Excretion and homeostasis
Fox Chapter 17, one figure from Chapter 6
How the kidneys function is way more interesting than you may have thought.
Summarizing, they throw the baby out with the bath water, then recover most
Consider the work of the kidneys
Artificial kidney (dialysis) 10 hr 2 times per week
This is why transplant important, and there is difficulty getting a compatable
Cell makes wastes that go into the plasma.
Heart pumps 7000 l/day (32 55 gal drums).
1/4 (8 55 gal drums) through kidneys
Glomerulus - Bowman's capsule passes (filters) 180 l/day.
And yet only 1 l of urine is produced per day.
Osmoregulation (for ions)
Hypertonic (concentrated), isotonic, hypotonic (dilute).
Nitrogenous waste (urea) is from catabolism of amino acids and nucleotides.
Ammonia (toxic) would be o.k. for small water animals where it can diffuse
There is a tradition in undergraduate biology to emphasize comparative aspects:
Malpighian tubule in insects puts out uric acid and rectum recovers water
and other molecules.
Uric acid is used in birds, reptiles, and insects, and water loss is minimized
The nitrogen story
Although 78% of the atmosphere is nitrogen in the form of N2, this is fairly
Thus there are these important processes: N2 to NH3 nitrogen fixation, NH3
to NO3- (nitrate) nitrification, NO3 to NH3 (nitrate reduction) in plant
Also nitrogen is recycled.
In Pacific, off the coast of Peru, the Humbolt current causes an upwelling
of nutrients, anchovies thrive, bird droppings (guano) were used as fertilizer.
El Nino (the Child, named not for misbehavior but because it comes near
Christmas) is a periodic climate misbehavior that disrupts this.
The uric acid story
In humans, mild accumulation of uric acid causes gout - crystals in joint
cause inflammatory response which is treated by NSAIDS (non-steroidal anti-inflammatory
drugs like prostaglandin inhibitors like indomethacin, ibuprophin, and aspirin).
Enzyme is inhibited by chronic treatment with allopurinol. Genetically pathological
uric acid accumulation which is Lesch-Nyhan syndome - children have bizarre
self mutilation from HGPRTase (hypoxanthine guanine phospho ribosyl transferase)
kidney, ureter, bladder, urethra
Pelvis=basin; Medulla=marrow; Cortex=bark ("medulla" and "cortex"
are terms used a lot, like in brain and in adrenal gland)
The blood supply is huge (1/4-15 of body at rest) and regulated (way less
Renal artery and vein branches near eachother
each kidney has 1 million nephrons:
Capsule, PCT, loop of Henle, DCT, collecting duct (this will be repeated
in other figures)
Blood flow in glomeruli
Notice "afferent" (toward) and "efferent" (away from)
arterioles, implies a portal system to next capillary bed iaround nephron
and in medulla
Glomerulus - Bowman's (glomerular) capsule
I picked just one figure, when the book uses several to develop the point
Blood pressure and osmotic pressure drives sieve
Green is protein that is too big to fit through.
Blue is all small molecules.
Na+ is actively transported, Cl- and H2O follow
Glomerulus - fenestrae (windows) in capillaries and slits between podocyte
pedicels make up sieve.
here is a
picture from the histology course
highlights glomerulus by dye injected into artery
large molecules dye do not pass
- small molecules dye passes through
blood proteins and cells do not pass
test if blood, cells or protein is present
Clearance test for filtration
One test of kidney function, specifically filtration, is inulin clearance
Inulin is an injected dye that is filtered but not resorbed.
Short of injecting inulin, an endogenous molecule, creatinine, can be assayed.
Resorption of glucose
Proximal Convvoluted tubule - bring back amino acids, glucose note active
(NaCl) vs passive (water) transport
Glucose is a special case.
(1) ATP is used in a Na+-K+ pump on basolateral cell surface
(2) glucose is cotransported with Na+ on apical cell surface
(3) Cells are joined so there are no other pathways
(4) recovery in capillary is by diffusion
Why an untreated diabetic has glucose in the urine is that this mechanism
is saturated and cannot recover all of the glucose filtered from high blood
Resorption of salt
Kangaroo rat - metabolic water, hypertonic urine
Ascending loop - salt resorbed but not water
Ascending loop of Henle - salt outward resorption is stimulated by aldosterone
Some passive water recovery is made possible because of high tonicity of
interstitial fluid in the medulla.
This is called the countercurrant system
A summary shows dilute in cortex, hypertonic in medulla
Kidney also secretes - pump out (penicillin)
TRANSPARENCY (from an intro book)
ADH (vasopressin) makes water follow back into interstitial fluid which
is hypertonic from salt
alcohol and caffeine inhibit ADH, hence diuresis (excessive urination)
affects water channels called aquaporins
regulation of ADH by negative feedback (from hypothalamus to pituitary)
and relation to thirst and water intake
This same concept was covered way back in Chapter 6.
The relation of thirst to water conservation via ADH
low blood pressure -> JGA (juxtaglomerular apparatus) makes renin
Renin causes Angiotensinogen (liver) -> angiotensin II- closes arterioles
High blood pressure ->atrial natriuretic protein ->(-) aldosterone
Filter, resorb (salt and water)
Sweat pores not as good -which is why gatorade tastes good to athletes
especially bad in cystic fibrosis (salty sweat) molecular genetics shows
a chloride channel defect
Exam questions from 2004 - 2011 relating to this outline
Uric acid: Answer either (1) Why would you take NSAIDS (non-steroidal anti-inflammatory
drugs) if your uric acid were high? or (2) Why would you dig up uric acid
from the islands off the coast of Peru?
reduce inflammation in a gout attack, for nitrogen fertilizer
In the glomerulus, fluid passes through the fenestrated capillary endothelium
plus (what?) on its way to Bowman's capsule.
pedicels of podocytes
Aldosterone. Answer one of the following: (1) Where specifically is it from?
(2) Where (specifically) does it act? (3) What would happen to an animal
who has no aldosterone?
zona glomerulosa in adrenal cortex, ascending loop of Henle, would lose
salt in the urine and crave salt
Angiotensin is activated in a low blood crisis; another hormone regulates
angiotensin activation. Answer either (1) Where is this other hormone secreted
from? or (2) What is this other hormone called?
JGA in kidney, renin
Why would it be advantageous for some animals to use uric acid instead of
urea to eliminate nitrogenous wastes?
less water is lost
Where does the efferent arteriole from the glomerulus go to next?
vasa recta, capillary bed around loop of Henle
Where (answer either cellular location or molecule) is energy used to resorb
glucose across a cell in the kidney tubule?
basolateral surface, sodium pump
ADH (antiduretic hormone, alias vasopressin). Answer (1) What channels are
regulated by ADH? or (2) Where (specifically) does ADH have its effects?
water channels (aquaporins), collecting duct
Why is it advantageous for some animals to use uric acid rather than urea
in their excretory systems?
less water is lost
26. "Upwelling of nutrients off the coast of Peru." Answer either
(1) What ocean current helps with this? Or (2) What is the climate abnormality
that disrupts current and upwelling?
Humboldt current, El Nino
27. Non-steroidal anti-inflammatory drugs (NSAIDS) inhibit the formation
of what mediator of inflammation?
Peritubular capillaries (the vasa recta) form part of the kidney's portal
system. Where is the other capillary bed?
A basement lamina separates two components of the glomerular sieve. Name
one of these two cellular components.
podocyte's foot processes and fenestrated capillary
Facilitated diffusion for glucose takes place on the basolateral surface
of a proximal tubule cell. For EITHER of the other two essential components
of glucose transport in this cell type, give BOTH the membrane transporter
PLUS the location of the membrane.
cotransport-apical, sodium pump-basolateral
What function does it serve to have salt but not water transport in the
ascending limb from the loop of Henle?
to increase the osmolarity of the interstitial fluid
Elimination of what hormone from your body would make you crave salt?
ACE=angiotensin converting enzyme: Answer EITHER (1) What hormone from the
kidney activates ACE? Or (2) For what disorder might you want to inhibit
People with gout have high levels of what substance?
Many people enjoy an electrolyte replacement beverage such as Gatorade if
they perspire a lot. They do not like such drinks if they pee a lot. Why
More salt is lost in sweat than in urine
For ADH (antidiuretic hormone = vasopressin), answer one of these (1) What
does it do to the membrane to facilitate transport? Or (2) Where, in the
kidney, does it have its effect?
Adds aquaporins (water channels) in the collecting duct
Blood arrives at the glomerulus for filtration. What do they call the blood
vessel that carries blood away from the glomerulus?
In addition to facilitated diffusion at the basolateral cell surface, what
is necessary for glucose transport in kidney tubule and intestinal cell?
(Include process and location.)
apical cotransport with Na+
What is the product of the juxtaglomerular apparatus?
High levels of what nitrogen-containing chemical cause gout?
Why are alcoholic beverages contraindicated to stay hydrated in times of
heat stress? (Make sure your answer says what happens to the relevant hormone
alcohol inhibits ADH, more water is lost through kidney
Cystic fibrosis is a channel for what ion?
Where are the cell bodies of the cells whose axon terminals release ADH
What does creatinine clearance test for?
In the intestine and the kidney tubule, three processes are needed for glucose
transport, (1) basolateral sodium pump, (2) basolateral facilitated diffusion,
and (3) apical... [your
Because of the portal system, the vessel carrying blood from the glomerulus
is not called a vein. What is it called instead?
If a kidney stone passed from the kidney to the bladder, what tube would
it go through?
What accumulates in Lesch-Nyhan syndrome?
By what mechanism are proteins excluded from the primary filtrate in the
size of sieve openings (podocytes and fenestrated endothelium
Why might you give a secretion blocker in conjunction with penicilin?
keep antibiotic from being pumped out by kidney
Why do cells in the proximal convoluted tubule need to pump sodium to reclaim
because of sodium-glucose cotransporter ion apical surface
In what tube does the final, ADH-dependent, water reclamation occur?
Instead of injecting inulin, what test is there for clearance assaying for
a substance already in the body?
Renin activates what hormone?
In the kidney tubules, salt and water are reclaimed. Only one substance
is actively transported. What substance? (Be specific.)
What hormone from the adrenal cortex is essential for salvaging salt in
There is a capillary bed in the glomerulus. Where is the other capillary
bed of this portal system?
Na+, Cl- and H2O are all recovered in the proximal convoluted tubule. Which
involve active transport?
Aquaporins in the collecting ducts are regulated hormonally. What are aquaporins?
At what location in the lumen of the kidney tubules is the tonicity the
loop of Henle (and maybe deep collecting duct)
Describe either how the kidney deals with inulin or, alternatively, what
specific aspect of kidney function inulin is used to test.
filters but does not retrieve, tests GFR=glomerular filtration rate
Considering how unreactive nitrogen gas (N2) is, how did it get into biological
molecules such as amino acids?
The glomeruli vs. the loops of Henle are in which two overall anatomical
portions of the kidney respectively?
In addition to the fenestrations in capillaries, what cellular architecture
is responsible for glomerular filtration?
pedicels of podocytes
What change in appetite would occur if the adrenal glands were removed?
you would crave salt
What is detected by the juxtaglomerular apparatus that makes these granular
cells release their renin?
pressure in afferent arteriole
If you drink very little and become thirsty, what pituitary hormone would
What are creatinine and inulin reapectively and what are they used for?
creatinine is already in body and inulin is injected, buth used to test
glomerular filtration since they are filtered but not resorbed
For glucose in the kidney, tell me the surface locations of the three transporters
cotransport apical, basolateral facilitated diffusion plus sodium pump
What should happen to the tonicity of urine if a drug that inhibits ADH
(antidiuretic hormone) were administered?
Why are drugs like aspirin called prostaglandin inhibitors?
they block synthesis by blocking the cyclooxygenase (COX)
What is the tube that connects the kidney with the bladder?
What do they call the blood vessel exiting the capillary bed that is in
Salt and water are recovered in the proximal convoluted tubule. What is
active and what is passive? Be specific.
sodium ion active, chloride and water passive
Why would a rat drink salty water after an adrenalectomy?
aldosterone which favors salt recovery would be missing
Where, in the nephron's components, are the aquaporins that are influenced
by ADH (antidiuretic hormone)?
What does the juxtaglomerular apparatus monitor and why is it in a good
location to do this job?
blood pressure, near afferent arteriole
From the renal pelvis, the urine flows to the bladder via what tube?
Why is it advantageous to have hypertonic interstitial fluid in the kidney
Then, if ADH is present, water will be salvaged from the collecting duct
Why would it be advantageous to position renin secreting cells where they
Blood pressure is monitored near the glomerulus for the emergency work of
angiotensin that rennin initiates
Drugs that inhibit prostaglandin synthesis might help with the symptoms
of gout. Why?
b/c it is the inflammatory response to the uric acid in the joint that is
What is wrong in Lesch-Nyhan syndrome children (HGPRTase deficiency)? (Your
answer can be behavioral or chemical.)
self-mutilation, uric acid accumulation
What blood vessel connects the two capillary beds of the nephron and hence
serves as the portal vessel?
the "arteriole" that is efferent from the glomerulus
Out of all the things a nephron does, inulin clearance tests for just one.
How is glucose transported at the apical surface of the cell of the kidney
apical is the co-transport with Na+
What would an adrenalectomy do a rat's specific appetites?
without aldosterone, there would be increased sodium appetite
What would inhibiting ADH do to the urine?
inhibiting antidiuresis, two negatives make a positive, so diuresis, more
(and more dilute) urine
How and where does ATP get used for glucose resorption in the kidney?
sodium pump on basolateral surface in proximal tubule
How do water and salt transport differ in the proximal convoluted tubule
vs. the ascending limb from the loop of Henle.
in both cases, sodium transport is active. Water follows in the PCT but
not in the ascending limb
By what molecular mechanism would ADH (antidiuretic hormone) make the collecting
duct recover water better?
In describing the work of the kidneys, some relevant volumes were graphically
described in terms of drums containing 55 gallons. Why were there 32 and
8 drums in that story?
32 volume of blood pumped daily, 8 through kidneys
"A disruption in the Humboldt current might have an effect on bird
droppings." Fill in a few of the details missing in that telegraphic
bird droppings - uric acid, nitrogen fertilizer, birds eat anchovies which
thrive b/c of Humboldt driving upwelling
In the portal system of blood flow in the kidney, describe the anatomical
localization of the second capillary bed (vasa recta).
surrounds each loop of Henle in medulla
In addition to foot processes (pedicels) of podocytes, how else is a fine-mesh
mechanical sieve achieved in the glomerulus?
Why would an adrenalectomy cause an animal to have a specific appetite for
loss of aldosterone makes kidneys lose salt
What change of appetitive behavior would accompany an increased secretion
of ADH (antidiuretic hormone)?
while kidneys wold conserve water, you would also be thirsty
For hormonal control originating from the juxtaglomerular apparatus, answer
either (1) What purpose does it serve? Or (2) Why is the location of the
juxtaglomerular apparatus ideal for monitoring this need?
emergency response to low blood pressure, near afferent arterioles
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