3.7 -homeostasis And The Kidney Flashcards
1
Q
Define homeostasis
A
The maintenance of a constant environment
2
Q
What does the internal environment consist of?
A
Tissue fluids (that bathe cells supply nutrients and removing waste), maintain glucose confrontation, pH, core temperature and solute potential.
3
Q
Why do we need to keep the concentration of body fluid at a constant and optimum level?
A
They protect cells from changes in the external environment, ensuring reactions continue at a constant and appropriate rate allowing cells to function normally despite external changes.
4
Q
What may alter within the body around a set point? (Dynamic equilibrium)
A
Body temperature, pH and water potential.
Constant changes occur but a set point is resumed (via homeostasis)
5
Q
What system controls homeostatic responses?
What do hormones operate by?
A
The endocrine system.
Negative feedback
6
Q
Define negative feedback
A
A change in a system that produces a second change, which reverses the first change.
7
Q
Give a general die statement about the process Of negative feedback
A
An output from an effector I.e a muscle or gland, reduced the effect of a stimulus and restores the system to its original level.
8
Q
Describe the steps of a generalised negative feedback loop
A
1) the set point for a factor is the norm at which the system operates
2) a receptor detects the level of the factor and its deviation from the set point
3) the receptor sends instructions to a co-ordinator or controller
4) the co-ordinator communicates with one or more effectors i.e muscles and glands, which make responses that are corrective procedures
5) the factor returns to normal monitored by the receptor and information is fed back to the effectors which stop making the correction
9
Q
Give an example of the negative feedback of glucose
A
If glucose concentration increases above the set point, insulin is secreted, reducing the glucose concentration by converting it to glycogen and increasing the rate at which it’s respired.
If the level falls below the set point, glucagon is secreted, which results in glycogen being converted to glucose.
10
Q
Describe the negative feedback of the body’s core temperature
A
If the body’s core temperature falls below a set point, increased respiration generates heat and construction of superficial blood vessels allows the body to retain it.
If the temperature rises above the set point, superficial blood vessels dilate, and heart radiates from the body, reducing its temperature.
11
Q
What happens during positive feedback?
A
An effective increases a change i.e a movement away from the norm cause a further movement away from the norm
12
Q
Describe how positive feedback is used during pregnancy
A
Oxytocin stimulates the contraction of the uterus at the end of a pregnancy. The contractions stimulate the production of more oxytocin which increases the stimulus I.e the uterine contractions
13
Q
Describe the process of positive feedback when you cut your finger
A
When the skin is cut, the first stage of clot formation is that platelets adhere to the cure surface. They secrete signalling molecules which attract more platelets to the site of the cut.
14
Q
Define excretion
A
The removal of metabolic waste made by the body
15
Q
Describe the metabolic process producing the compounds water and CO2?
In what are the compounds excreted?
What is the excretion organ?
A
Metabolic process= respiration
Compound excreted in air
Excretory organ= lungs
16
Q
Describe the metabolic process producing the compound urea.
In what are the compounds excreted?
What is the excretion organ?
A
Metabolic process= amino acid breakdown
Compound excreted in urine
Excretory organ= kidneys
17
Q
Describe the metabolic process producing the compound creatinine
In what are the compounds excreted?
What is the excretion organ?
A
Metabolic process= muscle tissue breakdown
Excreted in urine
Excretory organ= kidneys
18
Q
Describe the metabolic process producing the compound Uric acid
In what are the compounds excreted?
What is the excretion organ?
A
Metabolic process= nucleic acid breakdown
Compound excreted in urine
Excretory organ= kidneys
19
Q
Describe the metabolic process producing the compound bile pigments
In what are the compounds excreted?
What is the excretion organ?
A
Metabolic process= haemoglobin breakdown
Compound excreted in farces
Excretory organ= liver
20
Q
How is water removed from the body
A
Excreted as a metabolic Easter product of respiration
Secreted e.g in tears of saliva
Egested in faeces
21
Q
What are the two main functions of the kidney
A
Excretion (the removal of nitrogenous metabolic waste from the body)
Osmoregulation (the control of the water potential of the body’s fluids by regulating the water content)
22
Q
Define the term osmoregulation
A
The control of the water potential of the body’s fluids by the regeneration of the water content of the body
23
Q
Describe protein digestion briefly
A
Dietary protein is digested into amino acids, which are transported to the liver and then around the body where they are assimilated into protein
24
Q
What happens to excess amino acids?
A
They are deaminated in the liver and the amino group is converted to urea
Amino acid—> a-Keto acid + ammonia —> urea
25
Define the term deamination
The removal of an amino group from a molecule. Excess amino acids are deaminated in the liver, and the amine group is converted to urea.
26
What happens to other nitrogen containing waste products
They can also be converted to urea, although a low concentration of creatinine is released in both sweat and urine.
27
Where is urea carried to?
Urea is carried in the plasma to the kidneys and excreted in urine
28
List the parts of a human kidney
```
Renal artery (blood into kidney)
Renal vein (blood returned to general circulation)
Bowmans capsule (ultrafiltration)
Cortex
Medulla (contains loop of Henle and collecting duct)
Nephron
Pyramid
Pelvis (empties urine into the ureter)
Ureter (carries urine into the bladder)
```
29
Name the main features that are in the cortex
The glomerulus (containing the bowmans capsule) and the proximal/distal convoluted tubules
30
What are the main features in the medulla
The loop of henle and the collecting duct
31
What is the size of the kidney in an adult
Kidney is about:
15cm long
6cm wide
4cm thick
Urter is about:
30cm long
4mm in diameter
32
What are the main features of the kidney nephron?
```
Afferent arteriole (blood in)
Efferent arteriole (blood out)
Glomerulus
Bowmans capsule
Distal convoluted tubule
Proximal convoluted tubule
Vasa recta
Descending limb
Loop of Henle
Ascending limb
Collecting duct
```
33
How many nephrons are there in a human?
There are about a million nephrons in the kidneys, about 30mm long providing a large area for exchange
34
Where is the bloody carried in the kidneys nephron?
The afferent arteriole (a branch of the renal artery) brings the blood to the nephron, divides into about 50 capillaries in the glomerulus and is from there the filtered blood is carried by an efferent arteriole to the capillary network surrounding the proximal and distal convoluted tubules and the vasa recta.
35
Define the term ultrafiltration
Filtration under high pressure
36
Why does the blood arriving in the capillaries of the glomerulus have a high pressure?
1) The hearts contraction Increases the pressure of arterial blood
2) The afferent arteriole has a wider diameter than the efferent arteriole
37
By what is the blood entering the glomerulus separated from the Bowmans space?
Separated by 3 layers:
1) the wall of the capillary
2) the basement membrane
3) podocytes (the wall of the bowmans capsule)
38
Describe the structure of the capillary wall
A single layer of endothelium cells with pores called fenestrae, about 80nm in diameter
39
Describe the structure of the basement membrane
| Describe its role
An extra-cellular layer of proteins, mainly collagen and glycoproteins.
It acts as a molecular filter and is the selective barrier, acting like a sieve between the blood and the nephron
40
Describe the structure of the podocytes (wall of the bowmans capsule)
Made of squamous epithelial cells.
Each podocyte has multiple pedicels wrapped around the capillary pulling it closer to the basement membrane.
The gaps between the pedicels are called filtration slits.
41
What are the parts of the bowmans capsule
```
Afferent arteriole
Capillaries of the glomerulus
Capillary with fenestrae
Basement membrane
Podocyte
Path of filtrate
Cells of proximal convoluted tubule
```
42
Why is the high blood pressure in the capillaries of the glomerulus essential?
It forces solutes and water through the fenestrae if the capillaries through the basement membrane and through the filtration slits between the pedicels of the podocytes into the cavity of the bowmans capsule.
43
What does the glomerular filtrate contain
1. Water
2. Glucose
3. Salts
4. Urea
5. Amino acids
44
What molecules are too big to be filtered via ultrafiltration and hence remain in the blood
Blood cells
Platelets
Large proteins such as antibodies and albumin.
45
Describe the water potential in the blood that flows from the glomerulus into the efferent arteriole
It has a low water potential because much water has been lost and there is a high protein concentration remaining.
46
List the parts of the ultra structure of the wall of glomerular capillary and renal capsule
```
Fenestrae in capillary endothelium
Blood plasma
Water potential gradient
Hydrostatic pressure gradient
Basement membrane
Pedicel
Filtration slit
Podocyte cell of renal capsule wall
Bowmans space
Path of glomerular filtrate
```
47
What is the glomerular filtration rate?
The rate at which fluid passes from the blood in the glomerular capillaries into the bowmans capsule
48
What determines the glomerular filtration rate?
Determined by the difference in water potential between the two areas (the balance of their hydrostatic pressures and solute potentials).
49
Define the term selective reabsorption
The uptake if specific molecules and ions from the glomerular filtrate in the nephron back into the bloodstream
50
What useful molecules does the glomerular filtrate contain?
Glucose
Amino acids
Sodium ion
Chloride ions
51
What is the proximal convoluted tubule (PCT)?
It is the longest and widest part of the kidney nephron which carries the filtrate away from the bowmans capsule.
52
What process occurs at the proximal convoluted tubule?
The blood in the capillaries around the PCT reabsorbs all the glucose, amino acids, some of the urea, most of the water and sodium/chloride ions from the filtrate in the PCT.
53
How is the proximal convoluted tubule adapted from selective reabsorption?
1) large surface area because it is long and there are a million nephrons in the kidney
2) cuboidal epithelium cells in its walls who’s surface area is increased by microvilli
3) cuboidal epithelium cells also have invaginations called basal channels which increase surface area
4) many mitochondria providing ATP for active transport
5) a close association with capillaries
6) tight junctions between the cells of proximal convoluted tubule epithelium prevent molecules o from diffusing between adjacent cells or from the back into the glomerular filtrate
54
How does the PCT regulate he pH of the glomerular filtrate?
It exchanges hydrogen carbonate ions which increase the pH, with hydrogen ions which decrease the pH.
55
What % of salts in the filtrate are reabsorbed back into the blood during selective reabsorption?
70%
| Some reabsorption is passive but most uses active transport by membrane pumps.
56
How much of the glucose and amino acids are reabsorbed and how?
All of the glucose and amino acids are reabsorbed to the bloody by co-transport with sodium ions.
57
Describe the process by which glucose is reabsorbed.
A glucose molecule and two sodium ions bind to a transporter protein in the cuboidal epithelium cell membrane.
They enter the cell by facilitated diffusion, dissociate from the transporter and diffuse across.
Sodium ions are pumped into the capillary; glucose moves in by facilitated diffusion.
58
What is the alternate name of co-transport? Why?
Secondary active transport because active transport keeps the sodium ion concentration in the epithelial cell low, enhancing its diffusion into the cell carrying in the glucose.
59
What % of water of in the glomerular filtrate is reabsorbed?
Around 90%
| It is reabsorbed passively into the blood by osmosis as reabsorbed ions lower the water potential of the blood
60
What % of urea from the glomerular filtrate is reabsorbed?
About 50% if the urea and small protein in the glomerular filtrate is reabsorbed back unto the bloody by diffusion.
61
Why is there a steep concentration down which urea and proteins diffuse into the blood?
So much water has been lost from the filtrate that the concentration of urea and proteins in the glomerular filtrate is great and hence the concentration gradient is steep.
62
Define the key term secondary active transport
The coupling of diffusion e.g sodium ions, down an electrochemical gradient providing energy for the transport e.g of you’ve up it’s concentration gradient
63
What is reabsorbed in the distal convoluted tubule?
| What is it’s other role?
Some water and calcium/sodium ions
| It also has the role to regulate the ph of the filtrate.
64
List the parts of the proximal convoluted tubule and capillary
```
Endothelium
Capillary of vasa recta
Basement membrane
Microvillus brush border
Lumen of proximal convoluted tubule
Cuboidal epithelium
```
65
What happens in the proximal convoluted tubule if the glucose concentration in the filtrate is too high?
There are too few transport molecules in the membrane of the PCT to absorb all of the glucose and :: excess glucose will pass into the loop of Henle and be lost in the urine.
66
When may glucose be detected in the urine?
1) if the pancreas secreted too little insulin (type 1 diabetes) (insulin lowers blood glucose and glucagon radishes blood glucose)
2) insulin receptors in the surface membranes are damaged :: response of liver cells is reduced (type 2 diabetes or gestational diabetes)
67
What may happen if you loose too much glucose in your urine and you blood glucose concentration remains low?
```
Your pulse may race
Become dizzy/anxious/shakey
Become hungry
Irritable/sweaty
Concentration/co-ordination may deteriorate
Mouth/tongue becomes numb
Pass into a coma or
```
68
Where is water reabsorbed from to fight dehydration?
90% reabsorbed from the PCT
Some reabsorbed in the DCT (in the correx) and loop of Henle (in the medulla)
Also reabsorbed in the collecting duct
69
What parts of the nephron absorbs the same volume of water each time, and what can alter based on what the body needs?
The PCT and loop of Henle absorb the same volume each time
| The DCT and collecting duct reabsorbed varying values of water to operate the fine control of the body’s water content
70
Why can’t the PCT absorb all of the water in the filtrate?
Because excretory products have to be in solution to move through the nephron and out of the body
71
Describe the wall of the ascending limb
They are impermeable to water but fully permeable to ions
72
Describe the path of the filtrate through after the PCT
From the PCT it entrees the descending limb of the loop of Henle, Moves down into the Harpin Bend and up into the ascending limb.
73
What is the significance of the walls of the ascending limb being impermeable to water?
Allows for the active transport of sodium and chloride ions our of the filtrate in the tubule into the tissue fluid of the medulla.
This generates a low water potential in the tissue fluid of the medulla
74
What is the correlation between the length of the loop of Henle and the value of sodium/chloride ions actively transported from the tubule of the ascending limb into the tissue fluid in the medulla?
The longer the loop of Henle the greater the value of sodium/chloride ions actively transported into the tissue fluid of the medulla, and therefore the lower the water potential in the tissue fluid.
75
What happens to the water potential of the filtrate as it climbs from the bottom of the hairpin to the top of the ascending limb?
As it climbs there is greater active transport of ions and therefore the filtrate becomes increasingly dilute and water potential increases.
76
Describe the walls of the descending limb
The walls of the descending limb are permeable to water and slightly permeable to sodium and chloride ions
77
Describe what happens as the filtrate flows down the descending limb
Water diffuses out via osmosis into the tissue fluid of the medulla
Medulla :: has low water potential
Due to this the water :: moves into the vasa recta by osmosis (the capillaries surrounding the loop of Henle)
At the same time some sodium and chloride ions diffuse into the descending limb
78
When In the nephron is the filtrate at its most concentrated with the lowest water potential
At the bottom of the hairpin because as the filtrate moves down the descending limb it contains progressively less water and more ions
79
What is the counter-current multiplier effect in reference to the kidney nephron
It’s a process which enables the maximum concentration to be built up at the apex of the loop as the flow in the two limbs is in opposite directions increasing the concentration of solutes
80
What are the two purposes of the vasa recta?
1) delivers nutrients to the medulla cells
| 2) carries water reabsorbed from the glomerular filtrate in the nephron
81
Describe what happens once the filtrate reaches the top of collecting duct (in the cortex)
The collecting duct runs back down into the medulla which has a high solute concentration
Water diffuses out of the collecting duct via osmosis down a water potential gradient
The filtrate becomes more concentrated than the blood (is hypertonic to the blood)
By the time the filtrate reaches the base of the collecting duct it is urine
The water drawn out of the collecting duct via osmosis is reabsorbed into the vasa recta and into general circulation
82
What is the energy used to prevent water moving into the collecting duct via osmosis equal to?
The energy expended in pumping ions out of the ascending limb
83
What is osmoregulation?
It is the homeostatic function that maintain concentration of enzymes and metabolites so that the reaction within the cells occur at a constant and appropriate rate
84
How do humans gain their water?
90% from drinking and from food
| 10% from ‘metabolic water’(water released from the body’s reactions)
85
What is the receptor for osmoregulation?
| Why?
The hypothalamus (at the base of the brain) as its osmoreceptors monitor these solute potential in the blood.
86
What is the co-ordinator for osmoregulation?
The hypothalamus is also the co-ordinator as it signals the effect it to release stored antidiuretic hormone (ADH)
87
What is the effector in osmoregulation?
The posterior lobe of the pituitary gland as it relates stored ADH
88
Define the term Antidiuretic hormone (ADH)
It is the hormone produced in the hypothalamus and secreted by the posterior lobe of the pituitary gland.
It increases the permeability of the walls of the cells of the distal convoluted tubule and collecting duct to water, increasing its water reabsorption
89
What is Diuresis?
The production of a large volume of dilute urine.
90
What is a diuretic?
It is a compound (such as alcohol or coffee) that causes the production of a large volume of urine.
91
What process controls the volume of water reabsorbed by the Collecting duct and the distal convoluted tubule?
Negative feedback.
| It restores the normal water potential if the blood is diluted or becomes more concentrated.
92
What may cause a fall in water potential?
1) reducing water intake
2) sweating
3) intake of large amounts of salt
93
What happens if reduced water potential is detected by osmoreceptors in the hypothalamus?
Secretory granules carry ADH along axons from the hypothalamus to the posterior lobe of the pituitary gland from where ADG is secreted into the blood stream.
94
What happens after the blood containing increased values of ADH is carried to the kidneys?
- ADH increases the permeability of the walls of the distal convoluted tubule and the collecting duct to water
- more water is reabsorbed from there into the region of high solute concentration, low water potential in the medulla
- more water is reabsorbed from the medulla into the blood in the vasa recta
- the water potential of the blood is restored to normal
- the small volume of urine produced is relatively concentrated.
95
Describe the concentration of the urine of large volumes of ADH are secreted by the posterior lobe of the pituitary gland
The concentration is close to the concentration of the tissues near the apex of the loop of Henle and :: hypertonic to the body fluids
96
Describe briefly what happens if the water potential of the blood decreases after taking in a large volume of water
Less ADH is released by the posterior lobe of the pituitary gland
The permeability of the DCT and CD walls decreases
Less water leaves the DCT and CD via osmosis meaning that the water potential in the medulla is higher, decreasing the water potential gradient and allowing less water to be reabsorbed into the blood.
The water potential in the blood is restored to normal.
The body produces a large volume of more dilute urine.
97
What are aquaporins?
Intrinsic membrane proteins with a pore through which water molecules move.
98
How many types of aquaporins are known and how many are in the kidney?
There are 13 types of aquaporins known and 6 operate in the kidney
99
Describe the ADH mechanism (how ADH makes the walls of the collecting duct and distal convoluted tubule more permeable to water)
1- ADH bind to membrane receptors
2- Adenyl cyclase catalyses the production of cyclic AMP the second messenger
3- vesicles containing aquaporins in the cytoplasm move to and fuse with the cell membrane
4-Aquaporins are incorporated into the membrane
5- water molecules move in single file through their pores, down a water potential gradient
100
What stops the ADH mechanism?
When intracellular cyclic AMP levels fall, the aquaporins are removed from the cell membrane and they accumulate again in vesicles.
101
What happens if the kidney can’t complete it’s 2 functions (excretion and osmoregulation)
The body is unable to remove urea and so concentration can build up to toxic levels.
The body is unable to remove excess water so body fluids increase in volume and are diluted compromising metabolic reactions.
102
What are the most common causes of kidney failure?
1) Diabetes
2) High blood pressure (damage capillaries in the glomerulus which prevents ultrafiltration)
3) Auto immune disease (the body makes antibodies against its own tissues)
4) infection
5) crushing injuries (e.g traffic accident)!
103
Can the body remain healthy with only one kidney
Yes it can, there may be slight loss of kidney function later in life but life span is normal
104
What measures must be taken if both kidneys are compromised to reduce the concentration of waste products and control the volume of body fluids
1) reduce intake of certain nutrients e.g protein to reduce urea formation and ions e.g calcium and potassium
2) use drugs to reduce blood pressure
3) medications
4) dialysis
5) kidney transplant
105
What drugs can be used to reduce blood pressure?
1) calcium channel blockers dilate blood vessels and reduce blood pressure
2) beta blockers reduce the effect of Adrenalin, one affect of which is increased blood pressure as heart rate increases
3) Angiotensin-concerting enzyme (ACE) inhibitors reduce the effect of angiotensin (a hormone that constricts blood vessels increasing blood pressure)
106
What is used to combat a high potassium concentration in the blood?
What happens if it’s left untreated?
Treated with a combination of glucose and insulin.
| If untreated it leads to heart arrhythmias .
107
What is used to combat a High calcium concentration in the blood?
What happens if left untreated?
It is treated with bisphosphonates which decrease the activity of osteoclasts (cells that break down bone) and :: calcium accumulated in bone and less circulates in the blood.
If untreated it’s associated with heart disease; kidney stones and osteoporosis.
108
Briefly describe kidney dialysis
- Dialysis fluid has the same water potential as the blood but a low iron concentration and no urea. Inorganic ions, water and urea diffuse out of the blood across a selectively permeable membrane down their concentration gradients.
- The dialysis fluid contains glucose at the normal concentration of blood so none diffuses out of the blood.
109
What happens during haemodialysis
Blood is taken from an artery, and run through thousands of long, narrow fibres made of selectively permeable dialysis tubing.
The pores allow molecules in solution out into the dialysis fluid but not large proteins, blood cells or platelets.
The blood and dialysis fluid run through the machine in opposite directions, enhancing diffusion via a counter current mechanism.
The blood is returned to a vein.
110
What detects whether haemodialysis is harming a patient
Sensor in the dialysis fluid detects haemoglobin that would diffuse through if red blood cells were damaged.
111
What is a negative of haemodialysis
Kidney function is not addressed and :: many patients may become anaemia due to erythropoietin production, and the conversion of vitamin D into an active compound
112
Why may some people only have one kidney?
```
Born with one
Had one removed
Through illness
Through donation
Both were damaged and :: they Received a transplant
```
113
List the important parts of the continuous ambulatory peritoneal dialysis diagram (CAPD) (Oooh Catherine’s arse padded doe)
Peritoneum
Dialysis fluid in/out
waste moves out of capillaries
Peritoneal cavity containing dialysis fluid
114
What makes CAPD ambulatory
The patient can walk around, carrying on with normal activities while the dialysis operates.
115
Describe the process of continuous ambulatory peritoneal dialysis (CAPD)
The patient drains a 1-3dm3 bad of dialysis fluid through a catheter in the abdomen into the body cavity.
The peritoneum acts as the dialysis membrane and materials are removed from the blood in the capillaries into the dialysis fluid.
After about 40 minutes the dialysis fluid is drained from the abdomen, under gravity into an empty bag.
The process is repeated 4x daily.
116
What is the peritoneum?
The membrane lining the body cavity which has rich blood supplies.
117
What are the negatives of CAPD and what must patients do to counteract them.
Retention of liquid and a build up of potassium ions is common.
Patients must drink very little and avoid foods such as bananas and tomatoes which are high in potassium.
118
What must a donor and recipient be compatible in to be considered as a “match”
Must have the same ABO blood group and must be compatible in most of their HLA (human leucocyte antigens). Also a similar size and high risk donors are those over 50 with High blood pressure or diabetes.
119
How is rejection recognised?
- Increase in serum creatinine
- Increase in urea
- a reduction in the volume of urine
- kidney may feel tender.
120
Describe how a kidney transplant takes place.
The transplanted kidney is placed in the lower abdomen, in the groin.
The renal artery and vein emerging from the transplanted kidney are attached to the iliac artery and vein respectively.
The circulation to the new kidney is restored.
When the kidney resumes a healthy pink colour and urine is seen emerging from the ureter, the ureter is joined to the bladder.
121
What must a recipient of a donor kidney take?
Immunosuppressants
122
What are the negative associated with taking immunosuppressants?
- Rejection may still occur (normally within first 6 weeks)
- patients are more susceptible to infection, especially of urinary tract
- can cause increased risk of cancers
123
What are the two types of possible nephrons
1) cortical nephrons
| 2) juxtamedullary nephrons
124
Describe cortical nephrons
They have the glomerulus in the outer vortex and a short loop of Henle, which just penetrates the medulla.
125
Describe juxtamendullary nephrons
Their bowmans capsule is closer to the cortex’s boundary with the medulla. They have a long loop of Henle penetrating deep into the medulla.
126
What kind of organisms have majority cortical nephrons
Humans have mostly cortical nephrons.
Beavers and muskrats also have mainly cortical nephrons with very short loops of Henle to make very dilute urine as they live in wet habitats.
127
What organisms have mostly juxtamedullary nephrons?
Mammals such as Australian hopping mice live in arid habitats and :: they use their long loop of Henle to generate a very low water potential in the medulla and Male very concentrated urine, conserving water effectively.
128
Compare the habitats and length of loop of Henle for the following animals:
Beaver
Rabbit
Hopping mouse
Beaver: freshwater, very short LOH
Rabbit: mesic, short LOH
Hopping mouse: desert, long LOH
129
Define the term metabolic water
Water produced from the oxidation of food reserves
130
When is metabolic water produced?
Produced from the breakdown of food and its respiration.
131
Give an example of an organism that relies of metabolic water to survive
Xerocoles (desert animals) such as the kangaroo rat, live in hot/dry habitats, they do not drink and rely entirely on metabolic water.
132
How does the behaviour of desert animals preserve water?
They remain underground during the day.
Live in cool/humid burrows (reducing water loss by evaporation)
Some are nocturnal e.g scorpions :: less risk of dehydration as less water evaporates from their bodies at lower temperatures.
133
What May adaptations to conserve water be?
They may be anatomical, biochemical or behavioural
