Excretion

Do Now

Your Body’s Filter•Have you ever seen a water-purification system attached to a faucet?This system removes impurities from the water such as arsenic or other chemicals that can be harmful to people. As water passes through the filters contained in the system, the impurities are trapped on the surface of the filters. Eventually, the water that comes out of this purifier is free of the impurities.

Section 38-3

1. Your body has its own system for filtering blood. Why might the blood in your body need to be filtered?

2. What organ(s) do you think filters your blood?3. How do you think the filtered materials leave your body?

Checks and Balances

• Your body is amazingly maintaining homeostasis through an intricate system of checks and balances to satisfy your body’s needs and remove waste products that are not useful or toxic

Excretion

• Excretion = the process by which wastes are eliminated from the body

• The excretory system includes:– Lungs: excrete gaseous carbon dioxide from

cellular respiration– Rectum: excrete solid undigested remains

from food– Skin: excretes excess water, salts, urea– Kidneys and accessory organs

The Urinary System

• The urinary system rids the blood of wastes produced by the metabolism of nutrients and controls blood volume by removing excess water produced by body cells.

• The urinary system includes: – Kidneys– Urinary bladder– Connecting tubules:

• Ureter • Urethra

Kidney (Cross Section)

Cortex

Medulla

Vein Artery

Kidney

Ureter

Urinary bladder

Urethra

The Urinary SystemSection 38-3

Kidneys

• Most people have 2 kidneys located on either side of the spinal column on your lower back

• Ureters = tubes that carry urine from each kidney to the urinary bladder

• Urinary bladder = saclike organ that stores urine until it can be excreted

• The kidneys filter blood by removing urea, excess water and other wastes collected as urine and the clean filtered blood returns to circulation

Kidney Structure

• Inner part = renal medulla

• Outer part = renal cortex

• Functional units of the kidney = nephrons

• About 1 million nephrons in each kidney

• Each nephron has its own arteriole (small artery), venule (small vein), and network of capillaries to filter blood

Kidney Nephron

Cortex

Medulla Renal artery

Renal vein

Ureter

To the bladder

Bowman’s capsule

Glomerulus

Capillaries

Collecting duct

To the ureter

Loop of Henle

Artery

Vein

Figure 38–17 Structure of the Kidneys

Section 38-3

Filtration

• Blood enters a nephron through the glomerulus (network of capillaries) in Bowman’s capsule (cup-shaped structure)

• Blood is under high pressure causing fluid to flow from the blood into Bowman’s capsule = filtration

• The filtrate contains water, urea, glucose, salts, amino acids, and some vitamins

Reabsorption

• Most of the material removed from the blood at Bowman’s capsule makes its way back into the blood = reabsorption– 99% of water is reabsorbed into blood

Secretion

• Some materials, including hydrogen ions (H+) are transferred from the blood into the filtrate = secretion

Filtration

Most filtration occurs in the glomerulus. Blood pressure forces water, salt, glucose, amino acids, and urea into Bowman’s capsule. Proteins and blood cells are too large to cross the membrane; they remain in the blood. The fluid that enters the renal tubules is called the filtrate.

Reabsorption

As the filtrate flows through the renal tubule, most of the water and nutrients are reabsorbed into the blood. The concentrated fluid that remains is called urine.

Secretion

Substances such as hydrogen ions are transferred from the blood to the filtrate.

Figure 38–18 The Nephron

Urine

• The material that remains = urine containing urea, salts, water and other substances

• The loop of Henle conserves water and minimizes the volume of urine

• Urine is stored in the urinary bladder until it can be released from the body through a tube = urethra

Kidney Function

• The kidneys maintain homeostasis by: – Regulating the water content of the blood

(blood volume)– Maintaining blood pH– Removing waste products from the blood

Dialysis

• Although you are born with two kidneys, you can live with only one kidney.

• If both kidneys malfunction, a kidney dialysis machine can artificially filter blood

Vein

Artery

Shunt

Air detector Dialysis machine

Blood pump

Blood in tubing flows through dialysis fluid

Used dialysis fluid

Compressed air

Fresh dialysis

fluid

Figure 38–19 Kidney DialysisSection 38-3