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The Urinary/Excretory System
Excretion: the elimination of chemical wastes from the body
Lungs excrete CO2, skin excretes waste along with sweat.
Excretory Organs:
A. Lungs- CO2 diffuses from the capillaries surrounding the alveoli
into the air spaces and is removed during exhalation (some H2O
vapor is also removed)
B. Liver- a large, glandular organ that performs many functions
essential to human metabolism. Among its excretory activities
are:
1. Disposal of hemoglobin-old RBC’s are destroyed in the
liver and their hemoglobin is released. The liver converts
this hemoglobin to waste products called bile pigments.
The bile pigments are present in bile, which is stored in the
gall bladder and discharged into the small intestine. The
bile pigments are eliminated in fecal material (feces).
2. Disposal of nitrogenous wastes-nitrogenous compounds
are broken down in the liver, forming urea. Urea is
absorbed into the blood and removed from the blood by
the kidneys.
C. Sweat Glands1. Structure-sweat glands are small, coiled, tubular glands
found in the dermis of the skin. Their ducts lead to
openings in the epidermis called pores. Blood capillaries
surround the base of each sweat gland.
2. Function-H2O, salts, and some nitrogenous wastes diffuse
from the blood capillaries into the sweat glands and are
eliminated through the pores as sweat. The formation of
sweat is called perspiration.
3. Temperature regulation- main function of perspiration is
to help regulate the temperature of the body. When sweat
evaporates from the surface of the skin, it absorbs heat
from the skin tissues and carries it off into the air. The
effect is to cool the body. This is an example of negative
feedback and helps to maintain homeostasis
Excretory System: A system of organs that remove chemical waste from
the body. Most important organ of this system is the Kidneys.
When the body breaks down proteins into amino acids, the amino group
(NH2) produces ammonia (NH3) in the process, a poisonous compound
that the body quickly converts to urea, which gets removed in urine.
Kidneys: principal job is to remove urea, filter blood, and regulate water
in the bloodstream.
Found on either side of the spinal column, size of fists.
Renal Artery: blood flows into kidney thru renal artery
Renal Vein: after being filtered in kidney, blood exits thru renal vein
Ureter: tube that carries waste fluid from kidney to the urinary bladder
where it eventually is released from the body
Kidney filtration system removes from the blood – urea, excess water,
and other wastes. The functional unit of the kidney is the nephron. Each
kidney contains about 1 million nephrons.
Nephrons: kidney has millions of blood filtering units called nephrons.
Nephrons are found in the outer cortex and medulla of kidney.
Blood enters nephrons through an arteriole (small artery) and leaves
through a venule (small vein) after being filtered.
Renal pelvis: area of nephron where wastes and excess water are sent.
This waste and excess water collects into ducts that dump into ureter
which takes the waste to the urinary bladder.
Structure & Function of the Nephron:
A. Structure: the nephron contains a network of capillaries called a
glomerulus, enclosed in a cuplike capsule called the Bowman’s
capsule. The capsule is connected to a long, coiled tubule.
Capillaries are closely entwined around the tubule.
1. Glomerulus- tangle of capillaries which increase the pressure on
the blood forcing almost all the liquid out of the vessels.
2. Bowman’s Capsule- surrounds the glomerulus; catches all that has
been filtered out of the blood.
3. Proximal tubule- first part of tubule; good stuff that was forced
out is put back into the blood.
4. Loop of Henle- long loop in nephron tubule that separates good
from the bad (good-> back into the blood, bad-> stays in tubule)
5. Distal tubule- more separation of good from bad
6. Collecting duct (or tubule)- the concentrated bad stuff (filtrate)
empties into here, which leads to the ureter.
B. Function:
1. Filtration- as blood flows through the capillaries of the
glomerulus, H2O, salts, urea, amino acids, and glucose
diffuse out of the blood into the Bowman’s capsule. This
stage of the process is called filtration. It is non-selective.
2. Reabsorbtion- as the materials flow through the capsule
and the collecting tubule, some of the H2O, salts, amino
acids, and glucose are reabsorbed by active transport into
the capillaries surrounding the tubule.
3. Secretion- the fluid that reaches the end of the collecting
duct/tubule is mostly water, urea, some salts, H+ ions
(urine slightly acidic), and any drugs or toxins---fluid is
called urine.
Ureter: tube that carries waste fluid from kidney to the urinary bladder
where it eventually is released from the body
Urinary Bladder: Stores urine until released from the body
Urethra: tube that leads from the urinary bladder out of the body where
urine can be excreted.
Urine- clear, yellow (urochrome pigment from hemoglobin destruction),
usually slightly acidic (pH 6), sterile
Color, odor, and pH can change based on foods, drugs, toxins, bile.
Substances normally found in urine include: nitrogenous wastes,
water, various ions (always Na+ and K+ ions).
Abnormal components include: glucose (glycosuria-excessive intake
of sugary foods or diabetes mellitus), proteins (proteinuria--physical
exertion, pregnancy, glomerulonephritis, hypertension), pus- WBC’s and
bacteria (pyuria--urinary tract infection), RBC’s (hematuria—bleeding in
urinary tract from trauma, kidney stones, infection), hemoglobin
(hemoglobinuria—transfusion reaction, hemolytic anemia), bile
pigment (bilirubinuria—liver disease/hepatitis)
Normal urine output—1.0 to 1.8 liters (1000ml to 1800ml)/day
Oliguria- abnormally low urine output (between 100-400ml/day)
Anuria- abnormally low urine output (less than 100ml/day)
(not enough pressure in glomerulus for filtration)
Polyuria- excretes large volumes of urine and loses tremendous
amounts of salt and water to urine. Need to take in adequate amounts of
salts and fluids to avoid electrolyte imbalance and dehydration.
Malfunctions of the Excretory System
1. Kidney disease- includes various problems in which the kidneys
or nephrons are unable to function effectively in excreting wastes.
If problems are extreme, the person might have to go on dialysis;
machine will filter the blood to remove waste products.
2. Gout- form of arthritis in which excessive production of uric acid
leads to deposits of crystals in the joints, causing pain and stiffness.
Causes of gout include high fatty diet, alcohol, high blood pressure,
and stress.
3. Urinary tract infections- usually just a bacterial infection inside
the urethra, but if the infection travels up the ureters into the
bladder then into the kidney, you have serious pain and a serious
battle to get rid of the infection. May require hospitalization and
fluid therapy. Painful urination, urinary urgency and frequency,
fever, cloudy or blood-tinged urine
4. Kidney stones- When urine becomes extremely concentrated,
solutes such as uric acid salts form crystals that precipitate in the
renal pelvis called renal calculi, or kidney stones. Excruciating
pain occurs when they become wedged in a ureter. Surgery to
remove stones or ultrasound waves to shatter them and then
eliminate the sand-like remnants in the urine.