Anatomy of the Distal GI Tract Flashcards
(35 cards)
1
Q
What are the components of the distal GI tract
A
- Colon - Caecum, appendix, ascending, transvers and descending colon
- Rectum
- Anal canal
- Anus
2
Q
Whats the anatomy of Faecal continene
A
Control of the excretion of faeces- complex
- Needs holding area (rectum) to store faeces until appropriate do defecate
- Normal visceral affarents nerve fibres to sense the fullness of the rectum
- Functioning muscle sphincters - around the distal end of the GI tract to respond to the fullness
- To contract preventing defecation and relax allowing defecation
3
Q
What can affect faecal continence
A
- Neurological pathology - dementia, stroke, MS, trauma
- Medications
- Natural age-related degeneration of nerves innervation of muscle
- Consistency of stool
4
Q
Describe the anatomy of the pelvic cavity
A
- Lies within the bony pelvis
- Continues with the abdominal cavity
- Lies between the pelvic inlet (superior aspect) and pelvic floor
- Contains pelvic organs and supporting tissues
- Rectum - located within the pelvic cavity
5
Q
Which muscle formes the pelvic floor
A
Levator ani
Separates the pelvic cavity from the perineum
6
Q
Whats the significant of openings in the pelvic floor
A
Permits the distal parts of alimentary, anal and reproductive tracts to pass from the pelvic cavity into the perineum
7
Q
At what level does the sigmoid colon become the rectum
A
S3 - Recto-sigmoid junction
8
Q
When does the rectum become the anal canal
A
Anterior to tip of coccyx -just after passing through levator ani muscle
9
Q
What are locations of the rectum anal canal
A
- Anus is the distal end of the anal canal both- perineum
- Rectum - pelvis
10
Q
What is the rectal ampulla and whats its anatomy
A
- Lies immediately superior to the levator ani muscle
- Walls relax to accommodate faecal material
- contains functioning muscle and sphincters to hold faeces in the ampulla until appropriate to defecate
- Function: Stores faeces
11
Q
Describe the anatomical relations of the rectum
A
- Rectouterine/rectovesical pouch lies anterior to the superior rectum
- Males - the prostate gland lies anterior to the inferior rectum
- females - the vagina and cervix lies anterior to the inferior/middle rectum
12
Q
What is the superior rectum covered by
A
Peritoneum
13
Q
Describe the anatomy to the Levator ani muscle
A
- Forms most of the pelvic diaphragm along with Fascial covering
- Made up of a number of smaller muscles -> Puboccygeus, puborectalis and illeococcygeus
- Forms most of the pelvis floor and most of the peritoneum roof
- Skeletal muscle
14
Q
What are the functions of the levator ani muscle
A
- support for pelvic organs - most of the time tonically contracted
- Reflexively contracts further during increased intra-abdominal pressure - e.g coughing, Sneezing
- Relaxes during - urination and defecation
15
Q
What is the nerve innervation of the Levator ani
A
‘nerve to levator ani’
- Branch of the sacral plexus and pudendal S2,3,4
16
Q
Describe the anatomy of the Puborectalis muscle
A
- Part of levator ani
- function: maintaining faecal continence
- Contraction decreases the Anorectal angle - acting like a sphincter
- Skeletal muscle - controle
- When the rectal ampulla is relax and filled with faeces this muscle will help to maintain continence
17
Q
What is the anorectal angle
A
18
Q
Describe the anatomy of the anal canal and anal sphincter
A
- Anal canal is below the anorectal junction
Two anal sphincters
- 1 internal sphincter - Smooth muscle
- 1 external sphincter - Skeletal muscle
19
Q
Describe the anatomy of the internal anal sphincter
A
- Smooth muscle
- Forms superior 2/3rd of anal canal
- Contraction -> sympathetic nerves
- Contraction inhibited -> parasympathetic nerves
- Contracted all the time will only relax reflexively in responce to destension of the rectal ampulla
20
Q
Describe the External anal sphincter
A
- Skeletal muscle
- Inferior 2/3 of the anal canal - superior part of sphincter is continous with puborectalis muscle
- Contraction- sitmulated by pudendal nerve
- Voluntarliy contracted (along with puborectalis) in responce to rectal ampulla distension and internal sphincter relaxation
21
Q
What are the two important spinal cord levels
A
T12-L2 and S2-S4
22
Q
What types of fibres are carried within the S2-S4 nerves
A
-
Visceral afferents back to S2-S4 - Run with parasympathetics
* Function: sense Stretch, ischaemia -
Parasympathetic fibres from S2-S4 - Via pelvic spkanchic nerves, Synapse in walls of rectum
* Function: inhibit internal anal sphincter and sitmulate peristalsis -
Somatic motor form pundendal nerve and nerve to levator ani
* Function: Contraction of external anal sphincter and puborectalis
23
Q
What type of nerve fibres are carried within the T12-L2
A
-
Sympathetic fibres- Travel to inferior mesenteric ganglia - synapse then travel via periarterial plexus around branches of IMA
* Function: contraction of internal anal sphincter and inhibit peristalsis
24
Q
Whats the nerve supply to the external sphincter
A
pundendal nerve
25
Describe the **pundendal nerve**
* Branch of the **sacral plexus**
* **S2, S3, S4, Rami**
* Supplies **external anal sphincter**
* **Exits pelvis via -\> _Greater sciatic foramen_**
* **Enters perineum via -\> _Lesser sciatic foramen_**
* branches to supply structures of **perineum**
26
What happens when there is **pundenal nerve or sphincter damage**
During labour
* **Branches of pundendal nerve could be stretched**
* **Fibres within puborectalis or external anal sphincter muscle could be torn**
* **Result -\> weakness of muacle and faecal incontinence**
27
What is the **pectinate line** in the anal canal
* Marks the junction between the part of the embryo which formed the **GI tract (endoderm)** and the part which formed the **skin (ectoderm)**
* **Aterial supply, venous drainage, neve suppy and lympathetics all differ above and below the pectinate line**
* **Superior to line -\> visceral**
* **Interior to line -\> Parietal**
28
What are the differences above the pectinate line and below it
29
Describe the lymphatics of the pelvis
* **internal illiac nodes -** inferior pelvic structures
* **External iliac nodes -** lower limbs and more superior structures
* **Common iliac nodes -** drains from internal and external iliac nodes
* Common illiac then drains into **lumbar nodes**
30
What is the blood supply to the rectum and anal canal
* **The inferior mesenteric artery -** supplies hindgut (all the way to petinate line)
* The remainder of the GI Tract = **Internal iliac artery**
* There is some degree of anastomoses between these vessels
31
What is the venous drainage from the anal canal and the rectum
* **Inferior mesenteric vein - Hingut** - above pectinate line into the portal venous system
* **The internal illac vein - drains** below the pectinate line - into the systemic venous system
32
Whats the difference between **rectal varices and haemorrhoids**
1. **Varices -**
* **** form due to Dillation of collateral veins between portal and systemic venous system
* **Portal hypertension**
2. **Haemorrhoids**
* Prolapses of rectal venous plexus- not due to Porta hypertension
* **Raised pressure -** chronic constipation, straning and pregnancy
33
What is the **Ischioanal Fossae**
* Right and left fossae that lie each side of the **anal canal**
* **Filled with fat and loose connective tissue**
* The two fossae communicate with each other **posteriorly**
* **Infection in fossa - _Ischioanal abcess_**
34
What is the PR exam use for
To asses anal tone, the effectiveness/ Strenght of the external sphincter
* **Female:** palpate cervix anteriorly
* **Males:** palplate the prostate anteriorly
35
What are the different types of endoscopies for the distal GI tract
* **Proctoscopy -** rectum
* **Sigmoidoscopy -** sigmoid colon
* **Colonoscopy -** colon
