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Water, Electrolyte, and Acid-Base Balance - PowerPoint PPT Presentation


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Water, Electrolyte, and Acid-Base Balance. Function of Water : Most of cellular activities are performed in water solutions. 4% TBW. 40% TBW. Body Fluid . - makes up ~60% of total body weight (TBW) - distributed in three fluid compartments. . 16% TBW. 4% TBW. 40% TBW.

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slide2

Function of Water:

Most of cellular activities are performed in water solutions.

slide3

4% TBW

40%TBW

Body Fluid

- makes up ~60% of total body weight (TBW)

- distributed in three fluid compartments.

16% TBW

slide4

4% TBW

40%TBW

Fluid is continually exchanged between the three compartments.

16% TBW

slide5

4% TBW

40%TBW

Exchange between Blood & Tissue Fluid

  • - determined by four factors:
    • capillary blood pressure
    • plasma colloid osmotic pressure
    • interstitium Hydrostatic Pressure
    • Interstitium colloid osmotic pressure

16% TBW

slide6

4% TBW

40%TBW

Exchange between Blood & Tissue Fluid

- not affected by electrolyte concentrations

- Edema = water accumulation in tissue fluid

16% TBW

slide7

4% TBW

40%TBW

Exchange between Tissue Fluid & Intracellular Fluid

  • - determined by two:
  • 1) intracellular osmotic pressure
    • electrolytes
  • 2) interstitial osmotic pressure
  • electrolytes

16% TBW

slide8

Water Gain

Water is gained from three sources.

1) food (~700 ml/day)

2) drink – voluntarily controlled

3) metabolic water (200 ml/day) --- produced as a byproduct of aerobic respiration

slide9

Routes of water loss

1) Urine – obligatory (unavoidable) and physiologically regulated, minimum 400 ml/day

2) Feces -- obligatory water loss, ~200 ml/day

3) Breath – obligatory water loss, ~300 ml/day

4) Cutaneous evaporation -- obligatory water loss, ~400 ml/day

5) Sweat – for releasing heat, varies significantly

slide10

Regulation of Water Intake

- governed by thirst.

blood volume and osmolarity

peripheral volume sensors central osmoreceptors

hypothalamus

thirst felt

slide11

Regulation of Water Output

- The only physiological control is through variations in urine volume.

- urine volume regulated by hormones

slide12

1) ADH

dehydration

blood volume and/or osmolarity

hypothalamic receptors / peripheral volume sensors

posterior pituitary to release ADH

 H2O reabsorption

Water retention

slide13

2) Atrial Natriuretic Factor

 blood volume

atrial volume sensors

atria to release ANF

inhibits Na+ and H2O reabsorption

 water output

slide14

Dehydration

  • - decrease in body fluid
  • Causes
      • the lack of drinking water
      • 2) excessive loss of body fluid due to:
          • overheat
          • diabetes
          • overuse of diuretics
          • diarrhea
slide15

Edema

  • - the accumulation of fluid in the interstitial spaces
  • caused by:
    • increased capillary filtration,
    • or
    • 2) reduced capillary reabsorption, or
    • 3) obstructed lymphatic drainage
slide18

Major cations

    • Na+
    • K+
    • Ca++
    • H+
  • Major anions
    • Cl-
    • HCO3-
    • PO4---
slide19

Distribution of Electrolytes

Na+

K+

Ca++

Cell

PO4---

Cl-

Extracellular

space

slide20

Na+

K+

Ca++

Cell

PO4---

Cl-

  • SodiumNa+
  • Functions
  • - involved in generating action membrane potential of cells
  • make a major contribution to extracellular osmolarity.
slide21

Regulation of plasma Na+

  • Aldosterone

Na+

  • plasma Na+

 aldosterone

  • renal Na + excretion

 plasma Na +

plasma

slide22

Renin-angiotensin-II

renin

  • angiotensin-II

 aldosterone

 renal Na+ excretion

 plasma Na+

Na+

plasma

slide23

3) ADH

increases water reabsorption in kidneys

water retention

dilute plasma Na+

H2O

Na+

plasma

slide24

Atrial Natriuretic Factor

  • inhibits renal reabsorption of Na+ and H2O and the excretion of renin and ADH
  • eliminate more sodium and water

 plasma Na +

Na+

plasma

Na+

slide25

Sodium imbalance

    • hypernatremia
        • plasma sodium > 145 mEq/L,
    • hyponatremia
    • plasma sodium < 130 mEq/L
slide26

Na+

K+

Ca++

Cell

PO4---

Cl-

Potassium

Functions

- the greatest contributor to intracellular osmosis and cell volume

- determines the resting membrane potentials

- an essential cofactor for protein synthesis and some other metabolic processes.

K+

slide27

Regulation of Potassium

  • by aldosterone
    • Aldosterone
    • stimulates K+
    • secretion by the kidneys
    •  Plasma K+

K+

plasma

K+

slide28

Potassium Imbalance

    • hyperkalemia (> 5.5 mEq/L)
    • hypokalemia (< 3.5 mEq/L)
slide29

Na+

K+

Ca++

Cell

PO4---

Cl-

Chloride

- makes a major contribution to extracellular osmolarity

- required for the formation of stomach acid (HCl)

slide30

Regulation of Cl–

  • No direct regulation
  • indirectly regulated as an effect of Na+ homeostasis. As sodium is retained or excreted, Cl– passively follows.
  • Chloride Imbalance
      • hyperchloremia (> 105 mEq/L)
      • hypochloremia (< 95 mEq/L).
slide31

Na+

K+

Ca++

Cell

PO4---

Cl-

Calcium

slide32

Functions of Ca++

    • - lends strength to the skeleton
slide33

Functions of Ca++

    • - lends strength to the skeleton
    • - activates muscle contraction

[ Ca++ ]i

Contraction

Excitation

(Action Potentials)

(shortening)

slide34

Functions of Ca++

    • - lends strength to the skeleton
    • - activates muscle contraction
    • - serves as a second messenger for some hormones and neurotransmitters
slide35

Functions of Ca++

    • - lends strength to the skeleton
    • - activates muscle contraction
    • - serves as a second messenger for some hormones and neurotransmitters
    • - activates exocytosis
    • of neurotransmitters and
    • other cellular secretions
slide36

Functions of Ca++

    • - lends strength to the skeleton
    • - activates muscle contraction
    • - serves as a second messenger for some hormones and neurotransmitters
    • - activates exocytosis of neurotransmitters and other cellular secretions
    • - essential factor
    • in blood clotting.
slide37

Functions of Ca++

    • - lends strength to the skeleton
    • - activates muscle contraction
    • - serves as a second messenger for some hormones and neurotransmitters
    • - activates exocytosis of neurotransmitters and other cellular secretions
    • - essential factor in blood clotting.
    • - activates many cellular
    • enzymes
slide38

Dynamics of Calcium

Ca++

Ca++

Ca++

plasma

Ca++

slide39

Regulation of calcium

    • 1) parathyroid hormone (PTH):
slide40

Regulation of calcium

    • 1) parathyroid hormone (PTH):
      • - dissolving Ca++ in bones
      • - reducing renal excretion of Ca++

Ca++

Ca++

plasma

slide42

2) calcitonin (secreted by C cells in thyroid gland):

depositing Ca++ in bones

Ca++

Ca++

plasma

slide43

3) calcitrol (derivative of vitamin D):

- enhancing intestinal absorption of Ca++ from food

Ca++

Ca++

plasma

Ca++

slide44

Calcium imbalances

      • hypocalcemia (< 4.5 mEq/L)
      • hypercalcemia (> 5.8 mEq/L).
slide45

Phosphates

  • needed for the synthesis of:
      • ATP, GTP
      • DNA, RNA
      • phospholipids
slide46

Regulation of Phosphate

  • by parathyroid hormone
  • PTH
  • increases renal excretion of phosphate
  • decrease plasma phosphate
  • - no real phosphate imbalances

PO4---

plasma

PO4---

slide48

Acid

An acid is any chemical that releases H+ in solution.

Base

A base is any chemical that accepts H+.

slide49

pH

is the negative logarithm of H+ concentration, and an indicator of acidity.

  pH = - log [H+ ]

Example: [H+ ] = 0.1 M = 10 –7 M

slide50

pH

is the negative logarithm of H+ concentration, and an indicator of acidity.

  pH = - log [10 –7]

= 7 log 10 = 7

Example: [H+ ] = 0.1 M = 10 –7 M

slide51

pH

is the negative logarithm of H+ concentration, and an indicator of acidity.

  pH = - log [10 –8]

= 8 log 10 = 8

Example: [H+ ] = 0.01 M = 10 –8 M

0.01 M [ H+]=pH 8

 [ H+]= pH

0.1 M [ H+]=pH 7

 [ H+]=  pH

slide52

Normal functions of proteins (especially enzymes) heavily depend on an optimal pH.

pH7.35-pH7.45

slide53

Regulation of acid-base balance

1) Chemical Buffers

2) Respiratory Control of pH

3) Renal Control of pH

slide54

Buffer

is any mechanism that resists changes in pH.

slide55

pH 3.0

pH 6.8

acid

acid

H2O

pH 7.0

Buffer

pH 7.0

slide56

pH 11.0

pH 7.2

base

base

H2O

pH 7.0

Buffer

pH 7.0

slide57

Chemical Buffers

There are three major buffers in body fluid.

1) The Bicarbonate (HCO3-) Buffer

2) The Phosphate Buffer

3) The Protein Buffer

slide58

The Bicarbonate (HCO3-) Buffer System

  • H + HCO3- H2CO3 H2O + CO2
  • - reversible depending on the equilibrium between the substrates and products.
  • - The lungs constantly remove CO2.
slide59

H+ HPO42–H2PO4– + H

H3PO4

2) The Phosphate Buffer System

slide60

3) The Protein Buffer System

  • more concentrated than either bicarbonate or phosphate buffers
  • - accounts for about three-quarters of all chemical buffering ability of the body fluids.
  • The carboxyl groups release H+ when pH rises and amino groups bind H+ when pH falls.

H+

H+

NH2-CH2-CH2 CH2-CH2-COOH

slide61

Properties of Chemical Buffers

    • - respond to pH changes within a fraction of a second.
    • - Bind to Hbut can not remove Hout of the body
    • - Limited ability to correct pH changes
slide62

1)

H + HCO3- H2CO3 H2O + CO2

10

10

10

10

10

2)

H + HCO3- H2CO3 H2O + CO2

20

10

10

10

10

3)

H + HCO3- H2CO3 H2O + CO2

10

0

20

10

10

H2CO3 H2O + CO2

10

20

20

slide63

H + HCO-H2CO3 CO2 + H2O

Respiratory Control of pH

H + HCO-H2CO3 CO2 + H2O

slide64

 pH

  • stimulate peripheral/central chemoreceptors
  •  pulmonary ventilation
  • removal of CO2 and  pH

H + HCO3-

H2CO3

H2O + CO2

slide65

Limit to respiratory control of pH

    • The respiratory regulatory mechanism cannot remove H+ out of the body. Its efficiency depends on the availability of HCO3-.

H + HCO3- H2CO3 H2O + CO2

slide66

Renal Control of pH

  • The kidneys can neutralize more acid or base than both the respiratory system and chemical buffers.
  • a. Renal tubules secrete hydrogen ions into the tubular fluid, where most of it combines with bicarbonate, ammonia, and phosphate buffers.
  • b. Bound and free H+ are then excreted in urine.
slide67

The kidneys are the only organs that actually expel H+ from the body. Other buffering systems only reduce its concentration by binding it to another chemical.

  • 3. Tubular secretion of H+ continues as long as a sufficient concentration gradient exists between the tubule cells and the tubular fluid.
slide68

Disorders of Acid-Base Balance

  • Acidosis: < pH 7.35 , Alkalosis: > pH 7.45
    • Mild acidosis
    • depresses CNS, causing
    • confusion, disorientation, and coma.
    • Mild alkalosis
    • CNS becomes hyperexcitable.
      • Nerves fire spontaneously and overstimulate skeletal muscles.
    • - Severe acidosis or alkalosis is lethal.
slide69

Respiratory vs Metabolic Cause

  • Respiratory acidosis / alkalosis
    • - caused by hypoventilation or hyperventilation

Initial change

H + HCO- H2CO3 H2O + CO2

Emphysema

slide70

Respiratory acidosis / alkalosis

    • - caused by hypoventilation or hyperventilation
  • Metabolic acidosis or alkalosis
  • - result from any causes but respiratory problems

Diabetes

 production of organic acids

metabolic acidosis

Chronic vomiting

loss of stomach acid

metabolic alkalosis