Homeostasis Flashcards
(138 cards)
1
Q
What change the concentration of glucose in your blood?
A
Eating
Exercise
2
Q
Why does the blood glucose concentration need to be carefully controlled?
A
Because all cells need a constant supply to work.
3
Q
What is the concentration of glucose in the blood normally?
A
90g per 100cm3.
4
Q
What monitors the concentration of glucose?
A
Pancreas
5
Q
When does the blood glucose rise?
A
After eating food containing carbs
6
Q
When does the blood glucose fall?
A
After exercise as more glucose used in respiration to release energy.
7
Q
What controls the blood glucose concentration?
A
The hormonal system using two hormones:
Insulin
Glucagon
8
Q
How and where do hormones travel to?
A
travel in the blood to their target cells (effectors).
9
Q
What are insulin and glucagon secreted by?
A
clusters of cells in the pancreas called islets of Langerhans
10
Q
What cells secrete insulin?
A
Beta cells
11
Q
What cells secrete glucagon?
A
Alpha cells
12
Q
What does insulin do?
A
Lowers blood glucose concentraion when it’s too high
13
Q
How does insulin lower the blood glucose concentration when it’s too high?
A
- Insulin binds to specific receptors on the cell membranes of liver cells and muscle cells.
- It increases the permeability of muscle cell membrane to glucose which increases the glucose uptake and increases number of channel proteins.
- Insulin activates enzymes in liver and muscle cells that convert glucose into glycogen.
- The cells are able to store glycogen in their cytoplasm as an energy source.
- The process of forming glycogen from glucose is called glycogensis.
- Insulin also increases the rate of respiration of glucose especially in muscle cells.
14
Q
What process is involved in insulin lowering blood gluc. conc
A
Glycogensis
Glucose into glycogen
15
Q
How does glucagon raise the blood glucose concentraion when its too low?
A
- Glucagon binds to specific receptors on the cell membranes of liver cells.
- Glucagon activates enzymes in liver cells that break down glycogen into glucose.
- The process of breaking down glycogen is called glycogenolysis.
- Glucagon also activates enzymes that are involved that are involved in the formation of glucose from glycerol and amino acids.
- The process of forming glucose from non-carbs is called gluconeogenesis.
- Glucagon decreases the rate of respirstion of glucose in cells.
16
Q
What processes are involved in glucagon to raise the blood gluc. conc.
A
Glycogenolysis - glycogen broken down into glucose
Gluconeogenesis - forming glucose from non-carbohydrates
17
Q
Why do hormones have a slower response than nerve impulses?
A
Because they travel in the blood to their target cells.
18
Q
Why are hormones long lasting compared to nerve impulses?
A
They aren’t broken down as quickly as neurotransmitters so last longer.
19
Q
What does negative feedback mechanisms do?
A
Keep blood glucose concentration normal
20
Q
What makes glucose transporters available for facilitated diffusion
A
insulin
21
Q
What contain a channel protein?
A
Skeletal and cardiac muscle cels
22
Q
What is GLUT4?
A
A channel protein
It is a glucose transporter
23
Q
Where is GLUT4 stored in when the insulin levels are low?
A
Vesicles in the cytoplasn of cells.
24
Q
What triggers the movement of GLUT4 to the membrane?
A
When insulin binds to receptors on the cell-surface membrane.
25
How is glucose transported into the cell?
Through the GLUT4 protein by facilitated diffusion
26
What increases the blood glucose concentration other than glucagon?
Adrenaline
27
What is adrenaline?
A hormone that's secreted from your adrenal glands
28
When is adrenaline released?
When there's a low concentration of glucose in your blood due to stress or exercising
29
Where does adrenaline bind?
To receptors in the cell membrane of liver cells
30
What does adrenaline do (activate/ inhibit)?
* It activates glycogenolysis (the breakdown of glycogen to glucose).
* It inhibits glycogenesis (the synthesis of glycogen from glucose).
* Activates glucagon secretion (increasing the glucose conc).
* Inhibits insulin secretion (increasing the glucose conc).
* Gets the body ready for action by making more glucose available for muscles to respire.
31
What do adrenaline and glucagon act with?
A second messenger
32
How can both adrenaline and glucagon activate glycogenolysis inside a cell?
1. The receptors for adrenaline and glucagon have specific tertiary structures that make them complementary in shape to their respective hormones.
2. Adrenaline and glucagon bind to their receptors and activate an enzyme called adenylate cyclase.
3. Activated adenylate cyclase converts ATP into a chemcial signal called a second messenger.
4. The second messenger is called cyclic AMP (cAMP).
5. cAMP activates an enzyme called protein kinase A. Protein kinase A activates a cascade that breaks down glycogen into glucose (glycogenolysis)
33
What do the kidneys do?
excrete waste and regulate blood water potential
34
Explain the process of excretion of waste products
1. Blood enters through the **renal artery** and passes through the **capillaries** in cortex.
2. As the blood passes through capillaries in the corex of the kidneys, **substances** of **filtered** out of the **blood** and into **long tubules** that surround the capillaries = **ULTRAFILTRATION.**
3. **Useful substances** such as **glucose** and the right amount of **water** are then **reabsorbed** back into the blood = **selective reabsorption.**
4. Remaining **unwanted** substances **pass** along to the **bladder** and are **excreted as urin**.
35
Where is blood filtered?
At the start of the nephrons
36
Describe how urea is removed from the blood
1. Hydrostatic pressure / description of pressure / description of how pressure generated;
2. Causes ultrafiltration (Allow description of ultrafiltration) at Bowman’s capsule / glomeruli / renal capsule;
3. Through basement membrane;
4. Enabled by small size urea molecule;
37
Explain how urea is concentrated in the filtrate.
1. Reabsorption of water / by osmosis;
2. At the PCT / descending LoH;
3. At the DCT / CD
4. Active transport of ions / glucose creates gradient (in context);
38
Describe how ultrafiltration produces glomerular filtrate. (5)
1. Blood pressure / hydrostatic pressure;
2. Small molecules / named example;
3. Pass through basement membrane / basement membrane acts as filter;
4. Protein too large to go through / large so stays behind;
5. Presence of pores in capillaries / presence of podocytes;
39
Some people who have diabetes do not secrete insulin.
Explain how a lack of insulin affects reabsorption of glucose in the kidneys of a person who does not secrete insulin. (4)
1. High concentration of glucose in blood;
2. High concentration in tubule / in filtrate;
3. Reabsorbed by facilitated diffusion / active transport; Requires proteins / carriers;
4. These are working at maximum rate / are saturated;
5. Not all glucose is reabsorbed / some is lost in urine;
40
Some desert mammals have long loops of Henle and secrete large amounts of antidiuretic hormone (ADH).
Explain how these two features are adaptations to living in desert conditions. (6)
1. More water (from filtrate) reabsorbed / returned to blood / less lost in urine;
2. By osmosis;
3. From collecting duct / from end of second convoluted tubule;
4. Due to longer loop of Henle;
For loop of Henle, maximum 2 marks:
1. Sodium / chloride ions absorbed from filtrate in ascending limb;
2. Gradient established in medulla / concentration of ions increases down medulla;
For ADH, maximum 2 marks:
1. Acts on collecting duct / distal convoluted tubule / second convoluted tubule;
2. Makes cells more permeable / inserts aquaporins in plasma membranes;
41
Explain ultrafiltration process
1. Blood from the renal artey enters smaller arterioles in the cortex of the kidney.
2. Each arteriole splits into a structure called a glomerulus - a bundle of capillaries lopped inside a Bowmans capsule.
3. Ultrafiltration takes place in the bowmans capsule.
4. The arteriole takes blood into each glomerulus = the afferent arteriole.
5. The arteriole that takes blood away from the glomerulus = the efferent arteriole.
6. The efferent is smaller in diameter than the afferent arteriole so the blood in the glomerulus is under high pressure.
7. The high pressure forces liquid and small molecules in the blood out of the capillary and into the bowmans capsule.
8. The liquid and small molecules pass through three layers into BC and enters nephron tubules - the capillary wall, a membrane and the epithelium of the BC.
9. Larger molecules like proteins and blood cells can't pass through, so stay in the blood. The substances that enter the BC are known as the glomerular filtrate.
10. The glomerular filtrate passes along the rest of the nephron and useful substances are reabsorbed along the way.
11. Finally the filtrate flows through the collecting duct and passes out of the kidney along the ureter.
42
Summary of what ultrafiltration is
blood from renal artery enters smaller arterioles in the cortex of kidney
43
When does selective reabsorption take place
Takes place as the glomerular filtrate flows along proximal convoluted tubulue, through the loop of henle and along distal convoluted tubule.
44
Where do useful substances leave and where do they enter?
They leave the tubules of the nephrons and enter the capillary network that's wrapped around them.
45
What does the epithelium of the wall of the PCT have that provides a large surface area?
Microvilli
46
What do microvillis provide
A large surface area for the reabsorption of useful materials from the glomerular filtrate into the blood.
47
What solutes are reabsorbed along the PCT and how are they absorbed?
glucose by active transport and facilitated diffusion
48
How does water enter the blood?
What is it reabsorbed from?
By osmosis because the water potential of the blood is lower than that of the filtrate. Water is reabsorbed from the PCT, loop of henle, DCT and the collecting duct.
49
What is urine made up of?
* Water and dissolved salts
* Urea
* Other substances such as hormones or excess vitamins
50
What does urine not usually contain?
* Proteins and blood cells - they're too big to be filtered out of the blood.
* Glucose because it's actively reabsorbed back into the blood.
51
What is osmoregulation?
The homeostatic control of water potential of the blood
52
When does diabetes occur?
When blood glucose concentration is not controlled
53
What is diabetes mellitus?
A condition where blood glucose concentration can;t be controlled
54
Type 1 diabetes
* explain type 1 diabetes in terms of insulin
* what have some scientists found
* what is hyperglycaemia
* what it can lead to
* how its treated
* why does the treatment need to be carefully controlled
* what is hypoglycaemia
* The immune system attacks the beta cells in the islets of langerhans so they can't produce insulin.
* Some scientists have found that some people have a genetic predisposition to developing Type 1 diabetes. They also think viral infections trigger it.
* The blood glucose levels after eating rise and stays high - HYPERglycaemira (remember it as hyper = too much glucose/ energy).
* Can lead to deaths if left untreated. The kidneys can't reabsorb all this glucose, so some is excreted in the urine.
* Type 1 diabetes is treated with insulin therpy. Most people need regular insulin injections thruout the day but some use an insulin pump to deliver insulin continuously.
* Insulin therapy needs to be carefully controlled because too much insulin can produce a dangerous drop in blood glucose levels - HYPOglycaemia.
* Eating regularly and controlling simple carbs intake helps avoid sudden rise in glucose.
55
Type 2 diabetes
* when do people get it
* what is it linked to
* what are risk factors
* Explain what it is in terms of insulin/ when it occurs
* how can it be treated
*
* It usually occurs later in life than type 1.
* Its linked to obesity and is more likely in family history
* risk factors include; lack of exercise, age and poor diet
* It occurs when beta cells don't produce enough insulin or when the body's cells don't respond properly to insulin due to the insulin receptors on their membrane not working properly, so cells dont take up enough glucose. That means the blood glucose concentration is higher than normal.
* It can be treated by eating healthy, balanced diet, losing weight and regular exercise.
* Glucose lowering medication can be taken if diet and exercise can't control it.
* Insulin injections might eventually be needed
56
What do health advisors recommend to people to reduce risk of developing type 2 diabetes
1. eat a diet that's low in fat, suagr and salt with plenty of whole grains, fruit and vegetables.
2. take regular excercise
3. lose weight if necessary
4. campaigns like NHS's "change4life" aim to educate people on how to have a healthier diet and lifestyle.
5. encourage food industries to reduce advertising of junk food to improve the nutrional value of their products and use clearer labels.
57
How have some food companies attempted to make their products more healthy?
* using sugar alternatives to sweeten food/ drinks
* reducing the sugar, fat and salt content
58
What's used to determine the concentration of glucose solution?
Calorimetry
59
What\s the concentration of glucose in urine
Very low
0-0.8mM
60
What would it indicate if there's a higher concentration of 0-0.8mM?
Diabetes
61
Explain the step used to determine the concentration of glucose solution in a urine sample using calorimetry
1. Quanitative benedicts reagent when heated with glucose will lose its blue coloue. A brick red ISN'T produced.
2. You can use a colorimeter to measure the light absorbance of the solution after the quantitative benedicts test has been carried out.
3. The higher the conc. of glucose, the more blue colour will be lost, decreasing the absorbance of the solution.
62
What is serial dilution?
make several glucose solutions of different known concentrations
63
Give the steps using serial dilution
1. Line up five test tubes in a rack.
2. Add 10cm3 of the initial 4mM glucose solution to the first test tube and 5cm3 of distilled water to other four test tubes.
3. Then, 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. You now have 10cm3 of the solution that's half as concentrated as the solution in the first test tube (it's 2mM).
4. Repeat the process three more times to create solutions if 1mM, 0.5mM and 0.25mM.
64
What does the kidneys regulate?
The water potential of the blood
65
Why is water essential?
To keep the body functioning
66
What needs to be kept constant in the blood?
The amount of water
67
How is water lost?
* Excretion
* Sweat
* breathing
68
What is osmoregulation?
The control of water levels and mineral ions (salt) in the blood.
69
Give the location of osmoreceptors in the body of a mammal.
Hypothalamus.
70
If the water potential of blood is too low, what does that mean for the body?
It's dehydrated
71
When a person is dehydrated, the cell volume of an osmoreceptor decreases. Explain why. (only need point 1 and 2 to get full marks)
1. **Water potential** of blood will **decrease**;
2. So more **water** gets reabsorbed and **moves** from **osmoreceptor** into the **blood** from the tubules of nephrons by **osmosis.**
3. That means the **urine** is **more concentrated**, so **less** water is **lost** during excretion.
72
When is the urine more concentrated?
When a person is dehydrated and so less water is lost during excretion.
73
When a person is too hydrated, the cell volume of an osmoreceptor increases. Explain why.
// explain what happens when a person is over hydrated
1. Water potential of blood will increase/ is too high
2. Less water is reabsorbed by osmosis into the blood from tubules of nephrons.
3. Urine is more dilute, so more water is lost during excretion
74
When is the urine more dilute?
when the body is too hydrated, more water is lost during excretion
75
Where does the regulation of water potential take place?
* Loop of Henle
* DCT
* Collecting duct
76
The volume of water reabsorbed by the DCT and collecting duct is controlled by what?
Hormones.
77
What does the loop of Henle maintain?
A sodium ion gradient
78
Where is the loop of henle located?
In the medulla of kidneys
79
What is the loop of henle made up of?
Two limbs;
* descending limb
* ascending limb
80
What do the AL and DL control in the loop of henle?
The movement of sodium ions so that water can bd reabsorbed by the blood
81
The control of water balance in the body involves negative feedback.
(i) Describe what is meant by negative feedback.
where a change triggers a response which reduces the effect of a change
82
What is meant by homeostasis?
maintaining a constant internal environment;
83
Giving one example, explain why homeostasis is important in mammals.
temperature / pH;
optimum for enzymes / effect of pH / temperature on enzyme activity;
84
Cross-channel swimmers may suffer from muscle fatigue during which the contraction mechanism is disrupted. One factor thought to contribute to muscle fatigue is a decrease in the availability of calcium ions within muscle fibres.
Explain how a decrease in the availability of calcium ions could disrupt the contraction mechanism in muscles. (3)
1. cannot interact with / move tropomyosin from binding sites on actin;
2. myosin(heads) do not bind / actinomyosin not formed;
3. does not activate ATPase / energy not released from ATP;
85
Explain how the normal mice prevented their blood glucose concentration falling when they had not eaten for 48 hours.
1. Release of glucagon;
2. Leads to formation of glucose in liver (cells);
3. From non-carbohydrates / amino acids / fatty acids
86
Apart from the yoghurt, it was important that all of the mice were given the same food each day.
Give two reasons why it was important that all of the mice were given the same food each day.
1. Food is a factor affecting blood glucose / different foods contain different amounts of starch / glucose / sugar / carbohydrate;
2. To keep starch / fibre intake the same / similar;
87
When insulin binds to receptors on liver cells, it leads to the formation of glycogen from glucose. This lowers the concentration of glucose in liver cells.
Explain how the formation of glycogen in liver cells leads to a lowering of blood glucose concentration.
1. Glucose concentration in cell / liver falls below that in blood (plasma) which creates / maintains glucose concentration / diffusion gradient;
2. Glucose enters cell / leaves blood by facilitated diffusion / via carrier(protein) / channel (protein);
88
Adrenaline binds to receptors in the plasma membranes of liver cells.
Explain how this causes the blood glucose concentration to increase.
1. Adenylate cyclase activated / cAMP produced / second messenger produced;
2. Activates enzyme(s) (in cell so) glycogenolysis / gluconeogenesis occurs / glycogenesis inhibited;
89
Diabetic people who do not control their blood glucose concentration may become unconscious and go into a coma. A doctor may inject a diabetic person who is in a coma with glucagon.
Explain how the glucagon would affect the person’s blood glucose concentration. (2)
1. Glycogen to glucose / glycogenolysis by activating enzymes;
2. Gluconeogenesis;
90
Explain how the Loop of Henle works/ how water moves out
1. Near the **top** of the **ascending** limb, **Na+ ions** are **pumped** out into the **medulla** using **active transport.**
2. The **ascending limb** is **impermeable** to **water**, so the water **stays** **inside** the tubule. This creates a **low water potential in the medulla** because there's a **high concetration of ions.**
3. **Water** moves **out descending limb,** into **medulla** by **osmosis**. The **filtrates** then more **concentrated**.
4. **Bottom** of **ascending** limb, **Na+ **ions **diffuse** **into** **medulla**, **lowering water potential** in medulla. (Ascending limb is **impermable** to water so stays in tubule again).
5. **Water moves out of DCT** by **osmosis** and **reabsorbed** into the **blood**.
6. The three stages **increase the ion concentration** in the **medulla**, which **lowers the water potential.**
7. That causes water to **move out of collecting duct** by **osmosis**. The water in the medulla is **reabsorbed into the blood** through the capillary network.
91
What controls water reabsorption
hormones
92
What controls the water potential of the blood
osmoreceptors in th brain hypothalamus
93
What happens when the water potential decreases?
Water moves **out** of **osmoreceptor** cells by **osmosis** causing a **decrease** in the **volume**. That sends a **signal** to other cells in the **hypothalamus**, which sends a signal to the **posterior** **pituitary gland.** That causes the posterior pituitary to **release** a hormone called **ADH** (antidiuretic hormone) into the blood.
94
What does ADH stand for?
Antidiuretic hormone
95
What does ADH make the walls of DCT and collecting duct?
**More permeable** to water so **more water** can be **reabsorbed** from these **tubules** into the **medulla** and into the **blood** by **osmosis**. A small amount of **concentrated urine** is produced which means **less water is lost** from the body.
96
When is less water lost?
When the urine is concentrated
97
How does ADH change the water content of the blood when it's too low (dehydrated)?
1. The **water** **content** of the blood **drops**, so its **water potential drops.**
2. That is detected by **osmoreceptors** in the **hypothalamus**.
3. The **posterior pituitary gland** is **stimulated** to **release** **more ADH** into the blood.
4. More ADH means that the **DCT** and **collecting duct** becomes **more permeable** so **more water is reabsorbed** into the blood by **osmosis**.
5. A **small amount** of **highly concentrated urine** is produced and **less water** is **lost**.
98
How does ADH change the water content of the blood when it's too high (hydrated)
1. The **water content** of the blood **rises**, so it's **water potential increases.**
2. That's detected by **osmoreceptors** in the **hypothalamus**.
3. The **posterior pituitary gland** releases **less ADH** into the blood.
4. Less ADH means that the **DCT** and **CD** become **less permeable** so **less water** is **reabsorbed** into the blood by **osmosis**.
5. A **large amount** of **dilure urine** is produced and **more water** is **lost**.
99
n humans, when the stomach starts to become full of food, receptors in the wall of the stomach are stimulated. This leads to negative feedback on the desire to eat. Suggest why this negative feedback is important.
1. (Negative feedback) stops desire / wish to eat / appetite;
2. (This) limits amount eaten / stops eating;
3. Prevents / reduces risk of obesity / too much energy intake;
100
In this investigation, the higher the concentration of sucrose in a rat’s mouth, the higher the frequency of nerve impulses from each taste receptor to the brain.
(3)
If rats are given very high concentrations of sucrose solution to drink, the refractory period makes it impossible for information about the differences in concentration to reach the brain. Explain why.
1. (Refractory period) leads to discrete / separate nerve impulses / time when another nerve impulse can’t happen;
2. When maximum frequency reached / exceeded, no further increase in information / all (higher) concentrations of sucrose seem the same;
101
From which gland is ADH released?
pituitary
102
Use the information given;
explain how ADH increases the movement of water from the lumen of the collecting duct into the blood.
1. ADH causes vesicles containing aquaporins / aquaporins to be inserted into membrane / collecting duct wall / plasma;
2. water enters cell through aquaporins;
3. by osmosis / diffusion / down a water potential gradient;
4. (from cell) to capillary;
5. via interstitial fluid;
103
Suggest why diabetes insipidus is more common in males. (2)
1. because males only have one X chromosome / do not have Y chromosome;
2. a single copy of the recessive allele will be expressed;
104
A recessive allele which has harmful effects is able to reach a higher frequency in a population than a harmful dominant allele. Explain how. (3)
1. recessive alleles can be carried by individuals without showing effects / dominant allele always expressed;
2. organism that are carriers more likely to reproduce / affected organism less likely to reproduce;
3. therefore recessive alleles are more likely to be passed on / dominant alleles less likely to be passed on;
105
Changes in your external environment can affect your..
internal environment (blood and tissue fluid that surrounds your cells)
106
What does homeostasis involve?
The control systems that keep your internal environment roughly constant
107
What is vital for cells to function normally
keeping the internal environment stable.
108
What is particularly important to maintain?
The right core body temperature
Blood pH
109
Why is it important to maintain the right core body temp ad pH of blood
Temperature and pH affect enzyme activity and the enzymes control the rate of metabolic reactions.
110
What happens if the temperatures too high?
1. Enzymes denature
2. The enzymes molecules vibrate too much breaking the hydrogen bonds that hold them in their 3D shape
3. The shape of active site now changed and no longer works as a catalyst.
4. That means metabolic reactions are less efficient
111
What happens if the temperature is too low?
1. Enzyme activity reduced
2. Slows the rate of metabolic reactions
112
When do enzymes work best/ their highest rate of activity?
The highest rate of enzyme activity happens as their optimum temperature
37oC
113
What happens if the pH too high or too low?
1. Enzymes denatured
2. Hydrogen bonds that hold the 3D shape are broken so shape of enzymes active site is changed
3. no longer works as catalyst
4. metabolic reactions less efficient
114
optimum pH for highest enzyme activity
usually pH 7
some enzymes in the stomach tho work best in lower pH
115
Why is it important to maintain the right concentration of glucose in the blood?
because cells need glucose for energy
and blood glucose conc. affects the water potential of blood
116
What is the water potential of blood
The potential of water molecules to diffuse out of or into a solution
117
If the blood glucose concentration is too high, how is the water potential of blood affected?
its reduced to the point where water molecules diffuse out of cells into blood by osmosis which causes cells to shrivel up and die.
118
If the blood glucose concentration is too low, how is the water potential of blood affected?
cells unable to carry out normal activites as there isn't eough glucose for respiration to provide energy
119
What does homeostatic systems detect
a change and respond by negative feedback
120
What does homeostatic systems involve
receptors
a communication system
effectors
121
How is the information communicated?
Receptors
via. the nervous system or hormonal system to effectors
122
why do effectors respond to when a level is too high or low?
to counteract the change (bring it back to normal)
123
Negative feedback
Changes causes a response that leads to a reduction in that change.
The mechanism that restores the level to normal.
124
Why does negative feedback only work in certain limits?
If the change is too big, then the effectors may not be able to counteract it.
i.e. a huge drop in body temperature caused by prolonged exposure to cold weather may be too large to counteract.
125
What do multiple negative feedback mechanisms give and how?
more control because having more than one mechanism gives more control over changes in your internal environment than just one negative feedback mechanism
126
Having multiple negative feedback mechanisms means you can ____ increase or decrease a level so it returns to normal
actively
127
What would it mean if you had one negative feedback mechanism?
All you could do would be turn it on or turn it off. You'd only be able to actively change a level in one direction so it returns to normal.
128
What would having one negative mechanism cause
a slower response
less control
129
When does postive feedback mechanisms occur?
Happens when a homeostatic system breaks down i.e. if you're too cold for too long
130
What does a positive feedback mechanism do?
Amplifies the change
131
How do the effectors respond to positive feedback mechanisms?
Further increase the level away from the normal level.
132
What is positive feedback useful for?
Rapidly increasing something i.e. blood clot after an injury.
133
Explain blood clots forming
1. Platelets become activated and release a chemical - this triggers more platelets to be activated.
2. Platelets very quickly form a blood clot at the injury site.
3. The process ends with negative feedback when the body detects the blood clot has been formed.
134
How does hypothermia involve positive feedback?
1. Hypothermia is low body temp.
2. It happens when heat's lost from the body quicker than it can be produced.
3. As the body temp. falls the brain doesn't work properly and shivering stops - makes the body temp. fall even more.
4. Positive feeback takes body temp. further away from the normal level, and it continues to decrease unless action is taken.
135
Why isn't positive feedback involved in homeostasis
Because it doesn't keep your internal environment stable.
136
How is urea concentrated in filtrate?
1. Waters reabsorbed by osmosis
2. At PCT
3. At DCT
4. By active transport
137
How does a lack of insulin affect the reabsorption of glucose?
1. Increase in conc. of glucose in the blood and tubule.
2. Reabsorbed by facilitated diffusion.
3. Proteins required.
4. They work at a max. rate.
5. Not all glucose reabsorbed/ some lost in the urine.
138
How is urea removed?
1. HSP
2. Causes ultrafiltration thru the basement membrane
3. Small size urea molecules out
