Homeostasis Flashcards
why do multicellular organisms need a communication system
to respond when internal and external environment changes
coordinate organ function
what is cell signalling
communication between cells
electrical signals carried between by neurons or chemical signals as hormones
what is homeostasis
internal environment in maintained within set limits around an optimum
define negative feedback
self regulatory mechanisms return individual environment to optimum when there is a fluctuation
define positive feedback
a fluctuation triggers changes that results in an even greater deviation from normal levels
what are receptors and effectors
receptors=specialised cells located in sense organs that detect a specific stimulus
effectors=usually muscles or glands which enable a physical response to a stimulus
what is an ectotherm
organism that cannot regulate own body temperature
rely on external sources and behavioural responses
what is an endotherm
organisms that can regulate own body temperature
thermoreceptors send signals to hypothalamus triggering a physiological or behavioural response
how does the autonomic nervous system enable endotherms to thermoregulate
negative feedback
peripheral thermoreceptors detect changes changes in skin temperature
thermoreceptors in hypothalamus detect changes in blood temperature hypothalamus sends impulses to effectors in skin and muscles
explain the role of the skin in thermoregulation
vasodilation/constriction of arterioles supplying skin capillaries controls heat loss to surface
hair erector muscles contract and follicles protrude to trap air for insulation
evaporation of sweat cools skin surface
what is excretion
process of removing metabolic wastes to maintain metabolism
describe the gross structure of the liver
liver lobules: cylinders of hepatocytes arranged in rows and connected at the centre
hepatic vein: takes deoxygenated blood away from the liver
hepatic portal vein: contains product of digestion
hepatic artery: supplies oxygenated blood
bile duct: transports bile to gall bladder
outline the functions of the liver
site of gluconeogenesis, glycolysis, and glycogenesis
stores glycogen
deaminates excess amino acids forming ammonia and organic acids
detoxifies chemicals
describe the gross structure of the kidney
fibrous capsule:protects kidney
cortex:outer region consists of Bowman’s capsule, convulated tubules and blood vessels
medulla:inner region consists of collecting ducts, loop of henle and blood vessels
describe the blood vessels associated with a nephron
wide afferent arteriole from renal artery enters renal capsule and forms glomerulus:branched knot of capilaries which combine to form efferent arteriole
efferent arteriole branches to form capillary network that surrounds tubule
describe the sections of a nephron
bowmans capsule at start: cup shaped, surrounds golmerulus, inner layer of podocytes
PCT:series of loops surrounded by capillaries, walls made of epithelial cells with microvilli
loop of henle:hairpin loop extends from cortex to medulla
DCT:fewer capillaries than PCT
collecting duct: DCT from several nephrons empty into collecting duct leading to pelvis
describe the process of ultrafiltration
occurs in Bowmans capsule
high hydrostatic pressure in glomerulus forces small molecules out capillary fenestrations against osmotic gradient
basement membrane acts as filter
how are cells of the Bowman’s capsule adapted for ultrafiltration
fenestrations between epithelial cells of capillaries
fluid can pass between and under folded membrane of podocytes
what happens during selective reabsorption
occurs in PCT
useful molecules from glomerular filtrate are reabsorbed into the blood
how does the kidney produce urine
after selective reabsorption filtrate passes through loop of henle which acts as countercurrent multiplier and then through DCT where water and mineral ions are reabsorbed
more water is reabsorbed in collecting duct
remaining fluid (urine) contains only waste materials and water
what happens in the loop of henle
active transport of sodium and chlorine out of ascending limb
water potential of interstitial fluid decreases
osmosis of water out of descending limb
water potential of filtrate decreases going down descending limb
define osmoregulation
control of plasma water potential via negative feedback
explain the role of the hypothalamus in osmoregulation
osmosis of water out osmoreceptor in hypothalamus causes them to shrink
triggers hypothalamus to produce more ADH
