Category: Lessons

Embryology is the branch of biology that studies the prenatal development of gametes, fertilization, and development of embryos and foetuses. Additionally, embryology encompasses the study of congenital disorders that occur before birth, known as teratology.

Embryology can be mainly studied under two main divisions. They are EMBRYOGENESIS and ORGANOGENESIS.

Embryogenesis is the process of initiation and development of an embryo from a zygote (zygotic embryogenesis) or a somatic cell (somatic embryogenesis). Embryo development occurs through an exceptionally organized sequence of cell division, enlargement and differentiation.

Studying embryogenesis can be easier if we go through the topics below.

01 GAMETOGENESIS

• Origin and migration of the germ cells
• Male gonadal primordium
• Female gonadal primordium
• Spermatogenesis
• Oogenesis

02 FERTILIZATION

• Explaining the ovulation process
• Knowing the necessary steps which lead to spermatozoa being ready
• Describing how the enabling of the spermatozoa takes place
• Describing how the spermatozoon penetrates into the oocyte
• Knowing the process whereby a zygote is formed

03 IMPLANTATION

• Describe the histological structures of the endometrium
• Explain the phases of endometrial changes during the menstruation cycle
• Know the effects of the hypophysial hormones in the regulation of the menstruation cycle
• Explain the various stages of implantation
• Know the fundamental mechanisms of the implantation at the molecular level
• List the normal types of implantation and the anomalies of the extra-uterine pregnancies
• List the various possibilities for hindering an implantation and thus a pregnancy

04 EMBRYONIC DISC

• The differentiation of the embryonic germ layers, emanating from the trilaminar embryo
• The mechanism of gastrulation and especially the morphogenetic role of the primitive streak
• The arrangement of the intraembryonic mesoblast, its segmentation and the formation of the intraembryonic coelomic cavity
• The formation of the notochord and its role in the differentiations of nerve tissue
• The stages of neurulation and the first steps in the genesis of the central and peripheral nervous system

05 EMBRYONIC PHASE

• The differentiations of the germinal layers during the fourth week of development that lead to an individualization of the embryo.
• The key concepts of the embryonic period that describe the first stages of organogenesis.
• The various types of congenital abnormalities and be able to cite a few characteristic examples.

06 FOETAL PHASE

• The duration of the pregnancy and its various developmental stages.
• Various techniques of prenatal diagnostics.
• The differences among premature, full-term and post-term births.
• The intrauterine development of the child.
• Positions of the child during birth.
• Swiss legal aspects of pregnancy termination (abortion).
• Various causes of embryo-/ fetopathies and possibilities for therapy.
• Sensitivity of the embryo or foetus to teratogenic substances.

07 FETAL MEMBRANES AND PLACENTA

• name the foetal membranes and cavities together with their components and functions
• distinguish between the maternal and foetal parts of the placenta
• describe the macroscopic morphology of the placenta
• explain the development of the placental structures during pregnancy and their influence on the physiologic functions of the placenta
• name the structural and functional characteristics of the foetal blood circulation and the properties of the hemato-placental barrier
• list the endocrine functions of the placenta
• describe the peculiarities of twin pregnancies
• name the pathologies of embryonic development (ectopic pregnancy, hydatid mole, foetal erythroblastosis) in connection with the foetal membranes

08 CHROMOSOMAL AND GENE ABERRATION

• The difference between various kinds of chromosomal aberrations and gene mutations
• Possible causes of such disorders
• Interactions between genotype and the environment
• Polygeny and abnormalities
• General clinical symptoms of chromosomal aberrations

ORGANOGENESIS, in embryology, the series of organized integrated processes that transforms an amorphous mass of cells into a complete organ in the developing embryo. The cells of an organ-forming region undergo differential development and movement to form an organ primordium, or anlage. Organogenesis continues until the definitive characteristics of the organ are achieved.

01 MUSCULAR SYSTEM

• The origin of the three muscle types
• The development of the hypaxial and epaxial parts of the muscles based on the development of the somites and their differing innervation
• The histological development of muscle fiber to maturity
• The approximate segment level of the innervation of large muscle groups as well as the partial displacement
• Congenital muscle ailments and their causes which can be understood by knowing muscle development

02 CARDIOVASCULAR SYSTEM

• The first signs of heart development as well as the location of the cardiogenic tissues
• How the serial blood circulation system is converted to a parallel one during the course of embryonic development and which factors promote this development
• The processes that occur in the partitioning of the atria and ventricles.
• An enumeration of the arterial and venous systems with their various components that are near the heart
• The relationships of the pericardial cavity in adults, taking into account pericardial development
• The various nerves that are responsible for cardiac innervation

03 BLOOD AND LYMPHATIC TISSUES

• know the development from stem cells to differentiated blood cells
• know the location where erythropoiesis occurs
• have a concept of the functions of the various blood cells both before and after birth.
• know the organs of the lymphatic system
• know how they arise
• know the difference between cell-derived and humoral immunity
• have a concept of how immunological competence arises

04 RESPIRATION TRACT

• know the various prenatal stages of lung development.
• be able to list and localize the various cells that are typical for lung tissue.
• know the components of the blood-air barrier.
• be able to describe the development of the various somatic cavities.
• know where the pericardio-peritoneal duct lies.
• know the difference between the vasa publica and privata in the lungs.
• be able to explain the occurrence of fistulas between the esophagus and trachea based on your knowledge of the development of the two structures.
• know the various mechanisms in charge of the switch of the circulation systems at birth.

05 DIGESTION TRACT

• describe the various parts that are involved in forming the face.
• trace the development of the teeth.
• explain the innervation of the tongue from an embryologic point of view.
• list the derivatives of the individual pharyngeal arches.
• construct the relationship between the aortic and pharyngeal arches.
• describe the individual portions of the intestine and know their definitive location in the abdomen.
• describe the mesenteric relationships with the associated intestinal sections and blood vessels.
• determine which blood vessel is responsible for which intestinal portion.
• map out the course
• of the portal vein and explain it from an embryologic point of view.
• know the individual parts of the pancreas and explain their derivation.
• draw the relationships of the duodenal loops in a fetus.
• discuss the development of the urogenital sinus with respect to the formation of the hind gut and anus.

06 URINARY SYSTEM

• Describe the sequence of transitory and definitive anlagen of the upper urinary tract as well as their functions over the course of their development.
• Describe how the lower urinary tract forms from the cloaca.
• Explain some of the basic mechanisms that can lead to pathological development of the urinary system.

07 GENITAL SYSTEM

• list the genetic and hormonal factors that lead to sexual differentiation
• describe the steps that occur in the differentiation of the testicles and ovaries
• explain the formation of the internal and external genitals of both sexes
• name the abnormalities that indicated disorders in the most important mechanisms of genital development

08 NERVOUS SYSTEM

• describe typical features of the central and peripheral nervous systems
• distinguish between primary and secondary neurulation
• summarize the molecular mechanisms that underlie the development of the nervous system
• correlate the formation of the brain vesicle with the structures of the completely developed brain
• name the main functional divisions of the brain and the peripheral nervous system
• explain the histological and functional differentiation of nerve tissue cells (neurons and glial cells)
• describe and interpret the importance of the basic phenomena that occur during brain development (apoptosis, cell migration, splicing)
• explain the structural equivalents between embryonic development of the spinal cord and supraspinal centers
• sketch out blood circulation in the brain

Definitions

Anatomy is the study of the structure of the body. Knowing the structure of the body helps to understand the functions of the body such as digestion, respiration, circulation and reproduction. Studying about the functions of the body is known as physiology.

The body is a chemical and a physical machine. Therefore, it is subjected to certain laws. These are sometimes called natural laws. Each part of the body is engineered to perform a particular job. We call these functions. For each body function there is a particular body structure engineered to do it.

In the laboratory, anatomy is studied by dissection (SECT = cut, DIS = apart)

Body Types

No two people are built exactly alike. Even when we consider twins, there are many differences. But, we can group individuals into three major categories. These groups represent basic body shapes.

MORPH = body, body form

ECTO = all energy is outgoing

ENDO = all energy is stored inside

MESO = between, in the middle

ECTOMORPH = slim individuals

ENDOMORPH = broad individuals

MESOMORPH = body type between the two above. (This is basically the muscular average type)

Ectomorphs, slim people are more susceptible to lung infections. Endomorph are more susceptible to heart disease.

Note On Terminology

Each profession and each science has its own language. Lawyers have legal terminology. Physicians and other medical professions and occupations have medical terminology, and educators have objectives, domains, and curricula.

To work in a legal field, you should know the meaning of quid pro quo. To work in a medical field, you should know the meaning of terms such as proximal, distal, sagittal, femur, humerus, thorax, and cerebellum.

Kinds of Anatomical Studies

Microscopic anatomy is the study of structures that cannot be seen with the unaided eye. You need a microscope.

Gross anatomy by system is the study of organ systems, such as the respiratory system or digestive system.

Gross anatomy by region considers anatomy in terms of regions such as the trunk, upper member, or lower member.

Neuroanatomy studies the nervous system

Functional anatomy is the study of relationships between functions and structures.

Organization of The Human Body

The human body is organized into cells, tissues, organs, organ systems, and the total organism.

Cells are the smallest living unit of body construction.

A Tissue is a grouping of cells working together. Examples are muscle tissue and nervous tissue.

An Organ is a structure composed of several different tissues performing a particular function. examples include the lungs and the heart.

Organ systems are group of organs which together perform an overall function. Examples are the respiratory system and the digestive system.

The total organism is the individual human being. You are a total organism.

Regions of The Human Body

The human body is a single, total composite. Everything works together. Each part acts in association with ALL other parts. Yet, it is also a series of regions. Each region is responsible for certain body activities. These regions are:

Back and Trunk: The torso includes the back and trunk. The trunk includes the thorax(chest) and abdomen. At the lower end of the trunk is the pelvis. The perineum is the portion of the body forming the floor of the pelvis. the lungs, the heart, and the digestive system are found in the trunk.

Head and Neck: The brain, eyes, ears, mouth, pharynx, and larynx are found in this region.

Members: Each upper member includes a shoulder, arm, forearm, wrist, and hand. Each lower member includes a hip, thigh, leg, ankle, and foot.

Anatomical Terminology

As I mentioned earlier, you must know the language of a particular field to be successful in it. Each field has specific names for specific structures and functions. Unless you know the names and their meanings, you will have trouble saying what you mean. You will have trouble understanding what others are saying. You will not be able to communicate well.

What is a scientific term? It is a word that names or gives special information about a structure or process. Some scientific terms have two or three different parts. These parts are known as a PREFIX, a ROOT (or base), and a SUFFIX. An example is the word subcutaneous.

SUBCUTANEOUS means below the skin.

SUB means below. SUB is the prefix.

CUTIS means skin. CUTIS is the root.

A second example is the word myocardium.

MYOCARDIUM means the muscular wall of the heart.

MYO means muscle. MYO is a prefix.

CARDIUM means heart. CARDIUM is the root.

A third example is the word TONSILLITIS.

TONSIL is the root

ITIS is the suffix and means inflammation.

So, TONSILLITIS means an inflammation of the tonsils.

The Anatomical Position

The anatomical position is an artificial posture of the human body (Figure 1.2). This position is used as a standard reference throughout the medical profession.

We always speak of the parts of the body as if the body were in the anatomical position. This is true regardless of what position the body is actually in. In the anatomical position, the body stands erect. with heels together. Upper members are along the sides, with the palms of the hands facing forward. The head faces forward.

Planes of The Body

See figure 1.3 for the imaginary planes used to describe the body.

Sagittal planes are vertical planes that pass through the body from front to back. The median or midsagittal plane is the vertical plane that divides the body into right and left halves.

Horizontal (Transverse) planes are parallel to the floor. They are perpendicular to both the sagittal and frontal planes.

Frontal (Coronal) planes are vertical planes which pass through the body from side to side. They are perpendicular to the sagittal plane.

Directions

Superior means above. Inferior means below.

Anterior refers to the front of the body. A commonly-used substitute word is Ventral.

Posterior refers to the back of the body. A commonly-used substitute word is Dorsal.

Medial means toward or nearer the midline of the body.

Lateral means away from the midline or toward the side of the body.

Superficial means closer to the surface of the body.

Deep means toward the centre of the body or body part.

Proximal and distal are terms applied specifically to the limbs. Proximal means nearer to the shoulder joint or the hip joint. Distal means further away from the shoulder joint or the hip joint. Sometimes proximal and distal are used to identify the “beginning” and “end” of the GI tract-that portion closer to the stomach being Proximal while that further away being distal.

Names

Names are chosen to describe the structure or process as much as possible. An international nomenclature was adopted for anatomy in Paris in 1995. It does not use the names of people for structures. (The single exception is the Achilles tendon at the back of the foot and ankle.)

Names are chosen to identify structures properly. names identify structures according to shape, size, colour, function, and/or location. Some examples are:

TRAPEZIUS MUSCLE
TRAPEZIUS = Trapezoid shaped, like a rectangle with uneven sides.

ADDUCTOR MAGNUS MUSCLE
AD = toward
DUCT = to carry (function)
MAGNUS = very large (size)

ERYTHROCYTE
ERYTHRO = red (colour)
CYTE = cell

Cell Introduction

A cell is the microscopic unit of body organization. the “typical animal cell” is illustrated in figure 1.4. A typical animal cell includes a cell membrane, a nucleus, a nuclear membrane, cytoplasm, ribosomes, endoplasmic reticulum, mitochondria, Golgi apparatus, centrioles, and lysosomes, and I’ll talk a little about each of them.

Major Components of a “Typical” Animal Cell

Nucleus : The nucleus plays a central role in the cell. Information is stored in the nucleus and distributed to guide the life processes of the cell. This information is in a chemical form called nucleic acids. Two types of structures found in the nucleus are chromosomes and nucleoli. Chromosomes can be seen clearly only during cell divisions. Chromosomes are composed of both nucleic acid and protein. Chromosomes contain genes. Genes are the basic units of heredity which are passed from parents to their children. Genes guide the activities of each individual cell.

Cell Membrane : The cell membrane surrounds and separates the cell from its environment. The cell membrane allows certain materials to pass through it as they enter or leave the cell.

Cytoplasm : The semifluid found inside the cell, but outside the nucleus, is called the cytoplasm.

Mitochondria (plural) : Mitochondria are the “powerhouses” of the cell. The mitochondria provide the energy wherever it is needed for carrying on the cellular functions.

Endoplasmic Reticulum : The endoplasmic reticulum is a network of membranes, cavities, and canals. The endoplasmic reticulum helps in the transfer of materials from one part of the cell to the other.

Ribosomes : Ribosomes are “protein factories” in the cell. They are composed mainly of nucleic acids which help make proteins according to instructions provided by genes.

Centrioles : Centrioles help in the process of cell division.

Lysosomes : Lysosomes are membrane bound spheres which contain enzymes that can digest intracellular structures or bacteria.

Cell Multiplication (Mitosis)

Individual cells have fairly specific life spans. Some types of cells have longer life spans than others. During the process of growth and repair, new cells are being formed. the usual process of cell multiplication is called mitosis. There are two important factors to consider.

• From one cell, we get two new cells.
• The genes of the new cells are identical (for all practical purposes) to the genes of the original cell.

Hypertrophy / Hyperplasia

Hypertrophy and Hyperplasia are two ways by which the cell mass of the body increases.

With Hypertrophy, there is an increase in the size of the individual cells. No new cells are formed. An example is the enlargement of muscles due to exercise by the increased diameter of the individual striated muscle fibers.

With Hyperplasia, there is an increased in the total number of cells. An example of abnormal hyperplasia is cancer.

Atrophy is seen when there is a loss of cellular mass.