Hair Flashcards
Three types of hairs in animals:
- Vibrissa- tactile and sensitive whisker of many animals; largest and longest hair on the body. Ex: cat’s whisker
- Bristle - guard hair that provides animals with a protective coat; guard hairs can be readily identified and usually are distinctive in appearance.
- Wool- wool or fur hair provides insulation from wet and cold. These relatively short fine hairs cover the bodies of all mammals.
Four types of hairs on the human body:
- Primordial
- Lanugo
- Vellum
- Terminal
Primordial hairs:
Appear as early as the beginning of the 3rd month of gestation. The hair grows on the upper lip, eyebrows, palms and soles of the fetus. Gradually, these coarse whisker-like primordial disappear and the softer lanugo hairs develop over the entire body.
Lanugo hairs:
Found in fetal life, shed after 6th month of gestation. They are fine, soft, unmedullated and normally unpigmented hairs. The surface of lanugo hair is smooth and scales are indiscriminate. Lanugo hair is shed and replaced by vellum and terminal hairs. Lanugo hairs are observed on aborted fetus and can be useful in the investigation of infanticide.
Vellus hairs:
Spread uniformly over entire body. They are soft, fine, unmedullated and rarely exceed 2cm in length. Vellus hair cover the entire body except the soles of feet, palms of the hands, lips and nipples. The coarser terminal hair replace vellus at specific sites and specific epoch of life.
Terminal hair:
Found on the scalp, eyebrows and eyelashes (asexual hair). Puberty is accompanied by pubic and axillary hair growth. Growth on the face, chest, back, arms and legs is sex limited. Forensic hair examiner deals almost exclusively with terminal hair, most commonly encountering head and pubic hair.
Hair is:
An appendage of the skin that grows out of an organ known as the hair follicle.
The hair root:
That portion of hair that lies in the follicle, whereas the portion above the skin surface is called the shaft.
The base of the hair root is called:
The bulb
The bulb is surrounded by a mass of loose connective tissue called:
Dermal papilla
Hair is composed of a group of proteins called:
Keratins
__________protein chains are very complexed histologically and chemically owing to the multiplicity of protein molecules cross-linked to produce an integral structure.
Keratin
Microscopic examination of hair cross section reveals an outer layer of ________that surrounds the shaft, an inner darker portion called the_______, and in the center of the _______, a canal like structure called the __________.
Cuticular scales
Cortex
Cortex
Medulla
____________arranged on the hair somewhat like shingles on a roof, act as a protective layer.
Cuticular scales
The color of hair is due to ___________that are found principally in the cortex and presence of air bubbles in the medulla.
Pigment granules (melanin)
A ordinary _______is an excellent model of the various structural components of hair.
Pencil
The human hair_____is a thin translucent layer surrounding the hair shaft. The layer consist of overlapping, non-nucleated, pigment free cells that form scales. As many as six layers of scales have been revealed by scanning electron microscopy. The free ends of the scales point away from the root toward the distal end of the hair shaft.
Cuticle
_______is the middle layer of hair, which forms the innermost layer.
Cortex
The hair_____is the visible part of hair that protrudes through the skin.
Shaft
Hair consist of three layers:
Cuticle, Cortex and Medulla.
The hair_________is below the surface of the skin and interacts with associated structures within the dermis and hypodermis.
Root
_________is the innermost layer and present in large thick hairs.
Medulla
The middle layer of hair:
Cortex
The outer layer of hair:
Cuticle
Three phases of hair growth:
Anagen
Catagen
Telogen
The growth phase of hair in which it grows at 1cm per month. It begins with the papilla and can last 2 to 6 years. There are about 85% to 90% of hairs on the head in this phase at any given time.
Anagen
The_____known as the transitional phase, allows the follicles to renew itself. This phase lasts about two weeks. No hair growth in this phase.The hair follicles shrink due to disintegration and the papilla detaches and rests, cutting the hair strand off from its nourishing blood supply.
Catagen
The resting or shedding phase; the follicle remains dormant for 1 to four months. 10% to 15% of hair on the head are in this phase at any given time.
Telogen
