11 Air & Elektrolit

8/12/2019 11 Air & Elektrolit

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WATER & ELECTROLYTES

Editor:Husnil Kadri

Biochemistry Departement

Medical Faculty Of Andalas University

Padang


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Angiotensin Pathway


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Regulation of Water

The hypothalamic thirst center is

stimulated:

By a decline in plasma volume of 10%15%

By increases in plasma osmolality of 12%

Via baroreceptor input, angiotensin II, and

other stimuli


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Regulation of Water

Thirst is quenched as soon as we begin to

drink water

Feedback signals that inhibit the thirst

centers include:

Moistening of the mucosa of the mouth and

throat

Activation of stomach and intestinal stretchreceptors


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Regulation of Water Loss

Obligatory water losses include:

Insensible water losses from lungs and skin

Water that accompanies undigested food

residues in feces

Obligatory water loss reflects the fact that:

Kidneys excrete 900-1200 mOsm of solutes

to maintain blood homeostasis

Urine solutes must be flushed out of the body

in water


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Regulation of ADH

Factors that specifically trigger ADH

release include:

prolonged fever; excessive sweating,

vomiting, or diarrhea; severe blood loss;

and traumatic burns.


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Regulation of ADH


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Disorders of Water Balance:

Dehydration

Causes include: hemorrhage, severeburns, prolonged vomiting or diarrhea,

profuse sweating, water deprivation, anddiuretic abuse

Signs and symptoms: cottonmouth, thirst,

dry flushed skin, and oliguria Other consequences include hypovolemic

shock and loss of electrolytes


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Disorders of Water Balance:

Edema

Atypical accumulation of fluid in theinterstitial space, leading to tissue swelling

Caused by anything that increases flow offluids out of the bloodstream or hinderstheir return


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Edema

Hindered fluid return usually reflects an

imbalance in colloid osmotic pressures

Hypoproteinemialow levels of plasma

proteins

Forces fluids out of capillary beds at the

arterial ends

Fluids fail to return at the venous ends

Results from protein malnutrition, liver

disease, or glomerulonephritis


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Edema

Blocked (or surgically removed) lymph

vessels:

Cause leaked proteins to accumulate in

interstitial fluid

Exert increasing colloid osmotic pressure,

which draws fluid from the blood

Interstitial fluid accumulation results in lowblood pressure and severely impaired

circulation


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Electrolyte Balance

Electrolytes are salts, acids, and bases,but electrolyte balance usually refers onlyto salt balance

Salts enter the body by ingestion and arelost via perspiration, feces, and urine


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Sodium in Fluid and Electrolyte

Balance

Sodium salts:Account for 90-95% of all solutes in the ECF

Contribute 280 mOsm of the total 300 mOsmECF solute concentration

Sodium is the single most abundant cation inthe ECF

Sodium is the only cation exerting significantosmotic pressure


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Sodium reabsorption is almost always by

active transport

Na+enters the tubule cells at the luminalmembrane

Is actively transported out of the tubules by a

Na+-K+ATPase pump

Sodium Reabsorption:

Primary Active Transport


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From there it moves to peritubular

capillaries due to:

Low hydrostatic pressure High osmotic pressure of the blood

Na+reabsorption provides the energy and

the means for reabsorbing most othersolutes

Sodium Reabsorption:

Primary Active Transport


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Regulation of Sodium Balance:

Aldosterone

Sodium reabsorption

65% of sodium in filtrate is reabsorbed in the

proximal tubules 25% is reclaimed in the loops of Henle

When aldosterone levels are high, all

remaining Na+is actively reabsorbed


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Regulation of Sodium Balance:

Aldosterone

Adrenal cortical cells are directly

stimulated to release aldosterone by

elevated K+levels in the ECF

Aldosterone brings about its effects

(diminished urine output and increased

blood volume) slowly


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Regulatory Site Of Potassium:

Cortical Collecting Ducts

Less than 15% of filtered K+is lost to urineregardless of need

K+

balance is controlled in the corticalcollecting ducts by changing the amount ofpotassium secreted into filtrate

When K+levels are low, the amount ofsecretion and excretion is kept to aminimum


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Influence of Aldosterone

Aldosterone stimulates potassium ionsecretion by principal cells

In cortical collecting ducts, for each Na+

reabsorbed, a K+is secreted Increased K+in the ECF around the

adrenal cortex causes:

Release of aldosterone Potassium secretion

P t i B l


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Potassium Balance


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Regulation of Calcium and Phosphate

PTH promotes increase in calcium levelsby targeting:

BonesPTH activates osteoclasts to breakdown bone matrix

Small intestinePTH enhances intestinalabsorption of calcium

KidneysPTH enhances calciumreabsorption and decreases phosphatereabsorption

Calcium reabsorption and phosphateexcretion go hand in hand

R l ti f C l i d Ph h t


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Regulation of Calcium and Phosphate

Filtered phosphate is actively reabsorbed inthe proximal tubules

In the absence of PTH, phosphatereabsorption is regulated by its transport

maximum and excesses are excreted in urine High or normal ECF calcium levels inhibit PTH

secretion Release of calcium from bone is inhibited

Larger amounts of calcium are lost in feces andurine

More phosphate is retained


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Influence of Calcitonin

Released in response to rising blood calcium

levels

Calcitonin is a PTH antagonist, but itscontribution to calcium and phosphate

homeostasis is minor to negligible


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H dit di d f t b l t t


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Hereditary disorders of tubular transport


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Disorders of s odium and w ater m etabolism


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Hyponatremia and h ypernatremia


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R f


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Reference

1. Ivkovic, A and Dave, R. Renal review. ppt. 2008

2. Marieb, EN. Fluid, electrolyte, and acid-base balance. ppt.Pearson Education, Inc. 2004

3. Marieb, EN. The urinary system part B. ppt. 2004.

4. Silverthorn, DU. Integrative Physiology II: Fluid and Electrolyte

Balance. Chapter 20, part B. ppt. Pearson Education, Inc. 2004

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