Derivatives of endoderm | Embryology | First Aid Lectures | Lec6 #firstaidlectures #usmlelectures
Channel: Dr. Jamil Lectures
Date: 2023-03-18

In this lecture we will discuss about derivatives of endoderm,derivatives of forehut,midgut and hindgut ,Pharyngeal Appratus ,fused membrane,buccupharyngeal membrane and cloacal membrane.

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Endodermal Derivatives
● The embryo undergoes lateral folding and longitudinal folding due to rapid growth as
1. During lateral folding, right and left lateral folds
fuse with each other to form a cylindrical embryo
that can be visualized through a cross-section of
the embryo → It is better to visualize the gut
cavities and sections of the gut tube.
2. During longitudinal folding,head and tail folds to
fuse with each other that can be visualized through
a sagittal section of the embryo →It is better to
visualize the entire length of the gut tube that
distinguish the whole gut tube into sections of the
gut (foregut, midgut, hindgut) → It helps to
understand the derivations of the endoderm →This view
shows the connection between the gut and the yolk
sac.→It is also called Cranio-caudal Folding.
● The endoderm forms the epithelial lining of the gut tube and the
gut tube is divided into three sections/parts
a) Foregut b) Midgut c) Hindgut
★ Derivatives of Foregut
● Pharynx
● Esophagus
● Stomach
● First two parts of the duodenum (superior and descending
parts)
● Endoderm lining of foregut buds out and forms following
pouches that give rise to GIT-associated organs.
➢ Respiratory bud/diverticulum gives rise to respiratory
tract
➢ Hepatic bud gives rise to liver,gallbladder and head of
pancreas
➢ Pancreatic bud gives rise to the body and tail of
pancreas.
★ Derivatives of Midgut
● Last two parts of the duodenum (horizontal and ascending
parts)
● Jejunum
● Ileum
● Cecum
● Ascending colon
● Proximal 2/3 of the transverse colon
★ Derivatives of Hindgut
● Distal 1/3 of transverse colon
● Descending colon
● Sigmoid colon
● Rectum
● Anal canal
★ Pharyngeal Apparatus
● The primitive pharynx is derived from cranial end of endoderm and a bud from the
primitive pharynx forms the thyroid → Primitive pharynx
undergo vesiculation and differentiates into pharyngeal
apparatus that consists of
➢ Pharyngeal arches
➢ 4 Pharyngeal pouches
➢ Pharyngeal cleft
➢ The inner membranes of the pharyngeal
apparatus are lined by endoderm , the outer
membrane is lined by ectoderm and mesoderm
in the middle.
1st Pharyngeal pouch gives rise to middle ear/tympanic
cavity & auditory tube/eustachian tube.
2nd Pharyngeal pouch gives rise to tonsils (tubal
tonsils, pharyngeal tonsils, lingual tonsils, palatine
tonsils)
3rd pharyngeal pouch gives rise to thymus.
3rd and 4th pharyngeal pouches give rise to inferior parathyroid gland and superior
parathyroid gland respectively → 4th pharyngeal pouch also develops the
Parafollicular C cells (thyroid cells that are responsible for secretion of calcitonin →
calcitonin is hormone that decreases the blood level of calcium).
★ Fused Membranes
● The embryo also forms 2 fused membranes.
1. Buccopharyngeal membrane →an area of ectoderm directly fused to the
endoderm in the cranial region of the embryo and forms buccopharyngeal
membrane that gives rise to the mouth.
2. Cloacal membrane →An area of ectoderm directly fused to the endoderm in
the caudal end of the embryo and forms a cloacal membrane that gives rise
to the anus and urethra → The cloaca (area near cloacal membrane) will
bifurcate into 2 parts
➔ One part moves anteriorly to form the urogenital sinus, which
forms the following structures
➢ bladder
➢ urethra
➢ prostate gland (in males)
➔ 2nd part moves posteriorly to form the anal canal → The
pectinate line separates the endoderm and ectoderm derived
portions of the anal canal
➢ Superior 2/3 of anal canal by endoderm
➢ Inferior 1/3 by ectoderm


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