The Large Intestine Flashcards
what are the three main sections of the large intestine
- caecum
- colon
- rectum
what is the colon
the distal part of the gastrointestinal tract that extends away from the caecum at the right iliac fossa to the anal canal
what is the caecum
- the most proximal part of the large intestine, located between the ileum and the ascending colon.
- acts as a reservoir for chyme which it receives from the ileum
- found in the right iliac fossa of the abdomen, lying inferiorly to the ileocecal junction
- can be palpated if enlarged due to faeces, inflammation or malignancy
- continuous with the ascending colon
- intraperitoneal
which section of the large intestine is the most proximal
the caecum
where in the abdomen is the caecum located
right iliac fossa
when can the caecum become palpated
when there are faeces, inflammation or malignancy
what does the caecum derive its name from
inferior blind end - caecus means blind in latin
what is the caecum continouus with superiorly
the ascending colon
is the ascending colon within the peritoneum
no
what is found between the caecum and the ileum
the ileocaecal valve
what is the function of the ileocaecal valve
preventing reflux of large bowel contents into the ileum during peristalsis - thought to function passively
what can the colon be divided into
four parts; ascending, transverse, descending and sigmoid. the sections form an arch, encircling the small intestine
what are the four parts of the colon
ascending
transverse
descending
sigmoid
describe the ascending colon
beginning of the colon, and is a retroperitoneal structure which ascends superiorly from the caecum
rises upward and sits behind the peritonel, moving away from the caecum
how long is the colon
150cm
what is the transverse colon
the second section of the colon that extends from the right colic flexure to the spleen
the least fixed part of the colon, variable in position and is intraperitoneal
in what way is the transverse colon variable in position
can dip into the pelvis in tall and thin individuals
which section of the colon is the least fixed
the transverse colon
what is the descending colon
third section of the colon that is retroperitoneal in the majority of individuals, meaning it sits behind the peritoneum. located anteriorly to the left kidney
when does the descending colon become the sigmoid colon
when it begins to turn medially
describe the sigmoid colon
40cm long sigmoid colon located in the left lower quadrant of the abdomen, extending from the left iliac fossa to the level of the s3 vertebra. interperitoneal
journey gives the sigmoid colon its characteristic s shape
what is the hepatic flexure
the angle formed when the ascending colon becomes the transverse colon. also known as the right colic flexure, and marks the start of the transverse colon
where is the hepatic flexure
the 90 degree turn of the ascending colon by the liver where the transverse colon begins
what is the splenic flexure
the 90 degree turn as the transverse colon goes to the descending colon, also known as the left colic flexure.
where is the splenic flexure
where our spleen is, at the point where the transverse colon becomes the descending colon
what are the taenia coli
3 longitudinal bands of smooth muscle on the outside of the ascending, transverse and descending colon that help to differentiate between the large and small intestine
what is the haustra
circumferential contraction of the inner muscular layer of the colon
what are the appendice epipliocae
pouches of peritoneum filled with fat mainly on the transverse and sigmoid colon, though not the rectum
what is the rectum
the most distal segment of the large intestine, with an important role as a temporary store of faeces
describe the route of the rectum
begins as a proximal continuation of the sigmoid colon, that terminates into the anal canal
how is the rectum distinct from the colon
absence of haustrations, taenia coli and omental appendices
what do the rectal valves do
they support the weight of the faeces and slow movement to the anus, which produces the feeling of wanting to defecate. contains circular muscle
describe the internal haemorrhoidal plexus
a collection of veins in the rectum that communicate directly between the portal and systemic venous system
why do drugs given rectally act quicker than those taken orally
they bypass metabolism by passing through the gut
where is the internal haemorrhoidal plexus found
either side of the anal canal
what are the haemorrhoidal plexuses
big collections of veins located at the lower end of the rectum
what is the internal anal sphincter
involved in the involuntary control of the passage of faeces which gives the feeling wanting to go to the toilet. people gain control of it by 2
what is the external sphincter in control of
the voluntary control of expulsion of faeces
describe barium enema
filling the large intestine with diluted barium liquid while the x ray images are being taken. the barium enemas are used to diagnose disorders of the large intestine and rectum.
these disorders may include colonic tumours, polyps, diverticula and anatomical abnormalities
what are diverticula
abnormal out pouches
what are barium enemas used for
diagnosing disorders of the large intestine and rectum
what can be included in the disorders of the large intestine
- colonic tumours
- polyps
- diverticula
- anatomical abnormalities
what is the ileo-ceacal junction
this is the junction between the caecum and ileum, and is also known as a valve.
it is a fold of mucosa that allows chyme to pass from the small intestine to the large intestine
what leads off from the caecum
the vermiform appendix
does the caecum have an essential function in human beings
no
compare the structure of the large intestine to the small intestine (similarities)
the basic structures are the same:
- the same epithelium of simple columnar goblet cells
- intestinal crypts of leiberkuhn
- mucosal glands to produce mucous
describe the differences between the structure of the large intestine and the small intestine
large intestine lacks villi and has an incomplte layer of longitudinal muscle called taenia coli
ring like arrangement of haustrae
the mucosal folds can look like epithelium but they are not
describe the histological layers of the large intestine
- mucosa (epithelium) on the surface
- underlying lamina propria
- muscularis mucosae
- submucosa
- muscularis externa
what are crypts
the glands found in the epithelial lining of the small intestine and colon. covered by two types of epithelium - goblet cells and enterocytes
what are goblet cells
cells that secrete mucous
what do enterocytes produce
water and electrocytes
what are crypts and intestinal villi coverd by
goblet cells and enterocytes
where is the anal canal located
extraperitoneal between the anorectal junction and the anus
what are the zones of the anal canal
columnar zone
intermediate zone
cutaneous zone
what is the columnar zone of the anal canal
anal columns
anal cushions
valves
crypts of morgagni
dentate line
what is found in the intermediate zone of the anal canal
anoderm
what is found in the cutaneous zone of the anal canal
perianal skin
break down the blood supply of the anal canal
- above the dentate line is the superior rectal artery
- below the dentate line is the middle and inferior rectal arteries
how much of the anal canal is above the dentate line
two thirds
how much of the anal canal is found below the dentate line
a third
what supplies blood to the superior two thirds of the anal canal
the superior rectal artery
what supplies blood to the inferior third of the anal canal
middle and inferior rectal arteries
describe the venous drainage of the anal canal above the dentate line
superior rectal vein followed by the hepatic portal circulation
describe the venous drainage of the inferior third of the anal canal
middle and inferior rectal veins followed by the vena cava circulation
describe the innervation of the anal canal above the dentate line
inferior mesenteric plexus
pelvic splanchnic nerves
inferior hypogastric plexus
describe the innervation of the anal canal below the dentate line
pudendal nerve
what epithelium is found in the colorectal zone of the anal canal
simple columnar
what epithelium is found in the transitional zone of the anal canal
simple columnar and stratified squamous epithelium
what epithelium is found is the anoderm
stratified squamous non keratinised epithelium
what epithelium is found in the cutaneous zone
stratified squamous keratinised epithelium
what are the functions of the anal canal
faecal continence and defecation
what does the colon function in
absorption of fluids and electrolytes from the chyme within the small intestine as it passes into the caecum
what volume of chyme enters the large intestine from the ileum
0.5-1 litre
what does the colon absorb from the small intestine chyme
fluid and electrolytes
what can failure to absorb fluid and electrolytes lead to
diarrhoea
what is the role of the intestinal flora found within the large intestine
- fermenting dietary fibres like cellulose and lipids
- producing flatus (gas)
- synthesise some vitamins like the vitamin b complex and vitamin k
describe the vitamin b complex
8 different types of b vitamins
direct impact on energy levels, brain function and cell metabolism
helps prevent infections and good cell health, growth of red blood cells and nerve function
what is vitamin k
fat soluble and needed for blood clotting to help wound healing
describe the motility of the large intestine
- churning - similar to segmentation in the small intestine
- contraction of circular muscles to break things down locally
- squeezing action on chyme
- mainly in the caecum and the ascending colon
what are propulsive movements describing
the motility of the large intestine
what are the different propulsive movements of the large intestine
peristalsis and mass movements
describe peristalsis
short range peristalsis in transverse and descending colon, propelling semi solid faecel matter toward the rectum
describe mass movements
infrequent, more sustained contractions usually made after meals
what is rectal distension associated with
the desire to defaecate
what is defaecation
ejection of faecal matter from the rectum via the anal canal
an involuntary reflex
what are the muscles used for defaecation
the internal and external sphincters, composed of smooth muscle controlled by the autonomic nervous system
how can some diseases of the large bowel be managed
removal of a portion of the colon
describe how a colostomy occurs
proximal end of the gut tube is brough out through the abdominal wall, creating an opening called a stoma which can be emptied into a bag
a hole is made in the abdomen and the free end of the colon is pulled through the hole and stitched to the abdomen to create the colostomy
describe an ileostomy
a small bowel is diverted through an opening in the abdominal wall, creating a stoma. can be needed as either a temporary measure or permanent. could be done for healing after bowel cancer resection, to relieve inflammation of inflammatory bowel disease.
describe diarrhoea
characterised by excessively watery stools and is caused by gastrointestinal tract infections and failure of fluid absorption
could be associated with reduced colonic motility, as there is less mixing and less fluid absorption
results in dehydration and electrolyte imbalance
defined as loose stools for 3 or more times in a day
how is diarrhoea a killer
infection accounts for 1 in 9 deaths in children worldwide per year
describe constipation
- characterised by hard faeces, difficult to pass
- due to increased fluid absorption
- associated with gastrointestinal spasm, side effect of some drugs like opiates, and a role of dietary fibre
- Not defaecting at least 3 times per week, hard, dry and lumpy and straining when going to the toilet
- Associated with gastrointestinal spasm.
- the more dietary fibres that we have the less constipation we will experience
