Flashcards in Week 2 - Salivation and Swallowing and development Deck (81):
What is the end result of mastication and salivation?
-Formation of a food bolus for swallowing
How much saliva is produced per day?
What is the function of saliva?
-Lubricate and wet food
-Start digestion of carbohydrates
-Protection of oral environment
In what ways is the oral environment protected by saliva?
-Maintains teeth integrity by neutralising acid produced by bacteria
-Keeps mucosa moist to prevent ulceration
-Contains antibodies and WBCs to protect against bacteria
What is zerostomia? What are the consequences of this condition?
-Absence of saliva production
-Oral environment degrades at a very quick rate due to acid produced by bacteria
-Halitosis and poor dentition
What is saliva?
-Hypotonic watery secretion with mucus which is produced by glands in the mouth
What triggers saliva production above baseline?
-Senses of food including thought as a response from the brainstem
What are the three major salivary glands and their secretions?
-Parotid -> serous rich in enzymes (25%)
-Submandibular -> mixed (70%)
-Sublingual -> mainly mucus with no enzymes (5%)
What are the constituents of saliva?
-Water (hypotonic )
-Electrolytes -> Na, Cl at lower conc than plasma, Ca, I and K at higher conc than plasma
-Alkali -> HCO3 at higher conc than plasma
Why does saliva need to be hypotonic?
-Prevent water being drawn out of mucosa and being absorbed instead
Why is there a high concentration of calcium in saliva?
-Prevent teeth erosion
Why is iodide present in saliva?
Why is mucus present in saliva?
-To coat food bolus for easy swallowing
What enzymes are most prominent in saliva?
What type of glands are the salivary glands?
-Ducted, exocrine glands
Describe the glandular structure of salivary glands and the fuctions of specific parts
-Terminal tubulo-acinar structures
-Acinar cells are secretory
-Ductal cells are modificatory
What is stensons duct?
-Duct of parotid glands
What is whartons duct?
-Duct of submandibular gland
Describe the secretion from acinar cells
-Secretion is isotonic with ECF with a higher conc of I (via active transport)
-Secretion contains enzymes manufactured by acinar cells
Describe ductal modification
-There is little change in volume
-It is the solutes which are removed rather than solvent added to make a hypotonic fluid -> impermeable to water
-NaKATPase on basolat sets us gradient
-Na ions are removed from the secretion down gradient and Cl follows
-K Diffuses out into saliva down conc garient
Describe the differences in saliva during rest and stimulation. What accounts for these differences?
-During rest HCO3 is added to produce a neutral pH saliva and there is a low flow rate meaning there is sufficient time to remove Na. There are few enzymes secrted
-During stimulation excessive HCO3- added to produce an alkaline saliva and there is less Na removed due to the high flow rate and the limited removal rate of ions. Excessive enzyme secretion
Describe the control of secretion of saliva
-Parasympathetic stimulates acinar cells (via ach) to produce primary secretion and ductal modification
-sympathetic input to the glands reduced blood flow and thus limits salivary flow
-Ductal recovery of Na is influenced by aldosterone
What are the three phases of swallowing?
Describe voluntary phase of swallowing
-Food blus moved to pharynx under voluntary control
Describe pharyngeal phase of swallowing
-Afferent information from pharyngeal receptors reaches swallowing centre in brain stem which causes:
Closure of glottis
Inhibition of breathing
opening of oesophagus
Describe oesophageal phase of swallowing
-Upper 1/3 is striated muscle under voluntary control
-Lower 1/3 is smooth muscle under parasymp control and peristalsis propels bolus into stomach
What is the result of lateral embryonic folding in relation to GI tract?
-Ventral body wall formation
-Primitive gut tube formation
What is the result of craniocaudal folding in relation to the GI tract?
-Creates blind pockets of forgut and hindgut
What is different about the midgut to foregut an hindgut in the beginning of development?
-foregut and hind gut are blind diverticula
-Midgut has an opening at first and is continuous with yolk sac
When does development of primitive gut tube begin?
What is the stomatoduem?
What is the proctoduem?
Describe the length of the primitive gut tube
-Rubs from stomatoduem (blind foregut) to proctoduem (blind hindgut) with an opening at umbilicus (midgut)
Where is the intermal lining of the gut tube derived from?
Where is the future musculature and visceral peritoneum of the gut tube derived from?
-Splachnic mesoderm (of lateral plate mesoderm)
In which cavity is the primitive gut tube?
-Suspened in intraembryonic coelom
How is the primitive gut tube suspended in the furture peritoneal cavity?
-By a double layer of splanchnic mesoderm
Name the derivatives of the foregut
-Oesophagus to 1st portion of duodenum including pancreas, liver and gall bladder
Name the derivatives of the midgut
-From second part of duodenum where bileduct joins to proximal two thirds of transverse colon
Name the derivatives of the hind gut
-Distal 3rd transverse colon to pectinate line of anus
-Inclides intermal lining of bladder and urethra
From where does the foregut receive its blood supply?
From where does the midgut receive its blood supply?
-Superior mesenteric artery
From where does the hind gut receive its blood supply?
-inferior mesenteric artery
Name the branches of the celiac trunk
-Splenic artery -> giving left gastroepiploic artery
-Common hepatic artery -> giving right gastric, gastroduodenal (which gives right gastroepiploic and superior pancreaticoduodenal), proper hepatic artery (which gives left and right hepatic and cystic)
-Left gastric artery
What is specific about the blood supply to the duodenum?
-Supplied by gastroduodenal and superior pancreaticoduodenal proximal to bile duct entry (CT)
-Supplied by inferior pancreaticoduodenal distal to bile duct entry (SMA)
What is specific about the blood supply to the pancreas?
-Receives sup. panc.duo art from CT
-Receives inf. panc.duo art from SMA
Describe the branches of the superior mesenteric artery
-gives ileocolic, right colic and middle colic
Describe the branches of IMA
What forms the future peritoneal cavity?
What happens to the intraembryonic ceolom to divide it into the thoracic and abdominal cavities?
-Subdivided by the diaphragm
What is the peritoneal cavity?
-Potential space between the parietal and visceral peritoneum which should contain only a minute amount of fluid
What are mesenteries?
-Double layer of peritoneum which contain vessels and nerves and suspends the gut from the abdominal wall
From where do mesenteries form?
-From the splanchnic mesoderm which holds the primitive gut tube in the intraembryonic ceolom
Describe dorsal and ventral mesenteries
-Dorsal mesentery suspends entire gut ube from dorsal body wall
-Ventral mesentery only in the region of the foregut
What are the left and right sacs?
-The cavities created in the foregut due to dorsal and ventral mesentary
To which sacs do the left and right sacs contribute?
-Left sac contibutes to greater sac
-right sac contributes to lesser sac
Where is the lesser sac?
-Directly behind the stomach
Where is the greater sac?
-The sac you enter as soon as you open the peritoneum
What are omenta?
-Specialised regions of peritoneum
From where is the greater omentum formed?
From where is the lesser omentum formed?
What structure is related to the free edge of the ventral mesentery?
Describe the rotation of the stomach and its role in the formation of the sacs and omenta
-Stomach first rotates clockwise upon its longitudinal axis and it pulls the mesenteries with it so that a double fold of dorsal mesentery lies on the left and a double fold of ventral lies on the right
-The stomach then rotates upon its anterioposterior axis (dont forget in the fetus this is superioinferior axis) so that the cardia and pylorus move horizontally and the lesser sac moves inferiorly. This produces the final greater and lesser omenta.
What happens to the liver and right sac as the stomach is rotating?
-Begins to develop in the ventral mesentrey and is pushed to the right as the stomach rotates
-This forces the right sac behind the stomach which is now the lesser sac
What effect does rotation of the somach have on the vagus nerve?
-The vagus nerves become anterior and posterior to the stomach instead of left and right
What is a peritoneal reflection?
-A change in direction from parietal peritoneum to mesentry to visceral peritoneum and vice versa
What happens to organs when there is no mesentery?
-They are considered retroperitoneal eg kidneys
What is secondary retroperitoneal? Give an example
-Organs which began development in the peritoneum and had a mesentery but with successive growth and evelopment the mesentery is lost through fusion with the posterior abdominal wall
Why does the foregut originally include the lung bud? What happens to separate these two structures?
-Respiratory diverticulum appears in ventral wall of foregut
-Resp diverticulum thickens and tracheoesophageal septum grows separating respiratory tract anterior to GI tract
What are the consequences of abnormal tracheoesophageal septum positioning?
Why is the greater curvature present?
-Dorsal border of primordia of stomach grows faster
Apart from the liver, what other foregut structures develop in the ventral mesentery?
-Part of pancreas
Where does the pancreas develop?
-Ventral and dorsal mesentery
Describe the attachments of the liver to the anterior and posterior body walls and the diaphragm
-Liver attached to anterior bodywall as develops in the mesentery (by falciform ligament)
-Livver attached to posterior body wall by lesser omentum
-When diaphragm develops, the region of liver attached to the diaphragm is known as the bare area as not cobered by visceral peritoneum
Describe the development of the duodenum
-Develops from distal foregut and proximal midgut.
-Loops into right and into C shape when stomach rotates as well as being pressed against posterior abdominal wall causing fusion of the mesentery -> secondary retroperitoneal
-The lumen is obliterated due to speed of growth and then recanalised by the end of the embryonic period
What is mastication?
-Preliminary disruption of food (chewing)
Name 3 common causes of dysphagia
What is achalasia?
-A condition where the muscles of the lower oesophagus fail to relax and prevent passage of bolus
Why might someone have dysphagia following a cerebrovascular accident?
-Poorly coordinated peristalsis
What is odynophagia?