Homeostasis Flashcards
What is it?
The maintenance of a stable internal environment.
What happens if the temp/pH is too high?
Temp too high - enzymes could be denatured so homeostasis can aims to decrease it.
pH - needs to be perfect so enzymes don’t denature so if it’s too high homeostasis can decrease it.
Why do we need to control the conc of glucose in the blood?
Because cells need glucose for energy - it also effects the water potential of blood.
What happens if blood glucose conc is too high?
The water potential of blood is reduced to a point where water molecules diffuse out of cells into the blood by osmosis - cells shrivel and die.
What happens if blood glucose is too low?
Cells are unable to carry out normal activities because there isn’t enough glucose for respiration to provide energy.
Homeostatic systems detect…
A change and respond via negative feedback. They counteract the change to help keep things around the normal level.
Negative feedback only works with…
Certain limits - if the change is too big then the effectors may not be able to counteract it.
What are multiple negative feedback mechanisms?
Where more than one mechanism is used for each thing - gives more control.
Also means you can actively increase or decrease something until it turns back to normal.
If you only had one negative feedback mechanism…
All you could do would be turn it on and turn it off - would be slower and less control.
Some changes trigger a …
Positive feedback mechanism
What does a positive feedback mechanism do?
Rapidly activate something e.g. a blood clot after energy.
Platlets becomes activates and release a chemical - triggers more to be activated a this ends with negative feedback
How does Hypothermia involve positive feedback?
As body temp falls the brain doesn’t work properly and shivering stops - falls even more.
Positive takes the body temp even further away from normal level and it continues to decrease until action is taken.
Normal conc of glucose in blood:
90mg per 100cm3 of blood - monitored by pancreas cells.
When does glucose conc fall and rise?
Rises after eating foods containing carbohydrate
Falls after exercise as more glucose is used in respiration to release energy.
Two hormones released by pancreas:
Insulin
Glucose
What secrets the insulin and glucagon?
Islets of Langerhans - beta cells secrete insulin and alpha cells secrete glucagon into the blood.
How does insulin work?
When blood glucose conc is too high
- binds to specific receptors on membranes of liver and muscle cells
- increases permeability so cells take more glucose (increases number of channels)
- also activates enzymes in liver and muscle cells that concert glucose to glycogen - glycogenesis
- also increases rate of respiration.
How does glucagon work?
When blood glucose conc is too low
- glucagon binds to specific receptors on cell membranes of liver cells
- glucagon activates enzymes in liver cells that break down glycogen - glycogenolysis.
- also activates enzymes in the formation of glucose from glycerol and amino acid - gluconeogenesis.
- decreases rate of respiration.
Skeletal and cardiac muscle cells contain..
A channel protein called GLUT4 - this is a glucose transporter.
What happens to GLUT4 when insulin levels are low?
it’s stored in vesicles in the cytoplasm of cells and when insulin binds to receptors it triggers the movement of it to the membrane - glucose is then transported through it.
What is adrenaline?
A hormone that’s secretes from your adrenal grands when there’s a low conc of glucose in your blood.
What does adrenaline do?
When it binds to receptors in the cell membrane of liver cells it:
Activated glycogenolysis (breakdown of glycogen to glucose)
Inhibits glycogenesis (synthesis of glycogen from glucose)
Activated glucagon secreteion and inhibits insulin secretion
How can Adrenalin and glucagon activate glycogenolysis inside a cell? (3)
- they bind to their receptors and activate an enzyme called adenylate cyclase.
- this converts ATP into a chemical signal called second messenger - cyclic AMP.
- this activates an enzyme called protein kinesis A - activates lots of reactions which break down glycogen into glucose.
How can type 2 diabetes be prevented? (3)
- regular exercise
- eat a diet that’s low in fat sugar and salt
- lose weight
How have food companies responses to make their products more healthy: (2)
- using sugar alternatives
- reducing the sugar fat and salt in their food
When does type 2 diabetes occur?
When the B cells don’t produce enough insulin or when the body’s cells don’t respond properly to insulin - means the glucose conc is higher than normal.
What happens in Type 1 diabetes?
The immune system attacks the B cells so they can’t produce any insulin - this means after eating blood glucose levels remain and stay high (hyperglycaemia)
How is type 1 diabetes treated?
Insulin therapy - using an insulin pump and injections.
One of the main functions of the kidneys:
To excrete waste products e.g. urea.
As blood is passed through capillaries, substances are filtered out of the blood into long tubules - ultrafiltration.
Useful ones are reabsorbed and unwanted are urine.
What are nephrons?
The long tubules with the bundle of capillaries where the blood is filtered.
How does ultrafiltration start?
When blood from the renal artery enters the smaller arterioles in the vortex of the kidney
Each arteriolar splits into a structure called glomerulus.
Ultrafiltration:
- high pressure forces liquid and small molecules in the blood out of the capillary and into the bowman’s capsule
- these pass through 3 layers before they get to it and enter the nephron tubules (capilarrybwall, membrane and epithelium)
- large molecules can’t pass so they stay in the blood.
Substances that enter the bowman’s capsule are known as:
Glomerular filtrate.
What is the arteriole takes blood into each glomerulus is called…
The afferent arteriole.
The arteriole that takes the filtered blood away from the glomerulus is called..
The efferent arteriole
What forces the liquid and small molecules out of capillary?
The high pressure
The end of ultrafiltration:
- the glomerular filtrate passed along the rest of the nephron and useful substances are reabsorbed.
- finally the filtrate flows through the collecting duct and passed out of the kidney along the ureter.
Urine is usually made of: (3)
Urea
Water
Hormones and excess vitamins
Where does selective reabsorbtion happen?
Along the proximal convoluted tubule through loop of henle and along the distal convoluted tubule.
How is the epithelium of the wall of the PCT adapted?
Microvilli provide a large surface area for the reabsorption of useful materials from the glomerular filtrate into the blood.
What is osmoregulation?
It’s the way in which kidneys regulate the water potential of the blood and urine so the body has just the right amount of water.
What happens if the blood water potential is too low?
More water is reabsorbed by osmosis into the blood from the tubules of the nephrons - means urine is more concentrated so less water lost.
What happens if water potential of the blood is too high?
Less water is reabsorbed by osmosis into the blood from the tubules of the nephrons - means the urine is more dilute so more water is lost during excretion.
Where is the loop of Henle and what is it?
It’s made up of two lines which control the movement of sodium ions so that water can be reabsorbed by the blood - locates in the medulla of kidneys.
Loop of henle made of…
Ascending limb
Descending limb
Step 1
- at ascending limb, Na+ ions pumped out into the medulla - this is impermeable to water so water stays inside tubules so there’s a lower water potential in medulla - higher conc of ions.
Step 2
- lower potential in medulla than descending means water moves out into medulla - filtrate is more concentrated, water in the medulla reabsorbed into the blood.
Step 3
Near the bottom of ascending limb na* diffuse out into the medulla further lowering the water potential - this is impermeable to water so it stays in tubule
Water moves out of distal convoluted tubule and reabsorbed into blood
How is the water potential of blood monitored?
By cells called osmoreceptrs in a part of a brain called the hypothalamus.
What happens when you’re dehydrated? (5)
- water content of blood drops
- detected by osmoreceptors in hypothalamus
- posterior pituitary gland is stimulated to release more ADHD in blood
- more ADHD means the DCT and collecting duct are more permeable so more water is reabsorbed into blood
- small amount of highly concentrated urine is produced and less water is lost.
What happens when you’re hydrated?
- water content rises
- detected by osmoreceptors
- PPG releases less ADHD in blood
- less ADH means that the DCT and collecting dust becomes less permeable so less water is reabsorbed into blood by osmosis
- large amount of dilute urine is produced and more water is lost.
