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Chapter 9
Excretory System
 consists of the kidneys, ureters, urinary bladder
and urethra
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The kidneys
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How much do you know about
your kidneys?
http://www.betterhealth.vic.gov.au/BHCV2/BHC
ARTICLES.NSF/pages/Quiz_The_urinary_syste
m?OpenDocument
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Answers to kidney quiz
1.
2.
3.
4.
5.
6.
7.
8.
B
B
A
A
A
C
B
A
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URINARY SYSTEM - OVERVIEW
http://www.youtube.com/watch?v=qxb2_d9ilEw
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Kidney Structure
human kidney
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Functions of the kidneys
• removal of metabolic wastes (urea, uric acid)
from the blood and excretion to the outside of the
body
• regulation of blood pressure (aldosterone)
• regulation of ion (Ca2+, Na+) absorption
• regulation and conservation of water in the body
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Fig. 36.8
1. There are approximately 1 million nephrons in each kidney.
Why so many?
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The nephron
4 STAGES OF URINE
FORMATION
1.
Glomerular filtration –
into Bowman’s Capsule
1.
Solute Reabsorption –
from proximal tubule to
capillary
3.
Water Reabsorption –
from proximal tubule and
Loop of Henle to capillary
4. Tubular Secretion – from
capillary to distal tubule
Fig. 36.11
The
nephron
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Page 678
Urine Formation
Urine is the final product of the processes of:
• glomerular filtration: substances move from blood in
glomerulus to the Bowman’s capsule
• solute reabsorption: nutrients i.e. glucose, potassium and
sodium ions, and many other substances the body
can use
• water reabsorption
• tubular secretion
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Step 1: Glomerular Filtration
• The first step in urine formation is filtration of substances out
of the glomerular capillaries into the Bowman’s capsule
•Filtrate includes: water, sodium, chloride ions, glucose, amino
acids, urea, other small solutes
•Filtrate does NOT include: red and white blood cells, platelets,
plasma proteins
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Glomerular Filtrate and Urine
average amounts over a 24 hour period
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Step 2: Solute Reabsorption
• sodium, chloride,
glucose, amino
acids are actively
transported from
the filtrate to the
blood in the
proximal tubule
•There are many
mitochondria in the
cells of the proximal
tubule (for ATP)
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Step 3 WATER REABSORPTION
•Water reabsorption
begins in the
proximal tubule
(osmosis resulting
from active transport
of ions, glucose, etc
from filtrate into
blood)
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Step 4: Tubular Secretion
• transports substances
(such as H+, K+, drugs,
other solutes) from the
capillary into the distal
tubule
• active transport –
distal tubule has many
mitochondria for ATP
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Urine Composition
• about 95% water
• usually contains urea, uric acid, and creatinine (break
down product from creatine phosphate used up in
muscles)
• may contain trace amounts of amino acids and varying
amounts of electrolytes
• volume varies with fluid intake, diuretics (caffeine &
alcohol) and environmental factors (heat, humidity)
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Ureters
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Urinary Bladder
• hollow, distensible, muscular organ located within the
pelvic cavity, posterior to the pubic bone
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Urinary Bladder
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Urethra
• tube that conveys urine from the urinary bladder
to the outside of the body
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Urine
colour
chart
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Life-Span Changes
• kidneys appear scarred and grainy
• kidney cells die
• by age 80, kidneys have lost a third of their mass
• kidney shrinkage due to loss of glomeruli
• proteinuria may develop (protein in urine)
• renal tubules thicken
• harder for kidneys to clear certain substances
• bladder, ureters, and urethra lose elasticity
• bladder holds less urine
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ANIMATION REVIEW
http://www.sumanasinc.com/webcontent/ani
mations/content/kidney.html
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