Gastro Flashcards
What is the overall purpose of the GI tract and system?
The body lacks the ability to take in the larger and complex molecules in the diet straight to the cells and use them for energy. The GI tract has to aid in the cutting up of the macromolecules and get the sub-macro molecules into the blood. This process is absorption and digestion.
What 3 properties does the end product of digestion possess?
Isotonic (stop water movement inappropriately) to surrounding solution, correct pH and sterile.
What protection mechanisms does the stomach have against it’s own digestion mechanisms?
c
What is contained within excrement?
Residue, dead cells and waste products in the body.
What is the consequence of rate of digestion being lower than the rate of the eating?
Humans need a place to store food as the food is digested. Held and then released gradually from the stomach.
What are the two mechanisms that food is digested by?
Physical and chemical disruption (mastication, acid and enzymes)
What are the main roles of the stomach
Production of chyme, acid kills pathogens, storage of food, receptive relaxation to accommodate food, enzymic reactions for chemical reactions and muscular contractions for physical disruption and churning.
What needs to happen to chyme when it leaves the stomach and why?
It needs to be neutralised and made isotonic. THis is to protect the lower GI tract from the acidity of the stomach.
How does saliva aid digestion?
Lubricates the food and enables bolus formation. contains ptyalin (amalase) for breaking down starch and also contains salivery lipase which is key in new borns.
How does saliva act as a disinfectant?
Human saliva (although lacking nerve growth factor) contains several anti-microbials agents. these include IgA, lactoferrin and peroxidase.
Properties of saliva
Wet to protect the mucosa in the oral cavity,
Bacteriostatic
Alkaline and high calcium to protect the teeth
What induces saliva production?
Both sympathetic and parasympathtic stimulation.sympathetic increase secretions of mucosal composition and parasympathetic induces production of the enzyme rich serosal fluid.
Where and why does dilution and neutralisation of chyme occur?
Entry of acid into the duodenum induces the release of Secretin from s cells there. Secretin is released at a pH of 4.5. They induce the secretion of HCO3 and also fluid from the pancreas. The duodenum has it’s own intrinsic HCO3 production but it’s limited to the proximal portion of. This intrinsic mechanism involves the Anion exchanger and the CFTR in the apical membrane.
What are the 3 processes of movement in the stomach?
Propulsion
grinding
retro-propulsion
What mechanisms are in place to ensure the intragastric pressure remains lower?
receptive relaxation and gastric accommodation.
How is the intestine designed to optimize absorption?
Slow movement of chyme, massive surface area from microvilli and villi. Hepatic portal vein allows to maintain the steep concentration gradient.
Describe the fluid absorption and secretion in the GI tract.
Food- 1 litre in saliva- 1.5 litres in Gastric secretions- 2.5 litres in Water and alkali- 9 Litres in Small intestine- 12.5 litres out Large intestine- 1.35 Litres Faeces- 0.15 Litres
Describe the parotid gland
Develops in the 6th week of gestation and is the first salivary gland to be formed. They grow towards the ears and are closely associated with the mandibular ramus.
They are mainly serous glands and are anterior and inferior to the acoustic meatus.
Surrounded by a dense capsule the gland has short striated ducts and long intercalated ducts from which it contributes only 25% total salivary volume (which is high in alpha amylase)
Its blood supply is from the external carotid and innervation is entirely autonomic coming from the glossopharyngeal nerve.
Describe the composition of saliva
99.5% water Low Na High K plasma conc Ca Low Cl high HCO3 Mucos (mucopolysaccharides and glycoproteins) Anti microbial agents various enzymes Haptocorrin.
What is the role of haptocorrin?
Binds strongly to Vit B12 to protect it from being denatured in the stomach by HCL.
What are the 3 mechanisms of control of the GI tract?
Neural
Paracrine
Endocrine.
Describe the divisions of the ENS
Meissner’s/submucosal plexus- sub mucosa of the small and large intestine,
Mysenteric plexus- between the circular and longitudinal muscle,
Why is the ENS considered to be a mini brain?
As it can function almost in isolation of any autonomic input from the CNS
What are the neurotransmitters used in the ENS?
Ach is the most common
Vasoactive intestinal peptide has a role in the inhibition of intestinal smooth muscle and stimulation of intestinal fluid and electrolyte secretion. VIP can also be found in the CNS.
What two hormones induce the secretion of HCL from parietal cells?
Histamine and gastrin.
What are the main functions of saliva?
Aid in the physical and chemical disruption of food to enable easier bolus formation and swallowing.
It also contains a number of bacteriostatic molecules such as Iodine and also is also high in calcium and alkali which protects the teeth.
What is the role of incisors? molars?
Cutting
Crushing
What is the main muscle of mastication? innervation?
Masseter
Trigeminal nerve
What volume of saliva is produced per day?
1.5 Litres approx
Describe xerostomia
It is also termed dry mouth syndrome and is due to a relative lack of saliva production. Hyposalivation is one of many causes.
Signs and symptoms include
dental decay, oral candida, altered taste, pain/tingling in the mouth, dysphagia, thirst. Viscous saliva.
It is associated with other auto immune conditions such as sjogren’s syndrome or RA.
What are the 3 salivary glands? What properties do they all have as ducted exocrine glands?
Parotid (serous), submandibular (both), sublingual (mucosal)
Blinded ended tubes.
At the end are acinar cells
Along the tubes are the duct cells
The cell secretions from each cell type vary from being mucosal or serous.
What proportion of salivary production comes from each gland?
Parotid (serous) 25%
submandibular (both) 70%
sublingual (mucosal) 5%
Describe the properties of saliva in terms of osmolality and the issues that this implies.
Hypotonic to the solutions in the cells and in the body.
It must be made from more concentrated solutions.
There is no mechanism for just adding water
Therefore a very energy expensive process to remove ions from the solution using ATP must be used.
Describe the typical acinar secretion
isotonic to ECF, normal NA+ and K+, high I-. slightly less Cl-. HCO3- same and enzymes
How do the ductal cells modify the secretions
Don’t alter volume, Na+ falls, K+ rises, HCO3- (falls upon resting and rises when stimulated).
Why is HCO3 unusual in terms of its modification by the ductal cells?
As all other constituents are less modified in high secretion except itself.
What is the mechanism of acinar secretion?
Through the secretion of Cl- into the lumen which pulls in Na+ and water along with it.
What are the mechanisms of ductal modification?
NA/K ATPase sets up high K+ and low NA+ inside. Na+ diffuses in from duct and some K+ diffuses into duct.HCO3- taken up into the cell as it becomes C)2 and H20. HCO3 then passes into duct via AE. the remaining high K+ takes the high CL- out via a symporter.
What cells dictate volume of saliva?
Acinar
What cells dictate the composition of saliva?
Ductal
What controls the salivary secretion?
Predominantly comes from the autonomic nervous system.
Para (glossopharyngeal)= highest
Sym (superior cervical ganglion)= above a basal level but not as high as para
Aldosterone also acts to increase K+ conc and decrease Na+ conc (see addisons)
how does Ach effect the ductal cells?
Ach increases volume but leads to a lower level of Na+ being absorbed.
How does sympathetic stimulation have it’s effect on the salivary glands?
The effect in vivo is not observed but they increase flow of saliva. It is thought to be due to increased function of myoepithelial cells.
What are the three phases of swallowing?
Voluntary: separation of bolus
Pharyngeal: Pressure receptors in palate and anterior pharynx close glottis and inhibit respiration.
Oesophageal: 9 second rapid peristaltic wave that passes down to the stomach.
What are common causes of dysphagia?
Subdivided into lumenal and external.
Lumenal: fibrous rings, strictures, tumors
External: Right atrial enlargement, Aorta impingement, mediastinal tumor (lymph nodes in lungs or cardiac tumor), thymoma, thyroid tumor, nerve lesions to the major nerves in swallowing (parkinson’s, stroke, MS, etc)
Achalasia is where the oesophagus maintains inappropriate tone and gives rise to a rat’s tail and one cause of is chagas disease.
How can the process of swallowing be observed?
Using a barium swallow and a CT and using video fluroscopy.
How is stomach reflux prevented?
Acute angle of entry,
right crus of diaphragm acts to pinch the oesophagus,
mucosal folds act as a valve.
Describe development of the inguinal canal
During development, the gonads descend from their starting point on the posterior abdominal wall through the abdomen through the inguinal canal. The inguinal canal is formed from a peritoneum invagination called the procesessus vaginalis into the scrotal swelling.
Why does the intraembryonic coleum arise?
Due to the splitting on the lateral-plate mesoderm into the somatic and splanchnic. These both curve round but never reattach. This leads to a cavity being formed between the two layers.
Where does the primitive tube run from?
Stomatodeum (primitive mouth) and proctodeum (future anus)
How does the umbilical cord form?
Growth of the amniotic cavity puts pressure on the yolk sac and connection stalk such that they join and form the primitive umbilicus.
What is the allantois?
d
What structures are in the foregut? blood supply?
Oesophagus. stomach, pancreas, liver, gall bladder, proximal end of duodenum.
Celiac trunk
What structures are in the midgut? Blood supply?
Distal end of duodenum, jejunum, illium, cecum, ascedning colon, proximal 2/3 of transverse colon
Superior mesenteric artery
What structures are in the hind gut?
Distal 1/3 of transverse colon, descending colon sigmoid colon, rectum, upper annal canel, internal lining of bladder and urethra.
Inferior mesenteric artery
Describe the blood supply to the pancreas head
Superior pancreaticoduodenal-CT
Inferior pancreaticoduodenal-SMA
What is a mesentery? why do we have them? where do they form from? where are they?
A double layer of peritoneum suspending the gut tube from the abdominal wall.
They allow a conduit for blood and nervous supply and it also allows mobility.
Forms from the epithelium that lines the splanchnic mesoderm.
Dorsal mesentery= entire gut tube
Ventral mesentery= only in the foregut with a free edge.
Which side of the foregut mesentery becomes the greater sac?
The left sac contributes to the greater sac
What are Omenta? where are they? Roles?
They are specialized regions of peritoneum.
The greater arises due to folding of the liver and the long arm of peritoneum that arises dorsally fuses to form the greater omentum and above which is the omental bursa. The lesser omentum forms from the peritoneum that joins the liver, lesser curvature of the stomach and the duodenum. The dorsal mesentery has a free edge that allows conduction of the portal triad.
How do the sacs form?
This is due to rotation of the stomach and growth of the liver. This pushes the Right sac dorsally. There are several consequences of this. It puts the vagus nerve anterior and posterior to the stomach and causes the stomach to lie obliquely. Also it results in the creation in the greater omentum.
How does the stomach rotate?
Initially about 90 degrees clockwise (looking down the tube). This causes the greater curvature to lie on the left. Then a 90 degree rotation clockwise from looking at a chest anteriorly.
What is reflection of the peritoneum?
Where the peritoneum changes roles. I.e mesentery–> parietal etc
Define secondarily retroperitoneal
Began as having investment of peritoneum and had a mesentery but now the mesentery has been lost through fusion at the posterior abdominal wall.
Describe formation of the lung bud.
In the 4th week a respiratory diverticulum forms in the ventral wall of the foregut at the junction of the pharyngeal gut. This is ventral to the oesophagus.
This is divided by the tracheosophageal septum.
This can have many problems if the septum doesn’t fuse properly.
