Histology Learning System: This is an extensive site of histology images placed online. Images are organized by topic, anatomical figure, keyword, and thumbnails. The images cover the nervous, integumentary, circulatory, lymphatic, urinary, digestive, endocrine, respiratory and both male and female reproductive systems. There is an excellent Introduction on how to use the site and help pages. There are also appendices on Staining and Commonly Used Stains, Taxonomic Key to histological Organs, and a Glossary.
Anatomy Drill & Practice: This site covers the human body, the chemical, cellular, and tissue levels of organization, the integumentary system, skeletal system, muscular system, nervous system, cardiovascular system, respiratory system, digestive system, excretory system, and reproductive system.
This site not only includes images of and information on the above listed systems, but it also includes interactive drills and practice questions for students. NOTE: Flash required for the quizzes/practice questions.
Anatomy Drill & Practice: Test your knowledge of terms and structures related to anatomy for the following systems: human body, chemical level of organization, cellular level of organization, tissue level, integumentary, skeletal system, joints, muscle tissues & system, nervous tissue, spinal cord, spinal/brain/cranial nerves, sensory systems, senses, nervous system, endocrine system, cardiovascular, lymphatic, respiratory, digestive, urinary, and reproductive system. Note: This interactive quiz system requires that Flash be downloaded & installed on your computer to use it.
BioDigital Systems: Availble for free (individual) or for a fee (groups/businesses), this interactive system will first require you to sign in via your Facebook or Google account to gain access. Once inside the system, you can zoom and rotate your virtual skeleton. Eleven systems in total are able to view and examine. Note: this site allows you to repeatedly quiz yourself on all eleven systems that are covered within the site.
Structure of Skin: The skin is subdivided into three different regions - the epidermis, the dermis and the hypodermis (also known as the subcutaneous layer). The epidermis consists of four cell types (keratinocytes, melanocytes, Langerhans cells and Merkel cells), which are all spread out among five different layers. The five layers of the epidermis, starting from the topmost, are stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum and stratum basale. The epidermis is avascular, which means it does not contain any blood vessels. The surface portion of the epidermis consists of dead cells that contain large portion of keratin. Keratin is a protein that makes the skin virtually impermeable to water. The epidermis is attached to the dermis via a basement membrane. The topmost layer of the dermis is called the papillary layer. This layer is composed of connective tissue that contains extensions which extend into the epidermis. This holds the two layers together. The lower layer of the dermis is called the reticular layer. This layer is composed of a dense connective tissue made up of collagen and elastin. These two proteins give the skin its strength and elasticity. The reticular layer also contains other structures, such as blood vessels (arteries and veins), sweat glands, sebaceous (oil) glands, roots of hair follicles, arrector pili muscle and receptors. The lowest most layer of the skin is called the hypodermis. It is composed of macrophages, which eat up bacterial cells as well as adipose cells, which insulate the organism. It also contains its own network of protein fibers. The hypodermis not only insulates but also serves as an attachment point that connects the skin to the rest of the body.
Function of the Skin: The skin is the largest organ of the body, by size as well as by mass. It is a multifunctional organ, which implies that it consists of the four types of tissue that work together to carry out a certain set of functions. What are these functions? Our skin functions in (1) protection (2) immunity (3) sensation (4) thermal regulation and insulation (5) excretion and secretion (6) endocrine control (7) growth.