D3.3 Homeostasis Flashcards
D3.3.1—Homeostasis as maintenance of the internal environment of an organism
Variables are kept within preset limits, despite fluctuations in external environment. Include body
temperature, blood pH, blood glucose concentration and blood osmotic concentration as homeostatic
variables in humans.
D3.3.2—Negative feedback loops in homeostasis
Students should understand the reason for use of negative rather than positive feedback control in
homeostasis and also that negative feedback returns homeostatic variables to the set point from values
above and below the set point.
D3.3.3—Regulation of blood glucose as an example of the role of hormones in homeostasis
Include control of secretion of insulin and glucagon by pancreatic endocrine cells, transport in blood and
the effects on target cells.
D3.3.4—Physiological changes that form the basis of type 1 and type 2 diabetes
Students should understand the physiological changes, together with risk factors and methods of
prevention and treatment.
D3.3.5—Thermoregulation as an example of negative feedback control
Include the roles of peripheral thermoreceptors, the hypothalamus and pituitary gland, thyroxin and also
examples of muscle and adipose tissue that act as effectors of temperature change.
D3.3.6—Thermoregulation mechanisms in humans
Students should appreciate that birds and mammals regulate their body temperature by physiological and
behavioural means. Students are only required to understand the details of thermoregulation for humans.
Include vasodilation, vasoconstriction, shivering, sweating, uncoupled respiration in brown adipose tissue
and hair erection.
D3.3.7—Role of the kidney in osmoregulation and excretion
Students should understand the distinction between excretion and osmoregulation. Osmoregulation is
regulation of osmotic concentration. The units for osmotic concentration are osmoles per litre (osmol L−1).
D3.3.8—Role of the glomerulus, Bowman’s capsule and proximal convoluted tubule in excretion
Students should appreciate how ultrafiltration remove solutes from blood plasma and how useful
substances are then reabsorbed, to leave toxins and other unwanted solutes in the filtrate, which are
excreted in urine.
D3.3.9—Role of the loop of Henle
Limit to active transport of sodium ions in the ascending limb to maintain high osmotic concentrations in
the medulla, facilitating water reabsorption in the collecting ducts
D3.3.10—Osmoregulation by water reabsorption in the collecting ducts
Include the roles of osmoreceptors in the hypothalamus, changes to the rate of antidiuretic hormone
secretion by the pituitary gland and the resultant switches in location of aquaporins between cell
membranes and intracellular vesicles in cells of the collecting ducts.
D3.3.11—Changes in blood supply to organs in response to changes in activity
As examples, use the pattern of blood supply to the skeletal muscles, gut, brain and kidneys during sleep,
vigorous physical activity and wakeful rest.
