Ch. 26: Urinary System Flashcards
(165 cards)
1
Q
What main structures are involved in the urinary system?
A
Kidneys (2), ureters (2), urinary bladder, urethra.
2
Q
Ureters.
A
Transport urine from the kidneys (renal pelvis) to the urinary bladder. Retroperitoneal.
3
Q
Urinary bladder.
A
Stores urine and expels it into the urethra.
4
Q
Urethra.
A
Discharges urine from the body. Small tube leading from the internal urethral orifice in the floor of the urinary bladder.
5
Q
Kidney functions.
A
1) Waste excretion.
2) Regulation of blood ionic composition.
3) Regulation of blood pH.
4) Regulation of blood volume.
5) Regulation of blood pressure.
6) Maintenance of blood osmolarity.
7) Production of hormones.
8) Regulation of blood glucose level.
6
Q
Nitrogenous wastes.
A
Waste products that contain nitrogen. Urea, ammonia, creatine, uric acid, urobilin.
7
Q
How do the kidneys regulate blood ionic composition?
A
Adjust the amounts of Na+, K+, Ca2+, Cl-, HPO42- ions that are excreted in the urine.
8
Q
How do the kidneys regulate blood pH?
A
They excrete a variable amount of H+ into the urine and conserve HCO3-, which is an important buffer of H+ in blood.
9
Q
How do the kidneys regulate blood volume?
A
They conserve or eliminate water in the urine.
10
Q
How do the kidneys regulate blood pressure?
A
They secrete renin, which activates the RAA pathway and increases BP.
11
Q
How do the kidneys maintain blood osmolarity?
A
Maintain blood osmolarity at 300 mOsm/L by regulating loss of water and solutes in urine.
12
Q
Which hormones do the kidneys produce?
A
Calcitriol and EPO.
13
Q
How do the kidneys regulate blood glucose level?
A
Use glutamine in gluconeogenesis, and then release glucose into the blood.
14
Q
If ribs ___ and ___ are fractured, they can puncture the ______ and cause life-threatening damage.
A
11, 12, kidneys.
15
Q
Which kidney is slightly lower than the other because of the liver?
A
Right.
16
Q
Renal hilum.
A
Indentation near the center of the concave border of each kidney. The ureter, blood vessels, lymphatic vessels and nerves emerge from this indentation.
17
Q
What are the 3 layers of tissue around each kidney?
A
1) Renal capsule: deep, smooth, transparent sheet of dense irregular connective tissue, continuous with outer coat of ureter, barrier against trauma, helps maintain kidney shape.
2) Adipose capsule: middle, mass of fatty tissue surrounding renal capsule, barrier against trauma, holds kidney in place.
3) Renal fascia: superficial, thin layer of dense irregular connective tissue, anchors kidneys to surrounding structures and abdominal wall.
18
Q
Renal cortex.
A
Superficial region within the kidney. Extends from renal capsule to the bases of the renal pyramids and into the spaces between them. Divided into an outer cortical zone and inner juxtamedullary zone.
19
Q
Renal columns.
A
The portions of renal cortex that extend between the renal pyramids.
20
Q
Renal medulla.
A
Inner region within the kidney. Consists of renal pyramids.
21
Q
Parenchyma.
A
Functional part of the kidney. Renal cortex and renal pyramids together. Within the parenchyma are the nephrons, which are the functional units.
22
Q
Filtrate formed by the nephrons drains into…
A
Large papillary ducts which extend through the renal papillae and into minor or major calyces. A minor calyx receives filtrate from the papillary ducts of one renal papilla and delivers it to a major calyx. Once the filtrate enters the calyces, it becomes urine. From the major calyces, urine drains into the renal pelvis (single large cavity) and then out through the ureter to the urinary bladder.
23
Q
Each kidney has ___ major calyces and ___ minor calyces.
A
8-18, 2-3.
24
Q
_____ receive 20-25% of the resting cardiac output via the right and left __________ .
A
Kidneys, renal arteries.
25
Renal blood flow is ____ mL per minute.
1200
26
Within the kidney, the renal artery divides into...
Segmental arteries. Each segmental artery gives off branches that enter the parenchyma and pass through the renal columns between the renal lobes as the interloper arteries.
27
A renal lobe consists of...
A renal pyramid, some of the renal column on either side of the renal pyramid, and the renal cortex at the base of the renal pyramid.
28
Arcuate arteries.
At the bases of the renal pyramids, the interlobar arteries arch between the renal medulla and cortex, where they are known as arcuate arteries. Divisions of these arteries produce a series of cortical radiate arteries, which radiate outward and enter the renal cortex where they give off afferent arterioles.
29
Each nephron receives one afferent arteriole which divides into a...
Glomerulus. The glomerular capillaries reunite to form an efferent arteriole that carries blood out of the glomerulus. The efferent arterioles divide to form the peritubular capillaries which surround tubular parts of the nephron in the renal cortex. Extending from some efferent arterioles are vasa recta that supply tubular portions of the nephron in the renal medulla. Peritubular capillaries eventually reunite to form cortical radiate veins which receive blood from the vasa recta. Then the blood drains through arcuate veins to the interlobar veins running between renal pyramids.
30
How are glomerular capillaries different than other capillaries in the body?
They are positioned between 2 arterioles rather than between an arteriole and a venule.
31
Blood leaves the kidney through...
A single vein that exits at the renal hilum and carries venous blood to the inferior vena cava.
32
Renal nerves are part of which division of the nervous system?
Sympathetic division of ANS.
33
What does a nephron consist of?
A renal corpuscle, and a renal tubule.
34
Renal corpuscle.
Where blood plasma is filtered. Glomerulus and glomerulus/Bowman's capsule. Double-walled epithelial cup that surrounds the glomerular capillaries. Filtered fluid passes into the renal tubule. Within renal cortex.
35
Renal tubule.
PCT, nephron loop, DCT. Proximal denotes the part of the tubule attached to the glomerular capsule. Distal denotes the part of the tubule that is further away. Convoluted means the tubule is tightly coiled rather than straight. Within renal cortex.
36
The DCTs of several nephrons empty into...
A collecting duct. CDs then unite and converge into several hundred large papillary ducts which drain into the minor calyces.
37
Within a nephron, what does the nephron loop connect?
The PCT and DCT.
38
Cortical nephrons.
80-85% of nephrons. Their renal corpuscles lie in the outer part of the renal cortex. Short nephron loops that lie in the renal cortex and penetrate only into the outer part of the renal medulla. Nephron loops receive their blood supply from peritubular capillaries that arise from efferent arterioles.
39
Juxtamedullary nephrons.
15-20% of nephrons. Their renal corpuscles lie deep in the renal cortex close to the renal medulla. Long nephron loops that extend into the deepest region of the renal medulla. Nephron loops receive their blood supply from peritubular capillaries and vasa recta that arise from efferent arterioles. The ascending limb of this nephron loop consists of a thin ascending limb followed by a thick ascending limb. The lumen of the thin ascending limb is the same as in other areas of the renal tubule, it is only the epithelium that is thinner.
40
_____ nephrons enable the kidneys to excrete very dilute or very concentrated urine.
Juxtamedullary.
41
A single layer of ___ cells forms the entire wall of the glomerular capsule, renal tubule and ducts.
Epithelial.
42
What are the 2 layers of the glomerular capsule?
Visceral and parietal.
43
Visceral layer of glomerular capsule.
Modified squamous epithelial cells (podocytes). Pedicels wrap around the single layer of endothelial cells of the glomerular capillaries and form the inner wall of the capsule.
44
Parietal layer of glomerular capsule.
Simple squamous epithelium. Forms outer wall of capsule.
45
Fluid filtered from the glomerular capillaries enters which region of the glomerular capsule?
Capsular space between the visceral and parietal layers, which is continuous with the lumen of the renal tubule.
46
Proximal convoluted tubule.
Simple cuboidal epithelial cells. Brush border of microvilli on apical surface.
47
Which cells make up the descending limb and first part of the ascending limb of the nephron loop?
Simple squamous epithelium.
48
Which cells make up the thick ascending limb of the nephron loop?
Simple cuboidal to low columnar epithelium.
49
Juxtaglomerular apparatus.
Juxtaglomerular cells + macula densa. Regulates blood pressure within the kidneys.
50
Distal convoluted tubule.
Begins shortly after the macula densa. Principal cells, which have receptors for ADH and aldosterone. Intercalated cells, which play a role in the homeostasis of blood pH.
51
Signs of kidney dysfunction do not become apparent until function declines to less than ___ of normal because remaining nephrons adapt.
25%
52
Surgical removal of one kidney stimulates ____ of the remaining kidney.
Hypertrophy. The remaining kidney will be able to filter blood at 80% of the rate of 2 normal kidneys.
53
To produce urine, nephrons and collecting ducts perform which 3 basic processes?
1) Glomerular filtration.
2) Tubular reabsorption.
3) Tubular secretion.
54
Glomerular filtration.
Water and solutes in blood plasma move across the walls of glomerular capillaries, where they are filtered and move into the glomerular capsule and then renal tubule.
55
Tubular reabsorption.
As filtered fluid flows through the renal tubules and collecting ducts, tubule cells reabsorb 99% of the filtered water and solutes. The water and solutes return to the blood as it flows through the peritubular capillaries and vasa recta.
56
Tubular secretion.
As filtered fluid flows through renal tubules and collecting ducts, the renal tubule and duct cells secrete other materials into the fluid. Transfer of materials from the blood and tubule cells into the glomerular filtrate.
57
The rate of urinary excretion of any solute is...
Rate of glomerular filtration + rate of tubular secretion - rate of tubular reabsorption.
58
Glomerular filtrate.
Fluid that enters the capsular space of the glomerulus.
59
Filtration fraction.
The fraction of blood plasma in the afferent arterioles of the kidneys that becomes glomerular filtrate. Usually 150 L females, 180 L males.
60
Filtration membrane of glomerulus.
Glomerular capillaries and podocytes. Leaky barrier. Permits filtration of water and small solutes. Prevents filtration of most plasma proteins and blood cells. Consists of 3 filtration barriers.
61
What are the 3 filtration barriers of the filtration membrane of the glomerulus?
1) Glomerular endothelial cells.
2) Basement membrane.
3) Filtration slit.
62
Glomerular endothelial cells.
Leaky because they have large fenestrations. Permits all solutes in blood plasma to exit glomerular capillaries. Prevents filtration of blood cells. Mesangial cells are contractile cells that help regulate glomerular filtration, and they are in the cleft between afferent and efferent arterioles.
63
Basement membrane (of filtration membrane of glomerulus).
A layer of acellular material between the endothelium and podocytes consists of collagen fibres and negatively charged glycoproteins. The pores allow water and most small solutes to pass through. The negative charge of the glycoproteins repel plasma proteins, preventing their filtration.
64
Filtration slit.
Extending from each podocyte are thousands of pedicels that wrap around glomerular capillaries. The spaces between pedicels are filtration slits. A slit membrane extends across each filtration slit and permits the passage of molecules.
65
Less than 1% of which protein passes the slit membrane because it is slightly too big?
Albumin.
66
Why would the volume of fluid filtered by the renal corpuscle be larger than in other blood capillaries?
1) Glomerular capillaries present a large SA for filtration because they are long and extensive. While mesangial cells are relaxed, SA is maximal and glomerular filtration is very high.
2) Filtration membrane is thin and porous.
3) Glomerular capillary blood pressure is high because the efferent arterioles are smaller than the afferent arterioles.
67
Glomerular filtrations depends on which 3 pressures?
1) Glomerular blood hydrostatic pressure.
2) Capsular hydrostatic pressure.
3) Blood colloid osmotic pressure.
68
Glomerular blood hydrostatic pressure.
55 mmHg. Blood pressure in glomerular capillaries. Promotes filtration by forcing water and solutes in blood plasma through the filtration membrane.
69
Capsular hydrostatic pressure.
15 mmHg. Pressure exerted against the filtrated membrane by fluid already in the capsular space and renal tubule. Opposes filtration.
70
Blood colloid osmotic pressure.
30 mmHg. Due to presence of proteins in blood plasma. Opposes filtration.
71
Net filtration pressure =
GBHP - CHP - BCOP = 10 mmHg. A pressure of 10 mmHg causes a normal amount of blood plasma to filter from the glomerulus into the capsular space.
72
Glomerular filtration rate.
The amount of filtrate formed in all renal corpuscles of both kidneys each minute. 125 mL/min males, 105 mL/min females.
73
What may happen if the GFR is too high?
Needed substances will pass too quickly through the renal tubules to be reabsorbed.
74
What may happen if the GFR is too low?
All the filtrate will be reabsorbed, and wastes will not be adequately excreted.
75
Filtration ceases if GBHP reaches ____ mmHg because the opposing pressures are equal to this.
45
76
The mechanisms that regulate GFR operate by...
Adjusting blood flow into and out of the glomerulus and by altering the glomerular capillary SA available for filtration.
77
Which 3 mechanisms control the GFR?
1) Renal auto regulation.
2) Neural regulation.
3) Hormonal regulation.
78
Renal autoregulation of GFR consists of which 2 processes?
1) Myogenic mechanism.
2) Tubuloglomerular feedback.
79
Myogenic mechanism.
Elevated BP --> stretches the walls of the afferent arterioles --> smooth muscle fibres in the walls of the afferent arteriole contract to narrow the arteriole's lumen --> renal blood flow decreases --> GFR decreases to normal level.
Decreased BP --> afferent arterioles dilate --> GFR increases.
Normalizes renal blood flow and GFR within seconds after a change in BP.
80
Tubuloglomerular feedback.
The macula densa of the renal tubules provides feedback to the glomerulus.
Elevated BP --> filtered fluid flows more rapidly along the renal tubules --> PCT and nephron loop have less time to reabsorb Na+, Cl- and water --> macula densa cells detect increased delivery of Na+, Cl- and water, and inhibit release of nitric oxide from cells in JGA --> afferent arterioles constrict --> less blood flows into glomerular capillaries --> GFR decreases.
Decreased BP --> opposite --> GFR increases.
Slower than myogenic mechanism.
81
Blood vessels of the kidneys are supplied by which nerves? What do these fibres release?
Sympathetic ANS nerves.
They release NE, which causes vasoconstriction through the activation of alpha1 receptors, which are plentiful in smooth muscle fibres of afferent arterioles.
82
Describe the GFR at rest. Which mechanism prevails?
Sympathetic stimulation is low, so the afferent and efferent arterioles are dilated.
Renal autoregulation prevails.
83
Describe what happens to the GFR with moderate sympathetic stimulation, and with greater sympathetic stimulation.
Moderate: Afferent and efferent arterioles constrict, blood flow into and out of glomerulus is restricted, GFR is decreased slightly.
Greater: Vasoconstriction of afferent arterioles predominates, blood flow into glomerular capillaries is decreased, GFR is decreased more.
84
The lowering of renal blood flow has 2 consequences:
1) Reduces urine output which helps conserve blood volume.
2) Permits greater blood flow to other body tissues.
85
Which hormones regulate GFR?
1) Angiotensin II: Reduces GFR via vasoconstriction of afferent and efferent arterioles.
2) ANP: Increases GFR. Blood volume increases --> atria stretches --> ANP is released from atria --> glomerular mesangial cells are relaxed --> glomerular capillaries have increased SA available for filtration.
86
Which cells make the largest contribution to tubular reabsorption?
PCT cells (with help from epithelial cells).
87
Solutes reabsorbed by active and passive processes in tubular reabsorption:
Glucose, amino acids, urea, ions.
88
Which substances are secreted by tubular secretion?
H+, K+, NH4+, creatinine, drugs.
89
Tubular secretion has 2 outcomes:
1) The secretion of H+ helps control blood pH.
2) The secretion of other substances helps eliminate them from the body in urine.
90
Paracellular reabsorption of tubular reabsorption.
Fluid can leak between the cells in a passive process. Even though the epithelial cells are connected by tight junctions, the tight junctions between cells in the PCTs are leaky and permit some reabsorbed substances to pass between cells in peritubular capillaries.
91
Transcellular reabsorption of tubular reabsorption.
A substance passes from fluid in tubular lumen through the apical membrane of a tubule cell, across the cytosol, and into interstitial fluid through the basolateral membrane.
92
When renal cells transport solutes out of or into tubular fluid, how many directions can they move specific substances?
In one direction only. Tight junctions form a barrier that prevents mixing of transport proteins in apical and basolateral membrane compartments.
93
What ensures the one-way reabsorption of Na+ in renal tubules?
Absence of Na+/K+ ATPases in the apical membrane.
94
How much ATP do Na+/K+ ATPases in renal tubules use at rest?
6% of total ATP consumption.
95
Primary active transport of renal tubule reabsorption/secretion.
Energy derived from hydrolysis of ATP is used to move a substance across a membrane.
96
Secondary active transport of renal tubule reabsorption/secretion.
Energy stored in an ion's electrochemical gradient drives a substrate across a membrane. This couples movement of an ion down its electrochemical gradient to the movement of a second substrate against its electrochemical gradient.
97
____ of the reabsorption of water filtered by the kidneys occurs along with the reabsorption of solutes.
90%. Obligatory water reabsorption. The water is obliged to follow the solutes when they are reabsorbed. Occurs in PCT and descending limb of nephron loop because these areas are always permeable to water.
98
10% of the reabsorption of water filtered by the kidneys is _____ .
Facultative water reabsorption. Regulated by ADH. Occurs in collecting ducts.
99
Filtered fluid becomes tubular fluid once it enters the ____.
PCT.
100
The largest amount of solute and water reabsorption from filtered fluid occurs in the ____.
PCTs.
101
PCTs secrete a variable amount of which substances?
H+, NH4+, urea.
102
Filtered glucose, amino acids, lactic acid, and water-soluble vitamins are not lost in the urine. They are reabsorbed in the...
First half of the PCT by Na+ symporters located in apical membrane.
103
Na+-glucose symporter.
Secondary active transport.
2 Na+ and 1 glucose attach to symporter protein which carries them from the tubular fluid into the tubule cell. Glucose exits basolateral membrane via facilitated diffusion and diffuse into peritubular capillaries.
104
Na+-H+ antiporter.
Secondary active transport.
Carry filtered Na+ down concentration gradient into a PCT cell as H+ is moved from cytosol to lumen, causing Na+ to be reabsorbed into blood and H+ to be secreted into tubular fluid.
105
PCT cells produce ___ needed to keep the antiporters running.
H+.
CO2 diffuses from peritubular blood, or tubular fluid, or is produced --> carbonic anhydrase catalyzes the reaction of CO2 and H2O to H2CO3 --> H2CO3 dissociates into H+ and HCO3- --> HCO3- is reabsorbed in PCTs --> H+ is secreted into fluid within PCT lumen and reacts with HCO3- to form H2CO3 --> H2CO3 dissociates into CO2 and H2O --> CO2 diffuses into tubule cells and joins with H2O to form H2CO3 --> H2CO3 dissociates into H+ and HCO3- --> HCO3- level rises in cytosol, exits via facilitated diffusion transporters in basolateral membrane, and diffuses into blood with Na+.
For every H+ secreted into the tubular fluid of the PCT, 1 HCO3- and 1 Na+ are reabsorbed.
106
How does solute reabsorption in PCTs promote osmosis of water?
Each reabsorbed solute increases the osmolarity, first inside the tubule cell, then in interstitial fluid, and then in the blood.
107
Cells lining the PCT and descending limb of nephron loop are permeable to water because...
They have many aquaporin-1 molecules.
108
Which substances are no longer present as the fluid enters the nephron loop?
Glucose and amino acids.
109
In the nephron loop, is water reabsorption via osmosis automatically coupled to solute reabsorption?
No, because the apical membranes of the ascending limb of the nephron loop is impermeable to water.
110
Na2+-K+-2Cl- symporters.
Present in apical membranes of cells in the thick ascending limb of the nephron loop. Reclaim 1 Na+, 1 K+, and 2 Cl- from the fluid in the tubular lumen. Na+ and Cl- move into vasa recta, and the K+ move down its concentration gradient back into tubular fluid.
111
Little or no ____ is reabsorbed in the ascending limb of the nephron loop.
Water.
112
Fluid enters the nephron loop at a rate of...
40-45 mL/min
113
Fluid enters the DCTs at a rate of...
25 mL/min. 80% of the filtered water has now been reabsorbed.
114
Na+-Cl- symporters.
Apical membrane of early DCT.
115
Na+/K+ pumps and Cl- leakage channels in the _____ then permit reabsorption of Na+ and Cl- into the _____.
Basolateral membranes of early DCT, peritubular capillaries.
116
The early DCT is a major site where...
PTH stimulates reabsorption of Ca2+.
117
By the time the fluid reaches the late DCTs and CDs, ____ of the filtered solutes and water have returned to the blood.
90-95%
118
Principal cells in the late DCT and CD.
Reabsorb Na+. Secrete K+. Have receptors for aldosterone and ADH.
119
Intercalated cells in the late DCT and CD.
Reabsorb HCO3- and K+. Secrete H+.
120
How is Na+ transported in the late DCT and CD?
Pass through apical membrane of principal cells via Na+ leakage channels rather than symporters or antiporters.
121
Which 5 hormones affect the extent of Na+, Ca2+, and water reabsorption, as well as K+ secretion by renal tubules?
Angiotensin II, aldosterone, ADH, ANP, PTH.
122
Renin-angiotensin-aldosterone system.
Blood volume and blood pressure decreases --> walls of afferent arterioles are stretched less --> juxtaglomerular cells secrete renin --> sympathetic stimulation also stimulates release of renin from juxtaglomerular cells --> renin cleaves angiotensin from angiotensinogen --> ACE converts angiotensin I to angiotensin II.
123
What 3 ways does angiotensin II affect renal physiology?
1) It decreases GFR by causing vasoconstriction of afferent arterioles.
2) It enhances Na+ and water reabsorption in PCT by stimulating Na+-H+ antiporters.
3) It stimulates adrenal cortex to release aldosterone, which stimulates principal cells in CDs to reabsorb more Na+ and secrete more K+. The osmotic consequence of reabsorbing more Na+ is that more water is reabsorbed which causes an increase in blood volume and pressure.
124
Which hormone regulates facultative water reabsorption by increasing the water permeability of principal cells in DCT and CD?
ADH.
125
Which molecules are present inside tiny vesicles within principal cells?
Aquaporin-2. ADH stimulates insertion of the aquaporin-2-containing vesicles into the apical membranes via exocytosis.
126
How is ADH released?
When the osmolarity of plasma and interstitial fluid increases by just 1%, osmoreceptors in the hypothalamus detect the change, their nerve impulses stimulate ADH secretion, and principal cells become more water permeable so plasma and interstitial osmolarity decreases to normal.
Decreased blood volume can also stimulate ADH release.
127
Describe water reabsorption caused by ADH in the late DCT and CD in conditions of normal hydration.
Enough ADH is present to cause reabsorption of 19% of filtered water in the late DCT and CD. The urine is slightly hyperosmotic compared to blood.
128
Describe water reabsorption caused by ADH in the late DCT and CD in conditions of dehydration.
ADH concentration increases, causing an increase in the amount of filtered water that is reabsorbed in the late DCT and CD. The amount of filtered water that is reabsorbed in the late DCT and CD can increase from 19% to 19.8%. Less than 1% of filtered water remains unreabsorbed in the late DCT and CD, causing a low urine output. Very hyperosmotic urine compared to blood.
129
Describe water reabsorption caused by ADH in the late DCT and CD in conditions of overhydration.
ADH concentration decreases, causing a decrease in the amount of filtered water that is reabsorbed in the late DCT and CD. The amount of filtered water that is reabsorbed in the late DCT and CD can decreased from 19% to 0%. More than 1% of filtered water remains unreabsorbed in the late DCT and CD, causing a high urine output. Hypoosmotic urine compared to blood.
130
ANP.
Inhibits reabsorption of Na+ and water in the PCT and CD. Suppresses secretion of aldosterone and ADH. Increase the excretion of Na+ in urine. Increase urine output. Decreases blood volume and blood pressure.
131
PTH.
Low Ca2+ levels stimulates parathyroid glands to release PTH. Stimulates cells in early DCT to reabsorb more Ca2+ into blood. Inhibits phosphate reabsorption in PCT to promote phosphate excretion.
132
Which hormone controls whether dilute or concentrated urine is formed?
ADH.
133
What 2 things contribute to building and maintaining the osmotic gradient necessary for ADH to cause excretion of concentrated urine?
1) Differences in solute and water permeability and reabsorption in different sections of the long nephron loops and CDs.
2) The countercurrent flow of fluid through tube-shaped structures in the renal medulla.
134
Countercurrent flow.
The flow of fluid in opposite directions. Occurs when fluid flowing in one tube runs counter to fluid flowing in a nearby parallel tube.
135
What are the 2 types of countercurrent flow in the kidneys?
Countercurrent multiplication, and countercurrent exchange.
136
Countercurrent multiplication.
A progressively increasing osmotic gradient is formed in the interstitial fluid of the renal medulla as a result of countercurrent flow. Involves long nephron loops and juxtamedullary nephrons. The descending limb carries tubular fluid from the renal cortex into the medulla, and the ascending limb carries it in the opposite direction. The long nephron loops functions as a countercurrent multiplier. The kidneys use this osmotic gradient to excrete concentrated urine.
137
Steps of countercurrent multiplication.
1) Symporters in thick ascending limb cels of the nephron loop cause a buildup of Na+ and Cl- in the renal medulla.
2) Countercurrent flow through the descending and ascending limbs establishes an osmotic gradient in the renal muedlla (tubular fluid becomes progressively more concentrated as it flows along the descending limb and progressively more dilute as it moves along the ascending limb).
3) Cells in CDs reabsorb more water and urea.
4) Urea recycling causes a buildup of urea in the renal medulla (a small volume of concentrated urine is excreted).
138
Countercurrent exchange.
Solutes and water are passively exchanged between the blood of the vasa recta and interstitial fluid of the renal medulla as a result of countercurrent flow. Blood flows in opposite directions in the ascending and descending parts of the vasa recta. Vasa recta functions as a countercurrent exchanger. As blood flows along the descending part into renal medulla where the interstitial fluid becomes increasingly concentrated, Na+, Cl- and urea diffuse from interstitial fluid into the blood, and water diffuses from the blood into the interstitial fluid. Blood then flows into the ascending part of the vasa recta, where the interstitial fluid becomes increasingly dilute, causing Na+, Cl- and urea to diffuse back into the interstitial fluid, and water diffuse back into the vasa recta. This is how the vasa recta provides oxygen and nutrients to the renal medulla without diminishing the osmotic gradient.
139
The long nephron loop establishes the osmotic gradient in the renal medulla by _____ , and the vasa recta maintains the osmotic gradient in the renal medulla by _____ .
Countercurrent multiplication, countercurrent exchange.
140
Typical solutes found in urine.
Electrolytes, urea, creatinine, uric acid, urobilinogen, fatty acids, pigments, enzymes, hormones.
141
Normal volume and pH of urine.
1-2 L every 24 hours. 6.0 pH.
142
Solutes found in abnormal urine.
Albumin, glucose, RBCs, ketone bodies, bilirubin, casts, microbes.
143
Blood tests to measure kidney function.
Blood urea nitrogen (BUN) test = measures blood nitrogen which rises when GFR decreases in cases of renal disease or urinary obstruction.
Plasma creatinine measurement = measures blood creatinine which rises when creatine phosphate is catabolized in skeletal muscle and is not properly excreted, usually remains steady because excretion equals discharge from muscle, 1.5 mg/dL indicates poor renal function.
144
Renal plasma clearance.
Evaluates how effectively the kidneys are removing a given substance from blood plasma. Depends on glomerular filtration, tubular reabsorption, and tubular secretion.
Substance = (U x V) / P
--> U and P are the concentrations of the substance in urine and plasma
--> V is the urine flow rate in mL/min
145
Which drug is filtered but not reabsorbed or secreted so its clearance equals the GFR?
Inulin.
146
Which drug is used to measure renal plasma flow? What is renal plasma flow, and why would this drug be used to measure it?
PAH. Renal plasma flow is the amount of plasma that passes through the kidneys in 1 minute, and PAH would be used to measure renal plasma flow because it is filtered and secreted in a single pass through the kidneys.
147
What type of contractions of the muscular walls of the ureters push urine toward the urinary bladder?
Peristaltic. Also with the help of hydrostatic pressure and gravity.
148
How is backflow of urine prevented between urinary bladder and ureters?
As the bladder fills with urine, pressure within it compresses the oblique openings into the ureters. When this mechanism is not properly working, it is possible for microbes to travel up the ureters and infect the kidneys.
149
Mucosa of ureters.
Deepest layer. Mucous membrane. Transitional epithelium. Lamina propria of areolar connective tissue with collagen fibres, elastic fibres, and lymphatic tissue. Mucus secreted by goblet cells prevents the cells from coming into contact with urine.
150
Muscularis of ureters.
Intermediate layer. Inner longitudinal and outer circular smooth muscle (opposite to GI). Functions in peristalsis.
151
Adventitia of ureters.
Outer layer. Areolar connective tissue. Blood vessels, lymphatic vessels, nerves (all serve muscularis and mucosa). Anchors ureters in place.
152
What hold the urinary bladder in position?
Folds of peritoneum.
153
What is the urinary bladder capacity?
700-800 mL.
154
Trigone.
Small triangular area in the floor of the urinary bladder. The two posterior corners of the trigone contain the two ureteral openings. Smooth appearance because its mucosa is bound to muscularis.
155
Internal urethral orifice.
The opening into the urethra. Lies in anterior corner of trigone.
156
Mucosa of urinary bladder.
Deep. Mucous membrane. Transitional epithelium. Lamina propria. Rugae permits expansion of bladder.
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Muscularis of urinary bladder.
Detrusor muscle. Intermediate. Inner longitudinal, middle circular, and outer longitudinal smooth muscle fibres.
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Internal urethral sphincter.
Around opening into urethra. Circular fibres of muscularis.
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External urethral sphincter.
Inferior to urethra opening. Skeletal muscle. Modification of the deep muscles of the perineum.
160
Adventitia of urinary bladder.
Superficial. Posterior and inferior surfaces of bladder. Areolar connective tissue is continuous with that of ureters.
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Serosa of urinary bladder.
Over the superior surface of urinary bladder. Layer of visceral peritoneum.
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Micturition reflex.
Discharge of urine from the urinary bladder. Combination of involuntary and voluntary muscle contraction.
When the urine volume within the bladder exceeds 200-400 mL, pressure increases and stretch receptors in its walls transmit nerve impulses to spinal cord --> micturition center in S2 and S3 --> trigger spinal reflex. Parasympathetic impulses propagate to urinary bladder wall and internal urethral sphincter --> contraction of detrusor muscle, relaxation of internal urethral sphincter muscle, and inhibition of somatic motor neurons that innervate skeletal muscle in external urethral sphincter.
Urination takes place when the urinary bladder contracts and both sphincters relax.
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Urethra in males.
Discharges urine and semen. Passes through prostate, deep muscles of perineum, and penis. Consists of a deep mucosa and superficial muscularis. Lamina propria is areolar connective tissue with elastic fibres and a plexus of veins. Throughout the urethra, openings of ducts discharge mucus during sexual arousal and ejaculation.
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What are the 3 anatomical regions of the male urethra?
Prostatic urethra: passes through prostate, epithelium is continuous with urinary bladder, transitional epithelium, stratified columnar epithelium, pseudostratified columnar epithelium, muscularis is circular smooth, help form internal urethral sphincter. Contains the openings of ducts that transport secretions from the prostate, and the seminal vesicles and ductus deferent which deliver sperm into the urethra and provide secretions that both neutralize the acidity of the female reproductive tract and contribute to sperm motility and viability.
Intermediate urethra: shortest, passes through deep muscles of perineum, mucosa contains stratified columnar or pseudo stratified columnar epithelium, muscularis is circular skeletal, help form external urethral sphincter.
Spongy urethra: longest, passes through penis, stratified columnar epithelium, pseudo stratified columnar epithelium, nonkeratinized stratified squamous epithelium near the external urethral orifice. The openings of the ducts of the bulbourethral glands empty into this section of the male urethra.
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Urethra in females.
Posterior to pubic symphysis. External urethral orifice is located between clitoris and vaginal opening.
Mucosa: mucous membrane, transitional epithelium that is continuous with urinary bladder, nonkeratinized stratified squamous epithelium near external urethral orifice, stratified columnar epithelium, pseudostratified columnar epithelium, lamina propria.
Muscularis: circular smooth muscle fibres, continuous with urinary bladder.
