6C - Homeostasis Flashcards
What is homeostasis?
- maintenance of a stable internal environment
How does body temperature affect enzyme activity?
- if body temp is too high, becomes denatured.
- H bonds break due to heavy vibrations.
- Active site changes shape
- if body is too low, activity is reduced
What is the optimum body temperature for enzyme activity?
- 37 degrees celsius
How does blood pH affect enzyme activity?
- too high or too low; become denatured
- H bonds break and active site changes shape
What is the optimum pH for enzyme activity?
- pH 7 (neutral)
What is meant by ‘negative feedback’?
- receptors detect when a level is too high or too low
- effectors respond to counteract change, bringing the level back to normal
How does glucose concentration affect providing energy and water potential?
- too high; WP is reduced to where water diffuses out of cells by osmosis. Cells shrivel up and die
- too low; cells are unable to carry out normal activities due not enough glucose for respiration to provide energy
Why does homeostasis involve multiple negative feedback mechanisms?
- gives more control
- you can actively increase or decrease a level so it returns to normal
- one mechanism means a slower response and less control
What is meant by ‘positive feedback’?
- effectors respond to further increase the level away from the normal level
How is positive feedback used to form a blood clot?
- platelets become activated and release chemical - activates more platelets and so on
- they very quickly form blood clot at injury site
- process ends w/ negative feedback when body detects clot had been formed
How is positive feedback used for hypothermia?
- hypothermia = low body temp, happens when heat is lost quicker than it can be produced
- as body temp falls, brain doesn’t work properly and shivering stops
- positive feedback takes body temp further away from normal level
Which cells secrete insulin into the blood?
- Beta cells
Which cells secrete glucagon into the blood?
- Alpha cells
What is the first two steps in insulin lowering blood glucose concentration?
- insulin binds to specific receptors on membranes of liver cells and muscle cells
- increases permeability of membranes to glucose, so cells take up more glucose. Involves increasing no. of channel proteins
What are the 3rd and 4th steps in insulin lowering blood glucose concentration?
- insulin also activates enzymes in liver and muscle cells that convert glucose into glycogen
- cells are more able to store glycogen in cytoplasm, as an energy source
What are the 5th and 6th steps in insulin lowering blood glucose concentration?
- glycogenesis; forming glycogen from glucose
- insulin also increases rate of respiration of glucose, especially in muscle cells
What are the first two steps in glucagon increasing blood glucose concentration?
- binds to specific receptors on membranes of liver cells
- activates enzymes in liver cells that break down glycogen into glucose
What are the 3rd and 4th steps in glucagon increasing blood glucose concentration?
- glycogenolysis; breaking down glycogen into glucose
- also activates enzymes involved in formation of glucose from glycerol and amino acids
What are the 5th and 6th steps in glucagon increasing blood glucose concentration?
- gluconeogenesis; forming glucose from non-carbohydrates
- glucagon decreases rate of respiration of glucose in cells
How does negative feedback respond to a rise in blood glucose concentration?
- pancreas detects when its too high
- beta cells secrete insulin, alpha cells stop secreting glucagon
- insulin binds to receptors on liver and muscle cells
- cells take up more glucose, glycogenesis activated, cells respire more glucose
- less glucose in blood
How does negative feedback respond to a fall in blood glucose concentration?
- pancreas detects when its too low
- alpha cells secrete glucagon, beta cells stop secreting insulin
- glucagon binds to receptors on liver cells
- glycogenolysis activated, gluconeogenesis activated, cells respire less glucose
- cells release glucose into blood
How does adrenaline increase blood glucose concentration?
- binds to receptors in membrane of liver cells; activates glycogenolysis, inhibits glycogenesis
- activates glucagon secretion and inhibits insulin secretion
- gets ready for action by making more glucose available for muscles to respire
How can adrenaline and glucagon act via a second messenger?
- they bind to receptors and activate adenylate cyclase
- adenylate cyclase converts ATP into chemical signal (second messenger)
- second messenger is called cyclic AMP (cAMP)
- cAMP activates protein kinase A, which activates a cascade (chain of reactions) that involves glycogenolysis
What is Type 1 diabetes?
- immune system attacks beta cells in islets of Langerhans so they can’t produce any insulin
- after eating, blood glucose level rises and stays high (hyperglycaemia) and can result in death if untreated
- kidneys can’t absorb all this glucose, so some its excreted in urine
What is used to treat Type 1 diabetes?
- insulin therapy (regular injections, insulin pump
- eating regularly and controlling simple carbohydrate intake helps avoid sudden rise in glucose
Why must insulin therapy has to be carefully controlled?
- too much insulin can produce a dangerous drop in blood glucose levels (hypoglycaemia)
What is Type 2 diabetes?
- when beta cells don’t produce enough insulin or when body’s cells don’t respond properly to insulin
- cells don’t respond properly due to insulin receptors not working properly
What can cause Type 2 diabetes?
- linked w/ obesity and more likely in people w/ family history
- lack of exercise
- age
- poor diet
What is used to treat Type 2 diabetes?
- eating a healthy, balanced diet
- losing weight (if necessary)
- regular exercise
- glucose-lowering medication
- insulin injections
What do health advisors recommend that people do in order to reduce risk of Type 2 diabetes?
- eat a diet that’s low in fat, sugar and salt, w/plenty of whole grains, fruit and vegetables
- take regular exercise
- lose weight if necessary
What else have health advisors challenged the food industry to do?
- reduce advertising of junk food
- improve nutritional value of products
- use clearer labelling on products
How have some food companies attempted to make their products more healthy?
- using sugar alternatives to sweeten food/drinks
- reducing the sugar, fat and salt content of products
What is one issue on food companies’ response to criticism?
- some people believe that diet varieties aren’t as good for health as they’re claimed to be
- e.g some evidence suggests artificial sweeteners are linked to weight gain
What are nephrons?
- long tubules along with the bundle of capillaries where blood is filtered
- around one million in the kidney
What happens first in the filtration of blood?
- blood from renal artery enters smaller arterioles in cortex of kidney
What is the structure and function of a Bowman’s capsule?
- hollow ball containing a glomerulus (bundle of capillaries looped)
- where ultrafiltration takes place
What is the difference between afferent arterioles and efferent arterioles?
- afferent - takes blood into glomerulus
- efferent - takes filtered blood away from glomerulus
- efferent is smaller in diameter, so blood in glomerulus in under high pressure
What does this high pressure in glomerulus do?
- forces liquid and small molecules in blood out of capillary and into Bowman’s capsule
The liquid and small molecules enter what after getting into the Bowman’s capsule?
- capillary wall; a basement membrane and epithelium of Bowman’s capsule
What happens to the larger molecules?
- can’t pass through, so they stay in blood
What are the substances that enter the Bowman’s capsule called?
- glomerular filtrate
What are the last 2 stages of the filtration of blood?
- glomerular filtrate passes along rest of nephron and useful substances are reabsorbed along the way
- filrate flows through collecting duct and passes out of kidney along the ureter
Where does selective reabsorption take place?
- glomerular filtrate flows along proximal convoluted tubule (PCT), through loop of Henle, and along distal convoluted tubule (DCT)
What property does the microvilli in the epithelium of the wall of the PCT give?
- large SA for reabsorption of useful materials from filtrate into the blood
How are useful solutes e.g. glucose reabsorbed along PCT?
- active transport
- facilitated diffusion
Why does the water enter the blood by osmosis?
- because water potential of blood is lower than that of the filtrate
What is urine usually made of?
- water and dissolved salts
- urea
- other substances such as hormones and excess vitamins
What doesn’t urine usually contain?
- proteins and blood cells; too big to be filtered out of blood
- glucose; actively reabsorbed back into blood
What is osmoregulation?
- kidneys regulate WP of the blood (and urine), so the body has just the right amount of water
What happens when the water potential in blood is too low?
- more water is reabsorbed by osmosis into the blood from tubules of nephrons
- means urine is more concentrated, less water is lost through excretion
What happens when the water potential in blood is too high?
- less water is reabsorbed by osmosis into blood from tubules of nephrons
- urine is more dilute, so more water is lost during excretion
Where does the regulation of water potential mainly take place?
- loop of Henle, DCT and collecting duct
What is the first stage of control of movement of sodium ions for water absorption by loop of Henle?
- near top of ascending limb, Na+ ions pumped out into medulla using active transport
- ascending limb is impermeable to water, so water stays inside tubule
- creates low WP in medulla due to high concentration of ions
What is the second stage of control of movement of sodium ions for water absorption by loop of Henle?
- water moves out of descending limb into medulla by osmosis
- makes filtrate more concentrated
- water in medulla is reabsorbed into blood through capillary network
What is the third stage of control of movement of sodium ions for water absorption by loop of Henle?
- near bottom of ascending limb, Na+ ions diffuse out into medulla, further lowering WP in medulla
- ascending limb is impermeable to water, so it stays in tubule
What is the fourth stage of control of movement of sodium ions for water absorption by loop of Henle?
- water moves out of distal convoluted tubule (DCT) by osmosis and reabsorbed into blood
What is the fifth stage of control of movement of sodium ions for water absorption by loop of Henle?
- the first 3 stages massively increase ion concentration in medulla, which lowers WP
- causes water to move out of collecting duct by osmosis
- water in medulla is reabsorbed into blood through capillary network
What monitors the water potential of the blood?
- osmoreceptors in the hypothalamus
What happens when the water potential in the blood decreases?
- water will move out of osmoreceptor cells by osmosis
- causes cells to decrease in volume
- sends signal to hypothalamus, which send signal to posterior pituitary gland
- causes it to release antidiuretic hormone (ADH)
What does ADH do?
- makes walls of DCT and collecting duct more permeable to water
- means more water is reabsorbed from tubules into medulla and blood by osmosis
- small amount of concentrated urine is produced, less water is lost from body
How does ADH change water content of the blood when its too low?
- water content of blood drops, so WP drops
- detected by osmoreceptors in hypothalamus
- posterior pituitary gland releases more ADH into blood
- more ADH means DCT and collecting duct are more permeable, so more water is reabsorbed into blood
- highly concentrated urine produced, less water lost
How does ADH change water content of the blood when its too high?
- water content in blood rises, so WP rises
- detected by osmoreceptors in hypothalamus
- posterior pituitary gland releases less ADH into blood
- less ADH means DCT and collecting duct are less permeable, so less water is reabsorbed into blood
- large amount of dilute urine produced, more water lost
