Homeostasis Flashcards
what is homeostasis?
the maintenance of an internal environment within restricted limits in organisms, to respond to the external environment
the ability to return to the optimum point
why is homeostasis essential for proper functioning of organisms?
- to maintain a fairly constant internal environment (of pH and temperature) to let enzymes work at their optimum
- changes to the water potential of blood and tissue fluid may cause cells to shrink and expand
- allow for organisms to have a greater geographical range
what are the series of stages for the control of any self-regulating system?
OPTIMUM POINT, monitored by RECEPTOR, informs the COORDINATOR, send instructions to EFFECTOR, which creates a FEEDBACK MECHANISM
what is negative feedback?
when 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 are hormones and how do they work?
- produced in glands, secrete hormone directly into blood
- carried in blood plasma to target cells
- are effective in very low concentrations, but have widespread and long-lasting effects
what do the islets of Langerhan include?
alpha cells - larger and produce glucagon
beta cells - smaller and produce insulin
what is glycogenesis?
glucose into glycogen
what is glycogenolysis?
breakdown of glycogen to glucose
what is gluconeogenesis?
production of glucose from sources other than carbohydrates
what happens if the concentration of blood glucose increases too high?
lowers the water potential of the blood and creates osmotic problems that can cause dehydration
what are three factors that influence blood glucose concentration?
- directly from diet
- from hydrolysis in the small intestine of glycogen (glycogenolysis)
- from gluconeogenesis
How does insulin reduce the concentration of glucose in blood?
- increases rate of glucose absorption
- increases respiratory rate of cells
- increases rate of glycogenesis
- increases rate of conversion of glucose to fat
what happens to beta cells when the blood glucose concentration reduces?
they reduce their secretion of insulin (=negative feedback)
how does glucagon increase the concentration of glucose in the blood?
- attach to specific protein receptors on liver cell surface membrane
- activate enzymes that convert glycogen to glucose
- activate enzymes involved in gluconeogenesis (from amino acids and glycerol)
what happens to alpha cells when the blood glucose concentration increases?
they reduce their secretion of glucagon (=negative feedback)
how does adrenaline raise blood glucose concentration?
- attaches to protein receptors on the cell-surface membrane of target cells
- activate enzymes that cause the breakdown of glycogen to glucose in the liver
what can we say about the use of the two hormones insulin and glucagon?
they act in opposite directions, and are antagonistic
what are the two forms of diabetes?
Type I and Type II
what causes Type I diabetes and when?
due to the body being unable to produce insulin, normally begin in childhood
what causes Type II diabetes?
due to glycoprotein receptors on body cells being lost or losing their responsiveness to insulin, develops in people over 40 years
how to control Type I diabetes?
by injections of insulin, managing carbohydrate intake + exercise
how to control Type II diabetes?
regulating intake of carbohydrates + matching this to amount of exercise taken
what are the 7 parts that make up the kidney?
fibrous capsule, cortex, medulla, renal pelvis, ureter, renal artery, renal vein
what are the 9 parts and blood vessels associated with a nephron?
renal (Bowman’s) capsule, proximal convoluted tubule, Loop of Henle, distal convoluted tubule, collecting duct, afferent arteriole, glomerulus, efferent arteriole, blood capillaries
what 5 features resist the movement of filtrate out of the glomerulus?
-capillary endothelial cells
connective tissue and endothelial cells of blood capillary
-epithelial cells of renal capsule
-hydrostatic pressure of the fluid in the renal capsule space
-low water potential of the blood in the glomerulus
adaptations to allow glomerular filtrate from blood into renal capsule?
- podocytes within inner layer of renal capsule, have spaces between them which allows for filtrate to pass between the cells rather than through them
- endothelium of glomerular capillaries has spaces up to 100 nm between its cells
the proximal convoluted tubule reabsorbs nearly 85% of filtrate. how are three ways that it is adapted to do so?
it has epithelial cells that have:
- microvilli to provide a large SA to reabsorb substances from the filtrate
- infoldings at their bases to give a large SA to transferr reabsorbed substances into blood capillaries
- a high density of mitochondria to provide ATP for active transport
what are the two regions of the Loop of Henle?
- descending limb, narrow, thin walls that are highly permeable to water
- ascending limb, wider, thick walls that are impermeable to water
what happens at the distal convoluted tubule?
final adjustments are made to the water and salts that are reabsorbed
the pH is also controlled by selecting which ions to reabsorb
what are the adaptations of the distal convoluted tubule?
the cells that make up the walls have microvilli and many mitochondria that allow them to reabsorb material rapidly from the filtrate, by active transport.
how and why is the glomerular filtrate formed?
afferent arterioles -> glomerulus -> efferent arterioles
diameter of afferent greater than efferent and so there is a build up of hydrostatic pressure within the glomerulus
water and mineral ions are squeezed out of the capillary
why do blood cells and large proteins not exist in the filtrate?
they are too large to pass through the glomerulus into the renal capsule
what is the process of reabsorption of glucose and water by the PCT?
Na+ actively transported out into blood capillary - lowers Na+ conc
Na+ diffuse down a conc. gradient from lumen into epithelial cell lining - through carrier proteins by facilitated diffusion
specific carrier proteins that carry another molecule - co-transport
molecules that are co-transported into cells of PCT diffuse into blood - most other valuable molecules + water are reabsorbed
what is the role of the Loop of Henle?
responsible for water being reabsorbed from the collecting duct, thereby concentrating the urine so that it has a lower water potential than the blood
what are three ways in which the rise in solute lowers the water potential of blood?
- too little water consumed
- much sweating occurring
- large amounts of ions being taken in
how does the body respond to the drop in water potential of blood?
- osmoreceptors in hypothalamus detect fall
- water lost from osmoreceptor cells by osmosis
- osmoreceptor cells shrink and hypothalamus produces antidiuretic hormone (ADH)
- ADH passes to POSTERIOR pituitary gland, secreted into capillaries
- ADH passes in blood to kidney, increases permeability to water of cell-surface membrane of cells making up DCT + collecting duct
- specific protein receptors bind to ADH molecules, activates phosphorylase within cell
- vesicles move to, and fuse with, its cell-surface membrane
- aquaporins fuse with membrane and make the cell-surface membrane much more permeable to water
- ADH increases permeability of c.d to urea, lowers water potential as urea passes out
- water reabsorbed into blood - doesn’t increase but rather prevents it from getting lower. osmoreceptors send nerve impulses to thirst centre of brain
- osmoreceptors detect rise in water potential and send fewer impulses
- pituitary gland reduces release of ADH, permeability back to normal
what are two ways in which the fall in solute raises the water potential of blood?
- large volumes of water consumed
- salts used in metabolism or excreted not replaced in diet
how does the body respond to the rise in water potential?
- osmoreceptors detect rise, increases frequency of nerve impulses. pit. gland reduces release of ADH
- less ADH = decrease in permeability of c.d to urea + water
- less water reabsorbed
- more dilute urine produced, water potential of blood falls
- when normal again. osmoreceptors cause the pit. gland to raise ADH release back to normal levels
what are both of these responses examples of?
negative feedback
