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Situation:
The rectum lies in the posterior part of the lesser pelvis, anterior to the lower three pieces of the sacrum and the coccyx.
Extent:
It begins as a continuation of the sigmoid colon at the level of the third sacral vertebra (S3).
The rectosigmoid junction is marked by the end of the sigmoid mesocolon.
It ends by continuing as the anal canal at the anorectal junction, which lies 2–3 cm in front of and slightly below the tip of the coccyx — corresponding to the apex of the prostate in males
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Dimensions:
The rectum measures about 12 cm in length.
Its upper part has a diameter of about 4 cm, similar to the sigmoid colon, while its lower part dilates to form the rectal ampulla, which acts as a temporary fecal reservoir
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Course and Direction:
The rectum passes downward and backward, then downward, and finally downward and forward.
It shows two types of curvatures:
Anteroposterior curves:
Sacral flexure follows the concavity of the sacrum and coccyx.
Perineal flexure is the backward bend at the anorectal junction.
Lateral curves:
Upper convex to the right
Middle convex to the left (most prominent)
Lower convex to the right
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Relations:
Peritoneal relations:
Upper one-third – covered by peritoneum in front and on both sides
Middle one-third – covered only in front
Lower one-third – no peritoneal covering, lies below the rectovesical pouch (males) or rectouterine pouch (females)
Distance between anus and pouch floor: 7.5 cm in males, 5.5 cm in females
Visceral relations:
In males: upper two-thirds relate to the rectovesical pouch with intestinal coils; lower one-third to bladder base, ureters, seminal vesicles, deferent ducts, and prostate.
In females: upper two-thirds relate to the rectouterine pouch and intestines; lower one-third to vagina and uterus
The mucosa of the rectum is smooth and devoid of villi. It shows three permanent transverse folds, called Houston’s valves or rectal folds, which are semilunar in shape and project into the lumen.
Upper fold: to the left, about 12 cm from the anus.
Middle fold: to the right, about 8 cm from the anus — the most prominent, corresponding to the Kohlrausch’s fold, marking the junction of the upper two-thirds and lower one-third of the rectum.
Lower fold: to the left, about 5 cm from the anus.
These folds support the fecal column and help retain feces before defecation.
The rectum receives blood from three main arteries:
Superior rectal artery → continuation of the inferior mesenteric artery, supplies the upper part of the rectum.
Middle rectal arteries → branches of the internal iliac arteries, supply the middle portion.
Inferior rectal arteries → branches of the internal pudendal arteries, supply the lower part of the rectum and anal canal.
These arteries anastomose freely in the submucosa and muscular coats, forming a continuous longitudinal arterial network along the rectal wall.
Venous drainage follows the arterial pattern and is divided into three sets:
Superior rectal vein → drains into the inferior mesenteric vein, hence into the portal system.
Middle rectal veins → drain into the internal iliac veins, hence into the systemic circulation.
Inferior rectal veins → drain into the internal pudendal veins, also into the systemic system.
These connections between the portal and systemic systems form a porto-systemic anastomosis, clinically important in portal hypertension, leading to hemorrhoids.
Upper part: drains into the pararectal lymph nodes, then to inferior mesenteric nodes.
Middle part: drains into the internal iliac nodes.
Lower part: drains into the superficial inguinal nodes through the anal canal below the pectinate line.
The rectum is supplied by both autonomic and somatic nerves:
Sympathetic: from the L1–L2 spinal segments via the hypogastric plexus, causing contraction of internal anal sphincter and inhibition of peristalsis.
Parasympathetic: from S2–S4 (pelvic splanchnic nerves) via the inferior hypogastric plexus, responsible for rectal peristalsis and relaxation of the internal sphincter.
Somatic fibers: from the pudendal nerve, supplying the external anal sphincter (voluntary control).
The rectum is supported by:
Pelvic floor (levator ani muscles): especially the puborectalis, forming a sling around the anorectal junction and maintaining the anorectal angle.
Lateral ligaments of the rectum: condensations of pelvic fascia containing middle rectal vessels.
Fascial condensations: including Waldeyer’s fascia (rectosacral fascia), connecting the rectum to the sacrum.
Pelvic peritoneal reflections and rectal ampulla, which help maintain fecal continence.
The rectum is exposed by removing the sigmoid colon and reflecting the pelvic viscera.
Note the peritoneal reflections on its upper two-thirds and identify the three lateral mucosal folds within.
The lateral ligaments containing middle rectal vessels and pelvic fasciae (Waldeyer’s fascia) can be identified posteriorly.
In males, observe relations with prostate, seminal vesicles, and bladder base; in females, with posterior vaginal wall and uterus.
Hemorrhoids (piles): occur due to dilation of the rectal venous plexus, especially at the 3, 7, and 11 o’clock positions, representing sites of portosystemic anastomosis.
Internal hemorrhoids → above pectinate line (painless).
External hemorrhoids → below pectinate line (painful).
Rectal prolapse: due to weakness of pelvic floor (levator ani) and fascia, leading to downward displacement of rectal wall through the anal canal.
Rectal carcinoma: commonly develops near Kohlrausch’s fold; spreads through lymphatics to pararectal and internal iliac nodes.
Rectal examination (per rectal): essential to assess prostate in males, posterior vaginal wall in females, and rectal wall integrity.
Fistula-in-ano: infection of anal glands leading to fistulous tracts between the anal canal and perianal skin.
Rectal atresia: congenital absence or narrowing of the anal opening due to failure of cloacal membrane rupture.
Fecal incontinence: caused by damage to pudendal nerve or weakness of the external sphincter after obstetric or neurological injury.
The anal canal measures about 3.8 cm in length.
It extends from the anorectal junction (where the rectal ampulla narrows to pass through the pelvic diaphragm) to the anus, the external opening.
It is directed downward and backward, lying between the right and left ischioanal fossae which allow expansion during defecation.
The anorectal junction lies about 2–3 cm in front of and slightly below the tip of the coccyx, corresponding to the apex of the prostate in males.
The anus is situated about 4 cm below and in front of the coccyx, surrounded by pigmented skin arranged in radiating folds containing apocrine glands
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.Anteriorly
Both sexes: Perineal body
Males: Membranous urethra and bulb of penis
Females: Lower end of the vagina
Posteriorly
Anococcygeal ligament and tip of coccyx
Laterally
Ischioanal fossae on both sides
All around:
Enclosed by sphincter muscles, whose tone keeps the canal closed
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.The anal canal’s interior is divided into three parts based on epithelial lining and structure:
Lined by mucous membrane of endodermal origin.
Features:
6–10 vertical folds called anal columns (of Morgagni) containing radicles of superior rectal vein.
Anal valves – short transverse mucosal folds joining adjacent columns.
Anal sinuses – small depressions above each valve, containing anal glands (their secretions are odoriferous in lower animals).
The line joining anal valves forms the pectinate (dentate) line, representing the junction of endodermal and ectodermal regions.
Occasionally, small anal papillae may project from valves — remnants of the embryonic anal membrane
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.Lies below the pectinate line, appears bluish due to dense venous plexus.
Lined by stratified squamous epithelium, thin and glossy, without sweat glands.
Ends at the white line of Hilton, which marks the lower limit of this zone and corresponds to the interval between the subcutaneous external sphincter and lower edge of internal sphincter
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.Lined by true skin, containing sebaceous glands, sweat glands, and hair follicles.
Represents the ectodermal part of the anal canal
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.Formed by the thickened circular smooth muscle coat of the gut.
Surrounds the upper three-fourths (≈30 mm) of the anal canal.
Extends from the upper end of the canal to the white line of Hilton.
Under autonomic control — sympathetic stimulation causes contraction; parasympathetic causes relaxation.
Made of striated muscle fibers under somatic control via inferior rectal nerve and perineal branch of S4.
Surrounds the entire anal canal and consists of:
Subcutaneous part: encircles the anal margin.
Superficial part: attached anteriorly to perineal body, posteriorly to anococcygeal ligament.
Deep part: blends superiorly with puborectalis fibers.
In males, transverse perinei and bulbospongiosus insert anteriorly forming a plane of cleavage; in females, transverse perinei and bulbospongiosus fuse with the sphincter in the lower perineum
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.Formed by the fusion of puborectalis muscle with the longitudinal muscle coat of rectum at the anorectal junction.
Lies between the external and internal sphincters.
Descends as fibroelastic septa that insert into the skin around the anus (forming corrugator cutis ani), helping maintain anal integrity and anchoring the anal mucosa
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.A muscular ring at the anorectal junction formed by the union of:
Puborectalis muscle,
Uppermost fibers of the external sphincter, and
Internal anal sphincter.
Palpable during digital rectal examination.
Essential for rectal continence — its division results in incontinence.
It is less marked anteriorly, where puborectalis fibers are absent
Ischioanal (Ischiorectal) Space
Present on each side of the anal canal.
Triangular in coronal section and filled with fat and loose areolar tissue.
Allows distension of the anal canal during defecation and provides space for passage of inferior rectal vessels and nerves.
Pus in this space may spread widely and communicate with the opposite side through the deep postanal space.
Perianal Space
Surrounds the anal canal below the white line.
Contains:
Lower fibers of the external sphincter
External rectal venous plexus
Terminal branches of the inferior rectal vessels and nerves
Pus in this space tends to track either upward to the white line or outward to the perineal skin, rather than spreading to the ischioanal fossa
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.Submucous Space
Lies above the white line between the mucous membrane and internal sphincter.
Contains the internal rectal venous plexus and lymphatic vessels
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.Above the pectinate line:
Supplied by the superior rectal artery (branch of the inferior mesenteric artery).
Below the pectinate line:
Supplied by the inferior rectal arteries (branches of the internal pudendal arteries).
These two systems anastomose within the wall of the anal canal, ensuring continuous circulation
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.Internal Rectal Venous Plexus (haemorrhoidal plexus)
Lies in the submucosa.
Drains mainly into the superior rectal vein, but communicates freely with the external plexus and middle and inferior rectal veins.
Represents an important portosystemic anastomosis.
Veins at 3, 7, and 11 o’clock positions (in lithotomy) are large and prone to internal hemorrhoids
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.External Rectal Venous Plexus
Lies outside the muscular coat of rectum and anal canal.
Communicates with the internal plexus.
Drained by:
Inferior rectal vein → internal pudendal vein
Middle rectal vein → internal iliac vein
Superior rectal vein → inferior mesenteric vein
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Anal Veins
Arranged radially around the anal margin.
Communicate with internal plexus and inferior rectal veins.
Rupture due to excessive straining may produce perianal hematoma (external piles)
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.Above the pectinate line: to the internal iliac lymph nodes.
Below the pectinate line: to the medial group of superficial inguinal nodes.
The pectinate line thus forms a watershed between deep and superficial lymph drainage
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.Above the pectinate line:
Supplied by autonomic nerves:
Sympathetic: from inferior hypogastric plexus (L1–L2) → causes contraction of internal sphincter.
Parasympathetic: from pelvic splanchnic nerves (S2–S4) → causes relaxation of internal sphincter and initiates peristalsis.
Below the pectinate line:
Supplied by somatic nerves — inferior rectal nerve (branch of pudendal nerve) and perineal branch of S4 → control the external sphincter.
This zone is pain-sensitive, unlike the upper part
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.After identifying the anal canal, expose:
The ischioanal fossae laterally.
The internal and external sphincters.
The submucous and perianal spaces.
Trace the inferior rectal vessels and nerves from the pudendal canal to the anal margin.
Identify the pectinate line and note transitions in mucosal epithelium and vascular plexuses.
Internal hemorrhoids:
Dilatation of internal rectal venous plexus above pectinate line — painless bleeding.
External hemorrhoids:
Involve external venous plexus below pectinate line — painful and tender swellings.
Anal fissure:
Linear tear in lower anal canal, often due to constipation or trauma, producing severe pain during defecation.
Fistula-in-ano:
Abnormal epithelialized tract connecting anal canal to skin, often secondary to perianal abscess.
Ischioanal abscess:
Infection in ischioanal fossa leading to painful swelling; may spread contralaterally via the deep postanal space.
Incontinence:
Damage to anorectal ring or pudendal nerve results in loss of control over defecation.
Carcinoma:
Above pectinate line → lymph spread to internal iliac nodes;
Below pectinate line → spread to superficial inguinal nodes.
The anal canal shows distinct epithelial and structural changes at different levels, corresponding to its embryological origins.
Epithelium: Simple columnar (like rectal mucosa).
Lamina propria: Contains mucous glands and dense vascular plexuses (internal rectal venous plexus).
Muscularis mucosae: Present but thin.
Submucosa: Rich in veins, lymphatics, and connective tissue.
Muscular coat:
Inner circular layer → thickened below to form internal anal sphincter.
Outer longitudinal layer → continuous with conjoint longitudinal muscle coat of the rectum.
Epithelium: Stratified squamous non-keratinized; smooth, bluish appearance due to venous plexus beneath.
No glands or hair follicles.
Marks the transition from endodermal to ectodermal region.
Contains small anal glands that open into anal sinuses near the pectinate line.
Epithelium: Keratinized stratified squamous (true skin type).
Contains sebaceous and sweat glands, and hair follicles.
Beneath lies dense connective tissue, external venous plexus, and skeletal muscle fibers of the external sphincter.
Anal columns: Longitudinal mucosal folds with branches of the superior rectal vein.
Anal valves and sinuses: Sites of potential infection or abscess formation.
Internal and external venous plexuses: Represent the anatomical basis for hemorrhoids.
The anal canal develops from two embryological sources:
Endodermal (Hindgut) Part
Derived from the terminal part of the hindgut, which forms the rectum and upper two-thirds of the anal canal.
Lined by columnar epithelium.
Blood supply from superior rectal artery (inferior mesenteric artery).
Lymph drains to internal iliac nodes.
Nerve supply is autonomic (visceral) and insensitive to pain.
Ectodermal (Proctodeal) Part
Derived from the proctodeum (ectodermal depression on the embryo’s surface).
Forms the lower one-third of the anal canal.
Lined by stratified squamous epithelium (skin type).
Supplied by inferior rectal artery (from internal pudendal artery).
Lymph drains to superficial inguinal nodes.
Nerve supply is somatic (pudendal nerve) and pain-sensitive.
The cloacal membrane initially separates the endodermal hindgut from the ectodermal proctodeum.
Its rupture at 7th week of development establishes continuity between the two parts.
The line of fusion is marked in adults by the pectinate (dentate) line.
Imperforate anus: Failure of cloacal membrane to rupture.
Anal stenosis: Narrowing due to incomplete absorption of epithelial plug.
Ectopic anus: Abnormal migration of the anal opening.
Fistula-in-ano: Persistence of embryonic connections between the anal canal and perineal skin.
Anorectal agenesis: Failure of development of the hindgut part of the canal.
The middle lateral curvature of the rectum is the most prominent, and it is convex to the left side.
The chief vessels of the rectum are the superior rectal artery and superior rectal vein.
The perineal body and levator ani muscles form the main supports of the rectum.
The anal canal is surrounded by both internal (involuntary) and external (voluntary) sphincters which maintain continence.
Only the middle fibers of the external anal sphincter have a bony attachment.
The proximal 15 mm of the anal canal develops from the anorectal canal (endoderm), and the distal 23 mm develops from the proctodeum (ectoderm).
Primary hemorrhoids appear at 3, 7, and 11 o’clock positions (in the lithotomy position).
The rectum and anal canal together demonstrate dual blood, lymphatic, and nerve supply, explained by their dual embryological origin.
The pectinate line marks the junction between endodermal and ectodermal regions, distinguishing areas of visceral vs. somatic innervation and different lymph drainage.
Internal hemorrhoids (above the pectinate line) are painless, while external hemorrhoids (below it) are painful due to somatic innervation.
The anorectal ring formed by puborectalis, deep external sphincter, and internal sphincter is vital for continence.
Damage to the anorectal ring or pudendal nerve results in fecal incontinence.
The ischioanal fossae provide space for anal expansion during defecation, but infections here can spread bilaterally through the deep postanal space.
Rectal carcinoma often occurs at the rectosigmoid junction or ampulla; lymphatic spread depends on the level relative to the pectinate line.
Case:
A 40-year-old female patient presents with painless bleeding and a soft mass protruding from the anus during defecation
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Question 1:
What is the painless structure that bleeds during defecation?
Answer:
The patient is suffering from internal hemorrhoids (piles), which are caused by prolapse of the mucous membrane containing tributaries of the internal rectal venous plexus.
This venous plexus drains blood from the upper part of the anal canal (above the pectinate line) and is supplied by autonomic nerves, hence painless.
Question 2:
What are the reasons for this development?
Answer:
Varicosity of the internal rectal venous plexus due to increased venous pressure.
Irregular bowel habits and chronic constipation, leading to straining during defecation.
Prolonged standing or portal hypertension (commonly due to liver cirrhosis) increases pressure in the portal circulation, resulting in venous congestion.
The internal venous plexus lacks valves and is arranged in radial columns that bulge under pressure, forming piles at the classical 3, 7, and 11 o’clock positions in the lithotomy position
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.Clinical Correlation:
These piles bleed bright red blood during defecation because of rupture of varicose venous radicles.
The absence of pain distinguishes internal piles (autonomic innervation) from external piles (somatic innervation by pudendal nerve).
Chronic cases may lead to anemia and prolapse of the mucosa.
Management involves dietary fiber, avoiding straining, and in advanced cases, ligation or hemorrhoidectomy.
1. The upper part of the anal canal develops from:
A. Cloacal membrane
B. Ectodermal proctodeum
C. Endodermal hindgut (anorectal canal)
D. Mesoderm of urorectal septum
→ Answer: C. Endodermal hindgut (anorectal canal)
2. The lower part of the anal canal develops from:
A. Cloaca
B. Proctodeum (ectodermal invagination)
C. Hindgut endoderm
D. Allantois
→ Answer: B. Proctodeum (ectodermal invagination)
3. The line that marks the junction between endodermal and ectodermal parts of the anal canal is:
A. White line of Hilton
B. Pectinate (dentate) line
C. Anal verge
D. Anocutaneous line
→ Answer: B. Pectinate (dentate) line
4. Above the pectinate line, the epithelium is:
A. Stratified squamous keratinized
B. Stratified squamous non-keratinized
C. Simple columnar
D. Cuboidal
→ Answer: C. Simple columnar
5. Below the pectinate line, the epithelium is:
A. Simple columnar
B. Stratified squamous keratinized
C. Pseudostratified ciliated columnar
D. Transitional
→ Answer: B. Stratified squamous keratinized
6. The artery supplying the anal canal above the pectinate line is:
A. Middle rectal artery
B. Inferior rectal artery
C. Superior rectal artery
D. Median sacral artery
→ Answer: C. Superior rectal artery
7. The artery supplying the anal canal below the pectinate line is:
A. Superior rectal artery
B. Middle rectal artery
C. Inferior rectal artery
D. Inferior mesenteric artery
→ Answer: C. Inferior rectal artery
8. The vein involved in the development of internal hemorrhoids is:
A. Inferior rectal vein
B. Middle rectal vein
C. Superior rectal vein
D. External pudendal vein
→ Answer: C. Superior rectal vein
9. Internal hemorrhoids are painless because:
A. The mucosa is thick
B. It is supplied by autonomic nerves
C. It occurs below the pectinate line
D. The area lacks nerve endings
→ Answer: B. It is supplied by autonomic nerves
10. External hemorrhoids are painful because:
A. They occur above pectinate line
B. They involve internal rectal venous plexus
C. They are supplied by pudendal nerve (somatic)
D. They are small in size
→ Answer: C. They are supplied by pudendal nerve (somatic)
11. Which of the following marks the lower limit of the pecten?
A. Pectinate line
B. White line of Hilton
C. Anal verge
D. Anal sinus
→ Answer: B. White line of Hilton
12. The venous drainage below the pectinate line is mainly into:
A. Inferior rectal veins → internal pudendal vein
B. Middle rectal veins → internal iliac vein
C. Superior rectal vein → inferior mesenteric vein
D. Lumbar veins → azygos vein
→ Answer: A. Inferior rectal veins → internal pudendal vein
13. The lymph from the anal canal below the pectinate line drains into:
A. Pararectal nodes
B. Internal iliac nodes
C. Superficial inguinal nodes
D. Inferior mesenteric nodes
→ Answer: C. Superficial inguinal nodes
14. The nerve supply to the anal canal below the pectinate line is:
A. Inferior hypogastric plexus
B. Pelvic splanchnic nerves
C. Inferior rectal branch of pudendal nerve
D. Pelvic sympathetic chain
→ Answer: C. Inferior rectal branch of pudendal nerve
15. Which structure forms the internal anal sphincter?
A. Longitudinal muscle coat of rectum
B. Thickened circular smooth muscle of rectum
C. Levator ani
D. Puborectalis
→ Answer: B. Thickened circular smooth muscle of rectum
16. The external anal sphincter is supplied by:
A. Autonomic nerves
B. Inferior rectal nerve and perineal branch of S4
C. Pelvic splanchnic nerves
D. Hypogastric plexus
→ Answer: B. Inferior rectal nerve and perineal branch of S4
17. Which muscle forms the main sling for fecal continence at the anorectal junction?
A. Puborectalis
B. Ischiococcygeus
C. Superficial external sphincter
D. Bulbospongiosus
→ Answer: A. Puborectalis
18. The anorectal ring is formed by:
A. Pubococcygeus
B. Internal sphincter only
C. Puborectalis, deep external sphincter, and internal sphincter
D. Superficial external sphincter
→ Answer: C. Puborectalis, deep external sphincter, and internal sphincter
19. Which of the following represents the portosystemic anastomosis in the anal canal?
A. Superior and inferior rectal veins
B. Inferior rectal and external pudendal veins
C. Superior and middle rectal arteries
D. Internal pudendal and obturator veins
→ Answer: A. Superior and inferior rectal veins
20. A defect in partitioning of the cloaca by the urorectal septum leads to:
A. Rectal atresia
B. Anorectal agenesis with or without fistula
C. Anal fissure
D. Rectal prolapse
→ Answer: B. Anorectal agenesis with or without fistula
Q1. What is the total length of the anal canal?
A. Approximately 3.8 cm (1½ inches).
Q2. What is the direction of the anal canal?
A. It is directed downward and backward, following the axis of the pelvic outlet.
Q3. What are the parts of the anal canal?
A.
Upper part – mucous (endodermal).
Middle part – transitional zone (pecten).
Lower part – cutaneous (ectodermal).
Q4. What is the pectinate line?
A. A serrated line formed by the anal valves joining adjacent anal columns; it marks the junction of endodermal and ectodermal parts of the anal canal.
Q5. What is the significance of the pectinate line?
A. It marks differences in:
Epithelium – columnar above, squamous below.
Blood supply – superior rectal artery above, inferior rectal below.
Venous drainage – portal above, systemic below.
Lymph drainage – internal iliac above, superficial inguinal below.
Nerve supply – autonomic above (painless), somatic below (painful).
Q6. What are anal columns (of Morgagni)?
A. Longitudinal mucosal folds in the upper anal canal containing superior rectal vein tributaries.
Q7. What are anal valves and anal sinuses?
A.
Valves: Small transverse folds joining adjacent columns.
Sinuses: Small depressions above valves; may collect debris and become infected.
Q8. What is the white line of Hilton?
A. A line at the junction of the transitional and cutaneous zones, corresponding to the lower limit of the internal sphincter and upper limit of the subcutaneous external sphincter.
Q9. What are the sphincters of the anal canal?
A.
Internal sphincter – involuntary, smooth muscle (circular coat).
External sphincter – voluntary, skeletal muscle (striated).
Q10. What forms the anorectal ring?
A. Formed by the puborectalis, deep part of the external sphincter, and internal sphincter.
Q11. What is the function of the puborectalis muscle?
A. Acts as a sling at the anorectal junction, maintaining fecal continence.
Q12. What are the supports of the rectum?
A.
Pelvic diaphragm (levator ani)
Perineal body
Endopelvic fascia
Anal sphincters
Q13. Which arteries supply the anal canal?
A.
Above pectinate line: Superior rectal artery.
Below pectinate line: Inferior rectal artery.
Q14. Which veins form the portosystemic anastomosis in the anal canal?
A. Between superior rectal vein (portal system) and middle/inferior rectal veins (systemic circulation).
Q15. What are the common sites of internal hemorrhoids?
A. At 3, 7, and 11 o’clock positions (in lithotomy position).
Q16. Why are internal hemorrhoids painless?
A. Because the mucosa above the pectinate line is supplied by autonomic nerves.
Q17. Why are external hemorrhoids painful?
A. Because the skin below the pectinate line is somatically innervated by the pudendal nerve.
Q18. Where does lymph from the anal canal drain?
A.
Above pectinate line: Internal iliac lymph nodes.
Below pectinate line: Superficial inguinal lymph nodes.
Q19. What is the clinical importance of the ischioanal fossa?
A. It allows distension of the anal canal during defecation and can be a site of abscess or fistula formation.
Q20. What happens if the anorectal ring is damaged?
A. It leads to fecal incontinence due to loss of sphincteric control.
Q21. What are the common congenital anomalies of the anal canal?
A.
Imperforate anus
Anal stenosis
Anorectal agenesis with fistula
Rectovaginal or rectourethral fistula
Q22. What is the histological difference above and below the pectinate line?
A.
Above: Simple columnar epithelium.
Below: Stratified squamous keratinized epithelium.
Q23. Which nerve supplies the external anal sphincter?
A. Inferior rectal nerve (branch of pudendal nerve) and perineal branch of S4.
Q24. Which muscle forms the corrugator cutis ani?
A. Fibers of the longitudinal coat of rectum that extend to the skin around the anus, helping to wrinkle it.
Q25. What embryological event leads to formation of the anal canal?
A. Fusion of endodermal hindgut and ectodermal proctodeum after rupture of the cloacal membrane during the 7th week of development.
Q26. What is the cause of backflow of portal blood through rectal veins?
A. Portal hypertension, leading to dilatation of internal rectal veins and formation of piles.
Q27. What is the function of the conjoint longitudinal coat?
A. Connects the internal and external sphincters, supports mucosa, and maintains anal canal integrity.
Q28. What is the difference between upper and lower anal canal regarding pain?
A.
Upper part: Painless (autonomic innervation).
Lower part: Painful (somatic innervation).
Q29. What is the function of the perineal body in relation to the anal canal?
A. Acts as an anchoring structure for sphincters and maintains pelvic floor integrity.
Q30. What is the histological hallmark of the anal columns?
A. Presence of venous channels of the superior rectal vein within the mucosal folds.
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