8 — excretion in humans

Question 1

Chemical reactions in cells

Answer 1

• Anabolic reactions → build up complex molecules )simple→ complex)
  
  • Photosynthesis — synthesis of glucose usin CO2 n H2O
  • Formation of glycogen from glucose molecules
• Catabolic reactions → break down complex molecules (complex → simple)
  
  • Oxidation of glucose during respiration to form CO2 n water
  • Deamination of excess amino acids to form urea.

Question 2

Metabolism

Answer 2

The sum of all the chemical reactions within the body of an organism

Question 3

Metabolic waste products:

Answer 3

• CO2 → abnormally high lvl can cause hypercarbia (expires from body)
• Urea → excess amino acids deaminated to form Urea
  
  • Abnormally high conc can cause abdominal pain, nausea, vomiting, irregular heartbeat, muscular cramps
  • Produced in liver, excreted by kidneys
  • Aka waste product of amino acid metabolism in TYS 2014
• Mineral salts or ions
  
  • High lvl → lower wp in blood plasma → water exits tissue cells into blood by osmosis → cells crenated
• Water
  
  • Produced during aerobic respiration
  • High lvl in blood plasma → wp^ →water enters tissue cells, cells swell n burst
  • Metabolic water is water produced by metabolic reactions such as aerobic respiration carried out by cells in the body

Question 4

Excretion

Answer 4

Excretion is the removal of metabolic waste products, toxic substances and substances in excess of the body’s requirements. Excretion is impt to prevent accumulation of metabolic waste products & toxic substances in excess to toxic levels in the body.

Question 5

Ultrafiltration

Answer 5

Ultrafiltration is the process where most of the blood plasma and dissolved substances r forced out of the glomerulus into the bowman’s capsule by high hydrostatic blood pressure.

Question 6

Selective reabsorption

Answer 6

Selective reabsorption is the process where certain substances are reabsorbed from the filtrate back into the blood as they pass through nephrons.

Question 7

Egestion

Answer 7

Egestion is the removal of undigested material from the alimentary canal

Question 8

Osmoregulation

Answer 8

Osmoregulation is The control of water potential and solute concentration (level) in the blood to maintain a constant water potential in the body

Question 9

Osmoreceptors

Answer 9

Osmoreceptors are cells in the hypothalamus that detect changes in blood water potential

Question 10

Journey of urea

Answer 10

Proteins in food → excess amino acids → liver deaminates aa to form urea → diffuse from liver cells into tissue fluid down cg → dissolves into blood plasma → hepatic vein to heart → aorta → renal artery → kidney → being small molecules, r forced out of blood by high hydrostatic blood pressure during ultrafiltration at glomerulus across partially permeable basement membrane → BCap → urea in glomerular filtrate flows along nephron to collecting duct → ureter → urinary bladder → excreted in urine out of body thru urethra.

Question 11

Nephrons

Answer 11

• tiny kidney tubules where urine is formed; basic functional unit of a kidney.
  
  • **Function: - Responsible for urine formation.
• Ultrafiltration occurs at glomerulus + Bowman’s capsule
• Selective reabsorption of useful substances occurs mainly at PCT, and also at DCT, LoH, n CD. Resulting mixture of excess water, mineral salts n nitrogenous wastes pass out of collecting duct into ureter as urine to be stored in bladder.**
  
  • Surrounded by blood vessels connected to the renal artery n renal vein

Question 12

IF: walls of glomerulus leaky, predict 2 ways in which this might alter urine composition.

Answer 12

1. Presence of blood proteins in urine
2. Presence of RBCs in urine

Question 13

Ultrafiltration

Answer 13

1. Afferent arteriole lumen wider than efferent arteriole → high hydrostatic blood pressure by contraction of left ventricle in heart and due to higher resistance to blood flow at the efferent arteriole (narrow lumen) as compared to in glomerulus
2. Blood plasma forced out of glomerular blood capillaries into the Bowman’s Capsule → partially permeable basement membrane around glomerular capillaries filters small soluble molecules → small soluble molecules enter Bowman’s Capsule while large molecules r carried away by efferent arteriole

Filtrate: water and small molecules - (glucose, AA, mineral salts, urea)
- Not filtered out:
- Large molecules (plasma proteins, red/ white blood cells)
- Plasma proteins: fibrinogen, thrombin etc (needed in blood clotting)

Question 14

Adaptations of glomerulus:

Answer 14

• a network of blood capillaries → large SA for filtration process
• BC (blood capillaries) r 1 cell thick + hv tiny pores in capillary wall
• BC covered by thin partially permeable membrane impermeable to large molecules such as blood cells, platelets and proteins.

Question 15

Describe the role of glomerulus and venule.

Answer 15

Ultrafiltration occurs in A: glomerulus to force small substances like glucose, urea and water out of the glomerular capillaries into the Bowman’s capsule. Lumen of efferent arteriole s smaller than the afferent arteriole, high hydrostatic blood pressure forces out small substances out into Bowman’s capsule in ultrafiltration.

B: Venule brings substances that have been selectively reabsorbed along the nephron such as glucose and amino acids to the renal vein and back to the rest of the body.

Question 16

Why are proteins and glucose absent in urine?

Answer 16

Proteins are large molecules, hence it is unable to force through the partially permeable basement membrane of the glomerulus in the Bowman’s capsule during ultrafiltration and stays in the blood, therefore absent in urine.

Glucose are small molecules which can pass thru the partially permeable basement membrane during ultrafiltration into the glomerular filtrate but all glucose will be selectively reabsorbed at the PCT into the blood capillaries by diffusion n AT hence absent in urine.

Question 17

What happens if the length of the afferent arteriole lumen is reduced?

Answer 17

• Reduced or absence of high hydrostatic blood pressure in the glomerulus
• Ultrafiltration is less efficient or reduced
• Rate of urine production is reduced

Question 18

Selective reabsorption process

Answer 18

1. Glucose, AA and salts diffuse into cells lining proximal convoluted tubule by selective reabsorption.
2. All glucose and amino acids molecules will be selectively reabsorbed into the blood capillaries by diffusion and active transport in a healthy individual.
3. Most of the water molecules are reabsorbed by osmosis.

Details:
A. These molecules r actively transported into interstitial fluid (fluid betw cells lining PCT n capillaries)
B. And enters BC via diffusion
1. PCT → tissue fluid (by AT)
2. Tissue fluid → capillary: (by diffusion)

• Waste products passed out of nephron as urine
• > 80% of filtrate reabsorbed at the proximal convoluted tubule

Question 19

Water reabsorption

Answer 19

1. At Loop of Henle, some water is reabsorbed from the filtrate back into blood vessel via osmosis
2. At distal convoluted tubule (fine-tuning process), some salts r reabsorbed back into blood vessel via AT.
3. Blood pH regulated by selectively reabsorbing H+ ions.
4. At collecting duct, some water is reabsorbed back into blood vessel via osmosis
5. Remaining fluid in tubule passes out of collecting duct into renal pelvis to form urine

Question 20

Osmoregulation Answ tech

Answer 20

Loss/ intake of water (thru sweating to remove excess heat from body/drink water) → WP of blood decreases/ ^ -> stimulates hypothalamus in brain → hypothalamus stimulates pituitary gland release more/ less ADH into bloodstream → cells in walls of collecting ducts become more/ less permeable to water → more/ less water reabsorbed from collecting duct into BC →. Smaller/ larger volume & more/ less conc urine produced → WP of plasma returns to normal

Question 21

Describe and explain how reduced secretion of ADH would affect the composition of urine.

Answer 21

When pituitary gland secretes less ADH into the bloodstream → cells in the wall of the collecting ducts become less permeable to water → Less water is reabsorbed from the collecting ducts back into the blood capillaries → a larger volume of urine that is less concentrated is produced

Question 22

Kidney failure

Answer 22

Refers to the inability of the kidney to function properly, causing the accumulation of excretory products in the blood

Question 23

Causes and treatments for kidney failure

Answer 23

• Causes:
  
  • High blood pressure (hypertension)
  • Diabetes
  • Alcohol abuse
  • Severe accidents that cause physical dmg to kidneys
  • Complications from major surgeries
• Treatments:
  
  • Kidney transplant
  • Dialysis

Question 24

Diabetes mellitus

Answer 24

1. Islets of Langerhans in pancreas X secrete enuf insulin
2. Inability to convert excess glucose into glycogen to be stored in liver n muscle tissues
3. When glucose in blood is filtered into glomerular filtrate, not all the glucose can be reabsorbed from the kidney tubules
4. Glucose excreted in urine

Question 25

Dialysis

Answer 25

1. Blood drawn from vein in arm pumped thru tubing in dialysis machine
2. Partially permeable tubing bathed in specially controlled dialysis fluid
3. Small molecules such as urea n metabolic waste products diffuse out of tubing into dialysis fluid. Blood cells, platelets & large molecules remain.
4. Filtered blood returns to patient’s vein

(Conc of urea: blood entering dialysis machine > dialysis fluid out of machine > blood out of dialysis machine > dialysis fluid entering dialysis machine

Question 26

Dialysis fluid vs blood plasma

Answer 26

Similarities:
Contains digested food substances such as glucose, AA and mineral salts. Contains dissolved gases such as O2 and CO2

Differences:

Dialysis fluid: X
Blood plasma: Contains metabolic waste products

Dialysis fluid: Direction of flow opposite to blood plasma

Question 27

Features of a dialysis machine:

Answer 27

• dialysis fluid contains similar conc of essential substances as healthy blood but lacks nitrogenous waste, to prevent diffusion of essential substances out of blood
• Dialysis fluid does not contain metabolic waste products → establish a conc gradient to remove waste products & maintain correct solute composition & wp of blood
• Tubing in machine narrow, long coiled →^SA:V helps to speed up rate of exchange of substances betw patient’s blood n dialysis fluid
• Direction of blood flow is opposite to the flow of dialysis fluid → maintains conc gradient for removal of waste products.
• Dialysis tubing is immersed in dialysis fluid at. 37 DC to initiate heat loss from patient

Question 28

Describe and explain the changes in concentration of urea along the nephron as it passes from the renal arteriole into the urine. [6]

Answer 28

• Urea is transported in blood by the renal arteriole to the kidney to be excreted as metabolic waste products in urine [1]
• Glomerulus – urea molecule is small enough to pass through the partially permeable basement membrane to form part of the filtrate in the Bowman’s capsule through the process of ultrafiltration. [1]
• Concentration of urea in the filtrate increases as it moves through the nephron[1]
• Proximal convoluted tubule - Most of the water in the filtrate is selectively reabsorbed back into blood via osmosis but not urea, thus the filtrate becomes more concentrated in urea and lesser in volume. [1]
• Loop of Henle and distal convoluted tubule – some water and mineral salts are reabsorbed back into the blood, the filtrate becomes more concentrated with urea [1]
• Collecting duct – the effect of ADH can stimulate more / less water being reabsorbed into the blood, causing the final urine formed to be more / less concentrated in urea. [1]

Question 29

Explain why there is no glucose and protein present in the urine of a normal individual. [4]

Answer 29

• Protein molecules are too large [1] to pass through the partially permeable
  basement membrane at the glomerulus during ultrafiltration and are not
  filtered from the blood [1]
• Glucose molecules are small enough to pass through the partially
  permeable basement membrane at the glomerulus to be filtered during
  ultrafiltration into the Bowman’s capsule. [1]
• Selective reabsorption took place and all glucose molecules are
  selectively reabsorbed into the blood capillaries at the proximal
  convoluted tubule via active transport. [1]

Question 30

Explain how eating salty food would affect the composition of the urine.[6]

Answer 30

• Increase in salt concentration decreases water potential in blood plasma [1]
  Detected by hypothalamus which produce more ADH and stimulate
  pituitary gland to release more ADH. [1]
• Anti-diuretic hormone (ADH) increases the permeability of the collecting
  duct to water [1] and increases water reabsorption into the blood
  capillaries. [1]
• Hence decreasing the volume of water in urine produced and the urine is
  more concentrated with urea. [1]
• Excess salts which are not reabsorbed will also make up the concentrated
  urine. [1]

Question 31

Describe how the dialysis machine functions in the removal of metabolic waste products from the patient. [4]

Answer 31

1. Blood is drawn from a vein in the patient’s arm and pumped through a long dialysis tubing in the dialysis machine which separates the blood and the dialysis fluid, to increase surface area for faster diffusion to take place.
2. The dialysis tubing is bathed in dialysis fluid which contains similar concentrations of glucose, amino acids and other essential substances as blood to prevent net movement of useful substances out of blood via diffusion. [1]
3. Urea and other metabolic waste products diffuse out of the tubing down the steep concentration gradient from blood into the dialysis fluid as there are no metabolic waste products in dialysis fluid. [1]
4. Blood cells, platelets and big molecules (plasma proteins) stay in the tubing as they are too big to pass through the pores of the partially permeable membrane. [1]
5. Dialysis fluid flows in the opposite direction of blood to maintain constant steep diffusion / concentration gradient. [1]

Question 32

Compare and contrast between dialysis and kidney function. [6]

Answer 32

Similarities:

• Both involves partially permeable membrane to allow small molecules to filter/ pass through [1]
• Both help in the removal of metabolic waste products such as urea. [1]

Differences:
Movement of substances
D: Involves diffusion only
K: Involves diffusion and active transport

Processes:
D: Does not involve ultrafiltration and selective reabsorption.
K: Involves ultrafiltration and selective reabsorption.

Pressure
D: Pressure provided by dialysis machine.
K: Pressure provided by the left ventricle of heart & difference in diameter of lumen of efferent
arteriole and afferent
arteriole.

Hormones
D: Does not involve any hormones.
K: Involves ADH regulation

Fluid
D: Dialysis fluid is needed.
K: Dialysis fluid not required. Only
involved glomerular filtrate.

Urine concentration
D: Cannot produce more concentrated/diluted urine
K: Can produce more concentrated/
diluted urine

Transport mechanism
D: Involves concentration gradient for diffusion to occur
K: Use hydrostatic pressure during
ultrafiltration to force out the filtrate

Question 33

Describe how the break down product of amino acids is transported from the site of production to the site of removal in the human body. [5]

Answer 33

• Excess amino acids are deaminated in the liver cells to produce urea [1]which diffuse from the liver cells into the tissue fluid down the concentration gradient and dissolve into blood plasma. [1]
• The dissolved urea is transported into the heart by veins and out of the heart to the kidneys. [1]
• Urea being small molecules are forced out of the blood by high
  hydrostatic blood pressure during ultrafiltration at the glomerulus across a partially permeable basement membrane into the Bowman’s capsule. [1]
• Urea in the glomerular filtrate then flows along the kidney tubules/ nephron to the collecting duct and into the ureter to the urinary bladder and discharged in urine out of the body through the urethra. [1]

Question 34

Explain the change in the concentration of proteins between the blood plasma in the renal artery and the fluid in the nephron. [1]

Answer 34

High protein concentration in blood plasma in renal artery and no proteins in the
fluid of nephron and collecting duct as proteins are large molecules, which
cannot pass through the partially basement permeable membrane. [1]

Question 35

Compare the concentration of sodium ions at collecting duct and at loop of Henle in Figure 6.2 and give a reason for your answer [1]

Answer 35

Concentration of sodium ions at Z is higher than at Y because water has been
reabsorbed by selective absorption from the filtrate using osmosis (same or slightly reduced amount of sodium ions in a smaller volume of water). [1]
Or
Concentration of sodium ions at Z is lower than at Y because sodium ions needed by
the body are reabsorbed by selective reabsorption from the filtrate using active
transport and diffusion. [1]

Question 36

Suggest what would happen if the dialysis solution is not changed after five hours. [1]

Answer 36

No concentration gradient between blood and
dialysis solution, no net movement of nitrogenous
waste from the body to the cavity after 5 hours. [1]