RECTUM & ANUS ANATOMY -

RECTUM & ANUS ANATOMY

1. Longitudinal muscle
2. Circular muscle
3. Valve of Houston
4. Column of Morgagni
5. Levator ani muscle
A. Iliococcygeus
B. Pubococcygeus
C. Puborectalis
6. Anal crypt
7. Anal gland
8. Intersphincteric groove

Rectum & Anus Anatomy

The rectum and anus are the final parts of the digestive system, responsible for storing and eliminating waste (stool). They contain specialized muscles and structures to control bowel movements.

RECTUM

The rectum is the last part of the large intestine, approximately 12–15 cm (4.7–6 inches) long, leading into the anus. It stores stool until defecation.

Key Structures in the Rectum

Valve of Houston
- Three internal folds in the rectum that help slow down stool movement and prevent sudden urgency.
Longitudinal Muscle
- Runs along the length of the rectum, assisting in pushing stool toward the anus.
Circular Muscle
- Surrounds the rectum, controlling its diameter and aiding in stool movement.
Levator Ani Muscle
- A key pelvic floor muscle that supports the rectum and helps maintain continence.
- Includes:
  - Iliococcygeus – Supports pelvic organs.
  - Pubococcygeus – Helps control bowel movements.
  - Puborectalis – Forms a sling around the rectum, maintaining the anorectal angle to prevent leakage.
Peritoneal Reflection
- The area where the peritoneum (lining of the abdominal cavity) folds over the rectum.

ANUS

The anus is the opening at the end of the digestive tract, controlling stool expulsion. It is about 2.5–4 cm (1–1.5 inches) long and consists of specialized muscles and structures.

Key Structures in the Anus

Column of Morgagni
- Vertical ridges inside the anal canal that help guide stool movement.
Dentate Line
- A landmark inside the anal canal that separates the upper, nerve-insensitive part from the lower, pain-sensitive part.
Anal Crypts & Anal Glands
- Small pockets and glands near the dentate line that secrete mucus for lubrication.
Intersphincteric Groove
- A groove between the internal and external anal sphincters.
Anal Verge

The visible outer edge of the anus.

Anoderm

The specialized skin lining the anal canal, highly sensitive to touch and pain.

Corrugator Cutis Ani Muscle

A small muscle that causes the wrinkled appearance of the anus.

Muscles Controlling the Anus

Internal Anal Sphincter Muscle

A smooth (involuntary) muscle that stays contracted to prevent stool leakage.

External Anal Sphincter Muscle

A skeletal (voluntary) muscle that allows conscious control of bowel movements.

Conjoined Longitudinal Muscle

A muscle layer that connects the internal and external anal sphincters, helping maintain rectal function.

🔹 How the Rectum & Anus Work Together

✔ Rectum stores stool → Sphincters control release → Anus expels waste when appropriate

This complex structure ensures continence while allowing controlled defecation!