BI102 excretory system

osmoregulation

osmoregulation

regulates solute concentrations/ balances gain and loss of water, based on controlled movement of water and solutes across plasma membranes

excretion

gets rid of nitrogenous waste (ammonia converted into urea)

function of excretory system

1. excretion

2. osmoregulation (make sure blood has specific amounts of solutes and water)

what gives excretory system a high SA/V

nephrons

why does the excretory system have a high SA/V

maximizes blood filtration in kidneys (get rid of urea but keep water and salts)

how does water enter and leave cells

osmosis (diffusion of water from high to low concentration)

osmolarity

solute concentration (solutes divided by water)

how does osmolarity affect osmosis

1. isoosmotic = movement of water is the same in both ways

2. differ in osmolarity = movement is from hypo to hyper

what happens if cells are surrounded by hyperosmotic solution

net flow of water out of cell, cell shrivels

what happens if cells are surrounded by hypoosmotic solution

new flow of water into cell, cell lyses (bursts)

how can osmolarity be increased

more solutes or less water

how can osmolarity be decreased

less solutes or more water

how is ammonia produced

breakdown of nitrogenous molecules (proteins and nucleic acids)

how is ammonia excreted

dissolved in water and then excreted

3 forms of nitrogenous waste

ammonia, urea, uric acid

ammonia (toxicity, energy cost of production, water loss with excretion)

1. highly toxic

2. low energy required for production

3. lots of water loss when excreted

urea (toxicity, energy cost of production, water loss with excretion)

1. less toxic than ammonia

2. energetically expensive

3. less water required to excrete than ammonia

uric acid (toxicity, energy cost of production, water loss with excretion)

1. relatively nontoxic

2. more energetically expensive than urea

3. secreted with little water loss

what makes urea in humans

the liver

blood flow into kidneys

aorta, renal artery, glomerulus, peritubular capillaries

blood flow out of kidneys

peritubular capillaries, renal vein, inferior vena cava

flow of filtrate

bowman’s capsule, proximal tube, loop of henle, distal tubule, collecting duct, renal pelvis, ureter, urinary bladder, urethra

bowman’s capsule function

collects filtrate from glomerulus

proximal tubule function

surrounded by peritubular capillaries, carries filtrate to loop of henle, reabsorption of water and salt, molecules transported actively (salt) and passively (water) from filtrate into interstitial fluid and then peritubular capillaries

loop of henle descending limb function

reabsorption of water through channels formed by aquaporins, no ion channels for salt or solutes, movement driven by high osmolarity in intersitial fluid (hyperosmotic to filtrate), filtrate becomes more concentrated

loop of henle ascending limb function

salt (not water) diffuses from tubule into interstitial fluid from the thin segment and actively transported (requires lots of energy) from the thick segment into the interstitial fluid. no aquaporins, only ion channels, generates osmotic gradient in kidneys which causes osmosis in descending limb

distal tubule function

reabsorption of water and salt, salt actively transported, water passively transported (osmosis) from filtrate into interstitial fluid and then into peritubular capillaries.

collecting duct function

carries filtrate through medulla one more time and to the renal pelvis, reabsorption of water (here the number of aquaporins can be greatly modified), urine is hyperosmotic to body fluids

why is urine hyperosmostic

energy is spent transporting solutes to form concentration gradients in ascending limb

How much blood goes through kidneys per day and how much filtrate and urine are produced

1600 L blood filtered per day (300x total blood volume), 180 L filtrate produced, 1.5 L urine produced bc 99% of filtrate is reabsorbed

diuretic

substance that increases urine production

antidiuretic hormone (ADH)

makes collecting duct epithelium more permeable to water, decreasing urine production

what triggers release of ADH to help conserve water

increase in osmolarity

what does the binding of ADH to a receptor molecule lead to

temporary increase in aquaporin proteins in membrane of collecting ducts

what happens when blood osmolarity increases

1. hypothalamus detects

2. neurons generate thirst and ADH produced

3. ADH allows increased reabsorption in collecting duct

4. osmolarity returns to normal

what happens when blood osmolarity decreases

1. hypothalamus detects

2. neurons stop thirst, ADH reduced? to decrease water reabsorption

3. osmolarity returns to normal

why do mutations preventing ADH production cause severe dehydration and results in diabetes insipidus

they can’t decrease urine production so they’re dehydrated since they are urinating a lot

If you drink a diuretic like alcohol what happens to urine production and why

increased urine production because not putting as many aquaporins in collecting ducts

why is diabetes mellitus (types 1 and 2) and high bp linked to higher urination

they can’t put glucose into body as glycogen, glucose stays in blood, more solutes in blood means higher bp. more solutes in blood so higher blood osmolarity which means water flows into kidneys (nephrons) because concentration gradient is reversed, meaning more urine

why does drinking salt water result in severe dehydration

more solutes in blood, higher bp, water flows into kidneys because blood is hyperosmotic to interstitial fluid, concentration gradient reversed and more urine

what happens if blood osmolarity decreases when drinking lots of water

dont make ADH so less aquaporins on collecting duct, increased urination, fluids become hypoosmotic to cells, water rushes into cells and trillions of cells explode