Support and Movement | Human Skeleton, Muscles, Joints

In the intricate world of biology, the concepts of support and movement play a pivotal role in the survival and functionality of living organisms. The skeletal and muscular systems work in harmony to provide the necessary framework and mobility that enable animals, including humans, to interact with their environment. This chapter delves into the fascinating interplay between the skeletal system, which offers structural support and protection to vital organs, and the muscular system, which facilitates movement through contraction and coordination. By understanding the underlying mechanisms, such as the sliding filament theory and the various types of joints, students can appreciate how these systems contribute to locomotion and overall bodily function. This knowledge is not only essential for academic success, particularly in preparation for the MDCAT exam, but also lays the groundwork for a deeper understanding of human physiology and anatomy. As we explore the nuances of support and movement, we will also provide valuable resources, including MCQs and biology notes, to enhance your learning experience and ensure a comprehensive grasp of these fundamental concepts.

Table of Contents

• Support and Movement in Animals
• Human Skeletal System
• Endoskeleton
• Composition of Human Skeleton
• Gross Anatomy of Bones
• Structure of Bone Tissue
• Types of Cartilage
• Division of Human Skeleton
• Joints
• Arthritis

Definition

Support and movement refer to the biological systems that provide structural integrity and facilitate locomotion in organisms. In higher animals, the skeletal system, composed of bones and cartilage, works in conjunction with the muscular system to enable movement. The skeletal system serves as a framework that supports the body, protects vital organs, and allows for various movements through joints. Muscles, attached to bones via tendons, contract to create movement, while the nervous system coordinates these actions. This interplay between the skeletal and muscular systems is essential for maintaining posture, balance, and overall mobility, making support and movement critical for survival and functionality in living organisms.

Support and Movement in Animals

Support and Movement in Animals 🐾

Understanding how animals move and support their bodies is fascinating! The support and movement in animals are primarily facilitated by two crucial systems: the skeletal system and the muscular system. Let’s dive deeper into these systems and see how they work together to help animals thrive in their environments.

The Skeletal System 🦴

The skeletal system is like the framework of a house, providing structure and support. Here are some key points about the skeletal system:

• Composition: It is made up of bones and cartilage, which together create a rigid structure.
• Functions:
  • Support: It holds the body upright and maintains its shape.
  • Protection: Vital organs, such as the heart and lungs, are safeguarded by the bony cage of the ribcage and skull.
  • Movement: Bones serve as levers that muscles pull on to create movement.

The Muscular System 💪

The muscular system is what allows animals to move. It consists of three types of muscles:

1. Skeletal Muscles: These are attached to bones and are responsible for voluntary movements, like running or jumping.
2. Cardiac Muscles: Found only in the heart, these muscles pump blood throughout the body.
3. Smooth Muscles: These control involuntary movements, such as digestion and blood vessel constriction.

Nervous System Coordination 🧠

The nervous system plays a vital role in coordinating movements. Here’s how it works:

• Communication: The brain sends signals through the spinal cord to the muscles, telling them when to contract or relax.
• Adaptability: This system allows animals to adjust their movements based on their environment, whether they are climbing a tree or sprinting away from a predator.

The Musculoskeletal System in Action 🌟

The combination of the skeletal and muscular systems is known as the musculoskeletal system. This system is essential for a variety of activities, including:

• Walking and Running: Animals use their limbs to move efficiently across different terrains.
• Grasping: Animals like monkeys and humans use their hands to hold onto objects, climb, or manipulate their environment.
• Climbing: Many animals have adapted their skeletal and muscular structures to excel in climbing, showcasing their incredible adaptability.

In summary, the support and movement in animals are intricate processes that involve the harmonious interaction of the skeletal, muscular, and nervous systems. This remarkable adaptability allows animals to thrive in diverse environments, making them truly fascinating creatures!

For more information, check out our support and movement MCQs and support and movement biology notes to test your knowledge and learn even more! 📚✨

Support and Movement in Animals

Human Skeletal System

The Human Skeletal System: A Marvel of Support and Movement 🦴

The human skeletal system is an incredible framework that not only gives our bodies shape but also plays a crucial role in our overall health and functionality. With a total of 206 bones, this complex structure is essential for support and movement. Let’s dive deeper into its fascinating components!

Major Components of the Skeletal System

1. Axial Skeleton 🛡️

   • Structure: Comprising the skull, vertebral column, and rib cage.
   • Function:
     • Protection: Safeguards vital organs such as the brain, spinal cord, and thoracic organs.
     • Support: Provides a stable base for the body.

2. Appendicular Skeleton 🚶‍♂️

   • Structure: Includes the limbs (arms and legs) and girdles (shoulder and pelvic).
   • Function:
     • Facilitates Movement: Enables various activities like walking, running, and jumping.
     • Interaction with Environment: Allows us to engage with the world around us.

The Living Tissue of Bones

• Bone Composition: Did you know that bones are made of living tissue? They are dynamic structures that can grow, adapt, and repair themselves! This is crucial for maintaining strength and integrity throughout our lives.

• Bone Functions:

  • Support: Provides a framework that supports the body.
  • Movement: Works in conjunction with muscles to enable movement.
  • Blood Cell Production: The bone marrow, found within certain bones, is responsible for producing red and white blood cells.
  • Mineral Storage: Bones act as a reservoir for essential minerals like calcium and phosphorus.

Fun Facts About the Skeletal System! 🎉

• The human skull is made up of 22 bones that are fused together.
• The femur, or thigh bone, is the longest bone in the human body, while the stapes in the ear is the smallest!
• Babies are born with approximately 270 bones, but many fuse together as they grow, resulting in the 206 bones of adulthood.

Understanding the human skeletal system is essential for grasping how our bodies function. It not only provides support and movement but also plays a vital role in protecting our organs and producing blood. If you're interested in testing your knowledge, check out some support and movement MCQs or review support and movement biology notes for a deeper understanding!

Overview of the Human Skeletal System

Endoskeleton

The endoskeleton is a fascinating and essential feature of vertebrates, playing a crucial role in providing structural support and protection for internal organs. Unlike the exoskeletons seen in some invertebrates, which are external and rigid, the endoskeleton is an internal framework that grows along with the organism. This unique characteristic allows for greater flexibility and a wider range of movement, making it vital for the survival and adaptability of vertebrates.

What is an Endoskeleton? 🦴

The endoskeleton serves multiple functions, including:

• Support: It provides a sturdy framework that supports the body structure.
• Movement: The endoskeleton works in conjunction with muscles to facilitate movement.
• Protection: It shields vital organs, such as the heart and lungs, from injury.

Key Characteristics of Endoskeletons

1. Occurrence:
   - Found in a variety of vertebrates, including:

   • Mammals (e.g., humans, dogs)
   • Birds (e.g., eagles, sparrows)
   • Reptiles (e.g., snakes, lizards)
   • Amphibians (e.g., frogs, salamanders)
   • Fish (e.g., sharks, goldfish)

2. Composition:
   - The endoskeleton is primarily made up of:

   • Bone: A rigid connective tissue that forms the hard structure.
   • Cartilage: A more flexible connective tissue that provides cushioning and support.

3. Significance:
   - The endoskeleton is crucial for:

   • Supporting the body: It maintains shape and posture.
   • Facilitating movement: It allows for a wide range of motions, from running to flying.
   • Protecting vital organs: It encases and safeguards organs from external impacts.

Fun Facts About Endoskeletons! 🎉

• Did you know that the human skeleton is made up of 206 bones? This number can vary slightly due to individual differences.
• Some species, like certain fish, have a skeleton made entirely of cartilage, which makes them lighter and more agile in water!

In summary, the endoskeleton is a remarkable adaptation that enables vertebrates to thrive in diverse environments. Its ability to provide support and movement is essential for survival, making it a key topic in biology. For those looking to dive deeper, check out resources like support and movement MCQs and support and movement biology notes for more insights!

Endoskeleton Overview

Composition of Human Skeleton

The composition of the human skeleton is a fascinating topic that plays a crucial role in our ability to support and move. Let's dive deeper into the structure and function of our bones! 🦴

Overview of the Human Skeleton

The human skeleton is made up of 206 bones, which can be divided into two main categories:

1. Axial Skeleton:

   • Comprises the skull, vertebral column, and rib cage.
   • Provides central support and protects vital organs like the brain and heart.

2. Appendicular Skeleton:

   • Includes the limbs (arms and legs) and girdles (shoulder and pelvic).
   • Facilitates movement and interaction with our environment.

Bone Composition

Bones are not just rigid structures; they are complex organs made up of a unique matrix that includes:

• Collagen Fibers: These provide flexibility and tensile strength.
• Minerals: Primarily calcium phosphate, which gives bones their hardness and rigidity.

Key Components of the Skeleton

Understanding the components of the skeleton is essential for grasping how it supports our body. Here are the key players:

• Bones:

  • Rigid structures that form the skeleton and provide the framework for our body.
  • They also store minerals and produce blood cells.

• Cartilage:

  • A flexible tissue that cushions joints and allows for smooth movement.
  • Found in areas like the nose, ears, and between bones in joints.

• Bone Cells:

  • Osteoblasts: Responsible for bone formation.
  • Osteocytes: Mature bone cells that maintain bone tissue.
  • Osteoclasts: Cells that break down bone tissue, important for bone remodeling.

Fun Facts About Bones! 🎉

• The largest bone in the human body is the femur (thigh bone).
• The smallest bone is the stapes in the ear, which is about the size of a grain of rice!
• Bones are constantly being remodeled, with new bone being formed and old bone being broken down.

Importance of the Skeleton

The skeleton is vital for support and movement. It not only provides a framework for our body but also works in conjunction with muscles to enable us to perform various activities, from walking to jumping.

By understanding the composition and function of our skeleton, we can appreciate how it contributes to our overall health and mobility.

For those looking to explore this topic further, check out some support and movement MCQs or biology notes to deepen your knowledge! 📚

Human Skeleton Structure and Function

Gross Anatomy of Bones

The gross anatomy of bones is a fascinating topic that dives into the structural features of bones visible to the naked eye. Understanding these features is crucial for grasping how our skeletal system supports and facilitates movement. Let's break down the anatomy of a typical long bone, which serves as a prime example.

Main Regions of a Long Bone 🦴

A typical long bone consists of two main regions:

1. Diaphysis (Shaft):

   • This is the tubular shaft that runs along the length of the bone.
   • It plays a vital role in support and movement, providing leverage during various physical activities.
   • Inside the diaphysis lies the medullary cavity, which is filled with yellow bone marrow—a crucial component for fat storage and energy supply.

2. Epiphysis (Ends):

   • The epiphysis is the wider section at each end of the bone.
   • It is primarily involved in joint formation, connecting with other bones to facilitate movement.
   • The interior of the epiphysis contains spongy bone, which is lighter and provides structural support while housing red bone marrow—the site of blood cell production.

Key Features of Bone Anatomy 🔍

Here are some essential features to remember about bone anatomy:

• Bone Marrow:

  • This is the soft tissue found within the medullary cavity and spongy bone.
  • It is responsible for the production of blood cells, playing a critical role in our body's overall function.

• Compact vs. Spongy Bone:

  • Compact Bone: Dense and forms the outer layer, providing strength and protection.
  • Spongy Bone: Found mainly in the epiphysis, it is less dense and contains many small spaces, making it lightweight yet strong.

Importance of Bone Structure in Support and Movement 💪

The structural features of bones are not just for show; they are intricately designed to support and facilitate movement. Here’s how:

• Leverage: The diaphysis acts as a lever, allowing muscles to exert force and create movement.
• Joint Formation: The epiphysis connects with other bones at joints, enabling a range of motions from bending to rotation.
• Blood Cell Production: Healthy bone marrow is essential for producing red and white blood cells, which are vital for oxygen transport and immune function.

By understanding the gross anatomy of bones, we can appreciate how they contribute to our body's support and movement. Whether you're studying for support and movement MCQs or reviewing support and movement biology notes, knowing these details can enhance your comprehension of human anatomy!

Gross Anatomy of Long Bones

Structure of Bone Tissue

Bone tissue is a fascinating and specialized form of connective tissue that plays a crucial role in providing strength and support to our skeleton. Understanding its structure is essential for grasping how our bodies function and move. Let's dive into the two main types of bone tissue and their components!

Types of Bone Tissue 🦴

1. Compact Bone:

   • This is the dense outer layer of bones.
   • It provides strength and is essential for support and movement.
   • Compact bone is structured in a way that allows it to withstand compressive forces.

2. Spongy Bone:

   • Also known as cancellous bone, it is lighter and less dense.
   • Contains trabeculae, which are small, rod-like structures that provide structural support.
   • Spongy bone is typically found at the ends of long bones and within the interior of others, helping to reduce weight without sacrificing strength.

Key Components of Bone Tissue 🔑

• Osteons:

  • The functional unit of compact bone.
  • Composed of concentric rings of bone matrix, which are crucial for the bone's strength.
  • Each osteon contains a central canal that houses blood vessels and nerves.

• Bone Cells:

  • Osteoblasts: These cells are responsible for building new bone. They secrete the bone matrix and are essential for growth and healing.
  • Osteocytes: Once osteoblasts become trapped in the matrix they create, they transform into osteocytes, which maintain the bone tissue.
  • Osteoclasts: These cells break down bone tissue, a process vital for bone remodeling and calcium release.

• Matrix:

  • The matrix of bone tissue is composed of collagen fibers and mineral deposits (mainly calcium phosphate).
  • This combination provides both flexibility and strength, allowing bones to support our body while also being resilient to stress.

Fun Facts About Bone Tissue! 🎉

• Did you know that bones are constantly being remodeled? This means that old bone is broken down and replaced with new bone throughout your life!
• The human body has about 206 bones, and they all contain some form of bone tissue that contributes to support and movement.

Understanding the structure of bone tissue is not just about knowing the types and components; it's about appreciating how these elements work together to keep us moving and active! Whether you're studying for support and movement MCQs or reviewing your support and movement biology notes, knowing the ins and outs of bone tissue is essential for grasping the complexities of human anatomy.

Structure and Function of Bone Tissue

Types of Cartilage

Types of Cartilage

Cartilage is an essential flexible connective tissue that plays a crucial role in providing support and cushioning throughout various parts of the body. It is vital for maintaining the structure and function of many organs and joints. There are three primary types of cartilage, each with unique properties and functions that cater to specific needs within the body. Let’s dive deeper into each type!

1. Hyaline Cartilage 🦴

• Description: This is the most common type of cartilage found in the human body.
• Location:
  • Joints: Covers the ends of bones, allowing for smooth movement.
  • Rib Tips: Connects ribs to the sternum, providing flexibility.
  • Trachea: Keeps the airway open, ensuring proper airflow.
• Function:
  • Provides a smooth surface for joint movement.
  • Acts as a cushion to absorb shock during physical activities.

2. Fibrocartilage 💪

• Description: This type contains dense bundles of collagen fibers, making it tough and resilient.
• Location:
  • Intervertebral Discs: Acts as a shock absorber between the vertebrae.
  • Pubic Symphysis: Located between the left and right pubic bones, providing stability.
• Function:
  • Offers tensile strength, allowing it to withstand pressure and tension.
  • Absorbs shock, protecting bones during heavy lifting or high-impact activities.

3. Elastic Cartilage 🎶

• Description: This cartilage is characterized by a high concentration of elastic fibers, giving it flexibility.
• Location:
  • Ear: Provides shape and support while allowing for flexibility.
  • Epiglottis: Helps prevent food from entering the windpipe during swallowing.
• Function:
  • Maintains the shape of structures while allowing for bending and movement.
  • Provides support without compromising flexibility.

Summary of Cartilage Types

Understanding the different types of cartilage is essential for grasping how our bodies maintain support and movement. Each type serves a specific purpose, ensuring that we can move freely and without pain. Whether it's the smooth gliding of hyaline cartilage in our joints or the shock absorption of fibrocartilage in our spine, cartilage is a vital component of our musculoskeletal system.

For those interested in testing their knowledge, check out some support and movement MCQs or refer to support and movement biology notes for further study!

Types of Cartilage and Their Functions

Division of Human Skeleton

Understanding the Division of the Human Skeleton 🦴

The human skeleton is an incredible structure that serves as the framework for our bodies. It is divided into two main parts: the axial skeleton and the appendicular skeleton. This division is essential for grasping how our skeletal system is organized and how it functions to support and facilitate movement.

1. Axial Skeleton: The Core of Support 🛡️

The axial skeleton is the central part of our skeleton, and it includes:
- Skull: Protects the brain and supports facial structure.
- Vertebral Column: Composed of vertebrae, it safeguards the spinal cord and provides flexibility.
- Rib Cage: Encloses vital organs like the heart and lungs, offering protection while allowing for breathing.

Key Functions:
- Central Support: Acts as the main support structure for the body.
- Protection: Shields the brain and spinal cord from injury.

2. Appendicular Skeleton: Enabling Movement 🚶‍♂️

The appendicular skeleton is all about movement and includes:
- Limbs: Arms and legs that allow us to interact with our environment.
- Girdles: The shoulder girdle (scapula and clavicle) and pelvic girdle (hip bones) connect the limbs to the axial skeleton.

Key Functions:
- Facilitates Movement: Enables a wide range of motions, from walking to throwing.
- Interaction with Environment: Essential for activities like grasping, lifting, and running.

Fun Fact: Total Bones in the Adult Skeleton

Did you know that the adult human skeleton consists of 206 bones? This number can vary slightly due to individual differences, such as the presence of extra bones called accessory bones.

Why This Division Matters

Understanding the division of the human skeleton into axial and appendicular parts is crucial for:
- Studying Anatomy: Helps in learning about the body's structure and functions.
- Medical Applications: Essential for diagnosing injuries and conditions related to bones and joints.

By grasping these concepts, you can better appreciate how our bodies are designed for both support and movement. Whether you're preparing for exams with support and movement MCQs or reviewing support and movement biology notes, this foundational knowledge is key!

Division of the Human Skeleton

Joints

Understanding Joints: The Key to Support and Movement 🦴

Joints are essential components of our skeletal system, acting as the connections between bones that enable us to move and maintain flexibility. Without joints, our ability to perform daily activities—like walking, running, or even waving hello—would be severely limited! Let's dive deeper into the fascinating world of joints and their classifications.

What Are Joints? 🤔

Joints can be defined as the areas where two or more bones meet. They play a crucial role in providing support and movement to our bodies. Depending on their structure and function, joints can be classified into several categories:

Key Classifications of Joints

1. Fibrous Joints 🧩

   • Description: These joints are connected by dense connective tissue, primarily made up of collagen fibers.
   • Movement: Generally immovable.
   • Example: Sutures found in the skull, which protect the brain and maintain the shape of the head.

2. Cartilaginous Joints 🦷

   • Description: In these joints, bones are connected by cartilage, providing a cushion between them.
   • Movement: Allow for limited movement, making them more flexible than fibrous joints.
   • Example: Intervertebral discs in the spine, which help absorb shock and allow for slight movement.

3. Synovial Joints 💧

   • Description: The most common type of joint in the body, these joints have a fluid-filled cavity that allows for smooth movement.
   • Movement: Freely movable, enabling a wide range of motion.
   • Examples:
     • Knee Joint: Supports weight and allows for bending and straightening.
     • Elbow Joint: Enables the arm to flex and extend.

Why Are Joints Important? 🌟

• Facilitate Movement: Joints allow us to perform various movements, from simple actions like bending our fingers to complex activities like dancing.
• Provide Stability: They help maintain posture and balance, ensuring our bodies remain upright and coordinated.
• Absorb Shock: Certain joints, especially cartilaginous ones, act as shock absorbers, protecting bones from impact during physical activities.

Fun Facts About Joints! 🎉

• Did you know that the human body has over 200 joints? That's a lot of connections!
• The largest joint in the body is the knee, while the smallest is in the ear (the stapes bone).
• Regular exercise can help keep your joints healthy and improve flexibility!

By understanding the different types of joints and their functions, we can appreciate how they contribute to our overall support and movement. Whether you're studying for your biology exam or just curious about how your body works, knowing about joints is fundamental!

For more insights, check out our support and movement MCQs and support and movement biology notes to enhance your knowledge!

Classification of Joints in the Human Skeleton

Arthritis

Arthritis: Understanding the Basics 🦴

Arthritis is a common disorder that affects millions of people worldwide. It is characterized by inflammation of the joints, which can lead to pain, stiffness, and reduced mobility. This condition can significantly impact daily life, making it essential to understand its types, causes, and symptoms.

Key Types of Arthritis

There are several types of arthritis, each with unique characteristics. Here are the most prevalent ones:

1. Osteoarthritis (OA) 🦵

   • This is a degenerative joint disease that occurs due to the wear and tear of cartilage.
   • Commonly affects older adults, especially those who have experienced joint injuries or have a family history of OA.
   • Symptoms include:
     • Joint pain during or after movement
     • Stiffness, particularly in the morning or after sitting for long periods
     • Swelling and tenderness around the affected joints

2. Rheumatoid Arthritis (RA) 🤕

   • An autoimmune disorder where the immune system mistakenly attacks the joint tissues.
   • Can affect people of any age, but often begins in middle age.
   • Symptoms include:
     • Symmetrical joint pain (affecting both sides of the body)
     • Morning stiffness lasting more than 30 minutes
     • Fatigue and general malaise

3. Gout 🍷

   • Caused by the accumulation of uric acid crystals in the joints, leading to sudden and severe pain.
   • Often affects the big toe but can occur in other joints as well.
   • Symptoms include:
     • Intense pain that comes on suddenly, often at night
     • Redness and swelling in the affected area
     • Sensitivity to touch

Managing Arthritis: Support and Movement

Living with arthritis can be challenging, but there are ways to manage symptoms effectively. Here are some strategies to promote support and movement:

• Physical Therapy: Working with a physical therapist can help improve joint function and reduce pain through tailored exercises.
• Medication: Over-the-counter pain relievers and anti-inflammatory drugs can help manage symptoms.
• Lifestyle Changes:
  • Maintain a healthy weight to reduce stress on joints.
  • Engage in low-impact exercises like swimming or cycling to keep joints moving without excessive strain.
• Support Groups: Connecting with others who have arthritis can provide emotional support and practical tips for coping.

By understanding the different types of arthritis and implementing effective management strategies, individuals can enhance their quality of life and maintain their support and movement.

Types of Arthritis and Their Characteristics

Conclusion

In conclusion, the intricate interplay between the skeletal and muscular systems is fundamental to the concepts of support and movement in animals. The skeletal system provides the essential framework that shapes, supports, and protects vital organs, while the muscular system facilitates locomotion through coordinated contractions. Understanding the structure and function of bones, joints, and muscles is crucial for comprehending how these systems work together to enable movement. As you prepare for the MDCAT exam, focusing on the key concepts of support and movement, along with practicing relevant MCQs, will enhance your grasp of this essential topic in biology. Remember, mastering these concepts not only aids in your exam preparation but also lays the foundation for a deeper understanding of human physiology and anatomy.

FAQs

Q: What is the role of the skeletal system in support and movement?

A: The skeletal system provides structure, support, and protection for internal organs, while also enabling movement through its interaction with the muscular system. Together, they form the musculo-skeletal system, which is essential for locomotion in higher animals.

Q: How do joints contribute to movement?

A: Joints are connections between bones that allow for a range of movements. They can be classified into different types such as fibrous, cartilaginous, and synovial joints, each permitting varying degrees of mobility. The structure of joints facilitates smooth movement and flexibility in the skeletal system.

Q: What is the sliding filament theory?

A: The sliding filament theory explains how muscles contract. According to this theory, muscle fibers shorten as the thin (actin) and thick (myosin) filaments slide past each other during contraction, which is triggered by the interaction of myosin heads with actin binding sites.

Q: What are the different types of muscles involved in support and movement?

A: There are three types of muscles involved in support and movement: skeletal muscles, which are voluntary and striated; cardiac muscles, which are involuntary and found in the heart; and smooth muscles, which are involuntary and found in various organs. Each type plays a unique role in facilitating movement.

Q: How does the nervous system coordinate support and movement?

A: The nervous system coordinates the skeletal and muscular systems by sending signals that trigger muscle contractions and regulate joint movements. This coordination is essential for maintaining balance, posture, and executing complex movements.

Q: What is the significance of cartilage in the skeletal system?

A: Cartilage is a flexible connective tissue that provides cushioning at joints, supports structures such as the nose and ears, and allows for smooth movement between bones. It also plays a crucial role in the growth and development of long bones.

Q: What are the common disorders affecting support and movement?

A: Common disorders affecting support and movement include arthritis, which causes joint inflammation and pain; osteoporosis, which leads to weakened bones; and muscular dystrophies, which affect muscle strength and function. These conditions can significantly impact mobility and quality of life.

Q: How does exercise influence the musculo-skeletal system?

A: Regular exercise strengthens muscles, improves joint flexibility, and enhances bone density. It promotes better coordination and balance, which are essential for effective support and movement. Exercise also helps prevent injuries and conditions like osteoporosis.