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95 Cards in this Set
- Front
- Back
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What is homeostasis? |
The maintenance of a constant internal environment |
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Why is homeostasis important? |
To maintain temperature and pH for enzyme activity which control rate of metabolic reactions and correct blood glucose concentration |
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How does temperature affect metabolic reactions? |
Rate increases when temperature increases as more heat means more KE so molecules move faster so substrate more likely to collide with active site and energy of collision increases so more likely to be successful |
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What is the effect of a temperature that is too high? |
Over 40°c, reaction stops as enzymes vibrate more which breaks some hydrogen bonds holding 3D shape so active site changes and substrate no longer fits. |
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What is the effect of a temperature that is too low? |
Enzyme activity is reduced so slows rate of metabolic reactions |
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What happens if pH is too high or low? |
Enzymes become denatured so ionic and hydrogen bonds that hold 3d shape broken so active site shape changes and it no longer works as a catalyst |
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pH = |
-log[H+] |
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What is logarithmic scale? |
When every value is ten times larger than the value before as concentration can vary enormously so it's easier to compare values on a logarithmic scale and plot a large range on a graph |
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What happens if blood glucose concentration is too high? |
Water potential of blood reduced to a point where water molecules diffuse out of cells into the blood by osmosis which causes the cell to shrivel up and die |
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What is a negative feedback mechanism? |
Level change detected by receptors and pass info to nervous system to effectors which counteract the change and bring the level to normal |
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What are the benefits of having multiple negative feedback mechanisms? |
Actively increase or decrease a level so it returns to normal, faster response and more control |
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What is a positive feedback mechanism? |
Changes trigger a positive feedback mechanism which amplifies the change so effectors response to further increase the level away from normal |
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When does positive feedback happen? |
When a homeostatic system breaks down - not involved in homeostasis |
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What is a normal glucose concentration in the blood? |
90mg per 100cm³ of blood, monitored by cells in the pancreas |
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Where are insulin and glucagon secreted from? |
Islets of Langerhans, which contain beta and alpha cells |
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What do beta cells in islets of Langerhans do? |
Secrete insulin into the blood |
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What do alpha cells in the islets of Langerhans do? |
Secrete glucagon into the blood |
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What does insulin do? |
Lowers blood blood concentration when it's too high by binding to specific receptors on cell membranes of muscle/liver cells (hepatocytes). Increases permeability by increasing channel proteins in cell membrane of muscle cell membranes to glucose so cells take up more glucose. |
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What is the effect of insulin on enzymes? |
Activates enzymes in muscle and liver cells that convert glucosen into glycogen. Cells can store glycogen in cytoplasm as energy. Also, increases rate of respiration of glucose, especially as in muscle cells |
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What is glycogenesis? |
Forming glycogen from glucose, activated by insulin. |
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What is the effect of glucagon? |
Raises blood glucose concentration when it's too low by binding to specific receptors on the cell membranes of liver cells and activates enzymes that break down glycogen into glucose. |
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What is glycogenesis? |
Breaking down glycogen into glucose, using glucagon |
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What is the effect of glucagon on enzymes? |
Activates enzymes involved in the formation of glucose from glycerol and amino acids. |
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What is gluconeogenesis? |
Forming glucose from non-carbohydrates |
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What are the properties of hormones? |
Travel in blood to Target cells so slow and occur all over the body, broken down ore slowly so longer effect |
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How does negative feedback respond to a rise in blood concentration? |
Pancreas detects blood glucose concentration is too high, B cells decree insulin and a cells stop secreting glucagon. Insulin binds to receptors on liver and muscle cells which respond by decrease blood glucose concentration e.g.glycogenesis activated |
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How does negative feedback respond to a fall in blood concentration? |
Pancreas detects blood glucose I too low, a cells secrete glucagon and b cells stop secreting insulin, binds to receptors on liver cells which respond by increasing blood glucose concentration e.g. glycogenolysis activated |
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What are glucose transporters? |
Channel proteins which allow glucose to be transported across a cell membrane |
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What is the glucose transporter in skeletal and cardiac muscle cells? |
GLUT4 |
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What happens to GLUT4 when isulin is low? |
GLUT4 is stored in the vesicles in the cytoplasm of cells when insulin levels are low |
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What happens to GLUT4 when insulin binds to receptors on the cell surface membrane? |
GLUT4 moves to membrane so glucose can be transported into the cell through the GLUT4 protein by facilitated diffusion |
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What is adrenaline? |
Hormone secreted from adrenal glands when there's a low concentration of glucose in your blood, when you're stressed and when your exercising. |
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What does adrenaline do? |
Binds to receptors in cell membrane of liver cells and activates glycogenolysis, inhibits glycogenesis, activates glucagon secretion and inhibits insulin secretion, so increasing glucose concentration. |
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What is glycogenolysis? |
Breakdown of glycogen to glucose |
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What is glycogenesis? |
Synthesis of glycogen from glucose |
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What is the second messenger model? |
Adrenaline/glucagon bind to receptors outside cell but activate glycogenolysis inside cell. Binding of hormone to cell receptors activate enzyme on inside of cell membrane which produces chemical - second messenger |
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What does the second messenger do? |
Activates other enzymes in the cell to bring about a response |
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What do adrenaline and glucagon bind to to activate glycogenolysis? |
Receptors and activate enzyme called adenylate cyclase which converts ATP to cyclic amp which is a second messenger. cAMP activates enzyme called protein kinase A which activates a cascade that breaks down glycogen to glucose |
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What is type 1 diabetes? |
Immune system attacks b cells in islets of Langerhans so they can't produced insulin. After eating, blood glucose level ruses and stays high - hyperglycaemia. |
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How is type 1 diabetes treated? |
Some glucose excreted in urine if not absorbed by kidney. Insulin injections or pump. Controlled diet and eating regularly. |
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What is type 2 diabetes? |
Acquired later in life, linked with obesity, lack of exercise, age and poor diet. B cells dont produce enough insulin or cells don't respond properly to insulin as receptors on membranes don't work. |
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How is type 2 diabetes treated? |
Eating a healthy, balanced diet, losing weight and regular exercise. Glucose lowering medication. |
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What can type 2 diabetes cause? |
Kidney failure Visual impairment |
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What is the response of health advisors to the rise in type 2 diabetes? |
Diet low in fat, sugar and salt with plenty of while grains, fruit and vegetables, take regular exercise and lose weight if necessary. E.g. change for life |
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What is the response of food companies to the rise in type 2 diabetes? |
Make products more healthy by using artificial sweeteners but limited response as profit driven. Should improve nutritional value and use clearer labelling. |
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Where does blood enter the kidney through? |
The renal artery |
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Where does blood pass through after entering the renal artery? |
Passes though the capillaries in the cortex (outer layer) of the kidneys |
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What is ultrafiltration? |
Blood passes through capillaries in the cortex, substances are filtered out of the blood and into long tubules that surround the capillaries |
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What substances are reabsorbed into the blood? |
Useful substances such as glucose and the right amount of water - selective reabsorption |
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What happens to remaining unwanted substances after selective reabsorption? |
Remaining unwanted substances pass along to the bladder and excreted as urine |
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What are nephrons? |
Long tubules along with the bundles of capillaries where the blood is filtered - around one million in each kidney |
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Where does ultrafiltration take place? |
Blood from renal artery enters smaller arterioles in cortex of kidney, each arteriole splits into a glomerulus |
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What is the glomerulus? |
A bundle of capillaries looped inside a hollow ball |
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What is the afferent arteriole? |
Arteriole that takes blood into each glomerulus |
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What is the efferent arteriole? |
Arteriole that takes filtered blood away from the glomerulus |
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How are the afferent and efferent arterioles different? |
Efferent arteriole smaller in diameter than afferent so blood in the glomerulus is under high pressure |
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Why is important that the blood in the efferent arteriole is smaller in diameter? |
High pressure forces liquid and small molecules in the blood out of the capillary and into the Bowman's capsule |
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What three layers do liquid and small molecules pass through to get into the Bowman's capsule and enter the nephron tubules? |
Capillary endothelium, basement membrane and epithelium of Bowman's capsule |
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What can't pass through the three layers into the Bowman's capsule? |
Larger molecules like proteins and blood cells |
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What is the substance that enters the Bowman's capsule? |
Glomerular filtrate |
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What happens to the glomerular filtrate? |
Passes along the rest of the nephron and useful substances are reabsorbed along the way then Les through the collecting duct and passes out the kidney along the ureter |
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When does selective reabsorption? |
As the glomerular filtrate flows along the proximal convoluted tubule (PCT), through the loop of Henle, and along the distal convoluted tubule (DCT) |
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How is the PCR adapted for reabsorption of useful materials from the glomerular filtrate into the blood? |
Epithelium of the wall of the PCT has microvilli to provide a large surface area for reabsorption of useful materials from the glomerular filtrate |
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How are useful solutes reabsorbed along the PCT? |
Active transport and facilitated diffusion |
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Where do useful substances go when they leave the tubules of the nephrons? |
Enter the capillary network that's wrapped around them |
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How does water enter the blood? |
By osmosis because the water potential of the blood is lower than that of the filtrate |
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Where is water reabsorbed from? |
The PCT, loop of Henle, DCT and the collecting duct |
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What happens to the filtrate that remains in the PCT? |
Urine that passes along the ureter to the bladder |
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What is urine made up of? |
Water, dissolved salts, idea and other substances such as hormones and excess vitamins |
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Why doesn't urine contain proteins or blood cells? |
They're too big to be filtered out of the blood. Glucose is actively reabsorbed back into the blood so isn't found in urine either |
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How is water lost? |
Urea and waste products in solution during excretion, lost in sweat |
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What is osmoregulation? |
Kidneys regulate the water potential of the blood and urine so the body has just the right amount of water |
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What happens when the water potential of the blood is too low? |
More water is reabsorbed by osmosis into the blood from the tubules of the nephrons so urine is more concentrated so less water is lost during excretion |
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What happens when the water potential of the blood is too high? |
Less water reabsorbed by osmosis into the blood from the tubules of the nephrons so urine is more dilute so more water is lost during excretion |
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Where does water regulation take place? |
Reabsorbed into blood along almost all of the nephron and loop of Henle, DCT and collecting duct |
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Where is the loop of Henle located? |
In the medulla (inner layer) of the kidneys - made up of the two 'limbs' - descending and ascending limb |
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What do the limbs of the loop of Henle control? |
The movement of sodium ions so that water can be reabsorbed by the blood |
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What does the cortex of the kidney consist of? |
Bowman's capsules and the proximal and distal convoluted tubules |
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What does the medulla consists of? |
Loops of Henle and collecting ducts |
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What are the gaps in the endothelium? |
Fenestration - helps the filtration process |
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What are the cells that line the tubules? |
Podoctyes because they appear to have feet |
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What is a basement membrane? |
Continuous sheet of protein between the other two layers of cells that forms a continuous mesh so is the finest layer of the filter |
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How is the movement of sodium ions controlled in the loop of Henle? (1/8) |
Near top of ascending limb, sodium ions actively transported out into medulla, ascending limb impermeable to water so water stays inside tubule |
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How is the movement of sodium ions controlled in the loop of Henle? (2/8) |
Increases concentration of sodium ions in medulla so lowers water potential |
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How is the movement of sodium ions controlled in the loop of Henle? (3/8) |
Because there's a lower water potential in medulla than in descending limb, water moves out of descending limb into medulla by osmosis |
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How is the movement of sodium ions controlled in the loop of Henle? (4/8) |
Descending limb impermeable to ions so this makes glomerular filtrate more concentrated |
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How is the movement of sodium ions controlled in the loop of Henle? (5/8) |
Near bottom of ascending limb, sodium ions diffuse out into medulla, further lowering water potential in medulla. Ascending limb is impermeable to water. |
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How is the movement of sodium ions controlled in the loop of Henle? (6/8) |
Net result means solute concentration at any one level of loop is slightly lower in ascending loop than descending loop |
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How is the movement of sodium ions controlled in the loop of Henle? (7/8) |
Longer the loop, the more chance there is for this mechanism to build up a high sodium ion concentration |
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How is the movement of sodium ions controlled in the loop of Henle? (8/8) |
Longer the loop of Henle, greater the solute concentration and the more concentrated the urine eventually produced |
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What is the water that leaves the loop of Henle by osmosis and enters the surrounding network of capillaries? |
Vasa recta |
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How is the volume of water reabsorbed into the capillaries controlled? |
By changing the permeability of the DCT and the collecting duct |
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What monitors the water potential of the blood? |
Osmoreceptors in the hypothalamus |
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What happens when water potential of the blood decreases? |
Water moves out osmoreceptor cells by osmosis causing cells to decrease in volume which sends signal to other cells in hypothalamus which sends to signal to posterior pituitary gland which releases anti-diuretic hormone |
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What do ADH molecules bind to? |
Receptors in plasma membrane of cells in DCT/collecting duct, causing aquaporins to be inserted into plasma membrane, allowing water to pass by osmosis so more water reabsorbed from tubules into medulla, then blood by osmosis so conc. urine produced |
