Growth occurs through three main ways: multiplicative growth through cell division, auxetic growth through increased cell size, and accretionary growth through accumulation of substances between cells. The cell cycle consists of interphase (G1, S, G2 phases) and the mitotic phase (M phase). Cell division occurs through either mitosis in somatic cells or meiosis in germ cells. Mitosis results in two identical daughter cells through karyokinesis and cytokinesis, passing through prophase, metaphase, anaphase and telophase. Meiosis results in four haploid gametes through two cell divisions and one DNA replication, with its own prophase I, metaphase I, anaphase I, and tel

2. o Growth
o Cell Cycle
o Cell Division-
 Mitosis
 Meiosis

3. Growth: Increase in bulk of body.
3 ways of Growth
1. Multiplicative:- increase in cell no.
2. Auxetic:- increase in cell size.
3. Accretionary :- increase accumulation of intercellular
substances.

4. 1. Multiplicative growth: cell division causes increase in
cell no.
3 categories
A) Cat I : do not divide in post-natal period.
e.g.- nerve cells
B) Cat II : continuous loss is replaced by stem cells.
e.g.- epidermis of skin
-intestinal epithelial cell
-RBCs
C) Cat III : divides only in altered conditions.
e.g.- Liver in resection

5. 2. Auxetic growth : increase in cytoplasmic
volume.
e.g.- oocytes & some Neurons
 Nucleus is not sufficient to fulfill the nutritional
need. So surrounded by small cells to provide
nutrition.
3. Accretionary growth : increase accumulation
of intercellular substances
e.g.- connective tissue:- Bones & Cartilage.

6. CONTROL :-Local
Endocrinal
LOCAL:- During early embryonic life
ENDOCRINAL:-Affects rate Generally- Somatotropic hormone.
Affects rate Locally – Progesterone.
-by affecting General metabolic rate-Thyroid hormone
OR affecting protein synthesis-some Corticosteroid &
Somatotropic hormone
*local control is imp in wound healing in Adults.
*Chalones are imp. Which inhibits cell division normally.

7. CELL CYCLE
 Definition : is the period of time between the birth of the
cell & it’s own division to produce two daughter cells.
 Rate: - Short life span( fast turnover )
- according to demand as in healing of wounded skin
 Faulty coupling of replacement – Neoplasm
Phases of cell cycle
A. Interphase :- G1, S ,G2
B. Mitotic phase :- M

8. G1-Phase :-Responds to growth factors to initiates cycle
-once made, this is irreversible
-molecular machinery for cell cycle generated
G0 Phase/Quiescent phase- cells retain capacity for
proliferation but no longer dividing.
- GH can stimulate it to enter cell cycle.
S-Phase :- DNA Replication occurs
G2-Phase :-
-cell prepares for division
-period ends with start of breakdown of nuclear membrane
& onset of chromosomal condensation.
Timing :-
S phase :6-8hrs G1 phase : great variation
G2 phase : 2-4 hrs 2hrs in rapidly dividing to
M phase : 1-2 hrs >100hrs in some cells

9. Regulation of transitions between cell cycle phases
- Cyclins at there maximum abundance at G1-S,G2-M
transitions.
- High level cyclins protein activates CDKs
- Activation of various cyclin-CDK complex regulates G1-
S,G2-M transitions.
*There are check points in the cell cycle at which progress
will be arrested.
**P53 – Tumor suppressor gene

10. Mechanism of Cell Division
Division
-Direct/amitotic- random nuclear material distribution
-Indirect- a) Mitosis- somatic cells
b) Meiosis- Germ cells
Two events - Karyokinesis
- Cytokinesis

11. MITOSIS
Definition:-
“Mitosis is the process that results in the
distribution of identical copies of the parent
cell genome to the two daughter somatic
cells.”
Four phases:-
-Prophase
-Metaphase
-Anaphase
-Telophase

13. Prophase
 Condensation of chromatin
 Centriole separation & movement at opposite pole
 Microtubule formation, Aster formation
 Nucleoli disappears
 Nuclear membrane disintegration into vesicles to release
chromosomes
(**this event marks end of prophase)
Prometaphase
 Microtubules extends into central region
 Attaches chromosomes & move it towards
Metaphase/Equatorial plate or plane

14. Metaphase :-
 Chromosomes are in equatorial
plane/aster formation
 Arranged in ring viewed from poles
 Cytoplasmic movements during late
metaphase
 Centromere is doubled structure
Anaphase :-
 Centromere separates
 Chromosomes moves apart towards poles
 Infolding of cell equator begins & it
deepens during telophase as cleavage
furrow.

15. Telophase :-
 Chromosome decondense
 Nuclear membrane forms
 Nucleoli appears
 Cytoplasmic division continues
 Spindle remnants disintegrates
 cleavage furrow-
due to band of actin & myosin
INHIBITORS OF CELL CYCLE
Radiation exposure -chromosomal damage-inhibition of cell
cycle-ulceration of skin & mucous membrane
Chemical agents - Colchicine & It’s derivatives
(**imp. In Karyotyping & cancer therapy)

17. MEIOSIS
Definition:-
“The process in which two cell divisions
occurring one after the other, following only one
round of DNA replication; shows chromosomal
pairing and chromosomal seperation in the first
division and chromatid seperation in second;
leading to the formation of four haploid daughter
cells from a single 2n parent cell.”

18. Stages of meiosis
 Meiosis-I
o Prophase- I
- Leptotene
- Zygotene
- Pachytene
- Diplotene
- Diakinesis / Prometaphase
o Metaphase – I
o Anaphase – I
o Telophase- I
 Meiosis- II
o Metaphase – II
o Anaphase- II similar to mitosis
o Telophase- II

19. Prophase- I
Leptotene:-
 Long thin thread to beaded chromomeres
 End is attached to nuclear membrane
Zygotene
 Homologus chromosomes are arranged in pairs
lengthwise / Synapsis
 One paternal / one maternal

20. Pachytene:
 Chromosome splits longitudinally except at centromere
 Tetrad formation
Diplotene:
 Form chiasma
 Break by endonuclease & joined by ligases
 Cross over
 Imp. For continual reshuffling of the genes / structural
basis of hereditary diversity

21. Diakinesis / Prometaphase:
 Homologus centromeres pull apart
 Nuclear membrane & nucleolus disappear

22. Metaphase – I
 Homologus pairs of chromosomes
align in equatorial plane of spindle.
Anaphase – I
• Centromere do not divide
• Chromosome migrate to
the opposite pole

23. Telophase- I
 Chromosomes are haploid
 Reductional division

24. Meiosis- II
Metaphase – II
 Cell directly enter in meiosis- II
 Redistribution of genetic material
 DNA replication

25. Anaphase- II
 Centromeres divide
 Migrate towards opposite pole
Telophase- II
 Four gametes are formed
 Second meiotic is an equating division

28. Peculiarities of meiosis
1. Appearance & pairing of homologues
2. Crossing over chromosomes
3. Centromere do not divide
4. Reductional division