Lips

• Outer cutaneous surface• It consists of epidermis (stratified squamous

keratinized epithelium) and dermis (dense irregular connective tissue) with numerous hair follicles, sebaceous glands and sweat glands

• Red area• It is stratified squamous cornified epithelium

with numerous dermal papillae

• Inner wet surface or mucous membrane• It is stratified squamous epithelium and

lamina propria containing mucous glands

• The central core • It is made up of skeletal muscles with

intervening loose connective tissue

Pinealocytes

• The main cells of pineal gland, • The gland is located behind the 3rd ventricle

and between the two hemispheres of the brain.

• The primary function of the pinealocytes is the secretion of the hormone melatonin, a hormone important in the regulation of circadian rhythms.

circadian rhythm

• A is any biological process that displays an endogenous, entrainable oscillation of about 24 hours.

• These rhythms are driven by a circadian clock, and rhythms have been widely observed in plants, animals, fungi and cyanobacteria.

• The term circadian comes from the Latin circa, meaning "around" (or "approximately"), and diem ordies, meaning "day".

• The formal study of biological temporal rhythms, such as daily, weekly, seasonal, and annual rhythms, is called chronobiology.

• Although circadian rhythms are endogenous ("built-in", self-sustained), they are adjusted (entrained) to the local environment by external cues called zeitgebers, commonly the most important of which is daylight.

• In humans, the suprachiasmatic nucleus (SCN) communicates the message of darkness to the pinealocytes, and as a result, controls the day and night cycle.

• It has been suggested that pinealocytes are derived from photoreceptor cells.

• Research has also shown the decline in the number of pinealocytes by way of apoptosis as the age of the organism increases