Flashcards in GI Deck (252)
What must the GI tract convert food too?
What is the fluid balance of hype GI tract?
1.5 L saliva
2.5 L stomach secretions
9 L small intestine and pancreatic secretions
12.5L absorbed in small intestine
1.35L absorbed in large intestine
What does the lower oesophageal sphincter comprise of?
Acute angle of entry of oesophagus
Oesophagus passes through oesophageal hietus and right crux of diaphragm
High pressure in abdomen collapses oesophagus
Circular muscle of oesophagus
Folds of oesophageal mucus membrane
What are the functions of saliva?
Begin digestion of carbs
Moisten mucus membranes
Reduce breakdown of teeth
Why is saliva necessary in the mouth?
Non keratanized epithelium so vulnerable to dehydration
Mucus membrane exposed to external environment so vulnerable to infection
Teeth would decay rapidly without protection and maintainance
What are the constituents of saliva that aid its function?
What types of saliva are there?
Mucous - rich in mucin
Serous - rich in enzymes
Which salivary glands produce which types of saliva? What volume of saliva does each contribute?
Parotid - serous - 25%
Sublingual - mucus - 5%
Submandibular - both - 70%
What distinguishes the submandibular gland Histologically?
The presence of demilunes - serous glands that move back out of the acini during preparation.
What do the acinar cells secrete when making saliva?
An isotonic solution with normal cations, high iodine and consequently low chlorine ions.
How are acinar secretions modified by ductal cells?
Absorption of Na+ with less K+ excretion thus hypotonic
Exchange of Cl- for HCO3- thus alkali
How is a sodium gradient set up in saliva ductal cells?
Na+/K+ ATPase on basal membrane extrudes Na+ setting up a gradient in the cell drawing ductal Na+ in
Some K+ released into duct
Remainder of K+ excreted in cotransport with Cl- into the blood
How is HCO3- created within the ductal salivary cells?
Inward diffusion of CO2
Combination with H2O creating HCO3- and H+
H+ extruded into blood in exchange for Na+ down its gradient
How does resting saliva differ from stimulated saliva?
More hypotonic (less Na+, marginally higher K+) due to longer spent in duct
Less HCO3- and less enzymes as less stimulation for their release
How is saliva secretion controlled?
Stimulation (taste, smell, reflex) trigger increased parasympathetic stimulation to the glands - this causes increased secretion. Reduced sympathetic stimulation causes vasodilation resulting in increased blood flow
Stimulation of the sympathetic NS also increases gland activity but reduces blood flow, as a result secreation decrease
Which cranial nerves supply which salivary glands?
Parotid - CN IX - glossopharangeal
Sl and SM - CN facial via the chorda tympani
What is the term for:
Difficulty in swallowing
What can cause dysphagia?
Neurological causes - cve, myesthenia gravis, parkinsons, MS
Oesophageal causes - tumour, stricture, right atrial hypertrophy, enlarged aorta, achalaesia (lack of peristalsis due to enteric NS destruction).
How does lateral folding of the embryo contribute to the formation the GI tract?
Somatic mesoderm that surrounds the amniotic cavity pinches the yoke sac creating a tube suspended by splanchnic mesoderm lined with ectoderm.
What does craniocaudal folding cause in the GI tract?
Cuts the connection between the GI tract and the yoke sac down to one tube - the vitelline duct
What occurs at either end of the primitive gut tube?
Direct connections between endoderm and ectoderm - the stomatodeum and proctodeum
What does endoderm form in the GI tract?
What forms the GI tract muscles? What else does this layer form?
The splanchnic mesoderm.
Also forms the visceral peritoneum
What are the divisions of the gut?
Foregut - oesophagus to major duodenal papilla
Midgut - major duodenal papilla to 2/3rds along transverse colon
Hindgut - last 1/3rd of transverse colon to rectal canal (pectinate line)
How is the gut tube suspended in its cavity?
What splits this cavity?
The dorsal mesentery
Which section of the gut also has a ventral mesentery?
What does this do to the cavity?
Forgut - stomach to major duodenal papilla.
Divides the intraembryonic coelom into a right and left sac.
How do the mesenteries change around the stomach?
The stomach twists clockwise carrying the mesenteries with it. The stomach also tilts as the greater curvature (was posterior now right side) grows faster than the lesser. This causes the dorsal mesentery to become horizontal on its attachment to the bottom edge of the stomach.
What develops in the dorsal and ventral mesogastrium?
Dorsal - spleen
Ventral - liver
What does the ventral mesogastrium form in the adult?
The lesser omentum connecting the lesser curvature to the liver
The surroundings of the liver
The falciform ligament connecting the liver to the anterior abdominal wall