Homeostasis Flashcards
What is homeostasis?
The maintenance of of the internal environment within an optimum range
What happens if body temperature is too high?
Enzymes denature, as the hydrogen bonds in the tertiary structure break, altering the shape of the active site
What happens if body temperature is too low?
Enzyme activity decreases, so important reactions slow down
What happens if pH is not maintained?
Enzymes will denature, so can no longer catalyse important reactions
What happens if blood glucose is high? (Ψ)
- Ψ of blood is reduced, so water moves out of cells via osmosis and into the blood
- This makes cells flaccid and kills them
What happens if blood glucose is low?
- Insufficient glucose for respiration, so respiration rate decreases + energy falls
What is negative feedback?
A mechanism that restores the system to original level
How does negative feedback work?
- Change in the internal environment is detected by receptors
- Receptors are stimulated + send signal to effectors
- The effectors counteract the change
- But only in a specific range
Advantage of multiple feedback mechanisms
Faster response
What can cause changes in blood glucose conc? {2}
- Eating carbs (increase)
- Exercise (decrease)
Where is blood glucose conc monitored?
Pancreas
What happens when blood glucose is too high?
- Glycogenesis
- Receptors in the pancreas detect change
- Beta cells in the islets of Langerhans secrete insulin
- Insulin binds to receptors on hepatocytes which activates the conversion of glucose to glycogen
What happens when insulin binds to receptors? {3}
- Increases the permeability of cells by increasing the number of GLUT 4 channel proteins
- Glucose is used during respiration
- Glycogenesis
What happens when blood glucose is low (hepatocytes)?
- Glycogenolysis
- Receptors in the pancreas detect change
- Alpha cells from the islets of Langerhans secrete glucagon
- Glucagon binds to receptors on hepatocytes stimulating the conversion of glycogen to glucose
What happens when blood glucose is too low (muscle + cytoplasm of hepatocytes)?
- Gluconeogenesis
- Glycerol and amino acids are converted to glucose
How else can glucagon reduce blood glucose
- Slowing the rate of respiration
Why is insulin important? (Ψ)
- As without it blood glucose would not decrease, so Ψ would decrease and move out of cells via osmosis causing them to die
Why is glucagon important?
- As without it blood glucose would decrease, so there is not enough for respiration, therefore less energy to survive
How does adrenaline increase blood glucose?
- It is secreted from the adrenal glands
- It binds to receptors on hepatocytes
- It inhibits glycogenesis and activates glycogenolysis
- It also promotes the secretion of glucagon and inhibits the secretion of insulin
What are primary messengers?
- Messengers that do not enter the cell
- They exert an action on the cell membrane
- They activate another molecule or initiate a reaction
- Example; hormones
What are secondary messengers?
- They initiate and coordinate responses within a cell
- They are activated by the binding of primary messengers
- Example; cAMP (cyclic AMP)
What is adenylate cyclase?
- An enzyme that converts ATP to cAMP
What is protein kinase A?
- An enzyme activated by cAMP
- It triggers a cascade of reactions that results in glycogenolysis
What are the causes of type 1 diabetes?
- Beta cells are attacked by the immune system
- So become damaged and can no longer produce insulin
What is hyperglycaemia?
- When the body is unable to produce insulin to counteract the increase in blood glucose conc
- So it continues to increase
- Fatal if not treated
Name a treatment for type 1 diabetes?
- Insulin therapy; pump or injection
What is hypoglycaemia?
- When blood glucose conc is too low
What are the causes of type II diabetes? {4}
- Obesity
- Lack of exercise
- Age
- Family history
How does type II diabetes occur?
- When beta cells no longer produce enough insulin
- When the hepatocytes and muscle cells stop responding to insulin
Name treatments for type II diabetes
- Healthy diet
- Exercise
- Medication to lower glucose levels
- Insulin injections(rare)
Where does osmoregulation take place?
The nephron of the kidneys
What do the kidneys do if blood Ψ is too high?
- The blood reabsorbs less water from the kidneys
- So more is excreted making urine dilute
What do the kidneys do if blood Ψ is too low?
- The blood reabsorbs more water from the kidneys
- So less water is excreted and urine is more concentrated
What happens during filtration in the kidneys?
- Blood flows through the afferent arteriole at high hydrostatic Pa into the glomerulus
- As the afferent arteriole has a larger diameter than the efferent arteriole
- Small molecules forced out of the blood to the bowman’s capsule creating glomerular filtrate
- The efferent arteriole takes filtered blood back to the body
What happens during selective reabsorption? {3}
- Sugars such as glucose move back into the blood from the glomerular filtrate via active transport
- It takes place in the proximal convoluted tube (PCT), distal convoluted tube and loop of Henle
- Water moves back into the blood via osmosis as the Ψ of the blood is lower than the Ψ of the glomerular filtrate
What occurs after selective reabsorption?
- The rest of the filtrate(urine) enters the collecting duct and passes out of the kidneys down the ureters, into the bladder
Which limb is permeable to water?
Descending limb
How are substances selectively reabsorbed by the PCT?
- Na⁺ ions actively transported out of PCT to the blood via the Na-K pump, K⁺ ions are transported into the epithelium
- The conc in the epithelial cells decrease
- Na⁺ ions diffuse down the conc gradient to epithelial cells via co-transporter proteins
- AA + glucose are also co-transported in, increasing their conc
- Glucose + AA diffuse down conc gradient into the blood, maintaining a steep conc gradient
- Ψ of the blood decreases, in PCT increase, so water diffuses via osmosis into the blood
How is water reabsorbed in the collecting duct?
- Na⁺ ions are actively transported out of the A limb into medulla
- This decreases the Ψ in the medulla, A limb is impermeable to water so does not diffuse out
- D limb is permeable to water so water diffuses out to increase Ψ, + is reabsorbed by the blood
- Na⁺ ions diffuse out at the bottom of A limb decreasing Ψ in the medulla
- Collecting duct is permeable to water, so it diffuses out via osmosis + reabsorbed by the blood
Why is the ascending limb less permeable to water?
Due to its thick walls
What monitors blood Ψ?
Osmoreceptors in the hypothalamus
What does ADH stand for?
Anti diuretic hormone
What stimulates the release of ADH?
- When Ψ is low, water moves out of osmoreceptors via osmosis
- Causing the cell to shrink which is detected by the posterior pituitary gland
- The gland then releases ADH into the blood
What is ADH?
A hormone that binds to receptors on the cell membrane of the DCT and collecting duct
What happens when ADH binds to the receptors on the cell membrane?
- Vesicles containing aquaporins fuse with the cell membrane
- Aquaporins increase the permeability of the DCT and collecting duct
- So more water in reabsorbed into the blood
What is the special name given to epithelial cells of the Bowman’s capsule?
Podocytes
What happens if Ψ of the blood is low?
- The change is detected by osmoreceptors in the hypothalamus
- Stimulating the posterior pituitary gland to release lots of ADH
- ADH binds to receptors of cells lining DCT + collecting duct
- Causing more aquaporins to move to cell membrane
- DCT + collecting duct become more permeable to water
- So lots of water leaves via osmosis into the medulla
- So lots of water is reabsorbed by the blood so Ψ increases
What happens if Ψ of the blood is high?
- The change is detected by osmoreceptors in the hypothalamus
- Stimulating the posterior pituitary gland to release less ADH
- ADH bind to receptors on cells lining DCT + collecting duct
- So less aquaporins move to cell membrane
- So DCT + collecting duct are less permeable to water and less leaves via osmosis into the medulla
- So less water is reabsorbed by the blood so Ψ decreases
