Unit II Flashcards
Integumentary System
- Skin
- Hair
- Nails
- Mammary Glands
The 2 layers of skin are:
- Epidermis
2. Dermis
Epidermis is derived from
ectoderm
Dermis is derived from
Mesoderm
How does embryonic skin begin?
A single layer of surface ectoderm cells
What 2 layers does surface ectoderm create?
Periderm and the basal layer
Periderm:
Keratinized Layer
Basal layer
produces new cells
Vernix Caseosa
Whitish, greasy substance formed by secretions of sebaceous glands and exfoliated cells (periderm). It covers the skin of the fetus
Vernix Caseosa Functions
- Protects fetal skin from amniotic fluid (urea and uric acid are in the fluid)
- Lubricates the fetus to facilitate parturition
What replaces the periderm?
The stratum corneum
Sweat glands
down-growths of the epidermis into the dermis
Epidermal ridges
finger prints (dermatoglyphics)
Fingerprints of children with chromosomal abnormalities
Have a pattern
Melanocytes
Derived from neural crest cells and produce skin pigmentation
Albinism
An autosomal recessive genetic trait where a person lacks pigmentation in the skin, hair, and retina. They have the normal number of melanocytes but lack the enzyme tyrosinase (produces melanin)
Problems associated with skin cancer and the retina
Pigmentation is necessary to protect the skin and eyes from UV Radiation
Dermal Papillae
project up into the epidermis. Contain blood vessels and nerves
Hair buds
down-growths of the epidermis into the dermis
Dermal root sheath
mesenchyme surrounding the hair bulb
Arrector muscles of hairs
elevate the hair shafts and are responsible for “goosebumps”
Sebaceous gland
a small bud grows from the wall of the developing hair follicle
Lanugo
The first hairs to develop. Help hold the vernix cases in place
Fingernails reach the tips of the digits by week:
32
Toenails reach the tips of the digits by week:
36
Mammary crest (ridge)
A band-like thickening of the epidermis where mammary glands develop
Mammary buds
down-growths of the epidermis into the underlying mesenchyme which develops into lactiferous ducts
Polythelia
An extra nipple. More common in females. Always occurs along the mammary crest
Polymastia
An extra breast. Usually develops inferior to the normal breast but can occur anywhere along the mammary crest
Inverted Nipple
Can cause problems with baby’s latching.
- The nipple is everted and then inverts in adult hood is a sign of breast cancer
- A nipple that is always inverted is not a sign of breast cancer
Somites differentiate into:
- Sclerotome
2. Dermomyotome
Sclerotome
Gives rise to the vertebrae and ribs and is located ventromedially
Dermomyotome:
Gives rise to muscle and dermis of the trunk. Located dorsolaterally
Mesenchyme
Connective tissue made up of loosely woven sclerotomes
Mesenchyme differentiates into:
- Fibroblasts
- Chondroblasts
- Osteoblasts
Intramembranous Ossification
Bone develops from mesenchyme directly within membranous sheaths
Ex: Flat bones of the skull
Endochondral Ossification
Mesenchyme differentiates first into hyaline cartilage models and then ossifies
Ex: Limb and most other bones
Neurocranium
encloses the brain
Viscerocranium
forms the face
Neurocranium subdivides into:
- Membranous Neurocranium
2. Cartilaginous Neurocranium
Membranous Neurocranium
forms the skull vault
Cartilaginous Neurocranium:
forms the base of the skull
Membranous neurocranium ossification
intramembranous
What seperates flat bones at birth?
Fibrous tissue joints called sutures
Fontanelles
sheet-like fibrous areas where more than 2 bones meet
How many fontanelles are there?
6
Name the 6 fontanelles
- Anterior fontanelle
- Posterior Fontanelle
- Anterolateral fontanelle (paired)
- Posterolateral Fontanelles (paired)
Anterior Fontanelle
Largest, closes about 1.5 years after birth
Posterior Fontanelle
closes about 3 months after birth
Cartilaginous Neurocranium ossification
endochondral
Craniosynthosis
Prenantal fusion of cranial sutures
Scaphocephaly
premature fusion of the sagittal suture. Skull becomes long, narrow and wedge shaped (MOST COMMON)
Brachycephaly
premature fusion of the coronal suture. Produces high, tower-like skull
Acrania
Complete or partial absence of the neurocranium. Associated with major defects of the vertebral column and partial absence of the brain. Usually incompatible with life
Viscerocranium
bones of the face formed from neural crest cells of the first 2 pharyngeal arches
Sclerotomes differentiate into:
- Cranial part: loosely packed cells
2. Caudal part: densely packed cells
Anulus Fibrosus
formed of the uppermost cells of the caudal part
