Human development powerpoint with sound

Human Development

week 10

Explain the stages of development starting with fertilization and ending with the neonatal period.
Discuss the major events of the first, second, and third trimesters of development.
I addition we will discuss the formation process maxilla, mandible and cranium

Prenatal Development

Embryonic development

fertilization - 8 weeks

Fetal development

9 weeks - birth

Postnatal Development
time period from fertilization to birth = gestation= pregnancy

Stages of development

Fertilization:it is the process of fusion of mail and female germs to form zygote. Typically this cell contains 46 chromosomes and gametes contain 23 chromosomes
Taking place in ??
Viability of gametes:
Oocyte 12-24 h
Sperm 12-48 h

Single sperm fuses with oocyte

Cleavage

Blastocyst

with blastocoele cavity 64 cells
Morula
solid ball of cells 16 cells
Early division of zygote into multiple cells without increase in size. Cleavage is the mitotic division of cells in the early embryo which occurs in sequence of 2.4.8.16. 32,64 and so on


Zygote










• Implantation Embedding of blastocyst into uterine lining begins at day 7 end at 9th dayBall of mass cell called blastocyst. Out layer form trophoblast and inner layer form embryo.Trophoblast converted to chorion and finally establish to form placenta

Formation of Placenta

Development of placenta from edges of blastocyst
Placenta = organ that allow the embryo/fetus to exchange nutrients and waste.
Nutrient and gas exchange happens without actual blood exchange

Gastrulation: 3 Germ Layers Formed

Ectoderm (forms from epiblast)
Nervous system
Epidermis, epithelium lining skin mucosa of lips, nasal cavity, floor of mouth palate, exocrine sweat gland parotid gland. Enamel of teeth
Endoderm (forms from hypoblast)
Mucosae (eg: GI-tract
Associated glands
Mesoderm
Dentin, heart blood vessels etc.

day 12:

Embryogenesis

Following gastrulation, formation of viable embryo
Head fold and tail fold develop
Critical period organogenes
Teratogens, Teratology = ?
Rubella and syphilis
X-rays
FAS and smoking

Fetal development from 9th -38th weeks

Characteristics
1. rapid growth
2.tissue differentiations

Fetal development

Tissue and organ development
Face
Eyes
External genitalia
Limbs
Lung development
Nervous system

Pharyngeal Apparatus

The head and neck region of four week human embryo somewhat resemble these regions of a fish embryo of comparable stage


This explains the former use of designation branchial apparatus

Branchial is derived from the Greek word branchia or gill

Pharyngeal Apparatus

Pharyngeal apparatus consists of:

Pharyngeal arches

Pharyngeal pouches
Pharyngeal grooves/clefts
Pharyngeal membrane

Pharyngeal Arches

Pharyngeal arches begin to develop early in the fourth week as neural crest cells migrate into the head and neck region

The first pair of pharyngeal arches (primordium of jaws) appears as a surface elevations lateral to the developing pharynx


Soon other arches appear as obliquely disposed, rounded ridges on each side of the future head and neck regions

Each pharyngeal arch consists of a core of mesenchyme

Is covered externally by ectoderm and internally by endoderm

In the third week the original mesenchyme is derived from mesoderm

During the fourth week most of the mesenchyme is derived from neural crest cells that migrate into the pharyngeal arches

Pharyngeal Arches

By the end of the fourth week, four pairs of pharyngeal arches are visible externally

The fifth arch is rudimentary and are not visible on the surface of the embryo

The pharyngeal arches are separated from each other by fissures called pharyngeal grooves

Arches

Each arch contains
Cartilage
Cranial nerve
Artery
Muscle component


All neural crest origin

6 arches, only 5 form structures in humans

1, 2, 3, 4, and 6
5th fails to develop

1st Arch “Mandibular Arch”

Skeletal components
Meckel’s cartilage
Framework for mandible
Malleus head and neck
Incus body and short process
Muscles
Muscles of mastication
Anterior digastric
Mylohyoid
Tensor tympani
Tensor veli palatini
Nerve
CN V (Trigeminal)
Artery
Maxillary; external carotid

2nd Arch “Hyoid Arch”

Skeletal components
Reichert’s cartilage
Stapes
Malleus manubrium
Incus long process
Styloid process
Hyoid bone (lesser horn and upper body)

Muscles

Facial expression, buccinator, platysma, stapedius, stylohyoid, posterior digastric


Nerve
CN VII (Facial)

Artery

Stapedial

3rd Arch

Skeletal components
Hyoid (greater horn and lower body)
Muscles
Stylopharyngeus
Nerve
CN IX (Glossopharyngeal)
Artery
Common/Internal carotid

4th Arch

Skeletal components
Thyroid, epiglottic, cuneiform cartilages
Muscles
Cricothyroid, inferior constrictors
Nerve
Superior laryngeal
Artery
Subclavian, aortic arch

6th Arch

Skeletal components
Cricoid, arytenoids, corniculate
Muscles
All intrinsic muscles of larynx (except cricothyroid)
Nerve
Recurrent laryngeal
Artery
Pulmonary artery

Branchial Clefts and Pouches

4 clefts and 4 pouches
5th and 6th contribute to the 4th

Clefts provide “covering” to structures of the corresponding arch and pouch

Pouches

1st Pouch
Eustachian tube, middle ear, mastoid, inner layer of tympanic membrane

2nd Pouch

Tonsils, root of tongue, foramen cecum, pharynx(part)

3rd Pouch – ventral and dorsal wings

Ventral wing – Thymus
Dorsal wing – inferior parathyroid glands

Pouches

4th Pouch
Superior parathyroid glands
Parafollicular C-cells of thyroid gland


5th Pouch
Contributes to Parafollicular C-cells

6th Pouch

Contributes to laryngeal musculature and cartilage

Fate of Pharyngeal Arches

A typical pharyngeal arch contains:

An aortic arch, an artery that arises from the truncus arteriosus of the primordial heart

A cartilaginous rod that forms the skeleton of the arch


A muscular component that differentiates into muscles in the head and neck

A nerve that supplies the mucosa and muscles derived from the arch