5.2 Excretion as an example of homeostasis control Flashcards
(141 cards)
1
Q
What is excretion?
A
The emoval of metabolic waste from thr body.
2
Q
What is metabolic waste?
A
A substance that is produced in excess by the body by a metabolic activity. It may become toxic.
3
Q
Why must sbstances be excreted?
A
So they do not build up and inhibit enzyme activity or become toxic.
4
Q
What are the 3 main excretory products?
A
- Carbon dioxide from respiration.
- Nitrogen-compounds, such as urea (i.e. nitogenous waste)
- Other compounds, such as bile pigments found in feases.
5
Q
What is the differnence between excretion and egestion?
A
Egestion is the elimination of feases from the body. Feases are undigested remains of food and are not metabolic products.
6
Q
What are the main organs involoved in excretion?
A
- The lungs
- The liver
- The kidneys
- The skin
- The ureter
- The bladder
- The uretha
7
Q
How are the lungs a excretory organ?
A
Every living cell in the body produces carbon dioxide as a result of respiration. Carbon dioxide passes in to the blood stream, where is it transported to the lungs. In the lungs the csrbon dioxide diffuses into the avioli to be excreted as you breath out.
8
Q
How is the liver an exretory organ?
A
It has many metabolic roles and some of the products will be passes ino bile for excretion with the feases, for example, the pigment bilirubin.
The liver also converts excess amino acids into urea, they’re broken down by daemination. The nitogen-containing part of he molecule is combines with carbon dioxide to make urea.
9
Q
How are the kidneys an excretory organ?
A
The urea is passed into the bloodstream to be transported to the kidneys. Urea is transported in solution- dissolved in plasma. In the kidneys the urea is removed from the blood to become a part of urine. Urine is stored in the bladder before being excreted from the body via the uretha.
10
Q
How is the skin an excretory organ?
A
Sweat contains a rangex of substances including salts, urea, water, uric acid and ammonia. Urea, uric acid and ammonia are all excretory products.
11
Q
What happens is products of metabolism build up?
A
They can interfer with cell processes by altering the pH, so the the normal metabolism is prevented. Other metabolic products may act as inhibitors and reduce the activity of essential enzymes.
12
Q
How is carbon dioxide mosty transported in the blood?
A
Hydrogencarbonate ions.
13
Q
How are hydrogencarbonate ions formed?
A
Carbon dioxide + water = carbonic acid, then the carbon acid dissociates to release hydrogen ions and hydrogenvcarbonate ions. This occurs in the red blood cells, under the infuence the the enzyme carbonic anahydrase.
14
Q
During the formation of hydrogencarbonate ions, how does hydrogen ions affect the red blood cells?
A
They affect the pH of the cytoplasm in the red blood cells. The hydrogen ions interact with the binds within heamoglobin, changing the 3-dimential shape, reducing the affinity of haemoglobin for oxygen, affecting oxygen transport.
The hydrogen ions can combine with heamoglobin, forming haemoglobinic acid. The carbon dioxide that wasn’t converted to hydrogencarbonate ions can combine with heamoglobin forming carbaminohaemoglobin, both haemoglobonic acid and carbaminohaemoglobin are unaable to combine with oxygen, reducing oxygen transport further.
15
Q
During the formation of hydrogencarbonate ions, how can excess hydrogen ions affect the blood plasma?
A
They can reduce the pH, which could alter the structure of many proteins in the blood that help transport a wide range of substances around the body. Proteins in the blood act as buffers to resist the change in pH.
16
Q
What happens if a small change in pH caused by extra hydrogen ions is detected in the body?
A
Extra hydrogen ions are detected by the respirtory centre in the medulla oblongata of the brain. Causing an increase in the breathing rate to help remove excess carbon dioxide.
17
Q
What happens if the body detects a larger change in it’s pH caused by extra hydrogen ions?
A
If pH drops below 7.35, it may cause headaches, drowiness, restlessness, tremor and confusion. There also may be a rapid heart rate and changesin blood pressure. This is respiratory acidosis.
18
Q
What is repiratory acidosis?
A
If blodd pH drops below 7.35, it may cause headaches, drowiness, restlessness, tremor and confusion. There also may be a rapid heart rate and changesin blood pressure.
19
Q
What is respiratory acidosis caused by?
A
It can be caused by disease or conditions that affect the lings, such as emphsyma, chronic bronchitis, asthma or sevre pneumonia. Blockages of the airways due to swelling, a foreign object, or volmit can also cause respiratory acidosis.
20
Q
What is it called when the potentially toxic amino acid group is removed in the liver?
A
Deamination
21
Q
What toxic chemical can excsee amino acids form?
A
Ammonia.
22
Q
What less toxic compound is ammonia coverted to in the liver?
A
Urea
23
Q
Where is urea transported to from the liver? Why?
A
It is transported to the kidneys fpr excretion
24
Q
What happens to the remaining amino acids after ammonia has been removed?
A
The 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.
25
Equation for deamination?
Amino acid + Oxygen = Keto acid + Ammonia
26
Equation for the formation of urea?
Ammonia + Carbon dioxide = Urea + Water
27
What are liver cells called?
Hepatocytes.
28
What is the function of the liver?
To remove excess or unwanted substances from the blood and return substances to the blood to ensure concentrations are maintained.
29
What does the internal structure of the liver ensure?
It ensures that as much blood flows past as many liver cells as possible.
30
What are the 2 blood vessels that supply the liver with blood?
* The hepatic artery
* The hepatic portal vein
31
What is the role of the hepatic artery?
Oxygenated blood from the heart travels from the aorta via the hapetic artery. This supplies the liver with oxygen for aerobic repiration- they need lots so they carry out a lot of metabolic processes.
32
What is the role of the hepatic portal vein?
The blood is rich in products of digestion. The concentrations of substances will be uncontrolled as they have just entered the body from digestion in the intestines. The blood may also contain toxic compounds. It is important these substances dont circulate the body before the concetrations have been adjusted.
33
What path does bloof take to the heptic portal vein?
Deoxygenated blood from the digestive system enters the liver via the heptic portal vein.
34
What blood vessel leaves the liver?
The heptic vein.
35
What happens to blood travelling in the heptic vein?
The heptic vein rejoins the vena cava and the blood returns to the body's normal circulation.
36
What vessel is connected to the liver that isn't a blood vessel?
The bile duct.
37
What is bile?
Bile is a sectretion from the liver which has functions in digestion and excretion. It also contains some excretory products such as bile pigments like bilirubin, which leaves the body in feases.
38
What is the role of the bile duct?
The bile duct carries bile from the liver to the gall bladder, where it is stored until required to aid the digestion of fats in the small intestine.
39
How is the structure of the liver specialised so that blood has maximum contact with the liver cells?
The liver is divided into lobes which are further divided into lobules.
40
What is this part of the liver?
Hepatocytes- liver cells with lots of microvilli
41
What is this part of the liver?
Inter-lobular vessels.
42
What is this bit of the liver?
Intra-lobular vessels.
43
What is this bit of the liver?
Kupffer cell- specialised macrophage that breaks down and recycles old red blood cells.
44
What is this bit of the liver?
A sinusoid-the sinusoid is in close contact to the liver cells.
45
What is the role of hepatacytes?
They remove substances from the blood and return other substances to the blood.
46
When Kupffer cells breakdown red blood cells, what is one of the primary products?
One of the products of heamoglobin break down is bilirubin, which is one of the bile pigments excreted as part of the bile.
47
What happens to bile produced in the liver?
Bile is released into bile canaliculi. The bile canaliculi join together to form the bile duct, which transports bile to the gall bladder.
48
What is the structure of a hepatocyte?
They have a cuboid shape with many microvilli on their surface. Their cytoplasm is very dense and is specialised in the number of organells it contains.
49
What are the metabolic functions of hepatocytes?
* Protein sythesis
* Transforming and storage of carbohydrates
* Synthesis of cholesterol and bile salts
* Detoxification
50
What metabolic functions does the liver carry out?
* Control of blood glucose levels, amino acids, lipid levels
* Synthesis of bile, plasma proteins, cholesterol
* Sythesis of red bloof cells in the fetus
* Storage of vitamins A, D and B12, iron and glycogen
* Detoxification of alcohol, drugs
* Breakdown oof hormones
* Destruction of red blood cells
51
What is the orithine cycle?
A series of biovhemical reactions that convert ammonia to urea.
52
How is glycogen stored in the liver?
Sugar is stored as glucogen. The glycogen forms granules in the cytoplasm of the hepatocytes- this can be broken down to release glucose into the blood.
53
How much glycogen can the liver store?
It's able to store about 100-120g of glycogen, which makes up about 8% of the fresh weights of the liver.
54
What substances may be detoxified in the liver?
* Hygrogen peroxide
* Alcohol
55
By what process can toxins be rendered harmless?
* Oxidation
* Reduction
* Methylation
* Combination with another molecule
56
What does the liver contain what renders toxins harmless?
It contains enzymes inculuding:
* Catalase- converting hydrogen peroxide to oxygen and water.
* Cytochrome P450- a group of enzymes used to break down drugs. They are also used in other metabolic reactions such as electron transport during respiration.
57
How is alcohol detoxified in the liver?
Enthanol dehydrogenase enzymes break down alcohol, resulting in the compound ethanal, which is dehydrogented further by the enxyme ethanal dehydrogenase making a finak compound ethonoate (acetate).
58
What happens the ethanoate in the liver after alcohol has been detoxified?
This acetate is combines woth coenzyme A to from acetyl coenzyme A, which enters the process of aerobic respiration.
59
What is ghe equation for the detoxification of alcohol?
60
What happens to the livers function to breakdown fatty acids if its required to breakdown too much alcohol?
It would have used up its NAD stores, leaving insufficient to breakdown the fatty aacids. These fatty acids are than converted back to lipids and stored as fat in hepatocytes, causing the liver to become enlarged. This condition is known as 'fatty liver', which can lead to alcohol-related hepatitis or to cirrhosis.
61
What part of an amino acid is toxic?
The amine group
62
Why do excess amino acids undogo deamination?
It cannot be stored because the amino grouo makes them toxic, however, it would be wasteful to excrete the whole molecule.
63
What treatmeant do amino aacids undergo in the liver to remove and excrete the amino component?
Deamination followed by the ornithine cycle.
64
What is an equation tht describes the formsstion of urea?
65
What equation shows deamination?
66
Why must ammonia be converted to a less toxic form very quickly?
Beacuse it is so soluble and toxic.
67
What is ammonia combines with to create urea?
Carbon dioxide- this occurs in the ornithine cycle.
68
What occurs in the ornithine cycle?
Ammonia and carbon dioxide combine with the amino acid ornithine to produce citrulline. This is converted by argunine by the addition of further ammonia. The agrunine is then re-converted to ornithine by removal or urea.
69
Why is ammonia converted to urea?
Urea is less soluble and less toxic than ammonia. It can be be passed back into the blood and transported around the body to the kidneys.
69
Why is ammonia converted to urea?
Urea is less soluble and less toxic than ammonia. It can be be passed back into the blood and transported around the body to the kidneys.
70
What happens to urea in the kidneys?
Urea is flitered out of the blood and concentrated in the urine. Urine can be stroed in the bladder safely until it is realsed from the body.
71
How can the ornithine cycle be summarised in an equation?
Ammonia + carbon dioxide -> urea + water
72
What does a diagram of the ornothine cycle look like?
73
8 to 10 litres of blood pass into the kidneys every hour. Why must so much blood pass through the kidneys?
The kidneys remove metabolic waste – the concentration of metabolic waste in the blood must be kept low. The
wastes are concentrated in the urine so a large volume of blood is needed to make a small volume of urine. Many
of the cells in the kidney are active – they need a good supply of oxygen.
74
Why are the proximal and distal tubules convoluted?
This makes the tubules longer so there is a larger total surface area for the selective reabsorption that takes place.
75
Why is each nephron surrounded by capillaries?
The substances reabsorbed from the fluid in the nephron must be returned to the blood.
76
Why must reabsorbtion from the nephron be selective?
Useful substances, such as glucose and amino acids, must all be removed from the fluid in the nephron. Wastes,
such as urea and excess salts, should remain in the fluid so that they can be excreted as urine.
77
Why is it essential that most of the water is reabsorbed from urine?
A large volume of blood passes through the kidney. If the water in it is all lost in urine the body will dehydrate
very quickly. A terrestrial animal cannot find and drink enough water to replace all the water that passes through
the kidney.
78
What is a nephron?
A functional unit of the kidney.
79
What is ultrafiltration?
Filtration of the blood at a molecular level under pressure.
80
What vessel supplies the kidney with blood?
Renal artery
81
What vessel drains the kidney of blood?
Renal vein
82
What is the role of the kidney?
The kidneys remove waste from the blood and produce urine.
83
What 3 regions can be seen in the kidney surrounded by the rough capsule?
* The outer region is the cortex
* The inner region is called the medulla
* The centre in the pelvis, which leads to the ureter
84
What does the bulk of the kindey consist of?
Tiny tubules called nephrons.
85
Aproximetly how mnay nephrons does one kidney have?
One million
86
What path does a nephron take in the kidney?
Each nephron starts in the cortex at a cup-shaped structure called the Bowmans capsulse. The remainder of a nephron is a coiled tubule that passes through the cortex, forms a loop don into the medulla and back into the cortex, before joining a collecting duct that passes back down into the medulla.
87
The renal artery splits to form many different arterioles, which lead to a knot of capillaries in the kidney, what is this called?
The glomerulus.
88
What is the vessel going the the glomerulus called and what is the one travellling away called?
Going to- afferent arteriole
Going away- efferent arteriole
89
What is the glomerulus surrounded by in the kidney?
The bowmans capsule.
90
By what process is blood pushed into Bowman's capsule in the kidney?
Ultrafiltration
91
What does the filter between the blood in the capillary and the lumen of the Bowman's capsule consist?
* The endothilium of the capillary
* The basement membrane
* The epithelial cells of the Bowman's capsule
92
How does the endothilium of the capillary provide ultrafiltration?
There are narrow gaps between cells of the endothilium and the capillary wall. The cells of the endothilium also contains pores, called fenostrations. The gaps allow blood plasma and the substances dissolved in it to pass out of the capillary.
93
How does the basement membrane provide ultrafiltration?
The membrane consists of a fine mesh of collogen fibres and glycoproteins. This mesh acts as a filter to prevent the passage of molecules with a relative mass greater than 69,000. This means that most proteins (and blood cells) and held in the capillaries in the glomerulus.
94
How does the endothilial cells of the Bowman's capsule provide ultrafiltration?
These podocytes have many fingure like projections called majoe processes, on which are minor processes (or foot ptocesses) that hold cells away from the endothilium of the capillary. These projections ensure there are gaps between the cells- fluid from the clood can pass into the lumen of the Bowman's capsule.
95
After the Bowman's capsule, what are the three parts of the tubule that it leads to?
* Proximal convoluted tubule
* Loop of Henle
* Distal convoluted tubule
96
What happens to fluid from many nephrons that enter collecting ducts?
It passes down through the medualla to the pelvis at the centre of the kidney.
97
What is ultrafiltration?
The filtering of blood at the molecular level.
98
What ensures a pressure is maintained in the glomerulus in the Bowman's capsule?
The difference in diameters of the capillaries either side if the glomerulus- the afferent arteriole is wider than the efferent arteriole.
99
Why does a pressure need to ne maintained in the glomerulus?
To push fluid from the blood into the Bowman's capsule.
100
What does blood plasma contain?
* Water
* Amino acids
* Glucose
* Urea
* Inorganic mineral ions
101
What is left in the capillary after ultrafiltration?
Blood cells and proteins.
102
After ultrafiltration, why is the water potential low and why is this significant?
The presence of proteins means the blood has very low water potential- this ensures some of the fluid is retained in the blood.
103
What is glomerular filtrate rate (GFR)?
The rate at which fluid enters the nephrons.
104
What are monoclonal antibodies?
Antibodies made from one type of cell- they are specifc to one compementary molecule?
105
What is renal dialysis?
A mechanism used to artificiallly regulate the concentrations of solutes in the blood.
106
What is kidney failure?
The kidneys are completely unable to regulate the levels of water and electrolytes in the body or to remove waste products such as urea from the blood.
107
How can kidney function be assessed?
* By estimating the glomerular filtration rate (GFR)- normal reading is between 90-1290cm^3min^-1, below 10cm^3min^-1 indicates kidney failure.
* By analysing the urine for substances such as proteins.
108
What are some causes of kidney failure?
* Diabetes mellitus (type 1&2)
* Heart disease
* Hypertension
* Infection
109
What are the 2 treatments for kidney failure?
* Renal dialysis
* Transplant
110
What is the most common treatment for kidney failure?
Renal dialysis
111
What does renal dialysis include?
Waste products, excess fluid and mineral ions are removed from the blood by passing it over a **partically permeable dialysis membrane** that allows the exchange of substances between the blood and dialysis fluid.
112
What does the dialysis fluid contain for renal dialysis?
Contains the correct concentrartions of mineral ions, urea, water and other substances found in the blood plasma.
113
What are the 2 types of renal dialysis
* Heomodialysis
* Peritoneal dialysis (PD)
114
What happens in renal dialysis?
Blood from an artery or vein is passed into a machine that contains artificial dialysis membrane shapes to form many artificial capillaries, which increase the surface area for exchnage. These capillaries are surrounded by dialysis fluid, which flows in the opposite dirrection to the blood (countercurrent flow).
115
What must be added to the blood during haemodialysis?
Heparin is added to avoid clotting.
116
What must be removed from the blood before the blood is returned to the body via a vein in haemodialysis?
Any bubbles in the blood.
117
What happens in pertineal dialysis?
The dialysis mebrane is the bidy's own abdominal membrane (peritoneum). A surgon implants a permanent tube in the abdomen. Dialysis solution is poured throught the tube and fills the space between the abdominal walls and organs. After several hours, thez solution is drained.
118
Where is haemodialysis usually carried out?
In a clinic 2 or 3 times a week for several hours per session. Some patients learn how to do it at home.
119
Where does peritoneal dialysis?
Home or work- beacuse the patient can walk around while having the dialysis.
120
During a kidney transplant, what is the new kidney connected to?
To the blood supply andd the bladder.
121
What drugs would a kidney transplant need to take?
Immunosupressants to help prevent their immune system recognise the new organ as a foreign body.
122
What are some advantages of a kidney transplant?
* Freedom from time consuming renal dialysis
* Feeling physically fitter
* Improved qulity of life- able to travel
* Improved self-image
123
What are some disadvantages of a kidney transplant?
* Need to tske immunosupresant drugs- side effects inculding, fluid retention, hoigh blood pressure, susceptablity to infections.
* Need for major surgery
* Need for regular checks for signs of rejection
124
What can the urine be tested for?
* Glucose in the diagnostic of diabetes.
* Alcoho to determine blood levels in drivers.
* Many recreational drugs
* Human chorionic gonadotrphin (hCG) in the pregnancy testing.
* Anabolic syeroids.
125
What occurs in pregancy testing?
1. Urine is poured onto stick.
2. hCG binds to mobile attatched to a blue bead.
3. Mobile antibodies move down the test stick.
4. If hCG is present, it binds to fixed antibodies holding a bead in place - a blue line forms.
5. Mobile antibodies with no hCG attatched bind to another binding site to show the test is working.
126
What does anabolic steroids do?
They increase protein sysntheis in cells.
127
Why are non-medical usues for anacolic steroid contreversial?
They can give an advangate in competative sports and have dangerous side-effects.
128
What does testing for anabolic steroids include?
Analysing a unrine sample in a lab using gas chromotography.
129
What is an antidiuretic hormone (ADH)?
A hormone that conrols the permeabitlity of the collecting duct walls.
130
What is an osoreceptor?
A sensory receptor that detects changes in the water potenial.
131
What is osmoregulation?
The control of the water potential in the body.
132
What does osmoregulation involuve controlling the levels of?
Water and salt in the body.
133
Why is osmoregulation important?
The correct water balence between cells and the surounding fluids must be maintained to prevent water entering cells and causing lysis or leaving the cells and causing crenation.
134
What sources does the body gain watter from?
Food, drink and metabolism.
135
Where in the bodyy controls the water and salt content in the bdy?
In the kidneys.
136
Where are osmoreceptors found?
In the hypothalamus.
137
What will occur in the body when the water potenial of the blood is low?
1. Osmoreceptor cells lose water by osmosis and shrink.
2. This stimulates neurosecretory cells in the hypothalamus, producing and releasing more ADH.
3. AD noces down the axon to the terminal bulb in the posterior pituitary gland, where it is stored is vesicles then released by exocytosis.
4. ADH travel in the blood untill it binds too receptors on the collecting duct
5. This causing a chain of enzye controlled reactoins inside the cell.
6. Resulting in vesicles containing water-permeable chaneels (aquaporins) to fuse with the cell surface membrane making the walls more permeabketo water.
138
What is changed about the collecting duct if the water potential of the bloof is loe?
Vesicles containing aquaporins fuse with the cell surface membrane, making the wall more permeable to water.
139
What is changed about the collecting duct is the water potential of the blood is high?
Level of ADH will fall, causing the cell surface membrane to fold inwards to create new vesicles the remove water-permeable channels from the membrane- making the wall less permeable to water.
140
What is the half life of ADH?
20 minutes.
