Homeostasis Flashcards
Define homeostasis
Physiological control systems that maintain a constant internal environment
Summarise negative feedback system
Receptors detect change away from normal and mechanism activated to return body to normal
Summarise positive feedback system
A response resulting in effectors further amplifying the change away from the normal
Summarise how the body reacts to high blood glucose
- Receptors in pancreas detect increase
- Beta cells in islets of langerhans secrete insulin
- Insulin binds to receptor is liver and muscle to increase glucose permeability
- More glucose absorbed by diffusion
- Glycogenesis occurs and respiration increased
Summarise how the body reacts to low blood glucose
- Receptors in pancreas detect decrease
- Alpha cells islets of langerhans secrete glucagon
- Glucagon binds to receptors on liver cells
- Decrease in rate of respiration
- Gluconeogensis
- Glycogenolysis
Define glycogenesis
Breaking down of glycogen into glucose promoted by glucagon and adrenaline
Define glycogenolysis
The making of glycogen promoted by insulin
Define gluconeogenesis
The formation of glucose from other molecules promoted by glucagon
Summarise glucagon in the control of blood glucose
- Secreted by A cells the islets of langerhans
- When blood glucose low
- Attaches to liver receptors
- Increase blood glucose
- Decreases rate of respiration, causes glycogenesis and gluconeogensis
Summarise adrenaline in the control of blood glucose
- Secreted by adrenal glands
- When blood glucose low
- Attaches to liver receptors
- Increases blood glucose
- Causes glycogenolysis due to secretion of glucagon and inhibits glycogenesis due to inhibitng insulin
Summarise insulin in the control of blood glucose
- Secreted by B cells in the islets of langerhans
- When blood glucose high
- Attaches to liver and muscle cells
- Decrease blood glucose levels
- Causes glycogenesis and increase liver and muscle cell permeability to glucose
How does insulin increase cell permeability to glucose
- Glucose carrier proteins stored in vesicles within cell
- Insulin binds with receptors on the cell membrane
- Causes vesicle to fuse with cell membrane
- Carrier protein joins membrane and glucose absorbed by facilitated diffusion
Summarise the process of second messengers
- Hormone (adrenaline or glucagon) binds to receptors on target cell
- Enzyme on inside of the cell called adenyl cyclate activated and hydrolyses ATP into cyclic AMP
- AMP acts as non-competitive inhibitor and activates protein kinase A by changing tertiary structure
- Causes break down of glycogen (glycogenolysis)
Define diabetes
When blood glucose levels are not controlled fully
Distinguish between hyper and hypoglycaemia
Hyper = too much glucose and hypo = too little
Summarise Type I diabetes
- Immune system kills B cells so lack of insulin
- Occurs in children and young adults
- Hyperglycaemia after eating carbs
- Stays high and so glucose removed by kidneys in urine
- Insulin injections/pump
- Avoid simple carbohydrates
- Eat regular intervals and regular exercise
Summarise Type II diabetes
- Obesity, lack of exercise and poor diet
- Not enough insulin produced and liver and muscle cells do not respond due to lack of receptors
- Hyperglycaemia after eating carbs
- Stays high and so glucose removed by kidneys in urine
- Eat healthy, lose weight, regular exercise
- Drugs to reduce glucose, increase insulin production and sensitivity to insulin
Summarise the structure of a nephron
Afferent arteriole, bowman capsule containing glomerulus, efferent arteriole, proximal convoluted tubule, descending loop of henley, ascending loop of henley, distal convoluted tubule and collecting duct
Summarise ultrafiltration
- Blood flows into bowman capsule from afferent arteriole
- Glomerulus under high hydrostatic pressure due to wide afferent and thin efferent
- Small molecules and liquid are forced out of glomerulus into bowman capsule forming filtrate
- Large molecules do not fit through gaps in capillary walls, basement membrane and podocytes
- Filtrate moves into nephron
What does kidney filtrate contain
Glucose H2O Amino acids Ions Urea
Define selective reabsorption
When useful products are reabsorbed from the glomerulus filtrate by the PCT, loop of henley, distal convoluted tubule and collecting duct
Summarise selective reabsorption
- Capillaries wrap around nephron and useful substances reabsorbed
- Microvilli increase SA for absorption
- Urine produced once useful molecules removed
- Glucose and amino acids absorbed by facilitated diffusion, some urea remains due to simple diffusion and water moves in by osmosis
- Rest of glucose, amino acids and ions absorbed by active transport
How are substances absorbed in the proximal convuluted tubule
all the glucose/amino acids and some of the salts/water are sent back into blood
(from lumen of PCT, through cells lining PCT, into blood)
how:
salts (sodium ions) are actively transported from cells lining the PCT into the blood
this lowers sodium ion concentration in the cells, so sodium ions diffuse from the lumen of the PCT into the cells
as sodium ions move, they pull in glucose and amino acids with them via co-transport
glucose and amino acids build up in the cell, then diffuse into the blood
the movement of salt/glucose/amino acids into the blood, lowers it’s water potential, so water follows into blood by osmosis
Summarise how the function of the loop of henle
- Sodium and chloride ions actively transported out of ascending limb into medulla
- Lowers water potential of medulla
- Ascending limb impermeable to water
- Water moves out of descending limb by osmosis due to salty medulla and absorbed by capillaries
- Urine hence more concentrated
