Anatomy And Physiology Of Gastrointestinal System Pdf
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- Basic Anatomy and Physiology of the Gastrointestinal Tract
- Anatomy and physiology of the stomach
- Quick Anatomy Lesson: Human Digestive System
The function of the digestive system is to break down the foods you eat, release their nutrients, and absorb those nutrients into the body.
Basic Anatomy and Physiology of the Gastrointestinal Tract
The gastrointestinal tract GIT consists of a hollow muscular tube starting from the oral cavity, where food enters the mouth, continuing through the pharynx, oesophagus, stomach and intestines to the rectum and anus, where food is expelled. There are various accessory organs that assist the tract by secreting enzymes to help break down food into its component nutrients. Thus the salivary glands, liver, pancreas and gall bladder have important functions in the digestive system.
Food is propelled along the length of the GIT by peristaltic movements of the muscular walls. Information on re-publishing of our images.
The primary purpose of the gastrointestinal tract is to break food down into nutrients, which can be absorbed into the body to provide energy. First food must be ingested into the mouth to be mechanically processed and moistened. Secondly, digestion occurs mainly in the stomach and small intestine where proteins, fats and carbohydrates are chemically broken down into their basic building blocks. Smaller molecules are then absorbed across the epithelium of the small intestine and subsequently enter the circulation.
The large intestine plays a key role in reabsorbing excess water. Finally, undigested material and secreted waste products are excreted from the body via defecation passing of faeces. In the case of gastrointestinal disease or disorders, these functions of the gastrointestinal tract are not achieved successfully. Patients may develop symptoms of nausea, vomiting, diarrhoea, malabsorption, constipation or obstruction. Gastrointestinal problems are very common and most people will have experienced some of the above symptoms several times throughout their lives.
The gastrointestinal tract is a muscular tube lined by a special layer of cells, called epithelium. The contents of the tube are considered external to the body and are in continuity with the outside world at the mouth and the anus. Although each section of the tract has specialised functions, the entire tract has a similar basic structure with regional variations.
The innermost layer of the digestive tract has specialised epithelial cells supported by an underlying connective tissue layer called the lamina propria. The lamina propria contains blood vessels, nerves, lymphoid tissue and glands that support the mucosa.
Depending on its function, the epithelium may be simple a single layer or stratified multiple layers. Areas such as the mouth and oesophagus are covered by a stratified squamous flat epithelium so they can survive the wear and tear of passing food. Simple columnar tall or glandular epithelium lines the stomach and intestines to aid secretion and absorption.
The inner lining is constantly shed and replaced, making it one of the most rapidly dividing areas of the body! Beneath the lamina propria is the muscularis mucosa. This comprises layers of smooth muscle which can contract to change the shape of the lumen.
The submucosa surrounds the muscularis mucosa and consists of fat, fibrous connective tissue and larger vessels and nerves. At its outer margin there is a specialized nerve plexus called the submucosal plexus or Meissner plexus. This supplies the mucosa and submucosa. This smooth muscle layer has inner circular and outer longitudinal layers of muscle fibres separated by the myenteric plexus or Auerbach plexus.
Neural innervations control the contraction of these muscles and hence the mechanical breakdown and peristalsis of the food within the lumen. The outer layer of the GIT is formed by fat and another layer of epithelial cells called mesothelium.
The oral cavity or mouth is responsible for the intake of food. It is lined by a stratified squamous oral mucosa with keratin covering those areas subject to significant abrasion, such as the tongue, hard palate and roof of the mouth. Mastication refers to the mechanical breakdown of food by chewing and chopping actions of the teeth. The tongue, a strong muscular organ, manipulates the food bolus to come in contact with the teeth.
It is also the sensing organ of the mouth for touch, temperature and taste using its specialised sensors known as papillae. Insalivation refers to the mixing of the oral cavity contents with salivary gland secretions.
The mucin a glycoprotein in saliva acts as a lubricant. The oral cavity also plays a limited role in the digestion of carbohydrates. The enzyme serum amylase, a component of saliva, starts the process of digestion of complex carbohydrates.
The final function of the oral cavity is absorption of small molecules such as glucose and water, across the mucosa. From the mouth, food passes through the pharynx and oesophagus via the action of swallowing.
Book your health appointments online Find and instantly book your next health appointment with HealthEngine. Find health practitioners. Three pairs of salivary glands communicate with the oral cavity. Each is a complex gland with numerous acini lined by secretory epithelium. The acini secrete their contents into specialised ducts. Each gland is divided into smaller segments called lobes.
Salivation occurs in response to the taste, smell or even appearance of food. This occurs due to nerve signals that tell the salivary glands to secrete saliva to prepare and moisten the mouth.
Each pair of salivary glands secretes saliva with slightly different compositions. The parotid glands are large, irregular shaped glands located under the skin on the side of the face. They are situated below the zygomatic arch cheekbone and cover part of the mandible lower jaw bone. An enlarged parotid gland can be easier felt when one clenches their teeth.
The parotids produce a watery secretion which is also rich in proteins. Immunoglobins are secreted help to fight microorganisms and a-amylase proteins start to break down complex carbohydrates. They are found in the floor of the mouth, in a groove along the inner surface of the mandible. These glands produce a more viscid thick secretion, rich in mucin and with a smaller amount of protein. Mucin is a glycoprotein that acts as a lubricant. The sublinguals are the smallest salivary glands, covered by a thin layer of tissue at the floor of the mouth.
The main functions are to provide buffers and lubrication. The oesophagus is a muscular tube of approximately 25cm in length and 2cm in diameter. It extends from the pharynx to the stomach after passing through an opening in the diaphragm. The wall of the oesophagus is made up of inner circular and outer longitudinal layers of muscle that are supplied by the oesophageal nerve plexus.
This nerve plexus surrounds the lower portion of the oesophagus. The oesophagus functions primarily as a transport medium between compartments. The stomach is a J shaped expanded bag, located just left of the midline between the oesophagus and small intestine. It is divided into four main regions and has two borders called the greater and lesser curvatures. The first section is the cardia which surrounds the cardial orifice where the oesophagus enters the stomach.
The fundus is the superior, dilated portion of the stomach that has contact with the left dome of the diaphragm. The body is the largest section between the fundus and the curved portion of the J. This is where most gastric glands are located and where most mixing of the food occurs. Finally the pylorus is the curved base of the stomach.
Gastric contents are expelled into the proximal duodenum via the pyloric sphincter. The inner surface of the stomach is contracted into numerous longitudinal folds called rugae. These allow the stomach to stretch and expand when food enters. The stomach can hold up to 1. The functions of the stomach include:. Most of these functions are achieved by the secretion of stomach juices by gastric glands in the body and fundus.
Some cells are responsible for secreting acid and others secrete enzymes to break down proteins. The small intestine is composed of the duodenum, jejunum, and ileum. It averages approximately 6m in length, extending from the pyloric sphincter of the stomach to the ileo-caecal valve separating the ileum from the caecum. The small intestine is compressed into numerous folds and occupies a large proportion of the abdominal cavity. The duodenum is the proximal C-shaped section that curves around the head of the pancreas.
The duodenum serves a mixing function as it combines digestive secretions from the pancreas and liver with the contents expelled from the stomach. The start of the jejunum is marked by a sharp bend, the duodenojejunal flexure. It is in the jejunum where the majority of digestion and absorption occurs. The final portion, the ileum, is the longest segment and empties into the caecum at the ileocaecal junction.
The small intestine performs the majority of digestion and absorption of nutrients. Partly digested food from the stomach is further broken down by enzymes from the pancreas and bile salts from the liver and gallbladder. These secretions enter the duodenum at the Ampulla of Vater. The lining of the small intestine is made up of numerous permanent folds called plicae circulares. Each plica has numerous villi folds of mucosa and each villus is covered by epithelium with projecting microvilli brush border.
This increases the surface area for absorption by a factor of several hundred. The mucosa of the small intestine contains several specialised cells. Some are responsible for absorption, whilst others secrete digestive enzymes and mucous to protect the intestinal lining from digestive actions. The large intestine is horse-shoe shaped and extends around the small intestine like a frame.
It consists of the appendix, caecum, ascending, transverse, descending and sigmoid colon, and the rectum. It has a length of approximately 1.
Anatomy and physiology of the stomach
The stomach is a muscular, J-shaped organ in the upper part of the abdomen. It is part of the digestive system, which extends from the mouth to the anus. The size of the stomach varies from person to person, and from meal to meal. The stomach is part of the digestive system and is connected to the: esophagus — a tube-like organ that connects the mouth and throat to the stomach. The area where the esophagus joins the stomach is called the gastroesophageal GE junction.
This article — the fifth in a six-part series describes the physiology and functions of the large intestine, the last portion of the gastrointestinal tract, as well as common conditions of both the small and large intestine. In the large intestine — the final section of the gastrointestinal tract — absorption of water and electrolytes takes place and colonic bacteria complete the process of chemical digestion. The large intestine is also where faeces are formed from the remains of food and fluid combined with by-products of the body. Intestinal content is pushed back and forth by haustral contractions and antiperistaltic contractions, until faeces are finally pushed towards the anal canal by mass movements. This article, the fifth in a six-part series exploring the gastrointestinal tract, describes the anatomy and functions of the large intestine.
The human digestive system, also known as the digestive tract, the GI tract, the alimentary canal is a series of connected organs leading from the mouth to the anus. The digestive system allows us to break down the food we eat to obtain energy and nourishment. The digestive system -- which can be up to 30 feet in length in adults -- is usually divided into eight parts: the mouth, the esophagus, the stomach, the small intestine or "small bowel" and the large intestine also called "large bowel" or "colon" with the liver, pancreas, and gallbladder adding secretions to help digestion. These organs combine to perform six tasks: ingestion, secretion, propulsion, digestion, absorption, and defecation. The mouth starts the process by ingesting and mechanically breaking down the food we eat into a swallowable form, adding some early secretions to start the process of digestion.
The functions of the gastrointestinal tract and its accessory organs are essential for life. The process of digestion supplies nutrients to each and every cell in our.
Quick Anatomy Lesson: Human Digestive System
The gastrointestinal tract GIT consists of a hollow muscular tube starting from the oral cavity, where food enters the mouth, continuing through the pharynx, oesophagus, stomach and intestines to the rectum and anus, where food is expelled. There are various accessory organs that assist the tract by secreting enzymes to help break down food into its component nutrients. Thus the salivary glands, liver, pancreas and gall bladder have important functions in the digestive system. Food is propelled along the length of the GIT by peristaltic movements of the muscular walls. Information on re-publishing of our images.
The gastrointestinal system is responsible for the breakdown and absorption of various foods and liquids needed to sustain life. The new edition is a highly referenced and useful resource for gastroenterologists, physiologists, internists, professional researchers, and instructors teaching courses for clinical and research students. Clinical gastroenterologists, physiologists, and internists, as well as, professional researchers in gastroenterology, physiology, internal medicine, translational medicine and biomedicine. Chapter He serves as a reviewer on a variety of NIH, VA and other national study sections as well as international European study sections dealing with medical research in internal medicine and nutrition.
As adults, we know that a healthy digestive system is essential for good health because it converts food into raw materials that build and fuel our body cells. The organs of the digestive system can be separated into two main groups: those forming the alimentary canal and the accessory digestive organs. The alimentary canal, also called the gastrointestinal tract, is a continuous, hollow muscular tube that winds through the ventral body cavity and is open at both ends.
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