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Digestive System & Common Sickness ((Digestive System…
Digestive System & Common Sickness
Digestive System
Gastrointestinal tract / Alimentary canal
This is a tube that transfers food to the organs of digestion. It consists of a series of hollow organs joined in a long, twisting tube from the mouth to the anus. It consists of the:
Upper gastrointestinal tract
Esophagus
The Esophagus is a muscular tube which connects the pharynx to the stomach. It carries swallowed masses of chewed food. During the esophageal stage of swallowing, contractions and relaxations of the muscularis called peristalsis push the food bolus onward. At the inferior end of the esophagus is a muscular ring called the cardiac sphincter. This function of the cardiac sphincter is to close the end of the esophagus to and trap food inside the stomach, thus why we are able to eat food upside down.
Stomach
The stomach is a muscular sac that is located on the left side of the abdominal cavity. The average person's stomach is the size of their two fists places next to each other. This organ acts as a storage tank for food so that the body has time to digest large meals properly. It contains hydrochloric acid and digestives enzymes such as pepsin and gastric lipase that continue the digestion of food that began in the mouth. The stomach epithelial cells are protected from gastric juice by a 1-3mm thick layer of alkaline mucus.
Enzymes in the stomach
The Chief (zymogenic) cells secrete pepsinogen and gastric lipase
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Parietal cells produce hydrochloric acid and intrinsic factor
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G cells secrete gastrin
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Four regions of the stomach
The body: the large central portion of the stomach
The Fundus: the rounded portion left of the cardia
The Pylorus: the region of the stomach which connects to the duodenum. When the stomach is empty, the mucosa lies in large folds called rugae. The Pylorus communicates with the duodenum of the small intestine via a sphincter called the pyloric sphincter.
The Cardia: surrounds the opening of the stomach
Mechanical digestion in the stomach
Several minutes after food enters the stomach, gentle peristaltic movements called mixing waves pass over the stomach every 15-20 seconds. These waves macerate food, mix it with secretions of the gastric glands, and reduce it to a soupy liquid called chyme.
As digestion proceeds in the stomach, more vigorous mixing waves begin at the body of the stomach and intensify as they reach the pylorus. Each mixing wave forces several millimeters of chyme into the duodenum through the pyloric sphincter.
Pharnyx
The pharynx, or throat, is a funnel-shaped tube connected to the mouth. It is responsible for passing chewed food from the mouth to the esophagus. The pharynx also plays an important role in the respiratory system, as air from the nasal cavity passes through the pharynx to get to the larynx, and eventually the lungs. Because of the two roles it is required to play, it contains a flat of tissue known as the epiglottis that acts as a switch to route food to the esophagus and air to the larynx.
Duodenum
The duodenum is the first part of the small intestine and is a short structure (20-25cm long) which receives chyme from the stomach, pancreatic juice containing digestive enzymes and bile from the gallbladder. These digestive enzymes break down proteins and bile emulsifies fats into micelles. The duodenum contains Brunner's glands which produce a mucus-rich alkaline secretion containing bicarbonate. These secretions, in combination with bicarbonate from the pancreas, neutralize the stomach acids contained in the chyme.
Emulsifies: the breakdown of fat globules into tiny droplets, which provides a larger surface area on which the enzyme pancreatic lipase can act to digest the fats into fatty acids and glycerol
Micelles: a group of bile salts released from the liver which dissolves fatty acids and monoglycerides so that they can be absorbed into the small intestinal epithelial cells.
Epithelial: the tissue that forms glands or the superficial part of the skin and lines blood vessels, hollow organs, and passages that lead externally from the body.
Brunner's glands: glands in the submucosal layer of the duodenum that secrete alkaline mucus and a potent proteolytic enzyme
Mouth
Food begins its journey through the digestive system in the mouth, also known as the oral cavity. Inside the mouth are many accessory organs that aid in the digestion of food - the tongue, teeth, and salivary glands.
Lower gastrointestinal tract
Large intestine
The large intestine is divided into four principle regions. The overall function of the large intestine are the completion of absorption, the production of a few vitamins, the formation of faeces, and the expulsion of faeces from the body.
Anatomy
The large intestine is about 1.5m long and 6.5cm in diameter. It extends from the ileum to the anus and is attached to the posterior abdominal wall by its mesocolon (a double layer of peritoneum). The four principle regions of the large intestine are the cecum, colon, rectum, and anal canal.
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Most of the small intestine
Jejunum
This is the midsection of the small intestine, connecting the duodenum to the ileum. It is about 2.5 m long, and contains the circular folds also known as plicae circulares, and villi that increase its surface area. Products of digestion (sugars, amino acids, and fatty acids) are absorbed into the bloodstream here.
Ileum
The final section of the small intestine. It is about 3 m long, and contains villi similar to the jejunum. It absorbs mainly vitamin B12 and bile acids, as well as any other remaining nutrients.
Absorption in the small intestine
Vitamins
Fat-soluble vitamins A, D, E, and K are absorbed via simple diffusion. Most water-soluble vitamins, such as vitamin C, is also absorbed via simple diffusion but Vitamin B12, however, is absorbed in the ileum via active transport.
Water
The small intestine absorbs about 8.3 liters of fluid and passes the remainder into the large intestine, where the rest of it is absorbed. All water absorption in the GI tract occurs via osmosis (from the lumen of the intestines through epithelial cells and into blood capillaries). The absorption of water in the small intestine depends on the absorption of electrolytes and nutrients to maintain an osmotic balance witht he blood.
Lipids
All dietary lipids are absorbed via simple diffusion. Adults absorb about 95% of lipids present in the small intestine whereas newborn infants absorb only about 85% of lipids. As a result of their emulsification and digestion, triglycerides are broken down into monoglycerides and fatty acids. Most dietary fatty acids are long-chain fatty acids.
Amino acids, dipeptides, tripeptides
Most proteins are absorbed as amino acids through the process of active transport (mainly occurs in the duodenum and jejunum).
Monosaccharides
All carbohydrates are absorbed as monosaccharides. The small intestine is able to absorb an estimated amount of 120 grams per hour. Monosaccharides pass from the human lumen through the apical membrane via diffusion or active transport. For example, glucose and galactose are transported into epithelial cells of the villi via secondary active transport.
Function and histology
The walls of the small intestine is composed similar to the same four coats which make up the GI tract, however special features of the mucosa and submucosa facilitate the processes of digestion and absorption. The mucosa forms a series of fingerlike projections called villi. The large number of villi vastly increases the surface area of the epithelium available for absorption and digestion.
Villi: each villus has a core of areolar connective tissue; inside this connective tissue is an arteriole, a venule, a blood capillary network, and a lacteal. Nutrients absorbed by the epithelial cells covering the villus pass through the wall of a capillary to enter the blood.
Intestinal juice is a clear yellow fluid secreted in amounts of 1-2 liters a day. It contains water and mucus and is slightly alkaline. Pancreatic and intestinal juices provide a liquid which aids the absorption of substances from chyme as they come in contact with the microvilli.
Epithelial cells synthesize several digestive enzymes called brush-border enzymes, and insert them into the plasma membrane of the microvilli.
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Digestion in the small intestine
Mechanical
Segmentations
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Migrating motility complex
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Chemical
Lipids
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Carbohydrates
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Proteins
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Nucleic acids
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Accessory Organs
Organs that helps with digestion but is not part of the digestive tract. The accessory digestive organs consists of the:
Pancreas
The pancreas is an organ 6 to 8 inches long. It extends horizontally across the abdomen. Around 95 percent of the pancreas is exocrine tissue. The pancreas releases juices directly into the bloodstream, and enzymes / digestive juices are secreted directly into the small intestine. The pancreas also produces the hormone insulin and secretes it into the bloodstream, where it regulates the body's glucose or sugar level.
Liver
The liver is the largest gland in the body, weighing about three pounds in an adult. It plays a number of roles in metabolism and regulation. The liver lies inferior to the diaphragm and is protected by the ribs. The liver is divided into two primary lobes: a large right lobe and a much smaller left lobe.
Salivary glands
The salivary glands produce saliva, which keeps the mouth and other parts of the digestive system moist. It also helps break down carbohydrates and lubricates the passage of food down from the pharynx to the esophagus to the stomach. There are three main pairs of salivary glands: the parotid, the submandibular and the sublingual glands.
Partotid
Submandibular
Sublingual glands
Gallbladder
The gallbladder is a pear-shaped, hollow structure located under the liver and on the right side of the abdomen. Its primary function is to store and concentrate bile, a yellow-brown digestive enzyme produced by the liver. The gallbladder is part of the biliary tract.
Tongue
Your tongue helps out, pushing the food around while you chew with your teeth. When you're ready to swallow, the tongue pushes a tiny bit of mushed-up food called a bolus toward the back of your throat and into the opening of your esophagus, the second part of the digestive tract.
Common Sicknesses and Conditions
Adults
Allergy
a damaging immune response by the body to a substance, especially a particular food, pollen, fur, or dust, to which it has become hypersensitive.
Anxiety Disorders
group of mental disorders characterized by significant feelings of anxiety and fear
Asthma
deficiency of red cells or of haemoglobin in the blood, resulting in pallor and weariness.
Colds and Flu
cold, is a viral infectious disease of the upper respiratory tract that primarily affects the nose. The throat, sinuses, and larynx may also be affected. ... These may include coughing, sore throat, runny nose, sneezing, headache, and fever.
flu is a contagious respiratory illness caused by flu viruses. symptoms: fever or feeling feverish/chills
Depression
a respiratory condition marked by attacks of spasm in the bronchi of the lungs, causing difficulty in breathing. It is usually connected to allergic reaction or other forms of hypersensitivity.
Sleep Disorders
Depression (major depressive disorder) is a common and serious medical illness that negatively affects how you feel, the way you think and how you act. ... Depression causes feelings of sadness and/or a loss of interest in activities once enjoyed
Stroke
when blood flow to an area of the brain is cut off, brain cells get deprived of oxygen and start to die. abilities controlled by that area of the brain e.g. memory, muscle control are lost
Heart Attack
A heart attack occurs when a coronary artery becomes suddenly blocked, stopping the flow of blood to the heart muscle and damaging it.
Headache
Primary headaches are caused by the overactivity of/ problems with structures in the head that are pain-sensitive. e.g. blood vessels, muscles, and nerves of the head and neck also can result from changes in chemical activity in the brain.
Common Cold
The common cold is a viral infection of your nose and throat (upper respiratory tract). It's usually harmless, although it might not feel that way. Many types of viruses can cause a common cold.
Chicken Pox
Chickenpox is an infection caused by the varicella-zoster virus. It causes an itchy rash with small, fluid-filled blisters. Chickenpox is highly contagious to people who haven't had the disease or been vaccinated against it.
Today, a vaccine is available that protects children against chickenpox. Routine vaccination is recommended by the Centers for Disease Control and Prevention (CDC).
