y4.1 excretion 🫘

Question 1

why is it important to remove metabolic waste products from the body?

Answer 1

metabolic waste products can be harmful and prevent the maintenance of a steady state in the body if allowed to accumulate

Question 2

what is excretion?

Answer 2

excretion is the removal of toxic materials and metabolic waste products from organisms

Question 3

what is the difference between egestion and excretion?

Answer 3

egestion is the elimination of undigested material from the alimentary canal. these undigested materials were not formed within the cells and are not a product of metabolic processes

Question 4

structures of the urinary system

Answer 4

kidneys => ureters => bladder => urethra

Question 5

structures of a kidney

Answer 5

• cortex (outer ring)
• medulla (inner ring)
• renal pyramid
• nephrons
• renal pelvis (where renal pyramids empty into)

Question 6

structures of a nephron (in order)

Answer 6

renal artery => afferent arteriole => glomerulus => efferent arteriole => Bowman’s capsule => proximal convoluted tubule => loop of Henle => distal convoluted tubule => collecting duct

Question 7

what is ultrafiltration?

Answer 7

ultrafiltration is the non-selective filtering process which occurs at the glomerulus

Question 8

describe the process of ultrafiltration and what substances are found in the glomerular filtrate

Answer 8

1) the lumen of the afferent arteriole that brings blood into the glomerulus is wider than the efferent arteriole which brings blood away
2) blood enters the glomerulus more readily than it can leave, as a result blood dams up in the glomerulus, creating a high blood pressure which provides the main force for the filtration process
3) the pressure forces blood plasma out of the glomerular capillaries into the Bowman’s capsule along the whole length of the glomerulus
4) blood plasma that is forced out contains water and small molecules (glucose, amino acids, minerals and urea), forming the glomerular filtrate in the Bowman’s capsule
5) blood cells, platelets and large molecules (eg blood proteins, fats) remain in the blood which leaves the glomerulus via the efferent arteriole

Question 9

what is selective reabsorption?

Answer 9

selective reabsorption is the transport of useful substances from the filtrate back into the bloodstream. Solutes are reabsorbed by facilitated diffusion and active transport while water is reabsorbed by osmosis

Question 10

what is reabsorbed at the proximal convoluted tubule?

Answer 10

all glucose, amino acids and vitamins + 85% of water and ions

Question 11

what is absorbed at the loop of Henle?

Answer 11

water + ions

Question 12

what is absorbed at the distal convoluted tubule?

Answer 12

water + ions

Question 13

what is reabsorbed at the collecting duct?

Answer 13

the remaining water needed by the body

Question 14

composition of urine

Answer 14

96% water, 2% urea, 1.8% salts, 0.2% other nitrogenous substances

Question 15

how does a protein-rich diet affect urine composition?

Answer 15

more urea will be present in the urine because urea is formed when amino acids are deaminated in the liver

Question 16

how does a higher water intake affect composition of urine?

Answer 16

a higher water intake results in higher water potential of blood, hence a higher volume and lower concentration of urine is excreted

Question 17

how will a higher salt intake affect the urine composition?

Answer 17

higher concentration of salts will bee excreted in the urine

Question 18

how will having diabetes mellitus affect urine composition?

Answer 18

a diabetic patient is unable to store excess glucose as glycogen in the body, hence there is a high concentration of glucose in blood. howeverm the nephrons are unable to reabsorb all the glucose fast enough, a lot of glucose passes out in the urine

Question 19

what are the causes of kidney failure?

Answer 19

• high blood pressure
• diabetes
• alcohol abuse
• accidents to the kidney

Question 20

how does high blood pressure (as a result of diabetes) cause kidney failure?

Answer 20

(for diabetes, blood becomes more viscous and has to pump harder, increasing blood pressure)
- at high blood pressure, it results in capillary damage especially at the glomerulus which is already subjected to high pressure, and is one-cell thick
- this causes the glomerulus to become ‘leaky’, hence ultrafiltration can no longer occur, resulting in kidney failure

Question 21

what is the treatment for kidney failure?

Answer 21

dialysis

Question 22

what features of the dialyser aid with diffusion?

Answer 22

1) narrow tubing
- increase total surface area, allow more blood to come into contact with tubing walls
2) fresh dialysis fluid enters at the end nearer filtered blood, flowing in opposite direction of blood
- ensure waste products are completely removed before re-entering patient
3) dialysis fluid contains 0% urea, same concentration of solutes as blood
- provide a favourable concentration gradient for waste products to diffuse out of blood while ensuring useful solutes remain in blood
4) tubing is partially permeable
- allows small solutes (waste products) to diffuse through but not large proteins (blood cells)