Life Science Journal 2013;10(5s) http://www.lifesciencesite.com http://www.lifesciencesite.com lifesciencej@gmail.com 194 Histogenesis study of skin in sheep Sajjad Hejazi 1 , Sina Yaghoubi * 2 , Mohamadreza Delghandi 2 , Farzin Javid 3 1 - Departmenet of anatomy, Faculty of Veterinary Medicine,Tabriz branch,Islamic Azad University,Tabriz,Iran. 2 – Graduation of veterinary, Faculty of Veterinary Medicine,Tabriz branch,Islamic Azad University,Tabriz,Iran 3– Veterinary Student, Faculty of Veterinary Medicine,Tabriz branch,Islamic Azad University,Tabriz,Iran. *Corespondig auther Hejazi.sajjad@yahoo.com Abstract: Aim of this research is based on the study of face's skin in ((ghezel)) sheep.This study done on 100 sheep embryos. Mentioned embryos were sampled accidentally from Tabriz mechanized slaughter's house. Length of the collected embryo's were measured by X=2.1(Y+17) formula. Collected embryos were in the age of 40to130 days. After fixation of embryos in 10% formalin, samples from face (including single hair follicle's and sensitive hair follicles)gathered.After providing the histological samples and using hematoxilin-eosin coloring method, samples studied. In the first levels of developing the skin, epidermis layer was provided from a layer a basal (quboidal cells) and covered by a layer of squamus cells called periderm. In the 8 th week of pregnancy, interstitial layer was created because of germinal layer's proliferation and in the 14 th week of pregnancy the interstitial layer changed to a layer of spinosal cells. In the last one-third of the pregnancy form of the skin changed to keratinized. Appearing the hair follicles, fat glands and sweat glands started in 9 th week. Fat and sweat glands disconnected from hair follicle and simultaneously, myoepithelial cells appeared with sweat glands. Against all of the mammals that hair follicle grows by beveled angle, in sheep we are faced with perpendicular form of hair growth, in conclusion it's clear that the 13 th week of ewe's embryo's life is a sensitive period for appearing skin structures. While melanocytes, myoepithelial cells, fat and sweat glands appear in this week. From results of this research, it’s clear that the development pattern of ewe's embryo's skin is in accordance with human embryo. [Hejazi S, Yaghoubi S, Delghandi M, Javid F. Histogenesis study of skin in sheep. Life Sci J 2013;10(5s):194-198] (ISSN: 1097-8135). http://www.lifesciencesite.com . 35 Keyword: Histogenesis, Sheep, Skin 1. INTRODUCTION Skin is the heaviest organ of body by having 16% of its weight. Skin is made of epidermis which have a layer of epithelial cells that originate from ectoderm and derm and a layer of connective tissue that originates from mesoderm. Under skin, hypoderm or under skin tissue is located and its made of loose connective tissue, also a group of cells called fat- paniklus can be included in this layer. In fact, hypoderm is not accounted as a part of skin, never and less it connects the skin as a layer of loose connective tissue to the layers of under it, also this layer is in accordance with superficial fascia in anatomy.(6). At all, in developed skin, derm makes the thickest part, and hair follicle, sweat and fat glands are located on the deep part of the derma. Animal’s skin has to origins: 1: superficial layer for epidermis which is the improved form of superficial ectoderm. 2: deeper layer or derma which is provided from the develop of sub mesanshim layer.. Some usual parts 6f skin like hair follicle and sweat gland (apocrine in domestic animals) are placed in this area (5). In embryo's first growth levels, epiderm is covered with a single layer of epithelium and later they become a layer of periderm cells. (10.15). Derma is derivative of mesoderm and embryo's dermatomes. (12). In view of embryology, hair, hoof, and horn (ruminants) are derivative of ectoderm layer (12). Hair follicles have differences according to the sex and weight of animal. (14) On the other hand, thicknes of skin in sheep not only results from breed but also results from age, sex and weights. (11) Figure 1: Some of the collected embryos for sampling 2. Method: Statistical community in this research contains pregnant ewes from Ghezel , s breed, which are killed in Tabriz mechanized slaughtry. Samples include 100 male embryos which are disconnected from the uterus of pregnant ewes (Figure1).Sampling was completely random. After sampling age of the embryos measured,