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Flashcards in Renal Physiology Deck (185):
1

What is osmolarity?

Units
Which two factors can be used to calculate it?

Concentration of osmotically active particles in a solution

osmol/L or mosmol/L

1) Molar concentration of solution
2) number of osmotically active particles present


e.g. 150mM NaCl

molar conc = 150mM
No.of osmotically active particles = 2

therefore, osmolarity = 2X150 =300 mosmol/L

2

Osmolality

Units of osmol/kg water

For weak salt solutions (i.e. the body), osmolality and osmolarity are interchangeable

3

Osmolarity of body fluids?

300 mosmol/L

4

Tonicity

effect a solution has on cell volume

5

Isotonic - effect on cell

No change in cell volume

6

Hypotonic

Increase in cell volume if a cell is exposed to a hypotonic environment

7

Hypertonic

Causes a decrease in cell volume

Cell is losing water to its environment to try and dilute it

8

300mM urea solution vs 300mM sucrose- effect on RBC

Hypotonic

Therefore the RBCs lyse and burst

Cell membrane is more permeable to urea than sucrose

9

Total Body water consists of?

Intracellular fluid (ICF) - 67%
Extracellular fluid (ECF) - 33%

10

ECF can be broken down into?

Plasma (20% of ECF)
Interstitial fluid (~80%)
Lymph+ trans cellular fluid (negligible)

11

Purpose of a tracer?

Obtain the distribution of volume of a tracer and therefore the volume of the body fluid compartments

12

ECF tracer

Inulin

13

Plasma tracer

Labelled albumin

14

Total body water tracer

3H2O

15

How to measure distribution of volume of a tracer

1. Add a known quantity of tracer X (Qx; mol or mg) to the body

2. Measure the equilibration volume of X in the body [X]

3. Distribution volume (litres) = Qx(mol)/[X](mol/litre)

=====

16

Largest contributor to water loss in the human body?

Urine

17

Why can we not "turn off" urine output - especially if we are dehydrated or are exercising intensely

The body still needs to excrete metabolic waste products.

18

Ionic composition of major fluid compartments (ICF, ECF)

of Na+, K+, Cl-, HCO3-

Na+ in ICF = 10mM
Na+ in ECF = 140mM

K+ in ICF = 140mM
K+ in ECF = 4.5mM

Cl- in ICF = 7
Cl- in ECF = 115

HCO3- in ICF = 10
HCO3- in ECF = 28

19

Concentrations of which ions are essentially the same in plasma and interstitial fluid?

Sodium and bicarbonate

as are chloride ions

20

Main ions in ECF are

Na+, Cl- , HCO3-

21

Main ions in ICF

K+, Mg2+, and positively charged proteins.

22

Osmotic concentrations of ECF and ICF are the same/different?

Same

~300mosmol/L

23

What is Fluid shift?

what would happen if:

a) the osmotic concentration of the ECF increases

b) If the osmotic concentration of the ECF decreases

Movement of water between the ICF and ECF in response to an osmotic gradient.


a) if osmotic concentration of ECF increases, water will move from ICF--> ECF in order to dilute and equilibrate the two compartments. (e.g. dehydration) ECF is hypertonic compared to ICF.

Fluid in ICF decreases, ECF increases.

b) Overhydration. Too much water but not enough salt, so ECF is hypotonic vs ICF.

Water therefore moves from ECF to ICF.

Fluid in ICF increases, ECF decreases

24

Water loss/gain if ECF gains/loses NaCl.

ECF NaCl gain: ECF ↑ ICF ↓

ECF NaCl loss: ECF ↓ ICF ↑

25

Gain or loss of isotonic fluid?

No change in fluid osmolarity

Change in ECF volume only.

26

Regulation of ECF volume is vital for?

Long term regulation of blood pressure.

27

Electrolyte balance

Why is it important? (2)

rates of gain = rates of loss

Important for two reasons:

1) Total electrolyte concentrations can directly affect water balance (via changes in osmolarity)

2) The concentrations of individual electrolytes can affect cell function

Na+ and K+ are particularly important

28

Where is Na+ mainly present?

Is this ion a major determinant of ECF volume?

ECF.

Therefore it is a major determinant of ECF volume (water follows salt)

Vital to regulate Na+

29

>95% of which ion is intracellular?

Small leakages, or increased cellular uptake of this ion may lead to?

K+

Important in cell membrane potential

Muscle weakness --> paralysis

Cardiact irregularities --> cardiac arrest.

Must be closely monitored

30

Salt imbalance is manifested as?

Changes in ECF volume.

31

Recommended maximum salt intake per day?

6g.

32

Primary function of the kidneys?

Regulate volume, composition and osmolarity of the body fluids.

Controlled excretion of ions/water/other substances.

33

Structure of the kidney

• Outer renal CORTEX - granulated appearance
• Inner renal MEDULLA - striated appearance
• Renal pyramid
• Minor and major calyces.
• Renal pelvis
• Ureter

34

Functional unit of the kidney

Nephrons

~ 1 million in each kidney

35

Functional mechanism of the nephrons

1. Filtration
2. Reabsorption
3. Secretion

36

How much of cardiac output does the kidney receive?

~25%

37

Types of nephron (2)

1. Cortical nephron (80%)
2. Juxtamedullary nephron (20%)

38

How thick are the tubes of the nephron?

1 cell thick.

39

Blood supply of the nephron

Renal artery --> Afferent arteriole --> glomerulus --> Efferent arteriole --> Peritubular capillaries

40

Through which blood vessels are substances reabsorbed or secreted?

Peritubular capillaries

41

Bowman's capsule

Cup like sack at beginning of tubular component of a nephron.

Comes into close contact with glomerular capillary.

Plasma crosses to form tubular fluid.

--> proximal tubule --> loop of henge --> distal tubule --> collecting duct --> ureter

42

Initial fluid in the tubular component of the nephron is composed of?

After it enters the tubes, what is the fluid then known as?

Plasma.

Then known as TUBULAR FLUID

43

Differences between cortical (CO) and juxtamedullary (JM) nephron?

which produces a more concentrated urine?

• JM loop of henge is a lot longer
• JM don't have peritubular capillaries
• JM have VASA RECTA
• JM produces more concentrated

• CO has a short loop of henge
• Possess peritubular capillaries

44

***** Diameter of afferent arteriole is larger than the efferent arteriole's. Why? *****

Keeps glomerular capillary blood pressure constant due to the "back-dating" of blood in the capillaries.

45

Contraction of smooth muscle wall of afferent arteriole leads to

Narrow diameter --> reduce amount of blood going to glomerulus

Relaxation --> increased blood flow to capillary

46

Inner layer of Bowman's capsule is composed of what cell?

Podocyte.

Wrap around capillaries of glomerulus.

"Foot-like" extensions.

Interdigitate with extensions from neighbouring cell.

Gaps formed between adjacent podocytes are known as filtration SLITS

47

Gaps formed between adjacent podocytes are known as?

Filtration Slits

48

Why is there more filtration in glomerulus compared to other sites in the body?

Gaps between endothelial cells in the glomerulus are a lot larger ==> more filtration.

49

Juxtaglomerular apparatus

What cells form the juxtaglomerular apparatus

Specialised structure formed by the distal convoluted tube and the glomerular afferent arteriole.

• Granular cells - secrete RENIN
• Macula densa - detect/respond to levels of NaCl in the tubule

50

What do granular/juxtaglomerular cells do?

Secrete Renin when blood pressure in arteriole falls.

51

Macula densa function

detect/respond to levels of NaCl in the tubule

In response to elevated sodium, the macula densa cells trigger contraction of the afferent arteriole, reducing flow of blood to the glomerulus and the glomerular filtration rate

52

Extraglomerular mesangial cells

Function remains unclear.

53

What is urine

Modified filtrate of the blood

54

Renal processes

1. Glomerular filtration
2. tubular reabsorption
3. Tubilar secretion

55

20% of the plasma that enters the glomerulus is?

Filtered.

80% of the plasma that enters the glomerulus is not filtered and leaves through the efferent arteriole.

56

Renal tubule acts as a conveyor belt...

substances are added or removed as urinary filtrate moves from proximal to distal end.

57

Rate of excretion for any substance =

Rate of filtration + rate of secretion + rate of reabsorption

58

Rate of filtration of X =

Mass of X filtered into Bowman's capsule per unit time.

i.e. Rate of filtration of X = [X]plasma x GFR.

59

What is GFR

Normal value of GFR?

Glomerular filtration rate.
Rate at which protein-free plasma is filtered from the glomeruli into the bowman's capsule per unit time.

GFR = Kf x net filtration pressure.

Kf is the filtration coefficient - how "holey" the glomerular membrane is.

125ml/minute

60

Rate of excretion of X =

[X]urine x Urine production rate

61

Rate of reabsorption o X =

Rate of filtration of X - rate of excretion of X

62

Rate of secretion of X =

Rate of excretion of X - rate of filtration of X

63

If rate of filtration is greater than rate of excretion, what has occurred?

Net secretion.

64

Rate of filtration > rate of excretion

net reabsorption has occurred

65

Rate of urine production?

1ml/min

66

Filtration barriers of the glomerulus (3)

1. Glomerular capillary endothelium (barrier to RBC)

2. Basement membrane (basal lamina) (plasma protein barrier)

3. Slit processes of podocytes (plasma protein barrier)

67

Filtration Slits are formed between?

Adjacent podocytes' interdigitating processes.

68

How many layers must the fluid pass through from the glomerulus to the Bowman's capsule?

3.

1. Endothelial cell/pores
2. Basement membrane (negatively charged)
3. Podocyte slits

69

Electrical charge of the basement membrane of the glomerulus

Negative

Repels large plasma proteins.

70

Forces that comprise net filtration pressure (4)

Glomerular capillary blood pressure (BPGC) - 55mmHg

Capillary oncotic pressure
(COPGC) (i.e. proteins in the blood exerting a force) - 30mmHg

Bowman’s Capsule hydrostatic (fluid) pressure
(HPBC) - 15mmHg

Bowman’s Capsule oncotic pressure
(COPBC) - 0 mmHg

Net filtration = (55+0) - (15+30) = 10mmHg

71

Is filtration in the kidney active or passive?

Passive.

72

Largest/most important hydrostatic pressure? Main determinant of GFR.

Is it constant along the length of the capillary

Glomerular capillary blood pressure.

Remains constant along entire length of capillary

73

Why is oncotic pressure of bowman's capsule 0?

There should not be any proteins in Bowman's capsule.

74

Presence of plasma proteins (i.e. capillary oncotic pressure) does what

Tries to attract fluid from the Bowman's capsule back into the capillary

75

Increased GFR leads to (plasma, urine)

Filtering more plasma

Producing more urine

76

Decreased GFR leads to (plasma, urine)

Filtering less plasma, producing less urine

77

Regulation of renal blood flow and GFR (2)

1. Extrinsic regulation of GFR
- sympathetic control via baroreceptor reflex

2. Autoregulation of GFR (intrinsic)
- a) myogenic mechanism
- b) tubuloglomerular feedback mechanism

78

If arterial blood pressure increases thereby increasing...

Vasodilation

Blood flow to the glomerulus.

Increases glomerular capillary blood pressure

Increases net filtration pressure

Increases GFR

79

If arterial blood pressure falls, then...

Vasoconstriction

Glomerular capillary pressure decreases

Net filtration decreases

GFR decreases

80

Autoregulation in the kidneys prevents?

Short term changes in systemic arterial pressure affecting GFR

Renal Blood flow and GFR are protected from changes in MABP over wide range of MABP.

81

Can extrinsic control override intrinsic control?

Yes.

82

Myogenic autoregulation

If vascular smooth muscle is stretched (i.e. arterial pressure is increased), it contracts thus constricting the arteriole

83

Tubuloglomerular feedback

Involves the juxtaglomerular apparatus (mechanism remains unclear)

If GFR rises, more NaCl flows through the tubule leading to constriction of afferent arterioles

If there is increased salt in the blood, macula densa releases vasoactive chemical messengers, causing contraction of smooth muscle within wall of afferent arteriole and thus reducing GFR.

84

When would there be an increase in Bowman's capsule fluid pressure?

Kidney stones.

Opposes net filtration, decreases GFR.

85

Diarrhoea would cause an increase in

Capillary oncotic pressure

therefore a decrease in GFR.

86

Severely burned patients would lead to ...

Decreased capillary oncotic pressure

Burn patients lose/leak plasma proteins at site of burn.

Increased GFR.

87

Decreased Kf (decreased filtration coefficient)

Decreased GFR.

88

Plasma clearance

Equation.

• A measure of how effectively the kidneys can ‘clean’ the blood of a substance

• Equals the volume of plasma completely cleared of a particular substance per minute

• Each substance that is handled by the kidney will have it’s own specific plasma clearance value

Clearance of substance X = rate of excretion of X ÷ plasma concentration of X

i.e.

= ([X]urine x Urine flow rate)/ [X]plasma

in ml/min.

89

Inulin clearance is equal to

GFR.

• Freely filtered at glomerulus.
• Neither absorbed nor secreted
• Not metabolised by kidney
• not toxic
• easily measured in urine and blood

125ml of inulin-free plasma is returned to the circulation per minute.

90

Which substance is used to determine GFR in patients?

Creatinine.

91

Clearance of a substance which is filtered, completely reabsorbed and not secreted?

(need a number)

example of a substance.

Clearance = 0

e.g. Glucose

Also applies to a substance that is not filtered and not secreted.

92

substances which are filtered, partly reabsorbed and not secreted

Clearance < GFR

e.g. Urea

93

For substances which are filtered, secreted but not reabsorbed

Clearance > GFR

e.g. H+ ions.

All of the filtered plasma is cleared of a substance, and the peritubular plasma from which the substance is secreted, is also cleared

94

How much of all urea is reabsorbed back into the bloodstream?

50%

Other 50% is excreted.

95

If clearance < GFR (inulin clearance) then substance is REABSORBED

If clearance = GFR then substance is neither reabsorbed nor secreted

If clearance > GFR then substance is SECRETED into tubule

--

96

What substance is used to clinically calculate Renal Plasma Flow (RPF)?

Why

Para-amino hipputric acid (PAH) - an exogenous organic anion.

PAH is
a) freely filtered at glomerulus

b) secreted into the tubule (not reabsorbed)

c) completely cleared from plasma

i.e. all PAH in the plasma that escapes filtration is secreted from the peritubular capillaries.

97

Normal value of renal plasma flow?

650ml/min

= PAH clearance

98

Clearance marker - GFR marker and RPF marker

What properties should they have?

1. Non toxic
2) Inert
3. Easy to measure

a) A GFR marker should be filtered freely; NOT secreted or reabsorbed

b) An RPF marker should be filtered and completely secreted (i.e. no reabsorption)

99

Filtration fraction

Fraction of plasma flowing through the glomeruli that is filtered into the tubules.

= GFR/RPF

= 20% of plasma that enters the glomeruli is filtered.

100

Renal blood flow (RBP) equation

Renal plasma flow x (1/1-Haematocrit)

= 650 x 1.85

= ~1200ml/Min

roughly 24% of cardiac output.

101

Where does the vast majority of reabsorption occur in the nephron?

Proximal convoluted tubule

102

Roughly how many times is the plasma filtered per day?

65 times.

103

How much filtered fluid is reabsorbed in the proximal tubule per minute?

~80ml/min.

Meaning there is a 45ml.min flow into Loop of Henle

(125-80)

104

Is the fluid reabsorbed in the proximal tubule the same osmolarity as the filtrate?

Yes it is iso-osmotic

105

Substances reabsorbed and secreted in the proximal tubule

Reabsorbed
- sugars
- amino acids
- phosphate
- sulphate
- lactate

Secreted
- h+
- Hippurates
- Neurotransmitters
- Bile pigments
- Uric acid
- Drugs
- Toxins

106

Steps that constitute TRANSCELLULAR tubular reabsorption (5)

Substance has to

1. Make it across the basal membrane

2. Make it through the cell without being metabolised

3. Make it past the apical membrane e

4. make it through the lateral space/interstiital fluid

5. make its way across endothelial wall of capillary

107

Primary active transport

Energy is directly required to operate the carrier and move the substrate against its concentration gradient

108

Secondary active transport

The carrier molecule is transported coupled to the concentration gradient of an ion (usually Na+)

109

Facilitated diffusion

Passive carrier-mediated transport of a substance down its concentration gradient

110

Na+ reabsorption in the proximal convoluted tubule is achieved by?

An energy dependent Na+K+ ATPase transport mechanism at the basolateral membrane

111

Iso-osmotic fluid reabsorption across leaky proximal tubule epithelium is due to?

1) Standing osmotic gradient
2) Oncotic pressure gradient

Sodium ions leave the cell at the basolateral membrane via the sodium potassium pump.

Net movement of sodium sets up an electrchemcial gradient for the reabsorption of chloride (negative) paracellularly

Therefore we absorb NaCL

Water then follows the salt.

Water and salt enter peritubular capillary

112

How much glucose is reabsorbed by the proximal tubule?

100%

Glucose Leaves cell at basal membrane down its concentration gradient

It also sets up an osmotic gradient which water follows.

113

Renal threshold for glucose reabsorption?

10-12mmol/L

(normally humans have 4-5mmol so this is not a problem. it is an issue in diabetics)

114

Transport maximum (Tm) of glucose

2 mmol/min

Any glucose not being reabsorbed is excreted in the urine

115

Can secretory/reabsorption mechanisms become saturated?

Yes they can.

116

Percentage of all salt and water reabsorbed in the Proximal tubule?

Glucose and amino acids

~67%

100% of amino acids and glucose

117

How is Chloride reabsorbed in the proximal convoluted tubule? (which route)

Paracellularly

Na+ drives this reabsorption due to electrochemical gradient (negative chloride attracted by positive sodium ion)

118

Function of the Loop of Henle

Generates a cortico-medullary solute concentration gradient

This enables the formation of hypertonic (concentrated) urine

119

Fluid flow in the Loop of Henle is describe as?

Countercurrent flow

The loop functions as a countercurrent multiplier.

The loop and vasa rectae establish a hyper-osmotic medullary interstitial fluid.

120

Ascending Limb of the loop of henle

what is being absorbed?
what substance is this section of the loop of henge impermeable to?

> Na+ and Cl- are being reabsorbed along the entire length of the Ascending limb

-- thick upper AL: this is achieved by active transport
-- thin, lower AL: passive

> Impermeable to water

121

Descending Limb of the loop of henle

what is not reabsorbed?
Highly permeable to?

Does NOT reabsorb NaCl

Highly permeable to water

122

Na+ reabsorption in the thick ascending limb of the Loop of Henle.

What kind of transporter is present on the basal membrane?

What does this transporter transport?

Is there an electric gradient created?

Na+ and Cl- are reabsorbed in the thick ascending limb, but this region is impermeable to water.

Triple co-transporter is present on the basal membrane

Transports 1 Na+; 1 K+; 2 Cl- (2 positive and 2 negative charges = no current/electro gradient created)

123

Which drugs block the triple co-transporter?

Loop diuretics.

124

Potassium recycling in ascending limb

K comes in via triple co transporter, and moves down concentration gradient on apical membrane out of the cell.

Comes back into cell via Na+ K+ co transporter --> Na+ absorbed into interstitial fluid

Potassium joins chloride ions in a symport so that Cl- is also absorbed into interstitial fluid

Potassium recycled back into cell.

125

Triple co-transporter pumps solute from the thick ascending limb of Loop of Henle... 5 steps

shitty question I know

1. Solute removed from lumen of ascending limb (water cannot follow)

2. Tubular fluid is diluted and osmolality of interstitial fluid is raised

3. Interstitial solute cannot enter the descending limb

4. Water leaves the descending limb by osmosis

5. Fluid in the descending limb is concentrated

126

What kind of fluid moves on to the distal tubule? (hypo/hyper/iso)

Hypotonic.

127

Is there a decrease/increase of osmolality from beginning of loop of henge to the end of it?

There is a decrease in osmolality.

128

What 2 things are the main contributors to the corticomedullary concentration gradient?

Salt and urea

Distal tubule not permeable to urea.

129

Purpose of countercurrent multiplication?

Concentrate medullary interstitial fluid.

This enables the kidney to produce urine of different volume and concentration according to the amounts of circulating antidiuretic hormone (ADH = vasopressin)

130

Vasa rectae

Run alongside the long loop of henge of juxtamedullary nephrons.

Freely permeable to NaCl and water.

Capillary blood equilibrates with interstitial fluid cross the leaky endothelium

Blood osmolality rises as it dips down into the medulla (i.e. water loss, solute gained)

Blood osmolality falls as it rises back up into the cortex (water gained, solute lost)

Acts as a countercurrent exchanger.

Passive exchange across endothelium preserves medullary gradient - blood equilibrates at each layer.

Ensures that the solute is not washed away.

131

Essential blood flow through medulla tends to wash away NaCl and urea.
To minimise this problem (3)

1. Vasa recta capillaries follow hairpin loops

2. Vasa recta capillaries freely permeable to NaCl and water

3. Blood flow to vasa recta is low (few juxtamedullary nephrons)

132

High medullary osmolarity in presence of ADH produces?

Hypertonic urine?

133

Tubular fluid leaving the Loop of Henle entering the distal tubule is ____osmotic to plasma?

Hypo-osmotic (100 mosmol/L)

134

What does the distal tubule empty into?

Collecting duct

135

The collecting duct is bathed by progressively _________ concentrations of surrounding interstitial fluid as it descends through the medulla

Increasing concentrations (300-1200 mosmol/L)

136

Distal tubule and collecting ducts are major sites for?

Regulated by?

Regulation of ion and water balance

Regulated by hormones

137

Which hormones act in the distal tubules/collecting ducts? (4)

1. ADH (incr. water reabsorption)

2. Aldosterone (Na+ reabsorption; H+/K+ secretion)

3. Atrial natriuretic hormone (decreased Na+ reabsorption)

4. Parathyroid hormone (Ca2+ increased, decreased PO43- reabsorption)

138

Distal tubule has low permeability to?

Therefore?

Water and urea

Urea is concentrated in the tubular fluid (helps establish osmotic gradient in the medulla)

139

Distal tubule is made up of 2 sections - what are they referred to as?

"Early" and "late" distal tubule.

140

Early distal tubule transports and reabsorbs which ions?

Transport//
Na+
K+
2CL-

Reabsorption//

NaCl

141

Late distal tubule secretes/reabsorbs?

Reabsorption

Ca2+
Na+ (basal state)
K+ (basal state)

Secretion//

H+

K+ secretion when K+ secretory cells are activated.

142

Collecting duct is split into?

Early and late

143

Late collecting duct has (re ions; 2 things)

1. low ion permeability
2. permeability to water and urea influenced by ADH

144

Where is ADH secreted from?

Posterior pituitary

145

Where is ADH synthesised?

Octapeptide synthesised by the supraoptic and paraventricular nuclei in hypothalamus.

146

Size of ADH peptide?

Octapeptide.

147

Effects of ADH on collecting duct?

Increases permeability of luminal embrace to H2O by inserting new water channels (aquaporins)

148

Water channels formed by ADH stimulation are known as?

Aquaporins

149

Direction of water movement in presence of maximal ADH?

Water moves from the collecting duct lumen along the osmotic gradient into the medullary interstitial fluid

-> hypertonic urine formation.

Tubular fluid equilibrates with interstitial via aquaporins

150

In presence of minimal ADH, the collecting duct is ________ to water?

Impermeable to water.

No water reabsorption

Large, volume of dilute urine

151

Most important stimulus for ADH release?

Other stimuli

Hypothalamic osmoreceptors

Activation of left atrial stretch receptors (decreased atrial pressure --> increased ADH release) -- large changes in volume detected.

Stimulation of stretch receptors in upper GI tract exerts feed-forward inhibition of ADH

Nicotine stimulates ADH release

Alcohol inhibits ADH release

152

Effect of nicotine on ADH?

Stimulates ADH release.

153

Aldosterone - what kind of hormone is it?

Secreted from?

Steroid hormone.

Secreted by the adrenal cortex

154

When is aldosterone secreted? (2)

1. In response to rising [K+] or falling [Na+] in the blood (juxtaglomerular apparatus)

2. Activation of the RAA system.

155

Function of aldosterone

Stimulates Na+ reabsorption and K+ secretion

therefore na+ retention contributes to an increased blood volume and pressure

156

Where is majority of K+ is reabsorbed?

Proximal tubule

When aldosterone absent, rest is reabsorbed in the distal tubule.

157

Renin release control (3)

Released from granular cells in juxtaglomerular apparatus

1. Reduced pressure in afferent arteriole
-- more renin released, more Na+ reabsorbed, blood volume increased, BP restored.


2. Macula densa cells sense the amount of NaCl in the distal tubule
-- if NaCl reduced, more renin released, more Na+ reabsorbed

3. Increased sympathetic activity as a result of reduced arterial BP
-- granular (renin secreting) cells directly innervated by sympathetic nervous system, causes renin release.

158

Where does aldosterone increase Na+ reabsorption?

Distal tubule and collecting duct

159

Abnormal increase in RAA system can cause?

Hypertension

Fluid retention associated with congestive heart failure

160

Treatment of abnormal increase in RAA system?

Low salt diet

Diuretics (loop diuretics)

161

Atrial Natriuretic Peptide (ANP) - produced by?

released when

Cardiac cells, stored in atrial muscle cells.

released when these cells are mechanically stretched due to an increase in circulating plasma volume

162

What does ANP promote?

Excretion of Na+ and diuresis

Decreases plasma volume

Lowers blood pressure

163

Micturition is governed by 2 mechanisms - what are they

1. Micturition reflex

-- urinary bladder can accommodate up to 250-400ml of urine before stretch receptors within its wall initiate the micturition reflex. -

-- Causes INVOLUNTARY emptying.

-- simultaneous bladder contraction and opening of both internal and external urethral sphincters

2. voluntary control

-- micturition can be VOLUNTARILY prevented by deliberate tightening of the external sphincter and surrounding pelvic diaphragm

164

Regulation of erythropoiesis

Kidney produces erythropoietin --> stimulates stem cells in bone marrow --> produces RBCs --> increases 02 supply in tissues

if too low --> kidney produces erythropoietin

165

Is venous blood more acidic or alkaline than arterial blood?

More acidic

(presence of Co2)

166

Average pH of blood?

7.4

167

Fluctuations in [H+] can... (3)

Alter nerve, enzyme and K+ activity.

1. alter nerve activity. Acidosis can lead to depression of the CNS. Alkalosis can lead to overexcitability of the peripheral NS and later than CNS

2. [H+] exerts a marked influence on enzyme activity

3. Changes in [H+] influence K+ levels in the body

168

H+ is added from 3 sources (3)

1. Carbonic acid formation
2. Inoragnic acids produced during breakdown of nutrients
3. Organic acids resulting from metabolism


Input must equal output to maintain a constant H+ in body fluids

169

Strong acids dissociate ______ in solution

Completely dissociate

170

Weak acids dissociate ______ in solution

Partially dissociate

171

If acid [H+] is added to this system, equilibrium shifts towards...

the left

Protons are mopped up by A-, leading to formation of more HA

172

If a base is added to the system, equilibrium shifts to

The right

Base is tied up by combining with H+, allowing more HA to dissociate.

HA falls, A- rises.

the rise in pH (fall in [H+]) has been limited (buffered) by further dissociation of HA

173

Most important physiological buffer?

CO2-HCO3 buffer.

174

HCO3- concentration is controlled by which organ?

The kidneys

175

PCO2 is controlled by the?

Lungs

176

Normal arterial PCO2?

0.03

177

Normal HCO3- concentration in plasma?

24 mmol/L

178

Role of kidney in control of [HCO3-] plasma (2)

1. Variable reabsorption of filtered HCO3-

2. Kidneys can add "new" HCO3- to the blood

i.e. [HCO3-] in renal vein > [HCO3-] renal artery

179

Mechanism of [HCO3-] reabsorption in the proximal tubule

HCO3- disappears from the tubular fluid and appears in the interstitial fluid.

However, the same HCO3- ion does not cross the epithelium. (it is broken down into CO2 and H2O/converted into carbonic acid in the cell, and then reformed and exits the epithelial cell into the interstitial fluid)

180

When concentration of HCO3 in tubular fluid is low (reabsorption), secreted H+ combines with?

Phosphate

Therefore there is a net gain of HCO3- as the hydrogen phosphate (HPO4^2-_ basic) has mopped up the hydrogen ions and excreted it. therefore there is HCO3 "free", and it then becomes new.

181

How can amount of H+ be measured?

Titratable acid.

Measure amount fo strong base (NaOH) added to titrate the urine pH back to 7.4.

182

Max amount of titratable acid in a day?

40mmol

183

If 40mmol/day is added as titratable acid, how much "new" HCO3- has been gained?

40mmol (1 for 1)

184

What other substance acts as a buffer?

Ammonia

Combines with H+ to form ammonium ion.

185

H+ secretion by tubule does 3 things

A. Drives reabsorption of HCO3-

B. Forms "acid phosphate"

C. Forms ammonium ion