kidney Flashcards
1
Q
what are the different ways in which humans regulate their internal environment?
A
-thermoregulation
-osmoregulation
-excretion
1
Q
what is thermoregulation?
A
maintaining body temperature within a tolerable range
2
Q
what is osmoregulation?
A
regulating solute balance and gain/loss of water
3
Q
what is excretion?
A
removal of nitrogen-containing waste products of metabolism such as urea.
4
Q
when there’s a selectively permeable membrane, what are the two sides and what do they mean?
A
-hyperosmotic: higher solute concentration, less free H2O molecule
-hypoosmotic: lower solute concentration, more free H2O molecule
5
Q
what are the different components to osmoregulation?
A
1) controlling movements of solutes between internal fluids and the external environment
2) this also regulates water movement, which follows solutes by osmosis.
3) must also remove metabolic waste products before they accumulate to harmful levels.
6
Q
how do we maintain the composition of the cells of the body?
A
maintenance of the composition of body’s cells is primarily accomplished by managing the composition of the interstitial fluid that bathes the cells
7
Q
how do we regulate interstitial fluid?
A
regulate the interstitial fluid indirectly by controlling the composition of blood
8
Q
what do the kidneys do?
A
kidneys of vertebrates are specialized for the maintenance of fluid composition
9
Q
what is transport epithelium?
A
1) move specific solutes in controlled amounts in particular directions
2) are arranged into complex tubular networks with extensive surface area
10
Q
what determines the kind and direction of solutes that move across a transport epithelium?
A
molecular structure of plasma membranes determines the kinds and directions of solutes that move across the transport epithelium
11
Q
what happens when we want metabolic wastes to exit the body? what does this have an impact on?
A
most metabolic wastes must be dissolved in water when they are removed from the body so the quantity of waste products may have a large impact on water balance
12
Q
what is the breakdown of nitrogenous waste?
A
13
Q
what is the main nitrogenous waste I humans?
A
urea
14
Q
why is urea the main form of nitrogenous waste in humans? what is the advantage of urea?
A
Enzymes remove nitrogen in the form of ammonia (very toxic molecule).
Urea is synthesized in the liver by combining ammonia with carbon dioxide.
Main advantage of urea is its low toxicity, about 100,000 times less than that of ammonia
15
Q
what is the link between water and urea?
A
Urea can be transported and stored safely at high concentrations, reducing the amount of water needed for nitrogen excretion.
16
Q
why are animal cells sensitive? what is their relation to water?
A
Animal cells - which lack cell walls - swell and burst if there is a continuous net uptake of water or shrivel and die if there is a substantial net loss of water
17
Q
what is the best state of solution for an animal cell?
A
isotonic solution
18
Q
what happens to an animal cell in a hypnotic solution?
A
lysed
19
Q
what happens to an animal cell in a hyerptonic solution?
A
shrivelled
20
Q
true or false, the excretory system is central to homeostasis?
A
true
21
Q
what does erythropoietin do?
A
regulates RBC production
22
Q
what does renin do?
A
regulates blood pressure
23
Q
what does the excretory system?
A
1) disposes of metabolic wastes
2) controls body fluid composition by adjusting the rates of loss of particular solutes.
3) Producing erythropoietin (regulates RBC production)
and renin (regulates blood pressure)
4) Activating vitamin D
24
how does the excretory system produce urine?
1) blood is filtered and the collected fluid is called filtrate
2) composition of the collected fluid is adjusted by selective reabsorption of valuable substances and secretion of toxins and excess ions
3) excretion of the contents of the tubule.
25
what happens during the initial filtration of blood process, where the filtrate is formed?
involves filtration through the selectively permeable membranes of transport epithelia, largely nonselective
26
what does the transport epithelia retain during filtration?
These membranes retain cells as well as proteins and other large molecules from the body fluids
27
what forces the filtrate into the excretory system?
Hydrostatic pressure forces water and small solutes, such as salts, sugars, amino acids, and nitrogenous wastes, collectively called the filtrate, into the excretory system
28
what do nephrons do?
Each of your kidneys is made up of about a million filtering units called nephrons. Each nephron includes a filter, called the glomerulus, and a tubule. The nephrons work through a two-step process: the glomerulus filters your blood, and the tubule returns needed substances to your blood and removes wastes.
29
what are the layers of the nephrons?
cortex, inner medulla, outer medulla
30
what does the nephron look like?
31
what happens during reabsorption?
Use active transport to selectively reabsorb valuable solutes such as glucose, certain salts, and amino acids back into the blood.
- Nonessential solutes and wastes are left in the filtrate or added to it by selective secretion.
- Pumping of various solutes also adjusts the osmotic movement of water into or out of the filtrate.
32
what supplies blood to the kidney?
renal artery and a renal vein 9renal vein goes back to heart)
33
how many times of the total blood volume does the kidney filtrate?
In humans, the kidneys account for less than 1% of body weight, but they receive about 20% of resting cardiac output. Kidneys filter body’s entire plasma volume 60 times each day
34
how does urine exit the kidney?
Urine exits the kidney through a duct called the ureter, and both ureters drain through a common urinary bladder which empties via the urethra
35
what controls urination?
Sphincter muscles near the junction of the urethra and the bladder control urination
36
what are the two distinct regions of the kidney?
an outer renal cortex and an inner renal medulla
37
what does each nephron consist of?
Each nephron consists of a single long tubule and a ball of capillaries, called the glomerulus
38
what does each kidney region contain?
Both regions are packed with microscopic excretory tubules, nephrons, and their associated blood vessels
39
what is the bowman's capsule?
Blind end of the tubule forms a cup-shaped swelling, called Bowman’s capsule, that surrounds the glomerulus
40
what is the glomerulus?
ball of capillaries, called the glomerulus. The capillaries of the glomerulus are highly porous, part of nephron
41
how many nephrons does each kidney have?
millions
42
what's the glomerulus?
They are a type of capillaries. These capillaries are each contained within the Bowman's capsule and they are the only capillary beds in the body that are not surrounded by interstitial tissue
43
how does filtration occur?
Filtration occurs as blood pressure forces fluid from the blood in the glomerulus into the lumen of Bowman’s capsule
44
how does the filtration in the bowman's capsule occur?
Porous capillaries, along with specialized capsule cells called podocytes, are permeable to water and small solutes but not to blood cells or large molecules such as plasma proteins
45
what does the filtrate in Bowman's capsule contain?
Filtrate in Bowman’s capsule contains salt, glucose, vitamins, nitrogenous wastes, and other small molecules
46
after the bowman's capsule, where does the filtrate pass?
1) the proximal tubule
2) the loop of Henle, a hairpin turn with a descending limb and an ascending limb
3) the distal tubule which empties into a collecting duct, which receives processed filtrate from many nephrons.
47
what's the loop of henle?
a hairpin turn with a descending limb and an ascending limb
48
what is the distal tube?
the distal tubule which empties into a collecting duct, which receives processed filtrate from many nephrons
49
what do the ducts empty into?
The many collecting ducts empty into the renal pelvis, which is drained by the ureter
50
what are the different types of kidneys in the human body?
cortical and juxtamedullary
51
what are 80 percent of nephrons and where are they found?
about 80% of the nephrons, the cortical nephrons, have reduced loops of Henle and are almost entirely confined to the renal cortex
52
what are juxtamedullary nephrons?
The other 20%, the juxtamedullary nephrons, have well-developed loops that extend deeply into the renal medulla
53
which nephrons allow mammals to produce urine that is hyper osmotic to body fluids?
juxtamedullary nephrons
54
what are the nephrons and collecting ducts lined by?
The nephron and the collecting duct are lined by a transport epithelium that processes the filtrate to form the urine
55
what do the nephrons and collecting ducts reabsorb?
The nephrons and collecting ducts reabsorb nearly all of the sugar, vitamins, and other organic nutrients from the initial filtrate and about 99% of the water
56
what is the division of capillaries and arterioles in the nephrons?
The capillaries converge as they leave the glomerulus forming an efferent arteriole.
This vessel subdivides again into the peritubular capillaries, which surround the proximal and distal tubules.
Additional capillaries extend downward to form the vasa recta, a loop of capillaries that serves the loop of Henle.
57
true or false, the tubules and capillaries are immersed in interstitial fluid
true
58
what's the vasa recta?
Additional capillaries extend downward to form the vasa recta, a loop of capillaries that serves the loop of Henle.
59
what are aquaporins?
water channel proteins of the cell membrane
Aquaporins (AQP) are integral membrane proteins that serve as channels in the transfer of water, and in some cases, small solutes across the membrane.
60
true or false, there's a pore in the center of each aquaporin molecule
true
61
how does urine form
Filtrate from Bowman’s capsule flows through the nephron and collecting ducts as it becomes urine
62
what does the proximal tube do?
Secretion and reabsorption in the proximal tubule substantially alter the volume and composition of filtrate.
63
what do the cells of the transport epithelium do in the proximal tubule?
The cells of the transport epithelium help maintain a constant pH in body fluids by controlled secretions of hydrogen ions or ammonia
64
what do the proximal tubules reabsorb?
The proximal tubules reabsorb about 90% of the important buffer bicarbonate (HCO3-).
65
what exits the peritubular capillaries?
Drugs and other poisons pass from the peritubular capillaries into the interstitial fluid and then across the epithelium to the nephron’s lumen.
66
which valuable nutrients are reabsorbed, from the filtrate?
Valuable nutrients, including glucose, amino acids, and K+ are actively or passively (re)absorbed from filtrate
67
how is sodium transported out of the cells and into the interstitial fluid?
The epithelial cells actively transport Na+ into the interstitial fluid. This transfer of positive charge is balanced by the passive transport of Cl- out of the tubule.
As salt moves from the filtrate to the interstitial fluid, water follows by osmosis.
67
what is one of the most important functions of the proximal tubule?
One of the most important functions of the proximal tubule is reabsorption of most of the NaCl and water from the initial filtrate volume
68
describe the exterior side of the epithelium of the tubules?
The exterior side of the epithelium has a much smaller surface area than the side facing the lumen, which minimizes leakage of salt and water back into the tubule, and instead they diffuse into the peritubular capillaries (the difference in surface area may be due to the brush border..the presence of microvilli on the simple cuboidal epithelium
69
describe the descending loop of the loop of henley?
This transport epithelium is freely permeable to water but not very permeable to salt and other small solutes.
70
what is the link between the osmolality of the interstitial fluid and the movement of water in the descending tubule
For water to move out of the tubule by osmosis, the interstitial fluid bathing the tubule must be hyperosmotic to the filtrate.
Because the osmolarity of the interstitial fluid does become progressively greater from the outer cortex to the inner medulla, the filtrate moving within the descending loop of Henle continues to lose water.
71
where is the osmolality of the interstitial fluid greatest?
inner medulla
72
what happens in the ascending loop of henle?
In contrast to the descending limb, the transport epithelium of the ascending limb is permeable to salt, not water.
73
in the ascending tube, what diffuses out of the tubule?
As filtrate ascends the thin segment of the ascending limb, NaCl diffuses out of the permeable tubule into the interstitial fluid, increasing the osmolarity of the medulla.
The active transport of salt from the filtrate into the interstitial fluid continues in the thick segment of the ascending limb.
By losing salt without giving up water, the filtrate becomes progressively more dilute as it moves up to the cortex in the ascending limb of the loop.
74
what does the distal tube do?
The distal tubule plays a key role in regulating the K+ and NaCl concentrations in body fluids by varying the amount of K+ that is secreted into the filtrate and the amount of NaCl reabsorbed from the filtrate.
75
what do the proximal and distal tube have in common?
Like the proximal tubule, the distal tubule also contributes to pH regulation by controlled secretion of H+ and the reabsorption of bicarbonate (HCO3-).
76
what huge role does the transport epithelium have?
By actively reabsorbing NaCl, the transport epithelium of the collecting duct plays a large role in determining how much salt is actually excreted in the urine.
77
as we go down the collecting duct, what happens to the filtrate?
Collecting duct. By actively reabsorbing NaCl, the transport epithelium of the collecting duct plays a large role in determining how much salt is actually excreted in the urine.
As the collecting duct traverses the gradient of osmolarity in the kidney, the filtrate becomes increasingly concentrated as it loses more and more water by osmosis to the hyperosmotic interstitial fluid.
78
what happens in the duct, as we get to the inner medulla?
In the inner medulla, the duct becomes permeable to urea, contributing to hyperosmotic interstitial fluid and enabling the kidney to conserve water by excreting a hyperosmotic urine.
79
what is the state of the of the collecting duct epithelium due to?
controlled by hormones. There are modifications required to maintain homeostasis, blood pressure and osmolarity.
80
how does the osmorality of the filtrate change within the nephron?
81
what is responsible for the concentration of urine?
In a mammalian kidney, the cooperative action and precise arrangement of the loops of Henle and the collecting ducts are largely responsible for the osmotic gradients that concentrate the urine
82
in essence, what is the role of the nephron?
In essence, the nephrons can be thought as tiny energy-consuming machines whose function is to produce a region of high osmolarity in the kidney, which can then extract water from the urine in the collecting duct
83
what are the two primary solutes?
urea and NaCl
84
what do the juxtamedullary nephrons do?
The key to understanding the physiology of the mammalian kidney as a water-conserving organ is the actions of the juxtamedullary nephrons, which maintain an osmotic gradient in the kidney and use that gradient to excrete a hyperosmotic urine.
85
what does the counter-current multiplier allow for?
The ability of the mammalian kidney to convert interstitial fluid at 300 mosm/L to 1,200 mosm/L as urine depends on a counter-current multiplier between the ascending and descending limbs of the loop of Henle.
86
what happens in the descending limb?
As the filtrate flows from the cortex to the medulla in the descending limb of the loop of Henle, water leaves the tubule by osmosis
87
at what point is the filtrate at its most concentrated?
The osmolarity of the filtrate increases as solutes, including NaCl, become more concentrated until it reaches its highest osmolarity occurs at the elbow of the loop of Henle
88
how do the ascending and descending limb work together?
The descending limb produces progressively saltier filtrate, and the ascending limb exploits this concentration of NaCl to help maintain a high osmolarity in the interstitial fluid of the renal medulla.
89
what are the qualities that the loop of henle has that resemble a counter current system?
Although the two limbs of the loop are not in direct contact, they are close enough to exchange substances through the interstitial fluid.
The nephron can concentrate salt in the inner medulla largely because exchange between opposing flows in the descending and ascending limbs overcomes the tendency for diffusion to even out salt concentrations throughout the kidney’s interstitial fluid.
90
true or false, the direction of the vesa recta blood flow is opposite to the direction of the flow of the filtrate?
true. in the ascending tube of the loop of henle, the vesa recta blood id descending and vice versa
91
true or false, the vesa recta is a counter current system?
true
92
what happens in the ascending and descending part of the vesa recta?
As the descending vessel conveys blood toward the inner medulla, water is lost from the blood and NaCl diffuses into it.
These fluxes are reversed as blood flows back toward the cortex in the ascending vessel.
93
true or false, there's a steep osmotic gradient between the medulla and the cortex?
true
94
how is the steep gradient between the medulla and the cortex created?
This gradient is initially created by active transport of NaCl out of the thick segment of the ascending limb of the loop of Henle into the interstitial fluid
95
true or false the kidney consumes lots of ATP
TRUE
96
when is NaCl transported actively/passively?
97
what is the state of the filtrate as it gets to the distal tube?
By the time the filtrate reaches the distal tubule, it is actually hypoosmotic to body fluids because of active transport of NaCl out of the thick segment of the ascending limb.
98
what happens in the collecting duct?
As the filtrate descends again toward the medulla in the collecting duct, water is extracted by osmosis into the hyperosmotic interstitial fluids, but salts cannot diffuse in because the epithelium is impermeable to salt.
This concentrates salt, urea, and other solutes in the filtrate.
Some urea leaks out of the lower portion of the collecting duct, contributing to the high interstitial osmolarity of the inner medulla.
99
when is urine isosmotic to the interstitial fluid? what does this allow for?
Before leaving the kidney, the urine may obtain the osmolarity of the interstitial fluid in the inner medulla, which can be as high as 1,200 mosm/L.
Although isoosmotic to the inner medulla’s interstitial fluid, the urine is hyperosmotic to blood and interstitial fluid elsewhere in the body
ALLOWS FOR MINIMAL WATER LOSS
100
what do juxtamedullary nephrons allow for?
The juxtamedullary nephron is a key adaptation to terrestrial life, enabling humans to get rid of salts and nitrogenous wastes without squandering water
101
what can the kidney adjust for urine?
One important aspect of the human kidney is its ability to adjust both the volume and osmolarity of urine, depending on the water and salt balance and the rate of urea production.
102
what are the two cases where urine can vary?
With high salt intake and low water availability, a person can excrete urea and salt with minimal water loss in small volumes of hyperosmotic urine.
If salt is scarce and fluid intake is high, the kidney can get rid of excess water with little salt loss by producing large volumes of hypoosmotic urine (as dilute at 70 mosm/L).
Kidneys produce only small amounts
of urine if the body is dehydrated, or dilute urine if overhydrated
103
what is a countercurrent mechanism?
Accomplish this by using countercurrent mechanism: Fluid flows in opposite directions in two adjacent segments of same tube with hairpin turn
104
what is a countercurrent multiplier?
interaction of filtrate flow in ascending/descending limbs of nephron loops of juxtamedullary nephrons.
- Limbs of loop are not in direct contact but are close enough to influence each other’s exchanges with surrounding interstitial fluid
- The more NaCl the ascending limb actively transports out into ISF, the more water diffuses out of the descending limb
- The more water that diffuses out of the descending limb, the saltier the filtrate becomes
- Ascending limb then uses salty filtrate to further raise osmolality of medullary ISF
105
what is a countercurrent exchanger?
blood flow in ascending/descending limbs of vasa recta
- Vasa recta is highly permeable to water and solutes
- Flow of blood in vasa recta is also countercurrent (hairpin turn) so blood can exchange NaCl and water with surrounding interstitial fluid as it moves through adjacent parallel sections of gradient
- Blood inside vasa recta remains isosmotic with surrounding interstitial fluid
- Vasa recta is able to reabsorb water and solutes without undoing osmotic gradient created by countercurrent multiplier
106
what is ADH?
ADH is produced in hypothalamus of the brain and stored in and released from the pituitary gland, which lies just below the hypothalamus
107
what measures osmolality of blood?
osmoreceptors
108
what does ADH do?
ADH induces the epithelium of the distal tubules and collecting ducts to become more permeable to water
This reduces urine volume and helps prevent further increase of blood osmolarity above the set point
109
what is the negative feedback mechanism when it comes to ADH?
By negative feedback, the subsiding osmolarity of the blood reduces the activity of osmoreceptor cells in the hypothalamus, and less ADH is secreted
Conversely, if a large intake of water has reduced blood osmolarity below the set point, very little ADH is released
110
what happens with ADH if we drink a lot of water?
Conversely, if a large intake of water has reduced blood osmolarity below the set point, very little ADH is released.
This decreases the permeability of the distal tubules and collecting ducts, so water reabsorption is reduced, resulting in an increased discharge of dilute urine
111
what is the link between alcohol and ADH?
Alcohol can disturb water balance by inhibiting the release of ADH, causing excessive urinary water loss and dehydration (causing some symptoms of a hangover).
Normally, blood osmolarity, ADH release, and water reabsorption in the kidney are all linked in a feedback loop that contributes to homeostasis
112
what is the second regulatory mechanism?
A second regulatory mechanism involves a special tissue called the juxtaglomerular apparatus (JGA), located near the afferent arteriole that supplies blood to the glomerulus.
When blood pressure or blood volume in the afferent arteriole drops, the enzyme renin initiates chemical reactions that convert a plasma protein angiotensinogen to a peptide called angiotensin II.
Acting as a hormone, angiotensin II increases blood pressure and blood volume in several ways.
113
what converts angiotensinogen into angiotensinogen II?
renin
114
how does angiotensin II increase blood pressure?
1) It raises blood pressure by constricting arterioles, decreasing blood flow to many capillaries, including those of the kidney.
2) It also stimulates the proximal tubules to reabsorb more NaCl and water.
This reduces the amount of salt and water excreted and consequently raises blood pressure and volume.
3) It also stimulates the adrenal glands, organs located atop the kidneys, to release a hormone called aldosterone.
This acts on the distal tubules, which reabsorb Na+ and water, increasing blood volume and pressure.
115
what does aldosterone do?
This acts on the distal tubules, which reabsorb Na+ and water, increasing blood volume and pressure
116
what is the JGA?
A second regulatory mechanism involves a special tissue called the juxtaglomerular apparatus (JGA), located near the afferent arteriole that supplies blood to the glomerulus.
A drop in blood pressure triggers a release of renin from the JGA.
117
how do ADH and RAAS work together?
ADH alone would lower blood Na+ concentration by stimulating water reabsorption in the kidney.
But the RAAS helps maintain balance by stimulating Na+ reabsorption.
118
true or false, RAAS and ADH increase water reabsorption, but for different reasons
true!
119
what happens if we have a severe injury?
a situation that causes excessive loss of salt AND body fluids (an injury or severe diarrhea, for example) will reduce blood volume without increasing osmolarity.
The RAAS will detect the fall in blood volume and pressure and respond by increasing water and Na+ reabsorption
120
what hormone opposes RAAS?
The walls of the atria release ANF in response to an increase in blood volume and pressure.
ANF inhibits the release of renin from the JGA, inhibits NaCl reabsorption by the collecting ducts, and reduces aldosterone release from the adrenal glands.
These actions lower blood pressure and volume.
121
what are the three hormones used to regulate kidney?
Thus, the ADH, the RAAS, and ANF
122
what does the liver do?
For example, liver cells interact with the circulatory system in taking up glucose from the blood.
The liver stores excess glucose as glycogen and, in response to the body’s demand for fuel, converts glycogen back to glucose, releasing glucose to the blood.
The liver also synthesizes plasma proteins important in blood clotting and in maintaining osmotic balance in the blood.
Liver cells detoxify many chemical poisons and prepare metabolic wastes for disposal.
123
what does aldosterone do?
This acts on the distal tubules, which reabsorb Na+ and water, increasing blood volume and pressure
124
