Kidney Outline

“What do we want?
How do we get it?”
Water challenge….Log it!
 I. Functions of the
kidney
A. Remove metabolic wastes from the blood and
excretes them to the outside.
B. Help control the rate of RBC formation by secreting
erythropoietin.
C. Help regulate blood pressure by secreting renin.

D. Help regulate the absorption of calcium ions by

activating vitamin D.
E. Regulates the volume, composition and pH of body fluid
F. Forms urine.
 Location of the Kidneys
•Either side of the vertebral
column.
•Retroperitoneally located.
• Surrounded by fat.
•Upper border- 12th thoracic.
•Lower border- 3rd lumbar.
•Left kidney is 1.5-2 cm
higher.
 Renal Capsule Renal Cortex

Renal Sinus

Renal Pyramids
Renal Artery

Renal Vein

Renal Pelvis

Renal Columns

Ureter

Renal Medulla
 Blood Supply to the Kidney
 Afferent Arteriole-brings O2 blood in from the
renal artery.
 Glomerulus- a tight, knot-like, high pressure
capillary bed that is the site of blood filtration.
 Efferent arteriole- a narrow vessel that restricts
blood flow, helping to generate high pressure
in the glomerulus.
 Peritubular capillaries- a low-pressure capillary
bed that runs around the convoluted tubules,
absorbing fluid from them.
 Vasa recta- unbranched capillaries that are
similar in shape to the loops of Henle’, with a
descending limb and an ascending limb.
 Venules- carry deoxygenated and cleansed
blood to the renal vein.

http://www.youtube.com/watch?v=TzwPmz5V6Xg
 Nephron Structure
Bowman’s capsule- cup shaped
structure with a highly porous inner
wall, which collects fluid filtered from
the blood.
 Proximal convoluted tubule- a
highly twisted section of the
nephron, with cells in the wall
having many mitochondria and
microvilli projecting into the
lumen of the tubule.
 Loop of Henle- a tube shaped
like a hairpin, consisting of a
descending limb that carries
the filtrate deep into the
medulla of the kidney, and an
ascending limb that brings it
back out to the cortex.
Distal convoluted tubule- Another
highly twisted section, but with
fewer, shorter microvilli and fewer
mitochondria.
Collecting duct- a wider tube that
carries the filtrate back through
the cortex and medulla to the
renal pelvis.
 Ultrafiltration
 Blood (glomerulus)to urine (Bowman’s
capsule).
 Increased pressure in glomerulus.
 Fenestrae (pores) in walls increase fluid
transfer.
 Most solutes freely filter out, but proteins are
retained in the capillaries.

Ultrafiltration cont.
Fluids/particles pass thru pores
(fenestra) then basement
membrane, then past the
podocytes.
The amount of Glomerular filtrate
produced per day is about 180 L.
The average amount of urine
produced each day is 1.5 L.

HOW IS THIS
POSSIBLE???
 Osmoregulation:
The control of the water
balance of the blood, tissue or
cytoplasm of a living organism.
 Reabsorption
Almost all filtrate must be
reabsorbed into the bloodstream.
This occurs mostly in the Proximal
convoluted tubule.
Sodium (Na+ ) ions moved out by
active transport -- from the filtrate
to the space outside.
Chloride (Cl-) ions follow the
sodium ions.
Glucose molecules are co-
transported out of the filtrate into
the fluid outside the tubule.
Eventually this re-enters the
bloodstream.
Other molecules that are
reabsorbed are: amino acids,
mineral ion, small proteins, and
water.
 Loop of Henle
Job is to make the tissue fluid in the
medulla hypertonic compared to the
filtrate in the nephron.
This helps to reabsorb water.
 Descending limb-
impermeable to
ions (NaCl)
Ascending limb is
impermeable to
water, but
actively pumps
out NaCl.
Normally water
would follow by
osmosis.

Normal body fluids have a conc. of 300 mOsm. A gradient of 200 mOsm can
be created by the pump proteins. One osmole (Osm) is the solute potential of
one mole of dissolved solutes in a litre.
 Countercurrent Multiplier
System
As filtrate flows down the descending limb, the
increased solute concentration of the
interstitial fluid in the medulla causes water to
be drawn out of the filtrate until it reaches the
same solute conc. as the interstitial fluid.

This system is an example of a countercurrent

multiplier system. The fluid flows in opposite
directions, and it causes a steeper gradient of
solute conc. to develop than would be possible
with a concurrent system.
Cortex
Water leaves -
ion Chloride ions out
concentration in (sodium follows) -
filtrate increases ion concentration
in filtrate
decreases

Medulla Filtrate reaches maximum concentration

Cortex Collecting
duct
•Several nephrons
empty into one
collecting duct.
•The collecting duct
passes through the
progressively more
concentrated
medulla, losing
water by osmosis.
This water is
reabsorbed by the
capillaries.
•This water is
conserved, and a
highly concentrated
urine is produced.

Water reabsorbed into vasa

Medulla To ureter
recta, urine becomes more
concentrated
 Beaver

Human

The length of the loop of Henle is related

to the environment that the animal lives in.
A longer loop will conserve more water, so
animals in drier environments have longer
loops. Desert Rat
 Secretion
The cells of the tubules remove certain
molecules and ions from the blood and
deposit these into the fluid within the
tubules.
Example: Excess hydrogen ions (H+) are
combined with ammonia (NH3) to form
ammonium ions (NH4+) and transported
to the cells of the collecting ducts. Here
the NH4+ dissociates back into
ammonia and H+. Both are then
secreted into the fluid within the
collecting ducts (the protons by active
transport).
 Secretion cont.
 Tubular secretion of H+ is important in
maintaining control of the pH of the blood.

* When the pH of the blood starts to drop,

more hydrogen ions are secreted.
* If the blood should become too alkaline,
secretion of H+ is reduced.
* In maintaining the pH of the blood within
its normal limits of 7.3–7.4, the kidney can
produce a urine with a pH as low as 4.5 or as
high as 8.5.

 Excess potassium ions (K+) are also

disposed of by tubular secretion.
 ADH=Anti-diuretic Hormone
Controls water reabsorption in the
collecting duct.
If the solute concentration of the blood is too
high the hypothalamus detects this and causes
the pituitary to release ADH.
The presence of this hormone opens special
water channels in the cell membranes and
water is moved out of the urine and back into
the bloodstream.
If ADH is not present, all the fluids that reaches
the DCT and Collecting ducts are lost as urine.
 Water content of Water content of
the blood LOW the blood HIGH

Too much water drunk

Too much salt
or sweating

Brain
Brain
produces Water content
produces
More ADH of the blood normal
Less ADH

High volume of water Low volume of water

reabsorbed by kidney reabsorbed by kidney

Urine output Urine output

LOW HIGH

(small volume of (large volume of

Concentrated urine) dilute urine)
 Group Activity
Receive a card indicating if you are
going to focus on filtration, reabsorption
or secretion(R1, R2, S1, S2, F1, F2).
Go to my website and consult Kidney
Function Animation. With your team,
find the section of the kidney and
become an expert on your process to
teach the others.
Get into new group and teach your
process. (A,B,C,D)
 Kidneys vs. Malpighian tubules in
insects:
a. Arthropods (like insects and arachnids)
have circulating fluid known as hemolymph,
which is a mixture of tissue fluid and blood.
b. Osmoregulation is a form of homeostasis
whereby the concentration of hemolymph is
kept within a certain range.
c. When animals breakdown amino acids the
nitrogenous waste product is toxic and needs
to be excreted. In insects this is in the form of
uric acid (in mammals it is urea).
 d. Insects have tubes that branch off their intestinal
tract. These are known as Malpighian tubules. Cells
lining the tubules actively transport ions and uric acid
from the hemolymph through the walls and into the
lumen. The tubules empty their contents into the gut.
In the hindgut most of the water and salt are
reabsorbed while the nitrogenous waste is excreted
with the feces.

video
Dehydration Overhydration

Darkened urine due to increased Dilute urine and dilution of blood

solute concentration. solutes.

Tiredness due to decreased

muscle efficiency and increased
metabolic wastes in tissues.
Blood pressure can fall due to low May occur when large amounts of
blood volume. water are consumed without
replacing electrolytes lost during
exercise.
Heart rate increases. Body fluids hypotonic and may
make cells swell.

Body temperature regulation may Headache and nerve function

be affected due to inability to disruption.
sweat.
Treatment of Kidney Failure by Hemodialysis or
Transplant.
Common reasons for kidney failure: diabetes, and chronic
hypertension.
Hemodialysis- used when kidneys can no longer filter wastes
from blood properly.
Steady flow of blood passes over artificial semi-
permeable membrane.
Small waste products diffuse out.

Transplant- Receive a kidney from a living or deceased donor.

Gives freedom to travel, less chance of infection and other
complications. Rejection can occur.
Pathway of urine—
Kidney to ureter to
urinary bladder to
the urethra.

Decision to urinate
opens the external
sphincter and
allows urine to exit
the body.

See male vs.

female urethra next
slide.
Who gets bladder infections more often?
 Sources
 http://thumbs.dreamstime.com/thumb_129/1173760262A3GKzw.jpg
 http://faculty.irsc.edu/FACULTY/TFischer/images/Bowman%27s%20ca
psule.jpg