Integumentary System Development

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Questions and Answers

What are the two main layers of skin?

Epidermis and hypodermis

Epidermis and dermis (correct)

Dermis and subcutaneous layer

Epidermis and stratum corneum

Where does the epidermis originate from?

Surface ectoderm (correct)

Neural crest cells

Mesoderm

Dermatomes of somites

What is the role of the basal layer in the epidermis?

To proliferate and form various layers (correct)

To produce melanin

To protect against water loss

To provide sensory functions

Which layer of the epidermis is involved in continuous keratinization?

Stratum corneum Signup and view all the answers

What type of cells give rise to the dermis?

Mesenchyme from dermatomes Signup and view all the answers

From which region do mammary glands develop?

Axilla to inguinal region Signup and view all the answers

What type of glands arise from hair follicles?

Sebaceous glands Signup and view all the answers

Which of the following layers is not part of the typical epidermis structure formed by the end of the 5th month?

Stratum granulatum Signup and view all the answers

What structure forms the germinal matrix responsible for hair production?

Cells of the hair bulb Signup and view all the answers

What type of hair is first produced during development and aids in holding vernix caseosa?

Lanugo Signup and view all the answers

Which cells are responsible for producing melanin, contributing to hair color?

Melanoblasts Signup and view all the answers

What is the primary function of sebum produced by sebaceous glands?

Lubrication of skin and hair Signup and view all the answers

What physiological response is caused by the contraction of arrector pili muscles?

Goose bumps Signup and view all the answers

What structure is responsible for nourishing the epidermis?

Capillary plexus Signup and view all the answers

Which layer of the dermis is primarily composed of adipose tissue?

Reticular layer Signup and view all the answers

What is the function of skin appendages?

Serve specific functions like sensation Signup and view all the answers

Which part of the nail is considered the growing area?

Germinal matrix Signup and view all the answers

What structure overlaps the base of the nail plate?

Eponychium Signup and view all the answers

At what stage does angiogenesis of the dermis complete?

First trimester Signup and view all the answers

What is the primary component of the nail plate?

Keratinized cells Signup and view all the answers

Which term refers to the area under the free edge of the nail plate?

Hyponychium Signup and view all the answers

What forms the dermal papillae?

Epidermal thickenings Signup and view all the answers

Which structure is NOT considered a skin appendage?

Dermal papillae Signup and view all the answers

What is the inheritance pattern of generalized albinism?

Autosomal recessive disorder Signup and view all the answers

What factor is NOT typically associated with the etiology of vitiligo?

Hormonal changes Signup and view all the answers

Which cell type is classified as a tissue macrophage in the skin?

Langerhans cell Signup and view all the answers

Which structure does NOT derive from the intraembryonic mesoderm?

Epidermis Signup and view all the answers

What is a primary characteristic of albinism that affects the eyes?

Reduction of melanin in the retina Signup and view all the answers

During which gestational months do Merkel cells appear?

4th–6th months Signup and view all the answers

Which of the following is NOT a proposed trigger for vitiligo?

Genetic mutations Signup and view all the answers

What is the role of embryonic melanoblasts in the skin?

Synthesize melanin Signup and view all the answers

Which layer is part of the epidermal structure that contains melanocytes?

Epidermis Signup and view all the answers

How does oxidative stress relate to melanocytes?

Causes premature aging of melanocytes Signup and view all the answers

What marks the beginning of nail development?

Formation of nail field at the tip of fingers and toes Signup and view all the answers

By what week do fingernails typically reach the fingertips?

32 weeks Signup and view all the answers

Which structure persists at the base of the nail even after eponychium degenerates?

Cuticle Signup and view all the answers

What is the term for a painful condition caused by the ingrowth of the nail plate into the nail bed?

Onychocryptosis Signup and view all the answers

Which condition is characterized by inflammation of the nail folds leading to pus formation?

Onychia Signup and view all the answers

What does the term 'koilonychia' refer to?

Spoon-shaped nails Signup and view all the answers

What initiates hair development during fetal life?

Downgrowth of the epidermis into the dermis Signup and view all the answers

Which part of the hair bud develops into the hair bulb?

Inverted cup-shaped structure Signup and view all the answers

What is formed by the modification of the underlayer of the nail fold?

Nail matrix Signup and view all the answers

After birth, how much do nails grow in a week?

0.5 mm Signup and view all the answers

What is the primary role of melanin in hair development?

To determine the color of the hair Signup and view all the answers

Which type of hair replaces lanugo during the perinatal period?

Terminal hair Signup and view all the answers

What is the function of sebaceous glands in relation to hair follicles?

To secrete oil that protects and conditions hair Signup and view all the answers

What happens to the cells in the center of the alveoli of sebaceous glands?

They degenerate to produce sebum Signup and view all the answers

Which muscle is responsible for causing goose bumps upon contraction?

Arrector pili muscle Signup and view all the answers

Which component is primarily responsible for the formation of the dermis?

Mesenchyme from dermatomes of somites Signup and view all the answers

During the early development of the epidermis, which layer is characterized by cuboidal cells?

Deep layer of the epidermis Signup and view all the answers

From where do nails develop during embryonic growth?

Ectoderm at the tip of each digit Signup and view all the answers

Which type of cells contribute to the epidermis's stratified structure by proliferating and forming various layers?

Basal layer cells Signup and view all the answers

What is the significance of the periderm layer during the fifth month of development?

It undergoes keratinization and is gradually sloughed off Signup and view all the answers

What structures are derived from the ectoderm according to the development of the skin?

Hair follicles and sebaceous glands Signup and view all the answers

Which layer of the epidermis is responsible for continuous renewal and keratinization?

Stratum basale Signup and view all the answers

Which of the following is NOT a layer of the epidermis present by the end of the fifth month?

Stratum reticulare Signup and view all the answers

What forms the protective whitish sticky substance covering the skin of a newborn infant?

Vernix caseosa Signup and view all the answers

At what week do epidermal ridges become permanent?

18th week Signup and view all the answers

Which of the following is NOT a type of dermatoglyphic pattern?

Helix Signup and view all the answers

What is the primary role of melanoblasts during skin development?

To differentiate into melanocytes Signup and view all the answers

How do mature melanocytes contribute to skin pigmentation?

By extending dendrites to target keratinocytes Signup and view all the answers

Which scientist is known as the Father of Dermatoglyphics?

Dr. Harold Cummins Signup and view all the answers

By which month do melanoblasts invade the epidermis?

Third month Signup and view all the answers

What does the epidermal ridge pattern determine?

Individual fingerprints Signup and view all the answers

What is formed from the sclerotome in somite development?

Ribs and vertebral column Signup and view all the answers

What is the role of sebaceous gland secretions in relation to vernix caseosa?

To mix with shed epidermis for skin protection Signup and view all the answers

Where does the dermis of the limbs originate from?

Lateral plate mesoderm Signup and view all the answers

What happens to the layers of epidermis by the time of birth?

They are fully formed Signup and view all the answers

What is the likely diagnosis for a patient with a history of dry skin and prominent skin lines on palms and soles?

Ichthyosis Signup and view all the answers

What structure primarily forms the dermis on the dorsal aspect of the head and trunk?

Dermatome Signup and view all the answers

Which layer is NOT a part of the somite structure?

Neurodermis Signup and view all the answers

How many pairs of somites are typically formed during development?

40-45 pairs Signup and view all the answers

What is the inheritance pattern for most cases of ichthyosis?

Autosomal recessive Signup and view all the answers

What part of the somite contributes to the formation of striated muscle?

Myotome Signup and view all the answers

Where is dermis over most of the head and anterior aspect of the neck derived from?

Neural crest Signup and view all the answers

During which developmental period do somites appear?

Fourth week Signup and view all the answers

What is the primary function of dermal papillae in the papillary layer of the dermis?

To provide nourishment to the epidermis Signup and view all the answers

Which structure is responsible for the growth of the nail?

Germinal matrix Signup and view all the answers

What structure forms the overlapping epidermis around the base of the nail?

Eponychium Signup and view all the answers

What is the role of the reticular layer in the dermis?

To provide structure and strength Signup and view all the answers

During which developmental stage does the surface elevation known as epidermal ridges form?

Second trimester Signup and view all the answers

What is primarily contained in the capillary loops within dermal papillae?

Nerve endings Signup and view all the answers

What triggers the process of angiogenesis in the dermis?

Differentiation of mesenchyme Signup and view all the answers

What structure provides a soft, proximal region of the nail plate that overlies the nail bed?

Lunula Signup and view all the answers

Which skin appendage is NOT derived from the epidermis?

Mammary glands Signup and view all the answers

What component primarily composes the nail plate?

Keratinized cells Signup and view all the answers

Study Notes

Integumentary System Development

The Integumentary system (skin) is composed of two layers:
- Epidermis: derived from surface ectoderm
- Dermis: formed by mesenchyme derived from dermatomes of somites
Epidermis:
- Initially, a single-layered structure
- During the second month, forms two layers:
  - Periderm/epitrichium: superficial layer of flat cells
  - Basal/germinative layer: deep layer of cuboidal cells
  - Later, a third intermediate layer forms from the basal layer proliferation.
  - The basal layer is known as stratum germinativum due to its continuous proliferation
- During the third to fifth month, the epidermis transforms into stratified squamous epithelium with five layers:
  - Stratum basale
  - Stratum spinosum
  - Stratum granulosum
  - Stratum lucidum
  - Stratum corneum
- Keratinisation and desquamation are continuous processes, replacing peridermal cells
- Periderm layer gradually sloughs off into the amniotic fluid.
- Melanoblasts, McSCs and melanocytes express specific genes during development
Other epidermal cells:
- Merkel cells: pressure-detecting mechanoreceptors found in palms and soles, appearing in the fourth to sixth months.
- Langerhans cells: tissue macrophages migrating into the skin from the seventh week, formed by the primitive yolk sac and fetal liver hematopoiesis.
Clinical correlations:
- Albinism: Reduced/absent pigmentation in skin, hair, and eyes caused by abnormal melanin synthesis.
  - May be autosomal recessive or autosomal dominant.
- Vitiligo: Patchy loss of epidermal melanocytes resulting in depigmentation.
  - Etiology is multifactorial, possibly involving:
    - Genetic predisposition
    - Autoimmune destruction of melanocytes
    - Oxidative stress
    - Intrinsic melanocyte defects
  - May be triggered by stress or skin injury.
Dermis (Corium):
- By the 11th week, mesenchymal cells start producing collagen and elastic fibers.
- The dermis-epidermis junction initially is straight but develops regular, spaced thickenings (projections) that penetrate the dermis during the third and fourth months.
- These projections form the dermal papillae.
- Further epidermal thickening in these areas results in surface elevations (epidermal ridges).
- The dermis differentiates into two layers:
  - Papillary layer (superficial)
    - contains loops of capillary plexus and sensory receptors
  - Reticular layer (deep)
    - Contains collagen and adipose tissue.
Blood vessels in the dermis:
- Develop initially as endothelium-lined structures from mesenchyme.
- Primordial vessels develop into capillaries (angiogenesis)
- Angiogenesis in the dermis is complete by the end of the first trimester.
Skin Appendage Development:
- Nails
  - Develop at the tip of each digit from the ectoderm.
  - This ectoderm then migrates to the dorsal aspect
  - Nail field appears at the end of the 10th week as a thickened area.
  - U-shaped epidermal nail folds appear at the base of the nail field.
  - Fingernails reach the fingertips by 32 weeks; toenails reach the toe tips by 36 weeks.
  - After birth, nails grow about 0.5 mm per week.
- Hairs
  - Develop early (7-12 weeks) from epidermal downgrowths into the dermis.
  - Cells of the stratum germinativum proliferate to form a solid epithelial cord, eventually forming the hair bud.
  - The terminal part of the hair bud becomes club-shaped and forms the hair bulb.
  - The hair bulb is invaginated by mesenchymal condensation of the dermis, forming an inverted cup-shaped structure.
  - The dermis within the cup-shaped hair bulb is called the dermal papilla.
  - Cells at the summit of the dermal papilla form the germinal matrix, producing hair.
  - Peripheral cells of the developing hair follicle form the epithelial root sheath.
  - The dermis condenses around the sheath to form the dermal root sheath.
  - The germinal matrix proliferates to form the hair root, which is pushed outside the follicle as a hair shaft.
  - Melanoblasts migrate into the hair bulbs and differentiate into melanocytes.
  - Melanin from the melanocytes is transferred to proliferating cells of the germinal matrix, determining hair color.
- Glands
  - Sebaceous glands
    - Develop as buds from the epithelial root sheath of hair follicles.
    - Grow into the dermis and divide into branches to form alveoli and ducts.
    - Cells at the center of alveoli degenerate, producing sebum.
    - Sebum is released into the hair follicle and then to the skin surface.
  - Sweat glands
    - Develop as epidermal downgrowths, later becoming canalized.
  - Mammary glands
    - Arise from the surface ectoderm along a milk line extending from the axilla to the inguinal region.

Integumentary System Development

The skin is the largest organ in the body and is comprised of two main layers: the epidermis and the dermis.
The epidermis is derived from the surface ectoderm.
The dermis is formed by mesenchyme derived from dermatomes of somites.
The skin also includes appendages: nails, hair, and glands.

Epidermis Development

The epidermis initially forms as a single-layered structure.
During the second month of development, the epidermis differentiates into:
- Periderm: a superficial layer of flat cells.
- Basal layer: a deep layer of cuboidal cells.
The basal layer proliferates to form a third intermediate layer and is responsible for the continuous formation of the epidermis.
From the 3rd to 5th month of development, the epidermis undergoes further stratification, resulting in five distinct layers:
- Stratum basale
- Stratum spinosum
- Stratum granulosum
- Stratum lucidum
- Stratum corneum
The periderm is gradually sloughed off into the amniotic fluid by the 21st week.

Vernix Caseosa

The periderm and secretions from sebaceous glands mix to form a whitish, sticky substance called vernix caseosa.
Vernix caseosa protects the fetus's skin from maceration by amniotic fluid.

Epidermal Ridges

By the 11th week of development, cells of the stratum basale proliferate and extend into the dermis forming epidermal ridges.
These epidermal ridges, which become permanent by the 18th week, create a pattern of fingerprints on the palms, soles, and fingers.
The pattern is genetically determined.
There are four basic types of dermatoglyphic patterns: arches, whorls, loops, and composites.

Melanoblasts

Melanoblasts, derived from neural crest cells, migrate from the neural tube through the dermis to the epidermis and hair follicles.
These melanoblasts differentiate into melanocyte precursors in the basal layer of the epidermis.
Within the hair follicles, melanoblasts differentiate into melanocyte stem cells (McSCs).
Melanocyte precursors and McSCs ultimately mature into melanocytes in the epidermis and hair matrix.

Somites

The paraxial mesoderm differentiates into 40-45 pairs of somites.
Somites are formed between the 20th and 30th day of intrauterine life.
Each somite is a triangular structure with a cavity.

Somite Subdivision

Somites are divided into three components:
- Sclerotome: Forms the vertebral column and ribs.
- Dermatome: Forms the dermis of the back of the head and trunk.
- Myotome: Forms the striated muscles.

Dermis

The dermis is formed by the condensation and differentiation of mesenchyme underlying the surface ectoderm.
The mesenchyme that forms the dermis originates from three sources:
- Dermatomes: Forms the dermis of the dorsal aspect of the head and trunk.
- Somatopleuric Layer of Lateral Plate Mesoderm: Forms the dermis of the limbs, and the lateral and ventral aspects of the trunk.
- Neural Crest Cells: Forms the dermis over most of the head and anterior aspect of the neck.

Dermis Development

By the 11th week, mesenchymal cells in the dermis begin producing collagen and elastic fibers.
The junction between the dermis and epidermis becomes wavy, forming dermal papillae and epidermal ridges.
The dermis differentiates into two layers:
- Papillary Layer: Superficial layer containing capillary loops and sensory receptors.
- Reticular Layer: Deeper layer containing a high amount of collagen and adipose tissue.

Nail Development

The nail is formed from keratinized cells and is comprised of several components:
- Nail Plate: The body of the nail.
- Nail Bed: Highly vascular connective tissue.
- Hyponychium: Part of the epidermis under the free edge of the nail.
- Germinal Matrix: Growing area of the nail.
- Lunula: Proximal, half-moon shaped part of the nail plate overlying the nail bed.
- Cuticle: Overlapping epidermis around the base of the nail.
- Nail Walls: Folds of skin overlapping the sides of the nail.
- Perionychium: Includes the nail wall and cuticle area.
- Eponychium: Extension of the base of the nail plate.

Hair Development

Hair follicles are formed from invaginations of the epidermis into the dermis.
Cells of the hair bulb form a germinal matrix that produces hair.
The growing hair root is pushed through the follicle to the surface of the skin.
Melanoblasts migrate into the hair bulbs and differentiate into melanocytes, giving the hair its color.

Hair Types

Lanugo: Fine, soft, lightly pigmented hairs that appear first.
Terminal Hair: Coarser hairs that replace lanugo during the perinatal period and at puberty.

Arrector Pili muscle

Smooth muscle fibers differentiate from the mesenchyme surrounding the hair follicle.
These muscles connect the dermal root sheath to the papillary layer of the dermis.
Contraction of the arrector pili muscles causes goose bumps.

Glands of the Skin

The skin contains three types of glands:
- Sebaceous Glands: Produce sebum, an oily secretion.
- Sweat Glands: Produce sweat.
- Mammary Glands: Produce milk.
These glands are derived from the epidermis and grow into the dermis.

Sebaceous Gland Development

Sebaceous glands develop as a bud from the epithelial root sheath of a hair follicle.
This bud divides into branches, forming alveoli and ducts.
Cells in the center of the alveoli degenerate, producing sebum.
Sebum is released into the hair follicle and then to the surface of the skin.

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Test your knowledge on the development of the integumentary system, including the composition and layers of the skin. This quiz will cover the roles of the epidermis and dermis during early stages of development, along with the changes that occur over time. Perfect for students studying anatomy and physiology.