9. Anatomy of the jejunum, ileum & large intestine.pptx Flashcards
Ileum –> ________ –> Anus
Ileum --> Large intestine: caecum plus appendix; ascending colon; transverse colon; descending colon; sigmoid colon; --> Rectum and anal canal --> Anus
The jejunum begins at the _______ flexure, and the ileum ends at the _______ junction in the right iliac fossa. There is a ______ change from jejunum to ileum
The jejunum begins at the duodenojejunal flexure, and the ileum ends at the ileocaecal junction in the right iliac fossa. There is a gradual change from jejunum to ileum
Difference in position between the jejunum and ileum?
The jejunum lies in the upper left abdomen, while the ileum tends to be lower right and also in the pelvis
Difference between jejunum and ileum
Jejunum:
- Wider bored
- Thicker walled : because the permanent infoldings of the submucosa, the plicae circulares, are larger, more numerous, and more closely set in the jejunum
- Redder
Difference between jejunum and ileum
Jejunum:
- Wider bored
- Thicker walled : because the permanent infoldings of the submucosa, the plicae circulares, are larger, more numerous, and more closely set in the jejunum
- Redder
Peyer’s patches in mucous membrane of lower ileum along anti-mesenteric border
Difference in mesentery of jejunum and ileum
Mesentery of jejunum:
The mesenteric vessels form only one or two arcades, with long and less frequent branches passing to the intestinal wall
The fat is deposited near the root and is less obvious near the intestinal wall
Mesentery of ileum:
The ileum receives numerous short terminal vessels that arise from a series of three or four or even more arcades
The fat is deposited throughout so that it extends from the root to the intestinal wall
What are Peyer’s patches?
Aggregations of lymphoid tissue (Peyer’s patches) are present in the mucous membrane of the lower ileum along the antimesenteric border;
What is the ileocaecal valve?
Structure
Function?
A rudimentary structure, the ileocaecal valve consists of two horizontal folds of mucous membrane that project around the orifice of the ileum, situated at the junction of the small intestine (ileum) and the large
intestine
Its function is to limit the reflux of colonic contents into the ileum and possibly control the flow of ileal contents into the caecum
Mid gut derived structure send referred pain to…
Peri-umbilical area (T10)
Ileum and jejunum: Blood (arteries and venous), lymph and nerve supply?
Jejunal and ileal arteries from the Superior Mesenteric Artery and its ileocolic branch
The veins correspond to the branches of the SMA and drain into the superior mesenteric vein, which forms the portal vein
Lymph Drainage is to superior mesenteric nodes, which are situated around the origin of the SMA
Nerve Supply is derived from the sympathetic, lesser splanchnic nerve T10 and 11, and parasympathetic (vagus) nerves via the superior mesenteric plexus
What forms a sequence of vascular, anastomotic arcades in the mesentery?
SMA
Intestinal lymph drainage via the mesentery
There is a lacteal in the centre of each villus for the absorption of digested fats and lipids (chyle).
The chyle passes from the lacteals into mesenteric lymph channels that DO NOT pass through lymph nodes but converge on the cisterna chyli and passes through the diaphragm as the thoracic duct (the absorbed LIPID molecules are TOO BIG for the lymph node “filters”)
The intestinal wall is packed with lymphocytes, in the ileum these aggregate as Peyer’s patches.
Lymph absorbed from the intestinal wall again passes into mesenteric lymph channels, but these FILTER through the mesenteric nodes
Afferents from the mesenteric nodes converge on nodes at the root of the SMA
Afferents from the nodes on the SMA pass to the cisterna chyli
Meckels Diverticulum:
How is it formed?
Remnant of?
Side effects?
How is it formed?
As intestinal tract communicates with yolk sac, can leave behind a Meckel’s Diverticulum
Remnant of?
The Vitello-intestinal duct
Side effects?
May ulcerate causing signs and symptoms similar to appendicitis
Structures that make up colon
Consists of the caecum, ascending colon, hepatic (right) flexure, transverse colon, splenic (left) flexure, descending and sigmoid colon, rectum and finally anal canal
Function of colon?
Absorbs fluid and salts, dries out the chyme to form faeces
Peritoneum relations of colon?
The ascending and descending parts are retroperitoneal
The transverse and sigmoid colon are on a mesentery, i.e. intraperitoneal
3 distinctive external features of colon
- Possesses tags of fat - omental appendices (appendices epiploicae)
- Possesses 3 taeniae coli – condensations of the longitudinal muscle layer
- Possesses (sacculations) haustra of the colon
3 distrinctive internal features of the colon
- Lacks plicae circularis
- Lacks villi
- Lacks peyers patches
Caecum
Caecum, mesentery?
Relevance of peritoneal recesses around it?
How to find appendix in surgery?
Caecum not on a mesentry
Variable peritoneal recesses may form adjacent to caecum, appendix may be found in any of these recesses
The 3 taeniae coli converge in the caecum at the root of the appendix and may be a guide to its location during surgery
Appendix:
What is it?
Position?
What is it? The appendix is a narrow blind ended tube hanging from the caecum
Its submucosa is packed full of lymphoid tissue
Position?
Root of appendix at McBurney’s point – 1/3 up from ASIS to umbilicus
It is suspended on a short, but highly variable meso-appendix that transmits the appendicular vessels
Possibile structures affected by appendicitis?
The appendicular artery is close and parallel to the appendix distally, therefore it may be affected by an inflamed appendix and become obstructed causing gangrene and rupture of the appendix
Early appendicitis refers pain to….
The peri-umbilical region; if the appendicular artery travels with nerves from T10/11
As time passes when the parietal peritoneum is involved, the overlying skin is affected
Blood supply to the caecum and appendix?
All derived from the ileocolic artery from the SMA
- Anterior caecal artery
- Posterior caecal artery
- Appendicular artery (from posterior caecal)
[Hence lymph drainage is to nodes on the SMA]
Which section of the colon is mobile?
The sigmoid colon is mobile on a fan-shaped mesentery and hangs down into the pelvic cavity in the form of a loop
It may rotate upon itself: sigmoid volvulus.
What colonic structure can present as left sided appendicitis
Colonic diverticulae may become obstructed and mimic left sided “appendicitis”
Colon blood supply
SMA branches:
- Ileocolic to caecum
- Right Colic to ascending colon
- Middle colic to hepatic flexure and 2/3 transverse colon
IMA branches:
- Left colic to 1/3 transverse colon, splenic flexure, descending colon
- Sigmoid to sigmoid
These vessels cross the ureters and gonadal vessels
[Equivalent veins run with the arteries and drain to the portal vein; lymph drainage is to nodes on the SMA and IMA]
IMA: Supplies? Carries which nerves? Forms which anastomosis? Forms collateral in the event of what?
The inferior mesenteric artery (IMA) supplies the hindgut i.e. last 1/3 of transverse colon to rectum and proximal anal canal
Carries sympathetic nerves derived from T12 and parasympathetics from S 2, 3, 4 (NOT vagus) .
It forms an important anastomosis with the SMA the Marginal Artery (of Drummond)
May form a collateral circulation should the IMA become obstructed
Referred pain, which nerves supply which ___guts? Referred pain of each region?
Autonomic nerves run with the 3 arteries:
- Coeliac trunk to foregut
- Lower oesophagus, stomach, duodenum
- Refer to upper abdomen (T7 – 9) - Superior mesenteric to midgut
- Duodenum to 2/3 transverse colon
- Refer to peri-umbilical region (T10/11) - Inferior mesenteric to hindgut
- Refer to suprapubic region (T12)
Pancreatic secretion:
Characterics?
Factors that increase secretion?
Characteristics:
High HCO-3 (isotonic)
Pancreatic lipase, amylase and proteases
Factors that increase secretion:
Secretin
Cholecystokinin (CCK) (potentiates secretin)
Parasympathetic supply
What does the pancreas secrete?
into where?
Why?
Fluid into the duodenum
Composition: Aqueous, enzymes, high HCO-3
HCO-3: Neutralises stomach H+
Enzymes: Digest carbohydrates, proteins and lipids
