Homeostasis Flashcards
What is homeostasis
the maintenance of an internal environment within restricted limits in organisms
What factors are controlled by homeostasis
-Body temperature
-pH
-water potential
-blood glucose concentration
what is the internal environment made up of
tissue fluid
What does homeostasis ensure
The cells of the body are in an environment that meets their requirements and allows them to function normally despite external changes
Why is homeostasis important
-Enzymes are sensitive to changes in pH and temperature
-changes to the water potential of the blood and tissue fluid may cause cells to shrink or burst
-Organisms with the ability to maintain a constant internal environment are more independent of changes in the external environment
What is a control mechanism
self regulating system that involves a series of stages to control it
What are the stages of a control mechanism
-optimum point- point the system works best
-receptor-detects any deviation from optimum
-coordinator- coordinates information from receptor
-effector- often a muscle or gland, brings about change
-feedback mechanism-receptor responds to a stimulus created by the change by the effector
What is an example of a control mechanism
-(change)room temperature drops from 20 to 18
-(receptor)room thermostat signals that the temperature is below optimum
-(coordinator)Programmer checks that heating should be on at his time
-(Effector)Boiler fires up, pump circulates water and radiators become hot
-Room is raised to 20
-(feedback loop)circulation of air in room takes air at 20 from radiator to thermostat
How are control systems co-ordinated
Mostly by negative feedback
What is negative feeback
The change produced by the control system leads to a change in the stimulus detected by the receptor and turns the system off
What is positive feedback
When a deviation from an optimum causes changes that result in an even greater deviation from the normal
What is an example of positive feedback
Neurones where a stimulus leads to a small influx of Na+ ions
-This influx increases the permeability of the neurone membrane to Na+ ions, more enter, causing a further increase in permeability
Why do control systems have many receptors and effectors
Allows them to have separate mechanisms that each produce positive movement towards an optimum
What is an example of negative feedback
control of blood glucose
What does having separate negative control mechanisms in either directions
A greater degree of homeostatic control
Why is negative feedback important in maintaining a system at a set point
If the information is not fed back once an effector has corrected any deviation and returned the system to the set point, the receptor will continue to stimulate the effector and an over-correction will lead to deviation in the opposite direction
What are hormones
chemical messengers that are produced in glands and carried in blood plasma directly to target cells
Second messenger model
-Adrenaline binds to protein receptor in membrane of liver cell
-The binding of adrenaline changes the shape of the receptor
-This activates adenyl cyclase by changing its shape
-Adenyl cyclase then synthesises cAMP from ATP
-cAMP is called a second messenger
-The production of cAMP activates a-kinase
-a-kinase hydrolyses glycogen to release glucose
-glucose moves out of the liver cell into the blood by facilitated diffusion
What is the pancreas
A gland that produces enzymes for digestion and hormones for regulating blood glucose concentration
What do alpha cells produce
Glucagon
What do alpha cells detect
A fall in blood glucose concentration
What do beta cells produce
Insulin
What do beta cells detect
An increase in blood glucose concentration
Where are alpha and beta cells loctaed
Islets of Langerhans
Glycogenesis
conversion of glucose to glycogen
Glycogenolysis
breakdown of glycogen into glucose
Gluconeogenesis
production of glucose from sources other than carbohydrates
What is the role of the liver
regulating blood glucose concentration
-pancreas produces hormones and the liver is where they have the effect
Describe the sources of blood glucose
-from the diet
-glycogenolysis
-gluconeogenesis
Why is the regulation of blood glucose so important
-glucose is a substrate for respiration
-need a constant concentration of glucose
-if the concentration falls too low cells are deprived of energy and die
-brain cells are sensitive- only respire glucose
How do B cells detect change in blood glucose concentration
-have receptors that detect the stimulus of rise in blood glucose concentration
-respond by secreting the hormone insulin directly into the blood plasma
What is the result of insulin binding to receptors on body cells
-tertiary structure of the glucose carrier protein changes and causes them to open
-increase in the number of glucose carrier proteins in the cell surface membrane
-activation of enzyme that converts glucose to glycogen and fat
what are the ways blood glucose concentration is lowered
-increased rate of absorption of glucose into cells
-increase in respiratory rate of cells
-increased glycogenesis
-increased rate of conversion of glucose to fat
What are the actions of glucagon
-alpha cells detect a fall in blood glucose concentration
-glucagon attaches to specific receptors on cell-surface membranes o liver cells
-activates enzymes that convert glycogen to glucose
-activates enzymes involved in gluconeogenesis
Diabetes
A metabolic disorder caused by an inability to control blood glucose concentration
what is type 1 diabetes
body is unable to produce insulin and this normally begins in childhood and might be the result of an autoimmune disease where the body attacks its own cells (B cells)
what is the control of type 1 diabetes
-injections of insulin 2-4 times a day
the dose must match the glucose intake and to ensure this blood glucose is monitored by a biosensor
What is type 2 diabetes
normally due to glycoprotein receptors on body cells being lost or losing responsiveness to insulin
what is the cause of type 2 diabetes
-age
-overweight
what is the control of type 2 diabetes
-regulating the intake of carbohydrates in diet
-exercise
-might include insulin injections
-supplements to stimulate insulin
signs of diabetes
-high blood glucose concentration
-presence of glucose in urine
-need to urinate excessively
biosensor
a device that uses biological molecules to measure the level of certain chemicals
Osmoreregulation
the homeostatic control of the water potential of the blood
How many kidneys are there is mammals
2
what structures is the kidney made up of
fibrous capsule, cortex, medulla, renal pelvis, ureter, renal artery and renal vein
fibrous capsule
an outer membrane that protects the kidney
cortex
a lighter coloured outer region made up of renal capsules, convoluted tubules and blood vessels
medulla
a darker coloured inner region made up of loops of henle, collecting ducts and blood vessels
renal pelvis
a funnel shaped cavity that collects urine into the ureter
ureter
a tube that carries urine to the bladder
renal artery
supplies the kidney with blood from the heart via the aorta
renal vein
returns blood to the heart via the vena cava
Nephron
the functional unit of the kidney
renal capsule
the closed end at the start of the nephron. it’s cup shaped and surrounds a mass of blood capillaries known as the glomerulus
proximal/ distal convoluted tubule
a series of loops surrounded by blood capillaries
Loop of henle
a long hairpin loop that extends from the cortex into the medulla of the kidney and back again
collecting duct
a tube into which a number of distal convoluted tubules from a number of nephrons empty
glomerulus
a many branched knot of capillaries from which fluid is forced out of the blood
afferent arteriole
a tiny vessel that ultimately arises from the renal artery and supplies the nephron with blood
efferent arteriole
a tiny vessel that leaves the renal capsule
Describe ultrafiltration and the production of glomerular filtrate
-Afferent arteriole larger than efferent arteriole causing high hydrostatic pressure in the glomerulus
-Water, glucose, urea, mineral ions (glomerular filtrate) forced out of the capillary into the renal capsule
-Blood cells and proteins too large to pass through
-Movement of filtrate out of the glomerulus is resisted by capillary endothelial cells, epithelial cells of renal capsule, hydrostatic pressure of fluid in renal capsule, low water potential in the blood
Explain how the structure of a nephron enhances ultrafiltration
-Podocytes in renal capsule: have spaces between them to allow filtrate to pass round them not through them
-Endothelium of glomerular capillaries has spaces between the cells allowing fluid to pass round not through the cells
How do the enhancements of the nephron allow resistance to be overcome
the hydrostatic pressure of the blood in the glomerulus is significant to overcome the resistance and so filtrate passes from the blood into the renal capsule
Explain how glucose is reabsorbed in the proximal convoluted tubule (5 marks)
-Sodium ions actively transported out of epithelial cells lining the PCT into blood capillaries
-Higher concentration of sodium ions in the lumen of the PCT than the cells lining the PCT
-Sodium ions diffuse down their concentration gradient, by facilitated diffusion through carrier proteins from the lumen of the PCT into the epithelial cells lining the PCT
-Glucose and sodium ions are co transported from the lumen into the epithelial cells.
-There is a specific type of carrier protein to co transport glucose with the sodium ion.
-Glucose is moved by facilitated diffusion into the blood down the concentration gradient
Explain how water is reabsorbed in the PCT
-glucose, amino acid and ions moved out of the PCT by co-transport
-Increased the water potential in lumen of PCT
-water moves to the lower water potential in the capillary by osmosis
Explain how epithelial cells of the PCT are adapted for transport of substances
-lots of mitochondria
-provide ATP/energy for active transport of sodium ions
-microvilli
-increased SA for transport
Explain how a gradient of sodium ions in the medulla is maintained by the loop of Henle
-Sodium ions actively transported out of ascending limb into the medulla
-This lowers water potential in the interstitial region (area between the limbs of the loop of Henle). The impermeable walls of the ascending limb prevent water moving out
-Water passes out of the filtrate in the descending limb into the interstitial region, enter blood capillaries and moves away
-Water potential of filtrate decreases, becoming lowest at the hairpin
-Sodium ions diffuse out of the filtrate down a concentration gradient at the base of the ascending limb and further up are actively transported out (point 1)
-The water potential in the interstitial space between the ascending limb and the collecting duct is a gradient from highest water potential in the cortex to the lowest water potential in the medulla (highest ion concentration)
-Water leaves the collecting duct by osmosis down it’s concentration gradient and is carried away by blood vessels
Explain how the loop of Henle acts a counter current multiplier
The water potential of the filtrate in the loop of Henle reduces as it moves down, meeting interstitial fluid with an even lower water potential. This ensures a small but constant water potential gradient along the whole length of the loop of Henle. This also applies to the collecting duct.
Define osmoregulation
Maintenance of water potential of the blood plasma and therefore tissue fluid
Explain how the water potential of the blood is regulated
Water potential of the blood depends on the solutes as well as volume of water.
Water potential of the blood is detected, the hormone ADH is either secreted or stopped, the permeability of the collecting ducts to water is altered and more or less water is absorbed
Describe the roles of hypothalamus, posterior pituitary and antidiuretic hormone in osmoregulation
-Osmoreceptors in the hypothalamus detect a fall in the water potential of the blood (water is lost by osmosis from these cells and they shrink)
-This causes the hypothalamus to produce ADH
-ADH passes to the pituitary gland and is secreted into the capillaries
-ADH travels in the blood to the kidneys and increases the permeability of the DCT and collecting duct to water
-protein receptors in the membranes of the cells making up the walls of the DCT and collecting duct bind to ADH and cause activation of phosphorylase enzymes in the cell
-Phosphorylase causes vesicles in the cell containing aquaporins to move to and fuse with the cell membrane
-ADH also increases permeability to urea which passes out further lowering water around the collecting duct
-More water leaves the collecting duct and is reabsorbed into the blood
-When the above and drinking restore water potential of blood the osmoreceptors detect this and the process is reversed
