Human Body and Its Digestion System – all you need to know

This article will provide a deeper understanding of how these cells, tissues, and organs acquire their nutrients through the help of the digestive system.

The human digestive system is an interconnected multiple-organ system that is responsible for the breaking down of food into small enough particles for the body to absorb. These small food particles provide the nutrients that the body requires to achieve homeostasis. The required nutrients that the body desires are commonly known as carbohydrates, proteins, fats, vitamins, and minerals, which all support growth and cellular regeneration. The multiple organs that make up the digestive system start from the mouth and pass all the way through the body to the anus via the gastrointestinal tract. In addition to the gastrointestinal tract, the liver, the pancreas, and the gallbladder also aid in the digestion process. It is imperative that these organs are all functioning properly because they directly affect nutritional absorption and overall health. 

The digestive system serves as a remarkable network within the human body, playing a pivotal role in both nutrient absorption and energy production. Its intricate processes involve a series of interconnected organs and mechanisms that work harmoniously to break down ingested food into usable components that the body can utilize for various physiological functions.

At its core, the digestive system is responsible for converting complex macronutrients, such as carbohydrates, proteins, and fats, into simpler forms that can be readily absorbed by the body. This process begins as soon as food enters the mouth, where mechanical and chemical digestion commence. The food is broken down into smaller particles, and enzymes in saliva start breaking down carbohydrates, initiating the digestion of starches into simpler sugars.

This journey continues into the stomach, where gastric juices containing hydrochloric acid and enzymes further break down proteins into amino acids. From there, the partially digested food moves into the small intestine, where the bulk of nutrient absorption takes place. Enzymes from the pancreas and bile from the liver aid in the breakdown of fats, carbohydrates, and proteins into their building blocks—fatty acids, glucose, and amino acids. These nutrients are then absorbed through the intestinal walls into the bloodstream and transported to cells throughout the body.

The interconnectedness of organs and processes is essential for the efficient functioning of the digestive system. The mouth, esophagus, stomach, small intestine, and colon work seamlessly together, each contributing a vital role to ensure the breakdown and absorption of nutrients.

The Brain-Gut Connection

The intricate relationship between the brain and the gut, often referred to as the brain-gut connection or the gut-brain axis, highlights the profound influence of mental and emotional states on the digestive process. This dynamic interplay between these two systems plays a significant role in initiating, modulating, and even disrupting various aspects of digestion.

Explanation of the Brain’s Role in Digestion

The brain-gut connection plays a pivotal role in regulating appetite and satiety through a complex interplay of hormones and neural signals. When we eat, sensory input from the sight, smell, and taste of food triggers the brain to release hormones like ghrelin and leptin. Ghrelin, often referred to as the “hunger hormone,” stimulates appetite and promotes food intake, while leptin, known as the “satiety hormone,” signals fullness and inhibits further eating. Moreover, the gut communicates with the brain through the vagus nerve, relaying information about digestion and nutrient availability. This bidirectional communication between the brain and gut influences our perceptions of hunger and satisfaction, helping to regulate food intake and maintain energy balance. Disruptions in this intricate system can contribute to overeating, obesity, and other eating-related disorders, highlighting the importance of a balanced brain-gut axis for healthy appetite regulation.

Impact of Emotions and Stress on Digestion

Stress plays a significant role in the brain-gut connection and can have a profound impact on appetite regulation and eating behaviors. When the body experiences stress, the brain triggers the release of stress hormones, such as cortisol, which can affect appetite in various ways.

Stress-induced cortisol release can lead to changes in appetite hormones. For example, some individuals may experience an increase in ghrelin levels, leading to heightened feelings of hunger and cravings for high-calorie, comfort foods. This can contribute to overeating and weight gain over time. On the other hand, stress has been linked to decreased levels of leptin, the hormone responsible for signaling fullness. As a result, individuals under stress might have difficulty recognizing when they are satisfied, leading to excessive food consumption.

Furthermore, stress can disrupt the intricate neural communication between the brain and gut. The gut has a network of neurons known as the enteric nervous system, often referred to as the “second brain.” Stress can alter the function of this network, influencing gut motility, nutrient absorption, and sensitivity to appetite-related hormones.

The Mouth and Salivary Digestion

The mouth, often regarded as the gateway to the digestive system, is a crucial starting point for both physical and chemical digestion. Its intricate mechanisms set the stage for the efficient breakdown of food, ensuring the extraction of vital nutrients and energy from the ingested materials.

Role of the Mouth in Digestion

The mouth plays a dual role in digestion—physical and chemical. Physically, it breaks down food into smaller, more manageable particles through the mechanical action of chewing. This initial step increases the surface area of the food, making it easier for digestive enzymes to access and break down nutrients. Moreover, the mouth’s mechanical processing initiates the release of enzymes and promotes the mixing of food with saliva, a vital component in the chemical digestion process.

Salivary Enzymes and Carbohydrate Breakdown

Saliva, a complex fluid secreted by salivary glands, contains essential enzymes that initiate the chemical breakdown of carbohydrates. Amylase, a key enzyme found in saliva, begins the process of carbohydrate digestion by breaking down complex starches into simpler sugars like maltose. This enzymatic activity becomes especially significant when starchy foods like bread, rice, and potatoes are chewed, as amylase starts converting their carbohydrates into more digestible forms.

Chewing and Saliva Production for Efficient Digestion

Chewing serves as a pivotal initial step in the digestive process. Proper mastication not only breaks down food into smaller particles but also facilitates the mixing of food with saliva. Effective chewing exposes more surface area of the food to saliva and its enzymes, ensuring thorough carbohydrate digestion and nutrient release. Furthermore, chewing stimulates the production of saliva, which contains water, mucus, and electrolytes that lubricate the food and create a suitable medium for enzyme activity.

Swallowing and the Esophagus

Swallowing, an intricate physiological process, is a seamless orchestration of muscle contractions and coordinated movements that ensures the safe and efficient transport of food and liquids from the mouth to the stomach. At the core of this process lies the esophagus, a muscular tube connecting the throat to the stomach, which serves as a crucial conduit for bolus movement and the avoidance of discomfort.

Mechanics of Swallowing and the Role of the Esophagus

Swallowing, or deglutition, involves three distinct phases: the oral phase, the pharyngeal phase, and the esophageal phase. The esophagus takes center stage during the esophageal phase. After food is propelled to the back of the mouth, the upper esophageal sphincter relaxes, allowing the bolus to enter the esophagus. Muscular contractions, known as peristalsis, then propel the bolus downward, pushing it through the esophagus and towards the stomach. The lower esophageal sphincter subsequently relaxes, permitting entry into the stomach.

Importance of Proper Posture and Chewing

Proper posture and effective chewing play pivotal roles in preventing discomfort during swallowing. Maintaining an upright posture while eating allows gravity to aid in the smooth passage of food through the esophagus, reducing the risk of regurgitation and acid reflux. Additionally, adequate chewing breaks down food into smaller, more manageable pieces, easing its transition through the esophagus and minimizing the likelihood of blockages or discomfort. Insufficient chewing can lead to larger food particles that may not smoothly pass through the esophagus, potentially causing discomfort or even potential choking hazards.

Gastric Digestion in the Stomach

The stomach, a muscular and highly adaptable organ, plays a central role in the digestive process by further breaking down ingested food and mixing it with gastric juices. This intricate dance of mechanical and chemical processes sets the stage for efficient nutrient extraction and energy production.

Stomach’s Role in Breaking Down Food and Mixing with Gastric Juices

Upon entering the stomach, food encounters a series of rhythmic contractions known as peristalsis. These contractions mix the food with gastric juices, creating a semi-liquid mixture called chyme. The stomach’s muscular walls churn and mix the chyme thoroughly, exposing it to the digestive enzymes and hydrochloric acid present in the gastric juices. This mechanical breakdown, coupled with the chemical activity of the gastric juices, effectively begins the process of digestion.

Hydrochloric Acid and Enzymes for Protein Digestion

One of the stomach’s pivotal roles is protein digestion, facilitated by the presence of hydrochloric acid and specific enzymes. Hydrochloric acid maintains the stomach’s highly acidic environment, with a pH of around 1-2, creating an optimal milieu for protein breakdown. This acid denatures proteins, unfolding their complex structures and rendering them more susceptible to enzymatic attack.

Pepsin, a crucial enzyme secreted by specialized cells in the stomach lining, is responsible for breaking down proteins into smaller peptides. As the chyme mixes with gastric juices, pepsin cleaves peptide bonds, breaking proteins into fragments that can be further digested in the small intestine.

Journey through the Digestive Tract: Small Intestine and Colon

The small intestine and colon, the latter part of the digestive tract, continue the intricate process of nutrient absorption, waste elimination, and maintaining overall digestive health. Here, we dive into the multifaceted roles of these two segments in extracting nutrients, regulating water balance, and supporting optimal digestion.

Detailed Exploration of the Small Intestine’s Function

The small intestine, despite its name, is a lengthy and convoluted structure where the majority of nutrient absorption occurs. Divided into three sections—the duodenum, jejunum, and ileum—the small intestine is equipped with specialized structures called villi and microvilli. These finger-like projections greatly increase the surface area, maximizing nutrient absorption efficiency.

Here, various enzymes and secretions from the pancreas and gallbladder play vital roles. Pancreatic enzymes, including amylase, protease, and lipase, further break down carbohydrates, proteins, and fats, respectively. Bile, produced by the liver and stored in the gallbladder, emulsifies fats, breaking them into smaller droplets that are more accessible to digestive enzymes. This collaborative effort ensures that nutrients are broken down to their absorbable forms, such as glucose, amino acids, and fatty acids.

Colon Function, Water Absorption, and Formation of Feces

As the small intestine completes its role in nutrient absorption, undigested material and waste enter the colon, or large intestine. While nutrient absorption decreases here, the colon has a vital function: water absorption. The colon reabsorbs water and electrolytes from the remaining chyme, transforming it into a semi-solid mass known as feces. This process concentrates waste material while facilitating the body’s water balance.

The formation of feces involves the synthesis of mucus and the interaction of gut bacteria with undigested fiber and other components. The colon’s muscular contractions, called peristalsis, propel feces toward the rectum, preparing them for elimination.

Impact of Fiber on Colon Health and Regularity

Dietary fiber, a non-digestible component of plant-based foods, plays a pivotal role in colon health and regularity. Soluble fiber, found in foods like oats, beans, and fruits, forms a gel-like substance that slows digestion and aids nutrient absorption. Insoluble fiber, abundant in whole grains, vegetables, and seeds, adds bulk to feces, promoting efficient movement through the colon and preventing constipation.

Furthermore, fiber acts as a prebiotic, nourishing beneficial gut bacteria. These bacteria ferment fiber, producing short-chain fatty acids that provide energy for colon cells and support a healthy gut environment. A balanced and diverse gut microbiome contributes to immune function, inflammation regulation, and overall well-being.

The Gut Microbiome and Digestive Health

Introduction to the Gut Microbiome and its Significance

The gut microbiome is a dynamic community of bacteria, viruses, fungi, and other microorganisms that inhabit the digestive tract. This vibrant ecosystem plays a pivotal role in digestion, metabolism, and nutrient absorption. Gut bacteria help break down complex carbohydrates and fiber that the human body cannot digest on its own.

The Relationship Between Gut Bacteria and Immune Function

An essential aspect of the gut microbiome’s impact is its intricate connection with the immune system. Gut bacteria play a critical role in training the immune system to distinguish between harmless and harmful substances. They help regulate immune responses, promoting tolerance to beneficial microbes while activating immune cells to combat pathogens.

A well-balanced gut microbiome helps prevent immune dysfunction and excessive inflammation, which can contribute to autoimmune diseases and other health conditions. Imbalances in the gut microbiome, known as dysbiosis, have been linked to immune-related disorders, allergies, and chronic inflammation.

The Mucosal Barrier and Nutrient Absorption

The mucosal barrier, a remarkable shield lining the inner surfaces of the digestive tract, serves as a critical guardian of nutrient absorption and protection against pathogens. This part looks into the essential role of the mucosal barrier, factors that can compromise its integrity, and the nutrients vital for maintaining its health and functionality.

Importance of the Mucosal Barrier

The mucosal barrier acts as a dynamic interface between the body and the external environment, serving as the first line of defense against harmful substances and pathogens present in ingested food and liquids. This barrier consists of a layer of mucus, immune cells, and specialized cells that form a physical and chemical defense system, preventing harmful particles from entering the bloodstream while facilitating the absorption of vital nutrients.

Furthermore, the mucosal barrier plays a pivotal role in nutrient absorption. Nutrients are absorbed through the cells lining the small intestine, and a healthy mucosal barrier ensures efficient and selective passage of nutrients while preventing the entry of toxins and harmful microorganisms.

Factors Compromising the Mucosal Barrier

Several factors can compromise the integrity of the mucosal barrier, rendering it less effective in its protective and absorptive roles. Inflammation, triggered by factors such as stress, poor diet, or infections, can disrupt the tight junctions between mucosal cells, leading to increased permeability, also known as “leaky gut.” This condition allows harmful substances to pass through the gut lining and enter the bloodstream, potentially triggering immune responses and contributing to chronic diseases.

Certain medications, such as non-steroidal anti-inflammatory drugs (NSAIDs) and antibiotics, can also disrupt the mucosal barrier. NSAIDs may impair the protective mucus layer, making the gut more susceptible to damage, while antibiotics can alter the composition of the gut microbiome, potentially impacting the mucosal barrier’s function.

The Six Processes of Digestion

The process of digestion is a fascinating journey that begins the moment we take our first bite of food and ends with the elimination of waste from our bodies. This complex process involves six key stages: ingestion, secretion, mixing and movement, digestion, absorption, and excretion. Each stage plays a crucial role in breaking down the food we eat into nutrients that our bodies can use for energy, growth, and cell repair. In this article, we will delve into each of these six processes, exploring their importance in maintaining our overall health and well-being. So, let’s embark on this incredible journey through the human digestive system.

1. Ingestion – Ingestion occurs when food is introduced to the mouth and is in que to be broken down into smaller food particles.
2. Secretion – Secretion occurs in the mouth when salivatory glands release enzymes that speed up the breakdown process of food particles. 

III.  Mechanical Digestion – Mechanical digestion occurs in the mouth when the teeth mix and mash the food particles.

1. Digestion – Digestion is the chemical process of food particles chemically converting into the nutrients that the body requires.
2. Absorption– Absorption is the process by which the nutrients begin to disperse into the bloodstream.
3. Excretion (defecation) – Excretion is the last stage of the digestive process, where leftover waste is expelled as feces. 

Biochemical Pathway of the Human Digestive System

The food we consume every day provides our body with the necessary nutrients that it needs to function properly. Most of them contain a compilation of different essential nutrients that will be broken down in the body through a series of chemical reactions to obtain what it needs in the form that is best used by the cells (1 National Institute of Diabetes and Digestive and Kidney Diseases. (2020). Every part of the digestive system helps to move foods and liquids through the gastrointestinal tract which breaks them into smaller parts. Once they have been fully broken into small parts, they can be absorbed by the body as nutrients where they are needed (2 Belsley, S. (2023). 

What is the digestive System? 

The human digestive system is responsible for the process of digestion in our body. It is made up by the gastrointestinal tract or the GI tract, liver, pancreas and gallbladder. This digestive tract consists primarily of a group of organs that allow food and liquids to travel in our body during their processing as absorbable forms that can get into the bloodstream. The system also contains structures that carry out waste to its elimination and other organs necessary for the entire digestive process (3 Baguma-Nibasheka, 2019). The digestive system is uniquely formed to perform the specialized function of turning food into nutrients that the body uses for energy, muscle growth and cell repairing. Human body is aiming to get nutrients from digestion that includes carbohydrates, protein, fat, vitamins and minerals. Because protein, fat and carbohydrates are considered macronutrients, human body will need them in large amounts. Vitamins and minerals are labeled as micronutrients and although they are needed in smaller amounts, they play a crucial role in the body by carrying out functions from bone building to red blood cell production (1 National Institute of Diabetes and Digestive and Kidney Diseases. (2020).).

Digestive system components

To fully understand all of the parts and sections of the GI tract, it is important to start by defining the basic tissue layers of the system. The GI tract tissue consists of four concentric layers: mucosa, submucosa, muscularis externa and serosa. 

The innermost layer is the mucosa and it consists of other three layers called: epithelium, the lamina propia and muscularis mucosae. The mucosa is referred to as the mucous membrane because of the characteristic mucus production of the epithelium. The epithelium is in direct contact with ingest food and contains cells that secrete mucus, hormones and digestive enzymes. The lamina propia consists of small blood vessels, nerves and lymphatics. The muscularis mucosae are thin muscles that control mucosal blood flow and secretions (4 U.S. Department of Health and Human Services National Institutes of Health National Cancer Institute. (2023)).

The adjacent layer to the mucosa is the submucosa which is a connective layer that houses the major blood vessels, nerve plexus and lymphatics. The muscularis externa is a thick muscle layer that contains the inner circular muscles and the outer longitudinal muscles. The contractions of these layers (peristalsis) promote mechanical digestion and circulate more food to the digestive chemicals and move it along the canal. The serosa is the outer most layer and is made up of connective tissue that connects the tubular GI tract to the abdominal wall (3)(4)(5). (3 Baguma-Nibasheka, 2019) (4 U.S. Department of Health and Human Services National Institutes of Health National Cancer Institute. (2023)) (National Library of Medicine. (2016)

Alimentary Canal

Also known as the alimentary tract, it is approximately a 9 meters long tube (in total for most adults) that passes from the mouth to the anus and includes the following parts: 6

Mouth–   The mouth is the beginning of the whole digestive system and it begins working before taking the first bite. The scent of food triggers the salivary glands to secrete saliva, in turn causing the mouth to water. Once the food is added to a mouth full of saliva, the chewing process will become greatly effective in the breaking down of food particles. Saliva contains special substances such as enzymes that begin the process of breaking down food into a more absorbable form. The tongue also helps in the oral digestion phase by mixing the food with the enzymes provided by the saliva and helping move the food along into the pharynx and esophagus.

Pharynx- The pharynx is the section of the digestive system that receives food from the mouth and moves it into the esophagus.(6)(7)

Esophagus– The esophagus is a muscular tube that passes through the pharynx and into the stomach. The movement of food through the esophagus is through a unique process known as peristalsis. Peristalsis is a series of stomach muscle contractions and relaxation that mimics a wave-like effect descending the food into the stomach. However, right before the connection to the stomach, there is a special feature known as the “zone of high pressure,” or also mentioned as the lower esophageal sphincter. This sphincter operates like a valve by allowing food to pass into the stomach but prevents it from coming back into the esophagus.  (6)(7)

Stomach– The stomach is found at the lower end of the esophagus and at the start of the small intestines. It holds foods while they are being mixed with enzymes to follow the process of breaking down to a more usable form for the body to absorb (9). The primary function of the stomach is to prepare food for digestion and the proper absorption by the intestine. The agent responsible for the chemical digestion of foods in the stomach is the gastric acid, also known as stomach acid. This is a substance secreted by the parietal cells in the stomach and is formed by a combination of hydrochloric acid (HCL), sodium chloride (NaCl) and potassium chloride (KCl). Their purpose is to keep levels of pH very low at the stomach and produce a neutralization reaction with sodium bicarbonate (NaHCO3) after the digested bolus leave to the intestines. This reaction neutralizes the acid to prevent damaging on the intestines (10). The stomach uses strong chemicals that are capable of destroying organic matter. The reason why the mucosa itself is not affected by gastric acid is a simultaneous process that allows parietal cells to remain near neutrality. The H+ and Cl- ions are kept separate in parietal cells until they are needed and released for digestion. The hydrochloric acid doesn’t digest the mucosa because there are cells in this tissue that secretes large quantities of protective mucus that line in the mucosal surface. Some basic electrolytes like carbonic acid (HCO3) are inside the layer of mucus and neutralize any HCl that penetrates the mucus (11) (14).

Small Intestine- The small intestine is in the lower area of the abdomen inside a large membrane known as the peritoneum. It consists of three segments, the duodenum, jejunum, and ileum (lined up, could be more than 20 feet long).  The duodenum is responsible for the breaking down of food, and the jejunum and ileum are responsible for absorbing the nutrients for release into the bloodstream. These segments all aid in the digestion process by further breaking down food by using enzymes that are released from the pancreas and the liver. The contractions known as peristalsis also play a crucial role in this organ helping food to move and be mixed with digestive secretions. The duodenum is responsible for the breaking down of foods and the jejunum and ileum are in charge of absorbing the nutrients into the bloodstream (9)(6).

Large Intestine (colon)– Beginning at the bottom of the abdomen, the colon is a 5 to 7-foot-long muscular tube that is connected with the small intestine and the rectum. The large intestine is made up of the cecum, the ascending (right) colon, the transverse (across) colon, the descending (left) colon, and the sigmoid colon that connects to the rectum. By the means of peristalsis, waste from the digestive process is passes through the intestine. First, the waste is on its liquid form and finally it becomes solid as the water is removed. This stool is stored on the sigmoid colon until it is emptied into the rectum once or twice a day (6)

Rectum– The rectum is the section that connects the colon to the anus. The rectum is responsible for receiving the stool from the colon and sending the necessary signals to the brain to alert it of the preparation to defecate or excrete the stool. 

Anus– The anus is the last part of the digestive tract. Its main purpose is to detect the kind of stool that the system is trying to expulse and to prevent and activate expulsion. This is possible by the ability of the internal and external muscles to hold the stool until it can eventually be evacuated (7).

Accessory Organs

These organs are important for the digestive process but are not considered part of the digestive system. These accessory digestive organs are:

• Teeth, tongue and salivary glands: these parts of the oral cavity are responsible for chewing and kneading food as much as possible. The tongue mixes the food with enzymes in saliva that start the process of the system before they move along the pharynx and esophagus (12).

• Pancreas: it is found behind the stomach and is where the hormones and digestive enzymes are produced. Insulin, which is the hormone that helps to maintain blood-sugar levels in balance, is created on the pancreas. These digestive enzymes are important in the process of breaking down foods. People with diabetes could be resistant to insulin, not producing it or have a pancreas that doesn’t function properly (13). 

• Liver: it is the largest gland of the human body and is located right beneath the diaphragm. It has a variety of functions and among them are the creation of the bile, storing nutrients, converting toxins into harmless substances or allowing their elimination from the body. Bile is passed from the liver to the duodenum (section of small intestine). Blood flows from the digestive tract to the liver and it process and stores vitamins and nutrients. It is also considered the “detox” part of the body because of its function of removing byproducts produced by medication and alcohol (13).

• Gallbladder: it is a small organ located under the liver. The gallbladder stores the bile after it is made by the liver. After ingesting food, the small intestine produces a hormone that allows the gallbladder to send the bile to the small intestine. The bile is responsible for the breaking down of fats in foods (13).

• Steps of the Digestive System

The process of the digestive system can be summarized through the individual processes of ingestion, digestion, absorption and excretion.

Ingestion and Digestion

During ingestion, food is located in the mouth and the process begin by chewing. On the digestive process, there are two important forms of digestion that works in the breakdown of molecules, those are the mechanical and chemical digestion. The mechanical digestion allows food to be broken down and increases its surface which also makes the digestion and absorption of the nutrients easier. In this time, the food consumed becomes a “bolus” which is easier to swallow. Also during this time, the chemical digestion starts as saliva is secreted to protect the mouth from the mechanical digestion and to help with the breaking down of foods. Saliva contains enzymes that protects the mouth and promotes the swallowing. After the mechanical digestion and the chemical digestion with saliva is finished, the bolus is moved to the esophagus to continue down the throat by peristalsis. There is an esophageal sphincter in the esophagus that regulates the in and out movement of foods. The sphincter contracts when a person is not swallowing and conversely, it relaxes when the bolus is passing to allow it to arrive at the stomach. The chemical digestion also takes place at the stomach as the gastric juices break down the extracellular matrix of the bolus (14).

Absorption

The process of absorption of nutrients will begin in the small intestine. The villi and microvilli structures in our body help to increment the surface area of the cells in the intestinal lining with the purpose of helping the process of absorption. After this, the chyme (partly digested food) passes through the large intestine. The colon reabsorbs the water and other nutrients that the body could have used during the digestive process. While the ingested materials go through the intestines by peristalsis, nutrients are being absorbed and waste is left out as feces (15).

Excretion

This is the very final step of the digestive system and consists of the body expulsing the solid waste that the process has left in the form of feces. These feces are excreted by the anus ending the process of the ingested food.

Chemistry of Nutrients

Protein digestion happens in the stomach. Gastric acid along with enzymes starts to denature proteins for digestion. The chemical digestion of proteins continues in the small intestines, where the enzyme protease keeps breaking down the protein into amino acids, which are absorbed by the walls of the intestines into the bloodstream. The digestion of fats occurs in the small intestines. Molecules of fat are mixed with the bile, which is made by the liver and stored on the gallbladder. The bile helps to dissolve the fats and make them more water-soluble. In this form, fat enzymes known as lipases, can break the fat molecules easier into fatty acids and glycerol. Also, carbohydrates are broken into glucose at the lower levels of the small intestines. Water-soluble vitamins, like vitamin C and B, don’t need any type of chemical digestion because they are directly absorbed into the bloodstream through the small intestines. Bile is needed to move fat-soluble vitamins like A, D, E and K from the fat molecules before they can be absorbed. Different minerals could have different processes of absorption. As an example, potassium is absorbed directly by the bloodstream while calcium needs a carrier to get to the bloodstream (1).

The Biochemistry of the Digestive System 9

1. I. Biochemistry of Nutrients– Protein digestion takes place in the stomach with the help of enzymes and gastric acid to denature the proteins for digestion. This chemical digestion process of proteins continues in the small intestines, where the enzyme protease continues breaking down the protein into amino acids. Amino acids are absorbed by the walls of the intestines and delivered into the bloodstream to move throughout the body. The digestion of fats takes place in the small intestines with the help of bile. Bile helps to dissolve fats and make them more water-soluble. When these fat molecules are in the water-soluble state, they can be activated with certain enzymes such as lipase, which have the capability to divide the fat molecules with less activation energy into fatty-acids and glycerol. Water-soluble vitamins, like vitamin C and vitamin B are directly absorbed into the bloodstream through the small intestines without any chemical change needed because of the vitamins’ initial water-soluble state. Bile is needed to help move fat-soluble vitamins like A, D, E, and K from fat molecules before they can be absorbed and released into the bloodstream. Minerals have different processes of absorption, such as in the example of potassium, which is absorbed and directly released into the bloodstream. On the other hand, calcium needs a carrier to be absorbed and released into the bloodstream.

1. pH Balance- The stomach acid balance is important for the digestive system to maintain. If the stomach pH acid level is too high there may be trouble with proper digestion and the possibility of microbial overgrowth. If the body is unable to produce enough stomach acid, it is also unable to digest minerals and protein molecules, which could lead to amino acid deficiencies from unmetabolized proteins. The normal pH range of the stomach needs to be between 1.5 and 2.2. 

III. Enzymes- The digestive system requires enzymes to speed up chemical reactions that take place in the body. Digestive enzymes are produced naturally by the body, mainly coming from the pancreas, stomach, and small intestine.  Enzymes are affected by factors like pH levels, where they are sensitive to a small range of pH level differences.

The Benefits of Maintaining a Healthy Digestive System

A healthy digestive system is everything that a person should strive for if they desire to be a healthy person. The reason for this is that the digestive system could present itself to be the root cause of many different types of diseases. Maintaining a healthy digestive system is as important as maintaining health on the rest of the body. Choosing to maintain a healthy digestive system will also provide the immune system with the strong support it needs to fight off all the different diseases that can be found throughout the entire body. 

The digestive process is so fundamental in our bodies that ensuring its balance and health will account for the overall’s body health. Certainly, food and nutrients play a crucial role in our digestive system. Consuming fruits and vegetables would provide us with important amounts of fiber that would help the GI tract to stay “regular” also improving cardiovascular health and regulating sugar levels (16). Constipation can occur when food moves too slowly through the colon. Fiber is an excellent in absorbing water which would soften the stools and help them pass easily (17).

How to Make Your Digestive System Bulletproof 

The human body needs a variety of nutrients, vitamins and minerals to function properly, including the digestive health. It is really important to focus on obtaining vitamins and nutrients like vitamin C, D, A, calcium, potassium, iron and folic acid from whole foods, vegetables, nuts and fruits. Among the multiple variables that affect the health of our gut are:

• Fiber: Replacing fats and simple sugars for complex carbohydrates and whole grains can also be beneficial due to the increment of fiber and other nutrients that are important for the digestive process. A healthy digestion also requires the intake of enough fluids from water and the foods consumed (19).  Gut bacteria are the most abundant microbes in our intestines, and they also help us digest food. They can make essential vitamins, protect us against harmful germs, send signals to the immune systems and make small molecules to help the brain work. Bacteria play a critical role in our bodies and are essential for health. Studies have shown that variety of bacteria is more important than the absence or presence of a specific type. We can keep our gut microbiome healthy by consuming fermented foods rich in probiotics like kombucha, tempeh and also by eating more fibers from fruits and vegetables (23) (24).

• pH Balance: stomach acid is critical for the process of the digestive system. If the body is unable to make enough stomach acid, there could be an inadequate digestion and microbial overgrowth. The normal pH range of the stomach is 1.5 – 3.5. For the proper protein digestion, the pH of the stomach needs to be between 1.5 and 2.2. If the body is unable to produce enough stomach acid, it is also unable to digest minerals and protein molecules that could lead to amino acid deficiencies due to the lack of metabolized proteins. For this reason, it is imperative that we maintain the proper acidic conditions in the stomach. There are different options to maintain proper acidic levels like drinking more herbals beverages containing ginger. Ginger is recognized as a great booster for digestive juices. Fermented veggies such as sauerkraut and kimchi contain enzymes and probiotics that also help to improve digestive juices. You can also opt to consume liquids like shakes and smoothies when you are on a busy period because these foods don’t depend much on HCL production (25).

• Enzymes: they are essential in the body for the proper functioning of the digestive system. This type of proteins found in cells speed up chemical reactions in the body as a support for multiple tasks including breaking down of foods, destroying toxins and building muscle. Digestive enzymes are produced naturally by the body mainly in the pancreas, stomach and small intestine but can be affected by some factors that include the pH level of the stomach. They work better in a narrow pH range but if the environment is too acidic or too basic, the enzyme’s functions will be affected. Certain food choices can also influence the body’s enzymes activity. Also, there are that foods contain digestive enzymes that help to increase the naturally occurring enzymes in the body (18). 

• Hormones: there is no doubt on the important role that hormones play in the human digestive process. They are made and released by the cells in the mucus lining of the stomach and small intestines helping to stimulate digestive juices and organ movement. Hormones stimulate secretion of enzymes and contraction and emptying of the gallbladder. Other functions for the hormones are the stimulation on the secretion of water and bicarbonate from the pancreas and bile products along with inhibition of gastric secretion (19) (26). 

• Stress: Besides nutrition, paying attention to the body it’s an important factor that directly affects the digestive system. Creating time for relaxation and managing stress can positively improve the quality of the overall well-being of the body. Stress can affect the body in many different ways. Depending on the body’s reaction to certain strong feelings, food’s passage through the digestive system can speed up or slow down causing symptoms like abdominal pain and diarrhea. Because of this, it is fundamental to always try to keep some balance in everyday life. Going for a walk, exercising at least 30 min a day or engaging in some self-care activity can help improve the quality of life and the body’s health (16).

Optimal Nutritional Choices for Digestive Health

Optimal nutritional choices are a cornerstone of maintaining a well-functioning digestive system. This chapter explores how macronutrients, micronutrients, fiber-rich foods, and hydration contribute to efficient digestion, energy production, and overall gut health.

Role of Macronutrients in Digestion and Energy Production

Macronutrients—carbohydrates, proteins, and fats—are essential components of our diet, each playing a distinct role in digestion and energy production. Carbohydrates are a primary source of energy, broken down into glucose for immediate use or stored in the liver and muscles as glycogen. Proteins, crucial for growth and repair, are broken down into amino acids that serve as building blocks for various bodily functions. Fats, both dietary and stored, are essential for nutrient absorption, cell membrane structure, and hormone synthesis.

The digestive process begins in the mouth, where carbohydrates are broken down by amylase, an enzyme in saliva. Stomach acid and enzymes facilitate protein digestion, while bile emulsifies fats in the small intestine. The breakdown of macronutrients results in smaller, absorbable components that are utilized for energy and essential functions throughout the body.

Micronutrients for Enzymatic Reactions and Gut Health

Micronutrients, including vitamins and minerals, are vital for supporting enzymatic reactions that drive digestion and contribute to gut health. B vitamins, such as B6, B12, and folate, aid in the metabolism of macronutrients and support nervous system function. Minerals like magnesium, zinc, and iron are cofactors for various enzymes involved in digestion and nutrient absorption.

Vitamins A and D are particularly important for gut health. Vitamin A supports mucosal integrity and immune function, while vitamin D contributes to the maintenance of the gut barrier and modulates immune responses.

Hydration’s Role in Digestive Function and Constipation Prevention

Adequate hydration is essential for maintaining optimal digestive function. Water supports the breakdown of food, the movement of nutrients across cell membranes, and the passage of waste through the digestive tract. Insufficient hydration can lead to constipation, as water is reabsorbed from the colon, resulting in dry and hard stool.

Staying hydrated helps maintain the elasticity of the intestines, promoting smooth passage of stool and preventing discomfort. Additionally, consuming water-rich foods like fruits and vegetables contributes to overall hydration and supports digestion.

In conclusion, optimal nutritional choices are integral to maintaining digestive health and overall well-being. Macronutrients provide energy and support bodily functions, while micronutrients enhance enzymatic reactions and gut health. Dietary fiber and hydration play vital roles in promoting regular digestion, nourishing the gut microbiome, and preventing issues like constipation. By making informed nutritional choices, individuals can create a foundation for a healthy and efficient digestive system, fostering vitality and long-term wellness.

Conclusion

Undoubtedly, the digestive process plays many fundamental roles in the human body and its functioning. One of the most important aspects to take in consideration is the amount of simple and complex processes that occur inside the body at every second with the goal of taking the necessary resources that the body needs to be alive. For this, it is important to reflect about the habits and food choices that we implement in our daily life. Knowing how certain factors can affect our digestive health, we can determine what best accommodates to our specific needs looking for ways to improve our previous lifestyle.

Patient Testimonials

Lana Advincula, a patient from Texas, shares her positive experience with Dr. Haque, highlighting his informative and patient approach to healthcare. Lana appreciates Dr. Haque’s willingness to explain aspects of her health that she didn’t understand, demonstrating his commitment to patient education.

What sets Dr. Haque apart for Lana is his holistic approach to healthcare. Instead of merely treating symptoms, Dr. Haque seeks to identify the root cause of health issues. He focuses on the patient’s overall well-being rather than just addressing isolated health problems. This comprehensive approach has had a significant impact on Lana’s health journey.

Lana’s testimonial underscores the importance of a holistic approach to healthcare and the value of patient education. Her experience with Dr. Haque serves as a testament to the effectiveness of his methods and the positive impact they can have on patients’ lives. This case study highlights the need for more doctors like Dr. Haque in the community, who prioritize understanding the root cause of health issues and treating the patient as a whole.

She wrote:

“Dr. Haque is very informative. He will always have the patience to explain something you do not know especially about your OWN health! It is amazing to know that there are doctors that do not just treat symptoms BUT actually goes even further as to looking for the root cause of what is going on within the body. He helps your ENTIRETY and NOT just bits and parts of you. There should be more doctors like him in the community!” 

• Lana Advincula, Texas, Patient

Tyson Lewis, a patient from Houston, shares his transformative journey towards managing chronic inflammation in his knees under the guidance of Dr. Haque. Tyson had spent a full decade visiting different doctors, trying to find a solution for his chronic knee inflammation. However, he was often told that they didn’t know the cause or was simply prescribed pills and painkillers.

Upon consulting Dr. Haque, Tyson’s experience drastically changed. Dr. Haque helped Tyson understand that his kidney function and diet were the root causes of his inflammation. This newfound understanding allowed Tyson to address the underlying issues rather than just managing the symptoms.

Tyson’s story is a testament to Dr. Haque’s knowledge and his commitment to treating the problem, not just the symptoms. His experience serves as an inspiration for others dealing with similar health issues and underscores the importance of understanding the root cause of health problems. This case study highlights the transformative power of professional medical guidance and the significant role of patient education in managing health conditions.

He wrote:

“Cant say enough about tue clinic! DR Haque is very knowledgeable. Spent a full decade going to different doctors trying to get help for chronic inflammation in my knees only to be told they didnt know or to just to take a few pills and pain killers.  Dr Haque helped me to understand how my kidney function and my diet have been the causes this whole time! I would highly recommend him he will treat your problem not your symptoms!”

• Tyson Lewis, Houston, Patient

National Institute of Diabetes and Digestive and Kidney Diseases. (2020, December). Your digestive system & how it works. National Institutes of Health. https://www.niddk.nih.gov/health-information/digestive-diseases/digestive-system-how-it-works

Belsley, S. (2023). The stomach and its role in digestion. Laparoscopic.MD. https://www.laparoscopic.md/digestion/stomach

Baguma-Nibasheka M, Fracassi A, Costain WJ, Moreno S, Kablar B. Striated-for-smooth muscle replacement in the developing mouse esophagus. Histol Histopathol. 2019 May;34(5):457-467. doi: 10.14670/HH-18-087. Epub 2019 Jan 30. PMID: 30698269.

U.S. Department of Health and Human Services National Institutes of Health National Cancer Institute. (2023). Introduction to the digestive system. SEER Training Modules. https://training.seer.cancer.gov/anatomy/digestive/

National Library of Medicine. (2016). Hormones. MedlinePlus. https://medlineplus.gov/hormones.htm

References 

Patricia JJ, Dhamoon AS. Physiology, Digestion. [Updated 2022 Sep 12]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK544242/ 

Thursby E, Juge N. Introduction to the human gut microbiota. Biochem J. 2017 May 16;474(11):1823-1836. doi: 10.1042/BCJ20160510. PMID: 28512250; PMCID: PMC5433529.

Ogobuiro I, Gonzales J, Shumway KR, et al. Physiology, Gastrointestinal. [Updated 2023 Apr 8]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK537103/ 

Bewick GA. Bowels control the brain: gut hormones and obesity. Biochem Med (Zagreb). 2012;22(3):283-97. doi: 10.11613/bm.2012.032. PMID: 23092061; PMCID: PMC3900054.

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