Gemetogenesis : easy and brief handout

Gemetogenesis: easy and brief description 

Definition: it is the process of formation and development of male and female gametes

·         Gametes are derived from primordial germ cells.

·          It is formed in the epiblast during the 2^nd  week

·         Then  move to the wall of the yolk sac  during the 4^th week ,

·         these cells begin to migrate from the yolk sac to the developing gonad, where they arrive by the end of the 5^th week

Meiotic cell division :

Importance of meiotic cell division:

1. Restores the normal dioploid number of chromosomes from generation to   generation
2. crossovers- interchange of chromatid segments between paired homologous chromosomes

      3. Allows random assortment of maternal & paternal chromosomes between gametes

Oogenesis :

 Definition: it is the sequence of events by which oogonia are transformed into mature oocytes. 

This maturation begins before birth and completed after puberty and continues to the menopause (the permanent cessation of the menses)

Maturation of oocytes:

Before birth:

Primordial germ cells (arrived in the gonad by the end of the 5^th week)

Differentiate into oogonia ( at 5^th month its number reaches maximum about 7 million)

Primary oocytes : oogonia enlarge to form primary oocytes.

Primordial follicle – a primary oocyte with its surrounding flattened follicular epithelium.

Near the birth, the primary oocyte remain arrested in prophase of meiosis I(diplotene stage) and do not finished meiosis I before puberty

At puberty:

Primary follicle - follicular cell became cuboidal and zona pellucida begin to form

Growing follicle: follicular cells forming the stratified layer of granulose cells and well-defined zona pellucida

Secondary follicle: fluid filled spaces developed within the granulosa cells .  

Grafiaan follicle : single cavity formed within granulosa cell

Shortly before ovulation the primary oocyte completes the first meiotic division and became secondary oocyte .

The division is unequal, the secondary oocyte receives almost all the cytoplasm but the 1^st polar body receives very little.

The secondary oocyte begins 2^nd meiotic division but arrest at metaphase.

Meiosis II is completed only if the oocyte is fertilized.

Spermatogenesis

Definition: It is the sequence of events by which spermatogonia are transformed into mature sperms or spermatozoa.

This maturation process begins at puberty and continues into old age

In male the primordial germ cells remain dormant until puberty.

At puberty, after several mitotic divisions of the spermatogonia, primary spermatocytes (diploid)  are formed. They are the largest cells of seminiferous tubules and enters a prolonged prophase (22 days)

Each primary spermatocyte is completed meiosis I to form two haploid secondary spermatocytes

Subsequently, two secondary spermatocytes complete the meiosis II to form four spermatids   

Spermiogenesis :

Definition: The spermatids are gradually transforms into mature sperm or spermatozoa by a process known as spermiogenesis

These changes include:

1. loss of cytoplasm
2. formation of acrosomes which covers half the nuclear surface, derived from the golgi region of spermatid contain enzymes that assist penetration of corona radiata and zona pellucida during fertilization
3. condensation of nucleus
4. formation of neck, middle piece, and tail
5. the mitochondria arranged in the middle piece as mitochordial sheath

The time required for a spermatogonium to become a mature spermatozoon is approximately 74 days   

Terminology related with general embryology

Terminology related to general embryology

Gestational period: The whole gestation period is subdivided into three stages:

a)       Germinal period : it extends from 1^st to 3^rd week of development

b)       Embryonic period : it extends from the 4^th to 8^th week

c)       Foetal period: it extends from the third month up to termination of pregnancy  

Oocyte: the female germ or sex cell produced in the ovaries

Sperm: the male germ cell produced in the testes.

Blastocyst : after the morula enters the uterus from the uterine tube , a fluid filled cavity –  the blastocyst cavity –develops inside it . This change converts the morula into a blastocytes

Implantation: the process during which the blastocyst attaches to the endometrium and subsequently embeds in it. It occurs at 6 days after fertilization.

Gastrulation : formation of three layered embryonic germ disc

Embryo:   the developing human during its early stages of development. It extends to the end of the eighth week

Conceptus: the embryo and its adnexa or associated membranes

Fetus: after the embryonic period the developing human is called a fetus.

Gemetogenesis: it is the process of formation and development of male and female gametes

Zygote: Definition:this cell formed by the union of an oocyte and a sperm during fertilization

Cleavage: is a series of mitotic divisions that results in an increase in cells, blastomeres, which become smaller with each division.

Morula : the 12-16 cell stage of the early embryo at 3 days post conception

Menopause: the permanent cessation of the menses

Length of the pregnancy: from 1^st day of last menstrual period: 280 days or 40 weeks

                                            After fertilization: 266 days or 38 weeks

Embryonic period /period of organogenesis: most major organ and organs systems are formed during the third to eighth weeks and this period is called embryonic period or period of organogenesis.

Growth: means increase in bulk which takes place by cells division, increasing cell size or increased accumulation of intercellular substance

Differentiation: is a complicated process in which groups of cells assume special characteristics and functions

Totipotent cells: are able to produce a separate embryo under favorable conditions

Pluripotent cells: are groups of cells which produce specific type of tissue

easy explanation of non dis junction at mitosis, meiosis 1 and meiosis II

Non disjunction :

meiosis 1 : some time homologous chromosomes are failed to separate  in meiosis 1 cell division so one cell contain 24 chromosome and another cell contain 22 chromosome 

mitosis and meiosis 2 : some time sister chromatids of chromosome are failed to separate in mitotic and meiotic division 2 .

so after mitotic division one cell contain 45 chromosomes and another contain 47 chromosomes. As a result two abnormal somatic cells are developed .

In meiosis 2 , one cell contain 22 chromosomes and another cell contain 24 chromosome . As result two abnormal gamete are formed.

easy handout on hard palate

Hard palate

It is a septum which separate nasal cavity from oral cavity.

Formation :                                                                                             

1.       Anterior 2/3 by palatine process of maxilla

2.       Posterior 1/3 by horizontal plates of palatine bone

Sutures:

There are three sutures present in hard palate.

1.      Intermaxillary suture

2.      Interpalatine suture

3.      Palatomaxillary suture

Relations:

Anteriorly it is continuous with alveolar arches and gums

Posteriorly  it is attached with soft palate

Superiorly it is formed floor of nasal cavity

Inferiorly it is formed roof of oral cavity. Inferior surface bears following structures

1.       Incisive fossa : a small pit behind the incisive teeth , it is the lower opening of two incisive canal (right and left) . incisive canals transmit terminal part of nasopalatine nerve and greater palatine vessels  

2.       Greater palatine foramen: transmits greater palatine nerve and vessel

3.       Lesser palatine foramen: transmits lesser palatine nerve and vessel

Histology of hard palate :

It has two surfaces:

Histology of nasal surface of hard palate:

It is lined by pseudo-stratified ciliated columnar epithelium.

This epithelium contains intraepithelial gland.

Sub-endothelial connective tissue contains glands, blood vessels and lymph vessels.

 The epithelium and the sub-epithelial connective tissue are collectively known as the mucoperiosteum, which is firmly attached to the bony shelf of the palate.

Masticatory mucosa :

It is found in the gingival (gums) and the hard palate

1.      Lining epithelium: Keratinized stratified squamous epithelium and in some place parakeratinized .

Keratinized epithelium of hard palate likes skin but stratum lucidum layer is absent.

Criteria of parakeratinized stratified squamous epithelium :

·         Superficial cells have nuclei like keratinized stratified squamous epithelium but nuclei are pyknotic (highly condensed) remain until the cell is exfoliated and

·         cytoplasm is not intensely stain by eosin

  Rete ridges are present in epithelium they are deep invagination of epithelium with

   subepithelial connective tissue  

2.      Lamina propria is formed by connective tissue contain dense collagen fibres, blood vessels and nerves. Deep to lamina propria contain reticular fibre rich dense connective tissue which firmly bind the palatine mucosa to the periosteum. Hard palate is also containing large deposits of adipose tissue at its anterior part and mucous gland at its posterior part.

Blood supply : greater palatine artery (from the third part of the maxillary artery) which emerges from the greater palatine foramen and passes forwards around the palate (lateral to nerve) to enter the incisive canal and pass up into the nose

Vein: corresponding vein drain into pterygoid venous plexus and pharyngeal plexus.

Lymphatic drainage: retropharyngeal  and deep cervical lymph nodes

Nerve supply : by branches of maxillary nerve via pterygopalatine ganglion

1.       Anterior part is supplied by two nasopalatine nerves

2.       From incisive fossa to rest of the posterior part is supplied by greater palatine nerve .

Development:

1.       Primary palate develops  from intermaxillary prominence

2.       Secondary palate develops from palatine shelves from the maxillay prominence

Two palatine shelves of maxillary prominence unite and fused with  primary palate.

Summary of sympathetic nervous system

Sympathetic nervous system is the part of autonomic nervous system .

Functionally Nervous system can be divided into two part
somatic nervous system and autonomic nervous system .
Sympathetic system is the part of autonomic nervous system

•Like somatic nervous system autonomic nervous system has two parts •Motor part of autonomic system innervate smooth muscle, cardiac muscles  and most of the glands of the body
•Sensory part of autonomic system carry sensory impulse from viscera to the brain . Sensory parts of autonomic system usually ran along the sensory system of somatic system so we often perceive visceral pain in the body wall .

short description of sympathetic nervous system

Topics	Sympathetic nervous system
Out flow	it is also known as thoraco lumbar outflow T1 to L 2
Pre ganglionic fibres	Short
Post ganglionic fibres	Longer
Ganglia	Para vertebral sympathetic ganglia  is away from the target organ
Location of pre-ganglionic neuron	•       Lateral horn cells of all thoracic segments and upper two or three lumbar segments of spinal cord
Location of post-ganglionic neuron	•       Lateral: sympathetic trunk •       Collateral : coeliac, superior mesenteric ganglia •       Terminal ganglia: supra-renal medulla
	This system activate during emergency and works during stress and strain for fight or flight
	Liberates non adrenaline at postganglionic ending except eccrine type of sweat glands and most of the blood vessels of skeletal muscle
	This system is not essential for to life
Urinary bladder	It is the nerve of filling It contract (close) urethral sphincter and relax detrusor muscles
Heart	Cardiac muscles cells : increase force of contraction Coronary vessels :  vasodilator ( so supply of nutrition and oxygen increase in cardiac muscle cells  )
Lung:	Bronchodilator / Trachealis muscles relax so diameter of trachea increase Decrease secretion of tracheal glands
Stomach	Gastric musculature (smooth muscle cells ) is relax  but smooth muscle cells at the pyloric sphincter is contract (closer of pyloric sphincter )
Small gut	Inhibit peristalsis Vasoconstriction (vaso motor)
Summary : effect	•       Produce mass reaction •       Cutaneous blood vessels undergo vasoconstriction but, skeletal and coronary vessels are dilated thus supplying more blood to the muscles, heart, brain. Heart rate is increased, blood pressure and blood sugar are elevated , pupil and bronchi are dilated. Intestinal peristalsis is suppressed and the sphincters of gut are closed.
Eye	Pupil dilates
*Uterus	Uterine contraction Vasoconstriction
Salivary glands	_
Pancreas	_
Gastric glands	_
Adrenal glands	secretomotor
Vessels of Skeletal muscle	Vasodilatation
Sweat gland	secretomotor
Afferents	Convey most of the visceral pain except pelvic organ
Cells of origin of afferents fibres	Dorsal root ganglia of T 1 to L1/L2
Central control	Posterior part of hypothalamus

Summary of parasympathetic ganglion of head and neck region

Para-sympathic ganglion of head and neck

Topics	Ciliary	Pterygopalatine
Nucleus of origin	Edinger-westphal nucleus in midbrain	Superior salivary nucleus in pons
Site of ganglion	Posterior lateral to optic nerve in orbit	Pterygopalatine fossa inferior to maxillary nerve
Preganglionic pathway	3rd nerve via branch to inferior oblique muscle	Facial nerve via greater superficial petrosal nerve & nerve of pterygoid canal
Post-ganglionic pathway	Short ciliary nerves	Greater & lesser palatine nerves &  sphenopalatine nerves Lacrimal nerves
Organ of destination	Ciliary body Sphincter pupillae	Palate Nose Lacrimal gland

Topics	Sub-mandibular	Otic
Nucleus of origin	Superior salivatory nucleus in pons	Inferior salivatory nucleus in medulla
Site of ganglion	On hyoglossus muscle inferior to lingual nerve	Inferior to foramen ovale outside skull
Preganglionic pathway	Facial nerve via chorda tympani & lingual nerve	Glossopharyngeal nerve via tympanic & lesser petrosal branches
Post-ganglionic pathway	Lingual nerve	Auriculotemporal nerve
Organ of destination	Sublingual & submandibular glands	Parotid glands