chapter 13: excretion in humans

Question 1

what do the kidneys excrete

Answer 1

• water
• urea
• ions

Question 2

why must carbon dioxide be excreted?

Answer 2

• carbon dioxide can dissolve in water easily to form an acidic solution which can lower the pH of cells
• reduces enzyme activity needed for controlling metabolic reactions
• toxic!

Question 3

why must urea be excreted?

Answer 3

toxic!!

Question 4

describe the function of the kidneys

Answer 4

• filters the blood and excretes toxic waste products of metabolism and substances in excess requirements
• regulates water content

Question 5

describe the function of the ureters

Answer 5

tube connecting the kidney to the bladder

Question 6

describe the function of the bladder

Answer 6

organ storing urine as it is produced by the kidney

Question 7

describe the function of the urethra

Answer 7

tube connecting bladder to the external environment

Question 8

describe the role of the glomerulus in the filtration from the blood of water, glucose, urea and ions

Answer 8

ultrafiltration
* a knot of capillaries in the bowman’s capsule
* capillaries are narrower further into the glomerulus
* small molecules get forced out of glomerulus into bowman’s capsule, forming the filtrate

Question 8

describe the nephron

Answer 8

tiny structures in the cortex and medulla that filter the blood contents

Question 9

describe the reabsorption of the small molecules in the nephron

Answer 9

• selective reabsorption of glucose by active transport occurs only at the proximal convoluted tubule; many mitochondrianto provide energy for active transport
• salts are reabsorbed by diffusion at the loop of henle as well as water by osmosis

Question 10

what happens to the remaining fluid in the collecting duct?

Answer 10

forms urine containing concentrated urea, excess water, and excess ions

Question 11

describe the role of the liver in excretion

Answer 11

• assimilation: converts food molecules to other molecules that the body needs
• amino acids into proteins
  ——
• deamination: breaking down of excess amino acids and removing the nitrogen containing part to form urea
• enzymes in the liver break up the amino acid molecules
• carbon part turned into glycogen
• nitrogen turned into ammonia into urea which is dissolved in the blood and taken to the kidney to be excreted and a small amount is excreted in sweat

Question 12

list the consequences of high urea levels

Answer 12

• cell death
• reduced response to insulin, leading to diabetes
• deposits inside blood vessels