Urinary System Flashcards
(131 cards)
1
Q
What are the functions of the kidneys?
A
- primary regulator of fluid volume and ion concentration
- maintain constant composition and volume of body fluids
- stabilize osmolality
- secrete excesses/retain when source
is scarce
- selective excretion: important products are retained and waste is removed
- excretes foreign substances
- excrete body organic wastes: urea
(metabolism of proteins), bile
(degradation of hemoglobin)
- contribute to the acid balance by removing H+ and bicarbonate HCO3-
- produce glucose by gluconeogenesis
- produce erythropoietin to stimulate the formation of erythrocytes
- produce calcitriol (active form of vitD)
- produce renin (enzyme that regulates formation of angiotension II which regulates bp and aldosterone)
2
Q
Where are the kidneys located?
A
upper abdominal wall
3
Q
Where do arteries, veins and ureters enter through?
A
the renal hilus
4
Q
What is the general structure of the kidney?
A
Refer to slide 6&7 Urinary I
5
Q
What is the basic urine-forming unit?
A
nephron
6
Q
What is the structure of a nephron?
A
- glomerulus: filters blood
- tubular system composed of several sections: reabsorption of filtered substances, secretion of others
- blood supply composed of 3 capillary beds: glomerular capillaries, peritubular capillaries, vasa recta
7
Q
What is the vasa recta?
A
capillaries of the medulla
8
Q
Where is the glomerulus?
A
confined in the cortex, enclosed in the bowmans capsule
9
Q
What are some characteristics of the glomerulus?
A
- protein free fluid is filtered and accumulate in the bowmans space then enters the first part of the tubule = proximal tubulus
- composed of many parallel capillaries
- capillaries do not connect with venules
- capillaries connect with efferent arteriole that will feed the peritubular capillaries
10
Q
Where does blood enter in the glomerulus?
A
through afferent arteriole
11
Q
What is the tubular system?
A
Walls made of a single layer of epithelial cells
12
Q
What are the four parts of the tubular system and what do they do?
A
- proximal tubule: highly convoluted in the cortex
- loop of henle: hairpin structure in the medulla; composed of the descending thin limn, the ascending thin limb, and the thick ascending limb
- distal tubule: highly convoluted in the cortex
- collecting ducts: receive distal tubules from multiple nephrons, small ducts merge into large ducts and bring urine to the renal pelvis
13
Q
What is a special feature of the distal tubule?
A
initial part of distal tubule passes between the afferent and efferent arteriole of its own glomerulus using epithelial cells called macula densa
14
Q
What do adjacent smooth muscles in the distal tubules do?
A
juxtaglomerular, produce and secrete renin
15
Q
What are the three basic renal processes?
A
- glomerular filtration: filtration of plasma from glomerular capillaries into Bowmans space (glomerular filtrate)
- tubular reabsorption: movement of substance from tubular lumen to peritubular capillaries
- tubular secretion: movement of substance from peritubular plasma to tubular lumen
16
Q
What complex does the glomerulus contain?
A
complex network of capillaries and specialized structure designed to retain cells and medium and high molecular weight proteins
17
Q
What is GFR?
A
glomerular filtration rate is an important index of renal function
18
Q
What is the function of glomerular filtration?
A
production of a protein free filtrate of plasma, contains all the small solutes
19
Q
What are the three layers of the glomerular membrane?
A
Capillary endothelium: fenestrated on about 10% of their surface -> blocks cells, not blood constituents
basal lamina: mesh of protein fibers -> blocks most of the plasma proteins
inner epithelial layer of bowmans capsule (visceral epithelium): composed of podocytes -> last level of filtration between the fingers
20
Q
What does the glomerular membrane function as?
A
a fine sieve
21
Q
What layer of the glomerular membrane is the best size selection unit against proteins
A
basal lamina
22
Q
What layer of the glomerular membrane is negatively charged?
A
basal lamina, repulses proteins
23
Q
What forces govern giltration pressure in the glomerular capillary?
A
differences in hydrostatic and oncotic pressures
24
Q
What is filtration facilitated by in the glomerulus?
A
higher hydrostatic pressure of blood in capillaries (remains fairly constant along capillary)
25
What is filtration reduced by in the glomerulus?
hydrostatic pressure in bowmans space (normally low), plasma oncotic pressure within glomerular capillary
26
What are the characteristics of pressures throughout the glomerulus?
hydrostatic pressure fairly constant
rate of filtration higher in the first part of the capillary where osmotic pressure is lower
rate decreases further along while the osmotic pressure increases due to the proteins stuck in blood compartment
27
What is another primary determinant of the GFR?
permeability of the filtration barrier and the SA available for filtration are other primary determinants of the GFR
28
What is the equation for GFR?
GFR = Pf x Kf
Pf = net filtration pressure (average over entire glomerulus)
Kf = ultrafiltration coefficient (product of the filtration barrier permeability and SA)
29
What maintains the regulation of the GFR?
kidneys maintain tight control over GFR
hydrostatic pressure in glomerular space and oncotic pressure cannot be regulated
30
What is regulated in the glomerular capillaries?
since hydrostatic/oncotic pressure is not regulated, only blood flow in glomerular capillaries is regulated
affecting constriction level of arterioles will determine the hydrostatic pressure in capillaries
31
What are the two arterioles that control the regulation of blood flow in glomerular capillaries
afferent - enters glomerulus
efferent - exits glomerulus
32
Draw the diagram of the effect of arteriole constriction on the renal filtration and renal blood flow?
slide 22 urinary I
33
What are the two levels of control that will affect the blood hydrostatic pressure?
- renal modulation of systemic blood pressure and blood volume (extrinsic as it affects the entire body)
- intrinsic control of renal blood flow, glomerular capillary pressure, and ultra-filtration coefficient = autoregulatory mechanisms
34
What is involved in long standing falls in blood pressure, or when decreased bp is accompanied by decreased extracellular fluid volume
renin-angiotensin-aldosterone
35
How is renin release from juxta glomerular cells?
- reduced stretch of the renin cells in the renal afferent arterioles (baroreceptors)
- sympathetic nerve impulses: arterial baroreceptors respond to fall in bp by unbraking sympathetic nerve activity in kidney
36
Label the diagram of the juxtaglomerual apparatus
slide 25 urinary I
37
Draw the diagram of the effect of renin secretion
slide 26 urinary I
38
What is angiotensin II?
potent vasoconstrictor
39
What is the function of angiotensin II?
- acts to increase systemic BP and renal perfusion pressure
- stimulates release of aldosterone (adrenal cortex) and vasopressin (pituitary)
40
What does aldosterone do?
enhance sodium/water reabsorption
41
What does vasopressin do?
enhances urea and water reabsorption
42
What does augmented fluid uptake increase?
intravascular volume -> improves renal perfusion -> turn off renin release
43
Where does intrinsic autoregulation occur?
at the level of the kidney
44
What does autoregulation prevent?
short term changes in arterial bp to affect the GFR
45
How does autoregulation occur?
feedback mechanisms that allow the kidney to vary the resistance of the afferent arterioles
smooth muscle cells react to increase in stretch by contracting
cells in the macula densa (distal tubule) secrete an unidentified factor that stimulates smooth muscle contraction
46
Explain the autoregulation graphs?
slide 29 urinary I
47
What are two events occurring in the tubules?
- glomerular filtration = bulk movements (water+dissolved substances) -> tubular fluid composition close to a protein free plasma
- fluid transormed into urine through: reabsorption and secretion
48
What is reabsorption?
water and dissolved susbtance from tubular lumen to peritubular capillaries
49
What is secretion?
substances transported from the peritubular capillaries to the tubular lumen
50
What substances are reabsorbed?
substances important for the body
51
What are the two types of active reabsorption?
Primary active reabsorption
Secondary active reabsorption
52
What is primary active reabsorption?
- ATP is used to transport a substance against concentration gradient
- used for Na: Na/K pumps in the epithelial cells from the basolateral membrane pump Na towards interstitial fluid -> then Na diffuse in the capillaries
- since pumps maintain low levels of Na in the epithelial cells -> Na diffuses from the lumen
- K easily leaks back out of the cell in the itnerstitial fluid
53
What is secondary active reabsorption?
- transport of 1 solute coupled to transport of another (glucose coupled to Na transport)
- in addition to diffusion, Na also transported into epithelial cells by specific membrane transport proteins
- once inside the cells, glucose moves along the gradient to the capillaries
- other molecules like AA and several organic molecules use that transport
- H+ also couples to Na+, but moves towards the tubular lumen
54
What is passive reabsorption?
- when concentration of a substance (negative ions, drugs, environmental toxins) in the lumen increases to higher levels than in epithelial cells
- if cell membrane permeable to that substance then it diffuses back out of the tubular lumen
- molecular size and liposolubility determine what is passively reabsorbed
55
Is tubular secretion for all substances?
no, onyl select substances
56
What is tubular secretion?
from peritubular capillaries -> across tubular cells -> into lumen
57
What type of transport is tubular secretion done by?
- some by active transport: one system for organic acids, one system for organic bases
- some by secondary active transport (H+)
- some by passive diffusion
58
Where in the tubule does reabsorption of glucose occur?
only in the proximal tubule
59
How easily is glucose filtered?
as easily as water
60
What is glucose concentration in glomerular filtrate equivalent to?
plasma concentration
61
How does glucose move across the tube?
secondary active transport
62
Does the kidney participate in regulating glucose levels?
no, just prevents its loss
63
Does glucose normally appear in urine?
no, unless glucose concentration in plasma is extreme
64
What is the renal threshold for glucose?
the lowest plasma concentration at which glucose can be detected in urine
65
Draw/explain the graph of glucose levels in tubule vs plasma glucose?
slide 12/13 urinary II
66
What is diabetes mellitus?
glucose in urine (sweet pee)
67
What are the two main causes of diabetes mellitus?
1. insulin regulation of blood glucose does not work (lack of impaired insulin), glucose levels in plasma increase dramatically past the Tmax which causes overload in the kidney, resulting in glucose excretion
2. genetic defect affecting the transport mechanism of glucose in the proximal tubule which results in reduced Tmax, glucose is then excreted even when plasma levels are normal
68
Do protein pass through the glomerular membrane?
no, not normally present in glomerular filtrate except small peptides and small proteins
69
How are proteins reabsorbed?
by epithelial cells of the proximal tubules by endocytosis
70
What happens after proteins are reabsorbed?
broken down into amino acids in epithelial cells
71
Is protein in the urine normal?
no, glomerulus should not let them pass
72
What is the main reason for protein leakage?
imbalance of charge in glomerular membrane
73
What happens if the basal lamina loses its membrane charge/polarity?
basal lamina is negatively charged, proteins are negatively charged and are repulsed by negative membrane charges
74
How much ions are reabsorbed?
reabsorption of many ions equals the amount filtered = low concentration in urine
75
How is reabsorption of ions controlled?
hormonally controlled = regulated
76
What affects ion reabsorption/filtration?
for most ions, intestinal absorption affect the plasma levels and thus the filtration
77
What organ is the most important one for Na+ control
kidney
78
What is the most important factor that regulates extracellular and blood volumes?
Na+
79
What is special about Na+ transport?
Transport of other substances also coupled to na+ through secondary active transport such as reabsorption of glucose, AA, HCO3-, Cl- and PO4-
secretion of H+ and K+
80
How much energy spent in Na+ transport represents the total metabolism of the kidney?
80%
81
What are the steps for Na+ handling in the tubules?
1. Na+ filtered in the glomerulus enters tubular structure in tubular fluid
2. in the tubule Na+ moves from the lumen into the epithelial cells by 2 mechanisms
- diffusion through channels (passive mechanism)
- binding to a carrier on the cell membrane (associated with another substance)
3. from epithlial cytosol, Na+ is pumped into interstitial fluid by Na+/K+ pump
4. pushing Na+ from interstitial fluid to peritubular capillaries
82
What is the pressure like in the peritubular capillaries?
hydrostatic pressure low
oncotic pressure high (lots of protein)
83
What is the permeability of all of the parts of the tubule?
proximal tubule: porous
- site of most Na+ water reabsorption
loop of henle: less permeable
distal tubule and collecting duct: barely permeable to Na+ and water (tight junctions between epithelial cells)
however there is a little bit of permeability and reabsorption in the last part of distal tubule and collecting duct as it is under hormonal control
84
What stimulates Na+ reabsorption in the distal tubule and collecting duct?
aldosterone
85
What is aldosterone?
steroid hormone (liposoluble) synthesized and released by the adrenal cortex = mineralocorticoid
86
What does aldosterone induce?
synthesis of Na+ channels and pump in epithelial cells = increase Na+ transport from the lumen to the epithelial cell (channels) and from the epithelial cell to the interstitial fluid (pumps)
87
What happens if there is no aldosterone in terms of Na+ transport?
all the Na+ entering the distal tubule will be excreted in urine, death within a couple of days
88
Where does reabsorption of K+ occur?
inside cells, ECF content relatively low
89
How does reabsorption of K+ need to be maintained?
within a narrow range
90
Where is K+ reasborbed?
actively reabsorbed in proximal tubule
91
Where is K+ secreted?
distal tubule and collecting duct
92
How much of K+ that is filtered is reabsorbed?
100% filtered is reabsorbed, changes in K+ mainly due to secretion
93
What happens to K+ when Na+ reabsorbed?
When Na+ reabsorbed, K+ secreted and vice versa
94
What does K+ concentration control?
aldosterone release
95
Draw the chart of Na+ and K+ reabsorption/filtration
slide 23 urinary II
96
How much of Ca2+ is bound to proteins in plasma?
50%
97
What form of ca+ can be filtered in glomerulus?
free form only
98
Where does reabsorption occur of calcium?
regulated reabsorption occurs in the ascending limb of the loop of henle, the distal tubules and the collecting ducts
99
What stimulates reabsorption of calcium?
PTH
100
How much filtered calcium is excreted?
1-2%
101
What is important in maintaining blood volume?
tubular reabsorption of water
102
How does tubular reabsorption of water occur?
two mechanisms
- between epithelial cells, through tight junctions
- through epithelial cells (aquaporins)
103
What is tubular reabsorption of water influenced by?
since it is a diffusion process (osmosis) it is influenced by movement of Na+
104
Where does most tubular reabsorption of water occur?
in proximal tubule
105
Where are aquaporins present in the tubular system?
- ascending limb of loop of henle does NOT possess aquaporins
- in distal tubule and collecting duct, aquaporins up regulated by ADH from pituitary which increases water reabsorption
106
How does the kidney regulate water balance?
dilutes or concentrations urine in accordance with hydration state
107
What happens if you are deprived of water vs water loaded?
deprived of water: lower urine volume, much higher osmolality
water loaded: excrete larger volumes of urine with low osmolality
108
How does water movement occur in dilution of urine?
by osmosis through pores
109
What does dilution/concentration of urine depend on?
osmlarity of interstitial and tubular fluids in the kidney
110
What does handling of ions, urea and water do to the osmolarity?
creates increasing osmolarity from the medulla to the pelvis in the kidney, this enables urine to be secreted at a higher osmolarity than plasma
111
What are the three components of the concentration/dilution of urine?
1. hypertonic medullary interstitium: allows concentrated urine
2. dilution of the tubule fluid in the thick ascending limb and the distal convoluted tubule: allows diluted urine
3. variability in water permeability of collecting duct in response to vasopressin (ADH)
112
What are the two parts of the loop of henle?
descending limb (cortex -> medulla)
ascending limn (medilla -> cortex)
113
What do the epithelial cells in the ascending limb of the loop of henle pump?
actively pump Na+, accompanied by secondary active transport of K+ and Cl- (1Na+:1K+:2Cl-)
114
What do the epithelial cells in the descending limb of the loop of henle do?
no active pumps, highly permeable to water
115
What happens to the movements of ions/water in the loop of henle?
- ions pumped out in interstitial fluid in ascending limb while water is retained
- increase in osmolarity in interstitial fluid
- draws water out from the descending limb
- fluid entering ascending limb more concentration: more ions pumped out
- result is an osmolarity gradient from cortex to medulla
116
What happens when tubular fluid passes through the distal tubules and collecting ducts?
goes from cortex to medulla which results in an increase in interstitial osmolarity
117
When will water be allowed to exit the duct through the epithelial cells?
if ADH is present
118
What does ADH do?
stimulates the formation of aquaporins on the apical membrane of epithelial cells
119
What happens when ADH decreases?
when ADH decreases, the number of aquaporins decreases and water is not reabsorbed
120
Where is ADH produced?
hypothalamus, stored in post pit
121
How is ADH released in response to pressure?
Hypothalamic osmoreceptrs sense plasma osmotic pressure
- increased osmolaitity results in the increased stimulus for ADH release
- increased ADH release -> acts to insert aquaporins in distal tubules and collecting ducts
hypothalamic osmoreceptors also send excitatory signals to thirst centers in the hypothalamus
122
Draw the diagram for H20 resulting in ADH uptake?
slide 13 urinary III
123
What is the role of urea?
participates in maintaing the high interstitial osmolarity in the medulla
124
How much does urea account for of the osmolarity of the medullary interstitium?
40%
125
How permeable is the collecting duct epithelium to urea?
moderately permeable, moves into the interstitium, re-enters ascending limb loop of henle
126
What does recirculation of urea help to do?
to ensure required amount of urea is excreted even if urine volume is low
127
What is the importance of the vasa recta?
- Capillaries of vasa recta make hairpun bends (similar to loop of henle)
- osmolarity in capillaries follows medulla gradient
- result is ions and urea are responsible for the gradient along the loop of henle and remain in the interstitial fluid
- if not there is no osmotic gradient that would occur
128
How much of water is our body mass?
60-70%
129
Where is half the water in our body present in?
cells
rest is present in: interstitial fluid, blood plasma, lymph
130
What is the movement of water between compartments driven by?
hydrostatic and osmotic pressure (osmolarity difference)
131
Draw the three charts of the effects of blood volume on various things in urinary system?
slide 18-20 urinary III
