Skin Anatomy Quiz

Epidermis Layers

• Stratum spinosum is several layers thick, cells have dark nuclei and spiny projections.
• Stratum basale is the deepest layer of the epidermis and is a single layer of actively dividing cells.
• Keratinocytes, melanocytes, and Merkel cells are present in the stratum basale.

Dermis

• Found below the epidermis, composed of elastic and collagenous fibers.
• Contains sweat glands, sebaceous glands, nerve endings, and hair follicles.
• Composed of two layers:
  • Papillary layer is composed of loose connective tissues with many blood vessels.
  • Reticular layer is deeper and thicker than the papillary layer and is composed of dense and stretchable connective tissues.
• Papillae are fingerlike projections in the papillary layer that bring blood vessels near the epidermis and help to hold the two layers together.
• The arrangement of the papillae determines fingerprints.

Hypodermis or Subcutaneous Layer

• Not a part of the skin but connects the dermis to other organs.
• Stores fat, is a shock absorber, and anchors the skin to underlying structures.

Specific Appendages inside the Skin Layer

• Arrector pili muscles cause goosebumps.
• Sensory nerve fibers protect the body and are sensitive to temperature.
• Hair follicles contain nerve endings allowing a person to feel hair movement.
• Sebaceous glands associated with each hair follicle produce oil to condition hair and skin.
• Pores lubricate the skin.
• Meissner’s corpuscles in the dermis monitor the duration and extent of touch.
• Pacinian corpuscles are pressure sensitive receptors.

Hair

• Found everywhere in the body except palms, soles, lips, penis, and parts of the female genitalia.
• Dense distribution of hair on the scalp, face, pubic area, and underarms.
• Functions for protection:
  • from injury, sunlight, and heat loss (scalp hair)
  • from foreign particles (eyebrows and eyelashes)
  • from airborne particles (hairs in the nostrils).
• Also functions as a sexual attractant.
• Composed of the shaft, root, and bulb.
  • The shaft determines the curliness of the hair: round shaft (straight hair), oval shaft (wavy hair), and flat shaft (kinky hair).
  • The bulb is the enlarged base of the follicle.
  • The root is encased in an internal or epithelial root sheath (derived from the epidermis), and an external or connective root sheath (derived from the dermis).

Nails

• Composed of hard plates of highly keratinized cells.
• Formed from the stratum corneum of the epidermis.
• Cover and protect the dorsal surface of the fingernails and toenails.
• Help in grasping and picking small objects.

Overview of Skeletal System

• Bones are classified according to size and shape:
  • Long bones are typically longer.
  • Short bones are generally cube shaped.
  • Flat bones are thin, flattened, and usually curved.
  • Irregular bones have complex shapes.

The Skeletal System Consists of More Than Bones

• The human skeleton is made up of bones, ligaments, and cartilage.
• Ligaments are bands of dense and fibrous connective tissue that are essential for joint function.
• Cartilage is more flexible than bone but stiffer than muscle, found in the larynx, nose, between vertebrae, and at the ends of bones.

The Adult Human Skeleton Is Made Up of 206 Bones

• Skull - 22 bones
• Shoulder Girdle/Upper Extremities - 64 bones
• Thoracic Cage - 25 bones
• Vertebral Column - 33 bones
• Pelvic Girdle/Lower Extremities - 62 bones.

Age-Related Changes in Muscle Structure

• Lean muscle mass contributes up to 50% of total body weight in young adults, but this decreases to 25% by 75 to 80 years.

Typical Muscle Changes with Age

• Reduced muscle mass and increased fat mass.
• Reduced lower limb muscle cross-sectional area, beginning in early adulthood and accelerating after age 50.
• Decline in the number of muscle fibers, primarily affecting type II fast-twitch glycolytic fibers.

Sarcopenia

• Prevalence in Japanese community-dwelling older adults is 9.9% overall (9.8% among men, and 10.1% among women).