ib biology homeostasis

why does negative feedback used to control homeostatic variables

negative feedback reverses a change in variable. in homeostasis cases, that feedback would return a variable back to its set point.

role of pancreas in regulating blood glucose levels

detects change in blood glucose levels w/ the Islet of Langerhans to secrete insulin by beta cells and glucagon by alpha cells

when do the beta cells release insulin?

after eating to lower blood-glucose levels back to set level for homeostasis.

when do alpha cells release glucagon?

during fasting/exercise to convert stored glycogen to glucose in the liver, then secrete into the blood.

where are the beta and alpha cells located that secrete insulin and glucagon?

Islet of Langerhans in the pancreas

first event when blood glucose levels rise above normal range after a meal

pancreas detects high glucose levels and beta cells in the islets of langerhans in the pancreas secrete insulin into the blooodstream

second event when blood glucose levels rise above normal range after a meal

insulin travels through bloodstream to receptor sites on target cells, like liver, muscle cells, and adipose fat cells

third event when blood glucose levels rise above normal range after a meal

when binded on receptor sites, insulin acts as a key in the cell’s plasma membranes to open protein channels, allowing glucose to enter the cells through facilitated diffusion.

fourth event when blood glucose levels rise above normal range after a meal

target cells convert glucose (monomer) from blood into glycogen (polymer) to be stored (glycogenesis).

fifth event when blood glucose levels rise above normal range after a meal

muscle cells used increased amounts of glucose for aerobic respiration

diabetes 1 reaction to insulin

beta cells in pancreas damaged, so they can’t secrete insulin. autoimmune disease.

diabetes 2 reaction to insulin

liver and muscle cells don’t respond to insulin, though still being produced. they are immune to insulin. healthy-diet can treat.

how does thermoregulation in humans involve neg. feedback

• peripheral thermoreceptors monitor body temperature. send negative signals to thermoregulatory center in hypothalamus (brain).

• hypothalamus sends negative feedback responses to warm up/cool down body as needed (vasodilation, sweating, etc.)

physiological mechanisms humans use to reduce body temperature when overheating

• vasodilation: widening blood vessel, increasing blood flow allows more heat loss.

• sweating: release of water from sweat glands, water evaporates by absorbing heat energy from skin.

first physiological mechanism used to increase body temperature

vasoconstriction

vasoconstriction

narrowing of blood vessels, less blood increases blood vessels. reduces heat loss.

second physiological mechanism used to increase body temperature

shivering

shivering

caused by rapid involuntary contraction and relax. of skeletal muscles. this contraction needs atp energy. generation of atp by respiration releases heat energy to warm body.

third physiological mechanism used to increase body temperature

hair erection

hair erection

muscles in the skin contracting when the body’s cold pulls hairs up. upright hairs traps air underneath and insulates.

first step of ultrafiltration in the glomerulus and bowman’s capsule

unfiltered blood enters glomerular capillaries at high pressure, capillaries much narrower than arteriole that brings the blood to the nephron

second step of ultrafiltration in the glomerulus and bowman’s capsule

blood passes through three filtration barriers:

• fenestrated capillaries

• basement membrane

• podocytes

fenestrated capillaries

pores in capillary wall allow for plasma and small solutes to pass through, but not blood cells.

basement membranes

gelatinous, negatively charged glycoprotein layer, acting as a physical strainer by blocking large proteins and repelling negatively charged proteins.

podocytes

epithelial cells (foundational, protective cells) lining the capillaries w/foot-like extensions forming filtration slits, allowing small molecules to pass into capsule

third step of ultrafiltration in the glomerulus and bowman’s capsule

water and small solutes like amino acids, glucose, urea, and mineral ions pushed out of now filtered blood into the bowman’s capsule, forming glomerular filtrate.

plasma and blood cells remain in capillary.

descending limb of loop of henle

permeable to water, and is impermeable to sodium ions.

has many aquaphorins. water leaves through osmosis into high sodium concentration of medulla

ascending limb of the loop of henle

impermeable to water, actively transports sodium ions into medulla of kidney

creates high sodium ion concentration in medulla

loop of henle function

reduces the volume of the filtrate by transporting water and sodium ions into the medulla of the kidney.

• fluid that leaves the loop of Henle and enters the distal convoluted tubule is dilute urine

first step in preventing dehydration (osmoregulation)

hypothalamus stimulates pituitary gland to release ADH into blood,

binding to receptors on plasma membrane of cells lining collecting ducts, triggering cascade of reactions within cells

second step in preventing dehydration (osmoregulation)

aquaphorins switched from vesicles in cells to the cell walls (plasma membranes),

making conducting duct permeable to water

aquaphorins

membrane protein channels, facilitate passive transport of water molecules across cell membranes

third step in preventing dehydration (osmoregulation)

medulla has high soluble concentration due to sodium in loop of henle

fourth step in preventing dehydration (osmoregulation)

water reabsorbed from urine into medulla of kidney by osmosis

• produces concentrated urine, w/a high concentration of urea, reducing water loss from bodily fluids (yellow pee)

first step in regulating water after consumption of lots. (osmoregulation)

hypothalamus inhibits secretion of ADH,

• aquaphorins switched from plasma membranes to vesicles in cells in collecting ducts, reduces permeability of collecting ducts.

first step in regulating water after consumption of lots. (osmoregulation)

hypothalamus inhibits secretion of ADH,

• aquaphorins switched from plasma membranes to vesicles in cells in collecting ducts, reduces permeability of collecting ducts.

third step in regulating water after consumption of lots. (osmoregulation)

dilute urine is produced w/a relatively low concentration of urea (more clear)

blood supply patterns to skeletal muscles during sleep

overall metabolic rate low

• flow to muscles low

• flow to gut low

• flow to brain and kidneys constant

blood supply patterns to skeletal muscles during vigorous activity

• flow to muscles increases

• flow to gut decreases

• flow to brain remains constant, kidney reduced