A&P Chapter 4: Tissue Level of Organization

[Four Main Groups - Overview]

Epithelial Tissue

• Function: Covers body surfaces, lines cavities, forms glands

• Structure → Function: Tightly packed cells arranged in sheets → ideal for protection, absorption, and secretion

[Four Main Groups - Overview]

Connective Tissue

• Function: Binds, supports, protects, and integrates body parts

• Structure → Function: Cells are spread within an extracellular matrix → provides strength, support, and flexibility

[Four Main Groups - Overview]

Muscle Tissue

• Function: Movement through contraction

• Types: Skeletal (voluntary), smooth, cardiac

• Structure → Function: Excitable, contractile cells → generate force and movement

[Four Main Groups - Overview]

Nervous Tissue

• Function: Communication via nerve impulses

• Structure → Function: Excitable cells that transmit electrochemical signals → enable rapid coordination

3 Major Germ Layers/Embryonic Tissues

• Ectoderm (outer): forms nervous tissue and epithelium (skin)

• Mesoderm (middle): forms muscle and connective tissue (skeletal, muscular, and circulatory systems)

• Endoderm (inner): forms internal epithelial linings (digestive/respiratory tracts)

[Tissue Membranes]

Mucous Membrane

• Composed of epithelial tissue.

• Line body cavities that are open to outside (digestive tract, respiratory tract, urogenital tract)

• Wet/moist membranes because they secrete mucous = reduces friction and facilitates absorption/secretion

[Tissue Membranes]

Serous Membrane

• Composed of mesothelium (simple squamous epithelium), supported by areolar tissue

• Lines closed body cavities/organs

• Never exposed/connected to outside

• Secrete serous fluid = reduces friction

1. Types: pleura (lung), pericardium (heart), peritoneum (abdominal organs)

[Tissue Membranes]

Cutaneous Membrane (skin)

• Made of stratified squamos + areolar tissue + supported by dense irregular connective tissue

• Covers body surface

• Dry, relatively thick, and waterproof

[Tissue Membranes]

Synovial Membrane

• Line mobile joint cavities but don’t cover opposing joint surfaces

• Secretes synovial fluid

• Differs from epithelia because: develops within connective tissue, no basal lamina present, gaps between cells, and synovial fluid/capillaries exchange fluids

[Epithelial Tissues]

Functions of Epithelial Tissue

• Provides physical protection from abrasion, dehydration, and destruction

• Controls permeability (substances that enter/leave the body)

• Provides sensation: sensory nerves detect changes in environment

• Absorption/filtration

• Can produce secretions (glands)

[Epithelial Tissues]

Structure of Epithelial Tissue

• Sheets of tightly packed cells with little extracellular space

• Avascular (no blood vessels)

• Show polarity: apical surface (free/exposed) and basal surface (attached to basement membrane)

• Anchored by basement membrane/basal lamina.

  • clear layer/lamina lucida: contains glycoproteins + fine protein filaments

  • dense layer/lamina densa: bundles of coarse protein fibers = strength/filter

[Epithelial Tissues]

Characteristics of Epithelial Tissue

• Rapid regeneration (cells divide frequently)

• Cellularity: they form an effective barrier

  • Occluding junctions: form a barrier that isolates surfaces/deeper tissues from the lumen contents. Tight attachments = prevents passage of water/solutes.

  • Adhesion belt: locks together the webs of cells = strengthens region and prevents distortion/leakage at junctions.

  • Gap junction: permits chemical communication that coordinate cell activity. Two cells are held together by interlocking proteins (connexons) that serve as channels.

  • Desmosomes: provide firm attachments between neighboring cells by interlocking cytoskeletons.

    • Hemidesmosomes: attach basal surface to basement membrane.

  • CAM: cells adhesion molecules; transmembrane proteins that bind to each other/other materials. Present in adhesion belt/desmosomes.

[Epithelial Tissue]

Naming Epithelial Tissues

Arrangement

• simple: one layer thick

• stratified: more than one layer

• pseudostratified: false layers (look like more than one, but isn’t)

Shape

• squamos: thin, flat, irregular. look like fried eggs or pancake with butter (nucleus)

• cuboidal: equally wide and tall. hexagonal boxes with spherical nucleus in the center

• columnar: more tall than wide, resemble rectangles with elongated nuclei crowded into a narrow band near the basal lamina

[Epithelial Tissue]

Simple Squamos Epithelium

• Description: single layer of flattened cells with disc-shaped central nuclei

• Function: diffusion/filtration (can secrete lubricant)

• Locations: air sacs in lungs, kidney, linings of heart/lymphatic system

[Epithelial Tissue]

Stratified Squamos Epithelium

• Description: thick layers of flattened cells (can have keratinized/mitotic layer)

• Function: protection

• Locations: outer layer of skin, covers organs (mouth/female reproductive organs)

[Epithelial Tissue]

Simple Cuboidal Epithelium

• Description: single layer of cube-like cells with large spherical nucleus in center

• Function: absorption/secretion

• Locations: ovaries, kidneys, glands

[Epithelial Tissue]

Stratified Cuboidal Epithelium

• Description: rare in human body

• Locations: sweat glands, mammary glands, exocrine glands

[Epithelial Tissue]

Simple Columnar Epithelium

• Description: single layer of tall cells with round/oval nuclei (some can have cilia, goblet cells, or microvilli)

• Function: absorption, secretion of mucus/enzymes

• Locations:

  • non-ciliated: digestive tract (intestines), gallbladder, glands

  • ciliated: bronchi, uterine tubes, uterus

[Epithelial Tissue]

Stratified Columnar Epithelium

• Description: rare in human body

• Locations: lines large ducts (salivary glands/pancreas)

[Epithelial Tissue]

Pseudostratified Columnar Epithelium

• Description: single layer of cells of differing heights (nuclei at different heights)

• Function: secretion, propulsion by cilia

• Locations:

  • non-ciliated: male reproductive ducts

  • ciliated: respiratory tract

[Epithelial Tissue]

Transitional Epithelium

• Description: resembles both stratified squamos/cuboidal. basal cells are cuboidal/columnar

• Function: stretches readily + permits distension

• Locations: lines uterus, bladder, and urethra

[Glands]

Endocrine Glands

• “ductless” glands that produce hormones

• secret directly into interstitial fluids/bloodstream

  • ex: pituitary gland, adrenal gland, thyroid gland

[Glands]

Exocrine Glands

• have ducts

• secrete their substance either on body surfaces or within ducts

Different modes

• merocrine: most common; secrete products from secretory vesicles by exocytosis (ex: salivary glands)

• holocrine: accumulate products until cell ruptures. destroys the cell and must be replaced by cell division (ex: sebaceous glands of skin)

• apocrine: products accumulate within the cells then pinches off packets that contain the secretion (ex: mammary glands)

Cellular

• unicellular: goblet cells that produce mucin which mixes with water = mucus

• multicellular:

  • simple: single duct, doesn’t branch on its way to secretory cells

  • compound: duct divides one or more times on way to secretory cells

[Connective Tissue]

Characteristics of Connective Tissue

• most abundant/never exposed to outside

• all originate from mesenchyme

• ground substance: fills space between cells + surrounds extracellular fibers

Different kinds

• fibroblast cells: produce connective tissue proper

• chondrocytes: produce cartilage

• osteocytes: produce bone

• hemocytoblast cells: produce blood

Fibers

• elastic: slender, straight, stretchy

• collagen: thick, straight, form bundles = strong and resist stretching

• reticular: strong fibers that form branches

[Connective Tissue]

Functions of Connective Tissue

• establish structural framework

• transport fluids/materials

• protect delicate organs

• store energy reserves (triglycerides)

• defend body from invaders

[Connective Tissue]

Loose Connective Tissues (Connective Tissue Proper)

1. areolar tissue: most common, packing material. attaches skin to body parts. (AKA superficial fascia)

2. adipose tissue: fat; found deep in skin, forms layer of padding (made of adipocytes)

3. reticular tissue: provides support/resistance through tough/flexible network (stroma)

[Connective Tissue]

Dense Connective Tissue (Connective Tissue Proper)

1. dense regular: fibers oriented parallel to each other = strength along axis of collagen fibers. found in tendons and ligaments

2. dense irregular: non-parallel = interwoven network. provide strength in many directions

3. elastic: springy nature that allows extension/recoil

[Connective Tissue]

Ligaments

connect bones to bones

[Connective Tissue]

Tendons

connect bone to muscle

[Connective Tissue]

Fluid Connective Tissue

suspended in watery matrix that contains proteins

1. blood: flows in cardiovascular system

• plasma: watery matrix

• hemocytoblasts:

  • erythrocytes: red blood cells (transport oxygen)

  • leukocytes: white blood cells (defend body from disease)

  • thrombocytes: platelets (clotting)

2. lymph: flows in lymphatic system

• forms interstitial fluid

• passes through lymph nodes

[Connective Tissue]

Supporting Connective Tissue

protects soft tissues and supports weight of the body

1. cartilage: solid/rubbery matrix containing chondrocytes. surrounded by perichondrium

• hyaline cartilage: support + reduces friction; connects ribs to sternum, covers articular surfaces of bones, forms parts of nose

• elastic cartilage: flexible; ear

• fibrous cartilage: collagen fibers = strong; found in discs, knee, pubic

2. bone: solid matrix containing osteocytes. surrounded by periosteum.

• hollow, compact bone (osteons) on outside and spongy bone inside

[Muscle Tissue]

Skeletal Muscle

1. structure: long/cylindrical, striated, multinucleated

2. location: attached to bones

3. control: voluntary

4. function: body movement (locomotion), posture, generates heat (shivering)

[Muscle Tissue]

Cardiac Muscle

1. structure: short, branched, striated, single nucleus, connected by intercalated discs

• discs: anchoring junctions = hold cells together, gap junctions = signals and coordination

1. location: heart

2. control: involuntary

3. function: pumps blood, contracts in rhythm, acts as one unit

[Muscle Tissue]

Smooth Muscle

1. structure: spindle-shaped, non-striated, single nucleus

2. location: walls of organs (digestive tract, blood vessels)

3. control: involuntary

4. functions: moves materials through organs (food/urine), blood flow, regulates airways and secretions

[Muscle Tissue]

Composition

vascularized muscle tissue is made of elongated cells (fibers) containing myofilaments (actin/myosin proteins)

[Nervous Tissue]

Perception and Response of Nervous Tissue

1. input: sensory receptors monitors changes inside/outside the body

2. integration: processes and interprets the sensory input

3. motor output: effects a response to the stimulus

4. maintains homeostasis by acting as regulatory/control center

[Nervous Tissue]

Overview

1. nervous tissue is made of neurons (branching cells)

2. neurons are made of cell body (contains nucleus), dendrites (receives signals), and axons (send signals)

3. function: conduct electrical impulses and maintains homeostasis

4. neuroglial cells: cells surrounding the neurons that feed/support/protect them

5. location: brain, spinal cord, nerves

[Tissue Repair]

Capacity for repair

1. epithelial tissue: replaced by division of stem/undifferentiated cells

2. connective tissue: bone has continuous capacity; cartilage not as much

3. muscle tissue: poor capacity for renewal

4. nervous tissue: poor capacity for renewal

[Tissue Repair]

Characteristics

• fibrosis: process of scar formation

• if injury is extensive: granulation tissue is formed

• clinical connection: adhesions (from scar tissue) causes abnormal joining of adjacent tissues = intestinal obstruction

• nutrition is important to tissue repair

• proper blood circulation is essential to tissue repair

[Tissue Repair]

Steps/Phases

Cleanup

• remove debris, toxins, etc

• clot forms (stop bleeding)

• scab forms (protects wound)

Tissue Rebuilding

• fibroblasts: rebuild collagen/matrix

• angiogenesis: new blood vessels form

• new vascular tissue develops (granulation)

Remodeling

• wound contraction: edges pull together

• clot dissolves

• scar tissue can form

[Aging and Tissues]

• young people’s tissues repair rapidly and efficiently; process slows down with age

  • younger body is in a better nutritional state, better blood supply, faster metabolic rate

• when aging: tissues become thinner, drier, less elastic

  • collagen decreases

  • bone loses minerals = reduced height

  • cartilage deteriorates = joint stiffness

  • muscle atrophy (loss of mass)

[Disorders]

Homeostatic Imbalances

• epithelial tissue disorders are specific to individual organs: skin cancer (epidermis), peptic ulcer disease (epithelial lining of stomach/intestines)

• connective tissue disorder: most prevalent is autoimmune disorders (antibodies in immune system fail to distinguish foreign VS self = attacks body tissue)

  • Systemic lupus erythematosus: chronic inflammatory disease

Simple Squamos Epithelium

• single layer of flattened cells

• diffusion/filtration

• air sacs in lungs, kidney, lining of heart/lymphatic system

Simple Columnar Epithelial Tissue

• single layer of tall cells with round nuclei

• absorption, secretion of mucus/enzymes

• non-ciliated: digestive tract/intestines, galbladder

• ciliated: bronchi, uterus

Pseudostratified (ciliated) columnar epithelial tissue

• single layer of cells at differing heights so it looks like multiple

• secretion, propulsion if it has cilia

• non-ciliated: male reproductive ducts

• ciliated: respiratory tract

Simple Cuboidal Epithelium

• single layer of cube-like cells

• absorption/secretion

• ovaries, kidneys, glands

Stratified Squamos Epithelium

• thick layers of flattened cells

• protection

• outer layer of skin, organs

Loose Fibrous Connective Tissue

• primary packing material

• cushions organs

• binds tissues together

• provides flexibility

• immune defense

just helpful

Dense Regular Connective Tissue

• fibers are parallel = strength along axis

• found in tendons and ligaments

Loose Areolar Connective Tissue

Nervous Tissue

Adipose Connective Tissue

Hyaline Cartilage Connective

• support

• reduces friction

• connections ribs to sternum

• covers articular surfaces for bones

• forms part of nose

Bone Connective Tissue

Fluid (blood) Connective Tissue

Smooth Muscle Tissue

• non-striated, single nucleus

• walls of organs (digestive/blood vessels)

• involuntary control

• moves materials through organs, blood flow, and regulates airways

Cardiac Muscle

• short, striated, single nucleus, has intercalated discs

• heart

• involuntary control

• pumps blood, rhythmic contraction

Skeletal Muscle

• long, cylindrical, multi-nucleated. striated

• attached to bones

• voluntary control

• body movement (locomotion), posture, generates heat (shivering)

Elastic Cartilage Connective Tissue

• flexible

• ear

Fibrous Cartilage Connective Tissue

• collagen fibers = strong

• found in discs, knee, pubic

[Quiz]

What epithelial tissue forms superficial layer of skin?

Keratinized stratified squamos epithelium

Which epithelial tissue is found lining the kidney glomerulus and performs blood filtration?

Simple squamos epithelium

[Quiz]

This type of junction contains tiny fluid-filled tunnels called connexons which allow the movement of ions and small molecules between cells. It is found between muscles cells of the heart and in organs with smooth muscle tissue, such as the gastrointestinal tract.

Gap Junctions

[Quiz]

These types of cell junctions anchor adjacent cells together and resist their separation during contractile activities.

Adherens junctions and desmosomes

[Quiz]

What kind of epithelial tissue is best in locations that need to stretch?

Transitional Epithelial Tissue

[Quiz]

In intestinal tissue, what substance do white cells (Goblet cells) produce?

mucus

[Quiz]

What gland are hormones secreted from? (They enter right into the blood stream)

Endocrine gland

[Quiz]

Adipose tissue is used for all of the following EXCEPT:

1. energy stoage

2. cushion organs

3. oxygen supply

4. insulate/temperature control

3. oxygen supply

[Quiz]

What kind of tissue includes collagen-filled, rope-like structures such as ligaments and tendons.

Dense Connective Tissue

[Quiz - Answered for you]

Exocrine glands secrete their substances onto body surfaces/ducts. Match ducts with definitions.

1. Merocrine: salivary glands of oral cavity

2. Holocrine: sebaceous glands of the skin

3. Apocrine: mammary glands of the breast

Gap Junctions

Channels for sharing ions and signals between adjacent cells.

Desmosomes

Localized spot welds holding cells together against mechanical stress.

Hemidesmosomes

Anchors attaching the bottom of a cell to the basement membrane.

Adhesion Belts

Continuous bands linking the actin skeletons of neighboring cells

Tight Junctions

Watertight seals preventing fluid leakage between adjacent cells