digestive system Flashcards
What components make up the Digestive System?
The Digestive System consists of the alimentary tract or GI tract and accessory organs such as the salivary glands, liver, pancreas, and gallbladder.
What are the main parts of the GI tract?
The GI tract includes the mouth, oesophagus, stomach, small intestine, large intestine, and anus.
What is the role of the accessory organs in the digestive system?
Accessory organs are solid organs that support the digestive process but are not part of the GI tract. They include the salivary glands, liver, pancreas, and gallbladder.
Describe the two types of digestion.
Mechanical digestion involves the physical breaking up of foods, typically in the mouth and stomach. Chemical digestion uses enzymes and solvents to break up molecules into smaller absorbable units.
How are nutrients absorbed in the digestive system?
Nutrients are mostly absorbed through the small intestine into the blood by diffusion or active transport. Lipids and lipid-soluble vitamins enter lymphatic vessels instead.
What occurs during the secretion phase of digestion?
During secretion, enzymes and water are secreted to aid in the digestive process.
Explain the process of motility in the digestive system.
Motility involves the movement of food, nutrients, and waste through the GI tract using myogenic contractions for peristalsis and segmentation.
Why are macromolecules important for the digestive system?
Macromolecules provide an efficient storage method, reduce osmolarity when stored, and allow for controlled, gradual digestion to prevent rapid increases in osmolarity, known as dumping syndrome.
Describe the structure of the GI tract.
The GI tract is a continuous hollow tube, about 8 meters long from oesophagus to rectum, varying in diameter, and organized into four layers or tunics: mucosa, submucosa, muscularis externa, and serosa or adventitia.
What are the characteristics of the mucosa in the GI tract?
The mucosa includes an epithelium layer, lamina propria, and muscularis mucosae. The epithelium varies along the gut, being stratified squamous in the mouth, oesophagus, and anal canal, and simple columnar in the stomach and intestines.
Describe the submucosa of the GI tract.
The submucosa is thick, irregular connective tissue supporting the mucosa, containing neurones, blood vessels, and the submucosal (Meissner’s) plexus.
What is the role of the muscularis externa in the GI tract?
The muscularis externa consists of two layers of smooth muscle (inner circular and outer longitudinal) that help in peristalsis and segmentation, controlled by the myenteric (Auerbach’s) plexus.
Explain the difference between serosa and adventitia.
Serosa is the connective tissue surrounding stomach, small intestine, and large intestine within the peritoneal cavity. Adventitia is connective tissue attaching the oesophagus and rectum to surrounding structures outside the peritoneal cavity.
How is the GI tract controlled by the nervous system?
The autonomic nervous system controls the GI tract, with parasympathetic (stimulatory) innervation mainly from the vagus nerve and sympathetic (inhibitory) innervation from the splanchnic nerve, affecting secretion and motility.
What is the function of chewing in the digestive process?
Chewing not only prolongs the taste experience and helps detect problematic food but also involves a reflex that regulates the pressure of food against the gums, palate, and tongue to control jaw muscle contraction.
What is the function of the pancreas in the digestive system?
The pancreas secretes digestive enzymes that are crucial for the digestion of fats, carbohydrates, and proteins.
What role does the liver play in the digestive process?
The liver secretes bile salts which are essential for the digestion and absorption of fats in the small intestine.
Describe the function of the gallbladder in the digestive system.
The gallbladder stores and concentrates bile, which is produced by the liver and used in the digestion of fats.
What are the main functions of the small intestine in digestion and absorption?
The small intestine is the final stage of chemical digestion and the primary site for nutrient absorption, where digested macromolecules are absorbed into the bloodstream.
What processes occur in the large intestine related to digestion?
The large intestine is responsible for absorbing water, bacterial fermentation of undigested materials, and forming faeces.
Describe the structural organization of the tube wall in the GI tract.
The tube wall throughout the GI tract is organized into four layers called tunics: mucosa, submucosa, muscularis externa, and serosa or adventitia, each serving specific functions in digestion and structural integrity.
What specific adaptations are found in the epithelium of the GI tract?
The epithelium varies along the GI tract: stratified squamous in the mouth, esophagus, and anal canal for protection; simple columnar in the stomach, small and large intestines for absorption and secretion.
What is the role of the lamina propria in the GI tract mucosa?
The lamina propria is loose connective tissue beneath the epithelium, containing glands, blood vessels, and lymph vessels, contributing to the immune function and support of the mucosa.
What function does the muscularis mucosae serve in the GI tract?
The muscularis mucosae is a thin layer of smooth muscle that helps produce local movements of the mucosa to aid in the more efficient mixing of food with digestive secretions.
Describe the role of the submucosal glands in the esophagus and duodenum.
In the esophagus, submucosal glands secrete mucus to lubricate and protect the lining. In the duodenum, these glands secrete bicarbonate to neutralize stomach acid entering the intestine.
What is the enteric nervous system, and how does it function?
The enteric nervous system (ENS) consists of the myenteric and submucosal plexuses. It controls gut function independently of the CNS, regulating peristalsis, segmentation, and enzyme secretion.
How do the sympathetic and parasympathetic nervous systems affect salivation?
The parasympathetic system stimulates watery saliva production for digestion, while the sympathetic system produces thick, viscous saliva. Both are involved in different aspects of salivary gland function.
What reflex is involved in the process of chewing, and how does it work?
Chewing involves a reflex that regulates jaw muscle contraction. This reflex responds to the pressure of food against the gums, hard palate, and tongue, with mechanoreceptors signaling to reduce or increase jaw muscle pressure as needed.
What are the specific roles of the epithelium in the digestive system?
The epithelium serves several critical functions: it acts as a barrier separating the GI tract lumen from the body, absorbs products of digestion, and is responsible for the synthesis and secretion of digestive enzymes, hormones, and mucus.
Describe the specific contributions of the parasympathetic and sympathetic nervous systems to digestive system control.
The parasympathetic nervous system, mainly via the vagus nerve, stimulates increased secretion and motility throughout the GI tract, enhancing digestion. In contrast, the sympathetic system, primarily through the splanchnic nerves, inhibits these processes to slow digestion. Salivation is an exception where it’s stimulated by both systems, with parasympathetic input generating watery saliva and sympathetic input producing viscous saliva.
How do the structural layers of the GI tract contribute to its function?
Each layer of the GI tract contributes uniquely: The mucosa facilitates absorption and secretion, the submucosa supports the mucosa with nutrients and nerves, the muscularis externa enables movement of contents through peristalsis and segmentation, and the serosa or adventitia provides structural integrity and connection to surrounding tissues.
What is the role of the hepatic portal vein in liver function?
The hepatic portal vein is crucial as it carries all blood from the gastrointestinal tract to the liver. This blood is rich in nutrients but low in oxygen, which the liver processes for storage or detoxification.
Describe the hepatic artery’s function in the liver.
The hepatic artery supplies oxygen-rich blood to the liver, coming directly from the aorta, which is vital for maintaining the liver cells’ metabolic activities.
How do the liver’s dual blood supplies integrate within its structure?
The liver’s dual blood supply from the hepatic artery and portal vein mixes in the sinusoidal spaces, allowing hepatocytes to access both oxygen and nutrients efficiently. Blood is then collected by the central vein of each lobule, draining into the hepatic vein before entering the vena cava.
Explain the significance of the liver in metabolic regulation.
The liver plays a pivotal role in metabolic regulation by synthesizing glucose, cholesterol, and special proteins for blood clotting. It also converts excess glucose into glycogen for storage and can convert glycogen back to glucose as needed.
What are the specific functions of Kupffer cells in the liver?
Kupffer cells, as macrophages of the liver, are involved in removing bacteria and old red blood cells from the blood, contributing to the detoxification process and immune function within the liver.
How do hepatic stellate cells respond to liver damage?
Hepatic stellate cells, when activated by liver damage, transform from vitamin A-storing cells to myofibroblasts that produce collagen and other extracellular matrix proteins, contributing to liver fibrosis if persistently activated.
What is the role of bile in the digestive system?
Bile aids in the digestion and absorption of fats in the small intestine by emulsifying fats, which increases the surface area for enzyme action. Bile also helps in the elimination of bilirubin, which is a byproduct of the breakdown of red blood cells.
How is bile modified in the liver and its pathway to the intestine?
Bile produced by hepatocytes is collected in bile canaliculi, moves to bile ducts, and is modified by cholangiocytes which may add bicarbonate. It is stored and concentrated in the gallbladder until needed, then released into the small intestine via the common bile duct.
Explain the relationship between the liver and the spleen in bile pigment metabolism.
Bilirubin, a major bile pigment, is formed in the spleen from the breakdown of old or damaged red blood cells. It is then transported to the liver where hepatocytes process and secrete it into the bile, helping to give bile its characteristic yellow color.
Describe the physiological process of bile concentration in the gallbladder.
The gallbladder concentrates bile by absorbing water and electrolytes through its mucosal lining, which features folds called rugae. This process is driven by sodium and water transport mechanisms, increasing bile concentration by 5-20 times depending on the duration it remains in the gallbladder.
What triggers bile discharge from the gallbladder into the duodenum?
Bile discharge is triggered by the presence of fats in the duodenum, which stimulates the release of cholecystokinin (CCK) from the intestinal mucosa. CCK relaxes the sphincter of Oddi and contracts the gallbladder, promoting bile flow into the duodenum for fat digestion.
Discuss the role of cytochrome P450 enzymes in liver function.
Cytochrome P450 enzymes play a critical role in the liver by oxidizing cholesterol to bile acids, a process essential for the synthesis of bile salts. These enzymes are also vital in the metabolism of xenobiotics, contributing to the liver’s detoxification functions.
How does the liver regulate immune responses?
The liver regulates immune responses by filtering pathogens from the blood, with Kupffer cells phagocytizing bacteria and debris. It also plays a role in the systemic immune system by producing acute-phase proteins that modulate immune functions.
What is the structural and functional significance of the liver’s hexagonal lobules?
The liver’s lobules are hexagonal structures that optimize the liver’s processing capabilities. Each lobule contains a central vein and is surrounded by portal triads, efficiently arranging blood flow and bile secretion to maximize exchange between blood and liver cells.
Describe the significance of the bare area of the liver.
The bare area of the liver is the region that lacks the protective covering of Glisson’s capsule and directly contacts the diaphragm. This area facilitates the attachment and positioning of the liver within the abdominal cavity.
How is the liver protected and stabilized within the abdominal cavity?
The liver is stabilized by the falciform ligament and other peritoneal attachments, and protected by Glisson’s capsule, a fibrous sheath that covers most of the liver’s surface except for the bare area. These structures help maintain the liver’s position and integrity.
Describe the interaction between the liver and the vena cava.
After processing in the liver, blood collects in the central veins of each lobule, drains into the hepatic vein, and then into the inferior vena cava. This efficient routing ensures that detoxified and nutrient-enriched blood quickly re-enters systemic circulation.
What specific role do liver sinusoidal endothelial cells (LSECs) play in liver function?
LSECs line the liver sinusoids and are highly specialized for filtration, lacking a basement membrane which allows for the free exchange of molecules between blood and hepatocytes. They also play a crucial role in the immune response by presenting antigens and clearing pathogens.
How do hepatic stellate cells contribute to liver fibrosis?
Hepatic stellate cells, when activated by liver damage or inflammation, transform into myofibroblasts that produce excessive amounts of collagen and other extracellular matrix components, leading to liver fibrosis, which can progress to cirrhosis if unchecked.
Detail the process and significance of bilirubin conversion in the liver.
Bilirubin, transported to the liver bound to albumin, is taken up by hepatocytes, conjugated with glucuronic acid to make it water-soluble, and then secreted into bile. This conversion is crucial for the body’s ability to dispose of hemoglobin breakdown products effectively.
Explain the significance of the liver in energy metabolism.
The liver is central to energy metabolism, regulating blood glucose levels through glycogenolysis and gluconeogenesis. It also metabolizes fats and proteins, providing energy and synthesizing critical biochemicals necessary for body function.
What mechanisms does the liver use to detoxify blood?
The liver detoxifies blood by altering chemical structures of toxins through oxidation, reduction, or conjugation reactions, making them soluble and safe for excretion via bile or urine, primarily facilitated by cytochrome P450 enzymes.
How does the liver’s anatomical position affect its functions?
The liver’s position in the upper right quadrant of the abdomen, directly under the diaphragm and adjacent to the stomach and intestines, facilitates its roles in metabolizing substances absorbed from the digestive tract and regulating blood composition before it circulates widely.
What are the three pairs of salivary glands and their primary functions?
The salivary glands include the parotid (secretes saliva from the upper mouth), sublingual (secretes saliva from below the tongue), and submandibular (secretes saliva from the back of the mouth).
What are the main components of saliva and their functions?
Saliva is 99% water, aiding in softening, moistening, diluting, and acting as a solvent. It contains mucins (major glycoproteins) that form mucus, serving a lubricant function, alpha-amylase that breaks down polysaccharides, electrolytes that maintain tonicity and pH, and lysozymes that are bactericidal.
How is salivary secretion controlled?
Salivary secretion is controlled by both the parasympathetic and sympathetic nervous systems. The parasympathetic nerves (cranial VII and IX) increase watery saliva production, while the sympathetic nerve increases a small volume of viscous secretion rich in mucus and amylase.
Describe the phases of swallowing and their mechanisms.
Swallowing has three phases: oral (voluntary, pushes bolus back with the tongue), pharyngeal (involuntary, coordinated by the swallowing centre in the medulla, closes off nasopharynx, relaxes upper esophageal sphincter), and esophageal (bolus moves to stomach via peristalsis, lower esophageal sphincter relaxes for stomach entry).
What are the main functions of the stomach?
The stomach stores ingested material, dissolves food particles, initiates digestion, controls delivery to the small intestine, sterilizes ingested material, and produces intrinsic factor essential for vitamin B12 absorption.
What vitamins are lipid-soluble, and why is Vitamin B12 important?
Lipid-soluble vitamins include K, E, D, and A. Vitamin B12 is critical for blood formation, myelin sheath formation, and other functions. Deficiency can lead to pernicious anemia, which develops over three years due to B12 depletion.
What is the anatomy of the stomach and its main sections?
The stomach includes sections like the cardiac region, fundus, body, antrum, and pyloric region. It features layers such as mucosa, submucosa, muscularis (with an extra oblique muscle layer), and serosa. Rugae are mucosal foldings that help maintain pressure despite volume changes.
Describe the functional anatomy of the stomach.
The fundus and body of the stomach store ingested material and secrete mucus, HCl, pepsinogen, and intrinsic factor. The antrum is responsible for mixing, grinding, and secreting gastrin.
What is the process and control of stomach acid formation?
Stomach acid formation involves CO2 reacting with H2O to form carbonic acid, which dissociates into bicarbonate and protons. Protons are exchanged for potassium and move to the lumen, while bicarbonate is exchanged for chloride, which also moves to the lumen to form HCl. Control involves gastrin, histamine, acetylcholine, and prostaglandins affecting various receptors and pathways in parietal cells.
How do medications affect stomach acid production?
Medications like omeprazole and pantoprazole inhibit the proton pump to reduce acid production. Ranitidine and cimetidine decrease acid secretion by blocking H2 receptors. NSAIDs like ibuprofen and aspirin can cause peptic ulcers by reducing prostaglandin levels, which are necessary for inhibiting acid secretion.
What specific role does alpha-amylase play in saliva?
Alpha-amylase in saliva catalyzes the breakdown of polysaccharides like starch and glycogen into smaller disaccharides such as maltose and eventually into glucose, facilitating the initial digestion of carbohydrates in the mouth.
Explain the importance of maintaining pH in the mouth regarding dental health.
Maintaining the pH in the mouth is crucial because it affects the solubility of hydroxyapatite, the primary mineral that teeth are made of. A lower pH (more acidic) increases the risk of demineralizing teeth, leading to cavities and tooth decay.
How does the oral phase of swallowing ensure that food enters the pharynx properly?
During the oral phase, which is voluntary, the tongue pushes the bolus of chewed food to the back of the mouth towards the oropharynx, preparing it for the involuntary pharyngeal phase of swallowing.
What mechanisms prevent food from entering the respiratory tract during swallowing?
During the pharyngeal phase of swallowing, the soft palate lifts to seal off the nasopharynx, and the epiglottis closes over the laryngeal opening, directing the bolus safely into the esophagus and preventing food from entering the trachea.
Describe the receptive relaxation of the stomach.
Receptive relaxation refers to the reflex relaxation of the gastric fundus and body’s smooth muscle as the bolus enters the stomach, mediated by the vagus nerve. This process allows the stomach to expand to accommodate incoming food without increasing internal pressure significantly.
What are the specific roles of mucous neck cells, parietal cells, and chief cells in the gastric glands?
Mucous neck cells secrete mucus to protect the stomach lining. Parietal cells secrete hydrochloric acid (HCl) and intrinsic factor, which is crucial for vitamin B12 absorption. Chief cells secrete pepsinogen, the inactive precursor of pepsin, which is vital for protein digestion.
How do changes in blood pH occur postprandially and how is it managed?
Postprandial alkalization occurs when CO2 is lost from the blood near the stomach due to increased respiration, making the blood temporarily more alkaline. The body’s buffer systems quickly neutralize this change to maintain the blood pH at 7.4.
Detail the roles of gastrin, histamine, acetylcholine, and prostaglandins in controlling stomach acid production.
Gastrin, secreted into the blood, activates GQ protein receptors increasing calcium levels in parietal cells, enhancing acid production. Histamine activates GS protein receptors increasing cAMP levels for the same effect. Acetylcholine from the vagus nerve also increases calcium in parietal cells. Prostaglandins, however, inhibit acid secretion by reducing cAMP levels through GI protein receptors.
What are the anatomical features that facilitate the stomach’s ability to mix and grind stomach contents?
The stomach’s oblique muscle layer, part of the muscularis, enhances its churning and mixing abilities. Additionally, the antrum’s powerful muscle contractions contribute to the grinding of solid food particles, preparing them for digestion in the small intestine.
How do proton pump inhibitors and H2 receptor blockers work to manage stomach acid-related conditions?
Proton pump inhibitors (e.g., omeprazole, pantoprazole) block the final step in acid production by inhibiting the H+/K+ ATPase enzyme at the gastric parietal cell surface. H2 receptor blockers (e.g., ranitidine, cimetidine) reduce acid secretion by blocking histamine receptors on parietal cells, decreasing the activation of adenylate cyclase and subsequent cAMP production necessary for triggering acid release.
What specific actions do lysozymes in saliva have against bacteria?
Lysozymes in saliva act as bactericidal agents by cleaving the polysaccharide components of bacterial cell walls, effectively destroying bacteria and reducing the risk of infection in the mouth.
What triggers the reflex arc for salivary secretion when food is present in the mouth?
The presence of food in the mouth activates chemoreceptors and mechanoreceptors on the walls of the mouth and tongue, which detect the food’s chemical and physical properties, respectively. This sensory input triggers a reflex arc that initiates salivary secretion to begin the digestive process.
Describe the sequence of reflex contractions during the pharyngeal phase of swallowing.
During the pharyngeal phase, the presence of the bolus triggers a sequence of reflex contractions in the pharyngeal muscles, coordinated by the swallowing center in the medulla. This action propels the bolus toward the esophagus while simultaneously closing off the nasopharynx and covering the larynx to prevent aspiration.
Explain the mechanism and function of the upper esophageal sphincter (UOS) during swallowing.
The upper esophageal sphincter (UOS) relaxes as the bolus approaches during the pharyngeal phase of swallowing, allowing the bolus to enter the esophagus. After the bolus passes, the UOS contracts to prevent food reflux back into the pharynx, ensuring one-way movement of the bolus towards the stomach.
How does the lower esophageal sphincter (LOS) manage the transition of the bolus into the stomach?
The lower esophageal sphincter (LOS), or cardiac sphincter, relaxes as the peristaltic wave propels the bolus through the esophagus. This relaxation allows the bolus to enter the stomach smoothly. After the bolus passes, the LOS contracts to prevent gastric reflux, thereby protecting the esophagus from acidic stomach contents.
What is the role of the gastric fundus and body in accommodating varying volumes of ingested material?
The gastric fundus and body exhibit receptive relaxation—a reflex mediated by the vagus nerve that allows these regions to expand when food enters the stomach. This process increases the stomach’s volume from about 50ml to 1500ml without a significant change in internal pressure, facilitating the temporary storage of ingested materials.
Detail the protective mechanisms of the stomach against its own acidic environment.
The stomach protects itself from its acidic environment primarily through the secretion of mucus by surface mucous cells and mucous neck cells. This mucus forms a barrier that coats the stomach lining, preventing digestive enzymes and gastric acid from damaging the epithelial cells of the stomach wall.
What physiological role does mucus play in oral digestion?
Mucus in saliva, primarily composed of mucins and water, serves as a lubricant that facilitates the easy movement and swallowing of food by forming a slick coating on the food bolus and the oral surfaces.
How do the electrolytes in saliva contribute to oral health?
Electrolytes in saliva help maintain the tonicity and osmolarity of the oral environment and keep the pH constant. This is crucial for protecting tooth enamel by preventing the solubility of hydroxyapatite, the mineral that teeth are made of, especially in acidic conditions.
Explain the coordinated action of the stomach’s muscular layers in digestion.
The stomach’s muscularis layer includes an additional oblique muscle layer that, along with the circular and longitudinal layers, enhances the mechanical digestion of food. These muscle layers churn the stomach contents, mixing them thoroughly with gastric juices to form a semi-liquid substance called chyme, optimizing digestion before it moves into the small intestine.
How does the pyloric sphincter regulate the passage of stomach contents into the duodenum?
The pyloric sphincter, located between the stomach and the duodenum, regulates the passage of chyme from the stomach into the small intestine. It opens periodically in response to gastric contractions, allowing small amounts of chyme to pass into the duodenum, which prevents overloading of the intestine and optimizes nutrient absorption.
Detail the feedback mechanisms involved in regulating gastric acid secretion in response to food intake.
Gastric acid secretion is tightly regulated by neural and hormonal feedback mechanisms. When food enters the stomach, stretch receptors trigger the release of gastrin, which in turn stimulates acid production. Additionally, the presence of food prompts the release of acetylcholine and histamine, which further promote acid secretion. Negative feedback mechanisms involve the lowering of gastrin levels as the stomach empties and pH decreases, helping to modulate acid production.
What is the functional significance of the stomach’s rugae?
The rugae, or folds of the stomach lining, allow the gastric walls to expand significantly after the ingestion of a large meal. By unfolding, they increase the internal volume of the stomach without increasing pressure, which aids in the accommodation of varying amounts of food.
Discuss the roles of intrinsic factor in vitamin B12 absorption.
Intrinsic factor, secreted by the parietal cells of the stomach, is crucial for vitamin B12 absorption in the small intestine. It binds with vitamin B12 in the stomach and facilitates its transport through the small intestine, where it is eventually absorbed into the bloodstream. This process is vital for preventing pernicious anemia and maintaining healthy nerve function.
