Cytoplasm - Zagazig University Zoology Department

Zagazig University Zoology Department Faculty of Sciences Course Code : z 221  Cytoplasm Cytoplasm composed of three main components: 1-Cytoplasmic organelles A- membranous organelles: Mitochondria , Lysosomes, RER , SER, Golgi appa...

Zagazig University Zoology Department Faculty of Sciences Course Code : z 221  Cytoplasm Cytoplasm composed of three main components: 1-Cytoplasmic organelles A- membranous organelles: Mitochondria , Lysosomes, RER , SER, Golgi apparatus and secretory vesicles. B- Non membranous organelles: -Ribosomes - Microtubules (centrioles, cilia and flagella) -Microfilaments (tonofilaments, neurofilaments and myofilaments) 2-Cytoplasmic inclusions: a- stored food (glycogen and lipids) b- pigments: -exogenous (carotene & carbon particles) -endogenous (blood pigments, melanin & lipofusein) 3--Cytoplasmic matrix (cytosol) 1  1- Mitochondria Mitochondria are membranous organelles present in all animal cells.At light microscope level (LM) it appears in the form of either granules, short rod or threads. One or more of such mitochondrial types may be present in the same cell. At the electron microscope (EM) level: Mitochondria appears rounded or oval vesicles each being composed as following: 1) Outer Membrane: The outer membrane is smooth. It has a large number of special proteins called porins.The outer membrane is freely permeable to small molecules (nutrient molecules, ions, ATP and ADP molecules). 2) Inner Membrane: The inner membrane extends inwards forming a number of septa or partitions known as the internal ridges or cristae that increase its surface area enhancing its ability to produce ATP. The mitochondrial cristae are usually transverse but, it may appear tubular or longitudinal in direction as in steroid forming cells. The inner membrane permeable only to oxygen, carbon dioxide and water. 3) inter- membrane space : Is the space between the outer membrane and the inner membrane. 4) Matrix: The matrix is the space enclosed by the inner membrane.The matrix contains mixture of hundreds of enzymes, ribosomes, tRNA, several copies of the mitochondrial DNA 2  (mitochondrial genome), vitamins, proteins, lipids and carbohydrate. Number: The number of mitochondria present in the cell depends on its energy requirement. Inactive cells have relatively few mitochondria, while metabolically active cells such as liver cell (hepatocytes) contain large number of mitochondria (about 1000 in each). Functions: Functions of mitochondria vary according to the cell type in which they are present. 1-The most important function of the mitochondria is to produce energy so they are called the 'powerhouse of the cell'. 3. The food that we eat is broken into simpler molecules like carbohydrates, fats, etc., in our bodies. These are sent to the mitochondrion where they are further processed to produce charged molecules that combine with oxygen and produce ATP molecules. This entire process is known as oxidative phosphorylation. 2- It is important to regulate proper concentration of calcium ion level within the cell since it serves as storage tanks of calcium ions. 3-They also help in the building of certain parts of the blood and hormones like testosterone and estrogen. 4- Mitochondria in the liver cells have enzymes that detoxify ammonia. 5-mitochondria contain their own DNA and RNA.they may divide by simple binary fission. 2- The lysosomes It is a membrane-bound organelle found in the cytoplasm of eukaryotic cells.The name lysosome derives from the Greek words lysis, which means dissolution or destruction and soma which means the body. At EM level Lysosome appear as rounded spherical small membranous vesicles containing hydrolytic enzymes (They are known to contain more than 50 different enzymes) that capable of breaking down virtually all kinds of biomolecules, including proteins, nucleic acids, carbohydrates, lipids and cellular debris. Each lysosome bounded by a single thin membrane. 4 Function: Lysosome formed from the mature face of Golgi apparatus and they contain hydrolytic enzymes (protease, lipase, phospholipase and acid phosphatase). They fuse with foreign bodies (bacteria, virus, fungi..etc.) and the hydrolytic enzymes digest them. They also function in the normal replacement of cellular components. 1) Phagocytosis (cell eating) a- When a cell is attacked by a solid material (eg.bacteria), the plasma membrane will engulf this material by endocytosis forming a phagocytic vesicle or a phagosome inside the cell. 5  b- Primary lysosome (lysosome) fuse with phagosome forming secondary lysosome. The hydrolytic enzymes digest the contents of phagosome. c- The digested material inside its membranous boundaries form the residual body (indigestible materials such as pigments, myelin figures or lipids remain in residual body). d- These residual bodies may accumulate within the cell over the years (lipofuscin) or may be expelled through the plasma membrane on the cell surface by exocytosis. 6  Diagram showing the process of Phagocytosis (cell eating) in which a white blood cell such as macrophage or neutrophil can engulf microbes, pseudopodia surround microbes, which are taken into the cell, a vacuole forms around microbes and fuse with a lysosome, where hydrolytic enzymes destroy microbes, and debris is released by exocytosis. 7 II) Pinocytosis (cell drinking ): a) It is essentially similar to that of phagocytosis but the foreign material is fluid. b) When a cell is attacked by a liquid material (eg. alcohol), the plasma membrane will engulf this material by endocytosis forming a pinocytotic vesicle c) Primary lysosome will fuse with pinocytotic vesicle forming secondary lysosome. The fluid will be digested by hydrolytic enzymes. Multivesicular bodies (MVB) are formed as a result of digestion of fluid material. This MVB may remain inside the cell. Diagram showing the process of pinocytosis (cell drinking). 8  3) Autophagy Lysosome have the ability to digest some of useless organelles (eg. Mitochondria and endoplasmic reticulum ). Secondary lysosome fusion of the organelle will form autophagic vacuoles ). Diagram showing the process of autophagy. 9 3- Endoplasmic reticulum The endoplasmic reticulum is a network of membranous tubules, sacs and vesicles which are interconnected forming a sort of reticulum (network) in the cytoplasm. The sacs are called cisternae, present all over the cytoplasm extending between the cell membrane and the nuclear membrane. There are two types of ER: 1- Granular or Rough ER: Their surface membranes are studded (covered) with ribosomes. 2- A granular or Smooth ER: Their surface membranes are smooth with no ribosomes. Functions of RER It has an important role in the process of protein synthesis that will be secreted by the cell. RER is well developed in protein secreting cells eg. Pancreatic acinar cells. Role of RER in protein synthesis 10  1- Amino acids are arranged in a certain sequence on the ribosomes to form a specific polypeptide chain (protein) 2- The polypeptide chain will enter through the cisternae of RER. 3- The formed protein will be condensed at one end of RER where budding occur forming transfer vesicle. 4- Transfer vesicle transfer the formed protein from RER to the immature surface (cis –face) of Golgi apparatus. 5- Proteins accumulate within the saccules of the Golgi membranes and concentrated as they pass through the Golgi complex. 6- At the mature (trans) face , the Golgi sacculus as bud off to form secretory vesicles 7- A secretory vesicles (granule) move to the surface of the cell where its membrane fuses with the plasma membrane and opens to the exterior ( exocytosis ). 11  Functions of SER: 1- Lipid synthesis: Lipids and cholesterol derived compounds are synthesized in the SER. So this organelle is well developed in cells forming lipids eg. Steroid hormones. 2- drug detoxification: In liver cells SER can detoxify lipid soluble drugs. 3- glucogen storage: Much of glycogen stored in the liver cells lies between tubules of SER 4- Calcium distribution: SER regulates the intracellular calcium distribution. In striated muscle cell the sarcoplasmic reticulum (SER) is responsible for the storage of calcium.indeed, the 12  calcium level in SER control the contraction or relaxation of muscle cells. 4-Golgi apparatus: The Golgi complex is referred to as the manufacturing and the shipping center of the eukaryoric cell. The Golgi apparatus, also known as the Golgi complex, Golgi body or simply the Golgi, is an organelle found in most eukaryotic cells. It was identified in 1897 by the Italian physician Camillo Golgi and named after him in 1898. The appearance of the Golgi body varies also within the same cell depending on the physiological state of the animal. for example, in the intestinal epithelial cells of starved animal it appear as a small body occupies a small area of the cytoplasm , but after feeding, it gradually increase its size to occupy larger area in the cytoplasm. The position of the Golgi complex is almost characteristic for each cell type for example, in some secretory cells such as those of the exocrine pancreatic cells, it is always located within the secretory pole of the cell, between the nucleus and the free border of the cell. In nerve cells, the Golgi complex has a perinuclear position. Ultrastructure: The Golgi complex is composed of flattened saccules (small sacs). The saccules running parallel to each other and arranged in well defined stacks. Each stack of saccules in the Golgi complex has: 13  1- An immature face: known as the cis or receiving face which is usually convex in shape and is closely associated with the endoplasmic reticulum (nucleus). 2- A mature face: known as trans or shipping face which is generally concave in shape and is closely opposite to the cell membrane. The Golgi –apparatus exists in different types of vertebrate animal cells with the exception of the germ cells, in the form of a network of staks.But in the vertebrate germ cells, in all invertebrate cells and in plant cells the apparatus exists in the form of an individual stack of the saccules is sometimes refer to as dictyosome. 14 Chemical structure: The Golgi apparatus consists of protein and lipids combined together forming a lipoprotein complex. The lipid protein is found in a masked or invisible form being surrounded by protein films. Function 1. The Golgi complex may be referred as post office of the cell where the molecules are packaged, labelled and sent to different parts of the cell. 2. Concentration and condensation of the protein coming to it from RER by transfer vesicles. Transfer vesicles fuse with the immature face of Golgi and the contents will enter the saccules to be concentrated. 3. Package of the condensed protein and formation of secretory vesicles from the mature face of Golgi 4. Chemical modification of some secretory products.It adds carbohydrate to the protein molecules brought to it. 5. Segregation and package of hydrolytic enzymes and create lysosomes 6. It is also a major site of synthesis of carbohydrates. 7. The G. apparatus also considered to be engaged in other cellular activities, such as the formation of the acrosomes of sperm, the elaboration of the synovial fluid in joints and the formation of the enamel of teeth. 15 16  Molecular Structure of DNA History of DNA By the end of nineteenth century it has been recognized that chromosomes are the carriers of the inherited information. The genetic information of all living organisms is stored in deoxyribonucleic acid (DNA) of the chromosomes (except the RNA) viruses. DNA molecule is the most complex macromolecule of the cell. DNA from a single human cell extends in a single thread for almost 2 meters long!!!....It contains information equal to a library of about 1,000 books). Watson and Crick model of DNA (1953): Watson and Crick used the information of Franklin's X- ray photo of DNA and proposed their famous model of the structure of DNA molecule. According to their model, the DNA molecule is represented by a ladder –like structure.the side chains (backbone) of this ladder are made up of the pentose sugar (deoxyribose) and phosphate.The nitrogen bases held the two strands together through hydrogen bonds forming the cross-rungs of the ladder. DNA was made of 2 long stands that wind together to form double helix.  Molecular Structure of DNA The each DNA strand is made up of repeating units called nucleotides. Each DNA nucleotide is formed of three structures: 1- A Five- carbon Pentose sugar (deoxyribose ). 2- Phosphate group. 3- Nitrogenous base. DNA nucleotide Nucleotide subunits are linked by the formation of a phosphodiester bond between carbon atom number 3 of the sugar molecule of one nucleotide and the carbon atom number 5 of the sugar molecule of the next nucleotide with the phosphate group in between. The nitrogenous bases are linked to carbon atom number one of sugar molecules by glycosidic bonds. -2-  Molecular Structure of DNA The orientation of the two strands is antiparallel (i.e their 5 '→3 ' direction are opposite).This mean that the two ends of the chain are not the same.The chain has a 5 ' carbon (with a phosphate group on it ) at one end and a 3'carbon (with a hydroxyl group on it ) at the other end.This make the two strands of the helix run in opposite directions , one strand runs in the direction 5'→3' and the other strand runs in the direction 3 '→5'. The double helix of DNA has constant width (20 ˚A) which represents the diameter of the molecule this width is suitable to be occupied by be either (C) and (G) Joined by three hydrogen bonds or (A) and (T) joined by two hydrogen bonds (obligatory). This mean that, DNA had specific base-pairing between the nitrogen bases. The space is not suitable to be filled by two purines because the combination of them would be wider.At the same time the space between the two strands is not suitable to be occupied by two pyrimidines, this is because their width together would be narrower. The opposite combination ( cytosine with adenine and guanine with thymine) do not lead to favorable hydrogen bonding. Each strand is formed of chain of nucleotides arranged in a specific way called the “Complementary Rule” -3-  Molecular Structure of DNA Since the base pairing is specific, once the sequence of bases in one strand is known, the sequence of the other strand is also known. Thus, if one strand has the sequence 5' ACTAGAC 3' the other strand must have the following complementary sequence 3' TGATCTG 5'. Watson and Crick model of DNA (1953) -4- Molecular Structure of DNA -5-  Molecular Structure of DNA Nitrogenous base: There are two types of nitrogenous bases: Purines pyrimidines Includes guanine (G) and adenine (A) cytosine (C) and thymine (T) composed of five –membered ring fused a six membered ring to the six-membered ring glycosidic Carbon atom number 1 of Carbon number 1 of the linkage the sugar binds to sugar binds to nitrogen formed between nitrogen number 9 of the number 3 of the base purine base. Structural formula -6-  Molecular Structure of DNA Chargaff `s rules : In the same DNA molecule:- 1-number of purines = number of pyrimidines. 2-amount of adenine = amount of thymine. 3-amount of guanine= amount of cytosine. 5- So, A+G / T+C=1(purines/ pyrimidines)=1 6-the base ratio A+T / C+G varies widely among organisms, but always constant for any species (species specific). Base pairing -7-  Molecular Structure of DNA Genetic Diversity… Different arrangements of nucleotides in a nucleic acid (DNA) provides the key to DIVERSITY among living organisms. -8-  Molecular Structure of DNA Note: A nucleotide consists of a nucleoside and one phosphate group. A nucleoside consists of pentose sugar molecule and one nitrogenous base (A,T,G or C). -9-  Molecular Structure of DNA DNA Replication All living organisms possessing DNA as their genetic material ( prokaryotes or eukaryotes ) must duplicate their DNA before every cell division. DNA replication is the process of DNA synthesis where by a parent DNA molecule is faithfully copied giving rise to two identical daughter molecules. DNA replication occurs at polymerization rates of about 500 nucleotides per second in bacteria and about 50 nucleotides per second in mammals. DNA replication is a complex process achieved by means of a multienzyme complex called the replication apparatus or ( replisome ).  Semi-conservative Model: Watson and Crick showed that the two strands of the parental DNA molecule separate and each functions as a template for synthesis of a new complementary strand.. Because each of the two daughter molecules containing one old and one new strand , the process of DNA replication is said to be (semi-conservative). - 01 -  Molecular Structure of DNA Fig.A Fig.B - 00 -  Molecular Structure of DNA Replicons: Replication does not occur all at once, it occurs within small units of DNA duplex called (replicons). It always has an origin at which replication starts and then proceeds. Not all replicons replicate at the same time. Some replicate early and some replicate later. Replicons fuse as replication proceeds. The steps of DNA replication (semi-conservative model): 1-Initiation: 1-Begins at a specific DNA sequence called an origin of replication (initiation point ). 2- Unwinding and separation of the two DNA strands of the double helix by DNA-helicase enzyme. 3- The two separated strands are prevented from rewinding by binding with helix- destabilizing proteins (single strand DNA binding proteins (SSB), these proteins are able to bind to the single – stranded DNA without covering the bases so that they are still readable by DNA polymerase). Binding of helix-destabilizing protein to the separated DNA strands resulted in the formation of two replication forks (y-shaped). 4- The replication process thus initiates, and the replication forks proceed in two opposite directions along the DNA molecule. - 02 -  Molecular Structure of DNA ❷ Primer Synthesis: 1-The synthesis of a new, complementary strand of DNA using the existing strand as a template is brought about by enzymes known as DNA polymerases. In addition to replication they also play an important role in DNA repair and recombination. 2- DNA polymerases cannot start DNA synthesis independently, and require 3' hydroxyl group to start the addition of complementary nucleotides. This is provided by an enzyme called DNA primase which synthesizes a short stretch of RNA onto the existing DNA strands. This short segment is called a primer, and comprises 9-12 nucleotides. Once the primers are formed on both the strands, DNA polymerases can extend these primers into new DNA strands. ❸ Leading Strand Synthesis DNA polymerases can add new nucleotides only to the 3' end of an existing strand, and hence can synthesize DNA in 5' → 3' direction only. But the DNA strands run in opposite directions, and hence the synthesis of DNA on one strand can occur continuously. This is known as the leading strand.. Here, DNA polymerase III (DNA pol III) recognizes the 3' OH - 03 -  Molecular Structure of DNA end of the RNA primer, and adds new complementary nucleotides. As the replication fork progresses, new nucleotides are added in a continuous manner, thus generating the new strand. ❹ Lagging Strand Synthesis: On the opposite strand, DNA is synthesized in a discontinuous manner by generating a series small fragments of new DNA in the 5' → 3' direction. These fragments are called Okazaki fragments, which are later joined to form a continuous chain of nucleotides. This strand is known as the lagging strand since the process of DNA synthesis on this strand proceeds at a lower rate. Here, the primase adds primers at several places along the unwound strand. DNA pol III extends the primer by adding new nucleotides. - 04 -  Molecular Structure of DNA ❺ Primer Removal Although new DNA strands have been synthesized the RNA primers present on the newly formed strands need to be replaced by DNA. This activity is performed by the enzyme DNA polymerase I (DNA pol I). ❻ Ligation: After primer removal is completed the lagging strand still contains gaps or nicks between the adjacent Okazaki fragments. The enzyme ligase identifies and seals these nicks by creating a phosphodiester bond between the 5' phosphate and 3' hydroxyl groups of adjacent fragments. ❼ Termination This replication machinery halts at specific termination sites which comprise a unique nucleotide sequence. This sequence is - 05 -  Molecular Structure of DNA identified by specialized proteins called tus which bind onto these sites, thus physically blocking the path of helicase. When helicase encounters the tus protein it falls off along with the nearby single- strand binding proteins Two Summary: 1-Newly synthesized strands:- a-leading strand: - Is formed continuously toward replication fork (its template 5'→3'). - Is formed more rapidly than lagging strand. b- lagging strand: -Is formed discontinuously as a short fragments (Okazaki fragments) away from replication fork ( its template 3'→5'). - formed discontinuously due to: a- it grow in direction away from replication fork. b- DNA polymerase can synthesize DNA in only one direction by adding nucleotides to the 3' end of a DNA strand. The fragments link together by DNA-ligase. 2- DNA –helicase: Unwinds and separates DNA double helix at origin of replication. - 06 -  Molecular Structure of DNA 3- Destabilizing proteins : Prevent reformation of DNA double helix by attaching the separated DNA strands at the replication forks. 4-. DNA – polymerase: Add nucleotides to 3’ end of RNA -primer -enzyme of replication, - move in 5’ → 3’ directions - works at replication fork - uses energy by breaking down nucleoside triphosphate. 5- DNA –ligase: links Okazaki – DNA fragments of lagging strand by the formation of phosphodiester bonds. 6-. RNA –primer: Is formed of 9-12 RNA nucleotides, provides a 3’ end to which DNA polymerase can add nucleotide at beginning of DNA replication Later degraded & replaced with DNA –nucleotide. - 07 - Protein biosynthesis (synthesis) Is when cells build proteins. the process by which individual amino acids are connected to each other in a specific order dictated by the nucleotide sequence in DNA, which also involves the processes of transcription and translation. Cytoplasm Nucleus The protein synthesis involves two steps: 1-Transcription 2- Translation Transcription is the first of overall two protein synthesis steps and it hapeens in the nucleus. During transcription, the information encoded in the DNA is copied to a RNA molecule as one strand of the DNA double helix is used as a template. The RNA molecule is sent to the cytoplasm, which helps to bring all components required for the actual protein synthesis together – amino acids, transport RNAs, ribosomes, etc. In the cytoplasm the protein polymers are actually “synthesized” through chemical reactions – that is why the process is known as “protein synthesis” or even more precisely “protein biosynthesis”. Translation step which happens in the cytoplasm includes translation of the codons (nucleotide triplets) of the messenger RNA (mRNA) into the 20-symbol code of amino acids that build the polypeptide chain of the proteins. The process of mRNA translation begins from its 5′-end towards its 3′-end as the polypeptide chain is synthesized from its amino-terminal (N-end) to its carboxyl-terminal (C-end). There are almost no significant differences in the protein synthesis steps in prokaryotes and eukaryotes, however there is one major distinction between the structure of the mRNAs – prokaryotes often have several coding regions (polycistronic mRNA), while the eukaryotic mRNA has only one coding region (monocistronic mRNA). The main protein synthesis steps are: 1- Initiation 2- Elongation 3- Termination In most of the aspects, the process in eukaryotes follow the same simple protein synthesis steps as in prokaryotes. However there are specific differences that could be outlined. One important difference is that in prokaryotic cells the process of translation starts beforetranscription is completed. This coupling is defined because prokaryotes have no nuclear membrane and thus there is no physical separation of the two processes. Protein Synthesis Initiation The first of protein synthesis steps is initiation that cover the assembly of the translation system components and precedes the formation of peptide bonds. The components involved in the first step of protein synthesis are: 1- the mRNA to be translated 2- the two ribosomal subunits (small and large subunits) 3- the aminoacyl-tRNA which is specified by the first codon in the mRNA 4- guanosine triphosphate (GTP), which provides energy for the process – eukaryotes require also adenosine triphosphate!  5- initiation factors which enables the assembly of this initiation complex - prokaryotes have 3 initiation factors are known (IF-1, IF-2, and IF-3), while eukaryotes, there have over ten factors designated with eIF prefix. Two mechanisms are involved in the recognition of nucleotide sequence (AUG) by the ribosome, which actually initiates translation: 1. Shine-Dalgarno (SD) sequence - In Escherichia coli is observed sequence with high percentage of purine nucleotide bases, known as the Shine-Dalgarno sequence. This region is located close to 5’ end of the mRNA molecule, 6-10 bases upstream of the initiating codon. The 16S rRNA component of the small ribosomal subunit possess a complementary to the SD sequence near its 3'-end. Thus the two complementary sequences can couple, which facilitates the positioning of the 30S ribosomal subunit on the mRNA in proximity to the initiation codon. The mechanism is slightly different in eukaryotes because they do not have SD sequences. In eukaryotes, with the assistance of the eIF-4 initiation factors, the 40S ribosomal subunit binds close to a structure called “cap structure” at the 5-end of the mRNA and then moves down the messenger RNA sequence till it finds the initiating codon. However this process requires energy from ATP. 2. Initiating codon (AUG) - The initiating AUG triplet is recognized by a special initiator tRNA. In prokaryotes this event is facilitated by IF-2-GTP, while in eukaryotes by eIF-2-GTP and additional eIFs. The charged initiator transport RNA aproaches the P site on the small ribosomal subunit. In bacteria (and in mitochondria), a methionine is attached to the initiator tRNAan subsequently a formyl group is added by the enzyme transformylase, which uses N10-formyl tetrahydrofolate as the carbon donor – finally a N-formylated methionine is attached to the initiator tRNA. For comparison, in eukaryotes, the initiator transport RNA attaches a non formylated methionine. In both types of cells, this N-terminal methionine attached to the 5’-end is removed before the end of the translation. In the last step of the initiation, the large ribosomal subunit joins the complex formed by now, and thus a fully functional ribosome is formed. This complex has a charged initiating tRNA in the P site, and the A site empty. During this protein synthesis step is used the energy within the GTP on (e)IF-2, which gets hydrolyzed to GDP. The reactivation of (e)IF-2-GDP is facilitated by A guanine nucleotide exchange factor. Translation Elongation Translation elongation is second in protein synthesis steps. During the elongation step the polypeptide chain adds amino acids to the carboxyl end the chain protein grows as the ribosome moves from the 5' -end to the 3'-end of the mRNA. In prokaryotes, the delivery of the aminoacyl-tRNA to ribosomal A site is facilitated by elongation factors EF-Tu-GTP and EF-Ts, and requires GTP hydrolysis. In eukaryotes, the analogous elongation factors are EF-1α−GTP and EF-1βγ. Both EF-Ts (in prokatyotes) and EF-1βγ (in eukaryotes) function as nucleotide exchange factors. The peptidyl-transferase is an important enzyme which catalyzes the formation of the peptide bonds. The enzymatic activity is found to be intrinsic to the 23S rRNA found in the large ribosomal subunit. Because this rRNAcatalyzes the polypeptide bound formation reaction, it is named as a ribozyme. The transport RNA at the P site carries the polypeptide synthesized by now, while on the A site is located a tRNA, which is bound to a single amino acid. After the peptide bond has been formed between the polypeptide and the amino acid, the newly formed polypeptide is linked to the tRNA at the A site. Once this step is completed, the ribosome moves 3 nucleotides toward the 3'-end of the mRNA. This process is known as translocation - in prokaryotes, it requires the participation of EF-G-GTP and GTP hydrolysis, while the eukaryotic cells use EF-2-GTP and GTP hydrolysis again. During the translocation, the uncharged tRNA moves from the P to the E site and peptidyl- tRNA leaves the A site and go to the P site. This is an iterative process that is repeated until the ribosome reaches the termination codon. Termination of Translation Termination happens when the A site of the ribosome reaches one of the three termination codons (UAA, UAG or UGA). In prokaryotes, these codons are recognized by different release factors (abbreviated with RF). RF-1 is responsible for the recognition of termination codons UAA and UAG, while RF-2 - UGA and UAA. When these release factors bind the complex, this cause in hydrolysis of the bond linking the peptide to the tRNA at the P site and releases the nascent protein from the ribosome. Then a third release factor (RF-3-GTP) causes the release of RF-1 or RF-2 as GTP is hydrolyzed to GDP and single phosphate reqidue.In contrast, the eukaryote cells have just one release factor, eRF, which can recognize all three termination codons. A second factor is involved - eRF-3, with a similar function to the RF-3 in prokaryote cells. The protein synthesis steps summary  Zagazig University Faculty of Science Zoology Department Embryology of Vertebrates ‫ﻋﻠﻢ أﺟﻨﺔ اﻟﻔﻘﺎر ﺎت‬ Code : Z 312 Prof. Dr. Mostafa Ali Salem 8-1 Contents introduction Gametogenesis.Male reproductive system Female reproductive system Spermatogenesis Oogenesis The Early Development of Amphioxus Embryology of Toad (amphibia) Organ differentiation in vertebrate embryos Embryology or development of Chick (birds) Extra-embryonic Membranes Types of placenta Types of twines Embryology of human embryo Structure of the Eye Causes of infertility in men Some Causes of infertility in women 8-2 Teratogenicity  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Introduction Embryology is the branch of biology that studies the prenatal development of gametes (sex cells), fertilization, and development of embryos and fetuses. Additionally, embryology encompasses the study of congenital disorders that occur before birth, known as teratology. Cleavage is the very beginning steps of a developing embryo. Cleavage refers to the many mitotic divisions that occur after the egg is fertilized by the sperm. The ways in which the cells divide is specific to certain types of animals and may have many forms. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Embryology Embryology is the study of the early development of living organisms through the reproduction process Reproduction takes place in different ways: asexual and sexual. Asexual: buds or fragments Sexual: fusion of two gametes; a male gamete or sperm, with a female gamete or egg to form the zygote or fertilized egg.  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. „ Gametogenesis „ includes the formation of male germ cells (sperms), namely spermatogenesis, „ and that of the female germ cells (eggs or ova), called oogenesis. „ Sperm – or male gametes gg ) – or female gametes „ Ova ((eggs) g „ The Reproductive p System x Testes in males x Ovaries in females Gross Anatomy of Male Reproductive System: „ Testis „ Produce Sperms and Androgens. „ produce a male sex hormone (testosterone) „ Seminiferous tubules is the structural unit of testes., „ If Seminiferous tubules stretched out these could reach 300 to 350 meters Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. „ Vas Deferens „ Seminal Vesicle „ Epididymis - Sperm Storage - Complete of - sperm maturation. „ Prostate Gland (Ejaculatory Duct) Contributes production of the Milky Alkaline Fluid that assists Sperm Activation „ Cowper,s GlandDiagram of the whole testis showing the seminiferous tubules „ Contributes secretion of mucus to Semen „ Urethra (Penis) Organ of Copulation  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. T.s. in a mammalian testis showing seminiferous tubules Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Female Reproductive System x Ovaries x Duct System x Uterine tubes (fallopian tubes) x Uterus x Vagina x External genitalia Fallopian tubes: 1- Receive the ovulated oocyte 2- Cilia inside the fallopian tube slowly move the oocyte towards the uterus (takes 3–4 days) 3- Fertilization occurs inside the fallopian tube  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Hormones of the Ovary x Estrogen hormone x Produced by follicle cells x Cause secondary sex characteristics as : x Development of breasts x Widening of the pelvis x Onset of menses ‫ﺑداﯾﺔ اﻟﺣﯾض‬ x Progesterone hormone: x Produced by the corpus luteum x Its production continues until LH diminishes in the blood x Helps in maintaining the pregnancy x In the case of pregnancy, it stimulates the growth of the mammary glands. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Gametogenesis - means formation of gametes (Sperm & Ova). - Spermatogenesis Means formation of sperm ; male gametes. - Oogenesis Means formation of ovum ; female gametes. Spermatogenesis 1- Multiplication (proliferation) stage: Each primordial germ cell multiply by mitotic cell division giving rise to 2 spermatogonia (each with 2n chromosomes or diploid). 2- Growth stage: each spermatogonium (male gamete) grows in size into primary spermatocyte (2n). 3- Maturation stage: each primary spermatocyte divides meiotically into 2 secondary spermatocytes (each with n chromosome or haploid) and intern finally into spermatid  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Summary of spermatogenesis 8-11 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. A diagram of T.S. in a seminiferous tubule showing development of the sperm T.S. in a seminiferous tubule showing development of the sperm  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Structure Of The Sperm 1) The Head „ has two important features. a- The acrosome contains hydrolytic enzymes which are released when the sperm reaches an ovum. These enzymes digest the outer membrane of the egg, allowing penetration of the sperm. b- The nucleus (haploid) contains a single set of chromosomes (n) derived from the male. This will include either an 'X' or 'Y' chromosome, because of the way the XY separate during meiosis. 2) The Middle Section „ contains sugars in the semen to generate ATP in order to provide numerous mitochondria. These respire the energy for movement of the tail. 3) The Tail „ (Flagellum) contains microfilaments. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ‫ ﺗﻛوﯾن اﻟﺑوﯾﺿﺎت‬Oogenesis 1- multiplication stage: Each primordial germ cell multiply by mitotic cell division giving rise to 2 oogonia. (each is diploid, 2n): 46 chromosome 2- Growth stage: each oogonium (female gamete) grows in size and give primary oocyte (diploid; 2n): 46 chromosome 3- maturation stage: - the primary oocyte undergoes two meiotic cell division: the first gives rise to secondary oocyte (haploid, n, 23 chromosome) and primary polar body (discharge). the second the secondary oocyte undergoes second meiotic division giving rise to mature ovum (haploid, n, 23 chromosome) and secondary polar body (discharge).  Copyright © The he McGraw-Hill Companies, Inc. Permission required for reproduction reproducti or display. Very important x The first and second stages occur during the intra-uterine life till the 7 th month (primary oocyte). x At puberty and under the effect of the FSH the primary oocyte complete the first meiosis division forming the secondary oocyte and then second meiosis forming mature ovum x With each ovarian cycle many ova developed and one or two (sometimes three) ova reach the maturity and the others degenerate Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Graffian n Follicle  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. -The oocyte is viable for 12 to 24 hours after ovulation - Sperm are viable for 12 to 48 hours after ejaculation  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Types of Eggs „ Isolecithal: e.g. mammals, amphioxius „ Very little yolk, evenly distibuted „ Use Holoblastic cleavage- full cleavage „ Mesolecithal: e.g. amphibia; toad, Moderate yolk, Holoblastic - full cleavage „ Telolecithal: reptiles , birds „ Have an abundance of yolk Use Meroblastic cleavage ( partial cleavage) Types of Fertilization External Fertilization - Usu Usually sually llyy occur occurs o cur urrs iin n aquatic a atic c env environments e viron ronmentss whewhere w ere e both b h eg eggs e ggss a and nd d sp sperm s p m are e released intoo the e water er. er r. e.g.g fishess ((with h the e exception p n of sharks), )),, amphibia p iaia. - Such Suc ch h an animals a nimals ls s are a e known k ownn too re release ele easee a huge h ge e nu numbers nummber b rss of eggss and d spermss to o account forr the e lossess expected p d among g thesee cellss in n waterer. er r Internal Fertilization „ - occurs in most land animals. In this case,, the eggs gg remain within the g genital „ system of the female until they are fertilized fer by the sperms introduced into the female byy the male during g copulation. p „ e.g. mammals, reptiles, birds, some fishes like sharks s ‫اﻟﻘرش‬ Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. According to internal fertilization, the animals divide into three categories 1) oviparous animals ‫ﺑﯾوﺿﺔ‬ „ fertilized eggs are laid outside the female’s body. „ The embryo feeds on the yolk which fill the egg. „ This occurs in many reptiles, some cartilaginous fish, all birds. 2) ovo-viviparous ‫ﺑﯾوﺿﺔ وﻟودة‬ - fertilized eggs are retained in the female. - the embryo obtains its nourishment from the egg’s yolk and hatch in the female body then go out. - This occurs in some bony fish (such as the guppy, some sharks), some lizards, some snakes. 3) viviparous, ‫وﻟودة‬ „ the young develop within the female. „ The embryo receiving nourishment from the mother’s blood through a placenta. „ This occurs in most mammals.  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mechanism of Fertilization 8-21 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Steps of embryo development Blastula  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. The Early Development of Amphioxus Or embryology of Amphioxus „ The Development of Amphioxus represents the simplest type of chordate development. It Is described as holoblastic cleavage or complete cleavage. „ 1- The first-cleavage is vertical resulting in two equal halves, each half is called blastomere. „ 2- The second cleavage, is also vertical but it is at right angles to the first division, resulting 4 blastomeres which are all equal in size. „ The third cleavage is horizontal resulting 8 blastomeres, 4 small upper micrormeres toward the animal pole and 4 lower macromeres towards the vegitale pole. „ The fourth cleavage, is vertical forming 16-blastomeres (8- micromeres and 8- macromeres). „ The fifth cleavage a double vertical and a double horizontal furrows respectively, to form a 32-blastomeres stage which referred to the morula stage. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 8-24  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Blastula of Amphioxus „ At 4 blastomeres stage a cavity appearing inside of the dividing mass, this space increases in size. morula „ After the sixth division, cleavage becomes irregular, the cells arrange themselves in a single epithelial layer, this stage is spherical in shape and described as the blastula stage. Blastula of Amphioxus „ „ The blastula composed of small micromeres near of the animal pole and large macromeres near the vegetal pole Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ‫ ﻋﻣﻠﯾﺔ اﻟﺗﺑطﯾن‬Gastrulation in Amphioxus The formation of gastrula takes place as the following steps: „ 1- Flattening and invaginationof the macromeres. „ 2- Increasing of the depression-resulting in the approach of the macromeres to the micromeres. „ 4- Macromeres come in contact with the micromeres. „ 5- Blastoceol disappears and a new cavity appears which is known as primitive gut or archenteron. „ This stage is known as gastrula giving 2 layers: outer layer known as ectoderm (micromeres) and inner layer known as endoderm (macromeres). Summary in Amphioxus „ - The blastula in amhioxus composed of micromeres near of the animal pole and macromeres near the vegetale pole - The gastrula in amphioxus means formation of the ectoderm (micromeres) and endoderm (macromeres). 26 „  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Gastrula in Amphioxus micromeres macromeres m i c 8-27 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Development of the notochord and gut in Amphioxus „ 1- The notochord develops from the notochordal plate (endodermal in origin) which found below the neural plate. „ 2- It extends longitudinally forming the roof of the archenteron and lies below the neural plate. „ 3- The notochordal plate becomes curved ventrally and then it is transformed into a solid mass known as notochord. „ 4- The two ends of the endoderm fuse together forming a large canal which is gut.  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Embryology of Amphioxus Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Embryology of Toad (amphibia) The egg of the frog is mesolecithal.‫ ﻣﺘﻮﺳﻄﺔ اﻟﻤﺢ‬It is covered by pigment which is either black or brown. Near the vegetative pole there is a small area which free from pigment.Cleavage 1- The first cleavage as the same of Amphioxus resulting 2 equal blastomeres. 2- The second cleavage like the first, is vertical meridional) and at right angles to the first resulting 4 equal blastomeres.3- The third cleavage is horizontal, resulting 8 unequal 1blastomeres, 4 small micromeres and.seremorcam egral-4 4- The fourth cleavage is vertical producing seremorcam -8 :seremolsalb-16. And -8 micromeres 5- The fifth cleavage takes place by two horizontal planes producing ehT.seremotsalb -32 egavaelc htfif eht retfa tsol si egavaelc fo ytiraluger Blastula Stage The beginning of blastocoel appears firstly in 8-blastomeres stage among the inner margins of the cells. A hollow sphere of cells is produced. The roof the blastocoel is formed of 3-4 layers of small blastomeres, while the floor consists of a number of larger blastomeres..  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cleavage in a toad embryo Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Gastrulation in Toad ‫اﻟﺘﺒﻄﯿﻦ ﻓﻰ اﻟﻀﻔﺪﻋﺔ‬ „ It means rearrangement of blastula cells that transforms the blastula into a gastrula. „ The blastula develops a hole in one end and cells start to migrate into the hole; this forms the gastrula „ Characterized by cell movement. „ Blastocoel is gradually disappear and a new cavity is formed which called gastrocoel. „ The gastrula in toad is a three-layered embryo „ formation of three primary embryonic germ layers „ Endoderm (inner) „ Mesoderm (middle) „ Ectoderm (outer) „ The pattern of gastrulation in toad is affected by the amount of yolk.  Copyright © The McGraw-Hill Companies, Figure 47.10 Inc. Permission Gastrulation in a frogrequired embryofor reproduction or display. Gastrulation in Toad 8-33 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Neurulation and organogenesis in Toad 1- The dorsal part of the ectoderm becomes differentiated into a neural plate. 2- The lateral edges of the neural tube grow upwards and inwards until they meet together to form the neural tube. 3- The anterior part of this tube becomes enlarged to form the brain elihw , eht ot esir sevig ebut laruen eht fo tser ehtspinal cord. Neural plate Neural groove Neural tube  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Organ differentiation in vertebrate embryos (outcomes of the three germ layers) l.Ectoderm forms : Neural plate Nervous system. * Sense receptors. * Epidermis and epidermal derivatives: Hair, Sweat glands, Mammary glands , Linings of buccal cavity, nose and, Enamel of teeth.2- Mesoderm forms : *Notochord gives vertebral column. *Mesodermal somites, which form : Skeleton, Connective tissues , Heart, blood and blood vessels, Dermis, Muscles, Excretory system, Reproductive system, Peritoneum, and mesenteries. 3- Endoderm forms : Epithelium of alimentary canal, Liver , Pancreas, Thymus gland, Thyroid gland, Parathyroid gland Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Structure of the egg in birds (the hen)  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Embryology or development of Chick (birds) (‫اﻟﺗﻛوﯾن اﻟﺟﻧﯾﻧﻰ ﻓﻰ اﻟﻛﺗﻛوت )اﻟطﯾور‬ - The fertilized egg will travel through oviduct. It takes nearly 22 hours. Hence the early development of egg will take place in oviduct (until the blastula stage). -Incubation: -When the egg is laid, the development is stopped. For further development it is to be kept at 38°C. This is done by hen by sitting over the egg. This is called incubation. Artificially eggs are incubated in incubators. For the hatching of egg 21 days are required. Cleavage in the chick embryo Cleavage in birds: It is of meroblastic type 1 -The first cleavage :After five hours of fertilization the first cleavage will appear. vertical groove takes place near the middle part of the germinal disc, resulting incompletely into two blastomeres. 2- The second cleavage :4 -blastomeres horizontal groove occurs at right angle to the first one resulting into 4 blastomeres, connecting at the periphery of the germinal disc. 3- The third cleavage :8 -blastomeres consist mainly of two planes, each plane is parallel to the first groove producing 8 blastemeres in the form of two rows each of 4 cells. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cleavage in the chick embryo -The fourth cleavage) :16 blastomeres: - result 8 small central cell and 8 larger peripheral ones. In this way 16 blastomeres are formed. - After the fourth cleavage, the regularity of cell division is completely lost and blastoderm is formed. At this stage the cells are closely adhering to the underlying yolk.  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Blastula of Chick (birds) Blastula Formation: -The central portion of the blastoderm detaches itself from the underlying yolk and thus a subgerminal cavity is formed. -At this stage, the embryo is called blastula. The blastoderm at this stage is differentiated into 2 zones or outer area opaca and central area pellucid. 18 hours of incubation of chick embryo -The primitive streak lies in the middle of the area pellucida. -In the front, the primitive streak ends in a small pit, the primitive pit or Hensen's node. -formation of the neural plate and later the neural groove. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20 hours of incubation of chick embryo Embryology of chicken 20 hours of incubation: …………………………. 1 = Proamnion, 2 = Area opaca (dark), 3 = Area pellucida (transparent), 5 = Head fold, 6 = Neural groove, 7 = Neural plate, 9 = Hensen's node, 10 = Primitive streak embryology  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 24 hours of incubation of chick embryo 1- The primitive streak is fully formed 2- The notochord extends from the hensen's node. 3- The head fold and fore-gut develop 4-four pairs of somites are differentiated from the nd neural groove. mesoderm. 5- The neuro-ctoderm gives rise to the neural folds a 1 - Area opaca (dark), 2 - Area pelucida (transparent), 3 - Neural fold, 4 - head foldinag, 7- Mesodermal Somites, 10- Hensen's node, 11- Primitive streak embryology Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 48 hours of incubation of chick embryo 1. Characterized by appearance of flexure and torsion (bending ‫ اﻧﺛﻧﺎء‬and twisting ‫) اﻟﺗواء‬. 2. Completion of circulatory system. 3. Formation of two pairs of aortic arches. 4. Formation of the optic cup and lens vesicle. 5. Development of auditory vesicle. 6. formation of 28 somites 7. Development of extra-embryonic membranes 1 Amnion, 2 Metencephalon, 3 Mesencephalon, 4 Optic cup + lens, 5 Prosencephalon, 6 Otic vesicle 9 Ventricle, 12 Vitelline artery 13 Mesodermal Somite, 14 Spinal cord, embryology  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Extra-embryonic Membranes ‫اﻷﻏﺷﯾﺔ اﻟﺟﻧﯾﻧﯾﺔ‬ -they do not form parts of the embryo proper. -These membranes perform a number of functions during the development of the embryo , - They disappear at the time of hatching or labor. -T These membranes membran rannes appear in the amniotes amn include:: Reptiles, birds, and which inclu mammals. mamm mm mals. --Thee extraembryonicc membranes are: Amnion , chorion, allantois and yolk sac (not found in humans, but yolk aids in formation of RBC). Extra-embryonic Membranes in the Chick embryo (‫اﻷﻏﺷﯾﺔ اﻟﺟﻧﯾﻧﯾﺔ ﻓﻰ اﻟطﯾور )اﻟﻛﺗﻛوت‬ Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Extra-embryonic Membranes ‫اﻷﻏﺷﯾﺔ اﻟﺟﻧﯾﻧﯾﺔ‬ n ‫اﻟرھل‬ 1) Amnion „ y develop Embryos p within it „ The amniotic cavityy contains a fluid surrounding g the embryo y „ The amnion protects p the embryo y from mechanical shocks. „ The amniotic cavity prevents the adhesion T a of amnion to the different embryonic y membranes. 2) Yolk sacc ‫ﺢ‬ ‫ﻛﯾس اﻟﻣﺢ‬ „I reptiles and birds, the yolk sac In a stores a large ac lar e amount a of yyolk for nutrition of the embryo y until hatchingg of the egg. „BBut In mammals, it stores a little amount of yolk yo for nutrition of the embryo until formation of the placenta.  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Extra-embryonic Membranes ‫اﻷﻏﺷﯾﺔ اﻟﺟﻧﯾﻧﯾﺔ‬ 3) antoiiiss ‫ﺟﻖ‬ 3) Alla Allantois A Al ‫اﻟﺳﺟﻖ‬ ‫ﻖ‬ - Storage S of metabolic wastes wastees during ringg development - IIn birds aand reptiles thee allantoiss becomes the urinary b bladder. - IIn Human it form the umbilical cord which transfer the nutritive materials from the mother through the placenta placen cen n to th nta the embryo. 4) Cho 4) Chorion C n: ‫ﻰ‬ oriooon on: ‫اﻟﺳﻠﻰ‬ n (excretory system). - acts as a reservoir for the secretion - In birds and reptiles, the chorio-allantoic membrane acts as respiratory surface for the embryo until hatching. - In mammals, chorio-allantoic projections grow into the tissue of the uterus forming the placenta. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Extra-embryonic Membranes and placenta in the human embryo ‫اﻷﻏﺷﯾﺔ اﻟﺟﻧﯾﻧﯾﺔ واﻟﻣﺷﯾﻣﺔ ﻓﻰ ﺟﻧﯾن اﻻﻧﺳﺎن‬ Placenta - The placenta is a connection between foetal membrane and the inner uterine wall. - The blood of the mother and foetus do not mix at all in the placenta or at any other place. a.  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Types of Placenta A) Non-deciduate ‫ﻣﺷﯾﻣﺔ ﻏﯾر ﻣﺗﺳﺎﻗطﺔ‬ 1) Diffuse: ‫ﻣﻧﺗﺷرة‬ Almost the entire surface of the allantochorion is involved in formation of the placenta. Seen in horses and pigs. 2) Coty-ledonary: ‫ﻓﺻﯾﺔ‬ Multiple, discrete areas of attachment called cotyledons are formed by interaction of patches of allanto-chorion with endometrium. e.g. cattle, sheep, goats B) Deciduate Placenta ‫ﻣﺷﯾﻣﺔ ﻣﺗﺳﺎﻗطﺔ‬ 1) Zonary: ‫ﺣﻠﻘﯾﺔ أو ﺣﺎﻓﯾﺔ‬ The placenta takes the form of a complete or incomplete band of tissue surrounding the fetus. Carnivores (as in dogs, cats, bears, and elephants). 2) Discoid: ‫ﻗرﺻﯾﺔ‬ A single placenta is formed and is discoid in shape. Seen in Humans, monkeys and rodents Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Placenta in mammals ‫اﻟﻣﺷﯾﻣﺔ‬ Umbilical cord ‫اﻟﺣﺑل اﻟﺳرى‬ placenta  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Discoidal Placenta ‫اﻟﻣﺷﯾﻣﺔ اﻟﻘرﺻﯾﺔ ﻟطﻔل ﺣدﯾث اﻟوﻻدة‬ Placenta ‫اﻟﻣﺷﯾﻣﺔ‬ Umbilical cord ‫اﻟﺣﺑل اﻟﺳرى‬ 8-49 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. „ Functions of Placenta: „ 1. Nutrition: Food materials pass from the mother’s blood into the foetal blood through the placenta. „ 2. Respiration: Through the placenta oxygen passes from the maternal blood to the foetal blood, and carbon dioxide passes from foetal blood to maternal blood. „ 3. As an endocrine gland: secretes hormones such as estrogen, progesterone. „ 4. Excretion: Nitrogenous wastes such as urea pass from foetal blood into maternal blood. Very important - Harmful substances such as nicotine from cigarette and addictive drugs such as heroin can pass through placenta. Therefore, pregnant women should avoid cigarette and drugs. - Viruses and bacteria can pass through placenta  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Types of Twins ‫اﻟﺗواﺋم‬ 1) Monozygotic (identical) ‫ﺗواﺋم ﻣﺗﺷﺎﺑﮫ‬ - same sperm and same egg. - develop from one zygote, which splits and forms two similar embryos. - Each embryo with special amniotic membrane but they surrounded with one chorionic sac. -The two embryos with one placenta. -They similar in sex (two females or two males). 2) Dizygotic or non-identical ‫ﺗواﺋم ﻏﯾر ﻣﺗﺷﺎﺑﮫ‬ - Two different sperms fertilize two different eggs giving two different zygotes. Each embryo with separate amnion and chorion. Each embryo with a separate placenta might or might not be the same sex. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Types of Twins ‫أﻧواع اﻟﺗواﺋم‬ Non-identical twins  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Embryology yology of h human embryo week 10 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Prenatal Development Embryonic Fetal development development fertilization - 8 weeks 9 weeks - birth time period from fertilization to birth = gestation Postnatal Development p  Copyright © The McGraw-Hill McGraw Hill Companies, Inc. Permission required for reproduction or display. The T The first Trimester weeks s 1- 1-12 2; weight ~ 14 4g Cleavage Implantation Placentation Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Early division of zygote into multiple cells contents Blastocyst with blastocoele cavity  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Implantationn - embedding of blastocyst into uterine at day 7 Blastocyst - with blastocoele cavity Trophoblast - outer layer of cells Inner cell mass - will form embryo Trophoblast forms syncytial trophoblast- erodes into endometrium Cellular trophoblast - carries nutrients to inner cell mass Lacunae and primary villi formed by trophoblast All of these form placental tissues Fig 28-3 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Labor and Delivery „ After the end of 8 weeks: Fetal development „ Weekk 12 2: all organ systems formed „ st teratogenss not lethal anymore Most e – but produce major defects „ 3rd trimester mostly for size increase and maturity. Second and Third Trimester 22 weeks of gestation absolute minimum (normal?) Parturition: Expulsion of fetus and placenta due to fetal oxytocin n Stages of labor 1. dilation stage - cervix stretches 2. expulsion stage - fetus delivered 3. placental stage - placenta expelled  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (‫ ﻓﻰ أى ﺻورة ﻣﺎ ﺷﺎء رﻛﺑك‬,‫)اﻟذى ﺧﻠﻘك ﻓﺳواك ﻓﻌدﻟك‬ ‫اﻟﻌﯾن‬ Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Structure of the Eye 8-61 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Structure of the Eye „ Sclera: ‫اﻟﺻﻠﺑﺔ‬ protects the inner parts of the eye. We know it as the ‘White of the eye’. „ Conjunctiva: ‫اﻟﻣﻠﺗﺣﻣﺔ‬ - It keeps the eyes moist and clear by secreting small amounts of mucus and tears. „ Cornea: ‫اﻟﻘرﻧﯾﺔ‬ - It is the transparent layer of skin - The main role of the cornea is to refract the light that enters the eyes. - It functions like a window that controls and focuses the entry of light into the eye. - It helps to shield the eye from germs, dust, and other harmful matters.  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Structure of the Eye Iris: ‫اﻟﻘزﺣﯾﺔ‬ - It is a pigmented layer of tissues that make up the colored portion of the eye. -It regulates the amount of light entering through the pupil. The muscular iris moves to shrink the pupil if there is too much light and widen it if there is not enough. This is an involuntary function, controlled by the brain. - The choroid: ‫اﻟﻣﺷﯾﻣﯾﺔ‬ The choroid consists of blood vessels. It provide the retina with oxygen.  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Structure of the Eye „ Pupil: ‫اﻧﺳﺎن اﻟﻌﯾن‬ It is the small opening located at the middle of the Iris. It allows light to come in. „ Lens: ‫اﻟﻌدﺳﺔ‬ It is a transparent, the lens with the help of the cornea refracts light focused on the retina, therefore creating images on it. Copyright © The McGraw-Hill Companies, Inc. Permission Permiission required required for reproduction or display. layers y a ‫طﺑﻘﺎت اﻟﺷﺑﻛﯾﺔ‬ of retina 1. Pigment g cell layer y 2. Layer of rods & cones 3. External limiting limit membrane 4. Outer nuclear layer y 5. Outerr p plexiform layer y 6. Inner nuclear layery 7. Innerr p plexiform layer y 8. Ganglion g cell layer y 9. Nerve fiber layer y 10. Internal limiting limit 1 membrane  Copyright © The McGraw-Hill McGraw Hill Companies, Inc. Permission ion required require ed for reproduction or display. A ‫طﺑﻘﺎت ﺷﺑﻛﯾﺔ اﻟﻌﯾن‬ LAYERS OF RETINA Copyright © The McGraw-Hill McGraw Hill Companies, Inc. Permission Permiission required required for reproduction or display. layers y a ‫طﺑﻘﺎت اﻟﺷﺑﻛﯾﺔ‬ of retina „ The pigment epithelium: Function: - storage and synthesis of vitamin A. - Phagocytosis g y s of tips p of rods and cones - metabolic support rods and cones - It absorbs light and reflect it back towards the rods and cones.  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Photoreceptor cells (Rods and Cones) ‫ﻣﺳﺗﻘﺑﻼت اﻟﺿوء‬ - They are the actual light-sensitive elements. Rods:- ‫اﻟﻘﺿﺑﺎن‬ - they are responsible for vision at low light levels (scotopic vision). They do not mediate color vision. - Approx. 120 million cell. Cones :- ‫اﻟﻣﺧﺎرﯾط‬ - they are active at higher light levels (photopic vision), are capable of color vision and are responsible for high sharp vision. - There are 3 types of cones: single cones, double cones and triple cones. - Approx. 6 million cell Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Rods ‫ اﻟﻘﺿﺑﺎن‬and Cones ‫اﻟﻣﺧﺎرﯾط‬  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Causes of infertility in men ‫أﺳ ﺎب اﻟﻌﻘﻢ اﻟﺮﺟﺎل‬ 1- Low sperm count: The man ejaculates a low number of sperm. A sperm count of under 15 million is considered low. Around one third of couples have difficulty conceiving due to a low sperm count. 2- Low sperm mobility (motility): The sperm cannot “swim” as well as they should to reach the egg 3- Abnormal sperm: The sperm may have an unusual shape, making it harder to move and fertilize an egg. 4) Abnorma Abnormal A al semen s n may m not be able to carry the sperm effectively: This his sccan result from a- A medical condition: This could be a testicular infection, cancer, or surgery b- O Overheated testicles: Causes include an n un undescended ndescended sc d te testicle, esticle, ticle cle, varicose varic vein in the he scrotum, s the use of sauna, wearing tight clothes, and working in hot environments. c- E Ejaculation disorders: If the ejaculatory ducts are blocked, semen b blo en may be ejaculated into the bladder 5) Inflammation 5) Inflammation: In n: inflammation inflamma of the testicles may affect sperm production. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7) Illegal drugs: cocaine or alcohole can lower the sperm count 8) Some diseases: anemia, diabetes, and thyroid disease 9) Overweight or obesity: This may reduce the chance of conceiving 10) Mental stress: Stress can be a factor, especially if it leads to reduced sexual activity  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Some Causes of infertility in women ‫ﺑﻌض أﺳﺑﺎب اﻟﻌﻘم ﻓﻰ اﻟﻧﺳﺎء‬ 1- Smoking: Smoking significantly increases the risk of infertility in both men and women. 2- Alcohol: Any amount of alcohol consumption can affect the chances of pregnency 3- Diet: A lack of folic acid, iron, zinc, and vitamin B-12 can affect fertility. 4- Mental stress: This may affect female ovulation and male sperm production and can lead to reduced sexual activity Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 5- Ovulation disorders appear to be the most common cause of infertility in women. Ovulation disorders can be caused by disequilibrium of the female sex hormones: progesterone, estrogen, luteinizing hormone, as well as the follicle stimulating hormone, which are produced by the pituitary gland. These hormones are responsible for releasing the egg from the ovary at the appropriate time and the growth and development thereof. Hence, if there is an imbalance of these hormones, then ovulation disorders may occur which is the leading cause of such infertility in females.  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 6- Polycystic ovary syndrome (PCOS): The ovulation may not occur 7- Problems in the uterus or fallopian tubes can prevent the egg from traveling from the ovary to the uterus. 8- Endometriosis: Cells that normally occur within the lining of the uterus start growing elsewhere in the body 9- Radiation therapy: If this is aimed near the reproductive organs, it can increase the risk of fertility problems. 10- Illegal drugs: Some women who use cocaine may have fertility problems 11- Anti-inflammatory drugs : Long-term use of aspirin or ibuprofen may make it harder to pregnancy. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fetal Abnormalities ‫اﻟﺗﺷوھﺎت اﻟﺧﻠﻘﯾﺔ أو ﺗﺷوھﺎت اﻷﺟﻧﺔ‬  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Causes of malformationss ‫أﺳﺒﺎب اﻟﺘﺸﻮھﺎت‬ 40% Unknown 40 12 2-25 -25% 25 2 5% Genetic defects (Dow (Downwn’ n’s syndrome is the most common of this ggroup) p) 20% 20 2 0% % Interactions between hereditary factors and environmental factors 5%-9 5% -9% Maternal disease (diabetes ess an and nd seizure) n izure) or in infection ((German measles)) , chemicals,, X-ray- y and drugs. g Factors That Determine the Effects off Teratogens (‫)اﻟﻤﻮاد اﻟﻤﺸﻮه‬ 1-Dose - reachingg fetus 2-Time - of drugg exposure p 3-Duration - of exposure p 4-Environmental - factorss e.g g age or disease of the mother Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Types of Teratogenes 1- ppollution ollution a) physical Atomic and d nnu nuclear uc explosions e.g.: Hiroshima & Nagasakia Nagasaki ia. ia. b) chemical c ical call *leead ((p *lead (pb pb p pb2 b2+)) : from water watteer er pipes, pipes or car exhaust : miscarriage p scarriage (spontaneous abortion ), stillbirth irth rth ( deliv delive delivery veryy ooff a dead very d de dea baby ), and increased inc mortality rate during thee 1st year of life. Carbon monoxide CO : *Carbon from cigarette smoking, smoking car ca exhaust, exhaust austt, and annd incomplete inco plete ete combustion of coal. It bind binds ds to ds to Hb Hb d decreasing decrea ecrea reasing reasin asingg O2 supply to fetus hypoxia hy hypo ypoxia oxiaa spontaneous sp pont onta ntaneou nta nt taane ane us abortion, aneous abortio abortionon stillbirth, growth retardation, premature labor.  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. *Vinyl yl chloride y e: sperm perm damage ( w working in vinyl industry, their babies may be malformed ). *Mercury y: Minamata a ssyndrome me : A plastic ic ffactory poured is wastes, containing Hg, inn Mina Minarnata M ina naarnnata aBBay Hg is converted by microorganisms in H2O 2O to methyl Hg witch contaminated fish eating contaminated fish, the pregnant women wo gave birth to malformed & mentallyy retarded babies. 2- infections ( biological pollution ) : a-Viral - al : -GGerman measles (Rubella) ella)) : deafness,s, blindness, b ccataract, t, retinopathy, glaucoma, glaucoma a, microcephal microcephaly m ly,, m ly mental retardation tard. Attenuated virus causes damage to the t fetus, so give vaccine before pregnancy p g y byy three months - -Hepatitis, small pox, chicken pox : may cause abortion, Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. b-bacterial Syphilis: hydrocephalus & mental retardation, deafness, tooth malformation, meningitis & CNS disturbances. Tuberculosis : Wt. loss, refusal to suckle, hepato- splenomegaly c-protozoa toxoplasmosis : it is transmitted to pregnant women by feces of domestic cats & birds causing hydrocephalus, CNS disturbance, microcephaly, hepatosplenomegaly & blindness. 3- maternal diseases : uncontrolled diabetes mellitus, hyperthyroidism, teratogenicity & toxemia of pregnancy 4-Alcohol : Fetal Alcohol syndrome ( FAS ) : growth failure & delayed development, microcephaly & mental retardation , defects in the eye, face ( cleft palate) , congental abnormalities in heart, skin & kidneys.  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 5- 5-Drugs : -H Highly ighlyy te teratogenic eratogenicc drug drugs as"" thalidomide,warfarin d n ,corticosteroids , anticancer drugsg. -Th -The he following drugs are hazardous if given during the e 2nd nd o orr 3rd rd trimester, trim mester, some of them are hazardous also if given during the mester 1st trimester : 1-Androgens - g &p progesterone: g e: Musculization n of fetus. 2-Estrogens:Feminization - g of male e fetus,abnormal spermatogenesis. 6- malnutrition : Vit. A Vit anophthalmia p a. Vit. D Vit bone and teeth malformation. Folic acid malformations. Minerals as iron ( anemia ), Caa 2+ ( bone malformation )& K+ ( pre re- ree-term m labourr ). Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. References ,‫ اﻟﺠﺰء اﻷول واﻟﺜﺎﻧﻲ‬.‫ ﺑﯿﻮﻟﻮﺟﯿﺔ اﻟﺤﯿﻮان اﻟﻌﻤﻠﯿﺔ‬:‫ أﺣﻤﺪ ﺣﻤﺎد اﻟﺤﺴﯿﻨﻲ وأﻣﯿﻞ ﺷﻨﻮده دﻣﯿﺎن‬-.1968 ,‫ ﻣﺼﺮ‬,‫دار اﻟﻤﻌﺎرف‬ ‫ ﻣﻛﺗﺑﺔ‬.‫ اﻷطﻠس اﻟوﺻﻔﻲ ﻓﻲ اﻟﺗﺷرﯾﺢ وﺑﯾوﻟوﺟﯾﺎ اﻟﺧﻠﯾﺔ واﻷﻧﺳﺟﺔ واﻷﺟﻧﺔ‬:‫ ﺣﻣزة أﺣﻣد اﻟﺷﺑﻛﺔ‬-.2005 ,‫ ﻣﺻر‬,‫اﻟدار اﻟﻌرﺑﯾﺔ ﻟﻠﻛﺗﺎب‬ ‫ دار ﺧوارزم اﻟﻌﻠﻣﯾﺔ ﻟﻠﻧﺷر‬,‫ اﻟﻔﻘﺎرﯾﺎت وأﺳﺎﺳﯾﺎت ﻋﻠم اﻷﺟﻧﺔ‬:‫ ﻣﺻطﻔﻰ ﻋﻠﻰ ﺳﺎﻟم‬- 2010 ,(‫ﺟده واﻟﺗوزﯾﻊ )اﻟﻣﻣﻠﻛﺔ اﻟﻌرﺑﯾﺔ اﻟﺳﻌودﯾﺔ‬ Balinsky, B. (1981): An introduction to embryology.Fifth edition Saunders College Publishing. Bloom, W. and Fawcett, D. W. (1975): A text book of histology. W. B. Saunders Company, London. Bodemer, C. (1968): Modern embryology. Holt, Rinehart and Winston. Inc. Browder, L. (1980): Developmental biology. Saunders College , Philadelphia. Keith L. Moor (1983): The developing human – Clinically oriented embryology. W. B. Saunders Company, Canada.  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. -Mathews ws s, W. W.. ((1976 76): ) Atlas of descriptive p embryology. Macmillan Comp., p London and New York -Parker er, T. J. and er d Haswell ell, W. A.. (1966 ell 66): 66 ) A text book of zoology. gy St Martin's Press, New York. -Reith th, E.J. and Ross, M. H.. (1977 th 77): 77 ) Atlas of descriptive p histology. gy Harper p and Row Pub., New York and London. -Salem m, M. A.. (200404): 04 ) Functional morphology p gy and fine structure of the cornea and retina in the eye y of the mudskipper ppp fish, h Periophthalmus h, p s barbaruss (Gobiidae ae, ae e, Teleostei ei). J. ei Egypt. Ger. Soc. Zool.,., 45 45B: 5B:: 20 20- 0-55 55. 555 Good Luck