GI Session 2 Flashcards
Which gland mainly secretes serous saliva?
Parotid
Which gland mainly secretes mucous saliva?
Sublingual
Which gland mainly secretes mixed saliva?
Submandibular
What are the two modes of secretion of saliva?
By minor glands of which there are 100s to 1000s
Secretion by 3 pairs of large glands
How much saliva is produced per day?
0.5-1.5 l
Is saliva produced at a constant rate?
No, peaks in afternoon and troughs at night
What does salivary composition depend on?
Whether it is baseline or stimulated
What are the main components of saliva?
Water Mucus Antibodies Electrolytes esp calcium to protect teeth Enzymes Bacterial flora Epithelial cells
What control are minor salivary glands under?
ANS
What is the function of minor salivary glands releasing trace amounts of saliva?
Maintain hydration
Decrease friction
Prevent bacterial build up
What does failure of the minor sail vary glands lead to?
Dry mouth
Halitosis
Poor dental hygiene
What is the function of the mass-ejecting salivary glands?
Produce and store large amounts of saliva until release is stimulated by thought/sight/smell/taste of food
What are the three pairs of mass-ejecting salivary glands?
Parotids
Sublingual
Submandibular
What are the functions of saliva?
Soften solid food to prevent mucosal tearing Taste perception Soft tissue repair Maintain integrity of teeth Dilute and clear oral sugars Initiate oral phase of digestion Detoxification and buffering
What are the three general types of saliva?
Serous
Mucous
Mixed
Where is the parotid gland situated?
In front of and level with external ear with deep portions behind mandible Ramos
What is the secretory function of the parotid gland?
Secretes 25-30% of all saliva but only secretes serous
What do the salivary secretions of the parotid gland drain through?
Stenson’s ducts
What can develop on the duct which drains the parotid gland?
Accessory parotid
Where are the submandibular salivary glands located?
Floor of mouth
What is the secretory function of the submandibular glands?
Produces 65-75% of all saliva which is mixed but mainly serous and amylase rich
How are the submandibular glands drained?
Wharton’s duct which emerges either side of the lingual frenulum
Which system innervates the submandibular glands?
PNS
What is the secretory function of the sublingual salivary glands?
Smallest, produce less than 5% of all saliva which is mixed but mainly mucus
What controls secretion by sub lingual glands?
ANS control of BV supplying gland
What does the acinus do in the secretion of saliva?
Primary stage of production: secretes fluid isotonic with plasma
What happens in the secondary stage of saliva production?
Ions reabsorbed –> hypotonic saliva with low sodium and chloride and high potassium and bicarbonate
Which cells are involved in the secondary stage of saliva production?
Striated duct cells
What happens to the composition of saliva is production is increased?
Reduced time for second stage therefore saliva is more hypertonic and acidic
What cells make up a salivary secretory unit?
Myoepithelial cells
Acinus cells
Secretory cells
What does the saliva pass through on its exit of the salivary secretory unit?
Acinus –> intercalated duct –> striated duct –> excretory duct
How do serous salivary secretory units appear histologically?
Dispersed chromatin
Dark staining due to zymogens
Large striated ducts
How do mucous salivary secretory ducts appear histologically?
Nuclei flattened against BM
Condensed chromatin
Light staining
Smaller striated ducts
What can a mixed salivary gland consist of?
Serous and mucus acini whose ducts join
Acini with serous and mucous cells
What is seen in a mixed salivary gland where mucus cells predominate?
Serous cells form semilunar caps on the terminal part of the mucous acini
What occurs if ingested foods are not recognised as food?
Gag reflex
What does testing the gag reflex examine?
Integrity of soft palate sensation and motor innervation which must both be intact to initiate reflex
When can difficulties in swallowing be seen?
Congenital abnormalities of the mouth
Cerebrovascular accidents causing paralysis of soft palette nerves
Hypertrophy of pharyngeal tonsils
What divides the oral cavity into two parts?
Palatoglossal arch
What is the oral cavity divided into?
Anteriorly is the mouth proper
Posteriorly is the oropharynx
What happens in the oral phase of swallowing?
Preparatory phase: voluntary chewing of food to form bolus –> food bolus on tongue by pushing up onto hard palate –> bolus touches soft palate activating receptors on palatoglossal arch and pharyngeal tongue –> transit phase
What does the transit phase of the oral phase of swallowing result in?
Reflex activation of pharyngeal phase
What happens in the pharyngeal phase of swallowing?
Soft palate rises to close off opening between naso- and oropharynx –> hyoid bone and larynx rise to allow epiglottis to seal off airways –> tongue movement pushes food into oesophagus
What usually identifies failure of the pharyngeal phase of swallowing?
Nasal regurgitation
What happens in the oesophageal phase of swallowing?
Bolus enters UOS –> sphincter reflexively constricts –> primary peristaltic wave initiated below UOS by brain –> wave takes 10s to travel length of oesophagus
What happens in the oesophageal phase of swallowing if sensory fibres in the distended oesophagus sense bolus not cleared?
Fibres signal for central and enteric nervous systems to initiate a secondary peristaltic wave
What controls the lower oesophageal sphincter?
ANS by vagus nerve with time affected by hormones and natural variation
Why does the oesophagus have a small diameter?
To ensure downward movement of food
What causes the primitive gut to become tubular in the 4th week of development?
Lateral folding
What forms the cranial and caudal pockets from the yolk sac endoderm in the 4th week of development?
Craniocaudal folding
What can be said about structures developing close to embryonic divisions of the gut?
They have mixed blood supply
Which adult derivatives of the embryonic gut have mixed blood supply due to their embryonic origins?
Duodenum proximal to the bile duct
Duodenum distal to the bile duct
Pancreas
What gives blood supply to the GI tract?
3 midline branches of the aorta: coeliac trunk, SMA, IMA
What are the adult derivatives of the foregut?
Oesophagus Stomach Pancreas Liver Gallbladder Duodenum proximal to Spincter of Oddi
What are the adult derivatives of the midgut?
Duodenum distal to sphincter of Oddi Jejunum Ileum Caecum Ascending colon Proximal 2/3 transverse colon
What are the adult derivatives of the hindgut?
Distal 1/3 transverse colon Descending colon Sigmoid colon Rectum Upper anal canal Internal lining of bladder and urethra
Which aortic branch corresponds with which section of the embryonic gut?
Coeliac trunk - foregut
SMA - midgut
IMA - hindgut
When does the primitive gut tube begin to develop?
3rd week when it pinches off from the yolk sac cavity
What do the cranial and caudal pockets from yolk sac endoderm form?
Cranial –> foregut as blind diverticula
Caudal –> hindgut as blind diverticula
Where does the primitive gut tube from and to?
From stomatodeum to proctodeum with opening at the umbilicus
Where does the internal lining of the primitive gut tube derive and what will it become?
Endoderm –> future epithelial linings
Where is the external lining of the primitive Gut tube from and what will it become?
Splanchnic mesoderm –> gut wall musculature and visceral peritoneum
What suspends the primitive gut tube in the intraembryonic coelom?
Double layer of splanchnic mesoderm
Describe how the intraembryonic coelom develops to form the abdominal cavity.
Endoderm lined tube as one large cavity –> diaphragm splits into abdominal and thoracic cavities –> abdominal lined by 2 separate leaves of peritoneal membrane from somatic and splanchnic mesoderm –> leaves line cavity and invest in viscera
What is the peritoneal cavity?
A potential space in the abdominal cavity
What is a mesentery?
Double layer of peritoneum attaching but tube to abdominal wall
What is the function of a mesentery?
Allow conduit for blood and nerve supply
Allow for mobility
How does the mesentery suspending the embryonic gut tube form?
Splanchnic mesoderm surrounds primitive gut tube and condensation of this forms a mesentery
Where is mesentery found in the primitive gut tube?
Dorsal mesentery suspends entire gut tube form dorsal body wall
Ventral mesentery only suspends the foregut
What are omenta?
Specialised folds of the peritoneum
What is the greater omentum?
First structure seen on opening the anterior abdominal wall formed by the dorsal mesentery
What is the lesser omentum?
Formed by the ventral mesentery, free edge conducts the portal triad
What do the dorsal and ventral mesentery in the foregut region split the abdominal cavity into?
L and R peritoneal sacs
What is the left peritoneal sac?
Gives rise to the greater peritoneal sacs which is entered upon opening of the abdominal cavity and peritoneum
What is the R peritoneal sac?
Gives rise to lesser peritoneal sac which lies behind the stomach
What does rotation of the stomach around the longitudinal axis cause?
Formation of lesser and greater curvatures of the stomach
What happens to the mesentery as the stomach rotates 90 degrees around its longitudinal axis?
Fold as stomach moves –> bulge in dorsal mesentery as space between leaves increases
What aorta of the stomach are the mesenteries attached to?
Ventral mesentery –> lesser curvature
Dorsal mesentery –> greater curvature
What is the result for the innervation of the stomach following longitudinal rotation?
L vagus nerve innervating L side –> anterior wall
R vagus nerve innervating R side –> posterior wall
Where does the liver develop?
Within the leaves of the ventral mesentery
What happens during rotation of the stomach around the anteroposterior axis?
Dorsal mesentery bulge –> greater omentum and two leaves fuse
Move cardia and Pylorus from midline –> stomach lies obliquely
Moves lesser sac behind stomach
What is the definition of a retroperitoneal structure?
One that was never in the peritoneal cavity and never had a mesentery e.g. Abdominal aorta, kidney
What are secondary retroperitoneal structures?
Began development invested by peritoneum and had mesentery but with growth this has been lost through fusion with the posterior abdominal wall e.g. Duodenum except duodenal cap, pancreas
What is formed in the ventral mesentery?
Liver
Biliary system
Ucinate process and inferior head of pancreas
What is formed in the dorsal mesentery?
Superior head, neck, body and tail of pancreas
How do the respiratory primordium and oesophagus develop from the foregut?
Resp diverticulum buds off from oesophagus and enlarges –> tracheosophageal septum forms to create two separate tubes
What can result in disruption of the respiratory primordium and oesophageal development?
Proximal blind-ended oesophagus
Tracheosophageal fistula
What creates the greater curvature of the stomach?
Faster growth on the dorsal border
What indicates the position of the stomach primordium in the foregut?
Slight dilation of distal foregut
What is the earliest GI tract associated gland to develop?
Liver
How does the liver develop within the leaves of the ventral mesentery?
Hepatic bud forms in mesentery and grows rapidly to occupy a large proportion of the abdomen thus affecting development of lesser sac and peritoneum
What attaches the liver to the ventral body wall and travels up the anterior aspect of the liver where it splits?
Falciform ligament
What is the bare area of the liver?
Area not covered by visceral peritoneum as it develops in parallel where the liver is attached to the diaphragm
Where is the lesser omentum found during development of the liver?
Between liver and foregut
How does the duodenum develop?
Caudal foregut+cranial midgut –> grows rapidly –> stomach rotation pushes it right then against posterior abdominal wall –> c-shaped duodenum
What happens to the duodenal endoderm all lining in the 6th week of development?
Becomes so well developed lumen is obliterated
When is the duodenum lumen recanalised?
By the end of the embryonic period
What grows over the duodenum making it secondarily retroperitoneal except from its cap?
Parietal peritoneum to form fusion fascia so structure is mobilised
