Embryology ebook

Philadelphia: Saunders. Larsen's human embryology 5th ed. New York; Edinburgh: Churchill Livingstone. NLM ID: publisher page.

This online textbook edition is designed mainly for ART clinicians covering only the developmental period between oocytes to the preimplantation embryo. Links: Amazon. Hill National Library Australia holding. Molecular Biology of the Cell. New York: Garland Science; Baron S, editor. Medical Microbiology. Cite this page: Hill, M. Navigation Main page. Site map. Site updates. Recent changes. New images. Teaching Medicine. BGD2 Tutorial. Med Projects.

Sci Projects. Movies Movies. One Minute. Embryonic Start. Animal Models. In any case, pregnancy and childbirth are relevant to all ofus, and unfortunately, these processes often culminate in negative outcomes. Furthermore, prematurity and birth defects are the leading causes ofinfant mortality and major contributors to disabilities.

Fortunately, new strategies can improve pregnancy outcomes, and health care professionals have a major role to play in implementing these initiatives. However, a basic knowledge ofembryology is essential to the success ofthese strategies, and with this knowledge, every health care professional can play a role in providing healthier babies.

It stresses the clinical importance ofthe subject by providing numerous clinical examples that result from abnormal embryological events. The following pedagogic features and updates in the 14th edition help facilitate student learning. Also included in this section are chapters on placental and fetal development as well as prenatal diagnosis and birth defects.

Clinical Correlates: In addition to describing normal events, each chapter contains clinical correlates that appear in highlighted boxes. Clinical pictures and case descriptions are used to provide this information, and this material has been increased and updated in this edition. Genetics: Because ofthe increasingly important role ofgenetics and molecular biology in embryology and the study ofbirth defects, basic genetic and molecular principles are discussed.

Extensive Art Program: The artwork has always been designed to enhance understanding ofthe text and includes four-color line drawings, scanning electron micrographs, and clinical pictures. Firstly, the language has been kept simple. Care has been taken not to compress too many facts into an involved sentence. New words are clearly explained. Secondly, simultaneous references to the development of more than one structure have been avoided as far as possible.

While this has necessitated some repetition, it is hoped that this has removed one of the greatest factors leading to confusion in the study of this subject. Thirdly, almost every step in development has been shown in a simple, easy to understand, illustration. To avoid confusion, only structures relevant to the discussion are shown. As far as possible, the drawings have been oriented as in adult anatomy to facilitate comprehension. Fourthly, the chapters have been arranged so that all structures referred to at a particular stage have already been adequately introduced.

In an effort of this kind it is inevitable that some errors of omission, and of commission, are liable to creep in. To obviate as many of these as possible a number of eminent anatomists were requested to read through the text. Their suggestions have greatly added to the accuracy and usefulness of this book. Nevertheless, scope for further improvement remains, and the author would welcome suggestions to this end both from teachers and from students.

Cardiovascular System. Urogenital System. The Nervous System. After that we call it a fetus. The ovary is the female sex organ or gonad. They produce gametes. The process is called spermatogenesis. The process is called oogenesis. Spermatogenesis and oogenesis are together called gametogenesis. The fused ovum and sperm form the zygote. Genes are made of such strands of DNA. They are located on chromosomes.

The usual method of cell division, seen in most tissues, is called mitosis. Daughter cells resulting from a mitotic division are similar to the parent cell, and have the same number of chromosomes It is called meiosis.

The gametes resulting from meiosis have the haploid number of chromosomes The various gametes formed do not have the same genetic content. Stages of spermatogenesis are summarized in Fig. Spermatozoa are derived from rounded spermatids.

The process of conversion of a spermatid to a spermatozoon is called spermiogenesis Fig. The follicle has a cavity filled with fluid Fig. The cells of the theca interna produce oestrogens Fig. The follicle gradually increases in size and finally bursts and expels the ovum.

This process of shedding of the ovum is called ovulation. The corpus luteum secretes progesterone, which is essential for maintenance of pregnancy. The most obvious feature is a monthly flow of blood menstruation.

The menstrual cycle is also divided into the follicular phase in which changes are produced mainly by oestrogens , and the luteal phase in which effects of progesterone predominate. Both phases are of roughly equal duration. Just before onset of menstruation, the blood supply to superficial parts of the endometrium is cut off Fig. This part is shed off and there is bleeding.

The menstrual cycle is influenced by oestrogens, by progesterone, by the follicle stimulating hormone FSH and by the Luteinizing hormone LH.

The fertilized ovum is a large cell. It undergoes a series of divisions clevage. It has an inner cell mass covered by an outer layer of cells, the trophoblast. The morula now becomes a blastocyst. These layers are the epiblast and the hypoblast. Later, the epiblast differentiates into three germ layers, the ectoderm outer , the endoderm inner , the mesoderm middle. Cells of the hypoblast become flattened and line the yolk sac.

This is the amniotic cavity. Another cavity appears on the endodermal side. This is the yolk sac. They are soon separated from the latter by extraembryonic mesoderm. This mesoderm forms the connecting stalk. Here ectoderm and endoderm are not separated by mesoderm. A line drawn through the prochordal plate and the primitive streak divides the embryonic disc into right and left halves. It is made up only of ectoderm and endoderm. This is the notochordalprocess. This is the notochord.

Most of the notochord disappears. Remnants remain as the nucleus pulposus of each intervertebral disc. A wide strip of ectoderm overlying the notochord becomes thickened and forms the neural plate Fig.

The mesoderm next to the middle line is called the paraxial mesoderm. It undergoes segmentation to form somites. The mesoderm in the lateral part of the embryonic disc is called the lateral plate mesoderm. A strip of mesoderm between the lateral plate mesoderm and the paraxial mesoderm is called the intermediate mesoderm. The embryonic disc, which is at first flat, undergoes folding at the cranial and caudal ends.

These are the head and tail folds Fig. Lateral folds also appear. As a result of these folds, the endoderm is converted into a tube, the gut. It is divisible into foregut, midgut and hindgut. Caudally, the gut is closed by the cloacal membrane.

The umbilical cord develops from the connecting stalk. The ground substance of the umbilical cord is made up of Wharton's jelly derived from mesoderm. The cord is covered by amnion. The allantoic diverticulum arises from the yolk sac before formation of the gut Fig. After formation of the tail fold, it is seen as a diverticulum of the hindgut. The developing heart lies ventral to the cavity Fig. After formation of the head fold the pericardial cavity lies ventral to the foregut; and the developing heart is dorsal to the pericardial cavity Fig.

After formation of the head fold, it lies caudal to the pericardium and heart Fig. The liver and the diaphragm develop in relation to the septum transversum. This is called implantation. The villi are surrounded by maternal blood. Fetal blood circulates through capillaries in villi. All substances passing from mother to fetus and vice versa traverse this membrane. They consist of a central core of cytotrophoblast covered by syncytiotrophoblast.

As the placenta enlarges, septa grow into the intervillous space dividing the placenta into lobes. The fully formed placenta is about six inches in diameter and about g in weight. A placenta attached lower down is called placenta praevia.

It can cause problems during child birth. Further enlargement of amniotic cavity obliterates the uterine cavity. Fused amnion and chorion called membranes bulge into the cervical canal during child birth and help to dilate it. Epithelia lining external surfaces of the body, and terminal parts of passages opening to the outside are derived from ectoderm. Epithelium lining the gut, and of organs that develop as diverticula of the gut, is endodermal in origin.

Epithelium lining most of the urogenital tract is derived from mesoderm. In some parts, it is endodermal in origin. Mesenchyme is made up of cells that can give rise to cartilage, bone, muscle, blood and connective tissues. Blood cells are derived from mesenchyme in bone marrow, liver, and spleen. Lymphocytes are formed mainly in lymphoid tissues. Most bones are formed by endochondral ossification, in which a cartilaginous model is first formed and is later replaced by bone.

Some bones are formed by direct ossification of membrane intramembranous ossification. An area where ossification starts is called a centre of ossification. In the case of long bones the shaft or diaphysis is formed by extension of ossification from the primary centre of ossification.

Secondary centres of variable number appear for bone ends.