Session 3 Flashcards
what is physiological herniation of the midgut
it protudes into the abdominal wall as by week 6 it grows faster than the abdominal wall and into the umbilical cord
what is the midgut connected to
yolk sac
how does the mid gut rotate
it forms a loop with the superior mesenteric artery within the umbilical cord
the distal part of the loop develops a caecal bulge and the proximal part becomes convuluted
the midgut states while in the umbilical cord and then returns to the abdomen around week 10- 3x 90 degree rotations
where is the midget connected to the yolk sac
midpoint
what is meckel’s diverticulum
when the vitelline duct doesn’t obliterate and the contents can herniate out into the yolk sac through the umbilicus
what forms the transverse colon
The hindgut through the superior portion of the anal canal
how does the anal canal have 2 origins
At first the hindgut ends blindly at the cloacal membrane which separates it from the proctodaeum. When the membrane ruptures, the hindgut is connected to the exterior
where does recanalisation occur
oesophagus, bile duct and small intestine
when does canalisation occur
weeks 6-8
what is pyloric stenosis
hypertrophy of the pyloric sphincter
What is one consequence of pyloric stenosis
Vomiting in infants
What is gastroschisis
Failure of closure of the abdominal wall following folding of the embryo which results in gut tube and derivates outside the body cavity
What is an omphalocoele
Persistence of the physiological herniation of midgut
What divides the anal canal into superior and inferior parts
Pectinate line
What is the cloaca
A region at the end of the hindgut that divides into an anterior urugenital sinus and a posterior anorectal canal
What is the primary constituent of saliva
Water
What is contained in saliva that maintain oral hygiene
IgA, lysozymes and lactoferrin an initiate the process of digestion
What is xerostomia
Reduced flow of saliva in the oral cavity
What are the three paired salivary glands
Parotid
Submandibular
Sublingual
What is the primary regulator of saliva production
Autonomic system - parasympathetic
What causes dry mouth and what is the name for it
Xerostomia
Anything that reduces parasympathetic innervation
What are the three phases of swallowing
Oral
Pharyngeal
Oesophageal
Oral phase
Voluntary
Results i bolus being pushed back onto pharyngeal wall
Pharyngeal phase
Involuntary
Involves bolus moving from oral cavity ti the beginning of the oesophagus
Elevation of the soft palate to protect the nasopharynx
Elevation of the larynx (which closes the epiglottis)
Adduction of the vocal cords
Relaxation of the upper oesophageal sphincter.
What protects the nasal cavity during swallowing
Soft palate
What protects the respiratory tract during swallowing
Elevation of the larynx (which closes the epiglottis)and addiction of the vocal cords
Oesophageal phase
Involuntary
Involves closure of upper oesophageal sphincter to prevent reflux
Rapid peristaltic movement of the oesophagus propelling the bolus into the stomach
What is teh sensory component of the swallow reflex
The glossophryngeal nerve - cranial nerve 9
What innervates most of the muscles involved in the swallow reflux
Cranial nerve 10
What moves the bolus from the posterior aspect o the oral cavity to the oesophagus
Pharyngeal constrictor
How can you distinguish between the sublingual gland and submandibular gland
Submandibular sits medially and sublingual sits laterally
What is the main driver of Salivary secretion
Parasympathetic- increases production
Parotid sialography
Medium has been inserted using a thin catheter which allows us to look at the ducts in the gland
What is the difference of anatomy in babies
The epiglottis extend into the nasopharynx so there is a patent airway constantly as the neck grows the epiglottis descends- allows speech
Gag reflex
Mechanoreceptors -> glossopharyngeal nerve -> medulla -> vagus nerve -> pharyngeal constrictors
How does the muscle change down the oesophagus
Goes from voluntary skeletal muscle to involuntary smooth muscle
What is dysphagia
Difficulty swallow and can have a neural cause or a physical obstructive cause
Rule of 2’s meckels diverticulum
- 2% of population
- Located 2 feet proximal to ileo-caecal valve
- Detected in under 2s
- 2:1 ration M:F
which hindgut derivatice does not form part of the GI tract
bladder epithelia
what wedge of mesoderm separates the cloaca into separare urogenital and anorectal spaces
urorectal septum
what is the proctodeum
a layer of ectoderm overlying a depression where the anus will form
The anal canal is formed from both ectoderm and endoderm. In basic terms why is this significant?
Two different epithelia (stratified squamous and columnar)
Different pain receptors above and below pectinate line
Different blood supply/venous drainage and lymphatic drainage above and below pectinate line
Explain why salivary glands produce a less hypotonic saliva when they are activated compared to
when they are rest
When saliva is produced in volume it flows through the ducts quicker and so has less contact time with the
ductal cells. As a result, when active the saliva produced is less modified and has had less Na and Cl ions
removed and so is relatively hypertonic compared to saliva produced at rest.
Briefly describe how saliva ends up hypotonic when the initial solution produced by the acinar cells is
isotonic
The acinar cells of the salivary gland produce an isotonic solution.
This passes through the ductal cells (myoepithelial cells contract the acinus) where there is movement of ions
More Na and Cl ions are removed from the saliva than K and HCO3 ions secreted into the saliva and since the
ductal cells are relatively impermeable to water, the result is a relatively hypotonic solution
Briefly explain how acid secretion is inhibited when the stomach empties
Stretch is reduced so there is no direct stimulation of G cells by the vagus nerve.
D cells detect a drop in pH and release the hormone Somatostatin, which then goes and inhibits G cells from
releasing the hormone Gastrin
. Briefly explain why there is a transient rise in the pH of blood draining the stomach (alkaline tide)
when parietal cells are producing acid?
Carbonic acid dissociates into H+ ions and HCO3- ions in the cytosol of the stomach. The H+ is moved into the
stomach lumen by the proton pumps and the Bicarbonate ions are exchanged with Cl- on the basolateral
membrane. These Bicarbonate ions are then moved into the venous drainage of the stomach and temporarily
raise its pH
Briefly explain how it is possible to develop an adenocarcinoma in the lower oesophagus despite the
fact that this area is lined with stratified squamous epithelia?
If you have chronic reflux disease then you lower oesophageal epithelia can undergo a metaplastic change to
gastric columnar epithelia. If this becomes dysplastic then the result can be a carcinoma of glandular tissue, an
adenocarcinoma.
