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Organ System Anatomy, Physiology and Pathology - BPT06 > Urinary System Physiology > Flashcards

Urinary System Physiology Flashcards

1
Q

What do kidneys regulate?

A
  • Plasma ionic composition (keep ions that we need, pee ions that we don’t need).
  • Plasma volume and pressure (role in blood pressure).
  • Plasma osmolarity (keep overall concentration of solute constant) and pH (concentration of hydrogen ions).
  • Removal of metabolic wastes.
  • Number of red blood cells.
  • Vitamin D production.
    Each function is vital!
  • Concentration of calcium.
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2
Q

Sections of the Kidneys

A

Renal cortex: outer regions.
Medulla: inner regions.
Pyramids: conical sections of the medulla separated by renal columns.

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3
Q

Order in Which Urine is Collected

A

Papillae → minor calyces → major calyces → ureter

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4
Q

The Nephron

A

Functional unit of kidneys.
Filter the blood and form urine.
Composed of renal corpuscle and renal tubule.

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5
Q

Renal Corpuscle

A
  1. Glomerulus: high pressure capillary bed

2. Bowman’s capsule: proximal end that surrounds glomerulus.

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6
Q

Renal Tubule Composition

A
  1. Proximal tubule
  2. Loop of Henle
  3. Distal convoluted tubule
  4. Collecting duct
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7
Q

Juxtaglomerular Apparatus

A

Helps regulating blood pressure.

  1. Macula densa: cells of distal tubule.
  2. Granular cells (juxtaglomerular cells): secretion of renin (regulation of blood pressure).
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8
Q

Which parts of the nephron are in the cortex?

A

Renal corpuscles, proximal and distal convoluted tubule.

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9
Q

Which parts of the nephron extend into the medulla?

A 
Loop of Henle (has descending and ascending limb).
Collecting ducts (bring the forming urine to papillae).
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10
Q

Vascular System of the Nephron

A

Efferent arteriole form a 2nd capillary bed around renal tubule, supply blood to glomerulus.

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11
Q

Regulation of Composition of Plasma

A 
Exchange of solutes and fluids between plasma and filtrate.
Achieved through 3 functions: 
1. Filtration
2. Reabsorption
3. Secretion
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12
Q

Bowman’s Capsule

A

Captures and directs filtrate to proximal tubule.
Parietal layer: simple squamous epithelium.
Visceral layer: cells cover the glomerular capillaries. Form a sieve.

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13
Q

How much of plasma enters Bowman’s capsule?

A

10-20%

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14
Q

Filtration Based on Size

A

Glomerular capillaries are fenestrated (extra spaces that favor movement of fluid). Blood cells and large proteins cannot pass.

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15
Q

Glomerular Filtration

A

Creation of a filtrate with a composition very similar to plasma (no protein).

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16
Q

What is Glomerular Filtration Rate (GFR) Influenced by?

A
  1. Hydrostatic pressure: that fluid exerts on the surface of capillaries.
  2. Osmotic pressure: overall concentration of fluid/solute. (absence of proteins in filtrate results in pressure near zero).
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17
Q

What are the forces favoring filtration?

A

Glomerular capillary hydrostatic pressure (60 mmHg)*

Bowman’s capsule osmotic pressure (0 mmHg)

18
Q

What are the forces opposing filtration?

A

Bowman’s capsule hydrostatic pressure (15 mmHg)

Glomerular capillary osmotic pressure (30 mmHg)

19
Q

Glomerular Filtration Rate (GFR)

A

Volume of plasma filtered per unit of time.
125 mL/min. Entire plasma filtrates through in 20 min.
180L of filtrate a day. Massive reabsorption.
1,5L of urine a day.

20
Q

Renal Plasma Flow

A

Volume of plasma flowing through kidneys.

625 mL/min.

21
Q

How much of the plasma flowing through the kidneys will pass inside the renal tubule?

A

20% → 125 mL/min / 625 mL/min = 0.20

22
Q

Mean Arterial Rate vs. Glomerular Filtration Rate

A

MAP: General blood pressure.
If MAP increases, GFR will increase as well BUT we have a mechanism to regulate GFR (kept constant between 80 mmHg - 180 mmHg.

23
Q

GFR Regulation - Myogenic Regulation

A

Intrinsic control.
Increased MAP stretch smooth muscle in afferent arteriole. Contraction results in vasoconstriction. Increased resistance, decreased blood flow. Decreased pressure in glomerulus.

24
Q

GFR Regulation - Tubuloglomerular Feedback

A

Intrinsic control.
Macula densa sense a change in GFR. Secretion of paracrine signals. Smooth muscle contraction/relaxation in afferent arteriole.
Increased GFR: vasoconstriction
Decreased GFR: vasodilatation

25
Q

GFR Regulation - Extrinsic control

A

MAP < 80 mmHg
Sympathetic activation through baroreceptor reflex.
Vasoconstriction in afferent and efferent arterioles.
Increased resistance (helps increase MAP)
Decreased blood flow
Decreased GFR

26
Q

Tubular Reabsorption

A

Massive, mostly in proximal* and distal convoluted tubules. Substances needs to cross tubule epithelium and capillary endothelium.
Active transport across either apical or basolateral membrane in conjunction with facilitated diffusion across the other.

27
Q

Water Reabsorption

A

Follows active reabsorption of solute.

28
Q

Tubular Reabsorption - Proximal Tubule

A

70% of water, Na+, K+. 100% glucose, amino acids, other organic substances. Recovery of bicarbonate ions for blood’s pH homeostasis.
Mass absorber.

29
Q

Tubular Secretion - Secreted Substances

A 
Hydrogen ions
Potassium ions
Urea
Drugs
Ammonia
Creatinine
30
Q

Tubular Secretion - Aquaporin

A

Water channels that facilitates water reabsorption.

31
Q

Tubular Reabsorption - Loop of Henle

A

Recover Na+ and water.
Concentration of solute goes from isotonic 300 (descending) to 1200 hypertonic (bottom of loop) to 100 hypotonic (ascending).
Descending: aquaporin channels, unrestricted movement of water.
Ascending: completely impermeable to water.

32
Q

Tubular Reabsorption - Collecting Ducts

A

Fine tuning of water balance and blood pressure.
Water can only pass through aquaporins in response to hormonal signals.
Concentration of solute in tubular fluid depends on how much H2O we need, the more H2O is reabsorbed, the higher the concentration/osmolarity (low volume of urine).
Concentration in medulla increases with depth.

33
Q

Excretion

A

Elimination of solute and water from the body.

Amount = amount filtered + amount secreted - amount reabsorbed.

34
Q

Excretion Rate

A

Depends on:
- Filtered load (GFR x plasma concentration)
- Rate of secretion
- Rate of reabsorption
Excretion rate > filtered load: Secretion
Excretion rate < filtered load: Reabsorbed
But we can only determine net effect (cannot exclude one or the other)

35
Q

Acid Base Balance - Acidosis

A 
pH < 7.35
Depression of CNS
Cardiac arrythmias
Potassium retention
Fatal: pH < 6.8
Coma 
Respiratory failure
36
Q

Normal pH Range

A

7.38 - 7.42

maintained by lungs and kidneys

37
Q

Acid Base Balance - Alkalosis

A 
pH > 7.45
Increase CNS excitability
Potassium depletion
Fatal: pH > 8
Muscle seizures and convulsions
Spasms of respiratory muscles
38
Q

Bicarbonate Buffer System - Acid Base Disturbance

A

Major buffer system in plasma, minimizes changes in pH.
CO2 + H2O ⇆ H2CO3 ⇆ H+ + HCO3-
CO2 increases - H+ increases - pH decreases.
In order to maintain 7.4 pH: [HCO3-] / [CO2] = 20:1
- Immediate action
- Temporarily limit changes
- Cannot reverse changes in pH

39
Q

Respiratory Compensation - Acid Base Disturbance

A

Within minutes.
True homeostatic mechanism.
Increase ventilation → Decrease CO2 → Increase pH
Decrease ventilation → Increase CO2 → Decrease pH

40
Q

Renal Compensation - Acid Base Disturbance

A

If pH increases → Decrease in H+ secretion, decrease in HCO3- reabsorption (in order to maintain pH).
If pH decreases → Increase in H+ secretion, increase in HCO3- reabsorption, Increase HCO3- production (in order to maintain pH).

Organ System Anatomy, Physiology and Pathology - BPT06 (34 decks)

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