Tissues and Membranes

Tissues…

• The human body consists of trillion of cells, but they do not work independently

• The cell must work together to perform various tasks to keep the body in homeostasis

• In order for cells to work together, they form tissues

• To help study the various cells and the tissues they make, anatomists have subdivided the tissues into four major groups and those groups are further subdivided according to their cellular makeup

General Information…• Some tissues, such as epithelial, connective, muscle or

nervous, may or may not have surface modifications• Microvilli – contain microtubules which help increase the surface

area of the cell• Cilia – contain microfilaments which help move materials along

the outer surface of the cell• Cell junctions attach the cells of the tissues together forming

an excellent barrier• Three types of cell junctions1. Tight junction – prevents movement of materials between cells

and are usually found in epithelial cells2. Adhering junction – holds the cells together and are found in skin

and cardiac tissue3. Gap junction

Three Types of Cell Junctions

1. Tight junction – prevents movement of materials between cells and are usually found in epithelial cells

2. Adhering junction – holds the cells together and are found in skin and cardiac tissue

• Desmosomes – the junction is a “spot” between the cells

• Intermediate junctions – the junction appears as a “band” around the cells

3. Gap junction – transmits impulse and small ions from cell to cell and are found in heart, smooth, and some nerve cells

The Four Tissue Groups…Tissue Type Characteristic Type of cell within the

tissues

Epithelial

(cover)

Consists of cells that make up the inside or outside lining of organs

Squamous, cuboidal, columnar

Muscular

(movement)

Consists of cells that have the ability to contract and relax

Skeletal muscle, smooth muscle, cardiac muscle

Neural

(control)

Consists of cells that conduct impulses or cells that protect the nervous system

Neuron, glial

Connective

(support)

Consists of cells that have a matrix and typically fill internal spaces within the body

Adipose, areolar, blood, bone, cartilage, dense, reticular

Epithelia Characteristics…

• The cells fit closely together to form continuous sheets

• They are bound together at many points called cell junctions

• They always have one free surface called the apical surface, which is exposed to the body’s exterior or to the cavity of an internal organ it is lining

Epithelia Characteristics con’t…• They rest on a basement membrane, which is a

structureless material secreted by the cells

• They have no blood supply (avascular), therefore they depend on diffusion from capillaries under connective tissue for food and oxygen

• When well nourished, they can regenerate

Classification of Epithelia…

• Epithelia are classified according to:1. Cell arrangement

Simple – one layer of cells Stratified – two or more layers of cells All attached to a “basement” membrane

2. Shape If the cells are stratified, the free surface determines

the name There are four main types

i. Squamousii. Cuboidaliii. Columnariv. pseudostratified

Drawing Tissue…• Draw each of the different types of tissue

Bell Ringer…

• What makes tissue?

• What are the 4 types of tissue and what is each of their main functions?

• Draw a simple squamous epithelial tissue – label the basement membrane, the apical surface, and cell junctions

The cells of Epithelial Tissue…• Squamous cells

Flat and irregular in appearanceFound in the lining of the skinOur first line of defense

• Cuboidal cellsShaped like little squaresFound in the lining of the urinary tubesSecrete and absorb material

The cells of Epithelial Tissue con’t…• Columnar cells

Shaped like columns Found in the lining of the trachea Secrete and absorb material

• Glandular cells Obtain needed materials from the blood and use

them to make their secretion, which they discharge Two types of glands develop from epithelial sheets

i. Endocrine glandsii. Exocrine glands

The cells of Muscular Tissue…• Skeletal muscle cells

Are elongated cells with striationsFound making up the muscles associated with the

skeletal systemContract and relax under voluntary control

• Smooth muscle cellsAre elongated cells without striationsFound making up the uterus and blood vesselsContract and relax under involuntary control

The cells of Muscular Tissue con’t…• Cardiac muscle cells

Consists of intercalated discsFound making up only the heartContract and relax in a non-voluntary pulsating manner

The cells of Neural Tissue…

• Neurons make up neural tissueConsists of dendrites, soma and an axonFound making up the nervous system such as the

brain and spinal cordConduct impulses

Glial cellsHave a variety of shapes and sizesFound either nearby or surrounding the neuronsProvide protection for neurons

Connective Tissue

• Connective tissue represents the most diverse tissue group of the human body

• Even though cells are quite different from each other, they do have some commonality, which is they all have matrix of some sort

• The matrix is the material that surrounds the cells

The Major Matrix Types…

• There are 4 major matrix materialsa. Fiber – the fibers of the matrix can be long, slender fibers

or short, thick fibers

b. Liquid – liquids such as plasma

c. Solid – creates a tough, strong type of tissue

d. Gel – creates a tough but yet very flexible type of tissue

Bell Ringer…Identify each type of tissue and explain why you choose it

Bell ringer…

• What is the one common thing that all connective tissue has in common?

• What type of cells protect nerve tissue?

The cells of Connective Tissue…

• Adipose cellsAre round and appear empty, but they are full of

fatFound surrounding various organs of the bodyProvide insulationHave a fiber matrix

• Areolar cellsAre small and have long, thin fibers running

between them making up the matrixFound between our skin and muscle and provide

attachment of our skin to the muscle

The cells of Connective Tissue con’t…• Blood cells

Are small anucleated with a plasma matrixCan be found in our circulatory systemTransport oxygen and carbon dioxide to and from

other cells in the body

• Dense cellsAre parallel fibers in a fiber matrixMake up tendons and ligamentsTendons provide attachment of muscles to boneLigaments provide attachment of one bone to

another

The cells of Connective Tissue con’t…• Bone cell

Form concentric rings around a central canalCan be found in our bonesProvide strengthIn a solid matrix made of calcium phosphate

• Cartilage cellAre small and sit in a rather large lacunaCan be found within our jointsHave a gel matrix, which allows for flexibility

The cells of Connective Tissue con’t…• Reticular cell

Are small and have short, thick fibers running between themCan be found making up the framework of the liver, spleen,

tonsils, appendix, and thymus glandHave a fiber matrix that consists of short, thick fibers

Glandular tissue…

• Consists of one or more cells that make AND secrete a particular product called a secretion

• The secretion typically contains protein molecules in an aqueous fluid

2 Major Types of Glands

1. Endocrine glands Do not have ducts (ductless) Their secretions (all hormones) diffuse directly into the

blood vessels found with in the gland Ex – thyroid, adrenal, pituitary

2. Exocrine glands Have ducts in which their secretions empty through to get to

the epithelial surface Ex – sweat, oil, liver and pancreas (can be both internal and

external)

Cartilage types…

1. Hyaline cartilage Most widespread type Supporting structures of the larynx, voice box,

attaches the ribs to the sternum Covers the ends of bones where they form

joints

2. Elastic cartilage Found where a structure with elasticity is

desired – external ear

3. Fibrocartilage Forms the cushion-like discs between the

vertebrae of the spinal cord

Body Membranes…

• There are 4 major types of membranes in the bodya. Cutaneous membranes

b. Mucous membranes

c. Serous membranes

d. Synovial membranes

Cutaneous membrane…

• The cutaneous membrane is actually the skin

• It covers the entire body and is made up of squamous epithelial cells

Mucous membranes…

• Typically consist of columnar epithelial cells• Produce a mucus, which provides protection

to the tissue they line, such as the cavities that open to the outside of the bodyThe digestive tract – opens via the mouth and

anusThe respiratory tract – opens to the outside via

the mouth and noseThe reproductive tract – opens to the outside via

the vaginal openingThe urinary tract – open to the outside via the

urethral opening

Serous membranes…

• Produce serous fluid, which provides protection for the tissue they cover

• Are made of epithelial cells that are supported by connective tissue

• Line internal cavities of the body that are not open to the outsideThe pleural membranes – cover the lungsThe peritoneal membranes – cover organs such

as the stomach and liverThe pericardial membrane – covers the heart

Synovial membranes

• Produce synovial fluid

• This fluid helps to reduce abrasion at the joint site

• They are made of connective tissue

• They line the joints of the body

Tissue Injury…

• The body has many techniques for protecting itself from uninvited guests or injury at the tissue level:Intact physical barriers (skin and mucous membranes)CiliaStrong acid produced by glands in the stomach lining

Tissue injury…

• When tissue injury does occur, it stimulates both the body’s inflammatory and immune responsesInflammatory – a non-specific response that attempts to

prevent further injuryImmune response – extremely specific and attacks

recognized invaders – bacteria, viruses, toxins

Tissue Repair…

• a.k.a wound healing

• Occurs in two major ways:1. Regeneration- the replacement of destroyed cells by the

same kind of cells

2. Fibrosis – repair involves dense connective tissue, which forms scar tissue

Determining the type of repair…• The type of repair that occurs depends on:

1. The type of tissue damaged

2. The severity of the injury

• In general, incisions heal much more successfully than lacerations:

Incision – a clean cut Laceration – ragged tear

Steps in tissue repair…

1. The broken blood vessels bleed, causing inflammatory chemicals to be released

2. The local blood vessels dilate and become more permeable, allowing white blood cells, fluid and plasma/clotting proteins to enter the injured area

3. The clotting proteins construct a clot, which stops the loss of blood and holds the wound together preventing harmful bacteria from spreading to surrounding tissue

Steps…

4. The surface dries and forms a scab

5. Granulation tissue forms It is a pink delicate tissue composed mainly of

capillary buds that grow into the damaged area from the undamaged blood vessels

The capillaries are fragile and bleed easily (pick a scab – what happens)

Contains phagocytes the eventually dispose of the blood clot and fibroblast that synthesis collagen fibers (scar tissue) to permanently bridge the gap

Steps…6. The surface epithelium begins to regenerate and

makes its way across the granulation tissue just beneath the scab, which will then soon detach

7. The final result is a fully regenerated surface epithelium that covers an underlying area of fibrosis (the scar)

The scar is either visible or invisible depending on the severity of the wound

Each type of tissue is different…• Epithelial tissue – skin tissue and mucous membranes –

regenerate beautifully• Most fibrous connective tissue and bone tissue also

regenerate well• Skeletal muscle regenerates poorly, if at all• Cardiac muscle and nervous tissue within the brain and

spinal cord are only replaced by scar tissue

Why scar tissue is not beneficial…• Scar tissue is strong, but is not as flexible as most

normal tissue

• It also does not have the ability to perform the normal functions of the tissue it replaces

• This is why when scar tissue forms on any organ, it usually hampers the function of that organ

Developmental Aspects of Cells and Tissues…• Growth through cell division (mitosis) occurs through

puberty – why we grow• Cells/tissue exposed to fiction (epithelium) replace

lost cells throughout our lives• Connective tissues remain mitotic and forms repair

(scar) tissue• Muscle tissue becomes amitotic by the end of

puberty • Nervous tissue becomes amitotic shortly after birth

Amitotic tissues are severely handicapped by injury

Developmental aspects continued…• Neoplasms, both benign and malignant,

represent abnormal cell masses in which normal controls on cell division are not working

• Hyperplasia is the increase in size of tissues or organs that occurs when a tissue is strongly stimulated or irritated

• Atrophy is the decrease in size of tissues or organs that occurs when the organ is no longer stimulated normally