salts, urea and other substances (e.g. hormones).
* Urine doesn’t contain proteins or blood cells as too large to be filtered out of the blood.
* Glucose is also actively reabsorbed into the blood so is not usually found in urine.
82
Describe what the presence of glucose in the urine means.
* Glucose- actively reabsorbed into the blood so is not usually found in the urine.
* All the glucose should be reabsorbed- there should be no glucose in urine.
* If there is this may be due to diabetes meaning that there is **a high concentration of glucose in the blood/ filtrate so not all glucose is reabsorbed at the proximal convoluted tubule because co-transport/ carrier proteins are saturated- working at maximum rate.**
* It could also be due to the kidney not working properly.
83
Give an overview of selective reabsorbtion in the proximal convoluted tubule.
* Useful solutes e.g. glucose are reabsorbed along the PCT by active transport and facilitated diffusion, along with water.
* 85% of water reabsorbed into the nephrons occurs in the proximal convoluted tubule. The rest is reabsorbed from the collecting duct due to the loop of Henle.
84
How are the proximal convoluted tubules adapted to reabsorb substances into the blood?
| Hint: 4 points
* The epithelial cells have key features.
* Microvilli in the epithelium of the wall of the PCT provide a large surface area to reabsorb useful substances from the glomerular filtrate.
* Infoldings at the base give large surface area to transfer reabsorbed substances into the capillaries.
* High numbers of mitochondria provide ATP for active transport.
85
Describe the process of reabsorbtion in the PCT.
| Hint: 5 points
* Sodium ions- actively transported out of the cells lining the proximal convoluted tubule into blood capillaries which carry them away- sodium ion concentration lowered.
* Sodium ions diffuse down the concentration gradient from the lumen of the proximal convoluted tubule into the epithelial lining but only through specific carrier proteins by facilitated diffusion.
* The carrier proteins carrier are co-transporters- carry another molecule- (glucose, amino acids, chloride ions etc.) along with sodium.
* Molecules co-transported into the cells of the proximal convoluted tubule diffuse into the blood. All the glucose and most other valuable molecules are reabsorbed as well as water.
* Water enters the blood by osmosis because the water potential of the blood is lower than the filtrate due to the high concentration of ions being pumped into it.
86
Describe the key features of reabsorbtion in the loop of Henle.
| Hint: 5 points
* The loop of Henle maintains a gradient of sodium ions in the medulla.
* Loop of Henle- hairpin-shaped tubule- extends into the medulla (inner layer of the kidney).
87
Describe the effects of a longer loop of Henle/ what a thicker medulla involves.
* **Thicker medulla= longer loop of Henle.**
* Enables water to be reabsorbed from the collecting duct, and concentrates urine so that it has a lower water potential than blood
* Concentration of urine- related directly to the length of the loop of Henle- longer= more water can be reabsorbed from the glomerular filtrate as **increases the sodium ion concentration in the medulla- sodium ion gradient maintained for longer. Water potential gradient maintained so more water reabsorbed from the loop of Henle and collecting duct by osmosis.**
88
Describe the features of the loop of Henle.
* Has lots of mitochondria in its cell walls to produce large amounts of ATP for the process.
* Has two regions- control the movement of sodium ions so water can be reabsorbed by the blood.
* The descending limb- narrow- thin walls, highly permeable to water.
* Ascending limb- wider, thicker walls impermeable to water.
89
Describe how the loop of Henle works (and acts as a counter-current multiplier).
| Hint: 10 steps
1. **Sodium ions are actively transported out of the ascending limb** into the medulla using ATP produced by mitochondria.
2. The ascending limb is **impermeable to water, so water remains inside** and does not leave by osmosis and most stays inside the tubule. This creates a low water potential in the region of the medulla between the two limbs- interstitial region because of a high ion concentration.
3. Walls of descending limbs- permeable to water. Lower water potential in the interstitial space in the medulla than the descending limb- **water moves out of the descending limb** into the interstitial space by osmosis and **sodium ions enter.** This makes the glomerular filtrate in the descending limb more concentrated- ions can’t diffuse out as the descending limb isn’t permeable to them.
4. The filtrate progressively loses water as it moves down the descending limb lowering its water potential. It reaches its lowest water potential at the tip of the hairpin.
5. At the base of the ascending limb- sodium ions diffuse out of the filtrate into the interstitial space- lowering the water potential in the medulla as the ascending limb is impermeable to water so it stays in the tubule.
6. As the filtrate moves up the ascending limb more ions are actively pumped out so the filtrate develops a progressively higher water potential.
7. These steps massively increase ion concentration in the medulla- lowing the water potential in the interstitial space. The interstitial space between the ascending limb and the collecting duct has a gradient of water potential with the highest water potential (lowest ion conc.) in the cortex and an increasingly lower water potential (high ion conc.) further into the medulla.
8. This causes water to move out of the collecting duct by osmosis as it is permeable to water.
9. As water passes out of the filtrate its water potential is lowered but the water potential is also lowered in the interstitial space so the water continues to move out by osmosis down the whole length of the collecting duct. The counter-current multiplier ensures that there is always a water potential gradient drawing water out of the tubule.
10. The water in the medulla is reabsorbed into the blood by osmosis into the capillary network. Water in the interstitial space is reabsorbed into the blood by the capillaries through osmosis and is carried away.
90
How does ADH alter reabsorbtion in the loop of Henle.
* Water passes out of the collecting duct by osmosis through channel proteins specific to water- aquaporins.
* Antidiuretic hormone- ADH- alters the numbers of aquaporins and so control water loss.
91
Describe how the counter-current multiplier works in the loop of Henle.
* When two liquids flow in opposite directions the exchange of substances between them is greater than if they flowed in the same direction.
* Loop of Henle- counter-current flow means that the filtrate in the collecting duct with a lower potential meets interstitial fluid with an even lower water potential.
* Although the water potential gradient between the collecting duct and interstitial fluid is small it exists for the whole length of the collecting duct.
* There is a steady flow of water into the interstitial fluid- around 80% enters the interstitial fluid and hence the blood. If the two flows were in the same direction, less water would enter the blood.
92
Describe reabsorption in the distal convoluted tubule and collecting ducts.
| Hint: 6 points
* The distal convoluted tubule has microvilli and many mitochondria reabsorb materials rapidly from the filtrate by active transport.
* Makes final adjustments to water and salts that are reabsorbed and controls the pH of the blood by selecting which ions to reabsorb.
* The permeability of its walls become altered by the influence of various hormones.
* Water moves out of the distal convoluted tubules by osmosis and is reabsorbed into the blood.
* After the distal convoluted tubule, the filtrate enters the collecting duct where many nephrons empty. More water is reabsorbed from the collecting ducts using water potential gradients- osmosis facilitated by the sodium pumps in the loop of Henle.
* The filtrate- now called urine- leaves the collecting duct to the bladder- lost most of its water- has a lower potential- more concentrated by blood.
93
Give an overview of how osmoregulation works.
* Homeostatic control of osmoregulation is controlled by hormones that act on the distal convoluted tubule and collecting duct.
* Water potential of the blood- depends on concentration of solutes (glucose, proteins, ions) and the volume of water.
* Rise in solute concentration lowers the water potential.
94
What is the importance of osmoregulation.
* Water- essential for metabolic processes so amount in blood needs to be kept constant and water loss needs ot be mitigated.
* Kidneys regulate the water potential of blood and urine so the body has the right amount of water.
95
When is water lost from the body.
Water is lost during excretion oof urea in solution, and sweat.
96
Where does osmoregulation occur?
* Water is reabsorbed into the blood along almost the whole nephron.
* Regulation of water potential mainly takes place in the loop of Henle, distal convoluted tubule and collecting duct.
* The volume of water reabsorbed into the capillaries is controlled by the permeability of the distal convoluted tubule and the collecting duct which is controlled by hormones.
97
What are the features of urine affected by?
* Water potential of the blood affects the volume and concentration of urine.
* **Water potential may be affected by factors such as diet** (changes ion concentrations and water uptake).
98
What may low water potential in the blood be due to.
* Too little water being consumed.
* Too much sweating.
* Large amounts of ions being absorbed from diet.
99
Give an overview of what happens if the water potential of the blood is too low.
If water potential of the blood too low- dehydration- more water reabsorbed by osmosis into the blood from the tubules of the nephrons- urine is more concentrated- less water lost during excretion.
100
Describe the response that occurs when there is a fall in water potential- dehydration.
| Hint: 13 points
* Osmoreceptors in the **hypothalamus** of the brain **detect the decrease in water potential in the blood** as it causes **water to move out of osmoreceptor cells into the blood by osmosis.**
* Water loss causes osmoreceptor cells to shrink causing the hypothalamus to send signals to the posterior pituitary gland, which stimulates it to release antidiuretic hormone (ADH) into the blood.
* ADH moves through the blood into the kidneys and binds to specific protein receptors on the cell-surface membranes of the cells in the distal convoluted tubule and collecting duct leading to the activation of phosphorylase enzyme.
* Phosphorylase causes vesicles with plasma membranes with large numbers of aquaporins (water channel proteins) to move to and fuse with the cell-surface membrane, increasing the number of aquaporins in the membrane.
* The aquaporins allow water to pass through by osmosis making the cell-surface membrane of the cells in the DCT and collecting duct more permeable to water.
* More **ADH means the membranes in the walls of the distal convoluted tubule and collecting duct become more permeable to water so more water is lost and reabsorbed into the blood by osmosis.**
* ADH also increases the permeability of the collecting duct to urea which passes out, further lowering the water potential of the fluid around the duct.
* This combined means more water leaves the collecting duct by osmosis, down a water potential gradient, and re-enters the blood, so more water is reabsorbed from the tubules into the medulla and into the blood by osmosis.
* A **small volume of concentrated urine** is produced so less water is lost from the body.
* As the reabsorbed water came from the blood in the first place, it doesn’t increase the water potential of the blood but prevents it getting lower.
* Osmoreceptors send nerve impulses to the thirst centre of the brain to encourage the individual to drink more water.
* Osmoreceptors in the hypothalamus detect the rise in water potential and send fewer impulses to the pituitary gland.
* The pituitary gland reduces the release of ADH and the permeability of the collecting ducts to water and urea returns to original state. Example of negative feedback.
101
What may raise the water potential of blood?
* Large volumes of water consumed.
* Salts used in metabolism or excreted not being replaced.
* Fall in solute concentration
102
Give an overview of what happens if the water potential of the blood is too high.
If water potential of the blood too high- too hydrated- less water is reabsorbed by osmosis into the blood from the tubules of the nephrons- urine is more dilute, more water lost during excretion.
103
Describe the response of the body to a rise in water potential.
| Hint: 5 points
* Osmoreceptors in the hypothalamus detect the rise in water potential of the blood and increase the frequency of nerve impulses to the posterior pituitary gland to reduce release of ADH into the blood.
* Less ADH leads to a decrease in the permeability of the distal convoluted tubule and collecting ducts to water and urea.
* Less water is reabsorbed into the blood from collecting ducts and the distal convoluted tubule.
* A large volume of dilute urine is produced and the water potential of the blood falls.
* Water potential of the blood returns to normal- osmoreceptors in the hypothalamus cause the pituitary to raise ADH release back to normal- negative feedback
104
What could be the effect of drugs on reabsorbtion of water if they prevent the reabsorbtion of ions
If less ions are absorbed- **lower water potential of filtrate, less water is reabsorbed by osmosis in the collecting duct, distal convoluted tubule or loop of Henle.**
105
Draw a flow cahrt to show the proccess of returning blood water concentration to a normal level using osmoregulation.
Answer on revision card.
106
Label the diagram of what is reabsorbed in each section of the loop of Henle.
Answer on revision card.
107
Label the diagram of PCT with what happens.
Answer on revision card.
108
Draw a diagram showing the second messenger model of adrenaline/ glucose.
Answer on revision card.
109
Draw a flow chart of how blood glucose levels are returned ot normal.
Answer on revision card.
110
Draw a flow chart of negative feedback during heat loss.
Answer on revision card.
111
Label and describe the graphs of diabetes.
Answer on revision card.
