Lecture 11 - Alimentary 3 Flashcards
Where does the rectum extend between?
S3 to pelvic diaphragm
The ampulla is the superior more narrow section, true or false?
False
How do you distinguish the rectum from the sigmoid colon? (5)
- No mesentery
- Retroperitoneal
- No sacculations
- No epiploic appendices
- No taenia
What is the special feature of the mucous in the wall of the rectum?
The submucosa contains a venous plexus linking superior and inferior rectal veins
What are the 2 planes of curvatures in the rectum?
- Anterior to posterior - follows the curve of the sacrum (sacral flexure)
- Laterall - Right to Left (largest) then Right
Where and what kind of folds are temporary in the rectum?
Longitudinal and in the ampulla
What are the features of the permanent folds in the rectum? (4)
- Variable in number
- Size and shape but commonly three
- Include mucosa, submucosa and a variable amount of external muscle
- The folds produce lateral folds?
Which permanent fold of the rectum is the largest and most constant
The middle fold
Where is the middle fold located? Where are the other folds located in relation to this?
Immediately above ampulla and roughly at the level of the rectovesicular/uterine pouch. The others are 4cm above or below
The peritoneum is loosely attached to the rectum true or false?
True
Where is the peritoneum attached on the rectum (3 points)?
Upper 1/3 - anterior and sides
Middle 1/3 - anterior only
Lower 1/3 - no periteoneum
What does the reflection of the middle 1/3 attachment of the peritoneum form?
The rectovesicular pouch
What are the posterior relations of the rectum (3)?
Sacrum, coccyx and pelvic diaphragm
What are the lateral relations of the rectum (3)?
Sigmoid colon, ileum, pelvic diaphragm
What are the anterior relations of the rectum in the male? (5)
Rectovesicular pouch, base of bladder, ductus deferens, prostate, seminal vesicle
What are the anterior relations of the rectum in females? (3)
Rectovesicular pouch (Pouch of Douglas), uterus and vagina
How does the anal canal sit/run
Using it’s legs hah
Postero-inferiorly through the pelvic diaphragm (coccygeus) to anus
What is the sling of skeletal muscle at the rectoanal junction called?
Puborectalis
How many columns are in the upper part of the rectum
6-10
How are the lower ends of the columns joined?
Transverse folds or valves
What is the space between columns called?
Sinuses
What is the line of valves in the rectum called?
Pectinate or dentate or mucocutaneous line
Where is the cloacal membrane?
At the pectinate/dentate/mucocutaneous line
What is the cloacal membrane? (2)
Junction of mucosa with skin with its own blood supply
How do the different layers of mucosa change in the rectum?
From epithelium to simple columnar than a transitional zone or non keratinised stratified squamous epithelium
There are sphincters over the entire length of the anal canal true or false?
True
Where are the internal and external sphincters?
Upper 2/3 and lower 2/3 of the anal canal
What do the internal sphincters consist of?
Thickened circular layer of external smooth muscle which stop at the junction of skin
What do the external sphincters consist of?
A tube of skeletal muscle outside external muscle (3 parts)
The movement of the external sphincters is voluntary, true or false?
False, it is only partly voluntary
Where is the rectoanal junction?
At the level of the tops of the columns
The rectoanal junction is narrower than the ampulla, true or false?
True
What if a posterior relation to the anal canal?
Anococcygeal ligament (dense connective tissue which extends from coccyx to anal margin)
What are the anterior relationships to the anal canal?
Perineal body and membranous urethra/bulb of penis OR vagina
What is the lateral relation to the anal canal?
Ischiorectal fossa
How long does the bolus spend in the stomach and small intestine?
1-3 hours and 1-6 hours
How does the bolus move from the stomach to the small intestine
Segmenting contractions and peristalsis from one end to the other (motilin)
How does the bolus move from the ileum to the large intestine?
Gastrocolic reflex
What keeps the anus closed?
Muscle tone stimulated by sympathetic nerves
When does the muscle tone normally increase
When intraabdominal pressure rises e.g. coughing
What are 4 things that keep the anus closed?
muscle tone, puborectalis, reverse peristalsis and relaxation of muscle wall of rectum and sigmoid
Where is the faeces held prior to defecation?
In the ampulla
What sends the defecation reflex?
Medulla oblongata
Where is faeces voided from?
The splenic flexure down
What is defecation?
Rectal stretching
What are three things that occur during defecation?
Relaxation of sphincters and puborectalis
Peristalsis in descending and sigmoid colon increases
Contraction of abdominal muscles and diaphragm which raise abdominal pressure
What are the functions of the two pancreas?
Exocrine - digestive enzymes
Endocrine - Islets of Langerhans
What does the pancreas develop from?
Two outgrowths from the foregut (dorsal and ventral pancreatic bud)
How do the buds turn into the pancreas? (3)
1) Buds form a series of branching epithelial lined tubules arising from distal/caudal foregut
2) Form pancreatic ducts which then develop into acini
3) Islets also arise from tubule cells which then separate and come to lie in connective tissue between the tubules.
4) The ventral pancreas rotates posteriorly so that i ultimately lies behind the dorsal pancreas
5) The two primordia then fuse.
When does insulin secretion first begin?
10 weeks into gestation
What causes the ventral pancreas to rotate posteriorly so that it lies behind the dorsal pancreas?
Rotation of the stomach and differential growth
Which duct remains as the main pancreatic duct?
The ventral duct
What happens to the dorsal pancreatic duct during development (2)
The dorsal duct also rearranges to drain into the ventral duct the part most proximal the duodenum may persist as a minor pancreatic duct
What causes the pancreas to become retroperitoneal?
Pressure from adjacent organs pushes the pancreas against the abdominal wall and layers of peritoneum fuse
What does the ventral pancreatic bud form? (2)
The uncinate process and inferior head
What does the dorsal pancreatic bud form?
The rest of the pancreas
How long is the mature pancreas?
12-15 cm long
The entire mature pancreas is retroperitoneal true or false?
False, everything is retroperitoneal apart from the tail
Where does the mature pancreas extend from?
Duodenum to spleen behind the stomach
What are the four regions of the pancreas?
Head, uncinate process, body, tail
Where does the head and uncinate process lie?
Within the curve of the duodenum
What is posterior to the head and uncinate process (2)?
IVC and aorta
What is the uncinate process?
Lower extension of head behind superior mesenteric vessels
What do the anterosuperior faces of the body of the pancreas face?
Lesser and greater sac
Where does the transverse mesocolon attach to the pancreas?
Anterior angle of the body
Where does the tail travel?
It accompanies the splenic vessels into splenorenal ligament
Where does the main duct drain into?
The greater duodenal papilla in the posteromedial wall of descending duodenum.
What may the bile and main pancreatic duct unite to form?
The hepatopancreatic ampulla
Where would the accessory duct open if it exists?
2cm superior to the main duct
What is a defining feature of the main pancreatic duct?
A herringbone pattern of lobar ducts drain into the main duct
Where does the main pancreatic duct sit?
Within the pancreas towards posterior surface
