Urinary System Pt. 2 Flashcards
1
Q
What is reabsorption in the kidney?
A
Return of filtered water and solutes to blood. Most occurs in PCT. Essential because filtered volume exceeds plasma volume.
2
Q
What substances are reabsorbed?
A
Glucose, amino acids, small proteins, ions (Na⁺, K⁺, Ca²⁺, Cl⁻, HCO₃⁻, HPO₄²⁻).
3
Q
What is secretion in the kidney?
A
Transfer of materials from blood/tubule cells into filtrate. Helps manage pH. Eliminates toxins and foreign substances.
4
Q
What substances are secreted?
A
H⁺, K⁺, NH₄⁺, creatinine, certain drugs (e.g., penicillin).
5
Q
Where does most reabsorption occur?
A
Primarily in PCT (Proximal Convoluted Tubule). Continues along nephron loop. Variable amounts in DCT and collecting duct.
6
Q
Why is reabsorption necessary?
A
Volume entering PCT in 30 minutes > total plasma volume. Must return fluid to maintain blood volume. Preserves essential nutrients and ions.
7
Q
What are the functions of secretion?
A
pH regulation (H⁺ secretion), elimination of toxins, removal of foreign substances, enables substance testing via urinalysis.
8
Q
How is secretion useful clinically?
A
Enables urinalysis testing, helps monitor drug levels, indicates kidney function, shows presence of toxins.
9
Q
What makes reabsorption and secretion different?
A
Reabsorption: movement from tubule to blood. Secretion: movement from blood to tubule. Different substances involved, different purposes.
10
Q
What are the two main routes for reabsorption?
A
Paracellular (between cells)
Transcellular (through cells)
11
Q
What is paracellular reabsorption?
A
• Passive fluid leakage between cells • Through leaky tight junctions • Accounts for ~50% of ion reabsorption • No energy required
12
Q
What substances typically use the paracellular route?
A
• Water • Some ions (Na⁺, Ca²⁺) • Small molecules that can fit through tight junctions
13
Q
What is transcellular reabsorption?
A
• Movement directly through tubule cells • Three steps:
Enter through apical membrane
Cross cytosol
Exit through basolateral membrane
14
Q
Compare energy requirements of both routes:
A
• Paracellular: Passive (no energy needed) • Transcellular: Often requires energy (active transport)
15
Q
What are tight junctions?
A
• Connections between adjacent cells • Can be ‘leaky’ (PCT) or ‘tight’ (later segments) • Control paracellular transport • Act like seals between cells
16
Q
Why do kidneys use two routes for reabsorption?
A
• Increased efficiency • Energy conservation • Better control • Backup system if one route fails
17
Q
What are the key components of transcellular transport?
A
• Apical membrane (faces urine) • Cell cytosol • Basolateral membrane (faces blood) • Specific transporters on each membrane
18
Q
What determines if tight junctions are ‘leaky’ or ‘tight’?
A
• Location in nephron • PCT has leaky junctions • Later segments have tight junctions • Affects amount of paracellular transport
19
Q
How does the PCT differ from later segments in terms of reabsorption?
A
• PCT has leakier tight junctions • More paracellular transport possible • Higher overall reabsorption rate • Less selective reabsorption
20
Q
What is the key difference between paracellular and transcellular reabsorption?
A
• Paracellular: Movement between cells
• Transcellular: Movement through cells
21
Q
List characteristics of paracellular reabsorption:
A
• Occurs between cells
• Uses leaky tight junctions
• Passive process (no energy needed)
• Accounts for ~50% of ion reabsorption
Like water seeping between bricks
22
Q
List characteristics of transcellular reabsorption:
A
• Through cells (3 steps)
Enter through apical membrane
Cross cytosol
Exit through basolateral membrane
• Often requires energy
• Highly selective
Like going through security
23
Q
What substances typically use paracellular transport?
A
• Water
• Na⁺ ions
• Ca²⁺ ions
• Other small ions
24
Q
What substances typically use transcellular transport?
A
• Glucose
• Amino acids
• Proteins
• Specific ions requiring transporters
25
Compare advantages of both routes:
Paracellular:
• Energy efficient
• Rapid
• High capacity
Transcellular:
• Precise control
• Selective transport
• Can concentrate substances
26
What role do tight junctions play?
• Connect adjacent cells
• Control paracellular movement
• "Leaky" in PCT
• Act as barriers between cells
## Footnote
Like cement between bricks
27
What are clinical concerns with these pathways?
• Tight junction problems can cause:
Excess fluid loss
Electrolyte imbalances
• Can be affected by medications
• Important for drug transport
28
What drives paracellular transport?
• Concentration gradients
• Osmotic pressure
• No energy required
• Natural movement from high to low concentration
29
What drives transcellular transport?
• Active transport mechanisms
• ATP energy
• Specific transporters
• Can move against concentration gradients
30
What is the main function of sodium-potassium pumps in renal tubules?
• Move Na⁺ out of tubule cells into interstitial fluid
• Create and maintain low intracellular Na⁺ levels
• Enable continued Na⁺ reabsorption from filtrate
31
Why is it important to maintain low Na⁺ levels inside tubule cells?
• Creates concentration gradient
• Drives Na⁺ reabsorption from tubular fluid
• Enables continuous movement of Na⁺ into cells
• Maintains reabsorption efficiency
32
How do sodium-potassium pumps work?
• Use ATP energy (active transport)
• Move Na⁺ against concentration gradient
• Transport Na⁺ from lower to higher concentration
• Located in basolateral membrane
33
What drives Na⁺ entry through the apical membrane?
• Low intracellular Na⁺ concentration
• Concentration gradient from lumen to cell
• Maintained by Na⁺/K⁺ pump activity
• Passive movement down concentration gradient
34
What is the sequence of Na⁺ reabsorption via transcellular route?
Na⁺ enters cell through apical membrane
Crosses cytosol
Pumped out through basolateral membrane
Enters interstitial fluid
Absorbed into peritubular capillary
35
What is the overall importance of this mechanism?
• Regulates fluid balance
• Controls blood pressure
• Maintains electrolyte levels
• Ensures efficient Na⁺ reabsorption
36
How does this process relate to homeostasis?
• Helps maintain blood volume
• Regulates blood pressure
• Controls Na⁺ balance
• Supports fluid/electrolyte balance
37
Where are Na⁺/K⁺ pumps located in renal cells?
• Basolateral membrane
• Side facing interstitial fluid
• Away from tubule lumen
• Near peritubular capillaries
38
What happens if Na⁺/K⁺ pumps malfunction?
• Reduced Na⁺ reabsorption
• Disrupted concentration gradients
• Impaired kidney function
• Potential fluid/electrolyte imbalances
39
What are the two main types of active transport?
Primary active transport (uses ATP directly)
Secondary active transport (uses ion gradients)
40
What is primary active transport?
• Directly uses ATP energy • Moves substances against concentration gradients
## Footnote
Example: Na⁺/K⁺ pumps • Uses 6% of body's ATP at rest
41
What is secondary active transport?
• Uses ion gradients created by primary transport • No direct ATP use
## Footnote
Couples movement of multiple substances • Uses energy stored in electrochemical gradients
42
What is a symporter?
• Type of secondary active transport • Moves multiple substances in same direction
## Footnote
Example: Na⁺-glucose co-transport • Also called co-transporter
43
What is an antiporter?
• Type of secondary active transport • Moves substances in opposite directions
## Footnote
Example: Na⁺-H⁺ exchange • Also called exchanger
44
Why are transport proteins one-directional?
• Ensures controlled movement of substances • Prevents backward flow
## Footnote
Maintains concentration gradients • Increases transport efficiency
45
How does coupling work in secondary transport?
• Links movement of two substances • One substance moves down gradient
## Footnote
Energy released moves second substance • Saves ATP by using existing gradients
46
Where are different transport proteins located?
• Different proteins in different membrane regions • Specific to apical or basolateral membrane
## Footnote
Location determines transport direction • Arranged for efficient reabsorption/secretion
47
Why is the Na⁺/K⁺ pump important?
• Creates Na⁺ gradient for secondary transport • Maintains cell volume
## Footnote
Essential for reabsorption • Uses significant ATP (6% of body's total)
48
What drives water reabsorption in kidneys?
• Solute reabsorption
• Osmosis
• Movement from low to high solute concentration
• Follows solute movement
49
Define osmosis in kidney function:
• Movement of water from:
Low solute concentration areas
To high solute concentration areas
• Passive process
• Follows concentration gradients
50
What is obligatory water reabsorption?
• 90% of water reabsorption
• Automatically follows solute movement
• Occurs in PCT and descending limb
• Not regulated by hormones
51
What is facultative water reabsorption?
• 10% of water reabsorption
• Regulated by ADH
• Occurs mainly in collecting duct
• Adaptable to body's needs
52
Compare obligatory vs facultative reabsorption:
Obligatory:
• Automatic
• 90% of total
• PCT and descending limb
• No hormone control
Facultative:
• Controlled
• 10% of total
• Collecting duct
• ADH regulated
53
Where does water reabsorption occur?
Obligatory:
• PCT
• Descending limb of loop
Facultative:
• Collecting duct
54
How does ADH affect water reabsorption?
• Controls facultative reabsorption
• Increases collecting duct permeability
• Allows more water reabsorption
• Responds to body's hydration needs
55
Why is water reabsorption important?
• Maintains fluid balance
• Prevents dehydration
• Conserves water
• Supports homeostasis
56
What happens if water reabsorption fails?
• Dehydration risk
• Fluid imbalance
• Electrolyte disorders
• Increased urine output
57
What determines how much water is reabsorbed?
• Amount of solute reabsorption
• ADH levels
• Osmotic gradients
• Body's hydration status
58
Where are essential substances reabsorbed in the nephron?
• First half of PCT
• Via Na⁺-transporters (symporters)
• Complete reabsorption
## Footnote
Examples: glucose, amino acids, vitamins
59
What is a symporter?
• Transport protein that moves multiple substances
• Moves substances in same direction
• Uses Na⁺ gradient as energy source
## Footnote
Example: Na⁺-glucose symporter
60
How does the Na⁺-glucose symporter work?
Na⁺ and glucose bind to symporter
Na⁺ gradient pulls both molecules into cell
Glucose exits via facilitated diffusion
Enters peritubular capillaries
61
What creates the Na⁺ gradient for symporters?
• Na⁺/K⁺ pumps (active transport)
• Uses ATP energy
• Pumps Na⁺ out of cell
• Creates low intracellular Na⁺
62
What substances use symporters?
• Glucose
• Amino acids
• Phosphate ions
• Sulfate ions
• Lactate
• Water-soluble vitamins
63
Why is symporter transport important?
• Prevents loss of essential nutrients
• Energy efficient
• Selective transport
• Maintains homeostasis
64
How does glucose exit PCT cells?
• Via facilitated diffusion
• Through specific transporters
• Through basolateral membrane
• Into peritubular capillaries
65
Why use Na⁺ for co-transport?
• Strong concentration gradient exists
• Gradient maintained by active transport
• Provides energy for transport
• No additional ATP needed
66
Where are symporters located?
• Apical membrane
• Faces tubular fluid
• First half of PCT
• Luminal side of cells
67
What happens if symporters malfunction?
• Loss of essential nutrients
• Increased urinary excretion
• Potential deficiencies
• Metabolic imbalances
68
What is an Na⁺-H⁺ antiporter?
• Transport protein moving Na⁺ and H⁺
• Moves ions in opposite directions
• Na⁺ enters cell
• H⁺ secreted into tubule
69
What drives the Na⁺-H⁺ antiporter?
• Na⁺ concentration gradient
• Created by Na⁺/K⁺ pump
• Secondary active transport
• No direct ATP use
70
How is H⁺ generated for the antiporter?
• CO₂ + H₂O → H₂CO₃
• Carbonic anhydrase catalyzes
• H₂CO₃ → H⁺ + HCO₃⁻
• CO₂ from blood/metabolism
71
What are the outcomes of antiporter function?
• Na⁺ reabsorption
• H⁺ secretion
• HCO₃⁻ reabsorption
• pH regulation
72
Why is this process important?
• Maintains acid-base balance
• Regulates blood pH
• Conserves bicarbonate
• Controls sodium levels
73
Where does CO₂ come from?
• Peritubular capillaries
• Tubular fluid
• Cell metabolism
• Diffuses freely across membranes
74
What role does carbonic anhydrase play?
• Catalyzes CO₂ + H₂O reaction
• Forms carbonic acid
• Speeds up H⁺ production
• Essential for antiporter function
75
What happens to HCO₃⁻?
• Reabsorbed into blood
• Exits via basolateral membrane
• Maintains blood buffering
• One HCO₃⁻ saved per H⁺ secreted
76
What maintains the Na⁺ gradient?
• Na⁺/K⁺ pump
• Uses ATP
• Located on basolateral membrane
• Keeps intracellular Na⁺ low
77
What drives passive reabsorption in late PCT?
• Solute reabsorption
• Osmotic gradients
• Electrochemical gradients
• Water following solutes
78
What is Aquaporin-1?
• Water channel protein
• Located in PCT cells
• Enables rapid water movement
• Present in descending limb
79
Which solutes are reabsorbed passively?
• Chloride (Cl⁻)
• Potassium (K⁺)
• Calcium (Ca²⁺)
• Magnesium (Mg²⁺)
• Urea
80
How does Cl⁻ reabsorption affect other ions?
• Creates negative charge
• Attracts positive ions
• Promotes cation reabsorption
• Uses paracellular pathway
81
What happens when water is reabsorbed?
• Increases solute concentration
• Creates new gradients
• Promotes more reabsorption
• Maintains homeostasis
82
What are the pathways for solute reabsorption?
* Paracellular (between cells)
* Transcellular (through cells)
83
What creates the osmotic gradient?
• Initial solute reabsorption
• Concentration differences
• Movement into interstitial fluid
• Differential membrane permeability
84
Where does reabsorbed water go?
• Leaves tubular fluid
• Enters interstitial fluid
• Enters peritubular capillaries
• Returns to bloodstream
85
What role do electrochemical gradients play?
• Drive ion movement
• Create charge differences
• Promote passive transport
• Aid solute reabsorption
86
What is the osmolarity of fluid entering the nephron loop?
Similar to blood osmolarity
• Due to PCT osmosis
• Balanced solute/water reabsorption
• Isotonic to blood
87
What happens in the descending limb?
Water permeable
• Some water reabsorption
• Driven by osmosis
• Fluid becomes concentrated
88
Describe the ascending limb characteristics:
Impermeable to water
• Active solute reabsorption
• Little obligatory water movement
• Fluid becomes dilute
89
What happens to tubular fluid osmolarity in ascending limb?
Progressively decreases
• Due to solute reabsorption
• No water follows
• Becomes hypotonic
90
Compare descending vs ascending limb:
Descending:
• Water permeable
• Concentrates fluid
Ascending:
• Water impermeable
• Dilutes fluid
91
What ions are reabsorbed in ascending limb?
Sodium (Na⁺)
• Chloride (Cl⁻)
• Potassium (K⁺)
• Calcium (Ca²⁺)
• Magnesium (Mg²⁺)
92
Why is little obligatory water reabsorption important?
Allows flexible water handling
• Enables concentration/dilution
• Supports homeostasis
• Adapts to body needs
93
What creates osmotic gradients in nephron loop?
Active solute transport, Selective water permeability, Ion reabsorption, Concentration differences
94
What is the overall function of the nephron loop?
* Regulates fluid volume
* Controls osmolarity
* Prepares for further adjustment
* Maintains homeostasis
95
What is a Na⁺-K⁺-2Cl⁻ symporter?
• Transport protein • Moves 1 Na⁺, 1 K⁺, 2 Cl⁻ • Located in ascending limb • Moves ions from filtrate to cells
96
How is Na⁺ handled after entering the cell?
• Actively pumped out • Via Na⁺/K⁺ ATPase • Into interstitial fluid • Then into vasa recta
97
What happens to K⁺ after transport?
• Leaks back to lumen • Through K⁺ channels • Maintains gradient • Supports continued transport
98
How does Cl⁻ exit the cell?
• Through Cl⁻ channels • On basolateral side • Into interstitial fluid • Maintains ion balance
99
What drives the symporter?
• Na⁺ gradient • Created by Na⁺/K⁺ pump • Secondary active transport • Electrochemical gradient
100
How does Cl - moving into interstitial fluid VIA leaky channels affect other cations?
* Creates positive charge in lumen * Promotes paracellular transport * Affects Ca²⁺ and Mg²⁺ * Enables passive reabsorption
101
Where are these symporters located?
• Thick ascending limb • Apical membrane • Facing tubular lumen • Multiple per cell
102
What's the overall effect on tubular fluid in the ascending limb?
* Becomes more dilute * Solutes removed * No water follows * Osmolarity decreases
103
Why is K⁺ recycling important?
• Maintains gradient • Supports continued transport • Creates positive charge • Enables cation movement
104
What percentage of filtered water is reabsorbed before DCT?
• 80% already reabsorbed
• Additional 10-15% in early DCT
• Total ~90-95%
• Reduced flow rate
105
What ions are reabsorbed in early DCT?
• Sodium (Na⁺)
• Chloride (Cl⁻)
• Calcium (Ca²⁺)
• ~5% of filtered Na⁺/Cl⁻
106
How do Na⁺-Cl⁻ symporters work?
• Located on apical membrane
• Move Na⁺ and Cl⁻ together
• Into tubule cells
• From tubular fluid
107
What's on the basolateral membrane?
• Na⁺-K⁺ pumps
• Cl⁻ leakage channels
• Move ions to blood
• Via peritubular capillaries
108
What's PTH's role in the DCT?
• Stimulates Ca²⁺ reabsorption
• Inhibits PO₄³⁻ reabsorption
• Regulates Ca²⁺ balance
• Affects PCT phosphate handling
109
What enters the early DCT?
• Partially processed filtrate
• ~25 mL/min flow rate
• More concentrated fluid
• 20% of original water
110
What are the key functions of early DCT?
• Fine-tunes ion balance
• Regulates water reabsorption
• Controls Ca²⁺ levels
• Responds to hormones
111
How does PTH affect phosphate?
• Inhibits reabsorption in PCT
• Increases excretion
• Balances with calcium
• Maintains mineral homeostasis
112
What happens to reabsorbed ions?
• Enter tubule cells
• Pass through basolateral membrane
• Enter peritubular capillaries
• Return to bloodstream
113
Why is early DCT important?
• Further refines filtrate
• Hormone-responsive
• Fine-tunes electrolytes
• Prepares for final processing
114
What percentage of filtrate is processed before late DCT?
• 90-95% of water reabsorbed
• 90-95% of solutes reabsorbed
• Only 5-10% remains
• Final adjustments occur here
115
What are the two main cell types?
Principal Cells:
• Na⁺/K⁺ regulation
• Hormone responsive
Intercalated Cells:
• pH regulation
• K⁺/HCO₃⁻ handling
116
What do principal cells do?
• Reabsorb Na⁺
• Secrete K⁺
• Respond to aldosterone
• Respond to ADH
• Have aquaporin-2
117
What do intercalated cells do?
• Reabsorb K⁺
• Reabsorb HCO₃⁻
• Secrete H⁺
• Regulate pH
• Help maintain acid-base balance
118
How is Na⁺ reabsorbed?
Enters through leakage channels
Pumped out by Na⁺-K⁺ pumps
Moves to interstitial fluid
Enters peritubular capillaries
119
How is K⁺ secreted?
• Enters cells via Na⁺-K⁺ pumps
• Exits through leakage channels
• Amount varies with needs
• Present in both membranes
120
What hormones affect these processes?
Aldosterone:
• ↑ Na⁺ reabsorption
• ↑ K⁺ secretion
ADH:
• ↑ water reabsorption
• Controls aquaporin-2
121
What are aquaporin-2 proteins?
• Water channels
• ADH controlled
• In principal cells
• Enable water reabsorption
122
What determines water reabsorption?
• ADH levels
• Aquaporin-2 presence
• Osmotic gradients
• Body's hydration needs
123
What triggers RAAS activation?
• Decreased blood pressure
• Decreased blood volume
• Less stretch of afferent arterioles
• Juxtaglomerular cells release renin
124
What's the sequence of RAAS activation?
Renin release
Angiotensin I formation
ACE converts to angiotensin II
Effects begin
125
What does angiotensin II do to GFR?
* Causes vasoconstriction of afferent arterioles
* Decreases filtration
* Conserves water/solutes
126
How does RAAS affect sodium handling?
• Stimulates Na⁺-H⁺ antiporters
• Enhances Na⁺ reabsorption
• Increases water reabsorption
• In PCT
127
What's aldosterone's role in RAAS?
• Released by adrenal cortex
• Increases Na⁺ reabsorption
• Increases K⁺ secretion
• Promotes water retention
128
What organs are involved in RAAS?
• Kidneys (renin)
• Lungs (ACE)
• Adrenal cortex (aldosterone)
• Blood vessels
129
What's the main purpose of RAAS?
• Maintain blood pressure
• Regulate blood volume
• Control fluid balance
• Adjust kidney function
130
What hormones are part of RAAS?
• Renin (enzyme)
• Angiotensin I
• Angiotensin II
• Aldosterone
131
What's the end result of RAAS?
• Increased blood pressure
• Increased blood volume
• Restored fluid balance
• Normalized kidney function
132
Where is ADH released from?
• Posterior pituitary gland
• Also called vasopressin
• Released in response to dehydration
• Controls water balance
133
What's facultative water reabsorption?
* Optional water reabsorption
* Controlled by ADH
* Occurs in late DCT, and collecting duct
134
How does ADH affect water permeability?
• Increases water permeability
• In principal cells
• Via aquaporin-2 insertion
• In apical membrane
135
What triggers ADH release?
• Increased plasma osmolarity
• Decreased blood volume
• Dehydration
• Low blood pressure
136
How does the negative feedback work?
High osmolarity detected
ADH released
Water reabsorbed
Osmolarity normalized
ADH release decreases
137
What are aquaporin-2 proteins?
• Water channels
• Inserted into membrane
• Allow water passage
• ADH controlled
138
What happens without ADH?
• Low water permeability
• High urine output
• Dilute urine
• Risk of dehydration
139
What's Diabetes Insipidus?
• ADH deficiency/resistance
• Extreme water loss
• Up to 20L urine daily
• Severe dehydration risk
140
Where does ADH act?
• Late DCT
• Collecting duct
• Principal cells
• Apical membrane
141
What's the end result of ADH action?
• Increased water reabsorption
• Concentrated urine
• Restored blood volume
• Normalized osmolarity
142
How does high fluid intake affect urine?
• Higher urine volume
• More dilute urine
• Less water reabsorption
• Maintains balance
143
How does low fluid intake affect urine?
• Lower urine volume
• More concentrated urine
• More water reabsorption
• Conserves water
144
What's the starting osmolarity?
• Blood: 300 mOsm/L
• Filtrate: 300 mOsm/L
• Initially isotonic
• Changes in tubules
145
How does osmolarity change in descending limb?
• Increases
• Water reabsorbed
• Due to medulla gradient
• Becomes concentrated
146
How does osmolarity change in ascending limb?
• Decreases
• Solutes removed
• Water impermeable
• Becomes dilute
147
How does ADH affect urine concentration?
High ADH:
• More water reabsorbed
• Concentrated urine
Low ADH:
• Less water reabsorbed
• Dilute urine
148
What happens in the descending limb?
• Medulla has high osmolarity
• Water leaves by osmosis
• Fluid becomes concentrated
• Osmolarity increases
149
What happens in thick ascending limb?
• Na⁺, K⁺, Cl⁻ actively reabsorbed
• Water can't follow (impermeable)
• Solutes leave, water stays
• Osmolarity decreases
150
What happens without ADH?
• Low water permeability
• Less water reabsorbed
• More dilute urine
• Larger urine volume
151
How does osmolarity change in descending limb?
• Starts at ~300 mOsm/L
• Increases to ~1200 mOsm/L
• Due to water loss
• Into medulla
152
How does osmolarity change in ascending limb?
• Starts at ~1200 mOsm/L
• Decreases to ~100 mOsm/L
• Due to solute loss
• Water retained
153
What's the final urine osmolarity?
• 65-70 mOsm/L
• Very dilute
• Large volume
• Low solute concentration
154
What are symporters in ascending limb?
• Transport Na⁺
• Transport K⁺
• Transport Cl⁻
• Active reabsorption
155
Why is ascending limb water-impermeable?
• Prevents water following solutes
• Helps dilute filtrate
• Essential for concentration gradient
• Creates dilute urine
156
What's the role of the medulla?
• Creates concentration gradient
• Draws water from descending limb
• Receives solutes from ascending limb
• Key for urine concentration
157
What's the end result?
• More solutes reabsorbed
• Less water reabsorbed
• Large urine volume
• Low osmolarity
158
What makes concentrated urine possible?
• Osmotic gradient in medulla
• Juxtamedullary nephrons
• Countercurrent multiplier
• ADH action
159
What creates the osmotic gradient?
Different permeability in nephron sections
Countercurrent flow
Solute pumping from ascending limb
Water retention in tubules
160
What's the osmolarity range in kidney?
• Cortex: ~300 mOsm/L
• Deep medulla: ~1200 mOsm/L
• Creates concentration gradient
• Drives water reabsorption
161
What happens in descending limb?
• Water leaves by osmosis
• Into hypertonic medulla
• Fluid becomes concentrated
• Follows osmotic gradient
162
What happens in ascending limb?
• Na⁺-K⁺-2Cl⁻ symporters active
• Pumps solutes out
• Water stays in tubule
• Creates dilute fluid
163
How does urea contribute?
• Reabsorbed from collecting duct
• Recycled into medulla
• Increases osmotic gradient
• Requires ADH presence
164
What's the vasa recta's role?
• Maintains osmotic gradient
• Countercurrent exchange
• Prevents solute washout
• Matches nephron flow
165
What's the maximum urine concentration?
• Up to 1200 mOsm/L
• 4x plasma concentration
• Requires ADH
• Needs medulla gradient
166
What's countercurrent multiplication?
• Opposite flow directions
• Amplifies osmotic gradient
• Occurs in nephron loop
• Essential for concentration
167
What happens when ADH is present?
• Collecting ducts become water-permeable
• Tubular fluid concentrates
• Urea moves into medulla
• Increases medullary osmolarity
168
What is countercurrent flow?
• Fluids moving in opposite directions
• In parallel tubes
## Footnote
Examples: Descending/ascending limbs, Vasa recta blood flow
169
How do juxtamedullary nephrons help?
• Have long loops
• Act as countercurrent multiplier
• Create osmotic gradient
• Allow concentrated urine
170
How does urea contribute?
• Moves with water into medulla
• Increases medullary osmolarity
• Gets recycled
• Maintains gradient
171
What happens in ascending limb?
• Fluid flows up
• Solutes actively removed
• Water stays in tubule
• Dilutes tubular fluid
172
Why is the gradient important?
• Enables water reabsorption
• Allows urine concentration
• Responds to ADH
• Conserves water
173
What's the purpose of vasa recta?
• Maintains osmotic gradient
• Prevents solute washout
• Matches nephron flow
• Enables concentration
174
What's the end result?
• Concentrated urine formed
• Water conserved
• Wastes eliminated
• Homeostasis maintained
175
What's exchanged in vasa recta?
• Solutes (Na⁺, Cl⁻, urea) • Water • Oxygen • Nutrients
176
Why is vasa recta structure important?
• Forms loops like nephron • Allows countercurrent flow • Matches medulla gradient • Preserves concentration
177
What happens in descending vasa recta?
• Solutes enter blood • Water leaves blood • Blood osmolarity increases • Follows medulla gradient
178
What happens in ascending vasa recta?
• Solutes leave blood • Water enters blood • Blood osmolarity decreases • Preserves gradient
179
Why is countercurrent exchange needed?
• Preserves medulla gradient • Supplies oxygen/nutrients • Prevents solute washout • Supports concentration
180
How does blood osmolarity change?
• Enters ~300 mOsm/L • Changes with depth • Returns near starting level • Minimal net change
181
What's supplied to loop cells?
* Nutrients snd Oxygen
* From blood supply; Via vasa recta
182
How does this differ from multiplication?
• Passive vs active transport • Preserves vs creates gradient • In vasa recta vs nephron loop • Maintains vs builds concentration
183
What's the end result?
• Gradient maintained • Tissues nourished • Concentration preserved • Efficient kidney function
184
What is urinalysis?
• Examination of urine properties
• Checks physical/chemical aspects
• Shows metabolism state
• Reveals kidney function
185
What's normal urine composition?
• 95% water
• 5% solutes
• Volume: 1-2 L/day
• Contains waste products
186
What do blood tests measure?
• Blood Urea Nitrogen (BUN)
• Plasma creatinine
• Waste product clearance
• Kidney function
187
What's renal plasma clearance?
• Kidney efficiency measure
• Rate of substance removal
• Expressed in mL/min
• Shows filtration ability
188
What are ureter functions?
• Transport urine
• Use peristalsis
• Use gravity
• Use hydrostatic pressure
189
How is backflow prevented?
• Physiological valve
• Bladder pressure
• Compresses ureter openings
• When bladder full
190
Describe bladder function
• Stores urine
• 700-800 mL capacity
• Distensible organ
• Collapses when empty
191
What's creatinine significance?
• From muscle metabolism
• Normal: ~1.5 mg/dL
• Higher = poor function
• Kidney efficiency marker
192
Why check glucose clearance?
• Usually zero
• Complete reabsorption
• Abnormal = problem
• Diagnostic tool
193
What is micturition?
Discharge of urine
Also called urination
Involves muscle contractions
Both voluntary & involuntary
194
How does micturition control develop?
Starts with stretch receptors
Triggers spinal reflex
Control learned in childhood
Involves voluntary muscles
195
What's the urethra's role?
Carries urine out of body
From internal orifice
To body exterior
Final pathway for urine
196
What is stress incontinence?
Weak pelvic floor muscles
Leakage with physical stress
Due to abdominal pressure
During coughing/sneezing
197
What is urge incontinence?
Common in older adults
Sudden urge to urinate
Followed by involuntary loss
Unexpected discharge
198
What is overflow incontinence?
Due to blockage
Or weak muscle contractions
Affects bladder musculature
Causes incomplete emptying
199
What is functional incontinence?
Can't reach toilet in time
Physical mobility issues
Environmental barriers
Time constraints
200
What causes incontinence?
Various muscle weaknesses
Nerve problems
Physical barriers
Age-related changes
201
How are muscles involved in micturition?
Voluntary sphincters
Involuntary muscles
Pelvic floor muscles
Bladder muscles
202
What triggers urination?
Stretch receptors
Bladder fullness
Spinal reflex
Voluntary control
203
What are kidney stones?
• Mineral deposits in kidneys • Caused by concentrated urine • Symptoms: severe pain, blood • Treatment: fluids, lithotripsy
204
What causes UTIs?
• Bacterial infection • Poor hygiene • Short urethra (females) • Weak immune system
205
What is glomerular disease?
• Affects kidney filters • Types: glomerulonephritis, nephrotic • Shows protein/blood in urine • Causes swelling
206
Describe renal failure types
• Acute: sudden, reversible • Chronic: gradual, permanent • Causes: hypertension, diabetes • Needs dialysis/transplant
207
What is polycystic disease?
• Genetic disorder • Fluid-filled cysts form • Causes high blood pressure • Can lead to kidney failure
208
Signs of bladder cancer?
• Blood in urine • Frequent urination • Painful urination • Risk factor: smoking
209
What is dialysis?
• Blood filtering treatment • Types: Hemodialysis (machine), Peritoneal (abdominal) • For kidney failure
210
Renal failure symptoms?
• Fatigue • Swelling • Decreased urine • Waste buildup
