Rectum And Anal Canal Flashcards
What is the function of the rectum?
Temporary storage of faeces prior to defaecation
Doesnt contain faeces unless need the toilet
How is the structure of the longitudinal muscle on the outside of the rectum different to the rest of the colon?
Has continous band of outer longitudinal muscles
Which is different to the Taenia coli of the rest of the colon
How is the peritoneum related to the rectum?
Parts are extra peritoneal and others are Intra peritoneal
What stimulates the urge to defecate?
The stretching of rectum by faeces
What are the 3 arteries that supply blood to the rectum?
Superior rectal artery
Middle rectal artery
Inferior rectal artery
What blood vessel/artery does the superior rectal artery come from?
Is a continuation of the inferior mesenteric artery
What blood vessel/artery does the middle rectal artery come from?
Its a branch from the internal iliac artery
What blood vessel/artery does the inferior rectal artery come from?
Its a branch from the pudendal artery
What are the 2 types of venous drainage to the rectum and anal canal?
Portal drainage
Systemic drainage
What vein acts as portal drainage for the upper part of the rectum?
Superior rectal vein
What vein acts as systemic drainage for the distal part of the rectum/anus?
Internal iliac vein
How can peri-anal Varices develop?
There are Porto-systemic anastomosis between the superior rectal vein of the portal drainage and the internal iliac vein of the systemic drainage
Portal hypertension can lead to the veins draining the anasotomoses distending leading to Varices formation
What vein drains the hindgut into the portal system?
Inferior mesenteric vein
Where is the anorectal junction/start of the anal canal?
Proximal border of the anal sphincter complex
What muscle plays a crucial role in maintaining fecal continence?
How does it do this?
Puborectalis sling (part of puborectalis muscle)
It angles the anal canal posteriorly (when it points anteriorly faeces can pass through more easily)
What factors of the anal canal are needed for good continence?
Distensible rectum (can stretch)
Firm bulky faeces
Normal anorectal angle
Anal cushions
Normal anal sphincters
What are anal/haemorhoidal cushions?
Network of venous blood vessels smooth muscle and cartilage that aid continence
What are the 2 sections of the anal sphincter complex?
Internal involuntary sphincter
External voluntary anal sphincter
What type of muscle is the internal involuntary sphincter of the anal sphincter complex?
Circular smooth muscle
What type of control is the internal involuntary sphincter under?
Autonomics
What type of muscle is the external anal sphincter of the anal sphincter complex?
Striated muscle
What are the 3 parts to the external anal sphincter?
Deep section
Superficial section
Subcutaneous section
What is important about the deep section of the external anal sphincter?
What muscles does it mix with and join with?
Marks boundary of upper anal canal
Mixes with levator ani and joins pubs-rectalis to from the sling
What is the nerve supply to the external anal sphincter that is under voluntary control?
Pudendal nerve
What is the process of defaecation?
Mass movement (rapid peristalsis from the distal 1/3 of transverse colon)
Defecation reflex
Inc pressure in the rectum leads to either defecation or delay in defecation
What is th defecation reflex?
Distension in rectum due to faeces leads to contraction of rectum and sigmoid colon. Withi relaxation of the internal anal sphincter (involuntary) but contraction of external anal sphincter
Once pressure increases in the rectum, what is the next step to get defecation?
External anal sphincter (voluntary) relaxes
Puborectalis muscle relaxes
Valsalva manoeuvre
What affect does the relaxation of the puborectalis muscle have?
Makes the anus orientate more anterioly so the faeces have a more linear path from rectum to anus so easier passage
What is the valsalva maneuver?
When you strain/forcefully exhale with glottis closed
This increases Intra abdominal pressure helping pass the faeces
Look at the last slide, label the rectum and anus:
1 = pectinate/dentate line
2 = anorectal border
3 = rectum
4 = anus
5 = white line of anus
What is the significance of the pectinate line in the anus?
How do the cells differ either side?
Deep to the pectinate line (towards the rectum) = columnar epithelia
Superficial to the pectinate line (towards the entrance of the anus) = stratified squamous
How do the cells either side of the white line in the anus differ?
Distal end of the white line = keratinised squamous epithelia
Side of white line closer to the rectum = non keratinised squamous epithelia
What are anal cushions/haemorrhoids?
Venous plexus
Have connections between veins and some arteries
As they fill with blood act as extra tissue contributing to continence
What is the pectinate line the junction of?
Hindgut and proctoduem (Ectoderm)
How do pain receptors differ above and below the pectinate line?
Above pectinate line = visceral pain receptors (diffuse pain)
Below pectinate line = somatic pain receptors (specific pain)
What are the 2 types of haemorrhoids?
Internal haemorrhoids
External haemorrhoids
What causes internal haemorrhoids?
Loss of connective tissue support above the pectinate line
Why are internal haemorrhoids painless?
They occur above the pectinate line which have visceral pain receptors
How can internal haemorrhoids become painful?
Can enlarge and prolapse through the anal canal below the pectinate line
How are internal haemorrhoids treated?
Prevents increasing pressure of anal cushions:
Increased hydration /high fibre diet to basically prevent constipation
Avoid straining
Rubber band ligation
Surgery
Why are external haemorrhoids painful?
Anal cushions swelling below the pectinate line so has somatic pain innervation so is very specific and painful
What is the treatment of external haemorrhoids?
Surgery
What is an anal fissure?
Linear tear in the anoderm (ectoderm) below the pectinate line
How does and anal fissure present?
Usually occurs after passing hard stool
Pain of defecation
Haematochezia
What is Haematochezia?
Rectal bleeding
What is the general cause of anal fissures?
High internal sphincter tone
Reduced blood flow to anal mucosa
What is the treatment for anal fissures?
Basically preventing constipation:
-hydration
-dietary fibre
-analgesia
Warm baths
Meds trying to relax the internal anal sphincter too help with healing
What are some common causes of Haematochezia?
Diverticulitis
Angiodysplasia
Colitis (ulcerative colitis, infection, shigella and campylobacter)
Colorectal cancer (cancer erodes blood vessels)
Anorectal disease like haemorrhoids or anal fissures
Rare (upper GI bleed with fast transit time)
What is melaena?
When there is black tarry stools that are offensive smelling due to Hb being altered by digestive enzymes and gut bacteria
What causes melaeana?
Slow upper GI bleeds:
Peptic ulcer bleeds
Variceal bleeds
Upper GI malignancy
Oesophageal/gastric cancer
Gastritis
Meckels diverticulum
Iron supplements
Why are the stools black and tarry in melaena?
The haemoglobin gets altered by enzymes and gut bacteria as its past out in stool
