The Excretory System

1. Professor Gieraltowski Professor Meehan The Excretory System

2. The Excretory System • All organisms create _________ wastes through life processes. (salts, carbon dioxide, urea) • Some of these are toxic. For example, urea, which is created when amino acids are broken down, can build up and kill an organism. • The function of the excretory system is to filter toxic metabolic wastes and remove them from the body in order to maintain ___________.

3. The Excretory System • The excretory system comprises of three major organs: • The ____ • The _____ • The _______

4. Skin and Lungs The sweat perspired by the skin contains amounts of metabolic waste. This secretion of waste makes perspiration a minimal factor in excretion. However, the skin’s main function is temperature regulation. The lungs excrete carbon dioxide, water, and heat, all of which are products of cellular respiration. Oxygen diffuses into the capillaries while carbon dioxide diffuses out.

5. The Kidneys • The human body has two kidneys, which are located on either side of the lower back. • Kidneys filter wastes from blood and collect them as ______. • The wastes then travel through _______ to the bladder, where they are stored until excretion. • Urine is then excreted through a tube called the urethra.

6. Excretion through the Kidneys • Blood enters the kidney through the renal ______. • In the ______, structures called ________ remove materials (filtrate) from the blood. • The filtrate collects in ducts and passes through the ureter.

7. Nephrons Nephrons are the functional units of the kidney. There are approximately one million nephrons in each kidney. With the exception of the loops of Henle and collecting tubes, which both extend into the renal _______, nephrons are found in the renal cortex. Blood enters a nephron through an _______. It then passes through filtration structures, and leaves through a _______.

8. Flow of Wastes within a Nephron • Blood passes through a Bowman’s capsule in a network of capillaries called a _________. Water, urea, sugar, salt, amino acids, and some vitamins pass through the capillary walls. This forms the _____. Large particles remain in the blood. • The filtrate passes through the _______ tubule, which reabsorbs valuable nutrients, water, and salt from the filtrate, which is now urine.

9. Flow of Wastes within a Nephron • The urine passes through the loop of Henle. The descending loop absorbs water and the ascending loop absorbs salt, both using a concentration gradient. • The ______ tubule further removes water and salt from urine and secretes other substances such as hydrogen and potassium ions into it.

10. Blood Flow in a Nephron • Urine passes from the distal tubules of each nephron into the collecting duct, extending into the renal medulla. Depending on the amount of antidiuretic hormone (ADH) present, the collecting duct will allow water to diffuse through. The lower portion of a collecting duct is somewhat permeable to urea, which maintains homeostasis within the medulla.

11. Without a Kidney • As people have two kidneys, they can injure one and still survive. However, when both are damaged, an alternative must be found. • There are two commonly available options: • Transplant – A compatible donor with two healthy kidneys donates one. • Disadvantages – The immune system can reject transplanted kidneys, so the patient must take medication for the rest of his or her life to prevent this. • Dialysis – Blood is pumped through dialysis tubes and is returned to the body. • Disadvantages – Dialysis is costly and time-consuming.

12. Comparative Anatomy • In simple animals, such as the hydra, the entire body is in contact with the environment. Thus, _________ is the quickest and easiest way for the waste to be transported out of the body. • In a grasshopper, carbon dioxide diffuses into __________ and is expelled through spiracles on the animal’s exoskeleton. This also covers excretion through the lungs.

13. Comparative Anatomy (cont.) • In annelids, such as earthworms, the skin excretes carbon dioxide by means of diffusion. Other metabolic wastes are excreted from the nephridia through the nephriopores. This also serves the purpose of the lungs, which, in humans, also rid the body of carbon dioxide.

14. Vocabulary • arteriole • bladder • Bowman’s capsule • (renal) cortex • dialysis • distal tubule • filtrate • glomerulus • loop of Henle • (renal) medulla • nephron • proximial tubule • renal artery • renal vein • ureter • venule