GI system Flashcards
What is the masseter muscle and what is it supplied by?
Muscles that power the teeth in mastication. Supplied by a branch of the trigeminal nerve
Where does the oropharynx lie
Between nasopharyns and laryngopharynx
uvula to hyoid bone
What are the functions of saliva?
Lubrication of food
Initiation of carbohydrate digestion
Protection of oral environment
What are the components of saliva?
Water, electrolytes, alkali, bacteriostats, enzymes, mucus
How does the concentration of electrolytes and HCO3- in saliva compare to plasma?
Higher K+, I-, Ca2+ and HCO3-
Lower Na+ and Cl-
Which salivary glands secrete a mixture of serous and mucous saliva?
Submaxillary
Parotid are just serous
What effect does a high flow rate have on serous saliva composition?
Decreases time available for ductal modification so saliva is less hypotonic but it also increases HCO3- secretion so saliva is more alkaline
How does Na-K-ATPase control saliva composition?
NKA decreased internal sodium conc so sodium passively diffuses into duct cell from lumen. NKA also increases internal potassium conc. so there’s increased action of K+Cl- symporter so there’s decreased Cl- conc internally. This increases action of Cl-/HCO3- antiporter, bringing Cl- into the cell and bicarbonate out into lumen
What parasympathetic nerves are the parotid glands innervated by?
Otic ganglion glossopharyngeal nerve (9th cranial)
What parasympathetic nerves are the submandibular and sublingual salivary glands innervated by?
Facial nerve (7th cranial) Submandibular ganglion
Which muscarinic receptors are found in salivary glands?
M1
What sympathetic nerve supplied salivary glands?
Superior cervical ganglion
What movements are triggered in the pharyngeal phase of swallowing?
Inhibition of breathing
closure of glottis
Opening of upper oesophageal sphincter
Raising of larynx
What normally helps prevent reflux of stomach contents?
Lower oesophageal sphincter
angle of His
Crus of diaphragm
What does craniocaudal folding of embryo achieve in terms of gut development?
Creates cranial and caudal pockets from the yolk sac
What embryonic layers do the linings of the primitive gut derive from?
Internal linings derive from endoderm
External linings derive from splanchnic mesoderm. Develop into musculature and visceral peritoneum
What structures are part of the foregut?
Oesophagus
Stomach
Gall bladder, liver, pancreas
Duodenum proximal to ampulla of vater
What main artery supplies the foregut?
Coeliac trunk
Describe the blood supply to the pancreas head
From coeliac trunk via superior pancreaticoduodenal artery and from superior mesenteric artery via inferior pancreaticoduodenal artery
What structures are part of the midgut?
Duodenum distal to ampulla of Vater Jejunum Ileum Caecum Ascending colon Proximal 2/3rds of transverse colon
What structures are contained within the hindgut?
Distal third of the transverse colon Descending colon Sigmoid colon Rectum Upper anal canal Internal lining of bladder and urethra
What does the diaphragm do to the intraembryonic coelom?
Divides it into thoracic and abdominal cavities
What is the purpose of the mesentery that suspends the primitive gut from the abdominal wall?
Allows conduit for nerve and blood supply
Allows mobility when needed
How is the mesentery suspending primitive gut formed?
By condensation of double layer of splanchnic mesoderm
Where along the primitive gut tube is there ventral mesentery?
Only along the foregut
What are the origins of the greater and lesser omentum?
Greater omentum comes from dorsal mesentery
Lesser omentum comes from ventral omentum
What’s the significance of the free edge of the ventral mesentery?
Conducts portal triad in life and gives access to the lesser sac
Where does the greater sac originate from?
The left hand side division formed by dorsal and ventral mesenteries
What directions does the stomach rotate in?
Longitudinal 90degrees around it’s axis
Anteroposteriorly
What does rotation of the stomach achieve?
Pulls dorsal mesentery laterall, creating the lesser sac behind the stomach
Puts vagus nerves anterior and posterior to the stomach
Forms the greater omentum
Shifts the cardia and pylorus from the midline
Pulls developing liver to the right
How is development of GI and respiratory tract related?
Foregut extends from lung bud to liver bud. In week 4 respiratory diverticulum forms on ventral wall of foregut and develops, forming a tracheoesophageal septum, until respiratory primordium is a separate tube to the oesophagus.
What can happen if the tracheoesophageal septum is abnormally positioned?
Can get abnormal communications and fistulae or blind ending oesphagus
Which foregut glands develop in the ventral mesentery?
Liver, biliary system and uncinate process and inferior head of pancreas
Describe the process of intestinal looping
Midgut intestinal loop has cranial and caudal limbs that use the sma as their axis and connect to the yolk sac via the vitelline duct. In order to make space for the rapidly developing intestines and liver, the intestinal loop herniates out into the umbilical cord and then undergoes looping. In turns 180 degrees anticlockwise around its axis, bringing caudal limb superiorly and then returns to the abdominal cavity, there it completes a further 90 degree turn
Where’s the junction in an adult between cranial and caudal limb of embryonic midgut?
Within the ileum
What is meant by incomplete rotation of the intestinal loop?
If intestine only makes one 90 degree turn then there’s a left sided colon
What happens if there’s reversed rotation of intestinal loop?
May be one 90 degree turn clockwise then duodenum and cranial limb end up passing anteriorly to transverse colon. Can be prone to obstruction of the transverse colon
What are some examples of major midgut defects?
Sub-hepatic caecum if caecum doesn’t descend
Volvulus of colon to obstruct the duodenum
Compression of transverse colon by superior mesenteric artery
What can occur if the vitelline duct persists?
Vitelline cyst where cyst is joined either side by fibrous strands to umbilicus and intestine
Vitelline fistula where there’s direct communication between intestine and umbilicus
Meckel’s Diverticulum - diverticulum of ileum, connected to umbilicus via fibrous strand
What is meckel’s diverticulum?
Rule of 2’s - occurs in 2% of the population, 2 feet from ileocaecal valve, 2 inches in length with 2:1 ratio occurence in men:women
Can contain ectopic gastric or pancreatic tissue so is prone to inflammation. Similar presentation to appendicitis
Why might atresia/stenosis occur in GI tract?
In duodenum, oesophagus and bile duct, lumen gets obstructed by proliferating cells followed by recanalisation. If recanalisation fails either completely or partially, there’s atresia or stenosis
What causes pyloric stenosis?
Hypertrophy of circular muscle at pyloric sphincter. Presents in infants with projectile vomiting
What is gastroschisis?
Anterior abdominal wall fails to close completely in embryonic folding so normally folded intestines lie outside of body cavity. May be necrosis
What is omphalocoele/ examphalos?
Where intestinal loop fails to return to abdominal cavity after physiological herniation. Gut is outside of body, improperly folded, covered by amnion.
High likelihood of other developmental defects.
How is the anal canal formed?
Urogenital septum (mesoderm) descends to separate cloaca into anorectal canal and urogenital sinus. Sinus and canal are separated by perineal body exteriorly
What are the differences in nerve and blood supply between 2 parts of anal canal?
Below pectinate line - supplid by pudendal artery and nerve (s2-4) and drained by superficial inguinal nodes. Lined by stratified squamous epithelium. Sensitive to temperature, pain and touch.
Below pectinate line - supplied by IMA and pelvic nerves (s2-4) and drained by internal iliac nodes. Lined with columnar epithelium and sensitive to stretch only
What is the difference between an anorectal agenesis and an imperforate anus?
Imperforate anus is where anal membrane fails to rupture so there’s no communication of anal canal to outside. Anorectal agenesis is when there’s failure to form an anorectal canal
What is a hindgut fistulae?
Where hindgut makes inappropriate communications, eg rectum with bladder
What’s the difference between an indirect and a direct inguinal hernia?
Indirect hernias pass lateral to inferior epigastric vessels and occur through the deep inguinal ring whereas direct hernias pass medial to the inferior epigastric vessels and pass through a weakened area of tranversalis fascia called hesselbach’s triangle.
Indirect are normally of embryonic origin
What are the borders of hesselbach’s triangle?
Lateral - inferior epigastric artery
Medial - Lower lateral border of rectus abdominis
Inferior - medial inguinal ligament
Where is the inguinal canal?
Oblique passage between deep and superficial inguinal rings, between layers of anterior abdominal ,muscles. Runs parallel and superior to the medial inguinal ligament
What are the contents of the inguinal canal?
Ilioinguinal nerve
Spermatic cord or round ligament of uterus
How can an inguinal hernia be tested for?
By palpating either hesselbach’s triangle or the superificial inguinal ring and asking patient to cough. If a sudden impulse is felt then there is a hernia
Where do epigastric hernias occur?
In the midling between xiphoid process of sternum and the umbilicus through the linea alba. Commonly occurs in pregnancy or obesity
What is a Richter’s Hernia?
Where only part of the intestine protrudes through the defect, with the rest of the lumen remaining in the peritoneal cavity. At high risk of strangulation and perforation
What are spigelian hernias?
Hernia along semilunar lines of abdomen. Common in over 40s and the obese
Where do femoral hernias occur?
Into femoral canal through the femoral ring, bound laterally by femoral vein and medially by the lacunar ligament. Often presents as tender mass within femoral canal, inferolateral to pubic tubercle.
What are some complications of femoral hernias?
They compress the contents of the femoral canal and so they distend its walls. Also at high risk of strangulation due to the rigib borders of the femoral canal.
Can pass through saphenous opening into subcutaneous tissue of thigh where it can grow as it’s no longer contained by walls of canal
What is a divarication of recti?
Weakness in linea alba so rectus abdominis stretches apart. Often only cosmetic and most common in pregnancy and neonates
Why do umbilical hernia occur?
Most common in neonates. After ligation of umbilical cord, there’s weakness in abdominal wall as there is incomplete closure of umbilical ring so can be protrusion through umbilical ring.
Can be acquired, commonly in women or the obese.
Both often occur after increased intraabdominal pressure
What are the borders of the anterolateral abdominal wall?
Superiorly - cartilages of ribs 7-10 and xiphoid process of the sternum
Inferiorly - Inguinal ligament and superior margins of anterolateral aspects of pelvic girdle (iliac crests, pubic symphysis, pubic crests)
From anterior to posterior, what are the different layers of the anterolateral abdominal wall?
Skin Fatty layer of superficial subcutaneous tissue Deep membranous layer of subcutaneous tissue Superficial investing fascia External oblique muscle Intermediate Investing fascia Internal oblique muscle Deep investing fascia Transversus abdominis muscle transversalis fascia Extraperitoneal fat Parietal peritoneum
Roughly at which spinal level is the umbilicus?
L3
Where is heartburn most commonly felt?
In epigastric fossa which is a slight depression, just inferior to xiphoid process of the sternum
What is the linea alba?
An aponeurosis of abdominal muscles, that separates right and left rectus abdominis
What is the difference between the pubic crest and the pubic symphysis?
Crest is the upper margin of the pubic bones and the symphysis is a cartilaginous joint that unites these bones
What landmark marks the division between the thigh and abdominal wall?
The inguinal groove - skin crease just inferior to inguinal ligament
What is the arcuate line?
Where the posterior layer of the rectus sheath ends. It lies a third of the way down from umbilicus to pubic symphysis.
What nerve supplies the obliques and transversus abdominis?
Thoracoabdominal subcostal nerve, T6-T11
What is the rectus sheath?
A strong aponeurosis, made up of continuations of anterior and medial aponeuroses of the 3 flat muscles (obliques and transversus abdominis) which extend from mid-clavicular line to midline.
The sheath encloses rectus abdominis apart from below the arcuate line, where there’s no posterior covering
What are the layers, superficial to deep, surrounding rectus abdominis, above the arcuate line?
Skin Subcutaneous tissue External oblique fascia Internal oblique fascia Rectus abdominis Internal oblique fascia Transversus abdominis fascia Transversalis fascia Parietal peritoneum
What are the layers, superficial to deep, surrounding rectus abdominis, below the arcuate line?
Skin Subcutaneous tissue External oblique fascia Internal oblique fascia Transversus abdominis fascia Rectus abdominis Transversalis fascia Parietal peritoneum
What is the clinical significance of the arcuate line?
Used as marker in C-sections so incisions are made below this point to minimise structures cut through
Where is the pyramidalis muscle?
Enclosed in the rectus sheath, anterior to the inferior rectus abdominis. It’s attached to the anterior pubis and anterior pubic ligament and acts to tense the linea alba
What kind of an incision is one made along the linea alba?
Midine incision. Good for exploratory operations
Where do we cut in a transverse incision?
Along aponeurosis of external oblique muscle
Where do we cut in an appendicectomy?
At Mcburney’s point which is two thirds of the way from umbilicus to ASIS
What kind of incision is used in an appendicectomy?
Gridiron - Put scissors in and open and close to separate out muscle fibres, layer by layer
What is a pfannenstiel incision?
AKA suprapubic incision. Made at pubic hairline, transcects linea alba and rectus sheath. Used in OB-GYN operations, expecially c-sections
What’s the difference between a patent urachus and a patent vitelline duct?
Urachus connects bladder to umbilicus so can present either at birth or later in life due to outflow obstruction i.e. from prostatic hypertrphy.
Vitelline duct connects gut to umbilicus. Can cause various different problems such as vitelline cyst, meckel’s diverticulum or vitelline fistula (faecal matter comes out of umbilicus)
What is somatic referred pain?
Pain caused by noxious stimulus to the proximal part of a somatic nerve, that’s perceived in the distal dermatome of that nerve.
E.g. in shingles
What is visceral referred pain?
Visceral afferent pain fibres follow same route as sympathetic fibres back to spinal segment that gives rise to preganglionic sympathetic fibres. CNS then peceives the visceral pain as coming from the same somatic portion that’s supplied by that spinal cord segment
What stimuli can cause visceral referred pain?
Stretch, ischaemia, inflammation, Abnormally strong muscle contraction
Where is pain felt in renal or ureteric colic?
Right lower quadrant/right flank pain
What is felt in referred diaphragmatic irritation and what can cause it?
Blood pools in peritoneum so patient feels faint and lies down. Blood pools around diaphragm and this irritates the left diaphragm especially (no liver in the way) so there’s pain referred along the phrenic nerve (C3-C5) so is felt in left shoulder
What drains peritoneal fluid?
Lymphatics, especially of inferior diaphragm
Where are the openings of the peritoneum?
Completely closed in men.
In women there’s a communication via uterine tubes and vagina to the outside world
What is the peritoneum?
2 Continuous layers of mesothelium (simple squamous) membrane
What separates parietal peritoneum from the anterior abdominal wall?
Extrapertioneal connective tissue which is fatty and particularly dense posterior to linea alba and on inferior diaphragm
What is the embryological origin of peritoneum?
parietal from somatic mesoderm and visceral from splanchnic mesoderm
What is a mesentery?
A double layer of peritoneum that’s formed by invagination of peritoneum by an organ
What is the function of mesentery?
Connects organs to posterior abdominal wall
Provides pathways for nerves, blood and lymph vessels between abdominal wall and viscera (organs)
What is the greater omentum?
Four-layered, fatty, prominent peritoneal fold that goes from greater curvature of stomach and proximal duodenum, hangs down then loops back up to attach to anterior transverse colon
What is the function of the greater omentum?
Acts as the abdominal constable by migrating to infected viscera to wall off infection.
Also acts to cushion and insulate viscera
What is the lesser omentum?
A smaller, double-layered peritoneal fold that connects lesser curvature of stomach and poximal duodenum to the liver, via membranous hepatogastric ligament and the hepatoduodenal ligament which provides the thickened free edge. Lesser omentum also connects the stomach to the portal triad
What are peritoneal ligaments?
Double folds of peritoneum that connect organs either to another organ or to the abdominal wall
How does the liver connect to the abdominal wall?
Via the falciform ligament
What peritoneal ligament conducts the portal triad and what is the portal triad made up of?
Hepatoduodenal ligament
made up of hepatic artery, portal vein and bile duct
How does the stomach connect to the transverse colon?
By gastrocolic ligament/ greater omentum
Why do organs have bare areas?
To allow passage of neurovascular structures
What organs are retroperitoneal?
Suprarenal glands Aorta/IVC Duodenum (except cap) Pancreas Ureters Colon (ascending and descending) Kidneys Esophagus Rectum
What is the greater sac made up of?
Supracolic and infracolic compartments
What is the lesser sac?
An extensive sac like quality that lies posterior to the stomach, lesser omentum and adjacent structures. It’s limited superiorly by the diaphragm and coronary ligament of the liver and its inferior recess lies between superior layers of greater omentum but mostly gets sealed off in childhood.
It acts to allow free movement of the stomach on the structures posterior and inferior to it
What is the epiploic foramen?
AKA omental foramen. It’s how the greater and lesser sacs communicate. It’s situated posterior to the free edge of the lesser omentum and posterior to the gallbladder.
