Homeostasis

Question 1

Definition of homeostasis?

Answer 1

The maintenance of a constant internal environment

Question 2

Types of regulation?

Answer 2

Body temp - Thermoregulation
pH of blood - Conc of Co2
Blood Glucose conc - Glucoregulation
Blood water conc - osmoregulation

Question 3

Importance of temperature regulation?

Answer 3

Body temperature too high - enzymes denature - enzyme molecules vibrate too much - hydrogen bonds break - 3D shape breaks - active site changed - no longer works as catalyst - metabolic reactions less efficient
Body temperature too low - enzyme activity reduced - slow rate of metabolic reactions
Optimum temp - 37 degrees

Question 4

Importance of pH regulation?

Answer 4

If blood pH is too high or too low enzymes become denatured - hydrogen bonds that hold them in their 3D shape are broken - shape of active site is changed and no longer works as a catalyst - metabolic reactions are less efficient
Optimum pH - 7

Question 5

Importance of glucose regulation?

Answer 5

If blood glucose concentration is too high the water potential of blood is reduced - water diffuses out of cells by osmosis - cells shrivel up and die
If too low, cells are unable to carry out normal activities because there isn’t enough glucose for respiration to provide energy
Monitored by the pancreas which releases hormones (insulin and glucagon) from its endocrine glands

Question 6

Homeostasis by negative feedback

Answer 6

Uses receptors, a communication system and effectors
Receptors detect when levels are too low or too high - communicated through the nervous or hormonal system to effectors
Effectors respond to counteract the change by negative feedback
Has limits, can’t counteract too big of changes

Question 7

Effectiveness of multiple negative feedback systems?

Answer 7

Gives more control over changes
Can actively increase or decrease a level so it returns to normal
Only one negative feedback mechanism means you could only turn it off or on, you could only actively change a level in one direction
Only one would mean a slower response and less control

Question 8

Amplifying a change?

Answer 8

Some changes trigger a positive feedback mechanism - amplifies the change
Effectors respond to further increase the level away from the normal level
Positive feedback is useful to rapidly activate something - blood clotting after an injury
Can also happen when a homeostatic system breaks down
Is not part of homeostasis as it does not maintain the internal environment

Question 9

Postive feedback examples?

Answer 9

Clotting:
Platelets become activated and release a chemical - triggers more platelets to be activated - very quickly a blood clot forms at the injury site - ends with negative feedback when the blood clot has been formed
Hypothermia (breakdown of homeostatic system):
Low body temperature (below 35 degrees)
Happens when heat’s lost from the body quicker than it can be produced
Body temperature falls - brain doesn’t function properly - shivering stops - body temp falls faster
Positive feedback takes body temp further away from normal level

Question 10

Glucoregualtion: Blood glucose gets too high?

Answer 10

Intake of glucose rich foods
Rise in blood glucose level detected by B-cells in the islets of Langerhans in pancreas
B-cells release insulin
Insulin binds to specific receptors on the cell membranes of liver cells and muscle cells
Insulin increases permeability of muscle-cell membranes to glucose - cells take up more glucose - done by increasing number of channel proteins in the cells
Activates enzymes in the liver and muscle cells that convert glucose to glycogen - glycogenesis
Cells store glycogen in their cytoplasm as energy source
Insulin also increases the rate of respiration of glucose in muscle cells

Question 11

Glucoregualtion: Blood glucose gets too low?

Answer 11

Falls due to exercise or fasting
Fall in blood glucose level detected by alpha cells in the Islets of Langerhans in Pancreas
Alpha cells release glucagon which travels to target cells in the blood
Binds to specific receptors on liver cells
Glucagon activates enzymes in liver cells that break down glycogen into glucose - glycogenolysis
Glucagon activates enzymes that form glucose from non-carbohydrates - gluconeogenesis
Glucagon decreases the rate of respiration in cells

Question 12

Qualities of hormones in glucoregulation?

Answer 12

They travel in blood - slower than nervous impulses

Not broken down as quickly as neurotransmitters - effects last for longer

Question 13

Insulin and glucose transporters?

Answer 13

GLUT4 is a channel protein found in skeletal and cardiac muscle cells - is a glucose transporter
When insulin levels are low - GLUT4 is stored in vesicles in the cytoplasm
When insulin binds to the receptors it triggers the movement of GLUT4 to the membrane
Glucose can now be transported into the cell through GLUT4 protein by facilitated diffusion

Question 14

Work of adrenaline in glucoregualtion?

Answer 14

Adrenaline is a hormone secreted from the adrenal gland
During blood glucose concentration it is secreted - stressed or when exercising
Binds to receptors in the cell membrane of liver cells
Activates glycogenolysis (breakdown of glycogen to glucose)
Inhibits glycogenesis (Synthesis of glycogen from glucose)
Activates glucagon secretion and inhibits insulin secretion - increases glucose concentration
More glucose available for muscles to respire - body ready for action

Question 15

Adrenaline and glucagon working via a second messenger?

Answer 15

Receptors for adrenaline and glucagon have specific tertiary structures that make them complimentary in shape to their respective hormones
Adrenaline and glucagon bind to their receptors and activate an enzyme called adenylate cyclase
This converts ATP into a chemical signal called a ‘second messenger’
Second messenger is called cyclic AMP (cAMP)
cAMP activates an enzyme called protein kinase A
Activates a cascade - breaks down glycogen into glucose - glycogenolysis

Question 16

Type I diabetes?

Answer 16

Immune system attacks the B cells in the islets of Langerhans so they can’t produce insulin
Scientists think this is caused by a genetic predisposition or is triggered by a viral infection
After eating - blood glucose level rises and stays high - hyperglycaemia - can result in death - kidneys can’t reabsorb all the glucose - some is excreted through the urine
Treated with insulin therapy - regular insulin injections - insulin throughout the day - or insulin pump delivering it continuously - has to be monitored as too much insulin can produce a dangerous drop in blood glucose levels - hypoglycaemia
Eating regularly and controlling simple carbohydrate intake helps avoid sudden rises in glucose

Question 17

Type II diabetes?

Answer 17

Usually acquired later in life - linked with obesity and is more likely in people with a family history of the condition - also linked with lack of exercise or poor diet
Occurs when B cells don’t produce enough insulin or when the body’s cells don’t respond to insulin - occurs when the insulin receptors on membranes don’t work - cells don’t take up enough glucose - blood glucose is higher than normal
Can be treated with a healthy, balanced diet, losing weight and regular exercise
Glucose lowering medication can be taken if diet and exercise don’t work - eventually insulin injections may be required

Question 18

Type II diabetes as a growing health problem?

Answer 18

Increasingly common in the UK
Linked to increasing levels of obesity and lifestyles of low physical exercise and unhealthy diets
Can cause additional health problems - visual impairment + kidney failure
Health advisors are increasing trying to educate people

Question 19

Responses to tackle type II diabetes?

Answer 19

Eat a diet of low fat, sugar and salt with plenty of whole grains, fruit and vegetables
Take regular exercise
Lose weight if you’re a big fatty
NHS’s ‘Change4life’ - aim to educate on how to have a healthier diet and lifestyle
Health advisors have challenged the food industry to reduce advertising of junk food - to improve nutritional value - and to use clearer labelling on products - allows consumers to make healthier choices
Food companies have made some changes:
Using sugar alternatives to sweeten food/drinks
Reducing the sugar, fat and salt content of products
However there is pressure on companies to increase profits

Question 20

Calorimetry experiment: Theory?

Answer 20

Normally, the concentration of glucose in the ring is very low - 0.0.8mM
Higher concentrations may mean diabetes (or kidney failure)
Calorimetry can be used to determine the concentration of glucose in urine
Use of Quantitative Benedict’s reagent - different to normal Benedict’s reagent - when heated with glucose the initial blue colour is lost - but brick-red precipitate is not produced
Can use a colorimeter to measure the light absorbency of the solution after the quantitative Benedict’s test has been carried out
The higher the concentration of glucose, the more blue colour will be lost, decreasing the absorbance of the solution

Question 21

Calorimetry experiment: Setup?

Answer 21

Need to make several glucose solutions of different, known concentrations - serial dilution technique
To make five serial dilutions with a dilution factor of 2, starting with a glucose concentration of 4mM:
5 test tubes in a rack
Add 10cm3 of the 4mM glucose solution to the first test tube and then 5cm3 of distilled water to the other 4
Using a pipette, draw 5cm3 of the solution from the first test tube, add it to the distilled water in the second test tube and mix the solution thoroughly - now have 10cm3 of solution thats half as concentrated as the solution in the first test tube (its 2mM)
Repeat the process three more times to create solutions of 1mM, 0.5mM and 0.25mM

Question 22

Calorimetry experiment: method?

Answer 22

Need to make a calibration curve
Do a quantitative Benedict’s test on each solution (plus a negative control of pure water)
Use the same amount of Benedict’s in each case
Add quantitative Benedict’s reagent to a sample and heat in a water bath that been brought to the boil
Use a colorimeter (with a red filter) to measure the absorbance of the Benedict’s solution remaining in each tube
Use the results to make a calibration curve, showing absorbance against glucose concentration
Then test the unknown solution (urine) in the same way and use the calibration curve to find the concentration of the glucose in the sample

Question 23

Kidney function?

Answer 23

To excrete waste products, such as urea
Regulate the water potential of the blood
Substances from the blood in the capillaries in the cortex are filtered out by ultrafiltration
Glucose and some water is reabsorbed back into the blood - selective reabsorption
Remaining unwanted substances pass along to the bladder and are excreted as urine

Question 24

Ultrafiltration in the Glomerulus?

Answer 24

A bundle of capillaries looped inside the bowman’s capsule
The efferent arteriole is smaller in diameter than the afferent arteriole, so the blood in the glomerulus is under high pressure
Forces liquid and small molecules out of the capillary and into the Bowman’s capsule - urea, glucose, salts and water
Passes through three layers - to enter the Bowman’s capsule and go through to the nephron tubules - the capillary wall, the basement membrane and the epithelium membrane
Larger molecules like proteins and blood cells cant pass through
Substance that enter the nephron are called the glomerular filtrate

Question 25

Selective absorption in the PCT?

Answer 25

Proximate Convoluted Tubule
Epithelium of the PCT wall has microvilli to provide a large surface area for reabsorption
Glucose and other useful solutes are reabsorbed by active transport and facilitated diffusion
80% of water re-enters the blood by osmosis because the water potential of the blood is lower than that of the filtrate

Question 26

Loop of Henle

Answer 26

Countercurrent multiplier system
Ascending limb of loop of Henle is impermeable to H2O - permeable to Na+ and Cl- ions
Top half of ascending limb Na+ and cl- are actively transported out into the medulla
This lowers the water potential so H2O moves out by osmosis in the descending limb and is reabsorbed into the capillaries from the medulla - permeable to H2O but not Na+ or Cl-
As H2O moves out the filtrate becomes more concentrated so as it enters the ascending limb Na+ and Cl- initially move out by facilitated diffusion

Question 27

Selective absorption in the DCT?

Answer 27

More H20 is reabsorbed by osmosis

Substances such as K+, H, toxins, ethanol, drugs and other foreign substances are actively transported into the filtrate

Question 28

Selective absorption in the Collecting Duct?

Answer 28

Collecting duct under the control of the hormone ADH
ADH released when the water potential of the blood is too low so water needs to be reabsorbed from the filtrate
ADH causes the aquaporin channels in the collection duct to open, allowing H2O to leave the filtrate by osmosis, resulting in the production of only a small amount of very concentrated urine

Question 29

Where is osmoregulation monitored?

Answer 29

Osmoreceptors on the hypothalamus in the brain

Question 30

Osmoregulation: Decrease in water potential?

Answer 30

Sweating
Water potential lowers 
Detected by osmoreceptors in the hypothalamus
Feeling of thirst = drink
Posterior Pituitary gland secretes ADH
Aquaporin channels in collecting duct and DCT open = more permeable 
More water reabsorbed from filtrates
Small amount of concentrated urine

Question 31

Osmoregulation: Increase in water potential?

Answer 31

Drinking too much
High water blood potential
Water potential lowers
Detected by osmoreceptors in the hypothalamus
No feeling of thirst = don’t drink
Posterior Pituitary gland secretes less ADH
Aquaporin channels in collecting duct and DCT close = less permeable
Less water reabsorbed in urine