Nutrition, Structure and Function of Seven Parts of Digestive System - Essay Example

Nutrition Paper TASK Living organisms require nutrition for sustainability and to operate vital functions. Components of nutrition build up matter in the body and provide energy for the operation of metabolic reactions that are vital for the sustenance of life. While the materials that provide for these two requirements are called “nutrients”, “nutrition” is the sum of all processes through which living organisms derive matter and energy (Sizer and Whitney 2011). Nutrition includes all processes that are involved in consumption and utilization of food substances using which growth, repair and maintenance of essential activities occurs in the body. Overall, the nutritional requirements of a living organism are inversely proportional to its ability to create essential molecules on its own. Living organisms with lesser number of such biosynthetic abilities require more kinds of nutrients from their environment. Green plants for example have the ability to utilize simple inorganic molecules from the environment to synthesize their own complex molecules (Sizer and Whitney 2011). Energy derived from nutrition is a vital requirement for all basic life processes that include movement, sensitivity, and reproduction.For instance, energy is used for the contraction of muscles which aids movement (Paul 2014). Energy is required for the transfer of sensory nerve signals that facilitate memory, cognition and control. Every process involved in digestion, excretion, movement or reproduction requires energy in the form of ATP (adenosine triphosphate) which is the energy currency of the body (Sizer and Whitney 2011). TASK 2: Functions— Carbohydrates: These are the principle source of energy in the body. Complex carbohydrates such as starch are broken down in the body into glucose, a simple carbohydrate. It is broken down in cells to provide a source of energy (Chiras 2011).Carbohydrates are obtained from carbohydrate rich foods and converted to glucose. Glucose is stored in the liver as glycogen. The glucose is oxidised in cells through cellular respiration to produce ATP, which is the energy currency of the body. ATP is required for all the energy needs of the body such as contraction of muscles, functioning of other metabolic processes, respiration, etc. It is required for all the essential physiological functions of the cell (Wingerd 2013). Lipids:Lipids have a variety of functions in the body. Some are energy-rich and are stored in the body as fat reserves to provide energy in times of need. These reserves are broken down to release energy. Lipids release more than twice the energy released per gram of glucose. Lipids also insulate and protect the body and keep the internal body temperature constant. They cover and protect vital organs from damage due to external pressure or injury. Lipids also aid in digestion by dissolving fat soluble vitamins such as A, D, E and K apart from playing an important role in hormone production. Other lipids function as important structural components in living cells. For instance, linolenic acid and linoleic acid provide support for cell wall structure and are required for hormone production. Hormones such as testosterone and estrogen are formed from cholesterol which is a form of lipid (Chiras 2011). Proteins: These are the chief body building nutrients. These are required by the body to build up other proteins such as hormones and enzymes that participate in essential biochemical functions. Structural components such as collagen that make up fingernails and hair are also made of proteins. Proteins consumed in diet are broken down into amino acids that are again assembled in the body to build required proteins for muscle, tissue, enzymes and hormones. Enzymes are proteins that catalyse various biochemical processes in the body that are essential for metabolism (Chiras 2011). Food sources high or low in— Carbohydrates: Rich sources – cereal grains such as wheat, rice, millet, sorghum and corn, tubers such as cassava and potato. Cereal grains are seeds and so is the richest source of carbohydrates. They are thus staple foods for most people around the world. The entire grain has three parts; germ, endosperm, and bran. Bran which is the outer layer contains vitamin B and fiber, germ contains Vitamin B and E, Unsaturated fats, minerals, antioxidants and phytochemicals. It is part of the plant food that is not digested by the body. The soluble fats slow down the absorption of nutrients and emptying of the stomach besides facilitating the reduction of rise in insulin and glucose to improve the control of blood sugar. The insoluble fiber adds to the stool and reduces its transit time through the colon. It also reduces the time taken by bowels to carry waste products. Cereals are best consumed without removing their husk to retain dietary fibre content. Tubers such as potato and cassava are very high in carbohydrates and are best consumed boiled or baked rather than fried. Potato helps in lowering the blood pressure. They are great sources of potassium that keeps blood pressure under control. Apart from providing fiber, Vitamin B and C, once potatoes have been cooked and cooled, they become loaded with starch which revs up the body fat burn furnace. Given that both starch and fiber cannot be digested, they are fermented when they reach intestine, triggering the body to burn fats and slow down the absorption of nutrients. Frying increases the fat content of potatoes, too much consumption of which could lead to obesity. Potatoes are better consumed with the skin as it contains fibre. Poor sources – meat, poultry.Meat and poultry are rich in protein and fat, rather than carbohydrates. These low carbohydrate diets are thus most preferred by calorie conscious individuals who intend to avoid carbohydrate intake. Poultry meat is mainly high in low, lean fat proteins. The poultry meat helps in the growth and development of muscle besides supporting healthy body weight. It also aids in the weight loss of the body. Poultry also has nutrients such as zinc, iron, vitamin B12, Niacin, Vitamin B6, Riboflavin, Thiamin, Selenium and phosphorous which are very nutritious for the body. These nutrients helps in cell growth, regulate energy metabolism, and assists folate in making of red blood cells. (Desai 2000). Lipids:Rich sources – Oilseeds like sunflower, peanut, fruits such as olive and avocado; milk and butter. Oilseeds are rich sources of dietary fats and oils providing the body with essential fatty acids. They are also good sources of proteins (Sarwar et al. 2013). Vegetable oil is extracted from oilseeds and used in cooking. Olive oil, Sunflower oil, and safflower oil are good sources of lipids because they are rich in mono and polyunsaturated fats that are good for heart and overall health and reduce cholesterol. It has lignans which contains the plant antioxidant and estrogen qualities. It contains Omega-3 essential fatty acids that have heart healthy effects. It also contains both soluble and insoluble fiber that reduces the absorption of food and good for the skin. Fats (saturated fats) from animal sources such as meat, milk, cheese etc. are harmful as they elevate cholesterol levels and increase cardiovascular disease risk. High level of body cholesterol is dangerous for the body and affects working of the heart. Fish oil is a good source of omega 3 fatty acids that reduce cholesterol and harmful fats in the body. Omega-3 fatty acids lower the triglyceride levels and also lower the blood pressure in the body. Omega-3 fatty acids help in the reduction of osteoarthritis, rheumatoid, and death from heart disease. Poor sources – most fruits and vegetables lack fats and are rich in carbohydrates and vitamins. Fruits and vegetables contain minerals and vitamins. They also have a plant chemical called phytochemicals. Fruit and vegetables helps in body protection against diseases such as heart disease, cancer, hypertension, high blood pressure and cancer. They have very minimal sources of fats. They should be added to every meal for the protection functions as above. (Desai 200) Proteins: Rich sources – Fish, meat, eggs, poultry, milk, cheese, soybeans. Poor sources – most fruits and vegetables.Most plant derived foods such as whole grains, seeds, nuts and legumes are healthy sources of proteins because they provide essential amino acids along with dietary fibre and no cholesterol. Whole grains contain both soluble and insoluble fats that reduce the absorption of the nutrients and reduce the transit of tool to the colon. On the other hand, animal sources such as meat are bad sources of protein because they leave toxic residues in the body such as uric acid, metabolic wastes, etc. that cause autotoxemia, gout, arthritis, over acidity, etc. Egg is a good source of protein as it has all 20 amino acids in easily digestible form. Nutrients advise on the uptake of white meat to the body. (Desai 2000). TASK 3: S.No. Vitamin/Mineral Need Best Food Sources 1. Vitamin - A Helps in the developments of visual pigments and also in epithelial cell maintenance Yellow/green fruits and vegetables, liver, milk products, carrots. 2. Vitamin – C Required for collagen synthesis, has antioxidant properties, cell repair Broccoli, citrus fruits Broccoli is a rich source of vitamin C as well as fibre. Citrus fruits like orange and lemon are best consumed as liquid extracts in the morning. They are used as detox diets before breakfast to relieve the body of toxins. 3. Vitamin – D Bone formation, absorption of phosphorous and calcium Fish, vitamin D fortified milk Fish is a great source of vitamin and also omega 3 fatty acids that have many health benefits. It is recommended to have at least two servings of fish a week. 4. Vitamin - K Synthesis of blood clotting agents Liver, green leafy vegetables Green leafy vegetables are best eaten raw or boiled to save their vitamin content. They are also a rich source of fibre that aids in digestion and bowel movement. 5. Calcium Blood clotting, teeth and bone formation, muscle action and nerve transmission Canned fish, dairy products Dairy products include milk, cheese and yoghurt. 6. Phosphorous Synthesis of nucleic acids, energy transfer mechanism via ATP and formation of bone and teeth Soft drinks, meat, dairy products Soft drinks are also high in sugars and therefore need to be consumed in limited quantities. Meat with low fat content is considered healthy. (Source: Alters 2000) TASK 4: Structure and function of seven parts of digestive system (Stipanuk and Caudill, 2013): 1. Oral cavity/Mouth: It extends from lips to oropharynx. The roof is made of a soft palate bone posteriorly and a hard palate bone anteriorly. The tongue is attached to the soft palate. Teeth are present in the sockets of the mandible and maxillae. The cheeks, tongue and lips help move food between the lower and upper tooth for chewing (mastication). Salivary glands release saliva into the oral cavity and this helps in the mastication process. The enzyme ptyalin in saliva breaks down starches in the food to maltose. 2. Pharynx: Chewed food or bolus is then swallowed and transferred from mouth to pharynx. The pharynx is the passageway for bolus. It aids both digestion and respiration. It is 12.5 centimeters long and has three parts, namely nasopharynx, oropharynx and laryngopharynx. A hanging flap of connective tissue called epiglottisguides the passage of food into the oesophagus and prevents it from going into the respiratory tract. 3. Oesophagus: the oesophagus is a tubular organ and has a sphincter at each end. Through peristaltic action, the bolus passes through the oesophagus into the stomach. The sphincters at both end of the oesophagus permit only one way movement of food. 4. Stomach: The stomach has four anatomical regions – cardia, fundus, corpus, and pyloric antrum. The function of the stomach is digestion and absorption. It temporarily stores swallowed food, secretes HCl acid and zymogens for initiating digestion and endocrine hormones for food assimilation regulation. The stomach mixes up the food with digestive enzymes and macerates it into a semiliquid state. This partly digested food is called chyme. Some salts, water and lipid soluble substances are absorbed at this stage. 5. Small intestine: The chyme passes into the small intestine. It is a long tube like convoluted structure that extends from the pyloric sphincter of the stomach to the ileocaecal valve. It is has three regions, namely duodenum, jejunum and ileum. The pancreatic duct from pancreas and bile duct from liver open into the duodenum. Mucous is secreted in the small intestine by goblet cells and Bruner’s glands. Intestinal juice called succusentericus is also secreted by intestinal glands. Chemical digestion of food occurs in the small intestine through enzymes from bile (from liver) and intestinal juice. Microorganisms in the small intestine also contribute to digestion. The small intestine is also involved in absorption and uptake of nutrients from the digested food. The absorption is done through small finger-like projections in the intestine called villi which are covered with even smaller projections called microvilli. 6. Large intestine: It is 1.5 meter long and starts from the caecum and continues till the rectum. The caecum is a pouch like portion and is followed by ascending colon, transverse colon, descending colon and sigmoid colon. The large intestine is involved in absorption of water and electrolytes. Microbial activity of microorganisms present in the large intestine helps in folic acid and vitamin K synthesis and absorption. 7. Rectum and anus:Rectum is a small dilated tube that leads to the anal canal. Anal canal is 3.8 cm long and leads to the exterior. Two sphincters control the anal opening. Distention of rectum starts the defecation reflex that results in relaxation of internal anal sphincter causing defecation. TASK 5: Mechanical and chemical digestion of carbohydrates, proteins and fats (Marieb 2009): Mechanical digestion – Mechanical digestion begins in the mouth when teeth grind food into smaller particles. The food is mixed with saliva which contains salivary amylase. This enzyme breaks down starch into maltose. Thus mechanical and chemical digestion begins in the mouth itself. Mechanical digestion also occurs in the stomach where peristaltic mixing of the food particles occurs with digestive enzymes. Mechanical digestion also occurs in the intestines where segmental mixing further causes movement, digestion and propulsion of digested food. Mechanical digestion enables the mixing of food with digestive enzymes that breakdown carbohydrates, proteins and lipids. Chemical digestion – 1. Carbohydrates: The chemical digestion of carbohydrates is initiated in the mouth when the enzyme amylase present in saliva breaks down starch into maltose. Once the bolus reaches the stomach, the acidic environment stops amylase action. The next carbohydrate chemical digestion process occurs in the duodenum where chyme from the stomach is mixed with the digestive secretions from liver, pancreas and gallbladder. Amylase enzyme is present in pancreatic juice that breaks down starch and glycogen into disaccharides like maltose. These are then further broken down by enzymes like sucrases, maltases, lactases into monosaccharides that are absorbed in the intestines and transported to other cells in the body via bloodstream. 2. Protein: Protein digestion begins in the stomach where the enzyme pepsin plays an important role in protein digestion. It breaks down complex proteins into peptides which are short chains of amino acids. Protein breakdown also occurs in the duodenum where other enzymes like elastase, trypsin, chymotrypsin produced by pancreas act on the peptides, further reducing them into smaller peptides. These peptides are further broken down into single molecule amino acids with the help of peptidase enzymes. The simple amino acids are then absorbed in the intestines and transferred to other cells via the bloodstream. Lipids: The digestion of lipids occurs in the stomach with the help of gastric lipase and lingual lipase enzymes. However, a major portion of lipid digestion takes place in the small intestine with the help of the lipase enzyme produced by pancreas. When chyme is transported from stomach to duodenum, hormonal responses are stimulated with then trigger bile release. Bile is produced by the liver and stored until use in the gallbladder. Bile contains bile pigments, bile salts that emulsify the lipids, mainly triglycerides. Emulsification is the process in which large globules of lipids are broken down into several small lipid globules that are mixed in chyme. Because lipids are hydrophobic and water insoluble, bile salts (which have both hydrophilic and hydrophobic ends) interact with lipids by interfacing their hydrophobic sides with lipids and hydrophilic sides with water, therefore emulsifying the lipids in water to aid their digestion. This step is extremely important because lipases can only efficiently breakdown lipids when they are present as small aggregates. The lipase enzymes breakdown lipids into glycerides and fatty acids that can pass through a cell’s plasma membrane and enter the epithelial cells of the lining of intestines.The monoglycerides and long-chain fatty acids resulting from lipase action are surrounded by bile salts, forming micelles, which are tiny spheres. These micelles move into the villi of the small intestine where the monoglycerides and long-chain fatty acids diffuse out of the micelles, leaving them behind in the chyme. In the absorptive cells of the intestinal villi, these monoglycerides and long-chain fatty acids recombine to form triglycerides that again aggregate into globules and are coated with proteins. The large spheres of aggregates are called chylomicrons. These contain cholesterol, triglycerides and other fats and are covered in proteins. The surface of these aggregates is also made of phospholipid heads that are hydrophilic. These enable the movement of the chylomicrons in the aqueous environment without exposing the fats to water. The chylomicrons leave these intestinal absorptive cells through a process called exocytosis where they enter the lymphatic vessels. These then enter the bloodstream in the subclavian vein and are then transported to cells. TASK 6: Liver is the largest organ in the body weighing approximately between 1200 and 1500 gm in adults. It is a large, reddish-brown, firm triangular organ located in upper region of abdominal cavity (Geller and Petrovic 2012). It has a dominant right lobe and a smaller left lobe. It is made of pinkish-brown soft tissues covered by a capsule of connective tissue. The liver is connected to the abdominal cavity’s peritoneum at four locations, the falciform ligament, the left and right triangular ligaments and the coronary ligament. The liver has four lobes namely the left lobe, right lobe, caudate lobe and quadrate lobe. The left and right lobes are large and separated from each other by the falciform ligament. The caudate lobe is small and extends from the right lobe’s posterior side and wraps the inferior vena cava. The quadrate lobe is also small and is inferior to caudate lobe, extending from the posterior end of the right lobe and wrapping the gall bladder. The liver has bile ducts which are tubes that transport bile (Geller and Petrovic 2012). They form a branched structure called the biliary tree. The bile produced in liver cells drains in bile canaliculi, which are microscopic canals. These join together to form larger bile ducts throughout the liver tissue. The bile ducts join to form larger ducts called left and right hepatic ducts that carry bile from the left and right lobes. These two ducts joint to form one common hepatic duct to drain bile which joins with the cystic duct of the gallbladder to form a single duct called common bile duct which carries bile to duodenum in small intestine. A hepatic portal vein system supplies blood to the liver. This vein collects blood from stomach, pancreas, spleen, intestines and gall bladder and delivers it to the liver. The hepatic veins carry blood away from the liver into the vena cava. The liver is made of 100,000 lobules which are small hexagonal functional units whose blood vessels are connected by capillary-like tubes called sinusoids (Geller and Petrovic 2012). Each sinusoid has Kupffer cells (a kind of macrophage that captures and lyses old red blood cells) and hepatocytes (that perform metabolism, digestion, storage and bile production) (Geller and Petrovic 2012). TASK 7: Urea is produced in the liver via the urea cycle. Ammonia produced as a byproduct of amino acid metabolism is toxic for the human body and needs to be removed. Therefore, this ammonia is extracted by the liver from the blood stream and converted to urea. It is then released to be excreted by the kidneys. The urea cycle involves a series of enzyme catalysed reactions beginning with the formation of carbamoyl phosphate from ammonia (Walsh and Wright 1995). The liver is one of the major organs in the body, apart from kidneys, skin and intestinal tract, that eliminate toxins. It detoxifies toxin substances that are either produced in the body or enter from outside. The liver converts toxins that are fat soluble into water soluble ones that are then excreted. The removal of toxins occurs in two phases, oxidation and conjugation. In the first phase, toxin is neutralized or converted into active intermediates that are neutralized in the second phase. Through oxidation, reduction and hydrolysis, toxic substances are converted to less harmful substances. In the second phase, liver cells add glycine, cysteine or a sulphur molecule to the active intermediates created in phase one to make it less harmful and water soluble. It is then excreted via urine or bile (Lipman 2004). TASK 8: Kidneys filter blood, removing and excreting wastes into urine. Each kidney is approximately 6 cm wide, 3 cm thick and 12 cm long. Kidneys are bean-shaped and have an indentation called hilum, which leads into the renal sinus which is a large cavity. The renal artery enters the kidney and ureter and renal vein leave at the hilum (Bonewit-West, Hunt and Applegate 2014). The outer reddish region of the kidney is renal cortex which surrounds the renal medulla, a darker reddish brown zone comprising a series of renal pyramids that appear striated because of the presence of blood vessels and straight tubular structures. The wide pyramid bases lie adjacent to cortex and their pointed ends that are directed towards the kidney centre are called renal papillae. Portions of the renal cortex that extend between spaces between adjacent pyramids are called renal columns (Bonewit-West, Hunt and Applegate 2014). The functional tissue of the kidney is present in the cortex and medulla. The renal pelvis is the central region of the kidney that has a large cavity for collecting urine. The renal pelvis’s periphery is interrupted with calyces which are cup-like projections. The renal papillae of each pyramid are surrounded by minor calyx which collects urine from the pyramid. Many of the minor calyces converge, forming a major calyx from where the urine flows into the renal pelvis and subsequently into the ureter (Bonewit-West, Hunt and Applegate 2014). TASK 9: Nephrons are the functional units of the kidney. There are over one million nephrons in a kidney located in medulla and cortex. In each nephron, urine is formed after blood purification. Nephrons are made of a renal corpuscle and renal tubule. The renal corpuscle is made of glomerulus (having a cluster of capillaries), and Bowman capsule also called glomerular capsule. Blood enters through the afferent arteriole into the glomerulus and is filtered as it leaves through the efferent arteriole. The filtrate enters the glomerular capsule and then into the renal tubule (Bonewit-West, Hunt and Applegate 2014). This tubule carries the fluid away and comprises of the proximal convoluted tubule, nephron loop called Loop of Henle and a distal convoluted loop. The proximal convoluted tubule is highly coiled and then straightens and dips into the kidney’s medulla taking a U-turn and then ascending back into the cortex forming the Henle loop or nephron loop. It then descends and ascends back towards cortex into a coiled tube in cortex called distal convoluted tubule. Urine passes from nephron’s distal convoluted tubule into the collecting ducts which are straight tubules (Bonewit-West, Hunt and Applegate 2014). TASK 10: The kidney varies the kidney varies the volume and concentration of urine through the ADH hormone. The volume and concentration vary based on internal conditions of the body. The water content in blood is to be maintained at a specific level to avoid cell damage. Thus a balance is to be maintained between the amount of water gained and the amount of water lost from the body. This is achieved by the anti-diuretic hormone ADH. When the body loses a lot of water through sweat or when there is very low consumption of water, the hypothalamus detects the low water levels in blood (Bonewit-West, Hunt and Applegate 2014). It then sends a message to the pituitary to release the hormone ADH. The hormone is transported to the kidneys where it makes the renal tubules more permeable to water so that more water is reabsorbed into the blood. This results in concentrated urine with low amounts of water for excretion. Thus water is conserved until the level in blood is back to normal. On the other hand, when excess water is taken, release of the hormone into the blood is slowed down or stopped. As the kidneys do not save water, large volumes of dilute urine is excreted. This is the negative feedback mechanism of ADH (Bonewit-West, Hunt and Applegate 2014). References Alters, S (2000), Biology: Understanding Life, New York: Jones & Bartlett Learning. 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Stipanuk, MH, &Caudill, MA (2013), Biochemical, Physiological, and Molecular Aspects of Human Nutrition, London: Elsevier Health Sciences. Walsh, PA, & Wright, PA (1995), Nitrogen Metabolism and Excretion, New York: CRC Press. Wingerd, B (2013), The Human Body: Concepts of Anatomy and Physiology, London: Lippincott Williams & Wilkins. Read More