-
with a transparent, gelatinous
substance-the vitreous body (vitreous humor). This substance,
unlike aqueous humor, cannot be replaced
THE
NOSE:
·
The nasal
cavity is the main route of air entry and consists of a large irregular cavity
divided into two equal passages by a septum
·
The
posterior bony part of the septum is
limited by perpendicular plate of the ethmoid bone and the vomer
·
Anteriorly
it consists of hyaline cartlage.
·
The roof is
formed by cribriform plate of the
ethmoid bone.
·
The floor is
formed by the roof of the mouth and
consist of the hard palate in front and the soft palate behind.
·
The openings
to the nasal cavity includes the anterior and posterior nares.
·
The anterior
nares or nostrils are the openings from the exterior into the nasal cavity ,
nasal hair are found here coated in a sticky mucous
·
The
posterior nares are the openings from the nasal cavity into the pharynx
·
Paranasal
sinuses are cavities in the bones of the face and the cranium containing air
THE SKIN:
The skin and its accessory structures(hairs , nails and gland) are
organized as follows:-
·
The skin and
its accessory structures make the so called integumentary
System.
·
Integumentary means covering, it covers
the outside of the body
·
The integumentary system consists of the
skin and the accessory structures such as hair, nails and glands.
·
The skin rest on the hypodermis.
·
Hypodermis is located between the dermis and underlying deep fascia
·
Hypodermis is not a part of skin. It is
also known as subcutaneous tissue. This consists of loose connective tissue
with collagen and elastin fibres. The main cells in the hypodermis are the
fibroblasts, adipose cells and macrophages. Approximately half of the body
stored adipose tissue is in the hypodermis. Although the amount and location
vary with age, sex and diet.
·
The skin is made up of the two major
tissue layers,
o
Dermis
o
Epidermis
·
The dermis is divided into two layers
o
The
deeper reticular layer, is dense irregular connective tissue, is the main layer
of the dermis consisting of layers of interlacing collagen fibers. This layer
is of elastic and collagens are oriented more in some areas than others
creating tension lines (cleavage lines) and wrinkle lines in the skin.
o
The
more superficial papillary is called from projections called papillae that
extend toward the epidermis. It is less dense than reticular and sometimes
called loose connective tissue, it also contain large number of blood vessels
o
These
fibers provide skin tone and account for the strength and toughness of the
skin. The pattern of collagen fibers in a particular region determines the
characteristic
o
The
deep layer of the dermis contains hair follicles, with their associated smooth
arrector muscles and sebaceous glands.
o
Contraction
of the arrector muscles erects the hairs (causing goose bumps), thereby
compressing the sebaceous glands and helping them secrete their oily product
onto the skin.
o
The
dermis composed of , nerve endings, hair follicles, smooth muscles, glands, and
lymphatic vessels
- The nerve ending are varied in structure and function,
§ Free nerve endings are for pain,
itch, tickle and temperature sensation
§ Hair follicle receptors are for
light touch
§ Pacinian corpuscles are for
deep pressure
§ Meissner’s corpuscles for the
ability to detect simultaneous stimulation at two points on the skin
§ Ruffini’s end organs for touch or pressure
o
Skin
ligaments, consisting of numerous small fibrous bands, extend through the
subcutaneous tissue and attach the deep surface of the dermis to the underlying
deep fascia. The length and density of these ligaments determine the mobility
of the skin over deep structures.
·
Epidermis: The epidermis is a keratinized
stratified (layered) epithelium with a tough outer surface composed of keratin
(a fibrous protein).
o
The
epidermis is made up of several layers (strata of cells) which extends from the
deepest germinative layer to the surface stratum corneum namely
-
Basal layer (stratum basale)
-
Spinous or prickle cell layer (stratum
spinosum)
-
Granular layer (stratum granulosum),
-
Clear layer (stratum lucidum)
-
And cornified layer (stratum corneum)
o
The
outer layer of the epidermis is continuously or rubbed away with replacement of
new cells from the basal layer.
o
The
cells of epidermis include,
-
Most
of the cells are called keratinocytes because they produce protein called
keratin.
-
Melanocytes
which contribute to skin colour,
-
Langerhans’
cells which are part of immune system,
-
Merkel’s
which are specialized epidermal cells associated with nerve endings responsible
for detecting light touch and superficial pressure,
o
This
process renews the epidermis of the entire body every 25 to 45 days. The
epidermis is avascular (no blood vessels or lymphatics) and is nourished by the
vessels in the underlying dermis.
o
The
skin is supplied by afferent nerve endings that are sensitive to touch,
irritation (pain), and temperature.
o
Most
nerve terminals are in the dermis, but a few penetrate the epidermis.
The hair
·
A hair is divided into
o
Shaft , protrude above the surface of
the skin and
o
Root, the root is located below the
surface. The root is expanded to form the hair bulb. Most of the root and the
shaft of the hair are composed of columns of dead keratinized epithelial cells
arranged in three concentric layers
§ Medulla
– is the central axis of the hair consists of the two or three layers of the
cells containing soft keratin,
§ The
cortex – forms the bulk of the hair consisting of the cells containing hard
keratin,
§ The
cuticle is a single layer of cells that forms hair suface,
·
The hair follicle consists of a,
o
Dermal root sheath , is the portion of
the dermis that surrounds the epithelial root sheath
o
Epithelial root sheath , is divided into
external and internal part
o
The hair bulb is an expanded knob at the
base of the hair root. Inside the hair bulb is a mass of undifferentiated
epithelial cells, the matrix, which produced the hair and the internal
epithelial root sheath.
The Glands and a
Nail
·
The major glands of the skin are,
o
Sebaceous gland
o
Sweat glands
·
Sebaceous glands are located in the
dermis, are simple or compound alveolar glands that produce sebum, an oily,
white substance rich in lipids.
·
Sweat glands are of two types
o
Merocrine gland
o
Apocrine gland
o
Merocrine sweat glands are the most common type of sweat gland.
They are simple coiled tubular glands that open directly onto the surface of
the skin through sweat pores. When the body temperature starts to rise above
normal levels, the sweat glands produce sweat, which evaporates and cool the
body.
o
Merocrine gland are more numerous in the
palms of the hands and soles of the feet, but absent from the margin of the
lips, labia minora, and tips of the penis and clitoris
·
Apocrine sweat glands are compound
coiled tubular glands that usually open into hair follicles superficial to the
opening into hair follicles superficial to the opening of the sebaceous glands.
o
They are found in the axillae and
genitalia (scrotum and labia majora) and around the anus and do not help to
regulate temperature. They become active at puberty as a result of the
influence of sex hormones.
o
Their secretion contain organic
substance the 3-methyl-2-hexenoic acid, that are essentially odourless when
first released but quickly metabolized
by bacteria to cause what is known body odour.
·
Other glands include
- Ceruminous glands are modified merocrine glands located in the ear canal (external auditory meatus) produce cerumen (earwax)
- Mammary glands these are modified apocrine sweat glands located in the breast. They produce milk. This has been discussed in detail in the session of accessory organs of female reproductive system.
- Nail
·
A nail is a horn-like envelop covering the
dorsal aspect of the terminal phalanges
of fingers and toes
·
The parts of the nail are,
o
Matrix, the only living part of the nail. It is
situated behind and underneath the nail fold and produces the keratin which makes
up the nail plate. If the matrix is damaged, growth of the nail plate is
affected.
o Eponychium,
Dead skin that forms around the cuticle area. It can be lifted and trimmed during a
professional manicure treatment. Tends to be more prominent on males.
o Paronychium,
The 'live' skin that folds around the cuticle area, giving protection to the
matrix.
o Hyponychium,
The area of attachment between the nail plate and nail bed that lies underneath
the free edge. Anatomical terms of location: proximal and distal, end of the
nail.
o Nail plate,
the hard and translucent part of the nail composed of layers of keratin.
o Nail bed,
Tissue underneath the nail plate, responsible for the pink colour of the nail.
It also determines what shape the nail will grow. It is informally referred to
as "the quick", especially the end nearest the fingertip.
o Lunula,
The visible part of the matrix, a whitish crescent shape around the base of the
nail plate. Tends to only be visible in larger nails.
o Nail fold, A
fold of hard skin overlapping the base and sides of a fingernail or toenail
o Free edge or
distal edge, The part of the nail that extends past the finger, beyond the nail
plate. There should always be a free edge present to prevent infections.
o Nail groove,
Grooves that guide the direction of nail growth. They are located down the
sides of the nail fold.
The Tongue.
The Tongue is organized in the
following ways:
·
The
tongue is a highly muscular organ of deglutition, taste and speech
·
It is made up of skeletal muscles
covered by a mucous membrane. It has the root, tip and the body.
·
It is attached by its base to the hyoid
bone and by the lingual frenulum to the floor of the mouth.
·
There are two types of muscles forming
the tongue;
o
Intrinsic muscles; they originate and
insert in the tongue itself. An example of the intrinsic muscles includes
Genioglossus. They are responsible for changing the shape of the tongue such as
flattening and elevating the tongue during drinking and swallowing
o
Extrinsic muscles are those muscles that
insert into the tongue but originate from other structures such as hyoid bone.
An example of the muscles includes hyoglossus. They are responsible for
protruding and retract the tongue, move it from side to side and change its
shape.
·
The dorsal mucosa is covered by numerous
papillae; tiny projections, some of which bear taste buds. There are three
types of papillae; vallate, fungiform
and filariform (Fig. 1)
o
Circumvallate papillae, arranged in an
inverted V shape at the base of the tounge. Are the largest papillae
o
Fungiform pappilae; are situated mainly
at the tip ad the edge of the tongue.
o
Filiform papillae; are the smallest of
all three. Most numerous on the surface of the anterior two-thirds of the
tongue.
·
There are four basic taste sensation:
o
Sweetness; apex (tip)
o
Saltiness; lateral margins
o
Sourness; posterior part of the
tongue
o
Bitterness; posterior part of the tongue
·
Although it is commonly stated that
particular areas of the tongue are specialized to detect these different
tastes, evidence indicates that all areas of the tongue are responsive to all
taste stimuli. Each afferent nerve fibre is connected to widely separated taste
buds and may respond to several different chemical stimuli. Some respond to all
four classic categories, others to fewer or only one
·
Blood supply of the tongue is by lingual
branch of the external carotid artery and venous drainage is by lingual veins,
which joins the internal jugular vein.
·
Nerve innervations of the tongue is
through:
o
The hypoglossal nerve(12th cranial
nerves)
o
The lingual branch of the mandibular
nerves
o
The facial and glossophayngeal nerves
(7th and 9th CN) the nerves of taste.
o
The parasympathetic innervation of the
various glands of the tongue is from the chorda tympani branch of the facial
nerve
o
The postganglionic sympathetic supply to
lingual glands and vessels arises from the carotid plexus
Step no 4. Illustrated diagrams of sensory organs(
25minutes)
Activity:
Brainstorming. (5 minutes)
Ask the students to
mention the names to the letters representing unlabeled parts of the sensory
organ.
Eg. What does the
later A, B and C represents.
·
Write
their answers on a flipchart or chalkboard.
SUMMARIZE:
by
showing a well labelled diagram of the human cell.-
|
The following is the diagram of the human ear in
different views:-
Source: standring 2005
The following
is the diagram of the human Eye.
|
|
|
|
The eye ball
|
Source: www.student
The following
is the diagram of the human Skin.
The
dermis and hypodermis of the skin
|
Source:
standring 2005.
The
skin epidermis of the.
|
Source:
standring 2005.
layers
of the skin
|
|
|
Source:
standring 2005.
Hair
follicle
|
Source:
standring 2005.
The
nail
|
Source:
standring 2005.
The Tongue
Source:
Elsevier Ltd 2005.
Step no 5. Basic functions
of each sensory organ. (10minutes)
·
The basic functions of the ear includes the following:
o
Detection of
sound(hearing)
o
Maintaining
body balance/ equilibrium.
·
The basic function of the Eye includes the following:
o
The main function of an
eye is to focusing images of object on the retina
·
The basic function of the Nose includes the following:
o
The nose is the first of the respiratory passages
through which the inspired air passes.
o
To begin the process by which the air is warmed,
moistened and filtered
·
The basic function of the skin and the accessory
structures includes the following:
o
Protection
for the body from environmental effects, such as,
§ Abrasions,
§ Melanin absorb ultraviolet light and
protect underlying tissue,
§ Skin prevent the entry of
microorganisms and other harmful substances,
§ Prevent dehydration by reducing
water loss from the body because its lipids act as barrier to the diffusion of
water,
§ Nail protect the ends of the digits
from damage and can be used in defence,
§ Hair follicles act as insulator and
protect from ultraviolet light,
o
Temperature
regulation through sweat glands, blood vessels, and fat deposits,
o
Sensation
, the
integumentary system has
sensory receptors that can detect heat, cold,
pain, touch, temperature and pressure)
o
Synthesis
and storage of vitamin D, when exposed to ultraviolet light, the skin produces
a molecule that can be transformed into vitamin. D
o
Excretion
, small amount of waste products are lost through the skin and in gland
secretions
The
basic functions of the Tongue includes the
following:-
·
The
tongue is a highly muscular organ of deglutition, taste and speech
·
There are four basic taste sensation:
o
Sweetness; apex (tip)
o
Saltiness; lateral margins
o
Sourness; posterior part of the
tongue
o
Bitterness; posterior part of the tongue
Step no
6. The Key points(5minutes)
·
Ears are paired sensory organs comprising of auditory system, involved in
the detection of sound, and vestibular
system, involved with maintaining body balance/ equilibrium.
·
The eye is an organ of the sense of sight situated in the orbital cavity
·
The nasal
cavity is the main route of air entry and consists of a large irregular cavity
divided into two equal passages by a septum
·
The integumentary system consists of the
skin and the accessory structures such as hair, nails and glands.
·
The
tongue is a highly muscular organ of deglutition, taste and speech
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