Chapter 16
Urinary System and the Excretion
System
Urinary Organs
• Kidneys  Fist sized organs that are next to the
vertebrae
• Ureters  Tubes that connect the kidney and the
urinary bladder
• Renal Artery and Renal Vein  Takes blood to and
from the kidneys
• The urinary bladder  holds urine
• Urethra  tube that goes from the urinary bladder
and exits the body.
• Adrenal Gland  glands that are on top of the
kidneys that release hormones in the body
What does the Urinary System do
1. They remove metabolic wastes
2. They regulate the amount of water and salt
in the body
3. They regulate the blood ph level  should be
about 7.4
4. They release hormones into the blood
Removing Metabolic Wastes
=O
• The liver breaks down amino acids and this
makes Ammonia
• Ammonia is very toxic and the liver combines
carbon dioxide to make the less toxic Urea
• The kidneys will then filter the Urea out of the
blood
NH3 + CO2  NH2-C-NH2
• Creatinine is also excreted by the kidneys.
Creatinine is the product of creatine
phosphate metabolism
• Uric acid is excreted. Uric Acid is the product
of breaking down nucleotides
Water Salt Balance
• Kidneys maintain the appropriate amount of
ions in the blood
• Potassium ions K+
• Bicarbonate ions HCO3• Calcium ions Ca2+
The Kidney
• The kidney can be divided into 3 main parts
1. Renal Cortex  the section that is farthest to the
outside
2. Renal Medulla  the section that is in the middle
3. Renal Pelvis  the section that is on the inside
that goes into the ureter
Renal Cortex
Renal Artery
Renal Vein
Renal Medulla
Renal Pelvis
The Nephron
• The kidney is made up of millions of Nephrons
• The nephron is where the actual filtration occurs
• The blood flow is different than other areas of the
body. Each nephron has 2 capillary regions
Renal artery  Afferent arteriole Glomerulus  Efferent
arteriole  Peritubular capillary network  Renal Vein
Renal Artery
Afferent Arteriole
Glomerulus
Efferent Arteriole
Peritubular Capillary
Network
Renal Vein
Parts of the Nephron
• Bomans Capsule  this is the cup that surrounds the
glomerulus. Small molecules move from the blood into
the Bomans capsule. This process is called Glomerular
Filtration
• Proximal Convoluted Tubule  this comes after the
bomans capsule. Has many mitochondria for active
transport. This process is called Tubular Filtration
• Loop of Henle  Loop that descends into the renal
medulla. Reabsorbs water back into the blood
• Distal Convoluted Tubule  have many mitochondria
for active transport of molecules from the blood into
the tubule
• Collecting Ducts  Take wastes to the Ureter.
Renal Medulla
Renal Cortex
Glomerular Filtration
• Occurs in the Bomans Capsule (also called the
glomerular capsule)
• This has a high pressure going into the capsule.
Blood undergoes Pressure Filtration.
• Large things do not pass into the Bomans Capsule,
but small things do pass into the Bomans Capsule.
Small Enough to Pass
Water
Nitrogen wastes
Nutrients (glucose, amino
acids)
Salts (ions)
Too big to Pass
Formed Elements (Blood cells)
Proteins (fibrinogen)
Tubular Reabsorption
• This occurs in the proximal convoluted tubule.
• This is when molecules and ions move from
the tubule back into the blood.
• Nutrients are reabsorbed back into the blood.
• Ions are reabsorbed back into the blood. This
is done both passively and actively.
• Water is reabsorbed back into the blood.
Tubular Secretion
• This occurs in the distal convoluted tubule
• Active transport moves ions and molecules
from the blood into the tubule
• This moves hydrogen ions and nitrogenous
wastes
1. Glomerulus
2. Bomans Capsule
3. Afferent arteriole
4. Efferent arteriole
5. Peritubular network
6. Loop of Henle
7. Bomans Capsule
8. Renal Vein
9. Renal Artery
10. Proximal convoluted
tubule
11. Distal convoluted tubule
12. Collecting duct
Water – Salt Balance
• Reabsorption of water
– The descending portion of the loop of Henle has
water that moves back into the blood.
– The concentration of Salt is higher toward the
bottom of the loop of Henle
– The acending portion of the loop of Henle does
not allow water to pass through it.
Maintaining Homeostasis
• Antidiuretic Hormone (ADH) this hormone will
help regulate how much water is in in your
body
• If ADH is released then more water will be
absorbed out of the nephrons and into your
blood  this will make you NOT go Pee
• If you do not make ADH then your nephrons
will not absorb very much water and you will
go Pee more
• When will your Body release ADH?
• When will your Body not release ADH?
• ADH is made and released in a special gland in
the brain called the pituitary gland
• The hormone will help regulate the amount of
water in the blood and keep it in a state of
Homeostasis.
Reabsorption of Salt
• NaCl moves into the Bomans capsule by
Pressure Filtration
• In the Proximal Convoluted Tubule, about 67%
of the NaCl is reabsorbed back into the blood
• 25% of the NaCl is reabsorbed in the
ascending portion of the loop of Henle
• 7% of the NaCl is reabsorbed in the Distal
Convoluted Tubule
• The remaining 1% is part of the urine
Hormones and reabsorption of salt
• Aldosterone is a hormone that is released by
Adrenal Cortex
• The adrenal cortex is the gland that sits on top
of the kidneys
• Aldosterone causes Na+ ions to be reabsorbed
into the blood. When more sodium ions are
absorbed into the blood then more water is
absorbed into the blood.
Kidneys Maintain the bloods pH
• Breathing is the main way to maintain the pH of the
blood
– If blood is too acidic  Breathe more to get rid of CO2
– If blood is too basic  Breathe less to let H+ ions build
up
• Kidneys can also help regulate pH
– Blood is too acidic  kidneys excrete H+ ions and
reabsorb bicarbonate ions HCO3– Blood is too basic  Kidneys do not excrete H+ ions and
do not absorb bicarbonate ions HCO3-