ACID BASE BALANCE IN HUMAN PHYSIOLOGY, Summaries of Physiology

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Acid-base

balance

By- ABHIGYAN

CHAUHAN

Objectiv

es

Basics of Acid-base balance:

• (^) Define: acid and base.
• (^) Explain what is meant by strong and weak acids and bases
• (^) List and identify the names/formulas for the common strong acids and strong bases.
• (^) To explain the role of Henderson-Hasselbalch equation in acid-base regulation

Buffer systems:

• (^) To define buffer system and discuss the role of blood buffers and to explain their relevant roles

in the body

• (^) To describe the role of kidneys in the regulation of acid-base balance
• (^) To describe the role of lungs in the regulation of acid-base balance

What pH represent?

H+ concentration in the blood

What is the normal range of pH?

in general: 0-

in the blood: 7.35-7.

Extracellular fluid (ECF): 7.

What is the type of blood sample should be

taken to measure pH and Why?

Arterial blood sample (not venous),

because it represents the actual contents of

blood such as Oxygen, nutrients.. Etc.

How can we calculate the pH?

pH= 1/H+ concentration log

OR

pH= - log [H+]

Does pH in the body change?

Yes, like exercise body will add some hydrogen

to blood through lactic acid and change pH.

What is the survival range of pH in the blood?

Between 6.8 and 8. More or less will lead to death

When we said it is acidosis or alkalosis?

-pH less than 7.35 (acidosis)

-pH more than 7.45 (alkalosis)

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• (^) Strong acid = HCL (complete dissociation) - Weak acid = Lactic acid,CO2,H2CO3 “Carbonic acid” (Partial dissociation) - Strong base = NaOH (complete dissociation)
• (^) Weak base = NaHCO3,HCO3 (Partial dissociation)

Strong and weak acids and bases

1.Food that contain proteins and lipids are rich in

acids

2.The end cellular metabolism in mitochondria

produced CO2 which source of H+ from the

following reaction:

CO2 + H20 ↔ H2CO3 ↔ H+ + HCO 3

Why acids more than bases in our bodies?

Because it has higher CO2 concentration

than arterial blood

Why venous blood is more acidic than arterial?

-Most enzymes work only in specific pH

(change in pH → enzymes become inactive)

-Change in pH cause disturbance in electrolytes -

Can affect some hormones

• Acidosis can cause depression of synaptic ending

and lead to coma such as a patient with diabetes

ketoacidosis and Hypercalcaemia

-Alkalosis can cause convulsion , muscle twitching,

tetany and hypocalcemia

Why pH tightly regulated and small changes

in pH is a serious condition? -Acids are H+ donors

-Bases are H+ acceptors

What acids and bases?

-Chemical buffer system: (first line)

Buffer system ( immediately )

-Physiological buffer system: (second line)

1.Respiratory system ( from minutes to hours )

2.Renal system ( from hours to days ) The most

effective regulator of pH

Systems that regulate pH

Convert strong acids and bases to weak acids

and bases to maintain blood pH

The component of chemical buffer system

1. Bicarbonate buffer (intracellular and extracellular )
2. Phosphate buffer (intracellular and renal tubule fluid )
3. Protein buffer ( the most important intracellular )

What is the goal of chemical buffer systems?

pH of buffer must be the same or very close to

the pH of sites that buffer work in. to observe

the changes in pH.

The most important feature of chemical buffers

• (^) Bicarbonate buffer

What are the components of bicarbonate buffer

system?

• Sodium bicarbonate : NaHCO3 regulated by

kidney

• Carbonic acid: H2CO3 regulated by lungs through

equation:

CO2 + H2O → H2CO

Why it is the most important extracellular buffer

system?

Because it regulated by kidney and lungs

What is the concentration of HCO3 in the blood

and what it is called?

Its concentration in blood equals = 27mEq/L and is

called alkali reserve.

How bicarbonate buffer work?

We must have acid and base to react with each

other. Then:

How can we calculate blood pH through

bicarbonate buffer?

By Handerson-Hasselbalch equation:

Note that 6.1 represent pH of the buffer not the

blood

Respiratory mechanism

What are the components of system?

The only component regulated here is CO2 (carbon dioxide) which is volatile acids.

It cannot deal with fixed acids such lactic acids that accumulate in skeletal muscles.

(Fixed acids is regulated by kidneys)

What is the general mechanism?

pH can be adjusted by changing RATE and DEPTH of breathing.

Patient with acidosis → Hyperventilation → wash out CO 2 → increase

pH Patient with alkalosis → Hypoventilation → retain CO 2 → Decrease

pH

What happened if a healthy person has FAST hyperventilation?

He will stop ventilation after 15 seconds because amount of CO2 reduced

and

chemoreceptors in the brain will observe this reduction. Therefore, it will

inhibit ventilation.

What happened if a healthy person has chronic hyperventilation?

Patient with Anorexia will develop alkalosis due to reduction in CO2.

Renal mechanism

 What is the normal secretion of H+

and reabsorbation of HCO3 per day?

Secretion H+ = 4400 mEq/day

 Filtration HCO3 = 4320 mEq/day

 So, the 80 that remains must be

titers by ammonia and phosphate

buffer systems

 What is the general mechanism?

 Secretion of H+:

 1.Sodium/H+ counter transport (PCT, Thick

ascending loop and early DCT) 2.H+

pump (Late DCT and collecting ducts)

“phosphate buffer” 3.Secretion of H+ with

Thank you