Urinary Systems Flashcards
(132 cards)
1
Q
How will regulating electrolyte balance change pH levels?
A
- regulating electrolyte balance will change pH levels, because of H+ movement. Acidity = increase in H+ (low pH) , alkalinity = decrease in H+ (high pH)
2
Q
What are the 2 body fluid compartments?
A
- 2 compartments - intracellular fluid (ICF- inside cell) and extracellular fluid (ECF-outside cell)
Compartments interact with each other
3
Q
What is RCF further divided into?
A
- ECF is further divided into interstitial fluid (found between ordinary cells) and blood plasma (part of blood excluding WBC and RBC)
4
Q
How much fluid is there in the body?
A
- Fluid = important because of its abundance (60% in body)
5
Q
How is ICF separated from IF?
A
- ICF is separated from IF by cell membranes. IF seperated from blood plasma by by endothelium of blood capillaries
6
Q
Which is the larger body fluid compartment?
A
- ICF is larger compartment with 2/3s total, remaining 1/3 is ECF
7
Q
What is the ECF divided into?
A
- ECF divided into IF (3/4) and plasma (1/4)
8
Q
Where does all solutes and water leave?
A
ALL SOLUTES AND WATER THAT ENTERS LEAVES VIA ECF
9
Q
Are ICF and ECF at equilibrium?
A
- ICF and ECF are in osmotic equilibrium, water shifts between
10
Q
What can the water content per body depend on?
A
- Water content per body can depend on amount of adipose tissue (lipid rich)
- Since adipose tissue is low in water content and increase in adipose tissues leads to a decrease in total body weight attributed to water
11
Q
What is the IF and plasma divided by?
A
- IF and plasma divided by capillary walls, movement is isosmotic (moves freely)
- Capillaries have thin walls, achieve filtration or reabsorption depending on pressure that is present (hydrostatic or osmotic)
- Osmotic pressure in human plasma is 300 mOsm
- IF and plasma have similar pressures (plasma slightly higher) but this difference does not disturb isosmotic state
- ICF and ECF water cannot move freely as osmolarity inside cell is different to external environment and thus require transporters
12
Q
What is the electrolyte composition of IF and plasma? Where are differences seen?
A
- as IF and plasma are isosmotic which means they have similar concentrations of anions and cations
- ICF has very different concentrations
- big differences between freshwater, seawater and terrestrial organisms
- An animal in freshwater, the surroundings will have low concentration of solute, so animal will be hyperosmotic to the environment. Sea water animals will be opposite
13
Q
What are the 4 major sites of osmoregulation/ ion+ water exchange?
A
The major sites of ion and water exchanges are:
* skin (sweat)
* Respiratory system (dry and wet during breathing)
* Digestive tract (water and fluid absorption)
* Excretory system (urine and faecal matter)
14
Q
What is osmoregulation?
A
Osmoregulation = movement of water and solutes to maintain isosmotic state
15
Q
How do sponges and cnidarians carry out this process?
A
- sponges and cnidarians carry out this process with the lack of a circulatory system as they are in direct contact with the water (bulk flow), meaning its easier for them to regulate and exchange
- The wall of the sponge is full of spores that propel water into the spongocoel and out through the osculum
16
Q
How do freshwater fish carry out osmoregulation?
A
- Freshwater fish (FW) pose several challenges to osmoregulation
- Outer covering of fish is surrounded by integument which is impermeable to water, therefore lack direct contact and exchange with external environment
- FW are surrounded by an environment that is low in salt ions, however it has a higher concentration of salts in its body and thus is hyperosmotic to the environment
- The salts from the FW will eventually be lost to the ambient environment via the gills and at the same time there will be a large influx of water
- FW take in a lot of water, which has to be lost
17
Q
What is meant by water potential? How are salts used in fish?
A
- Water moves from an area with higher water potential to a region of lower water potential
- Movement across compartments is essential to re supply cells or tissues with raw materials, to void waste and maintain a proper composition of body fluids
- Intake of water can dilute the blood and bloat the fish
- Must use energy to expel water, but that also means salts are lost to environment
- More energy is used to take up these lost salts. This is done via active transport. The transporters that are in place take up Na+ and CL- and loose bicarbonate and H+ (electroneutral) with the help of ATP
18
Q
What are aquaporins and what are the 2 types?
A
- similar to ion channels but permit the passage of larger molecules
- They are water channels in plasma membrane, each AQP can transport 3 billion water molecules a second (!)
- A plasma memrbane lacking AQP transports water 5-50x slower
- Significant physiological role - urine formation, tears, and sweat
- They can be transcellular (through cell membrane) or paracellular (across different compartments)
19
Q
How is cell volume regulated?
A
- cells control volume by transporting solutes across the plasma membrane causing changes in osmotic pressure that induce movement of water
- Water will flow to a region of higher solute concentration
- If there is an imbalance in water content and the cell swells, the transport mechanisms will come into place to rectify this
20
Q
What is preformed water?
A
- ingesting food also ingests water
- Epithelium of a hummingbird consists of a single layer of cells bearing microvilli on the apical membrane
- Dissolved sugar molecules such as glucose and fructose must cross the epithelium from the intestinal lumen to the blood
- This is ingested preformed water, different from metabolic water
21
Q
What is metabolic water?
A
- metabolic water is formed when organic food molecules are aerobically catabolized as shown by the above reaction (glucose oxidation)
- The significance lies in the amount of water lost in this reaction. However there is still a net gain, water is not only gained by drinking but cells produce water too.
22
Q
What are the major causes of water loss in animals?
A
Water loss: respiratory, urinary and faecal route
* when you breathe in you gain water and when you breathe out you lose water
* Air entering the nose is warmed and humified by heat. The nasal passages are cooled by evaporative water loss, leading to a flow of cool air
* During expiration, the air is cooled and leads to a loss of water ,wetting the nasal passage
* Kidneys are regulatory rather than excretory organs, however it is clear that he excretory function of the kidney is central to the role of of the composition and volume of body fluids
- water loss also takes place through the faecal route, food is ingested that contains preformed water and is excreted through this route
23
Q
What are desert kangaroo rats a great example of?
A
- great example of how organisms deal with water respective to a challenging environment
- Desert kangaroo rats have been shown to conserve water better than lab rats
- An experiment was conducted where these rats were given 0 preformed water and they were given barley grain
- They made metabolic water to survive
- Interestingly these rats had a net gain of metabolic water compared to the lab rats
- More concentrated urea, less water and drier faeces
24
Q
What are the 3 forms of regulation of blood plasma?
A
- osmotic
- ionic
- volume
25
What is osmotic regulation of blood plasma?
* osmotic - regulation of osmotic pressure of an organisms body fluid, detected by specialised receptors to maintain homeostasis of the organisms water content
26
What is ionic regulation of blood plasma?
* Ionic - maintenance of the concentration of various ions in the bod fluids relative to one another. The urinary system plays a key role in this process
27
What is volume regulation of blood plasma?
* Volume - cell volume regulation is an important homeostatic function defining not only cell shape but balance between the ICF and ECF
28
What is meant by environmental challenges in regulation?
* animals face sporadic challenges introduced by the environment to their regulatory system
* Exchanges of ions and water between an animal and its environment can be obligatory and regulated
* Obligatory exchanges cover responses of an animal to factors that are beyond their physiological control (physical factors)
* regulated exchanges are physiologically controlled and required for maintained the internal homeostasis
29
What are the 2 types of osmoregulation?
* 2 types - osmotic regulator (eg shrimp) and an osmotic conformer (mussel)
* The best fit line is line of equality between osmotic pressure and ambient osmotic pressure
* A perfect regulatory won’t follow the trend of of the isosmotic line. However, the osmotic conformer will follow the trend of the isosmotic line
* Conformers tend to have the same osmotic pressure as the external environment whereas regulators keep osmolarity constant regardless of changes in the external environment.
30
What is a disadvantage of a conformer?
* A disadvantage for the conformers is that the cells may not have the ideal solute concentration for metabolism
31
What is a disadvantage for regulators?
* The disadvantage for regulators is that they utilise too much to keep internal solute concentration constant
32
What do animals display when it comes to osmoregulation?
* Animals display gradations or mixtures of osmotic regulation and conformity. Among animals that are osmoregulators, the regulation is limited to ranges of external osmotic pressure
* A crab is a good example of how regulators can conform. This is usually when FW animals face brackish waters, they regulate in FW but not in SW
* Remember the way an animal regulates depends on the environment in which it lives. Furthermore, if they do ever change their regulation, it is because they are migrating into a different environment. All these are forms of adaptation.
33
What determines the osmotic concentration gradient?
* Solutes contribute largely to the osmolarity and determines the osmotic gradient across membranes, and hence the direction of water movement.
34
What is present in extracellular space of most animals?
* Extracellular space of most animals is dominated by Na+ and Cl-. SW is mainly Na+ and CL- followed by reduced levels of K+, Mg2+ and Ca2+
* Ionoconformers have high levels of Na+ and Cl- close to that of SW, whereas ion regulators have low levels of Na+ and Cl-
* Osmoconformers have the same osmolarity as SW but maintain a different solute profile, much like that of an osmoregulation
35
What is volume regulation and haemolymph?
* hemolymph is the circulating fluid of an open circulatory system. In an open circulatory system, hemolymph flows through blood vessels
* Hemolymph of FW crabs is hyperosmotic to the surrounding water. Osmosis allows water to move in, which is eventually lost as urine
* KEY POINT - even though volume, osmotic and ionic regulation are distinct processes they are all integrated in one organism
36
SW vs FW? How is salinity calculated?
* some aquatic animals live in environments that are uniform and stable in their water-salt composition, like those in open ocean
* The salinity of water is calculated number of dissolved grams of dissolved inorganic matter in a kg of water
37
What are the 3 challenges faced by FW fish?
volume regulation - a constant influx of water into the organism due to an osmotic gradient
* Osmotic regulation - the water that enters, dilutes the blood and reduced osmotic pressure within the ECF
* ion regulation - due to excretion of excess water ions are constantly lost to the external environment
38
What does uptake of ions require in FW animals? What are FW in relation to their environment?
* for a FW fish, the uptake of ions from a highly concentrated solution requires the use of energy and therefore FW fish reabsorb ions from their kidneys
* Freshwater animals are hyperosmotic to the ambient environment, which means gain of water and loss of ions
* The more rapidly water is taken up, the faster it is lost by diffusion and the more energy it spends to carry counteract these processes
39
What 3 factors determine the rate of exchange?
* 3 factors determine the rate of exchange: permeability, surface area to volume ratio and magnitude of gradient
40
Describe the urine of freshwater fish? What is the U:P value?
* FW animals have a great influx of water and they void this by excreting copious amounts of urine
* Because urine production balances osmotic water gain, rate of urinary water excretion resembles the rate of water influx
* The urine of FW animal is hypo-osmotic (low concentrations of Na+ and Cl-) to their blood . This is defined as as the U:P ratio (urine to plasma)
* If U:P is less than 1, this signifies that the blood osmotic pressure is high due to lots of urine production
* When U:P is less than 1 for an ion, it signifies that the large amounts of urine production tend to raise plasma concentrations for that particular ion
* Therefore the kidneys not only solve the problem of volume regulation by excreting urine but aid in ionic and osmotic regulation by maintaining high osmotic pressures and an increased ion concentration in the blood
41
What are gills and what do they do?
* gills are a suitable organ for osmoregulation. Gills of various are active not only in gas exchange but also in ion transport, excretion of nitrogenous waste and maintaining acid-base balance
* gills play a central role in regulating osmotic stress. The epithelium separates the blood from the external water, which consists of several cell types: mucous cells, pavement cells and chloride cells
42
What is the pathology of the gills?
* the epithelium of the lamella consists of pavement cells and mitochondria, best suited for respiratory exchange
* The epithelium covering the gills have chloride cells, mitochondria and enzymes that assist with salt transport
43
How do freshwater fish utilise active transport?
* a significant way by which FW animals replenish lost Na+ and Cl- is active transport
* Active ion transport takes place in the gills which requires ATP which means this places demands on energy resources
* The mechanisms that pump Na+ and CL- from the external environment into the blood are typically different from each other. The cL- pump typically exchanges HCO3 for CL- (electroneutral)
* The na+ pump exchanges H+ (protons) for Na+ or NH4 (ammonium ions)
* The HCO3 and H+ are produced by anaerobic catabolism being formed by metabolically formed co2 and h20
44
How is homeostasis maintained in mammals?
* in mammals, internal Na+ homeostasis is maintained through Na+ re absorption via a variety of Na+ transport proteins with mutually compensating functions which are expressed in the nephrons
* Na+ homeostasis is achieved through the skin gill ionocytes namely Na+/H+ exchangers. Expressing H+ ATPase rich cells and Na+ and Cl- cotransporters.
45
What are the challenges faced by marine animals?
* for marine or SW animals the challenges are different . Let’s assume the ICF has an osmotic pressure of 300 mOsm.
* Osmotic pressure is governed by the solute concentration. The osmotic gradient between the marine animal and the SW is 700 mOsm
* Let’s assume FW animals have an ICF osmotic pressure of 300mosm, the osmotic pressure of the ambient environment is FW is very low. Hence a smaller osmotic gradient in comparison to marine animals
* therefore since the osmotic gradient is higher in marine animals, the challenges are equally high. In this case water moves in the opposite direction.
* SW has a very high salt concentration. Let’s assume a marine animal is drinking water, with this there is going to be a great influx of salt. The only choice the animal has is to expel all that excess salt, and the water as well
* Marine animals try to reabsorb as much water as possible and lose as much of salt as possible to maintain their ICF osmotic pressure
46
How can excess salt be secreted in marine animals?
* Not all animals have gills. With respect to gills, substances can move in and out as they are permeable to water.
* organisms that live on land have adapted and are able to secrete excess salt through glands. Some marine animals have glands on their bodies, seabirds have them in nasal passages
47
What is the principle role of the kidneys in marine fish?
* integuments are poorly penetrable to water. Marine fish drink water with a price of gaining excess salt. Because they are conserving water they will form small amounts of isosmotic urine. Principal role of the kidneys in marine fish is to get rid of excess salt through glands
48
What are the 2 classes of animals based on their ability to tolerate changes in external osmolarity?
* animals are classified on their ability to tolerate changes in external osmolarity
* Stenohaline animals can tolerate a narrow range of salt concentration
* Euryhaline animals can tolerate wide variation in osmolarities
49
What are the main functions of the mammalian kidney?
* main function of kidney is to regulate the composition of body fluids (osmotic balance), excretion of waste in the form of urine, pH balance, hormone production (kidneys produce a hormone that is similar to RBC production) and regulate blood pressure
50
What are the 4 main processes that contribute to urine formation?
Main processes that contribute to urine formation are - filtration, reabsorption, secretion and excretion.
51
What happens as soon as water and solutes leave the arterioles and enter the lumen of the bowman’s capsule?
* water and solutes leave the arterioles and enter the lumen of the bowman’s capsule forming an ultra-filtrate
* The renal tubules are line with cells so that ion and water can move freely, passing through this layer (reabsorbed)
* Certain type of molecules are secreted from the IF into the proximal tubule (PT) to be excreted as waste
* The glomerular filtrate contains all the constituents of the blood except blood cells and proteins
* Filtration in glomerulus is so extensive that 15-25% of water and solutes are removed from the plasma
52
How much filtrate is produced a day in humans?
* The filtrate that is produced is at a rate of 180L/day, however we don’t drink that much to compensate for the loss, this means that almost all the ions and water is reabsorbed into the blood stream
53
What are the 2 different arterioles in the kidney?
* There are 2 arterioles - efferent and afferent. Afferent transports blood towards the glomerulus and efferent transports the blood taway from the glomerulus
54
What is found on the inside of the glomerulus?
* Inside the glomerulus you have a network of capillaries with thin walls allowing easy movement of substances. These loops are also referred to as glomerular tufts. The key here is constant blood supply.
55
What is the main function of the glomerulus and what are the 3 layers?
* glomerulus acts as a filtration barrier, which has 3 layers. Endothelial cells, basement membrane and the podocytes. This is the filtration barrier
* The function is to keep blood and proteins into the body and allow passage of small molecules into the urine. The podocytes are modified epithelial cells that provide structural support
56
What is meant by the glomerulus having size selectivity?
* The glomerulus has size selectivity which means that molecules less than 1.8nm can be easily filtered (water, sodium, insulin and glucose). Molecules more than 3.6nm are not filtered (RBC - haemoglobin)
57
What is meant by the glomerulus having charge selectivity?
* Furthermore, the glomerulus has a charge selectivity, where negatively charged molecules cannot pass through that easily as all 3 layers shown above contain negatively charged glycoproteins
58
What 2 forces filter blood in the lumen?
Filtration of blood to form the filtrate in the lumen depend on certain forces - hydrostatic pressure (Hp) and oncotic pressure (Op)
59
What is ‘hydrostatic pressure’?
the pressure that the fluid exerts on the walls of the compartment, either the walls of the capillary or bowman’s capsule (pushing force)
60
What is ‘oncotic’ pressure?
is the pressure exerted by the plasma protein on walls of the compartment in which they are contained (pulling force)
61
What is the glomerular filtration rate? (GFR)
Glomerular filtration rate (GFR) - the rate at which the filtrate is generated. 120ml/min and 180l/day
62
What is meant by the term ‘clearance’?
the amount of fluid cleared completely of a certain substance
63
How is fluid movement in the glomerulus linked to starlings forces?
The hydrostatic pressure in the capillary is the major driving force pushing fluids from the blood into the lumen of the bowman’s capsule
* If the Hp is greater in capillary than bowman’s capsule, fluid will be pushed out
Due to presence of proteins the blood has a greater osmotic pressure than the lumen of the bowman’s capsule. This pressure is termed as the oncotic pressure
* The oncotic pressure present in the capillaries tend to pull fluids back in. The balance between the forces influences rate and direction of fluid movement.
64
What is the net filtration pressure? Why do we calculate GFR?
* pressure favouring filtration minus the pressures opposing filtration is your net filtration pressure
* In simpler terms - it is the glomerular capillary pressure (hydrostatic pressure within the capillaries) minus the intracapsular pressure (hydrostatic pressure within the lumen of the bowman’s capsule). This will give you net hydrostatic pressure. The net pressure minus the colloid osmotic pressure (oncotic pressure) will give you the net filtration pressure.
* The reason we calculate GFR is because it can be used to indentify kidney problems
65
What is the JGA?
* the JGA is a specialised region which is significant for sensing the blood pressure/flow into the kidney and producing hormones such as renin
* The JGA os a region where the afferent arterioles come into contact with the distal tubule
* On the outside of the afferent arterioles you have presence of JG cells that can sense blood pressure
66
What is renin?
* Renin is a hormone significant in blood pressure regulation and fluid balance
67
When will renin be excreted?
* Now let’s examine the function of these cells, when systemic blood pressure decreases, there is a decreased stretch of JG cells that release renin, renin will increase blood pressure back to normal.
* In another example, when the filtrate has a decreased flow rate, the macular densa cells sense this, leading to vasodilation to the afferent arteriole and renin secretion by JG cells. Renin will return flow rate back to normal `
68
What is the purpose of the JGA?
There is connection between blood pressure, osmolarity, blood flow and Na+ concentration. This is the purpose of the JGA.
69
What do the tubule epithelial cells do and why are they unique?
* after the filtrate passes the glomerulus and enters the lumen of the bowman’s capsule, it passes the PT. This section of the nephron is specialised from transport and is the area where most reabsorption occurs.
* One of the important things to note is that the epithelial cells of the tubule are unique, they are not very permeable to lots of substances -> they have lots of transport mechanisms on either side of the cell to help regulate the movement of ions
70
Why do tubule epithelial cells have tight junctions?
* The tubule epithelial cells have tight junctions which prevent paracellular transport and contain polarity which allows certain substances to move across such as proteins and pharmaceutical agents
71
How much fluid is reclaimed by PT and loop of Henle?
* PT reclaims 80% of the filtered fluid and thus epithelia have microvilli, lots of mitochondria and a large surface area
* Loop of hence reclaims 5-10%of the filtrate and plays a significant role in water conservation. One can observe the difference in epithelial cell structure between the descending and ascending limb, as they each play different roles in water conservation.
72
Why is ion re absorption important?
Reabsorption is critical in maintaining fluid and electrolyte balance in the system
73
How is urine modified by secretion?
* Secretion uses transporters found in the epithelial cells that lines the lumen of the PT. H+, K+, toxins and pharmaceuticals drugs move from blood into the lumen of the PT. This process requires energy.
* Important thing to note is by the time the fluid reaches the end of the PT, the osmolarity is 300 mOsm, isosmotic to the IF and plasma (no movement)
74
What is the structure of the tubule?
* the wall of the tubule is one cell thick; this epithelium separates the lumen from the IF. These epithelial cells are specialised for transport, bearing a dense pile of microvilli on their luminal (apical) surfaces.
* They are tied together by leaky tight junctions
* in all sections of the kidney tubule, Na+ diffuses into the epithelial cells from the tubular fluid because there is an electrochemical gradient favoring this movement
75
What is in high concentration early PT?
* In the early PT, the fluid is rich in glucose and amino acids, and much of Na+ entry into the cell occurs by means of co-transporters that bring about secondary active transport of glucose and amino acids
76
What is the key process occurring at the loop of Henle?
Counter current multiplication
77
Describe the differences between the descending and ascending limb of the loop of Henle?
* the loop is significant for water reabsorption. The descending limb (DL) is very permeable to water because it doesn’t have tight junctions.
* Epithelium cells of the DL have no active transport of solutes, highly permeable to water and impermeable to ion and urea
* The ascending limb (AL) is the exact opposite, impermeable to water, permeable to ions and impermeable to urea. The thick segment of the AL has active transport of ions
78
How is acid-base balance controlled?
* the collecting duct is the final phase and there’s lots of ions moving in different directions. One of which is H+
* The movement of H+ in either direction has a direct affect of pH, which signifies an acidic or basic environment
79
Describe the composition of mammalian blood plasma
* In mammalian blood plasma and in the primary urine concentration of bicarbonate is high but concentration of protons is low
80
What are the processes occurring that ensures reabsorption of bicarbonate in the proximal convuluting tubule?
Reabsorption of around 80% of bicarbonate takes place in the proximal convoluting tubule and continues in downstream sections of the nephron
* Protons are moved in the opposite direction, causing acidification of the intertubular fluid
* The final fine tuning of urine acidification and bicarbonate reabsorption takes place in the distal tubule and the collecting duct
* Alpha intercalated cells (acid-secreting) and beta intercalated cells (base-secreting) possess various sensors for bicarbonate, co2 or proton concentration
* Signals from sensor modulate expression, abundance in the plasma membrane or activity of transporters, pumps and channels on these cells
* These processes are also under hormonal control (aldosterone, angiotensin II etc)
81
What is the main purpose of countercurrent multiplication?
* the main purpose of counter current multiplication is to create concentrated urine with the loop of henle (LOH)
* There is a reason why the role of DL is water reabsorption and the role of AL is to pump ions out to the IF via active transport
* Remember at the end of the PT the osmolarity is isosmotic (300 mOsm as the PT is responsible of maximum reabsorption)
82
What is the main function of the DL? How is this function produced?
The main function of the DL is water reabsorption. Therefore,, because the osmolariy (Concentration of Na+) in the IF is high, water will move out from the DL into the IF, equilibriating the osmotic pressure.
* because the water moves out of the DL, the Na+ concentration within the DL will increase
* High concentration Na+ from the DL will move into the AL where the concentration of Na+ was initially low, due to Na+ being transported into the IF via active transport.
83
What happens in the AL and what does this create?
* High concentration of Na+ in the AL will pump out Na+ into the IF
* this is a constant cycle known as counter current multiplication, which creates a concentration gradient across the LOH. There is always a difference of 200 mOsm between the IF and tubular fluid.
84
What is the osmolarity of filtrate entering the Loop of Henle from the proximal tubule?
It is isosmotic to the interstitial fluid (IF), approximately 300 mOsm.
85
Why is isosmotic filtrate not ideal for concentrated urine formation?
Because no osmotic gradient exists to drive water reabsorption
86
What is the main goal in forming concentrated urine regarding osmolarity?
To create a 200 mOsm difference between the ascending limb (AL) and the interstitial fluid (IF).
87
How is the 200 mOsm difference achieved in the Loop of Henle?
By actively transporting Na⁺ from the ascending limb (AL) into the IF.
88
What osmolarity values result from Na⁺ transport out of the AL?
IF becomes 400 mOsm; AL filtrate becomes 200 mOsm
89
What was the initial osmolarity of the descending limb (DL) filtrate before Na⁺ movement from the AL?
300 mOsm (isosmotic to IF).
90
What concentration gradient forms between the DL and IF after Na⁺ transport from the AL?
IF is 400 mOsm, DL remains at 300 mOsm.
91
Why does water move out of the DL into the IF?
Due to the concentration gradient created by Na⁺ transport.
92
How long does water move out of the DL?
Until equilibrium is reached between DL and IF (400 mOsm).
93
What happens to the filtrate in the DL as water moves out?
It becomes more concentrated (increased osmolarity
94
Does water reabsorption change the osmolarity of the IF?
No, it remains constant despite water entering.
95
What happens after filtrate in the DL becomes concentrated
It moves into the AL.
96
What drives filtrate movement from DL to AL?
Continuous entry of new filtrate from the proximal tubule (PT
97
Why can’t Na⁺ be transported passively at the bottom of the AL?
Because it is isosmotic with the IF—no concentration gradient exists.
98
How is Na⁺ transported in the AL?
Via active transport into the IF.
99
What happens to remaining Na⁺ in the upper AL?
It is also actively transported into the IF to maintain the 200 mOsm gradient.
100
Where does any remaining Na⁺ from the AL go after transport
A: Into the collecting duct (CD).
101
Why does osmolarity increase deeper into the medulla?
Due to countercurrent multiplication.
102
What is meant by “countercurrent multiplication”?
Filtrate moves in opposite directions (countercurrent), and the concentration gradient is amplified (multiplication).
103
Why do desert animals have longer loops of Henle?
To enhance water conservation by maximizing water reabsorption.
104
What are the vasa recta?
* Vasa recta are specialised capillaries found around the JMN
* These capillaries specialise in creating this hyperosmotic environment to draw water out
105
What happens in the descending vasa recta?
Descending vasa recta - blood coming down from the cortex into the medulla is in contact with increased osmolarity IF. The Na+ will diffuse from the surrounding IF into the vasa recta
106
What happens in the ascending vasa recta?
* Ascending vasa recta - concentrated blood (increased osmolarity) will move towards the AL and will lose that concentrated Na+ to the diluted IF (refer to counter current multiplication to understand this mechanism)
107
Describe the vasa recta in relation to H2O
* descending vasa recta - dilute blood recta - dilute blood flowing from the cortex into the medulla will lose water to the concentrated IF (increased osmolarity)
* Ascending vasa recta - concentrated blood flowing towards the AL will gain water from the IF due to its increased osmolarity in the capillary
108
How does a steep concentration gradient benefit the CD?
* due to increased concentration gradient across the nephron, there is constant water reabsorption which creates concentrated urine
* The steep concentration gradient also benefits the CD which promotes water reabsorption from the CD
* Furthermore, urea also has the ability to move freely across the membranes. Urea can move across the AL, CD and the IF. Due to this movement and the constant influx of newly filtered urea, creates a concentration gradient, promoting water reabsorption from the DL
* CD has special transport proteins. UT-A1 and UT-A3, expressed by epithelial cells of the CD, aid in transport of urea from the CD to the IF
109
What does vasopressin do?
Recent research has shown that vasopressin (anti diuretic hormone) upregulates expression of UT-A1 and UT-A3, increasing the rate of urea transport
110
Where is vasopressin synthesised?
* hormone known as vasopressin (antidiuretic hormone) is synthesised in the hypothalamus. This takes place when ADH is released by a neuronal cell body which lies in the posterior pituitary gland
111
How is vasopressin release stimulated?
* In your hypothalamus you have the presence of osmoreceptors that are sensitive to osmolarity. An increased osmolarity causes release of vasopressin.
* Angiotensin II also acts on receptors in the hypothalamus causing vasopressin release. This part of the renin-angiotensin system.
* Another significant stimulus for vasopressin release is from the heart. They have receptors known as baroreceptors that sense change in blood pressure.
* When there is a decrease in water content in the blood, there is reduced Venus return. This is sensed by the receptors, leading to vasopressin release
* Mechanism of vasopressin: when osmolarity of the IF increases (decrease in water content vasopressin is released
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What is the mechanism of vasopressin?
* Mechanism of vasopressin: when osmolarity of the IF increases (decrease in water content vasopressin is released
* Vasopressin upregulates translocation of aquaporin (AQP-2) receptors on the apical side of the plasma membrane in the distal convoluted tubule and CD
* On the basolateral side of the membrane you always have presence of aquaporin-3 and 4
* When osmolarity in the IF increases (decrease in water content), vasopressin is released and upregulates translocation of AQP-2, leading to increased water reabsorption in the IF
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What is renin?
Renin is an enzyme secreted by juxtaglomerular (JGA) cells.
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Where are juxtaglomerular (JGA) cells located?
At the point where the Bowman's capsule meets the distal convoluted tubule.
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What specialized cells are located near the glomerulus in the DCT?
JGA cells and macula densa cells.
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What triggers the baroreceptor mechanism for renin release
: A drop in blood pressure in the afferent arteriole.
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How do baroreceptors influence JGA cells?
They signal JGA cells to release renin when blood pressure decreases.
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What nervous system stimulates renin release during stress?
The sympathetic nervous system
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What do macula densa cells detect?
Sodium (Na⁺) concentration in the distal convoluted tubule.
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What does a low Na⁺ level in the DCT suggest?
Low blood pressure.
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What happens when macula densa cells detect low Na⁺?
They stimulate JGA cells to release renin
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What is the ultimate goal of renin secretion?
To increase blood pressure and glomerular filtration rate (GFR).
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What is the substrate for renin?
Angiotensinogen, which is produced by the liver.
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What does renin convert angiotensinogen into?
Angiotensin I.
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Which enzyme converts angiotensin I to angiotensin II?
Angiotensin-converting enzyme (ACE).
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What is the function of angiotensin II?
It increases blood pressure and stimulates aldosterone secretion.
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What hormone does angiotensin II stimulate?
Aldosterone.
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Where does aldosterone act in the kidney?
In the distal convoluted tubule and collecting duct.
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What does aldosterone do to Na⁺ and K⁺ levels?
It increases sodium reabsorption and potassium secretion.
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What happens to water reabsorption when Na⁺ reabsorption increases?
Water reabsorption also increases.
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What is the overall effect of increased water reabsorption?
An increase in blood volume and blood pressure.
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What system does renin initiate?
The renin-angiotensin-aldosterone system (RAAS), which regulates blood pressure and fluid balance.
