Human Skeletal System: Structure, Function, and Bone Remodeling

What are the primary functions of the skeletal system?

Provides support for soft tissues, attachment for muscles, protects internal organs, stores minerals and fat, and produces blood cells in red marrow.

How many bones are in the human body?

206 bones.

What are the two main types of bone structure?

Compact bone and spongy bone.

What is compact bone?

A dense outer layer of bone with few internal spaces, forming most of the shaft of long bones.

What is spongy bone?

A latticework of bone found in small, flat bones and near the ends of long bones.

What is the role of the periosteum?

It nourishes the bones and contains blood vessels, nerves, and cells involved in bone growth and repair.

What is an osteon?

The structural unit of compact bone, consisting of osteocytes arranged in concentric rings around a central canal.

What is the function of osteoblasts?

They are cells that form new bone by depositing bone matrix.

What is the role of fibroblasts in bone repair?

They invade the clot formed after a fracture and secrete collagen fibers to form a callus linking the two parts of the bone.

What happens during the transformation from cartilage to bone?

Osteoblasts form a collar of bone around the cartilage model, then migrate to form spongy bone, while cartilage cells divide to lengthen the bone.

What hormones are involved in bone growth?

Growth hormone, thyroid hormones, testosterone, and estrogen.

What is osteoporosis?

A condition that occurs when bone is broken down faster than it is deposited, leading to weakened bones.

What are the two groups of the human skeleton?

Axial skeleton and appendicular skeleton.

What does the axial skeleton consist of?

Skull, vertebral column, sternum, and rib cage.

What is the function of the skull?

It protects the brain, houses structures of hearing, and provides attachment sites for head and neck muscles.

What are the two divisions of the skull?

Cranium and face.

What is the role of calcitonin in bone remodeling?

It decreases blood calcium levels.

What is the role of parathyroid hormone (PTH) in bone remodeling?

It increases blood calcium levels.

What is the growth plate also known as?

Epiphyseal plate.

What is the significance of the growth plate?

It allows for the lengthening of bones during growth.

What happens to the growth plate at the end of teenage years?

It thins, and the ends of the bone fuse with the shaft, preventing further lengthening.

What is the difference between a nondisplaced and a displaced fracture?

In a nondisplaced fracture, the ends remain aligned; in a displaced fracture, the ends must be realigned.

What is the function of osteoclasts?

They break down old bone during the remodeling process.

How does bone tissue respond to stress?

Bone tissue forms in response to stress and is absorbed in the absence of stress.

What is the role of estrogen in bone remodeling for women?

It enhances calcium absorption, stimulates bone formation, and inhibits bone breakdown.

What is the cavity in the shaft of long bones filled with?

Yellow marrow, a fatty tissue for energy storage.

What type of marrow fills the spaces of some spongy bones in adults?

Red marrow, where blood cells form.

What are fontanels?

Membranous areas connecting the bones of the cranium before and shortly after birth.

What is the purpose of fontanels?

They allow the skull to be compressed during birth and enable rapid brain growth during infancy.

At what age are fontanels replaced by bone?

By 2 years of age.

How many vertebrae are in the vertebral column?

26 vertebrae.

What are the types of vertebrae in the vertebral column?

7 cervical, 12 thoracic, 5 lumbar, 1 sacrum, and 1 coccyx.

What separates vertebrae from one another?

Intervertebral disks, which are pads of fibrocartilage.

What is scoliosis?

An abnormal curvature of the spine, often referred to as 'twisted disease'.

What is a 'slipped disk'?

A misnomer for a bulging disk that does not move out of place.

What can happen if a disk bulges inward?

It can press against the spinal cord, interfering with perception of incoming stimuli and muscle control.

What are floating ribs?

The last two pairs of ribs that do not attach to the sternum.

What is the function of the appendicular skeleton?

It allows movement and interaction with the environment.

What components make up the pectoral girdle?

Scapulae and clavicles.

What is the function of the pelvic girdle?

It supports the legs.

What are the three classifications of joints?

Fibrous, cartilaginous, and synovial.

What characterizes fibrous joints?

They are held together by fibrous connective tissue and most do not permit movement.

What is an example of a fibrous joint?

The immovable joints between the skull bones (sutures).

What type of movement do cartilaginous joints allow?

Very little movement.

What are synovial joints?

Freely movable joints that have a thin layer of cartilage and are surrounded by a capsule containing synovial fluid.

What are hinge joints?

Joints that allow motion in only one plane, such as the knee.

What are ball-and-socket joints?

Joints that allow motion in all planes, such as the shoulder.

What are the four primary tissue types in humans?

Epithelial, connective, muscle, and nervous tissue.

What is the function of epithelial tissue?

It covers body surfaces, lines cavities and organs, and forms glands.

What is the role of connective tissue?

It provides support and protection for organs and serves as a storage site for fat.

What does muscle tissue do?

It facilitates body movement and movement of fluids through the body.

What is the function of nervous tissue?

It conducts nerve impulses throughout the body.

What are the two structural characteristics of epithelial tissues?

A free surface specialized for protection, secretion, or absorption, and a basement membrane that binds epithelial cells to underlying connective tissue.

What are the three basic shapes of epithelial cells?

Squamous, cuboidal, and columnar.

What is the function of squamous epithelium?

It allows for diffusion of materials and provides a slick surface to reduce friction.

What is cuboidal epithelium specialized for?

Secretion and absorption.

Where is columnar epithelium typically found?

Lining the small intestine.

What type of epithelium has tall, column-shaped cells?

Columnar epithelium

What is the primary function of columnar epithelium?

Specialized for secretion and absorption

Where is columnar epithelium primarily located?

Lines the small intestine

What are the two main categories of epithelial glands?

Exocrine glands and endocrine glands

What do exocrine glands secrete?

Into ducts leading to body surfaces, cavities, or organs

How do endocrine glands differ from exocrine glands?

Endocrine glands lack ducts and secrete hormones into spaces just outside the cells

What is the most abundant and widely distributed tissue in the body?

Connective tissue

What are the components of connective tissue?

Cells in an extracellular matrix of protein fibers and ground substance

What types of fibers are found in connective tissue?

Collagen, elastic, and reticular fibers

What is the function of fibroblasts in connective tissue?

Produce protein fibers and are responsible for tissue repair

What are the two categories of connective tissue?

Connective tissue proper and specialized connective tissue

What characterizes loose connective tissue?

Contains many cells and fewer, loosely woven fibers; cushions organs and provides insulation

What is the function of dense connective tissue?

Made of tightly woven fibers; attaches bone to bone (ligaments) or bone to muscle (tendons)

What are the three types of cartilage?

Hyaline, elastic, and fibrocartilage

What is the primary function of bone tissue?

Protects and supports internal structures, facilitates movement, stores lipids, calcium, and phosphorus

What is the composition of blood?

A liquid matrix of plasma with red blood cells, white blood cells, and platelets suspended in it

What are the three types of muscle tissue?

Skeletal, cardiac, and smooth muscle

What is the main characteristic of skeletal muscle tissue?

Long, cylindrical cells with multiple nuclei and obvious striations; provides voluntary movement

Where is cardiac muscle tissue found?

In the wall of the heart; contracts to propel blood through the circulatory system

What is the function of smooth muscle tissue?

Propels substances or objects through hollow organs

What makes up nervous tissue?

Neurons and neuroglia

What is the role of neurons?

Generate nerve impulses and conduct them to other neurons, muscle cells, or glands

What are the three types of cell attachments?

Tight junctions, adhesion junctions, and gap junctions

What is the function of tight junctions?

Form a leak-proof seal between cells

What do organs consist of?

Two or more different tissues that work together to perform a specific function

What is an organ system?

A group of organs with a common function; there are eleven major organ systems in the human body

What is the role of membranes in the body?

Sheets of epithelium supported by connective tissues cover body cavities and organ surfaces

What are mucous membranes?

Mucous membranes line passageways that open to the exterior of the body.

What do serous membranes line?

Serous membranes line the thoracic and abdominal cavities and the organs within them.

What is the function of synovial membranes?

Synovial membranes line the cavities of freely movable joints.

What is the cutaneous membrane?

The cutaneous membrane, or skin, covers the outside of the body.

What are the two main body cavities?

The two main body cavities are the ventral cavity and the dorsal cavity.

What does the ventral cavity include?

The ventral cavity includes the thoracic cavity and abdominal cavity, separated by the diaphragm.

What does the dorsal cavity consist of?

The dorsal cavity consists of the cranial cavity, which encloses the brain, and the spinal cavity, which houses the spinal cord.

What is the integumentary system composed of?

The integumentary system is composed of skin and its derivatives, including hair, nails, sweat glands, oil glands, and wax glands.

What is the largest organ of the body?

The skin is the largest organ of the body.

List some functions of the skin.

The skin protects against bacterial invasion, UV radiation, prevents water loss, regulates body temperature, and synthesizes vitamin D.

What are the layers of the skin?

The skin has three layers: epidermis, dermis, and hypodermis (subcutaneous layer).

What is the epidermis?

The epidermis is the thin outer layer of the skin, composed of several layers of epithelial cells.

What is the dermis?

The dermis is the thicker inner layer of skin containing nerves, blood vessels, and glands.

What is the hypodermis?

The hypodermis, or subcutaneous layer, anchors the skin to underlying tissues and functions in protection, temperature regulation, and fat storage.

What determines skin color?

Skin color is determined by blood flow and the distribution and quantity of the pigment melanin.

What are the two forms of melanin?

The two forms of melanin are yellow-to-red and black-to-brown.