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 wastes2. They regulate the amount of water and salt

in the body3. They regulate the blood ph level should be

about 7.44. They release hormones into the blood

Removing Metabolic Wastes• 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

=O

• 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 parts1. Renal Cortex the section that is farthest to the

outside2. Renal Medulla the section that is in the middle3. Renal Pelvis the section that is on the inside that

goes into the ureter

Renal Artery

Renal Vein

Renal Cortex

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 CapillaryNetwork

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.

Rena

l Cor

tex

Rena

l Med

ulla

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 Too big to PassWaterNitrogen wastesNutrients (glucose, amino acids)Salts (ions)

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. Glomerulus2. Bomans Capsule3. Afferent arteriole4. Efferent arteriole5. Peritubular network6. Loop of Henle7. Bomans Capsule8. Renal Vein9. Renal Artery10. Proximal convoluted

tubule11. Distal convoluted tubule12. 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

-