Skin and Skeletal System: Structure, Function, and Bone Cells

Posted on Feb 13, 2025 in Human Biology

Skin Structure and Function

Skin: There are two types of skin:

  • Thick skin: Found on the palms of the hands, fingertips, and soles of the feet.
  • Thin skin: Covers most of the body and contains hair follicles, sebaceous glands, and arrector pili muscles.

Functions of the Skin

The skin provides:

  • Protection: From pathogens and the environment.
  • Sensation: Contains nerve endings for touch, pressure, temperature, and pain.
  • Body Temperature Regulation: Through sweat production and blood vessel dilation/constriction.
  • Prevention of Fluid Loss: Acts as a barrier to prevent dehydration.
  • Lipid Storage: Adipose tissue in the hypodermis stores fat.
  • Excretion: Eliminates salts and wastes through sweat.

Layers of the Skin

  • Epidermis: The topmost layer, responsible for keeping water in the body, preventing pathogens from entering, and regulating body temperature.
  • Dermis: The middle layer contains nerve endings that provide the sense of touch and heat. It also contains hair follicles, sweat glands, sebaceous glands, apocrine glands, lymphatic vessels, and blood vessels. The blood vessels in the dermis provide nourishment and waste removal for its own cells and the epidermis.
  • Hypodermis: The deepest layer attaches the skin to underlying bone and muscle and supplies it with blood vessels and nerves.

Stratum Layers of the Epidermis

The epidermis is composed of five layers:

  • Stratum Basale
  • Stratum Spinosum
  • Stratum Granulosum
  • Stratum Lucidum
  • Stratum Corneum

Cell Types in the Epidermis

  • Keratinocytes: Produce keratin, which provides protection from heat, water loss, microbes, and chemicals.
  • Langerhans Cells: Migrate from red bone marrow and protect against microbes.
  • Melanocytes: Produce melanin, which protects against UV radiation.
  • Merkel Cells: Touch receptors.

Skeletal System Structure and Function

Functions of the Skeletal System

  • Protection: Protects organs in the body.
  • Framework: Provides shape and support.
  • Movement: Bones anchor muscles to provide movement.
  • Blood Cell Production: Bone marrow produces white blood cells (WBCs), red blood cells (RBCs), and platelets.
  • Mineral Storage: Stores minerals such as zinc, potassium, iron, magnesium, manganese, traces of copper, selenium, strontium, calcium (main mineral for muscle contraction), phosphorus (other main mineral for cell structure, bones, and teeth), and phosphate.
  • Triglyceride Storage: Stores triglycerides in adipose cells of yellow marrow.

Axial Skeleton (80 Bones)

Composed of six parts:

  • Skull (22 total): Cranial Bones (8), Parietal (2), Temporal (2), Frontal (1), Occipital (1), Ethmoid (1), Sphenoid (1)
  • Ossicles (6 total): Malleus (2), Incus (2), Stapes (2)
  • Hyoid Bone (1 total)
  • Vertebral Column (26 total): Cervical vertebrae (7), Thoracic vertebrae (12), Lumbar vertebrae (5), Sacrum (1) (5 at birth), Coccyx (1) (4 at birth)
  • Thoracic Cage (27 total): Sternum (3), Manubrium (1), Body of sternum (1), Xiphoid process (1), Ribs (24)

Appendicular Skeleton (126 Bones)

Divided into six major regions:

  • Pectoral Girdles (4 total): Left & right Clavicle (2) and Scapula (2)
  • Arm and Forearm (6 total): Left & right Humerus (2; Arm), Ulna (2), Radius (2; Forearm)
  • Hands (54 total): Left and right Carpal (16; wrist), Metacarpal (10), Proximal phalanges (10), Middle phalanges (8), Distal phalanges (10)
  • Pelvis (2 total): Left and right os coxae (2; ilium)
  • Thigh and Leg (8 total): Femur (2) (thigh), Tibia (2), Patella (2; knee), and Fibula (2; leg)
  • Feet and Ankles (52 total): Tarsals (14) (ankle), Metatarsals (10), Proximal phalanges (10), Middle phalanges (8), Distal phalanges (10)

Bone Cells

  • Osteoclasts: Destroy bone.
  • Osteoblasts: Create bone.
  • Osteocytes: Maintain bone tissue.
  • Osteoprogenitor Cells: Involved in bone growth and repair.

Spongy and Compact Bone

Spongy and compact bone are two types of osseous tissue, or bone tissue. Compact bone is generally dense and heavy, and it makes up the hard outer surfaces of the bones. Spongy bone is less dense than compact bone, and it is typically very porous, giving it a sponge-like appearance. This type of bone is typically surrounded by compact bone. Also, in an adult, spongy bone typically contains more red bone marrow, while compact bone may contain yellow bone marrow.