Chapter 4
CHAPTER 4-TISSUES AND MEMBRANES
I. TISSUES-groups of cells located in a distinct region of the body that work together to carry out
a specific function.
A. Histology-the study of tissues.
B. Tissues differ from each other based on the types of cells that they contain and the
specific functions of those cells.
C. Tissues are most effectively observed using microscopes. In most cases, small tissue
sections are removed from the body, stained and prepared for observation on a
microscope slide.
II. TYPES OF TISSUES IN THE HUMAN BODY:
A. Epithelial Tissue
B. Connective Tissue
C. Muscle Tissue
D. Nerve Tissue
III. EPITHELIAL TISSUE (Epithelium-singular)-typically occurs as a sheet of cells that covers or lines
surfaces and cavities in the body.
A. General Features of Epithelial Tissue
1. The cells of epithelium are arranged in sheets and are packed closely together.
2. It is avascular-does not contain blood vessels. Epithelial cells are nourished by
nutrients that diffuse from blood vessels in the underlying connective tissue.
3. Epithelium has a nerve supply.
4. Epithelium has a high regeneration rate. Cell division occurs rapidly in epithelial
cells. This allows epithelial tissue to heal quickly.
5. Epithelial tissue has several major functions in the body including: protection,
absorption, filtration, excretion, secretion and sensory reception.
6. Nearly all substances received or given off by the body must pass through a layer of
epithelial tissue.
7. Two broad categories of epithelial tissue: Covering and Lining Epithelium and
Glandular Epithelium. We will focus on covering and lining epithelium in this
chapter-glandular epithelium will be covered when get to the Endocrine System.
B. Structure of Epithelial Tissue:
1. The Apical Surface-upper, free surface of epithelial tissue that is exposed to the
exterior or to a body cavity. This layer may contain fingerlike projections called
microvilli or hairlike structures known as cilia. Collectively, these structures are
referred to as a brush border and they aid in increasing the surface area of the
tissue.
2. All epithelial tissues rest upon and are supported by connective tissue.
a. Basement membrane-a layer of attachment between epithelial and
connective tissue. This structure functions by holding epithelial tissue in
place. This membrane also plays a key role in regulating the movement of
materials between the epithelium and the lower connective tissue.
1) 2 Layers of the Basement Membrane:
a) Basal lamina-secreted by the epithelial tissue. This layer
acts as a filter that determines which molecules will diffuse
from the underlying connective tissue. This layer is
composed primarily of proteins and sugars, thus it is
acellular.
b) Reticular lamina-secreted by connective tissue. This layer
functions by providing support to the overlying epithelial
tissue.
C. Organization of Cells in Epithelial Tissue
1. Arrangement of Cells in Epithelial Tissue
a. Simple epithelium-is only one cell layer thick. This type of epithelium is
found in areas where absorption, filtration and osmosis occur.
b. Stratified epithelium-is composed of two or more cell layers. This type of
epithelium is found in areas where protection is important.
c. Pseudostratified epithelium-has the appearance of being several cell layers
thick; however, it is only one cell layer thick.
2. Cell Shapes in Covering and Lining Epithelium
a. Squamous cells-are flat and scalelike.
b. Cuboidal cells-are boxlike, almost as tall as they are wide.
c. Columnar cells-are column or rectangular in shape.
d. Transitional cells-have the ability to change shape.
D. Two Broad Categories of Covering and Lining Epithelial Tissue (both are further subdivided
into specific types).
1. Simple Epithelium
2. Stratified Epithelium
E. Specific Types of Surface Epithelium
1. Simple squamous epithelium-composed of a single layer of flat cells.
a. Is a very thin tissue, so it is highly adapted for diffusion and filtration.
b. Forms endothelium, which lines blood vessels and many of
the hollow organs of the body.
c. Mesothelium-serous membrane that covers the ventral body cavity.
2. Simple cuboidal epithelium-lines glands and is involved in secretion and
absorption. This tissue is also found in the kidney tubules.
3. Simple columnar epithelium
a. Can be nonciliated (as in the gallbladder) or ciliated.
b. Is often covered by microvilli.
c. This tissue lines the digestive system from the mouth to the anus.
d. This type of tissue often contains goblet cells which produce mucus.
F. Specific Types of Stratified Epithelium:
1. Stratified Squamous Epithelium
a. This tissue can be keratinized (covered by the thick protein keratin) or
nonkeratinized.
b. Keratinized squamous epithelium makes up the bulk of the epidermis while
nonkeratinized squamous epithelium forms a covering over the tongue.
2. Stratified Cuboidal Epithelium-lines the sweat glands and a portion of the ovaries.
G. Pseudostratified epithelium-looks thick but is only one cell layer thick.
1. Pseudostratified columnar epithelium-located in the trachea and nasal cavity this
tissue can contain:
a. Goblet cells
b. Cilia
IV. CONNECTIVE TISSUE-the most abundant type of tissue in the human body.
A. Functions of Connective Tissue
1. Binds structures together
2. Provides support
3. Protects, provides immunity
4. Insulates, pads
5. Transports materials through the body
6. Movement
B. General Features of Connective Tissue
1. Has an extensive nerve supply
2. Most types are highly vascular
C. Structure and Organization of Connective Tissue
1. Connective Tissue is composed of three basic elements:
a. Cells-make up the bulk of most connective tissues.
1) The suffix blast refers to unspecialized, immature types of connective
tissue. EX: fibroblasts
2) The suffix cyte refers to mature types of connective tissue cells.
b. Fibers-provide support and strength to connective tissue. Collagen fibers,
elastic fibers and reticular fibers are three major types of fibers found in
connective tissue.
c. Matrix-the material that surrounds connective tissue cells. This material is
noncellular.
1) It can be fluid, gelatinous or solid.
2) Ground substance-fills the spaces around the connective tissue cells.
It is composed of matrix and fibers.
D. Mesenchyme-embryonic connective tissue. This type of tissue develops early in embryonic
development and specializes into the different connective tissues that make up the body.
Some mesenchyme tissue remains in the human body throughout our lives.
E. Types of Connective Tissue in the Body:
1. Areolar Connective Tissue- contains all three types of connective tissue fibers. This
tissue provides strength, support and elasticity to body structures. It is commonly
found beneath epithelial tissue.
a. It also serves as a packaging tissue in the body. When a body area becomes
inflamed, areolar tissue soaks up the excess fluid to prevent edema (swelling).
b. Areolar tissue is classified as a type of loose connective tissue since the fibers
in this tissue are loosely arranged. Areolar tissue can be stronger than steel.
2. Adipose Tissue-fat tissue.
a. Adipocytes-mature cells in adipose tissue. These cells are specialized for fat
storage. The fat is stored in a fat vacuole.
b. Adipose tissue functions as an insulator, a source of stored energy and as a
padding around body structures.
c. Adipose is also classified as a loose type of connective tissue.
d. Subcutaneous layer-composed of areolar and adipose tissue. This layer
attaches the skin to the underlying tissues and organs.
3. Reticular Tissue- contains only reticular fibers. It is a form of loose connective tissue. a. Is very common in lymph nodes, the spleen and bone marrow. This tissue holds
structures together and it can form a framework for blood cells to attach to.
4. Dense Regular Connective Tissue-fibers in this tissue are packed tightly together, thus,
it is referred to as being a dense type of connective tissue.
a. Typically contains collagen fibers which offer a great deal of strength to this
tissue. That said, this tissue provides strength, support to body structures.
c. Tendons- composed of dense regular connective tissue. These are connective
tissue cords that attach muscles to bone.
5. Dense Irregular Connective Tissue-fibers in this tissue have an irregular arrangement.
Again, this is a type of dense connective tissue. This type of tissue typically forms sheets that cover and protect organs and structures within the body.
a. This tissue is found in heart valves and in the periosteum (membrane that
covers bone). It also forms fibrous coverings over some organs.
6. Cartilage- is composed of fibers that are packed tightly together. It can withstand a
great deal of stress.
a. Chondrocytes-mature cartilage cells. These are located in open spaces known
as lacunae.
1) Matrix surrounds the lacunae.
2) Perichondrium-the membrane that surrounds cartilage tissue.
3) Cartilage has a greatly reduced blood supply and nerve supply. Due to
this is a very slow growing and healing type of tissue.
b. Chondroblasts-these are cells that secrete new cartilage matrix. These
develop into chondrocytes.
c. Types of Cartilage Tissue:
1) Hyaline Cartilage- most abundant type of cartilage in the body. It is
located at the ends of long bones. Hyaline cartilage greatly reduces
friction and it absorbs shock at the ends of bones. This type of cartilage
also makes up the bulk of the embryonic skeleton and it forms the
epiphyseal plates of bones. This is also referred to as articular cartilage. (cushion around growth plates)
2) Elastic Cartilage- is very similar to hyaline cartilage in structure. This
tissue forms the bulk of the ears, nose, glottis (voice box), and
epiglottis (flap that covers the trachea).
3) Fibrocartilage- typically forms pads in the human body. Can withstand
extreme pressure. Intervertebral discs and the pubic symphysis are
examples of fibrocartilage in the body.
7. Bone (Osseous) Tissue-due to its hardness, bone has the ability to support and protect
body structures. Along with cartilage, bone forms the skeleton of the body.
a. 2 Types of Bone Tissue: bone tissue is always growing and changing
1) Compact Bone-forms the external covering over all human bones.
a) This type of bone is composed of repeating units known as
Haversian Systems (Osteons).
b) Components of Haversian Systems:
1) Osteocytes- mature bone cells; are located in lacunae. Regulate all the activity of the bone itself
2) Lamella- rings of matrix. This matrix is composed of
mineral salts (which can be calcium carbonate or
calcium phosphate). Gives bone its structure
3) Canaliculi- small (microscopic) canals that extend from lacunae, through the lamellae of bone. Nutrients and wastes pass to/from osteocytes through these small canals.
4) Haversian (Central) Canals-holes in the center of each
Haversian System. These openings contain blood vessels
and nerves.
2) Spongy Bone -is not composed of Haversian Systems. This type of
bone is composed of thin plates of bone known as Trabeculae (small thin plates of bone). Trabeculae are composed of osteocytes and lamellae.
8. Blood- has a liquid matrix. ( a transport tissue)
a. Components of Blood:
1) Plasma-the liquid portion of blood. This is the matrix of blood. Plasma
contains a variety of dissolved compounds.
2) Formed Elements-cells and cell fragments in blood. The formed
elements in blood include the following:
a) Erythrocytes (Red Blood Cells)-involved in carrying oxygen to
body cells and carbon dioxide to the lungs. These lack a nucleus
and cannot divide. They do contain the red pigment hemoglobin.
b) Leukocytes (White Blood Cells)-function in fighting infection and
in providing immunity to the body. These do have a distinct
nucleus they can divide.
c) Thrombocytes (Platelets)-involved in blood clotting. (thrombo means clot, cytes means cell)
V. MUSCLE TISSUE- is composed of fibers that are capable of generating force for contraction.
A. The functions of muscle tissue include moving bones, providing body support and protection
and thermogenesis (heat production).
B. Muscle tissue is composed of numerous cells known as muscle fibers.
C. Types of Muscle Tissue in the Human Body:
1. Skeletal Muscle Tissue- attaches to and moves bones.
a. Is classified as being striated and voluntary.
2. Cardiac Muscle Tissue- located in the wall of the heart.
a. Is striated and involuntary. Brain, hormones tell cardiac muscle what to do (involuntary). Contracts and relaxes 70 times a minute- “heart rate”
b. Contains intercalated discs-swellings of the cell membrane of cardiac muscle
fibers. These hold cardiac muscle fibers together during muscle contraction.
3. Smooth Muscle Tissue- is located in the internal organs and blood vessels of the body.
a. Is nonstriated and involuntary. Mostly internal organs and blood vessels
VI. NERVOUS TISSUE-makes up the brain, spinal cord and nerves of the nervous system.
A. 2 Types of Cells in Nervous Tissue:
1. Neuroglia (Support Cells)-support, insulate and protect the nervous system.
2. Neurons-the primary types of nerve cells. These are capable of generating and
conducting impulses (electrical signals) throughout the body. Neurons cannot divide.
a. These function by responding to stimuli via impulse formation and conduction.
VII. TISSUE REPAIR- the process by which tissues replace dead or damaged cells.
A. Tissue repair can occur in two major ways:
1. By Regeneration- the replacement of destroyed tissue with the same kind of tissue.
2. By Fibrosis-the formation of fibrous connective tissue (Scar tissue) over injured tissue.
B. Epithelial and connective tissues have a high capacity for continuous renewal.
C. Muscle tissue repair can occur; however, it is generally a slow process.
D. Nerve tissue does not have much capacity for renewal.
VIII. TISSUE GROWTH
A. Hyperplasia-tissue growth that occurs as cells increase their number. Epithelium grows in this
fashion.
B. Hypertrophy-tissue growth that occurs as preexisting cells enlarge in size. Adipose and muscle
tissue exhibit this type of growth.
C. Neoplasia- development of a tumor (either benign or malignant). The tumor is known as a
neoplasm (new growth).
D. Metaplasia- occurs when one type of tissue changes to another type of tissue (ciliated
epithelium in smokers often changes to a stratified form of epithelium).
IX. TISSUE DEATH
A. Necrosis- premature, pathological death of tissue to trauma, toxins or infection.
B. Infarction- tissue due that occurs when blood supply is cut off to the tissue. Like a heart attack or cardiac infarction
C. Gangrene- results from infection or interrupted blood supply.
1. Decubitus ulcer
X. MEMBRANES IN THE HUMAN BODY-these cover and protect surfaces and structures in the body.
A. Types of Membranes in the Human Body:
1. Epithelial Membranes-composed of epithelial tissue and an underlying connective
tissue layer. Types of Epithelial Membranes Include:
a. Cutaneous Membrane- refers to the skin.
b. Mucous Membranes- line body cavities that open to the exterior of the body.
1) This includes the digestive, respiratory and urogenital tracts. All of
these systems are moist areas in the body.
2) These membranes are adapted for filtration (capture), absorption, and secretion.
3) These membranes often contain special secretory cells such as goblet
cells.
4) They form a protective barrier to prevent bacterial and viral invasion of
systems in the body.
c. Serous Membranes- line body cavities that do not open directly to the outside
of the body. These often cover organs in the body. These are composed of simple
squamous epithelium that covers a layer of areolar connective tissue.
1) These are made up of 2 distinct layers:
a) The Parietal Layer- attaches to the walls of body cavities.
b) The Visceral Layer-attaches directly to and covers internal
organs.
2) Serous membranes secrete a special lubricating fluid known as
serous fluid which lubricates the surfaces of the parietal and visceral
layers so that they easily slide across one another.
3) Serous membranes are often named for the organ that they
cover. Examples of this include: the pericardium, the pleural membranes, and the peritoneum.
2. Connective tissue membranes-Types:
a. Synovial Membranes- are composed entirely of areolar connective tissue. These
line joint cavities in the body. These membranes secrete a synovial fluid which
lubricates the cartilage at the ends of long bones in the body.
b. Meninges- Cover and protect the brain and spinal cord.
XI. EMBRYONIC/DEVELOPMENTAL ASPECTS OF TISSUES
A. The major tissues of the human body develop from the primary germ layers (endoderm- internal becomes our digestive organs, Mesoderm- middle layer becomes our muscle, ectoderm- external and becomes the skin in our nervous system) that form in embryonic development. Between 9-12 weeks everything is developed in endoderm but not fully functioning. Lungs are last to develop
B. All of the primary tissues and organs are in place by the end of the second month of embryonic
development. These tissues will continue to develop throughout the period of development.