Transcript Primary Germ Layers

Histology – Study of Tissues
Tissue
- Group of closely associated cells that are similar
in structure and work together to perform a
function.
- Cells are nearly always embedded in or surrounded
by nonliving matrix
- Most organs contain some of each of the four
main tissue types:
- Epithelial, connective, muscle, nervous
Embryonic Germ Layers
1. Endoderm
- inner layer which forms the lining of the
digestive system
2. Mesoderm
- middle layer which forms muscles,
bones, and blood vessels
3. Ectoderm
- outer layer that forms the skin and
nervous system
Primary Germ Layers
Epithelial Tissue
Serve to cover a body surface or line a cavity
Two main types:
1. Covering and lining epithelium
- all substances entering and leaving the body
must pass through
2. glandular epithelium makes-up the glands of the
body
Functions
A) Protection
- from mechanical and chemical injury
- from invasion by bacteria and viruses
B) Sensory
- specialized epithelium found in skin, nose, eye,
and ear
C) Secretion
- glandular epithelium secretes hormones, mucus,
digestive juices, and sweat
D) Absorption
- lining epithelium of intestines and respiratory systems
allow absorption of nutrients and gases
E) Excretion
- in kidneys and skin waste products are excreted
F) Filtration
- specialized epithelium in the kidneys filter waste
products from the blood
Characteristics of Epithelial Tissue
1. Cellularity
- composed almost entirely of cells
- very little extracellular material
2. Specialized contacts
- are held together in continuous sheets by many
lateral contacts
3. Polarity
- free surface = apical surface
- exposed surface
- cells often have microvilli or cilia attached to
increase surface area
- basal surface = attached
4. Basement Membrane
- basal lamina is a noncellular adhesive sheet that
attaches epithelial tissue to underlying structures
- serves as a selective filter
- important in healing of wounds
- reticular lamina is connective fibers produced by
underlying connective tissue
- cancerous epithelial cells can pass through the
basement membrane to underlying tissues
5. Innervated but avascular
- contains nerve endings, but no blood vessels
- nutrients must diffuse into the tissue from
underlying tissues
6. Regeneration
- as long as they receive nutrients they can
regenerate by mitosis
Classification of Epithelia
Each epithelium is given two names:
First name indicates number of cell layers:
A. Simple – single layer of cells
- often found in areas of absorption and filtration
B. Stratified – consists of two or more layers of cells
- found in areas of abrasion
Second name indicates the shape of the cells:
A. squamous – flattened and scale-like
B. cuboidal – cells are about as tall as they are wide
C. columnar – cells are taller and column shaped
Classification of Epithelial Tissues
Simple Squamous
- single layer of flattened
cells
- linings of alveoli, blood
vessels, and many
membranes
- absorption, filtration,
secretion
Simple Squamous lining of lung.
Simple cuboidal epithelium
Simple columnar epithelium
Pseudostratified ciliated epithelium
- lines trachea, bronchi, epididymis, and vas deferens
- protection and movement of mucus
Stratified squamous (keratinized) epithelium
- forms epidermis of skin, surface of cornea, lining of
mouth, esophagus, anus
- protection
Stratified Squamous (nonkeratinized)
epithelium
Transitional epithelium
- often found in areas that are subjected to stress and
tension changes, such as urinary bladder
- usually composed of 10 or more layers of cuboidal
cells
Glandular Epithelium
- specialized for secretory activity
- cells may function as unicellular or multicellular glands
Glands are classified as:
1. Exocrine
- discharge through ducts
- ex.: salivary glands
2. Endocrine
- secrete products directly into the blood or interstitial
fluid
- ex.: pituitary, thyroid, adrenals
Connective Tissues
Functions:
A. Binding and support
- tendons and ligaments hold bones and muscles to
each other
- in soft organs, connective tissue supports and binds
cells together
B. Protection
- bone and cartilage support and protect body organs
C. Insulation
- fat cushions, insulates, and protects body organs as
well as providing reserve energy fuel
D. Transportation
- blood transports materials within the body
Characteristics of Connective Tissue
1. Intercellular Matrix
- non-living material that makes-up most of the tissue
- cells are embedded in the ground substance
- gives different connective tissues their varying
qualities
- allows it to bear lots of weight, withstand tension, and
endure physical abuse
2. Common origin
- all originate from mesoderm
3. Various degrees of vascularity
Fibers in connective tissue:
A. Collagenous (white)
- tough, often in bundles, high tensile strength, nonelastic
- found in tendons and ligaments (tough, flexible
support)
- collagen is the most abundant protein in our bodies
B. Reticular fibers
- delicate fibers found in networks with elastic and
collagenous fibers
- slightly elastic
- found in lymphatic tissues (nodes) and supporting
small structures
C. Elastic fibers (yellow)
- tough, elastic fibers that are not found in bundles
- tough, expandable support
- in aorta, arteries, trachea, and bronchi
Four main categories of connective tissues
based on the matrix:
1. Fibrous
- extracellular fibers are predominant features
2. Bone
- has fibers and a hard mineral ground substance
3. Cartilage
- fibers with a specialized ground substance that traps
water to form a firm gel
4. Blood
- lacks fibers
- liquid matrix - plasma
Cells in connective tissues are designated by their suffix
as to what they do:
- blast – creates the matrix
- cyte – maintains the matrix
- clast – breaks down the matrix
Examples of Connective Tissues
A. Loose (Areolar)
- widely distributed
- ground substance is a soft viscous fluid
- collagenous and elastic fibers in a loose network
- elastic glue – holds, but allows movement
- found under skin – superficial fascia
B. Adipose Tissue
- same matrix and fibers as areolar, but majority of tissue
is composed of fat cells
- fat cells are large, round, and delicate w/ nucleus
- act as padding around organs, insulation for heat
conservation, and as a reserve energy storage site
Fat storage areas – males versus females
C. Reticular connective tissue
- spleen and lymph nodes
- function in filtering and cleaning the blood
D. Dense fibrous (regular) connective tissue
- mostly fibers packed densely in the matrix
- found in areas needing tensile strength and flexibility
- tendon, ligaments, dermis, scar tissue
E. Dense fibrous (irregular) connective
tissue - dermis
F. Bone tissue
- matrix of inorganic
calcium salts and
collagenous fibers
- osteocytes – bone
maintaining cells
- organized in Haversion
Systems - Osteons
osteocytes in lacunae
- lamellae – concentric
circles of matrix
- canaliculi – small canals
connecting lacunae -
G. Cartilage
- fiber matrix of collagenous and elastic fibers
- chondrocytes – cartilage generating cells that secrete
matrix and ground substance
- firm, tough and flexible
- lacks blood vessels
Fibrocartilage
Elastic Cartilage
H. Blood
- matrix = plasma
- 90% water w/ dissolved proteins, food, metabolic
wastes and dissolved gases
- formed elements made in bone marrow
- erythrocytes – red blood cells – carry oxygen
- leukocytes – white blood cells – defense against
microbes
- thrombocytes/platelets – help in clotting
Muscle Tissue
- highly cellular and well vascularized
- composed of contractile protein fibers called
myofilaments
Functions
- provide movement
- squeeze contents of internal organs
- generate heat
Striated vs. Nonstriated
- striated muscle is arranged so that it has a striped
appearance under the microscope
Voluntary vs. Involuntary
- voluntary muscles can be consciously controlled
Smooth muscle
- found in internal organs
- normally involuntary
- spindle-shaped cells w/ one
nucleus
Skeletal muscle
- voluntary muscles
responsible for movement
- long, cylindrical fibers
- striated
multinucleate
Cardiac muscle
- muscle of the heart
- branching fibers with
single nucleus
- intercalated discs
connect cells
- striated
Nervous tissue – functions in control mechanisms of the
body and in coordinating responses to the environment
Neurons
- nerve cells which transmit electrochemical signals
- soma = cell body
- axon – carries impulse away from soma
- dendrite – carries impulse toward soma
1. Afferent = sensory
- transmit impulses to CNS from sense organs
2. Efferent = motor, secretory, accelerator, inhibitory
- transmit impulses from CNS to muscles or effector
organs
3. Association
- within CNS
- run between afferent and efferent neurons
Neuroglia
- helper cells which nourish, protect, and insulate neurons
Membranes
- thin sheet of tissue that covers a structure or lines a
cavity
- most are derived from epithelial and connective tissues
1. Serous membranes
- line cavities that do not open to outside of body
- normally composed of simple squamous epithelium
- secretes fluid to decrease friction between structures
- parietal layer – covers the body wall
- visceral layer – covers the outer part of the organ
2. Mucous membranes
- line cavities that do open to the outside
- stratified squamous epithelium w/ connective tissue
below
- produces a fluid to trap particles or to keep
underlying tissues moist
3. Synovial membranes
- line synovial joints (mostly movable joints)
- produce a liquid that lubricates and cushions the joint
Tumors and Cancer
Neoplasms, also called tumors, are any abnormal growth
of cells
Benign tumors do not spread to other tissues and
normally grow slowly.
- cells tend to stay together and are often in a capsule
- normally not life threatening unless they interfere
with organ function
Malignant tumors, or cancers, are not encapsulated and
tend to spread to other regions.
- spread to other regions in blood or lymph
- metastasis – spread of a cancer
Cancer factors:
- genetic factors, carcinogens, age
Detection and Treatment
Cancer specialists are Oncologists
- early detection is important
1. Self-examination
- some cancers (breast and testicular for example) can
be detected by self-examination
2. Medical imaging
- radiography – x-ray photographs can find many
- mammography
- computed tomography (CT) – x-ray scanning
- magnetic resonance imaging (MRI)
- ultrasonography
3. Blood tests can detect abnormalities
4. Biopsy is removal and examination of living tissue
Without treatment cancer usually results in death.
A. Surgical removal
B. Chemotherapy
- uses cytotoxic compounds and antineoplastic drugs to
kill malignant cells
C. Radiation therapy
- uses x-ray or gamma radiation to destroy cancer
- used alone or with chemotherapy
D. Laser therapy
- uses an intense beam of light to destroy a tumor
E. Immunotherapy
- attempts to bolster the body’s own immune system
against cancer