Gastrointestinal Anatomy Flashcards
Mouth boundaries
From lips to palatoglossal arches, cheeks form walls
Floor is mylohyoid muscle
Oral cavity is teeth to oropharynx
Vestibule is between teeth and lips
Teeth
Made of dentine (pulp cavity containing nerves and vessels)
Crown covered in enamel
Anchored in sockets by periodontal ligament
Teeth and gums (gingivae) - superior and inferior alveolar nerves and vessels - from maxillary division at top, mandibular at bottom
Numbers of teeth per quadrant
Decididuous (milk) - 2 incisors, 1 canine, no premolar, 2 molar
Adult - 2 incisors, 1 canine, 2 premolar, 3 molar
Tongue
Made of muscles - intrinsic change shape, extrinsic move tongue
Root is anchored to mandible and hyoid bone
Stratified keratinised squamous epithelia
Covered in papillae - taste buds
Vallate papillae divide body from root of tongue
Nerve supply to tongue
All motor - hypoglossal nerve
Posterior 1/3 - sensation and taste from glossopharyngeal
Anterior 2/3 - sensation - mandibular, taste - facial
Looking into mouth
Palatoglossal arch in front
Then palatine tonsils
Palatopharyngeal arch
Muscles of mastication
Temporalis and massete - superficial
Medial and lateral pterygoid - deep
- supplied by mandibular branch of trigeminal
Deglutition
= swallowing
1) VOLUNTARY
- bolus to dorsum of tongue
- up against hard palate as mylohyoid contracts
- bolus to pharynx
- styloglossi and palatoglossi raise posterior part of tongue
2) INVOLUNTARY
- soft palate elevates, sealing off nasopharynx
- long pharyngeal muscles pull larynx upwards
- laryngeal orifice closed by aryepiglottic and oblique arytenoids
- pharyngeal constrictors constrict in sequence
- cricopharyngeus relaxes
3) INVOLUNTARY
- wave of peristalsis moves bolus down oesophagus
Palate
Hard palate - palatal processes of maxillae and horizontal plates of palatine bones
Soft palate - 5 muscles - tensor and levator veli palatine, palatoglossus, palatopharyngeus, uvular
Maxillary artery supplies
Sensory - maxillary division of trigeminal
Motor - mainly from pharyngeal plexus
Muscles of pharynx
External - constrictors
Internal - palatopharyngeus, salpingopharyngeus (by opening of eustachian tube in nasal cavity), stylopharyngeus (from back of ear)
Suprahyoid muscles
Geniohyoid - to chin
Mylohyoid - under tongue, floor of mouth
Digastric - mentum to hyoid to mastoid process
Stylohyoid - to bottom of chin
Infrahyoid muscles
Sternohyoid - to sternum
Omohyoid - to scapula
Thyrohyoid
Sternothyroid
Parotid salivary gland
Duct pierces buccinator (cheek), enters oral cavity opposite 2nd maxillary molar tooth
Glossopharyngeal nerve innervates
Running through - facial nerve, external carotid, superficial temporal and maxillary artery, retromandibular vein
Submandibular salivary gland
Duct opens adjacent to lingual frenulum under tongue
Facial nerve innervates
Sublingual salivary gland
Numerous small ducts open into floor of mouth along sublingual folds
Facial nerve innervates
Oesophagus
Starts at C6 (cricoid cartilage level), 25cm long
Mucosa stratified squamous epithelium
No serosal layer
Outer longitudinal and inner circular fibres
Four main constrictions of oesophagus
1) At C5, cricopharyngeal sphincter
2) At aortic arch
3) At left main bronchus
4) Cardiac sphincter, gastro-oesophageal junction
Arterial supply of oesophagus (and lymph)
Upper third - inferior thyroid artery
Middle - branch of thoracic aorta
Bottom third - left gastric artery
Lymph drains to posterior mediastinal nodes, left gastric nodes
Stomach
Longitudinal, oblique and circular muscle fibres
Columnar epithelium
Intraperitoneal
Nervous supply to stomach
Intrinsic - enteric NS - coordinates contractions and secretions
Extrinsic - autonomic - modify activity (parasymp increases)
Parasympathetic - anterior and posterior vagal trunks
Sympathetic - sympathetic trunks via coeliac plexus
Blood and lymph supply to stomach
Veins drain to portal system
Lymph to coeliac nodes
Splenic artery behind stomach to spleen
Gastroepiploic arteries run below to stomach and spleen
Lesser omentum
Two layers of peritoneum extending between liver and lesser curvature of stomach
Lesser sac
Between lesser and greater omentum
Subsection of peritoneal cavity, posterior to lesser omentum and stomach, anterior to retroperitoneal organs of posterior abdominal wall
Greater omentum
Two layers of peritoneum laying together -> 4 layers
Between greater curvature of stomach and transverse colon
Hangs like apron over intestines
Contains adipose tissue
Omental foramen is communication between lesser and greater omentum
Endoscopy
OGD = oesophagogastroduodenoscopy
- lie on left side, swallow tube
TOE = transoesophageal echocardiography
- ultrasound probe through oesophagus to view heart
Indicated after upper GI bleed, foreign body, gastric cancer, GORD
Oesophagus histology
Stratified squamous epithelia, to protect from acid reflux
Peristalsis mediated by muscularis externa
Submucosal glands, especially in lower oesophagus
Epithelia Lamina propria - not much, mainly gastric glands Muscularis mucosa Submucosa Circular muscle Longitudinal muscle (NO Serosa)
Gastro-oesophageal sphincter
LES has no marked thickening of circular muscle, so physiological NOT anatomical sphincter
Stomach cell types
PARIETAL - dominant cell type, large cells with bright pink cytoplasm and central dark nucleus
CHIEF - light grey cytoplasm, nucleus at base of cell, abundant in gastric glands
ENDOCRINE - light grey cytoplasm (look very similar to chief), but less abundant
MUCOUS NECK - empty spaces in surface epithelium, found at bottom of gastric pits and scattered
SURFACE EPITHELIAL - dominant type lining gastric pits, columnar epithelial, nucleus at base
Histology of duodenum
Abundant tall villi separated by crypts
Brunner’s glands (submucosal)
Paneth cells found here in crypts - prominent apical eosinophilic granules, for host defence as secrete anti-microbial factors
Ileum histology
Abundant smaller villi separated by crypts
Peyer’s patches (lymph) pack mucosa, covered by flattened epithelium with less obvious villi
Large intestine histology
No villi, just crypts
Mucosa has crypts filled with mucus-secreting goblet cells
Loose connective tissue forms submucosa
Crypts of Lieberkuhn - crypts packed with mucus-secreting goblet cells, for salt and water secretion
Duodenum
In epigastric region
1st part at L1, intraperitoneal
Rest is retroperitoneal as forms C shape around pancreas
Simple columnar epithelium with villi and circular folds (pilicae circulares)
Secretion stimulated by secretin - local hormone, and vagus nerve
Dual blood supply and lymph drainage - 1st 1/3rd is foregut (coeliac), then midgut (superior mesenteric). Major duodenal papilla marks change
Pancreas
In epigastric region
Retroperitoneal, but tip of tail intraperitoneal
Duct opens at major duodenal papilla
Endo and exocrine gland
Secretion stimulated by cholecystokinin and vagus nerve
Blood supply to pancreas
Splenic artery runs along top of body
Superior and inferior pancreaticoduodenal arteries run around head
Corresponding veins drain to portal system - splenic vein biggest, posterior
Spleen
Red and white pulp
For removal of old RBCs from blood, largest lymphoid organ
Sits under 9th-11th ribs on left - left hypochondriac region
Intraperitoneal
Splenic artery and vein supply
Superior/anterior - stomach
Inferior - left colic flexure, left kidney
DELICATE and vulnerable to injury - if rupture by blunt trauma, significant bleeding, left flank pain
Foregut surface anatomy
Liver - deep to ribs 5-11 on right, crosses midline
Gallbladder - behind tip of 9th costal margin
Pancreas - neck overlies L1-2, body and tail left and superior
Spleen - 9-11th ribs on left (only palpable at 3x normal size)
Referred pain by region
Foregut -> epigastric
Midgut -> umbilical
Hindgut -> hypogastric
Retroperitoneal refer to back
Liver
Largest gland in body - 1.5kg in adult
Right hypochondriac region, extending to epigastric
Intraperitoneal, covered in visceral peritoneum apart from bare area where joins to diaphragm
Right, left, caudate (top) and quadrate (bottom) lobes
Falciform ligament across front, attaches to abdominal wall at front and diaphragm above
Lymph to coeliac nodes
Porta
In porta hepatis, fissure
Carries hepatic portal vein (80% blood to liver), L + R hepatic arteries, bile duct
Hepatic portal vein - SMV (midgut), IMV (hindgut) and splenic vein (foregut) all feed in
Functions of liver
METABOLIC - fats, proteins, carbs
PRODUCTION - bile, plasma proteins, albumin, clotting factors, urea
STORAGE - glycogen, vitamins, minerals
IMMUNITY - produce immune factors and remove bacteria
HOMEOSTASIS - regulates glycogen release in response to glucagon or insulin from pancreas, produces heat for body temperature control
Embryological remnants in liver
Ligamentum teres (round at bottom of falciform) - old umbilical vein Ligamentum venosum (between left and caudate lobes) - old ductus venosus, shunt
Gallbladder
In right hypochondriac region
Intraperitoneal
Arterial supply from branch of right hepatic artery
To store and concentrate bile made by liver
Secretion stimulated by cholecystokinin, into duodenum
Biliary tree
Left and right hepatic ducts
Common hepatic duct
+ cystic duct from gall bladder
-> common bile duct
Gallstones
Form from bile pigments, cholesterol crystals so don’t show up on X rays
If dislodge -> pain and jaundice
Cholecystitis = acute inflammation
Biliary colic = cystic duct blocked, pain but no jaundice
Laporascopic cholescystectomy
= Lap chole
Scope in port superior to umbilicus
Inflate abdominal cavity with CO₂ to create space
Insert other ports
Isolate cystic duct and cystic artery
Make small cut, insert contrast, choleangiogram
Cut and clip cystic duct and artery
Cut through fat and fascia attached to posterior wall to liver
Insert bag, put gallbladder in
Saline solution into cavity to ensure no bleeding
Arcuate line
Half way between umbilicus and pubic symphysis
No posterior rectus sheath below
Inguinal canal
From ASIS to pubic tubercle
Anterior - skin, superficial fascia, external oblique aponeurosis
Posterior - medial - conjoint tendon (where transverse abdominus and internal oblique fuse at pubic tubercle)
- lateral - transversalis fascia
Roof - lower edge of internal oblique and transverse abdominus
Floor - inguinal ligament
Inguinal ring
Deep - opening in transversalis fascia lateral to lateral to pubic tubercle
Superficial - above and lateral to pubic tubercle
Contains spermatic cord and inferior epigastric vessels to testes in men
Or round ligament of uterus to anchor to abdominal wall in women
Below midinguinal ligament - femoral nerve
Below midinguinal point - femoral artery
Acute appendicitis
Interpreted as midgut pain as refers to umbilical region initially - as inflammation just in viceral peritoneum and appendix wall
As develops, pain localises to right iliac fossa
McBurney incision to remove
Hernias
The protrusion of tissue or an organ from the confines of its normal cavity to outside of that cavity
Inguinal hernia - above inguinal ligament
Femoral hernia - below inguinal ligament to exit abdominal cavity
Blood and lymph to small intestines
Blood supply from jejunal and ileal branches of superior mesenteric artery
Corresponding veins drain to portal system
Lymph drains along arteries to superior mesenteric lymph nodes
Features of jejunum
Larger, densely packed circular folds, larger villi
Deep red
Thicker mucosal wall
Few Peyer’s patches (lymphoid tissue)
More vascular - longer vasa recta, less arcades
Less fat in mesentery
Upper left quadrant, umbilical region
Intraperitoneal
Mesentery attaches to left of aorta to posterior abdominal wall
Features of ileum
Smaller, fewer, sparser circular folds Pale pink Thinner mucosal wall Many Peyer's patches (lymphoid tissue) Less vascular - shorter vasa recta, more arcades More fat in mesentery Lower right quadrant, hypogastric region Intraperitoneal Mesentery attaches to right of aorta to posterior abdominal wall
- terminal ileum is site for absorption of vitamin B12 with intrinsic factor from stomach
Location of branching of aorta
Passes into abdomen at T12 Coeliac trunk arises at L1 (high) SMA arises at L1 (low) Renal arteries arise at L2 IMA arises at L3 Bifurcation to form common iliac arteries at L4
Structure and function of large intestine
Principle function to absorb water
Venous drainage via SMV and IMV to portal vein
Ileocaecal valve prevents reflux from caecum to ileum
Ascending and descending colon - retroperitoneal
Transverse and sigmoid colon - intraperitoneal
Taeni coli
Thickened bands of muscle in large intestine, don’t go complete width of colon
Gives sacculated appearance
Free taeni coli - ascending colon
Omental taeni coli - transverse colon
Mesocolic taeni coli - descending colon
Rectum
Dilatable holding area in pelvis, above levator ani
Upper part - superior rectal artery from IMA, lymph to inferior mesenteric nodes
Lower part - middle rectal artery from internal iliac, lumph to internal iliac nodes
Anal canal is 4cm long tube, from anorectal ring to anus
Upper anal canal
Above pectinate line Derived from endoderm Simple columnar epithelium Stretch sensors - inferior hypogastric plexuses Superior rectal artery from IMA supplies Superior rectal vein to IMV drains Lymph to internal iliac nodes
Lower anal canal
Below pectinate line
Derived from ectoderm
Stratified squamous epithelium
Pain, temperature, pressure receptors - inferior rectal nerve
Inferior rectal artery supplies
Inferior rectal vein drains
Lymph to superficial inguinal group nodes
Anal pathology
Weakness in levator ani muscles -> incontinence or prolapse of rectum (and uterus in women)
Infection may seed next to anal canal at ischioanal fossa -> abscess formation
Potential portosystemic anastamoses site as dual system of blood drainage
