Excretory System
Maddie, Jess, Monica, Alyssa
The Urinary System (1, 2)
Consists of: 2 kidneys, 2
ureters, 1 urinary bladder, and
1 urethra
Function: To maintain homeostasis (a stable internal
environment) in the body by getting rid of excess water
and waste
image from
The Kidney (5)
Image from source 1
● Kidney contains millions of
nephrons which perform the
functions of the Kidney:
○ eliminate waste products
○ regulate water & what kind of
chemicals are in blood/body
○ maintains balance between
water/salt and acids/bases
● Which becomes urine
The Nephron (1)
Parts of Nephron:
•
Glomerulus (G & R)
o Bowman’s capsule (G) +
blood capillaries (R) =
Glomerulus
Proximal tubule (G)
Loop of Henle (B)
Distal tubule (P)
Collecting
duct (Y) involved in either transporting substances
Each
part of Nephron
•
•
•
•
into or out of the blood capillaries (R) which surround the
nephron.
Image from: http://4.bp.blogspot.com/_rSpBEx_JXa0/TSEcdlvs9fI/AAAAAAAAAUA/3i4Pmbmqnjg/s640/nephron.gif
Processes (1)
•
Urine forms in nephrons by 3 process:
o Filtration:
 separation of a liquid from some or all of the undissolved
particles through a selectively permeable membrane
o
Tubular Reabsorption:
 movement of substances out of nephron and into the blood
capillaries
o
Tubular Secretion:
 process by which substances move into the distal and
collecting tubules from blood capillaries
Nephron: Glomerulus (3, 5)
•
•
Function: filters out solutes (except
proteins) & water from blood into the
nephron
o raises blood pressure = forces
molecules into Bowman’s
capsule
o process called filtration
This fluid (called filtrate) made up of:
water, urea, salts (e.g. NaCl) ions
(e.g. H+, K+, HCO3-), glucose, amino
acids, vitamins, & (possibly)
drugs/poisons
Photo is from source 5
Bowman’s capsule (yellow)
+ blood capillaries (pale
beige) = Glomerulus
•
Nephron: Proximal Tubule (4, 6)
Function: Tubular reabsorption
(nutrients and other substances
returned to blood)
o active tubular reabsorption
 Movement of sodium, etc, by
transport proteins
o passive tubular reabsorption
 Osmosis
 Substances in filtrate move out
into blood as well
images from: http://waynesword.palomar.edu/images/osmosi2.gif
http://droualb.faculty.mjc.edu/Course%20Materials/Physiology%20101/Chapter%20Notes/Fall%202007/figure_18_15_labeled.jpg
Nephron: Loop of Henle (6, 7)
Function: sodium & water selectively reabsorbed in order to keep constant
concentration
descending part of loop =
outside fluid hypertonic with
sodium, therefore water leaves
by osmosis
as water leaves = sodium
NaCl
concentration in tubule
increases
o that’s why on ascending
part of loop = sodium
leaves tubule by diffusion > contents of tubule
Key:
become more dilute
=
•
•
•
•
•
Nephron: Distal Tubule (6)
Tubular Secretion: Solutes in
blood capillaries are accepted
and secreted into the nephron
Solutes are mainly H+ and K+
o Regulates sodium,
potassium, pH
Prevents foreign substances
(drugs) from accumulating in
blood
Nephron Collecting Duct (6)
•
Function: Controls how much water is
reabsorbed into the blood
Aldosterone allows for sodium to be
absorbed by blood capillaries by
stimulating sodium pumps = creates
L to H gradient need for osmosis
● ADH makes tubule more permeable
for water & w/ osmotic gradient =
allow more water in the filtrate to be
reabsorbed into the blood
● Amount of secretion of each based
on what the body needs
images from: http://droualb.faculty.mjc.edu/Course%20Materials/Elementary%20Anatomy%20and%20Physiology%2050/Lecture%20outlines/15_
•
http://content.answcdn.com/main/content/img/elsevier/vet/gr277.jpg
•
How does urine formation help
maintain homeostasis? (7)
• pH- kidneys help excrete extra hydrogen (h+ ions) from the blood into
•
•
•
urine through active transport
Ions- the excess ions such as sodium or calcium leave the body in the
urine
The Loops of Henle balances concentrations by osmosis
Collecting Duct - keeps more water in body or allows it to leave the body
Questions?
Bibliography
1.
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3.
4.
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7.
Taggart, Ralph. Cecie Starr. "Urinary System of Mammals." The Unity and Diversity of Life. Ninth
edition. Publisher.: Brooks/Cole, 2001. pg 750-752. Print. Biology
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