Intro to Anatomy Guide

INTRODUCTION TO ANATOMY
By: Tewodros Yesuf (Anatomist)
COLLEGE OF MEDICINE AND
HEALTH SCIENCES

Wk Course contents
1 Introduction to human Anatomy --- 2.5 hrs. Definition and divisions of Anatomy, Anatomical terminologies, Body Parts, Planes and Body
Movement
2 Muscular system (4 hrs)--Naming of skeletal muscles , Orientation of fibers, Relative position, Antagonistic Muscles, Synergistic Muscles, Major
skeletal muscles, Origin, Insertion, Action, Innervations, Blood supply
3 Body regions and cavities (4 hrs.) - Abdominopelvic regions and quadrants, Regional names and structures
4 Levels of structural organization (4 hrs.)--Chemical level of organization ,The cellular levels of structural organization, The tissue levels of
organization, The organ levels of organization, The system levels
5 Anatomy of skeletal system (3 hrs.) The Structure of a Typical Bone, Compact bone, The Histological Features of compact bone:, Osteon
(Haversian System), Central (Haversian) canal, Perforating (Volkmann’s) canal Spongy bone, The Histological Features of Spongy Bone,
Classification of Bones
6 RESPIRATORY SYSTEM (2 hrs) -Respiratory pathways, Anatomical divisions of Respiratory system: Upper respiratory zone, Lower respiratory zone
7 CIRCULATORY SYSTEM (4 hrs) -Cardiovascular system, Heart- structure , Circulatory roots, Lymphatic system
8 Anatomy of Accessory organs (2 hrs.)
9 ANATOMY OF THE EYE (2 hrs.)----Anatomy of the Visual System, Organization of the visual cortex, Visual cortex
10 Anatomy of the Ear and Face (2 hrs.)----Functional Anatomy of the Ear and face , Anatomy & excitation of central pathways
11
12
Anatomy of the nerve system (2 hrs) Types and structures of the cells of the nervous system , Structure and function, Protection and
coverings, Spinal nerves , General structures, coverings, Brain ventricles, Principal parts and their functions, Formation and circulation of CSF
Anatomy of the peripheral nervous system (PNS)-----2hrs --- Neural pathways, Autonomic nervous system (ANS), Divisions and structures, Cranial
nerves(I-XII) nerve plexus, Spinal nerves
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 Is the study of the structures of the human body, either regionally or systematically
 An understanding of anatomy is key to the practice of medicine and other areas of
health.
 The word “anatomy” comes from the Greek words “ana,” meaning “up,” and “tome,”
meaning “a cutting.”
 Traditionally, studies of anatomy have involved cutting up, or dissecting, organisms.
 Now, however, imaging technology can show us much about how the inside of a body
works, reducing the need for dissection.
Human anatomy : Definition
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subdivisions/types
Microscopic anatomy
Gross anatomy/macroscopic anatomy
Developmental anatomy-Embryology
Specialized branch of anatomy

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1. Microscopic anatomy –the study of very small structures, where a
magnifying lens or microscope is needed
-Cytology-internal structure of single cells
-Histology-study of tissues (groups of cells)
2. Macroscopic (Gross anatomy)- the study of large, easily observable
structures (by naked eye)
Regional anatomy: study of the body by dividing in to different body regions
Systemic anatomy : systemic approach of studying anatomy
Surface anatomy: study of internal structure in relation to overlying skin

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Regional anatomy (topographical anatomy)
• the head,
• neck
• trunk (subdivided into thorax, abdomen, back,
and pelvis/perineum), and
• paired upper limbs and lower limbs.

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Specialized branch of anatomy
Pathological anatomy: study of structural change cause by disease.
Radiographic anatomy: study of internal structures visualized by X- ray
Molecular biology: studies the composition, structure and interactions of cellular
molecules such as nucleic acids and proteins – that carry out the biological
processes essential for the cell's functions and maintenance.

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Levels of Organization
(how our body is organized)
Chemical level
 CHON-most
abundant elements

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Anatomical Terminology
Standardized anatomical language used to describe the body.
Anatomical position :the standard body “map”
 Is a standardized position used to describe body parts
clearly and consistently in relation to it.
 refers to the body position as if the person were
 Standing upright.
 Head, gaze (eyes), and toes directed anteriorly (forward).
 Arms adjacent to the sides with the palms facing anteriorly.
 Lower limbs close together with the feet parallel.
Anatomical position and terminologies

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Activity 1: Directional Terms
1. Complete the sentences below using the appropriate directional term from Table 1.2.
a. The sternum is___________ to the vertebrae.
b. The orbit is __________ to the oral cavity.
c. The heart is ___________ to the lungs.
d. The carpus is____________ to the brachium.
e. The right lung and right kidney are ________ .
f. The skin is ___________ to the bones.
g. The nose is ___________ and __________to the eyes.

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MOVEMENTS

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ANATOMICAL PLANE

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ABDOMINOPELVIC REGION AND QUADRANTS

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Body cavities
The cavities of the body house the internal
organs, which commonly referred to as the
viscera.

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Organ –skin, largest organ in the body(wt =4.5-5kg)
Function
 protection against bacteria and other harmful
agents/injury.
 It inhibits excessive loss of water and electrolytes.
 It produces a protective pigmentation to protect
the body against excessive exposure from the sun.
 It helps produce the body’s supply of Vitamin D.
 It regulate body temperature and has sensory
receptors
Integumentary system

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 is composed of 206 bones that, along
with cartilage, tendons, and ligaments,
make up the framework or skeleton of
the body.
ORGANS
• Bones, cartilages, ligaments, joints
FUNCTIONS
 Protects & supports body organs
 Framework for muscles & movement
 Hematopoiesis
 store minerals
The skeletal system

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ORGAN
 Skeletal,
 cardiac and
 smooth muscle
FUNCTION
• To create movement by working with bones, ligaments,
and tendons.
• To move food through the digestive system.
• To move blood through the body by pumping the heart.
• To produce heat.
• To provide protection to inner organs.
MUSCULAR SYSTEM

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Cardiovascular system
The heart
Blood vessels
 Artery
 Veins
 Capillary
Blood

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Lymphatic
system

How Cells Are Studied
• Cytology—study of cells
– Microscopes necessary
– Measured in micrometers (1/10,000 cm)
• Microscopy
– Using a microscope to view small-scale structures
– Staining techniques provide contrast
52

• Light microscope (LM)
– Produces a two-dimensional image
– Passes light through a specimen
– Glass lenses focus and magnify image
• Electron microscope (EM)
– Beam of electrons illuminates specimen
– Greater magnification than light microscope
– Greater ability to see details (resolution)
53

• Transmission electron microscope (TEM)
– Directs an electron beam through thin-cut sections
– Produces two-dimensional images
• Scanning electron microscope (SEM)
– Directs an electron beam across surface of specimen
– Generates a three-dimensional image onto a TV screen
54

Figure 4.1
55
Microscopic Techniques for Cellular Studies

Cell Size and Shape
• Cells vary greatly in size and shape
– E.g., an erythrocyte between 7–8 μm
– E.g., human oocyte has a diameter of 120 μm
– Most are microscopic
– Shapes vary: spherical, cubelike, columnlike, cylindrical,
disc-shaped, or irregular
56

Figure 4.3 57
The
Variety of
Cell Shapes

Common Features and General Functions
• Plasma membrane
– Forms outer, limiting barrier separating internal contents from
external environment
– Modified extensions of plasma membrane
o Cilia, flagellum, microvilli
• Nucleus
– Largest structure in cell; enclosed by a nuclear envelope
– Contains genetic material, DNA
– Nucleoplasm—inner fluid
• Cytoplasm
– Cellular contents between plasma membrane and nucleus
– Includes: cytosol, organelles, and inclusions
58

• Cytoplasmic components
– Cytosol (intracellular fluid )
o Viscous fluid of cytoplasm
o High water content
o Contains dissolved macromolecules and ions
– Organelles (“little organs”)
o Complex, organized structures within cells
o Unique shapes and functions
o Two categories
˗ Membrane-bound organelles
˗ Non-membrane-bound organelles
59

̶ Organelles (“little organs”) (continued )
o Membrane-bound organelles
˗ Enclosed by a membrane
˗ Separates contents from cytosol
˗ Includes endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes,
mitochondria
o Non-membrane-bound organelles
˗ Not enclosed within a membrane
˗ Composed of protein
˗ Includes ribosomes, cytoskeleton, centrosome, proteasomes
60

• Inclusions
– Cytosol stores temporarily
– Not considered organelles
– Molecules added to and removed from continuously
– E.g., pigments, glycogen, triglycerides
61

62
Figure 4.4
The Structure of
a Cell

• Cells perform general functions
– Maintain integrity and shape of a cell
o Dependent on plasma membrane and internal contents
– Obtain nutrients and form chemical building blocks
o Harvest energy for survival
– Dispose of wastes
o Avoid accumulation that could disrupt cellular activities
– Cell division
o Make more cells of same type
o Help maintain tissue by providing cells for new growth and
replacing dead cells
63

tewodros yesuf( introduction to anatomy) 65

Embryonic Development of Tissues
• Primary germ layers
• Endoderm
• Mesoderm
• Ectoderm
• Gastrulation—process of cell movement and
differentiation, which results in development
of primary germ layers.
• Histogenesis—the process by which the
primary germ layers differentiate into different
kinds of tissue tewodros yesuf( introduction to anatomy) 66

67
Figure 5.13
Primary
Germ Layers
and Their
Derivatives
tewodros yesuf( introduction to anatomy)

Basic tissues of the body

Epithelia (singular = epithelium)
• Cover the outer surface (of the body).
• line the luminal surface of tubular structures and cavities of the body are
called epithelia

Characteristic of epithelial tissue
• Very cellular with little intercellular space
(20 nm).
• Usually avascular
• Cells rest on a basement membrane
• adhere strongly to neighboring cells and
basal laminae
• epithelia subject to friction or other
mechanical forces.
• Cells show polarity- have two pole
• Cells may display surface modifications

Epithelial Tissue
• Types and locations
• Epithelium is divided into two types:
• Membranous (covering or lining) epithelium
• Glandular epithelium
• Locations
• Membranous epithelium—covers the body and some of its parts; lines the serous
cavities, blood and lymphatic vessels, and respiratory, digestive, and genitourinary tracts
• Glandular epithelium—secretory units of endocrine and exocrine glands

Epithelial Tissue
• Classification of epithelial tissue
• Classification based on
• Cell shape
• Squamous
• Cuboidal
• Columnar
• Pseudostratified columnar
• No of cells layer
• Simple
• stratified

Simple squamous epithelium
• One-cell layer of flat cells
• Permeable to many substances
• their height being much less as compared to their width.
Location
• Endothelium, Alveolar membrane, Mesothelial cells
Function
• It helps in rapid transport of substances diffusion of gases and filtration
of fluids.
Simple Cuboidal epithelium
• the height the same as width.
• rounded nuclei

Location of simple
cuboidal epithelium

Location
• follicles of the thyroid gland, in the ducts of many glands, and on
the surface of the ovary.
• choroid plexuses(plica choroida), the inner surface of the lens, and
the pigment cell layer of the retina.
• A cuboidal epithelium with a prominent brush border is seen in the
proximal convoluted tubules of the kidneys.
Function
• It is mainly concerned with secretory and absorptive functions.

Simple columnar epithelium
• Single layer of tall,
column-shaped cells
• Cells often modified
for specialized
functions—e.g.,
goblet cells
(secretion), cilia
(movement),
microvilli
(absorption)
• Often lines hollow
visceral structures

Location
• stomach and the large intestine.
• small intestine, and with a brush border in the gallbladder.
• Ciliated columnar epithelium lines most of the respiratory tract, the uterus, and the uterine tubes.
• efferent ductless of the testis
• middle ear and auditory tube
• ependymal lining the central canal of the spinal cord and
• the ventricles of the brain.

• Pseudostratified columnar epithelium
• Columnar cells of differing heights
• All cells rest on basement membrane but
may not reach the free surface above
• Cell nuclei at odd and irregular levels
• Found lining air passages and segments of
male reproductive system.
• Motile cilia and mucus are important
modifications.

Stratified epithelium
• Stratified squamous
(keratinized) epithelium
• Multiple layers of flat,
squamous cells
• Cells filled with keratin
• Covers outer skin on body
surface

• Stratified squamous (nonkeratinized) epithelium
• Lines vagina, mouth, and esophagus
• Free surface is moist
• Primary function is protection

Stratified Columnar or Cuboidal epithelium
Description
• This epithelium consists of two or more layers of columnar or cuboidal cells
Location
• Stratified cuboidal and columnar epithelium is seen in large ducts of
exocrine glands like sweat glands, pancreas, and salivary glands.

Function
• Like all stratified epithelia it is
protective in function and it
also helps in conducting the
secretion of the glands.

Stratified transitional epithelium
• Located in lining of hollow
viscera subjected to stress
(e.g., urinary bladder)
• Often 10 or more layers thick
• Protects organ walls from tearing

Connective Tissue
• Supports, protects, and binds organs
• Composed of Cells, protein fibers, and
ground substance
• Examples
o Tendons
o Ligaments
o Adipose tissue
o Cartilage
o Bone
o Blood

Functions of CT
• Physical protection
o Bones of skull and thoracic cage protect
delicate organs
o Adipose tissue protects kidneys and eyes
• Support and structural framework
o Bones, body framework
o Place for muscle attachment
o Cartilage keeps trachea and bronchi open
o Supportive capsules around kidney and
spleen
• Binding of structures 87
Functions of CT (continued )
• Storage
o Adipose CT is the major energy
reserve
o Bone, primary reservoir for
calcium and phosphorus
• Transport
o Blood carries nutrients, gases,
wastes between regions of body
• Immune protection
o Leukocytes protects body against
disease
o Immune response when necessary
o Extracellular matrix restricts
movement of disease-causing
organisms

Characteristics of Connective Tissue
• All CT shares three basic components:
cells, protein fibers, ground substance
• Cells
• Classes of CT have specific cell types
• Most cells not in direct contact with each
other
• Two classes of cells
o Resident cells
o Wandering cells

Resident cells
̶ Stationary, housed in CT
̶ Support, maintain, repair
extracellular matrix
• Examples of resident cells
• Fibroblasts
o Flat cells with tapered ends
o Most abundant resident cells in CT proper
o Produce fibers and ground substance of
extracellular matrix
• Adipocytes (fat cells)
o Appear in small clusters in some types of CT
proper
o Adipose connective tissue—dominant area of
large clusters
89
• Mesenchymal cells
o Embryonic stem cell
o Divides to replace damaged cells
o One replaces mesenchymal cell, other
becomes committed cell
• Fixed macrophages
o Relatively large, irregular-shaped cells
o Derived from monocytes (white blood
cells)
o Dispersed throughout matrix
o Phagocytize (engulf) damaged cells or
pathogens
o Release chemicals that stimulate immune
system/attract wandering cells

• Wandering cells
• Continuously move through CT
• Components of immune system
• Repair damaged extracellular matrix
• Types of leukocytes, white blood cells
• Protect body from harmful agents
Characteristics of Connective Tissue
90

Protein fibers
• Strengthen and support tissue.
• Three types:
• collagen fibers,
• reticular fibers,
• elastic fibers
Collagen fibers
o Unbranched, “cable-like” long fibers
o Strong, flexible, and resistant to stretching
o Appear white in fresh tissue
o Numerous in tendons and ligaments
91
Reticular fibers
oSimilar to collagen fibers but thinner
oForm branching, interwoven
framework
oTough but flexible
oAbundant in stroma (CT framework)
of
˗Lymph nodes
˗Spleen

Protein fibers (continued )
• Elastic fibers
o Contain protein elastin
o Stretch and recoil easily
o Help structures return to normal shape after stretching
o Found in skin, arteries, lungs
93

Ground substance
• Non cellular material
produced by CT cells
• Residence of CT cells and
protein fibers
• Consistency:
oViscous (e.g., blood)
osemisolid (e.g., cartilage)
oSolid (e.g., bone)
• Ground substance + protein
fibers = extracellular
matrix
94
Glycosaminoglycans (GAGs)
o Large molecule in ground substance
o Carbohydrate building blocks, some
with attached amines
o Types include
˗ Chondroitin sulfate
˗ Heparin sulfate
˗ Hyaluronic acid

Ground substance (continued )
̶ Proteoglycans
o Formed with GAG linked to a protein
o 90% carbohydrate in the form of GAGs
̶ Adherent glycoproteins
o Proteins with carbohydrates attached
o Bond CT cells and fibers to ground substance
o Includes: fibronectin, fibrillin, laminin
95

• All CT derived from mesenchyme
• Mesenchyme differentiates into adult connective tissues types
• CT proper
• Supporting CT
• Fluid CT
• Connective tissue proper is divided into two categories
• Loose CT
• Dense CT
Classification of Connective Tissue
96

CT proper
•Loose CT
• Fewer cells and protein fibers than dense CT
• Protein fibers are sparse and irregularly arranged
• Abundant ground substance
• Body’s “packing material”, supports structures
• Three types
1. Areolar
2. Adipose
3. Reticular
Classification of Connective Tissue
97

̶ Areolar CT
o Loose organization of collagen and elastic fibers
o Highly vascularized
o Contains all fixed and wandering cells of CT proper
o Ground substance is abundant and viscous
o Found in the papillary layer of dermis
o Major component of subcutaneous layer
o Surrounds organs, nerve and muscle cells, and blood vessels

̶ Adipose CT (fat)
o Composed mostly of adipocytes
o Two types
˗ White (stores energy, acts as insulator, cushions)
˗ Brown (found in newborns, generates heat, lost as we age)
o Adipocyte number remains stable
o Weight gain/loss due to adipocytes enlarging or shrinking

̶ Reticular CT
o Meshwork of reticular fibers, fibroblasts, leukocytes
o Structural framework of many lymphatic organs
˗ Spleen
˗ Thymus
˗ Lymph nodes
˗ Bone marrow

CT proper
Dense CT
• Mostly protein fibers
• Less ground substance than loose CT
• Collagen fibers predominate
• Three categories
1. Dense regular
2. Dense irregular
3. Elastic
Dense CT(continued )
Dense regular CT
oTightly packed, parallel collagen
fibers
oIn tendons and ligaments
˗ Stress typically applied in a
single direction
oFew blood vessels
oTakes a long time to heal

Dense irregular CT
oClumps of collagen fibers extend in all directions
oProvides support and resistance to stress in multiple directions
oExtensive blood supply
oFound in:
˗ Most of the skin dermis
˗ Periosteum of bone
˗ Perichondrium of cartilage
oForms capsules around some internal organs

Elastic CT
oBranching, densely packed elastic fibers
oAble to stretch and recoil
oFound in
˗ Walls of large arteries
˗ Trachea
˗ Vocal cords

Supporting CT
Two type : cartilage and bone
Cartilage
• Cartilage is a tissue that forms the ‘skeletal’ basis of some parts of the body.
• e.g., the auricle of the ear, or the lower part of the nose.
• firm to maintain its form, it is not rigid like bone.
• It can be bent, returning to its original form when the bending force is removed.

Characteristics of cartilage
• In all three forms, cartilage
– Cartilage is derived (embryologically) from mesenchyme.
– is avascular- has no blood supply
– receives nutrients by diffusion from capillaries in adjacent connective tissue
(perichondrium).
– Cartilage also lacks lymphatic vessels and nerves.

CONT….
• Cartilage has very limited ability for regeneration
• The greater part of the skeleton is cartilaginous in early fetal life.
• Replacement of cartilage by bone is called ossification.

Distribution of Elastic Cartilage
• Auricle (or pinna) and of the lateral part of the external acoustic meatus.
• The wall of the medial part of the auditory tube is made of elastic cartilage.
• The epiglottis and two small laryngeal cartilages (corniculate and
cuneiform) consist of elastic cartilage.
• The apical part of the arytenoid cartilage contains elastic fibres but the major
portion of it is hyaline.

Distribution of Fibrocartilage
Secondary cartilaginous joints or symphyses.
• IVD
• PS
• MSJ
• TMJ & SCJ
• Menisci
• Glenoidal labrum & acetabular labrum

Bone
 Bone is a specialized type of connective tissue.
 Is the main constituent of skeletal system functioning as:
 Support( structural framework)
 Storage of minerals (calcium, phosphorus, magnesium)
 Storage of lipids (yellow marrow)
 Blood cell production (red marrow)
 Protection( vital organs)

Bone matrix
1. The Organic Matrix
• This consists of a ground substance in which collagen fibres are
embedded.
• The ground substance consists of:
• Glycosaminoglycans
• proteoglycans and
• water
• Two special glycoproteins osteonectin and osteocalcin are present in
large quantity.
• They bind readily to calcium ions and, therefore, play a role in mineralization
of bone.

2. The Inorganic Ions
• predominantly calcium and phosphorus (or phosphate).
• Magnesium, carbonate, hydroxyl, chloride, fluoride, citrate, sodium and potassium
are also present in significant amounts.
• Most of the calcium, phosphate and hydroxyl ions are in the form of needle shaped
crystals that are given the name hydroxyapatite (Ca10 [PO4]6[OH]).

Bone cells
Bone contain four classes of
cells,
• the first three belong to
same cell lineage include:
• Osteoprogenitor cells,
• osteoblasts,
• osteocytes
• osteoclasts, are derived
from monocyte precursors

The Periosteum
• Covers external surface of bone
• two layers: outer and inner.
• The outer layer is a fibrous membrane.
• The inner layer is cellular (osteogenic
layer).
• Periosteum is richly supplied with blood.
• Many vessels from the periosteum enter
the bone and help to supply it.

Types of Bone
Based on histology
• Compact bone
• Spongy bone
Based on maturity
• Mature/ lamellar bone
• Immature/woven bone
Based on manner of development
• Cartilage bone
• Membrane bone.

Woven bone is non-lamellar
• characterized by random disposition of
type I collagen fibers.
• It is the first bone tissue to appear in embryonic
development and in fracture repair.
-is usually temporary
-is replaced in adults by lamellar bone
-Can be found in few places in the body
-Like sutures of the calvaria and in the
insertions of some tendons.

Structure of Cancellous Bone (spongy
Bone)
• Cancellous bone is made up of a
meshwork of bony plates or rods
called trabeculae.
• The trabeculae enclose wide spaces
that are filled in by bone marrow
• They receive nutrition from blood
vessels in the bone marrow.
• The trabeculae are covered externally
by vascular endosteum containing
osteoblasts, osteoclasts and
osteoprogenitor cells.

Structure of Compact Bone
• type of bone is also made up of concentric lamellae,
and is pervaded by lacunae (containing osteocytes),
and by canaliculi
• Most of the lamellae are arranged in the form of
concentric rings that surround a narrow Haversian
canal present at the center of each ring.
• The Haversian canal is occupied by blood vessels,
nerve fibres, and some cells.
• One Haversian canal and the lamellae around it
constitute a Haversian system or osteon

• interstitial lamellae –
part of compact bone
Between adjoining
osteons
• circumferential
lamellae-Near the
surface of compact bone
the lamellae are
arranged parallel to the
surface

Formation of bony skeleton
Begins before week 8 of embryo development
Ossification:-
• Intramembranous ossification –bone develops from a fibrous membrane
connective tissue.
• Endochondral ossification – bone formed by replacing hyaline cartilage( that
is being used as a framework)

Intramembranous Ossification
 Also called dermal ossification (because it occurs in the dermis)
 produces dermal bones such as mandible, maxilla and clavicle
 Formation of most of the flat bones of the skull
 Fibrous connective tissue membranes are formed by mesenchymal cells

Endochondral ossification
Begins in the second month of development
 is the formation with in hyaline cartilage
The cartilage serves as a blueprint/model
All bones bellow the skull, except the clavicle formed through this
way

Muscle Tissue
Skeletal, Cardiac and Smooth muscles

Introduction
• Muscle tissue is one the four basic tissues in the body
• It is composed of cells with contractility property.
• As in all cells, actin microfilaments and associated proteins generate the
forces necessary for the muscle contraction
• Contraction of muscles drives movement
• within organ systems e.g. blood through vessels
• body as a whole.

Introduction
• abundant synthesis of the myofibrillar proteins actin and myosin.
• Three types of muscle tissue
• can be distinguished on the basis of morphologic and functional
characteristic
• The structure of each is adapted to its physiologic role.

Introduction
• Skeletal muscle
• contains bundles of very long, multinucleated cells with cross-striations.
• Their contraction is quick, forceful, and usually under voluntary control.
• Cardiac muscle
• also has cross-striations
• composed of elongated, often branched cells
• Cells bound to one another at intercalated discs that are unique to cardiac
muscle.
• Contraction is involuntary, vigorous, and rhythmic

Introduction
• Smooth muscle
• consists of collections of fusiform cells
• lack striations
• have slow, involuntary contractions.
• In all types of muscle, contraction
• is caused by the sliding interaction of thick myosin filaments along thin actin filaments.
• The forces necessary for sliding
• are generated by other proteins affecting the weak interactions in the bridges between actin
and myosin.

Nervous tissue

introduction
• The human nervous system
• Most complex in the body
• Formed by network of many billion nerve cells called neurons
• and glial cells responsible for protection, nourishment, and support of neurons
• Anatomically, is organized into two major divisions
• Central nervous system
• Consisting of brain and spinal cord
• Peripheral nervous system
• Composed of cranial, spinal and peripheral nerves

General Characteristics of Neurons
• Neurons (nerve cells) have certain traits
• Excitability: responsiveness to a stimulus
• Stimulus causes change in cell’s membrane potential
• Conductivity: ability to propagate electrical signal
• Voltage-gated channels along membrane open sequentially
• Secretion: release of neurotransmitter in response to conductive activity
• Messenger is released from vesicle to influence target cell
• Extreme longevity: cell can live throughout person’s lifetime
• Amitotic: After fetal development, mitotic activity is lost in most neurons
135

Figure 5.12
139
Body
Membranes

• Mucous membrane
– Mucosa
– Lines compartments that open to external environment
– Includes: digestive, respiratory, urinary, and reproductive tracts
– Performs absorptive, protective, and secretory functions
– Formed from epithelium and underlying CT
o CT component, lamina propria
o Covered with a layer of mucus derived from goblet cells, multicellular glands, or both
Body Membranes
140

• Serous membrane
– Lines body cavities that do not open to external environment
– Simple squamous epithelium (mesothelium)
– Produces thin, watery serous fluid
o Derived from blood plasma
o Reduces friction between opposing surfaces
– Forms parietal and visceral layers
– Serous cavity is in between
Body Membranes
141

• Cutaneous membrane
– Skin
– Covers external surface of body
– Composed of
o Keratinized stratified squamous epithelium
o Underlying CT
– Protects internal organs and prevents water loss
Body Membranes
142

• Synovial membrane
• Lines some joints in body
• Composed of
o Areolar CT
o Covered by squamous epithelial cells lacking basement membrane
• Synovial fluid secreted by epithelial cells
o Reduces friction among moving bone parts
o Distributes nutrients to cartilage
Body Membranes
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