The Excretory System
By: Kaylie Corda, Finn Mahoney,
& Liana Tabtiang
The FUNction of the Excretory System
Source 2
The excretory system is a passive biological system that
removes excess, unnecessary materials from an organism,
so as to help maintain homeostasis within the organism
and thus prevent damage to the body.
The Excretory System
Source 1
The body’s blood filtration system begins with the kidneys.
Blood is pumped in from the heart and filtered in the
medullas of the kidneys. Cleaned blood is pumped back
into the body and filtered solution is collected in the Renal
Pelvis. Two tubes, the Ureters, drain the fluid from the renal
pelvis and empty it into the Urinary Bladder. The urethra
empties the urine from the bladder.
The Kidney
Source 1
● Two bean shaped organs that act as the body’s
blood filters and liquid waste generators
o the Cortex

spongy external tissue surrounding the kidney’s filters
o the Medulla


pyramid shaped
where blood is filtered
o the Renal Pelvis



sac in the interior of the kidney
collects filtered fluid from blood (liquid waste)
drained by the Ureter into the Urinary Bladder
Summary of the Kidney
Cortex (connective
tissue surrounding the
Medullas and Renal
Pelvis)
Renal Pelvis (sac in the
interior of the kidney
where urine is
collected)
Medullas (structures
through which
unfiltered blood is
passed)
Source 1, 3
Renal Artery (passes
unfiltered blood from
the heart to medullas
and nephrons (filtration
units within the
medullas)
Renal Vein (passes
filtered blood out to the
rest of the body)
Ureter (drains renal
pelvis into urinary
bladder)
The Medulla
Source 1, 3
● Several pyramid shaped medullas for blood filtration
within each kidney
● Within each medulla, unfiltered blood passes through
thousands of specific blood vessel structures called
nephrons
● The renal artery feeds blood to the medullas from the
heart and the renal vein transports the blood that has
already passed through the nephrons out to the rest of
the body
The Nephron
●
●
●
●
●
●
●
●
Source 1
Located on the border between the Cortex and Medulla
Act as vessel filters for the blood
Functional units of the kidney
Made up of a Glomerulus, Bowman’s Capsule, Proximal tubule, Loop of Henle,
Distal tubule, and Peritubular Capillaries
Glomerulus (a semipermeable membrane):
o a collection of tightly packed, looped blood vessels that are about 100 times
more permeable to water and small solutes
The Glomerulus is surrounded by the Bowman’s Capsule (an impermeable cup):
o Think of the glomerulus and Bowman’s Capsule as a permeable bag within an
impermeable one
Clean blood moves out of the Glomerulus and through the Peritubular Capillaries
back into the body
Waste filtrate (in the Bowman’s Capsule) moves through the Proximal tubule, Loop
of Henle, and Distal tubule, where the rest of the waste is added
Summary of the Nephron
Source 1
Glomerulus (collection of
Glomerular Capillaries)
Bowman’s Capsule
(surrounds glomerulus)
Renal Artery (feeds
unfiltered blood to the
Nephron)
Proximal Tubule (carries
filtrate)
Renal Vein (carries
cleaned blood to the rest
of the body)
Peritubular Capillaries
(capillaries carrying clean
blood around the Distal
and Proximal Tubules)
Loop of Henle (carries
filtrate)
Distal Tubule (carries
filtrate)
Collecting Duct (collects
filtrate and transports to
Renal Pelvis)
Urine Formation
Source 1, 3
Pressured Filtration: blood pressure generated by heart’s contractions filters blood by forcing
water and all solutes except proteins through the walls of the glomerular capillaries. The protein-free
filtrate moves out of the cupped part of the nephron and into the proximal tubule (first step in exit from
the body)
● Utilizes facilitated diffusion (through channel proteins and membrane) out of the blood and
into the filtrate along an artificially high pressure gradient
Tubular reabsorption: as the filtrate in the Bowman’s capsule passes along the proximal
tubule, Loop of Henle, and distal tubule, most of the water in the filtrate is drawn out from tubule and
into the peritubular capillaries surrounding the tubule and reabsorbed into the blood
● Utilizes facilitated diffusion (through channel proteins and membrane) out of the filtrate and
into the blood along an osmotic pressure gradient
Tubular secretion: as the blood moves through the peritubular capillaries, hydrogen and
potassium ions (H+ and K+) are pulled (diffused through the capillary wall and tubule wall) from the
peritubular capillaries (filtered blood) and into the tubules (bodily waste)
● Utilizes facilitated diffusion (through channel proteins and membrane) out of the blood and
into the filtrate along an electric charge gradient
Urinary Process
Source 1
● After leaving the distal tubule, urine is collected in the
Renal Pelvis
● Urine leaves the renal pelvis through the Ureter and
travels into the Urinary bladder
● Urine exits the urinary bladder through the Urethra.
Homeostasis and Urine Function
Source 3
● Regulates blood volume and pressure:
○ adjusts the volume of water in blood (through pressured filtration)
○ releases Erythropoietin (EPO) and Renin
■ EPO is a hormone that bonds with receptor proteins in the
bone marrow to stimulate red blood cell production
■ Renin is an enzyme that mediates extracellular volume, and
arterial vasoconstriction
● Regulates blood pH by balancing ion concentrations:
○ Hydrogen, Sodium, Potassium, and Chloride ions lost in urine
● Prevents valuable nutrient loss while excreting organic waste products
Resources:
1. Starr, Cecie and Taggart, Ralph. Biology: The Unity and Diversity of Life.
California: Brooks/Cole, 2001. Print.
1. Science Daily. “The Excretory System.” Science Daily. Web. 13 November
2014 <www.sciencedaily.com/articles/e/excretory_system.htm>
1. Napa Valley College. “The Urinary System.” Napa Valley College. Web 14
November 2014
<http://www.napavalley.edu/people/briddell/Documents/BIO%20105/_STA
RT_HERE_ch18_lecture.pdf>
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