Topic 16: Homeostasis Flashcards
What is homeostasis
The maintaining of a constant internal environment within an organism
Give three reasons why homeostasis is important
- To ensure the enzymes in your body that control biochemical reactions do not become affected by temperature and pH
- To ensure the water potential of cells remains constant so they do not lyse or crenate (burst or shrivel)
- By maintaining a constant internal environment organisms can handle a wide variety of external environments
State the parts of a control mechanisms that is self regulating
- Stimulus
- Receptor
- Coordinator
- Effector
- Feedback Mechanism
What are the two types of feedback
- Negative Feedback
- Positive Feedback
Briefly explain negative feedback
When the change produced leads back to the original (optimum point)
Briefly explain Positive Feedback
When the change produced leads further away from the optimum point
Give some examples of Negative feedback systems
- Temperature control
- Blood gluose control
- pH regulation
- Osmoregulation
- Hormone regulation
- Blood pressure regulation
Give some examples of positive feedback systems
- Birth
- Depolarisation in neurones
- Blood Clotting
- Milk Production
- Fever production
What is a consequence of your core temperature being too high
- H-bonds within the tertiary structure of the enzymes break
- Enzymes denature ad the active site is no longer complementary to the substrate
- So less Enzyme-Substrate complexes are formed
What is a consequence of your core temperature being too low
- Enzymes and substrates have less Thermal energy
- Less Kinetic energy
- So fewer Enzyme-Substrate complexes form
Why is it important to maintain pH within your body
- Any deviation in pH will break the bonds (H-bonds, ionic) within the tertiary structure of your enzymes
- So the enzyme denatures
- The active site changes shape, so it is no longer complementary to the substrate
- Less E-S complexes formed
Explain what happens when your blood glucose is too low (hypoglycaemia)
- Less glucose for respiration
- Less ATP is produced
- Processes requiring energy are less efficient/ cannot occur
- Death
Explain what happens when your blood glucose is too high (hyperglycaemia)
- Too much glucose will lower the water potential in your blood
- So water moves from the tissue into the blood via osmosis
- The kidneys will not be able to absorb all of the glucose
- So more water is lost in urin -> dehydration
Explain what happens in a positive feedback system
(3 marks)
- Receptors detect a change/ deviation from the regular parameters
- The effectors will respond to amplify the change
- Resulting in a greater deviation from the normal
What are hormones
Chemical messengers that coordinate a response
What produces hormones and where do they function
Produced in the endocrine glands
Move into the blood and function in the muscle / tissue they are targeting
What are two factors that influence your blood glucose levels
- Consumption of carbohydrates
- Rate of respiration
What part of the pancrease will release hormones for the regulation of blood glucose
Islets of Langerhans
What are the three hormones involved in the regulation of blood glucose
- Insulin
- Glucagon
- Adrenaline
What three processes does the liver undergo to regulate blood glucose
- Glycogenesis
- Glycogenolysis
- Gluconeogenesis
What happens with adrenaline when your body detects danger
- Adrenaline is released by your adrenal glands
- This results in more glucose being released from your glycogen stores in the liver
What happens in glycogenesis
Excess glucose is converted into glycogen
What happens in Glycogenolysis
Glycogen is hydrolysed back into glucose
What happens in gluconeogenesis
Glucose is created from non-carbohydrate stores in the liver
When will gluconeogenesis occur
When all your glycogen stores have been used up and you still need glucose, so it will be made from amino acids / glycerol.
What are the cells called that are in the Islets of Langerhands which detect a change in your blood glucose levels
Beta cells / Alpha cells
Which cells are responsible for secreting insulin when the blood glucose is too high
Beta cells
Which cells are responsible for secreting glucagon when blood glucose is too low
Alpha cells
Explain insulin action
- Insulin released by Beta cells within the islets of Langerhans
- Insulin binds to complementary receptors on the cell surface membrane of the target cell
- This causes more glucose channel proteins to fuse with the membrane, increasing permeability to glucose, so more glucose can enter via facillitated diffusion
- This also activates enzymes involved in glycogenesis, lowering the concentration of glucose within the cell, so glucose can enter via facillitated diffusion
Explain Glucagon action
- Alpha cells in the Islets of Langerhans will release glucagon
- Glucagon will attatch to complementary receptors on the cell surface membrane of the target cells (liver cells)
- This activates enzymes involved in glyocogenolysis, so more glucose is released, high concentration of glucose means it can move by facillitated diffusion into the blood
- Also activates enzymes involved in gluconeogenesis
Explain Adrenaline action
- Adrenaline is released by the adrenal glands in time of stress/danger
- Adrenaline attatches to complementary receptors on the target cells
- This activates enzymes involved in glycogenolysis
- This establishes a concentration gradient so more glucose can move by facillitated diffusion into the blood
Which of the two hormones that control blood glucose use the second messenger model
- Adrenaline
- Glucagon
(the ones that want to increase blood glucose when it is too low)
Explain the second mesenger model
- A hormone (glucagon / adrenaline) will bind to complementary receptors on the cell surface membrane
- This will activate G-protein, which will activate the enzyme adenylate cyclase
- Adenylate cyclase will convert ATP into cyclic AMP (cAMP)
- cAMP is the second messenger, and will activate protein kinase enzymes
- Protein Kinase enzymes will activate enzymes that hydrolyse glycogen into glucose.
What causes type 1 diabetes, and how do you treat it
- The beta cells within the islets of langerhans cannot produce insulin
- Treatment by insulin injections
What causes type 2 diabetes and how is it treated
- The receptors on the target (liver) cells lose their responsiveness to insulin
- Treated by regulating diet and exercising
What are some symptoms of Diabetes
Beyond the spec
- High blood glucose
- Presence of glucose in the urine
- Increased hunger and thirst
- Tiredness
- Weight loss
- Needing to urinate excessively
How is diabetes diagnosed
(Beyond the spec)
- Glucose tolerance test
- Patient takes a fasting blood glucose test
- Patient then chugs a glucose drink
- Glucose test is then taken every hour for 6 hours
Where are the nephrons found in the kidney
In the medulla of the kidney
Name the 6 structures in the nephron
- Glomelurus
- Renal capsule
- Proximal convulated tubule
- Loop of Henle
- Distal convulated tubule
- Colelcting duct
What is the function of the renal capsule
Formation of the glomerular filtrate due to hydrostatic pressue during ultrafiltration
What is the function of the Proximal Convulated tubule
To rebsorb water and glucose during selective reabsorption
What is the function of the Loop of Henle
Maintains a gradient of sodium ions in the medulla so water can be reabsorbed
What is the function of the Distal convulated tubule and the collecting duct
Reabsorption of water and filters the remaining liquid as urine
What happens during ultrafiltration
- Blood enters via the afferent arteriole and flows into the glomerulus. This causes high hydrostatic pressure within the glomerulus
- Water and small molecules are forced out of the gaps between the epithelial cells into the renal capsule and form the glomerulus filtrate. The filtrate is filtered out through the gaps, then the capillary basement membrane, and then podocytes.
- Large proteins and blood cells remain in the blood because they are too big, and then they leave via the efferent arteriole.
How many layers of filtration are there during ultrafiltration
3
What are the adaptations of the proximal convoluted tubule
- microvilli on the surface of the PCT to maximise surface area for reabsorption
-many channel/carrier proteins for facilitated diffusion - many carrier proteins for active transport
- many ribosomes to produce carrier/channel proteins via protein synthesis
- lots of mitochondria to provide energy for active transport
Where does selective reabsorption occur
In the proximal convoluted tubule
Explain selective reabsorption
- Sodium ions are actively transported from the epithelial cells lining the PCT into the capillaries. This creates a concentration gradient
- Sodium ions can then diffuse by facillitated diffusion from the filtrate in the lumen of the PCT, along with a glucose molecule, into the epithelial cells
- Glucose can then diffuse by facillitated diffusion from the epithelial cells into the capillaries
This is how all glucose is absorbed
Describe the pathway of the filtrate in the nephron
from glomerulus
- Glomerulus
- Renal capsule
- Proximal convoluted tubule
- Loop of Henle
- Distal convoluted tubule
- Collecting duct
Which limb of the Loop of Henle is impermeable to water and why
The ascending limb is impermeable, because it has much thicker walls
Explain what happens within the Loop of Henle?
- Sodium ions actively transported out of the filtrate in the ascending limb and into the interstitial fluid
- This lowers the water potential of the interstitial fluid
- This allows water to osmose out of the filtrate in the descending limb and into the capillaries
- At the base of the Loop of Henle, there is a very high water potential so sodium ions can just diffuse back into the filtrate
What happens in the distal convoluted tubule
- The filtrate arrives very dilute
- Water can osmose from the filtrate directly into the interstitial fluid which has a very low water potential
What will happen when blood has too low of a water potential
- Water will osmose out of the cells
- causing the cells to crenate
What will happen when blood has too high water potential
- Water will osmose out of the cells
- Causing them to lyse
Where are osmoreceptors found
In the hypothalamus
Where is ADH released from
Released from the post-pituitary
When will osmoreceptors produce more ADH
When they shrivel
Explain how ADH results in more concentrated urine
- ADH binds to the complementary receptors on the cell-surface membrane of the collecting duct
- This activates a phosphorylase enzyme in the cells
- The phosphorylase enzyme will cause vesicles containing aquaporins to move twards and fuse with the cell membrane and embed the aquaporins
- The aquaporins are channel proteins that allow water to osmose out of the cell, allowing more to be reabsorbed into the blood, resulting in more concentrated urine.
