Hair Follicle Anatomy

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Questions and Answers

What is the primary role of the dermal papilla in hair follicles?

To control the hair growth cycle (correct)

To facilitate the movement of companion cells

To determine the color of the hair

To provide nutrients directly to the hair shaft

What occurs if the dermal papilla is removed from the hair follicle?

Hair growth is immediately halted without any chance of regeneration

New papillae will not form and hair will become permanently absent

Hair growth will continue unaffected

They can regenerate leading to normal hair length over time (correct)

How does the dermal papilla interact with the developing hair follicle?

By surrounding the hair bulb entirely

By providing keratin to the hair shaft

By specifying follicle location, timing, and type (correct)

By influencing wound healing processes

What is the consequence of only destroying the papillae during electrolysis?

Regenerated papillae will lead to shorter hair Signup and view all the answers

What type of tissue is the dermal papilla derived from?

Fibroblasts Signup and view all the answers

What separates the dermal papilla from the germinative cells of the hair bulb?

Basement membrane Signup and view all the answers

What happens to hair growth if the dermal papilla, hair bulb, and lower one-third of the follicle are removed?

Shorter hairs will gradually grow due to new papillae formation Signup and view all the answers

Where do the stem cells that give rise to the germinative cells of the follicle reside?

Middle third of the follicle Signup and view all the answers

What distinguishes the inner root sheath (IRS) from the medulla in hair follicles?

The fusion of trichohyalin granules in the medulla Signup and view all the answers

Where are epidermal keratins predominantly found in hair follicles?

In the outer root sheath Signup and view all the answers

Which layer of the outer root sheath (ORS) is known as the companion cell layer?

The inner layer adjacent to the Henle layer Signup and view all the answers

What is the primary role of desmosomes in the outer root sheath (ORS)?

To attach ORS cells to each other and to the IRS Signup and view all the answers

What is indicated by the presence of keratin-like filaments in ORS cells?

They accumulate in the bulb near the dermal papilla Signup and view all the answers

Which cells are identified as the first to accumulate keratin-like filaments in the ORS?

Companion layer cells Signup and view all the answers

How does the number of layers in the outer root sheath change as it ascends the follicle?

It starts with one layer and increases to multiple layers Signup and view all the answers

What is the orientation of the filaments in the elongating ORS cells?

Circumferential orientation Signup and view all the answers

What is the primary characteristic that differentiates Type I and Type II IF proteins?

Acidity level Signup and view all the answers

How many keratin protein chains are estimated to be present in the cross-sectional area of the keratin intermediate filament?

32 Signup and view all the answers

What is one of the main components that provides tensile strength and toughness to hair?

Covalent disulphide cross-links Signup and view all the answers

Which of the following statements regarding the amino acid sequence of human Type I IF protein is correct?

It has been identified but not fully sequenced. Signup and view all the answers

What is characteristic of the matrix proteins found in human hair compared to wool?

They do not have HT proteins. Signup and view all the answers

What happens to hair when it is wet and heated?

Chemical bonds such as ionic and hydrogen bonds are disrupted. Signup and view all the answers

What is the molecular weight range of intermediate filament proteins as determined by SDS gel electrophoresis?

$50,500–76,000$ Signup and view all the answers

What percentage of half-cystine residues do IF proteins contain as a group?

Approximately 8 mole percent Signup and view all the answers

What is the region of the follicle below the bulge called?

Transient zone Signup and view all the answers

Which part of the follicle is referred to as the permanent zone?

Isthmus and infundibulum Signup and view all the answers

What characterizes the cells in the active cell division region of the lower bulb?

High nuclear to cytoplasmic ratio Signup and view all the answers

Which zone is involved in the keratin gene expression?

Upper bulb zone Signup and view all the answers

What is the function of the germinative cells in the lower bulb?

Cell division for hair growth Signup and view all the answers

What structure does the critical level refer to?

The level of the widest part of the dermal papilla Signup and view all the answers

The section of the follicle between the bulge and the sebaceous gland duct is called what?

Isthmus Signup and view all the answers

What occurs during the keratogenous zone?

Hardening of the fibre Signup and view all the answers

What does the old nomenclature for keratin proteins primarily categorize based on?

Presence of sulphur and glycine/tyrosine content Signup and view all the answers

What issue arose when epidermal keratin intermediate filaments (IFs) were sequenced?

The existing nomenclature failed to accommodate all identified proteins Signup and view all the answers

How are the Type II keratins classified within the proposed nomenclature system?

K1-K8 Signup and view all the answers

In the proposed system, how is the keratin IF gene symbol represented?

KRT Signup and view all the answers

What denotes the type of keratin IF in the symbol Km.nxpL?

The letter 'm' Signup and view all the answers

What proposal was made to address the nomenclature confusion?

Revise the nomenclature to include all keratin IFs Signup and view all the answers

What is indicated by the term KAPm.nxpL in the proposed nomenclature?

Keratin-associated proteins Signup and view all the answers

What is a limitation of the old nomenclature for keratin proteins?

It does not include low-sulphur keratins Signup and view all the answers

Study Notes

Follicle Structure and Zones

The region below the bulge of a hair follicle is termed the lower follicle or transient zone, regressing during the catagen phase.
The isthmus is the section between the bulge and sebaceous gland duct; the infundibulum extends from the isthmus to the epidermis.
The isthmus and infundibulum together form the permanent zone of the follicle, which remains intact through all hair cycle stages.
Follicles functionally divide into four zones based on cellular and biochemical activities:
- Cell proliferation and differentiation zone at the bulb's base
- Keratin gene expression zone in the upper bulb
- Keratogenous zone where fiber hardening occurs
- Zone of inner root sheath (IRS) degradation

Hair Bulb and Germinative Cells

The lower bulb is the active division area, particularly below the critical level and at the dermal papilla's apex.
Epithelial cells in this region are characterized by a high nuclear-to-cytoplasmic ratio and are termed germinative cells.
Germinative cells organize into layers, giving rise to the follicle and hair fiber; they differ from matrix cells to avoid confusion with keratin-associated proteins during keratinization.
Intermediate filaments in IRS cells likely contain keratin proteins, although definitive identification remains incomplete.

Outer Root Sheath (ORS)

The ORS, the outermost follicle layer, has its own autonomous cell population.
It consists of a single layer at the bulb base, increasing to multiple layers higher in the follicle, augmented by desmosomal connections.
Epidermal keratins, not hair-specific intermediate filaments, populate the ORS, with stem cells giving rise to germinative cells residing in the bulge just below the sebaceous gland.
The companion cell layer within the ORS assists in the movement of IRS and ORS during hair growth.

Dermal Papilla

Located at the base of the follicle, the dermal papilla is derived from dermal fibroblasts and plays a critical role in hair growth and cycle regulation.
It interacts with ectoderm during follicle development, specifying follicle properties.
Although surrounded by germinative cells, it is separated by a basement membrane and is essential for sustaining hair growth.
Removal of the papilla halts hair growth, but it can regenerate, leading to the potential for continued hair production despite disturbances.

Keratin and Hair Structure

Hair keratin intermediate filament (IF) proteins consist of types I and II, with distinct molecular weights and half-cystine residue content.
Keratin IFs integrate into microfibrils, forming coiled-coils with cross-sectional areas estimated to contain 32 protein chains.
The tensile strength of hair stems from the cross-linking of IF and keratin-associated proteins through covalent and non-covalent bonds.
Hair's structural integrity allows it to withstand significant force, although it can stretch when wet due to bond disruption.
Updates in keratin protein nomenclature are necessary to rectify historical classification issues and accommodate new discoveries.

Nomenclature of Keratin Proteins

A unified nomenclature for keratin proteins classifies Type I and Type II IF keratins under separate systems, which lack straightforward extensions.
A proposed revised system would classify keratin-associated proteins and hair keratins uniformly, resolving existing confusion in nomenclature.

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Description

This quiz focuses on the structural components of hair follicles, highlighting regions such as the lower follicle, isthmus, and infundibulum. Understand how these areas relate to the hair growth cycle, including the catagen phase. Test your knowledge of hair follicle anatomy and their functions.