internal 1st year || Veterinary Physiology

Answers to Question No. 1

a. Reflex

A reflex is a rapid, automatic, and involuntary response to a specific stimulus. It is a built-in, protective mechanism that helps the body maintain homeostasis and avoid danger without requiring conscious thought from the brain. A classic example is pulling your hand away from a hot surface before you even feel the pain.

b. Ganglia

Ganglia (singular: ganglion) are clusters of nerve cell bodies located outside the central nervous system (brain and spinal cord). They act as relay stations or processing centers for nerve signals in the peripheral nervous system. For example, dorsal root ganglia contain the cell bodies of sensory neurons.

c. All or none principle

This is a fundamental law of physiology stating that when a nerve cell (neuron) or muscle fiber is stimulated, it will respond to its fullest extent or not at all. There is no partial response. If the stimulus is strong enough to reach the threshold potential, a full action potential is generated. A weaker, sub-threshold stimulus will produce no response.

d. Stroke volume

Stroke volume is the amount of blood pumped out by the left ventricle of the heart in a single contraction or heartbeat. It is a crucial determinant of cardiac output and is typically measured in milliliters per beat (mL/beat).

e. ESR (Erythrocyte Sedimentation Rate)

ESR is a common hematological test that measures the rate at which red blood cells (erythrocytes) settle at the bottom of a test tube over one hour. A faster-than-normal rate often indicates inflammation in the body, as inflammatory proteins cause red blood cells to stick together and fall more quickly.

f. Hemostasis

Hemostasis is the body's natural process to stop bleeding and prevent blood loss after injury to a blood vessel. It is a complex cascade involving three main steps:

  1. Vascular spasm: The damaged blood vessel constricts.
  2. Platelet plug formation: Platelets adhere to the site of injury and clump together.
  3. Coagulation (clotting): A fibrin mesh forms to solidify the plug into a stable clot.

g. Rigor Mortis

Rigor mortis is the post-mortem stiffening of muscles that occurs after death. It happens because ATP (energy) production ceases, preventing the detachment of actin and myosin filaments within the muscle cells. This causes the muscles to become locked in a contracted state. It typically begins a few hours after death and passes after 24-48 hours as tissues break down.

h. Prehension

Prehension is the act of grasping or seizing feed and water and bringing it into the mouth. It is the first step of eating. Different species use different anatomical structures for prehension:

  • Cattle & Sheep: Use their tongue.
  • Pigs: Use their snout.
  • Horses & Rabbits: Use their lips and incisor teeth.
  • Cats & Dogs: Use their teeth (canines and incisors) and jaws.

Veterinary Physiology Insights: ECGs, Methemoglobin, and Protein Digestion

Today's post dives into the answers to three key questions in veterinary physiology, covering diagnostics, blood disorders, and fundamental nutrition.

a. Electrocardiography (ECG)

What it is: Electrocardiography is the technique of recording the electrical activity of the heart over a period of time using electrodes placed on the skin. The recording is called an electrocardiogram (ECG or EKG).

Principle: The heart's contractions are triggered by electrical impulses (action potentials) that travel through the heart muscle. These electrical currents can be detected on the body's surface.

The ECG Waveform: A typical ECG cycle consists of:

  • P Wave: Represents the depolarization (contraction) of the atria.
  • QRS Complex: Represents the depolarization (contraction) of the ventricles. This is the largest wave because the ventricular muscle mass is much bigger.
  • T Wave: Represents the repolarization (relaxation) of the ventricles.

Veterinary Use: ECG is a vital non-invasive diagnostic tool used to identify arrhythmias (abnormal heart rhythms), assess heart size, detect electrolyte imbalances, and evaluate the overall health of the heart in animals.

Clear diagram of a typical ECG waveform showing P wave, QRS complex, and T wave

A schematic of a normal ECG waveform. (Image: ResearchGate)

b. Methemoglobin

What it is: Methemoglobin is a dysfunctional form of hemoglobin where the iron atom in the heme group is in the ferric (Fe³⁺) state instead of the normal ferrous (Fe²⁺) state.

Consequence: Methemoglobin cannot bind and carry oxygen effectively. This leads to reduced oxygen delivery to the tissues, a condition known as methemoglobinemia.

Causes: It can be caused by:

  • Genetic defects (e.g., deficiency of the enzyme methemoglobin reductase).
  • Oxidizing agents (common in veterinary medicine), such as:
    • Certain drugs (e.g., acetaminophen/paracetamol in cats).
    • Chemicals (e.g., nitrates in contaminated water or fertilizers).
    • Plants (e.g., onions, garlic).

Clinical Signs: The blood appears chocolate brown instead of bright red. Affected animals show signs of oxygen starvation (cyanosis - blue/grey mucous membranes, weakness, rapid breathing, exercise intolerance) even if the blood oxygen pressure is normal.

c. Protein Digestion in Monogastric Animals

A "ray diagram" typically refers to a flowchart. Here is a simple flowchart outlining the process of protein digestion in monogastric animals (e.g., Pigs, Dogs, Humans):

PROTEIN
↓
1. MOUTH
Mechanical breakdown only.
↓
2. STOMACH
HCl denatures protein.
Pepsin → Polypeptides
↓
3. SM INTESTINE (Lumen)
Pancreatic enzymes (Trypsin)
→ Peptides
↓
4. SM INTESTINE (Brush Border)
Aminopeptidases
→ Free Amino Acids
↓
5. ABSORPTION
Into the bloodstream.

Process Description:

  1. Mouth: Only mechanical breakdown occurs.
  2. Stomach: HCl denatures proteins, and pepsin begins enzymatic breakdown into polypeptides.
  3. Small Intestine (Duodenum): Pancreatic enzymes further break down polypeptides into smaller peptides.
  4. Small Intestine (Brush Border): Enzymes on the intestinal lining break down the remaining peptides into individual amino acids.
  5. Absorption: Free amino acids are absorbed into the bloodstream to be used by the body. 
       ^ 
       | 
       | P Wave      QRS Complex      T Wave
       |  _---_      .-----.           _---_
       | /     \    /       \         /     \
Height |/       \  /         \       /       \
       |         \/           \_____/         \
       |         |             |   |           |
       +---------+-------------+---+-----------+---------> Time
       |         |             |   |           |
       |      Atria         Ventricles      Ventricles
       |    Depolarize      Depolarize     Repolarize
       |     (Contract)      (Contract)     (Relax)

A text-based representation of an ECG waveform.

Answers to Question No. 3

a. Blood Pressure

1. What is Blood Pressure?

Blood pressure (BP) is the pressure exerted by circulating blood on the walls of the blood vessels. It is typically expressed as Systolic pressure / Diastolic pressure (e.g., 120/80 mmHg).

Systolic Pressure: The peak pressure in the arteries during ventricular contraction (systole).

Diastolic Pressure: The minimum pressure in the arteries during ventricular relaxation (diastole).

2. How do we determine arterial blood pressure?

Direct (Invasive) Method: A catheter is inserted directly into an artery and connected to a pressure transducer.

Indirect (Non-Invasive) Method: Uses an inflatable cuff placed around a limb or tail.

Doppler Ultrasound: Uses a probe to detect the sound of blood flow returning.

Oscillometric Method: Machine detects oscillations in pressure within the cuff.

3. Factors influencing blood pressure:

Blood pressure is primarily determined by Cardiac Output (CO) and Total Peripheral Resistance (TPR): BP = CO × TPR.

Factors Affecting Cardiac Output
  • Heart Rate
  • Stroke Volume
    • Preload
    • Contractility
    • Afterload
Factors Affecting TPR
  • Diameter of arterioles
  • Sympathetic nervous system
  • Local metabolic factors
  • Hormones
  • Blood viscosity

b. Blood Clotting Factors and Intrinsic Mechanism

1. Names of Different Blood Clotting Factors:

Factor I: Fibrinogen
Factor II: Prothrombin
Factor III: Tissue Factor
Factor IV: Calcium ions
Factor V: Proaccelerin
Factor VII: Proconvertin
Factor VIII: Antihemophilic A
Factor IX: Antihemophilic B
Factor X: Stuart-Prower
Factor XI: Plasma thromboplastin
Factor XII: Hageman factor
Factor XIII: Fibrin stabilizing

2. Intrinsic Mechanism of Blood Clotting:

The intrinsic pathway is called "intrinsic" because all the factors needed for it are present within the blood.

1
Initiation: Factor XII contacts negatively charged surface, activates to XIIa
2
Amplification: XIIa activates XI to XIa, then XIa activates IX to IXa
3
Tenase Complex: IXa joins with VIIIa to activate X to Xa
4
Common Pathway: Xa forms prothrombinase complex, converts prothrombin to thrombin
Note: The intrinsic pathway is slower to start than the extrinsic pathway, but both are crucial for normal hemostasis.

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