The Digestive System L1 Flashcards
Main functions of the digestive system
- continuous supply of water
-electrolytes , vitamins , and nutrients
-remove the toxic residues
Oral Cavity is divided into 3 sections
- oral orifice- anterior opening of the oral cavity
- oral vestibule - space between the teeth and the lips
- oral cavity proper - the area of tongue and teeth
the roof is made by hard palate with soft palate attached to its posterior margin
- it acts as a flutter valve that can :
- swing up (elevate) to close pharyngeal isthmus , and seal off the nasopharynx from the oropharynx
- swing down ( depress) to close the oropharyngeal isthmus and seal off the oral cavity from the oropharynx
Tongue
- it is a mass of skeletal muscle covered in mucous membrane
- innervated by hypoglossal nerve
-main function - articulation , directing food into the oropharynx during deglutition
taste - papillae are mucosal elevations - fungiform , foliate and vallate papillae - taste buds
filiform papillae - do not have taste buds
Terminal sulcus divides tongue into - Anterior 2/3 - Facial nerve and Trigeminal nerve
- Posterior 1/3- by Glossopharyngeal nerve
- Hypoglossal nerve is the main motor nerve
Salivary glands types
Parotid gland – largest and main salivary gland.
* Located near the ear.
* Parotid duct opens in cheek opposite upper Molar
* Innervated by Glossopharyngeal nerve
Submandibular gland -
*Located at lower border of mandible
Sublingual gland – smallest and deepest gland
* Located in the floor of the mouth.
* Innervated by Facial Nerve
* Ducts open in the floor of the mouth.
Pharynx
Musculofascial half-cylinder that links oral and
nasal cavities to the larynx and esophagus.
The pharyngeal cavity is a common pathway for air and food.
Attached to base of the skull and at vertebra C 6 level, continues as esophagus
Based on anterior relationships the pharynx is subdivided into three regions
* Nasopharynx: anteriorly attached to nasal cavities through Choanae (posterior
apertures)
* Oropharynx: anteriorly opens into oral cavity (oropharyngeal isthmus)
* Laryngopharynx: anteriorly attached to larynx through superior aperture of larynx
(laryngeal inlet)
The 3 parts of the gut
- Foregut: starts at the abdominal oesophagus
end below the major duodenal papilla in duodenum. - Midgut: begins below major duodenal papilla
ends at the junction between the proximal 2/3 and
distal 1/3 of the transverse colon. - Hindgut: begins before the colic flexure
ends midway through the anal canal.
Organisation of gastrointestinal tract
Tissue layers
*Mucosa - Epithelium
Lamina propria
Muscularis mucosa
*Submucosa
*Muscularis Externa -
Circular layer
Longitudinal layer
*Serosa
Tissue layers
- Epithelium: Simple columnar epithelium with special characteristics
- Sub mucosa: connective tissue, arteries, veins, lymphatics and nerves
- Muscularis Externa: Smooth muscles
- Serosa: connective tissue, peritoneum in most parts
The Enteric Nervous System is arranged in two nerve plexus
- Myenteric nerve plexus (myenteric= “intestinal muscle”)
Located in the muscularis externa layer –
between inner circular layer and outer longitudinal layer.
It controls the processes of peristalsis and segmentation.
*Submucosal nerve plexus
Located within the submucosa.
It stimulates the glands in the mucosal layer to secrete mucous and
muscularis mucosa to contract rhythmically.
Peritoneum and Mesentery
A thin membrane that
* lines the walls of the abdominal cavity - Parietal peritoneum
* covers the viscera - Visceral peritoneum.
Peritoneal cavity is the space between the parietal and visceral layers
* Greater sac: main space bounded by Diaphragm superiorly and continuing
inferiorly into the pelvic cavity.
* Lesser sac (omental bursa) is a smaller subdivision of the peritoneal cavity
posterior to stomach and liver and is continuous with the greater sac through
omental (epiploic) foramen.
- Abdominal viscera are suspended in the peritoneal cavity by folds of peritoneum
( mesenteries )
Oesophagus
Muscular tube connecting pharynx and stomach
- Begins: inferior border of the cricoid cartilage opposite C6 vertebra
- Ends: the cardiac opening of the stomach opposite T 10 vertebra
after passing through Esophageal hiatus of diaphragm
- Mucosa: Stratified Squamous epithelium
Submucosa - Muscularis: skeletal muscles in Upper 1/3rd
lower 1/3rd has smooth muscles
-Serosa
the oesophagus part 2
Located in superior and then posterior mediastinum
- Anteriorly: left Atrium, left Bronchus, right Pulmonary artery
- Posteriorly: Thoracic duct, Hemi-Azygous vein and Aorta
- Arterial supply:
- Thorax- branches of thoracic Aorta and Bronchial arteries
- Abdomen- Ascending branches of the Left gastric artery
- Venous drainage:
- Azygos vein, and Hemiazygos vein
- Esophageal branches to the -Left gastric vein
- Lymphatic drainage:
- Posterior mediastinal and Left gastric nodes.
Oesophagus part 3 - oesophageal plexus
Esophageal plexus
Right and Left Vagus nerves
Just above the diaphragm, fibers converge to form
▪ Anterior vagal trunk
▪ Posterior vagal trunk
Efferent
*Upper - brachial branches (superior laryngeal) of Vagus nerve
*Lower - pre-ganglionic parasympathetic fibers that synapse in myenteric plexus
Afferent
*Pain- Greater Splanchnic nerves and
Periarterial plexuses around left gastric & inferior phrenic arteries.
*Function- Vagus nerve
Sympathetic stimulation and Parasympathetic stimulation
Sympathetic stimulation reduces peristaltic and secretory
activity of the intestine and causes vasoconstriction, reducing or
stopping gastrointestinal activity (fight and flight)
from T8 or T9 through T10 or T11 segments of the spinal cord and
reach the celiac plexus through the sympathetic trunks and greater
and lesser (abdominopelvic) splanchnic nerves.
Parasympathetic stimulation
increases peristalsis and secretion
activity of the intestine, restoring gastrointestinal activity (rest and
digest)
Stomach
It is the most dilated part of the gastrointestinal tract and has J-like shape
Positioned between the abdominal oesophagus and the small intestine.
Four parts/regions
* Cardia- surrounds the opening of the oesophagus into the stomach
* Fundus- the area above the level of the cardial orifice
* Body- the largest region of the stomach
* Pyloric part- which is divided into pyloric antrum and pyloric canal
* Pylorus most distal part- marked on surface by pyloric
constriction and contains a thickened ring of gastric circular muscle
pyloric sphincter
Corresponds with the lower border of vertebra L1 (transpyloric plane)
The Stomach part 2
*Greater curvature is a point of attachment for the gastrosplenic ligament and the
greater omentum
*Lesser curvature is a point of attachment for the lesser omentum;
*Cardial notch is the superior angle created when the esophagus enters the
stomach
*Angular incisure is a bend on the lesser curvature.
Wall structure
Mucosa:
Submucosa
Muscularis: Oblique, Circular and Longitudinal
Serosa
Small intestine
The small intestine is approximately 6 to 7 m long
* Extends from pyloric orifice of the stomach to ileocecal fold.
* Duodenum, jejunum and ileum.
Duodenum
First part of the small intestine- Located above the level of the umbilicus
C-shaped structure, adjacent to the head of the pancreas
- Superior: from the pyloric orifice of stomach to neck of the gallbladder,
Known as Duodenal cap and most duodenal ulcers occur in this part of the duodenum. - Descending: is just to right of midline and extends to lower border of vertebra LIII.
- Major duodenal papilla, common entrance for the bile and pancreatic ducts
- Minor duodenal papilla, entrance for the accessory pancreatic duct.
- Inferior: is the longest, crossing the inferior vena cava, aorta, and vertebral column.
- Ascending: passes upward to left and terminates at the duodenojejunal flexure.
Jejunum
Proximal two-fifths.
Located in the left upper quadrant of the abdomen.
* larger in diameter and has a thicker wall than the ileum.
* Mucosal lining of the jejunum is characterized by numerous
prominent folds that circle the lumen (plicae circulares).
* The less prominent arterial arcades and longer vasa recta
(straight arteries)
Ileum
It makes up the distal three-fifths of the small intestine
Located in the right lower quadrant.
* Compared to the jejunum, the ileum has thinner walls, fewer and less prominent
mucosal folds (plicae circulares).
* Shorter vasa recta, more mesenteric fat, and more arterial arcades
It opens at junction of cecum and ascending colon
Ileocecal fold, mucosal folds that surround the opening.
Acting as Sphincter, preventing reflux from cecum to the ileum.
Large Intestine
It extends from the distal end of the ileum to the anus
approximately 1.5 m
Consists of the Cecum, Appendix, Colon, Rectum, and Anal canal
It absorbs fluids and salts from the gut contents, thus forming faeces.
Features
* Taeniae Coli: arrangement longitudinal muscle in its walls into three narrow bands
* Haustra: Sacculations
* Omental Appendices: peritoneal-covered accumulations of fat
Caecum and Appendix
Caecum is the first part of the large intestine.
- It is inferior to the ileocecal opening and in the right iliac fossa
- It is continuous with the ascending colon at the entrance of the ileum
Appendix
- is a narrow, hollow, blind-ended tube connected to cecum.
- It has large aggregations of lymphoid tissue in its walls.
- It is suspended from the terminal ileum by the mesoappendix
Colon
Caecum continues upward as the Ascending colon through right flank.
In right hypochondrium Just below the liver, it bends, right Colic flexure (Hepatic
flexure )
Crosses the abdomen as the Transverse colon to the left hypochondrium
Below spleen, it bends downwards forming the left Colic Flexure (Splenic flexure )
Continues as the Descending colon through the left flank and into left groin.
It enters in pelvic cavity as the Sigmoid colon
Continues on the posterior wall of the pelvic cavity as the Rectum
and terminates as the Anal canal
Rectum / Anal Canal
Tubular structure but no Taenia, Haustrae, Appendices
Two Flexures(bends) ,Three constant transvers folds (Houston valves)
* Anal Canal: Stratified squamous epithelium
-Skeletal muscles makes external anal sphincter
Blood supply:
Superior Rectal arteries – Inferior mesenteric artery
Middle and Inferior Rectal arteries – Internal Iliac artery
Venous drainage:
Superior Rectal veins -Inferior Mesenteric vein (Portal circulation)
Middle and Inferior Rectal veins- Internal Iliac (systemic circulation)
Liver
Located primarily in the right upper quadrant just under the
right dome of diaphragm
extending into the left upper quadrant
* Diaphragmatic surface: Falciform ligament separates into right and left lobes
* Visceral surface: Stomach, Esophagus, IVC, Colon, Kidney
* Right lobe
* Left lobe
* Quadrate lobe
* Caudate lobe
Porta Hepatis- Portal vein, Hepatic artery and Bile duct
Liver lobule
Liver Lobule: cords of Hepatocytes arranged in octagonal
lobules with hepatic vein in center and bile duct, branch
of portal vein and hepatic artery at corners.
Billary tree
Right and Left Hepatic duct joins to form Common Bile duct
Cystic duct from Gall bladder opens into CBD
Gallbladder is a pear-shaped sac lying tucked under the
right lobe of the liver.
It stores and concentrates bile
* Rounded end is called Fundus
* main Body
* a narrow Neck
Common Bile duct + Main Pancreatic duct open in
duodenum at major duodenal papilla
Pancreas
The pancreas lies mostly posterior to the stomach
It extends across the posterior abdominal wall from duodenum, on right,
to spleen, on the left.
Head: lies within the C-shaped concavity of the duodenum.
Projecting from the lower part of the head is the uncinate process
Neck Portal vein forms Posterior to the neck of the pancreas
Body extends from the neck to the tail
Tail passes between layers of the splenorenal ligament to hilum of Spleen
Endocrine: islets of Langerhans- Glucagon, Insulin, Somatostatin, Polypeptide
Exocrine: digestive enzymes- Amylase(carbohydrates), Lipase(fats)
trypsin(proteins)
