Understanding Human Physiology: Past, Present, and Future

This article describes physiology, with a special focus on human physiology and its various branches. Here, learn about the past, present, future, and scope of physiology. In short, physiology refers to the study of living organisms.

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  1. Past: Developments of human physiology
  2. Present: Integration of Physiology with Modern Science
    1. Physiological function depends on
    2. Branches of Physiology:
  3. Future: Digital, Personalised, and Predictive Physiology
  4. Scopes in physiology
  5. Promising career
    1. Take-home message

Introduction:

Physiology refers to the study of the functions of living organisms. It is divided into many branches. We are concerned with Human Physiology. In Physiology, we learn about the mechanisms that control body functions.

Physiology is the branch of biological science that deals with the functioning of living organisms. It also describes the organs that initiate and control these functions.

A French physician, Jean Fernel (1497-1558), introduced the word “physiology” for the first time.

The word “physiology” is derived from a Greek word with a Latin equivalent, “Physiologia,” which means natural knowledge. Physiology comes from two words: physis, meaning ” nature”, and logia, which means” study”.

The ancient Greek phrase” nature origin” and its study indicate an innate scientific understanding of a living body’s station, functions, and mechanisms.

Physiology is the branch of life science that deals with body functions and how these functions occur in a controlled manner. It also describes the organs that initiate and maintain these functions.

A living organism comprises different organs that respond to environmental changes to survive. Body organs function in such a way that mild variations in the external environment cannot alter the body’s internal environment, which is maintained within a normal range by a mechanism known as homeostasis.

Past: Developments of human physiology

The study of human physiology has been ongoing for time immemorial. The first authentic available record is found in the Sushruta Samhita and Charak Samhita, dating back to around 600 BCE. They proposed that vata, pitta, and kapha regulate the body’s functions.

Documents reveal that the study of medical or human physiology started at the time of Hippocrates, i.e., late 5th century BC, in Greece.

Later, many scientists, philosophers, and thinkers contributed to the development of physiology. Some of them are Galen, Aristotle, Claude Berard, Walter B. Cannon, and many others.

However, their knowledge was speculative and descriptive, lacking scientific experimental support.

A breakthrough came with Galen (129–200 AD), a Roman physician who performed animal dissections and produced detailed anatomical and physiological texts. However, many of his theories were eventually discarded with the advent of new scientific procedures and technology.

William Harvey and many others in the 17th century revolutionised physiology by describing the functions of many organs and systems supported by experiments.

Present: Integration of Physiology with Modern Science

A living organism is composed of many different organs that respond to changes in both its internal and external environments. Any shift in physiology will impact an individual’s physical and mental functions. The study of physiology focuses on the organs, systems, and the biological basis of the human body’s operations.

Physiological condition refers to the normal function of the body, while pathological condition refers to altered physiology, or abnormal conditions.

Physiological function depends on

1. Biophysical processes

2. Biochemical processes,

3. Homeostatic control

4. Rapid and precise communication between cells occurs in various ways, for example, through chemical and electrical methods.

Animal experiments have provided deep knowledge of human physiology. Physiology is a core component of medical studies worldwide, and many universities offer bachelor’s, master’s, and doctoral degrees in the field of physiology.

Modern human physiology encompasses biology, physics, and chemistry, enabling a precise understanding at the cellular, tissue, organ, and systemic levels.

Today, physiology is not limited to describing functions but explaining them through evidence-based mechanisms.

Branches of Physiology:

1. Cellular and Molecular Physiology:

Cellular and molecular physiology explores the roles of ion channels, neurotransmitters, hormones, and genes in regulating various bodily functions.

2. Systems Physiology:

Cells form organs, and organs form systems such as the nervous, cardiovascular, respiratory, renal, endocrine, gastrointestinal, and reproductive systems. Systems Physiology is now studied with integrated perspectives.

3. Diagnostic and Imaging Advances:

Technologies such as MRI, CT scans, PET scans, echocardiography, and EEG enable the real-time observation of physiological processes. These tools provide insights into how systems respond normally.

4. Computational Physiology:

Physiological data is now being analysed through mathematical models and simulations. This computational approach facilitates the prediction of outcomes, simulation of diseases, and testing of potential treatments, thereby reducing reliance on invasive procedures or animal models.

5. Education and Research:

In medical education, physiology is taught not only as an academic subject but as a clinical science. It forms the backbone of medical science. Modern teaching aids, including the use of simulations, virtual labs, and interactive models, have significantly enhanced learning and retention.

6. Sports physiology:

Sports physiology deals with the study of the physiological challenges associated with sports. And how to deal with them in an integrated manner.

7. Genetic counselling:

Nowadays, genetic counselling is available to prevent many hereditary diseases.

Future: Digital, Personalised, and Predictive Physiology

The future of human physiology lies at the intersection of advanced technologies, artificial intelligence, genomics, and personalised medicine. The coming decades promise profound transformations in how we understand and apply physiological principles.

1. Artificial Intelligence:

AI can analyse massive physiological datasets, such as ECG recordings, imaging scans, and genetic data, to identify patterns and predict health outcomes.

2. Machine learning models will assist in diagnosing conditions like arrhythmias, respiratory failure, or hormonal imbalances based on real-time physiological inputs.

3. Personalised Physiology and Genomics:

Understanding the human genome has opened the door to personalised medicine. Future physiology will not generalise bodily functions but will consider an individual’s genetic, epigenetic, and environmental factors.

4. Bioengineering and Artificial Organs:

Bioengineered tissues or artificial organs may replicate physiological functions.

Organs-on-chips and 3D bioprinting aim to mimic real physiological responses, offering potential solutions for organ failure. Research is ongoing into bionic limbs that respond to nerve impulses, replicating natural movement.

5. Devices and Remote Monitoring devices at affordable prices are available:

Smartwatches, pulse oximeters, and biosensors are used to measure heart rate, oxygen concentration, respiratory rate, and blood glucose levels. Digital blood pressure machines enable you to measure your blood pressure accurately. These machines are available at affordable prices.

Devices to monitor additional parameters, such as hormone levels, electrolyte balance, and blood pressure in real-time, are in development.

6. Space and Extreme Physiology:

As humans venture into space and colonise new environments, understanding how extreme conditions affect physiology will become crucial. Microgravity research has already revealed changes in bone density, cardiovascular function, and immunity. Future studies will investigate methods for preserving human physiology under such conditions.

7. Neurophysiology and Brain-Machine Interfaces:

Neurophysiology is rapidly advancing with the development of brain-machine interfaces. Devices like Neuralink aim to decode brain signals to control prosthetics or communicate directly with computers. Such breakthroughs could revolutionise care for patients with paralysis or neurodegenerative disorders.

Scopes in physiology

Physiology is a primary subject of medical degrees worldwide. Many universities offer bachelor’s, master’s, and doctoral degrees in the field of physiology.

Physiology is an essential subject in medical education for M.B.B.S. degrees and is included in the 1st professional curriculum of M.B.B.S.

B.Sc. M.Sc. and PhD physiology courses are also available in many universities.

A physiologist may get posted in medical colleges as a tutor, assistant, associate Professor, or Professor.

Exercise physiology is the study of human physical activity and exercise. The word exercise comes from the Latin word drive forth.”

Exercise has been considered essential to human health for thousands of years in ancient cultures. The Greek physician Hippocrates recognized the importance of exercise and advocated for daily physical activity to maintain good health.

Many career opportunities exist in exercise physiology.

As physiology advances, several jobs are likely to increase in demand.

An exercise physiologist may pursue research work.

Physiologists can work in various clinical settings,

including fitness centers, community organizations, and corporate fitness.

Sports physiologists may start private fitness clinics.

A physiologist may also begin their general clinic.

Hospitals, community facilities, industries, and nursing homes may employ clinical physiologists.

Promising career

A physiologist has a promising career.

Physiology has a promising future, but it faces multifaceted challenges. With the advancement of science and technology, physiology is evolving rapidly. Integrating massive datasets requires strict data privacy protocols. The human body is a highly complex system, and simulations may not fully capture its intricacies.

Ethical concerns also surround interventions like gene editing or neural implants.

Take-home message

A persistent quest to understand life causes the evolution of human physiology.

Physiology is a fascinating and dynamic subject that underpins translational and clinical medicine, as well as the interface between the physical and life sciences. By studying human physiology, we gain insight into how the body maintains normal health and responds to and adapts to challenges in both internal and external environments.

Today, physiology is more integrated, evidence-based, and technologically empowered than ever. It is developing very rapidly.

Looking forward, it will become even more personalised, predictive, and digital, shaping the future of healthcare and medical science.

For M.B.B.S. students and aspiring doctors, mastering physiology is not just about passing exams — it is about developing a scientific foundation that will support every future clinical decision.

Hashtags: Hippocrates # homeostasis # exercise #physiology # sports physiology# divisions #clinical# scopes #

Internal Link: https://blog.totalphysiology.com/2022/01/homeostasis external-internal.html

External Link:

1.https://en.m.wikipedia.org/wiki

2. Entin, Pauline (n.d.)”ABrie” History of ExercisePhysiolPhysiology’rn Arizona University Retrieved 2017-06-30 from

http://jan.ucc.nau.edu/pe/exs336historyVA1.htm.

3. Ivy.John L.(2007). Exercise Physiology: Brief History and Recommendations Regarding Content Requirements for the Kinesiology Major. 59:34-411.

Bijay Krishna

Bile: Formation, Functions, and Health Implications

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Understanding Calcium: Benefits and Functions in the Body

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Understanding Intercellular Communication Mechanisms

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12 Simple Ways to Improve Your Lung Capacity

What is Vital Capacity?

Vital capacity (VC) is the air volume that can be expired by forceful effort, following maximal deepest possible inspiration.

The subject takes a deep breath of maximal inspiration and then breathes out forcefully. The volume of air expelled indicates vital capacity.

The total Tidal volume (TV), Inspiratory reserve(IRV), and Expiratory reserve volumes (ERV) make Vital capacity.

Vital capacity measures respiratory functions and indicates respiratory and overall health conditions. It indicates functions of higher brain and respiratory centers, strength of respiratory muscles, regular nerve supply to the respiratory muscles, and functions of the lungs and chest wall.

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You cannot change your age, sex, and height, but you can improve your posture, general health, and lung and muscle conditions by simple and effective methods.

Improving your vital capacity involves strengthening your respiratory muscles and optimizing lung function. Here are some simple, free, but effective steps:

Twelve simple ways are:

1. Maintain a normal weight.

2. Maintain hydration.

3. Ensure quality sleep for 6 to seven hours.

4. Take a balanced diet at regular intervals.

5. Avoid stress and strain.

6. Avoid pollution and ensure good quality of indoor air.

7. Quit smoking and avoid passive smoking.

8. Quit alcohol.

9. Practice deep breathing exercises, such as deep inhalations and exhalations, to expand your lungs fully and Diaphragmatic breathing, also known as belly or abdominal breathing.

10. Practice regular aerobic exercise, such as running, swimming, or cycling, and muscle-building exercises to strengthen your muscles, especially those of your back, chest, neck, and abdomen. Before starting the exercise program, follow the advice of a qualified healthcare provider.

11. Practice Yoga

Author doing Yoga.

12. Maintain a healthy lifestyle.

Remember, this is for informative purposes only, based on different sources of information.

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The Complement System: Role in Immunity

This article will discuss the role of the complement system in the body’s defense mechanisms, including its site of origin and mechanism of action.

Table of Contents

  1. Complement activation results in
  2. Site of synthesis
    1. Nomenclature of complement
    2. Main types of complements
  3. The complement system gets activated by three biochemical pathways-
  4. Functions of the Complement System:
  5. Mechanisms of Lysis
    1. Regulation of the Complement System
  6. Applied
    1. Diagnosis

Introduction

The complement system is crucial in the body’s defense against invading pathogens and tumor cells. Its components enhance the antibacterial activities of antibodies.

The complement system, or the complement cascade, consists of over 50 small inactive protein precursors in blood, body fluids, and tissues. They contribute about 10% of the globulin of plasma protein. The inactive form is known as zymogen. When stimulated by appropriate stimulus, proteases in the system cleave specific zymogen to release active enzymes.

Complement activation results in

1. Opsonization-to speed up phagocytosis.

2. Formation of ‘membrane attack complex (MAC) to cytolyse or cell killing and

3. Produce inflammation to attract phagocytic cells and other immunocompetent cells to the invasion site.

Site of synthesis

Hepatocytes synthesize complement molecules.

Monocytes, macrophages, platelets, and epithelial tissues of the gastrointestinal tract and urogenital tract also contribute in small amounts.

The complement system is a system of plasma enzymes. The liver synthesizes enzymes of the complement system. It comprises over 50 enzymes circulating in the blood and is responsible for cell killing by humoral and cellular immunity.

The precursors are zymogens, inactive enzymes in the blood, body fluids, and tissues. When stimulated, they become active enzymes at sites of infection locally and trigger events that exert effects when stimulated by an antigen-antibody complex or other pathways.

When in active form, they work in a sequence of cascade reactions to remove pathogens, kill pathogens, initiate and promote inflammation, and activate other immunological cells.

In a complement cascade system, an active complement enzyme formed by cleavage of its zymogen precursor then cleaves its substrate, another complement zymogen, to its active enzyme to form. This, in turn, cleaves and activates the next zymogen of the complement pathway. In this way, activating a small number of complement proteins at the start of the path, amplified by each successive enzymatic reaction, rapidly generates a significant complement response.

There are many regulatory mechanisms to prevent uncontrolled complement activation.

Nomenclature of complement

All components of the classical complements are designated by the letter C followed by a number, for example, C1. The number was allotted in the order of their discovery.

The products of the cleavage reaction of a complement are designated ‘b’ for large fragments and ‘a’ for small fragments.

Main types of complements

There are nine named complement enzymes in the complement system, and their names are C1, C2, C3, C4, C5, C6, C7, C8, and C9. Complement C1 has three subunits C1q, C1r, and C1s. The C1 complex has one molecule of C1q, two molecules of C1r, and two molecules of C1s.

Activating one complement of this system triggers cascade reactions that activate other system complements.

The complement system gets activated by three biochemical pathways-

The three pathways generate protease C3 convertase. The formation of C3 convertase is an early event of complement activation, and the formation of C5 convertase and onwards is a late event.

  1. Classical Pathway-Antibody- antigen complex binds with C1 and activates C1. Activated C1 triggers a sequence of reactions that activates C3. As the classical pathway requires the antigen-antibody complex for activation, it is involved in specific immune responses. Activation occurs when C1q binds to the Fc portion of pentamer IgM or six units of IgG monomer. C1q can bind directly to the pathogen surface.

These bindings cause conformational changes in the C1q molecules, which lead to the activation of C1r, which cleaves C1s.The C1r,s split C4 and C2 to form

C4——–C1r,C1s———–àC4a and C4b.

C2———C1r,C1s———-à C2a and C2b.

C4b and C2b form C3 convertase, which cleaves C3 into C3a and C3b.

C3b joins with C4b and C2b to make a (C4b, C2bC3b complex), which promotes the formation of C5 convertase. C4b and C3b can bind to the Fc portion of immunoglobulins.

2. Lectin Pathway:

The lectin pathway activates the complement system without the presence of an antibody. It occurs by antigen and C3 hydrolysis. Mannose-binding lectin (MBL)binds with mannose residues on the surface of the bacterial wall and stimulates the MBL-associated serine proteases MASP-1 and MASP-2, which split.

C4 to C4a and C4b and C2 into C2a and C2b.

C4b and C2b join to form the classical C3 convertase. MBL fixation on viral surfaces enhances the neutralization of viruses—complement system.

3. Properdin or Alternative pathway–

Alternative pathways do not depend on the antigen-antibody complex; they are essential to innate immunity.

The alternative pathway is always active at a low level. This is due to spontaneous C3 hydrolysis forming C3 convertase due to the breakdown of the internal thioesters bond.

C3b is formed, which is unstable in aqueous media. Factor H and I rapidly inactivate the C3 convertase.

Pathogens do not have complement regulatory proteins on their surfaces, but they do on the host cells. The alternative pathway distinguishes self from non-self due to the presence of complement regulatory proteins.

When a complement is activated on a host cell surface, the activation is limited by endogenous complement regulator proteins, which include CD35, CD46, CD55, and CD59. Host cells do not have cell surface C3b receptors, but foreign cells, pathogens, and abnormal cells may have many C3b receptors.

Polysaccharides on invading microbes’ bacterial cell walls, tumor cells interact with Properdin and initiate the complement system. Spontaneous hydrolysis of C3 forms active C3 that activates the complement cascade. and C5.

When active, the complement system causes invading microorganisms and tumor cells to lysis.

Each pathway generates a protease called C3 convertase. The reactions causing the formation of C3 convertase are early events of complement activation, which consists of triggered-enzyme cascades in which inactive complement zymogens are successively cleaved to yield two fragments, the larger of which is an active serine protease. The active protease remains at the pathogen surface and ensures that the next complement zymogen in the pathway is cleaved and activated at the pathogen surface.

The small peptide fragment is released from the reaction site and acts as a soluble mediator.

In the early events of complement activation, C3 convertase is formed that will bind to the pathogen surface. The formation of C3 convertase activity is pivotal in complement activation. Here, they cleave C3 to generate large amounts of C3b and C3a. The C3b molecule is the primary effector molecule of the complement system. C3a is a peptide mediator of inflammation.

The C3b molecules act as opsonins and react with phagocytes that have receptors for C3b. They also bind to the C3 convertase to form a C5 convertase that produces the C5a and C5b.

The C5a is an essential small peptide mediator of inflammation.

The C5b initiates the late events of complement activation. These comprise a sequence of polymerization reactions in which the terminal complement components interact to form a membrane-attack complex (MAC).The mac consists of C5b,C6,C7,C8,and polymeric C9.

Functions of the Complement System:

  1. Opsonization

Complements, especially C3b, coat the surface of pathogens, enabling efficient and prompt phagocytosis by phagocytic cells.

Opsonization is a process of coating the surface of pathogens with complement enzymes.

  1. Cell lysis:

Complements C5b, C6, C7, C8, and C9 form a membrane attack complex (MAC) that penetrates the cell membrane and leads to cell death.

  1. Inflammation

Active C3 (C3a)and C5(C5a) cause histamine release from granulocytes, mast cells, and platelets. Histamine is a potent vasodilator. Blood vessels dilate under the influence of histamine, increasing capillary permeability, so leucocytes and other cells come to the antigen-antibody complex site, causing inflammation.

4. Enhancement of antibody-dependent cell-mediated cytotoxicity

The complement system enhances antibody-dependent cell-mediated (ADCC) so that immune cells, for example, natural killer cells, destroy target cells.

Mechanisms of Lysis

1. The active complement from C5 to C9 causes perforation in the cell membrane of invading microorganisms and tumor cells. Ions enter the cell and cause its death.

2. Active C3 (C3a) and C5(C5a) release histamine from granulocytes, mast cells, and platelets. Histamine is a potent vasodilator. Blood vessels dilate under the influence of histamine, increasing capillary permeability, so leucocytes and other cells come to the antigen-antibody complex site.

3. Active C3of the system performs two functions-

It causes opsonization and phagocytosis of bacteria.

It activates other complement enzymes.

4. Active C5, C6, and C7 attracts WBCs to antigen-antibody reaction site.

Regulation of the Complement System

Complement control proteins in the blood and host cell membrane regulate the complement system and protect cells from it. Some inhibiting factors, such as C1 inhibitors and Factor H( FH), also exist.

Some genes produce complement control proteins; if one has defects, the synthesis becomes defective, causing several diseases.

Mutation in the genes of complement regulation causes diseases.

Applied

Excessive complement activity was responsible for severe COVID-19 symptoms.

In HIV infection, the complement system causes more damage to the body.

Although the complement system protects the body, it may cause damage beyond repair in stress and severe infections.

The complement system is essential in the pathogenesis of diseases like asthma and lupus erythematosus.

Deficiencies in the complement system increase susceptibility to infections.

Uncontrolled function and inappropriate activation of the complement system can cause autoimmune diseases, chronic inflammation, and tissue damage.

Diagnosis

1. Total complement activity test to measure complement activity.

2. Complement fixation test.

Blood Indices Explained

Absolute values of blood indices

Absolute blood indices are essential in diagnosing and typing anemias. A subject’s fundamental values are compared with arbitrarily set typical values. Blood indices have been discarded in favor of absolute corpuscular values. 

Table of contents

  1. Absolute values of blood indices
    1. Mean corpuscular volume (MCV):
    2. Mean corpuscular hemoglobin (MCH)
    3. Mean corpuscular hemoglobin concentration (MCHC)
    4. Colour Index (CI)
    5. MCD:
    6. MCAT:
    7. Red cell distribution width (RDW):

Mean corpuscular volume (MCV):

Mean corpuscular volume is the volume of a single red blood cell. It is expressed in cubic microns (µm3).

MCV= = PCV per 100 ml of blood divided by RBC count in millions / µL Multiplied by 10.

45/5×10 =90 µm3   (average value)

Range is 78 t0 94 µm3.

If MCV is above the normal range, the RBCs are known as macrocytes, and the condition is macrocytosis.

If MCV is less than the normal range, the RBCs are known as microcytes, and the condition is microcytosis.

If MCV is within the normal range, the RBCs are known as normocytes, and this condition is normocytic.

Mean corpuscular hemoglobin (MCH)

This is the average weight of (amount) of hemoglobin present in an RBC. It is expressed in picograms (10 -12 gm), which are micro-micrograms. We can calculate MCH if we know hemoglobin in grams per deciliter and RBC count in millions /microliter.

MCH= Hb in grams percent multiplied by ten and divided by the number of RBC in million per mm3  of blood.

If the values are

Hb =15 grams%

RBC count= 5 million/mm3.

MCH= 15/5 x10=30 average value.

Typical range is  28-32 picograms(pg).

Mean corpuscular hemoglobin concentration (MCHC)

This is the hemoglobin concentration in a single red blood cell. It indicates the amount of hemoglobin expressed as a percentage of the red blood cell’s volume.

MCHC= = Haemoglobin in grams per decilitre/PCV per 100 ml of blood multiplied by 100.

MCHC= 15/45 X 100= 33.3 % Average value.

The range is 32 to 38 %. ( 35 ± 3%).

In another way, MCHC can be calculated by the following formula

MCHC= MCH divided by MCV and multiplied by 100.

The MCHC value can not exceed 38% because RBCs cannot hold Haemoglobin beyond this metabolic limit—the Haemoglobin-Forming mechanism.

Therefore, RBC is never hyperchromic.

More than 99% of PCV is due to RBC.

MCHC is the most reliable. RBC count is not taken into consideration. Due to its large size, MCH may be high, up to 39 pg in a large red blood cell, but MCHC would be within the normal range.  

Colour Index (CI)

The color index is the ratio of Haemoglobin to RBC

Colour Index=haemoglobin % /RBC %

The normal range is 0.85 to 1.15 (1± 0.15).

The average is 1.

14.8 gm /dL hemoglobin is 100%, and 5 million/ µm3 RBC count is 100%.

The color index is low in iron deficiency anemia and high in macrocytic anemia.

RBC count and hemoglobin content may decrease simultaneously. Therefore, CI is not affected.

The color index has no clinical value.

MCD:

Red cell distribution width (MCD) can be measured by direct micrometric measurements of the red blood cells in a stained blood film.

MCAT:

MCD can measure central corpuscular average thickness (MCAT).

Red cell distribution width (RDW):

Red cell distribution width measures the variation in the size of red blood cells. It is calculated as a coefficient of variation (CV) or standard deviation (SD) and is usually part of a complete blood count.

A normal RDW is usually between 12 % to 15%.

A high RDW means there are abundant microcytes and macrocytes. This is seen in dimorphic anemia.

Other conditions associated with increased RDW are inflammation, malnutrition, and renal diseases.   

RBC size variation is known as Anisocytosis. (iso=same,cyto= cells.A=no.)

Variation in the shape of RBCs is known as Poikilocytosis.

blBL

Blood In a Test Tube for Tests Image created by the author with canva