Rectum And Anal Canal Notes

Rectum And Anal Canal

Prostatic Urethra Introduction

Situation: The part of urethra passing through the prostate gland is prostatic urethra.

Peculiarities: It is the zvidest and most dilated part of the male ♂ urethra. It is the narrozvest at the junction with the membranous urethra.

1. Internal features: Posterior wall of the prostatic urethra shows following features.

• The urethral crest, is a median longitudinal ridge of mucous membrane.
• The colliculus seminalis, an elevation on the middle of the urethral crest.
• The prostatic utricle, a blind sac about 6 mm long, which lies within the prostate.
• There is an orifice on the elevation through which prostatic utricle opens into the urethra.
• On each side of this orifice, there are openings of the ejaculatory ducts.
• There are two vertical grooves called prostatic sinuses situated one on each side of urethral crest.
• Each sinus presents the openings of 20 to 30 prostatic glands.

Read And Learn More: General Histology Question And Answers

Urethral Sphincters

1. Urethral Sphincters Proximal (internal) :

• It is formed by condensation of intermediate circular fibres of urinary bladder.
• It is involuntary. It is supplied by autonomous nerves. They are derived from vesical plexus.
•  It is damaged in men in following situations.
  • Bladder neck surgery
  • Transurethral resection of prostate
•  Functions: It may maintain continence when external sphincter has damaged.

2. Urethral Sphincters Distal (external): 

It is also called sphincter urethrae membranacea. 

• Components:
  • Urethral smooth muscle
  • Urethral striated muscle (of rhabdosphincter). It is most important component as it is capable of sustained contractions.
  • Pubourethral part of levator ani.
  • It is inserted into perineal body.

• Situation: Deep perineal pouch.
• Nerve supply: It is voluntary and supplied by perineal branch of pudendal nerve.

Internal Anal Sphincter

1. It is involuntary in nature.
2. It is local condensation of circular muscle coat.
3. It surrounds the upper 3/4th, i.e. 30 mm of the anal canal.
4. It extends from the upper end of the canal to the white line of Hilton.

Anal Sphincters

Anal sphincters external and internal:

Mucosal Folds Of Rectum

Two types of folds: Longitudinal and transverse

Two types of folds: Longitudinal and transverse (Contd.)

Question – 1: Describe the rectum under the following heads

1. Gross anatomy
2. Development, and
3. Applied anatomy.

Answer:

Rectum Of Introduction It is the distal part of hindgut and is present between sigmoid colon and anal canal.

1. Gross Anatomy:

1. Situation: It is situated in the posterior part of lesser pelvis.

• It lies in front of lower three pieces of sacrum and the coccyx.
• It begins as a continuation of the sigmoid colon at the level of vertebra S3.
• It ends by becoming continuous with the anal canal.
• Length: 12 cm.

2 . External features

3. Course and direction: It lies in the median plane. It shows two types of curvature in its course .

1. One curvature is in the beginning and other at the end.

2. Two anteroposterior curves

•  The sacral flexure of the rectum follows the concavity of the sacrum and coccyx.
• The perineal flexure of the rectum is the backward bend at the ano¬rectal junction.
• Three lateral curves.
• • Upper lateral:  Upper lateral curve is convex to the right.
  • Middle lateral: Middle lateral curve is convex to the left and is most prominent.
  • Lower lateral: Lower lateral curve is convex to the right.
    

4.  Relations:

1. Peritoneal relations:

• In the upper one-third, the peritoneum covers the anterior and lateral surfaces of the rectum.
• In the middle one-third, the peritoneum covers only the anterior surface.
• In the lower one-third, there is no peritoneum.

2. Visceral relations:

1.  Anteriorly:

Male ♂ :

• Upper two-thirds
  • Coils of the intestine pros
  • The rectovesical pouch contains a sigmoid colon.

• Lower one-third
  • Urinary bladder
  • The terminal part of the ureters
  • Seminal vesicles
  • Ductus deferens, and
  • Prostate.

Female ♀ :

• Upper two-thirds: Rectouterine pouch containing coils of small intestine.
• Lower one-third: Lower part of the vagina.

2. Posterior:  Relations are the same in males ♂   and females ♀

• Bones: Lower three pieces of the sacrum, and coccyx
• Ligament: Anococcygeal ligament.
• Muscles
  • Piriformis
  • Coccygeus, and
  • Levator ani.

• Vessels:
  • Median sacral
  • Superior rectal, and
  • Lateral sacral.

• Nerves:
  • Sympathetic chain
  • Ganglion impar (unpaired)
  • Anterior primary rami of S3, S4, S5 and
  • 1st coccygeal nerve, and the pelvic splanchnic nerves, lymph nodes lymphatics and fat.

5. Blood supply:

• Arterial supply:
  • The main blood supply of the rectum is by the superior rectal artery. It is the continuation of the inferior mesenteric artery.
  • The muscle wall of the rectum receives from the middle rectal artery which is a branch of the internal iliac artery.
  •  Small branches from the median sacral artery supply the back of the rectum.
    
• Venous drainage: There is a very free anastomosis between the tributaries of the venous system.
  • Superior rectal vein: The tributaries of this vein begin in the anal canal. It passes upward in the rectal submucosa. It pierces the muscular coat and unites to form a superior rectal vein. It continues upward as the inferior mesenteric vein.
  • Middle rectal vein: It drains mainly the muscular wall of the rectal ampulla. It opens into an internal iliac vein.

6. Nerve supply: It is supplied through superior rectal and inferior hypogastric plexuses.

•  The sympathetic fibres are derived from L1 and L2. These are vasoconstrictor and inhibitory to the rectal musculature and motor to the internal sphincter.
• Parasympathetic fibres are derived from S2, S3 and S4. These are motor to the musculature of the rectum and inhibitory to the internal sphincter.
  • The sensations of the distension of the rectum are also carried by the parasympathetic nerve.
  • Pain sensations are carried by both parasympathetic and sympathetic nerves.

7. Lymphatic drainage: The lymphatics of the rectum run along the arteries.

• The lymph vessels in the mucous membrane provide the first filter. The lymphatic vessels pierce the wall of the rectum.
• The lymphatics from the lower half of the rectum pass along the middle rectal vessels > internal iliac nodes.

2.  Development:

Chronological age: It develops in the 4th week of intrauterine life.

Germ layer: Endoderm and mesoderm.

Site: Caudal part of hindgut.

Source: The epithelium of the

• The upper part of the rectum is derived from the epithelium of the hindgut.
• The lower part of the rectum is derived from the dorsal part of the endodermal cloaca.
• Smooth muscles and connective tissues are derived from splanchnopleuric intra-embryonic mesoderm, surrounding the cloaca.

Anomalies:

• Imperforate anus: The commonest cause of imperforate anus is persistence of the anal membrane.
• Congenital rectovesical or rectourethral fistula.
• Congenital rectovaginal fistula.
• Ectopic anus.

3.  Applied Anatomy:

• Per rectal examination: The following structures can be palpated by a finger passed per rectum.
• In male ♂: In males, the posterior surface of the prostate, seminal vesical and vasa differentia are palpated.
• In females ♀: In females, the perineal body and the cervix are palpated.
• Proctoscopy: It is a visualization of the rectum and anal canal by proctoscopy.
• Sigmoidoscopy: It is a visualization of the sigmoid colon by sigmoidoscopy.
• Prolapse of rectum: It may be
  • Incomplete or mucosal prolapse of the rectum.
  • Complete prolapse or procidentia: The whole thickness of the rectal wall protrudes through the anus.

Blood Supply Of Anal Canal

Blood supply of anal canal:

White And Pectinate Lines Of Anal Canal

White and pectinate lines of the anal canal:

Question – 2: Describe the anal canal under the following heads

1. Gross anatomy
2. Development, and
3. Applied anatomy.

Answer:

Anal Canal Introduction:

The terminal part of the large intestine is called the anal canal. It is devoid of

1. Sacculations
2. Taenia coli
3. Appendices epiploic ae

1.  Anal Canal Gross Anatomy:

1. Situation: It is situated in the anal    between two ischiorectal fossae.

• Length: It is 4 cm long and situated about 4 cm in front and below the tip of the coccyx.
• Direction: Downwards, and backward.

2. Anal Canal External features:

• Extent: It extends from anorectal flexure (½ below and 1” in front of the tip of the coccyx) to the vertical slit between two buttocks.

3.  Anal Canal Relations:

1. Anterior relations are the structure at the base of urogenital  .

•  Perineal body
  • In male ♂:
    • Bulb of penis
    • Bulbospongiosus muscle
  • In female ♀:  Lower part of the vagina.

2.  Anal Canal  Posterior:  Anococcygeal ligament.

4.  Laterally:

• In the upper part: Levator ani.
• In the lower part: External anal sphincter.

5. Interior of the anal canal: It is divided by pectinate and Hilton’s white line into parts

• Upper part (above the pectinate line)
• Length is 15 mm. It is lined by a mucous membrane which shows 6-10 vertical folds.
• These folds are called anal columns of Morgagni. They are prominent in children. They are ill-defined in adults.
• The lower end of the anal columns is united to each other by short transverse folds of mucous membrane.
• These folds are called anal valves.
• Above each valve, there is a depression which is called the anal sinus.
• There are about 10 mucous-secreting anal glands. They open into the anal sinuses.
• The anal valves together form a transverse line called the pectinate line.
•  The middle part (between pectinate and Hilton’s lines):
  • This region is called the pecten or transitional zone.
  • There is no abrupt change in the esophagus to the stomach.
  • The lower limit of the pecten has a whitish appearance, hence it is called the white line of Hilton.
  • It is about 15 mm in length.
  • It is lined by a mucous membrane, which is bluish in appearance.
  • It contains a dense venous plexus which lies between the mucosa and muscle coat.
  • Mucous is less mobile as compared to the mucosa of the upper part.
  • Anal fissures are present in this zone.

• Lower part (cutaneous) (below Hilton’s line):
  • It is about 8 mm long.
  • It is lined by true skin containing sweat glands, sebaceous glands, and hair follicles.
  • The lining epithelium is stratified squamous keratinized.

Blood supply, nerve supply, and lymphatics of the anal canal:

Blood supply, nerve supply, and lymphatics of the anal canal(Contd):

2. Anal Canal Development:

Chronological age: It develops in the 7th week of intrauterine life.

Germ layer: Endoderm and ectoderm.

Site: Terminal part of the hindgut.

Sources:

• The upper two-thirds of the anal canal develops from the terminal part of the hindgut.
• The lower one-third develops from the proctodaeum.

Anomalies:

• Imperforate anus occurs in 1:5000 infants. It is more common in males ♂.
• It results from abnormal development of anorectal septum.
• Anal agenesis: The anal canal may end blindly.
• Anal stenosis.

3. Anal Canal Applied Anatomy:

•  Anal fissure: The lower end of anal columns is connected by small folds called anal valves.
  • In chronic constipated persons, the anal valves may be torn due to.
  • fecal mass catching on the fold of the mucous membrane.
  • The elongated ulcer is called anal fissure, which is very painful.
• Perianal abscess is due to the trauma to anal mucosa caused by fecal matter.

• Anal fistulae are due to the spread of inadequately treated anal abscesses. If the abscess opens only on one surface, it is called a sinus.
• Incontinence associated with rectal prolapse is due to trauma and spinal cord injury.
• Hemorrhoids are saccular dilatations of the internal rectal venous plexus.
  • They occur above the pectinate line and are, therefore, painless.
  • They bleed profusely during straining at stool.

6. Anal Canal Causes:

• Vessels are poorly supported by connective tissue
• They are valveless.
• Venous return decreases during defecation.
• Predisposing conditions
  • Portal hypertension resulting from cirrhosis
  • Pregnancy
  • Cancerous tumor.
  • Chronic constipation
• Precipitating factors
  • Familial tendency associated with leg vein varicosities.
  • The most dependent part of portal circulation