Head and neck

Vagus nerves

origin and travel route :

Vagus nerves are the only cranial nerves to extend beyond head and neck region.
Nerve fibers are from medulla, pass skull through jugular foramen, and descend through neck region into thorax and abdomen.

Targets, functions and types of neuron:

1. They are mixed nerves.
2. Almost all motor fibers are parasympathetic efferents, except those serving skeletal muscles of pharynx and larynx because they are involved in swallowing.
3. the visceral motor fibers are from the medulla oblongata to serve the heart, lungs and abdominal viscera and their functions are regulations of the heart beat, breathing, and digestive system activity.
4. The visceral sensory fibers transmit the sensory impulses from the thoracic and abdominal viscera, the carotid sinus, the carotid and aortic bodies and the taste buds of posterior tongue an pharynx to the medulla oblongata.
5. The somatic sensory fibers are from the posterior part of the external auditory meatus and the back of the ear and descend in the medulla.
6. They also carry proprioceptor fibers from muscles of the larynx and pharynx.

Comprehensive view of the upper limb structure an how it works

A Comprehensive View of the Upper Limb Structure
And How It Works


The human upper limbs include four elements:
§ The skeletal elements and their joints
§ The muscles that move those skeletal elements
§ The nerves that trigger those muscles to move those skeletal elements

First, the skeletal elements and their joints of the upper limb.

Bones of the appendicular skeleton on pectoral girdle and upper limbs including:
1. Clavicle (2): Clavicle is in superoanterior thorax; articulates medially with sternum and laterally with scapula.
2. Scapula (2): Scapula is in posterior thorax; forms part of the shoulder; articulates with humerus and clavicle.
3. Humerus (2): Humerus is the sole bone of arm; between scapula and elbow.
4. Ulna (2): ulna is the medial bone of forearm between elbow and wrist; forms elbow joint.
5. Radius (2): Radius is lateral bone of forearm; carries wrist.
6. Carpals (8 each hand): Carpals form a bony crescent at the wrist; arranged in two rows of four bones each.
7. Metacarpals (5 each hand): Metacarpals form the palm; one in line with each digit.
8. Phalanges (14 each hand): Phalanges form the fingers; three in digits 2-5; two in digit 1(thumb).

Cartilages between the bones of the upper limbs.
§ Skeletal cartilages----made of some variety of cartilage tissue, which consists primarily of water. The high water content of cartilage accounts for its resilience that is its ability to spring back to its original shape after being compressed.
§ The cartilage contains no nerves or blood vessels, is surrounded by a layer of dense irregular connective tissue.
§ The cartilages between bones of the upper limbs are all articular cartilages, which is one type of the hyaline cartilages. Hyaline cartilage cartilages provide support with flexibility and resilience.

Joints between the bones of the upper limbs are all synovial joints:
§ Acromioclavicular ---between scapula and clavicle--- plane type---rotation.
§ Shoulder---between scapular and humerus---ball and socket type---rotation,abduction,adduction,and circumduction (flexion and extension)
§ Elbow ---humurus and radius/ulna---hinge ---flexion and extension.
§ Proximal and distal radioulnar---radius and ulnar---pivot---supination and pronation
§ Wrist--- ulnar/radius and proximal carpals---plane----flexion/extension, adduction/abduction
§ Knuckle, metacarpophalanges---metacapals and phanlanges---condyloid---flexion/extension and adduction/abduction
§ Finger, interphalangeal (IP) proximal IP and distal IP---phalanges---hinge---flexion and extension

Second, the muscles that move the skeletal elements.

Skeletal muscles and movements
§ All the muscles in the upper limbs are skeletal muscles, which are the organs that attach to and cover the bony skeleton.
§ Different muscles provide different movements.
§ Major muscles of the upper limb and movement:
Major movement of the arm:
1. Deltoid---abduction, adduction, flexion and extension.
2. pectoralis major---flexiion, ratation, adduction.
3. Latissimus dorsi---extension, flexion, adduction, ratation.
4. coracobrachialis---flexiion and adduction.
5. biceps brachii---flexion.
6. brachialis---flexion.
7. brachoradialis---flexion and extension.
8. Teres minor--- rotation and adduction.
9. Teres major--- extention, ratation, and adduction.
10. Triceps brachii--- extensionand adduction.
11. Anconeus--- abduction and pronation, and extension.

Major movement of the wrist, hand, and fingers:
1. Pronator teres---pronation and flexion
2. Flexor carpi radialis---flexion and abduction
3. Ppalmaris longus---flexion.
4. Flexor carpi ulnaris---flexion and adduction, extension.
5. Abductor pollicis longs---abducts and extension.

At last, the nerves that trigger those muscles to move those skeletal elements.

§ Each muscle is served by one nerve, and artery, and by one or more veins, all of which enter or exit near the central part of the muscle and branch through its connective tissue sheaths.
§ Each skeletal muscle fiber is supplied with a nerve ending that controls its activity

Major nerves involve in the muscles of the upper limb:
1. Pectoralis major---lateral and medial pectoral nerves (c5-c8, and T1)
2. Latissimus dorsi---thoracordorsal nerves (C6-C8)
3. Deltoid---axillary nerve
4. Teres minor---axillary nerve
5. Coracobrachialis---musculocutaneous nerves
6. Triceps brachii---radial nerve (C6- C8)
7. Anconeus ---radial nerve
8. Biceps brachii--- Musculocutaneous nerve (C5- and C6)
9. Brachialis---Musculocutaneous nerve
10. Brachioradialis --- radial nerve
11. Pronator teres---Median nerve
12. Flexor carpi radialis---median nerve
13. Flexor carpi ulnaris---ulnar nerve (C7and C8)


Physiology of a skeletal muscle fiber
§ For a skeletal muscle fiber to contract, it must be stimulated by a nerve ending and must propagate an electrical current, or action potential, along its sarcolemma.
§ This electrical event causes the short-lived rise in intracellular calcium ion levels that is the final trigger for contraction.
The Neuronuscular Junction and the Nerve Stimulus
§ Skeletal muscle cells are stimulated by motor neurons of the somatic nervous system.
§ The motor neurons’ long threadlike extensions called axons travel, bundled within nerves, to the muscle cells they serve.
§ The axon of each motor of each motor neuron divides profusely as it enters the muscle, and each axonal ending forms a branching, neuromuscular junction with a single muscle fiber.
§ Each axonal terminal contains vesicles filled with the neurotransmitter acetylcholine(Ach), which is released when the action potential reaches the axonal terminal.
§ The sarcolemma is highly folded adjacent to the synaptic cleft, and Ach receptors are present in these junctional folds.
§ Ach diffuses across the synaptic cleft and attaches to receptors on the sarcolemma, opening ion channels and initiating depolarization of the sarcolemma.


The motor unit
§ A skeletal muscle contracts with varying force and for different periods of time in response to stimuli of varying frequencies and intensities.
§ Each muscle is served by at least one motor nerve, which contains axons of hundreds of motor neurons.
§ A motor neuron and all the muscle fibers it supplies are called a motor unit.
§ The cell bodies of the motor neurons reside in the spinal cord, an their axons extend to the muscle. In the muscle, each axon divides into a number of axonal terminals that are distributed to muscle fibers scattered throughout the muscle.
§ As a result, stimulation of a single motor unit causes a weak contraction of the entire muscle.

Coordination of all these skeleton, muscles and nerves, varies of movements can be represented by the upper limbs.

Reference cites:

A and P text book

google.com

Vertebral column and Peripheral nerves

Vertebral column and Peripheral nerves

Vertebral column

General Characteristics and Structure of the vertebral column

General Characteristics

1. Vertebral column also called the spine, the vertebral column is formed from 26 irregular bones connected and results in a flexible, curved structure.
2. Vertebral column serves as the axial support of the trunk, the spine extends from the skull to the pelvis, where it transmits the weight of the trunk to the lower limbs.
3. Vertebral column surrounds and protects the delicate spinal cord and provides attachment points for the ribs and for the muscles of the back and neck.
4. In the fetus and infant, the vertebral column consists of 33 separate bones, or vertebrae. Nine of them fuse to form two composite bones, the sacrum and the tiny coocyx. The remaining 24 bones persist as individual vertebrae separated by intervertebral discs.

General Structure

1. The vertebral column has five major divisions. The seven vertebrae of the neck are the cervical vertebrae, the next 12 are the thoracic vertebrae, and the five supporting the lower back are the lumbar vertebrae. The vertebral column becomes progressively larger from the cervical to the lumbar region.
2. Inferior to the lumbar vertebrae is the sacrum, which articulates with the hip bones of the pelvis. The terminus of the vertebral column is the tiny coccyx.
3. The view of the vertebral column from the side is four curvatures that shows the S shape. The cervical and lumbar curvatures are concave posteriorly; the thoracic and sacral curvatures are convex porteriorly.

General Structure of Vertebrae

1. All vertebrae have a common structural pattern. Each vertebra consists of a body or centrum, anteriorly and a vertebral arch posteriorly. The disc-shaped body is the weight-bearing region. The body and vertebral foramen. Vertebral foramina of the articulated vertebrae form the long vertebral canal, through which the spinal cord passes.
2. The vertebral arch is a composite structure formed by two pedicles and two laminae. The perdicles , short bony pillars projecting posteriorly from the vertebral body, form the sides of the arch. The laminae, flattened plates that fuse in the median plane, complete the vertebral arch posteriorly. Seven processes project from the vertebral arch. The spinous process is a median posterior projection arising at the junction of the two laminae. A transerse process extends laterally from each side of the vertebral arch. The paired superior and inferior articular processes protrude superiorly and inferiorly, from the pedicle-lamina junctions.

Regional Vertebral Characteristics

Cervical Vertebral Characteristics (C1-C7)

1. Body: small, wide side to side
2. Spinous process: short, bifid, projects directly posteriorly
3. Vertebral foramen: triangular
4. Transverse processes: Contain foramina
5. Superior and inferior articulating processes:superior facets directed superopsteriorly; inferior facets directed inferoanteriorly
6. Movements allowed: flexion and extension, lateral flexion, rotation, the spine region with the greatest range of movement

Thoracic Vertebral Characterstics (T1-T12)

1. Body: Larger than cervical, heart shaped, bears two costal demifacets
2. Spinous process: long, sharp, profects inferiorly
3. Vertebral foramen: circular
4. Transverse processes: Bear facets for ribs (except T11 and T12)
5. Superior and inferior articulating processes: superior facets directed posteriorly; inferior facets directed anteriorly
6. Movements allowed: rotation, lateral flexion possible but limited by ribs, flexion and extension prevented

Lumber Vertebral Characterstics (L1-L5)

1. body: massive, kidney shaped
2. Spinous process: short, blunt, projects directly posteriorly
3. Vertebral foramen: triangular
4. Transverse processes: Thin and tapered
5. Superior and inferior articulating processes: superior facets directed posteromedially; inferior facets directed anterolaterally
6. Movements allowed: flexion and extension, some lateral flexion, rotation prevented

Peripheral nervous system (CNS)

Definetion

The peripheral nervous system consists of sensory receptors, nerves conduting impulses to and from the CNS, their associated ganglia, an motor endings.

Sensory Receptors

1. Senroty receptors are specialized to respond to environmental changes (stimuli).
2. Sensory receptors include the simple receptors for pain, touch, pressure, and temperature found in the skin, as well as those found in skeletal muscles and tendons and in the visceral organs. Complex receptors (sense organs), consisting of sensory receptors and other cells, serve the special senses (vision, hearing, equilibrium, smell and taste).
3. Receptors are classified according to stimlus detected as mechanoreceptors, thermoreceptors, photoreceptors, chemoreceptors, and nociceptors, and according to location as exteroceptors, interoceptors, and proprioceptors.
4. The general sensory receptors are classified structurally as free or encapsulated nerve (receptor) endings fo sensory neurons. The free endings are mainly receptors for temperature and pain, although two are for light touch(Merkel discs and hair follicle receptors). The encapsulated endings, which are mechaoreceptors, include Meissner's corpuscles, Pacinian corpuscles, Ruffini's corpuscles, muscle spindles, Golgitendon organs, and joint kinesthetic receptors.

Sensation to Perception

1. Sensation is awareness of internal and external stimuli; perception is conscious interpretation of those stimuli.
2. The three levels of sensory integration are the receptor, circuit, and perceptual levels. Theselevels are functins of the sensory receptors, the ascending pathways, and the cerebral cortex, respectively.
3. Sensory receptors transduce(convert) stimulus energ via ulus strength is frequency coded. Adaptation (decrease response to a continuous or unchanging stimulus) is seen in all general receptors except pain and proprioceptors.
4. Perception --- the internal, conscious image of the stimulus that serves as the basis for response---is the result of cortical processing. Regions of the somatosensory cortex devoted to a particular body area reflect the number fo receptors in that area.

Nerves

1. A nerve is a bundle of neuron fibers in the PNS. Each fiber is enclosed by a perineurium, and the whole nerve is bundled by the epineurium.
2. Nerves are classified according to the direction of impulse conduction as sensory, motor, or mixed; most nerves are mixed. The efferent fibers may be somatic or autonomic.

Cranial Nerves

1. Twelve pairs of cranila nerves originate from the brain and issue through the skull to innervate the head and neck. Only the vagus nerves extend into the thoracic and abdominal cavities.
2. Cranial nerves are numbered from anterior to posterior in order of emergance from the brain. Their names reflect structures served or function or both.

Spinal Nerves

1. The 31 pairs of spinal nerves (all mixed nerves) are numbered successively according to the region of the spinal cord from which they issue.
2. Spinal nerves ar formed by the union of dorsal and ventral roots of the spinal cord and are short, confined to the intervertebral foramina.
3. Branches of each spinal nerve include dorsal and ventral rami, and a meningeal branch, and in the thoracic region, rami communicantes.
4. Ventral rami, except T1-T12, form plexuses that serve the limbs.
5. Dorsal rami serve the muscles and skin of the posterior body trunk. T1-T12 ventral rami give rise to intercostal nerves that serve the thorax wall and abdominal surface.
6. The cervical plexus (C1-C5) innervates the muscles skin of the neck nad shoulder. Its phrenic nerve serves the diaphragm.
7. The brachial plexus serves the shoulder, some thorax muscles, and the upper limb. It arises primarilu from muscles, and the upper limb. It arises primarily from C5-T1. Proximal to distal, the brachial plexus has roots, trunks, divisions, and cord. The main nerves arising from the cords are the axillary, musculocutaneous, median, radial, and ulnar nerves.
8. The lumbar plexus ( L1-L4) provides the motor supply to the anterior and medial thigh musclesand the curaneous supply to the anterior thigh and part of the leg. Its chief nerves are the femoral and obturator.
9. The sacral plexus (L4-S4)supplies the posterior muscles nad skin of the lower limb. Its principal nerve is th large sciatic nerve composed of the tibial and common fibular nerves.
10. Joints are innervated by the same nerves that serve the muscles acting at the joint. All spinal nerves except C1 innervate specific segments of the skin called dermatomes.

(Images are from Google.com and Yahoo.com; Letures are from A and P textbook)

Tissues of the human body

The Tissues of the human body

Four types of tissue:
Epithelial tissue
Connective tissue
Muscle tissue
Nervous tissue

Epithelial tissue:
Definition---is the covering, lining, and glandular tissue of the body.
Functions---Protection, absorption, excretion, filtration, secretion, and sensory reception.
Characteristics---exhibit a huge degree of cellularity, specialized contacts, polarity, avascularity, support from connective tissue, and high regenerative capacity.
Classification:
By arrangement---simple (one layer)
By cell shape---squamous, cuboidal, columnar

Combination terms:

Simple squamous epithelium
Description--- a single layer of flattened cells with disc-shaped central nuclei and sparse cytoplasm. The simplest of the epithelia.
Function---Allows passage of materials by diffusion and filtration I sites where protection is not important; secretes lubrication substances in serosae.
Location---Kidney glomeruli; air sacs of lungs; lining of heart, blood vessels, and lymphatic vessels; lining of ventral body cavity (serosae).

Simple cuboidal epithelium
Description---a single layer of cubelike cells with large, spherical central nuclei.
Function--- Secretion and absorption.
Location--- Kidney tubules; ducts and secretory portions of small glands; ovary surface.

Simple columnar epithelium
Description---Single layer of tall cells with round to oval nuclei; some cells bear cilia; layer may contain mucus-secreting unicellular glands (goblet cells).
Function---Absorption; secretion of mucus, enzymes, and other substances; ciliated type propels mucus (or reproductive cells) by ciliary action.
Location---Nonciliated type lines most of the digestive tract (stomach to anal canal), gallbladder, and excretory ducts of some glands; ciliated variety lines small bronchi, uterine tubes, and some regions of the uterus.

Pseudostratified columnar epithelium
Description---Single layer of cells of differing heights, some not reaching the free surface; nuclei seen at different levels; may contain goblet cells and bear cilia.
Function---Secretion, particularly of mucus; propulsion fo mucus by ciliary action.
Location---Nonciliated type in male’s sperm carrying ducts and ducts of large glands; ciliated variety lines the trachea, most of the upper respiratory tract.

Stratified cuboidal epithelia

Description---Quite rare in the body.

Location--- mostly found in the ducts of some of the larger glands(sweat glands, mammary glands).

Stratified columnar epithelium

description---a limited distribution in the body.

Location---pharynx, the male trethra, and lining some glandular ducts.

Stratified squamous epithelium
Description--- Thick membrane composed of several cell layers; basal cells are cuboidal or columnar and metabolically active; surface cells are flattened; in the keratinized type, the surface cells are full of kerative and dead; basal cell are active in mitosis and produce the cells of the more superficial layers.
Function--- Protects underlying tissues in areas subjected to abrasion.
Location--- Nonkeratinized type forms the moist linings of the esophagus, mouth, and vagina; keratinized variety forms the epidermis of the skin, a dry membrane.


Transitional epithelium
Description---Resembles both stratified squamous and stratified cuboidal; basal cells cuboidal or columnar; surface cells dome shaped or squamouslike, depending on degree of organ stretch.
Function--- stretches readily and permits distension of urinary organ by contained urine.
Location--- Lines the ureters, bladder, and part of the urethra.


Connective Tissue:

Definition---is the most abundant and widely distributed tissue of the body.
Functions---support, protection, binding, insulation, and transportation (blood).
Characteristics---originate from embryonic mesenchyme and exhibit matrix. Depending on type, a connective tissue may be well vascularized (most), poorly vascularized (dense connective tissue), or avascular (cartilage)

Structural Elements:
The structural elements of all connective tissues are extracellular matrix and cells.
Extracellular matrix consists of ground substance and fivers. It may be fluid, gel-like, or firm.
Each connective tissue type has a primary cell type that can exist as a mitotic, matrix-secreting cell (blast) or as a mature cell (cyte) responsible for maintaining the matrix. The chief cell type of connective tissue proper is the fibroblast; that of cartilage is the chondroblast; that of bone is the osteoblast; and that of blood-forming tissue is the hematopoietic stem cell.


Types of connective tissue:

Embryonic connective tissue
Description---Embryonic connective tissue; gel-like ground substance containing fibers; star-sharped masenchymal cells.
Function---Gives rise to all othe connective tissue types.
Location--- Primarily in embryo.
Connective tissue proper consists of loose and dense varieties.



Loose connective tissue:

Areolar
Description--- Gel-like matrix with all three fiber types; cells: fibroblasts, macrophages mast cels, and some white blood cells.
Function ---Wraps and cushions organs; its macrophages phagocytize bacteria; plays important role in inflammation; holds and conveys tissue fluid.
Location--- Widely distributed under epithelia of body e.g. forms lamina propria of mucous membranes; packages organs; surrounds capillaries.

Adipose
Description ---Matrix as in areolar, but very sparse, closely packed adipocytes, or fat cells, have nucleus pushed to the side by large fat droplet.
Function--- Provides reserve food fuel; insulates against heat loss; supports and protects organs.
Location---Under skin, around kidneys and eyeballs; within abdomen; in breasts.

Reticular
Description---Network of reticular fibers in a typical loose ground substance; reticular cells lie on the network.
Function--- Fibers form a soft internal skeleton that supports other cell types including white blood cells, mast cells, and macrophages.
Location---Lymphoid organs ( lymph nodes, bone marrow and spleen).

Dense connective tissue:
Dense regular
Description---Primarily parallel collagen fibers; a few elastic fibers; major cell type is the fibroblast.
Function---Attaches muscles to bones or to muscles; attaches bones to bones; withstands great tensile stress when pulling force is applied in one direction.
Location –Tendons, most ligaments, aponeuroses.

Dense irregular
Description--- Primarily irregularly arranged collagen fibers; some elastic fibers; major cell type is the fibroblast.
Function---Able to withstand tension exerted in many directions; provides structural strength.
Location--- Dermis of the skin; submucosa of digestive tract; fibrous capsules of organs and of joints.


Cartilage exists as
Hyaline
Description--- Amorphous but firm matrix; collagen fibers form and imperceptible network; chondroblasts produce the matrix and when mature lie in lacunae.
Function---Supports and reinforces; has resilient cushioning properties; resists compressive stress.
Location--- Forms most of the embryonic skelton; cobers the ends of long bones in joint cavities; forms costal cartilages of the ribs; cartilages of the nose, trachea, and larynx.

Elastic cartilage
Description---Similar to hyaline cartilage, but more elastic fibers I matrix.
Function ---Maintains the shape of a structure while allowing great flexibility.
Location--- Supports the external ear; epiglottis.


Fibrocartilage
Description---Matrix similar to but less firm that that in hyaline cartilage; thick collagen fibers predominate.
Function---Tensile strength with the ability to absorb compressive shock.
Location--- Intervertebral discs; pubic symphysis; discs of knee joint.


Bone (osseous tissue)
Description ---Hard calcified matrix containing many collagen fibers, osteocytes lie in lacunae. Very well vascularized.
Function ---Bome supports and protects; provides levers for the muscles to act on; stores calcium and other minerals and fat; marrow inside bones is the site for blood cell formation.
Location--- Bones

Blood
Description--- Red and white blood cells in a fluid matrix.
Function--- Transport of respiratory gases, nutrients, wastes and other substances.
Location--- Contained within blood vessels.



Nervous Tissue:


Description---Neurons are branching cells; cell processes that may be quite long extend from the nucleus-containing cell body; also contributing to nervous tissue are nonirritable supporting cells.
Function ---Transmit electrical signals from sensory receptors and to effectors.
Location ---Brain, spinal cord and nerves.



Muscle Tissue:

Definition---highly cellular, well-vascularized tissues that are responsible for most types of body movement.
Types of muscle tissue based on the structure and function: skeletal, cardiac, and smooth.

Skeletal muscle
Description---Long, cylindrical, multinucleate cells; obvious striations.
Function---Voluntary movement; locomotion; manipulation of the environment; facial expression; voluntary control.
Location--- I skeletal muscles attached to bones or occasionally to skin.



Cardiac muscle
Description--- Branching, striated, generally uninucleate cells that interdigitate at specialized junctions.
Function--- As it contracts, it propels blood into the circulation; involuntary control.
Location--- The walls of the heart.

Smooth muscle
Description--- Spindle-shaped cells with central nuclei; no striations; cells arranged closely to form sheets.
Function--- Propels substances or objects (foodstuffs, urine, a baby) along internal passageways; involuntary control.
Location--- Mostly in the walls of hollow organs.

organization of human body and embryonic development

Overall Structural Organizatioon of human body

The levels of structural organization of the body, from simplest to most complexes, are: chemical, cellular, tissue, organ, organ system, and organism.

Chemical level---tiny building blocks of matter, combine to form molecules, in turn, associate in specific ways to form organelles, basic components of the microscopic cells.

Cellular level---all cells have some common functions, but individual cells vary widely in size and shape, reflecting their unique functions in the body.

Organ level---a discrete structure composed of at least two tissue types that perform a specific function for the body.

Organ system---organs that work together to accomplish a common purpose make up an organ system.

Organismal level--- The highest level of organization, represents the sum total of all structural levels working together to promote life.

2. The eleven organ systems of the body are the integumentary, skeletal, muscular, nervous, endocrine, cardiovascular, lymphatic, respiratory, digestive, urinary, and reproductive systems. The immune system is a functional system closely associated with the lymphatic system.

Events of Embryonic Development

Formation and Roles of the Embryonic Membranes

Embryonic membranes:
Amnion ---protects the embryo; Amniotic fluid prevents
Embryonic parts from adhering and fusing together and allows the embryo freedom of movement.
Yolk sac ---forms part of the gut (digestive tube);
---Produces the earliest blood cells and blood
Vessels;
--- the source of primordial germ cells
Allantois ---forms umbilical cord
Chorion ---encloses the embryonic body and all other membranes

Gastrulation: Germ Layer Formation
• conceptus → embryo
(imagegoogle.com)

Three primary germ layers:

Ectoderm (outer skin) → nervous system and the skin
Mesoderm (inner skin) →epithelial linings of the digestive, respiratory, and urogenital systems and associated glands
Endoderm (middle skin) →virtually everything else.
(imagegoogle.com)


Organogenesis: Differentiation of the Germ Layers

By the end of the embryonic period, when the embryo is about 22 mm long from head to buttocks, all the adult organ systems are recognizable.


Derivatives of the Primary Germ Layers

Ectoderm:

All nervous tissue (including brain and spinal cord)
Epidermis of skin and epidermal derivatives (hairs, hair follicles, sebaceous and sweat glands, nails)
Cornea and lens of eye
Epithelium of oral and nasal cavities, of paranasal sinuses, and of anal canal
Endothelium of blood vessels and lymphatic
Tooth enamel
Epithelium of pineal and pituitary glands and adrenal medulla
Melanocytes
Some cranial bones and branchial cartilages (derived from neural crest)

Mesoderm:

Skeletal, smooth, and cardiac muscle

Cartilage, bone, and other connective tissue

Blood, bone marrow, and lymphoid tissues

Endothelium of blood vessels and lymphatics

Serosae of ventra body cavity

Fibrous and vascular tunics of eyes

Synovial memvraes of joint cavities

Organs of unogenital system (ureters, kidneys, gonads, and reproductive ducts)

Endoderm:

Epithelium of digestive tract (except that of oral and anal cavities)

Glandular derivatives of digestive tract (liver, pancreas)

epithelium of respiratory tract, auditory tube, and tonsils

Thyroid, parathyroid, and thymus glands

Epithelium of reproductive ducts and glands

Epithelium of urethra and bladder

1. Peiwen Wu
2. China 06/09/1974
3. No favorite Artist
4. I like BIO and want to be a nurse
5. I'm married and have two boys.