1. The Urinary System

2. Function of the Excretory System
The excretory system functions in ridding the body of nitrogenous wastes (urea, uric acid, ammonia) and other wastes.
It also regulates the amount of water and ions present in the body fluids.

3. Nitrogenous wastes

4. Overview of the Urinary System
Blood enters the kidneys through the renal artery.
Blood enters the nephrons.
Water,sugar,salt and wastes in the blood enter a cuplike structure in nephron.
Capillaries reabsorb most of the water,sugar, and salt.
The renal vein returns purified blood to be circulated.
Urine drains from each collecting tubule into funnel shaped areas of the kidney
Urine flows from ureters to the urinary bladder
Urine flows from the bladder through the urethra and out of the body.

5. Nephron Structure
Bowman’s capsule
loop of henle

6. Five Parts of the Nephron
1. Bowman’s capsule
2. proximal tubule
3. loop of Henle
4. distal tubule
5. collecting duct
glomerulus: “capilliary bed” = network of blood capillaries

7. The Formation of Urine
depends on three functions
1. Filtration
movement of fluids from blood into the Bowman’s capsule
2. Reabsorption
transfer of essential solutes and water from the nephron back into the blood
3. Secretion
movement of materials from the blood back into the nephron

8. Filtration
blood pressure forces water, urea, salts, and other small dissolved solutes from the blood in the glomerulus into the lumen of Bowman’s capsule
not all materials enter the capsule (e.g plasma protein, blood cells and platelets are too large to move through)

9. Pathway of the Filtrate
the nephric filtrates passes through the proximal tubule, the loop of Henle, and the distal tubule
the distal tubule empties into a collecting duct, which empties into the renal pelvis

10. Pathway of the Filtrate
1100 to 2000 L of blood flows through the kidneys each day
kidneys excrete only 1.5L of urine
Where’s the rest of the filtrate and water?

11. Reabsorption
The rest of the filtrate and water are reabsorbed into the blood in the process of reabsorption!
commences when the nephric fluid enters the the proximal tubule and continues to the loop of Henle and then the distal tubule
is the process by which materials required by the body are removed from the filtrate and returned to the blood
If all were converted to urine we would have to consume over 1L of water every 10 min to maintain homeostasis
(1mL/min of urine)
Occurs through active and passive transport - mitochondria provides energy for active

13. Reabsorption
almost ALL the sugar, vitamins, and other organic nutrients from filtrate and water are reabsorbed
helps to control the concentration of salts in body fluids
Both active and passive transport are used to pump these substances out of the nephron and back into the blood stream
If all were converted to urine we would have to consume over 1L of water every 10 min to maintain homeostasis
(1mL/min of urine)
Occurs through active and passive transport - mitochondria provides energy for active

14. Secretion
the proximal and distal tubules are the most common sites of secretion
VERY selective process involving mostly active transport
movement of wastes from blood into the nephrons

15. Secretion
nitrogen containing wastes, excess H+ ions and minerals such as K+ get secreted
cells containing mitochondria line the distal tubule
molecules are shuttled from the blood into the nephron

16. Homework Pg. 348 Q: 1-3 Pg. 352 Q: 1,3 Answer the following questions:
How does ADH help to ensure homeostasis?
Why is the liver important in the excretory system?