Cells & Tissues: What's The Relationship?

Alright, let's dive right into the fascinating world within us! Think of your body as a bustling city, where every structure and function is carefully organized. In this incredible metropolis, cells are like the individual building blocks, similar to the foundational work of Robert Hooke, who first observed cells. These cells, the basic units of life, then come together to form tissues, which are akin to specialized departments, such as the epithelial tissues that act as protective barriers. Understanding histology, the study of these tissues, is vital to figuring out how these departments cooperate. It really makes you think, doesn't it: what is the relationship between cells and tissues, and how do they work together to keep the entire city—your body—running smoothly, just like the interconnected studies at the National Institutes of Health (NIH) seek to uncover the mysteries of life?

Diving into the Microscopic World: Cells and Tissues - The Foundation of Life

Ever wondered what makes you, you? The answer, in its most fundamental form, lies in the microscopic realm of cells and tissues.

These tiny building blocks aren't just random specks; they're the very essence of life, orchestrating a symphony of functions that keep us going.

But why should we care about something so small? Because understanding cells and tissues is the key to understanding everything about how our bodies work.

Cells: The Basic Units of Life

Think of cells as the individual members of a highly skilled team, each with their own unique job.

Some cells are like tiny messengers, carrying information throughout the body. Others are like tireless workers, building and repairing tissues. Still others are like fierce protectors, defending us against invaders.

Cells are the fundamental units of life, performing diverse and essential functions.

From energy production to waste removal, cells are constantly working to maintain a stable internal environment – a state known as homeostasis.

Each cell, regardless of its specific role, contributes to the overall health and well-being of the organism.

Tissues: The Organized Workforce

Now, imagine those individual team members coming together to form larger groups, each specializing in a particular task. That's essentially what tissues are.

Tissues are groups of similar cells that work together to perform a specific function.

Epithelial tissue forms protective barriers. Connective tissue provides support and structure. Muscle tissue enables movement. Nervous tissue transmits signals.

These tissues aren't just randomly arranged; they're carefully organized to create complex organs and systems.

Think of your heart, your lungs, your brain – all intricate structures built from different types of tissues working in perfect harmony.

Each type of tissue contributes uniquely to the functionality of the organ and the overall system.

The Integrated Nature of Life

The magic truly happens when cells and tissues work together seamlessly.

Cells form tissues, tissues form organs, and organs form systems, all interconnected and interdependent.

Imagine a complex machine where each part relies on the others to function properly. That's how our bodies work, with cells and tissues playing the starring roles.

When this intricate system is disrupted – due to disease, injury, or genetic defects – the consequences can be significant.

Understanding the integrated nature of cells and tissues is crucial for maintaining health and addressing medical challenges.

By studying these microscopic components, we can gain valuable insights into the workings of life itself.

Cell Biology: The Foundation of Life

Diving into the Microscopic World: Cells and Tissues. The Foundation of Life.

Ever wondered what makes you, you? The answer, in its most fundamental form, lies in the microscopic realm of cells.

Cells are the basic units of life, and to truly understand biology, we need to zoom in and explore their fascinating world. It’s a journey into miniature marvels, where structure dictates function and processes are finely tuned to maintain life.

Unveiling the Cellular Structure: A World of Organelles

Imagine a bustling city, but instead of buildings and streets, it's filled with organelles, each with a specific job. The cell membrane acts as the city walls, controlling what enters and exits, and keeping the inner workings safe.

Inside, you'll find the nucleus, the control center containing the cell's genetic blueprint, DNA.

Think of DNA as the architect's plans, guiding every process within the cell.

Then there are the mitochondria, the power plants of the cell, generating energy in the form of ATP. These powerhouses fuel all cellular activities, from muscle contraction to protein synthesis.

Ribosomes are the construction crews, synthesizing proteins based on the DNA instructions.

The endoplasmic reticulum (ER) acts as a manufacturing and transport network, with the rough ER studded with ribosomes for protein production, and the smooth ER responsible for lipid synthesis and detoxification.

The Golgi apparatus is the packaging and shipping center, modifying and sorting proteins before sending them to their final destinations.

Lysosomes are the recycling plants, breaking down waste materials and cellular debris.

Each organelle plays a vital role, working in harmony to keep the cell alive and functioning optimally.

Essential Cellular Processes: The Engine of Life

Cells aren't just static structures; they're dynamic systems constantly engaged in essential processes.

Metabolism is the sum of all chemical reactions that occur within a cell, providing energy and building blocks for growth and repair.

It's a complex dance of breaking down nutrients and building complex molecules.

Protein synthesis is the process of creating proteins from amino acids, guided by the genetic code.

This is crucial for building enzymes, structural components, and signaling molecules.

Transport mechanisms allow cells to move materials across their membranes, taking in nutrients and expelling waste. This includes passive diffusion, facilitated transport, and active transport.

These essential processes are tightly regulated, ensuring that the cell functions efficiently and responds appropriately to its environment.

The Importance of Understanding Cells: A Foundation for Discovery

Cell biology is more than just memorizing organelle names and processes; it's about understanding the fundamental principles of life.

By unraveling the mysteries of the cell, we can gain insights into disease, develop new therapies, and ultimately improve human health. Whether you're a student, a researcher, or simply curious about the world around you, exploring the fascinating world of cell biology is a journey worth taking. So, buckle up and prepare to be amazed by the microscopic marvels that make us who we are.

Key Cellular Processes: Differentiation, Communication, Apoptosis, and Mitosis

Cells are the fundamental units of life, but what truly orchestrates the symphony of our bodies? It's a fascinating quartet of processes: differentiation, communication, apoptosis, and mitosis. These four processes are the cornerstones of development, function, and maintenance within our tissues and organisms. Let's dive into each of these crucial functions and explore their intricacies!

Cell Differentiation: Becoming a Specialist

Think of cell differentiation as a cell's journey to becoming a specialist.

Each cell starts with the potential to become any cell type in the body, much like a blank canvas.

However, through differentiation, cells embark on a path to acquire specialized structures and functions.

The Path to Specialization

Differentiation is guided by a complex interplay of genetic signals and environmental cues.

Specific genes are activated or deactivated, leading to the production of unique proteins.

These proteins then dictate the cell's shape, size, and function.

For instance, a muscle cell differentiates to produce large amounts of contractile proteins, enabling movement.

In contrast, a nerve cell differentiates to form long extensions, allowing for rapid signal transmission.

Cell Communication: The Art of Cellular Conversation

Cells aren't isolated islands; they thrive in a community, constantly communicating with each other.

This communication ensures that cells coordinate their activities to maintain tissue homeostasis and respond to changes in the environment.

Methods of Communication

Cells employ a diverse array of signaling molecules to "talk" to their neighbors.

These molecules can be hormones, growth factors, or neurotransmitters.

They bind to specific receptors on the surface of target cells, triggering a cascade of intracellular events.

This cascade ultimately alters the target cell's behavior.

Cell communication is vital for everything from coordinating muscle contractions to regulating immune responses.

Apoptosis: Programmed Cell Death

Death is an inevitable part of life, even at the cellular level.

Apoptosis, or programmed cell death, is a tightly controlled process that eliminates unwanted or damaged cells.

It's essential for normal development, tissue homeostasis, and preventing the spread of disease.

The Importance of Cellular Housekeeping

Apoptosis plays a critical role in sculpting tissues during embryonic development.

It also eliminates cells that are infected with viruses or have sustained DNA damage.

Dysregulation of apoptosis can have severe consequences.

Too much apoptosis can lead to degenerative diseases, while too little can contribute to cancer.

Mitosis: The Miracle of Cell Division

Mitosis is the process by which a single cell divides into two identical daughter cells.

It's essential for growth, repair, and asexual reproduction.

Steps to Replication

Mitosis is a carefully orchestrated process that involves several distinct phases.

During these phases, the cell's chromosomes are duplicated, separated, and distributed equally to the daughter cells.

The result is two genetically identical cells, ready to carry on the functions of their parent.

This process of cell division is responsible for building our bodies from a single fertilized egg.

It also ensures that tissues can repair themselves after injury.

By mastering these key cellular processes, we unlock deeper insight into the workings of life itself.

The Four Primary Tissue Types: A Symphony of Structure and Function

[Key Cellular Processes: Differentiation, Communication, Apoptosis, and Mitosis Cells are the fundamental units of life, but what truly orchestrates the symphony of our bodies? It's a fascinating quartet of processes: differentiation, communication, apoptosis, and mitosis. These four processes are the cornerstones of development, function, and maintenance. But what about the building blocks themselves? Let's explore the four primary tissue types – epithelial, connective, muscle, and nervous – and how they collaborate to form the remarkable architecture of the human body.]

Each tissue type has unique characteristics and roles, contributing to the overall functionality and vitality of our being. Understanding their structure and functions unlocks a deeper appreciation for the intricate design of life.

Epithelial Tissue: The Body's Versatile Barrier

Epithelial tissue acts as a protective barrier, a selective gatekeeper, and a secretory powerhouse, all rolled into one. Think of it as the body's first line of defense against the outside world.

It's also responsible for absorption and secretion in various organs.

Functions of Epithelial Tissue

Epithelial tissue performs many crucial tasks, including:

• Protection: Shielding underlying tissues from damage, dehydration, and invasion by pathogens.
• Secretion: Releasing hormones, enzymes, sweat, and other substances.
• Absorption: Taking in nutrients and other molecules from the environment.
• Filtration: Filtering fluids in the kidneys.
• Excretion: Ridding the body of waste products.

Types and Arrangements of Epithelial Cells

The shape and arrangement of epithelial cells are closely related to their function. You'll find them in various forms, such as:

• Squamous: Thin, flat cells ideal for diffusion and filtration (e.g., lining of blood vessels and air sacs of the lungs).
• Cuboidal: Cube-shaped cells involved in secretion and absorption (e.g., kidney tubules and glands).
• Columnar: Tall, column-shaped cells specialized for secretion and absorption (e.g., lining of the digestive tract).
• Transitional: Able to change shape, allowing organs to stretch (e.g., urinary bladder).
• Pseudostratified Columnar: Appears layered, but all cells attach to the basement membrane (e.g., lining of the trachea).

Epithelial cells can be arranged in single layers (simple epithelium) or multiple layers (stratified epithelium). This layering provides increased protection in areas subject to abrasion.

Connective Tissue: Providing Support and Structure

Connective tissue is the body's structural framework, providing support, connection, and separation. It's incredibly diverse, ranging from the hard matrix of bone to the fluid consistency of blood.

Roles of Connective Tissue

Connective tissue's main functions are:

• Support: Providing a framework for the body and its organs.
• Connection: Linking tissues and organs together.
• Protection: Cushioning and insulating organs.
• Transportation: Transporting fluids, nutrients, and waste products.
• Immunity: Housing immune cells that fight infection.

Types of Connective Tissue

Let's examine a few types of connective tissue:

• Bone: Provides rigid support and protects vital organs.
• Cartilage: Provides flexible support and cushions joints.
• Blood: Transports oxygen, nutrients, and waste products.
• Adipose: Stores energy, insulates the body, and cushions organs.
• Dense Connective Tissue: Tendons, ligaments
• Loose Connective Tissue: Underlies most epithelia

Fibroblasts and the Extracellular Matrix (ECM)

A key component of connective tissue is the extracellular matrix (ECM), a complex network of proteins and other molecules secreted by cells called fibroblasts. Fibroblasts are the workhorses of connective tissue.

The ECM provides structural support, regulates cell behavior, and facilitates cell-to-cell communication.

Muscle Tissue: The Engine of Movement

Muscle tissue is responsible for movement, enabling us to walk, talk, breathe, and perform countless other actions. It achieves this through contraction, shortening its cells to generate force.

Types of Muscle Tissue

There are three types of muscle tissue, each with its own unique characteristics:

• Skeletal Muscle: Attached to bones, responsible for voluntary movement. It appears striated (striped) under a microscope.
• Smooth Muscle: Found in the walls of internal organs, such as the stomach, intestines, and blood vessels. It's responsible for involuntary movements like digestion and blood pressure regulation. It has a smooth, non-striated appearance.
• Cardiac Muscle: Found only in the heart, responsible for pumping blood throughout the body. It's also striated but has unique features that allow it to contract rhythmically and continuously.

Nervous Tissue: The Body's Communication Network

Nervous tissue is the body's communication network, transmitting electrical signals throughout the body. It allows us to perceive our environment, think, feel, and control our actions.

Neurons and Glial Cells

Nervous tissue is composed of two main types of cells:

• Neurons: Generate and transmit electrical signals called nerve impulses.
• Glial cells: Support, protect, and nourish neurons. They play a vital role in maintaining the health and function of the nervous system.

Nervous tissue is found in the brain, spinal cord, and nerves. It's responsible for coordinating all of the body's activities.

Related Disciplines: Histology, Anatomy, and Physiology

After exploring the intricate world of cells and tissues, it's time to zoom out and appreciate the broader scientific disciplines that dedicate themselves to understanding these fundamental building blocks. Think of histology, anatomy, and physiology as interconnected lenses through which we view the miracle of life. Each provides a unique perspective, but they all work together to give us a complete picture.

Histology: Unveiling the Microscopic Architecture

Histology is your guide to the hidden world visible only through a microscope. Imagine yourself as an architect, but instead of designing buildings, you're studying the intricate arrangement of cells in tissues.

Histologists prepare tissue samples, carefully slicing them and staining them with dyes to highlight different structures. By examining these stained sections, they can identify tissue types, diagnose diseases, and unravel the mysteries of cellular organization.

It's like having a detailed map of the cellular landscape, allowing you to see how each component fits into the bigger picture.

Anatomy: Charting the Body's Grand Design

While histology focuses on the microscopic, anatomy takes a step back to examine the overall structure of the body. Anatomists study organs, systems, and their relationships to one another.

Think of anatomy as the art of understanding the whole human form.

They use techniques like dissection, imaging, and observation to map out the body's intricate design. Anatomy provides the framework for understanding how tissues and cells fit together to form functional units.

Physiology: Deciphering the Body's Inner Workings

Physiology is all about function– how cells, tissues, and organs work together to keep us alive and thriving. Physiologists explore the mechanisms that govern everything from muscle contraction to nerve impulses.

They investigate how the body maintains homeostasis, responds to stimuli, and performs its essential functions.

Physiology builds upon the knowledge gained from histology and anatomy to explain how structure relates to function. It's a dynamic field that constantly seeks to unravel the complexities of life's processes.

The Interconnectedness of It All

Histology, anatomy, and physiology aren't isolated fields. They're intertwined like the threads of a tapestry.

Understanding the microscopic structure of a tissue (histology) informs our understanding of its location and organization within the body (anatomy), which then helps us understand how it functions (physiology). For example, understanding the structure of lung tissue (histology) helps us understand how the lungs are organized within the respiratory system (anatomy) and how they facilitate gas exchange (physiology).

By integrating these three disciplines, we gain a complete and holistic view of the human body.

Think of them as different pieces of a puzzle that fit together to reveal the full picture of life.

Tools and Techniques for Studying Cells and Tissues

After outlining the disciplines that closely study cells and tissues, it's time to explore the practical side: the tools and techniques that allow us to actually see and analyze these microscopic marvels.

From the fundamental microscope to cutting-edge molecular techniques, these methods are essential for unlocking the secrets of cellular life. Let's dive in!

Essential Tools: The Foundation of Cellular Observation

These are the bread-and-butter techniques that form the basis of any cellular investigation.

Without them, much of what we know about cells and tissues would remain a mystery.

The Mighty Microscope: Window to the Microscopic World

Microscopes are the indispensable tool for visualizing cells and tissues.

They magnify tiny structures beyond the limit of the naked eye, revealing a world of intricate details.

Different types of microscopes offer varying levels of magnification and resolution.

Light microscopes are commonly used for basic observation, while electron microscopes provide incredibly high resolution for examining ultrastructural details.

Whether it's a simple observation of cell shape or a detailed study of organelles, the microscope is our primary window into the cellular realm.

Histological Staining: Painting the Cellular Canvas

While microscopes allow us to see cells, histological staining techniques enhance our ability to distinguish between different cellular components.

Staining involves applying dyes or chemicals that selectively bind to specific structures within cells and tissues, making them more visible under the microscope.

Hematoxylin and eosin (H&E) staining is a widely used technique that stains nuclei blue and cytoplasm pink.

This simple yet effective method allows pathologists to identify different cell types, assess tissue organization, and diagnose diseases.

Other staining methods, such as immunohistochemistry (which we'll explore later), target specific proteins to further refine our understanding of cellular function.

Advanced Techniques: Unlocking Cellular Secrets

Moving beyond basic observation, advanced techniques allow us to probe deeper into the molecular workings of cells and tissues.

These methods provide valuable insights into gene expression, protein activity, and cellular interactions.

Immunohistochemistry (IHC): Spotting Specific Proteins

Immunohistochemistry (IHC) is a powerful technique that uses antibodies to detect specific proteins within tissue samples.

Essentially, we're tagging a protein of interest with a marker that we can then visualize under a microscope.

How does it work? Antibodies are designed to bind specifically to the target protein.

These antibodies are then linked to a detectable label, such as a fluorescent dye or an enzyme that produces a colored product.

IHC is widely used in research and diagnostics to study protein expression patterns, identify tumor markers, and assess the effectiveness of drug treatments.

It's like having a GPS for specific molecules within a complex cellular landscape.

Cell Culture: Growing Cells in the Lab

Cell culture involves growing cells in a controlled laboratory environment, providing a powerful platform for studying cellular behavior and function.

Researchers can grow cells in specialized containers (like petri dishes or flasks) with the right nutrients, temperature, and other environmental factors.

This allows them to perform experiments on a population of cells.

Why is this important? Cell culture allows us to study cellular processes in isolation, without the complexity of the whole organism.

It’s valuable for drug discovery, toxicology testing, and basic research into cell biology.

Plus, it's an essential step in creating tissues for regenerative medicine!

When Things Go Wrong: Diseases and Conditions Related to Cells and Tissues

After exploring the amazing world of cells and tissues, and how they work together, let's face a difficult truth. Sometimes, these intricate systems break down, leading to disease. Here, we'll delve into some common conditions linked to cellular and tissue dysfunction, focusing on cancer, fibrosis, and inflammation. Understanding these processes is crucial for developing better treatments and, hopefully, preventing these conditions in the first place.

Cancer: Uncontrolled Growth

Cancer. Just the word itself can evoke fear. But what is cancer at its core? Simply put, it's a disease of uncontrolled cell growth. Our bodies have built-in mechanisms to regulate how cells divide and die. However, sometimes these mechanisms fail, leading to cells dividing uncontrollably and forming tumors.

The Breakdown of Cellular Regulation

So, how does this happen? Genetic mutations play a central role. These mutations can arise spontaneously during cell division or be caused by external factors like radiation or certain chemicals. These mutations can disrupt the cell cycle, allowing cells to bypass checkpoints that would normally prevent them from dividing with damaged DNA.

The Consequences of Uncontrolled Growth

The result is a mass of abnormal cells – a tumor – that can invade and damage surrounding tissues. Even worse, cancer cells can break away from the primary tumor and spread to other parts of the body through a process called metastasis. This is why early detection and treatment are so crucial. The sooner cancer is caught, the better the chances of preventing it from spreading and causing more damage.

Fibrosis: Too Much Connective Tissue

Imagine a scar forming after a cut. That's connective tissue doing its job, patching things up. But what happens when this process goes into overdrive? That's where fibrosis comes in. Fibrosis is the excessive accumulation of connective tissue, particularly collagen, in an organ or tissue.

The Impact of Excessive Connective Tissue Formation

Think of it like this: imagine you're trying to build a house but you're using way too much cement and not enough bricks. The structure becomes rigid and inflexible, hindering its normal function. Similarly, in fibrosis, the excessive collagen deposition distorts the tissue architecture, leading to impaired function.

Organs Affected by Fibrosis

Fibrosis can affect various organs, including the lungs (pulmonary fibrosis), liver (cirrhosis), heart (cardiac fibrosis), and kidneys (renal fibrosis). In each case, the excessive connective tissue interferes with the organ's ability to perform its normal functions, leading to a range of symptoms and complications.

Inflammation: The Body's Response

Inflammation is the body's natural response to injury or infection. It's a complex process involving immune cells, blood vessels, and inflammatory molecules. While acute inflammation is a necessary and beneficial process, chronic inflammation can be harmful.

The Role of Inflammation

Think of inflammation as a first responder to an accident. It sends in reinforcements (immune cells) to clean up the damage and start the healing process. Blood vessels dilate, bringing more blood flow to the area, resulting in redness and swelling. Inflammatory molecules signal to other cells to join the fight.

When Inflammation Becomes Chronic

However, when inflammation persists for a long time, it can damage healthy tissues and contribute to various diseases. Chronic inflammation has been linked to heart disease, arthritis, diabetes, and even cancer.

Causes of Chronic Inflammation

Chronic inflammation can be triggered by persistent infections, autoimmune disorders, and chronic exposure to irritants. Lifestyle factors, such as diet and stress, can also play a role. Understanding the causes and mechanisms of chronic inflammation is crucial for developing strategies to manage and prevent these debilitating conditions.

Real-World Applications: Tissue Engineering and Regenerative Medicine

After exploring the amazing world of cells and tissues, and how they work together, let's face a difficult truth. Sometimes, these intricate systems break down, leading to disease. Here, we'll delve into some common conditions linked to cellular and tissue dysfunction, focusing on how tissue engineering and regenerative medicine offer hope by harnessing our understanding of cells and tissues to repair, replace, or regenerate damaged or diseased parts of the body. It's not science fiction anymore; it's happening now!

Building New Tissues: The Foundation of Regeneration

Tissue engineering is a revolutionary field that combines cells, biomaterials, and growth factors to create functional tissues and even entire organs.

Think of it as building with biological LEGOs!

The possibilities are vast, offering potential solutions for everything from repairing damaged cartilage to creating artificial skin for burn victims. But how does it all work?

The Tissue Engineering Process: A Step-by-Step Guide

Here’s a breakdown of the typical tissue engineering process:

Cell Source Selection and Expansion

First, you need the building blocks: cells!

Researchers carefully select the appropriate cell type for the tissue they want to create.

These cells can come from the patient themselves (autologous), a donor (allogeneic), or even induced pluripotent stem cells (iPSCs), which can be programmed to become almost any cell type in the body. The beauty of autologous cells is that they minimize the risk of immune rejection.

Once the cells are selected, they need to be multiplied in a lab setting. This involves growing the cells in a controlled environment with the right nutrients and growth factors.

Scaffold Creation: The Blueprint for Tissue

Next comes the scaffold. Think of it as the mold or framework that guides the cells as they grow into the desired tissue shape.

Scaffolds are typically made from biocompatible materials that can be natural (like collagen or alginate) or synthetic (like polymers).

The ideal scaffold is biodegradable, meaning it will eventually break down and be absorbed by the body as the new tissue develops.

The scaffold's design is crucial, as it needs to provide the right structure and support for cell attachment, growth, and differentiation.

Cell Seeding and Culture: Bringing Life to the Scaffold

Now it's time to introduce the cells to the scaffold!

This process, called cell seeding, involves carefully placing the cells onto the scaffold, ensuring they are evenly distributed and have access to nutrients.

The seeded scaffold is then placed in a bioreactor, a specialized incubator that mimics the conditions inside the body.

The bioreactor provides the cells with the optimal temperature, oxygen levels, and nutrients to grow and differentiate into the desired tissue type. It also provides mechanical stimulation, mimicking movements of the body.

Implantation and Integration: The Final Step

Finally, the engineered tissue is ready to be implanted into the patient.

Once implanted, the tissue needs to integrate with the surrounding host tissue, forming functional connections and receiving a blood supply.

This is a critical step, as the new tissue needs to be able to survive and function within the body long-term.

Highlighting the Potential for Healing and Regeneration

Tissue engineering holds immense promise for revolutionizing healthcare, especially when it comes to healing and regeneration.

Here are just a few examples of how it's being used today and what the future holds:

• Skin Grafts for Burn Victims: Engineered skin can be used to replace damaged skin in burn patients, reducing scarring and improving healing.
• Cartilage Repair for Joint Injuries: Engineered cartilage can be implanted into damaged joints, relieving pain and restoring mobility.
• Bone Regeneration for Fractures: Engineered bone grafts can be used to repair fractures and bone defects, promoting faster healing and reducing the need for amputation.
• Organ Replacement: While still in its early stages, researchers are working on engineering entire organs, such as kidneys, livers, and hearts, to address the critical shortage of donor organs.

The potential of tissue engineering and regenerative medicine is truly transformative.

As technology advances and our understanding of cells and tissues deepens, we can expect to see even more groundbreaking applications in the years to come. This is an exciting time to be involved in the field of biomedical engineering and regenerative medicine!

So, there you have it! Hopefully, you now understand that cells and tissues are inextricably linked. Simply put, the relationship between cells and tissues is that cells are the basic building blocks, and when similar cells work together to perform a specific function, they form tissues. Think of it like bricks (cells) making up a wall (tissue). Pretty neat, huh?