kidneys

how does the volume of a cell depend on osmosis

if there are greater solute concentrations outside the cell than in, free water will flow out at cause the cell to shrink

if there is less solute concentrations outside the cell than in, free water will flow into the cell and cause it to swell

what is osmolarity

the number of moles of osmotically active solute per liter of solvent

what do excretory systems do

it controls the osmolarity and composition of extracellular fluids by excreting excess solutes while conserving valuable solutes and by eliminating toxic waste products through urine

what are the three processes of an excretory system

• filtration

• secretion

• reabsorption

what is filtration

blood plasma is filtered from capillaries into associated tubules. filtered extracellular fluid contains no cells or large molecules like proteins

important fact about the movement of water

there are no mechanisms for the active transport of water. the movement is due either to filtration or osmosis

who are osmoconformers

most invertebrates that live in seawater conform to the osmotic concentration of their environment over a fairly wide range of salinities

why do freshwater animals have to expend more energy than seawater animals in osmotic regulation

osmoconformity is not an option for freshwater animals. no cell can do without ions or nutrients, so freshwater animals always have to expend energy to conserve salts and excrete water

hypotonic regulation

marine invertebrates that maintain a constant osmotic concentration considerably below that of the environment

hypertonic regulation

marine invertebrates that maintain a constant osmotic concentration, and when they live in estuaries, seawater is diluted and thus will have osmotic concentrations above that of the environment

how can some marine invertebrates survive in a range of osmolarities

at high solute concentrations they are able to regulate hypotonically by actively transporting NaCl from their extracellular fluid out across their gill membranes.

at dilute concentrations they reverse the direction of transport of NaCl across their gills to maintain the osmolarity above that environment

what do all aquatic vertebrates regulate their osmolarity to

300 mOsm/L

how do terrestrial vertebrates regulate ionic concentrations

by conserving some ions and excreting others.

• a herbivore conserves sodium because plants are low in it, marine animals are high in sodium, so the birds that feed on that must excrete the excess

what is the most common nitrogenous waste

ammonia

what is the problem with ammonia being a common waste product

ammonia is highly toxic

how is ammonia dealt with

ammonia is highly toxic, so it must be excreted continuously to prevent its accumulation or it must be detoxified by conversion into urea or uric acid

Why do fish excrete ammonia instead of converting it into another less toxic waste?

Fish excrete ammonia because it is highly soluble in water and diffuses easily, allowing for simple continuous removal from their bodies.

what do mammals and amphibians excrete as their nitrogenous waste product

they excrete urea

why do some animals excrete urea

urea is quite soluble in water, but its excretion uses lots of water. mammals get around this issue by producing urine with a high concentration of urea, decreasing the water loss associated with its excretion

why do some animals excrete uric acid as their nitrogenous waste product

uric acid is not very soluble in water therefore uric acid tends to precipitate out and form a semisolid excretion. through this excretion system, water can be reabsorbed from the urine and reduce water loss.

what is the main excretory organ and functional unit of vertebrates

the main excretory organ is the kidney

the functional unit of the kidney is the nephron

what are the two components of the nephron

blood vessel component

tubule component

what does the blood vessel component of the nephron begin with

a knot of capillaries that are highly permeable and filter blood into the tubule component

what happens in the tubule component of the nephron

secretion and reabsorption in the tubules produce urine

how do marine bony fish conserve water

they minimize water loss by producing very little urine

what problems do marine bony fish experience

water loss and salt gain through gills

how do marine bony fish conserve water and get rid of salt

• drink sea water

• spend energy to actively transport ions out

• produce very little urine

• avoid uptake of certain ions in gut

what problems do freshwater fish experience

water gain and salt loss through gills

how do freshwater fish conserve salts and get rid of water

• produce copious dilute urine

• spend energy to transport salts in

• does not drink

what problems do terrestrial animals have

lose water continuously

how do terrestrial animals conserve water

• body coverings that reduce water loss

• drinking and eating moist foods

• kidneys can concentrate urine

what are the three main processes of the nephron

1. filtration

2. tubular reabsorption

3. tubular secretion

what happens in the filtration process of the nephron

each nephron has a glomerulus. the glomerulus is highly permeable to water, ions, and small molecules but impermeable to large molecules. Blood pressure drives the movement of water and small-molecular-weight solutes out of the glomerular capillaries

what is a glomerulus

the dense knot of capillaries on each nephron

what happens the in the tubular reabsorption process of the nephron

the filtrate from the glomerulus flows into the renal tubule. Cells in the renal tubule modify the filtrate by reabsorbing specific ions, nutrients, and water, returning these to the blood, and leaving behind and concentrating excess ions and waste products such as urea.

what happens in tubular secretion process of the nephron

the filtrate in the renal tubule is further modififed by tubule cells transporting substances into the tubule. These are substances that the body needs to excrete

how does blood enter the glomerular capillaries

via an afferent arteriole

how does blood leave the glomerulus

in an efferent arteriole

what is Bowman’s capsule

it contains the glomerulus

what are podocytes

highly specialized cells with numerous extensions, each with hundred of find precesses

where are podocytes

they are in direct contact with the glomerular capillaries. they wrap around the capillaries so that their processes interdigitate and intimately cover the capillaries

what does a glomerulus do

it filters the blood, producing a fluid that lacks cells and large molecules

what causes things to flow out of the glomerular capillaries

the arterial pressure of the blood entering the capillaries causes the filtration of water and small molecules out of the glomerular capillaries and into Bowman’s capsule

what does bowmans capsule do

acts as the initial, critical filtration unit of the nephron in the kidney, surrounding the glomerulus to collect plasma filtrate

what does renal tubules do

the composition of the filtrate that enters the renal tubule is similar to blood plasma without proteins. cells of the tubule actively reabsorb certain molecules from the tubule fluid.

what do kidneys do

they filter blood, process the filtrate into urine, and releases that urine into a duct called the ureter

what is a urethra

it excretes the urine from the bladder through a short tube that opens to the outside of the body

what are the two types of sphincter muscles surrounding the base of the urethra

• smooth muscle, controlled by autonomic nervous system

• skeletal muscle, controlled by the voluntary nervous system

what does the smooth sphincter muscle do

as the bladder fills, stretch receptors in the walls of the bladder triggers a spinal reflex that relaxes this sphincter causing urination

renal pyramids

structures that envelop kidney tissue

medulla

rental pyramids make up the internal core, or medulla

cortex

the cortex covers the medulla, and has a granular appearance because it contains all of the glomeruli

what occurs between the cortex and the medulla

the renal artery divides into many arterioles that serve the nephrons

in the same place, renal veins collects blood from the many venules that drain the peritubular capillaries

where are all the glomeruli located within the kidney

all of the glomeruli with their bowman’s capsules are located in the cortex

what are the initial segments of the renal tubules that come from the bowman’s capsules

the proximal convoluted tubules what

• proximal because they are closest to the glomerulus and convoluted because they are twisted

what is happening at the point where the proximal convoluted tubule enters the medulla

it becomes thin, straight, and descends directly down toward the tip of a renal pyramid. in the medulla the tubule turns and ascends back to the cortex, forming a loop of henle.

what does the ascending limb of the loop of henle become

it becomes the distal convoluted tubule when it reaches the cortex

• distal because it is farther from the glomerulus

where does the distal convoluted tubules of many nephrons join to?

many nephrons join a common collecting duct in the cortex.

where does the collecting duct go

the collecting duct descend back down through the renal pyramid, parallel to and past the tips of the loops of henle, and empty into the pelvis

organization of the blood vessels of the kidney

smaller arteries branch from the renal artery and radiate into the cortex, forming the afferent arterioles that carry blood to each glomerulus. each glomerulus is drained by an efferent arteriole

what is the vasa recta

a vascular network and the avenue by which water gets out of the renal medulla and back into the circulation

how much of the blood filtered by kidneys is peed out

the kidneys receive about 1,500 liters of blood per day. the glomeruli filters 12% of it - 180 liters. and because we pee out 2 liters per day, around 99% of fluid filtered is returned to the blood

where does reabsorption occur

the proximal convoluted tubule reabsorbs water and solutes from the glomerular filtrate

how does proximal convoluted tubule’s reabsorption work

solutes, glucose, and amino acids are actively transported out of the tubule fluid. Once in the interstitial fluid, the water + solutes are taken up by peritubular capillaries are returned to the venous blood.

osmosis’ role in PCT cell reabsorption

the active transport of solutes from the proximal tubule into the interstitial fluid causes water to follow osmotically

what is isosmotic reabsorption in the proximal convoluted tubule

the overall osmolarity of the fluid flowing through PCT doesn’t change. so the fluid that enters the loop of henle has same osmolarity as blood plasma, even if its composition is different.

how are mammals able to concentrate their urine

because of a countercurrent multiplier mechanism which is made possible by the loops of henle

anatomy and function of the descending limb in the loop of henle

cells of the descending limb and initial cells of ascending limb are thin, with no microvilli and few mitochondrial. they are not specialized for transport

anatomy and function of the ascending limb of the loop of henle

partway up the ascending limb, the cells become specialized for active transport. these cells are thick and have many mitochondria

function of the thick ascending limb of the loop of henle

the thick ascending limb of the loop of henle transports Na/Cl from the tubule fluid to the interstitial fluid. water cannot leave the ascending limb, so Na/Cl accumulates in the interstitial fluid.

what happens because the thick ascending limb is not permeable to water

water is trapped inside the tubule while electrolytes like sodium and chlorine are actively pumped out into the surrounding kidney tissue.

This makes the tubule fluid more diluted and the medulla more salty.

what happens because the thin descending limb is highly permeable to water and not permeable to solutes

the local interstitial fluid will become more concentrated by sodium and chlorine. that concentration pulls water out thereby making the limb more concentrated as you descend

function of the thin ascending limb being permeable to solutes and not permeable to water

as the concentrated tubule flows up the thin ascending limb, it is more concentrated than the surrounding interstitial fluid, so NaCl diffuse out.

what is the results of the countercurrent multiplier mechanism

the tubule fluid entering the distal convoluted tubule is more dilute than blood plasma, while the solutes left behind in the renal medulla establish a concentration gradient within its interstitial fluid

how does the concentration established by the loop of henle in the medulla stay constant

the vasa recta preserves the concentration gradient by being both permeable to water and solutes.

The descending limb of vasa recta loses water and gains solutes. the ascending limb experiences the opposite

aquaporins in the nephron

regions of the nephron that are highly permeable to water have greater numbers of aquaporins. thus they are abundant in PCT cells/descending limbs of loops of henle, but not in ascending limbs of the loop of henle.

what happens in the first portion of the distal convoluted tubule

sodium and chlorine are transported out and water cannot follow making the tubule fluid more dilute

what happens in the later sections of the distal convoluted tubule

the tubule becomes permeable to water, and water is then osmotically drawn from the fluid into the interstitial fluid. as it joins with the collecting dust, the tubule fluid osmolarity matches that of the blood plasma

reabsorption phase of distal convoluted tubule

most reabsorption occurs in the proximal convoluted tubule but depending on if a person is depleted or in excess of a substance it can reabsorb or excrete

concentration gradient and the collecting duct

the concentration gradient in the renal medulla creates an osmotic potential which pulls the water out of the tubule. the further down the collecting duct, the more the solute concentration increases.

what is the main solute in the collecting duct

urea

what happens when urea leaks out of the collecting duct

some urea leaks out into the interstitial fluid, the urea will diffuse back with the loop of henle. the recycling of urea increases the concentration gradient and therefore its ability to concentrate the urine.

how are pH changes dealt with in the kidney

by adding a buffer, like bicarbonate ions it can control the pH of the blood. the kidneys remove proton ions from the blood and return bicarbonate ions to the blood

how do pH changes occur in the kidney

filtered bicarbonate ions combine with secrete H+ in the tubule fluid to form H2O and CO2. this resulting CO2 diffuses back into the tubule cells, where an enzyme converts it into new bicarbonate to be reabsorbed into the bloodstream

what happens for each H+ secreted into tubule fluid

a bicarbonate ion is released into the blood

what does a constant glomerular filtration rate depend on

an adequate blood supply to the kidneys at an adequate blood pressure

how does dilation keep the glomerular filtration rate constant

dilation decreases resistance in arterioles and helps maintain blood pressure in glomerulus

what keeps glomerular filtration rate constant if dilation isn’t enough

kidney release enzyme, renin which converts a protein which is then acted on another enzyme to form angiotensin

how does angiotensin work to regulate the glomerular filtration rate

• it constricts the efferent renal arterioles, raising the resistance for blood leaving glomerulus

• it constricts peripheral blood vessels to elevate blood pressure

• release of a hormone aldosterone to stimulate sodium reabsorption makes water reabsorption more effective

• it stimulates thirst in the brain

what is macula densa

modified cells of the tubule where the renal tubule becomes the distal convoluted tubule

what is juxtaglomerular cells

modified arteriole cells where the renal tubule becomes the distal convoluted tubule

what does macula densa cells do

they sense the concentration of NaCl in the fluid entering the distal convoluted tubule. if NaCl level drops too low, the macula densa cells signal the juxtaglomerular cells to release renin and trigger the RAAS response.

what is RAAS response

When kidneys detect low blood pressure, low sodium, or reduced blood flow, they release the enzyme renin, which triggers a cascade creating Angiotensin II, a powerful vasoconstrictor that elevates blood pressure and releases aldosterone for fluid retention

glomerular filtration rate and the flow speed through loop of henle

at high GFR, there is high flow rate through loop of henle so less NaCl is reabsorbed through the thick ascending limb

at low GFR, there is slow flow rate through loop of henle so more NaCl is reabsorbed through the thick ascending limb

what do juxtaglomerular cells do

they release renin and trigger the RAAS response

what is antidiuretic hormone (ADH)

a hormone that stimulates cells of the collecting duct to insert aquaporins into their cell membranes.

a higher level of ADH means

the greater the number of aquaporins

what are the various factors that stimulate or inhibit ADH release

• osmoreceptors

• baroreceptors

what do osmoreceptors do

ADH helps regulate blood osmolarity by controlling water reabsorption. the osmoreceptors also stimulate thirst. this results in diluted blood