GI 2023.pptx

OFFICI AL Gastrointestinal A&P HEA1091 OFFICI AL Identify some of the organs of the GI tract Describe the functions of the GI tract Analyse the role of the stomach in the digestive process OFFICI AL Pharynx Ascending colo Sublingual Rectum Anus Transverse colon Oral cavity Tongue Pancreas Oesophagus...

OFFICI AL Gastrointestinal A&P HEA1091 OFFICI AL Identify some of the organs of the GI tract Describe the functions of the GI tract Analyse the role of the stomach in the digestive process OFFICI AL Pharynx Ascending colo Sublingual Rectum Anus Transverse colon Oral cavity Tongue Pancreas Oesophagus Parotid Duodenum Ileum Cecum Stomach Submandibular Descending colon Liver Salivary gland Gallbladder Pancreatic duct ommon bile duct Appendix Colon OFFICI AL OFFICI AL Contribution of Other Body Systems to the Digestive System Benefits received by the digestive Body system system Blood supplies digestive organs with Cardiovascular oxygen and processed nutrients Endocrine hormones help regulate Endocrine secretion in digestive glands and accessory organs Skin helps protect digestive organs and Integumentary synthesizes vitamin D for calcium absorption Mucosa-associated lymphoid tissue and other lymphatic tissue defend against Lymphatic entry of pathogens; lacteals absorb lipids; and lymphatic vessels transport lipids to bloodstream Skeletal muscles support and protect Muscular abdominal organs Sensory and motor neurons help regulate Nervous secretions and muscle contractions in the digestive tract Respiratory organs provide oxygen and Respiratory remove carbon dioxide Bones help protect and support digestive Skeletal organs Kidneys convert vitamin D into its active Urinary form, allowing calcium absorption in the small intestine OFFICI AL ALIMENTARY CANAL  Alimentary= Nourishment  This is a continuous tube that extends from the mouth to the anus through the thoracic and abdominopelvic cavities OFFICI AL OFFICI AL Alimentary canal Also known as the gastrointestinal (GI) tract, this is essentially a long tube. It begins at the mouth and ends at the anus, and in adults is around 10 metres long. The organs along its length have different functions, although structurally they are remarkably similar. The parts are: Mouth Pharynx Oesophagus Stomach Small intestine Large intestine Rectum and anal canal. OFFICI AL Accessory organs Various secretions are released into the alimentary tract, some by glands in the lining of certain organs, e.g., gastric juice secreted by glands in the lining of the stomach, and others by glands outside the tract. The latter are the accessory organs of digestion, and their secretions pass through ducts to enter the tract. They consist of: Three pairs of salivary glands The pancreas The liver Gall Bladder The organs and glands are linked physiologically as well as anatomically, in that digestion and absorption are coordinated and occur in stages, each being OFFICI AL Functions of the digestive system 1. Ingestion- Eating and drinking 2. Secretion of water, acid, buffers, and enzymes into lumen- Approx 7 litres per day!! 3. Mixing and propulsion- Alternating contractions and relaxation of smooth muscle mix food and secretions. OFFICI AL Functions of the digestive system 4. Digestion Mechanical digestion churns food- Teeth, then smooth muscle of the stomach and small intestine break down the food Chemical digestion – hydrolysis- The large carbohydrate, protein and nucleic acid molecules are broken down into smaller molecules 5. Absorption – passing into blood or lymph- Movement from the lumen of the GI tract. Vitamins, cholesterol and water from food do not undertake the digestive process 6. Defaecation – elimination of faeces- Indigestible substances, bacteria, cells from the GI tract and digested material that was not absorbed leave the body OFFICI AL OFFICI AL Layers OFFICI AL The walls of the alimentary tract are formed by four layers of tissue: Adventitia or serosa – outer covering Smooth muscle Submucosa Mucosa – mucosal lining. OFFICI AL The adventitia and serosa are like the bodyguards of the gastrointestinal (GI) system. The adventitia is more of a tough, connective tissue layer that provides support and structure to the organs in the digestive tract, kind of like a sturdy foundation. On the other hand, the serosa is a slick, smooth membrane that wraps around some parts of the GI organs, making sure things run smoothly. OFFICI AL The peritoneum is a big, thin membrane in your belly that acts like a protective sac. It contains a small amount of serous fluid, called peritoneal fluid, secreted by the peritoneal cells. It is richly supplied with blood and lymph vessels and contains many lymph nodes. It provides a physical barrier to local spread of infection. It has two layers: The parietal peritoneum, which lines the anterior abdominal wall The visceral peritoneum, which covers the organs (viscera) within the abdominal and pelvic cavities. OFFICI AL Voluntary skeletal muscle found in mouth, pharynx, upper 2/3 of oesophagus, and anal sphincter. The rest consists of two layers of smooth (involuntary) muscle. The muscle fibres of the outer layer are arranged longitudinally, and those of the inner layer are circular. Between these two muscle layers are blood vessels, lymph vessels and a plexus (network) of sympathetic and parasympathetic nerves, called the myenteric plexus. These nerves supply the adjacent smooth muscle and blood vessels. Contraction and relaxation of the muscle layers occur in waves, which push the contents of the tract onwards. This type of rhythmical contraction of smooth muscle is called peristalsis and is under the influence of sympathetic Musculari s OFFICI AL Submucos a This layer is a mix of loose connective tissue that links the muscles to the inner lining. It's like a support network for the muscles and contains blood vessels, nerves, and lymph vessels. The nerves create a submucosal plexus (Think of it as a communication hub that influences what happens on the inner surface of the organ), sending signals to the inner lining and its glands, OFFICI AL Mucosa – inner lining The mucosa has three layers. The top one is the mucous membrane (epithelium), followed by a thin layer of connective tissue supporting blood vessels and protecting against microbes. The deepest layer is a thin layer of smooth muscle that shapes the features of the tract wall, like gastric glands and villi. OFFICI AL At various spots in the tract, special glands release fluids into the tube, such as: Saliva from the oral glands Stomach juice from the stomach glands Intestinal juice from the intestinal glands Pancreatic juice from the pancreas Bile from the liver. These fluids, aka digestive juices, usually have enzymes that help break down food chemically. OFFICI AL Nervous control OFFICI AL The parasympathetic supply One pair of cranial nerves, the vagus nerves, supplies most of the alimentary canal and the accessory organs. Sacral nerves supply the most distal part of the GI tract. The effects of parasympathetic stimulation on the digestive system are: Increased smooth muscle activity, especially peristalsis. Increased glandular secretion. The sympathetic supply This is provided by numerous nerves that emerge from the spinal cord in the thoracic and lumbar regions. These form plexuses (ganglia) in the thorax, abdomen, and pelvis, from which nerves pass to the organs of the alimentary tract. The effects of sympathetic stimulation on the digestive system are to: Decrease smooth muscle activity, especially peristalsis, because stimulation of the myenteric plexus is reduced. OFFICI AL ORAL CAVITY The digestion starts here: Cutting and chewing (mechanical) Mixing with saliva (chemical) Food converted to a bolus which is swallowed and enters the oesophagus via the pharynx The bolus moves down the oesophagus vis peristalsis (and gravity) OFFICI AL OFFICI AL The oral cavity- Opening to the GI tract Hard palate Formed by the cheeks (lateral), tongue (floor) and palate (roof) Hard palate = bone Soft palate = mucous membrane Uvula = muscle Soft palate Uvula Cheek Tongue (reflected upwards) OFFICI AL When food is taken into the mouth, it is chewed (masticated) by the teeth and moved around the mouth by the tongue and muscles of the cheeks. It is mixed with saliva and formed into a soft mass, or bolus, ready for swallowing. V & VII Trigeminal and Facial OFFICI AL SALIVARY GLANDS OFFICI AL SALIVARY GLANDS Blood supply Arterial supply is by various branches from the external carotid arteries, and venous drainage is into the external jugular veins. Secretion of saliva Secretion of saliva is controlled by the autonomic nervous system. Reflex secretion occurs when there is food in the mouth and the reflex becomes conditioned so that OFFICI AL SALIVARY GLANDS OFFICI AL Functions The tongue plays an important part in: The tongue is composed of voluntary muscle. It is attached by its base to the hyoid bone and by a fold of its mucous membrane covering, called the frenulum, to the floor of the mouth Chewing (mastication) Swallowing (deglutition) Speech Taste OFFICI AL Nerve supplyMouth The hypoglossal nerves (12th cranial nerves), which supply the voluntary muscle The 5th cranial nerves, the nerves of somatic (ordinary) sensation, i.e. pain, temperature and touch The facial and glossopharyngeal nerves (7th and 9th cranial nerves), the nerves of taste. OFFICI AL PHARYNX Funnel shaped tube from the posterior nasal opening down to cricoid cartilage Skeletal muscle lined with mucous membrane Divided into 3 parts: Nasopharynx Oropharynx Laryngopharynx OFFICI AL PHARYNX The nasopharynx is important in respiration. The oropharynx and laryngopharynx are passages common to both the respiratory and the digestive systems. Food passes from the oral cavity into the pharynx and then to the oesophagus below, which is continuous. OESOPHAGUS Hollow muscular tube It is 20 - 40cm long and about 1 - 2cm in width The oesophagus begins in the laryngopharynx at C6 and extends down to T11 Responsible for carrying food from the pharynx to the stomach Runs posterior to the trachea and the heart Passes through diaphragm at the oesophageal hiatus The upper and lower ends of the oesophagus are closed by sphincters. The upper oesophageal sphincter prevents air entering the oesophagus during inspiration, and the aspiration of oesophageal contents. The lower oesophageal (cardiac) sphincter prevents the reflux of acid OFFICI AL OFFICI AL OFFICI AL OESOPHAGEAL CONSTRICTIONS The oesophagus has 3 normal constrictions: Upper oesophageal/cervical (C5/6) → due to cricoid cartilage Middle oesophageal/thoracic (T4/5) → due to the arch of aorta Lower oesophageal/abdominal (T10/11) → due to the oesophageal Why are these constrictions important? hiatus of the diaphragm OFFICI AL OFFICI AL Functions of the Mouth, Pharynx and Oesophagus Formation of a bolus Swallowing the bolus occurs in three stages. It is initiated voluntarily but completed by reflex (involuntary) action. OFFICI AL Oral stage With the mouth closed, the voluntary muscles of the tongue and cheeks push the bolus backwards into the pharynx. Pharyngeal stage The muscles of the pharynx are stimulated by a reflex initiated in the walls of the oropharynx and coordinated by the swallowing centre in the medulla. Involuntary contraction of these muscles propels the bolus down into the oesophagus as all other routes that the bolus could take are closed. The soft palate rises up closing off the nasopharynx, the tongue and the pharyngeal folds block the way back into the mouth, and the larynx is lifted up and forwards so that its opening is occluded by the overhanging epiglottis, preventing entry into the trachea. OFFICI AL Once in the pharynx, the bolus triggers a wave of involuntary muscle contractions that push it down the oesophagus to the stomach. Peristaltic waves only occur when swallowing starts, and the oesophageal walls are relaxed at other times. Before a peristaltic wave, the lower oesophageal sphincter, guarding the stomach entrance, opens to let the food pass. Normally, it prevents stomach acid from flowing back into the oesophagus. Factors preventing acid reflux include the stomach's attachment to the diaphragm, the angle of the oesophagus entering the stomach, and increased sphincter tone during activities like swallowing and defecation. The oesophageal walls are coated with mucus, making it easier for the food to slide down during swallowing. OFFICI AL PHASES OF DIGESTION Cephalic phase Smell, sight, thought or initial taste of food activates neural centers Prepares mouth and stomach for food to be eaten Gastric phase Neural and hormonal mechanisms promote gastric secretion and motility Intestinal phase Begins when food enter small intestine Slows exit of chyme from stomach Stimulates flow of bile and pancreatic juice OFFICI AL STOMACH Muscular expansion of the GI tract Located mainly within the epigastrium and umbilical region Inferior to the diaphragm Stores ingested food- holding reservoir (Can store up to 4 litres at one time) Continues mechanical digestion Secretes gastric juices for chemical digestion Converts food bolus into chyme OFFICI AL STOMACH ANATOMY The stomach is a roughly beanshaped, muscular sac which can be anatomically divided into different regions: Fundus Cardia Body Antrum Pylorus Lesser curvature Greater curvature OFFICI AL STOMACH ANATOMY The cardia- surrounds the opening of the oesophagus The fundus- The rounded portion, superior to and left of the cardia The body- The large central Portion The pylorus- pyl=gate orus=guard. Connected to the duodenum OFFICI AL STOMACH ANATOMY Separates the oesophagus with the stomach by the oesophageal sphincter Stomach separates with the duodenum by the pyloric sphincter -When the stomach is empty the sphincter is relaxed and open, and when the stomach contains food the sphincter is closed OFFICI AL OFFICI AL DIGESTION Mechanical digestion Mixing waves – creates chyme OFFICI AL Chemical digestion Digestion by salivary amylase continues until inactivated by acidic gastric juice The HCl in the stomach denatures salivary amylase and other proteins by breaking down the structure and, thus, the function of it. Covalent bond OFFICI AL Remember this….. How is Hydrochloric Acid produced? OFFICI AL Hydrochloric acid (HCl) is produced in the stomach by parietal cells, which are a type of cell lining the stomach walls. The process of hydrochloric acid production involves several steps: 1. Inside the parietal cells, carbon dioxide (CO2) combines with water (H2O) to form carbonic acid (H2CO3). 2. The enzyme carbonic anhydrase, which is present in the parietal cells, facilitates the rapid conversion of carbonic acid into bicarbonate ions (HCO3-) and protons (H+). 3. Swap: The bicarbonate ions go out of the cell and into the blood, while chloride ions (Cl-) from the blood come into the cell. 4. The protons, or hydrogen ions, are actively transported from the cytoplasm of the parietal cell into the stomach lumen via a proton pump called the hydrogen-potassium pump (H+/K+ pump or proton pump). 5. Chloride ion secretion: Chloride ions, which entered the parietal cells in exchange for bicarbonate ions, combine with the protons in the stomach lumen to form hydrochloric acid (HCl). OFFICI AL Gastrin 1. Stimulus for Gastrin Release: Gastrin release is triggered by various stimuli, such as the presence of food in the stomach, especially proteins, and the stretching of the stomach wall. When food is ingested, the stomach responds by releasing gastrin to prepare for the digestive process. 2. Gastrin Circulation: Once released, gastrin enters the bloodstream and is carried to its target cells, the parietal cells in the stomach lining. 3. Effect on Parietal Cells: Gastrin binds to specific receptors on the surface of parietal cells. This binding activates the parietal cells and stimulates them to secrete hydrochloric acid (HCl). 4. Hydrochloric Acid Production: The activation of parietal cells by gastrin results in several effects: o Increased production of hydrogen ions (protons) within the parietal cells. o Activation of an enzyme called H+/K+ ATPase, which pumps these hydrogen ions into the stomach's gastric pits. o 5. In exchange for the pumped-out hydrogen ions, potassium ions are taken up by the parietal cells. Feedback Mechanism: As the acidity in the stomach increases, it provides feedback to the G cells to reduce further gastrin release. This is a regulatory mechanism that prevents excessive acid production. OFFICI AL Somatostat in Production and Release: Somatostatin is produced by specialized cells called D cells, which are present in the stomach, pancreas, and other parts of the digestive system. In the stomach, D cells are found in the gastric glands. Trigger for Somatostatin Release: Somatostatin release is stimulated by factors such as low pH (acidity) in the stomach, the presence of partially digested food in the stomach, and the release of other hormones like gastrin. Essentially, somatostatin is released when there is a need to counteract or inhibit excessive gastric acid secretion. Inhibition of Gastrin: One of the primary actions of somatostatin is to inhibit the release of gastrin, another hormone that stimulates gastric acid secretion. Somatostatin acts directly on the G cells (gastric cells) in the stomach lining, reducing their activity and the release of gastrin into the bloodstream. Direct Inhibition of Parietal Cells: Somatostatin also acts directly on parietal cells, which are responsible for producing hydrochloric acid (HCl) in the stomach. When somatostatin binds to receptors on the surface of parietal cells, it inhibits the activity of the enzyme H+/K+ ATPase. This enzyme is crucial for pumping hydrogen ions (protons) into the stomach, leading to a reduction in gastric acid production. Inhibition of Other Digestive Processes: Besides inhibiting gastric acid secretion, somatostatin has inhibitory effects on other digestive processes, including the release of enzymes from the pancreas and the contraction of the gallbladder. Negative Feedback Mechanism: Somatostatin, through its inhibitory actions, provides a negative feedback mechanism. As the acidity in the stomach increases, somatostatin is released to inhibit further acid production and maintain a balance in the digestive environment. OFFICI AL Carbohydrates Started to be broken down in the mouth- Salivary amylase As the bolus enters the stomach, because of salivary amylase the carbohydrates are partially broken down Mechanical digestion breaks carbohydrates down further No chemical digestion of carbohydrates occurs in the stomach Chemical digestion begins again once in the small intestine OFFICI AL Lipid s Acidic Environment: The stomach is an acidic environment due to the presence of gastric acid (hydrochloric acid). Gastric lipase functions optimally in this acidic pH range. Action on Triglycerides: Gastric lipase primarily acts on triglycerides, which are the predominant form of dietary fats. Triglycerides consist of three fatty acid chains attached to a glycerol molecule. Gastric lipase is like a little worker in this stomach mixing bowl. It goes to these fat structures (triglycerides) and takes away one or two blocks (fatty acids). It does this through a process called hydrolysis, which is like breaking a bond that holds those blocks together. Gastric lipase is good at dealing with shorter chains of blocks, but it struggles a bit with longer chains. However, it still starts the process of breaking down the fats. Stomach's Mechanical Mix: While gastric lipase is doing its thing, your stomach is also OFFICI AL Proteins Chewing in the Mouth: Protein digestion begins in your mouth when you chew your food. Chewing breaks down food into smaller pieces, and saliva contains an enzyme called salivary amylase that starts breaking down carbohydrates. However, proteins are not significantly affected in the mouth. Stomach Acid and Pepsin: When the chewed food (bolus) reaches your stomach, it encounters a very acidic environment due to the presence of hydrochloric acid (HCl). This acid helps to create the right conditions for the action of an enzyme called pepsin. Activation of Pepsin: Pepsin is initially released in an inactive form known as pepsinogen by the stomach lining cells (Chief cells). The acidic environment of the stomach activates pepsinogen, converting it into pepsin. Pepsin is a protease enzyme, which means it breaks down proteins. Protein Breakdown: Activated pepsin starts breaking down large protein molecules into smaller fragments called peptides. Peptides are chains of amino acids, which are the building blocks of proteins. Mechanical Digestion: While the chemical breakdown of proteins is happening, the stomach is also doing some mechanical digestion—mixing and churning the food. This helps in distributing the stomach acid and enzymes throughout the food, ensuring better contact and digestion. It's important to note that the stomach doesn't break down proteins into individual amino acids; rather, it breaks them into smaller peptide fragments. Further digestion of these peptides into individual amino acids takes place OFFICI AL OFFICI AL OFFICI AL Mucous Synthesis of Mucus: Inside goblet cells, there is a process of synthesising mucus. Mucus is composed of water, mucin proteins, salts, and other substances. The key component, mucin, is a large and complex glycoprotein. Storage in Cytoplasmic Granules: Once synthesised, the mucus is stored in large cytoplasmic granules within the goblet cell. Stimulation for Release: Goblet cells are sensitive to various stimuli, such as irritation, infection, or mechanical stimulation. When these cells are triggered by such stimuli, it signals the goblet cell to release its stored mucus. Mucus as a Protective Barrier: Once released, mucus forms a protective layer over the epithelial surfaces. In the respiratory tract, for example, mucus helps trap and eliminate foreign particles, dust, and pathogens. In the digestive tract, mucus provides lubrication for the passage of food and protects the lining from OFFICI AL NERVE SUPPLY Sympathetic Reduce smooth muscle contraction Reduce secretion of hormones Parasympathetic Smooth muscle contraction Secretion of gastric juices ‘Rest & Digest’ OFFICI AL HYDROCHLORIC ACID PRODUCTION Produced by parietal cell Three production pathways Acetylcholine (ACH) Secreted by vagus at sight, smell, taste Gastrin Secreted as a result of food in stomach and distension of stomach ACH stimulates production of gastrin Histamine Secreted as a result of food in stomach ACH and gastrin lead to release of histamine OFFICI AL OFFICI AL ACID PRODUCTION Ach Gastrin Histamin e Parieta l Cell HCl OFFICI AL -Belong to a class of drugs called H2 (histamine-2) blockers or antagonist -H2-blockers inhibit the action of histamine on the cells, thus reducing the production of acid by the stomach. OFFICI AL ACID PRODUCTION Ach Gastrin X Histamin e Parieta l Cell HCl OFFICI AL