FRS 2. GI anatomy

Question 1

What is the peritoneal cavity?

Answer 1

the continuous area between the parietal peritoneum lining the abdominal wall
and the visceral peritoneum surrounding the abdominal organs = apotential space

contains a thin film of peritoneal fluid, which consists ofwater,
electrolytes, leukocytes and antibodies.

Question 2

What is the function of the fluid found in the peritoneal cavity?

Answer 2

o It acts as a lubricant, enabling the viscera to move freely over each other without any friction,
and allowing movements of digestion
o The antibodies fight infection.

Question 3

Why is the peritoneal cavity a potential space?

Answer 3

because excess fluid can accumulate in the peritoneal cavity resulting in ascites

Question 4

how is the peritoneal cavity divided?

Answer 4

The peritoneal cavity can be divided into the greater andlesser peritoneal sacs.

The greater sac comprisesthe majority of the peritoneal cavity.

The lesser sac (also known as theomental bursa) is smaller and lies posterior to the stomach and lesser
omentum.

Question 5

Describe the greater sac

Answer 5

Begins at the diaphragm superiorly, and continues to the pelvic cavity inferiorly

larger portion of the peritoneal cavity.

Further divided into two compartmentsby the transverse mesocolon (= mesentery of colon):

• Thesupracolic compartment
• Theinfracolic compartment

Question 6

Describe the supracolic compartment

Answer 6

compartmentlies above the transverse mesocolon between the diaphragm and
the transverse colon

Contains thestomach,liverandspleen.

Question 7

Describe the infracolic compartment

Answer 7

compartmentlies below the transverse mesocolon

▪ Contains thesmall intestine, ascending and
descendingcolon.
▪ Further divided intounequal left and right
infracolic spacesby the mesentery of the small
intestine

Question 8

What connects the supracolic and infracolic compartments of the greater sac?

Answer 8

connected by
theparacolic gutterswhich lie between the posterolateral
abdominal wall and the lateral aspect of the ascending or descending colon.

Question 9

What are Subphrenic (subdiaphragmatic) spaces?

Answer 9

Recesses in the greater sac between the liver and the diaphragm

Divided into left and right subphrenic spaces by the falciform ligament of the liver

Question 10

Describe the potential space of the Subphrenic (subdiaphragmatic) spaces

Answer 10

It’s a potential space that accommodates movement of the diaphragm
o Air accumulates here with perforated organs – visible as black spaces on x-ray
o Subphrenic abscesses during infection may arise due to accumulation of pus as a result of peritonitis
o Common on right side due to appendicitis
o Patients may experience referred pain in the shoulders with accumulation of blood/pus etc. as it stimulates C4 (diaphragm is innervated by C3,4,5)

Question 11

What is the Falciform ligament

Answer 11

o Fold of peritoneum that splits the subphrenic space into right and left subphrenic spaces
o Curved edge has a fibrous core called the ligamentum teres (round ligament of the liver)
▪ This is the location of the umbilical vein

NB: not a ligament but a fold of peritoneum

Question 12

Describe the Lesser Sac (Omental Bursa)

Answer 12

● Smaller subdivision of the peritoneal cavity
● Hollow space that is formed by the greater andlesser omentumand its adjacent organs
● Lies posterior to the stomach and lesser omentum.
● Allows the stomach to move freely against the structures posterior and inferior to it.

Question 13

What is the epiploic foramen,

Answer 13

situated posterior to the free edge of the lesser omentum.

Allows the greater and lesser sacs to communicate

Question 14

What structures surround the epiploic foramen?

Answer 14

o Anteriorly, there is the portal vein, the hepatic artery proper, and
the bile duct.
o Posteriorly, there is the inferior vena cava.
o Superiorly lies the caudate lobe of the liver
o Inferiorly lies the first part of the duodenum.

Question 15

Name the peritoneal folds within the peritoneal cavity

Answer 15

● Throughout the peritoneal cavity are numerous peritoneal folds that connect the organs with each other,
or to the abdominal wall.
● These folds are the omenta, the mesenteries and the peritoneal ligaments.

Question 16

What is the omentum?

Answer 16

double layered extensions or folds of peritoneum that pass from the stomach and proximal part of the duodenum to the adjacent organs in the abdominal cavity.
Consists of greater and lesser omentum

Question 17

What is the mesenteries?

Answer 17

double peritoneal layers formed as a result of invaginations created by organs.
o Connect the intraperitoneal organs with the body wall.

Question 18

What are the peritoneal ligaments?

Answer 18

consist of double layers of
peritoneum that connect an organ with another organ or to
the abdominal wall.
o Some of the folds contain vessels and nerves to
supply the viscera
o Others function to maintain the proper position of
the viscera in the abdominal cavity.

Question 19

Describe the greater omentum

Answer 19

● Consists of four layers of peritoneum
● Descends from greater curvature of stomach then folds back up and attaches to the surface of the
transverse colon
● Hangs loosely – functions as a “policeman” as it can stick onto regions of infection to prevent further
spread
● Also functions in plugging hernias

Question 20

Describe the lesser omentum

Answer 20

● Very small – attaches to the lesser curvature of the stomach and the liver
● Consists of two parts: the hepatogastric ligament and the hepatoduodenal ligament

Question 21

What is the oesophagus

Answer 21

Theoesophagusis a continuation of the pharynx at the level of C6

Question 22

Describe the descent of the oesophagus

Answer 22

Descends anterior to the vertebral column and posterior to the trachea, passing posterior to the aortic arch, and along the right side of the descending aorta.
Passes through the diaphragm at the level of T10 to end at the cardiac orifice of the stomach.

Question 23

What happens to the oesophagus during inhalation?

Answer 23

Held shut during inhalation by a sling of muscle, unlike the inferior vena cava
o This prevents gastric contents from entering the oesophagus with the increase in abdominal
pressure

Question 24

Describe the lining of the oesophagus

Answer 24

● Lamina propria (areolar connective tissue)
● muscularis mucosae (smooth muscle)
● Non-keratinised stratified squamous epithelium

Question 25

What is the benefit of squamous epithelial tissue?

Answer 25

associated with the lips, mouth, tongue, oropharynx, laryngopharynx, and the oesophagus, and allows protection from hot and cold temperatures, chemical attacks on the tissue, and abrasion from food particles.

Question 26

What are the two sphincters of the oesophagus?

Answer 26

- Upper Oesophageal Sphincter | - Lower Oesophageal Sphincter

Question 27

Describe the Upper Oesophageal Sphincter

Answer 27

● Comprised of striated muscle and is under constant voluntary control. ● Formed by a portion of the inferior constrictor muscle ● Opens to allow the food bolus to enter the oesophagus and closes to prevent the regurgitation of contents back into the pharynx.

Question 28

Describe the Lower Oesophageal Sphincter

Answer 28

● Formed by a portion of the diaphragm ● Constricts the oesophagus during respiration to prevent the contents of the stomach from regurgitating ● Mainly comprised of smooth muscle and is under involuntary control

Question 29

Describe the process of peristalsis

Answer 29

begins in the oesophagus and continues down tract ● Initially the circular fibres of the section of oesophagus superior to the bolus contract, narrowing the lumen and applying pressure to the bolus. ● The longitudinal fibres inferior to the bolus also contract, shortening this section and widening the lumen, allowing the bolus to move towards the stomach. ● These contractions travel in a wave along the oesophagus, propelling the food into the stomach.

Question 30

What are the 3 major functions of the stomach?

Answer 30

1. acts as a mixing compartment, breaking up food into chyme 2. Acts as a storage when food is eaten faster than digested 3. secretes gastric juice, which contains water, mucus, HCL, intrinsic factor and pepsinogen

Question 31

What are the regions of the stomach

Answer 31

- cardiac region - fundus - body - pyloric antrum - pyloric canal - pyloric sphincter - greater curvature - lesser curvature

Question 32

Describe the cardiac region of the stomach

Answer 32

Upper region of the stomach where the bolus from the oesophagus enters. Continuous with the oesophagus at the lower oesophageal sphincter.

Question 33

Describe the fundus of the stomach

Answer 33

Dome-shaped portion of the stomach that lies above its junction with the oesophagus.

Question 34

Describe the body of the stomach

Answer 34

The mid-portion of the stomach. | Bordered superiorly by the fundus and inferiorly by the pyloric antrum.

Question 35

Describe the pyloric antrum

Answer 35

A funnel-shaped section of the stomach. Lies between the body and pyloric canal.

Question 36

Describe the pyloric canal

Answer 36

A narrow section of the stomach. Lies between the pyloric antrum and pylorus. The pyloric antrum narrows toward the right to become the pyloric canal, surrounded by the pyloric sphincter, which joins the duodenum at the L1 level (transpyloric plane) to the right of the midline.

Question 37

Describe the | Pyloric sphincter

Answer 37

Strong ring of smooth muscle at the end of the pyloric canal | Controls the passage of food from the stomach to the duodenum.

Question 38

Describe the pylorus

Answer 38

The pylorus is a constriction separating the pyloric canal from the first part of the duodenum. Guarded by the pyloric sphincter.

Question 39

Describe the greater curvature

Answer 39

Extends from the oesophagus to the duodenum on the lateral border of the stomach. Provides attachment to the greater omentum, which drapes inferiorly from it.

Question 40

Describe the lesser curvature

Answer 40

Extends from the oesophagus to the duodenum on the medial border of the stomach and provides attachment to the lesser omentum.

Question 41

What is the cardiac notch

Answer 41

the acute angle between the left border of the abdominal oesophagus and the fundus of the stomach o acts as a valve to prevent reflux o During peristalsis muscles tug to make the angle sharper in order to prevent reflux o The angle is created by the collar sling fibres and the circular muscles around this (gastroesophageal) junction

Question 42

What is the angular notch?

Answer 42

small anatomical notch on the stomach located on the lesser curvature of the stomach near the pyloric end. o Its location varies somewhat with the state of distension of the internal organs o Used as a separation point between the right and left portions of the stomach. o An imaginary line drawn perpendicular to the lesser curvature of the stomach through the angular incisure makes up the boundary between the body of the stomach and pylorus.

Question 43

What is the transpyloric plane?

Answer 43

● Also known as Addison's Plane ● Upper transverse line, located halfway between the jugular notch and the upper border of the pubic symphysis ● It is also said to lie roughly a hand's breadth beneath the xiphoid process of the human sternum ● Normally cuts through the pylorus of the stomach, the tips of the ninth costal cartilages and the lower border of the first lumbar vertebra

Question 44

What are the layers of the stomach wall?

Answer 44

- serosa - muscularis - submucosa - mucosa

Question 45

Describe the mucosa of the stomach

Answer 45

the deepest layer of the stomach wall and consists of three layers; the epithelium, lamina propria, and muscularis mucosae.

Question 46

Describe the stomach epithelium

Answer 46

consists of a simple columnar secretory epithelium that secretes mucin, which when combined with water, produces mucus. The internal surface of the stomach is folded to form millions of gastric pits.

Question 47

Describe the lamina propria

Answer 47

Loose connective tissue that lies between the epithelium and the muscularis mucosae. Rich in capillaries, lymphatic vessels, and nerves and gastric glands.

Question 48

Describe the muscularis mucosae

Answer 48

Thin layer of smooth muscle that lies between the lamina propria and the submucosa. When it contracts, it compresses the gastric glands and helps to push out their contents into the lumen of the stomach.

Question 49

Describe the submucosa

Answer 49

Consists of connective tissue and a vascular plexus that supplies the mucosa. Allows the mucosa to move freely over the deeper structures.

Question 50

Describe the muscularis

Answer 50

In continuation with the oesophagus, there are three layers of smooth muscle fibres: oblique, circular, and longitudinal. They contract rhythmically to break up food in the stomach. Oblique muscular layer The deepest layer, the oblique muscular layer covers the cardiac region of the stomach and then sweeps along the lesser curvature. Circular muscular layer The middle layer, the fibres of the circular muscular layer encircle the stomach.  Longitudinal muscular layer The outer layer, the fibres of the longitudinal muscular layer run longitudinally. 

Question 51

Describe the serosa

Answer 51

The outer surface of the stomach is covered in a layer of peritoneum. It is continuous superiorly with the lesser omentum and inferiorly with the greater omentum.

Question 52

What cells line the gastric pits?

Answer 52

parietal cells, chief cells, and neck mucous cells.

Question 53

Describe the surface mucous cells

Answer 53

Columnar epithelial cells, surface mucous cells cover the entire internal surface of the stomach, extending down into the necks of the gastric pits.  Replaced every 3 to 6 days by the division of stem cells located in the walls of the gastric pits. Old damaged cells are sloughed into the stomach and digested.

Question 54

What is the function of the surface mucous cells?

Answer 54

Secrete a thick alkaline mucin which produces mucus when combined with water. This protects the underlying mucosa from self-abrasion by the acidity of the stomach.

Question 55

Describe the mucous neck cells

Answer 55

Low columnar epithelial cells, mucous neck cells are located in the neck region of the gastric glands. Contain mucin-bound vesicles towards their apex.

Question 56

What are the function of the mucous neck cells?

Answer 56

Secrete a soluble mucus in the active stomach.

Question 57

Describe the parietal (oxyntic) cells

Answer 57

Large oval epithelial cells. Located towards the apical half of the gastric glands, interspersed among the neck mucous cells.  They possess invaginations of the lumen that form thin channels called canaliculi, which have irregular microvilli edges, vastly increasing the cell's surface area. The canaliculi contain H+/K+ ATPase antiporters.  Their exact structures change depending on which phase they are in, and on stimulation, they increase the amount of microvilli by up to five times.

Question 58

Describe the function of the parietal cells

Answer 58

Secrete hydrochloric acid and an intrinsic factor.

Question 59

What are the chief cells?

Answer 59

Cuboidal epithelial cells. Located in the base of the gastric glands Found in the body of the stomach. They contain rounded nuclei and their cytoplasm is abundant with RNA.

Question 60

What is the function of the chief cells?

Answer 60

They secrete pepsinogen, which is converted into pepsin by hydrochloric acid, as well as gastric lipase, and rennin in infants.

Question 61

What are G cells?

Answer 61

Large, round enteroendocrine cells. G cells are often located amid chief cells, at the base of the gastric glands. They are most frequent in the fundus and body of the stomach, and can also be found in the duodenum.  They contain irregular nuclei surrounded by secretory granules.

Question 62

What is the function of G cells?

Answer 62

Secrete gastrin, which stimulates the parietal and chief cells to produce hydrochloric acid and pepsinogen. G cells also increase the motility of the stomach, and relax the pyloric sphincter.

Question 63

What are stem cells?

Answer 63

Low columnar epithelial cells, stem cells are located in the neck region of the gastric glands.  They have short microvilli on their apical surfaces.

Question 64

What is the function of stem cells

Answer 64

Give rise to all cell types found in the gastric mucosa; traveling upwards to replace surface mucous cells, and downwards to replace parietal, chief, and G cells.

Question 65

Describe the role of the stomach in mechanical digestion?

Answer 65

After a bolus of food is swallowed, it leaves the oesophagus and enters the stomach through the lower oesophageal sphincter.  Several minutes later, peristaltic movements called mixing waves help break down the bolus mechanically before it mixes with gastric juice and becomes a soupy liquid, called chyme. The lower oesophageal sphincter prevents the bolus from passing back into the oesophagus. The peristaltic movements rely on 3 layers of smooth muscle that alternately contract and relax: a longitudinal layer, a circular layer, and an oblique layer.  The contractions vary in intensity, beginning as gentle rippling movements near the cardia and fundus, and becoming more powerful as they progress through the body of the stomach, towards the pylorus the region of the stomach that connects to the duodenum, or small intestine.  The frequency of the peristaltic contractions is constant, always about 3 per minute.

Question 66

Describe gastric emptying

Answer 66

pyloric sphincter controls movement of chyme from pyloric antrum and pyloric canal into the duodenum. Peristaltic contractions squeeze out small volumes of chyme (~3 mL) into duodenum (gastric emptying) remaining chyme in pyloric region (about 27 mL) is forced back into the body of the stomach by retropulsion. mixing continues, forming chyme that can be processed by intestinal enzymes. rate of gastric emptying is normally ~2 -4 hrs, depends on content: Carbohydrates -rapidly, fats - slowly proteins -intermediate rate.

Question 67

What is a hiatus hernia?

Answer 67

hernia occurs when a part of the stomach protrudes into the chest through the oesophageal hiatus in the diaphragm. Two main types: o Sliding hiatus hernia (C) – The lower oesophageal sphincter slides superiorly. Reflux is a common complication, as the diaphragm is no longer reinforcing the sphincter. o Rolling Hiatus Hernia (D) – The lower oesophageal sphincter remains in place, but a part of the stomach herniates into the chest next to it.