Final Digestive Notes PDF

Overview of the Digestive System FUNCTION: Break down food into nutrients that can be delivered viz bloodstream to cell in the body to use and then eliminate wastes o Steps of food nutrient absorption: 1. Break down food into a form that cells can use. This process begins with mechanical and chemica...

Overview of the Digestive System FUNCTION: Break down food into nutrients that can be delivered viz bloodstream to cell in the body to use and then eliminate wastes o Steps of food nutrient absorption: 1. Break down food into a form that cells can use. This process begins with mechanical and chemical digestion in the mouth, stomach, and small intestine, where food is broken down into smaller molecules such as carbohydrates, proteins, and fats. 2. Absorb into bloodstream. Once food is broken down into smaller molecules, these nutrients are absorbed through the walls of the small intestine into the bloodstream. This absorption occurs through specialized structures called villi and microvilli, which increase the surface area for nutrient absorption. 3. Eliminate waste (anything that you were unable to absorb). Any undigested food particles, as well as waste products from the digestive process, are eliminated from the body through the large intestine in the form of feces. Digestive System Consists of two types of organs: 1. Organs of the alimentary canal (gastrointestinal (GI) tract or digestive tract) a. Mouth: Where digestion begins with mechanical (chewing) and chemical (enzymatic) breakdown of food. b. Pharynx: A common passage for both air and food, located behind the mouth. c. Esophagus: A muscular tube that transports food from the pharynx to the stomach through a process called peristalsis. d. Stomach: A muscular organ that continues the mechanical and chemical digestion of food, primarily proteins, through mixing and the action of gastric juices. e. Small Intestine: Consists of three parts: the duodenum, jejunum, and ileum. It is where most of the digestion and absorption of nutrients occur. f. Large Intestine (Colon): Absorbs water and electrolytes from undigested food, forming feces, and stores waste until it is eliminated from the body. g. Rectum: Stores feces until they are expelled through the anus during defecation. 2. Accessory organs - are organs that contribute to the process of digestion but are not part of the alimentary canal. These organs include: a. Liver: Produces bile, which aids in the digestion and absorption of fats in the small intestine. b. Gallbladder: Stores and concentrates bile produced by the liver, releasing it into the small intestine to aid in fat digestion when needed. c. Pancreas: Produces digestive enzymes (such as amylase, lipase, and proteases) that help break down carbohydrates, fats, and proteins in the small intestine. The pancreas also secretes bicarbonate ions to neutralize the acidic chyme from the stomach, creating a more favorable environment for enzyme activity. d. Salivary Glands: Secrete saliva, which contains enzymes like amylase that initiate the breakdown of carbohydrates in the mouth and help lubricate food for easier swallowing. e. Teeth & Tongue Food generally does not come into direct contact with accessory organs; teeth and the tongue are exceptions 2 types of digestions: 1. Mechanical Digestion: the physical breakdown of food into smaller particles through chewing and muscular contractions ( in the alimentary canal) a. Why it’s needed? i. Mechanical digestion breaks down food into smaller particles, increasing its surface area. This greater surface area allows enzymes and other digestive substances to act more efficiently, accelerating the chemical digestion process and facilitating the absorption of nutrients. 2. Chemical Digestion: is the process by which enzymes and other chemicals catalyze (speed up) the breakdown of large food particles into smaller molecules, facilitating nutrient absorption by the body. a. Carbohydrates: breaks down into glucose (amount of time it takes varies on the type of carb) i. Ex. bread, rice, pasta, potatoes, etc. b. Proteins: breaks down into amino acids i. Ex. chicken, beef, fish, eggs, etc. c. Lipids: breaks down into glycerol + fatty acids i. Ex. avocado, olive oil, butter, cheese, etc. Mouth Structure of the Orals Cavity (area behind the teeth) Need to know Anatomy o Upper/Lower Lip o Superior/Inferior Labial Frenulum: Attaches the lips to the gum o Vestibule: the space between your lips, cheeks, and gums. o It's like a little pocket where your teeth sit. o Lingual Frenulum: attaches the tongue to the floor of the mouth. o If it's too short or tight, it can cause speech problems or difficulty with certain tongue movements. In such cases, it may need to be altered through a surgical procedure to improve speech and tongue function. o Duct of Submandibular Gland: is a tiny tube that carries saliva from under your jaw to your mouth. o Uvula o Teeth Introduction: o The digestive system being in the Oral Cavity (mouth) o The Oral Cavity is not technically part of the alimentary canal. It houses 3 ACCESSORY ORGANS: § Teeth – mastication (mechanical breakdown) o Breaking down of food unto smaller pieces § Tongue o Mixes food and saliva and makes it into a small ball of food called bolus § Salivary Glands (located around the oral cavity) START OF THE DIGESTIVE PROCESSES o Parotid gland (octi = ear, so they are near the ear) o Sublingual gland (below the tongue) o Submandibular Gland (below the mandible) o Salivary Glands o Is the start to the digestive processes o Three pairs od salivary glands secrete saliva (fluid containing water, enzymes, mucus, and other solutes) thorough the duct (aka Ductus of the Submandibular gland) into the cavity o PARASYMPATHETIC N.S. role in the production in saliva § The parasympathetic nervous system plays a crucial role in stimulating saliva production within the oral cavity. By sending signals to the salivary glands, it prompts the release of saliva. These signals can be triggered by various stimuli, including the sight, smell, or mere thought of food. Activation of the parasympathetic nervous system enhances saliva flow, which in turn aids in the process of digestion, lubricates the mouth, and helps protect the teeth and oral tissues. SMALL OVERVIEW of process of production of Saliva 1. Stimulus detection The process begins with the detection of stimuli related to food consumption. This can include sensory cues such as the sight, smell, or even the thought of food. 2. VAGUS (11th carinal nerve) Activated by sensory signals that are transmitted to the brain, particularly the areas involved in processing taste and smell. From there, the brain sends signals through the Vagus nerve, which is a major component of the parasympathetic nervous system. 3. Stimulates Salivary Glands The Vagus nerve carries these signals to the salivary glands. The signals trigger the release of neurotransmitters that stimulate the salivary glands to produce saliva. 4. Saliva Production: As a result of the stimulation, the salivary glands begin to produce saliva. Saliva is composed of water, electrolytes, mucus, and enzymes, which are essential for the process of digestion and maintaining oral health. 5. Saliva Flow The produced saliva flows into the oral cavity through ducts connected to the salivary glands. This saliva helps moisten food, making it easier to chew and swallow. It also contains enzymes that begin the process of breaking down carbohydrates in food. 6. Digestive Preparation Additionally, saliva contains enzymes like amylase, which start breaking down carbohydrates into simpler sugars, initiating the process of digestion even before food reaches the stomach. Salvia (chemical Breakdown) o Function: Help moisten food o Made up of primary water. Electrolytes such as sodium, chloride, and potassium ions, and variable amounts of mucus, depending on the type of salivary gland; also contains; o Salivary Amylase – Break down Complex Carbs. § Salivary amylase is an enzyme found in saliva. Enzymes are pH Sensitive (normal pH level in the mouth is around 6.5-7) o Meaning that Salivary Amylase works best in 6.5-7 range § It breaks down carbohydrates into simpler sugars. § This process begins in the mouth, where salivary amylase starts breaking down complex carbohydrates. § The action of salivary amylase helps prepare food for further digestion in the stomach and small intestine. o Lysozyme – helps protect against bacterial infections in the oral cavity and stomach § Does not play a direct role in digestion. Instead, it functions primarily as an antimicrobial agent, breaking down bacterial cell walls to help prevent infections in the oral cavity and stomach. Pharynx/Esophagus Pharynx (throat) – posterior to nasal and oral cavities; consists of nasopharynx, oropharynx, and laryngopharynx: o Of these three divisions, only oropharynx and laryngopharynx are part of the alimentary canal o Like the oral cavity, both are lined with stratified squamous epithelium to protect them from abrasion by food Esophagus – muscular tube about 10’’ long; posterior to trachea; transport bolus from pharynx to stomach o Esophageal mucosa, lined with stratified squamous epithelium, contains esophageal glands, as does submucosa; secrete mucus to lubricate bolus as it passes through the esophagus o The Esophagus serves as a passageway to the stomach o Layers of the Esophagus (deep à superficial): o Mucosa - The innermost layer, consisting of epithelial cells that line the lumen of the esophagus. § These epithelial cells form a protective barrier and secrete mucus, which helps lubricate and protect the inner lining of the esophagus from damage caused by food passage and stomach acid. o Submucosa § The layer beneath the mucosa, containing blood vessels, lymphatic vessels, nerves, and glands. It provides support and nourishment to the mucosa. o Muscularis externa § The middle layer, composed of smooth muscle fibers arranged in circular and longitudinal layers. These muscles facilitate peristalsis, the rhythmic contractions that propel food down the esophagus. o Serosa § The outermost layer, consisting of connective tissue o The esophagus operates similarly to a vein in that it dilates (opens) to accommodate the passage of food when swallowing occurs, and it collapses or constricts once the food has passed through and there is no longer a need for it to remain open. o The valve that connects the esophagus to the stomach is called the Cardiac Sphincter o controls food entry into the stomach and prevents stomach acid from flowing back into the esophagus Stomach Anatomy: o The Stomach has 2 regions o Cardia – entry part of the stomach o Fundus o Body of the stomach o Pylorus – exiting part of the stomach o Curvatures o Lesser Curvature – aimed towards the liver § Lesser omentum (attaches the liver to the lesser curvature of the stomach and the beginning of the duodenum.) o Greater Curvature – aimed towards the spleen/Intestines § Greater omentum (attaches to the greater curvature of the stomach and extends downward, draping over the small intestines and other abdominal organs.) o Rugae of mucosa - are folds in the stomach lining that allow for expansion, contraction, and increased surface area for digestion and absorption. (allowing the stomach to be able to hold 1-1.5 liter of chewed food/liquid) Histology: o Gastric Pits: These are invaginations or depressions in the surface of the stomach mucosa. They extend down into the underlying gastric glands and serve as openings through which gastric juices are secreted into the stomach lumen. Gastric pits also contain mucus-secreting cells, which produce a protective layer of mucus that coats the stomach lining, preventing damage from stomach acid and digestive enzymes. o Gastric Glands: Found within the gastric mucosa, gastric glands are tubular structures that extend from the base of gastric pits. They consist of various cell types, including: o Mucous neck cells: Secrete acidic mucus. This prevents their mucus from neutralizing the aid produced by other cells known as parietal cells § More about digestions, less about protections o Parietal cells: Secrete HCL and Intrinsic factor § hydrochloric acid (HCl), which creates an acidic environment in the stomach (creates low pH) necessary for the activation of digestive enzymes and the breakdown of food particles and kill microorganisms § intrinsic factor, which is required for the absorption of vitamin B12. o Chief cells: Secrete pepsinogen, an inactive form of the enzyme pepsin, which is responsible for breaking down proteins into smaller peptides. § Pepsinogen is activated by low pH aka hydrochloric acid (HCl), o Enteroendocrine cells (DNES): Produces a hormone called gastrin, targets parietal , chief, mucosa cells to activate § Once gastrin is released, it targets various cells in the stomach: Parietal cells: Gastrin stimulates parietal cells to secrete hydrochloric acid (HCl). Chief cells: Gastrin stimulates chief cells to secrete pepsinogen, an inactive form of the enzyme pepsin, which aids in protein digestion. Mucous neck cells: Secrete acidic mucus this prevents their mucus from neutralizing the aid produced by other cells known as parietal cells. § Note: Parasympathetic Nervous System to tell Enteroendocrine cells to produce gastrin o Chyme mixture of food in the gastric juice (in the stomach) o Churning of the Chyme is mechanical digestion Moreover, chyme is the semi-fluid mixture of partially digested food and gastric juices that is produced in the stomach. The stomach muscles contract and relax rhythmically to mix and churn the chyme, breaking it down into smaller particles and thoroughly mixing it with gastric juices. This mechanical action helps to further break down food particles, mix them with digestive enzymes, and create a homogenous mixture that is easier to digest and absorb in the small intestine. Reverse peristalsis, also known as emesis or vomiting, is the involuntary expulsion of stomach contents through the mouth. This reflexive action is typically triggered by various factors such as the presence of toxins, pathogens, or excessive food in the stomach, as well as certain sensory cues or psychological factors. Reverse peristalsis helps the body expel harmful substances or relieve discomfort by emptying the stomach contents. o o The Small Intestine The small intestine is about 20’ long and about 1’-1½’ wide Has 3 parts: 1. Duodenum 2. Jejunum 3. Ileum Microscopic Anatomy o Modifications of small intestine for absorption o Small intestine’s length and other structural modifications provide huge surface area for nutrient absorption o Modifications include § Plica (Circular folds) Permeant folds that force chyme to slowly spiral through the lumen, allowing more time for nutrient absorption § Villi Fingerlike projections of mucosa with a core that contains dense capillary ben and lymphatic capillary called acetal for absorption § Microvilli Cytoplasmic extensions of mucosal cell that give fuzzy appearance called the brush border that contains membrane-bound enzymes brush border enzymes, used for final carbohydrate and protein digestion Duodenum o The duodenum is the first part of the small intestine, where partially digested food mixes with pancreatic juices and bile for further digestion. o Is going to produce 2 hormones o Secretin § Going to target 2 different places: Pancreas à to make/send HCO3 (bicarbonate) o Why is bicarbonate needed? § Bicarbonate = neutralizes the acidic chyme from the stomach, creating a more favorable environment for digestion and protecting the intestinal lining Liver à to make bile and sends it to the gallbladder to be stored o CCK (cholecystokinin) § Going to target 2 different places: Pancreas à to make and send enzymes such as: o Pancreatic amylase Remember that if it § It helps break down complex carbohydrates into simpler sugars ends in -gen then it o Pancreatic Lipase is inactive from and needs § It breaks down fats into fatty acids and glycerol, aiding in fat to be activated digestion and absorption o Trypsinogen § Trypsinogen is an inactive enzyme produced by the pancreas. It becomes activated into trypsin by enterokinase § Trypsin plays a crucial role in protein digestion by breaking down proteins into smaller peptides Chymotrypsinogen Chymotrypsinogen is an inactive enzyme produced by the pancreas. It becomes activated into chymotrypsin (protein digestion) by trypsin, another pancreatic enzyme Gallbladder à Send bile into the duodenum o bile breaks down fat droplets into smaller particles through emulsification, making them easier to digest and absorb in the small intestine. § emulsification = is a form of mechanical digestion breaking down large fat droplets into smaller ones for easier digestion and absorption. § Jejunum: o Middle section of the small intestine. o Approximately 2.5 meters (8.2 feet) long. o Responsible for absorption of nutrients, including carbohydrates, proteins, and a portion of fats. o Contains villi and microvilli to increase surface area for absorption. Ileum: o o o o Final section of the small intestine, connecting to the large intestine. Approximately 3.5 meters (11.5 feet) long. Responsible for further absorption of nutrients, including vitamin B12 and bile salts. Contains Peyer's patches, contributing to immune function. Hepatic Portal Circulation: ?????? Large Intestine o o o o o o o o o o Location: It follows the small intestine and is located in the abdominal cavity. Length: The large intestine is shorter but wider than the small intestine, measuring about 5 to 6 feet (1.5 to 1.8 meters) in length. Functions: o Absorption of water and electrolytes: The large intestine absorbs water and electrolytes from undigested food residue, converting the liquid chyme from the small intestine into solid feces. o Formation of feces: Feces are formed as undigested food, water, bacteria, and other waste products are processed and compacted in the large intestine. o Fermentation: Bacteria in the large intestine ferment undigested carbohydrates and fiber, producing gases and certain vitamins (such as vitamin K and some B vitamins). Segments: o Ascending colon: Begins at the cecum (the pouch-like structure where the small intestine meets the large intestine) and travels upward on the right side of the abdomen. o Transverse colon: Crosses the abdomen from right to left below the stomach. o Descending colon: Travels downward on the left side of the abdomen. o Sigmoid colon: Forms an S-shaped curve leading into the rectum. o Rectum: Stores feces before they are expelled from the body through the anus. Role in Defecation: The large intestine stores feces until they are expelled from the body during defecation. Diarrhea: o Characterized by loose, watery stools and increased bowel movements. o Causes include infections, dietary factors, medications, or medical conditions. o Results from inadequate water absorption in the large intestine. o Can lead to dehydration and electrolyte imbalances. Constipation: o Characterized by infrequent bowel movements or difficulty passing stools. o Causes include inadequate fiber or fluid intake, lack of physical activity, medications, or medical conditions. o Results from excessive water absorption in the large intestine. o Symptoms include straining and feeling of incomplete evacuation. o Treatment involves dietary changes, hydration, exercise, and medications if severe. E. coli (Escherichia coli): o Bacteria found in the intestines; some strains are beneficial. o Certain strains in the large intestine help synthesize vitamin K. Cellulose: o Indigestible carbohydrate found in plant cell walls. o Acts as dietary fiber, promoting digestive health and fermentation by gut bacteria. Vitamin K: o Essential for blood clotting and bone health. o Synthesized in the large intestine by bacteria, including certain strains of E. coli.