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OCR A level Biology HJ > Excretion an example of homeostatic control > Flashcards

Excretion an example of homeostatic control Flashcards

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1
Q

define metabolism

A

The sum of all these chemical reactions happening in the body

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2
Q

what would happen if waste products aren’t removed from the body?

A

If not removed, wastes would build up and become toxic or inhibit enzyme activity

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3
Q

define excretion

A

Removal of metabolic waste products from the body.

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4
Q

what are the 3 main waste products that need to be excreted?

A
  • carbon dioxide
  • bile pigments
  • nitrogen containing compounds, e.g. urea
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5
Q

is the removal of faeces considered excretion any why?

A

Faeces are an example of a substance that is removed from the body,but its removal is not classed as excretion. Most of the matter in faeces has neither entered cells nor taken part in any metabolic reaction. Faeces are therefore not metabolic products and so its elimination from the body is not classed as excretion but egestion.

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6
Q

why is the component of faeces that is excretion?

A

However, there is a small amount of bile pigment that enters the faeces from the liver. Bile pigment is a product of a metabolic reaction and so this component of faeces is excreted.

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7
Q

why does CO2 need to be continuously excreted?

A
  • CO2 is produced by all cells during respiration and travels in the blood to be ultimately excreted by the lungs
  • CO2+ H2O—> HCO3- H+
  • the H+ ions lower the blood pH which alters the tertiary structure of proteins in the blood which can have a damaging effect on the body.
  • after diffusing into the alveoli, CO2 is excreted as the person breathes out
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8
Q

what is deamination?

A

-the process in which amino acids are broken down in the liver and combined with CO2 to form the waste product urea.
THE REST OF THE AMINO ACID

amino acid + oxygen —->keto acid + ammonia

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9
Q

how is urea removed?

A

Urea travels in the blood, along with water,to the kidneys where it is removed and excreted as urine.

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10
Q

why is urea removed?

A

At high concentrations, urea increases the pH of the blood.It must be continuously excreted to maintain safe levels.

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11
Q

why are some of the amino acids in the body not excreted?

A
  • they’re very useful for the body so they are recycled
  • toxic amino groups are removed and converted to ammonia which combines with CO2 to make urea

-the remaining keto acid is used directly in respiration

amino acid + oxygen —->keto acid + ammonia

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12
Q

what are the 3 main blood vessels of the liver?

A
  • hepatic artery
  • hepatic portal vein
  • hepatic vein
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13
Q

what is the role of the hepatic artery?

A

carries oxygenated blood from the heart to the liver, allowing the liver cells to respire, thus carry out their functions

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14
Q

what is the role of the hepatic portal vein?

A

carries deoxygenated blood, high in absorbed nutrients, straight from the duodenum (a part of the small intestine) to the liver

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15
Q

what is the role of the hepatic vein?

A

carries deoxygenated blood away from the liver back to the heart, where it joins the vena cava

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16
Q

what are sinusoids?

A

special chambers where blood from both the hepatic artery and hepatic portal vein mix and pass into empty into branches of the hepatic vein called the intra- lobular vessel

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17
Q

where are the intra-lobular vessel?

A

these lie within the lobules which ultimately join together to form the hepatic vein

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18
Q

what is present in the blood in the hepatic portal vein?

A
  • uncontrolled concentrations of digestive products are present in blood entering the liver via the hepatic portal vein
  • the blood may even contain toxic substances absorbed from the intestine
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19
Q

what are liver cells called?

A

hepatocytes

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20
Q

what is the role of hepatocytes?

A

Hepatocytes remove excess substances and wastes, and secrete substances back into the blood to maintain their concentration within it.

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21
Q

what is the gall bladder?

A

The gall bladder is a small, pouch-like storage organ that lies next to the liver.

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22
Q

what connects the gall bladder and duodenum (in the small intestine)?

A

the bile duct

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23
Q

what is the role of the bile duct.

A

it carries bile to the small intestine for use in digestion

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24
Q

what is the structure of bile duct?

A

the bile duct is formed of specialised cavities called bile canaliculi which join together forming the duct, transporting bile to the gallbladder

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25
Q

what is the liver tissue divided into?

A

Liver tissue is divided into lobes further divided into repeating cylindrical structures called liver lobules.

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26
Q

what is a liver lobule made up of?

A

A liver lobule is made up of liver cells surrounded by cavities called sinusoids and canaliculi.

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27
Q

what happens when blood from the hepatic portal vein and hepatic artery when they meet?

A

Blood from the hepatic portal vein and hepatic artery meets and mixes at the sinusoids (channels in the liver cells), producing oxygenated blood that is high in nutrients:

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28
Q

what path does the blood take after it reaches the sinusoids?

A
  • Blood then travels down the sinusoids to the hepatic vein,passing closely by hepatocytes that line the sinusoid — the hepatocytes are able to remove and add substances to the blood
  • By the time blood reaches the end of the sinusoid the concentrations of its components have been modified and regulated
  • Sinusoids empty into branches of the hepatic vein (intra-lobular vessels) lying at the centre of each lobule. Intra-lobular vessels from different lobules join together to form the hepatic vein, which drains blood from the liver
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29
Q

what do the hepatocytes also produce?

A

The hepatocytes also produce bile which travels in the opposite direction to the blood.

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30
Q

where does the bile produced by the hepatocytes go?

A

The bile travels down bile canaliculi to the gall bladder.

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31
Q

what are the 2 main cells of the liver?

A
  • Hepatocytes

* Kupffer cells

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32
Q

what structures do hepatocytes have to support their general function of being involved in metabolic functions?

A

Hepatocytes are the main cells of the liver — they are metabolically active so contain many mitochondria. They do not have a specific function but are generally involved in metabolic functions

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33
Q

what are some general metabolic functions that hepatocytes are involved in?

A
  • cholesterol synthesis
  • storage of carbohydrates
  • detoxification
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34
Q

what is the role of kupffer cells?

A

are a type of macrophage which moves around within the sinusoids. They ‘clean’ the liver by breaking down and recycling red blood cells, whilst also protecting the liver from diseases.

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35
Q

what is the problem with the ammonia produced by the deamination reaction and how is it removed?

A

its highly toxic and very soluble so the ornithine cycle quickly converts ammonia into a less toxic from and prevents it from accumulating

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36
Q

what does ornithine cycle do?

A

The ornithine cycle combines toxic ammonia with carbon dioxide to produce the less soluble, less toxic urea.

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37
Q

what are the 3 intermediates in the cycle?

A
  • ornithine
  • citrulline
  • arginine
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38
Q

what is ornithine?

A

an amino acid

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39
Q

what are the steps of the ornithine cycle?

A
  1. Ammonia and carbon dioxide combine with ornithine (an amino acid) to produce citrulline, removing water in the process
  2. Further ammonia is added to the citrulline, producing arginine and removing water in the process
  3. Water is then added to arginine, removing urea in the process and re-converting the arginine back to ornithine again.

Once ornithine is reformed, the cycle can start again.

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40
Q

what happens to urea that is produced in the ornithine cycle?

A

Urea produced in the cycle travels in the blood to the kidneys where it is filtered out of the blood then concentraed and removed in urine. This process, therefore, ensures safe levels of amino acids.

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41
Q

what is the formula that summarises the ornithine cycle?

A

ammonia + carbon dioxide —> urea + water

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42
Q

why does the liver store carbohydrates?

A

to regulate blood glucose concentration

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43
Q

how does the liver regulate blood glucose conc? what happens when its too high and too low?

A

Glycogen stored in the liver (as cytoplasmic granules) is broken down and released into the blood when the body needs glucose.
• When blood glucose concentration is too high, the hepatocytes in the liver take in glucose and store it as glycogen
• When blood glucose concentration is too low, the hepatocytes in the liver release glucose into the blood

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44
Q

how is the regulation of blood glucose concentration regulated?

A

This is all coordinated by the action of glucagon and insulin, hormones made and released by the pancreas.

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45
Q

what is the role of glucagon?

A

• Glucagon — causes hepatocytes to release stored glucose

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46
Q

what is the role of insulin?

A

• Insulin — causes hepatocytes to take in glucose

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47
Q

what processes does the liver use to detoxify substances by modifying them?

A
  • Methylation
  • Oxidation
  • Reduction
  • Combining the toxins with other molecules
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48
Q

what enzymes in the liver help with detoxification?

A
  • catalase

- cytochrome P450

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49
Q

how does catalase help with detoxification?

A

An enzyme directly influencing hydrogen peroxide. Hydrogen peroxide (H2O2)is highly toxic and usually produced by cells. Catalase converts H2O2 into water and oxygen. The enzyme has a high turnover rate — one molecule of catalase can convert up to five million hydrogen peroxide molecules in a second.

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50
Q

how does the enzyme cytochrome p450 help with detoxification?

A

These enzymes are mainly involved in the breakdown of drugs such as paracetamol and cocaine. Their action can interfere with the functioning of some medicinal and recreational drugs which gives rise to unwanted side-effects. As P450 enzymes vary greatly between individuals different end products may be produced, explaining why some individuals experience side-effects that others do not.

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51
Q

why does alcohol need to be broken down?

A

its a toxic molecule which can depress nerve activity

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52
Q

how can alcohol be useful?

A

Alcohol contains chemical potential energy so can be used for respiration.

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53
Q

what is the process where alcohol is broken down?

A
  1. Ethanol is converted to ethanal, a reaction catalysed by ethanol dehydrogenase
  2. Ethanal is then dehydrogenated further to form ethanoic acid, catalysed by ethanal dehydrogenase
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54
Q

what is cirrhosis?

A

Excessive alcohol consumption can cause cirrhosis (fatty liver), a type of liver disease.

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55
Q

what leads to the cirrhosis?

A

• When too much alcohol is consumed it must be detoxified, using NAD in the process. NAD is also needed to oxidise and break down fatty acids for use in respiration• The utilisation of NAD stores to detoxify excessive alcohol levels leads to insufficient NAD to beak down fatty acids. The unmetabolised fatty acids are therefore converted back to lipids and stored as fat in hepatocytes, leading to a build-up of fat in the liver known as cirrhosis

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56
Q

what is the name of the process in which the liver converts excess glucose as glycogen ?

A
  • glycogenesis

- the glycogen is then stored as granules in the liver cells until the glucose is needed for energy

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57
Q

whats the difference between ultrafiltration and osmoregulation?

A

ultrafiltration-Filtration of blood at the molecular level under high pressure.

osmoregulation- controlling the body’s water potential

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58
Q

what are the 2 main roles of the kidney?

A
  • ultrafiltration

- osmoregulation

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59
Q

what are the 2 purposes of ultrafiltration?

A
  • To clean the blood — avoiding the build-up of toxic urea, which is otherwise excreted in the urine
  • Maintaining the concentration of ions in the body (this has a direct impact on the control of water potential)
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60
Q

what are the 2 main purposes of osmoregulation?

A

The kidneys’ second role, osmoregulation, ensures that the cells neither burst nor shrink:• If the water potential of the blood is too high, water enters cells, they swell and can eventually burst (cell lysis)• If the water potential of the blood is too low, water leaves the cells and the cells shrink, leading to crenation

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61
Q

whats the fibrous capsule?

A

Fibrous Capsule —the outer membrane that protects the kidney from mechanical forces

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62
Q

whats the cortex?

A

• Cortex — a lighter coloured outer region made up of renal (Bowman’s) capsules, convoluted tubules and blood vessels

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63
Q

whats the medulla?

A

• Medulla — darker coloured interior region made up of the loop of Henle, collecting ducts and blood vessels

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64
Q

whats the renal pelvis?

A

• Renal Pelvis — branches in the medulla that collect urine from the collecting ducts into the ureter

65
Q

whats the ureter?

A

• Ureter —the tube which collects urine and carries it for storage in the bladder

66
Q

whats the role of the renal artery?

A

• Renal artery — supplies kidney with blood under high pressure and a high flow rate to the kidneys

67
Q

whats the renal vein?

A

• Renal vein — drains blood from the kidneys, carrying the blood under lower pressure and low flow rate

68
Q

describe the structure of the glomerulus?

A
  • The renal artery splits to form multiple afferent arterioles with each going on to form a mesh/knot of capillaries called the glomerulus
  • Blood first enters the nephron via the glomerulus
  • Fluid from the blood is forced from the glomerular capillaries into the lumen of the Bowman’s Capsule, forming filtrate through the process of ultrafiltration
69
Q

whats the role of the bowmans capsule?

A

• The Bowman’s Capsule surrounds the glomerulus and is responsible for transporting the filtrate to the proximal convoluted tubule and hence the rest of the nephron as it is gradually converted into urine

70
Q

how is blood supplied to the glomerulus?

A

Blood is filtered in the glomerulus of the kidneys, forming the glomerular filtrate through the process of ultrafiltration. Blood is supplied to the glomerulus by the afferent arteriole (branch of the renal artery) and leaves via the efferent arteriole(branch of the renal vein)

71
Q

whys is the diameter of the efferent arteriole smaller than the afferent arteriole?

A

• The efferent arteriole has a smaller diameter than the afferent arteriole. This ensures that the blood passes into the glomerulus at a higher pressure than that at which it leaves

72
Q

why does the blood from the afferent arteriole have a higher pressure?

A

• This pressure pushes glucose, water and mineral ions out of the glomerulus and into the Bowman’s Capsule, forming the glomerular filtrate

73
Q

how is the blood in the bowmans capsule filtrated?

A

The blood pushed into the Bowman’s Capsule is filtered by the barrier which separates the fluid in the glomerulus and the fluid in the Bowman’s Capsule.

74
Q

what are the 3 layers that allow for ultrafiltration to occur?
(the barriers)

A
  • Glomerular endothelium
  • Basement membrane
  • Podocytes
75
Q

how does the structure of the glomerular endothelium relate to its function?

A

Cells of the glomerular capillary endothelium have spaces/holes between them to allow blood to pass through. These cells also contain pores called fenestrations. The gaps allow the blood to pass out of the capillary and between the cells rather than through them in order to form the glomerular filtrate.

76
Q

how does the structure of the basement molecule relate to its function?

A

The basement membrane lies adjacent to the glomerular endothelial cells. It is made up of a mesh of molecules, including collagen fibres and glycoproteins, which act as a filter, preventing molecules with a relative molecular mass greater than 69000 from passing through.

77
Q

what are some molecules that are too big to pass through the glomerular capillaries?

A

Red blood cells and some proteins are too large to pass through these gaps into the Bowman’s Capsule, hence are held in the glomerular capillaries. Small proteins,glucose, urea and amino acids are among the molecules small enough to pass through. Due to ultrafiltration, the composition of the filtrate in the Bowman’s Capsule is different from that of the blood.

78
Q

how does the structure of the podocytes relate to its function?

A

Podocytes are the epithelial cells of the Bowman’s Capsule and line its lumen (the inner-layer). They have foot-like extensions (minor processes), extending from the major processes (finger-like projections),allowing them to attach to the basement membrane. This ensures that there are gaps between them and they are held away from the capillary endothelium cells. This allows fluid to move between the podocytes rather than through the cells themselves.

79
Q

what does the nephron split into?

A
  1. Proximal convoluted tubule
  2. Loop of Henle
  3. Distal convoluted tubule
80
Q

water is reabsorbed into the nephron and what is excreted?

A

Water and certain ions are reabsorbed into the blood continuously throughout the nephron, and the remaining filtrate is excreted as urine.

81
Q

where are knuffer cells and what is their function?

A

the are attached to the walls of the sinusoids and they remove bacteria and break down old red blood cells

82
Q

what are canaliculi?

A

the tubes that connect the bile duct to the central vein

83
Q

what is the process used to excrete waste substances from the kidneys?

A

1-blood enters the kidney through the renal artery and then passes through capillaries in the cortex of the kidneys
2-as the blood passes through the capillaries, substances are filtered out of the blood and into the long tubules that surround the capillaries. This process is called ultrafiltration.
3-useful substances (e.g. glucose) are reabsorbed back into the blood from the tubules in the medulla and cortex -this is called selective reabsorbtion
4-the remaining unwanted substances (e.g. urea) pass along the tubules, then along the ureter to the bladder, where they’re expelled as urine.
5-the filtered blood passes out of the kidneys through the renal vein

84
Q

what is a nephron?

A

small tubes that make up the kidney which help filter the blood

85
Q

how is blood filtered in the nephron?

A
  • The renal artery splits to form multiple afferent arterioles with each going on to form a mesh/knot of capillaries called the glomerulus
  • Blood first enters the nephron via the glomerulus
  • Fluid from the blood is forced from the glomerular capillaries into the lumen of the Bowman’s Capsule, forming filtrate through the process of ultrafiltration
  • The Bowman’s Capsule surrounds the glomerulus and is responsible for transporting the filtrate to the proximal convoluted tubule and hence the rest of the nephron as it is gradually converted into urine
86
Q

what is the route that blood takes in the nephron?

A
  1. The filtrate passes from the Bowman’s Capsule into the proximal convoluted tubule. The proximal convoluted tubule is a series of loops made up of epithelial cells forming the brush border. This increases the surface area available for reabsorption
  2. The filtrate then enters the loop of Henle. This is a longloop that extends from the cortex into the medulla and back again
  3. From the loop of Henle, the filtrate goes into the distal convoluted tubule. This is a series of loops and is surrounded by fewer blood capillaries than the proximal tubule
  4. Finally, the filtrate passes into the collecting duct. Several distal convoluted tubules from multiple nephrons empty into this tube, and it becomes wider as it empties into the kidneys’ pelvis (at the centre of the kidney)
87
Q

what solutes are excreted and which are reabsorbed?

A

The main solute that is excreted is urea, whilst molecules such as glucose, amino acids, water and some mineral ions are reabsorbed

88
Q

where does reabsorbtion occur?

A
  • Most of the reabsorption occurs in the proximal convoluted tubule (around 85%of the fluid)
  • Reabsorption occurs with molecules moving from the glomerular filtrate in the tubule into the blood capillaries. This is defined as selective reabsorption
89
Q

what impact does the presence of proteins in the blood have?

A

Certain cells (e.g. blood cells) and proteins are left in the capillary as they are too large to pass into the filtrate. The presence of proteins in the blood gives rise to a low water potential which ensures water and the substances discussed above,are reabsorbed and not excreted

90
Q

what adaptations does the proximal convoluted tubule epithelial have to fulfill its function of reabsorbtion?

A
  • microvilli
  • cotransporters
  • the base of the epithelial cells
  • mitochondria
91
Q

how does microvilli allow the proximal convoluted tubule epithelial have to fulfill their function of reabsorbtion?

A

• Microvilli —the cell surface membrane at the top (side closest the lumen) of epithelial cells lining the tubule is highly folded, forming microvilli. This increases the surface area for reabsorption of substances from the filtrate and also allows more protein pumps and transporters to be inserted into the membrane to maximise reabsorption

92
Q

how do cotransporters allow the proximal convoluted tubule epithelial have to fulfill their function of reabsorbtion?

A

• Cotransporters in the cell surface membrane transport glucose and/or amino acids simultaneously with sodium ions from the tubule lumen into the cell

93
Q

how does the base of the epitheial cells allow the proximal convoluted tubule epithelial have to fulfill their function of reabsorbtion?

A

• The base of the epithelial cells (side closest to the blood capillary) —hasinfoldings,which increases the surface area to transfer reabsorbed substances into the blood capillaries. This membrane also contains sodium/potassium pumps which pump sodium ions out of the cell and potassium ions into the cell to maintain a concentration gradient across the membrane

94
Q

how does mitochondira allow the proximal convoluted tubule epithelial have to fulfill their function of reabsorbtion?

A

• Mitochondria — a high-density of mitochondria are present to provide ATP to drive reabsorption through active transport

95
Q

what mechanism is used to reabsorb useful solutes along the proximal convoluted tubule (PCT)?

A
  • useful solutes like glucose, amino acids, vitamins and some salts are reabsorbee aling the PCT by active transport and facilitated diffusion
  • some urea is also reabsorbed by diffusion
96
Q

why and how is water reabsorbed by the blood?

A

water enters the blood by osmosis because the water potential of the blood is lower than that of the filtrate. water is reabsorbed from the loop of Henle, DCT and the collecting duct

97
Q

what is present in the urine and what isnt?

A

Urine is made up of:

  • water and dissolved salts
  • urea
  • other substances such as hormones and excess vitamins

Urine doesn’t usually contain:

  • proteins and blood cells-they’re too big to be filtered out of the blood
  • glucose, amino acids and vitamins- they’re actively reabsorbed back into the blood
98
Q

what happens if the water potential of the blood is too low?

A
  • the body is dehydrated, more water is reabsorbed by osmosis into the blood from the tubules of the nephrons.
  • this means the urine is more concentrated, so less water is lost during excretion
99
Q

what happens if the water potential of the blood is too high?

A
  • the body is hydrated, less water is reabsorbed by osmosis into the blood from the tubules of the nephrons.
  • this means the urine is more dilute, so more water is lost during excretion.
100
Q

what controls the volume of water that is reabsorbed?

A

hormones

101
Q

what drives the movement of glucose and sodium ions into epithelial cell?

A

The movement of these molecules (glucose and sodium ions) into epithelial cells is driven by the concentration gradient created by pumping sodium out of the cell.

102
Q

where are sodium ions reabsorbed?

A

at the proximal convoluted tubule

103
Q

what are the steps in which ions are pumped out of the loop of Henle and ions are reabsorbed?

A

1-near the top of the ascending limb, Na+ and Cl- ions are actively pumped out into the medulla. The ascending limb is impermeable to water, so water stays inside the tubule. This creates a low water potential in the medulla, because there’s a high concentration of ions.

2- Because there’s a lower water potential in the medulla than in the descending limb, water moves out of the descending limb into the medulla by osmosis. This makes the filtrate more concentrated (the ions can’t diffuse out- the descending limb isn’t permeable to them). The water in the medulla is reabsorbed into the blood through the capillary network.

3-Near the bottom of the ascending limb Na+ and Cl- ions diffuse out into the medulla, further lowering the water potential in the medulla. (the ascending limb is impermeable to water, so it stays in the tubule.)

4-The first 3 stages massively increase the ion conc in the medulla, which lowers the water potential. This causes water to move out of the collecting duct by osmosis. As before, the water in the medulla is reabsorbed into the blood through the capillary network.

104
Q

what are the ascending and descending limb each impermeable to?

A
  • the ascending limb is impermeable to water

- the descending limb is impermeable to ions

105
Q

how is the amount of water that is reabsorbed into the collecting duct controlled?

A

the volume of water reabsorbed from the collecting duct into the capillaries is controlled by changing the permeability of the collecting duct

106
Q

what impact does the length of the loop of Henle and ascending limb have on an animal?

A
  • the longer an animals loop of Henle, the more water they can reabsorb from the filtrate.
  • when there’s a longer ascending limb, more ions are actively pumped out into the medulla, which creates a really low water potential in the medulla.
  • this means more water moves out of the nephron and collecting duct into the capillaries, giving a very conc urine
  • animals that live in areas where there’s little water usually have long loops to save as much water as possible
107
Q

how does the reabsorption of sodium ions work?

A

The reabsorption of sodium ions is carried out via pumps which use ATP to actively transport the ions.
• Sodium ions are pumped out of cells lining the tubule and into the blood via the sodium/potassium pump, resulting in a low sodium ion concentration within them
• Sodium ions then diffuse from the proximal tubule lumen into the cells through a co-transport protein (on the proximal tubule luminal side). The ions diffuse down the Na+ concentration gradient formed by the pumping of sodium ions out of the cell

108
Q

where are sodium ions reabsorbed?

A

the proximal convoluted tubule

109
Q

how does the reabsorption of sodium ions differ to the reabsorption of glucose ad amino acids?

A

the reabsorption of sodium ions is independent whereas the reabsorption of glucose or amino acids is dependent on the presence of sodium ions

110
Q

how does the reabsorption of glucose or amino acids work?

A
  1. Sodium ions are actively pumped out of the cells lining the proximal convoluted tubule and into the interstitial space (via the sodium/potassium pump) creating a concentration gradient (lower concentration of sodium ions inside the epithelial cell cytoplasm)
  2. Sodium ions diffuse down this concentration gradient, via facilitated diffusion, from the lumen of the proximal convoluted tubule into the epithelial cells. They do this through special carrier proteins called co-transporters
  3. The co-transporter simultaneously carries another molecule (e.g. glucose or amino acids) into the epithelial cell in a process known as secondary active transport
  4. The transport of these molecules into the epithelial cell reduces its water potential, therefore, water moves into the cell from the proximal convoluted tubule via osmosis
  5. The molecules which have been co-transported can then freely diffuse into the blood, moving down a concentration gradient, with water following them
111
Q

how are larger proteins reabsorbed?

A

by endocytosis

112
Q

what is the role of the loop of Henle?

A

The role of the loop of Henle is to decrease the water potential in the medulla.

This creates a water potential gradient extending into the medulla, allowing water (in urine within the collecting duct) to diffuse out along the whole length of the collecting duct.

113
Q

describe the structure of the descending limb

A

• The descending limb is thinner and permeable to both ions and water

114
Q

describe the structure of the ascending limb

A

• The ascending limb is thicker and impermeable to water. It also contains protein pumps which pump ions out into the interstitial fluid which surrounds the loop of Henle

115
Q

what is the name of the system that the loop of Henle is arranged in?

A

• The arrangement of the loop of Henle is called a hairpin countercurrent multiplier system

116
Q

how does the conc of glucose vary in different parts of nephron?

A

• Glucose — it is selectively reabsorbed in the proximal convoluted tubule,so its concentration decreases near the start of the nephron

117
Q

how does the conc of sodium ions vary in different parts of nephron?

A

• Sodium ions — initially diffuse into the ascending limb so the concentration rises, but then are actively transported out of the descending limb so the concentration falls. However, its concentration rises again in the distal convoluted tubule and collecting duct as water is removed since the water potential is lowered

118
Q

how does the conc of urea vary in different parts of nephron?

A

• Urea — concentration rises as water is removed from the tubule filtrate (lowers water potential)and is also actively transported into the nephron

119
Q

how does the conc of potassium ions vary in different parts of nephron?

A

• Potassium ions — are actively transported into the tubule filtrate and its concentration also rises as water is removed (with a fate similar to the sodium ions)

120
Q

where is ADH released form and what does it do?

A

Antidiuretic hormone (ADH) is released from the posterior pituitary gland.

It alters the permeability of the collecting ducts to water, thus controls how much water is lost in urine.

121
Q

what difference does and excess amount of ADH and a limited amount of ADH in the blood make?

A
  • If there is excess ADH in the blood, the collecting ducts are more permeable,and less water is lost in urine
  • If there is limited ADH in the blood, the collecting ducts are less permeable, and more water is lost in urine
122
Q

what is osmoregulation?

A

the monitoring of water potential in the blood to determine how much water to retain and how much to excrete.

123
Q

what can cause an increase in water potential?

A

An increase in water potential usually arises from excessive consumption of water, or salts being used up in metabolism and not being replaced in the diet.

124
Q

what can cause a drop in water potential?

A

A drop-in water potential can be caused by low water consumption (dehydration), excessive sweating, or, large amounts of ions being consumed in the diet.

125
Q

define osmoreceptors

A

Sensory receptors that detect changes in water potential and affects osmoregulation.

126
Q

how is the water potential of the blood detected?

A

The hypothalamus contains osmoreceptors (sensory receptors) which can detect the water potential of the blood. They do this by changing shape in response to their environment.

127
Q

what is the response of the osmoreceptors when the water potential in the blood is too low?

A

• When the water potential of the blood is , water moves out of the osmoreceptors causing them to shrink

128
Q

what is the response of the osmoreceptors when the water potential in the blood is too high?

A

• When the water potential of the blood is too high, water moves into the osmoreceptors causing them to swel

129
Q

how do osmoreceptors respond when they detect a change in shape?

A

Osmoreceptors detect this change in shape and pass the signal to specialised neurosecretory cells with their cell bodies in the hypothalamus which produce and release ADH

130
Q

what happens when osmoreceptors detect a fall in water potential?

A

• When osmoreceptors detect a fall in water potential, the neurosecretory cells respond, resulting in more ADH being secreted from the posterior pituitary gland

131
Q

what happens when osmoreceptors detect a fall in water potential?

A

• When osmoreceptors detect a rise water potential, the neurosecretory cells respond, resulting in less ADH being secreted from the posterior pituitary gland. Moreover, the ADH already in the blood is broken down

132
Q

what is ADH ?

A

antidiuretic hormone

-A hormone released by the hypothalamus that controls and determines the permeability of the collecting duct cell walls.

133
Q

how id ADH transported into the blood capillaries surrounding the posterior pituitary gland?

A

-via exocytosis

134
Q

Describe the method by which ADH is secreted by the pituitary gland.

A
  1. ADH attaches to membrane-bound ADH receptors on the cells of the collecting duct, activating intracellular enzyme-controlled reactions within the cell
  2. This causes vesicles containing aquaporins (specialised water-permeable channel proteins) to move to, and fuse with, the cell-surface membrane. As the number of water channels increases, the cell surface membrane becomes more permeable to water
  3. Water now moves out of the collecting duct and distal convoluted tubule by osmosis, entering the medulla and then the blood. This concentrates the urine (i.e. lowering its water potential) and reduces water loss so less urine is produced
135
Q

what is the role of ADH?

A

ADH works within the kidneys by increasing the permeability of the collecting duct and distal convoluted tubule epithelial cells to water

136
Q

what happens when the ADH levels fall?

A

f ADH levels fall in the blood however, the cell surface membrane invaginates (folds inwards), creating new vesicles which remove the aquaporins from the membrane. This results in the urine becoming more diluted (i.e. higher water potential) and more of it is produced as the walls become less permeable, therefore less water is reabsorbed from the collecting duct into the blood via osmosis

137
Q

How does the negative feedback loop of ADH work to decrease water potential?

A
  1. Osmoreceptors detect the rise in water potential and reduce stimulation of the neurosecretory cells, resulting in less ADH being released
  2. This leads to a fall in ADH concentration, and hence a fall in the permeability of the collecting duct to water and urea
  3. Therefore, less water is reabsorbed, and the urine becomes less concentrated (i.e. more dilute)
  4. Once the water potential of the blood has returned to normal, the osmoreceptors detect this and respond by increasing stimulation of the pituitary gland to raise ADH levels back to normal. This is an example of negative feedback
138
Q

How does the negative feedback loop of ADH work to increase water potential?

A
  1. Osmoreceptors detect the fall in water potential and increase stimulation of the neurosecretory cells, resulting in more ADH being released
  2. This leads to a rise in ADH concentration in the blood, and hence the permeability of the collecting duct to water and urea rises
  3. More water is therefore reabsorbed, and the urine becomes more concentrated(i.e. less dilute)
139
Q

what are some potential reasons for kidney failure?

A
  • High blood pressure (hypertension), which can damage the glomerulus
  • High blood glucose (e.g. resulting from diabetes mellitus) — which also damages the glomerulus
  • Infection
  • Heart disease
140
Q

how can you assess that there is kidney failure?

A

Kidney failure often results in molecules being present in the urine, such as proteins, that are usually too large to enter the filtrate (fluid filtered from the blood). Analysing urine for substances that are usually not present within it can be used to assess if the filtration mechanism has been damaged or not

141
Q

what are some problems arising from kidney failure?

A

1-waste products that the kidney would normally remove (e.g. urea) begin to build up in the blood. Too much urea in the blood causes weight loss and vomiting.

2-fluid starts to accumulate in the tissues because the kidney’s can’t remove excess water form the blood. This causes parts of the body to swell, e.g. the person’s legs, face and abdomen can swell up

3-the balance of electrolytes (ions) in the body becomes, well, unbalanced. The blood may become too acidic, and an imbalance of calcium and phosphate can lead to brittle bones. Salt build-up may cause more water retention

4-long-term kidney failure causes anemia - lack of haemoglobin

142
Q

whats glomerular filtration rate?

A

The volume (cm3) of fluid passing into the nephrons every minute

143
Q

what is the difference between a normal glomerular filtration rate and one which suggests there’s kidney failure?

A

A normal glomerular filtration rate (GFR) is 90-120 cm3min-1. A GFR of below 60 m3min-1suggests kidney disease and below 15 cm3min-1suggests kidney failure.

144
Q

what are the 2 main treatment options for kidney failure?

A
  • renal dialysis

- kidney transplant

145
Q

whats renal dialysis?

A

A mechanism utilised to artificially regulate the concentrations of solutes in the blood.

146
Q

how does renal dialysis work?

A
  • blood is passed over a partially permeable dialysis membrane. Dialysis fluid sits on the other side of the membrane and contains the correct concentrations of minerals, urea, water and other substances found in blood plasma but no waste products.
  • The partially permeable membrane allows the exchange of substances between the two fluids:
  • Substances more highly concentrated in the blood (e.g. urea) will diffuse down the concentration gradient into the dialysis fluid. This leads to the removal of waste products, excess fluid and mineral ions from the blood
  • Substances, such as glucose, at lower concentrations in the blood will diffuse across the membrane into the blood from the dialysis fluid
147
Q

what are the 2 types of renal dialysis?

A
  • haemodialysis

- peritoneal dialysis

148
Q

how is haemodialysis carried out?

A

Haemodialysis

  1. Blood is removed from an artery or a vein before being passed through a machine containing an artificial dialysis membrane in the form of many artificial capillaries
  2. Heparin is added to the blood to stop the blood from clotting in the dialysis machine
  3. The blood then moves into the thin capillaries (dialyser)where it interfaces with the dialysis fluid

In haemodialysis, the blood runs in the opposite direction to the dialysis fluid,which maximises the exchange of substances due to the use of the counter-current flow principle. The blood is then returned to the body after a few hours. Haemodialysis is performed a few times a week, usually at a hospital, although it can be done at home.

149
Q

how is peritoneal dialysis carried out?

A

Whilst haemodialysis removes blood from the body to clean it, peritoneal dialysis cleans the blood directly in the body.

  1. A tube is placed through the skin into the abdomen, through which the dialysis fluid is inserted
  2. It then uses the abdominal membrane (peritoneum) as a partially permeable membrane and interfaces with the blood

After diffusion across the peritoneum has occurred (normally takes around two hours), the dialysis fluid is removed. This method is advantageous as it allows patients to walk around whilst undergoing dialysis.

150
Q

how does a kidney transplant work?

A
  • The kidney is transplanted from one person to another and connected to blood vessels and the bladder in the lower abdomen
  • Immunosuppressants drugs are given to prevent the patient’s immune system rejecting the new kidney. Rejection often occurs as the new kidney will have antigens on its surface which are recognised by the immune system as foreign
151
Q

what are the advantages and disadvantages of kidney transplant?

A

advantages:

  • convenience: Less time consuming compared to renal dialysis
  • health:Greater physical fitness and wellbeing
  • other:No physical signs of chronic illness — better self-image and improved quality of life

disadvantages:

  • convenience: Need to take immunosuppressant drugs regularly
  • health:Side effects of immunosuppressants and have to undergo major transplant surgery
  • other:Need to be regularly checked for signs of rejection
152
Q

which chemicals are present in the urine and why?

A

any chemical with a relative molecular mass smaller than 69,000 passes from the blood into the urine if not reabsorbed further down the nephron.

This principle is used to test for a range of chemicals including:
• Alcohol and other recreational drugs
• Glucose
• Anabolic steroids
• Human chorionic gonadotrophin (hCG)
153
Q

why are we able to test for pregnancy?

A
  1. After fertilisation, an embryo implants into the lining of the uterus
  2. This causes the production of hCG — a hormone produced in the placenta
  3. hCG travels in the blood until it ultimately passes through the kidney nephron (it is small enough to be forced out of the blood in ultrafiltration)
  4. hCG can then be detected in the mother’s urine
154
Q

describe how a pregnancy test works

A
  1. The absorbent part of the testing stick is placed into the urine. The urine (containing hCG molecules) and travels up the stick until it meets labelled antibodies (linked with a coloured particle)
  2. The antibodies are complementary to the hCG molecules, and can bind to the hCG molecules to form a complex
  3. The complex then moves along the strip to another set of antibodies that are immobilised on the strip. These antibodies are complementary to hCG, and if it is present, the complex will bind to the immobilised antibodies
  4. The presence of the blue particles on the labelled antibodies causes a blueline to appear. If hCG is not present, there is no complex for the stable antibodies to bind to, hence, no blue line is visible
155
Q

what are the 2 windows for pregnancy testing kits for?

A
  • One to tell you whether you’re pregnant

* Another to confirm whether the test was accurate — the control window/zone

156
Q

what is the control zone?`

A

The control zone is where the immobilised antibodies are found hence a blue line appears when the antibody-colour complex successfully reaches it, regardless of whether or not hCG is present or not. If something goes wrong, the urine may not reach this point and no blue line will appear hence a faulty pregnancy testing kit can be identified.

157
Q

what are anabolic steroids and when are they used?

A

Anabolic steroids are a type of synthetic hormone that can be used to increase protein synthesis.
Their effect is pronounced in skeletal muscle where the protein synthesis results in an increase in muscle mass.

-For this reason, their use in sports is banned as they confer an unfair advantage.

158
Q

what is anabolic testing?

A

-testing the urine to try and detect anabolic steroids

Anabolic steroids have a half-life of 16 hours so a standard dose will be detectable after a few days.

159
Q

what is used to analyse whether he urine contains anabolic steroids?

A

gas chromatography

OCR A level Biology HJ (23 decks)

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