Revision as of 17:30, 28 September 2009

Integumentary System

Introduction

The skin provides a barrier between ourselves and our environment, it also contains specializations in different regions including hair, nails, glands and sensory receptors.

The two major tissue organizations of epithelial (ectoderm, epidermis) and mesenchyme (mesoderm connective tissue, dermis and hypodermis) are shown within skin. In addition, we have aslo extensive populating by melanocytes (neural crest) and sensory nerve endings.

It remains today as possibly the first epithelial specialization from which arose other epithelial specializations now located inside the body. The external skin specializations have many different roles and functions. This system is also an excellent model for distribution or "pattern" that is of interest.

Textbooks

Human Embryology Larson Chapter 14 p443-455
The Developing Human: Clinically Oriented Embryology (6th ed.) Moore and Persaud Chapter 20: P513-529

Objectives

Understand the embryonic origin and differentiation of the epidermis and dermis.
Understand the formation of hair and nails.
Understand the formation of sweat glands, mammary glands.
Understand the formation of teeth.
Brief understanding of associated abnormalities.

Skin Origins

Ectoderm forms the surface epidermis and the associated glands.
Mesoderm forms the underlying connective tissue of dermis and hypodermis.
Neural crest cells also migrate into the forming epidermis and the skin is also populated by specialized sensory endings.

Development Overview

Ectoderm and Mesoderm Origin

4 weeks

simple ectoderm epithelium over mesenchyme.

1-3 months

ectoderm- germinative (basal) cell repeated division of generates stratified epithelium.
mesoderm- differentiates into connective tissue and blood vessels.

4 months

basal cell- proliferation generates folds in basement membrane.
neural crest cells- (melanocytes) migrate into epithelium. These are the pigment cell of the skin.
embryonic connective tissue- differentiates into dermis, a loose ct layer over a dense ct layer. Beneath the dense ct layer is another loose ct layer that will form the subcutaneous layer.
Ectoderm contributes to nails, hair follictles and glands.
Nails form as thickening of ectoderm epidermis at the tips of fingers and toes. These form germinative cells of nail field.
Cords of these cells extend into mesoderm forming epithelial columns. These form hair follocles, sebaceous and sweat glands.

5 months

Hair growth initiated at base of cord, lateral outgrowths form associated sebaceous glands.
Other cords elongate and coil to form sweat glands.
Cords in mammary region branch as they elongate to form mammary glands. These glands will complete development in females at puberty. Functional maturity only occurs in late pregnancy.

Glands

Hair

Before birth we have embryonic hair that has an imporant role in binding the skins waxy protective coating against our watery environment.
After birth we have early postnatal hair that is gradually replaced by the mature form.
At puberty we have a second round of hair formation under endocrine regulation by sex hormones.

Fetal Hair

Month 5 - hair appears on the head and beginning of vernix caseosa deposition.
Month 6 - body is covered by fine hairs (lanugo) and the deposit of vernix caseosa is considerable. Skin papilla are developed and the free border of the nail projects from the corium of the dermis.
Month 8 - skin now completely coated with vernix caseosa, and the lanugo begins to disappear. Skin is also pink in colour and subcutaneous fat being deposited (hypodermis layer).
Month 9 - lanugo has largely disappeared from the trunk.

Teeth

Images

Hair histology
Dermatomes
Neonate hair

Glossary Links

Glossary: A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Numbers | Symbols | Term Link

Course Content 2009

Cite this page: Hill, M.A. (2026, October 28) Embryology 2009 Lecture 18. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/2009_Lecture_18

What Links Here?

@@ Line 11: / Line 11: @@
 * '''Human Embryology''' Larson Chapter 14 p443-455
 * '''The Developing Human: Clinically Oriented Embryology''' (6th ed.) Moore and Persaud Chapter 20: P513-529
-* Before We Are Born (5th ed.) Moore and Persaud Chapter 21: P481-496
-* Essentials of Human Embryology Larson Chapter 14: P303-315
-* Color Atlas of Clinical Embryology Moore Persaud and Shiota Chapter 15: p231-236
-* [http://www.nature.com/milestones/skinbio/index.html Nature - Milestones in Cutaneous Biology] "highlights groundbreaking advances in cutaneous biology over the past 100 years."
-* [http://www.ijdb.ehu.es/04023contents.htm International Journal Developmental Biology 2004 - Skin Development special issue]
 == Objectives ==

2009 Lecture 18: Difference between revisions