Anatomy

Question 1

anal Canal Lined By

Answer 1

The proximal anal canal is typically lined by columnar epithelium and the distal anus by squamous epithelium. The junction between the ectoderm and the endoderm, located at the midpoint of the anal canal, appears as an undulating demarcation referred to as the dentate line. Between the dentate line and the anal verge, the mucosa is lined by a modified squamous epithelium

Question 2

Hemorrhoids Supply

Answer 2

• receive their blood supply from six hemorrhoidal arteries
• The venous drainage is provided by the superior, middle, and inferior hemorrhoidal vessels, allowing for communication between the portal and systemic circulations.
• These vessels form direct arteriovenous communications within the cushions, and for this reason, hemorrhoidal bleeding is arterial rather than venous in nature.

Question 3

drainage above and below Dentate Line

Answer 3

Venous and lymphatic drainage above the dentate line flows into the internal iliac vessels;

below the dentate line, blood supply and drainage are provided by the inferior hemorrhoidal system.

Question 4

Internal and External Sphincter

Answer 4

The internal anal sphincter
- autonomically innervated smooth muscle and contributes between 50% to 85% of the resting tone of the anal canal.
- Anatomically, the internal anal sphincter is a thickened continuation of the circular layer of the muscularis propria of the distal rectum and occupies the distal 2 to 4 cm of the anal canal.

The external anal sphincter
- composed of the pelvic floor muscles enveloping the distal rectum and anus.
- The puborectalis muscle, often referred to as the rectal sling, is one of the main muscles contributing to the external anal sphincter.
- It originates at the pubis, passes around the rectum posteriorly, and returns to the pubis. The external anal sphincter is unique because it can be controlled both by the autonomic nervous system and by voluntary contraction

Question 5

Sphincters Nerve Supply

Answer 5

The internal anal sphincter
- sympathetic (L5) and parasympathetic (S2, S3, and S4) nerves.

The external anal sphincter
- the inferior rectal branch of the pudendal nerve (S2 and S3) and by the perineal branch of S4

Question 6

Interuption of the nerves of sphincter

Answer 6

• unilateral interruption of the pudendal nerve will not result in external anal sphincter dysfunction, but the loss of bilateral S3 nerve roots (e.g., by surgical transection) will typically result in fecal incontinence.
• If the S1 through S3 nerve roots remain intact only on one side, the patient is still expected to maintain control of the anal sphincters

Question 7

Which Nerve Transmit Sensation

Answer 7

The rectal branch of the pudendal nerve transmits anal sensation, and it is thought to play a role in maintenance of anal continence.

Question 8

Organized nerve endings and Function

Answer 8

Meissner corpuscles (touch)
Krause bulbs (temperature sensation)
Golgi-Mazzoni bodies (pressure)
genital corpuscules (friction).