7. Digestive System Flashcards
What are the 5 anatomical regions of the stomach?
- Cardia - entrance of the intra-abdominal oesophagus into the stomach; contains primarily mucous cells to provide lubrication for ingesta
2/3. Fundus and body - left and dorsal region of the cardia; food fills the fundus and then body; fundus and body contain primarily chief cells for the production of pepsinogen and parietal cells that produce hydrochloric acid (HCl); body has the greatest dilation capacity.
- Antrum - distal portion of the stomach, directed cranially; serves in in mechanical digestion containing many mucous cells as well as gastrin-secreting cells (g-cells) which stimulate HCl secretion from the parietal cells.
- Pylorus - anatomical sphincter between the stomach and duodenum; controls gastric outflow and prevents duodenal reflux.
What are the 4 layers of the stomach?
Deep to superficial
- Mucosa - surface epithelium, rugae; glanular lamina propria and lamina muscularis mucosa
- Submucosa - elastic layer of connective tissue; CRITICAL HOLDING LAYER
- Muscularis - outer longitudinal and inner circular smooth muscle fibres thicker in the region of the pylorus
- Serosa - smooth membrane with a thin layer of epithelial cells which offer minimal holding power for sutures
What is the main blood supply to the stomach?
Coeliac artery, which branches into the hepatic, left gastric and splenic arteries
Right gastric artery branches off the hepatic artery and anastomoses with the left gastric artery to supply the lesser curvature of the stomach
Hepatic artery then continues as the gastroduodenal artery and gives rise to the right gastroepiploic artery
Left gastroepiploic artery arises from the splenic artery and arborizes with the right gastroepiploic arter to supply the great curvature of the stomach
Venous drainage is via the gastrosplenic vein on the left and gastroduodenal vein on the right, which then empty into the portal vein
What is the nervous innervation to the stomach?
Parasympathetic fibres from the vagus nerves
Sympathetic fibres from the coeliac plexus
What is the lymphatic drainage to the stomach?
Gastric and splenic lymph notes to the hepatic lymph nodes
Describe healing of the stomach?
Rapid healing - rich blood supply and paucity (littleness) of intraluminal bacteria.
3-4 days postoperative:
- inflammation predominates, infiltration of neutrophils and macrophages to clean up cellular debris
- fibrin seal along serosa typically prevents leakage but surgical sutures are responsive for maintaining wound approximation
- migration of mucosal epithelium across wound bed
5-12 days postoperative:
- rapid acceleration of wound strength
- collagen-rich submucosa main source of fibroblasts for proliferative phase
Weeks following day 12 postoperative:
- maturation of gastrotomy scare
Long term complications uncommon
Describe food withholding in patients prior to surgery
Traditionally 8-12 hours recommended
However, withholding food does not reliably empty the stomach, lowers the pH and actually increases the risk of oesophagitis and postoperative stricture from gastro-oesophageal reflux
Small amounts of food at least 3 hours before the procedure have been shown to reduce gastric acidity and even the incidence of reflux
What electrolyte abnormalities may result from pyloric FBs?
Loss of potassium, sodium, hydrogen and chloride ions
Results in a hypokalaemic, hypochloraemic metabilic alkalosis
Monitor electrolyte values carefully in the perioperative and immediately postoperative period
What key considerations of gastric surgery should be considered?
Exteriorisation
- cannot usually be exteriorised from the abdomen
Contamination risk
- risks of ingesta spilling into abdomen
Visualisation
- requires adequate length abdominal incision extending from the xiphoid process of the sternum to a point caudal to the umbilicus
- may require a parapreputial skin incision in the male dog
- consider falciform ligament excision, especially in overweight and deep-chested dogs
- consider Balfour retractors or large Gelpi retractors in small dogs or cats as a substitute
Stay sutures
- can elevate proportion of the stomach before gastrotomy is made
- can also use Babcock forceps for this purpose
Barriers
- moist laparotomy swabs/sponges
- reduce gastric serosal abrasion if moist
Abdominal lavage
- 0.9% saline or hartmann’s
- 37-39 degrees celcius (warm)
- minimum 1 litre large dog, 500 ml cat
- ensure to suction remnant prior to closure
PPE
- consider clean and dirty surgical kit/gloves
- seperate kits for gastric vs abdominal closure
Perioperative antibiotics
- not required unless break in asepsis/ingesta spillage into abdomen
- relatively low population of bacteria within the stomach normally
What are the phases of healing in the stomach, with days?
Lag/reparative phase - day 1-3
Proliferative phase - day 3-14 = wound strength 80% normal
Maturation phase day 14 onwards = reaches 90% normal bursting strength
What are the benefits of the submucosa as the primary closure layer?
Greatest vascularity
Greatest collagen content
Greatest tensile strength
How should the stomach be closed?
2 layers - including submucosa in at least 1 of the layers
layer 1 - mucosa/submucosa = Cushing or Connell continuous inverting pattern; suture material may enter the lumen of the stomach; can use simple continuous approximating if Cushing or Lembert used for second layer
layer 2 - Cushing or Lembert pattern, can also use simple continuous approximating pattern
What type of needle is best for closure of the stomach?
Taper needle or taper point needle.
Cutting needles may lacerate the muscularis or submucosa during passage through those tissues
What clinical syndromes may be observed following antrectomy procedures?
Chronic vomiting
Alkaline reflux gastritis
Marginal (anastomotic) ulcer - more common in Billroth 2 procedures
Gastric dumping syndrome
Afferent loop syndrome - Billroth 2 procedure
What is a Billroth 1 procedure?
Used when resection of the antrum and/or body of the stomach.
Used to correct luminal disparity, with partial closure of the larger lumen.
What is a Billroth 2 procedure?
Gastrojejunostomy following partial gastrectomy (including pylorectomy).
Joins the jejunum to the stomach.
Describe a Billroth 1 vs 2 procedure
Describe the difference between an axial/sliding hiatal hernia and a paraoesophageal/rolling hiatal hernia.
How are hiatal hernias diagnosed?
Survey/contrast radiography
- gastric silhouette cranial to diaphragm
- dilated caudal mediastinal oesophagus (oesophagitis)
Endoscopy
- large gastro-oesophageal junction/large diaphragmatic hiatus
Fluroscopy
- specifically for hiatal hernias that undergo spontaneous reduction
Can medical therapy correct a hiatal hernia?
Usually only palliative
- mucosal protectants, e.g. sucralfate
- H2 blocking agents, e.g. omeprazole
Surgical correction usually required
Briefly describe the surgical management of a hiatal hernia
- surgical reduction of the oesophageal hiatus
- pexy of the cardia of the stomach to the diaphragm
- left-sided tube or incisional gastropext to place caudal traction on the stomach and reduce chances of reherniation
What % of patients post hiatal hernia repair experience continued regurgitation?
Up to 50%
Briefly describe the anatomy of the pancreas
- bilobar structure - right and left lobes
- lobes joined at pancreatic body
- angle formed between the pancreatic body by the two lobes is smaller in cats than dogs
- right = duodenal lobe; located in the peritoneal fold of descending duodenum; in cats the distal third curves cranially, giving a hook-like appearance ending close to the vena cava; easily exposed via the duodenal manoevre
- left lobe positioned in a dorsal fold of the omentum; begins at the pylorus and extends along the greater curvature of the stomach to the dorsal extremity of the spleen; exposure best achieved by retraction of the stomach and greater omentum cranially, which retracting the transverse colon caudally
- body of the pancreas is adjacent to the proximal duodenum
What is the vascular supply to the pancreas?
Arterial:
- tripartite
- cranial pancreaticodurodenal artery, terminal branch of the gastroduodenal arter
- pancreatitc artery, in 80% of dogs branching from the splenic artery and 20% the pancreatic artery
- caudal pancreaticoduodenal artery, arising from the cranial mesenteric artery
Venous:
- pancreaticoduodenal vein
- splenic vein
What innervates the pancreas?
Vagal nerve fibres, that when stimulated cause an increase in pancreatic juice production and secretion
Coeliac and superior mesenteric plexus innervate the blood vessels which supply the pancreas
What are the main differences in pancreatic duct anatomy between the dog and cat?
Dog:
- two pancreatic ducts
1. Pancreatic
2. Accessory
Cat:
- in 80% will only have accessory pancreatic duct
What are the fibrotic nodules (1-2 mm) commonly found on the pancreas of older dogs and cats?
Incidental findings, likely resulting from previous bouts of pancreatitis.
List indications for a partial pancreatectomy?
- focal pancreatic trauma
- isolated pancreatic masses, pseudocysts or abscesses
What percentage of the pancreas can be removed without affecting exocrine and endocrine function?
75-90%
Why should a total pancreatectomy NOT be attempted by an inexperienced surgeon?
Extremely difficult to remove right pancreatic lobe while sparing share blood supply to the duodenum.
List common surgical conditions of the pancreas?
- Insulinoma
- Gastrinoma
- Glucagonoma
- Exocrine pancreatic neoplasia
- Pancreatitis - controversial
- Pancreatic abscess
- Pancreatic pseudocyst
Why should careful handling of a pancreatic insulinoma occur?
Excessive manipulation can lead to increased insulin secretion, leading to a more profound hypoglycaemia
Briefly describe the key features of the anatomy of the small intestine.
Tethered by mesentery arising from the mesenteric root
Mesenteric artery and vein, intestinal lymphatics and large mesenteric nerve plexus arborise in the mesenteric root
Relatively immobile duodenum, long and mobile jejunum and short ileum
Duodenum:
- continuous with pylorus of the stomach
- position changes dependent on the colonic and bladder filling
- cranially has the right limb of the pancreas within the short mesoduodenum
- pancreatic ducts and CBD enter the duodenum
- 75% of dogs have two pancreatic ducts
- only 20% of casts have an accessory pancreatic duct
Jejunum:
- longest part of SI
- series of loops around the root of the mesentary
- contains cranial mesenteric vessels, lymphatics and mesenteric nerve plexus
- in contact with majority of organs, but rarely extends into the pelvic cavity
- covered ventrally and laterally by omentum
- cranial mesenteric artery branches into ileocolic and caudal pancreicoduodenal arterties before branching into 12-15 jejunal arcadial arteries, which in turn branch into terminal arcadial vessels which supple the jejunum by multiple vasa recti that penetrate and supply all layers of the intestinal wall
Ileum:
- terminal region of SI
- gross characteristic is an antimesenteric ileal vessel within the ileocolic fold, the artery arising from the ileocaecal artery
- mesenteric ileal artery is a branch of the ileocolic and last jejunal arteries
- ileum otherwise grossly the same as the jejunum
- joints the LI at the ileocolic valve
Describe healing in the small intestinal tract
- Lag
- days 1-4
- macrophages invade the wound and deliver cytokines that stimulate and facilitate fibroplasia and angiogenesis
- by day 3 epithelial migration, sealing the wound
- dehiscence most likely to occur within first 72-96 hours as fibrin seal is weakened by fibrinolysis
- all support from sutures - Proliferative phase
- day 3/4 to 14 days
- proliferation of fibroblasts
- marked increase in immature collagen production, resulting in rapid gain in wound bursting strength
- by day 14 wound strength will have reached normal levels - Maturation phase
- of little clinical importance
- continues from day 14 to day 180 (6 months)
- reorganisation and remodelling as the collagen fibres selectively resorbed/form important cross links
- process dependent on intramural tension
List examples of host factors that may affect wound healing in the small intestine.
Describe the pathophysiology of intestinal obstruction
Describe the pathophysiology of small intestinal strangulation
List and describe the clinical signs associated with small intestinal obstruction
List differential diagnoses for cats and dogs presenting with vomiting, diarrhoea and weight loss.
How is a small intestine obstruction diagnosed radiographically?
Comparing luminal diameter to the height of the body of the fifth lumbar vertebra at its narrowest point.
Should be < 1.6 in a normal intestine.
Ratio of > or = 1.95 gives a > 80% chance of SI intestine obstruction.
How should the enterotomy site be closed?
Holding layer of intestine = submucosa
Simple appositional suture patterns
Will lead to a small degree of eversion and inversion histologically, although clinical results are good
No double-layer closure as will reduce intestinal lumen and have poor submucosal apposition - will heal slower via secondary intention
Everting patterns should be avoided as may cause adhesions to develop
Describe types of assessments made with small intestine?
Describe the placement of a jejunostomy tube
Describe the appearance of SI with linear FBs?
Plication due to anchor effect
Describe the components of an intussusception?
Intussusceptum = invagination of a portion of the intestine
Intussuscipiens = into the lumen of another
Describe the anatomy of the perineum.
Describe a traditional herniorrhaphy technique
What are the advantages of the internal obturator muscle transposition? Describe the technique.
Advantages (over traditional herniorrhaphy):
1. reduces tension on approximating sutures, thus reduces distortion of the external anal sphincter
2. brings in additional muscular tissue and blood supply, improving healing and preventing breakdown
Recommended procedure of choice for bilateral or more severe perineal hernias.
Key point is to no pass more cranial than the caudal edge of the obturator foramen. This prevents concurrent damage to the obturator nerve and artery.
As elevation occurs 3 tendon bands will emerge.
Transect tendon medially to the point where it passes laterally over the body of the ischium to prevent damage to the sciatic nerve. Care to avoid the blood vessel that runs immediately cranial to the tendon.
Muscle is transposed medially and dorsally to fill the hernial defect.
