Digestive System A&P Exam III
Digestive System
Know the general functions of the digestive system.
1. Ingestion – taking in food and water
2. Propulsion – moving food through the GI tract. Includes swallowing, which is voluntary action in the mouth and pharynx, and peristalsis which is involuntary. Peristalsis is waves of smooth muscle contraction that move food through the esophagus, stomach, and intestines. Peristalsis is controlled by the enteric nervous system, as well as the autonomic nervous system. The sympathetic nervous system is related to fight or flight reflex, and therefore inhibits peristalsis and slows down digestion. This is because during fight/flight we have to direct our energy to our muscles to run or fight, and digestion is not a priority to escape the danger. The parasympathetic nervous system enhances and promotes digestive activity and peristalsis.
3. Mechanical digestion – physically breaking down food into smaller pieces- chewing in the mouth, churning in the stomach, and the segmentation contractions in the intestines.
4. Chemical digestion – smaller food particles have more surface area compared to volume, so they are more readily broken down by enzymes. Enzymes break complex molecules down into simple molecules
5. Absorption – transporting nutrients from the GI to the bloodstream mainly in the small intestine where there are villi and microvilli.
6. Elimination – eliminating undigested food and waste products from the body
Be familiar with the 4 layers of the GI tract. Know the type of tissue found in each and its general characteristics.
1. Mucosa – epithelial tissue with an underlying lamina propria which is connective tissue, and a thin layer of smooth muscle. Lamina propria contains blood vessels, lymphatic vessels, and glands.
2. Submucosa – dense irregular connective tissue. Rich in blood vessels and lymph vessels, also contains glands that secrete mucus and other substances. Also contains the submucosal plexus which controls secretions.
3. Muscularis – smooth muscles with an inner circular layer and an outer longitudinal layer. Contains the myenteric plexus that controls peristalsis.
4. Serosa – connective tissue, connects GI tract to surrounding organs, also the visceral peritoneum (part wrapping the organs like saran wrap) secretes a serous fluid that lubricates the GI tract and reduces friction as digestive contractions occur.
What are the two components of the enteric nervous system? Where are they located?
1. Myenteric Plexus (Auerbach's Plexus)
Location: Situated between the longitudinal and circular muscle layers of the muscularis externa.
Function: Primarily controls the motility of the GI tract, including peristalsis and the rhythmic contractions of the digestive muscles.
2. Submucosal Plexus (Meissner's Plexus)
Location: Found in the submucosa layer.
Function: Regulates local blood flow, absorption, and secretions of the GI tract. It helps coordinate the functions of the mucosa.
What is the peritoneum? Be familiar with the location of the greater and lesser omentum as well as the mesentery.
The peritoneum is a serous membrane that lines the abdominal cavity and covers most of the abdominal organs. It has two layers:
1. Parietal Peritoneum
Location: Lines the inner surface of the abdominal wall.
2. Visceral Peritoneum
Location: Covers the external surfaces of the abdominal organs.
Function:
Provides Support: Helps to hold the abdominal organs in place.
Lubrication: Produces serous fluid to reduce friction between organs during movement.
Greater Omentum
Location: Hangs down from the greater curvature of the stomach and drapes over the intestines.
Function: Acts as a fat storage site and contains immune cells to help fight infections in the abdominal cavity.
Lesser Omentum
Location: Stretches between the lesser curvature of the stomach and the liver.
Function: Provides a pathway for blood vessels, nerves, and lymphatics to reach the liver.
Mesentery
Location: Attaches the intestines to the posterior abdominal wall.
Function: Supports the intestines and contains blood vessels, nerves, and lymphatics that supply the intestinal wall.
List the basic components of saliva.
Basic Components of Saliva:
Water:
Primary Component: Makes up about 98-99% of saliva, providing the fluid medium for other components.
Electrolytes:
Includes: Sodium (Na⁺), potassium (K⁺), calcium (Ca²⁺), magnesium (Mg²⁺), bicarbonate (HCO₃⁻), and phosphate (PO₄³⁻).
Enzymes:
Salivary Amylase (Ptyalin): Begins the digestion of carbohydrates.
Lingual Lipase: Begins the digestion of lipids (fats).
Mucins:
Function: Glycoproteins that lubricate food, facilitating easier swallowing.
Antibacterial Compounds:
Includes: Lysozyme, lactoferrin, and immunoglobulin A (IgA), which help control bacterial growth.
Buffers:
Function: Maintain pH balance in the mouth to protect teeth and aid in digestion.
Metabolic Waste Products:
Includes: Urea and uric acid.
List factors that would promote or inhibit salivation.
Factors That Promote Salivation:
Sensory Stimuli:
Taste: Tasting food, especially acidic or sour foods, increases salivation.
Smell: The aroma of food can stimulate salivary glands.
Sight: Seeing appetizing food can trigger salivation.
Sound: Hearing the preparation of food (e.g., sizzling) can also promote salivation.
Neural Control:
Parasympathetic Nervous System: Activation of the parasympathetic nerves (via the facial and glossopharyngeal nerves) increases saliva production.
Chewing:
Mastication: The act of chewing stimulates the mechanoreceptors in the mouth, promoting saliva flow.
Psychological Factors:
Anticipation: Thinking about food can trigger the cephalic phase of digestion, leading to increased salivation.
Medications:
Cholinergic Drugs: Medications that stimulate the parasympathetic nervous system can increase salivation.
Factors That Inhibit Salivation:
Sympathetic Nervous System:
Stress and Anxiety: Activation of the sympathetic nervous system (fight or flight response) can inhibit salivation.
Medications:
Anticholinergic Drugs: Medications that block the action of acetylcholine can reduce saliva production.
Decongestants and Antihistamines: These medications can cause dry mouth as a side effect.
Dehydration:
Lack of Fluids: Dehydration reduces the body’s ability to produce saliva.
Certain Medical Conditions:
Sjogren's Syndrome: An autoimmune disorder that targets the salivary glands, leading to dry mouth.
Radiation Therapy: Treatment for head and neck cancers can damage salivary glands.
Aging:
Natural Decline: Salivary gland function can decrease with age, leading to reduced saliva production.
Smoking:
Tobacco Use: Smoking can impair salivary gland function, resulting in dry mouth
What causes mumps? What are some signs/symptoms?
Signs and Symptoms of Mumps:
Early Symptoms (similar to flu):
Fever
Headache
Muscle aches
Fatigue
Loss of appetite
Common Symptoms (usually appear 2-3 weeks after exposure):
Painful swelling of the parotid glands (salivary glands located near the ears), leading to puffy cheeks and a tender, swollen jaw.
Pain or tenderness around the swollen area.
Difficulty chewing or swallowing due to the swelling.
Severe Symptoms (rare, but more common in adults):
Inflammation of the testicles (orchitis), which can cause pain and swelling.
Inflammation of the ovaries (oophoritis) in females.
Inflammation of the pancreas (pancreatitis).
Inflammation of the brain (encephalitis) or the membrane covering the brain and spinal cord (meningitis).
Temporary or permanent hearing loss.
Prevention:
Vaccination: The MMR (measles-mumps-rubella) vaccine is highly effective in preventing mumps.
Hygiene Practices: Regular handwashing, avoiding close contact with infected individuals, and not sharing utensils or cups can help reduce the spread of the virus
Describe the process of deglutition.
Deglutition – swallowing
1. Oral Phase (Voluntary):
Preparation: The tongue collects and pushes the food to the back of the mouth.
Action: The tongue presses the food against the hard palate, forming a bolus.
Transition: The bolus is pushed into the oropharynx as the tongue moves upward and backward.
2. Pharyngeal Phase (Involuntary):
Reflex Action: Once the bolus reaches the oropharynx, the swallowing reflex is triggered.
Soft Palate: Elevates to close off the nasopharynx, preventing food from entering the nasal cavity.
Epiglottis: Moves down to cover the larynx, directing food away from the airway and into the esophagus.
Pharyngeal Muscles: Contract to push the bolus downwards towards the esophagus.
Upper Esophageal Sphincter: Relaxes to allow the bolus to enter the esophagus.
3. Esophageal Phase (Involuntary):
Peristalsis: Wave-like muscle contractions of the esophagus move the bolus toward the stomach.
Lower Esophageal Sphincter: Relaxes to allow the bolus to pass into the stomach, then contracts to prevent backflow of stomach contents.
What can cause acid reflux? What are some common treatments? How do they work?
Causes of Acid Reflux
Hiatal Hernia: When the upper part of the stomach and the lower esophageal sphincter (LES) move above the diaphragm.
Lifestyle Factors: Eating large meals, lying down immediately after eating, being overweight, and consuming certain foods and drinks like citrus, chocolate, caffeine, and alcohol.
Smoking: Damages mucus membranes and impairs muscle reflexes in the throat.
Pregnancy: Hormonal changes and pressure from the growing fetus can cause acid reflux.
Medications: Certain medications like aspirin, ibuprofen, and some blood pressure drugs.
Common Treatments
Lifestyle Changes: Avoiding trigger foods, eating smaller meals, losing weight, and not lying down immediately after eating.
Antacids: Over-the-counter medications like Tums and Rolaids that neutralize stomach acid.
H2 Blockers: Medications like ranitidine and famotidine that reduce stomach acid production.
Proton Pump Inhibitors (PPIs): Stronger acid blockers like omeprazole and esomeprazole that reduce acid production more effectively.
Surgery: In severe cases, a procedure to reinforce the LES may be recommended.
How Treatments Work
Antacids: Neutralize stomach acid to provide quick relief from heartburn.
H2 Blockers: Block histamine, which stimulates acid production, reducing acid levels in the stomach.
PPIs: Block the enzyme in the stomach lining that produces acid, providing longer-lasting relief.
Surgery: Tightens or reinforces the LES to prevent acid from flowing back into the esophagus.
Be familiar with the gross anatomy of the stomach.
Compare a pylorspasm to a pyloric stenosis.
Pylorospasm:
Definition: Intermittent, temporary spasms of the pyloric muscle.
Causes: Often related to irritation or inflammation, but the exact cause is not always clear.
Symptoms: Transient gastric outlet obstruction, leading to forceful non-bilious vomiting.
Diagnosis: Can be challenging to diagnose as it may mimic other conditions on imaging studies.
Treatment: Usually managed with medical treatment, such as medications to relax the pyloric muscle.
Pyloric Stenosis:
Definition: A condition characterized by the thickening and narrowing of the pyloric muscle, leading to persistent gastric outlet obstruction.
Causes: Often idiopathic, but may involve genetic and environmental factors.
Symptoms: Projectile vomiting, dehydration, weight loss, and a palpable olive-sized mass in the abdomen.
Diagnosis: Typically diagnosed with ultrasound, which shows thickened pyloric muscle and elongated pyloric channel.
Treatment: Surgical intervention (pyloromyotomy) to cut the thickened muscle and relieve the obstruction.
Comparison:
Nature: Pylorospasm is intermittent and temporary, while pyloric stenosis is persistent and requires surgical correction2.
Symptoms: Both conditions can cause vomiting, but pyloric stenosis is more severe and includes additional symptoms like dehydration and weight loss.
Diagnosis: Pylorospasm can be difficult to diagnose and may be mistaken for pyloric stenosis on imaging studies.
Treatment: Pylorospasm is usually managed medically, whereas pyloric stenosis requires surgery.
Memorize the various cell types present in the mucosa of the stomach. What substance(s) is secreted by each? What is the function of each enzyme or hormone? 1. Parietal Cells (Oxyntic Cells)
Secretes:
Hydrochloric Acid (HCl)
Intrinsic Factor
Function:
Hydrochloric Acid: Creates an acidic environment (pH 1.5-3.5) necessary for pepsin activation and protein digestion. It also kills bacteria.
Intrinsic Factor: Essential for the absorption of vitamin B12 in the small intestine.
2. Chief Cells (Zymogenic Cells)
Secretes:
Pepsinogen
Gastric Lipase
Function:
Pepsinogen: Inactive precursor of pepsin. When exposed to HCl, it is converted to pepsin, which digests proteins into peptides.
Gastric Lipase: Begins the digestion of lipids (fats) by breaking down triglycerides into free fatty acids and monoglycerides.
3. Mucous Cells (Neck Cells)
Secretes:
Mucus
Bicarbonate
Function:
Mucus: Forms a protective barrier on the stomach lining, preventing damage from gastric acid and enzymes.
Bicarbonate: Neutralizes the acid near the mucosal surface to protect the stomach lining.
4. G Cells (Enteroendocrine Cells)
Secretes:
Gastrin
Function:
Gastrin: Stimulates the secretion of HCl by parietal cells and promotes gastric motility.
5. D Cells
Secretes:
Somatostatin
Function:
Somatostatin: Inhibits the release of gastrin, thereby reducing HCl secretion.
6. ECL Cells (Enterochromaffin-like Cells)
Secretes:
Histamine
Function:
Histamine: Stimulates parietal cells to secrete HCl, working synergistically with gastrin and acetylcholine.
What is unique about the muscularis of the stomach? It has 3 layers rather than 2 like the rest of the GI. Inner oblique, middle circular, and outer longitudinal layers.
Summarize the main purpose each phase of digestion (cephalic, gastric and intestinal).
Cephalic Phase: Prepares the stomach for digestion via neural signals.
Gastric Phase: Enhances digestion within the stomach through neural and hormonal mechanisms.
Intestinal Phase: Regulates digestive processes in the intestines and controls gastric emptying.
Explain the regulatory processes of both the gastric and intestinal phases. Include neural and hormonal regulation as well as any other feedback mechanisms that exist.
Gastric Phase: Regulated by neural (local and vagal reflexes) and hormonal (gastrin) mechanisms. Feedback mechanisms ensure balance in acidity and gastric activity.
Intestinal Phase: Regulated by neural (enterogastric reflex) and hormonal (CCK, secretin, GIP) mechanisms. Feedback mechanisms slow gastric activity and promote digestion and absorption in the intestines.
Neural Regulation:
Distension of the Stomach: When the stomach is stretched by food, it activates stretch receptors.
Local Reflexes: These stretch receptors send signals to the enteric nervous system (ENS), which initiates local reflexes that enhance gastric motility and secretions.
Vagal Reflexes: Stretch receptors also send signals to the brain via the vagus nerve, which then sends signals back to the stomach to further enhance gastric secretions and motility.
Hormonal Regulation:
Gastrin:
Produced By: G cells in the stomach.
Stimulus: The presence of peptides and amino acids in the stomach, as well as stomach distension.
Function: Gastrin stimulates parietal cells to secrete hydrochloric acid (HCl) and increases gastric motility.
Feedback Mechanisms:
Negative Feedback: When the stomach pH becomes too low (high acidity), somatostatin is released, which inhibits the secretion of gastrin and HCl, thus preventing excessive acidity.
Intestinal Phase Regulation
Neural Regulation:
Enterogastric Reflex:
Trigger: The presence of chyme in the duodenum.
Function: This reflex inhibits gastric motility and secretions, slowing down the emptying of the stomach to allow time for digestion and absorption in the intestines.
Hormonal Regulation:
Cholecystokinin (CCK):
Produced By: I cells in the duodenum.
Stimulus: The presence of fats and proteins in the chyme.
Function: Stimulates the gallbladder to release bile, the pancreas to release digestive enzymes, and slows gastric emptying.
Secretin:
Produced By: S cells in the duodenum.
Stimulus: The presence of acidic chyme.
Function: Stimulates the pancreas to release bicarbonate to neutralize the acid and inhibits gastric secretions.
Gastric Inhibitory Peptide (GIP):
Produced By: K cells in the duodenum and jejunum.
Stimulus: The presence of fats and glucose in the chyme.
Function: Inhibits gastric motility and secretions, and stimulates insulin release.
Feedback Mechanisms:
Negative Feedback: As the chyme is processed and absorbed, the reduced stimulus leads to a decrease in the release of CCK, secretin, and GIP, thus allowing gastric activity to resume.
Memorize the components of pancreatic juice. Know the function of each constituent.
1. Enzymes:
Pancreatic Amylase:
Function: Breaks down carbohydrates into simpler sugars (maltose, maltotriose, and alpha-dextrin).
Pancreatic Lipase:
Function: Digests triglycerides into free fatty acids and monoglycerides.
Proteases (e.g., trypsinogen, chymotrypsinogen, procarboxypeptidase):
Function: Break down proteins into peptides and amino acids. These enzymes are secreted in their inactive forms (zymogens) and activated in the small intestine.
Trypsinogen: Converted to trypsin, which then activates other proteases.
Chymotrypsinogen: Converted to chymotrypsin by trypsin.
Procarboxypeptidase: Converted to carboxypeptidase by trypsin.
Nucleases (e.g., ribonuclease, deoxyribonuclease):
Function: Break down nucleic acids (RNA and DNA) into nucleotides.
2. Bicarbonate Ions (HCO₃⁻):
Function: Neutralize the acidic chyme from the stomach, providing an optimal pH for enzyme activity in the small intestine.
3. Water:
Function: Dilutes the chyme and aids in the transport and absorption of nutrients in the small intestine.
List 3 things that stimulate the acini of the pancreas. the acinar cells are specialized exocrine cells that produce and secrete digestive enzymes.
Appearance: These clusters have a grape-like structure, with the acinar cells surrounding small ducts.
Cholecystokinin (CCK):
Origin: Released by the I cells in the duodenum.
Function: CCK is a hormone that stimulates the acinar cells to secrete digestive enzymes in response to the presence of fats and proteins in the chyme.
Secretin:
Origin: Released by the S cells in the duodenum.
Function: Secretin is a hormone that primarily stimulates the ductal cells to secrete bicarbonate, but it also indirectly promotes enzyme secretion by enhancing the effects of CCK.
Vagal Stimulation:
Origin: Parasympathetic nervous system, via the vagus nerve.
Function: The vagus nerve releases acetylcholine, which stimulates the acinar cells directly to secrete digestive enzymes during the cephalic and gastric phases of digestion.
These stimuli ensure that the pancreas produces and secretes the necessary enzymes to aid in the digestion of food as it moves through the digestive tract.
Describe the unusual pattern of blood flow through a lobule within the liver. What is the purpose of this unusual circulatory route? Blood Flow Through a Liver Lobule:
Dual Blood Supply:
Hepatic Portal Vein:
Source: Carries nutrient-rich but oxygen-poor blood from the digestive organs (stomach, intestines, spleen, and pancreas).
Purpose: Delivers substances absorbed from the digestive tract to the liver for processing.
Hepatic Artery:
Source: Carries oxygen-rich blood from the systemic circulation.
Purpose: Supplies oxygen and nutrients necessary for liver cell (hepatocyte) function.
Blood Mixing in Sinusoids:
Liver Sinusoids:
Structure: Capillary-like spaces between rows of hepatocytes.
Function: Blood from the hepatic portal vein and hepatic artery mix in these sinusoids, bathing the hepatocytes in both oxygenated blood and nutrient-rich blood.
Kupffer Cells:
Location: Line the walls of the sinusoids.
Function: Act as macrophages to remove debris, bacteria, and worn-out blood cells.
Blood Flow Toward the Central Vein:
Central Vein:
Location: In the center of each liver lobule.
Function: Collects deoxygenated blood after it has passed through the sinusoids and hepatocytes.
Drainage into Hepatic Veins:
Pathway: Blood flows from the central veins into the hepatic veins.
Destination: Hepatic veins then empty into the inferior vena cava, returning blood to the heart.
Purpose of This Circulatory Route:
Nutrient Processing: The hepatic portal vein delivers nutrients directly from the digestive tract to the liver, where hepatocytes can process and store them.
Detoxification: The liver can remove toxins, drugs, and metabolites from the blood before it reaches the systemic circulation.
Metabolism: The liver metabolizes carbohydrates, fats, and proteins, regulating blood glucose levels and producing essential proteins.
Immune Function: Kupffer cells in the sinusoids help protect the body by removing pathogens and debris from the blood.
Be familiar with the biliary system. Be able to explain how bile is produced. Where is it made? What is it made up of? What stimulates its secretion? Give a detailed description of how bile makes its way from a hepatocyte to the duodenum. How do the pancreatic ducts merge with this system? Bile Production:
Location: Bile is produced by hepatocytes (liver cells) in the liver.
Components:
Bile Salts: Derived from cholesterol, essential for emulsifying fats.
Bilirubin: A byproduct of red blood cell breakdown, gives bile its color.
Cholesterol: Excreted in bile.
Phospholipids: Aid in fat digestion.
Water: Helps to dilute and transport bile constituents.
Electrolytes: Maintain the bile’s pH.
Stimulation of Bile Secretion:
Cholecystokinin (CCK): Released by the duodenum in response to fats in the chyme, stimulates the gallbladder to contract and release bile.
Secretin: Also released by the duodenum, stimulates the liver to produce more bile with a higher water content.
Vagal Stimulation: The parasympathetic nervous system stimulates bile production during the cephalic phase of digestion.
Pathway of Bile from Hepatocyte to Duodenum:
Bile Canaliculi:
Formation: Hepatocytes secrete bile into tiny channels called bile canaliculi.
Function: Collect bile from hepatocytes.
Bile Ductules and Ducts:
Flow: Bile canaliculi drain into bile ductules, which merge to form larger bile ducts.
Ducts: These bile ducts converge to form the left and right hepatic ducts.
Common Hepatic Duct:
Formation: The left and right hepatic ducts join to form the common hepatic duct.
Cystic Duct and Gallbladder:
Storage: The common hepatic duct joins with the cystic duct from the gallbladder, where bile is stored and concentrated.
Common Bile Duct:
Formation: The common hepatic duct and cystic duct merge to form the common bile duct.
Hepatopancreatic Ampulla (Ampulla of Vater):
Merging Point: The common bile duct joins with the pancreatic duct to form the hepatopancreatic ampulla.
Sphincter of Oddi:
Regulation: The sphincter of Oddi controls the flow of bile (and pancreatic juice) into the duodenum.
Duodenum:
Release: Bile is released into the duodenum, where it aids in the digestion and absorption of fats.
Pancreatic Duct Merging:
Main Pancreatic Duct: Carries digestive enzymes from the pancreas.
Merging: The main pancreatic duct joins the common bile duct at the hepatopancreatic ampulla.
Function: This convergence ensures that bile and pancreatic enzymes are released into the duodenum together, enhancing the digestive process.
Summary:
Production: Bile is produced by hepatocytes in the liver.
Components: Includes bile salts, bilirubin, cholesterol, phospholipids, water, and electrolytes.
Secretion Stimulated By: CCK, secretin, and vagal stimulation.
Pathway: Bile moves from hepatocytes through bile canaliculi, ductules, hepatic ducts, cystic duct, common bile duct, and finally into the duodenum via the hepatopancreatic ampulla and sphincter of Oddi.
Pancreatic Duct: Merges with the common bile duct at the hepatopancreatic ampulla, releasing enzymes and bile together.
Why might someone develop jaundice? Gall stones?
Jaundice:
Jaundice is a condition where the skin and the whites of the eyes turn yellow due to high levels of bilirubin in the blood. It can be caused by several factors, including:
Liver Diseases: Conditions like hepatitis, cirrhosis, or liver cancer can impair the liver's ability to process bilirubin.
Hemolytic Anemia: Excessive breakdown of red blood cells can lead to increased bilirubin production.
Bile Duct Obstruction: Gallstones, tumors, or inflammation can block the bile ducts, preventing bile from draining into the intestine.
Genetic Disorders: Conditions like Gilbert's syndrome can affect how the liver processes bilirubin.
Gallstones:
Gallstones are hardened deposits of digestive fluid that form in the gallbladder. They can cause symptoms if they block the bile ducts4. Common causes include:
Excess Cholesterol: When there's too much cholesterol in the bile, it can crystallize and form stones.
Excess Bilirubin: Conditions that increase bilirubin levels, such as liver disease or certain blood disorders, can lead to pigment stones.
Bile Stasis: If the gallbladder doesn't empty properly, bile can become concentrated and form stones.
Risk Factors: Female sex, middle age, obesity, rapid weight loss, and certain medications can increase the risk of gallstones4.
List and describe the unique features of the mucosa of the small intestine.
Villi: Increase surface area for absorption, contain blood and lymphatic capillaries.
Microvilli: Form the brush border, further increase surface area, and contain digestive enzymes.
Intestinal Glands: Secrete intestinal juice, contain Paneth cells and stem cells.
Goblet Cells: Secrete mucus to protect and lubricate the lining.
Enteroendocrine Cells: Secrete hormones that regulate digestion.
Peyer's Patches: Provide immune defense in the ileum.
Memorize all of the digestive enzymes that have been presented in class. Know which gland they are secreted by and the basic function of each. 1. Salivary Glands:
Salivary Amylase:
Secreted By: Salivary glands (parotid, submandibular, sublingual).
Function: Begins the digestion of carbohydrates by breaking down starches into maltose.
2. Stomach:
Pepsin:
Secreted By: Chief cells (as pepsinogen) in the stomach.
Function: Breaks down proteins into peptides. Pepsinogen is activated to pepsin by hydrochloric acid.
Gastric Lipase:
Secreted By: Chief cells in the stomach.
Function: Begins the digestion of fats by breaking down triglycerides into free fatty acids and monoglycerides.
3. Pancreas:
Pancreatic Amylase:
Secreted By: Acinar cells in the pancreas.
Function: Continues the digestion of carbohydrates by breaking down starches into maltose, maltotriose, and alpha-dextrin.
Pancreatic Lipase:
Secreted By: Acinar cells in the pancreas.
Function: Digests triglycerides into free fatty acids and monoglycerides.
Trypsin:
Secreted By: Acinar cells (as trypsinogen) in the pancreas.
Function: Breaks down proteins into peptides. Trypsinogen is activated to trypsin by enteropeptidase in the small intestine.
Chymotrypsin:
Secreted By: Acinar cells (as chymotrypsinogen) in the pancreas.
Function: Breaks down proteins into peptides. Chymotrypsinogen is activated by trypsin.
Carboxypeptidase:
Secreted By: Acinar cells (as procarboxypeptidase) in the pancreas.
Function: Breaks down peptides into amino acids. Procarboxypeptidase is activated by trypsin.
Ribonuclease:
Secreted By: Acinar cells in the pancreas.
Function: Breaks down RNA into nucleotides.
Deoxyribonuclease:
Secreted By: Acinar cells in the pancreas.
Function: Breaks down DNA into nucleotides.
4. Small Intestine (Brush Border Enzymes):
Maltase:
Secreted By: Enterocytes in the small intestine.
Function: Breaks down maltose into two glucose molecules.
Sucrase:
Secreted By: Enterocytes in the small intestine.
Function: Breaks down sucrose into glucose and fructose.
Lactase:
Secreted By: Enterocytes in the small intestine.
Function: Breaks down lactose into glucose and galactose.
Aminopeptidase:
Secreted By: Enterocytes in the small intestine.
Function: Removes the amino acid from the amino end of peptides.
Dipeptidase:
Secreted By: Enterocytes in the small intestine.
Function: Splits dipeptides into amino acids.
Enteropeptidase (Enterokinase):
Secreted By: Enterocytes in the small intestine.
Function: Converts trypsinogen into trypsin.
Summary:
Salivary Amylase: Carbohydrate digestion (salivary glands).
Pepsin & Gastric Lipase: Protein and fat digestion (stomach).
Pancreatic Amylase, Lipase, Trypsin, Chymotrypsin, Carboxypeptidase, Ribonuclease, Deoxyribonuclease: Carbohydrate, fat, protein, and nucleic acid digestion (pancreas).
Maltase, Sucrase, Lactase, Aminopeptidase, Dipeptidase, Enteropeptidase: Final steps in carbohydrate and protein digestion (small intestine).
Compare and contrast the terms: segmentations, peristalsis and peristaltic rush.
Segmentations
Definition: Segmentations are localized, rhythmic contractions of the circular muscles in the intestine.
Function: Mixes the intestinal contents, bringing the chyme into contact with the mucosa for absorption.
Frequency: Occurs more frequently in the small intestine.
Characteristics:
Non-propulsive: Does not move chyme forward significantly.
Segments: Creates alternating sections of contracted and relaxed muscle, dividing the intestine into segments.
Peristalsis
Definition: Peristalsis is a series of wave-like muscle contractions that move food through the digestive tract.
Function: Propels food, chyme, and waste through the digestive tract.
Frequency: Occurs throughout the entire digestive tract, from the esophagus to the intestines.
Characteristics:
Propulsive: Moves contents forward.
Waves: Involves coordinated contractions of circular and longitudinal muscles, creating waves of contraction and relaxation.
Peristaltic Rush
Definition: Peristaltic rush is an intense, powerful type of peristalsis.
Function: Rapidly moves contents through the intestines, often in response to irritation or the presence of harmful substances.
Frequency: Occurs in the intestines, particularly during episodes of severe irritation or infection.
Characteristics:
Rapid: Much faster than normal peristalsis.
Powerful: Strong contractions that quickly clear the intestines.
Comparison:
Segmentations vs. Peristalsis:
Segmentations primarily mix contents without significant forward movement, while peristalsis moves contents forward.
Segmentations occur mainly in the small intestine, whereas peristalsis occurs throughout the digestive tract.
Peristalsis vs. Peristaltic Rush:
Both are propulsive, but peristaltic rush is a more intense and rapid form of peristalsis.
Peristaltic rush is often a response to irritation or infection, whereas regular peristalsis is a normal part of digestion.
The processes involved in the absorption of nutrients can vary a great deal. Transport mechanism, location and regulatory factors can be different. Explain the mechanism of transport for carbs, proteins, lipids, electrolytes, vitamins and water. Do the molecules enter blood vessels or lacteals? Be sure to mention any regulatory factors. Carbohydrates
Transport Mechanism:
Monosaccharides (Glucose, Galactose): Absorbed via active transport (SGLT1) and facilitated diffusion (GLUT2).
Fructose: Absorbed via facilitated diffusion (GLUT5).
Location: Enterocytes in the small intestine.
Regulatory Factors:
Sodium: Active transport of glucose and galactose is coupled with sodium.
Entry: Enter blood vessels (capillaries).
Proteins
Transport Mechanism:
Amino Acids: Absorbed via active transport, often sodium-dependent.
Dipeptides and Tripeptides: Absorbed via peptide transporters (PEPT1), then hydrolyzed into amino acids inside enterocytes.
Location: Enterocytes in the small intestine.
Regulatory Factors:
Sodium: Active transport of amino acids is often sodium-dependent.
Entry: Enter blood vessels (capillaries).
Lipids
Transport Mechanism:
Monoglycerides and Free Fatty Acids: Form micelles with bile salts, absorbed by passive diffusion.
Chylomicrons: Inside enterocytes, lipids are re-esterified to triglycerides and packed into chylomicrons.
Location: Enterocytes in the small intestine.
Regulatory Factors:
Bile Salts: Essential for micelle formation and lipid absorption.
Entry: Enter lacteals (lymphatic vessels).
Electrolytes
Transport Mechanism:
Sodium (Na⁺): Absorbed via active transport and co-transport with glucose/amino acids.
Potassium (K⁺): Absorbed passively.
Calcium (Ca²⁺): Absorbed actively with the aid of vitamin D.
Chloride (Cl⁻): Absorbed passively and via co-transport with sodium.
Location: Enterocytes in the small intestine.
Regulatory Factors:
Hormonal Control: Calcium absorption is regulated by parathyroid hormone and vitamin D.
Entry: Enter blood vessels (capillaries).
Vitamins
Water-Soluble Vitamins:
Transport Mechanism: Absorbed via active transport and facilitated diffusion.
Location: Enterocytes in the small intestine.
Regulatory Factors: None significant for most, but vitamin B12 requires intrinsic factor for absorption.
Entry: Enter blood vessels (capillaries).
Fat-Soluble Vitamins (A, D, E, K):
Transport Mechanism: Absorbed with dietary fats via passive diffusion.
Location: Enterocytes in the small intestine.
Regulatory Factors:
Bile Salts: Essential for emulsification and micelle formation.
Entry: Enter lacteals (lymphatic vessels).
Water
Transport Mechanism: Absorbed via osmosis.
Location: Primarily in the small intestine, but also in the large intestine.
Regulatory Factors:
Electrolyte Balance: Water absorption follows osmotic gradients created by electrolyte absorption.
Entry: Enter blood vessels (capillaries).
Summary:
Carbohydrates: Absorbed as monosaccharides via active transport and facilitated diffusion; enter blood vessels.
Proteins: Absorbed as amino acids via active transport; enter blood vessels.
Lipids: Absorbed as micelles, re-esterified to triglycerides, and packed into chylomicrons; enter lacteals.
Electrolytes: Absorbed via various transport mechanisms; enter blood vessels.
Vitamins:
Water-Soluble: Absorbed via active transport and facilitated diffusion; enter blood vessels.
Fat-Soluble: Absorbed with dietary fats via passive diffusion; enter lacteals.
Water: Absorbed via osmosis; enter blood vessels.
Be familiar with the gross anatomy of the large intestine and be able to identify any unique histological features.
State the main functions of the large intestine.
State the main functions of the large intestine.
The large intestine plays several crucial roles in the digestive process. Here are its main functions:
1. Water and Electrolyte Absorption
Function: Absorbs the remaining water and electrolytes (such as sodium and potassium) from the indigestible food matter, converting it into a more solid form.
2. Formation and Storage of Feces
Function: Compacts the indigestible food matter into feces and stores it until it can be expelled during defecation.
3. Fermentation of Undigested Carbohydrates
Function: Houses a diverse microbiota that ferments undigested carbohydrates, producing gases (such as methane and carbon dioxide) and short-chain fatty acids, which are absorbed and provide additional energy.
4. Synthesis of Vitamins
Function: Bacteria in the large intestine synthesize certain vitamins, such as vitamin K and some B vitamins (like biotin), which are absorbed into the bloodstream.
5. Immunity
Function: Contains gut-associated lymphoid tissue (GALT) that plays a role in the immune response, protecting the body from pathogens.
6. Mucus Secretion
Function: Goblet cells in the mucosa secrete mucus, which lubricates the feces and protects the intestinal lining from mechanical damage and bacterial invasion.
Summary:
Water and Electrolyte Absorption: Essential for conserving water and maintaining fluid balance.
Formation and Storage of Feces: Prepares waste for expulsion.
Fermentation: Breaks down remaining nutrients and provides additional energy.
Vitamin Synthesis: Produces vitamins essential for various bodily functions.
Immunity: Helps protect against pathogens.
Mucus Secretion: Lubricates and protects the intestinal lining.
Distinguish between the gastrocolic, gastroileal and defecation reflex. What are the regulatory factors for each (or what initiates the reflex). 1. Gastrocolic Reflex
Definition: A reflex that increases motility of the colon in response to stomach filling.
Trigger: The presence of food in the stomach.
Mechanism:
Neural and Hormonal Signals: Stretching of the stomach walls sends signals via the vagus nerve and hormones (like gastrin) to the colon.
Response: This reflex causes increased peristalsis in the colon, moving contents towards the rectum.
Purpose: Facilitates the clearance of the colon, making room for incoming food.
2. Gastroileal Reflex
Definition: A reflex that promotes the passage of chyme from the ileum to the cecum.
Trigger: The presence of food in the stomach.
Mechanism:
Neural Signals: The stretching of the stomach and subsequent neural signals (vagus nerve) stimulate ileal peristalsis.
Hormonal Factors: Gastrin, released in response to stomach filling, also enhances ileal motility.
Response: This reflex causes the ileocecal valve to relax, allowing chyme to pass into the cecum.
Purpose: Helps coordinate the movement of digested food from the small intestine to the large intestine.
3. Defecation Reflex
Definition: A reflex that initiates the process of defecation.
Trigger: The distension of the rectum by feces.
Mechanism:
Stretch Receptors: Distension of the rectum activates stretch receptors in the rectal walls.
Neural Pathways: These receptors send signals to the spinal cord, which then sends motor signals back to the rectum.
Response: This reflex causes the internal anal sphincter to relax and increases peristalsis in the rectum and sigmoid colon.
Voluntary Control: The external anal sphincter, under voluntary control, must be consciously relaxed to allow defecation.
Purpose: Facilitates the expulsion of feces from the body.
Summary:
Gastrocolic Reflex: Increases colonic motility in response to stomach filling; triggered by the presence of food in the stomach.
Gastroileal Reflex: Promotes movement of chyme from ileum to cecum; triggered by the presence of food in the stomach.
Defecation Reflex: Initiates defecation; triggered by rectal distension.
Describe how each nutrient is absorbed and metabolized in the body.
Carbohydrates
Absorption:
Location: Absorbed in the small intestine (mainly the jejunum).
Process: Broken down into monosaccharides (glucose, fructose, galactose) by enzymes like amylase, maltase, sucrase, and lactase.
Transport:
Glucose/Galactose: Absorbed via active transport (SGLT1) with sodium.
Fructose: Absorbed via facilitated diffusion (GLUT5).
Entry: Enter blood vessels (capillaries).
Metabolism:
Pathway: Monosaccharides enter the liver via the portal vein.
Fate:
Glucose: Used for immediate energy, stored as glycogen (glycogenesis), or converted to fat.
Fructose/Galactose: Converted to glucose in the liver.
Proteins
Absorption:
Location: Absorbed in the small intestine (mainly the jejunum and ileum).
Process: Broken down into amino acids, dipeptides, and tripeptides by pepsin in the stomach and proteases (trypsin, chymotrypsin, carboxypeptidase) in the small intestine.
Transport:
Amino Acids: Absorbed via active transport, often sodium-dependent.
Dipeptides/Tripeptides: Absorbed via peptide transporters (PEPT1) and hydrolyzed inside enterocytes.
Entry: Enter blood vessels (capillaries).
Metabolism:
Pathway: Amino acids enter the liver via the portal vein.
Fate:
Amino Acids: Used for protein synthesis, converted to glucose (gluconeogenesis), or oxidized for energy.
Lipids
Absorption:
Location: Absorbed in the small intestine (mainly the jejunum).
Process: Broken down into monoglycerides and free fatty acids by lipases.
Transport:
Micelles: Formed with bile salts, absorbed by passive diffusion into enterocytes.
Chylomicrons: Lipids are re-esterified to triglycerides and packed into chylomicrons.
Entry: Enter lacteals (lymphatic vessels).
Metabolism:
Pathway: Chylomicrons enter the bloodstream via the thoracic duct.
Fate:
Triglycerides: Used for energy, stored in adipose tissue, or broken down into free fatty acids and glycerol.
Electrolytes
Absorption:
Location: Absorbed throughout the small intestine.
Process:
Sodium (Na⁺): Absorbed via active transport and co-transport with glucose/amino acids.
Potassium (K⁺): Absorbed passively.
Calcium (Ca²⁺): Absorbed actively with the aid of vitamin D.
Chloride (Cl⁻): Absorbed passively and via co-transport with sodium.
Entry: Enter blood vessels (capillaries).
Metabolism:
Purpose: Maintain fluid balance, nerve transmission, and muscle function.
Vitamins
Water-Soluble Vitamins:
Absorption:
Location: Absorbed in the small intestine.
Process: Absorbed via active transport and facilitated diffusion.
Entry: Enter blood vessels (capillaries).
Metabolism: Involved in various metabolic pathways as coenzymes.
Special Note: Vitamin B12 requires intrinsic factor for absorption.
Fat-Soluble Vitamins (A, D, E, K):
Absorption:
Location: Absorbed in the small intestine.
Process: Absorbed with dietary fats via passive diffusion.
Entry: Enter lacteals (lymphatic vessels).
Metabolism: Stored in the liver and adipose tissue, involved in various metabolic processes.
Water
Absorption:
Location: Absorbed primarily in the small intestine and some in the large intestine.
Process: Absorbed via osmosis.
Entry: Enter blood vessels (capillaries).
Metabolism:
Purpose: Essential for all bodily functions, maintains fluid balance, temperature regulation, and waste excretion.
Summary:
Carbohydrates: Absorbed as monosaccharides, metabolized for energy or storage.
Proteins: Absorbed as amino acids/peptides, used for protein synthesis, energy, or conversion to glucose.
Lipids: Absorbed as micelles/chylomicrons, used for energy or storage.
Electrolytes: Absorbed throughout the small intestine, maintain fluid balance and nerve/muscle function.
Vitamins: Water-soluble absorbed via active transport/facilitated diffusion, fat-soluble with dietary fats.
Water: Absorbed via osmosis, essential for fluid balance and all bodily functions.
Contrast the absorptive state and post absorptive state. Which hormones are involved in each? How is the regulation of blood glucose different? Absorptive State
Definition: The period during and shortly after eating when nutrients are being absorbed from the gastrointestinal tract.
Duration: Typically lasts about 4 hours after a meal.
Primary Hormone: Insulin
Source: Released by the beta cells of the pancreas.
Function: Promotes the uptake and storage of nutrients.
Glucose: Increases glucose uptake by cells, stimulates glycogenesis (formation of glycogen) in the liver and muscle, and inhibits gluconeogenesis (formation of glucose from non-carbohydrate sources).
Amino Acids: Promotes protein synthesis and uptake of amino acids by cells.
Fatty Acids: Stimulates lipogenesis (fat storage) and inhibits lipolysis (fat breakdown).
Postabsorptive State
Definition: The period when the gastrointestinal tract is empty and energy needs are met by the breakdown of body reserves.
Duration: Typically starts about 4 hours after a meal and lasts until the next meal.
Primary Hormones: Glucagon, Epinephrine, Cortisol, and Growth Hormone
Glucagon:
Source: Released by the alpha cells of the pancreas.
Function: Increases blood glucose levels by stimulating glycogenolysis (breakdown of glycogen) and gluconeogenesis in the liver, and promoting lipolysis.
Epinephrine:
Source: Released by the adrenal medulla.
Function: Stimulates glycogenolysis, gluconeogenesis, and lipolysis to increase blood glucose levels.
Cortisol:
Source: Released by the adrenal cortex.
Function: Promotes gluconeogenesis and the breakdown of proteins and fats.
Growth Hormone:
Source: Released by the anterior pituitary gland.
Function: Inhibits glucose uptake by cells, promotes lipolysis, and stimulates gluconeogenesis.
Regulation of Blood Glucose
Absorptive State:
Insulin: Lowers blood glucose levels by promoting the uptake of glucose into cells and its storage as glycogen.
Mechanism: Insulin increases the permeability of cell membranes to glucose, allowing it to be taken up by cells for energy or stored as glycogen.
Postabsorptive State:
Glucagon and Other Hormones: Raise blood glucose levels by promoting the breakdown of glycogen to glucose and the formation of glucose from non-carbohydrate sources.
Mechanism: Glucagon stimulates glycogenolysis and gluconeogenesis in the liver, releasing glucose into the bloodstream to maintain energy supply.
Summary:
Absorptive State: Dominated by insulin, promotes nutrient uptake and storage, lowers blood glucose.
Postabsorptive State: Dominated by glucagon, epinephrine, cortisol, and growth hormone, promotes nutrient mobilization, raises blood glucose.