Digestive Tract Overview PDF

The Digestive System Overview https://www.fh-krems.ac.at The digestive system is very efficient in extracting nutrients from food and drink. The alimentary canal is the passage that food takes from beginning to end. Food is broken down with the help of digestive enzymes in the body, and...

The Digestive System Overview https://www.fh-krems.ac.at The digestive system is very efficient in extracting nutrients from food and drink. The alimentary canal is the passage that food takes from beginning to end. Food is broken down with the help of digestive enzymes in the body, and provides fuel and all the nutrients that we need to live. These enzymes come from the digestive glands: Salivary glands, liver, and pancreas. Food enters the alimentary canal through the mouth, where food is chewed and mixed with saliva produced in the salivary glands. As food is chewed, it is broken down into smaller pieces. The food then forms a ball called a bolus. The bolus moves through the esophagus which is a fibromuscular tube located behind trachea and heart in the mediastinum. It connects the pharynx to the stomach. It moves food down from the mouth to the stomach through a process known as peristalsis. Peristalsis is the involuntary contraction and relaxation of muscles along the canal, an action that pushes the food through with wave-like movements. Peristalsis also helps food move through the intestines. The food then passes from the esophagus through a muscular valve called the esophageal sphincter. The stomach is a muscular sack of tissue where thehttps://www.fh-krems.ac.at partially digested food is In the small intestine, food is mixed with digestive enzymes and bile. The enzymes stem to the majority from the exocrine compound of the pancreas. Bile is produced in the liver and stored in the gallbladder. It breaks down the large fat droplets into smaller droplets that provide a larger surface area for the enzyme lipase to break the lipids down. Bile also neutralizes some of the stomach acid. This increase in pH will provide a better environment for the enzymes to function. The small intestine is also where digested nutrients are passed into the bloodstream. This absorption mainly happens in the jejunum. There are finger-like structures in the intestines called villi, which are there to increase the surface areas of the intestines to allow nutrients to pass into the bloodstream more efficiently. The large intestine is shorter and wider than the small intestine and is made up of two parts: the colon and the rectum. In the large intestine, water is reabsorbed and feces are stored in the rectum. Feces are then ultimately passed through the anus, leaving the alimentary canal. When stretched out, the alimentary canal can be 10 meters in length! https://www.fh-krems.ac.at Deciduous (Baby-) vs. Permanent ( Adult ) Teeth Upper jaw Humans have differently shaped teeth that do different jobs in mechanically breaking up food. The incisors are used for biting and tearing food. The canines are there to hold and cut food. Premolar and molars are using for crushing and chewing food. Lower jaw https://www.fh-krems.ac.at Saliva contains a digestive enzyme that further breaks down food: the amylase. https://www.fh-krems.ac.at  The stomach lies in the left upper quadrant of the abdominal cavity. The top of the stomach lies against the diaphragm. Behind the stomach is the pancreas. Two sphincters keep the contents of the stomach contained; the lower oesophageal sphincter at the junction of the oesophagus and stomach, and the pyloric sphincter at the junction of the stomach with the duodenum. The stomach is surrounded by parasympathetic (stimulant) and sympathetic (inhibitor) networks of nerves which regulate both the secretory activity of the stomach and the motor activity of its muscles (peristalsis). Gastroscopy Aspect Because it is a distensible organ, it normally expands to hold about one litre of food. The maximum gastric capacity in adults is between 2 and 4 litres. Cardia Body https://www.fh-krems.ac.at Antrum  Chief cells: basophilic, located in the bases of the glands; production of pepsinogen. Parietal cells: eosinophilic, located in the middle region of the glands; secretion of hydrochloric acid and intrinsic factor (needed for the absorption of vitamin B12 in the terminal ileum). Mucous neck cells: located in the neck of the glands; production of bicarbonate ions and mucus. https://www.fh-krems.ac.at https://www.fh-krems.ac.at The Dual Hepatic Blood Supply https://www.fh-krems.ac.at Micro- Anatomy Of The Liver The Lobule https://www.fh-krems.ac.at https://www.fh-krems.ac.at  Functions Of The Liver Albumin Production: Albumin is a protein that keeps fluids in the bloodstream from leaking into surrounding tissue. It also carries hormones, vitamins, and enzymes through the body. Amphylitic agent!!! Purifies Blood: All the blood leaving the stomach and intestines passes through the liver, which removes toxins, byproducts, and other harmful substances. Regulates Amino Acids: The production of proteins depend on amino acids. The liver makes sure amino acid levels in the bloodstream remain within their normal ranges. Produces Clotting Factors: Blood coagulants are created using vitamin K, which can only be absorbed with the help of bile, Resists Infections: As part of the filtering process, the liver also removes bacteria from the bloodstream. Stores Vitamins and Minerals: The liver stores significant amounts of vitamins A, D, E, K, and B12, as well as iron and copper ( co-enzymes) Processes Glucose: The liver removes excess glucose (sugar) from the bloodstream and stores it as glycogen. As needed, it can convert glycogen back into glucose. Alcohol antagonizes this mechanism. Secretes bile which passes through the bile duct to be stored in the gallbladder until needed. Bile juice is secreted from the liver on the food during its passage in the duodenum and it does not contain digestive enzymes , It emulsifies fats , dividing the large masses of fats into small globules to facilitate and accelerate the enzymatic action on fats that do not dissolve in water. https://www.fh-krems.ac.at Pancreatic juice is secreted from the exokrine compound of the pancreas on the food in the duodenum. Pancreatic juice includes Sodium bicarbonate , pancreatic amylase , Trypsinogen, and Lipase. Sodium bicarbonate neutralizes HCl and renders ( makes ) the medium alkaline ( pH = 8 ) Pancreatic amylase catalyzes the hydrolysis of glycogen and starch into maltose. Trypsin catalyzes the hydrolysis of protein into polypeptides. Lipase catalyzes the hydrolysis of emulsified fats into fatty acids and glycerol.  Small Intestine The length of the small intestine varies: The typical length is 3m–5m. It is approximately 2.5–3 cm in diameter in adults. The surface area of the human small intestinal mucosa, due to enlargement caused by folds, villi and microvilli, averages 20 square meters! The small intestine is divided into three structural parts. The duodenum is approx. 20 cm („12 fingers“ ) in length, and shaped like a "C“. It receives gastric contents from the stomach, together with digestive juices from the pancreas (digestive enzymes) and the liver (bile). The 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 gastric chyme. The jejunum is the midsection of the small intestine. It is about 2.5 m long, and contains the circular folds, and intestinal villi that increase its Villi are many folds in the inner wall of ileum surface area. Products of digestion (sugars, which cause an increase in the surface area of amino acids, and fatty acids) are absorbed into the bloodstream here. the small intestine that is subjected to the https://www.fh-krems.ac.at The ileum: The final section of the small intestine. absorption of digested food.  secrete mucin and create a protective mucus. layer antimicrobial peptides and immunomodulati Digested food is able to pass into the blood vessels in the wall of the ng proteins intestine through either diffusion or active transport. The small intestine is the site where most of the nutrients from ingested food are absorbed. Absorption of the majority of nutrients (chylus) into the lacteal (“milky”) vessels takes place in the jejunum. https://www.fh-krems.ac.at Absorption is the transfer of digested food to the blood or lymph through the mucosa of small intestine. Primary active transport, also called direct active transport, directly uses metabolic energy to transport molecules across a membrane. Substances that are transported across the cell membrane by primary active transport include metal ions, such as Na+, K+, Mg2+, and Ca2+. In Secondary active transport, also known as coupled transport. Energy is used to transport molecules across a membrane; It relies upon the electrochemical potential difference created by pumping ions in/out of the cell. Facilitated diffusion is the process of spontaneous passive diffusion of molecules or ions across a biological membrane via specific transmembrane integral proteins. Molecules and ions move along their concentration gradient (diffusion ). The transport relies on molecular binding between the cargo and the membrane-embedded carrier protein. https://www.fh-krems.ac.at The large bowel, is the last part of the gastrointestinal tract and of the digestive system. Water is absorbed here and the remaining waste material is stored in the rectum as feces before being removed by defecation. https://www.fh-krems.ac.at https://www.fh-krems.ac.at Gut microbiota ( gut microbiome ) are the microorganisms, including bacteria that live in the digestive tract. The gastrointestinal microbiome is the aggregate of all the genomes of gut microbiota. The gut microbiota has broad impacts, including effects on colonization, resistance to pathogens, maintaining the intestinal epithelium intact, metabolizing dietary and pharmaceutical compounds, controlling immune function, and even behavior through the gut-brain axis. The colon contains between 300 and 1000 different species. Bacteria also make up to 60% of the dry mass of feces. Over 99% of the bacteria in the gut are anaerobes. It is estimated that the human gut microbiota have around a hundred times as https://www.fh-krems.ac.at many genes as there are in the human genome.  The rectum acts as a temporary storage site for feces. It receives fecal material from the descending colon, transmitted through regular muscle contractions. As the rectal walls expand due to the materials inside, stretch receptors from the nervous system located in the rectal walls stimulate the desire to pass feces, a process called defecation reflex. An internal and external anal sphincter, and resting contraction of the puborectal sling, prevent leakage of feces (fecal incontinence). As the rectum becomes more distended, the sphincters relax and the expulsion of the contents of the rectum occurs. Expulsion occurs through https://www.fh-krems.ac.at contractions of the muscles of the