Homeostasis Flashcards
Homeostatis definition
Maintaining a constant internal environment within restricted limits
What happens when core body temperature becomes too high?
Hydrogen bonds break within enzymes - changes tertiary structure and shape of active site so less enzyme-substrate complexes
What happens when core body temperature becomes too low?
Enzymes have too low kinetic energy so less enzyme-substrate complexes so reduced metabolic rate
What happens when blood pH becomes too high?
Hydrogen bonds break within proteins - changes tertiary structure
What happens when blood pH becomes too low?
Hydrogen bonds break within proteins - changes tertiary structure
What happens when blood glucose concentration becomes too high?
Blood has lower water potential than cells so water leaves cells into blood via osmosis and cells lack water for hydrolysis reactions and as a solvent
What happens when blood glucose concentration becomes too low?
Glucose not provided to cells fast enough for a high enough rate of respiration
What happens when blood water potential becomes too high?
Water enters cells by osmosis - too much can cause cell lysis, too much water in blood causes high blood pressure
What happens when blood water potential becomes too low?
Water leaves cells into blood via osmosis so cells lack water for hydrolysis and as a solvent
What is an example of a biological negative feedback mechanism?
Regulating body temperature through vasodilation/constriction
What is an example of a biological positive feedback mechanism?
Depolarisation causing Na+ channels to open so more Na+ ions diffuse in which causes more depolarisation
What type of messenger are hormones and where are they produced/secreted from?
Chemical, glands
How are hormones transported around the body?
Through the bloodstream
Where do specific hormones act?
Protein binding receptors on TARGET cells
What causes blood glucose to increase?
Eating foods high in glucose/starch - absorbed into blood
What causes blood glucose to decrease?
Increase in cell respiration e.g. during exercise
Which cells produce insulin?
β-cells
What does insulin do?
Decreases blood glucose
What are the target cells for insulin?
Liver and muscle cells
What are the 2 ways insulin decreases blood glucose?
- Inserts more glucose channel proteins so glucose enters cells via facilitated diffusion
- Activates enzymes to convert glucose into glycogen for storage
What is the name of the process where glucose is converted into glycogen?
Glycogenesis
Which cells produce glucagon?
α-cells
Where is adrenaline released from?
Adrenal glands
What do glucagon and adrenaline do?
Increase blood glucose
What are the target cells for glucagon and adrenaline?
Liver cells
What are the 2 ways glucagon and adrenaline increase blood glucose?
- Activate enzymes that hydrolyse glycogen into glucose
- Activate enzymes that convert glycerol/amino acids into glucose
What is the name of the process when glycogen is hydrolysed into glucose?
Glycogenolysis
What is the name of the process when glycerol/amino acids are converted into glucose?
Gluconeogenesis
What is the secondary messenger pathway of glucagon and adrenaline?
- Binding of glucagon/adrenaline to their receptors activates adenylate cyclase
- Converts ATP to cAMP
- Activates protein kinase
- Activates enzymes for glycogenolysis
What is diabetes?
Individual is unable to lower blood glucose level
What can’t individuals with type 1 diabetes produce and why?
Insulin, pancreatic B cells have been destroyed
Why can’t people with type 2 diabetes lower their blood glucose level and what is type 2 diabetes caused by?
Insulin produced but insulin receptors don’t respond to insulin, caused by obesity
Why can’t people with type 1 diabetes take insulin orally?
Insulin is a protein so will be digested by stomach acid
Why are people with type 1 diabetes advised to eat complex carbohydrates rather than sugar?
Prevents rapid increase in glucose as glycosidic bonds need to be hydrolysed first before absorption
Why are people with type 2 diabetes advised to exercise regularly?
Glucose will be taken into cells from blood for respiration
What happens in the kidney?
Substances filtered out of blood, including water - useful substances reabsorbed back into blood, unwanted substances travel to bladder and are excreted
What happens in the kidney when blood water potential is too high?
Less water reabsorbed, greater volume of urine, less concentrated urine
What happens in the kidney when blood water potential is too low?
More water reabsorbed, smaller volume of urine, more concentrated urine
What are the 7 structures in a nephron?
Glomerulus
Basement membrane
Bowman’s capsule
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
Collecting duct
Describe the process of ultrafiltration, including what layers molecules pass through
- High blood pressure in glomerulus so water and small molecules e.g. glucose are forced out of pores in capillary endothelium and basement membrane
- Forms the glomerular filtrate in the tubule
- Proteins/cells too large to pass through so stay in the blood
What causes proteinurea (high quantity of protein in urine)?
Damage to the basement membrane
What is selective reabsorption?
85% of useful molecules and water are reabsorbed at proximal convoluted tubule into the blood
What are 3 ways epithelial cells lining the proximal convoluted tubule are adapted for absorption?
- Microvilli increase surface area for diffusion
- Many mitochondria to produce ATP for active transport
- Microvilli increases number of carrier proteins for facilitated diffusion
How is water reabsorbed at the proximal convoluted tubule and what causes water potential in the blood to be lower?
Osmosis, proteins in the blood that weren’t filtered
Why is glucose found in the urine of someone with diabetes?
High glucose concentration in blood so not all glucose reabsorbed at proximal convoluted tubule as all carrier proteins are occupied
What is the Loop of Henle involved in and how does it do this?
Involved in reabsorbing more water from glomerular filtrate by producing Na+ conc. gradient in the medulla
What happens at the ascending limb in the Loop of Henle?
Na+ ions are actively transported out and water remains as the ascending limb is impermeable to water - concentration decreases up the ascending limb
What happens at the descending limb in the Loop of Henle?
Na+ ions are actively transported in and water moves out via osmosis as the descending limb is permeable to water - concentration increases up the descending limb
What increases down the medulla?
Na+ concentration gradient
What is maintained along the whole length of the collecting duct and why?
Water potential gradient, medulla has a lower water potential than collecting duct
What does it mean when an organism has a longer Loop of Henle?
Greater Na+ concentration gradient so water potential gradient maintained for longer so more water reabsorbed from the collecting duct by osmosis
Describe how osmoregulation by ADH occurs when there is a decrease in blood water potential?
Water moves OUT OF osmoreceptors in the hypothalamus into the blood by osmosis so the posterior pituitary gland releases MORE ADH into blood so collecting duct becomes MORE permeable to water as MORE aquaporins in membrane so MORE water reabsorbed into blood via osmosis so urine volume DECREASES and becomes MORE concentrated
Describe how osmoregulation by ADH occurs when there is an increase in blood water potential?
Water moves INTO osmoreceptors in the hypothalamus into the blood by osmosis so the posterior pituitary gland releases LESS ADH into blood so collecting duct becomes LESS permeable to water as LESS aquaporins in membrane so LESS water reabsorbed into blood via osmosis so urine volume INCREASES and becomes LESS concentrated
