Med Term 3 > Urinary 3 > Flashcards

Urinary 3 Flashcards

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1
Q

Plasma composition is regulated via three processes.

What are they?

A
  1. filtration (forms glomerular filtrate)
  2. reabsorption (movement from tubular fluid to blood)
  3. secretion (movement from blood to tubular fluid)
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2
Q

Absorption and secretion occurs via what cells? What route is that?

What is another way that absorption/secretion can occur?

A

tubular cells - transcellular route (movement is highly dependent on secondary active transport)

between cells - paracellular route (movement depends on concentration/electrical gradient)

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3
Q

What type of blood vessels make up the glomerular capillaries?

A

fenestrated capillaries

(tiny blood vessels have small pores that allow water and small molecules to pass through while retaining blood cells and large proteins)

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4
Q

Why is the high surface area and thinness of glomerular capillaries important?

A

they facilitate efficient filtration

(large surface area increases volume of filtrate formed, and thin walls reduce the distance molecules need to cross, speeding up filtration)

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5
Q

What is the visceral layer of Bowman’s capsule made of?

A

podocytes

(specialised cells that wrap around capillaries and form filtration slits - helps selectively filter blood)

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6
Q

Where does the filtrate collect after passing through the glomerular capillaries?

A

bowmans space

(the cavity between the visceral and parietal layers of bowmans capsule where the filtrate is collected before entering the proximal convoluted tubule)

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7
Q

What is the role of Bowman’s space?

A

to collect glomerular filtrate

(acts as a reservoir for the filtrate before it moves into the tubule system for further processing)

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8
Q

What does the image show?

A

glomerular filtration membrane made of 3 layers

layer 1: endothelium of glomerular capillaries - composed of fenestrated endothelial cells - blocks cells and large proteins

layer 2: glomerular basement membrane - dense and negatively charged matrix of proteins like collagen and glycoproteins, acts as a selective and charge-selective barrier

layer 3: podocytes - specialised cells that make up the visceral layer of bowman’s capsule - foot like extensions called pedicels

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9
Q

What is the first layer of the glomerular filtration membrane?

What does it consist of?

A

endothelium of glomerular capillaries

consists of fenestrated endothelial cells that allow water and small solutes to pass while blocking blood cells and large proteins

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10
Q

How does the glomerular basement membrane (GBM) contribute to filtration?

What makes up the GBM?

A

acts as a selective and charge-selective barrier

dense matrix of proteins like collagen and glycoproteins - its negative charge repels negatively charged molecules preventing their passage

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11
Q

What are podocytes and where are they located?

What is a special feature of podocytes?

A

specialised cells that make up the visceral layer of bowmans capsule

they have foot-like extensions called pedicels that wrap around capillaries - forming filtration slits that further control what enters bowmans space

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12
Q

Which layer of the GFM prevents blood cells from entering the filtrate?

A

endothelium of glomerular capillaries

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13
Q

Which layer has a negative charge which repels negatively charged proteins, preventing them from being filtered?

A

GBM

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14
Q

Why aren’t most proteins filtered at the glomerulus?

A

GBM forms a barrier with protein fibrils and is negatively charged - repels many plasma proteins

(GBM mesh physically blocks larger proteins, negative charge repels negatively charged proteins like albumin)

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15
Q

Why is albumin normally retained in the blood?

A

because it is negatively charged and the GBM is also negatively charged

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16
Q

What two main properties of the glomerular filtration membrane prevent protein passage?

A
  • physical mesh of the GBM
  • negative charge of GBM
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17
Q

What prevents red blood cells from being filtered?

A

they are too large to pass through fenestrated endothelium of glomerular capillaries

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18
Q

What drives the movement of fluid across the glomerular filtration membrane?

A

glomerular blood hydrostatic pressure - blood pressure in the glomerular capillaries

(blood pressure inside the glomerular capillaries - pushes water and solutes out of the blood across the filtration membrane into bowmans space)

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19
Q

What opposes the filtration process?

A
  • capsular hydrostatic pressure (CHP)
  • blood colloid osmotic pressure (BCOP)

(CHP: pressure of filtrate in bowmans space pushing back)

(BCOP: osmotic pull of plasma proteins drawing water back into capillaries)

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20
Q

How is Net Filtration Pressure (NFP) calculated?

A

NFP = GBHP - (CHP + BCOP)

Net Filtration Pressure = high glomerular blood hydrostatic pressure - (capsular hydrostatic pressure + blood colloid osmotic pressure)

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21
Q

What is used to calculate eGFR and why?

A

creatinine

  1. byproduct of muscle metabolism (produced at relatively constant rate)
  2. freely filtered by glomerulus (passes easily through the glomerular filtration membrane into bowmans space)
  3. minimal reabsorption or secretion (in normal kidneys, it is mostly filtered and not reabsorbed = its blood levels reflects how well kidneys are filtering)
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22
Q

What is the purpose of renal autoregulation?

A

to maintain a consistent renal blood flow (RBF) and GFR

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23
Q

How is renal autoregulation achieved?

A

by changing the tone of the afferent and efferent arterioles

(constriction or dilation of these arterioles adjusts blood flow into and out of the glomerulus)

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24
Q
  1. What happens when the afferent arteriole constricts?
  2. What happens when the efferent arteriole constricts?
A
  1. capillary hydrostatic pressure decreases - drop in GFR
    (less blood enters the glomerulus so less is filtered into bowmans space)
  2. capillary hydrostatic pressure increases - increase in GFR
    (blood backs up in the glomerular capillaries, increasing filtration rate)
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25
What is the main site of reabsorption?
PCT
26
What transporters reabsorb glucose from the filtrate back into the blood?
SGLT1 and SGLT2 transporters, using the energy provided by the sodium gradient
27
What keeps intracellular Na concentration low?
Na+/K+ ATPAse
28
How does sodium movement from the filtrate drive reabsorption?
Na+ moves down its concentration gradient into PCT cells, bringing other solutes like glucose and amino acids along with it (secondary active transport)
29
What does the basolateral Na⁺/K⁺-ATPase pump do in the PCT?
it pumps 3 Na+ out of the cell and 2 K+ in using ATP, keeping intracellular Na+ low
30
What are aquaporins and which type is most important in the PCT?
aquaporins are water channels that allow water to move quickly through cells - AQP1 is the most prevalent in the PCT
31
What occurs in the following (Loop of Henle): 1. Descending Limb 2. Thin Ascending Limb 3. Thick Ascending Limb
1. water-permeable, solute-impermeable -> water leaves the tubule by osmosis - AQP1 channels help water move out quickly - urea and sodium diffuse in from the medullary interstitium - FILTRATE BECOMES MORE CONCENTRATED 2. impermeable to water, allows passive NaCl reabsorption - FILTRATE STARTS LOSING SALT BUT STAYS DILUTE IN WATER 3. impermeable to water, but actively pumps out salts - uses Na+/K+/2Cl- cotransporter (NKCC) to move Na+, K+, Cl- from tubule into the cell - K+ is recycled back into the tubule via ROMK channels - Cl- leaves the cell into tissue fluid via CLC-NKB channels - FILTRATE BECOMES VERY DILUTE, MEDULLA GETS SALTY, CONCENTRATES URINE
32
What is the permeability of the descending limb of the loop of Henle?
permeable to water but not to solutes (water leaves via AQP1 channels - concentrates the filtrate)
33
What happens to the filtrate in the descending limb?
becomes more concentrated as water leaves
34
What is the permeability of the thin ascending limb?
impermeable to water but allows passive NaCl reabsorption
35
What effect does the thin ascending limb have on filtrate?
filtrate loses some salt but stays dilute in water; the medulla starts to get salty
36
What is special about the thick ascending limb?
impermeable to water and actively pumps out, Na+, K+ and Cl- using the NKCC cotransporter
37
How are K⁺ and Cl⁻ handled in the thick ascending limb?
K+ is recycled back into the tubule via ROMK channels; Cl- leaves the cell into tissue fluid via CLC-NKB channels
38
Overall effect of the thick ascending limb?
filtrate becomes very dilute, and the medullary interstitium becomes very salty, creating the gradient needed to concentrate urine later
39
What fine-tunes the reabsorption of sodium, calcium and water, and is a site for active secretion of potassium and hydrogen ions?
the DCT
40
Where is calcium reabsorbed?
DCT
41
What are the two main cell types in the DCT and the collecting duct? What is their function?
1. principal cells - involved in uptake of sodium ions and extrusion of potassium ions - driven by a Na+/K+ ATPase on the basolateral membrane 2. intercalated cells - assist in acid-base control by controlling the levels of hydrogen and bicarbonate ions
42
What is the main function of principal cells?
they reabsorb sodium (Na+) and secrete potassium (K+)
43
What is the main function of intercalated cells?
they help regulate acid-base balance by controlling hydrogen (H+) and bicarbonate (HCO3-) ions
44
What does ADH do?
increases the permeability of the collecting duct to water, allowing reabsorption to concentrate the urine
45
What is renal clearance?
volume of plasma from which a substance is completely removed (cleared) by the kidneys per unit time
46
How do you calculate renal clearance?
urine creatinine conc X urine flow rate divided by plasma creatinine concentration
47
How much glucose is normally present in the urine of a healthy young person? Explain your answer.
none - glucose is normally fully recovered from the glomerular filtrate, by reabsorption into the peritubular capillaries from the proximal convoluted tubule (PCT) of each nephron
48
As you may know, the reference range for a random blood glucose sample, i.e. a blood glucose sample taken at random (i.e. a non-fasting sample) is 3.5-7.8 mmol/L. Based on this, and your knowledge of filtration/reabsorption, how many moles of glucose would be filtered each day by the kidneys of a young, healthy adult with a body surface area of 1.73 m2? Calculate a range from minimum to maximum moles of glucose filtered based on the range of blood glucose sample.
49
Where, within the nephron is glucose reabsorbed in a healthy individual?
in the PCT
50
How much glucose (in mmol) is reabsorbed per minute in a healthy individual at a plasma glucose concentration of 4 mmol/L? (Normal eGFR is 120 ml/min/ 1.73m2)
51
Glucose appears in the urine when the plasma glucose exceeds about 10 mmol/L. What is this level called?
renal threshold
52
Explain precisely why excess glucose that is not reabsorbed causes a diuresis.
when blood glucose is too high, proximal tubule can't reabsorb all of it - some of it spills into the filtrate as nephron reabsorbs water and electrolytes further along, glucose which is "left behind" becomes more concentrated glucose = osmotically active = holds water in tubule = less water is reabsorbed and more stays in urine = osmotic diuresis
53
What initial effect will the osmotic diuresis have on the osmolarity of plasma?
loss of extra water will concentrate solute in the ECF - will therefore increase osmolarity
54
A 19-year-old woman has consumed a very large amount of alcohol and become largely incapable. She has been vomiting repeatedly, and is now barely conscious, and her friends have brought her to the emergency department. 1. What is the immediate risk to this woman’s health? How should this be mitigated? 2. Her friends are embarrassed to note that she has wet herself. Why was her urinary bladder so full? Why has she voided spontaneously?
1. aspiration of vomit - mitigated by placing patient in recovery position 2. alcohol is a diuretic - suppresses ADH - makes collecting duct less permeable to water = more urine + as her urinary bladder fills, the pressure increases - in her debilitated state, she is unable to respond voluntarily, therefore when the pressure within the urinary bladder pressure reaches a critical level, the micturition reflexes activate spontaneously
55
A 19-year-old woman has consumed a very large amount of alcohol and become largely incapable. She has been vomiting repeatedly, and is now barely conscious, and her friends have brought her to the emergency department. Explain precisely what will have happened to her plasma osmolarity, and why.
plasma osmolarity will increase - blood level will be high which will increase osmolarity ALSO alcohol induced diuresis = selective loss of water and increase osmolarity further
56
A 19-year-old woman has consumed a very large amount of alcohol and become largely incapable. She has been vomiting repeatedly, and is now barely conscious, and her friends have brought her to the emergency department. What will be the effect of her vomiting on the composition of her blood? Explain why.
Fluid & electrolyte loss: Vomit is roughly isotonic with plasma, so vomiting causes loss of sodium (mainly) and water → risk of hyponatremia. Potassium: Usually preserved; significant loss only with prolonged/severe vomiting. Acid–base effects: Loss of gastric H⁺ (from HCl) → increased bicarbonate → metabolic alkalosis. Prolonged vomiting with large ECF loss → loss of bicarbonate → risk of metabolic acidosis. Volume effects: Loss of extracellular fluid (ECF) → hypovolemia. Hemoconcentration: Less plasma volume → relatively higher concentration of blood cells and proteins. 👉 Basically: vomiting = Na⁺ & fluid loss → hyponatremia + hypovolemia; acid–base imbalance (alkalosis first, acidosis if prolonged).
57
A 19-year-old woman has consumed a very large amount of alcohol and become largely incapable. She has been vomiting repeatedly, and is now barely conscious, and her friends have brought her to the emergency department. She cannot drink anything. Why can you not give her a simple infusion of water?
pure water = grossly hypotonic and would dilute ECF at point of infusion so much that surrounding cells and blood cells in local veins would lyse release of hB into plasma = harmful
58
A 19-year-old woman has consumed a very large amount of alcohol and become largely incapable. She has been vomiting repeatedly, and is now barely conscious, and her friends have brought her to the emergency department. She is given an infusion of 5% glucose in Hartmann's solution. Why will this work?
osmolarity of 5% dextrose is roughly the same as plasma = no local damage at site of infusion will occur glucose will however, enter cells and be metabolised over time leaving gradual increase in water in ECF = will help restore osmolarity towards normal
59
A 19-year-old woman has consumed a very large amount of alcohol and become largely incapable. She has been vomiting repeatedly, and is now barely conscious, and her friends have brought her to the emergency department. Slowly, the alcohol clears from her blood as it is metabolised in her liver. She wakes feeling ferociously unwell. She has a vicious headache- why might that be?
1. toxic by-product of alcohol metabolism = acetaldehyde and acetate 2. dehydration -> brain shrinkage -> stretches dura mater = activates pain receptors
60
A 19-year-old woman has consumed a very large amount of alcohol and become largely incapable. She has been vomiting repeatedly, and is now barely conscious, and her friends have brought her to the emergency department. How will you set about establishing whether she has a serious problem with alcohol addiction?
CAGE questionnaire (for a comprehensive evaluation, consult a GP who can provide further assessment and discuss available treatment options, which may include counselling, medication, and support groups such as Alcoholics Anonymous (AA)
61
An 86-year-old woman has multiple health problems and has been visiting her GP for regular checkups. For some time, her plasma albumin concentration has been low, and a urine dipstick test now shows significant protein in her urine. What is the difference between process that ensure there is no glucose or protein in the urine of a healthy person?
in a healthy person, glucose is freely filtered at the glomerulus but reabsorbed almost completely in the proximal tubule, so it doesn’t appear in urine protein, like albumin, is mostly blocked at the glomerulus due to its size and negative charge, and any small proteins that pass are reabsorbed in the proximal tubule KEY DIFFERENCE is that glucose is prevented from urine by TUBULAR REABSORPTION, while protein is prevented mainly by the GLOMERULAR FILTER
62
An 86-year-old woman has multiple health problems and has been visiting her GP for regular checkups. For some time, her plasma albumin concentration has been low, and a urine dipstick test now shows significant protein in her urine. List two classes of proteins found in plasma and indicate where each is made in the body.
albumin: made in liver globulins: made in variety of tissues including immune cells and liver
63
An 86-year-old woman has multiple health problems and has been visiting her GP for regular checkups. For some time, her plasma albumin concentration has been low, and a urine dipstick test now shows significant protein in her urine. What effect will low protein concentration in plasma have on the formation of tissue fluid and what clinical signs will this lead to?
albumin (plasma protein) creates ONCOTIC PRESSURE = pulls water from surrounding tissue (ISF) back into capillaries low plasma protein = oncotic pressure drops = less fluid is drawn back into capillaries = more fluid stays in the tissues (ISF) = OEDEMA clinical signs: ascites in abdomen or ankle swelling
64
An 86-year-old woman has multiple health problems and has been visiting her GP for regular checkups. For some time, her plasma albumin concentration has been low, and a urine dipstick test now shows significant protein in her urine. What will have changed in the nephron to lead to protein appearing in the urine?
glomerular barrier that normally prevents protein from entering the filtrate must have broken down (usually because of damage to glomerulus)
65
Aditya Ahluwalia, a 5 year old girl, comes to see you with her parents at the GP clinic. Her parents tell you she has been drinking excessively and passing lots of urine. Despite this, they say she seems to have lost weight and is sleepy, generally unwell and gradually more unresponsive. You suspect she might have type I diabetes mellitus. Her urine dip test is positive for glucose and her fingerpick glucose is 22 mmol/L. Other than glucose, what other result(s) might you expect to be abnormal on her urine dipstick test?
raised ketones - now required for metabolic energy as glucose cannot enter cells
66
You feel Aditya is more unwell than her parents expected and decide to call an ambulance for her. Due to poor staffing levels, you follow her in the ambulance and treat her as the SHO in A&E. You perform a blood gas analysis on her: pH: 7.15 (7.35 – 7.45) pCO2: 3.2 kPa (4.5 – 6.0) pO2: 9.5 kPa (10.6 – 14.5) HCO3: 18 mmol/L (19 – 24) Base excess: 0.01 (-2.0 – 2.0) Interpret this ABG.
met acidosis (low pH with low pCO2 and low bicarbonate)
67
What is the difference between Met Acidosis and Met Alkalosis?
met acidosis - primary decrease in bicarbonate in the blood - low pH <7.35 = acidemia - lungs compensate: blow Co2, hyperventilation -> low Co2 - can be caused by: DKA, renal failure, diarrhoea met alkalosis - primary increase in bicarbonate in the blood - high pH >7.45 = alkalemia - lungs retain Co2 = high Co2 - can be caused by: vomiting, diuretics
68
Aditya Ahluwalia, a 5 year old girl, comes to see you with her parents at the GP clinic. Her parents tell you she has been drinking excessively and passing lots of urine. Despite this, they say she seems to have lost weight and is sleepy, generally unwell and gradually more unresponsive. You suspect she might have type I diabetes mellitus. Her urine dip test is positive for glucose and her fingerpick glucose is 22 mmol/L. You notice that she is quiet and has a high RR, though her saturation is 100%. Why is this?
she has met acidosis, body trying to compensate by removing acidic Co2
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