this is the definition, subdivisions, terminologies and body planes that illustrate an introductory to Human Anatomy

1. DEBRE TABOR UNIVERSITY
COLLEGE OF MEDICINE & HEALTH SCIENCES
GENERAL ORIENTATION TO
HUMAN ANATOMY
1
Berhanu K. (MSc)
By Berhanu K. (MSc.)

2. 1.1 Definition
• The word “Anatomy “derived from the Greek term “anatome” (ana
= apart and tome = cutting). Therefore, anatomy means to cut
apart, divide or dissect.
• HumanAnatomy is the study of the structure of the human body and the
relationships among structures.
• It clarify normal structures of the body and their interrelationship.
• It is basic for any medical discipline
• Anatomy is closely related to physiology, the study of body
function.
• Although they are studied in separate courses, anatomy and
physiology are truly inseparable, because structure supports
function.
2
Berhanu K. (MSc)

3. 1.2 BRIEF HISTORY
 Is one of the old Biomedical sciences.
 It was first formally studied in Egypt - around 500 B.C
 Earliest descriptions of human anatomy were written on
papyruses- B/n 3000 and 2500 B.C
 It was taught in Greek by Hippocrates (460 - 377 B.C.E.)
 Aristotle (384-322 BC) was the first person to use the word
“anatome.”
 During renaissance artists & anatomists like Leonardo
davinci, Michelangelo, and Vesalius began to accurately
display and describe the parts of the human body.
 In 1543 the first comprehensive human anatomy book on
the structure of human body was published by Andreas
Vesaliu.
3
Berhanu K. (MSc)

4. 1.3 Subdivisions of anatomy
In the 19th century anatomy started to be divided into its
different parts.
 Gross (macroscopic) anatomy
is the study of the human body or its parts without the
help of a microscope.
 Microscopic anatomy
 the study of cells, tissues & organs of the body by the
help of microscope. It includes;
Cytology: study of cells
Histology: study of tissues
4
Berhanu K. (MSc)

5. Cont…
Developmental anatomy: anatomy of the structural
changes of an individual from fertilization to adulthood.
it includes embryology & postnatal development.
Other subdivisions:
 Applied (Clinical) anatomy:
– emphasizes aspects of bodily structure and function important in
the practice of medicine, dentistry, and the allied health sciences.
– It stresses clinical application.
 Surgical anatomy:
– is the study of anatomy in connection with surgical operations and
surgical procedures (e.g. anatomy of surgical incisions, anatomy of
surgical exposures…..).
5
Berhanu K. (MSc)

6.  Surface anatomy
• is the study of the surface landmarks of the underlying bony points,
muscles and tendons. It is also concerned with drawing on the
surface of the body the course of position of an internal structure
(e.g. surface anatomy of the heart, the lung or the main nerves and
vessels).
 Radiological anatomy:
• is the study of anatomy using radiological techniques e.g. X-rays,
ultrasound, CT scan and MRI to demonstrate the bones or some
internal organs as the heart, lungs, kidneys, stomach and intestine.
 Functional anatomy
 Descriptive anatomy
 Comparative anatomy
Berhanu K. (MSc) 6

7. 1.4.1 Regional or Topographic anatomy
 is the anatomy of certain related parts or divisions of the body
 Helps to know structural r/ship of portions of several systems
and for dissections of cadavers.
 Recognizes the body's organization by layers:
 skin
 subcutaneous tissue/ superficial fascia
 deep fascia
 muscles
 Neurovascular structures
 skeleton and cavities
7
Berhanu K. (MSc)
1.4 Approaches of Studying Anatomy

8. Regional anatomy cont…
 Head
Neck
Back
Upper limb
Thorax
Abdomen
Pelvis and perineum
Lower limb
8
Berhanu K. (MSc)

9. 1.4.2 Systems of the body
 an approach to anatomical study organized by organ systems
that work together to carry out complex functions.
 it is studying anatomy emphasizes the purposes of various
organs within a system.
The 11 human systems
Integumentary
 Skeletal
 Muscular
 Nervous
 Endocrine
Cardiovascular
 Respiratory
Digestive
 Urinary
Reproductive
 lymphatic/immune system
9
Berhanu K. (MSc)

10. 1.5 Anatomical Terminology
1.5.1 The Anatomical Position
 is a position used as a reference when describing
parts of the body in relation to each other.
 allow a standard way of documenting where one part
of the body is in relation to another, regardless of
whether the body is standing, lying down, or in any
other position.
 All anatomical descriptions are expressed in relation
to the anatomical position.
10
Berhanu K. (MSc)

11. CONT...
In anatomical position:
• Person is erect with the
head, eyes and toes pointing
forwardand facing the observer.
• The headlevel & eyes
facing directly anteriorly.
• Arms at the sides with
palms turnedforward.
• Feet are close together and flat on the
floor, parallel & directed forward.
11
Berhanu K. (MSc)

12. 1.5.2 Anatomical planes
Anatomical descriptions are based on four imaginary planes
(median, sagittal, frontal, and transverse) that intersect the
body in the anatomical position.
1. Median/Midsagittal plane: the vertical plane passing
longitudinally through the body, divides the body into right
and left halves. It defines the midline of head, neck, and trunk
where it intersects the surface of the body.
2. Sagittal planes : vertical planes passing through the body
parallel to the median plane. Parasagital is commonly used
term instead of it.
12
Berhanu K. (MSc)

13. Cont…
3. Frontal (coronal) planes:
 vertical planes passing through the body at right
angles to the median plane.
 divide the body into anterior(front) and posterior(back)
parts.
4. Transverse planes:
 passes the body at right angles to the median and
frontal planes,
 divide the body into superior (upper) and inferior
(lower) parts.
13
Berhanu K. (MSc)

14. 14
Berhanu K. (MSc)
Anatomical planes…

15. 1.5.3 Term of position and relation
1. Superior - above.
2. Inferior - below.
3. Cranial (rostral, cephalic) - nearer to the head.
4. Caudal - nearer to the tail
5. Anterior - in front.
6. Posterior – behind.
7. Ventral - in the direction of abdomen.
8. Dorsal - in the direction of the back.
15
Berhanu K. (MSc)

16. Terms of position….
9. Medial - nearer to the midline.
10. Median - at the median plane
11. Lateral - to the side.
12. Proximal – upper (nearer to origin).
13. Distal – lower( far away from origin).
14. Palmar - on the side of the palm of the hand.
15. Plantar - on the side of the sole of the foot.
16. Superficial - nearer to the body surface.
17. Deep - nearer to the center of the body.
16
Berhanu K. (MSc)

17. 17
Berhanu K. (MSc)

18. Berhanu K. (MSc) 18

19. 1.5.4 Terms of Laterality
 Bilateral - Paired structures having right and left
members (e.g., kidneys)
 Unilateral - on one side only (eg. Liver, spleen)
 Ipsilateral - something occurring on the same side of
the body. (eg. Liver and appendix, spleen and heart.
 Contralateral - occurring on the opposite side of the
body. (Eg. Liver and spleen)
19
Berhanu K. (MSc)

20. 1. 5.5 Terms of Movement
 Flexion: bending or decreasing the angle b/n the bones
or parts of the body
 Extension: straightening or increasing the angle
between the bones or parts of the body
 Abduction: moving away from the median plane in the
frontal plane
 Adduction: moving toward the median plane in a frontal
plane.
 Circumduction: circular movement that is a
combination of flexion, extension, abduction, and
adduction.
 Rotation: revolving a part of the body around its
longitudinal axis.
20
Berhanu K. (MSc)

21. Berhanu K. (MSc) 21

22. Terms of movement….
• Pronation : palm of the hand faces posteriorly and its
dorsum faces anteriorly
• Supnation: hand faces posteriorly and the palm faces
anteriorly
• Opposition: the mov’t by which the pad of the thumb is
brought to another digit pad
• Reposition: movement of the thumb from the position
of opposition back to its anatomical position.
• Protrusion: movement anteriorly
• Retrusion: movement posteriorly
22
Berhanu K. (MSc)

23. Inversion and eversion
These movements occur in the foot at the subtalar
(talocalcaneonavicular) joint
– inversion: The sole of the foot (its inferior surface) is directed
inwards.
– eversion: the sole is directed outwards.
23
Berhanu K. (MSc)
Other movements:
 Elevation:
• moving up
 Protraction:
• moving anteriorly
 Depression:
• moving down
 Retraction:
• moving
posteriorly

24. Berhanu K. (MSc) 24

25. 1.6 Body Cavities
25
Berhanu K. (MSc)

26. Body cavities cont…
 Body cavities are spaces within the body that house
internal organs. Bones, muscles, and ligaments separate the
various body cavities from one another.
 Dorsal cavity: protects the nervous system, and is
divided into two subdivisions
Cranial cavity is within the skull and encases the brain.
Vertebral cavity runs within the vertebral column and
encases the spinal cord.
 Ventral cavity/Cavities of Trunk: houses the internal
organs (viscera), and is divided into two subdivisions:
 Thoracic and
 Abdominopelvic cavity.
26
Berhanu K. (MSc)

27.  Thoracic cavity is subdivided into pleural cavities, the
mediastinum, and the pericardial cavity.
Pleural cavities – each houses a lung
Mediastinum – contains the pericardial cavity, and
surrounds the remaining thoracic organs.
Pericardial cavity – encloses the heart
The abdominopelvic cavity is separated from thoracic cavity
by the dome-shaped diaphragm.
27
Berhanu K. (MSc)

28. 28
Berhanu K. (MSc)

29.  Abdominopelvic cavity; composed of two subdivisions
Abdominal cavity – contains the stomach, intestines,
spleen, liver, and other organs.
Pelvic cavity – lies within the pelvis and contains the
bladder, reproductive organs, and rectum.
Ventral Body Cavity Membranes
 Parietal membrane- lines internal body walls
 Visceral membrane- covers the internal organs
 Serous fluid- separates the two membranes
- used for lubrication
29
Berhanu K. (MSc)

30. 2. Structural Levels Of Organization
 The human body extend from the smallest body structures
and their functions to the largest structure.
1) Atom [i.e. Carbon (C), Hydrogen (H), or Oxygen(O)] is the
least complex level. Atoms combine with (react with) other
atoms to form molecules.
2) Molecules [i.e. carbon dioxide (CO2), water (H2O)]. A
molecule is a particle composed of 2 or more joined atoms.
Molecules combine with other molecules to form
macromolecules.
3) Macromolecules (i.e. carbohydrates, lipids, proteins, nucleic
acids). A macromolecule is a large molecule and it combines
with other macromolecules to form organelles.
30
Berhanu K. (MSc)

31. 4) Organelles (i.e. cell membrane, nucleus, ribosome). An
organelle is a small organ of a cell, which performs a
particular function. Organelles collectively compose a cell.
5) Cells (eg. Hepatocytes, enterocytes, neurons, osteocytes…)
 The smallest independent units of life
 The basic unit of structure and function of living
organisms!
 Similar cells are arranged into tissues
6) Tissue (i.e. epithelial, connective, muscle and nervous tissues).
 A tissue is a group of similar cells that performs a
specialized function.
 Two or more tissues combine to form organ.
31
Berhanu K. (MSc)

32. 7) Organs (i.e. skin, heart, brain, liver, kidney…).
An organ is a structure consisting of a group of tissues that
performs a specialized function.
Two or more organs combine to form organ system.
8) Organ systems (i.e. respiratory, cardiovascular, digestive...)
An organ system is a group of organs that act together to
carry on a specialized function.
There are 11 organ systems. The eleven organ systems
collectively form the organism.
9) Human organism
An organism is the most complex level of organization
and is defined as an individual living thing.
32
Berhanu K. (MSc)

33. 33
Berhanu K. (MSc)

34. 3. THE CELL
34
Berhanu K. (MSc)

35. Berhanu K. (MSc) 35
3.1 INTRODUCTION
• A cell is the smallest independent functional and structural
unit of a living thing.
• The study of cell structure and its function is collectively
called cytology.
• The human body contains over 75 trillion cells each of
which perform a specific function.
 The two basic cell types
Prokaryotes: lack nuclear envelope, histones &
membranous organelles. Eg. bacteria and blue green algae
Eukaryotes: Has distinct nucleus surrounded by a
nuclear envelope, histones and membrane-limited
organelles. These include the protists, fungi, plant and
animal cells.

36. Berhanu K. (MSc) 36
The basic functional activities or properties of cells includes
metabolism, growth, regeneration, irritability (excitability),
movement, reproduction, aging and death.
Modern theory of cells:
1. All living things are made up of one or more cells.
2. Cells are the basic living units within organisms and the chemical
reactions of lifetake place within cells.
3. All cells arise frompre-existing cells.

37. 3.2 Cell Shapes and Sizes
• There are about 200 different types of cells in human body,
which there shape and size vary greatly.
A. Cell shapes
 Squamous: thin and flat & lines the esophagus and cover
the skin
 Polygonal: irregular, consists of about 4, 5 or more sides.
 Stellate: star like extensions of nerve cells
 Cuboidal: cube shaped, and they are as tall as they are
wide. eg. Liver cells
 Columnar: taller than wide & lines intestinal organs.
37
Berhanu K. (MSc)

38. Cell shapes….
 Spheroid/ ovoid: sphere like cells. Eg. Egg cells
 RBCs have a disc-like shape, called discoid
 There are also fusiform and fibrous (thread like) cells,
which are particularly present in smooth and skeletal
muscles, respectively.
Discoid shape - RBC
stellate
Nerve cells
Fibrous shape
Skeletal muscles
38
Berhanu K. (MSc)

39. Polygonal
Squamous Cuboidal Columnar
Stellate
Discoid shape - RBC fusiform Fibrous shape
Spheroid/ ovoid
39
Berhanu K. (MSc)

40. B. Cell Size
o Cell size is independent of body size but it shows relations
to differentiation and function.
o Because of the various functions that exist in our body, we
have cells with variable sizes.
For example:
 The human egg cell (ovum) has a diameter of about 0.15
- 0.20 mm.
 The human red blood cell (RBC) measures about 7.4 µm.
 A small human lymphocyte measures about 6 µm.
 The striated muscle fiber can be as long as 15 cm.
 The nerve cells with their processes can be more than 1
meter long.
Berhanu K. (MSc) 40

41. 3.3 Cell Extensions
• Two types of cellular extensions are cilia and flagella.
• Cilia are small hair like projections which beat to move
substances.
• The respiratory tract is lined with cilia which only beat in
one direction to move substances up from the lungs.
• Flagella are cellular projections which help the cell to move.
• A flagellum is found on sperm cells and helps them to
swim to fertilize the egg.
41
Berhanu K. (MSc)

42. Cell
Nucleus
Nuclear membrane
Chromatin skeleton
Nucleolus
Nucleoplasm
Cytoplasm
 Cell membrane
 Cytoplasmic matrix
(cytosol)
 Organelles
 Inclusions
42
Berhanu K. (MSc)
o A cell is composed of different structures that carry its complex
functions and these are grouped into two basic parts.
1. Cytoplasm: bounded by plasmalemma (cell membrane)
2. Nucleus: surrounded by nuclear membrane
3.4 Structural Composition of a Cell

43. Organelles
Commonly found
 Mitochondria
 Endoplasmic reticulum
 Golgi apparatus
 Centrioles
 Lysosomes
 Ribosomes
 Microbodies
Specialized
 Microfilaments
 Microtubuli
 Myofilaments (fibrils)
 Tonofilaments
 Neurofilaments
 Synaptic vesicles 43
Berhanu K. (MSc)
Organelles are permanent components of the cytoplasm of a cell while inclusions
like proteins, carbohydrates, lipids, pigments etc. are temporary components.

44. Berhanu K. (MSc) 44

45. Cell membrane (plasma membrane,
plasmalemma, cytolemma)
 It is a 7 - 10 nm thick barrier between the intra and extracellular
spaces.
 It is selectively permeable to substances entering and leaving the
cell and studded with proteins that regulate the flow of materials
in and out of the cell.
 Cell membrane is not visible in a light microscope.
 The cell membrane is composed of:
1. A layer of lipid molecule: consists of phospholipids and
cholesterol
This layer contains a hydrophobic (non-polar ) group
directed to the interior of the membrane and
45
Berhanu K. (MSc)

46. Berhanu K. (MSc) 46
a hydrophilic (polar or ionic) group directed towards the inner
and outer surfaces of the membrane.
2. Protein molecules: cover the lipid layer on either sides.

47. Functions of the cell membrane
• Permeability barrier: control the movement of substances
into and out of cells
• Keep the cells contents together and separate from other
cells
• Antigenic determinant of a cell.
• Transmembrane transport (e.g. nutrients, gases
electrolytes etc).
• Receptor for chemical messengers from other cells (e.g.
hormones, neurotransmitters).
47
Berhanu K. (MSc)

48. The two types of organelles:
A. Membranous
(membrane bounded)
1. Mitochondria
2. Endoplasmic reticulum
3. Golgi apparatus
4. Lysosomes
5. Peroxisomes
6. Endosomes
48
B. Non- membranous
(organelles that have
no membrane)
1. Ribosomes
2. Centriole
3. Microtubuli
4. Microfilaments
Berhanu K. (MSc)

49. Mitochondria
• thread like filamentous organelle (0.2 μm wide, up to 7 μm
long)
• Composed of an outer and an inner mitochondrial
membrane
 Outer mitochondrial membrane contains specialized
transmembrane transport proteins that allow
permeability to certain metabolic substrates
 An inner mitochondrial membrane thrown into
numerous folds, the cristae
Berhanu K. (MSc) 49

50. Mitochondria…
 The space between cristae is filled with a fine granular
mitochondrial matrix in which enzymes of the:
citric acid cycle,
fatty acid catabolism and
 protein synthesis are found
 The mitochondrial matrix contains a strand of
deoxyribonucleic acid (DNA) arranged as a circle in a
manner analogous to the chromosomes of bacteria.
 The matrix also contains ribosomes which have similar
structure with bacteria ribosome.
50
Berhanu K. (MSc)

51. Endoplasmic reticulum (ER)
o It is a network of double membranes that enlarge the
internal surface area of the cell for chemical or enzymatic
reactions.
o It consists of an irregular network of tubules forming
large, parallel and flattened saccular structures referred
to as cisternae.
Berhanu K. (MSc) 51

52. ER…
There are essentially two specialized types of ER.
1. Rough (granular) RER:
 has ribosomes attached to its outer limiting
membrane
 It contains ribophorins I and II (integral membrane
proteins.)
 Involved in protein synthesis which takes place in the
Ribosomes attached to it.
2. Smooth (agranular) SER:
 has no ribosomes attached to it and contains no
ribophorins I and II.
 involved in the synthesis of steroids, e.g. cells of adrenal
cortex and other endocrine glands.
52
Berhanu K. (MSc)

53. Golgi apparatus
o composed of several smooth membrane bounded flattened
saccules (vesicles, vacuoles) or cisternae.
o The saccules and cisternae are the structural units of the Golgi
complex.
Berhanu K. (MSc) 53

54. Regions of Golgi apparatus
 Cis (entry) face
 Forming (outer, convex) cisternae at side of the stack facing
the RER and transverse vesicle.
Trans (exit) face
 Maturing (inner, concave) cisternae at side of the stack facing
vacuoles & secretory granules
Berhanu K. (MSc) 54

55. Lysosome
 Lysosomes (Lyse = destroy, some = body)
 They are vesicles filled with hydrolytic enzymes
 Have more than 50 enzymes, active at an acid pH (acid
hydrolases)
 constitute the intracellular digestive system, that digests aged
cellular structures and foreign bodies.
Peroxisomes
 formed by budding from other organelles mainly from the SER.
 They contain oxidative enzymes that produce hydrogen
peroxide (H2O2)
used by some phagocytic cells to kill engulfed
microorganisms.
55
Berhanu K. (MSc)

56. Ribosome
• responsible for the synthesis of proteins from amino acids.
• They are composed of rRNA and proteins.
• In animal cells they are made up of two subunits
 Found in two forms
– Free ribosomes:
float in the cytosol; have no attachments to other
organelles.
 synthesize proteins for use inside the cell.
– Attached riosomes:
attached to the RER and nuclear membrane.
Involved in the synthesis of proteins destined for insertion
in the plasma membrane or for export from the cell.
Berhanu K. (MSc) 56

57. The Nucleus
o The nucleus or karyon is the most prominent structure in a
cell.
o One of the attributes that distinguishes eukaryotic from
prokaryotic.
o It serves as:
1. An archive of the cell.
2. The repository (storage place) of genome.
3. Source of informational macromolecules (t-RNA, m-
RNA, r- RNA) that initiate, coordinate and control
the synthetic activity of the cytoplasm.
57
Berhanu K. (MSc)

58. o Commonly cells contain one nucleus.
o But some cells have more than one nucleus, e.g. liver cells,
Osteoclasts
o Some cells lack nucleus, e.g. RBC, platelets, lens fibers.
Berhanu K. (MSc) 58
 major components of
a nucleus are:
1. Nuclear envelope
2. Chromatin
3. Nucleolus
4. Nuclear matrix

59. • Histology is the
scientific study of
tissues
 Tissues are
composed of similar
cells performing
similar functions.
 4 types of tissue
– Epithelial tissue
– Connective Tissue
– Muscular Tissue
– Nervous Tissue
59
4. HISTOLOGY
Berhanu K. (MSc)

60. 4.1 Epithelial tissue (epithelium)
Two types:
 Membranous
 glandular
A. Membranous/covering epithelium
Covers the body's surface
Lack blood vessels.
line inner body cavities and lumina (hollow portion body
tubes), and the covering of visceral organs.
Externally, provides protection from drying, injury and
bacterial invasion.
60
Berhanu K. (MSc)

61. Three main types
based on shape
 Squamous
- flat cells,
- found lining lungs and
blood vessels
 Cubodial
- cubed shaped cells,
- line the kidney tubules
 Columnar
- cells resemble columns,
- line the digestive tract
Three types based
on cell layers
Simple: single layer of cells
Eg. intestine
Stratified: two or more
layers of cells. eg. nose,
mouth, esophagus,
epidermis of skin.
Pseudostratified: appears to
be stratified but each cell
attached to the basement
membrane.
Berhanu K. (MSc) 61

62. Berhanu K. (MSc) 62

63. B. Glandular epithelium: form glands
– two types
• exocrine glands
–secretes products into ducts.
–e.g salivary and sweat
• endocrine glands
– secretes products into blood.
–e.g. pituitary and thyroid glands
63
Berhanu K. (MSc)

64. 4.2 Connective Tissue
- Most diverse, abundant, widely distributed, and
microscopically variable of the tissues
- Binds structures together
- Provides support and protection
- Fills spaces
- Stores Fat
- Cells are widely separated by a matrix
They are different types
i . Loose Connective Tissue
ii. Fibrous Connective Tissue
iii. Cartilage, Fat
iv. Bone
v. Blood
64
Berhanu K. (MSc)
connective tissue proper

65.  Basic components of connective tissue
• All CT share three basic components:
 cells
 protein fibers
 ground substance
 Cells
• connective tissue proper contains fibroblasts
• fat contains adipocytes,
• cartilage contains chondrocytes, and
• bone contains osteocytes.
• Blood contains, RBC, WBC, platelates
– Many CTs contain white blood cells such as macrophages, which
phagocytize foreign materials.
Berhanu K. (MSc) 65

66.  Protein fibers
• Three basic types of protein fibers:
 collagen fibers are strong and stretch-resistant
 elastic fibers are flexible and resilient
 reticular fibers form an interwoven framework
 Ground substance
– Nonliving material produced by the CT cells.
– composed of protein and carbohydrate and variable
amounts of water.
– Eg. Glycosaminoglycans, proteoglycans, glycoproteins…
Berhanu K. (MSc) 66

67. 67
4.3 Muscular Tissue
Composed of fiber that contain "actin" and "myosin"
microfilaments
Movement (muscular contraction) occurs when these
two interact
There are three types of muscular tissue:
• Skeletal muscle
• Smooth muscle
• Cardiac muscle
Berhanu K. (MSc)

68.  Skeletal muscle
 attaches to the bones, its function is to move skeleton
 is striated and under voluntary control
 its fibers are cylindrical
 are many nucleated
 have striated appearance
 is the fastest of all muscular contractions
 Smooth muscle
lacks dark bands, no striations
is an involuntary muscle
Found in the intestines, stomach, arteries
Muscles contract more slowly
can remain contracted for a longer period of time
68
Berhanu K. (MSc)

69. Cardiac muscle
 is present in the heart,
 responsible for the heartbeat
 have striated appearance
 Fibers appear branched, so that the contractions occur in
many directions
 is an involuntary muscle
69
Berhanu K. (MSc)

70. 4.4 Nervous Tissue
 Found in the Nervous system
Composed of neurons and neuroglial (Glial) cells
 Neurons
are the functional and structural units of nervous tissue.
are excitable cells that initiate and transmit nerve
impulses.
are mitotically inactive, i.e Do not divide (amitotic).
Neurons are composed of:
• Cell body - contains nucleus
• Dendrite - conducts impulse to the cell body
• Axon - conducts impulse away from the cell body
70
Berhanu K. (MSc)

71.  Glial Cells
Non- excitable; Support and protect the neurons
 Include:
astrocytes
oligodendrocytes
microglia
ependymal cells
Schwann cells (neurolemmocytes)
satellite cells
Those that encircle the fibers are called "Schwann" cells.
71
Berhanu K. (MSc)
Found in the CNS
Found in the PNS

72. 72
Berhanu K. (MSc)

73. 5. INTRODUCTION TO EMBRYOLOGY
 The study of the developmental events that occur during
the prenatal period
 The first 38 weeks of human development
• between fertilization and birth.
 A single fertilized cell (zygote) divides by mitosis to
produce all of the cells in the body.
73
Berhanu K. (MSc)

74.  Fertilization
• Two sex cells fuse to form a new cell containing genetic
material derived from both parents.
• Restores the diploid number of chromosomes.
• Determines the sex of the organism.
• Initiates cleavage.
• Fertilization occurs in the widest part of the uterine tube
(the ampulla).
• the union of an oocyte and a sperm during fertilization
results in Zygote.
Berhanu K. (MSc) 74

75. Cleavage: the series of mitotic cell divisions of the zygote
to form early embryonic cells, blastomeres
 After fertilization, the zygote begins to undergo a series of
divisions.
• Divisions increase the number of cells in the pre-embryo.
• After the third cleavage division, the cells become tightly
compacted into a ball called a morula (16 cells).
Blastocyst: morula enters the uterus and surrounded by a
fluid-filled cavity, blastocystic cavity.
• Forms two layer of cells
 Outer, Trophoblast = gives nutritional support
 Inner cell mass, embryoblast = embryo proper
75
Berhanu K. (MSc)

76. Implantation: is the process by which the blastocyst
burrows into and embeds within the endometrium.
• Begun about day 7; done by day 9
Trophoblast subdivides
• Cytotrophoblast
• Syncytiotrophoblast
Bilaminar Germinal Disc : By day 8, embroblast begins to
differentiate.
– Hypoblast layer: adjacent to blastocyst cavity
– Epiblast layer: adjacent to amniotic cavity
• Together called bilaminal germinal disc
76
Berhanu K. (MSc)

77. 77
Berhanu K. (MSc)

78. Extra embryonic membranes
 Amnion
• encloses the entire embryo in a fluid-filled sac called the
amniotic cavity to prevent desiccation.
• The amniotic membrane is specialized to secrete the
amniotic fluid that bathes the embryo.
Chorion
• The outermost extraembryonic membrane, is formed from
rapidly growing cells.
• These cells blend with the functional layer of the
endometrium and eventually form the placenta.
78
Berhanu K. (MSc)

79.  Placenta
• Functions in exchange of nutrients, waste products, and
respiratory gases between the maternal and fetal bloodstreams.
• Transmission of maternal antibodies to the developing embryo
or fetus.
• Production of hormones to maintain and build the uterine
lining.
Gastrulation: process of formation of the three embryonic germinal layers
• occurs during the 3rd week of development immediately after
implantation.
• Cells of the epiblast migrate and form the three primary germ
layers:
 Ectoderm
 Mesoderm
 endoderm.
79
Berhanu K. (MSc)

80. Differentiation of
ectoderm
• Notochord forms
in area of
primitive streak
This induces
neurulation.
• Neurulation is
Process of
formation of:
 Neural plate
 Neural folds
 Neural Groove
 Neural tube
3-80
Berhanu K. (MSc)

81. 3-81
Berhanu K. (MSc)
Five categories:
 Notochord
 Paraxial mesoderm
 Somites: most bone,
muscle, cartilage, dermis.
 Intermediate
mesoderm
Urogenital system
 Lateral plate mesoderm
Cardiovascular,
lining of body
cavities, CT of limbs
 Head mesenchyme
CT and musculature
of face
Differentiation of
Mesoderm

82. Differentiation
of Endoderm
• Linings of
digestive,
respiratory and
urinary tracts.
• Thyroid
• parathyroid
• thymus
• most of liver
• pancreas and
• gallbladder.
3-82
Berhanu K. (MSc)

83. Organogenesis
• Begins once the three primary germ layers have formed,
and the embryo has undergone folding.
• The upper and lower limbs attain their adult shapes, and
the rudimentary forms of most organ systems have
developed by week 8.
• By the end of the embryonic period, the embryo has the
outward appearance of a human.
 Fetus: is the developing human after the embryonic
period (8 weeks)and until birth.
• During the fetal period (9th week to birth), differentiation
and growth of the tissues and organs occur.
83
Berhanu K. (MSc)

84. THANK YOU
Berhanu K. (MSc) 84