Introduction to Human Anatomy PDF

INDRODUCTION TO HUMAN ANATOMY I. BASICS OF ANATOMY By Prof. DR. HODA ELAASAR PROFESSOR OF ANATOMY & EMBRYOLOGY Faculty of Medicine Cairo university MTI  Contents basic Anatomy Part I Introduction...

INDRODUCTION TO HUMAN ANATOMY I. BASICS OF ANATOMY By Prof. DR. HODA ELAASAR PROFESSOR OF ANATOMY & EMBRYOLOGY Faculty of Medicine Cairo university MTI  Contents basic Anatomy Part I Introduction Topic Page No. Anatomical terms 1 Skin & Fascia 4 Skeletal system 7 Muscles 16 Joints 21 Serous membranes and tendons 25 Cardiovascular system 27 Lymphatic system 34 Endocrine system 37 Nervous system 38  Anatomical Terms ILOs: By the end of the lecture, students should be able to: Describe the different anatomical positions of the human body. Recognize the meaning of the different anatomical terms Explain the meaning of the different movements of the human body Differentiate between different anatomical planes used in medicine Terms of Anatomical Position ❖ Anatomical erect position: The body is standing up, the face looks forwards, the upper limbs are stretched besides the body, and the palms are directed forwards. ❖ Supine position: The body lies on its back. ❖ Prone position: The body lies on its front. Terms of Anatomical Planes - Coronal plane: It is a vertical plane that divides the body into anterior and posterior halves or parts. - Median (Sagittal) plane: It is a vertical plane that divides the body into equal right and left halves. - Horizontal plane: It is a transverse plane that divides the body into upper (superior) and lowers (inferior) halves or parts. - Paramedian plane (Lateral sagittal plane): It is a vertical plane that runs parallel to the median plane dividing the body into two unequal parts. 1  Anatomical Terms of Locations Anterior (ventral): Near to the front of the body. Posterior (dorsal): Near to the back of the body. Upper (superior, cephalic): Towards the head. Lower (inferior, caudal): Towards the feet. Median: In the median plane. Medial: Near to the median plane. Lateral: Away from the median plane. Middle: Located at equal distance between two fixed points. Intermediate: A point located between two fixed points. Superficial: Near to the skin. Deep: Away from the skin. Proximal: Near to the root of the limb. Distal: Away from the root of the limb. Palmar: Refers to the front of the hand. Plantar: Refers to the ventral aspect of the foot. External: Near to the surface of a hollow organ. Internal: Near to the cavity of a hollow organ 2  Anatomical Terms of Joint Movements Flexion (bending): Approximation of two flexor or ventral surfaces. Extension (Straightening): Approximation of two extensor or dorsal surfaces. Abduction: Movement of the part away from the middle line (in fingers: from the axis of the middle finger, and in toes: from the axis of the second toe). Adduction: Movement of the part towards the trunk (in fingers towards the axis of the middle finger, and in toes towards the axis of the second toe). Circumduction: Successive combination of flexion, adduction, extension and abduction. Medial rotation: Internal or medial rotation of a part around its long axis. Lateral rotation: External or lateral rotation of a part around its long axis. Gliding: Sliding with no axial movement. Special Movements Pronation (in the forearm and the hand): Rotation of the forearm so that the palm of the hand looks backwards, and the thumb looks medially. Supination (in the forearm): Rotation of the forearm so that the palm of the hand looks forwards and the thumb looks laterally. Opposition: It is flexion and medial rotation of the thumb so as it gets in contact with the tips of the medial four fingers. Inversion (in the foot): The medial border of the foot is raised up and the sole looks medially. It is accompanied with plantar flexion of the foot. Eversion (in the foot): The lateral border of the foot is raised up and the sole looks laterally. It is accompanied with some degree of dorsiflexion of the foot. Lateral flexion of the trunk: Bending the trunk to one side. 3  The Skin and fascia ILOs: At the end of the lecture, students should be able to: Recognize layers of the skin and skin appendages Describe the structure and function of the superficial fascia. Explain the structure and function of the deep fascia in the human body. Determine sites of thickening of deep fascia and its importance The Skin ❖ Skin consisted of: I- Epidermis (outer epithelium): It i formed of stratified squamous epithelium covered by Keratin layer (horny layer) It invaginates the deeper layer (dermis) to form: a. Sweat gland b. Hair follicle c. Sebaceous glands 2- Dermis: Consists of collagen and elastic fibers, blood vessels, lymphatics and nerves. A tiny bundle of Muscle fibers named erectorpili muscle connects the side of hair follicle to the junction between dermis and epidermis. ❖ Skin pigments: The skin colour is affected by five pigments: 1. Melanin: Brown pigment which protects the skin against damage induced by the ultraviolet rays. 2. Carotenes: Yellow orange pigment. 3. Reduced hemoglobin: Purple 4. Oxyhemoglobin: Red 4 ❖ Skin appendages: I. Hair: there are two types of hair: a. Primary hair: It is the first hair that appears and covers the whole skin of the foetus inside the uterus. b. Permanent hair: It presents everywhere except in palms of hands, soles of feet, umbilicus and in certain areas of the external genital organs. It consists of root and shaft. Duct of sebaceous opens into the hair follicle. II- Nails: It develops from epidermis. It is formed of root body and free border. III- Sebaceous gland: It is located in the angle between hair follicle and the hair erector muscle. Their ducts open in the hair follicles. IV- Sweat glands: It is simple coiled tubular glands open on the surface of the skin. Fascia It is formed of sheets of fibroareolar C.T. lies deep to the skin and passes between muscles and organs. It is divided into: A. Superficial fascia: It lies beneath the skin and contains variable amount of fats. *Functions of superficial fascia: Retains warmth of the body. Acts as a reservoir of fat. Facilitates movement of skin. In the upper part of chest, it contains mammary gland. Acts as a soft bed for passage of vessels and nerves to skin. * Superficial fascia contains sheets of muscles in certain sites in the body: (a) In the face (muscles of expression). (b) In neck (platysma) 5  (c) In the palm (palmaris brevis) B. Deep fascia: * Structure: - It is a dense white fibrous layer that lies deep to the superficial fascia. - It covers the muscles or passes between the muscles to form intermuscular septa. - Almost absent in the face and the anterior abdominal wall. * Function of deep fascia: 1) Keeps the underlying structures in position. 2) Binds the muscle into groups and extends between them as intermuscular septa. 3) Helps circulation in veins and lymphatics, when muscle contract against their fascia, they compress veins and lymphatics. 4) It forms interosseous membranes that bind bones together. 5) In certain areas it forms tubular sheathes around vessels and nerves, eg. Carotid sheath in neck, femoral sheath in the thigh. 6) Formation of fibrous sheaths around flexor tendons of hands and feet. * Sites of condensation of the deep fascia: 1- At wrist and ankle joints to form flexor and extensor retinaculae holding the tendons of the long muscles in place to prevent their bowing during contraction of their muscles. 2- At the palm of the hand forming palmer aponeurosis to protect the underneath vessels and nerves. 3- At the sole of the foot forming planter aponeurosis to protect the underneath vessels and nerves. 4- At the lateral side of the thigh forming iliotibial tract giving an attachment to strong muscles of the lower limb helping the lower limb to act as one stick in standing position. 6  The skeletal system ILOs: At the end of the lecture, the student should be able to: Describe the general criteria of cartilage. Differentiate between different types of cartilage. Describe the three types of cartilage and mention their sites. Recognize the general features and functions of bones in man. Differentiate between different types of bones according to their developmental origin, type of ossification, and shape. Explain blood supply and growth of bones. Describe the layers and functions of periosteum. Identify the direction of nutrient foramina and the growing end of long bones It consists of: Cartilage. Bones I. Cartilage ❖ General properties: It is modified form of connective tissue. It is firm, flexible and avascular. It gets its nutrition by diffusion from the blood vessels of perichondrium. It has no nerves or lymphatics. It consists of mature cartilage cells (chondrocytes), fibers and matrix. It resists compression forces and friction. It can be subdivided into three types: 7  1. Hyaline Cartilage: Properties a. Translucent, b. Minimal amount of collagenous fibers. c. Rich in cartilage cells (single or in groups, cell nest) Sites: 1. Articular cartilage 2. Cartilage of respiratory passage as nose, Larynx, trachea 3. Costal Cartilages 4. Skeleton of fetus and epiphyseal plate 2- Yellow Elastic Fibrocartilage Properties: Contains yellow elastic fibers in the matrix with abundant cartilage cells Sites: 1. Ear pinna, External auditory meatus, Eustachian tube. 2. Some laryngeal cartilage as epiglottis. 3- White Fibrocartilage Properties: It is rich in dense white collagenous fibers with few numbers of cartilage cells Sites: 1. Intervertebral disc. 2. Laberum glenoidal and laberum acetebulare 3. Symphysis Pubis 4. Semilunar cartilage of knee and meniscus II. Bones 8 It is formed of calcified C.T. with hard matrix, it is formed of 206 separate bone. ❖ Classification of Bones: 1- According to their position in the body They are divided into: a) Axial skeleton: Skull, vertebral column, sternum & ribs b) Appendicular skeleton: Bones of the upper limb and lower limb. 2- According to the structure: There are two types of bones: compact (ivory) as the cortex of the shaft of long bones and cancellous (spongy) formed of bone trabeculae as in vertebrae. 3- According to the shape The bones are divided into: a) Long (tubular) bones: Each has a medullary cavity, a shaft called diaphysis and two ends called epiphyses. The area of junction between the shaft and epiphysis is called metaphysis e.g. humerus and femur. b) Short bones: Each is formed of a mass of spongy bone covered with a thin layer of compact bone e.g. carpal and tarsal bones. c) Flat bones: Each is formed of two tables of compact bone with a thin mass of spongy bone in between e.g. skull bones, scapula and ribs. d) Irregular bones: They are similar, in structure, to short bones but they have multiple processes e.g. vertebrae. e) Pneumatic bones: They are similar to flat bones but with absorption of the middle layer of cancellous bone. Their cavities are lined with mucous membrane, and they contain air as they communicate with the nasal cavity. They constitute the paranasal sinuses e.g. maxillary, frontal, sphenoid, ethmoid and mastoid air sinuses. They have the following functions: 1. Resonance of voice. 2. Lightening of the weight of the skull. 3. Protection of the brain. 9  4. Conditioning of air. f) Sesamoid bones: They are more or less rounded nodules of bones embedded in certain tendons and usually related to articular surfaces. Function: 1. Modify pressure exerted on tendons as they pass on bone. 2. Diminish friction between the tendon and the underlying bone. 3. Occasionally, alter the direction of pull of muscle. Examples: a) Patella: Largest sesamoid bone embedded in the tendon of quadriceps femoris b) Pisiform: It is embedded in flexor carpi ulnaris tendon. c) Fabella: it is located in the tendon of origin of gastrocnemius. 4- According to the methods of ossification: a. Membranous bones: A connective tissue membrane is transformed into a bone e.g. clavicle, skull cap and some facial bones. b. Cartilaginous bones: A model of cartilage is replaced by bone e.g. long bones of the limbs, the scapula, vertebrae, and ribs. ❖ Function of bones: 1- Act as a central axis. 2- Support of the body and transmit body weight. 3- Give form of the body. 4- Protect the underlying structures. 5- Give attachments to muscles. 6- Form joints that allow locomotion. 7- Form blood cells in the red bone marrow. 8- Store of calcium and phosphorus. 10 ❖ Blood Supply of Long Bones Long bones are supplied by: 1- Nutrient artery: Reaches the medullary cavity and divides into ascending and descending branches, which reach the metaphysis at the upper and lower end of the shaft. It supplies the bone tissue and bone marrow. 2- Epiphyseal arteries: They are numerous and enter the bone through its two epiphyses to supply them. 3- Metaphyseal arteries: They enter the bone through its two metaphyses to supply them. 4- Periosteal arteries: They come from the periosteum covering the shaft of the bone. They supply the cortex of the shaft and communicate freely with the nutrient vessels in the cortex. ❖ Nerve supply of bones: Sensory supply comes from surrounding nerves for both bone and periosteum. ❖ Bone Marrow it is a soft connective tissue situated in medullary cavities of the long bones and between trabeculae of the cancellous bone. - Types and distribution: 1- From birth till 2 years the whole bone marrow is red 2- During childhood fatty tissue (yellow marrow) gradually replaces the red marrow in the medullary canal of long bones 3- In older children and adults, red marrow is restricted to axial bones as well as clavicles and scapulae. 4- The yellow marrow in the long bones has the potential for conversion to active hemopoiesis in response to severe hematologic stresses. 11  ❖ The Periosteum It is rough fibrous sheath surrounding the bone except the articular surfaces. It consists of 2 layers: a) Superficial white fibrous layer. b) Deep layer of elastic fibers and osteoblasts, which is responsible for bone formation. ❖ Function: 1- Growth of bone in width. 2- Forming new bone in case of fracture. 2- Its blood supply supplies also the underlying bone. ❖ Growth of bones A- Increase in length This occurs at the epiphyseal plates of cartilages (called metaphysis) intervening between the epiphysis and diaphysis of the bone. The epiphyseal plate is responsible for growth of bone in length by proliferation of its cells. When the bone becomes mature, the epiphyseal plate stops division and ossifies resulting in bony fusion between epiphysis and diaphysis. The epiphyseal plate at one end of the shaft of long bone ossifies earlier than that at the other end, which continues adding bone to the shaft for another 2 to 3 years before it undergoes ossification as well. This end is called the growing end. Fusion of the epiphysis and diaphysis is under hormonal control. It occurs in females earlier than males by about 2 years. B- Increase in width: This is achieved by the osteoblast of the periosteum which is capable to form new bone even after removal of bone without removing the periosteum. 12 ❖ Location of the growing end in the long bones The growing ends of UL: It is located at the upper end of humerus and the lower end of ulna and radius. The growing ends of LL: It is located at the Lower end of the femur and the upper end of tibia and fibula. Accordingly, the direction of bone growth in length, which is represented by the direction of the nutrient foramina, follows the following statement: from the knee I flee to the elbow I go. The growing ends of bones are the reverse of the above-mentioned statement. 13  External Features of Bones  Articular surfaces: Articular surface: is the part of bone that shares in the formation of a joint. Facet: is a small articular surface. Condyle: is a knuckle-shaped articular surface. Epicondyle: is a small projection on a condyle giving attachment to a collateral ligament for the joint in which the condyle is involved. Trochlea: is a pulley-shaped articular surface. Caput (head): is the expanded end of a long bone. Capitulum: is a small head.  Projections: 1. Process: is a bony projection of a considerable size. 2. Spine: is a pointed process. 3. Hamulus and cornu (horn): are slender curved processes. 4. Styloid process: is a pencil-shaped process.  Elevations: Tubercle, tuberosity, and trochanter: They are localized roughened bony elevations of variable sizes. Line or ridge: Tt is elongated (linear) elevations of variable sizes. Crest: is an elongated (linear) bony projection with a flat surface having two lips.  Depressions: Fossa: is a rounded depression on a bony surface. Notch (incisura): is a rounded depression on a bony border. Groove and sulcus: are elongated (linear) depressions. The sulcus is deeper than the groove.  Defects (gaps): Foramen: is a hole in a bone. Canal: is a foramen of some length. Aperture: is a large foramen. Meatus: is a canal with a one closed end. 14  Fissure: is a cleft in a bone or between two bones.  Sex Differences in Bones: Female bones are lighter, shorter, and smoother in features than male bones. 15  Muscles ILOs: At the end of the lecture, the student should be able to: Differentiate between different types of muscle fibers. Classify skeletal muscles. Explain types of the muscle action. The muscles Discuss the about form nerve supply of skeletal ½ of body weightmuscles. and they have contractile ability. They are classified into three types: 1- Smooth muscles: Plane and spindle in shape. Supplied by autonomic fibers i.e. involuntary. Sites: Wall of blood vessels and viscera. 2- Cardiac muscle fibers: Striated but branched. Found in the heart. Supplied by autonomic fibers i.e. involuntary 3- Skeletal muscles: Striated, not branched, voluntary. Have bony attachments, an origin and insertion. Supplied by at least one somatic nerve and receive blood supply from surrounding blood vessels. 16  Skeletal muscles (striated) ❖ Types of striated muscles 1- Pale fibers: Rapid contraction and rapid fatigue. Located in prime mover muscles which start the movement. 2- Red fibers (high myoglobin content): Slow contraction but sustained. Located in antigravity muscles where continuous contraction is needed to maintain the posture of the body. - Examples: The gastrocnemius muscle is rich in pale fibers which is needed for rabid performance of movement. The soleus muscle is rich in red fibers where maintenance of the movement is required (maintenance of posture). ❖ Muscle Attachments: The muscle is attached at both ends where in contraction, one of the ends is fixed (the origin, usually the proximal end) and the other end is approximated to it (the insertion, usually the distal end). - Types of Muscle Attachments: 1. Attachment to bone: It is the commonest type. A muscle may be attached to bone either directly by fleshy fibres or by a tendon. 2. Attachment to a fibrous raphe: It is a band or septum of fibrous tissue through which 2 muscles fuse together e.g. mylohyoid muscle. 3. Attachment to deep fascia e.g. tensor fascia lata 4. Attachment to aponeurosis, which is a flat expanded tendon e.g. external oblique muscle. 5. Attachment to skin: A muscle is inserted into the dermis of the skin and by its contraction it could move the skin, e.g. facial muscles. 17  6. Attachment to an intermediate tendon: A muscle may have 2 fleshy bellies and an intermediate tendon in between; the bellies are inserted into this tendon, e.g. digastric muscle. 7. Attachment to cartilage: As in the muscles of the larynx e.g. cricothyroid muscle. ❖ Form of the Skeletal Muscles: The form of the skeletal muscles are divided according to the direction of the muscle fibers in relation to the line of pull into: a) Parallel fibers ( parallel to the line of pull): 1. Strap like: Sartorius 2. Quadrate: Quadratus femoris 3. Fusiform: Palmaris longus 4. Tendinous intersection: Rectus abdominus b) Oblique fibers (oblique to the line of pull): 1- Pennate fibers (feather like): Unipennate: Fibers attached to one side of the tendon: flexor pollicis longus Bipennate: Fibers at 2 sides of tendon: rectus femoris Multipennate: Series of bipennate: deltoid. Circumpennate: The fibers attached all around the tendon: tibialis anterior musc 2- Oblique non pennate: Triangular as temporalis Spiral as latissimus dorsi. Cruciate as masseter Circular as Orbicularis oculi 18 ❖ Muscle Action It is a range of contraction which produces a definite movement. - Factors affecting the action: 1- Length of the muscle fibers. 2- Number of fibers 3- Direction of the muscle fibers NB. Not all the muscle fibers contract at the same time so that the Maximum power of contraction achieved when all fibers of the muscle contract. The contracted muscle shortened by 2/3 of its original length. Tone of the muscle means the length shorter than distance. There is coordination and harmony during movements of different group of muscle. - Types of muscle actions: A. Prime movers (agonist): Start and maintain the movement e.g. brachialis to produce flexion of the elbow. B. Antagonistic muscles: Oppose the action of agonist e.g. triceps should relax in elbow flexion. C. Synergists: Support the agonists preventing unwanted movement. Sometimes the prime mover muscle crosses many joints before it reaches its insertion. So its contraction will move the desired joint (at the insertion) as well as the other joints crossed by the prime mover. In this case, other muscles called synergistic muscles will contract to eliminate the unwanted movements at the crossed joints. Therefore, the action of the prime mover on the desired joint becomes maximal. D. Fixator muscles: Stabilize the origin of the agonist so it can act efficiently e.g. to abduct the arm, the short muscles around the shoulder joint stabilize it during the contraction of the prime mover. 19 ❖ Blood supply of muscles: Derived from muscular branches of nearby arteries. When the artery to a muscle is accompanied by its nerve supply, they form what is called “neurovascular bundle”. ❖ Nerve supply of muscles: Each receives one or more motor nerve supply. When a muscle derived from several myotomes, it has multiple nerve supply. Many muscles, especially those concerned with posture, have also sensory nerve supply which carries proprioceptive sensation to CNS. 20  The Joints ILOs: At the end of the lecture, student should be able to: Describe the criteria of each type of the joints and giving examples for each one. Determine the movements allowed at different types of joints. Identify the factors that limit excessive movement of joints. Recognize the factors that stabilize the joints. Definition: is a meeting between two or more bones. Classification of Joints I- Fibrous Joints Bones are bound together by fibrous tissue. 1. The joints are almost immobile. 2. No cavity between articular surfaces. ❖ Types of fibrous joints: 1. Sutures: As in skull where the adjacent bone linked by sutural ligament: serrate, plane or squamous 2. Syndesmosis: The adjacent bones are linked by interosseous ligament e.g. inferior tibiofibular joint. 3. Gomphosis: Between teeth and adjacent bones (sockets) where the collagen fibers of the periodontal ligament run between tooth and socket. II- Cartilaginous Joints: 1. The articulating bones connected together by cartilaginous tissue. 2. Very limited degree of mobility may be allowed. 3. No cavity in this type of joints. 21 ❖ Types of cartilaginous joints a. Primary cartilaginous joints: It is temporary joint and disappears at certain age. No movement allowed e.g. epiphyseal cartilage between epiphysis and diaphysis of long bones. b. Secondary cartilaginous joints: the bones are connected by a fibro- cartilaginous disc, and it is permanent. Limited degree of movement is allowed. e.g. intervertebral discs and symphysis pubis. III- Synovial Joints They are characterized by: 1. Articular surfaces: Is covered by hyaline cartilage and separated from each other. 2. Joint cavity: It a Potential space. 3. Fibrous capsule: It covers the joint and is perforated by blood vessels, nerves and synovial membrane. 4. Synovial membrane: It lines the inner aspect of the capsule and non- articular parts inside the joint. It secretes synovial fluid. 5. Synovial fluid: It fills the joint cavity. It is secreted by the synovial membrane. It has the following functions: a. Lubrication of the articular surfaces. b. Nourishment of the articular cartilage. c. Phagocytosis of debris and foreign particles as it contains macrophages. 6. Ligaments: They enforce the capsule from outside 7. Intra-articular structures: May be present, for example: a. Articular disc. b. Menisci c. Ligaments d. Tendons 8. Movements: They are freely mobile with variable grades. 22  ❖ Movements of the synovial joints: Joints are classified according to their axes of movements into plane and axial joints: A- Plane joints Plane surfaces are in apposition and moves against each other permitting gliding movement, e.g. joints between articular processes of vertebrae and intercarpal and intertarsal joints B- Axial joints: where the articulating bones move around axis. According to the number of axes, these joints are classified into: 1- Uniaxial: a. Hinge joint: It is characterized by: 1. Moving around transverse axis 2. Has strong collateral ligaments. 3. Allowing flexion and extension only ❖ Examples: elbow, ankle and interphalangeal joints b. Pivot joint: It is characterized by: 1. Moving around longitudinal axis 2. Allowing rotatory movements ❖ Examples: superior and inferior radio-ulnar and atlanto-axial joints 2- Biaxial These joints move around two axes perpendicular to each other allowing flexion, extension, adduction and abduction. According to the shape of the articular surfaces, there are 3 types: a. Condylar: It consists of either 2 separate convex surfaces (condyles), which articulate with 2 concave surfaces, e.g. knee joint (bicondylar) or one condyle articulating with one concave surface e.g. temporomandibular joint (unicondylar). 23  b. Ellipsoid: It consists of one convex oval surface articulates with elliptical concave surface, e.g. wrist and metacarpo-phalangeal. c. Saddle: each surface is concave in one direction and convex at the perpendicular one, e.g. carpometacarpal of thumb. 3- Multiaxial joints: The movements occurs around axes. The articular surface consists of a global rounded head articulates with a concave cup-shaped cavity. They are called ball and socket joints and are the most freely mobile joints in the body, e.g. the shoulder & hip joints. ❖ Factors maintaining stability of the joints 1. Bony (skeletal) element: Shape and fitting of articulating surfaces. 2. Ligamentous element: Position and strength of ligaments as well as thickness and elasticity of the capsule 3. Muscular element: Strength of the surrounding muscles which are in direct contact with the joint capsule. 4. Intra-articular pressure: positive atmospheric pressure and negative intra-articular pressure help keeping the articulating surfaces in contact with each other. ❖ Arterial and nerve supply (Hilton’s law) Blood vessels cross the flexor aspect of joints to avoid stretching and tear of blood vessels. Hilton's Law: The nerve supply to a muscle acting on a specific joint gives a branch to supply this joint and another branch to supply the skin covering the same joint. 24  Serous Membranes ILOs: Br the end of the lecture, students should be able to: Locate the sites of serous membranes. Describe the function of the serous membranes. ❖ Structure It is formed of a closed sac lined with a single layer of squamous cells. It contains fluid for lubrication. The serous membrane is formed of: a. Visceral layer: Inner layer covering the organ or the part. b. Parietal layer: Outer layer is reflected from the visceral layer. c. Potential space: Between the 2 layers where thin film of serum-like fluid is present to facilitate the movement. ❖ Function a. It facilitates movement of the structure lined by it. b. It minimizes the friction between the mobile organ and the surrounding structures. ❖ Sites 1. Synovial sheath: Around the tendons of the muscles. 2. Synovial membrane: It is a serous sac inside the synovial joints to facilitate the movement of the joint. 3. Pericardium: Serous sac around the heart. 4. Pleura: Serous sac around the lungs. 5. Peritoneum: Serous sac lining the abdomen viscera. 6. Bursae: They are definite sacs; their walls are identical in structure to the synovial membrane of the joints. They occur where skin, ligament or tendon move over bony surfaces under conditions of pressure, to provide free movement and diminish friction between surfaces. Most bursae lie close to the joints, and sometimes communicate with synovial membrane of the joints. 25  Tendons They are tough whitish cords formed of parallel bundles of collagen fibres connected together by fibroareolar tissue. The tendon connects the muscle with the bone. Friction between it and the bone is minimized by a synovial sheath present around the tendon or by a bursa. Aponeurosis ▪ It is a flat expanded tendon usually of a flat muscle e.g. anterior abdominal wall muscles. ▪ It is poor in vasculature. Sometimes a non-flat muscle has an aponeurosis e.g. biceps brachii muscle which has bicipital aponeurosis. 26  Cardiovascular System ILOs: At the end of the lecture, the student should be able to: Recognise the three main circulations of the human body. Describe types of arterial anastomoses and their sites. Determine the sites of end arteries and its significance. Explain the importance of the arterio-venous shunt.. It is formed of two main structures: A) Heart B) Blood vessels. A- The Heart - It is Formed of 4 chambers: 1. Right atrium: It receives the deoxygenated blood from all parts of the body by 2 large veins; the superior vena cava (SVC) and the inferior vena cava (IVC). It sends its blood to the right ventricle through the tricuspid valve. 2. Right ventricle: It sends the deoxygenated blood through the pulmonary valve to the pulmonary trunk which divides into 2 pulmonary branches (right and left), one for each lung where oxygenation of the blood occurs. 3. Left atrium: It receives the oxygenated blood from both lungs through 4 pulmonary veins and pumps it to the left ventricle via mitral valve. 4. Left ventricle: It pumps its oxygenated blood to all parts of the body through the aortic valve, to the aorta and its branches. - The right 1/2 of the heart contains deoxygenated (venous) blood and the Left 1/2 of the heart contains oxygenated (arterial) blood. 27  - The heart is enclosed within 2 layers of serous pericardium surrounded by the fibrous pericardium. - The heart pumps about 70 C.C. of blood/beat and 5 liters/minute. Blood Circulation - Blood circulates in a closed circuit: From heart----large arteries----smaller arteries----arterioles-----smaller arterioles--------capillaries----venules----small veins-----large veins---- back to heart. - Types of blood circulations: The body contains 3 circulations: 1- The Pulmonary circulation (lesser circulation) 2- The Systemic circulation (greater circulation) 3- The Portal circulation 1- The pulmonary circulation: it is the passage of deoxygenated blood from the right ventricle to pulmonary arteries then to the lungs for gas exchange and its return from the lung, as oxygenated blood, to the left atrium via 4 pulmonary veins. 2- The Systemic Circulation (Greater circulation): The oxygenated blood is carried from the left ventricle through the aorta and its branches to all parts of the body for cell respiration. Then, the deoxygenated blood is collected and return to the right atrium by means of the superior and inferior venae cavae. 3- The Portal Circulation: The venous blood from stomach, spleen, pancreas and intestine is collected into portal vein which ends in the liver and not in the heart. The blood carried is rich in digested food substances and it is poured into the liver sinusoids (venous vessels) to be processed. Then the blood is drained into the hepatic veins to the inferior vena cava. Therefore, the portal circulation begins and ends by veins. 28  B- The Blood Vessels I. Arteries: They Are vessels carrying blood away from the heart. They give branches all over the body. They carry oxygenated blood except the pulmonary and umbilical arteries, which carry deoxygenated blood. ❖ Classification of arteries: 1- Large sized arteries: The tunica media of their wall is rich in elastic fibers, e.g. aorta 2- Medium sizes arteries: Muscular supplying limbs and organs 3- Small sized arteries: Muscular and arise from medium sized ones and goes more peripheral. 4- Arterioles: they arise from small arteries having thick wall and narrow lumen. They have projections into the lumen from their muscle layer called pre-capillary sphincter. They are the main source of peripheral resistance to blood flow to capillaries. ❖ Special types of arteries: 1- End arteries: no precapillary arteriolar anastomosis between adjacent arteries. Their interruption, due to any cause, results in death of the supplied organ. The following arteries are end arteries: a. Splenic b. Renal c. Pulmonary d. Metaphyseal e. Central artery of the retina. 2- Tortuous arteries: They supplied movable organs to give a way during different movements of the organ as: a. Lingual b. Facial c. Splenic d. Uterine 29  3- Coronary arteries: Blood supply to the heart is called coronary arteries. They contain elastic fibers in the 3 tunics to prevent closure of the coronaries during heart contraction. 4- Cerebral arteries: They resemble veins in having wide lumen, very thin wall as well as well-developed internal elastic lamina. ❖ Arterial Anastomosis The arteries unite with each other. The frequency of arterial anastomosis increases with increase distance from the heart i.e. the smaller arteries anastomose more frequently than the larger ones. - Importance 1. The anastomosis can provide alternative routes for blood flow to maintain the blood supply to the area where its main arterial supply is interrupted for any reason as in accident or disease. 2. It equalizes pressure in the communicating arteries. - Types of anastomosis: 1- End to end anastomosis (actual): The two ends of two arteries are connected together forming an arch. Example: palmar arches and stomach arteries. Cutting the anastomosis results in bleeding from both sides. 2- By terminal arterioles (potential): It occurs between side branches (collateral branches) of the main arteries. Sudden occlusion of the main arteries results in death of the supplied part while gradual occlusion gives chance to the collateral circulation to open and maintains the blood supply to the tissues beyond the level of obstruction e.g. Coronary arteries, and anastomoses around joint. NB.: Blood supply to the wall of the arteries is called Vasa Vasorum, which is derived from neighboring arteries. Nerve supply of the arteries arises from sympathetic fibers to produce vasoconstriction. 30  II- Veins ❖ Properties: They are blood vessels carrying blood from peripheries to the heart and usually carry deoxygenated blood, except the pulmonary and umbilical veins which carry oxygenated blood. The veins have thin wall and bigger calibers than the corresponding arteries for slower rate of blood flow. Venous pressure is much less than the arterial one and they do not pulsate. They are divided into superficial and deep veins. Deep veins usually accompany arteries while the superficial ones do not. In both hand and foot, the venous return is by the way of the dorsum to escape the pressure of the palm and sole which may constrict the veins. The large veins have a dead space around them to allow for great dilatation that takes place during increased blood flow e.g. femoral vein. Most of the veins especially those of the lower limbs contain valves formed by two cusps inside their lumena, which prevent back flow of the blood by gravity. ❖ Some veins have no valves: 1. SVC & IVC 2. Dural sinuses 3. Vertebral veins 4. Cardiac veins 5. Pulmonary veins 6. Hepatic & portal veins 7. Ophthalmic veins 8. Pelvic veins ❖ Factors helping venous return: In limbs: 1- Muscular contraction within the osteofascial compartments helps to squeeze veins pumping the blood towards the heart. 2- Valves prevent back flow of blood towards the periphery. 3- Arterial pulsation of the arteries accompanied the veins. 31  4- Deep fascia surrounding the muscle groups. Near thorax: The negative intra-thoracic pressure helps the venous return from the abdomen. In head and neck: The force of gravity helps the venous return. III- Connections between arteries and veins 1- Capillaries: They have narrow uniform diameter. They are found in all parts of the body except epidermis of skin, cornea and cartilage. 2- Sinusoids: they have wide irregular diameter and many pores. They are located in certain areas of the body e.g. liver, bone marrow, pituitary and parathyroid glands. 3- Arteriovenous shunt: ❖ Characteristics: It exists between smaller arteries and corresponding veins. Straight or coiled. Proximal to capillary bed Thick muscular wall Has sphincter rich sympathetic supply. Capable of complete closure, in this case circulation passes in the capillary bed as usual. When patent, the blood passes directly from the artery to vein by passing capillary bed. Poorly developed in newly-born infants. They develop rapidly in early years of life. Undergo atrophy and sclerosis in old age. ❖ Sites of arterio-venous shunt: Exposed parts of the body Mucous membranes of alimentary canal 32  The erectile tissue of the penis ❖ Significance of arteriovenous shunt: 1. Regulation of body temperature via the cutaneous arterio-venous anastomosis. 2. Facilitate the process of absorption where the arterio-venous anastomosis was closed during active absorption, the slow blood flow through the ordinary capillary bed gives enough time for active absorption. 3. Has role in erection. 33  The Lymphatic System ILOs: By the end of the lecture, the student should be able to: Describe the types and characters of lymph vessels. Discuss the shape, structure, sites and functions of lymph nodes Explain factors helping lymph drainage. The lymph is an intercellular fluid. ❖ The lymphatic system is formed of: 1. Lymphatic vessels 2. Lymphoid tissues: As lymph nodes, spleen, tonsils and thymus gland. 3. Free cells (lymphocytes): including B- and t- lymphocytes. 1- Lymph Vessels: - Formation: It starts as network. of lymph capillaries in the intercellular spaces where excess fluid is drained by "the lymph capillaries which is collected into lymph vessels. The lymph vessels are interrupted along their course by lymph nodes, which is a small bean-shaped bodies. There are 2 types of lymph vessels: a. Afferent lymph vessels: They open into the periphery of the lymph nodes at their convex borders and carry lymph to them. b. Efferent lymph vessels: They emerge from the hilum of the lymph nodes and carry the lymph away from them. The lymph vessels unite to form ultimately 2 main lymph trunks, thoracic duct and right lymphatic duct, open in the venous system at the root of neck. There are no lymphatics in certain tissues such as: a. Nervous system b. Bone marrow 34  c. Spleen d. Eye e. Avascular structures e.g. cartilage, cornea and hair. - Characteristics of lymph vessels: The superficial vessels follow veins while the deep ones follow arteries except the tongue. They have a thin irregular wall, which absorbs substances of high molecular weight (colloids) through wide pores in their walls. They have many valves, which make the flow of lymph in one direction. They drain a colorless fluid except intestinal lymph vessels, which drain milky lymph rich in fat, hence called lacteals. - Factors helping Lymphatic return: 1. Filtration pressure of capillaries. 2. Contraction of surrounding muscles and valves prevent passage of lymph to peripheries. 3. Pulsation of nearby artery 4. Intrathoracic negativity 5. May be by smooth muscles in the walls of large lymph trunk. 6. Peristaltic movement of the intestine 2- Lymphoid tissues 1- Lymph Nodes - Shape: Lymph nodes are oval or kidney-shaped small bodies. - Structure: Each lymph node consists of cortex and medulla. a. Cortex: Contains lymph follicles. It receives lymph via afferent vessels. b. Medulla: Devoid of follicles and leads to the hilum of the node. The lymph leaves the hilum by passing through an efferent vessel. - Site: They are located along the course of lymph vessels in groups in fixed sites: a. At the limb roots: axillary (in upper limb) and inguinal (in lower limb). b. In the neck: on both sides and at its junction with the head. c. In the chest: close to the trachea and bronchi and in the chest wall. d. Close to the abdominal and pelvic organs: near the big vessels. e. Around abdominal aorta and blood vessels of pelvis. 35  - Function of lymphatic system A- Lymph vessels: absorption of colloids from tissue spaces. B- lymph nodes: 1. Filtration of lymph from bacteria and foreign bodies. 2. Formation and production of lymphocytes 3. Defense mechanism: They form the sites of interaction between micro- organisms (antigens) and phagocytes and lymphocytes. 2- Thymus Gland It's a lymphatic organ and has endocrine function as it secretes thymosine hormone. It's formed by two lobes and present in the thorax just behind the sternum. The size of the thymus continues to increase in size until the age of puberty, and then it decreases in size with advance of age. 3- Spleen Site: It is a hemolymphatic organ present in the upper left part of the abdominal cavity beneath the left dome of the diaphragm, behind the stomach and protected by the 9th, 10th, and 11th ribs. Surfaces: it has a diaphragmatic smooth surface and a medial visceral surface which is related to the stomach, left kidney, pancreas, and left colic flexure. The hilum is present in the visceral surface. Size: it is not palpable, unless if it is enlarged at least three times. Functions: 1- In the fetus, the spleen has a role in the formation of the blood cells. 2- In the adult: the spleen stores and concentrates blood cells. So, in case of hemorrhage it pours the concentrated blood into circulation. 3- It destroys the old expired red cells. 4- It filters the blood from organisms or any harmful substances. N.B.: The lymph nodes filtrate the lymph, but the spleen filtrate the blood. 36  Endocrine System ILOs: By the end of the lecture, the student should be able to: Determine the site of each endocrine gland. Describe the function of the different endocrine gland. It is formed by glands which secretes hormones directly to the blood. (1) The Pituitary gland (the hypophysis) A small gland, in the size of a pea, which lies in the pituitary fossa (the sella turcica) in the middle part of the base of the skull, below the brain. It consists of: A) Anterior lobe: Is epithelial in origin and called the adenohypophysis; - Function: It secretes the important hormones which stimulate the growth and function of other endocrine glands and hence called "the master gland". B) Posterior lobe: Nervous in origin and is called the neurohypophysis; it is controlled by nerve fibers from the hypothalamus. (2) The Thyroid Gland: Situated in the lower part of the front of the neck clasping the larynx and upper part of trachea. It is formed of 2 lobes connected together by isthmus. It enlarges slightly in adolescence, menstruation and in pregnancy. Function: It secretes thyroxin which influence the metabolism of the cells of the body; its hyperfunction will increase the basal metabolic rate of the body. (3) The Parathyroid glands: Two pairs of small glands embedded in the posterior part of the thyroid gland. Function: They are very important because they secrete the hormone responsible for the calcium and phosphorus metabolism. 37 (4) The Suprarenal (adrenal) glands: Two glands, each one situated over the upper pole of the corresponding kidney. Each is formed of an outer part (the cortex) and an inner part (the medulla). Function: The cortex secretes cortisone and other essential hormones, The medulla secretes adrenaline and noradrenaline. (5) Pancreas: A mixed endocrine and exocrine gland which lies transversely on the posterior abdominal wall extending from the duodenum till the spleen. Function: Its endocrine part is called islets of Langerhans and it secretes insulin and glucagon hormones that regulate the blood glucose level (6) Gonads: They include the two testes in male and 2 ovaries in female. a. Testis: Oval firm organ lies inside the scrotum within a strong capsule. It is divided into 200-300 compartments; each contains 1-2 convoluted tubules called seminiferous tubules. Function: 1. Secretion of the male sex hormone: Testosterone hormone. 2. Formation of the sperms by the process of spermatogenesis. b. Ovary: It is an oval or almond-shaped organ. Attached to the lateral margin of uterus by round ligament of ovary. Function: 1. Secretion of the female sex hormones: Strogen and progesterone. 2. Production of ova (female germ cells) by the process of oogenesis. (7) Thymus gland: It is formed by two lobes and present in the thorax just behind the sternum. The size of the thymus continues to increase in size until the age of puberty, and then it decreases in size with advance of age. Function: It secretes thymosin hormone. 38  Nervous System ILOs: By the end of the lecture, the student should be able to: Classify parts of the nervous system. Determine the parts of the brain. Compare the spinal and cranial nerves. Discuss the two parts of the autonomic nervous system. The nervous system is formed of highly specialized nerve cells called neurons, which can receive stimuli, deal with them, and then transmit impulses to the effectors which may be muscles or glands. ❖ Parts of the neurons: it composed of Cell body or soma and processes of nerve cell called axon and dendrites. The nervous system is divided into: 1- Central nervous system (C.N.S). 2- Peripheral nervous system (P.N.S.): composed of: a. Somatic nervous system b. Autonomic nervous system 1- Central Nervous System: It is subdivided into brain and spinal cord which lie inside the skull and vertebral canal, respectively. They are covered by three membranes called Pia matter, Arachnoid matter, and Dura Matter. A- The brain is subdivided into: Two cerebral hemispheres, diencephalons, brain stem (Mid-brain, Pons, and Medulla) and cerebellum. B- The spinal cord is formed by H-shaped gray matter contains central canal inside and white matter outside. 39  2- Peripheral Nervous System: A- Somatic nervous system There are 12 pairs of cranial nerves attached to the brain and 31 pairs of spinal nerves attached to the spinal cord. - The Cranial nerves: They are 12 cranial nerves: 1. Nerves attached to the cerebrum: I- Olfactory nerve: for smell II- Optic nerve: for vision 2. Nerves attached to the midbrain: III- Oculomotor nerve: motor to eye muscles IV- Trochlear nerve: Motor to one muscle of the eye. 3. Nerves attached to the pons: V- Trigeminal: Sensory to the face and motor to the muscles of mastication. VI- Abducent: Motor to one muscle of the eye. VII- Facial: Motor to the muscles of the face, taste sensation and parasympathetic to salivary glands. VIII- Auditory (Stato-acoustic): For hearing and equilibrium. 4. Nerves attached to the medulla oblongata: IX- Glossopharyngeal: Sensory to the pharynx and tongue, motor to one muscle of the pharynx and parasympathetic to the parotid gland. X- Vagus: Motor to the muscles of the pharynx and larynx and parasympathetic to the structures in the thorax and abdomen XI- Accessory: Motor to muscles of the neck. XII- Hypoglossal: Motor to the muscles of the tongue. - Spinal Nerves: - The spinal cord gives attachment to 31 pairs of the spinal nerves which are distributed as follows: 40  8 cervical nerves; in the cervical region. 12 thoracic nerves: in the thoracic region. 5 lumbar nerves: in the lumbar region. 5 sacral nerves: in the sacral region. 1 coccygeal nerve: in the coccygeal region. - Each spinal nerve arises from the side of the spinal cord by 2 roots: (1) Dorsal root: Its fibers are sensory or afferent conveying sensations from the skin, joints, bones and muscles to the posterior horn cells of the grey matter of spinal cord. It has a ganglion attached to it. This ganglion consists of sensory nerve cells, and is called dorsal root ganglion. (2) Ventral root: Its fibers are motor or efferent. Its fibers arise from the anterior horn cells (A.H.Cs) situated in the anterior horn of the spinal cord. - The two roots unite to form nerve trunk, containing mixed fibers. - The nerve trunk divides into two rami; both contain mixed fibers: a- Anterior (ventral) primary ramus. b- Posterior (dorsal) primary ramus. B- The Autonomic nervous system: It is concerned with the involuntary activities. It is divided into: I. Sympathetic nervous system. II. Parasympathetic nervous system. I. Sympathetic Nervous System - Origin: Thoraco-lumbar outflow: It arises from the thoracic and upper 2 lumbar segments of the spinal cord. The Fibers (preganglionic fibers) passes in the anterior rami of the corresponding spinal nerves of the thoracic and upper two lumbar nerves to relay in sympathetic ganglion situated in two sympathetic 41  chains one in each side of the vertebral column, the fibers may not relay in the chain and relay in collateral ganglion. The relayed fibers (postganglionic) join the anterior rami of all spinal nerves to reach the effector organs. II. Parasympathetic Nervous System - Origin: Cranio-sacral outflow: It presents in the followings: a- Cranial nerves: Oculomotor, facial, glossopharyngeal and vagus. b- Sacral nerves: From the second, third and fourth sacral segments. The cranial outflow (preganglionic fibers) relays in parasympathetic ganglia of the head and neck. The sacral outflow relays in ganglia in the wall of the innervated viscous or near its wall. Function of both sympathetic and parasympathetic nervous systems ❖ Their function is complementary to each other: Sympathetic system prepares the body for activity, increases its capacity and arranges it for performing severe muscular effort as in emotional states, fight and fear. Parasympathetic stimulation is anabolic and energy preserving. It arranges the body for sleep and digestion. 42  References 1. Anderson, J.E. (1983): Grant's Atlas of Anatomy, 8th ed. Williams & Wilkins, london, Sydney, Baltimore, Los Angeles. 2. Clemente, C. D. (1997): A regional Atlas of Human Body, 4th ed. Williams & Wilkins, london, Sydney, Baltimore, Philadelphia, Tokyo. 3. Drake, R. (2009): Gray's Anatomy for students, 2nd ed. Churchill livingstone, UK, Philadelphia. 4. Martini, F.h.; Timmons, M.S. and Tallittsch, R.B. (2012): Human Anatomy-Atlases, 7th ed. Benjamin Cummings, London Dubai, Madrid, Paris Toronto, Sydney, HongKong, Tokyo. 5. Moore, K.L.; Agur, A.M.R and Dalley, A.F. (2006): Essential Clinical Anatomy, 4th ed. Lippincott Williams & Wilkins, london, Philadelphia, Baltimore, New York. 6. Netter, F.H. (2019): Atlas of Human Anatomy, 7th ed. W.B. Saunders Co. USA. 7. Olson, T.R. (1996): Student Atlas of Anatomy, International edition. Williams & Wilkins, london, Philadelphia, Baltimore,Bangkok. 8. Williams, P.L.; Bannister, L.H.; Berry, M.M. Collins, P.; Dyson, M.; Dussek, J.E.; and Ferguson, M.W.J. (1995): Gray's Anatomy, 38th ed., ELBS with Churchill livingstone, Edinburgh, London, Melbourne, New York. 43 INDRODUCTION TO HUMAN ANATOMY II. General Embryology By Prof. Dr. Hoda EL aasar Professor of Anatomy and Embryology Department of Anatomy and Embryology Faculty of Medicine Cairo Universit MTI  Contents basic Anatomy part II Embryology Topic Page No. Gametes 44 First Week Development 46 Second Week of Development 49 Third Week of Development 54 Embryonic Period 59 Fetal membranes 66 Fetal period 78  1 CHAPTER 1 Male & Female Gametes ILOs: By the end of this chapter, the student should be able to: ▪ Identify the morphology of mature sperm. ▪ Describe the mature ovum and its coverings. Male gametes (sperms) and female gametes (ova) are the reproductive cells that are formed from primordial germ cells by a process known as spermatogenesis and oogenesis, respectively. Site of formation: In the gonads (testis or ovary). Time of formation: ▪ In males, it starts at puberty and continues till old age. ▪ In females, it starts in the intrauterine life, then arrested to be continued from puberty to menopause through ovarian cycles. Ovulation occurs at the 14th day of the ovarian cycle. Morphology of mature gametes: I- Sperm: A human sperm is 55 microns long and consists of: ▪ Head: It is 4 microns long that contains: Condensed nucleus which carries hereditary material of the father (22 autosomes & X- or Y- sex chromosomes) mostly covered by acrosomal cap that has enzymes that facilitate penetration of covering of the ova (fertilization). Minimal cytoplasm. Cell membrane. ▪ Neck: It is narrow part between head and middle piece. ▪ Middle piece: It is 6 micron long and composed of mitochondrial sheath which is the source of energy for sperm motility. ▪ Tail: It is 45 microns long and composed of axial filament with cell membrane around most of it. The tail directs the movement of sperms towards the ovum, then helps fertilization. 44  2 II- Ovum: The diameter of mature ovum is about 120 microns. It consists of: A- Ootid which is the mature oocyte that carries: ▪ Nucleus that has the hereditary material of the mother (22 autosomes & X-Chromosome). ▪ Large cytoplasm which is the initial source of nutrition of the zygote ▪ Cell membrane. B- Zona pellucida: It is the glycoprotein coat around the ootid. It carries sperm receptors that attracts sperms prior to fertilization. C- Corona radiata: it is the outer cover that is formed of follicular cells derived from the ovary. 45  3 CHAPTER 2 FIRST WEEK OF DEVELOPMENT ILOs: By the end of this chapter the student should be able to: ▪ Identify the term fertilization and analyze its phases. ▪ Discuss the results of fertilization. ▪ Realize the meaning of cleavage and migration. ▪ Describe the formation of the blastocyst. FERTILIZATION Fertilization is the union between the male gamete (sperm) and the female gamete (ovum) to form the zygote. Site: In the ampulla of uterine tube. Mechanism: Capacitation of the sperms: It is the process of removal of glycoprotein coat that covers the acrosomal regions of the sperms in the female genital system. It takes about 7 hours to be completed. Phase I (Penetration of corona radiata): Only 300 – 500 sperms out from 200 – 300 million sperm / ejaculation will reach the ovum and start dispersion of corona radiata. Phase II (Penetration of zona pellucida): One sperm only passes through the zona pellucida by the following steps: ▪ Sperms bind to the zona at specific binding sites (sperm receptors). ▪ Sperms secrete acrosomal enzymes (acrosin- and trypsin- like substances) that dissolve a passage through zona. ▪ Only one sperm passes through the zona pellucida (acrosomal reaction) helped by movement of the tail. ▪ The head of the fertilizing sperm comes in contact with the plasma membrane of the secondary oocyte. Phase III (Penetration of cell membrane of the oocyte): It occurs by 46  4 the following steps: ▪ The plasma membranes of both sperm and ovum will fuse together. ▪ Then, fused plasma membranes (of sperm and oocyte) open to allow passage of sperm contents (nucleus, neck, middle piece and axial filament) to cytoplasm of the ovum, leaving sperm cell membrane on the outer surface of the oocyte. Events that occur after entrance of the sperm to cytoplasm of the oocyte: A. Cortical and zona reactions: after entrance of the fertilizing sperm, the oocyte releases lysosomal enzymes from cortical granules. These enzymes prevent polyspermy through: ▪ Changing sperm binding sites of the zona pellucida to prevent binding and passage of more sperms. ▪ Making the plasma membrane of the fertilized oocyte impenetrable to other sperms. nd B. The secondary oocyte completes nd the 2 meiotic division to form mature ovum (ootid) (23 Ch.) and 2 polar body (23Ch.). C. Male nucleus becomes larger (male pronucleus) and come to be in contact with nucleus of ootid (female pronucleus). D. Nuclear membranes of both male and female pronuclei fuse together to form nucleus of the zygote. Results of fertilization: 1. Formation of the zygote. 2. Determination of sex of the zygote either male (XY) or female (XX). 3. Restoration of diploid number (46 Ch.). 4. Start of cleavage and migration of the zygote from site of fertilization to site of implantation in the uterine cavity. 47  10 Cleavage and Migration Zygote divides mitotically, inside the zona pellucida coat, giving rise to smaller blastomeres (46 Ch.) in the followingstmanner: Two cell stage is formed in the 1 ndday. Four cell stage is formed in the 2 day. 16 cell rd stage (morula) followed by 32 and then 64-cell stage is formed in the 3 day. During cleavage, the morula th migrates inside the uterine tube to reach the uterine cavity at the 4 day by the following mechanisms: 1. Muscular peristalsis of the uterine tube. 2. The motion of the cilia of mucosal lining of the tube. Formation of the blastocyst: ▪ Zona pellucida starts to degenerate at the end of 5th day. ▪ Fluid pass through degenerating zona to form multiple spaces between cells of the morula. ▪ Gradually, those spaces fuse together to form a single cavity, called blastocele. This stage is named blastocyst. ▪ Blastocyst is composed of: 1. Outer cell mass (trophoblast) which is formed of a single layer of cells. 2. Inner cell mass (embryoblast) which is formed of a mas of cells on one side of the inner aspect of trophoblast. 3. Blastocele is the cavity of the blastocyst. 4. Embryonic pole is the side of the outer surface of blastocyst that corresponds to the embryoblast. 5. Abembryonic pole is the opposite side of the embryonic pole of the blastocyst. 48  20 CHAPTER 3 SECOND WEEK OF DEVELOPMENT ILOs: By the end of this chapter the student should be able to: ▪ Define the term implantation. ▪ Describe its mechanism. ▪ Detect the abnormal sites of implantation and ectopic pregnancy. ▪ Recognize different parts of "decidua” and the fate of each part. ▪ Trace the events that occur in the blastocyst changing it into" the chorionic vesicle. ▪ Describe the formation and structure of the chorionic vesicle. IMPLANTATION ▪ Definition: It is the process by which the blastocyst becomes embedded in the endometrium. ▪ Time: It starts at the 7th day and is completed at the 11th day. ▪ Site: In the endometrium of the upper part of the posterior wall of the uterus (near fundus), less frequent it occurs in the upper part of the anterior wall. N.B. : During implantation, endometrium (lining of uterus) is at the secretory phase of endometrial (menstrual) cycle. This phase is characterized by increased thickness of endometrium, increased number and size of endometrial cells, glands are spiral and rich with secretion and arteries are spiral showing arterio-venous anastomoses. ▪ Mechanism of implantation: It starts by adhesion of the blastocyst by its embryonic pole to the endometrium at the implantation site. Trophoblast proliferates at the embryonic pole to form a new layer of cells that has no cell walls, and this layer is called syncytiotrophoblast. This new layer secretes proteolytic enzymes that erode the endometrium and form the implantation 49  20 cavity. Blastocyst becomes embedded inside the implantation cavity. At the 9th day, the site of penetration by the blastocyst becomes blocked by fibrin clot. Two days later (11th day), endometrial epithelium overgrows and covers the fibrin clot. ▪ Changes of blastocyst during implantation: 1. Trophoblast differentiates into outer syncytiotrophoblast and inner cytotrophoblast, starting at the embryonic pole then extends all over the blastocyst. 2. Formation of amniotic and yolk sac cavities. 3. Formation of double layered embryonic disc (epiblast and hypoblast). ▪ Abnormal sites of implantation: A. Placenta Previa: Implantation occurs at the lower segment of uterus. It is of three types: 1. Placenta previa parietalis: The margin of placenta is near the internal os. 2. Placenta previa marginalis: The margin of placenta covers the internal os. 3. Placenta previa centralis: The center of placenta covers internal os. N.B. Internal os is the inner opening of cervical canal of uterus. Placenta previa is life threatening as: a. It leads to antepartum (before birth) maternal hemorrhage. b. It may lead to death of fetus. So, cesarean section is highly recommended in case of placenta previa. B. Ectopic pregnancy: Blastocyst is abnormally implanted outside the uterus in the following sites: ▪ Tubal in uterine tube which may occur in ampulla, isthmus or intramural parts. In this case, rupture of the tube is expected at the 8th week of pregnancy leading to severe internal hemorrhage. ▪ Ovarian on the surface of the ovary. ▪ Omental: in peritoneum (abdominal or pelvic). 50  20 Decidua - Definition: It is the endometrium of the uterus after implantation of the blastocyst. It is called decidua as it sheds during labor (Latin word deciduus, means falling off or shedding). It is exaggerated secretory phase of endometrium. - Features of decidua: Features of decidua are increased thickness of endometrium, increased number and size of endometrial cells, glands become spiral and full of secretions while arteries become spiral and show arterio-venous anastomoses. - Parts of decidua: 1. Decidua basalis: It is the part of decidua that lies between the implanted embryo and myometrium. 2. Decidua capsularis: It is the part of decidua that covers the embryo, separating the embryo from uterine cavity. 3. Decidua parietalis: It is the part of decidua that lines the rest of the uterine cavity. - Fate of decidua: ▪ Decidua basalis: persists as the maternal part of placenta and is known as decidual plate. ▪ Decidua capsularis and parietalis: come in contact and fuse together obliterating uterine cavity. They degenerate at last. Daily events during the second gestational week - At 8th day: ▪Blastocyst is partially implanted. ▪Trophoblast layer differentiates into inner cytotrophoblast and outer syncytiotrophoblast, starting at the embryonic pole of the blastocyst. ▪ Cells of the inner cell mass (facing the blastocele) become cuboidal to form a layer known as hypoblast. ▪ Amniotic cavity appears within cells of the embryoblast. The cells 51  20 adjacent to cytotrophoblast secrete amniotic fluid and are known as amnioblast cells. Amniotic cavity separates between amnioblast and epiblast of the embryonic disc. ▪ Epiblast and hypoblast form the bilaminar embryonic disc. - At 9th & 10th days: ▪ Blastocyst is completely implanted. ▪ Site of penetration is closed by fibrin clot. ▪ Flat cells (Heuser’s membrane) from hypoblast line the blastocele which is transformed into primary yolk sac. ▪ Syncytiotrophoblast extends to surround the cytotrophoblast of the whole blastocyst. ▪ Lacunae appear in the syncytiotrophoblast (Lacunar stage). - At 11th & 12th days: ▪ Endometrial epithelium grows and covers the fibrin colt. ▪ Lacunae are filled with maternal blood to form utero-placental circulation. ▪ Extra-embryonic mesoderm is formed between cytotrophoblast (externally) and embryonic disc with amniotic and yolk sac cavities (internally). Multiple spaces appear in the extraembryonic mesoderm. - At 13th day: Fusion between spaces in the extraembryonic mesoderm leads to formation of extraembryonic coelom (chorionic cavity). Now the blastocyst is termed chorionic vesicle and its wall is called chorion. The Chorionic cavity separates between somatic and splanchnic mesoderm. Somatic mesoderm lines cytotrophoblast and covers amniotic cavity while splanchnic mesoderm covers yolk sac. ▪ Connecting stalk is the part of the extraembryonic mesoderm that connects the caudal end of embryonic disc with the chorion. ▪ New generation of cells from hypoblast line the primary yolk sac to form secondary yolk sac. ▪ Pinching off a large part of the secondary yolk sac with marked reduction of its size. ▪ Formation of allantois that extends from caudal wall of yolk sac. ▪ Primary chorionic villi start to appear from the chorion. 52  20 ❖ Chorion: is the wall of chorionic vesicle. It secretes chorionic gonadotropin (CG) which maintains the corpus luteum (source of progesterone in the ovary) for 4 months. It is composed of (from internal to external): Somatic extraembryonic mesoderm. Cytotrophoblast. Syncytiotrophoblast. 53  3 11 CHAPTER 4: THIRD WEEK OF DEVELOPMENT ILOs By the end of this chapter, the student should be able to: Trace the changes that occur in the embryo during the 3 rd week of pregnancy. ▪ Describe the development of the chorionic villi at different stages (primary, secondary and tertiary). ▪ Cite the different parts of the 3ary villus and point to the function of each. ▪ Recognize the different parts of the chorion and indicate the fate of each. ▪ Define and describe gastrulation. ▪ Describe the different stages of formation of the notochord, discuss its important functions and indicate its fate. ▪ Review the site and differentiation of the extraembryonic mesoderm. ▪ Distinguish the different areas of the embryonic disc by the end of the 3rd week. The most characteristic events that occur during the third week of gestation are development of chorion and gastrulation of the embryonic disc. Development of Chorion The chorion is the wall of the chorionic vesicle. (Figs.III-11&12) Chorion is composed of somatic extraembryonic mesoderm, cytotrophoblast and syncytiotrophoblast (from internal to external). Chorionic villi are formed starting from the end of 2nd week. They are projections from the wall of chorionic vesicle (chorion). A. Chorionic Villi - Time of formation: They start formation at the end of the 2nd gestational week then continues 54  3 12 during the 3rd week. - Types: 1. Primary villi: Cytotrophoblast cells proliferate and push syncytiotrophoblast to form the primary villi which are separated from each other by lacunae filled with maternal blood. 2. Secondary villi: They are formed when somatic extraembryonic mesoderm enters the core of the primary villi. They are formed at the middle of the third week. 3. Tertiary villi: They are formed when fetal blood vessels appear in the mesoderm of secondary villi at the end of the third week. They are separated by intervillous spaces filled with maternal blood. Cytotrophoblastic shell is formed when cytotrophoblast cells penetrate syncytiotrophoblast at the apices of the stem villi and extend to surrounds chorionic villi and the intervillous spaces. Parts of the tertiary villus: Each villous is composed of: 1. Stem (anchoring) villus: It is the stem of the villous that extends between chorion and decidua basalis. 2. Free (floating or absorbing) villi: They are side branches from the stem villous that float in the maternal blood inside the intervillous spaces. They are responsible for exchange of nutrient and gases with maternal blood. - Parts of chorion: A. Chorion frondosum (chorionic plate): It is the part of the chorion that carries well developed tertiary villi that face decidua basalis. B. Chorion laeve: It is the rest of it the chorion that carries degenerating tertiary villi which are covered with decidua capsularis. - Fate of chorion: Chorion frondosum (chorionic plate) persists to share in the formation of placenta while chorion laeve degenerates. Gastrulation Gastrulation is the transformation of bilaminar embryonic disc into trilaminar disc. It starts by development of primitive streak and primitive node in the epiblast layer. 55  3 13 - Primitive streak: It appears in the midline of the caudal part of the embryonic disc as a median narrow groove with bulging sides. It is developed from proliferation and migration of epiblast cells towards the primitive groove. After its appearance, it is possible to identify the embryo’s cranio-caudal axis, ventral and dorsal aspects as well as its right and left sides. - Primitive node: It is a rounded bulge in the cephalic end of the primitive streak with middle depression known as primitive pit. - Invagination: Epiblast cells migrate towards the primitive groove to pass through it towards the hypoblast to form: Endodermal layer that replaces the hypoblast. Intra-embryonic mesoderm which forms middle layer in the embryonic disc. Notochord in the median region of the embryonic disc. The remaining epiblast layer is called ectoderm and its junction with amnion is called amnio-ectodermal junction. Finally, the embryonic disc becomes formed of 3 germ layers (ectoderm, mesoderm and endoderm). Buccopharyngeal membrane It is a rounded area of fusion between ectoderm and endoderm at the cranial part of the embryonic disc. Cloacal membrane It is a rounded area of fusion between ectoderm and endoderm at the caudal part of embryonic disc. - Shape and change of the embryonic disc At the beginning of the third week, the disc is oval in shape then due to spread of intraembryonic mesoderm, the cranial part becomes broader than the caudal part giving the disc the pear shape. 56  3 14 Notochord Notochord is the temporary axial skeleton of the embryonic disc. - Development: Prenotochordal process: It is formed by invagination of solid cord of cells from primitive pit. Prenotochordal process extends cranially in the midline between ectoderm and endoderm till the buccopharyngeal membrane. Notochordal canal: Primitive pit extends into the process transforming it into a canal. Its roof is in contact with the ectoderm while the floor is fused with endoderm. Neurenteric canal: It is temporary communication between amniotic cavity and yolk sac due to degeneration of floor of the canal together with median endoderm fused with it. Notochordal plate: It is the persisting roof of the canal that fuses with the remaining endoderm. Definitive notochord: Notochordal plate becomes folded upon itself to form solid cord (definitive notochord). Endoderm regenerates so amniotic cavity and yolk sac regain their separation from each other. - Importance of notochord 1. It is a temporary axial skeleton of the embryonic disc. 2. During folding, its firmness limits head fold. 3. Vertebral column is formed around it. - Fate of notochord Vertebral column and intervertebral discs are formed around the notochord which persists as nucleus pulposus inside the intervertebral disc. Intra-embryonic mesoderm Cells of intraembryonic mesoderm originate from the epiblast cells that migrate to primitive streak and primitive node. Then they slip through primitive groove and pit to invaginate between ectoderm and endoderm. Intraembryonic mesoderm forms the middle layer of embryonic disc transforming it into trilaminar disc (gastrulation). Intra-embryonic mesoderm is not present at the following sites: 57  3 15 1. Buccopharyngeal membrane. 2. Cloacal membrane. 3. Site of notochord. 4. Site of neural tube. At 17th day, intraembryonic mesoderm is divided into paraxial, intermediate and lateral plate-mesoderm. (For details see chapter V). 58  3 16 CHAPTER 5 EMBRYONIC PERIOD (4TH- 8TH) ILOs: By the end of this chapter, the student should be able to: ▪ Determine the embryonic period and its significance. ▪ List the different structures and organs derived from each of the three germ layers: ectoderm, mesoderm and endoderm. ▪ Trace the steps of formation of the central nervous system out of ectoderm. ▪ Follow the differentiation of subtypes of intraembryonic mesoderm (paraxial, intermediate and lateral plate) and cite the fate and derivatives of each subtype. ▪ Describe the process of folding of the embryonic disc and discuss its results. The embryonic period, or period of organogenesis, occurs from the 4th to the 8th week of development. It is the time when each of the three germ layers of the embryo gives rise to a number of derivatives. A-Derivatives of Ectoderm I- Central nervous system: Formation of central nervous system (Neurulation) is induced by growth factors secreted from developing notochord. It is developed through the following steps: Neural plate: It is the thickened median region of ectoderm which is formed by change of the shape of ectodermal cells to be columnar. It is formed at the median region between primitive node and buccopharyngeal membrane dorsal to notochord. Two strips of cells known as neural crest are present on both sides of the neural plate. Neural groove: It is a median depression in the neural plate with two elevated neural folds on both sides. Neural crests are present on both sides of neural folds. Fusions: Fusions between three structures occur as follows: 1. Neural folds fuse together, starting at the neck and extending in cranial and caudal directions to form a neural tube. The last 59  3 17 parts to be fused are cranial neuropore (closes at the 25th day) and caudal neuropore (closes at the 27th day). 2. Neural crest strips fuse together dorsal to the neural tube. Then it splits into two columns, dorsolateral to the neural tube. 3. The rest of ectoderm fuse together to cover the neural crest and neural tube forming surface ectoderm. Fate of neural tube: It forms the central nervous system (brain inside the skull and spinal cord in the vertebral canal). II- Neural crest: They are two strips of ectodermal cells on both sides of neural plate. - Development: During fusion of the neural folds, the two neural crests bands fuse together to form median single strip dorsal to neural tube that is covered by surface ectoderm. Then it divides into two longitudinal columns of cells on the dorsolateral aspect of neural tube. - Derivatives: Neural crest cells migrate to give rise to the following derivatives: Ganglia (sensory, sympathetic and parasympathetic). Cells (Schwann, glial, melanoblast and pigmented epithelium of iris). Adrenal medulla, arachnoid and pia mater. Some bones of the skull and enamel of teeth. Septum between ascending aorta and pulmonary trunk. III- Otic and lens placodes: They are ectodermal thickenings at the cranial part of the embryo. Otic placode forms otic vesicle and then the internal ear. Lens placode forms lens of the eye. IV- Other derivatives of ectoderm: Peripheral nerves. Sensory epithelium of ear, nose, eye, and epidermis of skin. Pituitary gland. Anterior part of oral cavity and lower part of anal canal. 60  4 18 B. Development of intraembryonic mesoderm: It is the layer that separates between ectoderm and endoderm. - Origin: Intraembryonic mesoderm cells originate from epiblast cells that invaginate through the groove of primitive streak and primitive pit. - Site: It is present between ectoderm and endoderm except in the following sites: a) Buccopharyngeal membrane. b) Cloacal membrane. c) Median region which is occupied by developing notochord and neural tube. - Differentiation: At the 17th day, the intraembryonic mesoderm is divided into 3 parts: 1. Paraxial mesoderm: It is the part of intraembryonic mesoderm that is present on both sides of notochord and neural tube. 2. Intermediate mesoderm: It is present between paraxial and lateral plate mesoderm. 3. Lateral plate mesoderm: It is the most lateral part of intraembryonic mesoderm. N.B.: Cells from cranial part of primitive streak form paraxial mesoderm. Cells from middle part of primitive streak form intermediate mesoderm. Cells from caudal part of primitive streak form lateral plate mesoderm. 1- Paraxial mesoderm: It is the part of the intraembryonic mesoderm on both sides of notochord and neural tube. - Segmentation: Paraxial mesoderm divides transversely into segments known as somites. Segmentation starts at the occipital region and extends caudally. Smaller segments of paraxial mesoderm are present cephalic to the first occipital somite and are called somitomeres. Somites: They are segmented masses of the paraxial mesoderm. - Time of segmentation: First pair appears in the 20th day, and then three pairs are formed per day till the 30th day (somite period). Then segmentation continues in a slower rate till the 35th or 40th day. - Number: They are 42 – 44 pairs of somites. 61  4 19 - Determination of the age of the embryo (Somite period) Number of somites - 1 Age in days = + 20 3 - Regional classification: There are 4 occipital, 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 8 – 10 coccygeal somites. - Differentiation of somites: Each somite is divided obliquely into: 1. Sclerotome: It is the ventromedial part of the somite that: ▪ Migrates medially and surrounds the notochord to form the vertebral bodies and intervertebral discs. ▪ Migrates medially and surrounds neural tube to form the neural arch of vertebrae. 2. Dermomyotome: It is the dorsolateral part of the somite that is further subdivided into: a) Dermatome: It forms the dermis of the skin whereas epidermis is formed from ectoderm. b) Myotome: It divides into dorsal part that forms skeletal muscles of the back of the body and ventral part that forms skeletal muscles of anterolateral aspect of body and limbs. N.B. Each spinal nerve divides into dorsal and ventral primary rami to supply divided parts of the myotomes. 2- Intermediate mesoderm: It lies between paraxial mesoderm and lateral plate mesoderm. It is partially segmented. It forms the urogenital system. 3- Lateral plate mesoderm: It is the part of intra-embryonic mesoderm that lies lateral to intermediate mesoderm. Lateral plate mesoderm on both sides are continuous together cranial to buccopharyngeal membrane. It is continuous with the extra-embryonic mesoderm at the margin of the disc. ❖ Intra-embryonic coelom: It is a horseshoe cavity that is formed in the lateral plate mesoderm. Its caudal ends communicate with extra-embryonic coelom at the margin of embryonic disc. It is divided into: 62  4 20 a) Pericardial cavity in median cranial part of the coelom. b) Peritoneal canals in the lateral part of the coelom. c) Pleural cavities between pericardium and peritoneal canals. Lateral plate mesoderm is split by intraembryonic coelom into: 1. Somatopleuric (somatic) mesoderm: It is the mesoderm that is present in contact with ectoderm. It forms connective tissue of anterolateral walls of the body as well as parietal layer of pleura, pericardium and peritoneum. 2. Splanchnopleuric (splanchnic) mesoderm: It is the mesoderm that is present in contact with endoderm. It forms smooth muscles and connective tissue of gut and respiratory tract, cardiac muscles as well as visceral pleura, pericardium and peritoneum. N.B. ▪ Cardiogenic area is the splanchnic mesoderm related to pericardium. ▪ Septum transversum is a mass of mesoderm cranial to pericardium (before folding) and caudal to pericardium (after folding). C-Derivatives of Endoderm Endodermal layer gives rise to: 1. Lining epithelium of: ▪ Digestive system except its beginning and end. ▪ Respiratory tract. ▪ Most of urinary bladder and urethra. ▪ Tympanic cavity and Eustachian tube. 2. Glandular epithelium: ▪ Parenchyma of liver, pancreas, thyroid, thymus, tonsils (palatine & nasopharyngeal) and parathyroid glands. 63  4 21 FOLDING It is the process by which the embryonic disc becomes folded upon itself. - Time of folding: It starts at the end of 3rd week and is completed at the end of 4th week. - Types of folding: 1. Cephalo-caudal folding: forming head and tail folds. 2. Lateral folding: It is the folding of sides of the embryonic disc. - Causes of folding: 1. Increase of longitudinal length of the embryonic disc due to growth of neural tube and somites leads to cephalo- caudal folding. 2. Expansion of amniotic cavity leads to folding in all directions. - Limitations of head & tail folds: Head fold is limited by relatively firm cranial end of notochord while tail fold is limited by relatively firm primitive streak. - Steps of folding: Expansion of amniotic cavity leads to ventral shift of amnio- ectodermal junction towards endoderm with subsequent incorporation of a part of yolk sac inside the folded embryo. The embryonic disc gradually bulges into the amniotic cavity. The embryo thus acquires a cylindrical shape: ▪ The ectoderm becomes on the outer surface of the embryo. ▪ It contains a cavity that is lined with endoderm called gut. ▪ The primitive umbilical ring is present on the ventral body wall and is surrounded by the amnioectodermal junction. ▪ The embryo becomes completely surrounded by the amniotic cavity bathing in the amniotic fluid. Cranio-cuadal elongation of the embryonic disc by the growth of neural tube and somites leads to formation of head fold and a tail fold due to cephalo-caudal folding. - Results of folding: a. The embryonic disc changes into cylindrical shape which has a body cavity. b. Amniotic cavity surrounds the cylindrical embryo. 64