Chapter 9 – Excretion and the
interactions of systems
Pages 306 - 310
Structures of the Excretory System
Structure
1. renal artery
Function
carries blood into the kidney from the aorta
2. renal vein
carries blood away from the kidney into the
inferior vena cava
carries blood away from the heart toward
the lower torso and legs
carries blood from the lower torso and legs
to the heart
removes wastes from the blood, thus
producing urine
carries urine from a kidney to the urinary
bladder
temporarily stores urine
3. aorta
4. inferior vena
cava
5. kidney
6. ureter
7. bladder
8. urethra
carries urine from the urinary bladder to the
exterior of the body
The Problem of Waste in a Human
Body
 A functioning system that produces waste uses
different methods to release waste from the system,
waste in the human body include excess water,
chloride and sodium ions, carbon dioxide, etc.
 The excretory system is used to eliminate these waste
from the fluids already in use, or are yet to be used, by
cells to function.
 The main organ of the excretory for separating useful
fluids and waste in the body is the kidney.
The Function of a Nephron in the
Kidney
• The function of Nephrons in the kidney can be
compared to the function of the pulmonary valve
in the human heart
• Nephrons are millions of microscopic structures
that filter away waste from the blood and
transforming it into urine
• The Nephrons are organized into 3 main regions,
a filter, a tube and a duct which can be viewed in
the image below
Pages 311 - 315
Urine Formation
 Four processes used for urine to be created:
 Glomerular filtration - moves filtrate (water and
solutes) from blood into nephron.
 Tubular reabsorption – removes useful solutes from
filtrate back into blood for reuse by body systems.
 Tubular secretion – moves additional wastes and
substances from blood into filtrate.
 Water reabsorption – returns water from the filtrate
back to blood for reuse.
Glomerular Filtration
 Start of urine formation, glomerular filtration:
 Water and dissolved substances are forced
from the blood in the glomerulus into the
Bowman’s capsule
 Capillaries of the glomerulus are very porous
and allow water and dissolved solutes to
easily pass through
 Pores are small enough that blood cells and
proteins cannot cross
 High pressure in the glomerulus (4x higher
than elsewhere), aides filtration
Tubular Reabsorption
 Tubular reabsorption – the recovery process
 Occurs in the loop of Henle
 65% of filtrate is reabsorbed to the body
 Reabsorption occurs via active and passive
transport
 Nutrients like sodium, glucose and other
solutes are actively transported back into blood
from filtrate.
 Negatively charged ions are passively absorbed
by electrical attraction
 Water is absorbed by osmosis
Tubular Secretion
 Occurs in distal tubule and collecting duct
 Excess hydrogen ions (H+) are secreted into the
distal tubule to maintain the pH of the blood
 Other substances not normally in the blood, such
as medication, are secreted into the distal tubule
filtrate
 Reabsorption and secretion in the distal tubule are
under the control of hormones
Water Reabsorption
 Water reabsorption occurs in the collecting
duct
 Filtrate still contains a lot of water
 The reabsorption of water in the collecting
duct causes the filtrate to become 4x as
concentrated by the time it exits the duct.
 The end product is approx. 1% of the volume
of the original filtrate and is now called urine
Summary
Part of the
Nephron
Function
Glomerulus
and bowman’s
capsule
Filtration - blood pressure forces water and
dissolved substances from the blood plasma
through the pores of the glomerular wall.
Bowman’s capsule receives filtrate.
Reabsorption – passive and active
reabsorption of water and ions from the
filtrate back to blood
Secretion – foreign components of blood are
secreted from blood into the filtrate
Loop of Henle
Distal tubule
Collecting duct Reabsorption – water is reabsorbed back into
blood. Final product is called urine.
Pages 316 - 325
Water Balance
 The solute concentration of blood remains
constant despite variations in the amount of
water we consume:
 If water intake is too high the kidneys allow
more water to pass into the urine
 If water is scare, the kidneys conserve water by
producing concentrated urine
Osmotic Pressure
 Osmotic pressure is the force generated by
water as it moves via osmosis
 The greater the concentration gradient the
higher the osmotic pressure
 Osmotic pressure affects many cellular
activities, especially the exchange of matter
between cells and blood.
 Blood volume influences blood pressure,
affecting the health of your cardiovascular
system
Regulating the Reabsorption of
Water
 The hypothalamus regulates mechanisms
maintain homeostasis:
•Hunger
•Thirst
•Blood
pressure
•Body
temperature
•Fluid balance
•Salt balance
 Osmoreceptors in the hypothalamus
measure osmotic pressure
 When you are dehydrated, blood
concentration increases and osmotic
pressure increases
 Osmotic receptors send a signal to the pituitary
gland to release ADH (antidiuretic hormone)
 ADH travels through the blood to the kidneys
and increases the permeability of the distal
tubule and collecting duct, allowing more
water to be reabsorbed
 If blood plasma is too dilute, osmotic pressure
is low
 Osmoreceptors stop or prevent the release of
ADH
 The distal tubules and collecting duct become
less permeable to water; more water is excreted
in the urine.
Reabsorption of Salts
 A drop in blood Na+ concentration
triggers a release of the hormone
aldosterone
 Aldosterone stimulates the distal tubules
and collecting ducts to reabsorb Na+
Urine Analysis
 Analyzing the physical and chemical
composition of urine enables physicians to
make inferences about an individual’s health
Disorders of the Excretory System
 Common excretory system disorders:
 Urinary tract infection (UTI) – due to
bacterial or viral infection
Can affect the bladder or urethra
 Characterized by urge to urinate, even
when no urine is formed
 Painful urination
 Brown or bloody urine

 Kidney Stones – due to crystalline
formations in the kidney
 Maybe caused by: recurrent UTIs,
insufficient water consumption, low activity
levels
 Treatment may include ultrasound shock
waves to break down stones
to be passed via
urethra; large stones
may require surgery
Problems with Kidney Function
 Nephrons can regenerate and restore kidney
function after short-term injuries.
 A person can survive on as little as 1/3 of one
kidney.
 If 75% or more of the nephrons are destroyed,
urine output is inadequate to maintain
homeostasis
 Kidney function may be replaced by kidney
transplant or through dialysis
Dialysis
 Two types of dialysis:
 Hemodialysis – artificial membrane in an
external device acts as an artificial kidney
 Peritoneal dialysis – utilizes the peritoneum
(intestinal membrane) as the dialysis
membrane.
Hemodialysis
Peritoneal Dialysis
Kidney Transplant
 Dialysis is not intended to be a long-term
treatment for kidney failure
 Kidney transplant organs can come from
cadaveric donors or from living donors
 Individuals can function normally with one
kidney
 The success rate of kidney transplant is 9095% with the aide of anti-rejection drugs