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Anatomy
Tuesday 10/5
Lecture #23
Just to remind you that in the body we have two kinds of cells:
1. Somatic cells (diploid):
 The word "somatic" is derived from the Greek word sōma, meaning
"body".
 Cells that can divide through mitosis and differentiate into diverse
specialized cell types. For example, in mammals, somatic cells make
up all the internal organs, skin, bones, blood, muscles and
connective tissue.
 Everyone knows that every cell has 46 chromosomes (23 pairs) each
pair of chromosomes comprises one chromosome inherited from the
father and one inherited from the mother.
 In mitosis, chromosomes cross each other’s and mixing between
them will happen then they will be separated. At the end, each
chromosome will have paternal and maternal features (hek b9eer
a5tela6 alansab y3ne al baby momkn ykon loon 3yonh la aboh o
$fayfoh la omoh o $3rato la jdetoh).
 As result of mitosis, two identical daughter cells are produced.
 Two identical: means each one has 46 chromosomes because they
are duplicated.
2. Germ cells:
 Cells that can differentiate through meiosis.
 As a result of meiosis, two non-identical cells; actually one is
produced and the other is polar body (fra6h) because meiosis
happens in two stages; meiosis І and ІІ.
Oogenesis happens within the ovary of female embryo at the fifth
week and the cells are produced called; oogonia (ovum to-be).
 No. of oogonia before birth is around 700,000.
 No. of oogonia after birth is around 1-2 million.
Oogensis>>>oogonia>>>23 chromosomes.
Spermatogenesis>>>sperm>>>23 chromosomes.
At puberty age:
 Males will produce testosterone and develop secondary sexual
characteristics like; moustache.
 Female reproductive cycle has 3 phases:
1. Proliferation phase>>reproduction phase (to build) that is controlled
by estrogen from pituitary gland.
2. Secretion phase coz endometrial is thick and blood vessels are
enlarged congested mucus secretion is more why????????? To
provide media to the zygote to be for good implantation and this
phase controlled by progesterone.
3. Bleeding phase>>shedding phase>>removing the endometrial.
The ideal cycle is 28 days and the middle is 14 days.
At day 14, ovulation occurs and secondary oocyte produced (at 14
years old) that was oogonia controlled by luteinizing hormone
Mature 2nd oocyte lives 24 hrs and sperm lives minutes.
2nd oocyte is covered from the outside by corona radiata and fro
inside zona pellucida.
300,000,000 sperms produced and 300 only will reach ovum in the
fallopian tube in the ampulla and there they will compete each
other that has the capacity to penetrate the corona radiata and
zona pellucida.
After fertilization; female pronuclues and male pronuclues (23
single chromosomes for each) from inside and cell membrane
outside the 2nd oocyte closes and nuclear membranes unite to form
the zygote and meiosis is finished and mitosis starts that gives
morula and morula gives blastocyst.
When one sperm penetrate the ova, depolarization of the cell
membrane occurs.
When mitosis starts; the morula that consists of mass of cells; will
enter the uterine cavity during the secretory phase where there
will be fluids that interside the morula and form the blastocyst
cavity.
Blastocyst formation begins at day 5 after fertilization in humans
and ends at 7th day that cells will compact (compactation) at the
embryonic pole and the blastocyst cavity around it.
Early implantation at day 21-22 and complete implantation occurs
at day 28 that’s why sometimes, the woman thinks it’s the
menstrual cycle but it’s not. (Sorry if this point is not well
understood but I didn’t get it well).
Fertilization · Oocyte activation · Zygote · Cleavage · Morula ·
Blastomere · Blastocyst .inner cell mass.
Pregnancy:
 2nd week: bilaminar embryonic disc formation with:
 2 layers: epiblast (ectoderm to be) and hypoblast (endoderm to
be).
 2 cavities: amniotic cavity and yolk sac.
 3rd week: trilaminar embryonic disc formation with:
 3 layers: endoderm (inside), mesoderm (middle) and ectoderm
(outside).
Due to the flat trilaminar embryonic disk; the embryo will form and
it will be cylindrical.
Stomodeum: is ectoderm (2lanbe3aja al5arejyh) and forms the
mandible, maxilla, teeth and hard palate.
Oropharyngeal isthmus separates between the endoderm and the
ectoderm.
Anterior two thirds of tongue and hard palate are ectoderm
Posterior 3rd of tongue and soft palate are endoderm.
All the orifices in the body are ectodermal in origin.
 4th week:
 GI: hindgut, foregut and midgut.
Membrane around the stomodeum (MOUTH TO BE) which is
endoderm and ectoderm, should be open to make the communication
between the mother and her baby.
Which means the baby takes what he needs from the mother
through the amniotic cavity and what he doesn’t need goes through
the GI.
 By the end of the 4th week: Stomodeum surrounded by 5
prominences:
 2 maxillary: right and left.
 2 mandibular: right and left.
 1 frontonasal.
 By the end of 4th week:
Upper part of GI ~~ foregut~~ pharynx (to-be)
This primitive pharynx is soft so it’s supported by horse-shoe
condensations that come from the mesoderm and are called
pharyngeal arches.
pharyngeal arches:
 They are 6 in no.
 1,2,3,4 and 6 well developed but 5 not.
Pharyngeal apparatus consists of:
1. Pharyngeal arches: when mesoderm arises and forms elevations.
2. Pharyngeal clefts: between the arches there are external
inveginations (ectoderm).
3. Pharyngeal pouch: internal invaginations (endoderm).
4. Pharyngeal membrane: double membrane that separates the pouch
from cleft.
Each arch has its own; nerve supply, arterial supply, muscles,
cartilage, ligament and bone.
Five arches are separated by 4 ectodermal clefts from outside and
by 5 endodermal pouches from the inside. That’s why palatine
tonsils originate from the pouches.
Only the 1st cleft contributes to final appearance of the other
derivatives like; external auditory meatus and the outer surface of
tympanic membrane.
And the 2nd will go down and cover the 3rd and the 4th to form
platysma muscle.
Pouches:
 Endodermal in origin.
 4 in no.
 Outside pouching gives Eustachian tube; also auditory tube or
pharyngotympanic tube is a tube that links the nasopharynx (upper
part of the pharynx) to the middle ear.
 1st pouch gives the internal auditory meatus.
Mandibular arch (1st arch):
 Supplied by maxillary artery.
 Innervated by trigeminal nerve.
 Gives development for muscles of mastication, anterior belly of
digastrics and mylohoid.
"Hold your head high, stick your chest out. You can make it. It gets dark
sometimes, but morning comes. Keep hope alive."
Dedicated to: my best friends; DamDom, Atheer, Noody,
Hadoo$,Rnoo$, Asool and SoSo……………..LUV YA:);)
DONE BY: Safa’a IsmaiL