1. Unit 4: Human Systems BIOLOGY 20
Excretory System
Unit 4:
Human Systems
BIOLOGY 20

2. 10 minutes
Find out all you can about the excretory system function!!

3. Human Excretory System
Structures:
Kidney
Renal Artery
Renal Vein
Ureter
Bladder
Urethra
Inferior Vena Cava
Aorta

4. Urinary System
Renal Arteries branch off of the aorta and carry blood to the kidneys
Ureters carry the waste to the bladder
The bladder stores maximum 600mL of urine; a sphincter muscle prevents the urine from entering the urethra until urination
Upon urination, the urine enters the urethra and is excreted

5. Structure of the Kidneys
There are three basic structures found within the kidneys:
(1) The Cortex - Outer layer of connective tissue
(2) The Medulla - Inner layer, found below the cortex
(3) Renal Pelvis - Joins the kidney with the ureter (hollow)

6. Real Kidney

7. Nephrons Nephrons are the functional units of the kidneys
( slender tubes)
Nephrons are supplied with blood from the afferent arterioles (3), which branch into the capillary bed or the glomerulus (2)
Filtered blood is carried away from the nephron via the efferent arterioles (4)
The glomerulus is the interface between the circulatory system and the excretory system
The Bowman’s capsule (1) surround each funnel like part of the nephron
The Bowman’s capsule, the afferent and efferent arterioles are all found in the cortex

9. The Bowman’s Capsule
The Bowman’s capsule is the place where waste products pass from the blood to the kidneys to form urine

10. Proximal and Distal Tube and Loop of Henle
The Bowman’s capsule tapers into a small thin tubule, called the proximal tubule (5)
The waste is then carried to the Loop of Henle (8), which descends into the medulla
Urine then moves through the distal tubule (6) and then into the collecting ducts (7), which collect the urine from many nephrons, which merge in the pelvis of the kidney

11. Review http://www.youtube.com/watch?v=glu0dzK4dbU

12. Importance of The Kidneys
The cells of your body obtain energy by converting complex molecules into simpler ones
Most of these molecules are toxic to your body
The body must have systems which remove waste, e.g.. Liver, Large Intestine, Kidneys

13. Deamination
Deamination is a process that occurs in the liver to help remove a toxic substance
Recall protein contains a nitrogen molecule, which must be removed upon protein break down
The by-product of deamination is ammonia, which is highly lethal
Two molecules of ammonia and CO2 combine to form urea or uric acid, main components of urine, which is a less toxic substance to the body
Urea is filtered through the glomerulus and in to the nephron

14. Formation of Urine Urine formation depends on three functions:
(1) Filtration: Accomplished by the movement of fluids from the blood into the Bowman’s capsule
(2) Reabsorption: Involves the transfer of essential solutes and water from the nephron back into the blood
USEFUL SUBSTANCES THE BODY NEEDS
Secretion: Involves the movement of materials from the blood back into the nephron
WASTE PRODUCTS THE BODY DOES NOT NEED

15. Nephron Diagram and Function
Draw a diagram of the nephron with the following labels AND list the function of each structure on your diagram
Renal artery, renal vein
Afferent arteriole, efferent arteriole
Glomerulus
Bowman’s Capsule
Proximal and Distal tubule
Loop of Henle (descending and ascending)
Collecting Ducts
Capillary Network

17. Filtration
Each nephron has an independent blood supply
In the glomerulus, a high pressure filter is created (8 kPa as opposed to 2 kPa)
Filtration occurs when dissolved solutes pass from the walls of the glomerulus into Bowman’s capsule, moving from an area of high pressure to low pressure
Dissolved solutes include water, NaCl, glucose, urea, amino acids, and hydrogen ions
Not all materials in the blood will be filtered into Bowman’s capsule (i.e. blood cells, plasma proteins and platelets)

18. Filtration

20. Reabsorption Why is it important?
Think about this….
600mL fluid flows through kidneys each minute
120mL of that fluid is filtered into nephron
If none of this fluid was reabsorbed, you would form 120mL of fluid every minute (remember your bladder is full at 600mL)!
You would have to drink 1 L of water every 10 minutes to maintain homeostasis!
AND you would have to “pee” every 5 minutes!!
About 119mL of fluid and solutes is reabsorbed, the remaining 1mL forms urine

21. How Does Reabsorption Occur?
Reabsorption occurs when solutes are pumped back into the blood from the nephron
Occurs by both active and passive transport in the proximal tubule
Na+ is actively pumped out of the nephron, causing Cl- , HCO3- to be drawn out of the nephron due to attractive forces
Glucose and amino acids are reabsorbed
Water follows (osmotic gradient)
Energy for active transport is supplied via cell respiration, and is limited
Thus excess salts/glucose remain in the nephron and are urinated out of the body

23. Filtration and Reabsorption

24. Secretion
Secretion is the movement of wastes from the blood to the nephron
Examples include nitrogen-containing wastes, histamines, excess H+ ions and other minerals
Drugs, alcohol
Secretion occurs using active transport

25. Secretion

26. Water Balance Urine output depends on water input and water use
An increase in water intake will increase water output
Exercise, or a decrease in water will cause a decrease in water output

27. Student Centre Animations
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