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Biology - Module 5 > 5.1.2 - Excretion as an example of homeostatic control > Flashcards

5.1.2 - Excretion as an example of homeostatic control Flashcards

1
Q

What does excretion mean?

A

The process of removing metabolic waste products from the body

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2
Q

Which products are removed via excretion?

A
  • Carbon dioxide
  • Bile pigment
  • Nitrogenous waste
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3
Q

What are the 3 blood vessels connected to the liver?

A
  • Hepatic artery
  • Hepatic portal vein
  • Hepatic vein
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4
Q

What does the hepatic artery do?

A

Supplies oxygenated nutrient poor blood from the heart

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5
Q

What does the hepatic portal vein do?

A

Supplies deoxygenated nutrient rich blood from the digestive system

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6
Q

What does the hepatic vein do?

A

Carries deoxygenated blood out of the liver and to the heart

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7
Q

What is the liver primarily made up of?

A

Hepatocytes

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8
Q

What are hepatocytes surrounded by?

A

Capillaries called sinusoids

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9
Q

What are sinusoids connected to?

A
  • Hepatic artery
  • Hepatic portal vein
  • Central vein
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10
Q

What does the central vein do?

A

Connects to hepatic vein

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11
Q

What are the 3 functions of the liver?

A
  • Stores glycogen which helps control blood glucose levels
  • Breaks down toxic substances such as alcohol
  • Breaks down excess amino acids
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12
Q

How does the liver break down excess amino acids?

A

It removes the amine group from an amino acid in a process called deamination and converts this amine group into ammonia. The remainder of the amino acid is used in respiration.

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13
Q

How is urea formed?

A

Ammonia is highly toxic and highly soluble in blood so the liver combines it with carbon dioxide to form urea which is less toxic and soluble using a series of reactions called the Ornithine cycle. Once urea is produced it is excreted in urine.

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14
Q

What is the main role of the kidneys?

A

To filter blood and produce urine which removes harmful waste products and controls the water potential of the blood (osmoregulation)

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15
Q

What is the structure of a nephron?

A
  • Glomerulus
  • Bowman’s capsule
  • Proximal convoluted tubule
  • Loop of Henle
  • Distal convoluted tubule
  • Collecting duct
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16
Q

What is the glomerulus?

A

A mass of blood capillaries and it is supplied blood by the afferent arteriole.

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17
Q

What does the efferent arteriole do?

A

Carries blood away from the glomerulus and branches into a network of capillaries that surround the rest of the nephron which ensures the whole structure has a short diffusion pathway to the blood.

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18
Q

What is the first step of water being absorbed into the nephron?

A

Ultrafiltration

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19
Q

Where does ultrafiltration take place?

A

Glomerulus and Bowman’s capsule

20
Q

What happens during ultrafiltration?

A
  • The difference in diameters between the afferent and efferent arterioles causes high hydrostatic pressure in the glomerulus
  • This forces water, urea and other small substances (glucose and ions) to pass through gaps in the capillary’s endothelium, the basement membrane and podocytes forming glomerular filtrate
21
Q

What is the second step of water being absorbed into the nephron?

A

Selective reabsorption

22
Q

Where does selective reabsorption take place?

A

Proximal convoluted tubule

23
Q

What happens during selective reabsorption?

A
  • Sodium ions in the epithelial cell are actively transported into the blood
  • Sodium ions and other substances in the tubule lumen are then transported into the epithelial cell via facilitated diffusion using co-transport proteins
  • These substances then travel down their concentration gradient into the blood
  • Water is transported into the blood by osmosis
24
Q

What adaptations does the proximal convoluted tubule have?

A
  • Epithelial cells contain mitochondria to produce ATP for active transport
  • Membrane contains a large number and variety of co-transport proteins
  • Microvilli increase the surface area for diffusion
  • Short diffusion distance through one epithelial cell
25
Q

What happens in the loop of Henle?

A
  • In the ascending limb sodium ions are actively pumped from the filtrate into the medulla
  • This creates a water potential gradient and causes water to pass out of the descending limb via osmosis
  • In the medulla sodium ions and water are reabsorbed into the blood
  • This loss of sodium ions causes the water potential of the filtrate to gradually increase up the ascending limb
  • The loss of water causes the water potential of the filtrate to gradually decrease down the descending limb
  • This countercurrent mechanism maintains the water potential gradient along the length of the loop of Henle
26
Q

How does the loop of Henle vary in length for organisms with limited access to water?

A

The loop is longer meaning the water potential gradient is maintained for a longer distance which allows more water to be reabsorbed giving more concentrated urine

27
Q

What happens in the distal convoluted tubule and the collecting duct?

A

Water is reabsorbed into the blood depending on the permeability of the structures.

28
Q

What do osmoreceptors do?

A

Detect changes in the blood’s water potential and produce ADH

29
Q

Where are osmoreceptors found?

A

In the hypothalamus

30
Q

Where is ADH stored?

A

In the posterior pituitary gland

31
Q

What happens when the blood water potential decreases?

A
  • Osmoreceptors detect the decrease
  • They stimulate the posterior pituitary gland to release more ADH
  • This increases the reabsorption of water by increasing the distal convoluted tubule and collecting duct’s permeability to water
  • This increases the blood water potential and produces a smaller volume of more concentrated urine
32
Q

What happens when the blood water potential increases?

A
  • Osmoreceptors detect the increase
  • They reduce stimulation of the posterior pituitary gland so it releases less ADH
  • This decreases the reabsorption of water by decreasing the distal convoluted tubule and collecting duct’s permeability to water
  • This decreases the blood water potential and produces a larger volume of less concentrated urine
33
Q

What are the 3 main uses of urine samples?

A
  • Pregnancy tests
  • Drug tests
  • Medical diagnosis
34
Q

How are urine samples used in pregnancy tests?

A
  • Pregnant women produce a hormone called hCG
  • This hormone enters the urine and pregnancy tests give a positive result if they detect hCG
  • The tip of the pregnancy test contains monoclonal antibodies attached to coloured beads and these antibodies are all complementary to hCG
  • The sample of urine is taken at the tip and it moves across the length of the strip
  • As it passes through the section with antibodies any hCG in the sample binds to the antibodies
  • The next zone contains immobilised antibodies which are also complementary to hCG so the hCG antibody complexes bind to these as well and stop here creating a blue line
  • Antibodies that aren’t bound to hCG move further down to a zone containing immobilised antibodies that are complementary to the unbound antibodies so these 2 antibodies bind together and this produces a 2nd line which is the control line showing that the test is working correctly
35
Q

How are urine samples used in drug tests?

A
  • In the body many drugs are broken down into substances that are excreted in urine
  • Some of these substances can be identified using complementary antibodies and others are tested using gas chromatography
  • Gas chromatography involves turning the urine into a gas to separate and identify the different substances in it
36
Q

What is an example of a class of drugs identified using gas chromatography?

A

Anabolic steroids which are taken to increase muscle mass

37
Q

How are urine samples used in medical diagnosis?

A
  • A high level of glucose in the body can diagnose diabetes
  • The presence of nitrites can diagnose a bacterial infection
  • A lack of toxic substances such as urea can indicate kidney damage
38
Q

What is the glomerular filtration rate?

A

The rate at which they filter the blood

39
Q

How does kidney failure affect the glomerular filtration rate?

A

It decreases the GFR

40
Q

How is the glomerular filtration rate estimated?

A

By measuring the concentration of creatine in the blood which is a waste substance used by the muscles that is normally excreted in the urine. Therefore a high concentration of creatine suggests the blood isn’t being filtered effectively which could indicate kidney damage

41
Q

What are the factors affecting the glomerular filtration rate?

A
  • It declines with age
  • Men generally have more creatine in their blood than women which is because they tend to have a higher muscle mass
42
Q

How does kidney failure affect the electrolyte balance?

A

The concentrations of ions and charged compounds are not maintained meaning there may be excess potassium ions in the body and incorrect sodium ion levels

43
Q

What are the 2 types of dialysis?

A

Haemodialysis and peritoneal dialysis

44
Q

How does haemodialysis work?

A
  • They pass the patient’s blood through a dialysis machine
  • This machine contains an artificial partially permeable membrane that separates the blood from the dialysis fluid
  • This fluid has a similar composition to blood but it doesn’t contain urea which ensures glucose doesn’t diffuse out but that urea does
  • To make sure all of the urea is removed the blood and dialysis fluid move in opposite directions which maintains a concentration gradient along the length of the machine
45
Q

How does peritoneal dialysis work?

A
  • Takes place inside the body and the dialysis fluid is inserted into the stomach
  • Substances are exchanged through the lining of the abdomen which is called the peritoneal membrane
46
Q

What are the advantages of kidney transplants as a treatment for kidney failure?

A
  • The patient doesn’t have to go through dialysis which can have bad side effects
  • This makes the treatment less expensive and the transplanted kidney can last for years
47
Q

What are the disadvantages of kidney transplants as a treatment for kidney failure?

A
  • There aren’t enough donors for transplants
  • There is the risk that the patient’s body may reject the donor kidney
  • Immunosuppressants increase the patient’s susceptibility to other diseases

Biology - Module 5 (7 decks)

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