Human Anatomy I: Tissues, Skin & Bones

Some Basic Ideas Anatomy describes the physical parts of an organism Physiology describes the way in which those parts work, alone and in combination Most organisms are organized into different levels: Cells Tissues: groups of cells performing some specific function Organs: groups of tissues performing some specific function Organ systems: groups of organs performing some specific function

Tissue Types There are 4 main kinds of tissues Epithelial Tissue Connective Tissue Muscle Tissue Nerve Tissue Most organs are a combination of two or more tissues

Epithelial Tissue Serves as covering or lining of various body parts Involved in both absorption of material and secretion of material Cells can vary in shape: Squamous cells are flat; found in areas where diffusion important Cuboidal cells are cubes; involved in secretion and absorption Columnar cells are rectangular: also used for secretion and absorption Tissue can vary in # of layers: Simple epithelium has one layer Stratified epithelium has 2 or more; can be different cell types

Clockwise from upper left: simple columnar; simple cuboidal; stratified squamous

Connective Tissues Perform a variety of functions All consist of two components: Living cells, scattered in a… Non-living matrix secreted by these cells Some examples include: Bones Cartilage Adipose (fatty) tissue Blood Ligaments tendons

Major Organ Systems

Integumentary System Or, more commonly, skin! Major functions include: A barrier to injury or invasion by other organisms A (very large) sensory organ Production of body covering (hair, scales, feathers) Production of various substances (toxins, pheromones, lubricants, etc.) Body cooling (via sweat) Assistance with respiration

General Anatomy of the Skin I Outermost layer is the epidermis Living epithelial cells towards interior Outer layer of dead cells, many filled with keratin (helps prevent water loss)

General Anatomy of the Skin II Middle layer is the dermis Contains primarily connective tissue, plus nerves, blood vessels, muscles, sensory organs Hairs and glands appear to come from this region, but actually are infoldings of the epidermis

General Anatomy of the Skin III Inner layer is the hypodermis, or subcutaneous layer Mostly a layer of adipose tissue, which helps… Cushion underlying organs In heat retention Also contains some nerves and blood vessels

2 Primary Skin Glands in Humans Sweat Glands, with two types: Eccrine sweat glands occur over most of body Release a clear fluid, mostly water with dissolved salts Apocrine sweat glands are found mostly in groin, armpits, face Release more viscous and odor-causing fluid Sebaceous Glands Release a thicker, oily/waxy fluid called sebum Helps lubricate hair follicles

Human skin also possesses a number of different kinds of sensory receptors (for temperature, pressure or touch, pain)

Skeletal System Major functions include: Protection for internal organs Attachment points for muscles Some animals possess a hydrostatic skeleton Body is a fluid-filled “bag” under pressure which animal can push against Others have an external skeleton, or exoskeleton Still others possess an internal skeleton

Above are some hydrostatic skeletons, in a roundworm and an earthworm Above are some hydrostatic skeletons, in a roundworm and an earthworm. To the right is a shed exoskeleton of a cicada.

Anatomy of the Human Skeleton The axial skeleton consists of bones along the midline of the body Includes skull, spinal column, ribcage, sternum The appendicular skeleton is everything else Includes arm bones, leg bones, pelvic girdle, pectoral (shoulder) girdle

Axial skeleton Appendicular skeleton

3 Components of Skeleton Bones: the hardest part of the skeleton Cartilage: more flexible than bone Ligaments: a type of connective tissue linking two bones NOTE: tendons link muscles to bones, but we’ll look at these with muscles

Bone Structure Bones may be long, short, flat, or irregular in shape Most bones have a dense region of compact bone, and a less dense region of spongy (or cancellous) bone Within the spongy bone of long and flat bones is red marrow Involved in production of red blood cells Within the shaft region of long bones is yellow marrow Mostly fat storage Can be converted to red marrow in emergencies

Long bones above, flat bones below

The Inside of Bones The living cells in bones are called osteocytes Osteocytes are found within spaces called lacunae Osteocytes produce bone, which is the non-living matrix part Osteocytes are arranged (at least in compact bone) in groups called osteons, or a Haversian system In the middle of each osteon is a canal containing blood vessels to nourish the osteocytes

Joints Joints occur where two bones come into contact and can move relative to each other At the end of each bone is a layer of cartilage Ligaments link bones Fluid usually fills space between bones to reduce friction and wear