Presented by:Dr. Jamal GiriResident (1st Year)

Development of Branchial

arches

Contents Introduction.

Basic embryology.

Development of Branchial arches.

Derivatives of Branchial arches.

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Embryology

Embryo Greek word “Embryon”= unborn

The branch of biology that deals with the formation, early growth, and development of living organisms.

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Ovum Embryo Foetus

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Gametogenesis Spermatogenesis

Spermiogenesis

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Gametogenesis (cont..) Oogenesis

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Ovulation

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Fertilization Ampulla of the fallopian tube

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1st week

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End result of first week. implanted

blastocyst

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2nd week (week of two’s) Trophoblast differentiates into two layers:

cytotrophoblast and syncytiotrophoblast.

Embryoblast forms two layers: epiblast and hypoblast. (Bilaminar)

Formation of 2 cavities: amniotic and yolk sac cavities.

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9-day blastocyst (Bilaminar disc)

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13-day blastocyst (uteroplacental circulation established).

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3rd week Gastrulation:

Primitive streak formation. Invasion of epiblast cells. Formation of 3 germ layers

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Which is the most important time of human life?

"It is not birth, marriage, or death, but gastrulation, which is truly the most

important time in your life."

Lewis Wolpert (1986) 20

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Notochord formation Days 16-18 Primitive node epiblast

cells invaginate and migrate anteriorly towards prochordal plate – Notochordal process.

Represents early midline axis of the embryo

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Neurulation Notochord induces the

overlying ectoderm to thicken and differentiate into neural plate.

Neural groove

Neural tube

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Neural crest cells Transient,

multipotent, migratory cell population unique to vertebrates.

“4th germ layer.”

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4th week- The body takes shape Folding of the

embryo in the cranio-caudal plane.

From a flat disc to a C-shaped embryo.

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Process of folding

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5th-8th week (2nd month) Embryo first looks

recognizably human.

All major organs are in place.

Head is disproportionately large.

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Actual size of embryo

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The branchial arches Greek “Branchia”

means gill. Develop adjacent to

primitive pharynx.

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Branchial apparatus Pharyngeal arches Pharyngeal

pouches Pharyngeal clefts

or grooves Pharyngeal

membrane

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Development of Branchial arch Neural crest cells migrate into the head

and neck region (4th week)

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The endodermal wall of the foregut is separated from the surface ectoderm by a layer of mesoderm.

Soon after, the mesoderm is arranged in the form of six bars.

5th arch soon degenerates.

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Pharyngeal arch components A typical pharyngeal

arch contains:

Cartilaginous rod (skeleton of arch)

Muscular component Nerve Artery

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Derivatives of branchial arches Head and neck region of human beings

develop from these branchial arches.

Skeletal derivatives Muscular derivatives Nerves supply Arterial supply

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Skeletal derivatives

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Skeletal derivatives

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Muscular derivatives

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Nerve supply/derivatives

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Arterial derivatives Arch I : Part of the maxillary artery Arch II : Hyoid and stapedial arteries Arch III : Part of the carotid system Arch IV : Left side-arch of aorta, Right

side-right subclavian artery Arch VI : Pulmonary arteries

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Pharyngeal pouches The endoderm of

the pharynx lines the internal aspects of pharyngeal arches and passes into balloon like diverticula called pharyngeal pouches

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Pharyngeal Grooves or Clefts These grooves

separate the pharyngeal arches externally

Out of four pairs only first pair persists as the external acoustic meatus.

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Pharyngeal Membranes The endoderm of the

pouches contacts the ectoderm of the pharyngeal grooves and form the double layered pharyngeal membranes.

First pharyngeal membrane becomes the tympanic membrane, others obliterate 47

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