Skeletal System and Skin Structures

Overview

This study guide covers essential topics in the anatomy and physiology of the skeletal system and skin structures, focusing on bone identification, structure, and classification, as well as sweat gland distribution.

Skin Structures and Sweat Glands

The skin is the largest organ of the body and contains various structures, including sweat glands, which play a key role in thermoregulation.

• Skin Structures: Includes the epidermis, dermis, and hypodermis, as well as accessory structures such as hair follicles, sebaceous glands, and sweat glands.

• Sweat Glands Distribution: Sweat glands are distributed throughout the skin, with higher concentrations in areas such as the palms, soles, and forehead. There are two main types: eccrine (widely distributed, important for cooling) and apocrine (found in axillary and genital areas, active after puberty).

• Function: Sweat glands help regulate body temperature and excrete waste products.

• Example: Eccrine glands are most numerous on the palms and soles, while apocrine glands are concentrated in the armpits.

Subdivisions of the Skeletal System

The skeletal system is divided into two main subdivisions, each with distinct functions and components.

• Axial Skeleton: Comprises the skull, vertebral column, and thoracic cage. Provides support and protection for the brain, spinal cord, and thoracic organs.

• Appendicular Skeleton: Includes the bones of the limbs and girdles (pectoral and pelvic). Responsible for movement and interaction with the environment.

• Example: The femur is part of the appendicular skeleton, while the vertebrae are part of the axial skeleton.

Major Bones of the Skull and Fontanel

The skull consists of several major bones that protect the brain and form the structure of the face. In infants, fontanels are soft spots that allow for growth and development.

• Major Bones: Frontal, parietal, temporal, occipital, sphenoid, and ethmoid bones.

• Fontanel: The anterior fontanel is the largest and is located at the junction of the frontal and parietal bones. It allows for expansion of the skull during early development.

• Example: The occipital bone forms the back of the skull, while the frontal bone forms the forehead.

Bone and Bone Markings: Axial vs. Appendicular Skeleton

Bones have specific markings that serve as attachment points for muscles, ligaments, and tendons, and are used to distinguish between axial and appendicular components.

• Axial Skeleton Markings: Includes features such as the foramen magnum (occipital bone), spinous processes (vertebrae), and costal facets (thoracic vertebrae).

• Appendicular Skeleton Markings: Includes the greater and lesser tubercles (humerus), acetabulum (pelvis), and trochanters (femur).

• Example: The acetabulum is a socket in the pelvic bone for the femur head.

Microscopic Anatomy of a Long Bone

Long bones have a complex internal structure that supports their function in movement and support.

• Diaphysis: The shaft of a long bone, composed mainly of compact bone.

• Epiphysis: The ends of a long bone, containing spongy bone and red marrow.

• Medullary Cavity: Central cavity containing yellow marrow (fat storage).

• Periosteum: Dense connective tissue covering the bone surface.

• Endosteum: Lines the medullary cavity.

• Example: The femur has a thick diaphysis for weight-bearing and epiphyses for joint articulation.

Compact vs. Spongy Bone

Bones are composed of two main types of tissue: compact and spongy bone, each with distinct characteristics.

• Compact Bone: Dense and strong, forms the outer layer of bones. Contains osteons (Haversian systems) for structural support.

• Spongy Bone: Porous and lightweight, found in the epiphyses of long bones and inside flat bones. Contains trabeculae and red marrow.

• Comparison Table:

Hyoid Bone

The hyoid bone is a unique structure in the neck that does not articulate with any other bone.

• Location: Situated in the anterior neck between the mandible and larynx.

• Function: Supports the tongue and serves as an attachment for muscles involved in swallowing and speech.

• Example: The hyoid bone is fractured in cases of strangulation.

Bones of the Vertebral Column and Thoracic Cage

The vertebral column and thoracic cage protect vital organs and provide structural support.

• Vertebral Column: Consists of cervical (7), thoracic (12), lumbar (5), sacral (5 fused), and coccygeal (4 fused) vertebrae.

• Thoracic Cage: Includes the ribs (12 pairs), sternum, and thoracic vertebrae.

• Function: Protects the spinal cord, heart, and lungs; supports body posture.

• Example: The cervical vertebrae allow for neck movement, while the thoracic cage protects the heart and lungs.

Bones of the Pectoral and Pelvic Girdle

The pectoral and pelvic girdles connect the limbs to the axial skeleton and facilitate movement.

• Pectoral Girdle: Composed of the clavicle and scapula; attaches the upper limb to the trunk.

• Pelvic Girdle: Formed by the hip bones (ilium, ischium, pubis); supports the lower limb and protects pelvic organs.

• Example: The scapula provides attachment for shoulder muscles, while the pelvis supports the weight of the upper body.

Additional info: For further study, refer to a terminology checklist for the skeletal system to reinforce key terms and concepts.