Excretion Powerpoint
Urinary System
Based on: Mader, S., Inquiry Into Life, McGraw-Hill
Anatomy of
the Kidney
Based on: Mader, S., Inquiry Into Life, McGraw-Hill
The Human Kidney & Nephron
Urine Formation in the Nephron

Urine formation in the nephron is a
continuous process starting in the
glomerulus and bowman’s capsule followed
by the proximal convoluted tubules, loop of
henle, distal convoluted tubules and finally
ending in the collecting duct.
Glomerulus and Bowman’s
Capsule
 Process
= Pressure filtration
 High blood pressure in afferent
arteriole
 Small soluble molecules pushed out of
blood through capillaries of glomerulus
and collected in Bowman’s capsule
Filterable
- small
and
soluble (pass from blood into
Bowman’s Capsule)
Non-Filterable –
large (remain in blood)
“Good stuff” *** “Bad Stuff”
“Good Stuff”
Water
Glucose
Salts
Amino
acids
vitamins
Blood cells Histamines
Platelets Penicillin
Proteins
Urea
Uric acid
“Bad Stuff”
*** Loss of all these permanently would result in dehydration, low blood
pressure, starvation and death.
Proximal Convoluted Tubules
Selective Reabsorption
 Movement of “good stuff” from the
filtrate to the proximal convoluted
tubules into bloodstream of the
peritubular capillary network.
 Glucose, amino acids, vitamins, minerals
 Accomplished by passive transport
(diffusion, osmosis, and facilitated
transport) and by active transport

Water is reabsorbed due to osmotic pressure
caused by plasma proteins and ions in the blood
Step 1: Na+ ions actively reabsorbed
Step 2: Cl- ions follow passively
Step 3: water moves passively into bloodstream
* Threshold levels: Reabsorption occurs only until this
is reached. For example, glucose has a high
threshold level where as urea has a low threshold
level

Summary of Selective Reabsorption
Reabsorbed Filtrate
components
Nonreabsorbed
Filtrate Components
(move back into bloodstream) (remain in nephron tubules)
Mostly water
Some water
Nutrients (glucose, Nitrogenous waste
amino acids) Excess salts (ions)
Required salt (ions)
Distal Convoluted Tubule
Tubular Secretion
 Active transport of any unfilterable waste
molecules or foreign substances (because
they were too large to be originally filtered)
from the blood into the distal convoluted
tubules, so that these materials will become
part of the urine

Substance actively added to the filtrate
in the distal convoluted tubules
Hydrogen ions
 Cretinine
 Drugs –
penicillin,
histamines

Loop of Henle and Collecting Duct
Maintaining water-salt balance
 Counter-current exchange
 Excretion of hypertonic urine is
dependent upon the reabosption of water
from loop of henle collecting duct
 Loop of Henle, which descends into the
renal medulla, is made up of two limbs;
the descending limb and the ascending
limb

Loop of Henle
NaCl diffuses out of lower portion of
ascending limb
 Na+ is actively pumped out of upper portion
of ascending limb, Cl- follow passively
 Ascending limb is impermeable to water,
therefore water cannot move through it
 As a result, osmotic gradient is set up within
tissues of renal medulla. The concentration of
salt is greater in the direction of the inner
medulla.

Due to osmotic gradient between renal
medulla and nephron tubules, water moves
by osmosis out of both descending limb of
loop of Henle and collecting duct.
 This movement of water out of filtrate is
responsible for concentrating the urine into
hypertonic solution

NaCl out
passively
Descending Limb
Increase [ ]
of solute
Ascending Limb
NaCl out
actively
H2O
Water comes
out due to
high Salinity
Nephron
Based on: Mader, S., Inquiry Into Life, McGraw-Hill
Video
Urine moves from the
collecting ducts through the
kidney pelvis to the ureter
Based on: Mader, S., Inquiry Into Life, McGraw-Hill
Incontinence (urine leakage)

More than 10 million Americans
experience incontinence

Most do not seek treatment

Treatment can improve or eliminate the
problem 90% of the time
Causes of Incontinence
Stress incontinence: leaking small amounts of
urine when coughing, lifting, or exercising
Urge incontinence: the bladder suddenly and
unexpectedly contracts and expels urine
Overflow incontinence: bladder cannot
completely empty so urine dribbles
Treatments for Incontinence






Kegel exercises to strengthen the urinary
sphincter
Medicines that increase the sphincter’s ability
to contract
Surgery to strengthen the pelvic muscles or
to lift the bladder
Retrain the bladder to increase its storage
capacity (allowing 3-4 hours between
urinating)
Drugs to prevent urge incontinence
Surgery to remove part of prostate gland if
responsible for overflow incontinence
Kidney stones form in the kidney
pelvis. There are types of stones.
•Calcium stones
(most common)
•Uric acid stones
•Bacteria caused stones
•Cystein stones
Based on Mayo Clinic Health Letter
Urinary Tract Infection (UTI)

Second most common infection following
respiratory infections

UTI occur when bacteria (E. coli) from the
digestive tract get into the opening of the
urinary tract and multiply

Bacteria first infect the urethra, then move
to the bladder and finally to the kidneys

UTI tend to occur more in women than men
Women may have more UTIs than men because:
1) they have a shorter urethra, allowing quicker
access to the bladder
2) the urethral opening is nearer the anus
3) intercourse may result in UTIs in women
Based on: Harvard Medical School Family Health Guide
Symptoms of UTIs
 Urge
to urinate but only small
amount of urine produced
 Pain and burning sensation in
bladder
 Fever
 Blood in urine
Diagnosis and Treatment
Doctors check urine for white and
red blood cells and bacteria
 Bacteria grown in culture to
determine which antibiotic will work
the best
 UTIs are treated with antibiotics and
are often cured within 1 or 2 days

Kidney Disease and Ethnicity

Kidney disease 26 million Americans
African Americans five times likely to
require dialysis or kidney transplant
 Possible reasons

◦
◦
◦
◦
Lack of health care
Genetic component
Diabetes
Hypertension