Human nose

The visible part of the human nose is the protruding part of the face that bears the nostrils .
The shape of the nose is determined by the ethmoid bone and the nasal septum , which consists mostly of cartilage and which separates the nostrils. On average the nose of a male is larger than that of a female .

The nose has an area of specialised cells which are responsible for smelling (part of the olfactory system ). Another function of the nose is the conditioning of inhaled air, warming it and making it more humid. Hairs inside the nose prevent large particles from entering the lungs. Sneezing is usually caused by foreign particlesirritating the nasal mucosa, but can more rarely be caused by sudden exposure to bright light (called the photic sneeze reflex ) or touching the external auditory canal . Sneezing is a means of transmitting infections because it creates aerosols in which the droplets can harbour microbes.

Human ear

The ear is the organ that detects sound . It not only receives sound,but also aids in balance and body position. The ear is part of the auditory system .
The word "ear" may be used correctly to describe the entire organ or just the visible portion. In most mammals, the visible ear is a flap of tissue that is also calledthe pinna and is the first of many steps in hearing . In humans, the pinna is often called the auricle . Vertebrates have a pair of ears, placed somewhat symmetrically on opposite sides of the head. This arrangement aids in the ability to localize sound sources.

Our Teeth

Teeth (singular tooth ) are small, calcified , whitish structures found in the jaws ( Mouths ) of many vertebrates that are used to breakdown food .
Some animals, particularly carnivores , also use teeth for hunting or for defensive purposes. The roots of teeth are embedded in the maxilla (upper jaw) or the mandible (lower jaw) and are covered by gums . Teeth are made of multiple tissues of varying density and hardness.
Teeth are among the most distinctive (and long-lasting) features of mammal species. Paleontologists use teeth to identify fossil species and determine their relationships. The shape of an animal 's teeth is related to its diet.

For example, plant matter is hard to digest, so herbivores have many molars for chewing and grinding. Carnivores , on the other hand, need canines to kill prey and to tear meat.
Mammals are diphyodont , meaning that they develop two sets of teeth. In humans , the first set (also called the "baby", "milk","primary", and " deciduous " set) Normally starts to appear at about six months of age, although somebabies are born with one or more visible teeth, known as "Neonatal teeth."

Normal tooth eruption at about six months is known as Teething and can be painful.
Some animals develop only one set of teeth (Monophyodont) while others develop many sets (polyphyodont). Sharks ,
For example, Grow a new set of teeth every two weeks to replace worn teeth. Rodent incisors grow and wear away continually through gnawing, which helps maintain relatively constant length. The industry of the beaver is due in part to this qualification. Many rodents such as voles (but not mice ) and guinea pigs , as well as rabbits , have continuously growing molars in addition to incisors.
Dental trauma refers to trauma to the face, mouth, and especially the teeth lips and periodontium. The study of dental trauma is called "Dental traumatology".

A human tongue

The tongue is a muscular hydrostat on the floors of the mouths of most vertebrates whichmanipulates food for mastication . It is the primary organ of taste ( gustation ), as much of the upper surface of the tongue is covered in papillae and taste buds . It is sensitive and kept moist by saliva , and is richly supplied with nerves and blood vessels . In humans a secondary function of the tongue is phonetic articulation.

[ 1 ] The tongue also serves as a natural means of cleaning one's teeth.

[ 2 ] The ability to perceive different tastes is not localised in different parts of the tongue, as is widely believed.

[ 3 ] This error arose because of misinterpretation of some 19th century research

Endocrine glands

Endocrine glands are glands of the endocrine system that secrete their products, hormones , directlyinto the blood rather than through a duct. The main endocrine glands include the pituitary gland , pancreas , ovaries , testes , thyroid gland , and adrenal glands . The hypothalamus is a neuroendocrine organ. Other organs which are not so well known for their endocrine activityinclude the stomach , which produces such hormones as ghrelin .
Local chemical messengers, not generally considered part of the endocrine system, include autocrines , which act on the cells that secrete them, and paracrines , which act on a different cell typenearby.
The ability of a target cell to respond to a hormone depends on the presence of receptors, within the cell or on its plasma membrane, to which the hormonecan bind.
Hormone receptors are dynamic structures. Changes in number and sensitivity of hormone receptors may occur in response to high or low levels of stimulating hormones.
Blood levels of hormones reflect a balance between secretion and degradation/ excretion . The liver and kidneys are the major organs that degrade hormones; breakdown products are excretedin urine and feces.
Hormone half-life and duration of activity are limited and vary from hormone to hormone.