kidney function I: filtration, reabsorption, and secretion Flashcards
(110 cards)
1
Q
What waste products are excreted by the kidney?
A
Urea (from protein catabolism)
Uric acid (from nucleic acid breakdown)
Creatinine (from muscle creatine)
Hormone metabolites (e.g., growth hormone metabolites)
End products of hemoglobin breakdown
Foreign chemicals (e.g., drugs, pesticides)
2
Q
What are the three main aspects of body fluid composition controlled by the kidney?
A
Volume regulation (linked to sodium concentration)
Osmoregulation (water balance)
pH regulation
3
Q
What hormones act on the kidney?
A
Anti-diuretic hormone (ADH)
Aldosterone
Natriuretic peptides
Parathyroid hormone
Fibroblast growth factor 23 (FGF23)
4
Q
What hormones are produced by the kidney?
A
Renin
Activated vitamin D3 (calcitriol)
Erythropoietin
Prostaglandins
5
Q
A
6
Q
label 1-5 on the diagram
A
7
Q
A
8
Q
A
9
Q
A
10
Q
What are the two types of nephrons in the kidney?
A
Cortical nephrons (85%)
Juxtamedullary nephrons (15%).
11
Q
Where are cortical nephrons located?
A
In the outer 2/3 of the cortex.
12
Q
What is a key characteristic of cortical nephrons?
A
they have a short Loop of Henle.
13
Q
Where are juxtamedullary nephrons located?
A
In the inner 1/3 of the cortex.
14
Q
What is a key characteristic of juxtamedullary nephrons?
A
They have a long Loop of Henle.
15
Q
A
16
Q
What is the primary function of juxtamedullary nephrons?
A
They are responsible for producing concentrated urine.
17
Q
how many arterioles in the nephron
A
2 sets - afferenet and efferent
18
Q
how many capillary beds in the nephron
A
2 sets - glomeruli and peritubular in series
19
Q
What are the basic renal processes?
A
- Glomerular Filtration
- Tubular Reabsorption
- Tubular Secretion
- Metabolism (e.g., glutamine)
20
Q
What is glomerular filtration?
A
The movement of fluid and solutes from the glomerular capillaries into Bowman’s space. About 20% of plasma that enters the glomerulus is filtered into Bowman’s space.
21
Q
What is tubular secretion?
A
The secretion of solutes from the peritubular capillaries into the tubules.
22
Q
What is tubular reabsorption?
A
The movement of materials from the filtrate in the tubules back into the peritubular capillaries.
23
Q
What is the equation for renal excretion?
A
24
Q
A
24
What determines the filtration of plasma constituents?
Filtration depends on molecular size, charge, and shape. Most plasma constituents are freely filtered, except proteins.
25
How does molecular size affect filtration in the glomerulus?
Molecules <7 kDa (e.g., glucose, inulin) are freely filtered.
Molecules between 7-69 kDa (e.g., myoglobin) are partly filtered.
Molecules >69 kDa (e.g., albumin) are excluded.
26
How does molecular charge affect filtration?
Negatively charged molecules (dextrans) are filtered the least.
Uncharged molecules are partly filtered.
Positively charged molecules are filtered the most.
27
Are cells and large proteins normally filtered across the filtration barrier?
No, cells and large proteins are not normally filtered.
28
Why are certain drugs and ions not freely filtered?
They bind to plasma proteins, preventing filtration.
29
Give an example of how drugs bind to plasma proteins.
Acidic drugs bind to albumin.
Basic drugs bind to α1-acid glycoprotein.
30
What percentage of plasma calcium (Ca²⁺) is freely filtered?
Only 60% of plasma Ca²⁺ is freely filtered, as 40% is bound to proteins.
31
What conditions can result in abnormal filtration of proteins or blood cells?
Infection, glomerular damage, or very high blood pressure.
32
What are the clinical consequences of glomerular damage?
Proteinuria: Protein in urine.
Haemoglobinuria: Haemoglobin in urine.
Haematuria: Red blood cells in urine
33
What is Glomerular Filtration Rate (GFR)?
The volume of fluid filtered from the glomeruli per minute (ml/min).
34
What three factors determine GFR?
Net filtration pressure
Permeability characteristics
Surface area
35
How is GFR regulated?
GFR is regulated by both neural and hormonal input.
36
What happens if GFR increases, assuming other factors remain equal?
A higher GFR means greater excretion of salt and water.
37
What are the two main forces involved in glomerular filtration (Starling's forces)?
Hydrostatic pressure difference
Colloid osmotic pressure difference
38
How does plasma flow across a capillary wall based on hydrostatic pressure?
Plasma flows from a high hydrostatic pressure to a low hydrostatic pressure.
39
How does plasma flow across a capillary wall based on colloid osmotic pressure?
Plasma flows from a low colloid osmotic pressure to a high colloid osmotic pressure.
40
What are the two main opposing Starling forces in glomerular filtration?
Hydrostatic pressures (60 mmHg - 15 mmHg)
Colloid Osmotic/Oncotic pressures (29 mmHg - 0 mmHg)
41
How is net glomerular filtration pressure calculated?
Net glomerular filtration pressure = (Glomerular hydrostatic pressure - Capsular hydrostatic pressure) - (Glomerular oncotic pressure - Capsular oncotic pressure)
(60 - 15) - (29 - 0) = 16 mmHg
42
Why is the oncotic pressure in Bowman’s space considered to be zero?
The protein concentration in Bowman’s space is so low that it does not generate significant oncotic pressure.
43
What is the net filtration pressure in the glomerulus?
16 mmHg
44
What is the filtration pore size of glomerular capillaries?
15 nm
45
What is the filtration pore size of most other capillaries, including peritubular capillaries?
5-12 nm
46
what 3 things does GFR depend on
1. starling forces involved in filtration
2. permeability characteristics of filtration interface
3. surface area of filtration interface changeable
47
What is the normal glomerular filtration rate (GFR) in humans?
125 ml/min, which equals 180 liters/day of filtrate formed.
48
How does the GFR compare to filtration in other body capillaries?
It is much higher, with the kidneys filtering 180 liters/day, whereas other capillaries filter only 4 liters/day.
49
How much urine is typically excreted per day?
1.5 liters/day.
50
Why is urine output much lower than the total amount of filtrate produced?
Because reabsorption occurs, where nearly 99% of filtered water is reabsorbed back into the body.
51
52
53
What is the primary mechanism for glucose and amino acid reabsorption in the proximal tubule?
Na⁺-coupled co-transporters facilitate reabsorption.
54
what 3 ways does proximal reabsorption of organic nutrients happen
55
What are the two types of glucose transporters in the kidney?
SGLT (Sodium-Glucose Linked Transporter) – Na⁺-dependent glucose co-transporter (secondary active transport).
GLUT (Glucose Transporter) – Facilitated diffusion transporter.
56
How does glucose enter the proximal tubular cells from the filtrate?
Via SGLT (Sodium-Glucose Linked Transporter), using Na⁺ gradient to move glucose against its concentration gradient into the cell.
57
How does glucose exit the proximal tubular cells into the blood?
Via GLUT (Glucose Transporter), using facilitated diffusion to move glucose down its concentration gradient into interstitial fluid and then into the blood.
58
What maintains the Na⁺ gradient needed for glucose reabsorption?
Na⁺-K⁺-ATPase pump, which actively pumps Na⁺ out of the cell into the blood, maintaining a low intracellular Na⁺ concentration.
59
How is the filtered load of glucose related to plasma glucose concentration?
The filtered load is linearly proportional to plasma glucose concentration.
60
What happens to glucose reabsorption at plasma glucose levels below 200 mg/dl (11 mM)?
Glucose is completely reabsorbed and does not appear in the urine.
61
What is the renal threshold for glucose, and what happens beyond this level?
The renal threshold is 200 mg/dl.
Beyond this, glucose transporters become saturated, and glucose starts appearing in the urine (glycosuria).
62
What does the "reabsorbed" line in the graph represent?
It shows the maximum glucose reabsorption rate as plasma glucose concentration increases.
63
How is glucose excretion calculated?
Excreted glucose = Filtered glucose - Reabsorbed glucose
Before the threshold, excretion is zero.
After the threshold, excretion increases as plasma glucose rises.
64
Where are amino acids reabsorbed in the nephron?
In the proximal tubule (PT).
65
How are different amino acids transported in the nephron?
Different transporters exist for different amino acid groups, including positively charged (basic) amino acids.
66
How many amino acid transporters are present in the nephron?
At least 8 amino acid transporters.
67
How many of these amino acid transporters are Na⁺-dependent?
6 transporters are Na⁺-dependent.
68
How is the majority of filtered protein reabsorbed?
Reabsorbed in the proximal convoluted tubule (PCT) via endocytosis.
Degraded into amino acids for reuse.
69
Why is protein reabsorption important in the kidney?
It helps in the inactivation of small polypeptide hormones, such as insulin and growth hormone.
70
What substances are transported using Na⁺-coupled transporters in the proximal convoluted tubule (PCT)?
Glucose, amino acids, phosphate, and sulphate.
71
What substances undergo passive reabsorption in the PCT?
Urea, chloride, potassium, and calcium.
72
How is bicarbonate reabsorption related to acid-base balance in the PCT?
Bicarbonate reabsorption is related to H⁺ secretion, which is important for acid-base balance.
73
How many stages of secretion in the proximal tubule?
It is a two-stage process involving basolateral and luminal membrane transporters.
74
What type of transporters are involved in proximal tubule secretion?
Broadly selective transporters.
75
Why is secretion in the proximal tubule important for some molecules?
It is the only means of excretion for some protein-bound molecules.
76
What type of molecules are secreted as organic acids (anions) in the proximal tubule?
Endogenous molecules, drugs, and diagnostic agents.
77
Give examples of endogenous organic acids secreted in the proximal tubule.
Bile salts, fatty acids, prostaglandins.
78
name some drugs that are secreted as organic acids in the proximal tubule.
Penicillin, furosemide.
79
What is an example of a diagnostic agent secreted as an organic acid?
Para-aminohippuric acid (PAH).
80
How do organic anions (OA⁻) enter the proximal tubule epithelial cell?
Via organic anion counter-transporters on the basolateral membrane.
81
How do organic anions (OA⁻) enter the tubule lumen?
Via ATP-dependent primary active transporters on the luminal membrane.
82
What type of molecules are secreted as organic bases (cations) in the proximal tubule?
Endogenous molecules and drugs.
83
Name some endogenous organic bases secreted in the proximal tubule.
Creatinine, histamine, choline, dopamine.
84
Provide examples of drugs that are secreted as organic bases in the proximal tubule.
Atropine, cimetidine, and morphine.
85
How do organic cations (OC) enter proximal tubule cells?
Via facilitated diffusion transporters.
86
How do organic cations (OC) enter the tubule lumen for excretion?
Via counter-transporters.
87
What is renal clearance?
The volume of plasma that is cleared of a substance in a given time.
88
What is the formula for renal clearance?
Renal Clearance = (U × V) / P
U = Concentration of substance in urine
V = Volume of urine per minute
P = Concentration of substance in plasma
89
Why is inulin clearance used to measure GFR?
Inulin is:
Freely filtered
Not reabsorbed
Not secreted
Not metabolized
Easily measured
90
Is inulin used clinically to measure GFR?
No, inulin is used experimentally.
91
What substance is routinely used in the clinic to estimate GFR?
Creatinine
92
Why is creatinine used instead of inulin for estimating GFR?
Creatinine is produced endogenously and does not require infusion like inulin, making it more practical for clinical use.
93
What happens when a substance undergoes net reabsorption?
Clearance is less than 120 mL/min (e.g., most solutes).
94
What happens when a substance is neither reabsorbed nor secreted?
Clearance equals 120 mL/min (e.g., inulin).
95
What happens when a substance undergoes net secretion?
Clearance is greater than 120 mL/min (e.g., para-aminohippuric acid (PAH)
96
What does Fick’s principle state when applied to the kidney?
The amount of a substance entering the kidney via the renal artery equals the sum of the amount leaving through the renal vein and the amount excreted in the urine.
97
What is the function of ADH (Antidiuretic Hormone)?
ADH is released by the posterior pituitary and promotes water reabsorption in the collecting duct.
98
Where is aldosterone produced, and what is its function?
Aldosterone is produced by the adrenal cortex and promotes sodium reabsorption in the collecting ducts.
99
What is the role of natriuretic peptides in kidney function?
Natriuretic peptides are produced by cardiac cells and promote sodium excretion in the collecting ducts.
100
What is the function of parathyroid hormone (PTH)?
PTH is produced by the parathyroid gland and promotes renal phosphate excretion, calcium reabsorption, and vitamin D production.
101
What is the role of FGF23 (Fibroblast Growth Factor 23)?
FGF23 is produced by osteocytes and promotes renal phosphate excretion while inhibiting vitamin D production.
102
What is renin, and where is it produced?
Renin is released by the juxtaglomerular apparatus, leading to angiotensin II formation, which promotes sodium retention and vasoconstriction.
103
What is the function of erythropoietin?
Erythropoietin is produced in the kidney and stimulates red blood cell formation in the bone marrow.
104
What role do prostaglandins play in the kidney?
Prostaglandins are produced in the kidney and regulate renal vessel tone.
105
What is the active form of Vitamin D3, and what does it do?
The active form of Vitamin D3 is calcitriol (1,25-dihydroxycholecalciferol), which promotes calcium and phosphate absorption in the gut.
106
What is the general equation for flow along tubes?
Flow along tubes = (Pressure difference along tube) / (Resistance), i.e., (P1 - P2) / Resistance.
107
What is Poiseuille’s Law for resistance to flow?
Resistance = (8Lη) / (πr⁴)
where L = vessel length, r = radius of vessel lumen, and η = blood viscosity.
108
How is flow related to pressure difference, vessel radius, length, and viscosity?
Flow = (Pressure difference × πr⁴) / (8Lη).
109
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