Page 6 - Fundamentals of anatomy physiology
P. 6
Watch the > ™ on Endochondral Ossification.
Increasing the Length of a Developing Long Bone (Steps 5–7) NEW There is one
During the initial stages of ossification, osteoblasts move away from the primary c oordinating Spotlight
ossification center toward the epiphyses. But they do not complete the ossification of Figure for every A&P Flix
the model immediately, because the cartilages of the epiphyses continue to grow. The available in MasteringA&P.
region where the cartilage is being replaced by bone lies at the metaphysis, the junction
between the diaphysis and an epiphysis. On the diaphyseal (shaft) side of the metaphysis, The explanation is
osteoblasts continually invade the cartilage and replace it with bone, while on the
epiphyseal side, new cartilage is produced at the same rate. The situation is like a pair of built directly into the
joggers, one in front of the other. As long as they are running at the same speed, they can illustration for efficient
run for miles without colliding. In this case, the osteoblasts and the epiphysis are both and effective learning.
“running away” from the primary ossification center. As a result, the osteoblasts never
catch up with the epiphysis, and the bone continues to grow longer and longer. The all-in-one-place
5 Capillaries and osteoblasts 6 The epiphyses eventually become filled 7 At puberty, the rate of epiphyseal presentation means no
migrate into the epiphyses, flipping back and forth
creating secondary with spongy bone. The metaphysis, a cartilage production slows and the between narrative and
ossification centers. relatively narrow cartilaginous region called rate of osteoblast activity accelerates. illustration to get the
the epiphyseal cartilage, or epiphyseal As a result, the epiphyseal cartilage full story.
Hyaline cartilage plate, now separates the epiphysis from the gets narrower and narrower, until it
Epiphysis diaphysis. On the shaft side of the ultimately disappears. This event is
metaphysis, osteoblasts continuously called epiphyseal closure. The former
invade the cartilage and replace it with location of the epiphyseal cartilage
bone. New cartilage is produced at the becomes a distinct epiphyseal line
same rate on the epiphyseal side. that remains after epiphyseal growth
has ended.
Articular cartilage
Articular cartilage Epiphyseal line
Spongy
bone
Metaphysis Epiphyseal Spongy
Periosteum cartilage bone
Compact
bone Diaphysis Medullary
cavity
Secondary Within the epiphyseal cartilage, the
ossification chondrocytes are organized into zones. A thin cap of the original cartilage
model remains exposed to the joint
center Chondrocytes at the cavity as the articular cartilage. This
epiphyseal side of the cartilage prevents damaging the
cartilage continue to joint from bone-to-bone contact.
divide and enlarge.
Chondrocytes degenerate
at the diaphyseal side.
Osteoblasts migrate upward
from the diaphysis and
cartilage is gradually
replaced by bone.
SPOTLIGHT Figure 5–3 SPOTLIGHT OFigvuerer1v6i–e2w of the Autonomic Nervous System Watch the > ™ on the Contraction Cycle. NEW Spotlight Figure
The Epidermis Coaching Activities
Consists of two divisions
BASIC ORGANIZATION OF THE EPIDERMIS Stratum One Spotlight F igure in each
corneum Sympathetic Division (Thoracolumbar) chapter now has an assignable
The epidermis consists of stratified squamous epithelium. Coaching Activity in MasteringA&P.
It is separated from the dermis by a basement membrane. Basement Preganglionic fibers from both the thoracic and upper lumbar spinal segments synapse in
The stratum basale and the underlying dermis interlock, membrane ganglia near the spinal cord. These axons and ganglia are part of the sympathetic division, or
strengthening the bond thoracolumbar (thor-a-kō-LUM-bar) division, of the ANS. In this division, the preganglionic
between the two. The Dermis fibers are short, and the postganglionic fibers are long. The sympathetic division brings about Parasympathetic Division (Craniosacral)
Epidermis what is often called the ”fight or flight“ response because it readies the body for a crisis that
may require sudden, intense physical activity. Preganglionic fibers originating in either the brain stem (cranial nerves III, VII, IX, and X) or the
epidermis forms epidermal Basement sacral segments of the spinal cord are part of the parasympathetic division, or craniosacral
Preganglionic Neurons division, of the ANS. The preganglionic fibers synapse in terminal ganglia, located close to the
ridges, which extend into membrane Preganglionic neurons are located in target organs, or intra-mural (murus, wall) ganglia, within the tissues of the target organs. In this
the lateral gray horns of spinal division, the preganglionic fibers are long, and the postganglionic fibers are short. The parasym-
the dermis and are Epidermal ridge segments T1–L2. pathetic division brings about what is often called the ”rest and digest“ response because it
conserves energy and promotes sedentary activities, such as digestion.
adjacent to dermal Dermal Thin skin LM ϫ 200 Ganglia
Ganglia are located near the spinal Preganglionic Neurons
papillae that project into papilla Thin skin contains four cord. Preganglionic fibers release Preganglionic neurons in brain
layers of keratinocytes, and ACh (excitatory), stimulating stem and in lateral portion of
the epidermis. Dermis is about as thick as the wall ganglionic neurons. anterior gray horns of S2–S4.
of a plastic sandwich bag
LAYERS OF THE EPIDERMIS (about 0.08 mm). Target Organs Ganglia
Most postganglionic fibers release Ganglia are in or near the target
The layers of the epidermis are best shown in a sectional view of thick skin. Thick skin contains NE at neuroeffector junctions. organ. Preganglionic fibers release
ACh (excitatory), stimulating
a fifth layer, the stratum lucidum. Because thick skin also has a much thicker superficial layer ganglionic neurons.
(the stratum corneum), it is about as thick as a standard paper towel (about 0.5 mm). Target Organs
All postganglionic fibers release
Surface Epidermis Characteristics ACh at neuroeffector junctions.
Stratum corneum
Basement t.VMUJQMFMBZFSTPGGMBUUFOFE
EFBE
JOUFSMPDLJOH
membrane LFSBUJOPDZUFT
t8BUFSSFTJTUBOUCVUOPUXBUFSQSPPG
t1FSNJUTTMPXXBUFSMPTTCZJOTFOTJCMF
perspiration
Stratum Stratum lucidum t"QQFBSTBTBHMBTTZMBZFSJOUIJDLTLJOPOMZ
corneum
Stratum granulosum t,FSBUJOPDZUFTQSPEVDFLFSBUPIZBMJOBOELFSBUJO
t,FSBUJOGJCFSTEFWFMPQBTDFMMTCFDPNFUIJOOFS
and flatter
t(SBEVBMMZUIFQMBTNBNFNCSBOFTUIJDLFO
UIF
PSHBOFMMFTEJTJOUFHSBUF
BOEUIFDFMMTEJF
Stratum Stratum spinosum t,FSBUJOPDZUFTBSFCPVOEUPHFUIFSCZ
lucidum desmosomes
Stratum basale t%FFQFTU
CBTBMMBZFS
t"UUBDINFOUUPCBTFNFOUNFNCSBOF
Dermal t$POUBJOTCBTBMDFMMT TUFNDFMMT
papilla
NFMBOPDZUFT
BOEUBDUJMFDFMMT .FSLFMDFMMT
Epidermal
ridge Thick skin LM ϫ 200 Dermis
EPIDERMAL RIDGES OF THICK SKIN 1PSFTPGTXFBU Sympathetic activation KEY Parasympathetic stimulation KEY
gland ducts “Fight or flight”response “Rest and digest” response
Fingerprints reveal the pattern of epidermal ridges. Preganglionic fibers Preganglionic fibers
This scanning electron micrograph shows the Epidermal Postganglionic fibers Postganglionic fibers
ridges on a fingertip. ridge
Thick skin SEM ϫ 20
The Epidermis Overview of the Autonomic Nervous System
Chapter 5, page 180 Chapter 16, pages 560-561
