Motility of GI tract

Question 1

What are the primary functions of the gastrointestinal (GI) tract?

Answer 1

The primary functions of the GI tract include ingestion of food, digestion (mechanical and chemical), motility, and secretion.

Question 2

What does ingestion refer to in the context of the GI tract?

Answer 2

Ingestion refers to the process of taking in food and the formation of a bolus (a small rounded mass of chewed food).

Question 3

What is digestion in the GI tract?

Answer 3

Digestion in the GI tract involves both mechanical and chemical processes that break up food particles into smaller pieces.

Question 4

What is the role of motility in the GI tract?

Answer 4

Motility refers to the movements of the organs and the bolus within the GI tract, which facilitate the mechanical digestion of food particles.

Question 5

What is secretion in the context of the GI tract?

Answer 5

Secretion refers to the release of digestive agents (such as enzymes, acids, and mucus) by various organs of the GI tract, which enables the chemical digestion of food particles.

Question 6

What is the role of absorption in the GI tract?

Answer 6

Absorption refers to the process of taking up and transferring the digestion products from the GI tract into the bloodstream or lymphatic vessels for distribution throughout the body.

Question 7

What is the function of storage/elimination in the GI tract?

Answer 7

The GI tract also serves the purpose of storing non-digested food particles temporarily and eliminating them through the process of defecation.

Question 8

What are the protective functions of the GI tract?

Answer 8

The GI tract provides mechanical, chemical, and immunological protection not only for its own organs but also for the rest of the body, defending against potential harmful food components and pathogens.

Question 9

What is the primary function of the esophagus?

Answer 9

The esophagus primarily serves as a transportation pathway for food, facilitating the movement of ingested food from the mouth to the stomach.

Question 10

What are the main functions of the stomach?

Answer 10

The stomach functions as a storage organ, where food is held temporarily. It also secretes digestive juices, mixes the food with gastric acids, and initiates the digestion process.

Question 11

What is the primary function of the small intestine?

Answer 11

The small intestine has multiple primary functions, including the secretion of digestive enzymes, mixing of food with these enzymes, digestion of nutrients, and absorption of digested products into the bloodstream.

Question 12

What are the primary functions of the large intestine?

Answer 12

The large intestine primarily focuses on the digestion of remaining food particles, limited absorption of water and electrolytes, and the formation of feces for elimination from the body.

Question 13

What is the basis of motility in the GI tract?

Answer 13

Motility in the GI tract is primarily governed by the coordinated contraction of smooth muscle.

Question 14

Are there any exceptions to smooth muscle contraction in the GI tract?

Answer 14

Yes, the upper esophagus and external anal sphincter are exceptions as they are composed of striated skeletal muscle and are under voluntary control.

Question 15

How is smooth muscle organized in the GI tract?

Answer 15

Smooth muscle in the GI tract is organized into connected bundles of outer longitudinal and inner circular muscle layers in the muscularis, allowing for involuntary contractions.

Question 16

How does smooth muscle facilitate coordinated contraction?

Answer 16

Smooth muscle consists of single units with gap junctions, which enable electrical coupling and contraction as a functional syncytium. This allows for coordinated contractions of the smooth muscle fibers.

Question 17

What is the arrangement of smooth muscle fibers in the GI tract?

Answer 17

Smooth muscle fibers are arranged in bundles within the muscularis layer, with outer longitudinal and inner circular layers, enabling involuntary contraction of the muscle.

Question 18

What is segmentation in the context of smooth muscle contraction in the GI tract?

Answer 18

: Segmentation is a type of smooth muscle contraction that is responsible for mixing the food within a specific segment of the GI tract. It involves bursts of circular muscle contraction and relaxation, resulting in back and forth pendular movements.

Question 19

What is peristalsis in the context of smooth muscle contraction in the GI tract?

Answer 19

Peristalsis is a type of smooth muscle contraction that facilitates the propulsion of food through the GI tract. It is triggered by local distension and involves contraction behind the bolus (food mass) and relaxation in front of it, creating a wave-like movement.

Question 20

What is required for peristalsis to occur in the GI tract?

Answer 20

Peristalsis relies on the presence of a functional myenteric plexus, which is a network of nerve fibers located between the circular and longitudinal muscle layers of the GI tract. It coordinates the sequential contraction and relaxation of smooth muscles during peristaltic movements.

Question 21

How many stages are there in swallowing (deglutition)?

Answer 21

There are three stages of swallowing: oral, pharyngeal, and esophageal.

Question 22

What happens during the oral phase of swallowing?

Answer 22

The oral phase of swallowing is under voluntary control. The tongue pushes against the hard palate and contracts to force the lubricated bolus (a mass of chewed food) into the oropharynx.

Question 23

Which phases of swallowing are under voluntary control?

Answer 23

Only the oral phase of swallowing is under voluntary control. The pharyngeal and esophageal phases are both involuntary.

Question 24

What occurs during the pharyngeal phase of swallowing?

Answer 24

The pharyngeal phase is an involuntary passage of food through the pharynx into the esophagus.

Question 25

What happens during the esophageal phase of swallowing?

Answer 25

The esophageal phase is the involuntary passage of food from the pharynx to the stomach.

Question 26

What triggers the pharyngeal phase of swallowing?

Answer 26

The presence of the bolus stimulates the glossopharyngeal nerves, which then activate the swallowing center located in the medulla oblongata.

Question 27

Which cranial nerves are involved in the motor control of the pharyngeal phase?

Answer 27

Motor efferents from the trigeminal (CN V), glossopharyngeal (CN IX), and vagus (CN X) nerves are involved in coordinating the muscular contractions during the pharyngeal phase.

Question 28

What are some of the specific actions that occur during the pharyngeal phase of swallowing?

Answer 28

During the pharyngeal phase, the soft palate elevates over the posterior nares, the epiglottis closes off the larynx, respiration is temporarily inhibited, and the upper esophageal sphincter (UOS) relaxes. Additionally, the contractions of the pharyngeal muscles propel the bolus into the esophagus.

Question 29

What occurs during the oesophageal phase of swallowing?

Answer 29

In the oesophageal phase, primary peristaltic waves consisting of both striated (upper 1/3) and smooth muscle contractions propel the bolus through the oesophagus. Stretch receptors in the oesophagus trigger secondary waves, facilitating peristalsis. The enteric nervous system (ENS) and intrinsic myenteric plexus, along with extrinsic vagal control, help coordinate peristalsis.

Question 30

What is the structure of the oesophagus?

Answer 30

The oesophagus is a muscular tube approximately 25 cm long, running from the pharynx to the stomach. It is semi-collapsible and channels substances into the stomach via peristalsis. The submucosal layer of the oesophagus contains multiple mucous glands that produce lubricating mucus to aid the movement of the bolus. There are sphincters located at both the superior and inferior ends of the oesophagus to close it when food is not being swallowed.

Question 31

How does the oesophagus propel the bolus towards the stomach?

Answer 31

The circular and longitudinal smooth muscles lining the oesophagus work together. The bolus stimulates stretch receptors within the oesophagus, allowing the enteric nervous system (ENS) to identify the bolus’s location. This coordination triggers peristalsis, which propels the bolus towards the lower oesophageal sphincter (LOS). As the bolus approaches the LOS, the pressure in the oesophagus overcomes the pressure gradient, allowing the bolus to enter the stomach. This change in pressure prevents acid reflux.

Question 32

What is the function of GI sphincters?

Answer 32

GI sphincters serve as smooth muscle valves that separate different regions of the GI tract through tonic contraction.

Question 33

Why does the GI tract require sphincters?

Answer 33

The GI tract requires sphincters to prevent the backward movement (reflux) of the contents within the GI tract. The sphincters act as barriers, ensuring that the flow of contents progresses in the desired direction.

Question 34

How do GI sphincters work?

Answer 34

GI sphincters maintain a state of tonic contraction, which creates a barrier between different segments of the GI tract. When necessary, such as during swallowing or passage of materials, the sphincters relax to allow the controlled movement of contents.

Question 35

Why is the Enteric Nervous System (ENS) referred to as the “second brain”?

Answer 35

The ENS is colloquially referred to as the “second brain” because it is a complex network of neurons located solely within the gastrointestinal (GI) tissue. It exhibits autonomous control over GI functions.

Question 36

What are the two complex plexi within the ENS and their respective function

Answer 36

The ENS consists of two main plexi:

Myenteric (Auerbach’s) plexus: Controls GI motility and contraction. It is located in the muscular layer of the GI tract.
Submucosal (Meissner’s) plexus: Controls glandular secretions and blood flow. It is located in the submucosal layer of the GI tract.

Question 37

What is the intrinsic control mechanism of the ENS?

Answer 37

The ENS is truly autonomous and can regulate GI motility and secretion independently. It functions as an intrinsic control mechanism within the GI tract.

Question 38

How does the ENS interact with the central nervous system (CNS)?

Answer 38

Extrinsic autonomic sympathetic and parasympathetic innervation from the CNS allows for central modification of GI functions, providing additional regulatory control

Question 39

What are the main components of the GI tract regulated by the ENS?

Answer 39

The ENS regulates GI motility, contraction of the longitudinal and circular muscles, secretions from glands, and blood flow in the GI tract. It plays a crucial role in coordinating and controlling various functions.

Question 40

What is the extrinsic regulation of the GI tract?

Answer 40

The autonomic nervous system (ANS) provides extrinsic regulation of the GI tract. It consists of sympathetic and parasympathetic pathways that help control the enteric nervous system (ENS).

Question 41

How does the parasympathetic pathway regulate the GI tract?

Answer 41

In the parasympathetic pathway, postganglionic fibers innervate smooth muscle and secretory cells in the GI tract. Acetylcholine (ACh) is the dominant neurotransmitter, stimulating motor and secretory activity. The parasympathetic regulation is primarily, but not exclusively, achieved through the vagus nerve (CN X).

Question 42

What is the role of the sympathetic pathway in GI regulation?

Answer 42

The sympathetic pathway inhibits motor and secretory activity in the GI tract. It also stimulates sphincter contraction and constriction of blood vessels. The sympathetic signals are transmitted through the prevertebral ganglia.

Question 43

What are the main effects of parasympathetic stimulation on the GI tract?

Answer 43

Parasympathetic stimulation promotes increased motor activity, secretion of digestive enzymes and hormones, and relaxation of sphincters in the GI tract. It generally facilitates digestion and absorption processes.

Question 44

How does sympathetic stimulation affect the GI tract?

Answer 44

Sympathetic stimulation inhibits GI motility and secretion. It causes constriction of sphincters and blood vessels in the GI t

Question 45

What are the three primary motor functions of the stomach?

Answer 45

The stomach has three primary motor functions: storage, mixing, and emptying.

Question 46

How does the stomach function in storage?

Answer 46

The vagovagal reflex, involving afferent and efferent nerves along with the vagus nerve (CN X), mediates receptive relaxation. This reduces muscle tone, allowing the stomach to function as a reservoir for storing stomach contents.

Question 47

What is the role of the stomach in mixing?

Answer 47

Slow peristaltic waves initiated in the body of the stomach move the stomach contents towards the pyloric antrum. Foodstuff is forced back and forth in a process called propulsion and retropulsion, promoting further mixing and digestion. This cyclic movement helps produce chyme.

Question 48

How is emptying of stomach contents regulated?

Answer 48

The emptying of stomach contents into the duodenum is highly regulated. Primary inhibitory feedback signals from the small intestine play a significant role. More powerful peristaltic contractions build to force chyme into the duodenum. The regulation of emptying involves excitatory signals from the enteric nervous system (ENS), autonomic nervous system (ANS) neuronal stimulation, hormonal factors (such as motilin), as well as inhibitory signals from the ANS, duodenal enterogastric reflexes, and hormones (such as cholecystokinin or CCK).

Question 49

What are the regulatory mechanisms involved in the emptying of the stomach?

Answer 49

The emptying of the stomach is regulated by excitatory signals from the enteric and autonomic nervous systems, as well as hormonal factors such as motilin. Additionally, inhibitory signals from the ANS, duodenal enterogastric reflexes, and hormones like CCK play a role in regulating the rate of emptying.

Question 50

How is the lower gastrointestinal tract (GIT) defined anatomically?

Answer 50

The lower GIT refers to the anatomical components of the gastrointestinal tract that are located inferior to the suspensory muscle of the duodenum, also known as the ligament of Treitz.

Question 51

What is the significance of the suspensory ligament of the duodenum?

Answer 51

The suspensory ligament of the duodenum serves as a landmark that distinguishes the upper and lower gastrointestinal tract. It is the point at which the lower GIT begins. However, there is some debate about the exact location that differentiates the upper and lower GIT.

Question 52

What components are included in the lower GIT?

Answer 52

The lower gastrointestinal tract (GIT) includes the small intestine, large intestine, rectum, and anus. These structures are responsible for further digestion, absorption of nutrients, and elimination of waste materials from the body.

Question 53

What is the function of the small intestine in the lower GIT?

Answer 53

The small intestine is responsible for the majority of nutrient digestion and absorption. It consists of the duodenum, jejunum, and ileum and plays a crucial role in extracting essential nutrients from ingested food.

Question 54

What is the role of the large intestine in the lower GIT?

Answer 54

The large intestine, also known as the colon, is involved in the absorption of water and electrolytes from undigested food residues. It also facilitates the formation and storage of feces before elimination.

Question 55

What are the rectum and anus responsible for in the lower GIT?

Answer 55

The rectum serves as a temporary storage site for feces until they can be expelled from the body through the anus. The anus, equipped with sphincter muscles, controls the release of fecal matter during defecation.

Question 56

What are the three main components of the small intestine?

Answer 56

The small intestine consists of three main components:
i) Duodenum - the shortest part of the small intestine.
ii) Jejunum - an intermediate-sized component.
iii) Ileum - the longest part of the small intestine.

Question 57

What is the role of motility in the small intestine?

Answer 57

Motility patterns in the small intestine play a crucial role in facilitating digestion and absorption of nutrients. The coordinated contractions and movements of the small intestine help propel the chyme, mix it with digestive enzymes, and ensure maximum exposure to the absorptive surfaces.

Question 58

How is the surface area for absorption increased in the small intestine?

Answer 58

The small intestine provides a large surface area for absorption through various structural features. These include circular folds (plicae circulares), villi projections on the mucosa, and microvilli on the apical surface of the epithelial cells, collectively known as the “brush border.” These structures significantly increase the absorptive surface area.

Question 59

What are the two main types of motility in the small intestine?

Answer 59

i) Mixing and circulation: This type of motility allows for maximum exposure of chyme to the absorptive epithelium. It involves segmental contractions and movements that help mix the chyme with digestive enzymes and facilitate absorption.
ii) Propulsion: This type of motility involves the coordinated contractions that propel the chyme aborally (towards the lower parts of the digestive tract), allowing for the progression of digestion and absorption through the small intestine.

Question 60

How is motility in the small intestine controlled?

Answer 60

Motility in the small intestine is primarily regulated by intrinsic motor patterns, which are modified by hormonal and autonomic nervous system (ANS) neural stimuli. These coordinated motor patterns ensure proper mixing and propulsion of the chyme.

Question 61

What is segmentation in the context of small intestine motility?

Answer 61

Segmentation refers to a type of motility pattern in the small intestine that facilitates mixing. Stretch receptors in the intestinal wall trigger myenteric stimulation, leading to localized contractions of the circular smooth muscle. This segmentation process helps mix the chyme with digestive enzymes and promotes optimal absorption. Importantly, there is no net movement of chyme during segmentation.

Question 62

What is propulsive peristalsis in the small intestine?

Answer 62

Propulsive peristalsis is another motility pattern in the small intestine that involves the movement of chyme in a net direction. Similar to segmentation, stretch receptors trigger myenteric stimulation, but in this case, it results in coordinated contractions that propel the chyme aborally (towards the lower parts of the digestive tract).

Question 63

How are small intestine motility and digestion regulated by hormones?

Answer 63

Hormones play a significant role in regulating small intestine motility. Excitatory hormones such as gastrin, cholecystokinin (CCK), insulin, and motilin stimulate motor activity and enhance digestion and absorption. In contrast, inhibitory hormones such as secretin and glucagon help modulate small intestine motility and promote proper coordination between different digestive processes.

Question 64

What is the gastroenteric reflex?

Answer 64

The gastroenteric reflex is a reflex pathway that is activated by gastric distention. It involves the activation of the myenteric plexus in the small intestine, which promotes peristalsis throughout the length of the small intestine. This reflex helps propel the chyme and facilitates its movement from the stomach to the large intestine.

Question 65

What is the migrating motor complex (MMC)?

Answer 65

The migrating motor complex (MMC) is a series of frequent peristaltic contractions that occur in the small intestine between meals. The MMC helps move the content of the small intestine, including any residual food particles or bacteria, towards the large intestine. The MMC is under intrinsic enteric control and is regulated by the hormone motilin. Its absence can lead to bacterial overgrowth in the small intestine.

Question 66

What is the role of the ileocecal valve?

Answer 66

The ileocecal valve is a sphincter-like structure located between the end of the ileum (last part of the small intestine) and the beginning of the colon (large intestine). The ileocecal valve controls the emptying of chyme from the small intestine into the colon. It helps regulate the flow and prevents backflow of contents between the two regions of the gastrointestinal tract.

Question 67

What is the large intestine?

Answer 67

The large intestine, also known as the colon, is a portion of the gastrointestinal tract that extends from the ileum (end of the small intestine) to the rectum. It is approximately 6 meters in length and consists of four main sections: the ascending colon, transverse colon, descending colon, and sigmoid colon.

Question 68

What are the primary functions of the large intestine?

Answer 68

The large intestine performs two primary functions:

Absorption of water and electrolytes: In the proximal (upper) part of the large intestine, water and electrolytes, such as sodium and potassium, are absorbed from the remaining chyme (digestive residue) that enters from the small intestine. This helps maintain fluid and electrolyte balance in the body.
Formation and storage of feces: In the distal (lower) part of the large intestine, the remaining indigestible materials, bacteria, and waste products are processed to form feces. The large intestine also serves as a storage site for feces until they are eliminated through the rectum.

Question 69

: How is motility regulated in the large intestine?

Answer 69

Motility in the large intestine is primarily controlled by intrinsic enteric control, which is then modified by neural and hormonal stimuli. The motility patterns in the large intestine include mixing contractions, propulsive peristalsis, and mass movements.

Question 70

What are mixing contractions in the large intestine?

Answer 70

Mixing contractions in the large intestine are known as haustral churning. These contractions occur in the haustra, which are the sac-like compartments along the colon. Haustral churning involves alternating contractions and relaxations of the circular muscles in the colon, allowing for mixing and mixing of the contents. This helps facilitate further absorption of water and electrolytes and promotes the formation of feces.

Question 71

What is propulsive peristalsis in the large intestine?

Answer 71

Propulsive peristalsis in the large intestine involves coordinated contractions of the circular and longitudinal muscles. These contractions propel the fecal matter forward through the colon, moving it from one haustrum to the next. Propulsive peristalsis helps to advance the fecal material towards the sigmoid colon and rectum for eventual elimination.

Question 72

What are mass movements in the large intestine?

Answer 72

Mass movements in the large intestine are forceful peristaltic contractions that occur two to three times per day. These movements involve a powerful coordinated contraction of the circular and longitudinal muscles, pushing a significant amount of fecal material into the sigmoid colon and rectum. Mass movements are responsible for the urge to defecate and play a crucial role in the elimination of waste from the body

Question 73

What is the defecation reflex?

Answer 73

The defecation reflex is a reflexive mechanism that initiates the process of defecation, which is the elimination of feces from the body. It is triggered when the rectum becomes distended with fecal matter.

Question 74

How is the defecation reflex initiated?

Answer 74

The defecation reflex is initiated when stretch receptors in the rectum detect the presence of fecal material and send signals to the enteric nervous system (ENS) and the parasympathetic division of the autonomic nervous system (ANS).

Question 75

What happens during the defecation reflex?

Answer 75

Activation of the ENS and parasympathetic ANS leads to involuntary contraction of the longitudinal muscles in the rectum. This contraction opens the internal anal sphincter, allowing fecal matter to enter the anal canal.

Question 76

What happens to the external anal sphincter during defecation?

Answer 76

The external anal sphincter, which is under voluntary control, is relaxed voluntarily to allow defecation. This relaxation is achieved through conscious effort.

Question 77

What is emesis?

Answer 77

Emesis, also known as vomiting, is the forceful expulsion of the contents of the stomach through the mouth. It is a physiological mechanism to remove harmful or toxic substances from the body.

Question 78

What are the three phases of emesis?

Answer 78

The three phases of emesis are:
i) Nausea: It is characterized by unpleasant feelings, unease, and distress, often accompanied by a sensation of the need to vomit.
ii) Retching: Retching involves labored respiratory movements and contractions of the muscles of the abdomen, thoracic wall, and diaphragm. It is the prelude to vomiting and helps generate the necessary pressure for emesis.
iii) Expulsive phase (emesis): This is the actual vomiting phase, where there is involuntary emptying of the gastric contents. The pressure gradient caused by abdominal and diaphragmatic contractions opens the lower esophageal sphincter (LOS), allowing the contents to be expelled.

Question 79

What happens during the expulsive phase of emesis?

Answer 79

During the expulsive phase, the abdominal and diaphragmatic muscles contract forcefully, generating a pressure gradient that leads to the opening of the lower esophageal sphincter (LOS). This allows the gastric contents to be expelled through the mouth.

Question 80

How is the airway protected during emesis?

Answer 80

During emesis, the airway is protected to prevent aspiration of vomitus into the lungs. The epiglottis covers the trachea, preventing the entry of vomitus into the respiratory tract, while the soft palate covers the nasopharynx, blocking off the nasal passages.

Question 81

What is the emetic reflex?

Answer 81

The emetic reflex is the physiological mechanism that triggers vomiting. It is controlled by the vomiting center located in the brainstem, specifically the medulla.

Question 82

How is motion sickness related to the emetic reflex?

Answer 82

Motion sickness, such as seasickness or car sickness, can trigger the emetic reflex. The inner ear’s labyrinth, which is responsible for balance, detects motion and sends signals to the chemoreceptor trigger zone (CTZ) in the brain. The CTZ, located outside the blood-brain barrier, is innervated by the vestibulocochlear nerve (CN VIII) and can detect certain chemicals in the bloodstream associated with motion sickness.

Question 83

How does the CTZ communicate with the vomiting center?

Answer 83

The CTZ communicates with the vomiting center in the medulla via neurotransmitters, particularly serotonin (5HT) and dopamine (DA). These neurotransmitters bind to their respective receptors in the vomiting center, triggering the vomiting reflex.

Question 84

: What role do acetylcholine (ACh) and serotonin (5HT) play in the emetic reflex?

Answer 84

ACh and 5HT are neurotransmitters involved in the emetic reflex. ACh acts on muscarinic receptors in the vomiting center, while 5HT acts on both 5HTergic and DA receptors. Activation of these receptors in the vomiting center initiates the vomiting response.

Question 85

Where is the labyrinth located, and how does it contribute to the emetic reflex?

Answer 85

The labyrinth is part of the inner ear’s vestibular system, responsible for maintaining balance. It detects motion and sends signals to the CTZ via the vestibulocochlear nerve (CN VIII). The labyrinth’s stimulation, particularly by motion, can trigger the emetic reflex.