CHAPTER 4: TISSUE 1

4 main types of tissues

1. Epithelial: Epithelium, sheets of cells that cover the exterior surfaces of the body, lines internal cavities and passageways, and forms certain glands.

2. Connective: binds the cells and organs of the body together and functions in protection, support, and integration of all parts of the body.

3. Muscle: excitable, responding to stimulation and contracting to provide movement, and occurs as three major types: skeletal (voluntary), smooth and cardiac muscle in the heart.

4 Types of Tissues 2

4. Nervous: excitable, allowing the propagation of electrochemical signals in the form of nerve impulses that communicate betwee3n different regions of the body.

View of Tissues 3

ORGAN 4

The next level of organization is the organ. This is where several types of tissue come together to form a working unit.

Embryonic Origin of Tissues:

Zygote, fertilized egg. First embryonic cells generated have the ability to differentiate into any type of cell in the body. Totipotent- each has the capacity to divide, differentiate, and develop into a new organism. As this cell proliferation continues, three major cell lineages are established within the embryo. At the point each lineage forms the distinct germ layers from which all of the tissues and organs of the human body eventually will form.

Germ Layers 5

Each germ layer is identified by its relative position:

• Ectoderm: outer

• Mesoderm: middle (muscle tissue)

• Endoderm: inner (nervous tissue)

Epithelial tissue originates in all three

Layers.

Tissue Membranes 6

• Tissue membrane: thin layer or sheet of cells that covers the outside of the body (ie. skin), the organs (pericardium), internal passageways that lead to the exterior of the body (abdominal mesenteries), and the lining of the moveable joint cavities. There are two basic types of tissue membranes:

1. Connective tissue: formed solely by connective tissue. Encapsulates organs, such as the kidneys, and line our movable joints. Synovial membrane: type of connective tissue membrane that lines the cavity of a freely movable joint. (shoulder, knee and elbow). Synovial fluid is a natural lubricant allows for movement.

Tissue Membranes – continued 7

2. Epithelial membrane: composed of epithelium attached to a layer of connective tissue. (skin). Mucous membrane a composite of connective and epithelial tissues. Sometimes called mucosae, these membranes line the body cavities and passageways that open to the external environment and include digestive, respiratory, excretory, and reproductive tracts. Mucous is produced by the epithelial exocrine glands, covers the epithelial layer. The underlying connective tissue is called lamina propria (own layer), helps support the fragile epithelial layer.

Tissue membranes – continued 8

Serous membrane: epithelial membrane composed mesodermally derived epithelium called the mesothelium, that is supported by the connective tissue. These membranes those cavities that do not open to the outside, and they cover organs located within those cavities. They are essentially membranous bags, with mesothelium lining the inside and connective tissue outside. Serous fluid secreted by the cells of the thin squamous mesothelium lubricates the membrane, reduces abrasion and friction between the organs. Serous membranes are identified according to location. Three serous membranes line the thoracic cavity; two pleura that cover the lungs and pericardium that covers the heart. The peritoneum is the serous membrane in the abdominal cavity that covers abdominal organs and forms double sheets of mesenteries that suspend many of the digestive organs.

Tissue membranes – continued 9

Skin is the epithelial membrane call the cutaneous membrane. Stratified squamous epithelial membrane resting on top of connective tissue. The apical surface of this membrane is exposed to the external environment and is covered with dead, keratinized cells that help protect the body from desiccation and pathogens.

Tissue membranes – continued 10

Epithelial Tissue 11

Epithelial tissue: essentially large sheets of cells covering all the surfaces of the body exposed to the outside world and lining the outside of organs. Epithelium also forms much of the glandular tissue of the body. Other areas exposed to the outside are airways, the digestive tract, as well as the urinary and reproductive systems, all which are lined with epithelium. Hollow organs and body cavities that do not connect to the exterior of the body, which lines blood vessels and serous membranes, are lined by endothelium.

The epithelia lining the skin, parts of the mouth and nose and the anus develops from the ectoderm. Cells lining the airways and most of the digestive system originate in the endoderm. Epithelium that lines vessels in the lymphatic and cardiovascular systems derives from the mesoderm and called an endothelium.

Epithelial Tissue – continued 12

• Epithelial tissue are nearly completely avascular. No blood vessels cross the basement membrane to enter the tissue and nutrients must come by diffusion or absorption from underlying tissue or surface.

GENERALIZED FUNCTIONS:

• Provides the body’s first line of protection from physical, chemical and biological wear and tear. Gatekeeper’s of the body controlling permeability and allowing selective transfer of materials across a physical barrier. All substances that enter the body must cross an epithelium. Many are capable of secretion and release mucous and specific chemical compounds onto their apical surfaces. Epithelium of the small intestines releases digestive enzymes. Cells lining the respiratory tract secrete mucous.

Epithelial Tissue 13

Classification of Epithelial Tissues 14

• Classified according to the shape of the cells and number of the cell layers format. Cell shapes: Squamous (flattened and thin), Cuboidal (boxy, as wide as it is tall), Columnar (rectangular, taller than it is wide).

• Simple epithelium: organized as a single layer of cells

• Stratified epithelial: formed by several layers of cells

• Pseudostratified: tissue with a single layer of irregularly shaped cells that give the appearance of more than one layer.

Simple Epithelium 15

Simple squamous epithelium: appearance of thin scales. Places where this type of tissue is found. Alveoli of the lungs where the gases diffuse, segments of the kidney tubules, lining of capillaries and interior of blood vessels.

Endothelium: epithelial tissue that lines vessels of the lymphatic and cardiovascular system. Made up of a single layer of squamous cells.

Mesothelium: forms a surface layer of the serous membrane that lines body cavities and internal organs. Primary function is to provide smooth and protective surface. Secrete a fluid that lubricates the mesothelium.

Simple Epithelium – continued 16

• Simple cuboidal epithelium: nucleus of the box-like cells appear round and generally located near center of cell. Active in secretion and absorption of molecules . Observed in the lining of the kidney tubules and ducts of glands.

• Simple columnar epithelium: nucleus of the tall column-like cells tend to enlongated and located in the basal end of the cell. Active in absorption and secretion of molecules. Forms the lining of some sections of the digestive system and parts of the female reproductive tract. Ciliated columnar found in lining of the fallopian tubes and parts of the respiratory system.

Simple Epithelium – continued 17

• Pseudostratified columnar: appears to stratified but consists of a single layer of irregularly shaped and differently sized columnar cells. Found in the respiratory tract where some of the cells have cilia.

Stratified Epithelium 18

• Stratified Epithelium: consists of several stacked layers of cells. Protects against physical and chemical wear and tear.

• Stratified Squamous epithelium: most common type in the human body. Top layer may be covered with dead cells filled with keratin. Example –Mammalian skin.

• Stratified Cuboidal epithelium: function is protective tissue. Found in sweat glands, salivary glands and mammary glands.

• Stratified columnar epithelium: Secretes and protects. Found in the male urethra and the ducts of some glands.

• Transitional epithelium: only found in the urinary system, specifically in the ureters and urinary bladder. Bladder empty, the epithelium is convoluted and has cuboidal cells. Bladder fills with urine it loses its convolutions and goes from cuboidal to squamous.

Stratified Epithelium: 19

• Simple cuboidal epithelium: active in secretion and absorptions of molecule. Observed in the lining of the kidneys and in the ducts of glands.

• Simple columnar epithelium: active in secretion and absorption of molecules. Form the lining of some sections of the digestive systems and parts of the female reproductive tract. Ciliated columnar epithelium: contains cilia and is found in the lining of the fallopian tubes and parts of the respiratory system. The cilia helps remove particulate matter.

• Pseudostratified columnar epithelium: found in the respiratory tract, where some cells have cilia.

Summary of Epithelial Tissues 20

Glandular Epithelium: 21

• A gland is a structure made up of one or more cells modified to synthesize and secrete chemicals. Glands can be classified two ways.

Endocrine gland: ductless gland that releases secretions directly into surrounding tissues and fluids. These secretions are called hormones. Released through interstitial fluid, diffused into the bloodstream and delivered to targets. Endocrine system part of the major regulatory systems coordinating the regulation and integration of body responses. Examples: anterior pituitary, thymus, adrenal cortex, gonads.

Glandular Epithelium- continued 22

Exocrine gland: secretions leave through a duct that opens directly, or indirectly to the external environment. Secretions that lead to the epithelial surface. Mucous, sweat, saliva and breast milk are examples. They are all discharged through tubular ducts.

• Glandular structure: Exocrine glands are either unicellular or multicellular.

Unicellular are scattered single cells, such as goblet cells- mucous secreting “gland” interspersed between columnar epithelial cells of mucous membranes. These are found in the small and large intestines.

Glandular Epithelium- continued 23

Multicellular exocrine glands: secretes directly into an inner cavity. Line the internal cavities of the abdomen and chest and release secretions directly into the cavities.

Methods and types of secretions: 24

• Merocrine secretion: most common type. Secretions enclosed in vesicles where contents is released by exocytosis. Sweat – example

• Apocrine secretion: Sweat glands of the armpits. These types of glands continue to secrete and produce contents with little damage to the cells.

• Holocrine secretion: Sebaceous glands that produce oils on the skin and hair. These types of glands rupture and destroy the entire gland cell. It accumulates it secretion and releases only when it bursts.

Modes of Glandular Secretion 25

Secretions 26

• Glands are also named after the products they produce. The serous gland produces watery, blood-plasma-like secretions rich in enzymes such as alpha amylase, whereas the mucous gland releases watery to viscous products rich in the glycoprotein mucin. Both serous and mucous glands are common in the salivary glands of the mouth. Mixed exocrine glands contain both serous and mucous glands and release both types of secretions.

Connective tissue 27

Functions of Connective Tissues:

• Support and connect other tissues (from the connective tissue sheath that surrounds muscle cells, to tendons that attach muscles to bone and the skeleton that supports the positions of the body.

• Protection: fibrous capsules and bones that protect delicate organs and the skeletal system. Specialized cells defend the body from microorganisms that enter the body. Blood and lymph transports fluid, nutrients, waste and chemical messengers. Adipose cells store surplus energy in the form of fat and contributes to the thermal insulation of the body.

Embryonic Connective tissue 28

• The mesodermal layer of the embryo is where all connective tissue derives. Mesenchyme – stem cell line from which connective tissues are later derived. Mucous connective tissue (Wharton’s jelly) –embryonic connective tissue forms in the umbilical cord. This tissue is no longer present after birth.

Classification of Connective tissue: 29

• Connective tissue proper includes loose connective tissue and dense connective tissue. Both tissues have a variety of cell types and protein fibers suspended in a viscous ground substance. Dense connective tissue is reinforced by bundles of fibers that provide tensile strength, elasticity, and protection. In loose connective tissue, the fibers are loosely organized, leaving large spaces in between.

• Supportive connective tissue—bone and cartilage—provide structure and strength to the body and protect soft tissues.

• In fluid connective tissue - lymph and blood, various specialized cells circulate in a watery fluid containing salts, nutrients, and dissolved proteins.

Connective Tissue Examples: 30

Connective tissue proper Supportive connective tissue Fluid connective tissue

Loose connective tissue

Areolar

Adipose

Reticular

Cartilage Hyaline

Fibrocartilage

Elastic

Blood

Dense connective tissue

Regular elastic

Irregular elastic

Bones

Compact bone

Cancellous bone

Lymph

Connective Tissue Proper 31

• Fibroblasts – present in all connective tissue. Most abundant cell found in connective tissue proper.

• Fibrocyte – less active form of fibroblasts, second most abundant cell type of connective tissue proper.

• Adipocytes – store lipids as droplets that fill most of the cytoplasm. Two types: white and brown. Brown adipocytes – store lipids as many droplets and have high metabolic activity. White adipocytes –store lipids in a single large drop and metabolically less active. Effective in storing large amounts of fat as seen in obese individuals.

• Mesenchymal cell – multipotent adult stem cell. Needed for repair and healing of damaged tissue.

Connective Tissue Proper – continued 32

• Macrophage – large cell derive from monocyte. Essential component of the immune system.

• Mast cells – has many cytoplasmic granules. Histamine is produced when a mast cell reacts to an irritation(inflammatory mediator, which causes vasodilation and increased blood flow at the site of injury or infection and heparin. Part of the immune system.

Connective Tissue Fibers 33

Three main types of fiber secreted by fibroblasts:

Collagen fiber: flexible, have great tensile strength, resist stretching, and give ligaments and tendons their characteristic resilience and strength.

Elastic fiber: after being stretched or compressed, it will return to its original shape. Elastic tissues found in skin. Elastic ligaments of the vertebral column.

Reticular fiber: found throughout the body, but most abundant in the reticular tissue of the soft organs, liver and spleen.

Loose Connective Tissue: 34

Found between many organs where it acts both to absorb shock and bind tissues together. It allows water, salt, and various nutrients to diffuse through to adjacent or imbedded cells and tissues.

oAdipose tissue: consists mostly of fat storage cells. White adipose tissue - most abundant and contributes mostly to lipid storage and be serve as an insulation from cold temperature and mechanical injuries. It can be found protecting kidneys and cushioning the back of the eye. Brown adipose tissue – more common in infants, baby fat. Reduced amount in adults, found mainly in the neck and clavicular regions of the body. Thermogenic.

Loose Connective Tissue – continued: 35

oAreolar tissue – fills in spaces between muscle fibers, surrounds blood and lymph vessels, supports organs in the abdominal cavity.

oReticular tissue – mesh-like supportive framework for soft organs, lymphatic tissue, spleen and liver.

Dense Connective Tissue 36

Contains more collagen fibers than loose connective tissue. Displays a greater resistance to stretching. Two major categories:Dense Regular: fibers are parallel to each other, enhances tensile strength

and resistance to stretching in direction of fiber orientation. Makes up ligaments and tendons. In ligaments – not all fibers are parallel. Dense regular elastic tissue – allows the ligament to return to its original length after stretching. Ligaments in the vocal folds and between the vertebrae are elastic.Dense Irregular: direction of fiber is random. Gives the tissue greater

strength in all directions and less strength in one particular direction. Example: dermis of the skin (dense irregular connective tissue). Strength of arterial walls and ability to regain original shape after stretching. (Dense irregular elastic tissue.

Supportive connective tissue: 37

Two major forms that allow the body to maintain its posture and protect internal organs. Cartilage and Bone.

Cartilage: Chondrocytes- cartilage cells. Cartilaginous tissue is avascular, all nutrients need to diffuse through the matrix to reach the chondrocytes. This makes for a very slow healing of cartilaginous tissue.

Cartilage tissue 38

Three types of cartilage tissue:

1) Hyaline cartilage: most common type in the body. Found in the rib cage and nose, covers bones where they meet to form movable joints. Allows for continued growth until adulthood.

2) Fibrocartilage: tough. Located in the knee and jaw joints and the intervertebral discs.

3) Elastic cartilage: gives rigid support as well as elasticity. Tug at your ear lobes and notice they return to their initial shape. External ear contains elastic cartilage.

Supportive connective tissue – continued 39

Two major forms that allow the body to maintain its posture and protect internal organs. Cartilage and Bone.

Bone: hardest connective tissue. Provides protection to internal organs, supports the body. Osteocytes are located in the lacunae and are the main cells of the bone. Bone is highly vascularized. This type of tissue can recover in a relatively short times from an injury.

Cancellous bone: looks like a sponge under the microscope. Lighter than compact bone (solid and has greater structural strength). Found in the interior of some bones and at the ends of long bones.

Fluid connective tissue 40

Blood and lymph are fluid connective tissues.

• Erythrocytes: red blood cells (RBCs) transports oxygen and some carbon dioxide.

• Leukocytes: White blood cells (WBCs) defends against potentially harmful microorganisms or molecules.

• Platelets: cell fragments involved in blood clotting.

Muscle Tissue and motion 41

Characterized by properties that allow movement. Excitable, respond to a stimulus. Contractile, can shorten and generate a pulling force. Bones –causes contractions of muscles causes bone to move. Some movement is voluntary (under conscious control) or involuntary (not under conscious control). Classified into three types according to structure and function:1. Skeletal: attached to bone. Makes possible locomotion, facial

expressions, posture and other voluntary movements of the body. 40% of body mass made up of skeletal muscle. Can generate body heat by contraction and participates in thermal homeostasis. Involuntary movement of shivering. Striations, cylindrical cells and multiple nuclei are observed in skeletal muscle. Mitochondria are the hard working cells found in abundance in this type of muscle.

Classified into three types according to structure and function – continued 42

2. Cardiac: forms the contractile walls of the heart.

3. Smooth: this type of tissue contracts involuntary for movements in internal organs. Digestive, urinary, and reproductive systems as well as arteries and airways.

Tissue Histology Function Location

Skeletal

Long cylindrical fiber,

striated, many

peripherally located

nuclei

Voluntary movement, produces heat, protects

organs

Attached to bones and

around entrance points to

body (e.g., mouth, anus)

Cardiac

Short, branched,

striated, single central

nucleusContracts to pump blood Heart

Smooth

Short, spindle-shaped,

no evident striation,

single nucleus in each

fiber

Involuntary movement, moves food, involuntary

control of respiration, moves secretions,

regulates flow of blood in arteries by contractionWalls of major organs and

passageways

Nervous Tissue 43

Characterized by being excitable and capable of sending and receiving electrochemical signals that provide the body with information.

Two main classes of cells make up nervous tissue: the neuron and neuroglia.

1. Neurons: propagate information via electrochemical impulses, called action potentials, which are biochemically linked to the release of chemical signals. Responsible for the transmission of the nerve impulse.

The Neuron 44

Neuron 45

Three main parts:

Cell body: includes most of the cytoplasm, the organelles and the nucleus.

Dendrites: branch off the cell body and appear as thin extensions.

Axon: long “tail” extends from the neuron body and can be wrapped in an insulating layer known as the myelin (formed by accessory cells). Synapse: gap between nerve cells, or between a nerve cell and its target (muscle or gland)

Neuroglia or Glial Cells: 46

Classified as having a simple support role.

Astrocyte: named for their distinctive star shape.

Oligodendrocyte: produce myelin in the brain and spinal cord.

Schwann: produces myelin in the peripheral nervous system.

Tissue Injury 47

Inflammation is the standard, initial response of the body to injury. It limits the extent of injury, partially or fully eliminates the cause of injury, and initiate repair and regeneration of damaged tissues.

Necrosis or accidental cell death causes inflammation.

Acute inflammation resolves over time by healing the tissue.

Inflammation persisting becomes chronic and leads to diseased conditions. Arthritis and tuberculosis are examples.

4 cardinal signs of inflammation: Redness, swelling, pain and local heat. Loss of function may also be a sign.

Aging 48

The skin and other tissues become thinner and drier, reducing the elasticity, contributing to wrinkles and high blood pressure. Gray hair and so on and so forth. Joints stiffen due to loss of cartilage.

Incidence of heart diseases, respiratory syndromes and type 2 diabetes increases with age. Wound healing is slower accompanied by a higher frequency of infection due to the immune system declining.

When you begin to use your muscles, they can atrophy which is a loss of mass.

The progressive impact of aging on the body varies considerably among individuals, but studies indicate that exercise and healthy lifestyle choices can slow down the deterioration of the body that comes with old. So to try and slow the rate of aging, one must modify stress, exercise and diet.