Notes for medical students on general physiology.


is defined as the Study of nature.

general physiology

Human Physiology

Study of all the processes that make the human body a living being.


A process of maintenance of the nearly constant internal environment. Coined by Sir Walter Cannon, an American Physiologist.

Extracellular fluid (ECF)

It is approx. 14 liters (1/3rd of total fluid). It consists of plasma (3 liters ) and interstitial fluid (11 liters ). It is measured using Inulin.

Intracellular fluid (ICF)

It is approx. 28 liters  (2/3rd of total fluid).


It accounts for about 55% of blood and is measured using Evan Blue-T1824


Movement of molecules from an area of higher concentration to that of lower concentration


It refers to the movement of water molecules from a region of high water conc. to that of lower water conc. across a semipermeable membrane.


Osmolar conc. expressed as osmoles per liters of solution. Blood has an osmolarity of 285-306 mOsm/Lt.

Osmolar Gap

Difference between measured osmolarity and estimated osmolarity.
a.Estimated osmolarity = 2 Na+ (mEq/lt) + glucose /18 (mg %) + urea / 2.8 (mg %)
b.increased by ethanol, methanol, wthylene glycol, acetone and mannitol.

Milieu interieur

refers to the internal environment. Coined by Claude Bernard.

Intercellular connections

a.Tight junctions(Zona occuldens): surround the apical regions of epithelial cells as in intestinal mucosa, choroid plexus, and renal tubules. Formed by occludens, junctional adhesion molecules(JAMs) and claudins. Permit the paracellular pathway.
b.Desmosomes: consists of apposed thickenings of cells. Consists of cadherins.
c.Hemidesmosomes: attach cells to the basal lamina. Consists of integrins.
d.Gap junction: consists of connexones, each of which consists of 6 subunits connexins.

Ubiquitin-Proteasome Pathway

Process of protein degradation by first binding of ubiquitin protein (74 amino acids) and then degradation by proteasome.

Nernst Potential

Potential across a membrane that exactly opposes the net diffusion of a particular ion across the membrane. Also known as Equilibrium potential.
a. For K+ = -94 mV
b. For Na+ = +61 mV
c. For Cl- = -76 mV
d. For Ca++ = +125 mV

Action Potential

A brief, all-or-none depolarization of the membrane potential, reversing polarity in neurons, it has a threshold and a refractory period and is conducted without decrement.

Local/ Graded Potential

A mild local change in the membrane potential of variable amplitude and duration has no threshold or a refractory period and is conducted decrementally. Eg: Motor end plate potential, Excitatory (or inhibitory) post-synaptic potential, pacemaker potential, etc.

Resting membrane potential

the diffusion potential across a resting i.e. unstimulated cells. A resting cell is about 100 times more permeable to potassium than sodium.


A change in the resting potential of the membrane towards zero as a result of sodium influx through voltage-gated sodium channels.


The process by which the membrane potential returns to its resting state as a result of efflux of potassium ions through voltage-gated potassium channels.

Absolute refractory period

The period in the action potential during which an excitable tissue cannot respond to a second stimulus, no matter how strong it is.

Relative refractory period

The period in the action potential during which an excitable tissue can respond to a second stimulus, provided it is greater than threshold strength.

All-or-none phenomenon

Once an action potential has been elicited at any point on the membrane of a nerve fiber, the depolarization travels all over the membrane if the conditions are right, or does not travel if the conditions are not right.


Minimum strength of stimulus that can elicit a biological response, without considering time duration.

Utilization time

Duration for which a stimulus of rheobase strength needs to be applied to elicit a biological response.


Duration in which a stimulus twice the rheobase strength needs to be applied to elicit a biological response. Excitability is inversely proportional to chronaxie.
a.For nerve: 0.01 – 0.1 micro sec
b.For skeletal muscle: 0.5 – 1 micro sec
c.For cardiac muscle: 3 – 5 micro sec
d.For smooth muscle:100 – 200 micro sec

Denervation Hypersensitivity

Heightened response of a tissue or organ following denervation due, in part, to an up-regulation of receptors on the post-synaptic membrane.

Wallerian regeneration

Degenerative changes seen at the distal end of neuron after nerve injury.
Retrograde regeneration Degenerative changes seen at the proximal end of neuron after nerve injury.


Physiological junction between two neurons.
a. It may be axo-dendritic, axo-axonic or axo-somatic.
b. A synapse may be electrical synapse or chemical synapse.

Neuromuscular junction

also known as motor end plate or myoneural junction. It consists of synaptic cleft or synaptic space (20 – 30 nm) with multiple sub-neural folds.
Some channels:
a. Cl C channel: Dimer
b.Epidermal Na channel: Trimer
c.Aquaporins: Tetramer
d.Rest all channels are pentamer.

Applied Physiology of some channels:

a. Chloride channel: Cystic Fibrosis
b. Potassium channel: Bartner syndrome
c. Ryanodine-Calcium channel: Malignant hypothermia
Some amino acids found in our body, but not incorporated in any proteins:
a. Ornithine
b. Taurine
c. 5-hydroxytryptophan
e. T4

Clotting Factors

  • Fibrinogen—-Factor I
  • Prothrombin—-Factor II
  • Tissue factor—-Factor III; tissue thromboplastin
  • Calcium —-Factor IV
  • Factor V—- Proaccelerin; labile factor; Ac-globulin (Ac-G)
  • Factor VII —-Serum prothrombin conversion accelerator (SPCA); proconvertin; stable factor
  • Factor VIII—–Antihemophilic factor (AHF); antihemophilic globulin (AHG); antihemophilic factor A
  • Factor IX —–Plasma thromboplastin component (PTC); Christmas factor; antihemophilic factor B
  • Factor X—- Stuart factor; Stuart-Prower factor
  • Factor XI—-Plasma thromboplastin antecedent (PTA); antihemophilic factor C
  • Factor XII —-Hageman factor
  • Factor XIII—–Fibrin-stabilizing factor
  • Prekallikrein—–Fletcher factor
  • High-molecular-weight kininogen—–Fitzgerald factor; HMWK (high molecular- weight kininogen)