Excretion in Humans

Question 1

What is anabolism?

Answer 1

Chemical reactions where simple substances are built up into more complex ones

Question 2

What is catabolism?

Answer 2

Chemical reactions in which complex substances are broken down into simpler ones

Question 3

What is metabolism?

Answer 3

The sum of all chemical reactions in the body

Question 4

When is water formed during metabolism?

Answer 4

1. Cellular respiration
2. Condensation reactions

Question 5

When are salts produced during metabolism?

Answer 5

Reactions between acids and bases (eg. stomach to intestines)

Question 6

What are the 3 main types of nitrogenous wastes?

Answer 6

1. Urea
2. Uric acid
3. Creatinine

Question 7

Why is excretion necessary?

Answer 7

To ensure that metabolic wastes and toxic substances do not accumulate to a level that becomes harmful to our body.

Question 8

Describe the structure of the kidneys

Answer 8

• Two main regions, renal cortex (outer( and renal medulla (inner)
• In the renal medulla there are renal pyramids
• In the kidney there are also numerous nephrons, spanning between the medulla and the cortex
• There are two blood vessels to the kidney, the renal artery and vein
• The kidney also connects to the ureter that is a tube leading to the bladder

Question 9

Describe the structure of a nephron

Answer 9

1. Bowman’s capsule: Cup like structure, found in outer region of kidney
2. Glomerulus: A knot of blood capiliaries in the Bowman’s capsule
3. Afferent arteriole: Small branch of the renal artery that carries blood into the glomerulus
4. Efferent arteriole: Transports blood away from the glomerulus
5. Proximal convoluted tubule: Convoluted tubule that straightens out into the medulla
6. Loop of Henle: U shaped portion that extends deeper into the medulla and back into the cortex
7. Distal convoluted tubule: Tubule that enters into the medulla again and becomes convoluted again
8. Collecting duct: Several nephrons open and empty their contents into the collecting duct which connects to the ureter

Question 10

What are the two processes of urine formation?

Answer 10

1. Ultrafiltration
2. Selective reabsorption

Question 11

Describe the process of ultrafiltration

Answer 11

1. High blood pressure in the glomerulus: afferent arteriole wider than efferent arteriole, creates high blood pressure known as hydrostatic pressure–> forces blood plasma out of glomerulus and into Bowman’s capsule
2. Selectively permeable membrane of the basement membrane that wraps around the glomerulus only allows small molecules like water, glucose, amino acids, urea and others to pass through.
3. These form the glomerular filtrate that enter the Bowman’s capsule while larger particles remain in the glomerulus and pass into the efferent arteriole

Question 12

Describe the process of selective reabsorption

Answer 12

1. The recovery of essential substances from glomerular filtrate
2. In the proximal convoluted tubule, all glucose and amino acids, most water and mineral salts are reabsorbed via diffusion, osmosis and active transport into the surrounding blood capiliaries and transported out of the kidney through the renal vein (80% of filtrate reabsorbed here)
3. In the loop of Henle some water is reabsorbed
4. In the distal convoluted tubule some salts and water is reabsorbed
5. In the collecting duct, some water is reabsorbed
6. Substances that remain in the tubule (urea, uric acid, creatinine, excess water) will then be excreted as urine

Question 13

What substances can be found in healthy urine?

Answer 13

Urea, uric acid, creatinine, excess water and mineral salts

Absolutely no glucose, proteins,

Question 14

Define

Osmoregulation

Answer 14

The control of water potential and solute concentration in the body to maintain a relatively constant water potential in the body

Question 15

How does osmoregulation take place in the body?

Answer 15

Low water potential in body
1. Osmoreceptors in the hypothalamus monitor the water potential of the blood
2. Antidiuretic hormones (ADH) is produced in the hypothalamus and released by the pituitary gland (below the hypothalamus)
3. ADH increases water reabsorption by increasing the permeability of kidney tubules to water in 2 regions: distal convoluted tubule and collecting duct

Vice versa for high water potential

Question 16

What are some causes of kidney failure?

4 causes

Answer 16

1. Medical conditions (high blood pressure, diabetes etc)
2. Heavy alcohol consumption
3. Bacterial infection
4. Major surgery or injury to the kidneys

Question 17

What are some symptoms of kidney failure?

2 symptoms

Answer 17

1. Decreased urine output
2. Fluid retention, causing swelling in legs, ankles or feet

Question 18

What treatment options are there for kidney failure?

Answer 18

1. Kidney transplant
2. Dialysis

Question 19

What is the function of dialysis and how does it work?

Answer 19

A dialysis machine mimics the function of the kidneys. It cleans the patient’s blood from metabolic waste products and toxins

1. Blood is drawn from a vein and pumped through a dialysis machine
2. Dialysate is pumped into the machine as well
3. The tubing wall -that the blood is within- is partially permeable, allowing small molecules (such as the waste products) to diffuse out of the tubing and into the dialysate while large molecules remain
4. The dialysate with the waste products is drained out of the machine and filtered blood is returned to the vein in the patient’s arm.

Question 20

What are some features of a dialysis machine?

4 features

Answer 20

1. Same concentration of essential substances in dialysate and blood; no net movement of essential substances
2. Absence of metabolic waste products in dialysate; creates a steep concentration gradient for waste products to diffuse out of the blood
3. Tubing of dialysis machine is long, narrow and coiled; increase SA:V ratio, rate of exchange of substances
4. Countercurrent flow in dialysis machine; direction of blood flow opposite to flow of dialysate; creates a larger portion of machine with a steeper concentration gradient

Question 20

How does solute concentration affect blood pressure?

Answer 20

1. If there is a high solute concentration; there will be a low water potential, hence water will diffuse in by osmosis and increase the volume of blood, increasing blood pressure
2. If there is a low solute concentration, there will be a high water potential, hence water will diffuse out by osmosis and decrease the volume and fluidity of blood, decreasing blood pressure and efficiency of flow

Question 20

What causes kidney stones?

Answer 20

• Chemicals are found in high concentration in urine, may form crystals.
• These crystals can grow into larger stones and make their way through the urinary tract
• If they get stuck, it can cause pain

Question 20

What are symptoms of kidney stones?

4 symptoms

Answer 20

1. Feeling of intense need to urinate
2. Urinating more often
3. Burning feeling during urination
4. Urine that is dark or red due to blood

Question 20

What are some treatments for kidney stones?

3 treatments

Answer 20

1. Wait for it to pass
2. Surgery
3. Shock wave lithotripsy

Question 21

How does high blood pressure cause kidney failure to occur?

Answer 21

With high blood pressure, the amount of pressure exerted by the afferent arteriole is very high onto the capiliaries of the glomerulus. The capiliaries cannot withstand so much pressure and rupture, disrupting blood flow into the nephron.