A2 CH12 Homeostasis and the kidney Flashcards
1
Q
What is homeostasis?
A
The maintenance of the internal environment within tolerable limits
2
Q
How does the body accomplish homeostasis?
A
The body uses negative feedback to accomplish homeostasis
3
Q
What is negative feedback?
A
When a change in the system produces a second change, which reverses the first change
4
Q
How does negative feedback work?
A
- There is a change from the set point which is the input
- A receptor detects the change from the set point and sends instructions to a coordinator or controller
- A Coordinator detects signals from the receptors and coordinates a response via effectors
- An effector bring about changes to the system in order to return it to the set point
- The output brings the change back to the set point, and it monitored by the receptor and information is bed back to the effectors which stop making the correction
5
Q
How does glucose concentration in the plasma use negative feedback?
A
- If glucose concentration increases above the set point, insulin is secreted
- The insulin reduces the glucose concentration by converting it to glycogen and increasing the rate at which it is respired
- If glucose concentration falls below the set point, glucagon is secreted
- The secretion of glucagon results in glycogen being converted into glucose
6
Q
What does the body do when glucose concentration increases?
A
It secretes insulin
7
Q
How does insulin decreases glucose concentration?
A
Insulin converts glucose to glycogen and increases the rate at which it is respired
8
Q
What does the body do when glucose concentration falls below the set point?
A
The body secretes glucagon
9
Q
How does glucagon increase glucose concentrations?
A
Glucagon results in glycogen being converted into glucose
10
Q
How does the use negative feedback to maintain the body’s temperature?
A
- If the body’s temperature falls below the set point, increased respiration generates heat, and the constriction of blood vessels near the skin’s surface reduce heat loss
- If the body’s temperature rises above the set point, blood vessels near the skin’s surface dilate, and heat radiates from the body, reducing its temperature
11
Q
What does the body do when the body’s temperature falls below the set point?
A
- the body increases respiration to generate heat
- Blood vessels near the skin’s surface constrict to reduce heat loss
12
Q
What does the body do when the temperature rises above the set point?
A
The blood vessels near the skin’s surface dilate, and heat radiates from the body, reducing its temperature
13
Q
How does positive feedback work with oxytocin at the end of pregnancy?
A
Oxytocin stimulates the contraction of the uterus at the end of pregnancy. The contractions stimulate the production of more oxytocin
14
Q
How does positive feedback work when there is a cut in the skin?
A
When the skin is cut, platelets move to the cuts surface which secrete signaling molecules that attract more platelets to the cuts surface
15
Q
What is excretion?
A
The removal of metabolic waste made by the body
16
Q
What is excreted from respiration?
A
Carbon dioxide and water
17
Q
What is excreted from the deamination of excess amino acids?
A
Urea
18
Q
What are the 2 main functions of the kidney?
A
- Excretion
2. Osmoregulation
19
Q
What is osmoregulation?
A
The control of the water potential of the body’s fluids by the regulation of the water content of the body
20
Q
How is urea produced?
A
- Protein is digested into amino acids, which are transported to the liver and then around the body
- Excess amino acids are deaminated (removal of an amine group / NH2 group) in the liver and the amino group is converted into urea
- Urea is carried in the plasma to the kidneys and excreted as urine
21
Q
What are kidneys covered by?
A
The renal capsule
22
Q
Where does the kidney receive blood from?
A
The renal artery
23
Q
From the kidney, where does blood return back to the general circulation system?
A
The renal vein
24
Q
Where does the blood from the renal artery go?
A
It is filtered at the cortex in the bowman’s capsule
25
What structures of the nephron does the medulla contain?
The loop of Henle and the collecting ducts
26
Where does the collecting duct carry urine to?
The pelvis, then the ureter, then to the bladder
27
What is the structure of the kidney nephron?
- There are many kidney nephrons and they are long providing a large area for exchange
- There is an afferent arteriole which is a branch of the renal artery bring blood to the nephron which divides into many capillaries in the glomerulus (enclosed by the bowman's capsule)
- The filtered blood is carried by the efferent arteriole to a capillary network surround the proximal and distal convoluted tubules, and the vasa recta which is a capillary network surround the loop of Henle
28
What is the vasa recta?
The capillary network surrounding the loop of Henle
29
What is ultrafiltration?
Filtration under high pressure
30
Where does ultrafiltration occur?
Occurs in the bowman's capsule where small molecules including water and urea are removed from the blood
31
Where does the blood at the capillaries of the glomerulus come from?
The afferent arteriole
32
Why do the capillaries of the Bowman's capsule have a high pressure?
- The heart's contraction increases the pressure of arterial blood
- The afferent arteriole has a wider diameter than the efferent arteriole
33
What is the blood entering the glomerulus and the bowman's capsule separated by?
The bowman's space
34
What is the bowman's space comprised of?
1. Single layered capillary epithelium which has spores called fenestrae
2. Basement membrane of the bowman's capsule acts like a sieve between the blood and the nephron
3. Wall of bowman’s capsule is made of squamous epithelial called called podocytes, filtrate passes between their branches which are called pedicels
35
What does the high blood pressure in the capillaries of the glomerulus do?
it forces solutes and water through the fenestrae of the capillaries, through the basement membrane, and the filtration slits between the pedicles into the cavity of the bowman’s capsule
36
What are the solutes and water forced into the bowman's capsule called?
Glomerular filtrate
37
What does the glomerular filtrate contain?
- Water
- Glucose
- Salts
- Urea
- Amino acids
38
What is the maximum relative molecular mass of substances that can be forced out into the bowman's capsule?
68000
39
What substance that has a relative molecular mass smaller than 68000 remain in the blood?
HCG hormone that is used to detect pregnancy
40
What type of substances don't get filtered out and remain the blood?
blood cells, platelets, large proteins such as antibodies
41
Why does the blood that flow from the glomerulus into the efferent arteriole have a low water potential?
because water has been lost / filtered out and there is a high protein concentration remaining
42
What is the filtration rate?
the rate at which fluid passes from the blood in the glomerular capillaries into the bowman’s capsule
43
What determines the filtration rate?
the factors resisting the movement of filtrate
44
What is the movement of filtrate resisted by?
- Capillary epithelium
- Basement membrane
- Wall of bowman’s capsule
- Hydrostatic pressure in capsule
- Low water potential of the blood in glomerulus
45
What is selective reabsorption?
The uptake of specific molecules and ions from the glomerular filtrate in the nephron back into the bloodstream
46
Where does selective reabsorption take place? And what happens?
Occurs in the proximal convoluted tubule where useful substances such as water, glucose and amino acids and reabsorbed, but urea is not
47
Why is selective reabsorption important?
Glomerular filtrate contains wastes that the body needs to eliminate, but also useful molecules and ions (glucose, amino acids, sodium and chloride ions)
48
How are proximal convoluted tubules adapted for reabsorption?
- Cells lining the tubule have a large surface area as they have microvilli and basal channels (infoldings of the membrane in contact with the capillary)
- Large surface area as they are long and there are many nephrons in the kidney
- Many mitochondria providing ATP for active transport
- Close association with capillaries which creates a short diffusion pathway
- Tight junctions between proximal convoluted tubule cells which prevent molecules from diffusing between adjacent cells or back into the glomerular filtrate
49
What substances are reabsorbed into the blood during selective reabsorption?
Mineral ions, salts, glucose, amino acids, water, some urea and small proteins are reabsorbed into the blood
50
How are mineral ions and salts reabsorbed?
Mineral ions and salts are reabsorbed by facilitated diffusion and active transport
51
How are glucose and amino acids reabsorbed?
Glucose and amino acids are reabsorbed by secondary active transport using co-transport
52
How does co-transport work when reabsorbing glucose molecules?
1. A glucose molecules and two sodium ions bind to a transporter protein and enter the cell by facilitated diffusion
2. They diffuse across the cell and sodium ions are pumped into the capillary, glucose moved in by facilitated diffusion
53
Why is co-transport a type of secondary active transport?
Co-transport is secondary active transport because active transport keeps the sodium ion concentration in the epithelial cell low, enhancing its diffusion into the cell carrying in more glucose
54
How is water reabsorbed?
By osmosis
55
How is some urea and small proteins reabsorbed?
By diffusion
56
Why do some urea and small proteins get reabsorbed even though they are not useful?
This is because so much water has been lost, the concentration in the filtrate is high, so urea and small proteins diffuse down a steep concentration gradient
57
What describes the filtrate when it is at the base of the proximal convoluted tubule?
Filtrate at the base of the proximal convoluted tubule is isotonic with the blood plasma as the filtrate has lost a lot of substances back to the blood
58
Why is it important for glucose to be reabsorbed?
Glucose is an energy source and it would be a disadvantage to the body if it were lost
59
What happens when the glucose concentration becomes too high?
there won't enough transport molecules in the membrane cells of the proximal convoluted tubules to absorb it all, so glucose would pass through the loop of Henle and be lost in urine
60
What are some causes of high glucose concentrations?
- Type 1 diabetes where the pancreas secretes too little insulin
- Type 2 diabetes or in some pregnant women where the response of liver cells to insulin is reduced because insulin receptors on surface membranes are damaged
61
Where is the majority of water reabsorbed?
Majority of water is reabsorbed in the proximal convoluted tubule by osmosis
62
After the majority of water is reabsorbed, where does the rest of the water get reabsorbed?
The rest of the water is reabsorbed in the loop of Henle at the medulla, distal convoluted tubule at the cortex, and the collecting duct
63
Where in the kidney nephron does the same volume of water get absorbed?
Proximal convoluted tubule and loop of Henle
64
Which parts of the kidney nephron reabsorb varying volumes of water depending on the body's needs?
Distal convoluted tube and the collecting duct
65
What part of the loop of Henle is impermeable to water?
The ascending limb
66
What is the ascending limb's role in selective reabsorption?
They actively transport sodium and chloride ions out of the filtrate in the tubule into the tissue fluid in the medulla
67
What does a longer loop of Henle allow?
More ions can be pumped out into the medulla
68
What water potential does the loop of Henle have?
a low water potential
69
As the filtrate climbs from the bottom of the hairpin, what happens?
More ions are transported out so the filtrate becomes increasingly dilute and its water potential increases
70
What part of the loop of Henle is permeable to water?
the descending limb
71
As the filtrate flows down the ascending limb, what happens?
Water diffuses out by osmosis into the tissue fluid of the medulla which as a low water potential
72
What is the descending limb permeable to?
Water and slightly permeable to sodium and chloride ions
73
Where does the water move to after it has diffused out of the descending limb?
The water moves into the vasa recta
74
What is the mechanism of selective reabsorption?
This mechanism is a counter-current multiplier because the flow in the two limbs are in opposite directions and the concentration of solutes is increased
75
When the collecting duct runs back down into the medulla, what happens?
It passes through the region with low water potential so water diffuses out of the collecting duct by osmosis down the water potential gradient
76
What happens to the water if the loop of Henle is longer?
The water potential in the medulla is even lower as more ions are pumped out of the ascending limb, so more water leaves the collecting duct by osmosis
77
What can the filtrate in the collecting duct be described as?
The filtrate becomes more concentrated than the blood
78
By the time the filtrate reaches the base of the collecting duct. what is it?
Urine
79
Where does the water in the medulla go?
Water in the medulla is reabsorbed into the vasa recta and goes back into the general circulation
80
Why is the counter-current multiplier mechanism good for selective reabsorption?
It ensure that the concentration of the filtrate is always lower than the tissue fluid in the medulla
81
Why is osmoregulation important in animals?
it maintains the concentrations of enzymes and metabolites, and prevents cells from bursting or crenating
82
Where is ADH produced and secreted?
ADH is a hormone produced in the hypothalamus and is secreted by the posterior pituitary
83
What does ADH do?
ADH increases permeability of the cells of the distal convoluted tubule and collecting duct walls to water, increasing water reabsorption
84
What mechanism is used in osmoregulation?
Negative feedback and it controls the volume of water reabsorbed. It restores the normal water potential if the blood is diluted or more concentration
85
Why would animals be overhydrated?
- excess water intake
| - low salt intake
86
Why would animals be dehydrated?
- low water intake
- sweating
- High salt intake
87
What triggers the release of more or less ADH?
Water potential of the blood is controlled by receptors called osmoreceptors in the hypothalamus, which respond by triggering the release of more or less ADH into the blood from the posterior lobe of the pituitary gland
88
What is osmoregulation controlled by?
negative feedback
89
What happens when water potential in the blood is low?
1. Low water potential is detected by osmoreceptors in the hypothalamus
2. ADH is secreted by the posterior lobe of the pituitary gland into the bloodstream to be carried to the kidneys
3. ADH increases the permeability of the walls of the distal convoluted tubule and the collecting duct to water
4. More water is reabsorbed into the medulla which has a low water potential
5. Urine produced is more concentrated
90
What happens when the water potential in the blood is high?
Less ADH is released so the permeability of the distal convoluted tubule and collecting duct wall decreases so less water is reabsorbed to the blood, body produces a larger volume of more dilute urine
91
What is the ADH mechanism?
1. ADH binds to membrane receptor proteins found on the surface of cells lining the distal convoluted tubule and collecting duct walls
2. The binding of ADH triggers vesicles containing intrinsic membrane proteins called aquaporins containing pores that allow water to move, to fuse with the cell membrane
3. Aquaporins allow water to pass through the walls down the water potential gradient
4. When ADH concentration falls, aquaporins are removed from the cell membrane
92
What happens when the kidney fails?
The body it is unable to remove urea, so its concentrations increase to toxic levels. The body also is unable to remove excess water so body fluids increase in volume and are diluted, disrupting metabolic reactions
93
What are some common causes of kidney failure?
- Diabetes
- High blood pressure damaging the capillaries in the glomerulus preventing ultrafiltration
- Auto-immune disease
- Infection
- Crushing injuries
94
What treatments are there to regulate solute concentration in kidney failure?
- Low protein diet
- Drugs to reduce blood pressure
- Medication to control blood potassium and calcium levels
- Dialysis
- Kidney transplant
95
Why is a low protein diet recommended for patients with kidney failure?
Low protein diet reduces concentration of excess amino acids, and hence concentration of urea
96
What types of drugs reduce blood pressure and how do they do it?
- calcium channel blockers that dilate blood vessels
| - Beta blockers reduce the effect of adrenaline which increases blood pressure as the heart rate increases
97
Why is taking medication to control blood potassium and calcium levels important for a patient with kidney failure?
- High potassium concentration in the blood leads to heart disease
- High calcium levels lead to kidney stones
98
How does dialysis work?
- Uses dialysis fluid that contains glucose at the same concentration as the blood, but has no urea and a low ion concentration
- Using dialysis results in urea, some ions and water diffuse out of the blood, but glucose remains
99
What must be checked before a kidney transplant?
That the donor and patient must have compatible blood groups
100
What type of drugs must be taken after a kidney transplant and why?
Immunosuppressive drugs must be taken to prevent organ rejection
101
What are the 2 types of dialysis?
1. Haemodialysis
| 2. Peritoneal dialysis
102
How does haemodialysis work?
- It uses a dialysis machine
- Blood is taken from a patient's artery and it is passed through a dialyser containing selectively permeable dialysis tubing and dialysis fluid
- Counter current is used when blood and dialysis fluid move in opposite directions to ensure maximum transfer
- Heparin is added to thin the blood and prevent it from clotting
103
How does peritoneal dialysis work?
- Passes dialysis fluid into the peritoneum through a catheter
- Peritoneum contains many capillaries which exchange materials with the dialysis fluid
- Process is repeated several times a day
104
What is a advantage and disadvantage of peritoneal dialysis?
- Advantage is that the patient is able to move around
| - Disadvantage is that it is less effective than haemodialysis as fluid retention is likely
105
How do plants make all the proteins that they need?
- Plant cells combine ammonium ions with alpha-keto-glutarate, making the amino acid glutamate
- Glutamate is converted into any amino acid by transamination with alpha-keto acids
106
What is transamination?
Transamination is an enzyme catalysed reaction that transfers an amino group to an alpha-keto acid making an amino acid
107
Why don't plants excrete nitrogen containing molecules?
Plants synthesis only the amino acids and proteins that they need, so they don't excrete nitrogen containing molecules
108
Why are animals less than plants at transamination?
- Animals eat protein, and make the molecules they need from from the constituent amino acids
- They cannot store any amino acids they don’t need, so these excess amino acids are deaminated and converted into another molecule which is excreted
109
What do freshwater fish excrete?
ammonia
110
What are some key points about excretion in fish?
- Ammonia is highly soluble in water but very toxic so it cannot be stored
- Large surface area of fish gills allow ammonia to diffuse out rapidly and it is immediately diluted by surrounding water
111
What do birds, reptiles and insects excrete?
uric acid
112
Why do reptiles excreting uric acid allow them to survive in dry environments?
- Uric acid is non-toxic so it requires very little water to dilute it
- Conversion of ammonia to uric acid requires a lot of energy but little water is needed
- Allows these animals to conserve water and survive in dry environments
113
What is an advantage for birds excreting uric acid?
since small volumes of water is needed, it reduces their weight for flight
114
What do mammals excrete?
Urea
115
What are some key points about mammals excreting urea?
- Urea is less toxic than ammonia so it requires less water to dilute it
- Requires energy to convert ammonia to urea
- Prevent dehydration as less water is needed to excrete it
116
Why is the concentration in the medulla higher than the loop of Henle's?
Ion pumps in the ascending limb increase concentration in the medulla so it is higher than the loop of Henle’s
117
Why is urine more concentrated in a longer loop of Henle?
Low water potential in the medulla enhances water reabsorption from the descending limb and the collecting duct, resulting in a more concentrated urine
118
What are the 2 types of nephrons?
- Cortical nephrons
| - Juxtamedullary nephrons
119
Describe the structure or cortical nephrons
Glomerulus in the outer cortex and a short loop of henle which just penetrates the medulla
120
What types of nephrons do animals at low risk of dehydration mostly have?
- Animals such as beavers which are not at risk of dehydration have mostly cortical nephrons with very short loops of Henle, they made very dilute urine
121
Describe the structure of the juxtamedullary nephron
- Bowman’s capsules are in the inner cortex, close to the medulla
- Long loop of Henle which penetrated deep into the medulla
122
What types of animals have mostly juxtamedullary nephrons?
Animals that live inn dry habitats such as camels
123
Why do animals that live in dry habitats have mostly juxtamedullary nephrons?
This is so they can generate a very low water potential in the medulla and make very concentrated urine, conserving water efficiently
124
What is metabolic water?
Metabolic water is water produced from the oxidation of food reserves
125
What types of animals rely entirely on metabolic water?
Xerocoles which are desert animals
126
What behaviour do desert animals have?
- Most desert animals remain underground during the day, where it is cool and humid to reduce water loss by evaporation
- Some desert animals are also nocturnal and are at less risk of dehydration as less water evaporates from their bodies at lower temperatures
127
Why do desert animals remain underground during the day?
Because it is cool and humid underground and this reduces their water loss by evaporation
128
Why are some desert animals nocturnal?
Less water evaporates from their bodies at lower temperates so it reduces their risk of dehydration
