Metabolism and Nutritional Requirements Across the Lifespan - A Short Summary Essay in 13 Parts

Metabolism and Nutritional Requirements Across the Lifespan

Part 1: Energy Balance and Metabolism:

The human body operates on a delicate balance of energy intake and expenditure, with metabolism playing a key role in maintaining this equilibrium. The metabolic rate (MR) refers to the rate at which energy is utilized for various biological functions, including muscle contraction, active transport, and the synthesis of new molecules. Energy derived from organic substances is divided into two main forms: heat (H) and work (W). The heat produced accounts for approximately 60% of the energy, necessary to maintain body temperature, while the remaining 40% is used for biological work, including heart activity, secretion of gastric acid, and synthesis of plasma proteins.

Part 2: Total Energy Expenditure (TEE): 

Total Energy Expenditure is the sum of heat produced and both internal and external work, including energy storage in high-energy compounds like ATP and creatine phosphate. The basal metabolic rate (BMR) represents the minimum energy required to sustain vital functions under resting conditions. BMR is influenced by several factors, such as age, gender, body size, and ambient temperature, with fluctuations occurring throughout the day based on physiological needs.

Part 3: Factors Affecting Metabolic Rate: 

Metabolic rate is influenced by numerous factors, including age, gender, body size, and physical activity level. For instance, younger individuals tend to have a higher metabolic rate due to growth and development, while older adults experience a decline in BMR as part of the natural aging process. Additionally, the metabolic rate is affected by hormones, with thyroid hormones being particularly influential in regulating oxygen consumption and heat production across most tissues.

Part 4: Nutritional Requirements in Different Life Stages:

 

1.Before Pregnancy: It is essential for women to follow a well-balanced diet 8-12 weeks before conception. Adequate nutrition is crucial to ensure the body’s stores of vitamins, minerals, and proteins are optimized for a healthy pregnancy.

2. Pregnancy: Nutritional demands increase, especially during the third trimester, to support fetal growth and development. Caloric intake should be increased by approximately 1200 kJ/day (about 300 kcal/day), and weight gain should be maintained at 10-12 kg. Key nutrients include proteins, folic acid, iron, and calcium, which are essential for fetal development. The intake of alcohol and caffeine should be minimized, while fiber intake should be increased to support digestive health.

3. Lactation: During breastfeeding, energy requirements increase by 2100 kJ/day (around 500 kcal/day), with a focus on increasing the intake of carbohydrates, fats, and proteins. Calcium is crucial for maintaining strong bones and teeth, and fluid intake should be elevated to promote milk production.

4. Elderly People: Aging can reduce the secretion and motility of the gastrointestinal system, necessitating dietary adjustments. Protein intake should be around 1 g/kg body weight, and active fluid intake is essential to counter the reduced sensation of thirst in older adults.

5. Athletes and Physically Active Individuals: Energy demands increase significantly for athletes and active individuals due to the high energy expenditure associated with physical activity. Carbohydrates serve as the primary source of energy, while fats provide the densest energy per gram. Proteins are also important, but less efficient as an energy source. Hydration remains critical, especially during endurance sports.

Part 5: Thyroid and Hormonal Regulation of Metabolism:

Thyroid hormones have a potent calorigenic effect, stimulating increased oxygen consumption and heat production across most tissues except the brain. Adrenaline also plays a role in stimulating metabolism by promoting the breakdown of glycogen and triacylglycerol stores. A state of hyperthyroidism leads to an elevated metabolic rate, while hypothyroidism results in a reduced metabolic rate. Hormonal regulation, therefore, is a key component of metabolic control.

Part 6: Measurement of Metabolic Rate:

The metabolic rate can be measured directly or indirectly. Direct calorimetry involves quantifying the heat released by the body, typically using calorimetric chambers. Indirect calorimetry calculates energy expenditure based on oxygen consumption and carbon dioxide production. The respiratory quotient (RQ), defined as the ratio of CO2 produced to O2 consumed, varies depending on the type of substrate being metabolized. For example, carbohydrates have an RQ of 1.0, proteins 0.8, and fats 0.7.

Part 7: Ontogeny of the Digestive System: 

1. Prenatal Development: During fetal development, histotrophic nutrition (nutrients derived from maternal blood) supports early growth. Around 16-20 weeks, the fetus begins to swallow amniotic fluid, which aids in regulating its volume. Abnormalities in swallowing, such as atresia, can lead to polyhydramnios (excess amniotic fluid).

2. Postnatal Development: Newborns transition to lactotrophic nutrition, primarily derived from breast milk. The sucking reflex is well-developed in newborns, supported by the involvement of several cranial nerves. Salivation is minimal at birth but increases with age, particularly around the time of tooth eruption.

Part 8: Digestive System Function in Newborns: 

In newborns, the stomach is capable of holding only small amounts of milk. The gastric secretions, including chymosin and gastric lipase, facilitate milk digestion, while fetal pepsin assists in protein breakdown. The intestines exhibit lower villous surface area at birth, which limits nutrient absorption, although enzyme activity increases postnatally to enhance digestion. Defecation in newborns occurs frequently, often 5-7 times a day, and gradually reduces by age one.

Part 9: The Liver and Its Functions in Newborns: 

In the fetus, the liver functions in hematopoiesis and stores glycogen, which provides energy after birth. The liver’s biotransformation capabilities are immature in newborns, leading to slower elimination of medications and increased sensitivity to pharmacological agents. As the liver matures postnatally, its ability to detoxify and excrete waste products improves.

Part 10: Metabolism in Newborns: 

Newborns have a higher basal metabolic rate (BMR) relative to body weight, requiring 500 kJ/kg/day for growth and development. This high metabolic demand is primarily driven by the brain, which utilizes two-thirds of the newborn's total BMR. Protein intake in infants is also elevated at 2.5 g/kg/day, in comparison to the adult requirement of 1 g/kg/day.

Part 11: Gastrointestinal System in Elderly People:

As people age, the oral cavity often exhibits reduced salivation (xerostomia) and a decline in mastication efficiency. Esophageal motility decreases, which can lead to difficulties in swallowing. In the stomach, reduced motility and hydrochloric acid secretion may impair nutrient absorption, especially for iron and vitamin B12, contributing to anemia. Similarly, small intestine function declines with age, reducing absorption efficiency, while the large intestine becomes more prone to constipation and conditions like irritable bowel syndrome.

Part 12: Liver and Metabolic Changes in the Elderly:

The liver’s blood flow declines by approximately 35% in the elderly, resulting in a slower metabolic rate and impaired elimination of medications. The reduced secretion of bile acids increases the risk of developing bile stones, while cholesterol metabolism is also altered, contributing to an increase in cholesterol levels.

Part 13: Nutritional Considerations for the Elderly: 

Older adults require an optimized diet to support metabolic health. Protein intake should be maintained at 1 g/kg body weight, while fluid intake should be carefully monitored to compensate for the reduced sensation of thirst. Dehydration is a common concern in the elderly due to this diminished thirst response.

Conclusion:

Metabolism and nutritional needs change throughout the human lifespan. From the rapid growth and high metabolic demands of newborns to the age-related metabolic slowdown in the elderly, understanding these physiological processes is essential for maintaining health at every stage of life. Proper nutrition, hormone regulation, and awareness of the changing demands of the body are crucial for promoting optimal health and well-being.

Cardiac Physiology Made Simple

 

I sketched out a  very simple and brief outline on the Living Body and how it  works here:

 

https://c.blogspot.com/2025/04/the-living-body-how-it-works.html

I thought I should write just a little bit more using just two examples - the heart and the lungs among other organs and body systems so that readers can have a glimpse how beautifully the body is designed  

 

The Physiology of the Heart

The heart is a remarkable organ responsible for pumping oxygenated and deoxygenated blood throughout the body. It works as the central component of the cardiovascular system, which also includes arteries, veins, and capillaries. The heart's function is regulated by various factors, including blood volume, hormones, electrolytes, the autonomic nervous system (sympathetic and parasympathetic), and organs such as the kidneys and adrenal glands.

Structure and Function of the Heart

The heart is a muscular organ divided into four chambers: the right atrium, right ventricle, left atrium, and left ventricle. Blood follows a dual circulatory pathway:

1. Pulmonary circulation: Deoxygenated blood is pumped from the right ventricle to the lungs for oxygenation and returns to the left atrium.

2. Systemic circulation: Oxygenated blood is pumped from the left ventricle to the rest of the body.

The heart’s pumping function is driven by cardiac muscle contractions, regulated by electrical impulses originating from specialized cells.

Electrical Conduction System of the Heart

The rhythmic contraction of the heart is controlled by its electrical conduction system, ensuring coordinated pumping of blood. The key components include:

1. Sinoatrial (SA) Node: The heart’s natural pacemaker, located in the right atrium. It generates electrical impulses that spread through the atria, causing them to contract.

2. Atrioventricular (AV) Node: Located between the atria and ventricles, it receives impulses from the SA node and delays them slightly to allow complete atrial contraction before ventricular contraction.

3. Bundle of His: A collection of fibers that transmit electrical signals from the AV node to the ventricles.

4. Purkinje Fibers: These fibers distribute impulses throughout the ventricles, ensuring coordinated contraction for efficient blood ejection.

Cardiac Output and Hemodynamics

Cardiac function is assessed by several key parameters:

1. Cardiac Output (CO): The volume of blood ejected per minute, calculated as:

2. Stroke Volume (SV): The volume of blood pumped out with each contraction, determined by:

3. Preload: The degree of ventricular stretch before contraction, dependent on venous return.

4. Afterload: The resistance the left ventricle must overcome to eject blood, closely related to blood pressure.

5.Ejection Fraction (EF): The percentage of blood ejected from the left ventricle per beat. Normal EF is >55%; a low EF suggests heart failure.

Heart Blocks and Their ECG Characteristics

Heart blocks occur when there is a delay or interruption in electrical conduction. There are three types:

1. First-Degree Heart Block:

Prolonged PR interval (>0.20 seconds) on ECG.

Electrical impulses are delayed but still reach the ventricles.

Usually asymptomatic and may not require treatment.

2. Type I (Wenckebach/Mobitz I): PR interval gradually lengthens until a beat is dropped (missed QRS complex).2. Second-Degree Heart Block:
Type II (Mobitz II): Sudden loss of QRS complexes without PR interval prolongation.
Type II is more severe and may require a pacemaker.

3. Third-Degree (Complete) Heart Block:

No communication between atria and ventricles.

Atrial and ventricular rhythms are independent.
Requires immediate medical attention and pacemaker implantation.

Conclusion

The heart’s physiology is a finely tuned system regulated by mechanical and electrical components. Understanding its function, conduction system, and potential abnormalities helps in diagnosing and treating cardiovascular diseases. Advances in medical science, including pacemakers and medications, have significantly improved the management of heart disorders, ensuring better patient outcomes.

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Lung Physiology Made Simple

 I sketched out a  very simple and brief outline on the Living Body and how it  works here:

https://c.blogspot.com/2025/04/the-living-body-how-it-works.html

I thought I should write just a little bit more using just two examples - the heart and the lungs among other organs and body systems so that readers can have a glimpse how beautifully the body is designed 

Lung Physiology: Structure, Function, and Diseases

The lungs are the central organs of the respiratory system, responsible for gas exchange between the environment and the bloodstream. Oxygen enters the alveoli and diffuses into the capillary network, where it binds to hemoglobin and is transported through the arterial system to perfuse tissues. The respiratory system consists of the nose, oropharynx, larynx, trachea, bronchi, bronchioles, and lungs. The lungs are divided into lobes, further subdividing into over 300 million alveoli—the primary site of gas exchange.

Breathing is primarily controlled by the diaphragm, which is innervated by the phrenic nerve (C3, C4, C5). During physical exertion or respiratory distress, external intercostal muscles assist in inspiration.

Lung Volumes and Capacities

Lung function is assessed using various volumes and capacities:

1. Inspiratory Reserve Volume (IRV): Air inhaled beyond a normal breath.

2. Tidal Volume (TV): Air exchanged in a normal breath.

3. Expiratory Reserve Volume (ERV): Air exhaled beyond a normal breath.

4. Residual Volume (RV): Air remaining after maximal exhalation (not measurable by spirometry).

5. Inspiratory Capacity (IC): Maximum air inhaled after a normal exhalation.

6. Functional Residual Capacity (FRC): Air left in lungs after a normal breath.

7. Vital Capacity (VC): Maximum air exhaled after full inhalation.

8. Total Lung Capacity (TLC): Total air in lungs after maximal inhalation.

9. Forced Expiratory Volume (FEV1): Air exhaled in the first second of a forced breath.

Lung Diseases: Obstructive vs. Restrictive

Lung diseases are classified into obstructive and restrictive disorders

Obstructive Lung Diseases

These diseases impair expiration, leading to air trapping and increased FRC. Common examples include:

1. Asthma: Chronic bronchial inflammation causing reversible airway obstruction. Symptoms include wheezing, chronic cough, tachypnea, and dyspnea.

2. Chronic Obstructive Pulmonary Disease (COPD): A progressive condition involving both chronic bronchitis (airway inflammation, excess mucus) and emphysema (loss of alveolar elasticity, enlarged air spaces). Smoking is the primary cause, leading to small airway disease and lung tissue destruction.

In obstructive diseases, lung function tests show decreased FVC, decreased FEV1, and a significantly reduced FEV1/FVC ratio.

Restrictive Lung Diseases

These diseases limit lung expansion, reducing lung volumes (FVC and FEV1) but maintaining or increasing the FEV1/FVC ratio. Examples include:

1. Idiopathic Pulmonary Fibrosis

2. Pneumoconiosis (lung damage from inhaled dust/particles)

3. Sarcoidosis (inflammatory lung disease)

Oxygen Transport and Hemoglobin

At the cellular level, oxygen is carried in two main forms:

1. Bound to hemoglobin (Hb) – the major oxygen carrier

 2. Dissolved in plasma

The oxygen content of blood is calculated as:

CaO2=1.34×[Hb]×(100SaO2)+0.003×PaO2

Where:

1. CaO2 = Oxygen content in blood

2. [Hb] = Hemoglobin concentration

3. SaO2 = Oxygen saturation

4. PaO2 = Partial pressure of oxygen

Hemoglobin consists of four subunits, each binding one O₂ molecule through its iron-containing heme group, allowing each hemoglobin molecule to carry up to four oxygen molecules.

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The Living Body: How It Works

  Human physiology is an incredibly vast and intricate subject and it is only possible for me to write a very short article on this subject in notes form as an introduction. 

It took me four years to learn physiology as a pure subject in a university for my undergraduate degree, and 3 - 4 times again, but with far less details  as part of pre-clinical medicine. 

Just to give my gentle lay readers  an idea how the human body works, I can only give an  overview of the cells, tissues, organs, and systems of the human body and just one or two sentences about  their functions. 

I have provided some good books on this subject - some books run into several chapters containing hundreds of pages, others more than a thousand pages.  Readers may buy them for further reading.  

Introduction: 

Human physiology is the study of how the human body functions at various levels, from the cellular to the systemic. The body is composed of trillions of cells that form tissues, which in turn form organs and organ systems. These systems work in concert to maintain homeostasis, ensuring the survival and proper functioning of the organism. This article provides an overview of the fundamental units of the body, their functions, and the role of the blood, lymphatic, and immune systems.

Cells: The Building Blocks of Life

Cells are the fundamental units of life in the human body. Each cell type has specific functions necessary for maintaining bodily processes. Major cell types include:

• Epithelial cells – Form protective barriers and are involved in absorption, secretion, and sensation.

• Muscle cells (myocytes) – Facilitate movement and include skeletal, cardiac, and smooth muscle cells.

• Nerve cells (neurons) – Transmit electrical signals for communication within the body.

• Blood cells – Include red blood cells (oxygen transport), white blood cells (immune defense), and platelets (clotting).

• Connective tissue cells – Support and bind other tissues, including fibroblasts, chondrocytes (cartilage), and osteocytes (bone).

Tissues: Structural and Functional Units

The human body is composed of four primary tissue types:

1. Epithelial Tissue – Covers surfaces, lines cavities, and forms glands.

2. Connective Tissue – Provides structural support, stores energy, and facilitates immune responses.

3. Muscle Tissue – Enables movement through contraction.

4. Nervous Tissue – Facilitates communication via electrical and chemical signals.

Organs and Organ Systems

Organs are structures composed of multiple tissue types that perform specific functions. These organs are organized into systems that work together to maintain health and homeostasis. Major systems include:

1. Circulatory System

• Composed of the heart, blood vessels, and blood.
• Functions to transport oxygen, nutrients, hormones, and waste products throughout the body.

2. Respiratory System

• Includes the lungs, trachea, bronchi, and diaphragm.

• Facilitates gas exchange by delivering oxygen to the blood and expelling carbon dioxide.

3. Digestive System

• Consists of the mouth, esophagus, stomach, intestines, liver, and pancreas.

• Breaks down food, absorbs nutrients, and eliminates waste.

4. Nervous System

• Comprises the brain, spinal cord, and peripheral nerves.

• Regulates body functions through electrical and chemical signaling.

5. Endocrine System

• Consists of hormone-secreting glands (e.g., thyroid, adrenal glands, pancreas).

• Controls metabolism, growth, and homeostasis via hormonal regulation.

6. Skeletal System

• Composed of bones, cartilage, and joints.

• Provides structural support, facilitates movement, and protects organs.

7. Muscular System

• Includes skeletal, smooth, and cardiac muscles.

• Enables voluntary and involuntary movements.

8. Urinary System

• Consists of the kidneys, ureters, bladder, and urethra.

• Filters blood, removes waste, and regulates fluid balance.

9. Reproductive System

• Includes male and female reproductive organs.

• Responsible for reproduction and hormone production.

Blood, Lymph, and Immune Systems

Blood System

Blood is a vital connective tissue responsible for transporting oxygen, nutrients, and hormones. It consists of:

• Red blood cells (erythrocytes): Carry oxygen via hemoglobin.

• White blood cells (leukocytes): Play a role in immune defense.

• Platelets (thrombocytes): Aid in clotting and wound healing.

• Plasma: The liquid component that carries nutrients, hormones, and waste products.

Lymphatic System

The lymphatic system consists of lymph nodes, lymphatic vessels, the spleen, and the thymus. It functions to:

• Transport lymph (a fluid containing white blood cells) and remove toxins.

• Assist in immune defense by filtering pathogens.

• Maintain fluid balance and absorb dietary fats.

Immune System

The immune system protects the body from pathogens through two main types of immunity:

• Innate immunity: First line of defense (e.g., skin, mucous membranes, inflammatory response).

• Adaptive immunity: Involves specific responses via T-cells and B-cells that produce antibodies.

Conclusion

The human body is an intricate and highly coordinated system that relies on specialized cells, tissues, and organs to function effectively. The integration of various physiological systems ensures survival, adaptation, and overall well-being. Understanding these fundamental components allows for a deeper appreciation of human health and disease.

References for Further Reading

1. Guyton, A. C., & Hall, J. E. (2020). Textbook of Medical Physiology. Elsevier.

2. Marieb, E. N., & Hoehn, K. (2018). Human Anatomy & Physiology. Pearson.

3. Tortora, G. J., & Derrickson, B. (2020). Principles of Anatomy and Physiology. Wiley.

4. Alberts, B., Johnson, A., Lewis, J., et al. (2015). Molecular Biology of the Cell. Garland Science.

5. Abbas, A. K., Lichtman, A. H., & Pillai, S. (2019). Cellular and Molecular Immunology. Elsevier.

6  Best and Taylor’s Physiological Basis for Medical Practice is indeed a classic, and The Living Body by the same authors is also a great resource.  

The Mystery on The Chemistry of Life

"I will praise thee; for I am fearfully and wonderfully made: marvellous are thy works; and that my soul knoweth right well".

(Psalm 139: 14)

First of all, I need to apologise that this article has a high content of biochemistry that may not be accessible to the general reader. But not to worry, I have an intended purpose for this for another mind-searching article I shall write later. 

I know biochemistry is a very complex and difficult to understand topic. I too find it difficult despite my strong undergraduate background in chemistry, biology and medicine. In fact, I have just written 3 very brief revisions courses in chemistry here:   

Revision course in Inorganic Chemistry 

https://scientificlogic.blogspot.com/2025/04/inorganic-chemistry-revision-in-nutshell.html

Revision course in Physical Chemistry 

https://scientificlogic.blogspot.com/2025/04/a-short-revision-in-physical-chemistry.html

Revision course in Organic Chemistry 

https://scientificlogic.blogspot.com/2025/04/a-short-revision-in-organic-chemistry.html

So, not to worry,  my initial purpose here is to bring you through a  very, very brief journey to mind-blow ourselves how complex our body has been designed by an Intelligent Design for an intended purpose. Are we ready? Let's go! 

Our bodies are composed of millions of chemical compounds, these compounds interact through various chemical reactions to sustain life. An example is digestion where food is digested into smaller molecules that the body can absorb involving complex chemical reactions and enzymes. Then there are chemical bonds which are interactions between atoms that allow them to form molecules and structures essential for life.

So, the biochemist will tell us life is nothing but just  a set of chemistries. But who designed it to work that way when we are still alive? Let us look at some examples of the types of chemistries that are going on in our living body. 

Later on, in separate articles I shall explain if there is a soul behind that controls all these highly complex chemistries. But that can come later. Let us first have a quick look at some of these chemistries  

Lipids are key elements in the chemistry of life, forming membranes and storing energy, while nucleic acids (DNA and RNA) are fundamental to heredity and store genetic information.


Carbohydrates are essential biomolecules that provide energy for living organisms whereas carboxylic acids are a biologically important class of molecules, including amino acids and fatty acids, which are essential for building proteins and lipids.


Then there are enzymes that are biological catalysts that speed up chemical reactions in living organisms, enabling processes like digestion and metabolism, let alone the various types of hormones.


Then what about signalling molecules involved in cellular signalling? These chemistries taking place in a living body touches on the vast and intricate world of biochemical processes that sustain life. All these chemistries can only take place when the body is still living and alive. They completely stop when life ceases.

Let me expand upon these examples systematically  starting with metabolic pathways when there is still life in the body.

Metabolic pathways are a series of biochemical reactions that convert molecules into usable forms of energy and essential biomolecules. For example, we have the most famous of all - the Krebs Cycle (Citric Acid Cycle) the key metabolic pathway in cellular respiration, occurring in the mitochondria, where acetyl-CoA is oxidized to produce ATP, NADH, and FADH₂.

Then there is glycolysis which is the breakdown of glucose into pyruvate, yielding ATP and NADH in the cytoplasm.


Electron Transport Chain (ETC) is the final stage of cellular respiration, where electrons from NADH and FADH₂ drive ATP production through oxidative phosphorylation.


Beta oxidation is the breakdown of fatty acids into acetyl-CoA for energy production.


In digestion and biomolecule breakdown of carbohydrate digestion we have enzymes like amylase that break down starch into maltose and eventually glucose for energy.


In protein digestion, proteins are hydrolysed by pepsin, trypsin, and peptidases into amino acids for cellular functions.


Lipid digestion is when lipases break down triglycerides into glycerol and free fatty acids, aided by bile salts in the intestines.


There are also chemical bonds in biological molecules such as covalent bonds. Strong bonds holding atoms together in molecules, such as peptide bonds in proteins and phosphodiester bonds in DNA. Hydrogen bonds are weak but essential bonds stabilizing DNA’s double helix and protein structures.

Next, are ionic bonds formed between charged biomolecules, such as in salt bridges in protein folding.


Lipids in life have their biological roles such as phospholipids that are essential for cell membrane structure, forming the lipid bilayer.


Triglycerides store energy in adipose tissues, and steroids (e.g., cholesterol) serve as precursor to hormones like cortisol, testosterone, and oestrogen.

In genetics we have nucleic acids and genetic information. DNA (Deoxyribonucleic Acid) stores genetic instructions for protein synthesis, while RNA (Ribonucleic Acid) functions in gene expression (mRNA, rRNA, tRNA).


ATP (Adenosine Triphosphate) is a nucleotide that acts as the energy currency of the cell.


In carbohydrates and energy production there are monosaccharides (e.g., glucose, fructose) that are simple sugars used for immediate energy. Disaccharides (e.g., sucrose, lactose) are broken down into monosaccharides for absorption. Polysaccharides (e.g., glycogen, starch, cellulose) are energy storage and structural components in plants and animals.


Then we have carboxylic acids and their biological importance. For example, amino acids are the building blocks of proteins, containing carboxyl (-COOH) and amino (-NH₂) groups.


Fatty acids are essential components of lipids, playing a role in membrane fluidity and energy storage.

Let's consider enzymes as biological catalysts. Digestive enzymes like amylase, protease, and lipase break down macromolecules.


There are also metabolic enzymes like hexokinase in glycolysis and ATP synthase in oxidative phosphorylation, while DNA polymerase facilitates DNA replication.


In life, we also have hormones and their regulatory functions. For example, there are peptide hormones (e.g., insulin, glucagon) that regulate blood sugar.

Steroid hormones (e.g., cortisol, oestrogen, testosterone) influence metabolism, reproduction, and stress responses, whereas thyroid hormones (e.g., T3 and T4) control metabolism and development.


Ah! The living body also produces signalling molecules for cellular communication. Examples include neurotransmitters (e.g., dopamine, serotonin, acetylcholine). These mediate nerve signal transmission. There are also cytokines (e.g., interleukins, tumour necrosis factor that are involved in immune responses.


The living body also has second messengers (e.g., cAMP, Ca²⁺, IP₃) that transmit signals inside cells.

G-Proteins mediate receptor signalling pathways, activating intracellular responses. Each of these processes is essential for maintaining life, ensuring homeostasis, and responding to environmental changes.


When I was an undergraduate student, and even when I went further to  study other systems of medicine at postgraduate levels, I found biochemistry truly fascinating, as it reveals the intricate molecular dance that sustains life. Yes, indeed biochemistry is quite complicated and difficult to understand as it involves so many pathways.

Strangely, initially I asked myself, why was it that  these pathways don't inhibit, interfere or crash with each other - each going their own pathway without 'traffic lights'? These biochemical pathways operate harmoniously without interference.


Indeed, initially I thought it is quite remarkable that millions of biochemical reactions occur simultaneously in the body without "traffic lights" to regulate them. However, this seemingly chaotic system is actually highly organized, thanks to several fundamental biochemical principles that ensure order and efficiency.


Later when my knowledge in biochemistry became more advanced, I realized that there are some key factors that prevent biochemical pathways from interfering or crashing into each other. Let me give some examples:


Compartmentalization of reactions are when cells use specialized organelles to separate different biochemical pathways. For example, glycolysis occurs in the cytoplasm, while the Krebs cycle and oxidative phosphorylation take place in the mitochondria.

DNA replication happens in the nucleus, while protein synthesis (translation) occurs in the cytoplasm (ribosomes).


Fatty acid synthesis takes place in the cytoplasm, whereas fatty acid breakdown (β-oxidation) happens in the mitochondria.


This physical separation prevents conflicting reactions from interfering with each other. Then we have enzyme specificity and regulation. Enzymes are highly specific to their substrates, meaning each enzyme only catalyzes one type of reaction. For example, hexokinase phosphorylates glucose but does not act on other molecules.


Feedback inhibition prevents unnecessary reactions. For example, when ATP levels are high, enzymes in glycolysis slow down to avoid excess energy production.


Another biochemical control is called Allosteric Regulation (Molecular "Traffic Control").


Some enzymes have allosteric sites where regulatory molecules can enhance or inhibit their activity.

An example is, phosphofructokinase-1 (PFK-1), a key glycolysis enzyme, is inhibited by ATP and activated by AMP, ensuring energy is only produced when needed.


In a living body chemistry, signalling pathways coordinate activities where cells communicate via hormones and signalling molecules, which regulate biochemical reactions. For example, insulin signals cells to take up glucose and store energy. Glucagon signals cells to break down glycogen when energy is needed.


Calcium ions (Ca²⁺) act as second messengers in muscle contraction, neurotransmission and enzyme activation.

There are also temporal regulations (timing of reactions) where certain reactions only occur when needed (e.g., DNA replication happens only during the S-phase of the cell cycle).


In a living body there are also circadian rhythms that regulate metabolic processes based on the body’s internal clock (e.g., melatonin secretion at night).


The living body has molecular crowding and organization. Despite the high concentration of molecules inside cells, molecular interactions are not random. Macromolecular complexes (e.g., ribosomes, proteasomes) help streamline biochemical processes.

The living body controls protein degradation and recycling to prevent build-up of unnecessary or misfolded proteins, the ubiquitin-proteasome system degrades and recycles proteins, ensuring only functional biomolecules are present.


In summary, the complexity of chemistries taking place in a body that has life in it, even though it looks like biochemical reactions should crash into each other, they don’t, because of precise spatial, temporal, and regulatory control mechanisms. These self-organizing principles are so intricate that they almost resemble a carefully designed traffic system without actual "traffic lights."


Perhaps this is another example of the astonishing intelligence embedded in nature. Does this level of organization could have evolved randomly, or does it suggest an underlying design? - The Hands of God who created us so wonderfully. 

Once again may we conclude with this verse:

"I will praise thee; for I am fearfully and wonderfully made: marvellous are thy works; and that my soul knoweth right well".

(Psalm 139: 14)

Chemical Life?

I have just written about the vast knowledge of our human brain here: 

https://scientificlogic.blogspot.com/2025/04/the-vast-knowledge-of-our-human-brain.html

This leads me to continue with another topic about 'chemical life and chemical evolution" which some scientists explain that's how life originated. 

They claim that life began on Earth as a result of some random combination of biomolecules.  Earth is about 4.5 billion years old. Scientists think that by 4.3 billion years ago, Earth may have developed conditions suitable to support life. The oldest known fossils, however, are only 3.7 billion years old. So how did these biomolecules spring into life randomly without the breath of life breathed into them? As far as I know such undirected processes have never been demonstrated or observed in the laboratory and are never likely to be observed. It is true that artificial life of some kind has been created by chemists such as Crate Venter using sophisticated techniques to mimic the DNA found in living things. "The creation of an artificial life form, even if achieved, could never occur unless directed by some highly skilled and intelligent people - never by an undirected natural process"  in the words of Professor Edgar Andrews. I concur this myself. 

 In other words, there must be an Intelligent Designer behind the scenes. 

To me, this profound question strikes at the heart of one of the greatest mysteries of science, the origin of life. The idea that life arose through chemical evolution is a fascinating yet deeply unresolved topic, one that has been debated for decades. Let me take you on a journey through what is known, what remains unknown, and the ultimate question of whether life could arise without an Intelligent Designer.

First we ask ourselves what is "chemical evolution"?

Chemical evolution refers to the hypothetical natural process by which simple chemical compounds gradually organized themselves into complex biomolecules, leading to the emergence of the first self-replicating life forms. Scientists hypothesize that this process occurred in several stages:

Stage 1: Formation of Simple Organic Molecules (Prebiotic Chemistry)

a). Earth's early atmosphere, possibly rich in methane (CH₄), ammonia (NH₃), hydrogen (H₂), and water vapor (H₂O), provided the raw materials. 

In 1953, the Miller-Urey experiment showed that when electrical sparks (simulating lightning) were applied to such a mixture, it produced amino acids, the building blocks of proteins.

Other studies suggest that organic molecules could have come from hydrothermal vents at the ocean floor or even arrived from meteorites (as seen in the Murchison meteorite, which contained amino acids).

Stage 2: Formation of Polymers (Proteins, RNA, and Lipids)

(a). Amino acids and nucleotides must have linked together to form proteins and RNA/DNA.

(b). However, this is a major challenge, as these molecules tend to break down in water rather than form complex chains.

(c). Some researchers propose that clay minerals or hydrothermal vents provided surfaces that stabilized the molecules and catalysed their formation.

Stage 3: Self-Replication and the "RNA World"

(a). The discovery that RNA can act both as genetic material and as a catalyst (ribozymes) led to the RNA world hypothesis—that early life was based on self-replicating RNA molecules.

(b). Yet, no one has been able to demonstrate how a fully self-replicating RNA molecule could form spontaneously.

Stage 4: Encapsulation into Protocells

(a). Life needs a membrane to separate itself from the environment.

(b). Lipid molecules naturally form micelles and vesicles in water, which could have served as primitive cell membranes.

(c). Some experiments have shown that vesicles can grow and divide spontaneously, but they do not yet exhibit life-like behaviour.

 The Unsolved Mystery: How Did "Life" Truly Begin?

Despite these hypotheses, there is a fundamental gap between chemical evolution and biological life:

(a). No self-replicating system has ever emerged spontaneously in a lab.

(b). Information storage and transmission (such as the genetic code) remains unexplained—how did life "know" how to encode its functions?

(c). The complexity of even the simplest bacteria exceeds anything that could arise by pure chance alone.

Even if all biomolecules formed spontaneously, life requires organization, purpose, and self-replication, none of which have been demonstrated without an intelligent guiding force.

Is an Intelligent Designer Necessary?

My intuition is one that many scientists and philosophers share. Could it be that life was deliberately designed? Here are some of my key thoughts:

1. The fine-tuning of the universe for life, such as the precise physical constants, suggests a non-random design.

2. The sheer complexity of biological information in DNA resembles an engineered system rather than a random accident.

3. Even the most advanced synthetic biology (like Craig Venter’s artificial genome) requires intelligence and planning, suggesting that unguided natural processes alone would struggle to achieve the same.

If life indeed emerged without a guiding intelligence, why have we never observed such a process occurring again in nature? If it happened once, why not twice, or countless times?

My personal conclusion is, the search continues since Science has not yet explained the origin of life in a definitive way, and perhaps it never will. What we do know is that chemical evolution alone does not yet account for the leap to true life.

Does this mean there is an Intelligent Designer? Many, including some of the greatest scientific minds believe so. The question is not merely scientific but also philosophical and theological.

I leave this thought to my readers. Perhaps life’s true origin lies beyond what science alone can uncover. If the universe operates with intelligence, then perhaps, as I have always suspected, there is indeed a Higher Designer behind it all.