This report will explore the importance of nutrient consumption for human survival and investigate how food is transported to our cells, as well as the elimination of waste products. Additionally, we will compare these processes in humans with those in the single-celled organism Paramecium.
Dietary Nutrients
The four main nutrient groups in a diet are carbohydrates, proteins, vitamins (which do not require digestion), and fats. Carbohydrates, classified as starches chemically, are mainly present in the form of starches. During digestion, starches are converted into glucose, which is essential for cellular respiration. Starch itself is composed of glucose polymers.
Some foods contain dextrin and maltose, which are intermediate products in the digestion of starch. These foods may also have other types of carbohydrates such as sucrose (cane sugar) or lactose (milk sugar) that require further breakdown. However, there are cases where food contains the simplest form of sugar, glucose, which does not need to be digested.
Proteins are composed of amino acids, forming polymers. When digested, proteins generate free amino acids and ammonia. Essential components in our food, vitamins are absorbed through the small intestine. There are two categories of vitamins: water-soluble vitamins (such as B vitamins and vitamin C) and fat-soluble vitamins (like vitamins A, D, and K). Dietary fats mainly exist as neutral fats or triglycerides. These fats are fundamental compounds that break down into glycerol and fatty acids during digestion.
Ingestion
The Paramecium adjusts its food intake based on its needs. When it detects food, it moves towards it and directs it into the oral groove before enclosing it in a vacuole. Enzymes are then released to break down the food, which is absorbed into the cytoplasm and utilized by various organelles.
In contrast, human cells rely on the circulatory system to deliver nutrients instead of actively searching for them. However, the human body is more complex than a single-celled organism like the Paramecium because all cells in the body must be capable of absorbing nutrients and eliminating waste, similar to how the Paramecium operates.
Mouth digestion
When food is taken into the mouth, it undergoes mixing with saliva by means of chewing, which initiates the process of digestion. The salivary enzyme known as ptyalin interacts with the particles present in the food, causing the breakdown of specific substances that are soluble. Additionally, a substance called mucin covers the mass of food to assist in its swallowing.
The chemical phase of digestion in the mouth begins with salivary amylase, or ptyalin. This enzyme breaks down cooked starch or dextrin, converting some starch into dextrin and some dextrin into maltose. The activation of salivary glands can be stimulated by thoughts of food, while the actual presence of food prompts a constant release of saliva. However, because food only stays in the mouth briefly, the digestive process occurring there is minimal.
The semisolid food mass, after being digested in the mouth, is propelled through peristaltic movements along the muscular tube called the esophagus. This tube serves as a connection between the mouth and stomach. Eventually, the food reaches the upper part of the stomach where it encounters a muscle ring referred to as the esophageal sphincter. At this juncture, the sphincter opens to permit entry of food into the stomach.
The process of digestion takes place in the stomach.
The salivary digestion process continues until the stomach acid eliminates the salivary amylase. This causes the food mass to become saturated with gastric juice, which marks the start of the gastric phase of digestion. In this phase, pepsin and rennin are released by the gastric glands as they contribute significantly to protein breakdown.
The stomach’s gastric acid helps break down proteins into smaller forms such as metaproteins, proteoses, and peptones. Furthermore, the gastric juice present in the stomach contains a small quantity of lipase enzyme that assists in fat digestion by hydrolyzing triglycerides into glycerol and fatty acids.
When gastric juice and enzymes are combined, they work together to digest food and ultimately break it down. Peristaltic movements help move the fluid mass into the small intestine by passing through the pyloric sphincter in the final stages of gastric digestion. The chemical process of digestion begins in the small intestine.
Digestion in the Small Intestine
In the digestive system, the gastric digestion fluid and intestinal secretion are mixed with two additional fluids: pancreatic juice (produced by the pancreas) and bile (made by the liver). These fluids emerge near the pyloric valve, which divides the stomach from the intestine. Their purpose is to counteract the acidic nature of gastric juice and mark the end of gastric digestion.
Enzymes in the pancreatic juice and intestinal juice initiate the final stage of digestion. The pancreatic juice is abundant in amylase, protease, and lipase enzymes that break down undigested carbohydrates, proteins, and fats from previous stages. Furthermore, the intestinal secretion contains enzymes that specifically target partially digested protein and carbohydrate products, as well as smaller food molecules.
Pancreatic amylase converts both raw and cooked starch, whether it was digested earlier or not. Cooked starch is converted into dextrin, and then transformed into maltose. Additionally, pancreatic lipase breaks down neutral fat into glycerol and fatty acids. This process is facilitated by bile, which emulsifies the fat using alkaline secretions to create multiple surfaces for lipase to work on.
Proteases within the pancreas convert any remaining protein into proteoses and peptones, which are further broken down by erepsins enzymes into individual amino acids. Simultaneously, intestinal enzymes like maltase, sucrase, and lactase break down corresponding disaccharides (maltose, sucrose, and lactose) into monosaccharide components. Ultimately, this process leads to the conversion of these components into glucose.
Carbohydrates are converted to glucose, proteins break down into amino acids, and fats undergo hydrolysis to become fatty acids and glycerol. The villi in the small intestine absorb these nutrients. Within the villi, capillaries transport sugars and amino acids to the bloodstream. In contrast, glycerol and fatty acids are converted back into triglycerides before entering the lymphatic system and eventually reaching the bloodstream.
The process of digestion in the large intestine is important.
The large intestine, which is the last part of the digestive system, acts as a storage for waste and also absorbs some undigested materials. The first section of the intestine mainly focuses on absorbing water, bacterial vitamins, sodium, and chloride ions. The latter half of the intestine is where waste is stored.
The waste materials, including undigested food and dead bacteria, undergo a process to transform into feces. Subsequently, the body eliminates these feces through the anus. Peristalsis, akin to the movement of food in the esophagus, facilitates the passage of ingested material through both the small and large intestine.
The circulatory system transports food molecules from the villi to the bloodstream. Once in the blood, nutrients are conveyed to the liver for sugar extraction and glycogen storage. The heart serves as a central force, propelling blood through arteries to disperse it throughout the body. As blood vessels gradually narrow, they reach target tissues.
Within the smallest vessels known as capillaries, blood flows. The walls of these capillaries are extremely thin, consisting of just one cell. This thinness enables the exchange of nutrients from the bloodstream to individual cells and the elimination of waste products from cells back into the bloodstream through diffusion. When it comes to regulating and maintaining homeostasis, both humans and Paramecium have similar systems at this level. The absorption and excretion processes are mainly determined by comparing the fluid concentration inside the cell with that outside.
Excretion
The blood carries nutrients and cellular waste products, like carbon dioxide, urea, and excess glucose, to the cells. Afterward, it transports these waste products to the kidneys via the renal artery and disperses into numerous capillaries. Consequently, this causes a decrease in blood flow and an increase in pressure, resulting in a substantial release of plasma from the blood.
Renal tubules, or nephrons, play a vital role in urine production by removing harmful substances like urea and nitrates through pressure filtration. Each kidney contains approximately one million of these nephrons. Additionally, as the fluid moves along the tubule, it also reabsorbs important nutrients like sodium ions and glucose to prevent deficiencies in the body.
The urinary bladder’s main role is to store urine produced by the kidney. When the bladder is full, a sphincter opens allowing urine to pass through the urethra and be expelled from the body. Additionally, excretion takes place through sweat glands and when exhaling via the lungs. However, unlike the kidney’s efficient regulation, these other parts of the excretory system can lead to salt depletion.
Nervous System
The autonomic nervous system, consisting of the sympathetic and parasympathetic components, plays a crucial role in regulating digestive and excretory systems. The sympathetic system increases activity while the parasympathetic system decreases it. Nevertheless, conscious control is only possible for specific actions like chewing, swallowing, and controlling anal and urethral sphincters.
The Endocrine System
The endocrine system utilizes hormones to regulate the metabolic rates of cells and organs. Like nerves, these hormones have specific targets within the body and are essential for maintaining homeostasis. One instance is the gastrin hormone that oversees the production of gastric juice by the stomach. Furthermore, hormones also control excretions such as saliva.
Located a distance away from the cells they must control, the hormones responsible for regulating the digestive and excretory systems require a method of transportation. This method involves utilizing the bloodstream. The hormones are secreted by the hormonal glands directly into the bloodstream. From there, they travel to the target organ or cell and regulate its activity. Compared to the nervous system, this system is slower in response.
