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A-level biology > A2 - Unit 1 - Excretion > Flashcards

A2 - Unit 1 - Excretion Flashcards

1
Q

What is excretion?

A

The removal of metabolic waste from the body

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2
Q

What is metabolic waste?

A

Consists of waste substances that may be toxic or are produced in excess by the reactions inside cells

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3
Q

What is deamination?

A

The removal of the amine group from an amino acid to produce ammonia

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4
Q

What are the main two products in large amounts in the body?

A

Carbon dioxide from respiration

Nitrogen-containing compounds such as urea

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5
Q

Where is carbon dioxide produced in the body?

A

In every living cell as a result of respiration

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6
Q

Where is urea produced in the body?

A

In the liver from excess amino acids

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7
Q

Where is carbon dioxide excreted from the body?

A

Passed from the cells of respiring tissues into the bloodstream.
It is transported in the blood (mostly in the form of hydrogencarbonate ions) to the lungs.
In the lungs the carbon dioxide diffuses into the alveoli to be excreted as we breathe out

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8
Q

Where is urea excreted from the body?

A

Produced by breaking down excess amino acids in the liver. This process is called deamination. The urea is then passed into the bloodstream to be transported to the kidneys the urea is removed from the blood to become a part of urine
Urine is stored in the bladder before being excreted via the urethra

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9
Q

Why must carbon dioxide be removed from the body?

A

Excess CO2 in the body produces hydrogencarbonate ions with also formed hydrogen ions. The hydrogen ions compete with oxygen for space on the haemoglobin and reduces oxygen transport
CO2 also combines with haemoglobin to produce carbaminohaemoglobin. This molecule has a lower affinity for oxygen than normal haemoglobin
Excess CO2 can cause respiratory acidosis, CO2 dissolves in the blood plasma to produce carbonic acid, acid dissociates to release hydrogen ions and lowers the pH of the blood

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10
Q

Why must nitrogenous compounds be removed from the body?

A

Body cannot store proteins or amino acids
Contain almost as much energy as carbohydrates
Transported to liver
Potentially toxic amino group removed (deamination)
Initially forms ammonia, which is transported to less soluble and less toxic compound urea
Remaining keto acid can be used directly in respiration to release its energy or it may be converted to a carbohydrate or fat for storage

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11
Q

What is the hepatic portal vein?

A

An unusual blood vessel that has capillaries at both ends - it carries blood from the digestive system to the liver

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12
Q

What two sources of blood is the liver supplied with?

A

Oxygenated blood from the hear

Deoxygenated blood from the digestive system

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13
Q

Why is oxygenated blood from the heart supplied to the liver?

A

Blood travels from the aorta, via the hepatic artery into the liver. Supplied the oxygen which is essential for aerobic respiration.
Liver cells are very active as they carry out many metabolic processes, requiring ATP for energy

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14
Q

Why is deoxygenated blood from the digestive system supplied to the liver?

A

Enters liver via hepatic portal vein. This blood is rich in the products of digestion.
Conc of various compounds will be uncontrolled, blood may contain toxic compounds that have been absorbed in the intestine

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15
Q

How does blood leave the liver?

A

Via the hepatic vein. Rejoins the vena cava and the blood returns to normal circulation

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16
Q

What does the bile duct do?

A

Carries bile from the liver to the gall bladder where it is stored until required to aid the digestion of fats in the small intestines

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17
Q

How are cells arranged inside the liver?

A

Liver divided into lobes, further divided into lobules
Hepatic artery and hepatic portal vein run between, and parallel to the lobules
Blood from both vessels mixed and passes along a special chamber called a sinusoid
Hepatic vein drains blood from the liver
Blood that flows along the sinusoid is in very close contact with liver cells, able to remove molecules from the blood and pass molecules into the blood

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18
Q

Give 4 metabolic functions of the liver cells

A

Protein synthesis
Transformation and storage of carbohydrates
synthesis of cholesterol and bile salts
detoxification

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19
Q

What are Kupffer cells?

A

Specialised macrophages

Move about within the sinusoids and are involved in the breakdown and recycling of old red blood cells

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20
Q

What is the primary function of Kupffer cells?

A

Appears to be the breakdown and recycling of old red blood cells

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21
Q

What is bilirubin?

A

One of the waste products from the breakdown of haemoglobin

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22
Q

What is urea?

A

An excretory product formed from the breakdown of excess amino acids

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23
Q

What is the ornithine cycle?

A

The process in which ammonia is converted to urea. It occurs partly in the cytosol and partly in mitochondria, as ATP is used

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24
Q

What 6 functions does the liver have?

A

Control of blood glucose levels, amino acid levels, lipid levels
Synthesis of red blood cells in the fetus, bile, plasma proteins, cholesterol
Storage of Vitamins A, D and B12, iron, glycogen
Detoxification of alcohol, drugs
Breakdown of hormones
Destruction of red blood cells

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25
How is urea formed from amino acids?
Amino acid --------> ammonia ---------> urea ^ ^ deamination ornithine cycle
26
What equation can the ornithine cycle be summarised as?
Ammonia + carbon dioxide ---> urea + water
27
What is detoxification?
The conversion of toxic molecules to less toxic or non-toxic molecules
28
How is ethanol detoxified in the body?
Ethanol -> ethanol -> ethanoic acid -> acetyl coenzyme A And acetyl coenzyme A is used in respiration
29
What is produced in the detoxification of alcohol?
NAD is converted into reduced NAD
30
What happens if you consume too much alcohol?
If the liver has to detoxify too much alcohol it has insufficient NAD to deal with the fatty acids These fatty acids are then converted back to lipids and are stored in hepatocytes, causing the liver to become enlarged
31
What is a nephron?
The functional unit of the kidney A microscopic tubule that receives fluid from the blood capillaries in the cortex and converts this to urine which drains into the ureter
32
What is the glomerulus?
A fine network of capillaries that increases the local blood pressure that increases the local blood pressure to squeeze fluid out of the blood Surrounded by a cup or funnel-shaped capsule which collects the fluid and leads into the nephron
33
Explain the structure of the kidney
Outer region called the cortex Inner region is called medulla Centre called the pelvis which leads into the ureter
34
What four things is the nephron divided into?
Proximal convoluted tubule Loop of Henle Distal convoluted tubule Collecting duct
35
What is selective reabsorption?
Useful substances are reabsorbed from the nephron into the bloodstream while other excretory substances remain in the nephron
36
How does the composition of fluid change in the nephron?
PCT fluid is altered by the reabsorbed of all the sugars, most salts and some water 85% of the fluid reabsorbed here Descending limb of the loop of Henle, water potential of the fluid is decreased by addition of salts and removal of water Ascending limb, water potential increased as salts are removed by active transport Collecting duct, water potential is decreased again by the removal of water Ensures the final product has low water potential
37
What are afferent vessels?
Bring blood into the organ
38
What are efferent vessels?
Vessels carry blood away from the organ
39
What is ultrafiltration?
Filtration at a molecular level - as in the glomerulus where large molecules and cells are left in the blood and smaller molecules pass into the Bowman's capsule
40
What are podocytes?
Specialised cells that make up the lining of the Bowman's capsule
41
Why are the afferent arteriole and the efferent arteriole different diameters?
to put the blood in the capillaries under increased pressure The pressure difference tends to push fluid from the blood into the Bowman's capsule that surrounds the glomerulus
42
What does the lumen of the Bowman's capsule consist of?
Endothelium of the capillary Basement membrane Epithelial cells of the Bowman's capsule
43
How is the endothelium of the capillaries adapted for ultrafiltration?
Has narrow gaps between its cells that blood plasma and the substances dissolved in it can pass through
44
How is the basement membrane of the Bowman's capsule adapted for ultrafiltration?
Consists of a fine mesh of collagen fibres and glycoproteins Act as a filter to prevent the passage of molecules with a relative molecular mass of greater than 69000 Means that most proteins (and all blood cells) are held in the capillaries of the glomerulus
45
How are the epithelial cells of the Bowman's capsule adapted for ultrafiltration?
Called podocytes Have a very specialised shape Many finger-like projections called major processes These ensure that there are gaps between the cells Fluid from the blood in the glomerulus can pass between these cells into the lumen of the Bowman's capsule
46
What is filtered out of the blood during ultrafiltration?
``` Water Amino acids Glucose Urea Inorganic ions (sodium, chlorine, potassium) ```
47
What is left in the capillary during ultrafiltration?
Blood cells and proteins are left in the capillary The present of proteins means that the blood has a very low water potential. Low water potential ensures some fluid is retained in the blood
48
Why is a very low water potential in the capillary in ultrafiltration helpful?
It is important to help reabsorb water at a later stage
49
What is selective reabsorption?
As fluid moves along the nephron, substances are removed from the fluid and reabsorbed into the blood. Most reabsorption occurs from the proximal convoluted tubule, where about 85% of the filtrate is reabsorbed
50
What is reabsorbed at the selective reabsorption stage?
All the glucose and amino acids and some salts are reabsorbed along some of the water
51
What cells in the proximal convoluted tubule are specialised to achieve reabsorption?
Microvilli Co-transporter proteins Sodium-potassium pumps Many mitochondria
52
What is the purpose of microvilli in the lining of the proximal convoluted tubule?
increase the surface area for reabsorption
53
What is the purpose of co-transporter proteins in the lining of the proximal convoluted tubule?
Transport glucose or amino acids, in association with sodium ions, from the tubule into the cell. This is facilitated diffusion
54
What is the purpose of the sodium-potassium pumps in the lining of the proximal convoluted tubule?
Opposite membrane of the cell, close to the tissue fluid and blood capillaries, is also folded to increase its surface area. This membrane contains sodium-potassium pumps that pump sodium ions out of the cell and potassium ions into the cell
55
What is the purpose of the many mitochondria in the proximal convoluted tubule?
This indicates that an active, or energy-requiring, process is involved, as many mitochondria will produce a lot of ATP
56
How does reabsorption occur?
Sodium-potassium pumps remove sodium ions from the cells lining the proximal convoluted tubule Reduces the concentration of sodium ions in the cell cytoplasm Sodium ions transported into the cell along with glucose or amino acid molecules by facilitated diffusion As glucose and amino acid concentrations rise inside the cell, these substances are able to diffuse out of the opposite side of the cell into the tissue fluid Process may be enhanced by active removal of glucose and amino acids from the cell From the tissue fluid these substances diffuse into the blood and are carried away Reabsorption of salts, glucose and amino acids reduces the water potential in the cells and increases the water potential in the tubule fluid. This means that ware will enter the cells and then be reabsorbed into the blood by osmosis Larger molecules, such as small proteins that may have entered the tubule, will be reabsorbed by endocytosis
57
What are microvilli?
Microscopic folds of the cell surface membrane that increase the cell surface area of the cell
58
What are co-transporter proteins?
Proteins in the cell surface membrane that allow the facilitated diffusion of simple ions to be accompanied by transport of a larger molecule such as glucose
59
What is facilitated diffusion?
Diffusion that is enhanced by the action of proteins in the cell membrane
60
What are sodium-potassium pumps?
Special proteins in the cell surface membrane that actively transport sodium and potassium ions against their concentration gradients
61
What is a hairpin countercurrent multiplier?
The arrangement of a tubule in a sharp hairpin so that one part of the tubule passes close to another part of the tubule with the fluid flowing in opposite directions. This allows exchange between the contents and can be used to create a very high concentration of solutes
62
What is osmoregulation?
The control and regulation of the water potential of the blood and body fluids. In humans the kidneys control the water potential of the blood
63
Describe the structure of the loop of Henle
Descending limb that descends into the medulla and an ascending limb that ascends back out to the cortex
64
How is the arrangement of the loop of Henle functional?
``` Allows salts (sodium and chloride ions) to be transferred from the ascending limb to the descending limb The overall effect is to increase the concentration of salts in the surrounding medulla tissue, giving the tissue fluid in the medulla a very low (very negative) water potential ```
65
How does the water potential in the descending limb become more negative?
Due to: loss of water by osmosis to the surrounding tissue fluid Diffusion of sodium and chloride ions into the tubule form the surrounding tissue fluid
66
How does the water potential in the ascending limb become less negative?
Because: At the base of the tubule, sodium and chloride ions diffuse out of the tubule into the tissue fluid Higher up on the tubule, sodium and chloride ions are actively transported out into the tissue fluid The wall of the ascending limb is impermeable to water, so water cannot leave the tubule The fluid loses salts but not water as it moves up the ascending limb
67
What is the distil convoluted tubule?
The coiled portion of the nephron between the loop of Henle and the collecting duct
68
What is ADH?
(Anitdiuretic hormone) Released from the pituitary gland and acts on the collecting ducts in the kidneys to increase their reabsorption of water
69
What are osmoreceptors?
Receptor cells that monitor the water potential of the blood.
70
What is the hypothalamus?
A part of the brain that contains neurosecretory cells and various receptors that monitor the blood
71
What are neurosecretory cells?
Specialised cells that act like nerve cells but release a hormone into the blood. ADH is manufactured in the cell body and passes down the axon to be stored in the terminal bulb. If an action potential passes down the axon then ADH is released from the terminal bulb
72
What is the posterior pituitary gland?
The hind part of the pituitary gland, which released ADH
73
Where is water gained in the body?
Food Drink Metabolism (respiration)
74
Where is water lost in the body?
Urine Sweat Water vapour in exhaled air Faeces
75
How do osmoreceptors work?
If the blood has a low water potential then water is moved out of the osmoreceptor cells by osmosis, causing them to shrink. This causes stimulation of the neurosecretory cells
76
How can you alter the permeability of the collecting duct?
Walls of the collecting duct respond to the level of ADH in the blood Cells in the wall have membrane-bound receptors for ADH ADH binds to these receptors and causes a chain of enzyme-controlled reactions inside the cell End result is to insert vesicles containing water-permeable channels (aquaporins) into the cell surface membrane Makes the walls more permeable to water If there is more ADH in the blood, more water-permeable channels are inserted Allows more water to be reabsorbed by osmosis into the blood
77
What happens to the body if there is less ADH in the blood?
The cell surface membrane folds inwards to create new vesicles that remove water-permeable channels from the membrane This makes the walls less permeable and less water is reabsorbed by osmosis into the blood More water passes out in the dilute urine
78
What is the water potential of the blood monitored by?
Osmoreceptors in the hypothalamus of the brain
79
What happens when the water potential of the blood is very low?
The osmoreceptor cells lose water by osmosis | This causes them to shrink and stimulate neurosecretory cells in the hypothalamus
80
What are the neurosecretory cells and what do the do?
Specialised neurones Produce and release ADH ADH is manufactured in the cell body of these cells, which lies in the hypothalamus ADH flows down the axon to the terminal bulb in the posterior pituitary gland It is stored there until needed
81
What happens when the neurosecretory cells are stimulated?
They send action potentials down their axons and cause the release of ADH
82
How does ADH reach its target cells?
Enters the blood capillaries running through the posterior pituitary gland It is transported around the body and acts on the cells of the collecting ducts (its target cells)
83
When is less ADH released?
Once the water potential of the blood rises again
84
What is half-life?
The half-life of a substance is the time taken for its concentration to drop to half its original value
85
How do you remove ADH from the body once it has had its desired effect?
It has a half-life of 20 minutes | Therefore the ADH present in the blood is broken down and the collecting ducts will receive less stimulation
86
What is dialysis?
The use of partially permeable membrane to filter the blood
87
What is the dialysis membrane?
A partially permeable membrane that separates the dialysis fluid from the patient's blood in a dialysis machine
88
What is dialysis fluid?
A complex solution that matches the composition of body fluids
89
What is haemodialysis?
Blood is taken from a vein and passes through a dialysis machine so that exchange can occur across an artificial partially permeable membrane
90
What is peritoneal dialysis?
Dialysis fluid is pumped into the body cavity so that exchange can occur across the peritoneal membrane
91
What are the three causes of kidney failure?
Diabetes mellitus (both type I and type II sugar diabetes) Hypertension Infection
92
What are the two main treatments for kidney failure?
Dialysis | Transplant
93
How does haemodialysis work?
Blood from the vein is passed into the machine that contain an artificial dialysis membrane Heparin is added to avoid clotting, and any bubbles are removed before the blood returns to the body Haemodialysis is usually performed at a clinic three times a week for several hours at each session, but some patients learn to carry it out at home
94
How does peritoneal dialysis work?
The filter in the body's own abdominal membrane First, a surgeon implants a permanent tube in the abdomen Dialysis solution is poured through the tube and fills the space between the abdominal wall and organs After several hours, the used solution is drained from the abdomen PD is usually performed in several consecutive sessions daily at home or work As the patient can walk around having dialysis, the method is sometimes called ambulatory PD
95
When someone is having a kidney transplant do they leave the old ones in? Where might someone get a kidney from?
The old kidneys are left in place unless they are likely to cause infection or are cancerous The donor kidney can be from a living relative who is willing to donate one of their healthy kidneys or from someone who has died
96
What happens during a kidney transplant?
Patient is under anaesthesia, the surgeon implants the new organ into the lower abdomen and attaches it to the blood supply and the bladder. Many patients feel much better immediately after the transplant, which is the best life-extending treatment for kidney failure However the patient's immune system will recognise the new organ as a foreign object and produce a reaction. Patients are given immunosuppressant drugs to help prevent rejection
97
What is human chorionic gonadotrphin (hCG)?
A hormone released by human enbryos; its presence in the mother's urine confirms pregnancy
98
What are monoclonal antibodies?
They are identical because they have been produced by cells that are clones of one original cell
99
What are anabolic steroids?
Drugs that mimic the action of steroid hormones that increase muscle growth
100
What is gas chromatography?
A technique used to separate substances in a gaseous state.
101
What is a chromatogram?
A chart produced when substances are separated by movement of a solvent along a permeable material such as paper or gel
102
What are the advantages of kidney transplants?
Freedom from time-consuming dialysis Diet less limited Feeling better physically A better quality of life e.g. able to travel No longer seeing oneself as chronically ill
103
What are the disadvantages of a kidney transplant?
Need immunosuppressants for the life of the kidney Need major surgery under general anaesthetic Risks of surgery include: infection, bleeding and damage to surrounding organs Frequent checks for signs of an organ rejection Side effects: anti-rejection medicines cause fluid retention and high blood pressure, immunosuppressants increase susceptibility to infections
104
How does pregnancy testing work?
When pregnant, hCG is present in the mothers urine Pregnancy tests are manufactured with monoclonal antibodies These antibodies are specific and will only bind to hCG not other hormones Soaks a portion of the test strip with urine Any hCG in the urine will attach to an antibody that is tagged with a blue bead As a result the antibodies carrying a blue bead and attached to hCG are held in one piece forming a blue line There is always one blue line as a control, a second blue line indicates pregnancy
105
How do you test for anabolic steroids?
Anabolic steroids increase protein synthesis within cells Results in a build up of cell tissue, especially in the muscles Have a half life of 16 hours Testing involves analysing a urine sample in a laboratory using gas chromatography or mass spectrometry In GC the sample is vaporised in the presence of a gaseous solvent and passed down a long tube lined by an absorption agent Each substance dissolves differently in the gas and stays there for a unique, specific time Eventually the substance comes out of the gas and is absorbed onto the lining This is then analysed to create a chromatogram

A-level biology (18 decks)

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