Chapter 8: Excretion in Humans

Question 1

urea

Answer 1

• excess amino acids transported to liver for deamination
• part of amino acid molecule removed and converted to urea

Question 2

Excretion

Answer 2

removal of metabolic waste products, toxic substances & substances in excess of body’s requirements

Question 3

ultrafiltration

Answer 3

• afferent arteriole wider than efferent arteriole creates hbp in glomerulus
• blood plasma forced out of glomerulus blood capillaries into Bowman’s capsule
• filtered blood: glomerulus filtrate (small soluble substances- water, a.a. , salts, glucose, urea)

Question 4

how is glomerulus suited to urine formation

Answer 4

• glomerulus: network/knot of blood capillaries- large surface area for filtration
• blood capillaries walls: one cell thick- tiny pores
• blood capillaries: covered by a thin partially permeable membrane- only allow small soluble molecules to pass thru, impermeable to blood cells, platelets & proteins

Question 5

selective reabsorption

Answer 5

glomerulus filtrate passes along nephron , useful substances are reabsorbed into surrounding capillaries
water: osmosis
salts: active transport
glucose and a.a. : active transport

Question 6

what is absorbed at where

Answer 6

PCT: water (osmosis), glucose & a.a. (active transport), mineral salts (diffusion & active transport)

LoH: water (osmosis), mineral salts (active transport)

DCT: water (osmosis), mineral salts (active transport)

collecting duct: water (osmosis)

Question 7

osmoregulation

Answer 7

control of water potential and solute concentration in the blood, to maintain a constant water potential in the body

Question 8

ADH

Answer 8

antidiuretic hormone (ADH)
produced by hypothalamus
released by pituitary gland, increases water reabsorption at nephrons

Question 9

why r kidneys important

Answer 9

1. excretory organs, play a role in excreting metabolic waste (urea, excess water & mineral salts) in the form of urine
2. osmoregulators: regulate water potential and solute concentration in blood, maintain constant water potential in blood

Question 10

causes of kidney failure

Answer 10

• hbp
• diabetes
• alcohol abuse
• severe accidents that physically damage kidney
• complications from undergoing major surgery

Question 11

dialysis fluid: same conc of essential substances in blood

Answer 11

essential substances (glucose, a.a. , mineral salts) do not accidentally diffuse out of blood into dialysis fluid

if patients blood lack these substances, these substances will diffuse from dialysis fluid into blood

Question 12

dialysis fluid: no metabolic waste products

Answer 12

sets up a conc gradient for waste products to diffuse into dialysis fluid, waste products removed from blood

maintains correct solute composition and water potential of blood

Question 13

tubing in dialysis machine is narrow, long and coiled

Answer 13

increase SA:V, helps speed up rate of exchange of substances between patients blood no dialysis fluid

Question 14

direction of blood flow opp to flow of dialysis fluid

Answer 14

maintains conc gradient for removal of waste products