excretion

Question 1

why is excretion important?

Answer 1

if the toxic materials remain in the body, the internal environment fluctuate and continuation of metabolic processes is hindered

Question 2

define excretion

Answer 2

it is the removal of waste products that were formed during metabolic reactions in the body cells

Question 3

products of excretion

Answer 3

co2, excess water and salt, products from deamination in the liver (eg urea), products from detoxification of substances such as alcohol

Question 4

what are nitrogenous excretory products?

Answer 4

deanimated excess amino acids

includes: uric acid, creatinine, ammonia

Question 5

how are bile pigments excreted?

Answer 5

bile pigment is formed from break down of haemoglobin of rbcs and it is excreted through urine, sweat and expired/exhaled air

Question 6

formation of urea

Answer 6

enzymes in the liver deaminate the excess amino acids by removing amino groups. the leftover amino acids cannot be used and are converted to ammonia. ammonia is quite toxic to all cells so it is combined with carbon dioxide to form urea. its removal from the body requires a lot of water

Question 7

formation of uric acid

Answer 7

uric acid is formed from the breakdown of nucleic acids (DNA, RNA) from the cell of the food consumed and from metabolic reactions of nucleic acids and ATP. it is almost insoluble in water and cannot diffuse into the body cells so it is harmless to cells. it requires a lot of energy but little water to remove

Question 8

formation of creatinine

Answer 8

it is mainly derived froma nitrogen-containing molecule called creatine found in muscle cells

Question 9

what does urine consists of?

Answer 9

it consists of urea, water and smaller amounts of creatinine and uric acid

Question 10

what does the urinary system consists of?

Answer 10

kidneys and the nephrons within it, the ureters, urinary bladder and urethra

Question 11

what is the kidney made up of?

Answer 11

1. fibrous capsule
2. renal cortex
3. renal medulla
4. renal pelvis
5. renal vein
6. renal artery
7. ureter

Question 12

what is the fibrous capsule?

Answer 12

it is the outer membrane that surrounds the kidney and serves as a protection layer

Question 13

what is the renal cortex?

Answer 13

it is the lighter-coloured outer region which consists of the Bowman’s capsule, convoluted tubules and blood vessels

Question 14

what is the renal medulla?

Answer 14

it is the darker-coloured inner region made up of the loop of Henle, collecting duct and blood vessels

Question 15

what is the renal pelvis?

Answer 15

it is a funnel-shaped cavity that drains urine into the ureter

Question 16

what does the nephron consist of?

Answer 16

1. Bowman’s capsule
2. Proximal convoluted tubule
3. Loop if Henle
4. Distal convoluted tubule
5. Collecting duct

Question 17

what is the Bowman’s capsule?

Answer 17

it is the closed end at the start of the nephron. it is cup-shaped and it contains a mass of blood capillaries aka the glomerulus. Its inner layer is made up of a thin layer of specialised cells known as podocytes

Question 18

what is the proximal convoluted tubule?

Answer 18

it is a series of loops surrounded by a dense network of peritubular capillaries. Its walls are made up of epithelial cells with microvilli

Question 19

what is the Loop of Henle?

Answer 19

it is the long loop that extends from the cortex region to the medulla region and back up again. It is surrounded by peritubular capillaries.

Question 20

what is the distal convoluted tubule?

Answer 20

it is the series of loops that is surrounded by a less dense network of peritubular cells than proximal convoluted tubule. Its walls are also made up of epithelial cells with microvilli

Question 21

what is the collecting duct?

Answer 21

it is a tube in which multiple distal convoluted tubules empty. it is lined by specialised cells and becomes increasingly wide as it drains into the renal pelvis

Question 22

what are the blood vessels associated with each nephron?

Answer 22

1. Afferent arteriole
2. Glomerulus
3. Efferent arteriole
4. Peritubular capillaries

Question 23

what is the afferent arteriole?

Answer 23

it is the tiny vessel arising from the renal artery that enters the Bowman’s capsule in the nephron
it supplies the nephron with bloodn

Question 24

what is the glomerulus?

Answer 24

network of capillaries from which fluids are forced out of the blood due to the high hydrostatic blood pressure

Question 25

what is the efferent arteriole?

Answer 25

it is the tiny vessel leaving the Bowman's capsule and its lumen diameter is narrower than that of afferent arteriole. this causes the increase in the hydrostatic blood pressure in the glomerulus

Question 26

what are the peritubular capillaries?

Answer 26

they are a dense network of blood capillaries which surrounds the convoluted tubules and loop of Henle. they reabsorb mineral salts, glucose and water from them and merge to form venules which are further merged to form the renal vein.

Question 27

what are the stages of urine formation?

Answer 27

Ultrafiltration, selective re-absorption and secretion

Question 28

what happens during ultrafiltration?

Answer 28

Due to the high hydrostatic pressure created as a result of the difference in lumen diameter between the afferent and efferent arteriole, most of the components of blood apart from plasma proteins and blood cells are forced out of the glomerulus and into the Bowman's capsule to form the glomerulus filtrate. Since this process relies on the steepness of the hydrostatic pressure gradient, it can be affected by changes in blood pressure.

Question 29

How is the glomerulus filtrate determined?

Answer 29

Ultrafiltration does not select for which substance can enetr the nephron tubule. Molecular size determines which substances can enter. The capillary walls of the glomerulus is made up of one layer of endothelial cellswith pores between them which are large enough for blood cells and protein molecules to pass through. However, the basement membrane of the Bowman's capsule only allows small molecules like urea, glucose and water to enter it, thereby preventing plasma protein and red blood cells from entering the nephron tubule

Question 30

What happens during selective-reabsorption?

Answer 30

Useful substances such as glucose and amino acids are actively transported out of the nephron tubules and into the interstitial fluid and back into the peritubular blood capillaries. hence only the excretory waste materials remain the glomerular filtrate

Question 31

what happens at the loop of henle?

Answer 31

Selective-reabsorption of amino acids and glucose lowers the water potential of the intertitial fluid and water potential in the glomerular filtrate is higher. This results in a large amount of water being reabsorbed along the loop of Henle. At the ascending limb of the loop of henle, active transport of salt from the glomerular filtrate occurs which increases the rate of osmosis by increasing the water potential in the glomerular filtrate.

Question 32

what happens at the distal convoluted tubule and collecting duct?

Answer 32

The walls of the ascending limb of the loop of Henle is impermeable to water but the walls of the end of the distal convoluted tubule and collecting duct are not. Hence the rate of osmosis is high due to the high water potential of the glomerular filtrate as a result of active transport of salt out of it. forms concentrated urine

Question 33

what are some the structural features of the nephron for selective re-absorption?

Answer 33

1. parts of nephron are very coiled, this increases surface area to volume ratio and increases time taken for glomerular filtrate to travl through the nephron thus giving more time for selective reabsorption to occur 2. epithelial cells of coiled tubules contains many mitochondria. more energy released for reabsorption of substances via active transport

Question 34

what happens during secretion?

Answer 34

Certain substances like creatinine, hydrogen ions and drugs are removed from the peritubular capillaries and into the distal convoluted tubule and collecting duct

Question 35

what is kidney failure?

Answer 35

it is when the kidneys are unable to function properly, resulting in the accumulation of waste products in the blood

Question 36

what causes kidney failure?

Answer 36

obstruction of blood supply to the kidneys, diabetes and high blood pressure

Question 37

how to treat kidney failure?

Answer 37

patients have to undergo dialysis where waste products such as urea are removed from the blood before it is returned to the vein

Question 38

how does dialysis work?

Answer 38

1. Blood is drawn from a vein in the patient's arm 2. Blood is pumped into the dialysis machine through a tubing 3. the semi-permeable tubing is bathed in dialysis fluid 4. small molecules (eg urea) and metabolic waste products diffuse from the tubing and into the fluid 5. larger molecules like red blood cells remain in the tubing 6. filtered blood is returned to the a vein in the patient's arm

Question 39

features of dialysis machine

Answer 39

1. fluid contains same concentration of amino acids, glucose and mineral salts as the blood to esnure no net movement of these essential substances from blood to the fluid. if the blood lacks any of these substances, they will diffuse from the fluid and into the blood 2. metabolic waste is absent in the fluid to create a steep gradient for the diffusion of excretory products into the fluid 3. dialysis tubing is long and coiled to increase surface area to volume ratio for increase rate of diffusion of substances it is semi-permeable so that large molecules like protein and red blood cells are retained in the blood while small molecules like urea is removed 4. dialysis fluid flows from opposite direction to maintain steep concentration gradient for removal of waste products