Embryo Exam 2

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Integumentary System

skin and its glands, hair, nails, mammary glands

2 layers of skin

epidermis and dermis

Epidermis

derived from ectoderm

Dermis

derived from mesoderm

2 layers of embryonic skin

periderm and basal layer

Periderm

keratinized layer, primarily dead cells

Basal layer

produces new cells

Vernix caseosa

Whitish, greasy substance formed by secretions of sebaceous glands and exfoliated cells. Covers skin of fetus.

Function of vernix caseosa

protect fetal skin from amniotic fluid

lubricates fetus for parturition

Epidermal ridges

Develop from basal layer and produce patterns on surface of fingertips, palms of hand, and soles of feet.

Genetically determined, individually unique.

Form basis of fingerprint analysis.

Dermatoglyphics

fingerprint analysis

Melanocytes

come from neural crest cells

produce skin pigmentation

Yes

Does albinism have a normal number of melanocytes?

Tyrosinase

What enzyme does albinism lack?

Arrector muscles

What elevates the hair shafts and are responsible for ‘goosebumps?

Sebaceous gland

A small bud grows from the wall of the developing hair follicle to form a ___?

Fine lanugo

first hairs to form

Function of fine lanugo

hold vernix caseosa in place

32 weeks

When do fingernails reach the tips of the digits?

36 weeks

When do toenails reach the tips of the digits?

Prematurity

What is suggested when nails do not reach the tips of the digits at birth?W

Along mammary crests

Where are mammary glands of all mammals found?

True

T/F: Development of lactiferous ducts and nipples is identical in males and females at birth

Puberty

When does the female breast enlarge due to development of mammary glands?

Rudimentary

In males, the lactiferous ducts remain ___________ throughout life.

Polythelia

extra nipple, more common in females

Polymastia

extra breast, usually develops just inferior to normal breast

can occur anywhere along mammary crest (NOT AT MIDLINE)

Inverted nipple

occurs when nipples fail to evert, can cause issues with babies latching

Breast cancer

Indicated by an everted nipple that inverts during adulthood

When does the paraxial mesoderm become segmented into somites?

Week 3

Sclerotome and dermomyotome

Two parts of each somite

Sclerotome

located ventromedially, gives rise to vertebrae and ribs

Dermomyotome

located dorsolaterally, gives rise to muscle and dermis

Mesenchyme

loosely woven embryonic connective tissue formed from sclerotomes

contains stem cells

Fibroblasts, chondroblasts, osteoblasts

Mesenchyme may differentiate into ________

Intramembranous ossification

bone develops directly from mesenchyme directly within membranous sheaths

Intramembranous

What type of ossification develops the flat bones of the skull?

Endochondral ossification

mesenchyme differentiates into hyaline cartilage models, which then ossify

Neural crest cells

Mesenchyme which forms the skull is derived primarily from ______.

Teratogens

Due to their migration, neural crest cells are susceptible to ____________.

Membranous Neurocranium

forms skull vault or calvaria

Cartilaginous neurocranium

forms the base of the skull

Intramembranous ossfication

How is the membranous neurocranium formed?

Sutures

Fibrous tissue joints that separate the flat bones of the skull at birth

Anterior fontanelle

large fontanelle, closes 1.5 years after birth, ‘soft spot’

Posterior fontanelle

fontanelle that closes 3 months after birth

Anterolateral and posterolateral fontanelles

Which fontanelles are found in pairs?

Fontanelle

Sheet-like fibrous areas where sutures widen at points where more than two bones meet.

Function of fontanelles and sutures

Allow molding of fetal cranium to birth canal during parturition

Cartilaginous neurocranium

Formed by endochondral ossification, forms base of skull

Craniosynostosis

general prenatal fusion of cranial sutures

Scaphocephaly

premature fusion of sagittal suture, results in long, narrow, and wedge-shaped head

Scapocephaly

most common type of craniosynostosis

Brachycephaly

premature fusion of coronal suture, produces high, tower-like skull

Acrania

complete/partial absence of neurocranium, often associated with major defects of vertebral column, usually incompatible with life.

Meroencephaly

major defects of vertebral column and partial absence of brain

Cranial and caudal part

2 parts of each sclerotome

Cranial part

loosely packed cells in a sclerotome

Caudal half of one sclerotome and cranial half of the one below it

What forms each vertebral column?

Centrum and left/right neural arches

3 primary centers of ossification for each vertebra

5

How many secondary ossification centers are there in the vertebra after puberty?

Puberty

When do the five centers of ossification appear in the vertebra?

Klippel-Feil Syndrome

condition with short neck, fused cervical vertebrae, restricted neck movement, and low hairline posteriorly

Hemivertebrae

results when one of two chondrification centers of vertebral centrum fail to appear

Hemivertebrae

common cause of congenital scoliosis

Lumbar ribs

most common accessory nerve, usually produces no symptoms

Cervical ribs

usually attached to C7, may produce neurovascular symptoms through compression of brachial plexus or subclavian artery

Pectus excavatum

variation in which there is a concave depression in lower sternum

Pectus carinatum

chest juts out, AKA pigeon chest

Appendicular skeleton

made of pectoral girdle, upper limb, pelvic girdle, lower limb

Diaphysis

portion of long bone formed from its primary ossification center

Clavicle

first bone to undergo ossification and the only bone that goes through both types

Ends of long bones

Where are epiphysis found?

Before birth

When most primary centers of ossification appear

After birth

when most secondary centers of ossification appear

Achondroplasia

most common type of dwarfism, characterized by normal sized head with bulging forehead and indented nasal bridge

Mesoderm

The muscular system develops almost from ___________.

Eye sphincter and dilator muscles, smooth muscles of sweat and mammary glands

Exceptions to muscular system derivations, NOT derived from mesoderm

Skeletal muscle

muscle from somites derived from paraxial mesoderm

Smooth muscle

muscle from splanchnic mesoderm surrounding the gut

Cardiac muscle

muscle from splanchnic mesoderm surrounding heart tube

Before birth

When do most skeletal muscles develop?

Epaxial

division of myotome that is located dorsally

Hypaxial

division of myotome that is located ventrally

Posterior primary ramus

Rami that supplies epaxial division

Anterior primary rami

Rami that supplies hypaxial division

Cervical region

Hypaxial division region that gives rise to scalene, geniohyoid, infrahyoid, and prevertebral muscles

Thoracic region

Hypaxial division region that gives rise to intercostal muscles and muscles of anterior abdominal wall

Lumbar region

Hypaxial division region that gives rise to quadratus lumborum muscle

Sacral and Coccygeal Region

Hypaxial division region that gives rise to pelvic diaphragm, external anal sphincter, perineal muscles (underlying external genitalia)

External, internal, and innermost intercostal

Ventrolateral muscle layers in the thorax from hypaxial divisions

External oblique, internal oblique, transversus abdominis

3 ventrolateral muscle layers in the abdomen

Rectus abdominis and infrahyoid muscles

Formed by the ventral longitudinal column of muscle at the ventral end of the hypaxial divisions.

Mastication, facial expression, pharynx, and larynx

Myoblasts (not somites) from pharyngeal arches give rise to muscles of

2-4

Which occipital myotomes are the tongue muscles derived from?

myoblasts

What do limb muscles develop from? These surround the developing bones and originate from the somites and undergo regulated migration.

Splanchnic mesoderm surrounding the endoderm

What is smooth muscle in the gut derived from?

Somatic mesoderm adjacent to endothelium of these vessels

What are the smooth muscle in walls of blood and lymph vessels derived from?

4th week

When is the heart muscle evident by?

Purkinje fibers

Specialized bundles of cardiac muscle fibers with larger diameter than ordinary cardiac msucle fibers and have fast-conducting gap junctions. Form conduction system of the heart whcih controls its rhythmic beating.