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Physiology (Term 2) > Urinary 3 > Flashcards

Urinary 3 Flashcards

1
Q

What is Plasma clearance?

A

The volume of plasma cleared of a particular substance per minute

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2
Q

Urine Excretion and Plasma Clearance:

Give examples

A
  1. Plasma clearance rate for a substance filtered but not reabsorbed or secreted
  2. Plasma clearance rate for a substance filtered and reabsorbed
  3. Clearance rate for a substance filtered and secreted
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3
Q

Urine Excretion and Plasma Clearance:

Give an example for each type

A

(a) For a substance filtered and not reassorbed or secreted, such as inulin, all of the filtered plasma is cleared of the substance
(b) For a substance filtered, not secreted, and completely reabsorbed, such as glucose, none of the filtered plasma is cleared of the substance
(c) For a substance filtered, not secreted, and partially reabsorbed, such as urea, only a portion of the filtered plasma is cleared of the substance
(d) For a substance filtered and secreted but not reabsorbed, such as hydrogen ion, all of the filtered plasma is cleared of the substance and the peritubular plasma from which the substance is secreted is also cleared (clearance rate higher than the filtration rate)

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4
Q

What can be used to determine the filtration fraction?

A

•Clearance rates for inulin and PAH can be used to determine the filtration fraction:

–Filtration fraction = GFR- Glomeruluar filtratration rate (plasma inulin clearance)/ renal plasma flow (plasma PAH-para aminohippuric acid clearance)

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5
Q

The kidneys can excrete urine of varying concentrations depending on body needs

What does ECF osmolarity depend on?

A

–The ECF osmolarity depends on the relative amount of H2O compared to solute

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6
Q

Describe the establishment of the Vertical Osmotic Gradient by Countercurrent Multiplication system

A

It is a vertical osmotic gradient in the interstitial fluid that surrounds the nephrons in the kidney

–Driven by a seriees of leeks and pumps in the descending and ascending limbs of a long Henle’s Loop (juxtamedullary nephrons as opposed to the cortical nephrons)

— Allows tight regulation of the osmolarity of water (and urine) being excreted

–Countercurrent multiplication

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7
Q

Describe the change in osmolarity of the interstitial fluid that surrounds the kidney nephrons from cortext to medulla in milliosmoles per litre (mOsm/L)

A

The further we go into the centre of the kidney, the higher the osmolarity of the interstitial fluid that the nephrons are bathed in:

  • In the cortext there is an osmolarity that is similar to extracellular fluid (around 300 mOsm/L)
  • As we move into the medulla there is an increase in osmolarity up to 1,200 mOsm/L
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8
Q

Explain Countercurrent Multiplication

A
  1. The active salt pump in the ascending limg establishes a 200 mOsm/L gradient at each horizontal level
  2. As the fluid flows forward several “frames” a mass of 200 mOsm/L fluid exits into the distal tubule and a new mass of 300 mOsm/L fluid enters from the proximal tubule
  3. The ascending limb pump and descending limb passive fluxes reestablish the 200 mOsm/L gradient at each horizontal level
  4. Once again, the fluid forward several “frames”
  5. The 200 mOsm/L gradient at each horizontal level is established once again
  6. The final vertical gradient is established and maintained by the ongoing countercurrent multiplication of the long loops of henle
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9
Q
A
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10
Q

Descending limb- cortical collecting duct-medullary collecting duct

A

This shows the osmolarity contained within the different tubular components of the nephron

It also shows the difference NaCl pumps and the osmotic movements of H2O

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11
Q

What is vasopressin also known as?

What is its function?

A
  • Also known as antidiuretic hormone (ADH) and arginine vasopressin (AVP)
  • It is a peptide hormone released from the posteriour pituitary gland which binds to its receptor on the distal tubule and collecting ducts luminal epitherial cells causing the movement of aquaporins towards the luminal membrane, allowing H2O to be removed
  • Controls Variable H2O Reabsorption in the Final Tubular Segments

Allows kidney to control:

–Regulation of H2O reabsorption in response to a H2O Deficit

–Regulation of H2O reabsorption in response to a H2O excess

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12
Q

How does vasopressin cause water to be reabsorbed from the distal and collecting ducts of the nephron when needed?

A
  1. Blood-borne vasopressin binds with its receptor sites on the basolateral membrane of a principal cell in the distal or collecting tubule.
  2. This binding activates the cyclic AMP (cAMP) second-messenger pathway within the cell.
  3. Cyclic AMP increases the opposite luminal membrane’s permeability to H2O by promoting the insertion of vasopressin-regulated AQP-2 water channels into the membrane. This membrane is impermeable to water in the absence of vasopressin.
  4. Water enters the tubular cell from the tubular lumen through the inserted water channels.
  5. Water exits the cell through different, always open water channels (either AQP-3 or AQP-4) permanently positioned at the basolateral border, and then enters the blood, in this way being reabsorbed.
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13
Q

Compare a water defefit and eater excess

A
  • (a) In the face of a water deficit:

Vasopressin present: distal and collecting tubules permeable to H2O

Small volume of concentrated urine (up to 1200mOsm/L) excreted; reabosorbed H2O picked up by peritubular capillaries and conserved for the body

  • (b) In the face of a water excess:

No vasopressin present:distal and collecting tubules impermea- ble to H2O

Large volume of dilute urine; (as low as 100 mOsm/L) excreted; no H2O reabsorbed in distal portion of nephron; excess H2O eliminated from body in urine

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14
Q

What is the function of the vasa recta?

A

•Preserve the Vertical Osmotic Gradient by Countercurrent Exchange

–Allows the blood to leave the medulla and enter the renal vein essentially isotonic to incoming arterial blood

–Tracks the Loop of Henle

–Looped structure, slow flow, prevents loss of gradients

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15
Q

Is water reabsorption fully linked to solute reabsorption?

A

•Water reabsorption is only partially linked to solute reabsorption

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16
Q

How does the hypothetical pattern of flow differ from the actual pattern of flow?

A
17
Q

Describe the reasbsorption of Na+ and H2O by the proximal tubule

A

Na+:

67%

Active; uncontrolled; plays a pivotal role in the reabsorption of glucose, amino acids, Cl-, H2O and urea through different mechanisms, sometimes through co-transporters e.g. glucose/sodium transporter or through passive movement

H2O:

65%

Passive; obligaotry osmotic reabsorption following active Na+ reabsorption that also occurs in the proximal tubule

18
Q

Describe the reasbsorption of Na+ and H2O by the loop of Henle

A

Na+:

25%

Active, uncontrolled; NaCl reabsorption from the ascending limg helps establish the medullary interstitial vertical osmotic gradient, which is important in the kidney’s ability to produce urine of varying concentrations and volumes, depending on the body’s needs

H2O:

15%

Passive; obligatory osmotic reabsorption from the descending limb as the ascending limb extrudes NaCl into the interstitial fluid (that is, reabsorbs NaCl)

19
Q

Describe the reasbsorption of Na+ and H2O by the distal and collecting duct tubules

A

Na+:

8%

Active; variable and subject to aldosterone control; important in the regulation of ECF volume and long-term control of blood pressure; linked to K+ secretion and H+ secretion

H2O:

20%

Passive; not linked to solute reabsoprtion; variable quantities of “free” H2O reabsorption subject to vasopressin control; driving force is the vertical osmotic gradient in the medually interstitial fluid established by the long loops of Henle; important in regulating ECF osmolarity

20
Q

Acid: Base balance

How is this balance maintained throughout the body

A

Although buffering systems resist changes in pH this would eventually fail without the kidney. Urine is usually mildly acidic (pH 6.0)

The pH of extracellular fluid has to be kept within a very narrow range (7.35-7.45) and the body has mechanisms to maintain this pH:

  • Chemical buffers (occur in the blood and inside cells)
  • Respiratory buffers (allow us to regulate CO2 removal)
  • Renal buffers
21
Q

The kidney can regulate pH by adjusting 3 related factors:

A
  1. H+ excretion
  2. HCO3- excretion
  3. NH3 secretion
22
Q

How does H+ enter urine?

A

H+ enters urine by excretion (minor) and secretion (major)

23
Q

How do you calculate Filtration of H+?

A

Filtration of H+ = [H+] x GFR

24
Q

Renal H+ Regulation: In proximal tubule

A
  • H+ is secreted by H+ ATPase (active) and Na+-H+ antiporters (2-secondary°active)
  • Hence, H+ secretion and Na+ reabsorption are linked (for every Na+ moelcule reabsorbed, a molecule of H+ will be secreted)
25
Q

Renal H+ Regulation: In distal/collecting ducts

What are the 2 different cell types?

A

Intercalated cells (found between principal cells)

There are two types of intercalated cells:

Type A – H+ secretion, HCO3- absorbing (more active)

Type B – HCO3- secreting, H+ absorbing

26
Q

Describe the movement of ions in intercalated cells

A

The diagram shows mechanisms involved in secreting H+ and and absorbing Cl-

  • In the α-intercalated cell→ The H+ ATPase pump is involved and there is a K+/H+ antiporter and Cl- is absorbed into the intercalated cell via a HCO3- (bicarbonate) antiporter

This cell is good at sparing bicarbonate produced metabolically and secreting hydrogen when needed

  • In the β-intercalated cell →H+ is reabsorbed by a K+/H+ antiporter or a H+ ATPase pump and Cl- is absorbed into the intercalated cell via a HCO3- (bicarbonate) antiporter
27
Q

What are the causes of renal failure?

A

–Infectious organisms

–Inappropriate immune responses

–Obstruction of urine flow

–Insufficient renal blood supply

28
Q

What are the types of renal failure?

A

–Acute or chronic (graded from 1-5 where 1 is the mildest and 5 is renal failure)

–End-stage (long term) individual would require dialysis

29
Q

What are the potential ramifications of renal failure?

A
  • Uremic toxicity→ Caused by retention of waste products
  • Metabolic acidosis→ Caused by the inability of the kidneys to adequately secrete H+ that is continually being added to the body fluids as a result of metabolic activity caused by the action of too much acid on enzymes
  • Potassium retention→ Resulting from inadequate tubular secretion of K+. Altered cardiac and neural excitability as a result of changing the resting membrane potential of excitable cells
  • Sodium imbalance→ Caused inability of the kidneys to adjust Na+ excretion to balance changes in Na+ consumption. Elevated blood pressure, generalised edema, and congestive heart failure if too much Na+ is consumed, hypotension and circulatory shock if too little Na+ is consumed
  • Phosphate and calcium imbalance→ arising from impaired reasbsorption of these electrolytes. Disturbances in skeletal structures caused by abnormalities in deposition in deposition of calcium phosphate crystals, which harden bone
  • Loss of plasma proteins→ as a result of increased leakiness of the glomerular membrane Edema caused by a reduction in plasma-colliod pressure
  • Inability to vary urine concentration→ as a result of impairment of the countercurrent system. Hypertonicity of body fluid if too much H2O IS ingested and hypotonicity if too little is ingested
  • Hypertension→ arising from the combined effects of salt and fluid retention and vasoconstrictor action of excess angitotensin II
  • Anemia→ caused by inadequate erythropoetin prodcuction
  • Depression of the immune system→ caused by toxic levels of wastes and acids increased susceptibility to infections
30
Q

Urine is Temporarily Stored in the Bladder:

What needs to be considered?

A
  1. Role of the bladder
  2. Role of the urethral sphincters
  3. Micturition reflex
  4. Voluntary control of micturition
  5. Urinary incontinence
31
Q

Describe the refelex control processes in urination

A

Reflex control of the urinary bladder:

  1. Bladder fills with urine
  2. Detected by mechanoreceptors (stretch receptors)
  3. This activated the parasympathetic nervous system
  4. Which stimulates the bladder to contract
  5. This causes the internal urethral spincter to mechanically open when the bladder contracts
  6. Causing urination
32
Q

Describe voluntary control of the urinary bladder

A
  1. External urethral sphincter remains closed even when its stimulated by motor neurons
  2. External urethral sphincter opens when motor neuron is inhibited
33
Q

Describe the relationship between pressure and volume

A
34
Q

What are the two systems that work to maintain the osmotic gradient?

A
  • Countercurrent multiplication
  • Vasa recta
35
Q

What happens with ammonia secretion?

A

Ammonia (NH3) binds to free H+ in the filatrate and becomes ammonium ion (NH4+) which cannont be reabsorbed so by secreting ammonia you can lock away hydrogen and make sure it doesnt get reabsorbed

Physiology (Term 2) (24 decks)

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