Other Sense Organs of Human Body : Skin, Sense of Taste, Female Breasts ,Tear Gland, Sense of Smell

3D Picture of Human skin Created By Me (Manash Kundu)

SKIN:
The skin is the largest organ in the body and has a surface area of about 1.5 to 2 m square in adults and it contains glands, hair and nails.There are two main layers:
1) Epidermis

2) Dermis
Between the skin and underlying structures is a layer of subcutaneous fat.

3D Page of Human Skin in My Biology-World Software

 

Epidermis:
The epidermis is the most superficial layer of the skin and is composed of stratified keratinised squamous epithelium, which varies in thickness is different parts of the body.It is thickest on palms of the hands and soles of the feet.There are no blood vessels or nerve endings in the epidermis, but its deeper layers are bathed in interstitial fluid from the dermis, which provides oxygen and nutrients and drained away as lymph.
      
There are several layers(strata) of cells in the epidermis which extend from the deepest germinative layer to the surface stratum corneum ( a thick horny layer). The cells on the surface are flat, thin, non nucleated,dead cells or squames, in which the cytoplasm has been replaced by the fibrous protein keratin.These cells are constantly being rubbed off and replaced by cells that originated in the germinative layer and have undergone gradual change as they progressed towards
the surface.Complete replacement of the epidermis takes about a month.The maintenance of healty epidermis depends upon 3 process being synchronised:

1) Desquamation(shedding) of the keratinised cells from the surface.
2) Effective keratinisation of cells approaching the surface.
3) Continual cell division in the deeper layers with newly formed cells being pushed to the surface.

Hairs, secretions from sebaceous glands and ducts of sweat glands pass through the epidermis to reach the surface.
       
The surface of the epidermis is ridged by projections of cells in the dermis called papillae. The pattern of ridges is different in every individual and the impression made by them is the fingerprint.The downward projections of the germinative layer between the papillae are believed to aid nutrition of epidermal cells and stabilise the 2 layers, preventing damage due to shearing forces.Blister develop when trauma causes separation of the dermis and epidermis and epidermis and serous fluid collects between the 2 layers.Skin colour is affected by various factors:-

Melanin:
A dark pigment derived from the amino acid tyrosine and secreted by melanocytes in the deep germinative layer, is absorbed by surrounding epithelial cells.The amount of genetically determined and varies between different parts of the body, between people of same ethnic origin and between ethnic groups.The number of melanocytes is fairly constant so the differences in colour depend on the amount of melanin secreted.It protects the skin fromthe harmful effects of sunlight.Exposure to sunlight promotes synthesis of melanin.

The percentage saturation of haemoglobin and the amount of blood circulating in the dermis give white skin its pink colour.

Excessive level of bile pigments in blood and carotenes in subcutaneous fat give the skin a yellowish colour.

Dermis:
The dermis is tough and elastic.It is formed from connective tissue and the matrix contains collagen fibres interlaced with elastic fibres. Rupture of elastic fibres occur when the skin is overstreched, resulting in permanent striae, or strech marks that may be found in pregnancy and obesity.Collagen fibres bind water and give the skin its tensile strength,but as its ability declines with age,wrinkle develop.Fibroblasts, macrophages and mast cells found in the dermis.Underlying its deepest layer there is a  areolar tissue and varying amounts of adipose tissue.The structure in the dermis are:
Lymph vessels:
Sensory nerve endings:
Sweat glands and their ducts:
Hairs,arrector pili muscles and sebaceous glands:

3D Picture of Human skin Created By Me (Manash Kundu)

 
Sensory nerve endings:
Sensory receptor(specialised nerve endings) sensative to touch, temperature, pressure and pain are widely distributed in the dermis. Incoming stimuli activate different types of sensory receptors. The skin is  an important sensory organ through which individual receive information about their environment. Nerve impulses generated in the sensory receptors in the dermis, are conveyed to the spinal cord by sensory nerves, then to the sensory area of the cerebrum
where the sensations are perceived.
Sensory Receptors:                                                                             Stimulus:
Meessner`s corpuscle                                                                         Light pressure
Pacinian Corpuscle                                                                             Deep pressure
Free nerve ending                                                                                Pain

Sweat Glands:
Sweat glands are widely distributed throughtout the skin and  are most numerous in the palms of the hands, soles of the feet axillae and groins.They are composed of epithelial cells.The bodies of the glands lie coiled in the subcutaneous tissue. Some ducts open onto the skin surface at tiny depressions, or pores and others open into hair follicles do not become active until puberty.In the axilla they secrete an colourless milky fluid which, if decomposed by surface microbes, causes an unpleasant odour.The functions of this secretion are not known. Sweat glands are stimulated by sympathetic nerves in response to raised body temperature and fear.

Hairs:
These are formed by a down-growth of epidermal cells into the dermis or subcutaneous tissue, called hair follicles. At the base of the follicle is a cluster of cells called the bulb.The hair is formed by multiplication of cells of the bulband as they are pushed upwards ,away from their source of nutrition, the cell die and become keratinised.The part of the hair above the skin is the shaft and the remainder, the root.

Functions of the skin:


1) Protection:
Defence action barrier against:
Invasion by microbes:
Chemical:
Physical Agents e.g. Mild trauma,Ultraviolet light:
Dehydration:

2) Regulation of body temperature:

3) Heat production:
 The Muscles:- Contraction of skeletal muscles produces a large amount heat and the more strenuous produces a large amount heat and the more strenuous the muscular exercise, the greater the heat produced.Shivering also involves skeletal muscle produced.

The liver is very metabolically active:-

The digestive organs:-  Produces heat during peristalsis and during the chemical reactions involved in digestion.

4) Heat Loss:

5) Formation of vitamin D:

6) Cutaneous Sensation:

7) Absorption:

8) Excretion:

3D Picture of Human Tongue Created By Me (Manash Kundu)

 

SENSE OF TASTE:
4 fundamental sesations of taste have been described -sweet, sour, bitter, and salt.This is probably an oversimplification
because perception varies widely and many tastes cannot be easily classified.However, some tastes consistently stimulate
taste buds in specific parts of the tongue:

1) Sweet and salty mainly at the tip.
2) Sour, at the sides.
3) Bitter, at the back.

The sense of taste triggers salivation and the secretion of gastric juice.It also has a protective function, e.g. when foul-tasting food is eaten, reflex gagging or vomiting may be induced.The sense of taste is impared when the mouth is dry.because substances can only be `tasted` when in solution.

3D Picture of Human Female Breast Created By Me (Manash Kundu)

 

BREASTS
The breasts or mammary glands are accessory glands of the female reproductive system. They exist also in the male, but in only a rudimentory form. In the female, the breasts are small and immature until puberty.Thereafter they grow and develop under the influence of oestrogen and progesterone.During pregnancy these hormones stimulates further growth.After the baby is born the hormone prolactine from the anterior pituitory stimulates the production of milk, and oxytocin from the posterior pituitory stimulates the release of milk in response to the stimulation of the nipple by the sucking baby, by a positive feedback mechanism.

Structure:
The mammary glands consist of glandular tissue, fibrous tissue and fatty tissue.Each breast consists of about 20 lobes of glandular tissue, each lobe being made up of a number of lobules that radiate around the nipple. The lobule consist of a cluster of alveoli that open into small ducts, and these unite to form large excretory ducts called lactiferous ducts. They form dilatations or reservoirs for milk. leading from each dilatation, or lactiferous sinus is anarrow duct that opens on to the surface of nipple.
    
The nipple is small conical eminence at the centre of the surrounded by the a pigmented area, the areola.On the surface of areola are numerous sebaceous glands , which lubricate the nipple during lactation.

Function:
The mammary glands are only active during late pregnancy and after childbirth, when they produce milk lactation.Lactation is stimulated by the hormone prolactin.

3D Picture of Human Tear Gland Created By Me (Manash Kundu)

 

LACRIMAL APPARATUS (Tear Gland) :
For each eye this consists of:

1 Lacrimal gland  and its ducts.
2 lacrimal canaliculi.
1 lacrimal sac
1 Nasolacrimal duct.

The lacrimal glands are exocrine glands situated in recesses in the frontal bones on the lateral aspect  of each eye just behind the supraorbital margin. Each gland is approximately the size and shape of an almond, and is composed of secretory epithelial cells.The glands secrete tears composed of water, mineral salts, antibodies, and lysozyme,a bactericidal enzyme.
 
The tears leave the lacrimal gland by several small ducts and pass over the front of the eye under the lids towards the medial canthus where they drain into the 2 lacrimal canaliculi; the opening of each is called the punctum.The 2 canaliculi lie one above the other, separated by small red body, the caruncle.The tears then drain into the lacrimal sac,which is the upper expanded end of nasolacrimal duct.This is the membranous canal approsimately 2 cm long, extending from the lower part of the lacrimal sac to the nasal cavity, opening at the level of inferior concha. Normally the rate of secretion of tears keep pace with the rate of drainage.When a foreign body or other irritant enters the eye the secretion of tears is greatly increased and the conjunctival blood vessels dilate.Secretion of tears is greatly increased and the conjunctival blood vessels dilate. Secretion of tears is also increased in emotional states, e.g. crying, laughing.

Functions:
Washing away irritating materials, e.g. dust, grit.
The bacteriocidal enzyme lysozyme prevents microbial infection.
Its oiliness delays evaporation and prevents drying of the conjunctiva. 

3D Picture of Human Nose created By Me (Manash Kundu)

 

OLFACTORY NERVES:
These are the sensory nerves of smell. they originate as specialised olfactory nerve endings(Chemoreceptor) in the mucous membrane of the roof of the nasal cavity above the superior nasal conchae. On each side of the nasal septum nerve fibres pass through the cribriform plate of the ethmoid bone to the olfactory bulb where interconnections and synapses occur. From the bulb, bundles of nerve fibres form the olfactory tract , which passes backwards to the olfactory area in the temporal lobe of the cerebral cortex in each hemisphere where the impulses are interpreted and odour perceived.

Physiology:
The human sense of smell is less acute than in other animals. Many animals secrete odorous chemicals called pheromones that play important part in chemical communication in, for example, territorial behavior, mating and bonding of mothers and their newborn offspring.The role of pheromones in human communication is unknown. All odorous materials give off volatile molecules which are carried into the nose with the inhaled air and even very low concentrations, when dissolved in mucus, stimulate the olfactory chemoreceptors.
    
The air entering the nose is warmed, and convection currents carry eddies of inspired air to the roof of the nasal cavity. Sniffing concentrates volatile molecules in the roof of the nose.This increases the number of olfactory receptors stimulated and thus the perception of smell.The sense of smell affect the appetite may improve and vice versa.When accopanied bt sight of food, and an appetising smell increases salivation and stimulates the digestive systems.The sense of smell may create long lasting memories, especially for distinctive odours, e.g. hospital smells,favourite or least-liked foods.

3D Picture of Human main Sense Organs Created By Me (Manash Kundu)