Y khoa, y dược - Chapter 7: The gastrointestinal system

Chapter 7The Gastrointestinal System IntroductionA healthy digestive system is fundamental to support human life. Its ability to extract nutrients from the food we eat affects our general well-being in health and our response to illness in ill-health. Disorders of the digestive system range from mild and self-limiting to severe and life-threatening, but affect everyone to some extent and at some point during their life. This presentation provides a general overview of the digestive system, and then explores its components in greater detail. Overview of the Digestive System The digestive system is divided into two areas: the gastrointestinal (GI) tract (gut) the accessory digestive organsThe GI tract is a 4.5m continuous tube (lumen) from the mouth to the anus. Between these ends it is divided into the pharynx, oesophagus, stomach, small intestine and large intestine. The walls of the GI tract have four layers: mucosa, submucosa, muscularis externa and serosa. The accessory digestive organs are exocrine glands and include the salivary glands, liver and pancreas. The Digestive System The Splanchnic CirculationThe digestive system is supplied by the splanchnic circulation. The liver only receives 20% of its blood supply from the hepatic artery. The remainder comes from the hepatic portal vein, which brings nutrient-rich blood from the gut for processing in the liver before it returns to the systemic circulation. Main Functions of the Digestive System Ingestion – food and drink being taken into the GI tract via the mouth Propulsion – swallowing and peristalsis Digestion Secretion – release of digestive juices for lubrication and digestion Absorption – final components of digestion are transported across the membrane of the GI tract into the circulation · Elimination – passing of undigested material, bacteria and excreted substances as faeces, also known as defecationThe Stomach The stomach is an expandable storage sac between the oesophagus and the duodenum. It is located below the diaphragm, in the left upper quadrant/epigastrium. Gastric juice is secreted by exocrine gastric glands which lie in deep gastric pits. The cellular composition of the gastric glands and the type of secretions differ between locations in the stomach. The Stomach Function When food enters the mouth, salivation increases to hydrate and lubricate the food with mucous. Mechanical digestion commences with mastication. The tongue forces food against the hard palate and mixes it with saliva, softening it and forming a bolus. Chemical digestion begins with the breakdown of starch by salivary amylase into smaller glucose molecules.Once in the stomach, the food bolus is subjected to further mechanical digestion.Vomiting Vomiting, or emesis, is a reflex mechanism which protects the digestive system from toxins. Vomiting is controlled by the vomiting, or emetic, centre in the brain, and is precipitated by many peripheral and central causes, including;Over-distension of the stomach or intestine Irritation by drugs, chemicals, bacteria or blood Stimulation of the gag reflexMotion sickness Severe headaches and rising intracranial pressure Stimulation of the vomiting centre by drugs such as opiates and cytotoxics Particular sights, smells or emotions Developing & Delivering Expert Care: Nausea and Vomiting:Caring for a patient who is experiencing nausea and vomiting is common. Excessive vomiting results in dehydration and electrolyte disturbances. The NHS National Library for Health produces guidance for the management of nausea and vomiting in pregnancy and palliative care. Commonly used drugs include: Cyclizine, Metoclopramide & prochlorperazineGastrointestinal Bleeding Peptic ulcer disease (PUD) is the commonest cause of GI bleeding. Peptic ulcers occur in the stomach, but more frequently in the duodenum. Gastric ulcers (GU) form when acid and pepsin erode the lining of the stomach where the protective mucosa is already damaged. If damage is severe enough or involves a blood vessel bleeding occurs.PUD is also the 2nd commonest cause of dyspepsia. Dyspepsia is most often caused by the reflux of stomach acid into the oesophagus.Developing & Delivering Expert Care: Intravenous fluid therapy is targeted at replacing intravascular (IV) and/or extracellular (EC) fluid volume deficits. Intravascular fluid volume (IVFV) deficit usually occurs as the result of blood loss.Extracellular fluid volume (ECFV) deficits are associated with other forms of fluid loss, such as dehydration. There are two main types of IV fluid available: crystalloids and colloids. The best fluid for the replacement of blood loss is blood itself. This is the only fluid which contains the oxygen-carrying component – haemoglobin The LiverThe liver is the largest gland in the body and occupies the right upper quadrant. It is divided into the left and right lobes and is composed of hexagonal units called lobules. Each lobule contains a central vein, which drains into the vena cava. At each corner of the lobule is a portal triad – a bile duct, a branch of the hepatic artery and a branch of the hepatic portal vein. The bile ducts converge to form the common hepatic duct. The Liver - FunctionThe liver is one of the most important organs in the body and has the unique ability to completely regenerate itself following removal of up to 75% of its size. It has numerous functions, many of which are associated with its vital role in processing nutrient rich blood from the GI tract. Its main digestive function, however, is the production of 1L of yellow/green bile everyday. The Gallbladder & PancreasThe gallbladder is a pear-shaped sac, which lies on the posterior surface of the liver and protrudes below the right lobe. The gallbladder neck opens into the cystic duct, which combines with the common hepatic duct to form the common bile duct. This is joined by the main pancreatic duct before it joins the duodenum at the sphincter of Oddi. The pancreas is located in the epigastrium/left upper quadrant and has both exocrine and endocrine functions. The exocrine tissue is composed of acinar cells, which produce the enzymatic component of pancreatic juice. These cells drain into pancreatic ducts which converge to form the main pancreatic duct. The Liver, Gallbladder & Pancreas Gallstones Gallstones are very common, particularly in women, the incidence increases with age. They are often composed of cholesterol; hence they are also associated with a high-fat diet. Gallstones cause a range of diseases, including:Cholecystitis - when stones block the outflow of bile. The bile becomes concentrated and infected leading to a swollen and oedematous gallbladder. Pancreatitis - when pancreatic enzymes become prematurely activated. Autodigestion of pancreatic tissue causes local inflammation and oedema. The activated enzymes leak into the systemic circulation causing fluid shifts, hypovolaemia and damage to other organs. The Small Intestine The small intestine is a 6m tube, which extends from the pyloric sphincter of the stomach to the ileocaecal valve of the large intestine, and is divided into three sections: Duodenum – 25cm long and containing the sphincter of Oddi where the common bile duct joins the small intestineJejunum – 2.5m long Ileum – 3.5m longThe small intestine provides a massive surface area for absorption due to deep folds in the mucosa and finger-like villi covered in microvilli. Once each food group has been broken down into small enough molecules, they are absorbed through the small intestine lining by diffusion, passive or active transport into either the blood or lymph capillaries. Scenario Ethel Higgins is a 78 year old retired cleaner who has been readmitted by her GP for non-specific symptoms of weakness, lethargy and depression. She was discharged a month ago following a fall at home which resulted in a fractured neck of femur. She is still only able to walk short distances around her house with a Zimmer frame. Mrs Higgins lives alone, has no family, close friends or home help. On assessment Mrs Higgins is awake but withdrawn and her vital signs are within normal limits for her age. She reports no past medical history and is not taking any medication. Whilst helping her undress you notice that she is very thin and the surgical wound on her hip is not fully healed. ContinuedMrs Higgins received seemingly appropriate treatment for her previous presenting complaint – repair of a hip fracture, but her subsequent fundamental needs have been neglected. On discharge Mrs Higgins has been unable to mobilise enough to acquire or prepare her food and as a result has become malnourished. Evidence is found in her low energy levels, underweight appearance and delayed wound healing. This is an example of where malnutrition is both a cause and consequence of ill-health. Malnutrition – The Facts Malnutrition is a global problem affecting one in three people worldwide. Whilst it is often predominately associated with developing countries it is still relatively common in the UK. Approximately 5% of the British population are considered underweight. However, the proportions are much higher in the elderly.Malnourished patients present a significant strain on health services, with longer hospital stays and approximately 50% greater costs. The consequences of malnutrition include:Poor immunity Delayed wound healing and response to illness Reduced muscle strength and fatigue Impaired respiratory and cardiovascular functionApathy and depression Apathy and Depression Mrs Higgins’s care will focus upon excluding other causes for her symptoms through history and examination. This should include blood tests to assess for electrolyte disturbances, and anaemia etc. The extent of malnutrition should be measured objectively by nutritional assessment using a validated tool. She will then require appropriate nutritional support under the guidance of a dietician. Of paramount importance is the assessment of Mrs Higgins’s social situation and the introduction of appropriate services to ensure the situation doesn’t recur on discharge.All patients should be screened for malnutrition by an appropriately trained healthcare professional. This should occur on admission to hospital or a care home, on initial registration with a GP, on a first outpatient appointment or when there is clinical concern. Screening should be repeated weekly for inpatients. General questions should be posed to patients and carers. Malnutrition Universal Screening ToolThere are many nutritional assessment tools available. One example is the ‘Malnutrition Universal Screening Tool’ (MUST) (BAPEN, 2003). Height and weight measurements are used to calculate the body mass index (BMI). The MUST also takes account of recent unplanned weight loss and the effect of acute illness. The score establishes the overall risk of malnutrition and guides the user in planning appropriate care. ExerciseIdentify which tools are used in your clinical areasWhat interventions are then undertaken to correct malnutrition?Large IntestineThe large intestine (colon) extends from the ileocaecal valve to the anus. It is 1.5m in length, but has a larger diameter than the small intestine. Its mucosa contains many mucous-secreting goblet cells, but no villi, and is colonised by a wide variety of bacterial flora. Subdivisions include the caecum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum and anal canal. FunctionMain functions of the colon are absorption of remaining water, storage and elimination of faeces. Faeces is comprised of a small amount of water, undigested food residues, mucous, bacteria and sloughed mucosal cells. Arrival of faeces in the rectum initiates the defecation reflex, which provides the urge to defecate. This causes the sigmoid colon and rectum to contract, and the internal anal sphincter to relax forcing faeces towards the external anal sphincter. Opening of this is under voluntary control, and defecation is aided by contraction of the abdominal muscles against a closed glottis. ConclusionApplication of digestive anatomy and physiology is vital for understanding normal human function. Gaining knowledge on the role nutrition plays in both health and illness and the development of a range of skills reflecting the ‘Essence of Care’ is essential for nursing practice.