6C - homeostasis Flashcards
1
Q
what do organisms have to run efficiently?
A
different control systems that ensure their internal conditions are kept relatively constant
2
Q
what does homeostasis involve?
A
physiological control systems that maintain the internal environment within restricted limits
3
Q
what is homeostasis?
A
maintenance of a constant internal environment in an organism
4
Q
what does homeostasis ensure?
A
it ensures the cells are in an environment which allows them to carry out their function
5
Q
what does homeostasis act to do?
A
bring any fluctuations in line with the set point
6
Q
why is homeostasis important?
A
-to ensure that enzymes which control metabolic reactions are working at their optimum rate
-to ensure a constant blood glucose concentration
-if organisms can resist fluctuations in their internal environments, they are less reliant on their external
environment
7
Q
what do homeostatic mechanisms require?
A
information to be transferred between different parts of the body
8
Q
which systems allow information to be transferred between different parts of the body?
A
-the nervous system
-the endocrine system
9
Q
examples of physiological factors that are controlled by homeostasis in mammals:
A
-core body temperature
-blood pH
-concentration of glucose in the blood
-water potential of the blood
10
Q
what is a hormone?
A
a chemical substance produced by an endocrine gland and carried in the bloodstream / they are chemicals which transmit information from one part of the organism to another and bring about a change
11
Q
what do hormones do?
A
they alter the activity of one or more specific target organs
12
Q
what are hormones used to control?
A
functions that do not need instant responses
13
Q
what is the endocrine system?
A
the endocrine glands that produce hormones in animals
14
Q
what is a gland?
A
a group of cells that produces and releases one or more substances (secretion)
15
Q
examples of glands in the body:
A
-thyroid gland (thyroxine)
-pancreas (insulin)
-testes (testosterone)
-ovaries (oestrogen)
16
Q
what is the pituitary gland?
A
the master gland at the base of the brain
17
Q
endocrine glands have… and why?
A
a good blood supply
↳ when they make hormones they need to get them into the blood plasma as soon as possible so they can travel around the body to the target organs to bring about a response
18
Q
what can hormones affect?
A
-hormones only affect cells with receptors that the hormone can bind to
-receptors have to be complementary to hormones for there to be an effect
19
Q
where are hormone receptors found?
A
these are found on the cell surface membrane or inside cells
20
Q
the human nervous system consists of…
A
CNS – the brain and the spinal cord
(PNS) – all of the nerves in the body
21
Q
what does the nervous system allow us to do?
A
it allows us to make sense of our surroundings and respond to them and coordinate and regulate body functions
22
Q
how is information sent through the nervous system?
A
information is sent through the nervous system as nerve impulses – electrical signals that pass along nerve cells known as neurones
23
Q
what is a nerve?
A
a bundle of neurones
24
Q
what do neurones coordinate?
A
the activities of sensory receptors, decision-making centres in the central nervous system, and effectors such as muscles and glands
25
what is vital for enzymes activity?
a stable core temperature and blood pH are vital for enzyme activity (if the temperature or pH of the tissue fluid surrounding cells is too high or too low it can negatively affect the rate of important enzyme-controlled reactions)
26
what do enzymes have associated with temperature?
**a specific optimum temperature** - the temperature at which they catalyse a reaction at the maximum rate
27
what do lower temperatures do to enzymes?
either prevent reactions from proceeding or slow them down
28
how do lower temperatures impact enzymes? (steps)
1) molecules move relatively slow
2) lower frequency of successful collisions between substrate molecules and active site of enzyme
3) less frequent enzyme-substrate complex formation occurs
4)substrate and enzyme collide with less energy → less likely for bonds to be formed or broken
29
how to higher temperatures affect enzymes? (steps)
1) molecules move more quickly
2) higher frequency successful collisions between substrate molecules and active site of enzyme
3) more frequent enzyme-substrate complex formation
4) substrate and enzyme collide with more energy, making it more likely for bonds to be formed or broken (allowing the reaction to occur)
30
what do very high temperatures do to enzymes? (steps)
as temperatures continue to increase, the rate at which an enzyme catalyses a reaction drops sharply, as the enzyme begins to denature
31
how do very high temperatures affect enzymes? (steps)
1) bonds holding the enzyme molecule in its precise shape start to break
2) this causes the tertiary structure of the the enzyme to change
3) this permanently damages the active site, preventing the substrate from binding
4) denaturation has occurred if the substrate can no longer bind
(high temperatures cause the hydrogen bonds between amino acids to break, changing the conformation of the enzyme)
32
what approximate temperature do enzymes denature around?
very few human enzymes can function at temperatures above 50°C → this is because humans maintain a body temperature of about 37°C, therefore even temperatures exceeding 40°C will cause the denaturation of enzymes
33
what do enzymes have associated with pH?
all enzymes have an optimum pH or a pH at which they operate best,
enzymes are denatured at extremes of pH
34
how do pH fluctuations affect enzymes?
1) hydrogen and ionic bonds hold the tertiary structure of the enzyme together
2) below and above the optimum pH of an enzyme, solutions with an excess of H+ ions (acidic solutions) and OH– ions (alkaline solutions) can cause these bonds to break
3) this alters the shape of the active site, which means enzyme-substrate complexes form less easily
4) eventually, enzyme-substrate complexes can no longer form at all
5) at this point, complete denaturation of the enzyme has occurred
35
what can indicate an enzymes optimum environment?
where an enzyme functions/is found can be an indicator of its optimal environment
36
what does the amount of glucose present in the blood affect?
the water potential of the blood and the availability of respiratory substrate for cells
37
what is the normal glucose concentration for human blood?
roughly 90mg per 100cm³
38
what is glucose required for?
cellular respiration
39
effects of insufficient amounts of glucose:
brain cells can become rapidly damaged or die if they do not receive a sufficient supply of glucose
(glucose is the only respiratory substrate that can be used in the brain) / if the water potential of the blood is too high, water will move into cells by osmosis and can cause them to burst
40
effects of overly high amounts of glucose:
if the blood glucose concentration is too high then the water potential of the blood with lower and water will leave surrounding cells by osmosis and prevent normal cell function
41
what do most homeostatic control mechanisms of organisms use?
they use negative feedback to maintain homeostatic balance and keep certain physiological factors, within certain limits
42
what is negative feedback?
the condition being regulated is brought back to a set value as soon as it is detected to have parted from it
43
what are the components of negative feedback control loops?
1) a receptor (or sensor) – to detect a physiological factor
2) coordination system (nervous system and endocrine system) – to transfer information between different parts of the body
3) an effector to carry out a response
44
steps of negative feedback:
1) stress or disturbance changes the internal environment
2) change/physiological factor is detected by receptors
3) receptor sends information through the nervous system to the brain or spinal cord
4) the brain activates corrective measures
4) corrective measures counteract the change back toward set point
45
in a negative feedback loop there are usually…
two corrective mechanisms
↳ one for when the factor becomes too low (causes the factor to decrease)
↳ one for when the factor becomes too high (causes the factor to increase)
46
what do negative feedback loops do?
reduce the effect of the original stimulus to keep a factor within a normal range
47
what is positive feedback?
when the deviation of the condition from the predetermined state is enhanced
48
what happens in positive feedback loops?
they enhance the effect of the original stimulus, which produces a response that causes the factor to deviate from the normal range
49
examples of positive feedback:
the entry of sodium ions into the axon after an action potential is reached
50
feedback inhibition:
-the end product in a metabolic pathway binds to an enzyme at the start of the pathway
-this process stops the metabolic pathway and so prevents further synthesis of the end product until the end product concentration decreases
-the higher the concentration of end product, the quicker the metabolic pathway stops
51
bone repair & positive feedback:
the osteoblast cells enhance the effect of the original stimulus (insulin) - positive feedback
52
where is glucose carried?
-it is carried around the body in solution in the blood plasma
-it's a small molecule so can easily move out of the blood capillaries into the tissue fluid
53
when does blood glucose increase?
following ingestion of food or drink containing carbohydrates
54
when does blood glucose fall?
after exercise / if you have not eaten
55
which organ is key in blood glucose control?
the pancreas, it detects changes in the blood glucose level & secretes two hormones that control blood glucose level
56
what does the pancreas contain?
it contains endocrine tissue made of a group of cells called the islets of langerhans
57
what does the islets of Langerhan contain?
two cell types:
α cells that secrete the hormone glucagon
β cells that secrete the hormone insulin
58
what other hormone is important for blood glucose concentration?
adrenaline, which is released by the adrenal glands
59
what do a and B cells act as?
the receptors that initiate the response for controlling blood glucose concentration
60
what are the effectors in response to insulin?
the liver, muscle and fat cells
61
steps of insulin secretion:
(an increase in blood glucose concentration)
1) blood glucose levels increase
2) B cells detect a rise in blood glucose concentration
3) B cells secrete the hormone insulin into the bloodstream
4) insulin makes the liver cells more permeable to glucose, and activates enzymes which convert glucose to glycogen
5) glucose is removed from the blood and stored as glycogen in cells
62
what do target cells possess?
glucose transporter proteins in their surface membranes
63
what do glucose transporter proteins allow for?
the uptake of glucose molecules via facilitated diffusion
64
the action of insulin
insulin binds to glucose transport proteins on the cell surface membrane of target cells
binding causes...
1) a change in the tertiary structure of glucose transport proteins (they open)
2) an increase in the number of glucose carrier molecules in the cell surface membrane
→ an increase in glucose uptake
3) the activation of an enzyme that converts glucose into glycogen or fat
65
glycogenesis steps:
1) once glucose has entered a liver cell an enzyme rapidly converts it to glucose phosphate
2) different enzymes then convert glucose phosphate into glycogen
(this helps to lower glucose concentration within the liver cells, a steep diffusion gradient is maintained between the blood in the capillaries and the liver cells)
66
why is an increase in glucose transport proteins important?
increased respiration → lowered blood glucose concentration
67
what happens when there is a low blood glucose level?
1) it is detected by the α cells in the pancreas
2) α cells secrete glucagon
3) β cells respond by stopping the secretion of insulin
68
what can control of blood glucose concentration by glucagon be used to demonstrate?
the principles of cell signalling
69
what are the effectors in response to glucagon?
liver cells
70
the second messenger model:
1) a cells detect lower blood glucose levels and secrete glucagon into the bloodstream
2) glucagon binds to receptors on the surface of the liver
3) the binding causes G protein to be activated
4) activated G protein activates adenylyl cyclase (through shape change), and the adenyl class catalysis the conversion of ATP into cAMP (cyclic AMP/2nd messenger)
5) cAMP activates the enzyme kinase which catalyses the hydrolysis of glycogen to glucose (glycogenlysis)
71
glycogenolysis
the hydrolysis of glycogen back into glucose in the liver
72
glyconeogenesis
glucose is created from non-carbohydrate stores in the liver
-this occurs if all glycogen has been hydrolysed into glucose and your body still needs more glucose
(glycerol + amino acids → glucose)
73
glycogenesis
the conversion of excess glucose into glycogen in the liver
74
what does hormone do when secreted?
increases the concentration of blood glucose
75
role of adrenaline
(second messenger model)
1) adrenaline attaches to receptors on the surfaces of target cells, this causes G protein to be activated and to convert ATP into cAMP
2) CAMP activates an enzyme (kinase) that can hydrolyse glycogen into glucose (glycogenolysis)
76
which three ways can glucose enter the bloodstream?
-absorption in the gut following carbohydrate digestion
-hydrolysis of glycogen stores
-non-carbohydrates such as lipids, lactate and amino acids that have been converted to glucose
77
what happens when there is excess glucose in the blood from a carbohydrate-dense meal?
it is removed through increased glucose uptake into muscle, fat and liver cells and glycogenesis
78
what happens when there is insufficient glucose in the blood for metabolic needs?
it is rapidly released from storage molecules through glycogenolysis and gluconeogenesis
79
what happens to the levels of insulin and glucagon present in the blood?
they are constantly regulated and adjusted in order to maintain the blood glucose concentration at a mostly constant level
80
what is diabetes?
a disease when blood glucose concentration cannot be controlled naturally
81
how does diabetes affect blood glucose concentration?
insulin function is disrupted which allows the glucose concentration in the blood to rise
82
how does diabetes affect urine?
1) the kidneys are unable to filter out this excess glucose in the blood and so it often appears in the urine
2) the increased glucose concentration also causes the kidneys to produce large quantities of urine, making the individual feel thirsty due to dehydration
83
what is type 1 diabetes?
caused by the body being unable to produce insulin, there are uncontrolled high blood glucose levels
84
causes of type 1 diabetes:
starts in childhood, due to an autoimmune response whereby the body’s immune system (T cells) attacks the β cells of the islets of Langerhans in the pancreas
85
how does type 1 diabetes affect an individual?
-the lack of insulin also affects glycogen stores which results in an individual feeling fatigued
-if the blood glucose concentration reaches a dangerously high level after a meal then organ damage can occur
86
treatments of type 1 diabetes:
treated with insulin injections and a diabetes appropriate diet
87
what is type 2 diabetes?
when receptor cells on the target cells lose their responsiveness to insulin - the person still makes insulin but their cells are resistant to it and don't respond as well as they should (reduced sensitivity)
88
which type of diabetes is more common?
type 2
89
causes of type 2 diabetes:
-poor diet
-lack of exercise
90
treatment of type 2 diabetes:
-a carbohydrate-controlled diet
-an exercise regime
91
risk factors for type 2 diabetes:
-being over age 40
-obesity
92
why is obesity a big risk factor for type 2 diabetes?
a person who is obese may consume a diet high in
carbohydrates, and over-production of insulin results in resistance to it developing
93
what do people with poorly controlled diabetes often have alongside it and why?
high blood pressure
↳ the high blood glucose concentration lowers the water potential of the blood which causes more water to move from the tissues into the blood vessels by osmosis
↳ there is a larger volume of blood within the circulatory system which causes blood pressure to increase
94
explain why the protein insulin must be administered intravenously rather than orally
Insulin is a protein, if it was taken orally it would be digested by the enzyme protease found in the gut before entering the bloodstream.
95
correlation
an association or relationship between variables
96
causation
when one variable has an influence or is influenced by another
97
which graphs are often used to show correlations?
scatter diagrams are used to identify correlations between two variables to determine if a factor does increase the risk of developing a disease
98
why is the percentage of the population that are obese in the UK rising?
it is thought to be due to the western diet - composed of energy-rich 'fast foods' and a sedentary lifestyle
99
TIP:
when analysing data and studies it is always important to remember that risk factors interact with each other
100
hypoglycaemia
-if a person's blood glucose concentration drops below about 600mg dm they can rapidly lose consciousness
-the brain is very sensitive to drops in the amount of glucose in the blood as they can only respire glucose
-cells need a constant supply of glucose as it is the main respiratory substance
101
hyperglycaemia
-very high concentrations of glucose in the blood → drop in the water potential (more negative) in the blood
-water then moves out of cells causing dehydration → the cells will start to shrivel and die
102
glucose in a healthy person:
around 800mg per dm²
103
how is body temperature controlled?
the control centre for temperature is the hypothalamus
104
what are ectotherms?
cold blooded animals, they can’t regulate own body temp and rely on the external environment to control their core temperature
105
how do ectotherms respond to low temperatures?
-will try to increase core temperature
-for example, by moving into a sunny area rather than staying in a shady area
106
how do ectotherms behave inhigh temperatures?
-ectotherms are more active in the heat
-in areas that are warmer, ectotherms have higher activity levels as they do not have to conserve energy to maintain their core temperature in these areas
107
how do ectotherms respond to high temperatures?
-of an ectotherm is too hot, it will try to decrease it’s core temperatures
-this can be through simple measures, such as moving into a shady area rather than a sunny area
-could be through moving to increase the rate of respiration and release heat as waste
108
how do ectotherms behave in low temperatures?
-ectotherms are less active in cooler conditions
-i areas that are cooler, ectotherms have lower activity levels, due to conserving heat to maintain their core temperature in these areas
109
what are endotherms?
endotherms are able to produce heat through metabolic processes. this means that they have a high metabolic rate
110
how do endotherms use the environment
111
low temp responses
112
low temp flow diagrams
113
high temp responses
114
high temp flow diagrams
115
how many kidneys do humans have and what do they do?
humans have two kidneys → they are an osmoregulatory and excretory organ
116
what does the fact that the kidney is an osmoregulatory organ mean?
they regulate the water content of the blood (vital for maintaining blood pressure)
117
what does the fact that the kidney is an excretory organ mean?
they excrete the toxic waste products of metabolism (such as urea) and substances in excess of requirements (such as salts)
118
what does the renal artery do?
carry oxygenated blood (containing urea and salts) to the kidney
119
what does the renal vein do?
carries deoxygenated blood (that has had urea and excess salts removed) away from kidneys
120
what is the ureter?
a tube that carries urine from kidneys to bladder
121
what is the bladder?
it stores urine (temporarily)
122
what is the urethra?
it releases urine outside of the body
123
what surrounds the kidney?
a tough outer layer known as the fibrous capsule
124
what is beneath the fibrous capsule?
the kidney has three main areas:
-the cortex
-the medulla
-the renal pelvis
125
what does the cortex contain?
the nephron’s….
glomerulus
Bowman’s capsule (renal capsule)
proximal convoluted tubule
distal convoluted tubule
126
what does the medulla contain?
the loop of Henle and collecting duct of the nephrons
127
what is the renal pelvis?
where the ureter joins the kidney
128
what does each kidney contain?
millions of tiny tubes - nephrons that are associated with blood vessels
129
what is the nephron?
the functional unit of the kidney – the nephrons are responsible for the formation of urine
130
what does the bowman’s capsule of a nephron surround?
the glomerelus (a knot of capillaries)
131
what occurs at the glomerulus?
ultrafiltration
132
blood flow at the glomerulus:
blood enters the glomerulus from the renal artery, blood flows through the afferent arteriole and into the glomerulus and out of the efferent arteriole
133
how does the process of filtration occur?
in two stages:
-ultrafiltration
-selective reabsorption
134
what is ultrafiltration?
small molecules are filtered out of the blood and into the Bowman's capsule of the kidney nephron, forming glomerular filtrate
135
what is selective reabsorption?
useful molecules are taken back from the filtrate and returned to the blood, after reabsorption is complete the remaining filtrate forms the urine
136
what happens when urine is formed?
it flows out of the kidneys, along the ureters and into the bladder, where it is temporarily stored
137
the steps of ultrafiltration:
1) blood flows through the glomerulus
2) the afferent arteriole is wider than the efferent arteriole (narrow) resulting in high hydrostatic pressure in the blood in the glomerulus compared tho the renal capsule
3) high hydrostatic pressure forces small, soluble molecules out of the blood and into the bowman’s capsule
138
which small, soluble molecules are forced out during ultrafiltration?
glucose, amino acids, urea, water, ions
139
which substances remain in the blood during ultrafiltration?
blood cells and large proteins remain in the blood as they are too large to pass through the fenestrations in the capillary
140
features that aid ultrafiltration:
-the basement membrane between the capillary endothelium and the epithelium of the bowman’s capsule
141
features of the capillary endothelium:
gaps (fenestrations) between the endothelial cells allow small molecules to pass through this layer
142
features of the basement membrane:
a mesh layer of proteins/collagen that small molecules can pass through
143
features of the epithelium of the bowman’s capsule:
-the epithelium cells of the Bowman’s capsule have many finger-like projections (podocytes) between which there are gaps for small molecules to pass through
-podocytes wrap around capillaries
-podocytes secrete and maintain the basement layer and stop large molecules from entering the filtrate
144
the glomerular filtrate contains… what is aimed to be done with these molecules?
reabsorb:
glucose, ions, water, amino acids
expel:
urea & some water
145
where does most selective transportation occur?
in the proximal convoluted tubule
146
which other structures of the nephron are involved in selective reabsorption?
the loop of Henle and collecting duct
147
features that aid selective reabsorption:
the lining of the PCT is composed of a single layer of epithelial cells, which are adapted to carry out reabsorption in several ways, they have:
-microvilli
-co-transporter proteins
-many mitochondria
-tightly packed cells
147
PCT adaptation: microvilli
many microvilli on the cell surface membrane that faces in contact with the filtrate fluid
↳ this increases the surface area for reabsorption
(more co-transport proteins in membrane)
148
PCT adaptation: co -transporter proteins
many co-transporter proteins in the luminal membrane
↳ each type of co-transporter protein transports a specific solute (e.g. glucose or a particular amino acid) across the luminal membrane
149
PCT adaptation: many mitochondria
these provide ATP for sodium-potassium (Na+/K+) pumps in the basal membranes of the cells
150
PCT adaptation: cells tightly packed together
this means that no fluid can pass between the cells (all substances reabsorbed must pass through the cells)
151
which molecules are involved in reabsorption?
-sodium ions (Na+)
-chloride ions (Cl-)
-sugars and amino acids
152
mechanisms of reabsorption:
-sodium ions are transported from the PCT into the tissue fluid by active transport
-the positively charged sodium ions creates an electrical gradient, causing chloride ions to follow by diffusion
-sugars and amino acids are transported into the surrounding tissues by co-transporter proteins, which also transport sodium ions
153
what is intended to be reabsorbed in the PCT?
glucose and water
154
steps of reabsorption:
1) sodium-potassium pumps in the cells that line the PCT actively transport sodium ions out of the epithelial cells and into the blood, where they are carried away
2) this lowers the concentration of sodium ions inside the epithelial cells, causing sodium ions in the filtrate to diffuse down their concentration gradient into the epithelial cells
3) these sodium ions move via co-transporter proteins in the membrane
4) as the sodium ions diffuse, the proteins transport another solute at the same time, e. g. glucose or an amino acid
5) once inside the epithelial cells these solutes diffuse down their concentration gradients into the blood
155
how much of the components of the glomerulus are reabsorbed?
-a high proportion of sodium ions & glucose are reabsorbed into the blood
-65% of water in the filtrate is reabsorbed
156
how is water reabsorbed in the PCT?
-movement of ions, sugars, and amino acids into the surrounding tissues → lowered water potential of the tissues / wp of blood exceeds that of tissues → l water leaves the PCT by osmosis
157
what happens to urea in the PCT?
urea could diffuses into the blood
because so much water is reabsorbed, the concentration of urea actually increases in the filtrate as it flows down the tubule
158
important organelles in selective absorption:
**mitochondria** - provided the ATP for active transport
**ribosome** - to synthesise transport proteins
RER
golgi apparatus
159
where does reabsorption of water and salts occur?
the loop of Henle
160
what does it mean if there is lots of glucose in the blood plasma?
the glucose that has been reabsorbed is too much, the water potential of blood has been lowered
(glucose transporter proteins are too saturated)
161
what is the loop of Henle?
a U-shaped tubule within the kidney nephron, it starts in the renal cortex, it descends into the renal medulla
162
why is the loop of henle important?
the conservation of water → it makes it possible for urine to be excreted with a higher concentration than the blood (it helps to concentrate the urine)
163
the ascending limb is…
-impermeable to water
-wider than the descending limb
-permeable to ions
164
the descending limb is…
-highly permeable to water
-narrower than the descending limb
-impermeable to ions
165
what does the loop of Henle facilitate?
the exchange of water and solutes between the tubule and surrounding interstitial fluid, which lets the kidney produce concentrated urine
166
steps of concentrating the urine:
(water moving through the collecting duct)
1) the ascending limb is impermeable to water, the cells here actively transport Na+ and Cl-ions out of the filtrate & into the surrounding tissue fluid
2) as the two limbs are very close to each other, this produces a high concentration of Na+ and Cl ions around the descending limb
3) the walls of the descending limb are permeable to water / the fluid that flows down this part of the loop is surrounded by tissue fluid with a high concentration of ions (low water potential)
4) water moves out of the descending limb by osmosis down the water potential gradient into the tissue fluid
5) at the same time, Na+ and Cl- ions diffuse into the descending limb down their concentration gradient
6) the outward movement of water and the inward movement of ions increases the concentration of ions inside the tubule
7) at the hairpin, the fluid inside the tubule is very concentrated (water potential decreases)
8) the low water potential in the medulla created by the ascending limb also enables the reabsorption of water from the collecting duct by osmosis
167
what effect does the length of the loop of Henle have?
This means the longer the loop, the higher the concentration will be, therefore more water will be able to be reabsorbed and a smaller volume of urine will be produced.
168
6 marker about water in the PCT:
1) in the ascending limb, sodium ions are actively removed
2) the ascending limb is impermeable to water
3) in the descending limb, sodium ions move in
4) in the descending limb, water moves out as it is permeable to water (due to lower water potential in the medulla)
5) a longer loop leads to lower water potential in the tissue fluid
6) water leaves the collecting duct/DCT by osmosis
169
steps of the filtrate in the collecting duct:
1) water moves from the filtrate in the collecting duct into the medulla, and then into surrounding capillaries (by osmosis) to be carried away
2) water continues to exit the filtrate as it moves through the collecting duct, because of the low water potential established by the loop of Henle in the surrounding medulla
3) urine leaving the collecting duct has a very low water potential, as most water has been reabsorbed into the blood
170
what is the countercurrent multiplier?
the loop of Henle operates as a countercurrent multiplier system, intensifying the salt gradient in the kidney medulla
171
how is the countercurrent multiplier set up?
1) as filtrate moves down the collecting duct, it loses water, decreasing its water potential (the filtrate is least concentrated at the deepest part of the loop of Henle)
2) however, due to the pumping of ions out of the ascending limb of the loop of Henle, especially deeper in the medulla, the water potential of the surrounding tissues in the medulla is even lower than in the collecting duct
3) **this allows water to continue to move out of filtrate down the whole length of the collecting duct**
172
what is the purpose of the countercurrent multiplier?
the countercurrent system concentrates urine, and ensures that there is always a water potential gradient drawing water out of the collecting duct.
-if the flows were parallel, less water reabsorption would occur
173
what is osmoregulation?
the water potential of body fluids
174
how is blood water potential monitored?
by osmoreceptors found in an area of the brain known as the hypothalamus
175
what happens if osmoreceptors detect a decrease in water potential?
1) osmoreceptors shrink
2) nerve impulses are sent along these sensory neurones to the posterior pituitary gland
3) these nerve impulses stimulate the posterior pituitary gland to release ADH
4) ADH molecules enter the blood and travel throughout the body
5) ADH causes the kidneys to reabsorb more water
6) this reduces the loss of water in the urine
176
the effect of ADH on the kidneys:
-ADH causes the membrane of the collecting dusts more permeable to water
-ADH does this by causing an increase in the number of aquaporins in the luminal membranes of the collecting duct cells
177
ADH action with low water potential in the blood:
1) the collecting duct cells contain vesicles, the membranes of which contain many aquaporins
2) ADH binds to receptors on the DCT surface, leading to the activation of phosphorylase
3) this triggers the activation of the enzyme phosphorylase
4) aquaporins are activated, causing the vesicles to fuse with the luminal membrane of the collecting dusk
5) this increases the permeability of the membrane to water
6) as the filtrate in the nephron travels along the collecting duct, water molecules move from the collecting duct (high water potential), through the aquaporins, and into the blood plasma in the medulla (low water potential)
7) as the filtrate in the collecting duct loses water it becomes more concentrated
8) a small volume of concentrated urine is produced
9) this flows from the kidneys, through the ureters and into the bladder
178
ADH action with high water potential in the blood:
1) osmoreceptors in the hypothalamus are not stimulated
2) no nerve impulses are sent to the posterior pituitary gland
3) no ADH released
4) aquaporins are moved out of the luminal membranes of the collecting duct cells
5) collecting duct cells are no longer permeable to water
6) the filtrate flows along collecting duct but loses no water and is very dilute
7) a large volume of dilute urine is produced
8) his flows from the kidneys, through the ureters and into the bladder
179
urine when dehydrated:
more concentrated
-urea (stinky)
-more yellow
-higher volume
-more reabsorption in the collecting duct
180
urine when hydrated:
less concentrated
-paper yellow
-not stinky
-lower volume
-less reabsorption in the collecting dusk
181
what happened to osmoreceptors when water potential is low?
osmoreceptors in the hypothalamus detect this and shrivel
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