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BMS2031 Body Systems > Urine Formation > Flashcards

Urine Formation Flashcards

1
Q

How many nephrons are there in a human kidney?

A

1 million

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2
Q

What is unique about a glomerulus as a capillary bed in terms of the vessels present?

A

The is an afferent renal arteriole and an efferent renal arteriole instead of an arteriole and a venule.

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3
Q

List the major sections of a nephron in order of fluid passing them.

A

Glomerulus, Bowman’s capsule, proximal tube, descending loop of Henle, ascending loop of Henle, distal tubule, ureter.

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4
Q

What are the three processes involved in urine formation?

A

Glomerular filtration, tubular reabsorption, tubular secretion.

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5
Q

What is glomerular filtration?

A

The passive, non-selective movement of fluid and solutes from the glomerular capillaries into the Bowman’s capsule

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6
Q

What substances move into the Bowman’s capsule during glomerular filtration?

A

Most substances, excluding proteins.

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7
Q

How does filtrate in the Bowman’s capsule differ from that in the plasma?

A

It lacks proteins (0.02% content)

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8
Q

How much of plasma passing through the glomerulus is filtered?

A

20%

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9
Q

What is tubular reabsorption?

A

Movement of materials (beneficial substances) from the renal tubules into the peritubular capillaries.

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10
Q

What is tubular secretion?

A

Movement of solutes (exogenous substances, H+, ammonium ions) from peritubular capillaries into the tubules.

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11
Q

Why can glomerular capillaries have relatively high pressures (55 mmHg vs 18)?

A

Due to the presence of two arterioles instead of a venule.

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12
Q

What are the 3 glomerular filtration layers?

A

Endothelium- single celled
Non-cellular basement membrane
Epithelial lining of Bowman’s capsule- single celled.

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13
Q

What special structures are present in capillary endothelium in the glomerulus?

A

Fenestrae/pores. These are not present in other capillaries

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14
Q

What are the special structures on

A

Podocytes (foot-like processes)

Filtration slits in between podocytes.

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15
Q

What force favours glomerular filtration?

A

High glomerular hydrostatic pressure (BP in capillaries)

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16
Q

What forces oppose glomerular filtration?

A

High blood colloid/oncotic osmotic pressure

High capsular hydrostatic pressure (pressure of liquid in Bowman’s capsule).

17
Q

What gives rise to high blood colloid osmotic pressure (30mmHg)?

A

Presence of plasma proteins that can not cross membranes.

18
Q

How is the GFP calculated?

A

GFP = Pgc - (Pbc + Pi gc)

19
Q

What would a low GFR indicate?

A

Reabsorption is increased and wastes are not excreted.

20
Q

What would a high GFR indicated?

A

Inadequate reabsorption and substances that shouldn’t be lost are lost in urine.

21
Q

How much of the plasma passing through the Bowman’s capsule in excreted as urine?

A

1%

22
Q

Is the process of reabsorption of sodium active of passive?

A

Active.

23
Q

How much of reabsorption of filtrate is controlled hormonally?

A

10%

24
Q

What is the transport maximum, why does it occur and what are the units for it?

A

The limit to the rate at which the solute can be transported into the peritubular capillaries due to saturation of carrier molecules.
Units: mg/min

25
Q

What is the relationship between filtration of glucose and plasma concentration?

A

Filtration is proportional to the concentration.

26
Q

When is the filtration of glucose no longer proportional to the plasma concentration of glucose?

A

Once the transport maximum (Tm) is reached.

27
Q

What is the renal threshold for glucose (point at which glucose appears in urine)?

A

300mg/100mL

28
Q

Why is the medullary interstitial hyperosmotic gradient important in human kidneys?

A

It allows to concentrate (hyperosmotic) urine.

29
Q

What are the two types of nephrons in the human kidney?

A

Cortical and Juxtamedullary.

30
Q

How do the Cortical and Juxtamedullary nephrons differ in terms of glomerulus position?

A

Cortical: in the cortex
Juxtamedullary: border of cortex and medulla

31
Q

How do the Cortical and Juxtamedullary nephrons differ in terms of the length of the loop of Henle?

A

The loop of Henle is longer in juxtamedullary nephrons and protrudes into the medulla when compared to cortical nephrons.

32
Q

What percentage of human nephrons are juxtamedullary?

A

25%

33
Q

What is the function of the vasa recta in juxtamedullary nephrons?

A

Preserve the hyperosmotic gradient to act as countercurrent exchangers.

34
Q

Is the descending loop of Henle permeable to sodium and water?

A

Permeable to water

Impermeable to sodium.

35
Q

What occurs in the ascending loop of Henle?

A

Sodium is actively transported out.

36
Q

What occurs in the cortical and medullary collecting ducts?

A

Water leaves the ducts, following a concentration gradient.

BMS2031 Body Systems (10 decks)

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