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A Level Biology > Module 5 - Homeostasis and Excretion > Flashcards

Module 5 - Homeostasis and Excretion Flashcards

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1
Q

What is excretion?

A

The removal of metabolic waste products from the body e.g. urea, urine and Carbon dioxide.

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2
Q

What are the 3 main metabolic waste products in mammals?

A
  • Carbon dioxide
  • Bile pigments
  • Nitrogenous waste products (urea)
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3
Q

Where is Carbon Dioxide produced as metabolic waste?

A

It is a product of respiration which is excreted from the lungs.

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4
Q

Where are bile pigments produced as metabolic waste?

A

Formed from the breakdown of haemoglobin from old red blood cells in the liver. They are excreted from the liver into the small intestine via the gall bladder and bile duct. They colour faeces.

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5
Q

Where is Nitrogenous waste products (urea) produced as a waste product?

A

Formed from the breakdown of excess amino acids by the liver. All mammals produce urea as their nitrogenous waste. Fish produce ammonia while birds and insects produce Uris acid. Urea is excreted by the kidneys in the urine.

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6
Q

What are the roles of the liver?

A
  • Involved in homeostasis
  • stores glycogen
  • can form less toxic substances for, highly toxic substances in the body (detoxification)
    • assimilation, maintaining levels in blood.
  • process nutrients absorbed from the small intestine
  • secretes bile into small intestine
  • rich in blood supply
  • carbohydrate metabolism
  • Deamination (breakdown) of amino acids
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7
Q

What is another word for a liver cell?

A

Hepatocyte

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8
Q

Describe 3 features of a hepatocyte

A
  • Large nucleus
  • Prominent Golgi apparatus
  • Lots of mitochondria (metabolically active)
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9
Q

Describe the rate of replication of a hepatocyte?

A

Can regenerate very quickly

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10
Q

Where does blood arrive into the liver from? (in what proportion)

A
  • Hepatic portal vein (75% of blood supply + assimilates)
  • Hepatic artery (25%)
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11
Q

Where does the hepatic portal vein travel from?

A

Travels from stomach, small intestine and spleen

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12
Q

Where does the hepatic artery travel from?

A

From heart

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13
Q

What is the difference between the hepatic portal vein and the hepatic artery?

A

Hepatic portal vein contains assimilates whereas the hepatic artery doesn’t.

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14
Q

What is a sinusoid?

A

Area where blood from the hepatic portal vein and hepatic artery mix - this takes place in order to increase oxygen content.

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15
Q

What is the role of Kuppfer cells?

A
  • Protect against disease (act as macrophages)
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16
Q

Where are Kuppfer cells located?

A

Located in Sinusoids

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17
Q

What travels to the gall bladder that is produced by hepatocytes?

A

Bile carried in a bile canaliculus

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18
Q

What type of blood does the hepatic portal vein and hepatic artery deliver to the liver?

A

Oxygenated blood

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19
Q

Describe how the body responds to an increase in blood glucose levels?

A
  • Increase in blood glucose levels
  • Insulin is released from the pancreas
  • Glucose is converted to glycogen
  • Blood glucose levels return to homeostatic levels
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20
Q

Describe how the body responds to a decrease in blood glucose levels?

A
  • Decrease in blood glucose levels
  • Glucagon is released from the pancreas
  • Glycogen is converted back to glucose
  • Blood glucose levels return to homeostatic levels
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21
Q

Where can glycogen be stored?

A

In hepatocytes, in the liver

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22
Q

What two processes take place in the liver?

A
  • Deamination
  • The Ornithine cycle
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23
Q

What is deamination?

A

Amino acids cannot be stored. Excess Amino Acids are Deaminated in the liver. The removal of the amine group

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24
Q

Describe the word formula of deamination

A

Amino Acid + Oxygen ——> ammonia + keto acid

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25
Q

Describe what happens to amino acids during deamination

A
  • Enzyme causes removal of the amine group along with the hydrogen.
  • Simultaneous oxidation of the remainder of the molecule.
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26
Q

What are the 2 products of deamination?

A
  • Ammonia
  • Keto acid
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27
Q

What is ammonia (include chemical formula)

A

Highly toxic and highly soluble substance
- NH3

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28
Q

Where can keto acid be used?

A

Used in respiration

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29
Q

Describe the formula of an amino acid

A

R
I
NH2 — —-C—- —COOH
I
H

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30
Q

What is the chemical formula of ammonia?

A

NH3

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31
Q

What is the chemical formula of keto acid?

A

R
I
C - COOH
II
O

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32
Q

What is the Ornithine cycle?

A

The production of urea from ammonia.
- Ammonia is highly toxic and soluble and can damage the brain if it accumulates. Therefore it is converted to urea and transported to the kidney for excretion in the urine.

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33
Q

Describe the word equation for the Ornithine Cycle.

A

Ammonia + Carbon dioxide —> Urea + water

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34
Q

Describe the chemical formula for the Ornithine cycle

A

2NH3 + CO2 —> CO(NH2)2 + H2O

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35
Q

Describe the role of Ornithine in the ornithine cycle

A
  • Ornithine is present
  • Ammonia and CO2 is added to Ornithine making citrulline.
  • Urea is then removed forming arginine.
  • Water is then removed forming Ornithine
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36
Q

What is detoxification?

A

The breakdown of toxins produced in the body, which may be produced as a result of metabolic activity.

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37
Q

What are examples of toxins that people choose to put in their bodies?

A
  • Alcohol
  • Other drugs
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38
Q

What is an example of a breakdown of a toxin?

A
  • The breakdown of hydrogen peroxide, a by-product of metabolic activity.
  • This takes place as hepatocytes contain the enzyme catalase, that splits hydrogen peroxide into oxygen and water.
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39
Q

What is homeostasis?

A

Maintaining optimum internal conditions, despite changes in the external environment.

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40
Q

What does Homeostasis control?

A
  • Body temperature
  • Composition of blood (e.g. glucose, concentration of minerals & ions).
  • pH levels
  • urea & CO2 - being expelled from the body
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41
Q

Describe the process of a positive feedback.

A

Change detected. <-
I I
I I
I I
Response reinforces change I
I I
I I
I I
Conditions change ————— I

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42
Q

What are examples of positive feedback cycles?

A
  • Hypothermia
  • Child birth (hormone called ‘oxytocin’ released causing contraction, building up faster and faster until contractions are fast for the birth to take place
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43
Q

Describe the negative feedback cycle?

A

Ideal conditions - increase detected - responses lower levels - ideal conditions restored

Ideal conditions - decrease detected - responses raise levels - ideal conditions restored

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44
Q

What are examples of negative feedback cycles?

A
  • Blood glucose levels
  • Body temperature
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45
Q

What is an endotherm

A

Animals that maintain a fairly stable internal body temperature through primary internal physiological mechanisms (birds mammals)

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46
Q

What is an ectotherm?

A

Animals that rely on heat sources outside their body to regulate temperature (fish, amphibians, reptiles, invertebrates).

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47
Q

What types of animals are endotherms?

A

Birds and mammals

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48
Q

What types of animals are ectotherms?

A

Fish, amphibians, reptiles, invertebrates

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49
Q

What are behavioural responses ectotherms use to warm up?

A
  • Basking/exposing themselves in the Sun - orienting their bodies to face the sun to receive maximum exposure to the sun.
  • Pressing their bodies against the warm ground
  • Endothermic metabolic reaction - e.g. muscle contraction and vibration, to increase cellular metabolism.
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50
Q

What are behavioural responses ectotherms use to cool down?

A
  • Shelter from the sun by seeking shade.
  • Press their bodies against cool surfaces, or move into available mud or water.
  • Orientate their bodies to have minimal exposure to the sun.
  • Reduce the level of movement to reduce the levels of metabolic heat being generated.
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51
Q

What are physiological responses do ectotherms carry out to affect their body temperature?

A
  • Dark colours absorbs more radiation, therefore colder climates may have animals that have darker skin than in warm climates.
  • Some ectotherms can alter their heart rate to increase/decrease their metabolic rate.
52
Q

What type of feedback cycle controls body temperature in endotherms?

A
  • Negative
53
Q

Describe the process of restoring homeostatic temperatures after after a rise in core temperature.

A
  • Rise in temperature
  • Thermoregulatory centre in hypothalamus detects change
  • Nervous system and hormonal system carry signals to skin, liver and muscles.
  • Less heat generated and more heat lost.
  • Temperature falls
54
Q

Describe the process of restoring homeostatic temperatures after after a fall in core temperature.

A
  • Fall in temperature
  • Thermoregulatory centre in hypothalamus detects change
  • Nervous system and hormonal system carry signals to skin, liver and muscles
  • More heat generated and less heat lost
  • Temperature rises
55
Q

What changes in the body takes place when there is a rise in temperature?

A
  • Vasodilation
  • Increased sweating
  • Reducing the insulating effect of hair/feathers
56
Q

What changes in the body takes place when there is a fall in temperature?

A
  • Vasoconstriction
  • Decreased sweating
  • Shivering
  • Raising the body hair or feathers
57
Q

How does vasodilation reduce body temperature?

A
  • Arterioles near the surface of the skin dilate.
  • The arteriovenous vessels constrict.
  • This forces the blood through the capillary network, close to the surface.
  • Heat is then lost as blood cools.
58
Q

How does increased sweating reduce body temperature?

A

The sweat on the skin’s surface will cool the blood, which will be closer to the surface due to vasodilation.

59
Q

How does reducing the insulating effect of hairs/feathers reduce body temperature?

A
  • Erector pili muscles relax, meaning that hairs/feathers lay flat.
  • This avoids trapping an insulating layer of air.
60
Q

How does vasoconstriction lead to an increase in body temperature?

A
  • The arterioles near the surface of the skin constrict. The arteriovenus vessels dilate so there is low levels of blood flow through capillaries.
  • This means that not much blood is close to the surface and looses heat via radiation.
61
Q

How does decreased sweating lead to an increase in body temperature?

A

As the core temperature falls, rates of sweating decrease and sweat production will stop entirely. This greatly reduces cooling by the evaporation of water from the surface of skin, although some evaporation from the lungs still continue.

62
Q

How does shivering lead to an increase in body temperature?

A

As the temperature falls, the body may begin to shiver. This is the rapid, involuntary contracting and relaxing of the large involuntary muscles in the body. The metabolic heat from the exothermic reactions warm up the body.

63
Q

How does raising the body hair/feathers lead to an increase in body temperature?

A
  • As body temperature falls, the erector pilli muscles in the skin contract, pulling the hair/feathers of the animal erect. This traps an insulating layer of air and so reduces cooling through the skin.
64
Q

What are 3 advantages of being an endotherm?

A
  • Can maintain a stable body temperature
  • Can live in different climates
  • Remains active even at low temperatures
65
Q

What are 3 disadvantages of being an endotherm?

A
  • High energy demand - more need for food (more metabolic activity)
  • Higher risk of overheating
66
Q

What are 3 advantages of being an ectotherm?

A
  • Low energy demand - less need for food
  • Can survive for longer without food
  • More energy can get put towards growth
67
Q

What are disadvantages of being an ectotherm?

A
  • Has to rely on the environment for heat
  • Can’t live in some climates
  • Less active in cool temperatures
  • Higher risk from predators
  • Can’t take advantage of food
68
Q

What are 2 types of thermoreceptors?

A
  • Core thermoreceptors in hypothalamus (detect blood temperature)
  • Peripheral thermoreceptors in skin (detect external temperature)
69
Q

Where are core thermoreceptors located?

A

Hypothalamus

70
Q

How does core thermoreceptors detect changes in temperature?

A

Detect blood temperature

71
Q

Where are peripheral thermoreceptors located?

A

Skin

72
Q

What are the different parts of the kidney?

A
  • Renal cortex
  • Renal medulla
  • Renal Pelvis
  • Renal Artery
  • Renal vein
  • Ureter
73
Q

Describe the journey of different parts of a nephron

A
  • Bowman’s capsule
  • Proximal Convoluted Tubule
  • Descending Limb
  • Loop of Henle
  • Thick Ascending Limb
  • Distal convoluted tubule
  • Collecting duct
74
Q

What is the Bowman’s structure?

A

Cup-shaped structure that contains the glomerulus, a tangle of capillaries. More blood goes into the glomerulus than leaves it, due to the ultrafiltration process that takes place.

75
Q

What is the proximal convoluted tubule?

A

The first coiled region of the tubule after the Bowman’s capsule, found in the cortex of the kidney. This is where many of the substances needed by the body are reabsorbed into the blood.

76
Q

What is the Loop of Henle?

A

A long loop tubule that creates a region with a very high solute concentration in the tissue fluid deep down in the kidney medulla. The descending loop runs from the cortex through the medulla to a hairpin at the bottom of the loop. The ascending limb travels back up through the medulla to the cortex.

77
Q

What is the distal convoluted tubule?

A

A second twisted tubule where the fine-tuning of the water balance of the body takes place. The permeability of the walls to water vary in response to the levels of ADH (Antidiuretic Hormone) in the blood. Further regulation of the ion balance and pH of the blood also takes place in the tubule.

78
Q

What does ADH do?

A

Affect the permeability of the walls of the distal convoluted tubule and collecting duct

79
Q

What is the collecting duct?

A

The urine passes down the collecting duct through the medulla to the pelvis. More fine-tuning of the water balance takes place - the walls of this part of the tubule are also sensitive to ADH.

80
Q

Describe the stages of ultrafiltration

A

Lumen of capillary
I
Capillary endothelium
I
Basement membrane
I
Bowman’s capsule epithelium (made of podocytes)
I
Lumen of Bowman’s Capsule

81
Q

What is the role of capillary endothelium in ultrafiltrarion?

A

The Glomerulus is supplied with blood by a relatively wide afferent (incoming) arteriole from the renal artery. The blood leaves through a narrower efferent (outward) arteriole and as a result there is considerable pressure in the capillaries of the glomerulus. This forces the blood out through the capillary wall - which is one cell thick - and acts like a sieve.

82
Q

What is the role of the Basement Membrane in ultrafiltration?

A

-Main filtration mechanism
- Fluid passes through the basement membrane. It is made up of a network of collagen fibres and other proteins that make up a second ‘sieve’. Most of the plasma contents can pass through the basement membrane but blood cells and many proteins are retained in the capillary because of their size.

83
Q

What is the role of Bowman’s capsule epithelium?

A
  • Contains podocytes that have extensions called ‘pedicels’ which wrap around the capillaries, forming slits that prevent any cells, platelets or large plasma proteins that get through capillary endothelium and basement membrane from entering the tubule.
84
Q

What is the glomerular filtration rate?

A

The volume of blood that is filtered through the kidney in a given time.

85
Q

Describe how effective ultrafiltration is?

A

The filtrate which enters the capsule contains glucose, salt, urea, and many other substances in the same concentrations as they are in the blood plasma. The process is so efficient that up to 20% of the water and solutes are removed from the plasma as it passes through the glomerulus.

86
Q

What % of filtrate is reabsorbed in the proximal convoluted tubule?

A

85%

87
Q

What is reabsorbed in the PCT (Proximal Convoluted Tubule)?

A
  • Glucose
  • Amino Acids
  • Some salts
  • Some water
88
Q

Describe the process of the reabsorption of glucose

A
  1. Sodium ions (Na+) are transported by a Na+/K+ pump using energy from ATP, out of the Proximal Convoluted Tubule (PCT) epithelium, across the basal membrane.
  2. Lower Na+ concentration inside the PCT epithelium.
  3. Na+ concentration gradient from PCT lumen to the PCT epithelium.
  4. Na+ diffuses from the lumen of PCT into the PCT epithelium via a cotransport protein - glucose comes with it (even against concentration gradient).
  5. Glucose diffuse down concentration gradient across the basal membrane via a carrier protein.
  6. Water follows down water potential by osmosis.
  7. There are many mitochondria to provide energy for Na+ to be actively transported.
89
Q

What is the role of the loop of Henle?

A

Facilitate the production of urine that is more concentrated than the blood.

90
Q

The loop of Henle acts as a counter-current multiplier - what does this mean?

A

The fluid in the medulla is increasingly concentrated (lower potential) compared to the filtrate in the nephron.

91
Q

What is the purpose of having a more concentrated area in the medulla compared to the cortex?

A

Facilitates reabsorption of water in the collecting duct.

92
Q

What happens at the descending limb at the Loop of Henle?

A
  • Water moves out of the nephron by osmosis
  • Water moves into surrounding capillaries
  • No active transport of Na+/Cl-
93
Q

What happens at the ascending limb of the Loop of Henle?

A
  • Na+/Cl- pumped out (active transport)
  • Walls are impermeable to water so none can follow by osmosis
  • Fluid left in nephron becomes more dilute, tissue fluid develops high concentration/low water potential
94
Q

What is ADH?

A

Antidiuretic hormone

95
Q

What does ADH do?

A

Increase permeability of distal convoluted tubule and collecting duct

96
Q

How does ADH increase the permeability of the distal convoluted tubule and collecting duct walls?

A

ADH travels in the blood from the pituitary gland to the collecting duct.
- It binds to receptors on the cell membrane
- This triggers the formation of cyclic AMP (cAMP), a secondary messenger.
- Vesicles fuse to the cell surface membrane
- The vesicles’ membrane contains aquaporins, making the cell membrane permeable to water.

97
Q

What type of feedback cycle is ADH involved in?

A

Negative feedback cycle

98
Q

What in the brain is responsible for the negative feedback of osmoregulation?

A

Pituitary gland - Releases ADH (Antidiuretic hormone)

Hypothalamus - osmoreceptors are sensitive to the concentration of inorganic ions in the blood and are linked to the release of ADH.

99
Q

Describe the different levels of ADH when water is in short supply vs excess water available

A

Short supply - high levels of ADH
Excess supply - low levels of ADH

100
Q

What are causes for kidney failure?

A
  • Infection which causes damage/destruction of the podocytes’ and tubules’ structure
  • Raised blood pressure - lead to damaged epithelial cells and basement membrane of the Bowman’s capsule.
  • Genetic conditions - e.g. polycystic kidney diseases
  • Diabetes
  • Old age
101
Q

How might you assess kidney failure?

A
  • Urine composition analysis
  • Glomerular filtration rate
102
Q

What are two components you could look for in urine composition analysis that would indicate a problem with the kidney?

A
  • Protein in the urine - if the basement membrane or podocytes of the Bowman’s capsule are damaged, they no longer act as filters and large plasma proteins can pass into the filtrate.
  • Blood in the urine - another symptom that the filtering process is no longer working
103
Q

What are the effects of kidney failure?

A
  • Loss of electrolyte balance
  • Build up of toxic urea in the blood (toxic urea accumulation)
  • High blood pressure (hypertension)
  • Weakened bones
  • Pain and stiffness in joints
  • Anaemia (lack of production of red blood cells)
104
Q

What is the normal GFR (Glomerular Filtration Rate)?

A

90-120cm^3

105
Q

What GFR (Glomerular Filtration Rate) is considered kidney failure?

A

<15cm^3

106
Q

What does an eGFR (estimate Glomerular filtration rate) measure?

A
  • Creatinine
107
Q

What is the eGFR units?

A

cm^3/min

108
Q

What are 2 potential treatments for kidney failure?

A
  • Dialysis (haemodialysis and peritoneal dialysis)
  • Transplant
109
Q

What are 2 different types of dialysis?

A
  • Haemodialysis
  • Peritoneal dialysis
110
Q

What is haemodialysis?

A
  • Involved a dialysis machine.
  • Blood leaves artery and flows into the dialysis machine
  • flows between partially permeable dialysis membrane, in a countercurrent exchange system to maximise the exchange that takes place.
  • These membranes mimic the basement membrane of the Bowman’s capsule.
111
Q

What is the purpose of blood and dialysis fluid flowing in a countercurrent exchange system?

A

Maximise the exchange that takes place.

112
Q

What is peritoneal dialysis?

A
  • Dialysis that takes place inside the body which makes use of membranes formed by the lining of the abdomen - peritoneum.
  • Dialysis fluid introduced using catheter.
  • The fluid is drained off as urea and excess mineral ions move out of the blood into the tissue fluid.
113
Q

What are advantages of kidney transplantation over dialysis?

A
  • Transplant means that dialysis isn’t required.
  • Better quality of life (dialysis 3 times a week of 4 hours)
  • Dialysis reduces life expectancy - 15 years, transplant - 40 years
  • Low risks associated with kidney transplantation - 98% not having major complications with surgery.
114
Q

What are the disadvantages of kidney transplantation over dialysis?

A
  • Kidney may be rejected
  • Need to wait for suitable donor - gap between demand and supply is increasing
  • Requires immunosuppressants - can result patient’s ability to fight infection and puts them at a higher risk of cancer.
115
Q

What is one way of identifying diabetes via urine testing?

A

Glucose in the urine

116
Q

What is one way of identifying muscle damage via urine testing?

A

Large amounts of creatinine in the urine

117
Q

What hormone is produced by the placenta?

A

hCG (human chorionic gonadotrophin)

118
Q

What hormone is used to detect pregnancy?

A

hCG (human chorionic gonadotrophin)

119
Q

What are monoclonal antibodies?

A

Antibodies from a single clone of cells that are produced to target particular cells or chemicals in the body.

120
Q

How can monoclonal antibodies be produced in mice?

A
  • Mouse injected with hCG to make antibody
  • B-cells that make antibodies are removed and fused with myeloma (cancer cell that divides rapidly)
  • This creates cell known as ‘hybridoma’
  • This creates many antibodies are collected and purified.
121
Q

How can urine be used to test for anabolic steroids?

A

Steroids are excreted in the urine. Therefore the presence of a steroids can be tested for.

122
Q

Why is urine used to test for drugs?

A

It is possible to find drugs or metabolites in the urine.

123
Q

How long does different drugs stay in the system?

A

Ethanol - 6-24hours
Cannabis - 22 hours - 30 days
Cocaine - 2-5 days

124
Q

Where can urine testing be applied to real life?

A
  • Detect anabolic steroids to prevent cheating in sport
  • Detect hCG to indicate a positive pregnancy
  • Detect drugs or metabolites which someone may have taken illegally
125
Q

Describe the stages of pregnancy testing

A
  1. Wick soaked in urine.
  2. Contains mobile monoclonal antibodies with small coloured beads attached.
  3. These antibodies only bind to hCG, forming hCG/antibody complex.
  4. Urine moves up the test trip.
  5. Immobilised monoclonal antibodies arranged in a line with a coloured line appearing if she is pregnant.
  6. At the second strip, immobilised monoclonal antibodies bind to mobile monoclonal antibodies, despite whether they are bound to hCG or not.
  7. This suggests that the test is working, if the second coloured line appears.

A Level Biology (13 decks)

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