44 Osmoregulation and Excretion Flashcards
(123 cards)
1
Q
What is the process by which organisms maintain their solute concentration?
A
Osmoregulation
2
Q
As an organism takes in solutes, what odes osmosis dictate will happen to its water intake?
A
It will increase.
3
Q
What would happen if animals did not properly osmoregulate?
A
Their cells would become swollen or shrivelled form too much or too little water.
4
Q
How is the solute concentration with regard to osmosis quantified?
A
With the property “osmolarity” which relates to the total solute concentration expressed as moles per litre.
5
Q
What is the unit of osmolarity most often used?
A
milliOsmoles per litre (mOsm/L)
6
Q
What is the osmolarity of sea water?
A
1,000 mOsm/L
7
Q
What is the osmolarity of human blood?
A
300 mOsm/L
8
Q
In what direction does water flow through from osmosis?
A
A hypoosmotic solution to a hyperosomotic solution
9
Q
How does hyperosmotic differ from hypertonic and so on?
A
Hypertonic etc. refers to the what happens i.e. water moves to it, as opposed to hyper osmotic which refers simply to the relative concentration of solutes with no implication of water movement.
10
Q
What are the basic strategies to respond to chaining osmotic conditions?
A
Be a osmoregulator or an osmoconformer
11
Q
What type of animals are osmoconformers?
A
All osmoconformers are marine animals (but not all marine animals are osmoconformers, nor are any freshwater fish)
12
Q
Where do osmoconforming marine animals typically live?
A
Areas with constant osmolarity, such as the sea.
13
Q
Could they be freshwater osmoconformers? Why?
A
No, to be an osmoconformer the animal must be isoosmotic with the water. In freshwater the osmolarity is essential 0 whereas the fish would have a higher osmolarity from all the cells and products they produce.
14
Q
Based on their ability to tolerate osmotic change, what can animals be grouped into and what do these groups denote?
A
“Stenohaline” organisms can only tolerate a narrow range of osmolarity whereas “euryhaline” organism can tolerate a wide range of osmotic conditions.
15
Q
Are osmoconformers typically stenohaline or euryhaline?
A
Stenohaline (narrow range of osmotic condition) as the sea has a relatively constant osmolarity.
16
Q
What is an example of a euryhaline osmoconforming organism?
A
Barnacles that tolerate begin covered and uncovered as the tide goes in and out.
17
Q
What is an example of a euryhaline osmoregulator?
A
Salmon etc. that spend part of their life in freshwater and part of their life in the ocean
18
Q
How is osmoregulation achieved in marine invertebrates?
A
Most marine invertebrates are osmoconformers so face no significant osmoregulatory difficulties.
Since the ion concentration of specific solutes does differ between their cells and the ocean they do have to actively transport some out i.e. chloride ions.
19
Q
How is osmoregulation achieved in marine vertebrates?
A
Most marine invertebrates, and a few marine vertebrates, are osmoregulators.
Since they have a lower solute concentration in their body than the ocean there is a strong tendency for water to be lost from them, possibly causing dehydration.
To rectify this marine fish such as cod drink large volumes of water to replace the water that is lost. In the gills cells called “chloride cells” actively transport sodium out of the body, while allowing sodium ions to follow passively.
In the kidneys, excess calcium, magnesium, and sulfate ions are ex- creted with the loss of only small amounts of water.
20
Q
What marine animals have a distinct osmoregulation strategy and what is is?
A
Chondrichthyans (Cartilaginous animals like sharks)
While they have a lower salt concentration they have a higher osmolarity than the sea water. This is achieved because the shark has a high concentration of urea in its cells. This osmolarity is also increased by the presence of TMAO (trimethylamine oxide), an organic molecule that protects against the urea
21
Q
How does the situation of freshwater fish differ form marine fish and how does this affect their osmoregulatory strategies?
A
They must be hyperosomotic to the water, as they could not tolerate the slow solute concentration of fresh water.
They are therefore adapted to drink very little water and excrete any water that enters through diffusion with their very dilute urine. They maintain their salts by eating food and from uptake across the gills.
In freshwater fish “chloride cells” of the gills actively transport Cl- ions into the body, with Na+ following passively.
22
Q
How do salmon adapt to moving between fresh and salt water environments?
A
When living in rivers and streams, salmon osmoregulate like other freshwater fishes,
producing large amounts of dilute urine and taking up salt from through their gills.
When they migrate to the ocean, salmon produce more of the steroid hormone cortisol, which increases the number and size of salt-secreting chloride cells. Salmon in salt water excrete excess salt from their gills and produce only small amounts of urine.
23
Q
What is extreme dehydration called in animals?
A
Desiccation
24
Q
What is it called when animals that can survive without water called?
A
Anhydrobiosis
25
What type of animals typically undergo anhydrobiosis?
Small invertebrates that live in ponds that often dry up or that live in the film of water between soil particles.
26
What is an example of an animal that can undergo anhydrobiois?
Tardigades (‘water bears’), some roundworms (nematodes)
27
What is a typically adaptation that allows animals to undergo anhydrobiosis?
They produce a disaccharide called trehlose that replaces the water in their cells during dormancy
28
How do insects prevent freezing during winter?
The can produce trehalose, a disaccharide that replaces water in their cells and thus prevents the formation of ice crystals.
29
What are some typical adaptions that prevent animals from losing water?
Insect exoskeletons have a waxy layer like the waxy cuticle.
Land snails have shells
Humans and many animals have layers of dead keratinised skin cells on their surface.
30
In desert animals, with what mechanism is the majority of water gained?
Metabolism i.e. eespiration
31
How are solutes and waste products move throughout the body?
In transport epithelia.
32
How can many sea birds drink salt water?
They have "nasal glands” that consist of capillaries that wrap around “secretory tubules” so that the NaCl diffuses out of the blood. These secretory tubules carry the NaCl to a central duct which secretes it out of the bird’s nostrils.
Note that this process uses countercurrent exchange.
33
What leads nitrogenous waste?
The break down of proteins and nucleic acids for energy or conversion to carbohydrate or fats etc.
When these breakdowns occur an enzyme removes the nitrogen in the form of NH2 amino groups, which become ammonia.
34
What is the issue with ammonia nitrogenous waste?
It is highly toxic and for example disrupts oxidative phosphorylation.
35
What animals release nitrogenous waste in the form of ammonia?
Pretty much only fish and marine invertebrates (not sharks) as they can release the ammonia in a very dilute form as they are surrounded by plentiful water to dilute it.
36
How do fish/marine invertebrate lose nitrogenous wastes?
In many inverte-brates, ammonia release occurs across the whole body surface. In fishes, most of the ammonia is lost as NH4 across the epithelium of the gills. The kidneys excrete only minor amounts of nitrogenous waste.
37
In what form do many land animals release nitrogenous waste?
Urea.
38
What animals specifically use urea excretion?
Mammals, most amphibians, sharks and some bony fish
39
Why is urea excretion beneficial over ammonia?
Ammonia can only be tolerated at very low concentrations and thus would have to be very dilute. Therefore a large, bulky, heavy bladder would be needed.
This need to dilute the ammonia would also lead to significant water loss during urination.
40
How and where is ammonia converted to urea?
In the liver, where is is combined with CO2
41
What disadvantage does urea formation have?
It takes energy
42
What form of excretion do frogs use?
In their tadpole stages they use ammonia excretion as it does not require energy and since they live in water it can be easily diluted.
As adults frogs use urea excretion of nitrogenous waste.
43
What alternative to urea production is used by some animals?
Uric acid production
44
What animals specifically excrete waste in the form of uric acid?
Many reptiles, birds, insects and land snails
45
What are the advantages of uric acid production?
Uric acid is even less toxic than urea and does not readily dissolve in water. This means the organism that produces it does not need to dilute it as much.
In animals that live in the desert this is beneficial as it means less water loss through excretion.
In other animals like birds this is beneficial as it means that they don’t need large bladders to dilute the nitrogenous waste.
46
What mammals produce uric acid and under what circumstances?
All mammals including humans produce some uric acid form the metabolism of the amino acid purine.
47
What can an inability to break down the amino acid purine cause?
Uric stones in the bladder (why?)
Also gout, a form of joint inflammation caused by purine crystals forming in the joints.
48
What form of nitrogen waste do embryos secrete?
In amphibians the embryos of the egg release urea as their eggs have no shells.
Reptile and bird eggs have shells that are permeable to gases but not liquids so uric acid is produced due to its low toxicity.
49
What is the general purpose of excretory systems
To filter usable products out and thus package the waste appropriately i.e. into urea.
50
What drives filtration?
Hydrostatic pressure of the blood.
51
What is the waste filtered by the kidney called?
Filtrate.
52
What animals have distinct excretory systems?
Flatworms, annelids and insects
53
What is the excretory system of flatworms called?
Protonephridia
54
What is the structure of Protonephridia excretory systems?
Through out their body is a matrix of tubules that branch off into dead ends called ‘flame bulbs’
Each flame bulb has a cap cell which includes a cavity with cilia that beats water to draws water and solutes from the interstitial fluid through the flame bulb, releasing filtrate into the tubule network where it is excreted as urine.
55
What excretory systems do annelids have?
Metanephridia
56
What is the structure of the metanephridia excretory systems?
Each segment of the worm has metanephridia that are immersed in the fluid of the coelom.
The metanephridia consist of a collecting tubule into which the coelomic fluid and the solutes it contains diffuse in through the aid of berating CILLIA. Transport epithelia transport and useful substance out of the collecting tubule and transfer them to the neighbouring capillaries.
The collecting tubule terminated in a bladder with an opening to the outside.
57
What does coelom refer to?
Body cavity
58
What is the excretory system of insects called?
Malpighian tubes
59
What animals use Malpighian tubes?
Insects and some other terrestrial arthropods.
60
How do malpighian tubes work?
Malphigian tubes branch of from the rectum of the insect as dead ends.
The Malphigian tubes extend throughout the hemolymph of the insect. They do not perform filtration so instead transport epithelium transfer the salts, water and nitrogenous wastes into the lumen of the malpighian tubule.
These wastes are then transferred to the rectum where they mix with solid waste from the stomach. Near the anus some H2O ions and valuable organic molecules are reabsorbed.
61
What special adaption do some insects have to maximise their water intake?
They can absorb water through their anus.
62
What is the the excretory system seen in vertebrates?
The kidney system.
63
What is the arrangement of the human excretory organs?
Two kidneys (left and right) at the base of the ribs are connected to two ureters (left and right) which carry the filtrate to the urinary bladder in the hips.
The urinary bladder then releases the urine through the urethra.
64
What is the artery and the vein that feed the kidney called?
Renal veins/artery
65
What is the basic structure of the kidney?
It has an outer layer called the renal cortex and a middle layer called the renal medulla.
At the centre is the renal pelvis where tubules of urine from the renal cortex and medulla drain into.
66
What types of nephrons are found in kidneys?
Cortical nephrons and juxtamedullary nephrons.
67
How do cortical and juxtamedullary nephrons differ?
Cortical nephrons extend only through the renal cortex. Juxtamedullary nephrons extend through the cortex and into the renal medulla.
68
Why are juxtamedullary nephrons important?
They are essential for producing urine that is hyper osmotic to blood, a key water saving adaption of mammals.
69
What type of nephron is most common in the kidney?
Cortical
70
What is the structure of a nephron?
Each nephron consists of a single long tubule as well as a ball of capillaries called the glomerulus. The blind end of the tubule forms a cup-shaped swelling, called Bowman’s capsule, which surrounds the glomerulus. Filtrate is formed when blood pressure forces fluid from the blood in the glomerulus into the lumen of Bowman’s capsule. Processing occurs as the filtrate passes through three major regions of the nephron: the proximal tubule, the loop of Henle (a hair- pin turn with a descending limb and an ascending limb), and the distal tubule. A collecting duct receives processed filtrate from many nephrons and transports it to the renal pelvis.
71
How are nephrons provided with blood?
Each nephron is supplied with blood by an AFFERENT arteriole, an offshoot of the renal artery that branches and forms the capillaries of the glomerulus. The capillaries converge as they leave the glomerulus, forming an EFFERENT arteriole. Branches of this vessel form the peritubular capillaries, which surround the proximal and distal tubules. Other branches extend downward and form the vasa recta, hairpin-shaped capillaries that serve the renal medulla, including the long loop of Henle of juxtamedullary nephrons.
72
What is the concentration of fluid from the Bowmans’s capsule similar to and why is this?
The blood plasma as the solutes it contain (except proteins and blood cells) freely diffuse out of the glomerulus and into bowman’s capsule.
73
What does the filtrate from Bowman’s capsule contain?
Salts, glucose, amino acids, vitamins, nitrogenous wastes, and other small molecules.
74
Through what major regions does the filtrate flow through after Bowman’s capsule?
1) Proximal tubule
2) Descending limb of the loop of Henle
3a) Thin segment of ascending limb of Henle
3b) Thick segment of ascending limb of Henle
4) Distal tubule
5) Collecting duct.
75
What happens at the proximal tubule of the nephron?
H+ ions are actively transported into tubule and ammonia passively enters.
NaCl and nutrients are actively transported out of the tubule. Bicarbonate ions, Water and potassium leave passively.
76
What happens at the descending limb of loop of Henle the nephron?
Aquaporin channels allow water to diffuse out. There are almost no channels for salts etc.
77
What happens at the thin segment of ascending limb of Henle of the nephron?
Because the water left during the descending loop of Henle, at the thin segment of the ascending loop the filtrate has a relatively high concentration of NaCl. Therefore it leaves in this region that is impermeable to water.
78
What happens at the thick segment of ascending limb of Henle of the nephron?
The movement of NaCl out of the filtrate continues, although here is is actively transported into the interstitial fluid by the epithelium. This region is still impermeable to water so the filtrate continue to get more and more dilute.
79
What happens at the distal tubule of the nephron?
The filtrate is now in the cortex which has a lower osmolarity than the medulla, allowing water to passively diffuse out. NaCl continues to be actively transported. HCO3- also leaves the distal tubule but unlike at the proximal tubule it leaves through active transport. K+ and H+ ions are actively transported in. (not that K+ ions left passively at the proximal tubule)
80
What happens at the collecting duct of the nephron?
As the duct passes through the outer medulla NaCl is actively transported out. When it reaches the inner medulla some urea diffuse OUT. This loss of solutes also leaves to some more water leaving through osmosis, further concentrating the urine.
81
How come when chloride ions are transported the sodium ions follow?
The Na+ ions are attracted to the oppositely charge Cl- ions.
82
What are the capillaries that encircle the loop of henle called?
Peritubular capillaries.
83
How does NaCl get actively transported out of the proximal tubule? What does this facilitate
The Na+ is actively transported, causing the oppositely charged Cl-
84
How does water leave the proximal tubule?
The actively removed salts cause the water to leave through osmosis.
85
When solutes leave the tubules and loop of Henle, where do they go?
Inter the interstitial fluid before being absorbed by the per tubular capillaries.
86
Why is proximal tubule particularly important?
It helps maintain blood pH in two ways.
First by actively transporting H+ ions in it directly decreases acidity.
It also filters out bicarbonate ions that that they renter the blood where they act as pH buffers.
87
How does the proximal tubule ensure that the H+ ions do not passively leave the tubule?
They form ammonia which in its aqueous form NH4+ acts as a buffer and thus traps the H+ ions.
88
How are toxins processed in the liver excreted?
These toxins pass from the peritubular capillaries into the interstitial fluid. They then enter the proximal tubule, where they are actively secreted from the transport epithelium into the lumen.
89
How does the descending loop of Henle ‘convince’ the water to leave the tubule?
For water to leave through osmosis the outside must be hyperosmotic. This condition is met by the fact that the osmolarity of the kidney interstitial fluid increases from the outer cortex to the medulla.
Therefore the filtrate loses water and thus increase in solute concentration all along its journey down the descending limb.
90
Why is the NaCl that leaves the thin segment of the ascending loop of Henle important?
It maintains the osmolarity of the interstitial fund of the medulla.
91
Why does some urea LEAVE the urine at the collecting duct?
The small quantity that leaves helps maintain the osmolarity of the medulla whilst also helping water leave through osmosis.
92
What is a unique ability of the mammalian excretory system?
To produce urine that is hyper osmotic to blood.
93
What models does the loop of Henle follow?
Two-solute model.
94
What is the two solute model?
The model the loop of henle uses through its two main solute: NaCL and Urea
As the filtrate descends through the loop of Henle it loses water through Osmosis and thus develops a greater solute potential. However the loss of Solute 1 (NaCl) from the ascending loop means that as the filtrate descends and increases in osmolarity, the osmolarity of the surrounding medulla also increases and thus osmosis continues.
As the water descends again through the collecting duct the same passive loss of water occurs due to the removal of a second solute: urea
95
What phenomena does the countercurrent system exploit?
It is a countercurrent system. More specifically it is a “countercurrent multiplier system” as it uses active transport to intensify this effect.
96
What prevents the capillaries of the vasa recta from dissipating the gradient by carrying away the high concentration of NaCl in the medulla’s interstitial fluid?
the descending and ascending vessels of the vasa recta carry blood in opposite directions through the kid- ney’s osmolarity gradient. As the descending vessel conveys blood toward the inner medulla, water is lost from the blood and NaCl is gained by diffusion. These fluxes are reversed as blood flows back toward the cortex in the ascending vessel, with water reentering the blood and salt diffusing out.
97
What do the nephrons of mammals focus on and what tradeoff does this bring?
It focuses on producing highly concentrated urine. However as a consequence of this it expends a lot of energy, such as by active transport.
98
How do kidneys differ between animals?
Mammals of the desert must produce highly concentrated urine. Therefore their nephrons have loops of Henle extend deeper into the medulla.
Mammals like beavers that live with plentiful water have shorter loops of loop of Henle.
99
What adaptations do the excretory system of birds?
Birds have juxtamedullary nephrons like mammals but they do not extend as far into the medulla. Instead uric acid excretion is their primary method of water loss prevention.
100
What adaptations do the excretory system of reptiles have?
They have only cortical nephrons.
However, the epithelium of the chamber from which urine and feces leave the body (the cloaca) helps conserve fluid by reabsorbing water from these wastes. (they also secrete water-saving uric acid)
101
What adaptations do the excretory system of freshwater fish and amphibians have?
These animals live in hypo osmotic environments so must constantly lose water. Their kidneys have many nephrons to produce filtrate at a high rate.
Freshwater fishes conserve salts by reabsorbing ions from the filtrate in their distal tubules, leaving water behind. Frogs gain salts by absorbing them through their skin.
When on land, and water-loss prevention is a priority, frogs can reabsorb water through the epithelium of the urinary bladder.
102
What adaptations do the excretory system of marine bony fish have?
They have fewer nephrons, all of which lack distal tubules.
The main function of kidneys in marine bony fishes is to get rid of divalent ions (those with a charge of 2+ or 2+) i.e. Ca2+, Mg2+, SO42- Marine fishes take in divalent ions by drinking lost of sea water. They remove these ions by secreting them into the proximal tubules of the nephrons and excreting them in urine. Secretion by the gills maintains proper levels of mono- valent ions (charge of 1+ or 1- like Na+ and Cl-)
103
Why is it important that an organism can regulate the osmolarity of its urine?
If that person is dehydrated then highly osmotic urine is produced to save water.
This takes considerable energy so if the person is not dehydrated more dilute urine is produced.
104
What are the main pathways that act to regulate the kidneys?
Antidiuretic hormones, the ‘Renin-Angiotensin-Aldosterone system’
105
What can cause an increase in blood osmolarity?
An intake of salty foods or water loss through perspiration etc.
106
What causes the release of ADH?
‘Osmoreceptors’ cells in the hypothalamus monitor the blood osmolarity. If it increases above a set point it triggers the release of ADH from the posterior pituitary.
107
What are the effects of ADH?
It causes thirst as water intake would restore the blood osmolarity to normal.
When ADH reaches the kidneys it causes the epithelium of the collecting ducts to become more permeable to water.
This causes more water to be reabsorbed. This increases the water in the blood and thus restores the osmolarity.
As a consequence of this increased water uptake the urine becomes more concentrated and more highly osmotic.
108
What is urination also called?
Diuresis
109
What does an ‘antidiuretic’ drug do>
Decreases urination.
110
How specifically does ADH increase water reabsorption?
ADH binds to a membrane receptor and thus causes the release of cAMP as a second messenger.
This triggers vesicles inside the cell which have aquaporins then fuse to the plasma membrane of the collecting duct cell through exocytosis.
Thus more aquaporins are added to the plasma membrane so that water absorption is increased.
111
How does a decrease in ADH trigger a reduction in water absorption?
The aquaporins added to the plasma membrane of the cells in the collecting duct are removed through endocytosis.
112
What is condition in which ADH does not cause the proper response?
‘Diabetes insipidus’ in which the urine is always hight dilute hence the name meaning “to pass through having no flavour"
113
What is the ‘renin-angiotenisn-aldosterone system’ also known as?
RAAS
114
What is ‘RAAS’?
The ‘renin-angiotensin-aldosterone system'
115
What is the general function of the RAAS?
To increase blood pressure and blood volume.
116
Where is the RAAS initiated?
In the juxtaglomerular apparatus (JGA), a specialized tissue consisting of cells of and around the afferent arteriole that supplies blood to the glomerulus.
117
What does the JGA do in the RAAS?
It monitors the blood volume and pressure and if it detects a drop causes the release of the enzyme renin.
118
What happens when renin is released by the JGA?
It catalyses certain chemical reaction which cleaves the plasma protein (part of the blood plasma) angiotensin into angiotensin II.
This Angiotensin II causes a direct response while also stimulating the adrenal glands to release ‘aldosterone'
119
What is ‘JGA’?
The ‘juxtaglomerular apparatus’ i.e. of the afferent artery that supplies the glomerulus.
120
How does the RAAS lead to the desired effects?
The ‘angiotensin II’ produced as an intermediate causes arterioles to constrict and thus raises blood pressure.
The aldosterone causes more Na+ and H2 to be absorbed in the distal tubules and thus increases blood volume.
121
Why are both the ADH and RAAS system needed?
During typical dehydration water is lost and thus the blood osmolarity increases causing the release of ADH.
Under some circumstances the blood volume could decrease without an increase in osmolarity. This could occur when a large amount of body fluids are lost such as from a wound or diarrhoea. This would not affect osmolarity so wouldn’t cause the release of ADH. Conversely the RAAS system, which measures blood volume directly, would continue to function.
122
Besides ADH and the RAAS system, what affects the kidneys to maintain homeostasis?
Atrial natriuretic peptide (ANP), opposes the RAAS. The walls of the atria of the heart release ANP in response to an increase in blood volume and pres- sure.
ANP inhibits the release of renin from the JGA, inhibits NaCl reabsorption by the collecting ducts, and reduces aldosterone release from the adrenal glands.
This lowers blood volume and pressure.
123
What is TMAO?
trimethylamine oxide. This chemical allows Clark cells to withstand high urea levels and thus helps in osmoregulwtion
