Hemorrhoidal arteries and rectal arteries are branches of

Reading File

Finding Sources

Reading File

The rectal/hemorrhoidal arteries are branches of three different parent arteries, depending on which level of the rectum and anal canal they supply:

Rectal (Hemorrhoidal) Arteries and Their Parent Vessels

Artery	Also Called	Parent Artery	Region Supplied
Superior rectal artery	Superior hemorrhoidal artery	Inferior mesenteric artery (IMA) - terminal branch	Rectum and upper anal canal (down to dentate line)
Middle rectal artery	Middle hemorrhoidal artery	Internal iliac artery (directly, or via inferior gluteal artery)	Lower rectum, around the level of the levator ani
Inferior rectal artery	Inferior hemorrhoidal artery	Internal pudendal artery (branch of the internal iliac artery)	Anal sphincters and anal canal distal to pectinate line

Key Points

Superior rectal artery = the terminal branch of the inferior mesenteric artery (IMA), after it gives off the sigmoid branches. It is the main blood supply to the rectum, descending posteriorly and bifurcating into right and left branches within the rectal wall.
Middle rectal arteries = arise from the internal iliac artery (via internal pudendal or inferior gluteal). They are considered inconstant and not the major supply.
Inferior rectal arteries = branches of the internal pudendal artery, which itself is a branch of the internal iliac artery. They supply the anus distal to the pectinate line.
All three arteries form a rich anastomotic network within the rectal wall, which is why the rectum can remain viable even after ligation of the superior rectal artery during sigmoid/rectal resections.
Hemorrhoids proper are supplied by terminal branches of the superior hemorrhoidal artery.

Sources: Fischer's Mastery of Surgery, 8e; Mulholland & Greenfield's Surgery, 7e; Sleisenger & Fordtran's Gastrointestinal and Liver Disease

Pectinate and dentate line

Finding Sources

Reading File

Loading Image

Here is a complete breakdown of the pectinate line / dentate line - they are the same structure, just two names for it:

Pectinate Line = Dentate Line

They are identical - the same anatomical landmark with two names:

Dentate line - named for its tooth-like (dental) saw-toothed appearance
Pectinate line - named for its comb-like (pectinate) serrated appearance

Location: 2-3 cm proximal to the anal verge, at the midpoint of the anal canal.

Embryological significance: Marks the junction between endoderm (above) and ectoderm (below) - i.e., the embryonic proctodeum junction.

The Key Differences: Above vs. Below the Dentate/Pectinate Line

Feature	ABOVE the Line	BELOW the Line
Embryology	Endoderm (hindgut)	Ectoderm (proctodeum)
Epithelium	Columnar/transitional mucosa	Stratified squamous epithelium (anoderm)
Arterial supply	Superior rectal artery (from IMA)	Inferior rectal artery (from internal pudendal)
Venous drainage	Superior rectal vein → IMV → portal system	Inferior rectal vein → internal iliac → systemic
Nerve supply	Autonomic (sympathetic + parasympathetic) - visceral	Somatic (inferior rectal nerve) - highly sensitive
Pain sensation	Absent - only pressure sensation	Present - very sensitive to pain, touch, temperature
Lymphatic drainage	Internal iliac nodes + inferior mesenteric nodes	Inguinal lymph nodes
Hemorrhoids	Internal hemorrhoids (above)	External hemorrhoids (below)

Structures at the Dentate Line

Columns of Morgagni: 6-14 longitudinal mucosal folds above the dentate line - result of funneling of the rectum into the anal canal
Anal crypts: Small pockets at the bases of the Columns of Morgagni; site of cryptitis and can lead to anal fistulas/abscesses
Anal glands: Located at the dentate line; secrete mucus for lubrication; if blocked → abscess/fistula
Anal papillae: Mucosal tips of the anal glands at the dentate line (can become hypertrophied and mimic a polyp)

Clinical Importance

Hemorrhoids: Internal hemorrhoids arise above the dentate line (painless because no somatic innervation); external hemorrhoids below it (painful). Hemorrhoid banding must be placed above the dentate line to avoid pain.
Anal fissure: Posterior commissure is relatively ischemic (less well-perfused) - most fissures occur here.
Anal cancer: The dentate line determines the type - tumors above tend to be adenocarcinomas; squamous cell carcinomas arise from the squamous/transitional zone.
Lymph node spread: Cancers above drain to internal iliac/inferior mesenteric nodes; cancers below drain to inguinal nodes - this changes staging and surgical approach.
Biopsy: Tissues above the dentate line can be biopsied with little/no anesthesia (no somatic pain); below requires local anesthesia.

Sources: Sleisenger & Fordtran's Gastrointestinal and Liver Disease; Schwartz's Principles of Surgery, 11e; Pfenninger & Fowler's Procedures for Primary Care, 3e

Pecten line and dentate line

Finding Sources

Reading File

This is an important distinction - the pecten and the dentate/pectinate line are not the same. Here is the full breakdown:

The Three Landmarks of the Anal Canal

The anal canal has three distinct lines from top to bottom:

Anorectal junction (top)
        |
   Columns of Morgagni
        |
   DENTATE / PECTINATE LINE  ← (1) saw-toothed line, anal valves
        |
   ANAL PECTEN (transition zone)
   (smooth, white, nonkeratinized squamous epithelium)
        |
   ANOCUTANEOUS LINE = "WHITE LINE OF HILTON"  ← (2) intersphincteric groove
        |
   True perianal skin (bottom)

Pectinate Line (= Dentate Line)

The upper landmark
Formed by the bases of the anal columns (Columns of Morgagni) joined by the anal valves
Has a saw-toothed / comb-like (pectinate) appearance
Located ~2-3 cm above the anal verge
Marks the approximate position of the cloacal membrane in the fetus
Embryological junction between endoderm (above) and ectoderm (below)

Pecten (Anal Pecten)

The zone between the pectinate line and the anocutaneous line
A smooth, pale/white strip of mucosa
Lined by nonkeratinized stratified squamous epithelium
Highly sensitive to pain (somatic innervation)
Also called the anal transitional zone (ATZ) distally
Ends at the anocutaneous line (white line of Hilton) below

Anocutaneous Line = White Line of Hilton

The lower landmark
Corresponds to the intersphincteric groove (junction between internal and external anal sphincters)
Where nonkeratinized squamous epithelium transitions to true keratinized skin with hair follicles and glands
Palpable as a slight groove during examination

Summary Table

Feature	Pectinate/Dentate Line	Anal Pecten	Anocutaneous Line (White Line)
What it is	A line/junction	A zone/strip of mucosa	A line/junction
Location	~2-3 cm above anal verge	Between dentate and white line	At intersphincteric groove
Epithelium	Transition (columnar above → squamous below)	Nonkeratinized squamous	Transitions to keratinized skin
Embryology	Site of cloacal membrane	Ectodermal	Ectodermal
Clinical relevance	Internal vs. external hemorrhoids; lymph drainage watershed	Anal fissures classically here; very pain-sensitive	Marks internal/external sphincter junction

In short: The dentate/pectinate line is the upper serrated junction; the pecten is the smooth pale zone below it; and the white line of Hilton (anocutaneous line) marks the lower end of the pecten where it becomes true skin.

Sources: Gray's Anatomy for Students; Color Atlas of Human Anatomy Vol. 2 (Internal Organs)

This is a shared conversation. Sign in to Orris to start your own chat.