Rectum and Anal Canal Flashcards
How long is the rectum?
How is it different to the rest of the colon?
Describe its shape and position relative to Sacrum
- 12-15cm
- Continuous band of outer longitudinal muscle
- Curved and anterior to sacrum
Is the Rectum Intra or extraperitoneal?
Some parts are Intra, some are Extra
Describe the arterial blood supply to the rectum
Superior part;
- Superior rectal artery (from IMA)
Middle part;
- Middle rectal artery (from Internal Iliac)
Inferior part;
- Inferior rectal artery (from Pudendal)
Describe the Venous drainage of the rectum
- Superior parts: Superior rectal vein drains becomes IMV which is part of portal circulation
- Inferior parts: Drained by Internal Iliac Vein
(Anastamoses exist between SRV and IIV)
What is significant about the Systemic-Portal anastomoses in the Rectum?
Can become varies in Portal Hypertension
Where does the anal canal begin?
At the proximal border of the anal sphincter complex
The rectum points anteriorly, the anal canal points posteriorly.
What muscle is responsible for this?
What is significant about this?
- Puborectalis
- This is a feature of continence
What are 5 factors that allow the anal canal to be involved in Continence?
- Distensible rectum
- Firm bulky faeces
- Normal anorectal angle (Via Puborectalis)
- Anal cushions
- Normal anal sphincters
What are the Anal Cushions and their function?
- Network of blood vessels (usually venous)
- Which increase the sphincter mechanism of the anus, when they swell/ blood passes through
What are the 2 parts to the Anal Sphincter Complex?
- Internal sphincter (Involuntary)
- External sphincter (Striated muscle)
Describe the Internal Anal Sphincter
What percentage of resting anal pressure does this contribute to?
- A thickening of circular smooth muscle
- Under autonomic control
80%, so very important in resting Anal Pressure
Describe the External Anal Sphincter
(20% of resting anal pressure)
What nerve innervates the sphincter?
3 components;
- Superficial
- Subcutaneous
- Deep: Demarcates upper anal canal, mixes with fibres from Levator Ani, Joins Puborectalis-rectalis to form sling
Pudendal nerve
List 3 ways the Defecation Reflex leads to Increased pressure in rectum
What stimulates this reflux?
- Contraction in rectum and sigmoid colon
- Relaxation of Internal Anal Sphincter
- Contraction of External Anal Sphincter
- Distension of rectum
Increased pressure in rectum can lead to either DELAY or DEFECATION
List 4 ways it leads to Defecation
- Relaxation of External Anal Sphincter
- Relaxation of Puborectalis
- Forward peristalsis in rectum and sigmoid colon
- Valsalva manoeuvre (Increased ab pressure)
Increased pressure in rectum can lead to either DELAY or DEFECATION
List 3 ways it leads to Delay
- Contraction of External Anal sphincter
- Contraction of Puborectalis
- Reverse peristalsis in rectum
The Anal Canal contains the Dentate/ Pectinate line.
What is this?
Junction between Hindgut and Proctodeum
Compare the pain receptors and epithelia above and below the Dentate/ Pectinate line
Above;
- Visceral pain receptors (So poorly localised, vague pain)
- Columnar
Below;
- Somatic pain receptors
- Strat. Squamous
What are Haemorrhoids?
What are the 2 classifications?
Symptomatic anal cushions, Internal and External
Internal- most common, above Pectinate line
Describe Internal Haemorrhoids in 4 ways
- Relatively painless (Visceral pain receptors)
- Caused by loss of CT support
- Enlarge and prolpase through anal canal
- Bright red blood and Itching
How do we treat Internal Haemorrhoids in 4 ways?
- Increased hydration/ high Fibre diet
- Avoid strain
- Rubber band ligation (around base, will necrose and fall off)
- Surgery
Describe the 4 grades of Internal Haemorrhoids
1: No prolapse, just prominent vessels
2: Prolpase upon bearing down, spontaneous reduction
3: Prolapse upon bearing down, needs manual reduction
4: Prolapse, inability to be manually reduced
Describe External Haemorrhoids in 3 ways
- Very painful
- Tend to thrombose
- Good outcomes for surgery
What is an Anal Fissure?
How does it present?
Linear tear in the Anoderm (Strat Squamous part of anal canal lying below Pectinate line)
- Painful defecation
- Haematochezia
Anal fissures can be caused by passing a hard stool (but also after diarrhoea)
What are 2 possible underlying causes?
- High internal anal sphincter tone
- Reduced blood flow to anal mucosa
How do we treat an Anal Fissure in 3 ways?
- Warm baths
- Medication to relax internal anal sphincter
- Hydration, Pain relief, Dietary fibre
List 6 causes of Haematochezia
- Diverticulitis
- Colitis (IBD, Infective)
- Angiodysplasia (small vascular malformation in bowel wall)
- Colorectal cancer
- Anorectal disease (Haemorrhoids, anal fissure)
- Upper GI bleeding (Large bleed with fast transit)
Does an Upper GI bleed present with Haematochezia or Melena?
Haematochezia, if it is a large bleed with fast transit
Melena, normally
Describe Melena in 2 ways
List 3 uncommon causes
- Black tarry stools
- Offensive smelling
- Gastritis
- Meckel’s diverticulum
- Iron supplements
List 4 causes of Upper GI bleeding that would result in Melena
- Varices
- PUD (Peptic Ulcer Disease)
- Upper GI Malignancy
- Oesophageal/ gastric cancer
