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Excretion Flashcards

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1
Q

What is excretion?

A

Removal of metabolic waste from the body

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2
Q

What are the main excretory products?

A
  • CO2 from respiration
  • Nitrogen containing compounds such as urea
  • Bile pigments
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3
Q

What are the main excretory organs?

A
  • The lungs
  • The skin
  • The liver
  • The Kidney
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4
Q

How is CO2 excreted by the lungs?

A
  • CO2 is passed from the cell or respiring tissues into the bloodstream, where it is transported (mainly in the form of HCO3- ions) to the lungs
  • In the lungs CO2 diffuses into the alveoli to be excreted as you breathe out
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5
Q

How does the liver excrete substances?

A

The liver is involved in many metabolic processes and some of the substances produced in these will be secreted into the bile for excretion with the faeces

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6
Q

How is urea excreted from the body?

A

Urea is passed into the blood stream to be transported to the kidneys, in the kidneys the urea is removed from the blood by ultrafiltration, the urea becomes a part of the urine. Urine is then excreted by the urethra

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7
Q

How is the skin an excretory organ?

A

Sweat is excreted from the skin, sweat contains a range of substances including salts, water, urea, uric acid and ammonia. Water and salts aren’t excretory products but can be an important part of homeostasis, maintaining the water potential of the blood

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8
Q

Why is it important for products of metabolism to be excreted?

A

Build up of metabolic products could be fatal as some of the products are toxic, other metabolic products can act as inhibitors and effect the activity of essential enzymes

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9
Q

Which products of metabolism are toxic?

A

CO2 and NH3, they interfere cell processes by altering the pH of the cells and therefore preventing normal metabolism

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10
Q

How can CO2 affect RBCs and haemoglobin?

A
  • CO2 dissolves in water to form Carbonic acid which dissociates inside the red blood cells under the influence of carbonic anhydrase to form H+ and HCO3-, the H+ ions can have many negative effects on haemoglobin and the RBCs
  • H+ affects the pH of the cytoplasm of the red blood cells
  • H+ affects the tertiary structure of the haemoglobin and reduces haemoglobin’s affinity for oxygen which affects oxygen transport, the H+ can then combine with the haemoglobin to form haemoglobinic acid
  • The CO2 that isn’t converted into HCO3- can combine directly with haemoglobin to form carbaminohaemoglobin
  • Haemoglobinic acid and carbaminohaemoglobin aren’t able to combine with oxygen, therefore reducing oxygen transport even further
  • In the blood plasma excess H+ ions can reduce the pH of the plasma, maintaining pH of blood plasma is essential as a change in pH can alter the structure of many proteins in the blood that help transport substances around the body, proteins in the blood act as a pH buffer to resist the change in pH
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11
Q

What is the body’s response to excess H+ ions in the blood plasma?

A

Excess H+ ions are detected by chemo receptors and this information is transmitted to the medulla oblongata in the brain and breathing rate is increased to get rid of excess CO2

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12
Q

What happens to the body if the blood pH drops below 7.35?

A

It causes headaches, drowsiness, restlessness, tremor and confusion. There may also be rapid changes to blood pressure and heart rate, this is called respiratory acidosis

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13
Q

What happens to excess amino acids?

A
  • They are deaminated to produce ammonia and a keto acid
  • Amino acid + oxygen → keto acid + ammonia
  • Ammonia then combines with CO2 to form the less toxic compound urea and water, the urea is then transported to the kidneys for excretion
  • 2NH3 + CO2 → CO(NH2)2 + H2O
  • The remaining keto acid can be used directly for respiration or may be converted to a carbohydrate or fat for storage
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14
Q

What is the function of the hepatic artery?

A

Oxygenated blood from the heart travels from the aorta to the liver via the hepatic artery, this provides oxygen for aerobic respiration which is essential as the liver cells are very active as they carry out many metabolic processes. Many of these processes require ATP so it is important that the liver has a good supply of oxygen to produce this ATP from respiration

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15
Q

What is the function of the hepatic portal vein?

A

Deoxygenated blood from the digestive system enters the liver via the hepatic portal vein, this blood is rich in the products of digestion. The concentration of these substances are uncontrolled as they have just entered the body as products of digestion. It is important that this blood enters the liver to so the products of digestion in the blood have their concentrations regulated and toxic products removed

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16
Q

How does blood leave the liver?

A

Via the hepatic vein, the hepatic vein rejoins the vena cava and blood returns to the normal circulation

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17
Q

What is the final vessel connected to the liver that isn’t a blood vessel?

A

Bile duct

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18
Q

What is bile?

A

A secretion from the liver which has functions in digestion and excretion

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19
Q

What is the function of the bile duct?

A

The bile duct carries bile from the liver to the gall bladder where it is stored

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20
Q

What is the function of bile?

A
  • Bile aids the digestion of fats in the small intestine

- Bile also contains some excretory products such as the pigment bilirubin which will leave the body with faeces

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21
Q

What is the liver divided into?

A

Lobes which are further divided into lobules

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22
Q

Which vessels in the liver are known as the inter-lobular vessels?

A
  • Branch of hepatic artery
  • Branch of hepatic portal vein
  • Branch of bile duct
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23
Q

Which is the intra-lobular vessel?

A

Hepatic vein

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24
Q

What is an inter-lobular vessel?

A

Vessels that split into smaller vessels and run between and parallel to the lobules

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25
Q

What is a sinusoid?

A

When branches from the hepatic artery and hepatic portal veins enter the lobule the blood from the two vessels mix and enter a special chamber called the sinusoid, the sinusoid is lined with hepatocytes

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26
Q

What is a liver cell called?

A

A hepatocyte

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27
Q

What is the function of the liver cells lining the sinusoids?

A

These hepatocytes can withdraw substances from the blood and add certain substances back into the blood

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28
Q

What are Kupffer cells and what are their function?

A
  • Specialised macrophages that move around within the sinusoids, they breakdown and recycle old RBCs
  • One of the products of the breakdown of haemoglobin is bilirubin which is a pigment that is excreted as part of the bile
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29
Q

What is the bile duct made up of?

A

Bile canaliculi

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30
Q

What is at the centre of each lobule?

A

Branch of the hepatic vein known as the intra-lobular vessel

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31
Q

Where do sinusoids empty the blood that has flowed through them into?

A

When blood has passed through the sinusoid the concentrations of many of the substances in the blood have been modified and regulated. The blood is then emptied into the intra-lobular vessel. The branches of the hepatic veins from different lobules join together to form the hepatic vein which transports deoxygenated blood into the heart via the vena cava

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32
Q

Describe the structure of a hepatocyte

A

A hepatocyte is relatively unspecialised, they have a simple cuboidal shape and their surface is lined with many microvilli to maximise SA for absorbing substances from the blood by diffusion. Their cytoplasm is very dense and specialised with the organelles it contains to help them carry out the many metabolic processes that the liver is involved in

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33
Q

What is the outer region of the kidney called?

A

The cortex

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34
Q

What is the inner region of the kidney called?

A

The medulla

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35
Q

What is the centre of the kidney called?

A

The pelvis

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36
Q

What does the renal artery split into?

A

Many afferent arterioles which each lead to the knot of capillaries called the glomerulus

37
Q

Where does blood enter the glomerulus?

A

Afferent arteriole

38
Q

Where does blood leave the glomerulus?

A

Efferent arteriole

39
Q

Where does blood go once it leaves the efferent arteriole?

A

It enters more capillaries surrounding the rest of the tubule (nephron) which then come together to form the renal vein

40
Q

What is a nephron?

A

A tiny kidney tubule

41
Q

What is ultrafiltration?

A

Where blood is pushed out of the glomerulus and into the lumen of the Bowman’s capsule

42
Q

What are the three layers of filtration between the glomerulus and the lumen of the bowman’s capsule?

A
  • Endothelium of capillary, the cells of the endothelium of the capillary have small gaps between them. The endothelial cells also contain pores called fenestrations
  • The basement membrane, a fine mesh of collagen fibres and glycoproteins, it acts as a barrier to prevent large molecules from passing through, therefore proteins and blood cells are contained in the capillaries of the glomerulus
  • Epithelial cells of the bowman’s capsule, these cells (called podocytes) have a specialised structure. They have many finger-like projections called major processes, on each major process is a minor process (foot process) that hold the cells (podocytes) away from the endothelium of the capillary. The foot processes also ensure that there are gaps between podocytes
  • Fluid from the blood passes through the endothelium of the capillary, through the basement membrane and finally through the podocytes into the lumen of the bowman’s capsule where it is now called filtrate
43
Q

What is the benefit of having three layers of filtration rather than just one as seen in formation of tissue fluid?

A

Makes it less likely for plasma proteins and erythrocytes to enter the bowman’s capsule

44
Q

What does the bowman’s capsule lead into?

A

The rest of the tubule (nephron) which has three parts:

  • Proximal convoluted tubule
  • Loop of Henle
  • Distil convoluted tubule
  • The fluid of many nephrons enters the collecting ducts which passes down through the medulla and into the pelvis at the centre of the kidney
45
Q

Which substances are selectively reabsorbed from the urine?

A

Amino acids, glucose and water

46
Q

What is filtered out of the blood in the glomerulus into the lumen of the bowman’s capsule?

A

Amino acids, glucose, water, urea, mineral ions (Na+, Cl-, K+)

47
Q

Why is the concentration of urea in the urine much higher than in the glomerular filtrate?

A

Because most of the water is selectively reabsorbed in the PCT meaning there is the same amount of urea in a much smaller volume meaning the concentration of urea is higher in the urine after the urine passes through the PCT and selective reabsorption has taken place

48
Q

What happens in the PCT?

A

Fluid is altered by the reabsorption of sugars, most mineral ions and some water. Around 85% of all fluid is reabsorbed here, cells here have a highly folded surface producing a brush border which increases surface area

49
Q

What happens in the descending limb of the loop of Henle?

A

Water potential of fluid is decreases by addition of mineral ions and the removal of water

50
Q

What happens in the ascending limb of the loop of Henle?

A

Water potential is increased as mineral ions are removed from the ascending limb by active transport

51
Q

What happens in the collecting duct?

A

Water potential is decreased again as water is selectively reabsorbed, the final product in the collecting duct is urine

52
Q

How are cells in the PCT adapted for selective reabsorption?

A
  • Cell surface membrane in contact with tubule fluid is highly folded to increase surface area for reabsorption
  • Cell surface membrane also contains special cotransporter proteins that transport glucose and amino acids in association with sodium ions, from the tubule into the cell
  • Opposite membrane of the cell that is close to the capillary and tissue fluid is also folded to increase its surface area
  • Cytoplasm of the proximal convoluted tubule contains many mitochondria, this is to actively pump sodium ions out of the the cells lining the tubule and into the blood
53
Q

Describe the mechanism of selective reabsorption of glucose and amino acids

A
  • Sodium ions are actively pumped out of the cells lining the tubule and into the the capillaries, potassium ions move the other way
  • Sodium ions being pumped out causes concentration of sodium ions in the cytoplasm of the cells lining the PCT to decrease, this creates a concentration gradient
  • Sodium ions diffuse down their concentration gradient into the PCT cells from the lumen of the PCT (from the urine) through a special cotransporter protein. The sodium ions cotransport glucose and amino acids against their concentration gradient
  • The movement of these substances into the cell reduces the water potential of these cells, this causes water to follow by osmosis
  • Glucose and amino acids diffuse into the blood, water follows by osmosis
54
Q

How does the glomerulus maintain a higher pressure than the lumen of the bowman’s capsule?

A

The afferent arteriole is wider than the efferent arteriole, the difference in diameters ensures that the blood in the glomerulus capillaries has a higher pressure than that of the lumen of the bowman’s capsule. This pressure difference causes fluid from the blood to be pushed into the lumen of the bowman’s capsule

55
Q

How can larger molecules be reabsorbed if they happen to enter the filtrate?

A

By endocytosis

56
Q

Describe the mechanism of reabsorption in the loop of Henle

A
  • Mineral ions enter the descending limb, this decreases the water potential at the top of the descending limb, as the tubule descends deeper into the medulla the water potential inside the tubule decreases
  • As the fluid rises up the ascending limb, mineral ions leave the ascending limb which increases the water potential. At the base of the ascending limb, mineral ions move out by diffusion, more mineral ions move out at the base meaning the water potential of the medulla is lower towards the bottom of the loop of Henle
  • At the top of the ascending limb, mineral ions are transported out of the ascending limb by active transport. This happens in smaller quantities than at the bottom of the ascending limb where ions move out by diffusion, this is why the water potential is lower towards the bottom of the loop of Henle as there are more ions moving out of the tubule at the bottom
  • The movement of ions out of the ascending limb means that the water potential of the urine at the top of the ascending limb is higher than the water potential of the blood meaning there is always a water potential gradient so water is always able to be reabsorbed in the collecting duct
57
Q

What is the arrangement of the loop of Henle known as?

A

A hairpin counter-current multiplier

58
Q

When the urine reaches the pelvis does it have a high or low water potential?

A

A low water potential as selective reabsorption has occurred, concentration of urea and minerals is higher than that in the blood

59
Q

Where are K+ ions actively transported into the tubule?

A

In the DCT

60
Q

When is your urine dilute?

A

When you have drunk a lot of fluid or on a cool day. You need to conserve less water, the walls of the collecting duct become less permeable, this means less water will be reabsorbed into the blood

61
Q

How does the hairpin countercurrent multiplier work?

A
  • The loop of Henle has an ascending and descending limb meaning that the urine is flowing down in the descending limb and up in the ascending limb
  • Mineral ions move out of the urine in the descending limb, this lowers the water potential of the medulla, at the base of the descending limb they move out by diffusion and at the top of the descending limb they move out by active transport, mineral ions move out in greater quantities at the bottom as they diffuse out instead of being actively transported out as they are at the top of the ascending limb
  • The water potential of the urine is lower at the bottom of the loop of Henle as mineral ions have diffused into the ascending limb as urine moves towards the bottom
  • The water potential is highest at the top of the ascending limb to maximise reabsorption of water in the collecting duct
  • The water potential is maximised at the top of the ascending limb by ions being actively transported out of the ascending limb and the top of the ascending limb being impermeable to water
  • The water potential of the urine at any point in the loop of Henle is higher than the medulla, this maximises the amount of reabsorption taking place
62
Q

What is osmolality?

A
  • The concentration of solutes in a fluid measured in mOsm kg-1
  • A high osmolality means low water potential
63
Q

Why is the concentration of glucose and amino acids very low?

A

They’re selectively reabsorbed at the PCT

64
Q

Why is the concentration of mineral ions higher in the urine than the filtrate?

A
  • As a lot of water is reabsorbed which increases the concentration of ions as there is the same amount of ions in a smaller volume , however, mineral ions are also reabsorbed at the PCT and at the loop of Henle, this decreases the concentration of mineral ions in the urine
  • The effect of water being reabsorbed has a slightly greater effect than the ions being reabsorbed so the concentration of mineral ions is slightly higher in the urine than in the filtrate
  • K+ ions are also actively transported into the the DCT for excretion causing their concentration to rise
65
Q

What is ADH?

A

A hormone that regulates the permeability of the walls of the collecting duct

66
Q

At what points of the loop of Henle is water reabsorbed?

A

The top of the descending limb, the bottom of the loop

67
Q

At what point of the loop of Henle do ions move into the loop?

A

Ascending limb

68
Q

At what point do ions move out of the loop?

A

The base of the ascending limb by diffusion and the top of the descending limb by active transport

69
Q

When is your urine concentrated?

A

On a hot day, or when you have drunk little fluid, the walls of collecting duct become more permeable to water so more water is reabsorbed, you produce a smaller volume of urine hence a higher concentration as same amount of urea in a smaller volume

70
Q

What is the body’s response to water potential of the blood decreasing

A
  • When a decrease in water potential of the blood is detected by osmoreceptors in the hypothalamus, these osmoreceptors stimulate neurosecretory cells that cause ADH to be secreted by the pituitary gland
  • ADH binds to membrane bound receptors on the cells in the walls of the collecting duct, this causes a cascade of enzyme controlled reactions inside the cell
  • These reactions cause vesicles with water-permeable channels called aquaporins in their membranes to fuse with the cell surface membrane, this means that the walls of the collecting duct, now containing aquaporins, are more permeable to water so more water is reabsorbed at the collecting duct
71
Q

What is the bodies response to an increase in blood water potential?

A
  • Water potential of blood increases, this is detected by osmoreceptors in the hypothalamus
  • These osmoreceptors signal for the pituitary gland to secrete less ADH
  • The cell surface membrane folds inwards to create new vesicles which removes aquaporins from the membrane
  • This makes the walls of the collecting duct less permeable to water, meaning less water is reabsorbed by osmosis into the blood
  • More water passes down the collecting duct meaning there is a greater volume of urine which is more dilute (has a higher water potential)
72
Q

How do osmoreceptors signal for the pituitary gland to release more ADH?

A
  • When the water potential of the blood is low, the osmoreceptors lose water by osmosis causing them to shrink, this stimulates neurosecretory cells
  • Neurosecretory cells are specialised neurones that produce and release ADH, the ADH then moves down the axon to the terminal bulb in the pituitary gland where it is stored in vesicles until the neurosecretory cells are stimulated
  • When the neurosecretory cells are stimulated this causes the release of ADH from the pituitary gland by exocytosis
73
Q

What happens to ADH in the blood when water potential rises again?

A

It is broken down, it has a half life of about 20 minutes

74
Q

What are polyclonal antibodies?

A

Antibodies that are all specific to the same antigen but each specific to a different epitope on the same antigen

75
Q

What are monoclonal antibodies?

A

Antibodies that are all specific to the same antigen

76
Q

What could indicate CKD?

A

A GFR of lower than 60cm3min-1

77
Q

What is haemodialysis?

A
  • Blood is passed from an artery or vein into a machine that contains an artificial dialysis membrane that is shaped into many artificial capillaries to maximise exchange
  • Dialysis fluid (containing the correct concentrations of mineral ions, urea, glucose, water, amino acids and other substances found in the blood plasma) flows in these artificial capillaries in the opposite direction to the blood to create a countercurrent effect which maximises the rate of diffusion
  • Heparin is added to avoid clotting and any bubbles are removed from the blood
  • This method of dialysis is performed at a clinic two or three times a week
78
Q

What is peritoneal dialysis?

A
  • The dialysis membrane is the body’s own abdominal membrane, a surgeon implants a permanent tube in the abdomen
  • Dialysis solution is poured into the tube and fills the space between the abdominal wall and organs, after several hours the solution is drained from the abdomen
79
Q

Describe the process for a pregnancy test

A
  • Once a human embryo is formed, it produces a hormone called hCG
  • Urine is poured onto the test stick
  • hCG binds to mobile antibodies attached to a blue bead
  • Mobile antibodies bound with hCG move down the stick with the urine
  • hCG binds to fixed antibodies, this holds the blue bead in place, a blue line forms
  • Mobile antibodies with no hCG attached bind to another fixed site to show the test is working, a blue line appears here also
80
Q

What are the main functions of the liver?

A
  • Control of blood glucose levels, amino acid levels and lipid levels
  • Synthesis of bile, plasma proteins and cholesterol
  • Synthesis of red blood cells
  • Storage of glycogen, iron and various vitamins
  • Detoxification of alcohol and drugs
  • Breakdown of hormones
  • Destruction of red blood cells
81
Q

How does the liver store glycogen?

A

The liver stores sugars in the form of glycogen, the liver can store approx. 100g of glycogen, it stores this as granules in the cytoplasms of the hepatocytes. It can be converted into glucose when blood glucose levels fall an more can be produced when blood glucose levels rise

82
Q

What is the function of catalase?

A

Converts hydrogen peroxide to water and oxygen

83
Q

What is cytochrome p450?

A

Breaks down cocaine and various other medicinal drugs

84
Q

Describe the process of alcohol detoxification

A
  • Ethanol is converted to ethanal, catalysed by an enzyme called ethanol dehydrogenase, 2H is removed and NADH is formed
  • Ethanal is converted to ethanoic acid catalysed by ethanal dehydrogenase and 2H is removed and NADH is formed
  • Ethanoic acid is converted to Acetyl CoA which enters the Krebs cycle
85
Q

How is the condition ‘fatty liver’ caused?

A

If someone drinks too much alcohol then the liver has to use up its NAD stores to detoxify the alcohol meaning fatty acids can’t be broken down into molecules that can be used in respiration. These fatty acids are then converted back to lipids causing the liver to become enlarged

86
Q

What is the equation for the reaction between an amino acid and oxygen to from a keto acid and ammonia?

A

2NH2-CHR-COOH + O2 → 2CRO-COOH + 2NH3

87
Q

Describe the process of the ornithine cycle

A
  • Ammonia and CO2 combine with ornithine to produce citrulline, a water molecule is removed
  • This is converted into arginine by the addition of further ammonia and removal of another water molecule
  • Arginine is then converted to ornithine by the removal of urea and addtion of a water molecule
88
Q

What are the three amino acids involved in the ornithine cycle?

A
  • Ornithine
  • Citrulline
  • Arginine

Biology A Level (21 decks)

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