B16 Homeostasis Flashcards
What is homeostasis
The maintenance of a stable internal environment
Why is homeostasis important
For cells to function normally and for optimum enzyme activity for metabolic reactions
What happens when body temperature is too high
- enzymes vibrate too much due to higher kinetic energy
- this breaks the hydrogen bonds that hold them in their 3D shape
- shape of the enzymes active site is altered so ES complexes can’t form
- rate metabolic reactions slow down
What happens if blood pH is too high/ low
- hydrogen bonds holding enzymes in their 3D shape are broken
-shape of enzymes active site is altered
- enzyme denatures
- metabolic reactions slow down
What happens if blood glucose conc is too high
- the water potential of blood is greatly reduced to a point where water molecules diffuse out of the cells into the blood via osmosis
- cells shrivel up and die
How do homeostatic systems work
Receptors detect when a level is too high or too low
Info is communicated via the nervous system or hormonal system
Reaches the effectors which counteract the change and restores the level
What is negative feedback
Restores systems to their original level by reversing a change in the body
Why is having multiple negative feedback mechanisms useful
You can actively increase or decrease a level so it returns to normal
Gives more control
Faster response
What is a positive feedback mechanism
Amplifies a detected change
Which organ controls the blood glucose concentration
Pancreas
Insulin is secreted from
Beta cells in islets of Langerhans
Glucagon is secreted from
Alpha cells in islets of Langerhans
Insulin
Lowers blood glucose conc
Glucagon
Increases blood glucose conc
How does insulin lower blood glucose conc
5 things
Binds to specific receptors on liver and muscle cells and increases their permeability of glucose so glucose can more easily diffuse into cells
This causes more carrier proteins to move to the cell membrane
Stimulates glucose -> amino acids/fats/lipids
Increases the rate of respiration
Stimulates glycogenesis
Explain how the formation of glycogen in liver cells leads to a lowering of blood glucose conc
Glucose conc in cells creates a glucose conc gradient
Glucose leaves the blood via facilitated diffusion
How does glucagon work
Binds to specific receptors on liver cells
Stimulates gluconeogenesis and glycogenolysis by activating enzymes from the second messenger model
Decreases the rate of respiration
Where is adrenaline released from
Adrenal glands
How does adrenaline work
Stimulates glycogenolysis
Secretion of glucagon
Inhibition of insulin
How does the 2nd messenger model work
1) 1st messenger binds to receptors on liver cell
2) This activates adenylyl cyclase
3) This stimulates the conversion of ATP -> cAMP
4) cAMP activates protein kinase A which activates a cascade of reactions that break down glycogen to glucose
What happens in type 1 diabetes
The immune system attacks the Beta cells in the islets of Langerhans so they can’t secrete insulin
What is the main issue for people with type 1 diabetes
Hyperglycaemia as after eating the blood glucose level rises and stays high
How can type 1 diabetes be treated
Insulin therapy
Eating regularly
Controlling simple carbohydrates intake
What happens in type 2 diabetes
When Beta cells don’t produce enough insulin OR when the body’s cells don’t respond properly to insulin
Risk factors causing Type 2 Diabetes
Obesity
Lack of exercise
Age
Poor diet
Treatments for type 2 Diabetes
Eating a healthy balanced diet
Losing weight
Regular exercise
Eventually insulin injections
How you can indicate if someone has diabetes
By using colorimetry to indicate blood glucose conc in someone’s urine
Colorimetry basic steps
1) Using quantitative Benedict’s Reagent
2) Use a colorimeter to measure the light absorbance of the solution after the Benedict’s test has been carried out
3) The higher the conc of glucose the more the blue colour will be lost which would decrease the absorbance of the solution
4) Plot a calibration curve showing absorbance against glucose conc
What is quantitative Benedict’s Reagent
When heated with glucose, the blue colour will just be lost. No brick red precipitate will be formed
How to make serial dilutions
1) line up 5 test tubes
2) add 10cm of initial whatever conc glucose solution to the first test tube
3) add 5cm of distilled water to each of the other 4 test tubes
4) use a pipette to draw out 5cm from first test tube and transfer to the second test tube and mix
5) repeat till 5th test tube
Each will be half conc compared to test tube before it
Function of the kidneys
Regulating water potential of the blood
Excrete waste products e.g. urea
Ultrafiltration process
Blood enters from afferent arteriole under high hydrostatic pressure and enters the glomerulus
The higher pressure forces small molecules out of the capillary’s via podocytes and through the basement membrane into the Bowman’s capsule
Larger molecules such as proteins and blood cells are unable to pass through as they are too large.
Differences between afferent and efferent arterioles
Afferent is larger in diameter/ larger lumen as it needs to withstand higher pressures than efferent
Selective reabsorption
Useful substances leave the tubules and enter the capillary network around them e.g.
Glucose via active transport and facilitated diffusion at pct
Water enters the blood via osmosis as WP of blood is lower than in the filtrate. This diffusion occurs at pct loop of henle dct and collecting duct
How is the pct’s epithelial cells adapted for selective reabsorption
Microvilli to provide a large surface area
Many ribosomes to provide channel proteins for facilitated diffusion of glucose
Many mitochondria for production of ATP for active transport of glucose
What is urine made up of
Water
Dissolved salts
Hormones
Excess vitamins
How is water lost
Sweat
Excretion
Breathing
Osmoregulation definition
The regulation of the water potential of blood through kidneys
Loop of Henle
Near the top of ascending limb, Na+ ions are pumped out into the medulla using active transport. The ascending limb is impermeable to water so no water is lost or gained. This creates a low WP in the medulla as there’s a high conc of ions
Low WP in medulla means water moves out the descending limb into the medulla via osmosis. Therefore filtrate becomes more concentrated as ions can’t diffuse out of descending limb. Water in medulla is reabsorber into the blood via capillary network.
Near the bottom of the ascending limb, Na+ ions diffuse out into medulla which furthers the lowering of the WP in the medulla.
Water moves out the DCT via osmosis and is reabsorbed by the blood
The lower WP of the medulla means water can move out of the collecting duct via osmosis
Where are osmoreceptors found and what do they do
Hypothalamus
They monitor the WP of blood
What happens when there’s a low WP in the blood
Water moved out of the osmoreceptors via osmosis
This causes the cells to decrease in volume
This send a signal to other cells in the hypothalamus which sends a signal to the posterior pituitary gland
This gland releases ADH
How does ADH work
More ADH means DCT and collecting duct becomes more permeable to water so more water is reabsorbed into the blood via osmosis
Negative feedback definition
When a change triggers a response which reduces the effect of the change
Why is glucose found in the urine of a person with untreated diabetes
3 marks
They have a high blood glucose concentration
They have high glucose concentration in filtrate
Not all the glucose can be selectively reabsorber into the blood
As channel and carrier proteins are working at maximum rate
Describe role of glucagon/ insulin
-> activates enzymes
Main issue for people with Type 2 Diabetes
Faulty receptors so less responsive to insulin
What does a thicker medulla mean
A longer loop of Henle
