Embryology of the Hindgut - PowerPoint Presentation

Slide1

Embryology of the Hindgut

a.al-nuaimi@sheffield.ac.uk

abdulameerh@yahoo.com

Prof. Abdulameer Al-Nuaimi

E-mail:

Slide2

Large Intestine

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Slide3

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Rectum and Anal Canal

Anal valves

(

Pectinate

line)

Slide4

Male Pelvis

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Female

Pelvis

Slide5

Blood supply of the large intestine

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Slide6

Development of the Hindgut

The hind gut is the caudal part of the primitive gut, it develops into: the left third of the transverse colon,

descending colon, sigmoid colon, rectum and anal canal.In early embryonic life, the hindgut has dorsal mesentery. During development, the

Transverse colon retains its dorsal mesentery and remains intraperitonealDescending colon swings to the left side, loses its mesentery and is fixed in a retroperitoneal position.

Sigmoid colon

retains its mesentery and remains in an intraperitoneal position.

Slide7

Rectum

and

anal canal have got no mesentery, they develop below the intraperitoneal space; they are infraperitoneal

organs

Peritoneal cavity

Rectum

Anal canal

Sagittal section shows the

Peritoneal cavity and

infraperitoneal

organs

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Slide8

Formation of Rectum and Anal canal

Caudal end of the hindgut dilates to form the cloaca

which is situated below the peritoneal cavity. The cloaca is connected to the allantois (

Primitive Urogenital Sinus) anteriorly.Cloaca is

a common opening through which the digestive, urinary and reproductive system that

exit.

During

development,

the cloaca is

divided, so that the digestive system ends separately from the urinary and reproductive

system.

T

he

urinary and reproductive system separate as well.

Slide9

Cloaca

is endodermal in origin, it is covered by ectoderm (Proctodeum) at its ventral surface. The ectoderm in this region develops during the folding of the outer body wall

. The ventral boundary of the cloaca is called the Cloacal membrane,

it represents

the opposed

layers

of

ectoderm

and

endoderm

Slide10

Parietal

mesoderm

Visceral mesoderm

(

Langman’s

Medical Embryology)

Cloaca

Hindgut

Yolk sac

Slide11

Allantois

Cloacal

membrane

Ectoderm (

Proctodeum

)

Urorectal

septum

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The

Cloaca

at its early development

Vitelline

duct

Cloaca

Ectoderm

The

mesoderm

at the angle between the allantois and the hindgut proliferates

and forming

a

septum

called

urorectal

septum

.

The septum extends caudally to divide the cloaca into:

1-

Primitive urogenital sinus

ventrally.

2-

Anorectal

canal

dorsally.

Endoderm

Mesoderm

Ectoderm

Ectoderm

Slide12

As the embryo grows,

further downwards extension

of the urorectal septum takes place , it reaches the

cloacal membrane and divides it into 2 parts:

1-

anterior part called

urogenital

membrane.

2- posterior part called

anal membrane

.

The

Urorectal

septum raises

the ectoderm between the

urogenital membrane and the anal membrane, forming

the

perineal

body

.

Slide13

Anal Pit

And Anal

membrane

Anal Canal

Stages of development of anal canal

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Opening of

Urogenital

sinus

Urorectal

septum

Perineal

body

Urogenital

Memb

.

Anal

memb

.

urogenital sinus

Anorectal

canal

Cloacal

memb

Urorectal

septum

Perineal

body

Slide14

Development of Anal canal

Anorectal canal (endodermal in origin),

forms the mucosa of rectum and the upper 2/3 of Anal canal.The lower 1/3 of anal canal is derived from the

Ectoderm (proctodeum). It develops through proliferation of the mesenchyme around the anal membrane. This

creates an ectodermal

depression called

the

Anal Pit

.

The anal pit

depression is roofed by anal membrane.

At

the

7

th

week

of

development, the anal membrane ruptures

and establishes continuity between the upper 2/3 and lower 1/3 of the Anal Canal.

M

esoderm

surrounding the

anorectal

canal forms the

muscles

of rectum and anal canal.

Slide15

Anal pit

Anal membrane

Lower 1/3

a

nal canal

Ectoderm

(

Proctodeum

)

Upper 2/3 anal canal

Anorectal

canal

Anal pit

Ectoderm

Lower 1/3 anal canal

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Development of anal canal

Anorectal

canal

A

B

C

(

D

A

Slide16

The junction between the upper 2/3 (Endodermal in origin) and lower third (Ectodermal in origin) of Anal Canal is delineated by the

Pectinate line ( a remnant of the

proctodeum). At this line the Endothelial lining changes from Simple columnar to a Stratified Squamous Epithelium. On top of this line are the Anal Columns (Endodermal in origin).

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White line

Anal canal

(anal

columns)

Slide17

Lower 1/3 of anal canal

is lined superiorly by a stratified squamous non-keratinized epithelium (zona hemorrhagica).

It is lined inferiorly by a stratified squamous keratinized  epithelium (zona cutanea). The junction between them is Hilton's white line.

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Anal canal

zona

hemorrhagica

zona

cutanea

Slide18

Blood supply and Nerve supply of the anal canal

The upper 2/3 of anal canal is Endodermal in origin, thus it is supplied by the Superior rectal artery, branch of the inferior mesenteric artery (the artery of the hindgut). The nerve supply is by Autonomic nervous system.

The lower third of anal canal is ectodermal in origin (skin), thus it is supplied by the Inferior Rectal arteries which are branch of internal pudendal

arteries. The nerve supply is by the inferior rectal nerve, a branch of the pudendal nerve (Somatic system).

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Blood supply

of

the anal canal

Slide19

Summary

1-The hindgut has dorsal mesentery.2-Transverse colon and sigmoid colon are intraperitoneal,

descending colon is retroperitoneal. Rectum, and anal canal are infraperitoneal parts of the hindgut.3- Hindgut ends into the cloaca which gives rise to anaorectal

canal and urogenital sinus.4- Upper 2/3 of anal canal develops from the endoderm while the lower 1/3 develops from ectoderm.

Slide20

Congenital anomalies of GIT

Slide21

Esophageal Atresia

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EA = Oesophageal Atresia

TEF = Tracheo oesophageal fistula

oesophagus

Trachea

Slide22

 omphalocele

(failure of retraction of midgut

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Slide23

Failure of rotation of

Midgut

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Slide24

Congenital anomalies of biliary system

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Slide25

Anular

Pancreas

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Slide26

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Slide27

Meckel’s

Diverticulum (Frequency of occurrence)Meckel’s Diverticulum

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Meckel’s

Diverticulum = Remnant of

vitelline

duct

15cm

46cm

91cm

162cm

4%

24%

44%

28%

Slide28

Meckel’s

Diverticulumwww.google.co.uk/search?

Slide29

Meckel’s Diverticulum

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Ileum

Meckel’s

Diverticulum

Slide30

Some congenital Anomalies of the anal canal

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(Imperforated anus

)

(

)

(

)

(

)

Slide31

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(

Urorectal Fistula)

Slide32

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Imperforated anus

After Surgery

Before Surgery

Slide33

Thank You

Thank You