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Renin Angiotensin Mechanism.

Accessory structures of the skin

 Integumentary System: Accessory structures of the skin.

Introduction:

  • Integument means “Covering”, this system is made of structures which provide covering to the body.

  • Skin along with subcutaneous tissue and accessory structures like hair, sweat glands etc. forms integument of the human body.

  • Skin shows presence of various accessory structures like,

    • Hair,

    • Sebaceous Glands,

    • Sudoriferous Glands (Sweat Glands).

    • Ceruminous glands.

Hair:

  • The hairs are formed by downgrowth of epidermal cells in the dermis or subcutaneous tissue.

  • Hair has three layers,

    • Cuticle.

    • Dermis,

    • Medula.

  • The base of the hair follicle is a cluster of cells called “Papila of Bulb”.

  • The visible part of hair that comes out of the skin is called as “Shaft” while the part not visible to the eye and is present in the dermis is called the root of hair.

  • The cells of the bulb as it grows are pushed forward, as they go away from the site of nourishment they become dead and keratinized.

  • The melanocytes present in hair bulbs pushes “melanin” the coloring pigment in the hair cells, the inability of these cells to produce melanin replaces the coloring pigment with air bubbles resulting in white hair.

  • The reduced growth rate, reduced blood supply or destruction of hair bubble cells by immune response causes loss of hairs producing baldness condition is called Alopecia.

  • Characteristics of the hair are controlled by genetics and hormonal effects.

Sebaceous Glands:

  • These consist of secretory epithelial cells derived from the same tissue as the hair follicles. 

  • They secrete an oily substance, sebum, hair follicle only.

  • Present on all body parts except the palms and soles.

  • Sebaceous glands present on  glans penis, labia minora, lips open directly on skin.

  • Sebum keeps the hair soft, flexible and gives it a shiny appearance.

  • On the skin it provides waterproofing and acts as a bactericidal and fungicidal agent, preventing infection. 

  • It also prevents drying and cracking of skin, especially on exposure to heat and sunshine. 

  • The activity of these glands increases at puberty and is less at the extremes of age, rendering the skin of infants and older prone to the effects of excessive moisture.

Sudoriferous Glands (Sweat Glands):

  • Widely distributed throughout the skin and are most numerous in the palms of the hands, soles of the feet, axillae and groins.

  • They are formed from epithelial cells.

  • The two main types are as following;

    • Apocrine Sweat Glands.

    • Eccrine Sweat Glands.

  1. Eccrine Sweat Glands:

  • They are numerous in number, and are present on the skin of almost all organs of the body except skin of glans penis, clitoris, margins of the lips.

  • They are numerous on the forehead, palms and soles.

  • They pour their secretion i.e. sweat directly onto the skin surface through minute openings.

  • The sweat produced by eccrine sweat glands is a thin clear liquid containing water , salts, glucose, urea, uric acid etc.

  • The main function is thermoregulation.

  • They get activated soon after the birth of the individual.

2. Apocrine Sweat Glands:

  • They are concentrated in the axial, areola and groin area.

  • They pour their secretion in the hair follicle.

  • The sweat produced by apocrine sweat glands is thick liquid containing the ingredients like eccrine sweat but additionally contains Lipids and Proteins.

  • When released the Proteins and lipids the sweat gets decomposed by bacterial action producing a typical body odor.

  • They get activated at puberty.

  • They are not involved in thermoregulation rather they get activated at emotional stress and sexual excitement.

Nails:

  • Nails are plates of tightly packed, hard, dead keratinized epidermal cells.

  • They are similar to horns, hoofs and scales in the animals.

  • Each nail consists of a nail body, a free edge, and a nail root.

  • Nails have a variety of functions:

    • Protection.

    • Support.

    • Grip to hold small objects.

    • Scratching and grooming.

 Ceruminous Glands:

  • Modified sweat glands in the external ear, called ceruminous, produce a yellowish waxy lubricating secretion called “Cerumen”.

  • Cerumen provides a sticky barrier that prevents the entrance of foreign bodies, such as insects. 

  • Cerumen also waterproofs the canal and keeps bacteria and fungi from entering cells.

Commonly Asked Questions.

  1. Name different accessory organs of the human integumentary system.

  2. Write a short note on,

    1. Hair.

    2. Sweat Glands.

    3. Nails.

    4. Ceruminous glands.
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