renal Flashcards
1
Q
renal =
A
kidney
2
Q
kidney regulates
A
the plasma of the blood
3
Q
renal functions
A
- regulate our blood volume and pressure (maintain water conc and fluid volume, inorganic ion composition within a constant range)
- maintain the acid-base balance
- excrete (urea, uric acid, creatinine, bilirubin, foreign chemicals)
- synthesis of new glucose molecules to provide energy (gluconeogenesis)
- secrete a number of hormones (EPO, renin, 1,25-dihydroxyvitamin D)
4
Q
sodium
A
higher conc in ecf
5
Q
potassium
A
higher conc in intracellular compartment
6
Q
chloride
A
higher conc in ecf
7
Q
bicarbonate
A
higher conc in ecf
8
Q
phosphate
A
higher conc in intracellular compartment
9
Q
aquaporins
A
specialized water-selective channels in the plasma membrane of cells; responsible for rapid diffusion of water
10
Q
one osmole is equal to
A
one mole of solute particle that is dissolved in water
11
Q
osmolarity
A
the number of solutes per volume of solution expressed in moles per liter
how many solute particles that are dissolved per unit volume of water
12
Q
water conc is always recorded i
A
osmoles
13
Q
pure water =
A
high water conc
14
Q
pure water =
A
high water conc
15
Q
a region with higher osmolarity has a
A
lower water conc as it contains more solute molecules
16
Q
osmotic pressure
A
opposing pressure required to stop osmosis completely
will push and prevent water from coming into the cell, to prevent them from taking on water and bursting
17
Q
tonicity
A
determined by the con of non-penetrating solutes of an extracellular solution
18
Q
isotonic
A
the inside of the cell and the extracellular environment have the same osmolarity
19
Q
hypertonic solution
A
extracellular medium has a higher osmolarity than inside the cell; cell with shrink
20
Q
hypotonic solution
A
extracellular medium has a lower osmolarity than inside the cell; cell will swell or bulge out
21
Q
water moves in and out of cells through
A
aquaporins
22
Q
extracellular fluid compartment =
A
plasma, which stays within the blood vessels, and the interstitial fluid
23
Q
kidneys can regulate the volume of the
A
plasma
24
Q
movement of water and solutes from the interstitial fluid compartment to the plasma is called
A
absorption
25
movement of water and solutes from the plasma to the interstitial fluid is called
filtration
26
how does fluid move between the plasma and the interstitial fluid compartments
capillary hydrostatic pressure
27
capillary hydrostatic pressure
the pressure exerted by a fluid; blood flows through the capillary and exerts pressure on the walls of the capillaries, pushes fluid out of the capillary
28
interstitial fluid hydrostatic pressure
pressure of the interstitial fluid on the walls of the capillary, pushes fluid into capillaries
29
what is the contribution of the plasma proteins to fluid movement
proteins are large and sometimes charged; cannot move in and out of capillaries easily
30
why these is osmotic force due to plasma protein conc
a lot of plasma proteins means there are more proteins and less water conc inside the capillary than outside; water will try to move into the capillary
31
why is there osmotic force die to interstitial fluid protein conc
proteins have a difficult time crossing the capillary, but some will escape into interstitial space; these proteins will draw fluid out of the capillary
32
the net pressure determines
the direction of fluid movement
33
staling forces
four factors that determine the net filtration pressure
34
net filtration pressure at arterial end of capillary
more filtration of fluid as the net filtration pressure is positive; fluid moves out of the capillaru
35
net filtration pressure at venule end of capillary
more absorption of fluid as the net filtration pressure is negative; fluid moves into the capillary
36
homeostasis is controlled mostly by
the kidneys
37
kidney location
retroperitoneal
38
hilum
inner concave part of kidnet
39
ureters
drain the formed urine from the kidneys and empty into the bladder
40
bladder
storage organ or sac for the formed urine
- receives innervation from ans, emptying is controlled by parasympathetic and sympathetic inputs
41
micturition
process of releasing the urine outside the body, uriniation
42
2 regions of kidney
cortex (outer portion)
medulla (inner portion)
43
nephron
functional units of kidneys, where urine is made
- 1 mil nephrons in kidney
contain renal corpuscle and renal tubule
44
renal corpuscle
bulb-like structure attached to renal corpuscle is a long tube called the renal tubule
tufts of capillaries (glomerulus) sits in Bowman's capsule
45
renal tubule segments
proximal convoluted tubule, loop of henle, distal convoluted tubule, collecting ducts
46
proximal convoluted tubule
close to the renal corpuscle, twisted
47
loop of henle
a hairpin that bends, divided into descending (travels downward) and ascending (travels upwards) limb
- ascending limb has a thicker segment and a thinner segment
48
distal convoluted tubule
far away from the renal corpuscle, drains its contents into a main tube called the collecting duct
49
collecting duct
each nephron has its renal corpuscle and the renal tubule which drain into the collecting duct
empties into the renal pelvis of kidney
50
initial blood filtering component of a nephron
renal corpuscle
51
blood pathway in renal corpsucle
enters through afferent arteriole, goes through several twists and turns, and then exits through the efferent arteriole
51
bowman's capusle
outer wall of bowman's capsule surrounds bowman's space
- filtrate enters bowman's space once the blood has been filtered
- outer wall of bowman's capsule is made up of epithelial cells
51
podocytes
cells closest to which come in contact with glomerular capillaries
have foot-like processes
51
ultimate outcome of renal corpuscle
development of a hollow tube which becomes the bowman's cup and continues in as the tubule
51
three stages of development of renal corpuscle
stage 1: when the kidneys are forming during fetal life
- a nephron will develop first as a blind-ended tube (no opening)
- tube is lined by a layer of epithelial cells sitting on a basement membrane
stage 2:
- growing tuft of capillaries penetrate the expanded end of tubules
- tubule invaginates/indents
- the capillaries continue to move closer to the epithelial cell layer
- basal lamina is trapped inbtw endothelial cells pf cap and epithelial layer
- epithelial layer differentiates into parietal (outer) and visceral (inner) layer
stage 3:
- the outer layer does not fuse with the inner layer (space btw them)
- parietal layer eventually flattened to become wall of Bowman's capsule, visceral layer becomes podocyte cell layer
51
podocytes are arranged around
the external surface of the glomerular capillaries
- podocytes are interlocked; the foot process of one podocyte (which are cytoplasmic projections) interlock with those of another podocyte
- btw the interlocking podocytes are filtration slits
51
3 layers of the glomerular capillary
endothelial layer, basement membrane, podocytes
52
anatomy of glomerular capillary
endothelial cell is fenestrated to allow for filtration
endothelial cells sit on a basement membrane (gel-like mesh structure composed of collagen proteins and glycoproteins)
podocytes are found outside the basement membrane with filtration slits through which fluid moves
the foot projections wrap around the capillary and leave slits between them
- foot process increase surface area for filtration
52
two types of nephrons
cortical (85%) juxtamedullary (15%)
one type sits closer to the cortex (cortical) and the other type sits closer to the medullary area (juxta)
-- renal corpuscles are always found in the cortex --
53
cortical nephron
renal corpuscle of the cortical nephron always found in cortex
tubule segment, collecting duct, distal convoluted tubule proximal tubule mostly located in cortex
54
juxtamedullary nephron
close to the medulla area
loop of henle and ascending limb are found in renal medulla
- create osmotic gradients in the interstitial space or outside the loop of henle -> physiologically regulate the conc of urine
55
3 types of renal processes
filtration, reabsorption, secretion
- cortical nephrons perform these three basic functions
- juxtamedullary nephrons perform these three basic function and regulate the conc of urine
56
blood supply to kidney
receive ~20% of the total cardiac output
brought through renal artery which enters the kidney through a curved concave portion known as the hilum area
57
afferent arteriole
branches off from the renal artery and diverges into the capillaries of the glomerulus
arteriole the brings blood into the glomerulus capillary network
58
efferent arteriole
blood exits the glomerulus through the efferent arteriole
branches around to form a set of capillaries called the peritubular capillary network (found around the proximal convoluted tubules) - fuse together to form the renal vein
59
vasa recta
capillaries that are found mostlu associated with juxtamedullary nephrons in the medullary portion of the kidney
- important in forming the osmotic gradient
60
glomerular filtration
fluid in the blood is filtered across the capillaries of the glomerulus and into bowman's space
- blood is brought to the kidneys by the renal artery and then enters the glomeruli through the arterioles, where it undergoes glomerular filtration
61
tubular reabsorption
the movement of a substance from inside the tubule into the blood
- glucose is reabsorbed by the body as it is very important as an energy source
62
tubular secretion
movement of nonfiltered substances from the capillaries into the tubular lumen
- waste products that did not undergo filtration can be removed from the blood by tubular secretion
63
urinary excretion
blood is filtered at the glomeruli, and then substances are added, or secreted, to the tubules, while other substances are reabsorbed; urine containing unwanted products is excreted from out body
64
3 layers that substances move across from the lumen of the glomerular capillaries into the bowman's space
capillary endothelial layer, basement membrane, podocytes with filtration slits
- when blood is passing though the3 glomerulus, almost everything moves out of the glomerular capillaries into bowman's space except large proteins (albumin) and blood cells -> pores and basement membrane have negative charges
65
what is filtered through the glomerulus
water, electrolytes, glucose, amino acids, fatty acids, vitamins, waste products (urea, uric acid, creatinine)
66
what is non filtered
plasma proteins, blood cells, large anions, anything bound to plasma proteins (calcium)
67
ultrafiltrate
the cell-free fluid that has come into bowman's space and, except for the plasma proteins and blood cells, contains mostly all the substances at the same conc as in the plasma
- the conc of a substance filtered through the filtration layers is the same in the plasma and in the filtrate
68
proteinuria
a condition where some of the proteins that are not supposed to pass through the filtration barrier show up in the filtrate and ultimately in the urine
- does not occur under healthy conditions
69
glomerular capillary hydrostatic pressure (Pgc)
hydrostatic pressure of the blood that is found in the glomerular capillaries
- 60mmHg
- this pressure pushes fluid into Bowman's space, or from the capillary side into bowman's space; favors filtration
70
bowman's space hydrostatic pressure (Pbs)
fluid pressure in bowman's space
- 15mmHg
- opposes filtration
71
osmotic force due to proteins in the plasma (pigc)
due to the proteins that are present in the plasma
- proteins in the glomerular capillaries act as a solute
- there is a greater solute conc in the capillaries due to the presence of the proteins and less water; this causes the movement of fluid from bowman's space into the glomerular capillaries by osmosis
- 29mmHg
- opposes filtration
72
net glomerular filtration pressure is the sum of the 3 forces
Pgc - Pbs - PIgc
60 - 15 - 29 = 16mmHg
positive filtration pressure which pushes fluid or water containing the substances that are filtered into bowman's space
- the positive pressure pushes the protein-free filtrate from the plasma out of the glomerulus into bowman's space
73
what factor would contribute to an inc in glomerular filtration rate
high blood pressure
74
what factor would contribute to a decrease on the glomerular filtration rate
an inc in protein conc in the plasma would inc the protein content in the glomerular capillaries, decreasing the glomerular filtration rate
75
plasma volume entering the afferent arteriole =
100%
76
filtration fraction
only 20% of the volume is filtered into bowman's space
- the rest of the volume leaves through the efferent arterioles into the peritubular capillaries and eventually back into the main circulation
- of the 20% that is filtered, 19% is reabsorbed and enters the peritubular capillaries
- less that 1% of the volume that was filtered is excreted to the external environment
77
glomerular filtration rate
the volume of fluid filtered from the glomerulus into the bowman's space per unit time
~125mL/min or 180L/day
- used to look at health of kidneys
78
factors that affect gfr
- net glomerular filtration pressure (blood pressure)
- neural and endocrine control
- permeability of the corpuscular membrane
- surface area available for filtration
79
autoregulation
gfr remains fairly constant
regulated by changes in the myogenic reflex as well as by the tubuloglomerular effect
80
constriction of the afferent arteriole
- due to the myogenic arteriole
- constriction increases resistance to flow through the afferent arteriole
- renal blood flow to the glomerulus has decreased due to an inc in the resistance in the afferent arteriole
- a dec in renal blood flow reduces the hydrostatic pressure of the glomerular capillary (Pgc) resulting in a dec in gfr
81
4 scenarios that can alter gfr
- constrict afferent arteriole: Pgc will dec -> dec gfr
- constrict efferent arteriole: volume of blood builds up in glomerular capillaries -> inc hydrostatic pressure in the glomerular capillaries -> inc gfr
- dilate efferent arteriole: dec resistance -> renal blood will drain rapidly -> dec in capillary hydrostatic pressure -> dec gfr
- dilate afferent arteriole: inc in blood flow into the afferent arteriole -> inc in hydrostatic pressure -> inc gfr
82
mechanisms which change arteriolar resistance
- myogenic response - arteriole smooth muscle contracts or relaxes in response to inc or dec in pressure
- hormones/neurotransmitters released from autonomic neurons may act on arterioles and alter resistance
- tubular glomerular feedback - in juxtaglomerular apparatus, controls the autoregulatory processes and affect the glomerular filtration rate
* myogenic response and tubuloglomerular effect play a role in autoregulation of the gfr
83
juxtaglomerular apparatus (JGA)
a specialized structure formed by the distal convoluted tubule and the glomerular afferent arteriole
- next to glomerulus
84
3 cell types that contol gfr
macula densa
juxtaglomerular cells
mesangial cells
85
macula densa
cells on wall of distal tubule at the junction where the ascending limb is beginning to form the distal tubule; in very close proximity to the glomerulus
- sense an increased sodium load along with increased flow of fluid through the distal tubule
- secrete vasoactive compounds
- by paracrine effects changes afferent arteriole resistance
-- adenosine is a paracrine factor which has an effect on arteriolar resistance by signaling jg cells
- part of the JGA
86
juxtaglomerular cells
also called granular cells
sit on top of the afferent arteriole
- innervated by sympathetic nerve fibers which can change the resistnace of the afferent arteriole
- release renin which controls afferent arteriole resistance
- part of the JGA
87
mesangial cells
found in the triangular region btw the afferent and efferent arterioles
- not considered part of the JGA
- when they contract, they allow podocytes to contract
- shrink the surface area of the glomerular filtration surface
- play a role in controlling the filtration surface area which affects the glomerular filtration rate
88
role of the macula densa in tubuloglomerular feedback
when increased fluid volume flows through the distal tubule there is a feedback effect on the glomerular structure in controlling the gfr
- inc in gfr -> inc in flow to the tubule -> flow past the macula densa increases -> paracrine factors from the macula densa are secreted -> paracrine factors act on the afferent arteriole -> afferent arteriole constricts -> resistance in the afferent arteriole inc -> hydrostatic pressure drops in the glomerulus (Pgc drops) -> dec gfr
89
filtered load
the amount of a substance that is filtered by the kidneys per day, or how much of the load is filtered into bowman's space
- substances filtered at the glomerulus are non-protein substances of non-protein bound substances
- calculated by multiplying the gfr by the con of the substance in the plasma
90
substance excreted in urine < filtered load
reabsorption has occurred
91
substance excreted in urine > filtered load
secretion has occurred
92
a substance may be filtered and secreted
- only 20% of the substance X is filtered into bowman's space and the remaining 80% enters the peritubular capillaries
- as a small amount of substance X is filtered, most of substance X was secreted into the urine from the peritubular capillaries
- the body did not retain any of substance X, but secreted 100% of the peritubular substance X into the urine
93
a substance may be filtered and partially reabsorbed
- only 20% of substance Y is filtered into Bowman's space and the remaining 80% enters the peritubular capillaries
- substance Y should be found in the ultrafiltrate at the same conc per unit volume but the amount of substance Y excreted in the urine is slightly less than the filtered load
- this means that there is partial reabsorption of substance Y back into the peritubular capillaries
94
a substance may by filtered and completely reabosrbed
- only 20% of substance Z is filtered into bowman's space and the remaining 80% enters the peritubular capillaries
- this situation is the ideal situation for blood glucose
95
renal handling of inulin
filtered only and what is filtered is excreted completely in the urine
- no secretion or reabsorption
96
renal handling of creatinine
filtered only and what is filtered is excreted completely in the urine
- no secretion or reabsorption
97
renal handling of electrolytes
filtered and partially reabsorbed
98
renal handling of glucose and amino acids
filtered and completely reabosrbed
99
renal handling of organic acids and bases
filtered and secreted
- whatever amound of substance is in the peritubular capillaries is secreted into the urine
- para-aminohippuric acid (PAH) - an organic acid that undergoes filtration and secretion often used clinically to measure renal plasma flow
100
average values of components that undergo filtration and reabsorption
water - 99% reabsorbed, 1.8L/day excreted
sodium - 99.5% reabsorbed, 3.2g/day excreted
glucose - 100% reabsorbed, 0g/day excreted
urea - 44% reabsorbed, 30g/day excreted
101
2 pathways of reabsorption
diffusion occurs mostly in tight junctions -- minor
mediated transport involving transporters (transepithelial transport - a substance will move from the tubular lumen into the cell, then out into the interstitial space and into the peritubular capillaries) -- main
102
mediated/transepithelial transport mechanism
major component of reabsorption
a substance moves from the tubular lumen across the cell, into the interstitial fluid and then into the peritubular capillaries
substance moves from apical membrane and across the basolateral membrane in reabsorption
103
reabsorption of sodium
inside the proximal tubule cell, there is a low conc of na (maintained through Na/K pump in basolateral membrane)
the low conc inside the cell causes na to move into the cell from the tubule lumen; once in the cell, it is pumped out into the interstitial fluid through the Na/K pump
then moves into the peritubular capillaries by diffusion or bulk transport
104
reabsorption of glucose
in the proximal tubule glucose is reabsorbed by active transport on the luminal side by sglt protein, facilitated diffusion on the basolateral side using carrier protein glut
- involves sodium-linked or sodium-dependent glucose reabsorption -> slgt uses inwardly directed sodium conc gradient to drive the influx of glucose into the cell against the conc gradient
once glucose enters the cell where the conc of glucose is high, glucose moves out of the cell into the interstitial fluid
105
graph a (linear line)
filtration rate of glucose is proportional to your plasma glucose conc
if your plasma glucose inc, the filtration rate of glucose will inc
106
graph b
initially, when plasma glucose conc increases reabsorption by the kidney will increases; linear relationship
- after 300mg/100mL plasma, the graph reaches a plateau -- this is the transport maximum (Tm)
- at transport max all the sglt proteins that transport glucose from the lumen to the peritubular capillaries are saturated (all the binding sites are occupied and cannot transport any more glucose, the graph plateaus)
107
graph c
normally glucose should not be found in the urine but will show up if the body's limit for handling glucose has been reached and there is no additional reabsorption of glucose
- 300mg/100mL
- this occurs in a diabetic person
108
diabetes mellitus
capacity to reabsorb glucose is normal, but filtered load is greatly increased and is beyond the threshold level to reabsorb glucose by the tubules
- sglt are functionally correct
- too much glucose in their blood due to insulin not working correctly
109
renal glucsuria
benign glucosuria or familial renal glucosuria
genetic mutation of the Na/glucose cotransporter, that normally mediates active reabsorption of glucose in the proximal tubules
- mutations of sglt result in the inability to transport glucose from the luminal side and across to the peritubular capillaries
- filtered load may be small/normal but glucose shows up in the urine bc sglt cannot transport glucose
110
reabsorption of urea
freely filtered at the glomerulus (conc of urea in bowman's space and in plasma are the same)
electrochemical gradient drives anion reabsorption (sodium and anions are moving out the lumen, water now flows out of the lumen)
urea diffuses down its conc gradient
*urea reabsorption is dependent upon water reabsorption*
111
tubular secretion
substances move from the peritubular plasma to the tubular lumen
- involves hydrogen ions and potassium ions
substances secreted: penicillin, choline, creatinine
- coupled to reabsorption of na
112
renal clearance
a way of measuring of quantifying how well the kidneys are functioning
- how well they clear or move substances
- looks are excretory products
measures the volume of plasma from which a substance is completely removed from the kidney per unit time
113
renal clearance formula
clearance of "S" = UsV/Ps
mass = UsV
114
clearance on inulin
used to measure clearance
polysaccharide not found normally in the body
filtered by the renal corpuscle but is neither reabsorbed nor secreted by the tubule
- 7.5L/hr, 180L/day
115
clearance of creatinine
product of muscle metabolism
filtered, not reabsorbed, but undergoes slight secretion
slightly overestimates gfr, but can be used clinically to estimate the gfr, or measure kidney function
- gfr is inversely proportional to the plasma conc of the substrate
116
clearance of substance X is > the gfr (125mL/min), substance X is being
secreted
117
clearance of substance X is < gfr (125mL/min), substance X is being
reabsorbed
118
ion transport in the nephron
Na is actively reabsorbed
Cl is transported passively when Na is pumped out of the cell
K is secreted into the tubules mainly by cells of the distal and collecting ducts
119
proximal convouted tubule
reabsorbs majority of the water and non-waste plasma solutes
major site of solute secretion, except potassium
120
loop of henle
creates an osmotic gradient in the interstitial space
121
distal convoluted tubule
site of major physiological control for water reabsorption
major homeostatic mechanisms of fine control of water and solute to produce urine
122
what is taken out (reabsorbed) and what is added back (secreted)
proximal convoluted tubules: 80% reabsorptive and secretory activities
loop of henle: little water, but large amounts of ions are reabsorbed
distal convoluted tubules: 12-15% reabsorption occurs here
nutritionally valuable substances are completely reabsorbed
123
water reabosrption
dependent on na reabsorption
vasopressin or antidiuretic hormone (ADH) regulates water reabsorption by regulating specific aquaporins in the collecting ducts
124
water transport in proximal tubule
67% of the filtered water is reabsorbed
passive mechanism
aquaporin type 1 channels
open and allow water to diffuse through or be reabsorbed
no hormonal regulaion
125
water transport in the loop of henle
15% of the filtered water is reabsorbed
passive mechanism
mainly the descending limb of the loop of henle
aquaporin type 1 channels
no hormonal regulation
ascending limb is impermeable to water
salt reabsorption through thick ascending limb of loop of henle
126
water transport in distal tubule
no water reabsorption as no aquaporins
127
water transport in large distal tubule and collecting ducts
8-17% of the filtered water is reabsorbed
varies depending on the body's state of hydration
different types of aquaporins in the large distal tubule and the collecting ducts
vasopressin control of specific aquaporins
128
generation of a hyperosmolar interstitial fluid environment in the renal medulla
goal: to generate a hyperosmolar environment in the interstitial fluid (on the outside of the tubules)
rate of absorption of sodium and water is very proportional when the filtrate moves into bowman's space and through the proximal convoluted tubules -300milliodmoles
net result: gradient different (btw interstitial space and ascending limb) of 200mOsm created
129
what happens in the descending limb of the loop of henle
the osmolarity in the ascending limb of the loop of henle has decreased from 300mOsm to 200mOsm due to the active transport of NaCl from the tubule lumen to the interstitial fluid
- a net movement of water occurs out of the descending limb and the ascending limb continues to actively pump out solute (NaCl)
130
fluid movement along descending limb of loop of henle
begin: 300mOsm
water moves out, increasing osmolarity to 400
bottom of hairpin: 1400mOsm a gradient is also created in the interstitial space
131
multiplication
as fluid moves down the loop, the gradient is multiplied and at the very bottom, it is very hyperosmolar
132
fluid in ascending limb
100mOsm at top of ascending limb; hypoosmotic compared to normal plasma osmolarity
different btw descending and ascending limb is always 200mOsm
133
what happens to water moving into the interstitial space
juxtamedullary nephrons create the hyperosmolar gradient
juxtamedullary nephrons have vasa recta around them - take up water and empty into renal vein
134
water conservation through loop of henle
short loop - does not need to conserve water
long loop - needs to conserve more water; hyperosmolar gradient is greater to conserve more water
135
vasa recta
blood vessels that run parallel to the loop of henle
136
counter current blood flow
blood flows through in one direction and goes out the other direction
137
why is a hyperosmotic interstitial gradient created
to absorb water into the interstitial space
138
nephrons that create the gradient
juxtamedullary nephrons
- loops of henle extend down into the medulla with vasa recta around them
- vasa recta create loop-like circuits at each gradient level, to maintain the salt gradient that the nephron tubules have created
- blood flow in the vasa recta is in the opposite direction to fluid flow in the loop of henle
139
purpose of the vasa recta
permeable to both solutes and water, allowing them to move in and out
when the filtrate is moving from the proximal tubule into the descending limb of the loop of henle, water moves out as the descending limb is permeable to water
NaCl from the ascending limb will enter the vasa recta
osmolarity of blood is about 300mOsm when it enters the vasa recta, is about 1200mOsm at the bottom of the loop of the vasa recta
140
how does the vasa recta help in the countercurrent exchange
blood flow in the vasa recta serves as countercurrent exchangers
- helps in maintaining the Na and Cl gradient
- gradient is not washed away
blood flow in medulla is low
- less than 5% of the total renal blood flow and is sluggish
- prevents solute loss
the capillaries are freely permeable to ions, urea and water and they move in and out of the capillaries in response to the conc gradients
141
recycling and trapping of urea
minimal uptake of urea by vasa recta and recycling urea in the interstitial space helps in maintaining high osmolarity in the medulla
- 15% of the original amount is excreted
142
why is there a need for concerntrated urine
kidneys save water by producing hyperosmotic urine
143
mechanisms used to maintain the hyperosmotic environment of the medulla
- counter current anatomy and opposing fluid flow through the loop of henle
- reabsorption of NaCl in ascending limb
- impermeability of ascending limb to water
- trapping of urea in medulla
- hairpin loops of vasa recta maintains the hyperosmotic interstitium in medulla
144
basis for body fluid volume regulation
- water reabosrption is dependent on sodium reabsorption
- the sodium com and the extracellular body fluid volume are closely linked
- any changes in total body sodium ion conc cause changes in blood volume and blood pressure
- plasma osmolarity is mainly determined by measuring plasma sodium con
- volume of water reabsorption dictates how much water will be excreted
- physiological control of water reabsorption/excretion is exerted by antidiuretic hormone
145
diuresis
void/produce a large amount of urine
146
antidiuresis
reduction in or suppression of the excretion of a large volume of urine
147
antidiuretic hormone (ADH)
peptide hormone
made in hypothalamus
cell in the hypothalamus sense the osmolarity of the plasma and the release adh
cells sense reduction on plasma volume
neurosecretory cells in the hypothalamus that make adh are found in the supraoptic nucleus (SON)
site of action of adh: collecting ducts
148
aquaporins
water channels
many types
aqp1 in proximal convoluted tubules
aqp2,3,4 in the collecting ducts
- aqp2 insertion on the luminal side is regulated by adh via aqp2 gene transcription
- aqps on the basolateral membranes are not regulated by adh (3 and 4)
149
how does adh regulate aquaporin 2 in collecting ducts
adh/vasopressin binds to the receptor on the cell -> activates adenylyl or adenylate cyclase -> ATP is converted to cAMP -> activates protein kinase A -> phosphorylates proteins -> transcription factors are activated -> aquaporin 2 protein is up-regulated -> aquaporin 2 proteins are inserted into the luminal membrane -> water can move from the tubular lumen into the cell -> water then diffuses out of the cell into the interstitial fluid via aquaporin 3 and 4
* ADH binds to receptor on cell and through G-protein coupled mechanism, transcription factors are activated and AQP-2 is up-regulated
-- water moves across apical membrane through AQP-2 and out basolateral membrane through AQP-3 and 4
- if levels of ADH are very low, AQP-2 channels will be recycled or taken back by endocytosis
150
water diuresis
all of the water flows through the lumen of the nephron tubules and is excreted producing a large volume of urine
- absence of adh leads to diuresis
151
diabetes insipidus
associated with large quantities of urine
central: failure to release the adh from the posterior pituitary
nephrogenic: adh is secreted in a normal matter from the pituitary but the hormone does not function normally - problem with receptor or intracellular signaling pathway - problem within the cells of the nephron
152
thirst
water deprication -> osmolarity of plasma will inc -> osmoreceptors in hypothalamus are stimulated -> inc release of adh -> retention of water
153
osmotic diuresis
excess solute in urine is always associated with high levels of water excretion
uncontrolled diabetes mellitus
154
mechanisms of na regulation when low
short-term handling of low levels - baroreceptors regulate gfr
long-term handling of low levels - aldosterone facilitate Na reabsorption
- renin, angiotensin II needed for aldosterone secretion
155
mechanism of na regulation when high
atrial natriuretic peptide (ANP)
- regulates gfr and inhibits Na reabsorption
- inhibits aldpsterone actions
156
baroreceptors
used for short-term regulation of low plasma volume (low Na levels)
nerve endings sensitive to stretch
located in carotid sinus, aortic arch, major veins, intrarenal (JG cells of JGA)
- can sense changes in blood volume, peripheral resistance
- inc/dec in blood pressure causes -> inc/dec in stretch -> inc/dec in nerve impulse frequency
- info processed in medulla oblongata
- activation of the ans
157
role of the baroreceptors
low plasma sodium conc -> low plasma volume -> low arterial blood pressure -> baroreceptors sense a lower stretch of the arterial walls -> baroreceptors reduce their rate of firing -> medullary cardiovascular center adjusts the autonomic outflow to correct the low blood pressure -> increased activity of sympathetic renal nerves -> increased constriction of the afferent renal arterioles -> decreases the glomerular filtration rate -> decreases sodium that is excreted in the urine -> increase the sodium levels in plasma
158
aldosterone
a steroid hormone secreted from the adrernal cortex
low plasma volume associated with low sodium triggers its release
long term
acts on cells of the distal tubule and the cortical collecting ducts
- induces the synthesis of sodium transport proteins (used for sodium reabsorption)
- reduces sodium excretion
159
na reabsorption in the cortical collecting duct
- basolateral membrane contains Na/K pump
- luminal membrane contains channels that allow sodium to diffuse into the cell and channels that allow potassium to leave the cell
- aldosterone acts to up-regulate or synthesize proteins that move sodium into the collecting duct cells
160
what regulates aldosterone secretion
na content in diet regulates sodium secretion
high na intake = low aldosterone secretion
low na intake or depletion = high aldosterone secretion
- angiotensin II acts on the adrenal cortex to control the secretion
161
renin
enzyme
the sensor for low sodium chloride conc in the blood
converts angiotensinogen to angiotensin I
162
angiotensinogen
gets converted to angiotensin I the angiotensin II using angiotensin converting enzyme (ACE)
163
ACE inhibitor
drug to manage high blood pressure by bocking the ACE enzyme
- reduces the plasma sodium conc by blocking conversion of angiotensin I to angiotensin II ultimately the release of aldosterone -> sodium will not be reabsorbed, lost in urine as well as water, lowering blood pressure
164
how does aldosterone regulate Na levels
a reduction of NaCl in the filtrate -> inc in renin secretion -> angiotensinogen converted to angiotensin I -> angiotensin I converted to angiotensin II -> angiotensin II stimulates aldosterone released from the adrenal cortex -> aldosterone increases the synthesis of sodium transport proteins in the collecting ducts -> increase sodium reabsorption -> less sodium is excreted in the urine -> plasma levels brought back to normal
165
what stimulates renin release
decreased stretch or a decreased activity in the stretch receptors due to the low circulating volume
- renal sympathetic nerves directly innervate the juxtaglomerular cells
dec in plasma volume decreases blood pressure in the kidney -> stretches juxtaglomerular cells less; these cells are stretched less -< inc secretion of renin
dec in gfr glowing past macula densa -> dec sodium delivery to macula densa -> inc renin secretion
166
intrarenal baroreceptors
the juxtaglomerular cells located in the walls of the afferent arterioles
167
renin-angiotensin mechanism initiates in response to
- sympathetic stimulation of renal nerves
- dec in filtrate osmolality
- dec blood pressure
168
factors that affect renin release (JG cells receive three inputs)
- sympathetic input from the extrarenal baroreceptors (outside the kidney)
- intrarenal baroreceptors
- signals from the macular densa
169
role of atrial natriuretic peptide (ANP)
important for regulating high levels of sodium
synthesized and secreted by cardia atria
site of anp action: on cells of several tubular segments, inhibits aldosterone, inhibits na reabsorption, increases gfr and na excretion
170
what stimulates anp secretion
increase na conc
inc blood volume
atrial distention - stretch of the atria (true sensor)
171
hyperkalemia
excess K in the blood
172
regulation of potassium
physiologically regulated by aldosterone
- aldosterone secreting cells in the adrenal cortex are sensitive to extracellular k
- aldosterone acts on cortical collecting ducts to inc secretion of k in the urine in response to a high extracellular k conc
173
aldosterone stimulates both
na reabsorption and k secretion in the cortical collecting ducts
174
acid
releases H in solution
175
base
accepts H in solution
176
acids produced by our body
volatile acid (carbon dioxide, carbonic acid)
nonvolatile acids (organic and inorganic acids from other sources than CO2, phosphoric acid, sulfuric acid)
hydrochloric acid
177
sources of hydrogen gain
- generation of h from co2
- nonvolatile acids, generated from protein metabolism
- from loss of bicarbonate in diarrhea
- from loss of bicarbonate in urine
178
sources of hydrogen loss
- vomiting
- in urine
- from hyperventilation
179
buffers
compounds that can bind to H and form a hydrogen-buffer conjugate
- reversible reaction
- composed of a weak acid and its conjugate base
- modify or adjust the change in ph following the addition of acids or bases
180
types of buffers
- bicarbonate (extracellular buffer)
- phosphate ions and associated proteins (intracellular buffer)
- hemoglobin (intracellular buffer)
181
role of kidneys and lungs in acid-base balance
when the respiration rate is not high enough, the passage of blood through the peripheral tissues generates h
CO2 + H2O -><- (carbonic anhydrase) H2CO3 -><- H + HCO3
182
what causes respiratory imbalances
hyperventilation, hypoventilation, respiratory malfunction causes H imbalance
inc H conc stimulates ventilation
dec H con inhibits ventilation
183
lungs play a
short-term homeostatic role
184
kidneys are the
long-term ultimate balancers
185
alkalosis
decrease of plasma H conc
kidneys excrete more bicarbonate
186
acidosis
increase of plasma H conc
kidney cells synthesize new bicarbonate and send it to blood
187
reabsorption of HCO3-
acidosis: plasma H has inc
bicarbonate is added to the blood
dependent on H secretion
active process
normally most if the HCO3- is reabsorbed
occurs in proximal tubule, ascending loop of henle, and cortical collecting duct
transport mechanism of H is different depending on part of the tubule segment
188
mechanisms 1 in response to acidosis: addition of HCO3- to plasma
when more H is secreted than there is HCO3- in the lumen to bind the H:
- extra H binds to HPO42- (intracellular buffer)
- HCO3- is still generated by tubular cells and diffuses into plasma
- NET GAIN of HCO3- in plasma
189
mechanism 2: addition of HCO3- to plasma
cells from proximal tubule are only involved
- uptake of glutamine from glomerular filtrate or peritubular plasma
- NH4+ and HCO3- are formed inside the cells
- NH4+ is actively secreted via the Na/NH$ counter transport into the lumen
- HCO3- is added to plasma
190
respiratory acidosis
occurs as a result of decreased ventilation
inc blood Pco2
occurs in emphysema
kidney compensates by secreting H and lowers plasma H
191
respiratory alkalosis
occurs as a result of hyperventilation
dec blood Pco2
happens in high altitude
kidney compensates by excreting HCO3-
192
metabolic acidosis
occurs in diarrhea (loss of bicarbonate ions)
severe exercise
diabetes mellitus
results in inc ventilation
results in inc H secretion
193
metabolic alkalosis
occurs after prolonged vomiting
results in dec ventilation
results in inc HCO3- excretion
