Study of the microscopic structure of the human organism co related with the development, function and clinical significance.

It is derived from Greek term” anatome” meaning cutting apart.

EMBRYOLOGY

It is the study of the formation and development of the embryo from the moment of its inception upto

the time when it is born as an infant.

Gonads: no: of chromosomes in an organism=23 pairs/46 no.

                                    ♂-----44 autosomes –XY

                                    ♀----44 autosomes  - XX

Karyotyping : Classification of   chromosomes based upon their differences that enable us to identify each chromosome individually.

Spermatogenisis : The process of formation and development of spermatazoan .

                               Formed in the wall of the seminiferous tubules of testes.

Spermiogenesis (spermateleosis)  : The process of transformation of a circular spermatid to a spermatozoan.

Mature spermatozoan: Has a head, a neck middle piece and a principal piece or tail. Head is covered with a cap called acrosome.

Length -50-60 microns

Golgi apparatus forms the acrosomic cap.

Nucleus forms head.

Mitochondrion forms the sheath of middle piece.

Proximal centriole comes to lie in the neck.

Distal centriole becomes ring shaped and forms the annulus.

Axial filament grows out from the centriole and is present in middle piece and tail.

                               Viability of spermatozoa =4 days.

Ovulation: The shedding of ovum from the ovary.

Corpus luteum- It is an important structure derived after the rupture of ovarian follicle to shed the ovum.

                               It secretes hormone progesterone.

                               Viability of ovum =24 hrs

 Menstrual cycle: Divided into 4 phases

1.Post menstrual phase

2.Proliferative

3.Secretory(premenstrual)

4.Menstrual

   Follicular phase ---post menstrual + proliferate phase -~   Oestrogen 

   Luteal phase – secretory +menstrual phase -~ progesterone

   Size of Oocyte— 120u.

Approximate number of occytes at puberty—around 40,000.

Approximate number of ova liberated during reproductive period of   female—around 300 to 400.

Time required for formation of spermatozoa from spermatogonium—64 days.

Fertilized ovum reaches uterine cavity—by 4 days.

Implantation of ovum (fertilized) occurs—about 7th day.

Primitive uteroplacental circulation begins—by end of 2nd week.

Number of somites in embryo — 42 to 44.

Time of somite formation —  21 to 30th day.

Organogenesis —  from 4th to 8th weeks.

Formation of primary ovary in a female takes place by 8th week

Differentiation of genital organs

1.Persons with two X chromosomes are female; those with one x and one y are male.

2.Y chromosome bears a gene responsible for production of a testis determining factor.

3.Interstitial cells in testis produce testosterone .It forms a complex with certain receptor proteins which attaches itself

 to DNA. This causes the mesonephric duct to develop as in male.

4.Presence of dihydrotestosterone .

5.Sertoli cells produce mullerian inhibiting substance .This causes regression of paramesonephric ducts.

Genital swellings in male differentiate into scrotum whereas in a female, they form labia majora.

The mesonephric duct in a female develops into Gartner's duct.

The Mullerian ducts in male develop into appendix testes whereas in a female, they develop into uterus and uterine tubes.

In female, the homologue of prostatic glands are paraurethral glands.

FOETAL CIRCULATION

    Differs from adult circulation in

a) Source of oxygenated blood is not the lung but the placenta.

b) Oxygenated blood from placenta comes to foetus through umbilical vein and joins the left branch of portal vein.

 Small portion passes through the substance of the liver to I V, but the greater part passes direct to I V through the ductus venosus. 

Changes at birth: 1) umbilical artery contracts.

2) Lumen of umbilical veins and ductus venosus occludes and this takes place a few minutes after birth.

3) Ductus arteriosus occludes by about 10 th day.

4) Pulmonary vessels increase in size.left atrial pressure rises than that of right atrium and leads to closure of foramen ovale.

Remnant of

Umbilical artery -  medial umbilical ligament

Left umbilical vein  - ligament teres of the liver

Ductus venosus   - Ligamentum venosum

Ductus arteriosus - Ligamentum arteriosum

OSTEOLOGY

Study of bones.

Bones are divided according to their

1)Position       

Human skeleton -------axial}  bones of skull, vertebral column, ribs,        sternum, hyoid.

                                       -------appendicular} bones of pectoral, pelvic girdle ,upper and lower limbs

2) Shape

Long bones: eg: Femur, tibia, humerus, ulna, radius, and fibula

Short long bones: eg: Metacarpals, metatarsals, phalanges

Short bones: eg: Carpals, tarsals

Flat bones: eg : Scapula , sternum, ribs, parietal and frontal.

Pneumatic bones : Maxillary ,sphenoid , ethmoid, mastoid part of temporal bone.

Irregular bones: eg: Vertebrae, skull bones

Sesamoid bone: eg: patella, pisciform, fabella

2)Structure

Compact bone =consisting of haversian system

Cancellous (spongy) bone = consisting of irregularly placed lamellae.

Diploic =consisting of inner and outer tables of compact bone with intervening porous layer.

3)Development

Ecto chondral bones: which develop in membrane (membranous)

Endochondral bones: which develop in cartilage. (cartilageneous)

Total no of bones ---206

                               Upper limbs-64

                               Lower limbs-62

                               Vertebrae-33

                               Skull        -  29(14-facial bones

                                              -  14- cranial bones , hyoid bone )

                               Sternum-1

                               Ribs- 12 pairs

Longest bone---femur

Smallest bone---stapes

Strongest part in human body- Enamel of teeth

Largest sesamoid bone ---  Patella developing in quadriceps.

Microscopic unit of a bone: Haversian system (secondary osteone)

Ossification

Process  of gradual bone formation.

a)Ossification in membrane (direct)—easy process

Eg: clavicle, bones of face,vault of skull.

b)Ossification in cartilage (Indirect) ---gradual process.

Eg: bones of limbs, trunk.

Secondary cartilage bone: eg: neck of mandible, sternal end of clavicle.

Primary centres of ossification may be single or multiple ,appear before birth between 6th – 8th week of foetal life

except cuneiform ,navicular bones .

Secondary centres of ossification are multiple and appear after birth except lower end of femur.

Ossification of acetabulum is complete at 16-17 years

Growing ends of bones of upper  limb—upper end of humerus & Lower end of radius and ulna                                                 

Growing ends of bones of lower limbs ---- lower end of femur & Upper limbs of tibia and fibula

In long bones, growing ends fuse with shaft at 20 yrs and opposite ends at about 18 yrs.

In other bones it is between 20-25 yrs.

Types of epiphysis are :

 a) Pressure epiphyses - located at pressure points like joints 

 b) Traction epiphyses:  subjected to traction by pull of muscles when located at the muscular attachment

 c) Atavistic epiphyses: centre appearing in the part of bone which was orginally a separate bone in evolution   eg : Coracoid

     process of scapula.

Hyaline cartilage has a tendency to get calcified in later years of life.

Skull bones—22 bones

Facial bones (14)-paired-nasal, maxillae, zygomatic, palantine, lachrymal, inferior nasal connchae.

                                                            Unpaired-mandible, vomer

Cranial bones (14)-paired- parietal, temporal, ear ossicles

                                                              Unpaired- frontal, ethmoid, sphenoid, occipital.

Carpal bones- 8 bones Lat  TO medial (Proximal) Scaphoid, lunate, triquetral, pisiform

                                             (Distal)—Trapezium, trapezoid, capitate, hamate.

Tarsal bones-7 bones (proximal) Talus, calcaneus

(distal) medial cuneiform, intermediate cuneiform, lateral cuneiform, cuboid.

Largest and strongest of tarsal bones—Calcaneus

Paranasal sinuses  4 pairs : Frontal, sphenoidal, ethmoidal, maxillary.

Largest of all air sinuses ---Maxillary sinus (Antrum of Highmore)

Foramina of skull

Anterior cranial fossa :

1.Foramen caecum: lies between the alae of crista galli of ethmoid and frontal crest. Transmits an emissary vein.

Middle cranial fossa:

2.Optic canal (foramen): Transmits optic nerve, opthalmic artery.

3.Superior orbital fissure: Bounded by lesser wing above, greater wing below and body of sphenoid medially.

Divided  by three compartments  by common tendinous ring.

Transmits –superior and inferior divisions of oculomotor, nasociliary nerve, abducent nerve, trochlear nerve, frontal nerve,

 lacrimal nerve, lachrimal artery, orbital branch of middle meningeal artery, superior ophthalmic vein,recurrent meningeal

 branch of lachrymal artery, inferior ophthalmic vein.

4.Foramen rotundum---transmits maxillary nerve.

5. Foramen ovale --- transmits mandibular nerve,accessory meningeal artery ,lesser superficial petrosal nerve, emissary vein.

6. Foramen spinosum--- transmits middle meningeal artery, nervus spinosus

7. Foramen lacerum--- transmits Internal carotid artery.

8. Carotid canal---- transmits internal carotid artery with plexus,    emissary veins, meningeal lymphatics.

Posterior cranial fossa:

         9. Jugular foramen --- transmits 9th,,  10, 11th cranial nerves.

        10. Foramen magnum---largest foramen in skull.

                                    Divided into anterior small compartment: Apical ligament

                                                                                    Upper band of cruciate ligament

                                                                                    Condylar parts on sides.

Posterior large compartment: lower end of medulla oblongata, 2 anterior and one posterior spinal artery, veins joining

venous plexus, lower part of tonsil of cerebellum, vertebral artery, sympathetic plexus, spinal root of accessory nerve.

Ribs: 12 in number on each side.

True ribs—1-7th

False ribs--- 8-12th

Floating ribs --- 11-12th

Atypical ribs—1, 2, and 10.11, 12th.

Folds of duramater

                               Falx cerebri – encloses superior sagittal sinus, inferior sagittal sinus, straight sinus

                               Tentorium cerebelli- encloses transverse sinuses, posterior petrosal sinuses.

                               Falx cerebelli—encloses occipital sinus

                               Diaphragma sellae—encloses anterior and posterior intercavernous sinuses.

Important points in skull

1.Bregma: meeting of coronal and sagittal sutures.site of anterior fontanelle, closes at 11/2 yrs of age.

2 .Lambda: meeting of sagittal and lambdoid sutures .site of posterior fontanelle ,closes at 2-3 months of age.

3. Nasion : meeting point of internasal and fronto nasal sutures.

4. Inion : centre of external occipital protruberance.

5. Pterion : area formed by meeting of frontal, squamous part of temporal ,parietal, greater wing of sphenoid.deep to

this lies anterior branch of middle meningeal artery, middle meningeal vein ,stem of the lateral sulcus.

6. Asterion : point  at the postero inferior angle of parietal bones.

Diaphragm

Inferior aperture (outlet )of thorax.

Aortic opening—T12- transmits Aorta, thoracic duct, Azygos vein

Oesophageal opening—T10-transmits oesophagus, gastric nerves, oesophageal branches of left gastic artery.

Venecaval opening --- T8 transmits  inferior venecava, branches of right phrenic nerve.

                                                     CEREBROSPINAL FLUID (CSF)

Definition

CSF is a modified tissue fluid in the central nervous system. It is contained in the ventricular system of brain and the

subarad space of brain and spinal cord. CSF replaces lymph in the CNS. It acts as a sensitive mirror which reflects

diseases of the na system. Formation

1.The bulk of the CSF is formed by choroid plexuses of the lateral ventricules, and the lesser amounts by the choroid plexus

the third and fourth ventricles.    '    

2.Possibly it is also formed by the capillaries on the surface of the brain and spinal cord.    

Circulation            

CSF passes from the lateral ventricles to the third ventricle through foramina of Monro (interventricular foramina). From

 ventricle it passes to the fourth ventricle through cerebral aqueduct. From fourth ventricle the CSF passes to the subarachnoid

around the brain and spinal cord through the foramen of Magendie and foramina of Luschka.

Absorption

1.CSF is absorbed chiefly by the arachnoid villi and granulations, and is thus drained to the cranial venous sinuses.

2.It is also absorbed partly by the perineural lymphatics around I, II, VII and VIII cranial nerves

3.And also by the veins related to the spinal nerves.

Rate of Formation

200 cc/hour, 5000 cc/day.

Total Quantity           About 150 cc. Pressure:60-150 mm of fluid (or water). Composition

Proteins                   20-40 mg per 100 cc.

Sugar                      50-75 mg per 100 cc.

Chlorides                 720-750 mg per 100 cc.

Cells                        0-5 per cubic mm

Functions

It is (a) protective, (b) nutritive, and (c) excretory to the CNS.

Applied Anatomy

1.