Case 4 Anatomy Flashcards
what does the small intestine extend from and to?
pyloric sphincter to the ileocecal junction
what is the function of small intestine?
main site of digestion and absorption
what are structural adaptions present in the small intestine to increase surface area for absorption?
- Plicae circulares = circular folds in the mucosa that can be seen with the naked eye
- Villi = finger-like projections of the mucosa
- Microvilli = microscopic protrusions from the luminal surface of the intestinal cells
how is most of the small intestine suspended? what does this arrangement ensure?
- from the posterior abdominal wall by the mesentery
- this arrangement ensures that the coils of the jejunum and ileum are freely mobile
which parts of the intestines have a mesentery?
the small intestine is differentiated from the large intestine by the presence of a mesentery (exceptions being no mesentery in the duodenum, and presence of a mesentery in the transverse and sigmoid colons)
how long is the root of the mesentery?
approx. 15cm long
along what is the root of the mesentery attached to the posterior wall?
a Iine that extends from the left side of the 2nd lumbar vertebra to the (right I think) sacroiliac joint
how do blood vessels, lymphatics and nerves supply the small intestine? what is the benefit?
- they enter at the root of the mesentery and pass through it to supply the small intestine
- this arrangement prevents tangling and trapping of the neurovascular structures
what is the main site of digestion?
duodenum
how long is the duodenum and what does extend from and to?
- C-shaped tube
- approximately 25cm long (12 finer breadths)
- extends from the pyloric sphincter to the jejunum
what is the duodenum divided into?
divided into four parts (sometimes referred to numerically (first, second, third or fourth) but may be specifically named: • First = superior part • Second = descending part • Third = horizontal part • Fourth = ascending part
describe the pancreas’ relation to different parts of the duodenum
head of the pancreas sits in the C-shape of the duodenum, it therefore lies inferior to the superior part, medial to the descending part and superior to the inferior part
what are the anterior relations of the duodenum? (each part)
- Superior part = quadrate lobe of liver & gallbladder
- Descending part = fundus of gallbladder, right lobe of liver, transverse colon, coils of small intestine
- Horizontal part = root of mesentery, coils of jejunum
- Ascending part = beginning of root of mesentery and coils of jejunum
what are the posterior relations of the duodenum?
- Superior part = lesser sac, gastroduodenal artery, bile duct, portal vein, inferior vena cava
- Descending part = hilus of right kidney
- Horizontal part = right ureter, inferior vena cava, aorta
- Ascending part = left margin of aorta
what opens into the descending duodenum?
minor and major papillae
what is the most distal part of the foregut?
descending duodenum
what does the superior duodenum have attached to it?
part of the lesser omentum attached to its superior border and part of the greater omentum attached to its inferior border
what is the ascending duodenum supported by?
suspensory muscle of the duodenum (ligament of Treitz)
double fold of peritoneum suspending the duodenojejunal flexure from the retroperitoneum
which part of the duodenum is intraperitoneal?
superior duodenum has an intraperitoneal section
where is the duodenum continuous with the jejunum?
at the duodenojejunal junction
what is the blood supply to the duodenum?
- The first two parts of the duodenum are foregut structures and the third and fourth parts are midgut structures, therefore the duodenum receives arterial blood from both the coeliac trunk and superior mesenteric artery
- The parts of the duodenum proximal to the major duodenal papilla are supplied by the superior pancreaticoduodenal artery, a branch of the gastroduodenal artery which arises from the coeliac trunk
- The parts of the duodenum distal to the major duodenal papilla are supplied by the inferior pancreaticoduodenal artery, a branch of the superior mesenteric artery
how long is the jejunum?
approx. 2.5m long
what does the ileum extend from and to?
from the distal end of the jejunum to the ileocaecal junction
how long is the ileum?
approx. 3.6m long (longest section)
what happens in the jejunum?
most absorption
however, where is the only site of vitamin B12 absorption?
terminal ileum
what is the blood supply of the jejunum and ileum?
superior mesenteric artery
how does the SMA supply the jejunum and ileum?
- It enters the mesentery at the root of the mesentery and divides into about 15-18 branches
- The arteries unite to form loops termed arcades
- The arcades give rise to straight vessels, vasa recta, which project to the intestinal wall
compare the jejunum and ileum
- arcades
- vasa recta
- vascularity
- diameter
- colour
- fat in mesentery
- where
- wall thickness
Jejunum: • Fewer, large arcades • Long vasa recta • More vascular • Wider in diameter • Redder in colour • Less fat in mesentery • Mostly located in left upper quadrant of infracolic compartment • Thicker walled
Ileum: • Many, short looped arcades • Short vasa recta • Less vascular • Narrower in diameter • Paler in colour • More fat in mesentery • Mostly located in right lower quadrant of the infracolic compartment • Thinner walled (basically less everything but more fat)
where is there the highest abundance of plicae circulares in the small intestine?
proximal jejunum
histologically, how can the duodenum be differentiated from other parts of the small intestine?
- the presence of Brunner’s glands
(secrete an alkaline fluid which exerts an anti-acid function by coating the duodenal epithelium, therefore protecting it from the acid chyme of the stomach)
histologically, how can the ileum be differentiated from other parts of the small intestine?
- by the presence of Peyer’s patches
small masses of lymphatic tissue
what are the functions of the large intestine?
- water absorption
- synthesis of vitamins
- storage of undigested food
- formation and excretion of faeces
how does the length and diameter of the large intestine compare to that of the small intestine?
large intestine is shorter than the small intestine, but much larger in diameter
what is the large intestine divided into?
the caecum, ascending colon, hepatic flexure, transverse colon, splenic flexure, descending colon, sigmoid colon, rectum and anal canal
what is special about the large intestine?
- teniae coli
- epiploic appendages
- haustra
- semilunar folds
what are the teniae coli?
three distinct strips of muscle formed from the longitudinal fibres of the muscularis externa
what are the epiploic appendages?
small fat-filled sacs that project from the outer wall of the intestine
what are the haustra?
sacculations in the wall of the large intestine
what are semilunar folds?
folds on the internal wall of the intestine between the haustra
what is the blood supply of the large intestine?
- The regions proximal to the distal third of the transverse colon are midgut structures and therefore supplied by the superior mesenteric artery
- Those distal to this point are hindgut structures and therefore supplied by the inferior mesenteric artery
what are the arteries supplying the large intestine?
- Superior mesenteric
- Middle colic
- Right colic
- Ileocolic
- Caecal (anterior & posterior)
- Appendicular
- Marginal
- Inferior mesenteric
- Left colic
- Sigmoidal
- Superior rectal
where is the caecum located?
in the right inguinal abdominal region
what lies posterior to the caecum?
psoas major
what is the arterial supply of the caecum?
- anterior and posterior caecal arteries
- they arise from the ileocolic branch of the SMA
what opens into the caecum and where?
- Two orifices open into the posteromedial wall of the caecum
- One is the ileal orifice and the other is the orifice of the appendix
where does the ileal orifice open into the caecum? what does this consist of? what does this do?
- ileocaecal valve
- consists of two horizontal folds of mucous membrane, one above and one below the ileal orifice
- it is debatable whether the ileocaecal valve prevents reflux of caecal contents into the ileum but it may control the flow of the contents from the ileum into the colon
what does the appendix represent?
tip of the caecum that fails to enlarge during development
describe the appendix wall
it presents the 4 basic layers of the gastrointestinal tract and a lumen of variable diameter
what is the lumen of the appendix like throughout life?
lumen is wide in young children, obliterated by middle age and narrow in adolescence
which age group is most prone to appendicitis?
adolescents
how does the length of the appendix vary between individuals?
ranges from 6 - 13cm
what is the position of the tip? how can the appendix be located?
- position is also variable – it may coil up behind the caecum, hang down into the pelvis, project up lateral to the caecum or project up anterior or posterior to the ileum
- this can make it difficult to find during appendicectomy
- the appendix may be located by following the three bands of the teniae coli as they descend over the caecum and converge at the base of the appendix
in relation to surface anatomy, where is the base of the appendix located?
at McBurney’s point
where is McBurney’s point located?
two-thirds of the way along an imaginary line that extends laterally from the umbilicus to that anterior superior iliac spine (the line goes laterally and inferiorly = oblique)
what is the mesentery of the appendix like and called?
suspended from the mesentery of the small intestine = mesoappendix
where are the appendicular artery and vein found?
running through the mesoappendix
where does the appendicular artery arise from?
ileocolic artery (or posterior caecal or ileal artery?)
what does the appendicular vein drain via and into what?
drains via the ileocolic vein into the superior mesenteric vein
what is the lymphatic system of the appendix like? what does lymph drain into? then into what?
- appendix is rich in lymphoid tissue
- lymph from the appendix drains into the ileocolic nodes
- efferent vessels from these nodes drain into superior mesenteric nodes
what do afferent pain fibres from the appendix accompany and where do they enter the spinal cord?
- accompany the sympathetic (got to be sympathetic because of the pain) fibres
- enter the spinal cord at the level of T10
where is pain from the appendix perceived?
in the umbilical abdominal region
how long is the ascending colon? what’s its route?
- approx. 13 cm
- it extends upwards through the right lower quadrant and turns as it reaches the liver forming the hepatic flexure
what are the anterior relations of the ascending colon?
- greater omentum
- coils of the small intestine
- anterior abdominal wall
what are the posterior relations of the ascending colon?
- iliac crest
- iliacus muscle
- quadratus lumborum
what crosses behind the ascending colon?
- ilioinguinal
- iliohypogastric nerves
(they arise from L1 spinal segment)
what is the largest portion of the colon?
transverse colon
how long is the transverse colon?
approx. 38cm
describe the course of the transverse colon
extends from the hepatic flexure, hangs down and crosses the abdomen ascends towards the spleen, it turns at the splenic flexure where it leads into the descending colon
is the transverse colon intra or retroperitoneal?
intraperitoneal
what is the transverse colon suspended by from what?
by the transverse mesocolon from the anterior border of the pancreas
what is attached to the superior and inferior borders of the transverse colon?
- The transverse mesocolon attaches to the superior border of the transverse colon
- The greater omentum is attached to the lower border of the transverse colon
what are the anterior relations of the transverse colon?
- greater omentum
- anterior abdominal wall
what are the posterior relations of the transverse colon?
- coils of ileum
- coils of jejunum
- head of pancreas
- second part of duodenum
what is the transverse mesocolon?
The transverse mesocolon is a broad, meso-fold of peritoneum, which connects the transverse colon to the posterior wall of the abdomen – it’s continuous with the two posterior layers of the greater omentum, which, after separating to surround the transverse colon, join behind it and are continued backward to the vertebral column, where they diverge in front of the anterior border of the pancreas
how long is the descending colon?
approx. 25cm
what is the route of the descending colon?
descends from the splenic flexure, passes through the left upper and left lower quadrants and becomes continuous with the sigmoid colon
what are the anterior relations of the descending colon?
- greater omentum
- coils of the small intestine
- anterior abdominal wall
what are the posterior relations of the descending colon?
- iliac crest
- iliacus muscle
- lateral border of left kidney
- quadratus lumborum muscle
- transversus abdominis muscle
what crosses posterior to the descending colon?
- femoral nerve
- iliohypogastric nerve
- ilioinguinal nerve
- lateral cutaneous nerve of the thigh
where does the sigmoid colon meet the rectum?
S3
- forms an S-shaped loop as it extends between the descending colon and the rectum
what attaches the sigmoid colon to where?
sigmoid mesocolon to the posterior pelvic wall
how is the junction (rectosigmoid junction) between the sigmoid colon and the rectum marked?
- by changes in the muscle layer
- the teniae coli disappear and are replaced by a complete layer of longitudinal muscle
how long is the rectum?
approx. 13cm
what does the rectum pass down in front of?
S3-S5 and coccyx
what happens to the rectum at the level of the tip of the coccyx?
it pierces the pelvic diaphragm and becomes continuous with the anal canal
the rectum is not straight, what flexures are apparent?
- sacral flexure of the rectum
- anorectal flexure
- superior and inferior lateral flexures
- intermediate lateral flexure
what is the sacral flexure?
this flexure follows the curve of the sacrum and coccyx
what is the anorectal flexure? what important for?
the sharp postero-inferior angle where the rectum pierces the pelvic diaphragm – important in maintaining faecal continence
where are the superior and inferior lateral flexures located?
on the left side of the rectum
where is the intermediate lateral flexure located?
on the right side of the rectum
where is the rectum in terms of the peritoneum?
partially retroperitoneal and partially below the level of the peritoneum (subperitoneal)
what are the anterior relations of the rectum?
- Vagina (females)
- Prostate (males)
- Seminal vesicles (males)
- Base of bladder (males)
- Coils of intestine
what are the posterior relations of the rectum?
- Sacrum
- Coccyx
- Median sacral artery
what is the dilated distal end of the rectum called?
rectal ampulla (bigger area than would expect)
what does the puborectalis do?
is the portion of the levator ani muscle that forms a sling around the rectoanal junction, pulling it forward and forming the anorectal flexure
what are the transverse folds of the rectum? how formed?
- on the inside of the rectum a number of permanent semi-circular folds are evident
- these are made from folds in the mucosa and circular muscle layers
how long is the anal canal?
approx. 4cm
in which direction does the anal canal extend from the rectal ampulla?
downward and backward
what is the anococcygeal body?
fibrous structure that lies posterior to the anus
what lies lateral to the anus?
ischioanal fossa
what is the perineal body?
fibrous structure that lies anterior to the anus
what is the pectinate line?
(dentate line) demarcates where the upper half of the anus joins the lower half (not only in structure but also in neurovascular supply (reflecting the differing embryological origin)) (above the dentate line the epithelium is a mucous membrane like the rest of the gastrointestinal tract and below the dentate line the epithelium is considered cutaneous) (the dentate line is formed by the anal columns, which consists of a series of anal sinuses (which drain anal glands))
upper half of the anal canal
- lymph drainage
- arterial supply
- venous drainage
- Lymph drains to inferior mesenteric nodes via lumbar nodes
- Arterial supply – superior rectal branch of IMA
- Superior rectal vein drains to portal system via IMV and splenic
lower half of anal canal
- lymph drainage
- arterial supply
- venous drainage
- Lymph drains to superficial inguinal nodes
- Supplied by inferior rectal branch of pudendal artery
- Inferior rectal vein drains to internal iliac via pudendal vein
upper half of anal canal
- are anal columns present
- what epithelium
- what derivative
- Anal columns present
- Columnar epithelium
- Hindgut derivative
lower half of anal canal
- are anal columns present
- what epithelium
- what derivative
- No anal columns present
- Stratified squamous epithelium
- Derived from proctodeum
upper half of anal canal
- what innervation
- where nerve fibres from
- what sensitive to
- Innervated by ANS
- Nerve fibres from hypogastric plexus (the superior hypogastric plexus receives contributions from the two lower lumbar splanchnic nerves L3-L4?)
- Sensitive to stretch
lower half of anal canal
- what innervation
- what sensitive to
- Innervated by inferior rectal branch of pudendal nerve
* Sensitive to pain, temperature, touch and pressure
