Skin and its appendages

Skin functions to protect the body from microorganisms and dehydration, to synthesize some chemicals and hormones, for sensation of heat, cold, pressure, touch and pain, to regulate temperature

Skin is a cutaneous membrane with an outer epidermis, the thicker dermis deep to it, and the hypodermis also called the subcutaneous fat layer, as the deepest layer. It is where hypodermic syringes place medications.

Skin cells include keratinocytes (about 90%) that make keratin, a tough, fibrous, protective protein and melanocytes (about 5%), which produce melanin, the pigment of skin, among others

Outer layer of skin is the epidermis. Five sublayers are the:

Stratum corneum- waterproof outer layer. Cells are dead.

Stratum lucidum- filled with a clear protein called eleiden. Cells are anuclear

Stratum granulosum has granules of proteins. Lysosomes are activated with degeneration of nuclei and

cytoplasm

Stratum spinosum- has desmosomes and lots of RNA to make proteins. Appears spiny

Stratum basale-the only layer that is alive where cells undergo mitosis (still dividing). About 10% undergo mitosis each day. From mitosis to sloughing off of stratum corneum is about 35 days.

Inner layer, the dermis has two sublayers. Collagen (leather) protein is most prevalent protein.

Papillary layer has ridges. The epidermis conforms to them to make fingerprints (for ID and gripping)

Reticular layer is where most sensory receptors and facial muscles in skin are located.

Color in skin

Tyrosine---------- (tyrosinase)--àmelanin (lack of enzyme is albinism). Enzyme altered by UV, ACTH, MSH

Blood flow- pink color (visible in nail beds and lips). Lack leads to blue (greyish) color (cyanosis)

Jaundice (liver failure) leads to yellowing. Particularly a problem in neonates.

Carotene can cause yellowing

Nails are made of keratin. Nail body forms at the nail root proximal to the nail. Under the nail is the nail bed. The epidermis overhangs the nail to make a cuticle. This is an area of concern in medicine as fungal infections get under the cuticle. The lighter area at the bottom is the lunula (little moon)

Hair is made in the papillary layer of the dermis. The papilla or hair root is alive and undergoing mitosis. It is fed by blood vessels in the skin. The hair shaft is not alive. Every hair has a gland called a sebaceous gland associated with it. The gland makes sebum which provides a lubricating waxy protective layer over the skin. Every hair also has a muscle called ___ associated with it. The muscles make the skin stand up in goosebumps as a result of fear or cold. (This is an evolutionary adaptation that is more useful for other mammals).

Glands of skin

Sebaceous glands- make sebum (protective against dessication and infection)

Ceruminous glands make cerumen (ear wax). Prevents dessication and infection in ear

Sudoriferous (sweat) glands are either eccrine or apocrine. They release perspiration to regulate temperature and eliminate some waste (ammonia and urea)

Eccrine Apocrine

Present from birth Present from puberty

No strong odor Strong odor

Thermal regulation Emotional sweating

All over the body Concentrated in axilla, around anus, and around areola of breast

Skeletal tissues

Types of bone- long bones, short bones, flat bones, irregular bones. Short, flat, and irregular bones are spongy, or cancellous bone with spines called trabeculae (spelling of Latin words ending in a is a or ae depending on singular or plural. Both are pronounced the same). They are covered with an outer layer of compact bone.

Long bones are hollow. They are made of a kind of bone called compact bone. Parts are the long shaft, or diaphysis, and the ends, or epiphyses. The inside hollow cavity is the marrow or medullary (Latin for middle) cavity. It is lined with the endosteum- a fibrous layer. The outside has a fibrous outer layer, the periosteum, with allows for attachment of tendons and ligaments. Articular cartilage is found at the ends of articulating bones (bones making a joint with another bone)

Microscopic structure of bone: Compact bone has a structure of multiple concentric circles of bone. The circles are called lamellae. They are made of individual spaces in which cells live, called lacunae. Each set of concentric circles of living bone is called a Haversian system, or osteon. It has a Haversian canal in the center where blood flows. Tiny blood vessels called canaliculi (little canals) carry blood out from the center. Transverse Volksmann’s canals connect the osteons

Cancellous, or spongy bone, has spikes of bone tissue called trabeculae.

Cells of bone

Mature cells are osteocytes (non-dividing osteoblasts)

Cells that make bone are osteoblasts

Cells that break down bone are osteoclasts.

Bone is a living tissue. Exercise builds it up. Lack of calcium can cause it to break down.

Composition of bone: a protein called collagen and a gelatinous mixture of other proteins and polysaccharides secreted by the bone cells, and a crystalline mineral called hydroxyapatite (made of calcium and phosphorus). The minerals make it hard while the collagen gives it tensile strength and keeps it from becoming brittle.

Bone marrow can be yellow (fat) or red (hematopoiesis). Red marrow is found in all bones in neonate. In adults it is found in the ends of humerus and femur, the bodies of the ribs and of the vertebrae. (Proximal end of femur used for bone marrow transplant).

Development of bone is osteogenesis

Endochondral ossification occurs in most bones. New bone forms in cartilage between the epiphyses and diaphysis of the bone at either end as it grows. The bones fuse under the influence of hormones (particularly estrogens) at puberty

Intramembraneous ossisfication occurs in a few flat bones (such as the skull) which grow outward into the periosteum rather than lengthwise.

Cartilage has cells called chondrocytes

Hyaline, fibrous, and elastic cartilage have slightly different structural characteristics for slightly different functions. (Review types of cartilage). Cartilage has poor blood flow and heals very slowly.

Growth of cartilage is interstitial (within- usually in childhood) or on the outside (appositional).