Anatomy 4 (lecture 6)

Question 1

Purpose of the rectum?

Answer 1

To store faeces until it is appropriate to defecate

Question 2

What type of nerves sense “fullness” of the rectum?

Answer 2

Normal visceral afferent nevre fibres

Question 3

What is required to control the excretion of faeces?

Answer 3

A holding area (the rectum)
Normal visceral afferent nerve fibres
Functioning muscle sphincters
normal cerebral function (to control the appropriate time to defecate
(these can all be affected by a neurological pathology e.g. dementia, MS)

Question 4

What factors, apart from neurological pathology, can affect faecal continence?

Answer 4

Medications
Natural age-related degeneration of nerve innervation of muscle
Consistency of stool

Question 5

What does the pelvic cavity lie between?

Answer 5

Pelvic inlet and pelvic floor

Question 6

What muscle forms the pelvic floor?

Answer 6

Levator ani muscle - forms the musculofascial inferior part of the pelvic cavity

Question 7

Why must there be opening in the pelvic floor?

Answer 7

To permit the distal parts of the alimentary, renal and reproductive tracts to pass from the pelvic cavity into the perineum

Question 8

At what vertebrae level does the sigmoid colon become the rectum?
What is this called?

Answer 8

Anterior to S3

The rectosigmoid junction

Question 9

At what anatomical point does the rectum become the anal canal

Answer 9

Anterior to the tip of the coccyx just prior to passing through the elevator anti muscle

Question 10

What is the anus?

Answer 10

The distal end of the anal canal

The orifice through which faeces pass

Question 11

What out of rectum, anal canal and anus are located in the perineum and what are located in the pelvis?

Answer 11

Rectum = pelvis

Anal canal and anus = perineum

Question 12

What is the rectal ampulla?

What do the walls of this do to accommodate faecal matter?

Answer 12

The dilated part of the rectum where faeces are stored until they are eliminated via the anal canal (lies immediately superior to the elevator ani muscle)
Walls can relax to accommodate faecal matter

Question 13

What covers the superior rectum?

Answer 13

Peritoneum

Question 14

What pouch lies anterior to the superior rectum? - in males and females

Answer 14

Rectouterine pouch (in females)
Rectovesical pouch (in males)

Question 15

In males, what lies anterior to the inferior rectum?

Answer 15

The prostate gland

Question 16

In females, what lies anterior to the inferior/ middle rectum?

Answer 16

Vagina and cervix

Question 17

What is the pouch between the uterus and bladder in females?

Answer 17

Vesicouterine pouch

Question 18

What forms the pelvic diaphragm (aka pelvic floor)? - also most of the roof of the perineum

Answer 18

Mostly the elevator ani muscle along with the fascial coverings

Question 19

What are the 3 smaller muscles that makes up the elevator ani muscle?

Answer 19

Iliococcygeus muscle (ileum to coccyx)
Pubococcygeus (pubic bone to coccyx)
Puborectalis (pubic bone to rectum)
Under voluntary control - skeletal muscle

Question 20

What is the purpose of the elevator ani muscle? (3)

Answer 20

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
Muscle must relax to allow defecation (and urination) to occur

Question 21

What is the elevator ani muscle supplied by?

Answer 21

“Nerve to levator ani”

A branch of the sacral plexus and pudendal (S2, 3, 4)

Question 22

What is the part of the elevator ani muscle that is particularly important for maintaining faecal continence?
Skeletal/ smooth muscle?

Answer 22

The puborectalis

Skeletal

Question 23

What does contraction of the puborectalis do?

Answer 23

Decreases the anorectal angle (acting like a sphincter)

Question 24

What does the puborectalis do when the rectal ampulla is relaxed and filled with faeces?

Answer 24

voluntarily contracts and helps to maintain continence

Question 25

What is the junction at which the anal canal begins?

Answer 25

The anorectal junction

Question 26

How many anal sphincters are there and what type of muscle supplies each?

Answer 26

2 Internal (smooth muscle) External (skeletal muscle) Can control external but not internal

Question 27

What parts of the anal canal is the external and internal anal sphincters found in?

Answer 27

``` Internal = superior two thirds External = inferior two thirds (superior part of the external sphincter is containers with the puborectalis muscle) ```

Question 28

What stimulates/ inhibits contraction of the internal anal sphincter?

Answer 28

Stimulated by sympathetic nerve i.e. sphincter is close | Inhibited by parasympathetic nerve

Question 29

What stimulates the external anal sphincters?

Answer 29

Pudendal nerve

Question 30

Describe the state of the internal anal sphincter in terms of contraction?

Answer 30

Contracted all the rime, relaxes in response to distension of the rectal ampulla

Question 31

Describe the state of the external anal sphincter in terms of contraction?

Answer 31

Voluntarily contracted (along with puborectalis muscle) in response to rectal ampulla distension and internal sphincter relaxation

Question 32

When deciding which nerve fibre types are carrying out which function, what does it mean if the structure is in the pelvis?

Answer 32

It is in the body cavity and therefore supplied by sympathetic, parasympathetic and visceral afferents

Question 33

When deciding which nerve fibre types are carrying out which function, what does it mean if the structure is in the perineum?

Answer 33

Body wall and therefore somatic motor and somatic sensory

Question 34

In terms of the nerve supply to the rectum/ anal canal, what happens with the sympathetic fibres - where do they travel? What do they do? (2)

Answer 34

Sympathetic fibres from T12-L2 travel to the inferior mesenteric ganglia, synapse, then travel via the periarterial plexuses around branches of the IMA causing contraction of the internal anal sphincter and inhibit peristalsis

Question 35

In terms of the nerve supply to the rectum/ anal canal, what happens with the parasympathetic fibres - where do they travel? What do they do? (2)

Answer 35

Parasympathetic fibres from S2 - S4 pass via the pelvic splanchnic nerves, synapse in walls of the rectum and inhibit internal anal sphincter, stimulate peristalsis

Question 36

In terms of the nerve supply to the rectum/ anal canal, where do the visceral afferents run back to? What do they run with? What do they sense?

Answer 36

S2-4 Run with parasympathetics Sense stretch, ischaemia, etc.

Question 37

What provides somatic motor supply? | What does this cause?

Answer 37

``` Pudendal nerve (S2-S4) and nerve to levator ani (S3, S4) Contraction of the external anal sphincter and puborectalis ```

Question 38

Where does the pudendal nerve come from? | what anterior rami form it?

Answer 38

Branch of the sacral plexus | S2, S3, S4 (S2, 3 and 4 keeps the pelvis off the floor)

Question 39

What does the pudendal nerve exit the pelvis via? | Where does it enter the perineum?

Answer 39

The greater sciatic foramen (branches to supply structures of the perineum) Through the lesser sciatic foramen

Question 40

What can happen to the pudendal nerve during labour?

Answer 40

Can be stretched

Question 41

How can labour cause faecal incontinence?

Answer 41

Fibres within the puborectalis or external anal sphincter muscle could be torn resulting in weakened muscle

Question 42

What is the line which marks the junction between the part of the embryo which formed the GI tract (endoderm) and the part that formed the skin (ectoderm)?

Answer 42

Pectinate line - can see division (ridges and change in mucosa) in individuals

Question 43

``` Comparing above and below the pectinate line: Nerve supply? Arterial supply? Venous drainage? Lymphatic drainage? ```

Answer 43

Above: Autonomic, From inferior mesenteric artery, to portal venous system (IMV), inferior mesenteric nodes (internal iliac nodes) Below: Somatic/ pudendal, from internal iliac artery, to systemic venous system (internal iliac), superficial inguinal nodes

Question 44

What structures do lymph vessels tend to lie alongside?

Answer 44

The arteries

Question 45

What are the main groups of lymph nodes draining the pelvic organs and what do each drain?

Answer 45

``` Internal iliac (drains inferior pelvic structures) External iliac (draining lower limb, and more superior pelvic structures) Common iliac (drain the lymph from the external and internal iliac nodes) Lymph raining through the common iliac nodes then drains to the lumbar nodes ```

Question 46

Where does the hindgut extend to?

Answer 46

The proximal had of the anal canal (the pectinate line)

Question 47

What is the blood supply to the: Proximal half of the anal canal? Distal half?

Answer 47

Proximal = inferior mesenteric artery Distal half = internal iliac artery (degree of anastomoses between these)

Question 48

Venous drainage of anal canal: Proximal half? Distal half?

Answer 48

Proximal = inferior mesenteric vein | Distal half = internal iliac vein

Question 49

What is the venous plexus?

Answer 49

A soft plexus of veins that sit around the anus When it is prolapses it forms haemorrhoids (these are completely different to rectal varies which are related to portal hypertension)

Question 50

What causes rectal varrices

Answer 50

Dilation of collateral veins between the portal and systemic venous systems due to portal hypertension

Question 51

What causes haemorrhoids?

Answer 51

Prolapses of rectal venous plexuses (not related to portal hypertension - caused by raised pressure e.g. chronic constipation)

Question 52

What are the name of the fossae which lie on each side of the anal canal? What are these filled with

Answer 52

Ischioanal fossae | Fat and loose connective tissue (communicate with each other posteriorly)

Question 53

What is an infection within the ischioanal fossae called?

Answer 53

An ischionala abcess