Feacal continence of the GI tract

Question 1

What does the control of excretion of feaces require?

Answer 1

A “holding area” (the rectum) to store faeces until appropriate to defecate
Normal visceral afferent nerve fibres to sense “fullness” of the rectum
Functioning muscle sphincters around the distal end of the GI tract to respond to this “fullness”
To appropriately contract, preventing defecation, and to relax, allowing defecation
Normal cerebral function to control the appropriate time to defecate

Question 2

What can feacal continence be affected by?

Answer 2

neurological pathology
Affected by medications
Affected by the natural age-related degeneration of nerve innervation of muscle
Affected by consistency of stool

Question 3

What is the Levator ani muscle?

Answer 3

pelvic floor

Question 4

Describe the pelvic cavity?

Answer 4

Lies within the bony pelvis

Continuous with abdominal cavity above

Lies between pelvic inlet and pelvic floor

Contains pelvic organs and supporting tissues

Question 5

What do openings in the pelvic floor allow?

Answer 5

alimentary, renal and reproductive tracts to pass from the pelvic cavity into the perineum

Question 6

What happens at S3?

Answer 6

“Recto-sigmoid junction”

Sigmoid colon becomes rectum

Question 7

Where does the rectum become anal canal?

Answer 7

the tip of the coccyx

Question 8

Are the anal canal and anus in the pelvis or perineum?

Answer 8

perineum

Question 9

What is the purpose of the 3 lateral folds of the rectum?

Answer 9

staggering effect and allows expansion (walls can relax to accommodate faecal material)

Question 10

What are the 3 parts of the pelvic diphragm?

Answer 10

Pubococcygeus
Puborectalis
Iliococcygeus

Question 11

What is the role of the Levator ani muscle?

Answer 11

Provides continual support for the pelvic organs - tonically contracted most of the time
Reflexively contracts further during increase in intra-abdominal pressure, e.g. coughing, sneezing
The muscle must relax to allow defecation (and urination) to occur

Question 12

What innervates the Levator ani muscle?

Answer 12

“nerve to levator ani”: (a branch of the sacral plexus) pudendal (S2, 3, 4) - keep the guts off the floor

Question 13

What is the Puborectalis?

Answer 13

Part of the levator ani muscle

Particularly important for maintaining faecal continence

Contraction of it decreases the anorectal angle, acting like a sphincter

This is a skeletal muscle: contraction is under voluntary control

Question 14

Describe the internal anal spinchter?

Answer 14

smooth muscle
involuntary - contraction is inhibited by parasympathetic nerves
thickening of muscle - an enlargement
Superior two thirds of anal canal

Question 15

Describe the external anal spinchter?

Answer 15

skeletal muscle
voluntary - contraction is stimulated by the pudendal nerve
Inferior two thirds of anal canal

Question 16

What is below the anorectal junction?

Answer 16

anal canal

Question 17

What applies to a structure if it is above the levator ani muscle?

Answer 17

In pelvis
Body cavity
Sympathetic, parasympathetic and visceral afferent

Question 18

What applies to a structure if it is below the levator ani muscle?

Answer 18

In perineum
Body wall
somatic motor and somatic sensory

Question 19

What is the role of the sympathetic fibres? Where do they leave from?

Answer 19

T12-L2: travel to inferior mesenteric ganglia – synapse - then travel via periarterial plexuses around branches of IMA.

Contraction of internal anal sphincter
Inhibit peristalsis

Question 20

Where do visceral afferents run to? What do they do?

Answer 20

S2-S4
Run with parasympathetics
Sense stretch, ischaemia etc.

Question 21

What is the role of the parasympathetic fibres? Where do they leave from?

Answer 21

S2-S4: via pelvic splanchnic nerves, synapse in walls of rectum

Inhibit internal anal sphincter
Stimulate peristalsis

Question 22

What is the pudendal nerve a branch of?

Answer 22

sacral plexus

S2, S3, S4 anterior rami

Question 23

What could happen to the pudendal nerve during labour?

Answer 23

be stretched or damaged which leads to incontinence

Question 24

What is the importance of the pectinate line?

Answer 24

Marks the junction between the part of the embryo which formed the GI tract (endoderm) and the part that formed the skin (ectoderm).
-check lecture

Question 25

What are organs above the pectinate line derived from?

Answer 25

endoderm

visceral

Question 26

What are organs below the pectinate line derived from?

Answer 26

ectoderm

parietal

Question 27

What is the trend of the lymphatics in the GI system?

Answer 27

follow arteries

Question 28

What supplies the hindgut?

Answer 28

inferior mesenteric artery

Question 29

What supplies the anus and anal canal?

Answer 29

internal iliac artery

Question 30

What vein drains below the pectinate line?

Answer 30

internal iliac vein

Question 31

What are rectal varices?

Answer 31

Dilation of collateral veins between portal and systemic venous systems

Question 32

What are haemorrhoids? What causes them?

Answer 32

Prolapses of the rectal venous plexuses

Raised pressure e.g. chronic constipation, straining, pregnancy

Question 33

What is an Ischioanal fossae? What is an infection within it called?

Answer 33

bottom fat

infection within the ischioanal fossa is called an ischioanal abscess