Lecture Notes - Chapter 49
Homework - Review questions
Organization of the Body
All vertebrates share the same basic body plan, with similar organs performing similar
functions.
I.
Levels of Organization in the Body
1) Cells
2) Tissues 3) Organs –
4) Organ systems –
During development in the uterus, there are three types of embryonic tissues,
or germ layers: endoderm, ectoderm, and mesoderm. These three tissues then
differentiate into the different cell types and tissues of the human body. The
differentiated cells can be grouped into four different types of tissues - epithelial –
- connective –
- muscle –
- nerve –
II. Epithelial Tissues
Covers every surface of the body, from the epidermis of the skin to the lining of the
digestive tract.
Provide a barrier between the internal and external environments, and are selective in the
passage of substances across this membrane.
also provides sensory surfaces, and secretes materials onto the surface of the membrane.
Some epithelial tissues become modified to form glands.
Usually one or a few cells thick, and constantly undergoing cell turnover.
Two general classes of epithelium - simple and stratified. These are further subdivided
into squamous, cuboidal, and columnar, based on the shape of the cells in the surface
layer.
A. Simple Epithelium –
-
One cell layer thick.
Simple squamous - cells are flat and irregularly shaped, and allow easy
pasage of molecules across the membrane
-
Simple cuboidal - cells are about as tall as they are wide
-
Simple columnar - cells are taller than they are wide
B. Stratified Epithelium
-
Several cells layers thick.
Stratified squamous - found in epidermis of the skin.
C. Glands –
-
derived from invaginations of epithelium.
Two major types of glands:
 Exocrine glands - the gland and the epithelial surface are connected by a
duct, which empties the secreted product out onto the surface.
Examples –

Endocrine glands - ductless. The connections with the epithelium were
lost during development. The secretions produced by these glands are
called hormones, which enter the blood vessels and are carried to their
target tissues.
Examples –
III. Connective Tissue
Divided into two classes: connective tissue proper, and special connective tissues.
Connective tissue proper can be subdivided into loose and dense connective tissues.
Special connective tissues include blood, cartilage, and bone.
All have abundant extracellular material (matrix).
A. Loose connective tissue –
-
composed of cells scattered within a gelatinous mass of proteins called
ground substance.
Also present – protein fibers such as collagen, elastin, and reticulun, all
produced by fibroblasts.
Other cells present include mast cells, macrophages and adipose cells.
B. Dense connective tissue
-
contains tightly packed collagen fibers.
Dense regular c.t. - collagen fibers run parallel to one another (tendons)
Dense irregular c.t. – collagen fibers are more scattered (organ coverings)
C. Cartilage
-
ground substance is made of glycoprotein
collagen fibers are packed in a way that results in a firm, flexible tissue that
does not stretch.
provides cushion for adjoining bones.
produced by chondrocytes.
Avascular, aneuronal tissue
D. Bone
-
forms where cartilage becomes hardened by calcification.
crystals of calcium phosphate are laid down by osteoblasts.
Compact bone contains osteons with lamellae, lacunae, canaliculi, and
Haversian canals
E. Blood
-
the extracellular matrix of blood is the fluid plasma.
cells include erythrocytes, leukocytes, and thrombocytes
the plasma of blood also contains all the other substances transported to and
from the cells of the body, including sugars, amino acids, salts, and
numerous protein molecules.
IV. Muscle Tissue
Muscle cells work together to provide the actions necessary to create movement of an
organism, in part or as a whole, or of movement of materials within the body.
The cells are packed with the protein filaments actin and myosin, which work together to
produce contraction of the muscle cell.
There are three types of muscle tissue: smooth, skeletal, and cardiac.
Skeletal and cardiac muscles are “striated” due to the arrangement of the actin and
myosin filaments.
A. Smooth muscle
-
organized into sheets of spindle-shaped cells, each containing a centrally
located nucleus.
found predominantly within the walls of blood vessels and portions of the
digestive system, as well as in the iris of the eye.
under involuntary control, and is stimulated by hormones or nerve impulses.
B. Skeletal muscle
-
-
this is attached to the bones of the body by connective tissue structures
called tendons.
The muscle cells are called muscle fibers, and are arranged parallel to one
another with several nuclei per fiber oriented out along the periphery of the
cell.
Each muscle fiber contains structures called myofibrils, which are composed
of very ordered arrays of actin and myosin.
Contraction of the muscle fibers is the result of nerve impulses which are
under the voluntary control of the organism.
C. Cardiac muscle
-
-
composed of muscle cells which are smaller and contain only one centrally
located nucleus.
interconnections between these cells appear as stairsteps, and are called
intercalated discs.
Cells are able to communicate with one another through gap junctions in
these discs in order to coordinate the overall contraction of the entire muscle
(heart).
Under involuntary control, though can be affected by the nervous system
V. Nerve Tissue
Cells of the nervous system are called neurons.
The neuron consists of a cell body, dendrites, and an axon.
Many axons of the body are covered by a protective layer called the myelin sheath.
Sensory neurons carry information from the sensory organs to the CNS
Motor neurons carry information from the CNS to the muscles and glands.
The axons of motor neurons and the dendrites of sensory neurons are bundled together
into structures called nerves.
The brain and spinal cord are collectively called the central nervous system.
The nerves that carry impulses to/from the CNS are part of the peripheral nervous
system.
The structural support within the CNS is provided by many cells collectively called
neuroglia.
In the PNS, structural support is provided by the Schwann cells, which provide a
insulating myelin sheath.