Lecture 15- Rectum and anal canal anatomy Flashcards
how long is the rectum
12-15cm long passes through the pelvic floor
anatomy of the rectum
- Has a continuous band of outer longitudinal muscle
- Curved shape anterior to sacrum
- Parts covered in peritoneum (some parts extraperitoneal)
function of the rectum
where does the anal canal start
- Starts at the proximal border of the anal sphincter complex
anatomy of the anal canal
- Rectum points anteriorly
- Puborectalis sling changes the direction of anatomy
- Ana canal points posteriorly
Anal is involved in continence
- Factors required:
- Distensible rectum
- Firm bulky faeces
- Normal anorectal angle
- Anal cushions
- Normal anal sphincters
blood supply the rectum
blood supply to rectum is from sevral arteries that for a plexus
- superior rectal artery
- middle rectal artery
- inferiro rectal
superior rectal artery is a continuation of the
inferior mesenteric artery
middle rectal artery is a continuation of the
internal iliac
inferior rectal artery is a contiuation of the
pudendal artery
venous drainage of the rectum
- portal draiange through superior rectal vein
- systemic driange through internal iliac vein
- portional for porto-systemic anastomosis
anal sphincter complex comprises
- internal involuntary sphincter
- external anal sphincter
internal involuntary sphincter
- thickening of circular smooth muscle
- under autonomic control (80% of resting anal pressure)
External anal sphincter is
striated muscle–> under more voluntary control
- External anal sphincter is striated muscle
- Deep section
- Upper anal canal
- Mixes with fibres from Levator ani
- Joins with puborectalis to form sling
- Superficial and subcutaneous section
- Nerve supply- pudendal nerve- conscious control
- 20% of resting pressure
process of dafaecation
- mass movement
- defecation reflex
- stimulus= distension in rectum
- responses
- contraction in rectum and sigmoid colon
- relaxation of internal anal sphincter
- contraction of external anal sphincter
- increased pressure in rectum
- delay of defaecate
- delay
- contraction of external anal sphincter
- contraction of puborectalis muscle
- reverse peristalsis in rectum
- defaecate
- relaxation of external anal sphincter
- relaxation of puborectalsis muscle
- forward peristalisis in rectum and sigmoid colon
- valsalva maneuver (increased abdominal pressure)
valsalva maneuver
increased abdominal pressure
where is the dentate canal found
the anal canal
what is the dentate line in the anal canal
junction of hindgut and proctodaeum (ectoderm)
above the dentate line what sort of pain receptors are there
visceral pain receptors
above the dentate line what sort of cells are found
columnar epithelium
below the dentate line what sort of pain receptors are found
somatic pain receptors
below the dentate line what sort of epithelium is found
stratified squamous epithelia
visceral opain receptors type of pain
vague, not localized
somatic pain
sharp well localised- very painful
haemorrhoids are caused by
problems with anal cushions
anal cushions
- (PLEXUS OF BLOOD VESSELS FORMS PART OF CONTINCNECE)
plexus of blood vessels which form anal cushions
- Divided into 3+ areas of tissues called anal cushions
- posterior
- antirior
- lateral
- Play a role in anal continence
- There are connections between the veins and some arteries
- Present from birth and a normal finding
haemorrhoids can be classified as…
internal or external haemorrhoids
Internal haemorrhoids found
above the dentate line
external haemorrhoids
found below the haemorrhoid line
features of internal haemorrhoids
- Loss of connective tissue support
- Above dentate line
- Relatively painless
- Enlarge and prolapse through anal canal
- Bleed bright red blood
- Pruritus’
treatment for internal haemorrrhoids
- Increased hydration/ high fibre diet - soften stool
- Avoid straining
- Rubber band ligation
- Surgery
grading of haemorrhoid: grade 1
no prolapse just prominent blood vessels
stage 2 internal hameorrhoids
prolapse upon bearing down, but spontaenous reduction
grade 3 internal haemorrhoids
prolapse upon bearing down requiring manual reduction
stage 4 intenral haemorrhoid
prolapse with inability to be manually reduced
external haemorrhoids are found
below dentate line
features of external hameorrhoids
- below dentate line
- swelling o anal cushions which may then thrombose
- painful ++
- surgery has good outcome
anal fissure
linear tear in andoderm (usually posterior midline)
cause of anal fissure
- High internal and sphincter tone
- Reduced blood flow to anal mucosa
- passing of hard stool
symtoms of anal fissure
- Pain on defaecation ++
- Haematochezia
- Haematochezia
Hematochezia is the passage of fresh blood per anus, usually in or with stools.
causes of haemotochezia most common
diverticulitis
other causes of haematochexia
- Diverticulitis’s
- Angiodysplasia (small vascular malformation in boewl wall)
- Colitis
- IBD
- Infective
- Colorectal cancer
- Anorectal disease
- Haemorrhoids
- Anal fissure
- Upper GI bleeding (least common)
- Large bleed with fast transit
malaena
- Black tarry stools
- Offensive smelling
- Due to Hb being altered by digestive enzymes and gut bacteria
- Common causes of melaena
- Upper GI bleeding
- Peptic ulcer disease
- Variceal bleeds
- Upper GI malignancy
- Oesophageal/ gastric cancer
- Uncommon causes of melaena
- Gastritis
- Meckels diverticulum
- Iron supplements
