Glossary

9.3 Absorption and assimilation of nutrients

6 min read•august 14, 2024

The is a nutrient powerhouse. Its unique structure, with circular folds, , and , maximizes surface area for efficient uptake of carbs, , and fats. Specialized transporters and enzymes work together to break down and absorb these nutrients.

Absorbed nutrients then enter the bloodstream or . The liver plays a crucial role in processing and distributing these nutrients throughout the body. Various factors, including digestive disorders, medications, and genetics, can impact nutrient absorption and overall digestive health.

Nutrient Absorption in the Small Intestine

Anatomy and Surface Area Enhancement

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  • The small intestine is the primary site of nutrient absorption, with its large surface area enhanced by circular folds, villi, and microvilli
  • Circular folds (valves of Kerckring) increase the surface area by 3-fold and slow the passage of chyme
  • Villi are finger-like projections that increase the surface area by 10-fold and contain capillaries and lacteals for nutrient absorption
  • Microvilli are microscopic projections on the apical surface of enterocytes that increase the surface area by 20-fold, forming the brush border

Carbohydrate Absorption

  • are broken down into monosaccharides (glucose, fructose, galactose) by brush border enzymes (lactase, sucrase, maltase)
  • Glucose and galactose are absorbed via (SGLT1), which uses the sodium gradient established by the Na+/K+ ATPase
  • Fructose is absorbed by facilitated diffusion through glucose transporter type 2 ()
  • GLUT2 also facilitates the basolateral exit of monosaccharides from enterocytes into the bloodstream

Protein Absorption

  • Proteins are digested into amino acids, di-, and tripeptides by various (aminopeptidases, carboxypeptidases, endopeptidases)
  • Amino acids are absorbed by specific amino acid transporters, which can be sodium-dependent or independent (e.g., neutral, basic, and acidic amino acid transporters)
  • Di- and tripeptides are absorbed by the proton-coupled peptide transporter , which uses the H+ gradient established by the Na+/H+ exchanger
  • Inside the enterocyte, di- and tripeptides are further hydrolyzed into amino acids by cytoplasmic peptidases

Lipid Absorption

  • , primarily triglycerides, are emulsified by and hydrolyzed by into monoglycerides and free fatty acids
  • These products form with bile salts, which facilitate their absorption into enterocytes by passive diffusion
  • (A, D, E, and K) are incorporated into micelles and absorbed along with dietary lipids
  • Inside the enterocyte, monoglycerides and free fatty acids are re-esterified into triglycerides and packaged into for lymphatic transport

Lymphatic System in Lipid Absorption

Chylomicron Formation and Exocytosis

  • After absorption into enterocytes, monoglycerides and free fatty acids are re-esterified into triglycerides by the enzymes monoacylglycerol acyltransferase (MGAT) and diacylglycerol acyltransferase (DGAT)
  • Triglycerides are packaged with cholesterol, phospholipids, and apolipoproteins (ApoB-48, ApoA-I, ApoA-IV) to form chylomicrons in the endoplasmic reticulum and Golgi apparatus
  • Chylomicrons are exocytosed from enterocytes into the intercellular space and enter the lymphatic capillaries called lacteals

Lymphatic Transport and Circulation

  • The lymphatic system, particularly the thoracic duct, transports chylomicrons and other lipoproteins from the intestines to the bloodstream, bypassing the liver
  • Chylomicrons enter the bloodstream via the left subclavian vein, where they circulate and deliver triglycerides to peripheral tissues expressing (LPL)
  • LPL is anchored to the capillary endothelium by heparan sulfate proteoglycans and hydrolyzes triglycerides in chylomicrons, releasing free fatty acids for uptake by adjacent tissues (adipose, muscle)
  • As triglycerides are hydrolyzed by LPL, chylomicrons shrink and become , which are enriched in cholesterol and apolipoprotein E (ApoE)
  • Chylomicron remnants are taken up by the liver via the LDL receptor and LRP1 (LDL receptor-related protein 1) for further processing and recycling of components

Liver's Role in Nutrient Metabolism

Carbohydrate Metabolism

  • The liver plays a central role in the metabolism of carbohydrates absorbed from the intestines
  • Hepatocytes extract glucose from the blood and store it as glycogen () when levels are high, such as after a meal
  • During fasting, the liver releases glucose through (breakdown of glycogen) and (synthesis of glucose from non-carbohydrate precursors like amino acids and glycerol)
  • The liver also converts excess glucose to fatty acids () when glycogen stores are full, contributing to the synthesis of triglycerides and VLDL particles

Protein Metabolism

  • Amino acids are taken up by the liver and used for protein synthesis, including the production of , clotting factors, and acute-phase proteins
  • Excess amino acids are catabolized by the liver, with their carbon skeletons used for glucose production (gluconeogenesis) or oxidized for energy
  • The liver converts ammonia, a byproduct of amino acid catabolism, into for excretion by the kidneys, preventing neurotoxicity

Lipid Metabolism

  • The liver is essential for lipid metabolism, as it synthesizes and secretes lipoproteins (VLDL, HDL), cholesterol, and bile acids
  • Hepatocytes package triglycerides, cholesterol, and apolipoproteins (ApoB-100, ApoE) into VLDL particles for export to peripheral tissues
  • The liver also synthesizes HDL particles, which participate in reverse cholesterol transport, removing excess cholesterol from peripheral tissues and returning it to the liver for excretion or recycling
  • Hepatocytes oxidize fatty acids for energy production, especially during fasting or prolonged exercise, through the process of in mitochondria and peroxisomes

Vitamin and Mineral Storage

  • Hepatocytes store fat-soluble vitamins (A, D, E, and K) and regulate their release into the circulation as needed
  • (retinol) is stored in hepatic stellate cells and released bound to retinol-binding protein (RBP) for transport to target tissues
  • The liver hydroxylates vitamin D to its active form, , which is further activated in the kidneys to 1,25-dihydroxyvitamin D
  • The liver stores and releases minerals such as (ferritin and hemosiderin) and copper (ceruloplasmin) to maintain homeostasis
  • Hepatocytes synthesize , the primary iron transport protein in the blood, and , a key regulator of iron homeostasis

Factors Affecting Nutrient Absorption

Digestive Disorders

  • Digestive disorders, such as , , and , can impair nutrient absorption by damaging the intestinal lining or causing inflammation
  • Celiac disease is an autoimmune disorder triggered by gluten, leading to villous atrophy and of nutrients (iron, calcium, fat-soluble vitamins)
  • Crohn's disease and ulcerative colitis are inflammatory bowel diseases that cause intestinal inflammation, ulceration, and scarring, disrupting nutrient absorption

Surgical Interventions

  • Gastrointestinal surgery, such as or resection of the small intestine, can reduce the surface area available for absorption and lead to nutrient deficiencies
  • (RYGB) and biliopancreatic diversion (BPD) are bariatric procedures that bypass segments of the small intestine, potentially causing malabsorption of iron, calcium, and fat-soluble vitamins
  • Small bowel resection, performed for conditions like Crohn's disease or intestinal tumors, can result in and malabsorption of nutrients

Microbial Imbalances

  • Bacterial overgrowth in the small intestine () can interfere with nutrient absorption and cause malabsorption
  • SIBO occurs when excessive bacteria colonize the small intestine, competing for nutrients and producing metabolites that damage the intestinal lining
  • , beneficial microorganisms like Lactobacillus and Bifidobacterium, can promote nutrient absorption by maintaining a healthy gut microbiome and supporting intestinal barrier function

Medications and Substance Use

  • Certain medications, such as , , and , can alter digestive processes or bind to nutrients, reducing their absorption
  • Proton pump inhibitors (PPIs) reduce stomach acid production, which can impair the absorption of calcium, magnesium, and vitamin B12
  • Antibiotics can disrupt the gut microbiome, leading to diarrhea and malabsorption of nutrients
  • Cholestyramine, a bile acid sequestrant used to treat hypercholesterolemia, can bind to fat-soluble vitamins and reduce their absorption
  • can impair the absorption and metabolism of nutrients, particularly water-soluble vitamins (B-complex and C), by damaging the intestinal lining and interfering with nutrient transport systems
  • Aging can lead to decreased production of digestive enzymes, reduced intestinal motility, and changes in the gut microbiome, all of which can affect nutrient absorption
  • , a condition common in older adults, results in decreased stomach acid production and impaired absorption of vitamin B12, calcium, and iron
  • Reduced intestinal motility can lead to constipation and bacterial overgrowth, further compromising nutrient absorption

Genetic Factors

  • Genetic factors, such as mutations in nutrient transporter genes or enzymes involved in nutrient metabolism, can impact an individual's ability to absorb and utilize specific nutrients
  • is caused by a deficiency in the brush border enzyme lactase, leading to malabsorption of lactose and gastrointestinal symptoms
  • is a genetic disorder characterized by mutations in the LDL receptor gene, impairing the liver's ability to clear LDL cholesterol from the bloodstream
  • is an inherited disorder of iron metabolism, causing excessive iron absorption and accumulation in tissues, leading to organ damage

Key Terms to Review (49)

25-hydroxyvitamin D: 25-hydroxyvitamin D, also known as calcidiol, is the primary circulating form of vitamin D in the body and is produced in the liver from vitamin D3 or D2. This compound plays a crucial role in calcium homeostasis and bone health, as it helps to regulate the absorption of calcium and phosphorus from the diet.
Absorption: Absorption is the process by which nutrients from digested food are taken up by the cells lining the gastrointestinal tract and transported into the bloodstream for use by the body. This vital function connects the breakdown of food to the assimilation of essential nutrients, highlighting the intricate relationship between digestive processes, nutrient uptake, and the regulation of bodily functions.
Albumin: Albumin is a type of protein found in the blood plasma that plays a crucial role in maintaining osmotic pressure and transporting various substances, including hormones, vitamins, and drugs. Its presence is vital for proper nutrient absorption and assimilation as it helps in the distribution of nutrients throughout the body and regulates fluid balance by retaining water in the bloodstream.
Alcohol consumption: Alcohol consumption refers to the intake of alcoholic beverages, which can affect various physiological processes in the body. The body absorbs alcohol mainly through the stomach and small intestine, leading to its rapid assimilation into the bloodstream. This process has implications for nutrient absorption and can influence overall metabolic health, as alcohol can interfere with the body's ability to process essential nutrients effectively.
Antibiotics: Antibiotics are a type of medication used to treat infections caused by bacteria. They work by either killing bacteria or inhibiting their growth, making them essential tools in managing bacterial infections and preventing their spread within the body. Understanding how antibiotics interact with the body's systems is crucial for effective absorption and assimilation of nutrients, as they can impact the overall health and functionality of the digestive system.
Atrophic gastritis: Atrophic gastritis is a medical condition characterized by the thinning of the stomach lining, leading to inflammation and a reduction in gastric acid production. This condition can impact the absorption and assimilation of nutrients, as the stomach plays a crucial role in breaking down food and facilitating nutrient uptake. The reduction in stomach acid can also hinder the digestion of certain nutrients, making it important to understand its implications on overall health.
Bariatric surgery: Bariatric surgery refers to a range of surgical procedures designed to aid in weight loss by making changes to the digestive system. These surgeries can significantly impact the absorption and assimilation of nutrients, often resulting in reduced calorie intake and altered nutrient absorption, which can lead to both weight loss and potential nutritional deficiencies.
Beta-oxidation: Beta-oxidation is a metabolic process in which fatty acids are broken down in the mitochondria to generate acetyl-CoA, NADH, and FADH2 for energy production. This process is crucial for the utilization of fatty acids as a fuel source during periods of fasting or prolonged exercise, linking it directly to nutrient assimilation and energy metabolism.
Bile Salts: Bile salts are steroid acids derived from cholesterol that play a crucial role in the digestion and absorption of fats in the small intestine. They emulsify dietary fats, breaking them into smaller droplets, which increases the surface area for digestive enzymes to act upon and promotes the efficient absorption of fatty acids and fat-soluble vitamins.
Carbohydrates: Carbohydrates are organic compounds made up of carbon, hydrogen, and oxygen, primarily serving as a major source of energy for the body. They can be classified into simple sugars, complex carbohydrates, and fibers, playing crucial roles in digestion and the absorption of nutrients. Understanding carbohydrates is essential for comprehending how our bodies utilize these macronutrients during digestion and the subsequent assimilation of nutrients into the bloodstream.
Celiac disease: Celiac disease is an autoimmune disorder where the ingestion of gluten leads to damage in the small intestine. This condition affects nutrient absorption and assimilation, as the immune response to gluten causes inflammation that harms the intestinal lining, making it difficult for the body to properly absorb essential nutrients from food.
Cholestyramine: Cholestyramine is a bile acid sequestrant used primarily to lower cholesterol levels in the blood by binding bile acids in the intestine. This action prevents the reabsorption of bile acids, leading the liver to use more cholesterol to produce new bile acids, thereby lowering serum cholesterol levels. Its connection to nutrient absorption is significant because it can also affect the absorption of certain vitamins and minerals.
Chylomicron remnants: Chylomicron remnants are the leftover particles formed after chylomicrons have delivered dietary lipids to tissues and have undergone lipolysis. These remnants play a crucial role in lipid metabolism as they transport residual triglycerides, cholesterol, and fat-soluble vitamins back to the liver for further processing and assimilation.
Chylomicrons: Chylomicrons are lipoprotein particles formed in the intestines after the ingestion of dietary fats. They play a crucial role in the absorption and assimilation of nutrients by transporting triglycerides, cholesterol, and fat-soluble vitamins from the intestine to other tissues in the body via the lymphatic system and bloodstream.
Crohn's Disease: Crohn's disease is a chronic inflammatory bowel disease that causes inflammation of the gastrointestinal tract, leading to a range of digestive issues. This condition can affect any part of the GI tract, from the mouth to the anus, but most commonly affects the end of the small intestine and the beginning of the large intestine. The inflammation can disrupt the absorption and assimilation of nutrients, leading to malnutrition and various complications.
De novo lipogenesis: De novo lipogenesis is the metabolic process through which the body converts excess carbohydrates and proteins into fatty acids, which are then stored as fat. This process primarily occurs in the liver and adipose tissue and plays a crucial role in energy balance, particularly when dietary intake exceeds energy expenditure. By synthesizing fat from non-fat sources, de novo lipogenesis helps maintain metabolic homeostasis and regulates nutrient storage.
Familial hypercholesterolemia: Familial hypercholesterolemia is a genetic disorder characterized by extremely high levels of low-density lipoprotein (LDL) cholesterol in the blood, leading to an increased risk of cardiovascular diseases at a young age. This condition arises from mutations in genes responsible for the metabolism of cholesterol, particularly the LDL receptor gene, which plays a crucial role in removing LDL cholesterol from circulation. As a result, individuals with this disorder often experience early onset atherosclerosis and heart disease.
Fat-soluble vitamins: Fat-soluble vitamins are a group of vitamins that dissolve in fats and oils, allowing them to be absorbed through the intestinal tract along with dietary fat. These vitamins, which include A, D, E, and K, play crucial roles in various bodily functions, including vision, bone health, antioxidant protection, and blood clotting. Unlike water-soluble vitamins, they are stored in the body's fatty tissues and liver, which can lead to potential toxicity if consumed in excessive amounts.
Gluconeogenesis: Gluconeogenesis is the metabolic process through which organisms generate glucose from non-carbohydrate substrates. This process primarily takes place in the liver and to a lesser extent in the kidney, allowing the body to maintain blood glucose levels during periods of fasting or intense exercise. It utilizes precursors like lactate, glycerol, and amino acids, highlighting the body's ability to adapt to energy demands.
Glut2: GLUT2 (Glucose Transporter Type 2) is a high-capacity glucose transporter found primarily in the liver, pancreas, kidneys, and small intestine. It plays a critical role in the absorption and regulation of glucose levels in the body, allowing for the transport of glucose across cell membranes into cells where it can be used for energy or stored. This transporter is essential for the efficient uptake of glucose during nutrient absorption and maintaining overall metabolic homeostasis.
Glycogenesis: Glycogenesis is the biochemical process through which glucose molecules are converted into glycogen for storage in the liver and muscle tissues. This process is essential for maintaining blood sugar levels and providing energy reserves, especially during times of fasting or increased energy demand. Glycogenesis is tightly regulated by hormones and is a key aspect of carbohydrate metabolism, linking the intake of nutrients to energy homeostasis.
Glycogenolysis: Glycogenolysis is the biochemical process of breaking down glycogen into glucose, which is then released into the bloodstream to be used for energy. This process is crucial for maintaining blood sugar levels, especially during periods of fasting or intense physical activity, ensuring that the body has a readily available source of fuel when needed. Glycogenolysis plays a vital role in energy metabolism and is closely linked to both nutrient absorption and athletic performance.
Hemochromatosis: Hemochromatosis is a genetic disorder characterized by excessive absorption of dietary iron, leading to iron overload in the body. This condition can result in damage to various organs, including the liver, heart, and pancreas, and it significantly impacts the body's ability to manage iron levels effectively. Understanding hemochromatosis is crucial because it highlights the delicate balance of nutrient absorption and the potential consequences of dysregulation.
Hepcidin: Hepcidin is a peptide hormone produced by the liver that plays a crucial role in regulating iron homeostasis in the body. It controls the absorption of dietary iron and the release of iron from macrophages and liver stores, ensuring that the body maintains adequate iron levels while preventing overload.
Inflammatory bowel disease: Inflammatory bowel disease (IBD) refers to a group of chronic inflammatory conditions affecting the gastrointestinal tract, primarily including Crohn's disease and ulcerative colitis. These conditions can disrupt the normal absorption and assimilation of nutrients, leading to various complications, while also involving complex regulatory mechanisms of gastrointestinal function to manage inflammation and maintain homeostasis.
Insulin: Insulin is a peptide hormone produced by the beta cells of the pancreas that plays a crucial role in regulating glucose metabolism and maintaining blood sugar levels within a normal range. By facilitating the uptake of glucose into cells, insulin supports energy production and storage, thereby contributing to homeostasis within the body.
Iron: Iron is a vital trace mineral that plays a crucial role in various physiological processes, particularly in the formation of hemoglobin in red blood cells, which is essential for transporting oxygen throughout the body. This mineral is also involved in energy production, immune function, and DNA synthesis, highlighting its importance in nutrient absorption and assimilation.
Lactose intolerance: Lactose intolerance is the inability to properly digest lactose, a sugar found in milk and dairy products, due to a deficiency in lactase, the enzyme responsible for breaking down lactose. This condition leads to gastrointestinal symptoms such as bloating, diarrhea, and abdominal pain after consuming lactose-containing foods. Understanding lactose intolerance is important as it highlights issues related to nutrient absorption and the regulation of gastrointestinal function, affecting how individuals manage their diets and health.
Lipids: Lipids are a diverse group of hydrophobic organic molecules that are insoluble in water but soluble in nonpolar solvents. They play crucial roles in storing energy, forming cell membranes, and serving as signaling molecules in the body, connecting them significantly to the absorption and assimilation of nutrients.
Lipoprotein lipase: Lipoprotein lipase (LPL) is an enzyme located on the surface of endothelial cells that hydrolyzes triglycerides in lipoproteins into free fatty acids and glycerol. This process is crucial for the absorption and utilization of dietary fats, allowing these components to be taken up by tissues such as muscles and adipose tissue for energy or storage.
Lymphatic System: The lymphatic system is a network of vessels, tissues, and organs that work together to transport lymph, a fluid containing infection-fighting white blood cells, throughout the body. This system plays a crucial role in maintaining fluid balance, absorbing fats from the digestive system, and facilitating immune responses by filtering lymph through lymph nodes and other structures.
Malabsorption: Malabsorption is a condition where the intestines do not properly absorb nutrients from the food consumed. This can lead to deficiencies in essential vitamins, minerals, and other nutrients, causing a range of health issues. Understanding malabsorption is critical because it can affect growth, metabolism, and overall health, linking closely to how nutrients are absorbed and assimilated in the body.
Micelles: Micelles are small, spherical aggregates of surfactant molecules that form in aqueous solutions, with hydrophilic (water-attracting) heads facing outward and hydrophobic (water-repelling) tails tucked away inside. They play a crucial role in the digestion and absorption of dietary fats, enabling the emulsification of lipids to facilitate their transport across the intestinal epithelium into the bloodstream.
Microvilli: Microvilli are tiny, finger-like projections found on the surface of epithelial cells, especially in the intestines and kidneys. They increase the surface area of the cell, enhancing its ability to absorb nutrients and other substances. Their presence is crucial in maximizing the efficiency of absorption processes within the gastrointestinal tract, as they provide more surface area for interactions with digested food and facilitate nutrient assimilation.
Pancreatic lipase: Pancreatic lipase is an enzyme produced by the pancreas that plays a critical role in the digestion of dietary fats. It breaks down triglycerides into free fatty acids and glycerol, allowing for their absorption in the intestines. This enzyme is essential for effective fat digestion and is regulated by several factors, including hormonal signals and the presence of bile salts.
Pept1: Pept1, or the peptide transporter 1, is a high-affinity proton-coupled transporter responsible for the absorption of di- and tripeptides in the small intestine. This transporter plays a critical role in the assimilation of dietary proteins by facilitating their uptake into enterocytes, which are the cells lining the intestinal wall. By allowing these smaller peptide fragments to enter the cells, pept1 helps ensure efficient nutrient absorption during digestion.
Peptidases: Peptidases are enzymes that catalyze the hydrolysis of peptide bonds in proteins, breaking them down into smaller peptides or amino acids. These enzymes play a crucial role in digestion, helping the body to absorb and utilize nutrients from the proteins consumed in food. By converting proteins into smaller units, peptidases facilitate the absorption of amino acids in the intestines, ensuring that the body has the necessary building blocks for various biological functions.
Probiotics: Probiotics are live microorganisms, mainly bacteria and yeasts, that provide health benefits when consumed in adequate amounts. They play a crucial role in maintaining gut health by balancing the microbiota in the gastrointestinal tract, which can influence digestion, nutrient absorption, and overall well-being.
Proteins: Proteins are large, complex molecules made up of long chains of amino acids, essential for the structure, function, and regulation of the body's tissues and organs. They play crucial roles in various biological processes, including enzyme activity, muscle contraction, and immune responses. Proteins are vital in nutrition as they are one of the main macronutrients that the body needs for growth, repair, and maintaining overall health.
Proton Pump Inhibitors: Proton pump inhibitors (PPIs) are a class of medications that reduce the production of stomach acid by blocking the proton pump in the stomach lining. By inhibiting this enzyme, PPIs effectively lower acid secretion, which is crucial in managing conditions like gastroesophageal reflux disease (GERD) and peptic ulcers, thereby impacting the absorption and assimilation of nutrients in the digestive system.
Roux-en-y gastric bypass: Roux-en-y gastric bypass is a surgical weight-loss procedure that alters the digestive system by creating a small pouch from the stomach and connecting it directly to the small intestine, bypassing a significant portion of the stomach and duodenum. This procedure not only limits food intake but also affects nutrient absorption, making it crucial for understanding how weight loss surgery impacts the body’s ability to absorb and assimilate nutrients.
Short bowel syndrome: Short bowel syndrome is a medical condition that occurs when a significant portion of the small intestine is missing or has been surgically removed, leading to malabsorption of nutrients. This condition can severely impact the body's ability to absorb essential nutrients, fluids, and electrolytes from food, resulting in various nutritional deficiencies and complications. The reduced absorptive surface area compromises the assimilation of nutrients and can result in symptoms like diarrhea, weight loss, and dehydration.
SIBO: SIBO stands for Small Intestinal Bacterial Overgrowth, a condition where excessive bacteria grow in the small intestine, which is normally a relatively sterile environment. This overgrowth can disrupt the absorption and assimilation of nutrients, leading to various gastrointestinal symptoms and nutritional deficiencies. SIBO can result from various factors, including anatomical abnormalities, motility disorders, or the use of certain medications, all impacting nutrient absorption.
Small intestine: The small intestine is a long, coiled tube in the gastrointestinal tract where most digestion and absorption of nutrients occurs. It connects the stomach to the large intestine and is divided into three sections: the duodenum, jejunum, and ileum. This structure plays a crucial role in breaking down food with the help of digestive enzymes and facilitating the absorption of nutrients into the bloodstream.
Sodium-dependent glucose transporter: The sodium-dependent glucose transporter (SGLT) is a type of membrane protein that facilitates the transport of glucose into cells using the energy from sodium ion gradients. This transporter plays a crucial role in nutrient absorption in the intestines, as it allows for the uptake of glucose alongside sodium, which is vital for energy metabolism and maintaining cellular functions.
Transferrin: Transferrin is a glycoprotein that plays a critical role in iron transport within the bloodstream. It binds to iron ions and facilitates their delivery to various tissues and cells in the body, ensuring that iron is available for essential processes such as hemoglobin synthesis and cellular metabolism. Transferrin's ability to regulate iron levels is crucial for maintaining homeostasis, preventing both iron deficiency and overload.
Urea: Urea is a nitrogenous compound produced in the liver through the urea cycle and is a primary component of urine, playing a crucial role in the body's way of excreting excess nitrogen. This compound helps regulate the body's nitrogen balance and is vital for maintaining homeostasis. As a waste product resulting from protein metabolism, urea connects closely with kidney function, urine formation, and nutrient assimilation.
Villi: Villi are small, finger-like projections that line the inner surface of the small intestine, significantly increasing the surface area for nutrient absorption. These structures play a vital role in maximizing the efficiency of nutrient uptake as digested food passes through the intestinal tract, allowing for a more effective assimilation of essential nutrients into the bloodstream.
Vitamin A: Vitamin A is a fat-soluble vitamin essential for various bodily functions, including vision, immune system performance, and skin health. It plays a critical role in the absorption and assimilation of nutrients by aiding in the proper functioning of epithelial tissues and supporting cellular communication.
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