BMS 150 Week 10: Gastrointestinal Tract Overview

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Questions and Answers

Which hormone is released by S-cells and is responsible for reducing motility during digestion?

Glucagon

Pancreatic peptide YY

Secretin (correct)

Somatostatin

What type of digestion involves physically cutting and crushing food to increase its surface area?

Biological digestion

Chemical digestion

Metabolic digestion

Mechanical digestion (correct)

What is the primary function of cholecystokinin in the digestive process?

Absorbing nutrients

Inhibiting stomach acid secretion

Stimulating gastric motility

Triggering the release of pancreatic enzymes (correct)

Which statement accurately describes somatostatin?

It has multiple functions including reducing gastric acid secretion. Signup and view all the answers

What effect do peptides or free fatty acids have on digestion?

They trigger the release of cholecystokinin. Signup and view all the answers

What is the primary function of the gastrointestinal tract?

To transport and break down food products for absorption Signup and view all the answers

Which component is NOT involved in regulating gut motility?

Hormonal receptors in the liver Signup and view all the answers

Which function does the gut microbiome primarily serve?

Maintaining relationships with the immune system and intestinal health Signup and view all the answers

Which of the following statements about gut dysbiosis is true?

It can lead to pathological implications. Signup and view all the answers

Which types of substances does the gastrointestinal tract help absorb?

Carbohydrates, amino acids, and fats Signup and view all the answers

Which vitamins require the incorporation into micelles for absorption?

Vitamins A, D, E, and K Signup and view all the answers

The relationship between dietary factors and the microbiome suggests that:

Dietary fiber is crucial for maintaining a healthy microbiome. Signup and view all the answers

In which part of the intestine is the majority of vitamin B12 absorbed?

Ileum Signup and view all the answers

What is the role of enteric hormones in GI function?

They regulate the gut motility and digestive processes. Signup and view all the answers

What is a significant consequence of taking antibiotics on the gut microbiome?

They often lead to a decrease in microbial diversity. Signup and view all the answers

How is iron transported into enterocytes during absorption?

Through divalent metal transporter 1 (DMT1) Signup and view all the answers

What is the approximate number of cells in the human microbiome?

100 trillion Signup and view all the answers

What term is used to describe the collection of all organisms living in and on the human body?

Microbiota Signup and view all the answers

What can happen if food is transported too quickly through the digestive system?

Food might not be fully digested before entering the duodenum. Signup and view all the answers

Which hormone is released by I-cells in response to certain stimuli during digestion?

Cholecystokinin Signup and view all the answers

What is a potential consequence of food staying in the stomach for too long?

Irritation of the local mucosa. Signup and view all the answers

What type of cells respond to mechanical stimulation such as distention in the gastrointestinal tract?

Smooth muscle cells and Interstitial Cells of Cajal (ICC) Signup and view all the answers

What is one effect of the presence of peptides or free fatty acids in the digestive system?

Stimulating the release of insulin from beta-pancreatic cells. Signup and view all the answers

What is the main function of the muscularis layer in the GI tract?

Propulsion of contents through the tract Signup and view all the answers

Which type of epithelium is typically found in high-absorption areas of the small intestine?

Simple columnar with microvilli Signup and view all the answers

What role do goblet cells play in the GI tract?

Secreting mucus for lubrication Signup and view all the answers

Which structure is responsible for the majority of secretion in the submucosa layer of the GI tract?

Submucosal (Meissner's) plexus Signup and view all the answers

What is a key function of the serosa/adventitia layer in the GI tract?

Providing structural support and allowing mobility Signup and view all the answers

How do microvilli contribute to the function of the mucosa in the GI tract?

Enhancing nutrient absorption surface area Signup and view all the answers

Which layer of the GI tract wall contains a large plexus of neurons and plays an immune role?

Submucosa Signup and view all the answers

What type of cell is primarily responsible for the endocrine functions in the mucosa of the GI tract?

Enteroendocrine cells Signup and view all the answers

What is a key function of the gut microbiome related to immune health?

It strengthens gut integrity and regulates immune function. Signup and view all the answers

Which of the following influences the development of an infant's gut microbiome the most?

The mode of delivery at birth. Signup and view all the answers

What change is observed in the gut microbiota of formula-fed infants compared to breastfed infants?

More diverse microbiota with increased Enterobacteriaceae. Signup and view all the answers

By what age does the composition of a child's gut microbiome become similar to that of an adult?

2.5 years. Signup and view all the answers

Which factor is NOT mentioned as influencing the composition of the gut microbiota?

Age-related hormonal changes. Signup and view all the answers

What percentage of AAD cases is accounted for by C.difficile?

10-25% Signup and view all the answers

Which condition is NOT associated with antibiotic use in childhood?

Type 2 diabetes Signup and view all the answers

Which component is reduced in the gut microbiome due to dysbiosis?

Bifidobacteria Signup and view all the answers

What is a symptom of pseudomembranous colitis caused by C.difficile?

Watery diarrhea Signup and view all the answers

Which of the following indicates an increase in white blood cells in the context of C.difficile infections?

Leukocytosis Signup and view all the answers

In which condition is a dysbiotic gut microbiome primarily thought to play a role?

Obesity Signup and view all the answers

What is the effect of reduced richness in gut microbiome diversity?

Increased risk of immune disorders Signup and view all the answers

Which of the following best describes the primary effect of antibiotics on the gut microbiome?

Alteration of gut microbiota composition Signup and view all the answers

What is the primary function of the hepatic portal vein?

To transport poorly-oxygenated, nutrient-rich blood to the liver Signup and view all the answers

Which veins combine to form the hepatic portal vein?

Superior mesenteric vein and splenic vein Signup and view all the answers

What is the correct order of blood flow involving the hepatic portal vein?

Artery → capillary → portal vein → capillary → vein → right atrium Signup and view all the answers

Which structure primarily receives blood from the hepatic portal vein?

Liver Signup and view all the answers

Which statement accurately describes the blood supplied by the hepatic portal vein?

The blood is nutrient-rich but poorly-oxygenated. Signup and view all the answers

What type of diet is associated with a higher percentage of Prevotella in the infant microbiota?

Rich in starch, fiber, and plants Signup and view all the answers

Which short-chain fatty acid is produced during fermentation of indigestible carbohydrates?

Acetate Signup and view all the answers

How do short-chain fatty acids (SCFAs) contribute to intestinal health?

Enhance luminal pH regulation Signup and view all the answers

What is a potential risk factor associated with trimethylamine oxide (TMAO)?

Higher risk of atherosclerosis Signup and view all the answers

What metabolic function does the gut microbiome influence related to appetite?

Increased appetite regulation Signup and view all the answers

What is a key role of bile acids modified by the gut microbiome?

Changing energy metabolism Signup and view all the answers

Which bacterial activity is responsible for producing indoles that influence the immune response?

Metabolism of tryptophan Signup and view all the answers

What correlation exists between the presence of different bacterial species and intestinal integrity?

Various species correlate with changes in epithelial cell function. Signup and view all the answers

Which hormone is primarily responsible for increasing stomach acid secretion?

Gastrin Signup and view all the answers

What is the main function of secretin in the gastrointestinal system?

Promoting bicarbonate and water secretion from the pancreas Signup and view all the answers

Which type of enteroendocrine cell is located in the stomach and releases histamine?

ECL cell Signup and view all the answers

Closed enteroendocrine cells differ from open cells in that they:

Do not contact the lumen Signup and view all the answers

How do motilin's main functions contribute to digestive processes?

Promotes the migrating motor complex during fasting Signup and view all the answers

Which hormone is involved in regulating satiety and also promotes insulin secretion?

Glucagon-like peptide Signup and view all the answers

What role does the muscularis mucosa serve in the gastrointestinal tract?

Increasing folding of the mucosa Signup and view all the answers

Enteroendocrine cells generally serve what primary role in the digestive system?

Releasing hormones affecting digestion Signup and view all the answers

Which statement accurately describes open enteroendocrine cells?

They can sense luminal contents and secrete granules towards the blood Signup and view all the answers

Which type of enteroendocrine cell is primarily responsible for stimulating enzyme secretion in the pancreas?

I cell Signup and view all the answers

Which type of movement is specifically responsible for the propulsion of food through the gastrointestinal tract?

Peristalsis Signup and view all the answers

What is the primary role of Enteric Nervous System (ENS) in the gut?

Regulating gut motility Signup and view all the answers

Which statement best describes the relationship between bacteria in the gut microbiome and human physiology?

They have a bidirectional relationship that impacts health. Signup and view all the answers

Which of the following factors is least likely to influence the composition of the gut microbiota?

Personal exercise routine Signup and view all the answers

What role do hormones play in gastrointestinal motility?

Hormones can both stimulate and inhibit motility. Signup and view all the answers

Which condition is primarily linked to an imbalance in the gut microbiome?

Irritable bowel syndrome Signup and view all the answers

Which structure in the GI tract is most involved in nutrient absorption?

Duodenum Signup and view all the answers

What is a potential consequence of prolonged antibiotic use on gut health?

Overgrowth of harmful bacteria Signup and view all the answers

What is the primary role of interstitial cells of Cajal (ICC) in the gastrointestinal tract?

Generating slow waves that regulate muscle contractions Signup and view all the answers

Which movement is characterized by waves of smooth muscle contractions that propel food bolus through the GI tract?

Peristalsis Signup and view all the answers

In what part of the gastrointestinal tract does segmentation primarily occur?

Small and Large Intestine Signup and view all the answers

What is a suspected function of the migrating motor complex (MMC)?

Cleaning the intestinal tract during fasting Signup and view all the answers

Which system is primarily involved in autonomically regulating GI motility?

Enteric Nervous System (ENS) Signup and view all the answers

What effect does norepinephrine have on the excitability of smooth muscle in the gastrointestinal tract?

Decreases excitability Signup and view all the answers

Which structure is responsible for facilitating communication between the CNS and the ENS?

Vagus Nerve Signup and view all the answers

What is stimulated by the distention of smooth muscle cells in the gastrointestinal tract?

Enhanced smooth muscle contraction Signup and view all the answers

How does the sympathetic nervous system generally affect gastrointestinal motility?

Opposes motility and digestive secretions Signup and view all the answers

Which cell type is primarily responsible for the regulatory processes within the submucosal plexus?

Interneurons Signup and view all the answers

What is the primary bacterial species composition in the microbiota of infants on a starch, fiber, and plant diet?

Bacteroidetes (57.7%) and Actinobacteria (10.1%) Signup and view all the answers

Which short-chain fatty acid (SCFA) is produced through the fermentation of dietary fibers by gut microbiota?

Acetic acid Signup and view all the answers

What impact do short-chain fatty acids (SCFAs) have on intestinal integrity?

They regulate mucus production. Signup and view all the answers

Which of the following metabolites is produced from the metabolism of choline, phosphatidylcholine, and L-carnitine?

Trimethylamine (TMA) Signup and view all the answers

What is a consequence of the absence of Prevotella in the microbiota of infants with a diet high in sugar, starch, and animal protein?

Decreased gut microbiome diversity Signup and view all the answers

How do bile acids modified by the gut microbiome influence metabolism?

They promote insulin insensitivity. Signup and view all the answers

What role do indoles play in the gut microbiome?

Support intestinal barrier function Signup and view all the answers

What primary effect do SCFAs have on epithelial cells in the gut?

They modulate mucosal immune function. Signup and view all the answers

What is the primary function of salivary amylase in the digestive process?

Breaking down carbohydrates Signup and view all the answers

What role does the Na+/K+ pump play in carbohydrate absorption?

It supports Na+/glucose co-transporter function Signup and view all the answers

Which transporter is responsible for the absorption of dipeptides and tripeptides into enterocytes?

PepT1 Signup and view all the answers

What characterizes the absorption of fat greater than 10-12 carbons long?

They are converted into chylomicrons after re-esterification Signup and view all the answers

What is the consequence of overly rapid transit of chyme through the digestive system?

Inadequate time for chemical digestion Signup and view all the answers

Which molecule can pass through enterocytes without modification?

Free fatty acids Signup and view all the answers

Which active transporters are involved in the absorption of nucleic acids?

Nucleoside transporters Signup and view all the answers

How are absorbed amino acids released into the bloodstream?

They cross the basolateral membrane of enterocytes Signup and view all the answers

What condition can result from impaired fat absorption, leading to excessive fat in the stool?

Steatorrhea Signup and view all the answers

Which carbohydrates can be transported across the epithelial cells of the small intestine?

Monosaccharides only Signup and view all the answers

What is the role of the swallowing center in the pharyngeal stage of swallowing?

To coordinate the activity of vagal nuclei Signup and view all the answers

What is the primary consequence of secondary peristalsis in the esophagus?

Emptying of food into the stomach Signup and view all the answers

What is the physiological mechanism of the lower esophageal sphincter (LES) during peristalsis?

Relaxes to allow easy propulsion of food into the stomach Signup and view all the answers

What characterizes achalasia in terms of esophageal motility?

Inability of the LES to relax properly Signup and view all the answers

Which condition results from impaired smooth muscle relaxation at the lower esophageal sphincter?

Achalasia Signup and view all the answers

What might cause dysphagia due to obstructive disorders?

Development of non-malignant growths in the esophagus Signup and view all the answers

Which disorder is characterized by high-amplitude contractions and intense chest pain?

Nutcracker esophagus Signup and view all the answers

What is the significance of barium swallow imaging in diagnosing esophageal conditions?

To visualize structural abnormalities in the esophagus Signup and view all the answers

Which type of esophagitis is often associated with immunosuppression?

Infectious esophagitis Signup and view all the answers

What type of esophageal pathology results in difficulty swallowing due to muscular dysfunction?

Dysphagic diseases Signup and view all the answers

What condition is often characterized by a grayish-white pseudomembrane on an erythematous base?

Candidiasis Signup and view all the answers

What is the result of the relaxation of the lower esophageal sphincter (LES)?

Facilitation of food entry into the stomach Signup and view all the answers

Which nerve is primarily responsible for sending afferent sensory input during swallowing?

Glossopharyngeal nerve Signup and view all the answers

What is a key characteristic of diffuse esophageal spasm?

Dysphagia accompanied by chest pain Signup and view all the answers

Study Notes

Overview of Gastrointestinal Tract

The gastrointestinal (GI) tract manages food transport and nutrient absorption.
Approximately 60 tonnes of food pass through the GI tract over a human lifetime.
Functions include digestion, absorption, and immune responses to environmental factors.

Gut Physiology

Gut motility is regulated by interstitial cells of Cajal (ICC), smooth muscle cells, and both enteric and central nervous systems.
Hormonal secretions impacting motility include:
- Promoting motility: Cholecystokinin (I-cells), Serotonin (enterochromaffin cells), Gastrin (G-cells), Motilin (Mo-cells), Insulin (beta-pancreatic cells)
- Reducing motility: Secretin (S-cells), Somatostatin (D-cells), Pancreatic peptide YY (pancreatic cells), Glucagon (alpha-pancreatic cells)

Digestion

Digestion entails breaking down macromolecules via mechanical (chewing, churning) and chemical processes.
Mechanical Digestion: Involves reduction of food particles to increase the surface area for chemical digestion.
Chemical Digestion: Enzymatic breakdown that allows nutrient absorption.

Absorption Processes

Fat-soluble vitamins (A, D, E, K) require micelle formation for absorption, mainly occurring in the duodenum; Vitamin B12 is absorbed in the ileum.
B-vitamins and Vitamin C are absorbed using Na+ cotransporters.
Iron absorption takes place in the duodenum through the divalent metal transporter 1 (DMT1).

The Human Microbiome

The microbiome comprises ~10^14 cells, including bacteria, viruses, and fungi, with a virus-to-bacteria ratio of ~5:1.
It plays a significant role in digestion, nutrient absorption, and overall intestinal health.
A balanced microbiome is crucial for preventing gut dysbiosis and associated health issues.

General GI Tract Histology

The GI tract's structure includes four main layers:
- Mucosa: Responsible for absorption and secretion, contains epithelial cells, goblet cells (mucus secretion), and enteroendocrine cells.
- Submucosa: Contains blood vessels and neurons (Meissner’s plexus).
- Muscularis: Composed of smooth muscle layers responsible for propulsion; contains Auerbach’s plexus.
- Serosa/Adventitia: Connective tissue providing support and mobility.

Pathological Implications

Gut dysbiosis can lead to various digestive disorders and health issues, highlighting the importance of a balanced microbiome.
Dietary factors and antibiotic use significantly influence microbiome composition and health.

Gut Microbiome Functions

Harvests energy from undigested nutrients, aiding nutrient absorption.
Strengthens gut integrity and shapes intestinal epithelium structure.
Regulates immune function and intestinal motility.
Offers protection against pathogenic microbes.
Produces essential nutrients, including Vitamin K2 and short-chain fatty acids (SCFAs).
Functions as an endocrine organ, influencing various bodily processes.

Gut Microbiome Development

Birth method influences initial gut microbiota:
- C-section leads to lower Bacteroides and higher Clostridium species.
- Vaginal birth reflects maternal microbiota characteristics.
Initial nutrition impacts gut flora:
- Breastfed infants show high levels of Bifidobacterium.
- Formula-fed infants exhibit lower Bifidobacterium and altered E. coli and Clostridium difficile ratios.
- Undernourished infants may have increases in enteropathogens like Enterobacteriaceae.
By age 2.5, a child's gut flora resembles that of an adult, remaining stable with minor fluctuations throughout life.

Diet and Gut Microbiome

Genetic, dietary, and medication factors influence gut microbiota composition.
Dietary examples:
- Starch, fiber, and plant-rich diets yield 10.1% Actinobacteria and 57.7% Bacteroidetes in infants.
- A diet high in sugar, starch, and animal protein leads to lower Actinobacteria (6.7%) and Bacteroidetes (22.4%) with absent Prevotella.

Short-Chain Fatty Acids (SCFAs)

Produced during fermentation of indigestible carbohydrates by gut microbiota.
Key SCFAs include acetate, propionate, and butyrate.
Promote intestinal integrity through regulating pH, mucus production, providing epithelial cell fuel, and modifying immune functions.
Influence metabolism aspects such as appetite regulation, energy expenditure, glucose homeostasis, and immunomodulation.

Microbiome Metabolites

Trimethylamine (TMA): Metabolized from choline and L-carnitine, linked to atherosclerosis and thrombosis risk via conversion to TMAO.
Bile Acids: Liver-produced substances modified by gut microbiota, correlated with energy metabolism changes, including cholesterol and insulin sensitivity.
Indoles: Derived from tryptophan metabolism, play a role in maintaining the intestinal barrier and influencing immune responses.

Gut Microbiome and Intestinal Integrity

Bacterial diversity correlates with epithelial function and structure.
Non-pathogenic E. difficile accounts for 10-25% of antibiotic-associated diarrhea (AAD) cases, with symptoms ranging from mild diarrhea to severe pseudomembranous colitis.
Childhood antibiotic use is associated with various health issues (asthma, diabetes, IBD, mental illness) attributed to dysbiosis, resulting in reduced microbial richness and shifts in bacterial populations.

Enteroendocrine Cells (DNES)

Located in the stomach and small intestine; involved in hormonal secretion.
Open and closed cells regulate hormonal release through different mechanisms (e.g., sensing luminal contents vs. other stimuli).
Key enteroendocrine cells and their functions include:
- D cells: Somatostatin release, inhibiting nearby hormone secretion.
- G cells: Gastrin secretion for increasing stomach acid release.
- I cells: CCK secretion, stimulating pancreatic enzymes and gallbladder contraction.
- L cells: Glucagon-like peptide for insulin secretion and satiety.
- S cells: Secretin for bicarbonate and water secretion from the pancreas.

Abdominal Venous Vasculature Overview

Inferior mesenteric vein combines with splenic vein to form hepatic portal vein.
Hepatic portal vein transports nutrient-rich blood from abdominal organs to the liver, facilitating nutrient metabolism and detoxification processes.

Swallowing and Esophageal Mechanics

The trachea closes during swallowing, inhibiting respiration.
Vocal cords approximate, the larynx raises, and the epiglottis covers the vocal cords.
The upper esophageal sphincter (UES) relaxes during swallowing.
Pharyngeal peristalsis moves food toward the stomach.

Nervous Control of Swallowing

Swallowing is regulated by the swallowing center located in the medulla.
Sensory input from the pharynx and esophagus activates the swallowing center.
The swallowing center coordinates activities through vagal nuclei while inhibiting the respiratory center.
Pharyngeal phase of swallowing occurs within 2 seconds, briefly interrupting respiration.

Esophageal Movements

Secondary peristalsis occurs in response to retained food or reflux, continuing until the esophagus is cleared.
Initiated by intrinsic neural circuits and vagal afferent fibers.

Lower Esophageal Sphincter (LES)

The LES, located 1-2 cm below the diaphragm, remains tonically constricted.
During peristalsis, the LES relaxes to allow food entry into the stomach, preventing reflux.

Esophageal Manometry Insights

High resting pressure of the UES contrasts with low resting pressure of the LES.
Post-food passage, the LES exhibits higher pressures due to activity of NO and VIP-secreting vagal branches.

Pathologies of the Esophagus

Common conditions range from dysphagia (difficulty swallowing) to inflammatory, metaplastic/neoplastic, and vascular diseases.
Motility disorders include nutcracker esophagus, resulting in intense chest pain, and achalasia, characterized by impaired LES relaxation.

Achalasia Features

Achalasia presents with dysphagia, chest pain, and regurgitation.
Primary achalasia: Idiopathic failure of inhibitory neurons leading to increased LES tone.
Secondary achalasia: Caused by diabetes or infections like Trypanosoma cruzi, leading to esophageal dilatation and failure of peristalsis.

Imaging and Studies

Barium swallow studies visualize motility disorders such as diffuse esophageal spasm and achalasia.
Manometry studies provide insights into pressure variations in the esophagus.

Esophagitis

Infectious esophagitis may indicate immunosuppression, commonly caused by HSV, CMV, or fungi like candidiasis.
Autoimmune disorders like Crohn's disease or scleroderma can also impact the esophagus.

Gastrointestinal Tract Overview

The GI tract transports approximately 60 tonnes of food over a lifetime, aiding in digestion and absorption.
Functions include decontamination of food and maintaining non-human cell interactions with the immune system.

GI Motility

Three primary movements in the GI tract: peristalsis (propels food), segmentation (mixes food for absorption), and migrating motor complex (cleanses intestines).
Interstitial cells of Cajal serve as pacemakers, coordinating muscle contractions.

Enteric Nervous System (ENS)

ENS composed of sensory, motor, and interneurons is organized into submucosal and myenteric plexuses, regulating GI motility and secretions.
The CNS influences GI function through vagus and pelvic splanchnic nerves.

Nutrient Transport in the GI Tract

Digestion and absorption occur primarily in the small intestine, where chemical digestion is crucial.
Carbohydrates are absorbed as monosaccharides via specific transporters like SGLT1 and GLUT-5.

Absorption Mechanisms

Proteins, nucleic acids, and fats undergo specific digestion to permit absorption via various mechanisms.
Fats are absorbed as chylomicrons through passive diffusion, entering lymphatics.

Short-Chain Fatty Acids (SCFA)

SCFAs, produced during fiber fermentation by gut microbiota, play roles in intestinal integrity, immune function, and metabolism.

Gut Microbiome Connections

The balance of bacterial species affects epithelial function and overall health.
Dietary factors shape the microbiome, influencing absorption and potential pathological conditions.

Dietary and Antibiotic Influences

Diet impacts microbiome diversity and functionality.
Antibiotics can disrupt microbial balance, influencing gut health.

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Description

This quiz covers the fundamentals of the gastrointestinal tract, including gut physiology, motility, digestion, absorption, and regulation. Additionally, it explores the microbiome's role in health and its relationship with human physiology. Prepare to test your understanding of these essential concepts.