THE EXCRETORY SYSTEM
Excretory System



Some call it the “urinary system”, but more than just
urine is excreted from our bodies
Excretion = removing unnecessary components from
an organism
Examples:
 Lungs
excrete CO2
 Skin excretes ions/salts in the form of sweat
 Kidneys excrete urine
 We
are gong to focus on this part of the excretory system
Major Function




Disposing of wastes and excess ions
Regulation of blood volume and chemical makeup
Regulation of blood pressure
Manufacturing and storage of urine
Organs

Kidney


Ureters


Tubes that connect kidney
to bladder and transport
urine
Urinary Bladder


Form urine
Store urine
Urethra
External opening to the
body where urine passes
 In males, the urethra does
double duty and can pass
semen AND urine

Kidneys

Located in the upper
lumbar region
 Protected


by the 12th rib
Adrenal gland sits atop
the kidney
When cut lengthwise, it
has 3 regions
Kidney-Regions

Renal cortex
 Outer

region
Renal medulla
 Contains
“medullary
pyramids”

Renal pelvis
 Connects
to ureters that
will send urine to the
bladder
Nephrons

Each kidney contains over a million nephrons
 Nephron
= structural and functional unit of the kidney
 Responsible for forming urine
Nephron

Each nephron consists of 2 main structures
 Glomerulus
 Knot
 Renal
of capillaries
tubule
 Glomerular
capsule
 Proximal convoluted tubule
 Loop of Henle

Ascending and descending loops
 Distal
convoluted tubule
 Collecting duct
Urine Formation

3 processes
 Filtration
 Tubular
reabsorption
 Tubular secretion

Rule of thumb: whatever is not reabsorbed from the
nephron will be found in the urine
Filtration

The glomerulus acts as a filter and the filtrate
goes into the glomerular capsule
 Will

eventually be found in urine if not reabsorbed
Filtration = nonselective passive process
 Only
salts, glucose, urea, amino acids can pass
through into the glomerular capsule
 Proteins and RBCs = too large
Tubular Reabsorption


Begins as soon as the filtrate enters the proximal
convoluted tubule and continues through all the
tubes
Salts, amino acids, and water are reabsorbed back
into the bloodstream
Tubular Secretion

Essentially reabsorption in reverse
 The


body is trying to get rid of these substances
Hydrogen, potassium, certain drugs
Whatever is left in the nephron will go into the
collecting duct and will eventually exit the body
What’s Next?

The filtrate that passes
through the collecting duct
will drain into the renal pelvis



It is called “urine” at this point
This is connected to the
ureters and will transport the
urine to the urinary bladder
When voided, the urine will
pass through the urethra and
into the outside world
Let’s Talk About Pee


Every 24 hours, 1-1.8 liters are produced
Urine = nitrogenous wastes and unneeded
substances
Characteristics of Urine

Generally clear and pale- to deep-yellow
 Why
is urine yellow?
 From
a pigment called urochrome that results from the
body’s destruction of hemoglobin

When formed, urine is sterile
 Means

there is no bacteria
Why does urine smell?
 The
longer the urine sits, it gets exposed to bacteria
and they eat the urine solutes and cause the ammonia
odor
Characteristics of Urine

Urine pH is slightly acidic, but this can vary based
on diet
 Lots
of protein and whole-wheat products? ACIDIC
 Vegetarian diet? BASIC
Characteristics of Urine

Composition
 Sodium,
potassium, urea, uric acid, creatinin, ammonia,
bicarbonate ions

Things that should NOT be found in urine:
 Glucose,
bile
blood proteins, RBCs, hemoglobin, WBCs, and