Physiology is among the most important topics from NEET MDS point of view as it forms the basic building blocks of some of the highly scoring and significant subjects such as Oral Medicine, Pathology and General medicine. The biggest challenge for students preparing for NEET MDS is that the students find themselves forgetting the topics they took days to finished. Here arises the biggest confusion as to which subjects should be approached when and how. The article aims to highlight the preparation strategy that must be followed when you are preparing for Physiology. Let us first take a look at list of standard books to refer & most important topics that you cannot afford to leave out at any cost.

Given below are the list of Questions MERITERS experts will answer that are essential for an effective and efficient preparation:

1. What is the subject wise Weightage?
2. Which Books to refer?
3. How much Time should be allocated to the subject?
4. How much Time should be allocated to each Topic?
5. How many times should the subject be Revised?
6. What is the Ideal time to Start the subject?
7. What are the Important Topics for NEET MDS?
8. Types of Questions asked?

What is the subject wise Weightage?

8-12/240 Questions (4%)

Standard books to refer:

Ganong’s Review Of Medical Physiology

Author : Barrett 

INR 1,221 Buy on Amazon

Guyton & Hall Textbook of Medical Physiology

Author : Mario Dr. Vaz, Tony Dr. Raj, Kurpad Dr Anura

INR 1,495 Buy on Amazon

How much Time should be allocated for the Subject?

• Theory reading – 4 Days
• MCQ Practice- 10-15 Days

How much Time should be allocated to each Topic?

• Theory reading – 3-4 Hours
• MCQ Practice-  5-8 Hours

How many Times should the subject be Revised?

• 4-6 times revision is required

What is the Ideal time to Start the subject?

• 3rd quarter of the preparation 
• After completing 13-14 subjects

Physiology – Important Topics

What Type of Questions were asked in NEET?

1. Single best answer

• Fact Based (Memory)
• Concept based
• Numerical/Value Based

2. Image based questions

3. True or false type questions

Please watch the above featured video for more detailed explanation about this article.

We hope this blog will assist you in preparing this subject meticulously for MDS entrance exams.
Prepare judiciously..

SOURCE: MERITERS!!

4 SIMPLE ACID-BASE DISORDERS

• Metabolic acid-base disorder presents as an imbalance between bicarbonate, the primary extracellular buffer, and fixed, aka, non-volatile, acids.
• Respiratory acid-base disorder presents as an imbalance between bicarbonate and carbon dioxide, the volatile acid.
• Acid-base Disorders are distinguishable by their arterial blood profiles, compensatory respiratory and renal mechanisms, and common causes.

ACIDEMIA

pH < 7.35

Metabolic acidosis

• Bicarbonate < 20 mEq/L
• Caused by either a gain in hydrogen ions and/or a loss of bicarbonate, which lowers pH.
• Consequently, the arterial blood profile shows reduced bicarbonate concentration and elevated hydrogen ion concentration.
• In response to a drop in pH, the respiratory systemcompensates with hyperventilation:
  • Excess carbon dioxide is “blown off,” which lowers the partial pressure of carbon dioxide in the blood; the arterial blood profile reflects this.
• Though slower to respond, renal bicarbonate conservation and acid excretion produce a more effective and longer-lasting pH elevation.

Anion Gap

Causes of metabolic acidosis into at least two categories: those associated with a normal anion gap (AG), and those associated with an elevated anion gap.

• In a routine blood test, only some cations and anions are measured; the anions that are not measured constitute the “anion gap.”
  • Because the total concentration of anions must be equal to the total concentration of cations, we know that the anion gap, the unmeasured anions, must be equal to:
    The measured cations (usually sodium) minus the measured anions (usually bicarbonate and chloride).
  • A normal average anion gap value is 12 mEq/L (typical range = 8 – 16 mEq/L).
• Thus, an increased anion gap indicates that bicarbonate, a measured anion, has been lost and replaced by the unmeasured ions
• A normal anion gap indicates that chloride is the ion that replaced the lost bicarbonate, which makes sense given that it is the other measured anion in the anion gap equation.
• Common causes of a normal anion gap include:
  • Diarrhea
  • Renal tubular acidosis
  • Renal failure
  • Hyperchloremia
  • Addison disease
  • Acetazolamide
  • Spironolactone
  • Saline infusion
• Common causes of an increased anion gap include MUDPILES:
  • Methanol intoxication (methanol is also called “wood alcohol,” commonly found in antifreeze and industrial settings)
  • Uremia
  • Diabetic ketoacidosis
  • Paraldehyde (which is sometimes used to treat alcoholism and certain convulsive and mental disorders)
  • Iron overdose
  • Lactic acid
  • Ethylene glycol poisoning (ethylene glycol is a compound commonly found in antifreeze)
  • Salicylate ingestion (key ingredient in aspirin, poisoning is common in children)

Respiratory acidosis

• Pco2 > 44 mmHg
• Caused by a gain in carbon dioxide and bicarbonate.
• The degree of change in pH depends on the duration of the disorder:
  • The pH is more reduced in acute acidosis than in chronic because, in chronic acidosis, sufficient time has elapsed for renal mechanisms to have some effect.
• There is no respiratory compensation when the respiratory system is itself the source of the imbalance.
  • To raise pH, the nephrons conserve bicarbonate and excrete hydrogen ions; notice that this is similar to the renal response to metabolic acidosis.

Caused by:

• Hypoventilation
  • Inhibition of the medullary respiratory center, which can be induced by sedatives or brainstem lesions
  • Neuromuscular defects that inhibit the anatomical structures responsible for ventilation
  • Gas exchange defects, such as COPD.

ALKALEMIA

pH > 7.45

Respiratory alkalosis

• Pco2 < 36 mmHg
• pH is increased in proportion to the duration of the disorder.
• There is no respiratory compensation for respiratory-induced acid-base disturbances.
• Nephrons excrete excess bicarbonate and reduce titratable acid and ammonium ion secretion to conserve hydrogen ions; this is similar to the renal response to metabolic alkalosis.

Caused by:

• Hyperventilation, which “blows off” too much carbon dioxide and lowers its arterial partial pressure.
  • Stimulation of the medullary respiratory center, hypoxemia (low blood oxygen), and physical or mental distress.

Metabolic alkalosis

• Bicarbonate > 28 mEq/L
• Caused by a loss of hydrogen ions and/or a gain in bicarbonate, which raises pH.
• Consequently, the arterial blood profile shows elevated bicarbonate concentration, and decreased hydrogen concentration.
• In response to elevated pH, hypoventilation retains carbon dioxide, which increases its arterial partial pressure; this is reflected in the arterial blood profile.
• The nephrons increase bicarbonate excretion, and, by reducing secretion of titratable acids and ammonium, conserve hydrogen ions; these actions lower pH.

Most commonly caused by

• Vomiting (HCL is lost from the body)
• Loop and thiazide diuretics, which increase bicarbonate excretion in the urine.
  • Vomiting and diuretics cause extracellular fluid volume contraction, which, as we’ve learned elsewhere, triggers hormonal responses that increase bicarbonate reabsorption and maintain the metabolic alkalosis.
• Hyperaldosteronism (excessive aldosterone secretion) causes over-excretion of hydrogen ions.

KEY PRINCIPLES:

Volatile acid is the product of aerobic cellular respiration, which releases carbon dioxide. As we’ve learned elsewhere, when carbon dioxide interacts with water in the body fluids, carbonic acid forms.

• “Volatile” refers to the fact that carbon dioxide is expired by the lungs

Non-volatile acids are the products of protein and phospholipid metabolism

• They include sulfuric acid and phosphoric acid
• They are excreted in the urine as titratable acids

Because enzymes and other proteins only function at particular pH values, the body must regulate the acidity of the intra- and extracellular fluids.

• Three lines of defense against acid-base imbalance:
  • In the body, fluids (chemical mixtures), called buffers, minimize pH changes until hydrogen balance can be regained.
  • The respiratory system expires carbon dioxide, the source of volatile acid.
  • The urinary system excretes the non-volatile, aka, fixed, acids.
  • These systems operate interdependently to maintain an arterial blood plasma pH of 7.4.

Acid Production by Body Tissues

• Body tissues produce acids, including carbon dioxide, sulfuric acid, and phosphoric acid
  • Each of these acids releases hydrogen ions that must be buffered in the body fluid compartments.

Buffering in Fluid Compartments

• Intracellular compartment of body tissues = proteins and organic phosphates
• Intracellular compartment of red blood cells = hemoglobin
• Extracellular fluid = bicarbonate, which is the most important extracellular buffer, and, phosphate and proteins.

Acid Removal

• In the Lungs
  • When carbonic acid reaches the lungs, it dissociates to form carbon dioxide, which is expired in ventilation.
  • When pH falls, increased ventilation triggers to release excess carbon dioxide.
    Rapidly, the partial pressure of carbon dioxide drops, and the acidity of the blood is reduced.

• In the Kidneys
  • Nephrons reabsorb bicarbonate from the filtrate, and excrete hydrogen ions as tritratable acids and ammonium in the urine.
  • Nearly all of the filtered bicarbonate is reabsorbed from the proximal tubule.
  • Some hydrogen ions attach to ammonia and are secreted into the filtrate as ammonium; some of this ammonium is then reabsorbed from the thick ascending limb (where it participates in countercurrent multiplication in the renal interstitial fluid).
  • In the alpha-intercalated cells of the distal nephron, ammonium is again secreted into the tubular fluid, along with phosphoric acid. Phosphoric acid forms when hydrogen ions attach to phosphate, and is often referred to as “titratable acid”
  • Ammonium and phosphoric acid formation and secretion involve bicarbonate synthesis and reabsorption; this new bicarbonate contributes to the extracellular buffers.
  • Both mechanisms are responsive to aldosterone, which is a hormone secreted by the adrenal cortex secreted in response to low pH.

Clinical correlations

• Aldosterone deficiency inhibits ammonium excretion, and causes type 4 renal tubular acidosis. Because potassium excretion is also inhibited by aldosterone deficiency, this type of acidosis is characterized by hyperkalemia.
• Alkalosis is a consequence of excessive removal of hydrogen ions from the body fluids; as a result, the blood becomes more alkaline).
• Acidosis is the opposite: excessive hydrogen ions are added to the blood or retained; the blood becomes more acidic. Retention of acids can be a sign of renal failure.

Key Principles of Acids and Bases:

Acids and bases are defined by their ability to donate or accept hydrogen ions

• Acids are chemical substances that can donate/release, hydrogen ions in water.
• Bases, aka, alkalines, are chemical substances that can accept hydrogen ions.

pH

• pH is a measure of the concentration of hydrogen ions in solution
• pH scale displays the concentration of hydrogen ions from 0 – 14.
  • An acidic solution has a pH less than 7; it has a high concentration of hydrogen ions.
  • A neutral solution has a pH of 7
  • A basic solution has a pH of greater than 7; it has a lower concentration of hydrogen ions.
• Calculation of pH:
  • Negative logarithmic function.

pH values for human bodily fluids:

• Gastric juice, which is secreted by organs of the digestive system, has a pH value around 2; its acidity aids in food digestion.
• Saliva is slightly acidic, but much closer to neutral than are the gastric juices.
• For comparison, pure water has a neutral pH, 7.
• Arterial blood has a pH of approximately 7.4

Homeostasis

Biological organisms are constantly adding acids to their bodily fluids during metabolism, but our blood is slightly basic.

• Intra- and extra-cellular buffers operate to maintain homeostasis.
  • Buffers minimize changes of pH in solutions; they reversibly donate or accept hydrogen ions.
• Example: Bicarbonate buffer system:
  When hydrogen ions are added to the extracellular fluid, they combine with bicarbonate to produce carbonic acid, which is a weaker acid.
  • If the extracellular fluid becomes too basic, the reaction can be reversed:
    Carbonic acid can dissociate to form hydrogen ions and bicarbonate; when pH increases (becomes more alkaline), carbonic acid dissociates to form bicarbonate, which is a base, and hydrogen ions.

Clinical Consequences

• If the body cannot maintain homeostasis due to pathology, disturbances in bodily fluid pH inhibit enzymatic reactions.
  -Thus, failure to regulate pH causes a range of clinical symptoms associated with acidosis (too high blood acid content) or alkalosis (too low blood acid content); elsewhere, we discuss how the kidneys and lungs work to maintain homeostatic pH levels.