Our Skin

– The skin is the outer protective covering of the body
– It has a tough structure
– It form integumentary system together with:
Its glands
Its hair
Nails
– This part of our body (the skin) is the most familiar for us
– Attentions normally given to the skin + components:
We scrub, cream, and coat it with make up
We cut, shave, and curl its hair
We manicure its nails


Learning Objectives
– List the 6 functions of the skin and explain how each is important in homeostasis
– Compare the structure and functions of the epidermis with that of the dermis
– Describe the subcutaneus layer
– Describe the functions of sweat glands and sebaceous glands
– Give the functions of hair and nails and describe the structure of hair
– Explain the function of melanin
Introduction
– The skin is the outer protective covering of the body
– It has a tough structure
– It form integumentary system together with:
Its glands
Its hair
Nails
– This part of our body (the skin) is the most familiar for us
– Attentions normally given to the skin + components:
We scrub, cream, and coat it with make up
We cut, shave, and curl its hair
We manicure its nails
The skin is important in communication.
– You may shake hands, stroke, kiss, and squeeze
Involuntary change in the skin reflect emotional state
– You may blush with embarrassment
– You may blanch with fear or rage
– You may redden with excertion
– You may sweat excessively when anxious
Skin can also be used as general health indicators
– Appearance
– Coloration
– Temperature
– Feel

The six functions of the skin

To protect the body against injury and against disease organisms
– The skin is the body’s first line of defense against harmful bacteria & other agents of disease
To receive the information about the outside world
– Within the skin there are sensory receptors
– These receptors detect touch, pressure, heat, cold, and pain
To prevent drying out
– The skin prevent loss of body fluid so that the cells do not dry out
To help maintain body temperature
– Involves the role of capillary network and sweat glands in the skin
– Sweating is a mechanism to maintain the body temperature (regulating the body’s temperature system)
The skin has sweat gland
– Function in excreting waste and excessive water from the body
The skin contains important compound for Vit D
– It is converted into vit D if exposed to the UV rays of the sun

The anatomy of the skin

The skin consists of two main layers:
– The outer epidermis
– The inner dermis
Beneath the skin is an underlaying subcutaneous layer

(gambar)


The epidermis

The thickness of the epidermis over the body is about a piece of paper
However, it consists of several sublayers
It consists of stratified epithelial tissue
The outer cells are continuously wear off
They are immediately replaced by new cells
New epidermal cells are constantly produced in the deepest sublayer of the epidermis
Each cell is mostly filled with a tough waterproofing protein called keratin
The cells at the surface of the skin resemble dead scales
They are closely packed together and serve as a waterproof protective covering for the body

The dermis

This is a thick layer of skin beneath the epidermis (Fig. 3.1)
It consists of dense connective tissue (mainly composed of collagen fiber)
The functions of collagen fiber:
– Responsible for mechanical strength of the skin
– Resposible for skin plasticity
Components found in the dermis:
– Blood vessels
– Nerve system
– Follicles
– Glands
The upper portion of the dermis, has many small finger-like elevations
These project into the epidermal tissue
In these elevations, extensive network of capillaries functions:
– To deliver O2 and nutrients to the cells of epidermis
– In regulating temperature


The subcutaneous layer

The subcutaneous layer beneath the dermis is also called superfisial fascia
This layer consists of:
– Loose conective tissue
– A lot of adipose (fat) tissue
Help protect underlaying organs from mechanical shock
Insulate body (conserve heat)
As food source
Responsible for characteristic male and female body shape
This layer attach the skin to the muscle and other tissues beneath

Sweat glands and sebaceous glands


Sweat glands
– Each gland is a tiny coiled tube in the dermis or subcutaneous
– It has a duct that extend up through the skin and opens onto the surface (Fig 3.1)
– In all area of the skin, there are 3 millions of them
– These glands help to maintain the body temperature
An increase in body temperature is caused by muscle contraction and metabolic activity
Heat is needed for evaporation
The body become cooler as the sweat evaporates from the body
– Sweat glands excrete water, salts, and small amount of nitrogen wastes
– Certain sweat glands are sometimes associated with hair
– These are concentrated in a few specific areas of the body, such as:
Armpits
Genital area
– These glands discharge into the folicle
– Their secretion is thick, sticky, and mainly odorless
– However, some bacteria that inhabit the skin surface are able to decompose this secretion
– This bacterial activity cause the secretes become odorous
– That’s why we need deodorant and antiperspirant to replace the odor and reduce moisture
– Emotional stress or sexual stimulation promote secretion of these glands
Sebaceous glands:
– Also known as oil glands
– Generally attach to hair follicles
– They are connected to each hair follicle by little ducts (the site through which the glands release their secretes or an oily substance called sebum)
– They are found numeously on the face and sculps
– The functions of this sebum:
Lubricate the surface of the skin
Oils the hairs
Prevent water loss
Inhibit bacterial growth
As antifungal
– During childhood, the glands are relatively inactive
– At puberty, they are activated by increased secretion of male hormone (both in male and females)
– The hormon activity can lead to acne
– This condition is very common during adolescence

– In some cases:
The sebum accumulates in the duct of the subaceous glands and hair folicle and block it, forming a blackhead (comedo)
In a blackhead, sebum and dead cells contaning the dark pigmen melanin block the duct
The Melanin cause black color of the skin
Sometimes the ducts of the sebaceous gland ruptures
This allowing the sebum spill into the dermis
This cause the skin to become inflamed and a pimple may form

Hair and nails

Hair is found on all skin surfaces, except the palm and soles
It serves a protective function
The components of hair:
– The shaft: the hair that we see
– The root: the portion below the skin surface
Hair follicle (fig. 3.2): the root + epithelial and connective tissue
– Get supply of nutrients from connective tissue that contains capillaries
Hair:
– Each hair consists of cells
– The cells multiply, manufacture keratin as they move outward, and die
The shaft:
– Consists of dead cells and their products
– We can cut it without any sensation of pain
The hair follicle
– Control the growth of hair
– As long as it remains intact, new hair will continue to grow
– The follicle is associated with tiny bundles of smooth muscle
– It contract in response to cold or fear hair stand up
Nails:
– Help protect the end of the fingers and toes
– They develop from horny epidermal cells
– Consists mainly of a closely compressed, tough keratin
– The actively growing area is the white crescent (lanula) at the base of the nails
– Beneath the nails, capillaries are found (make the to look pink)


Melanin

At the lowest layer of the epidermis, there are cells that produce pigment granules distributed scatteredly
These pigment granules are composed of a type of protein called melanin
The melanin gives color to hair and skin
Skin color is inherited
A person with dark skin, the pigment cells are more active and produce more melanin
Melanin is an important protective screen against the sun as it absorb UV
When the melanin is not able to absorb all the UV rays, the skin become inflame or sunburned
Excessive exposure to the sun rays can cause:
Skin cancer
Wrinkles
Dark-skinned people have more melanin
They are more resistance to sun rays that can cause wrinkles, sunburn, or even cancer
Other type of skin pigment:
Carotene (yellowish pigment found in asian people)