Psalm 139:14  “Thank you for making me so wonderfully complex! Your workmanship is marvelous—how well I know it.”

David was not offering a vague compliment to God.  He was praising God for His personal care in creating him.  He recognized that he was not an accident, not a simple collection of parts, and not a self-made being.  He was the workmanship of a wise and loving Creator.

David says, “I am wonderfully complex.”  Other translations say, “fearfully and wonderfully made.”  The point is that the human body inspires reverent awe.  The more we learn about it, the more we have reason to say with David: “Your workmanship is marvelous—how well I know it.”

Consider some ordinary circumstances that we experience every day—sleeping, waking, walking, stepping into the cold, and entering a warm room.  These may seem simple to us.  But behind each simple experience is an astonishing coordination of organs, nerves, hormones, blood vessels, muscles, and countless living cells.

## While We Sleep

When we go to sleep, it may appear that we simply “shut down.”  But sleep is not a shutdown.  It is more like a carefully scheduled night shift.

Throughout the night, the brain guides us through repeating cycles of non-REM sleep and REM sleep.  During those cycles, our circulation, breathing, hormones, immune system, brain activity, and muscle control are continually adjusted.

While we sleep, the brain carries out important maintenance.  It helps strengthen and organize memories.  Things we learned, experienced, or struggled to understand during the day can be sorted and stabilized in our memory.  That is one reason why, after sleeping on a problem, a person may wake up with clearer thinking.

The brain also becomes more active in clearing away certain waste products that build up while we are awake. In a sense, while we rest, the brain is doing its own housekeeping.

Sleep also helps regulate emotions and restore attention.  After a proper night’s sleep, we are generally better able to focus, make decisions, and respond calmly to situations.  When sleep is shortened or disturbed, we often feel that effect immediately in our patience, judgment, and concentration.

But it is not only the brain that is busy.  The body is also in a repair mode. Sleep supports tissue recovery, wound healing, muscle recovery, and ordinary cell maintenance.  The immune system remains active, organizing defenses against infection.  Hormones involved in hunger, fullness, and blood-sugar regulation are also influenced by sleep.

Even the heart and lungs adjust.  During deeper sleep, heart rate, breathing rate, blood pressure, and body temperature generally decrease.  That gives the cardiovascular system a lower-workload period. Then, during REM sleep, the picture changes.  The brain becomes highly active, dreams may become vivid, the eyes move rapidly beneath the eyelids, and breathing and heart rate can become more irregular.

During this stage, God designed an especially remarkable safeguard: most of the body’s voluntary muscles are temporarily switched off.  This is called REM atonia. In effect, while the mind may be dreaming of running, talking, or moving, the body is usually prevented from acting out the dream.

So even while we are unconscious and unable to direct any of these processes, the body is being maintained, protected, repaired, and prepared for a new day.  We did not command it to do those things.  We did not coordinate those systems. God designed them to function faithfully while we sleep.

## When We Awaken

Then morning comes, and we awaken. Again, what seems simple is actually an extraordinary transition.

As we wake, our heart rate and blood pressure begin rising from their lower sleeping levels.  Breathing becomes more responsive to activity, posture, conversation, and light.  If we sit up or stand, blood naturally tends to shift downward because of gravity.  But the autonomic nervous system immediately makes adjustments in blood-vessel tone and heart rate to help maintain enough blood flow to the brain.

Our core body temperature also begins to rise as the body shifts into its daytime pattern.  Metabolism moves away from the lower-energy state of overnight fasting toward the needs of movement, thought, work, and eating.

Hormones participate too.  Cortisol, often called a stress hormone, is not merely harmful. In its normal daily pattern, it helps mobilize energy and support alertness.  Its level rises during the late night and early morning, helping prepare us for wakefulness.

But waking is not always instantaneous in the mind.  We may be on our feet while part of the brain is still catching up.  That groggy state is called sleep inertia.  The parts of the brain involved in planning, judgment, and clear decision-making may take some time to fully return to their best performance.

Is that not remarkable?  As we move from sleep to wakefulness, no committee inside us has to meet.  No one has to tell the heart when to increase its pace, the blood vessels when to adjust, the hormones when to rise, or the brain when to shift from sleep to alertness.  The Creator built those patterns into us.

## When We Decide to Walk

Now consider something as ordinary as deciding to walk across the room.

Before the first step is taken, the brain has already begun preparing the body.  Areas of the brain involved in planning movement send signals down through the spinal cord to activate the muscles needed for posture, balance, and walking.

At the same time, the brain sends a “get ready” signal to the autonomic nervous system.  Heart rate, blood pressure, and breathing can begin adjusting even before the working muscles have fully signaled their need for more oxygen.

Then the balance system springs into action.  The eyes, the inner ear, the muscles, the joints, the tendons, and the feet all send continual reports to the brain.  The trunk, hips, knees, ankles, and feet make countless small corrections so that we do not fall.  One leg supports the body while the other swings forward.  Then they trade roles, again and again, with remarkable timing.

As the leg and hip muscles contract, they need more energy.  They use ATP, the immediate energy currency within cells.  They consume oxygen and fuel.  They produce carbon dioxide and heat.  In response, nearby blood vessels widen and send increased blood flow to the working muscles.

Meanwhile, the heart increases its pumping activity.  Blood flow is prioritized toward the muscles, heart, and brain.  The calf muscles do more than move us forward; with each contraction, they compress veins in the legs and help push blood back toward the heart.  One-way valves in those veins help keep the blood moving in the correct direction.

For the first few seconds, the muscles use immediately available energy stores.  Then, as walking continues, they rely increasingly on oxygen-based energy production, using a blend of blood glucose, stored carbohydrate, and fat.

All this happens when a person simply decides, “I will walk over there.”

We may think we are merely taking a few steps.  But beneath those steps is a coordinated system of thought, nerve impulses, balance signals, muscle contractions, heart action, blood-vessel adjustments, gas exchange in the lungs, and cellular energy production.

## When We Step Into the Cold

Suppose we walk outside into a cold environment.  Again, the body responds immediately.

Special temperature sensors in the skin detect the cold and send messages to the brain.  The brain’s temperature-control center, the hypothalamus, begins protecting the body’s core temperature.

Blood vessels in the skin constrict.  Less warm blood is sent to the hands, feet, ears, nose, and outer skin.  The fingers may feel cold, and the skin may become pale.  In effect, the body forms a cooler outer shell in order to preserve warmth for the brain, heart, and internal organs.

Goosebumps may appear as tiny muscles attached to hair follicles contract. In animals with thick fur, this helps trap a layer of warm air.  In humans it does not provide much insulation, but it is still evidence of an ancient protective system built into the body.

The heart may work harder as blood vessels narrow.  Blood pressure can rise. If the cold continues, muscle tension increases.  We instinctively pull in our arms, tighten our posture, hunch our shoulders, or seek shelter.  The body is trying to conserve heat.

If more heat is needed, shivering begins.  These are rapid, involuntary muscle contractions.  The movement may not accomplish useful work outwardly, but it produces heat.  The body is using fuel in order to protect the vital organs from dangerous cooling.

Even breathing is affected.  Cold, dry air can cool and dry the nose, throat, and airways.  For some people, especially those with asthma, it can trigger coughing, chest tightness, wheezing, or shortness of breath.

Again, we did not consciously arrange any of this.  We did not instruct the vessels to constrict, the muscles to shiver, or the brain to protect the core temperature. God’s design immediately responds to the environment.

## When We Enter Warmth

Now suppose we step back into a warm environment.  The response largely reverses.

The body reduces its heat-conserving measures.  Skin blood vessels relax and widen. Warm blood flows more freely to the hands, feet, face, and skin.  Fingers that were cold may tingle, ache, or turn pink as circulation returns.

Shivering stops.  Goosebumps flatten.  The body no longer needs to keep every bit of heat inside.

In this situation, the skin becomes something like a radiator.  The body brings warm blood from the core toward the skin surface so excess heat can be released into the surrounding air.

If the environment is very warm, the body uses another remarkable system: sweating. Sweat itself does not cool us simply because it is wet.  It cools us when it evaporates from the skin and carries heat away.

That is why humidity makes hot weather feel more difficult.  In dry air, sweat can evaporate more readily.  In humid air, it remains on the skin, and the body has a more difficult time getting rid of excess heat.

The heart may beat faster to deliver blood to the skin for cooling while still supplying the brain, muscles, and internal organs.  The body must carefully balance all of those demands.

## Marvelous on Every Level

These are only a few examples of God’s marvelous workmanship in ordinary situations.

Sleeping. Waking. Standing. Walking. Feeling cold. Becoming warm.  These are things we do every day without giving them much thought.  Yet in each situation, the body is coordinating systems beyond anything we could consciously manage.

And what we have described is only at the organ-system level: the brain, heart, lungs, blood vessels, muscles, nerves, skin, and glands.

But for those systems to work, there are millions upon millions of actions occurring at the cellular level.  Nerve cells are transmitting signals.  Muscle cells are contracting. Blood cells are carrying oxygen.  Immune cells are identifying threats.  Hormones are carrying messages.  Cells are producing energy, repairing damage, removing waste, and responding to changing conditions.

Every moment, countless processes are taking place in precise order and at the proper time.

We did not design those systems.  We did not start them.  We do not have to keep giving them instructions.  Even when we are asleep, unconscious, distracted, or unable to think about them, they continue to operate.

David’s words are therefore deeply meaningful:

> “Thank you for making me so wonderfully complex!  Your workmanship is marvelous—how well I know it.”

The more we consider the body—not merely as a machine, but as a living, integrated, self-regulating creation—the more we have reason to praise Jehovah.  His workmanship is not only marvelous in the great things we see in creation.  It is marvelous in the quiet, hidden processes taking place inside each one of us every second of every day.