“Oh GOSH! Reflecting on Hackteria's Collaborative Practices in a Global Do-It...
SKINvvvvvvvv (INTEGUMENTARY SYSTEM).pptx
1. SKIN (INTEGUMENTARY SYSTEM)
• This is the largest organ of the body, about
2mm thick covering the whole body of
multicellular organisms.
• The skin has two layers;
1. Epidermis (outer layer)
2. Dermis (inner layer)
NTONI WILBER-skin and genetics
3. Stratum Corneum
• Outermost layer consisting of many layers of
dead squamous cells.
• What is left of these cells is their flattened
cytoplasmic fibrous protein (keratin),
glycogen and phospholipids.
• Water proof and acts a barrier to pathogens
and chemicals
NTONI WILBER-skin and genetics
4. Stratum lucidum
• Made up of flattened/squamous epithelial
cells
• Many with degenerated nucleus and in some
without the nucleus
• These cells exhibit shiny character, giving the
layer a homogeneous translucent appearance
NTONI WILBER-skin and genetics
5. Stratum Granulosum
• This is a thin layer with two to five layers of
flattened rhomboid cells
• The cytoplasm of these cells contains
granules of a protein called keratohyalin the
precursor of keratin.
NTONI WILBER-skin and genetics
6. Stratum Spinosum
• It is also known as the prickle cell layer
• It is comprised of cells that possess some
spine like protoplasmic projections by which
they are connected to one another.
NTONI WILBER-skin and genetics
7. Stratum basale
• This is the base of the epidermis where
mitosis takes place, new cells are continually
being produced, pushing the older cells
toward the skin surface.
• As dead cells are worn off the skin’s surface,
they are replaced by cells from the lower
layers.
NTONI WILBER-skin and genetics
8. Stratum basale cont’d
• There are some projections (rete ridges)
which extend down to the dermis.
• These projections provide epidermal
anchoring to the dermis and nutritional
function.
NTONI WILBER-skin and genetics
10. Epidermis cont’d
• Melanocytes - large cells interspersed in
basal layer
• Langerhans cells - Antigen presenting cells
• Merkel Cells - Nerve endings within
epidermis
• Other structures - Hair, sebaceous glands
and ducts of sweat glands
NTONI WILBER-skin and genetics
11. Dermis
• Connective tissue layer made up of dense &
stout collagen fibres, fibroblasts and
histocytes.
• Collagen fibres have elastic property and
capable of storing water.
NTONI WILBER-skin and genetics
12. Superficial papillary layer
• Projects into epidermis, Contain blood
vessels, lymphatic, and nerve fibres.
• Has some pigment containing cells called
chromatophore.
• The papilla are surrounded by rete ridges
extending from the epidermis
NTONI WILBER-skin and genetics
13. Reticular layer
• Made up of reticular and elastic fibres.
• These fibres are found around the hair bulbs,
sweat glands and sebaceous glands.
• This layer also contain mast cells, nerve
endings, lymphatics, epidermal appendages
and fibroblasts
NTONI WILBER-skin and genetics
15. Function of skin
1. Protective Function
2. Sensory Function
3. Regulation of Body Temperature
4. Regulation of Water and Electrolyte Balance
5. Excretory function
6. Absorptive Function
7. Secretory Function
NTONI WILBER-skin and genetics
16. Appendages of the skin
1. The hair follicles with hairs
2. Nails
3. Sweat glands
4. Sebaceous glands
5. Mammary glands
• Below the Dermis – subcutaneous tissue
helps in temperature regulation
NTONI WILBER-skin and genetics
18. DNA, Genes and Chromosomes
1. Genetic material of both eukaryotes and
prokaryotes is DNA (deoxyribonucleic acid).
2. DNA has two chains, each made of
nucleotides composed of a deoxyribose
sugar, a phosphate group and a base.
3. The chains form a double helix
NTONI WILBER-skin and genetics
19. DNA
• There are four bases in DNA
A - adenine
G - guanine
C - cytosine
T - thymine
• In RNA, U (uracil) replaces T
NTONI WILBER-skin and genetics
22. DNA cont’d
The sequence of bases determines the
genetic information.
Genes are specific sequences of
nucleotides that pass traits from parents to
offspring.
NTONI WILBER-skin and genetics
23. Chromosomes
• Genetic material in cells is organized into
chromosomes
• Eukaryotes generally have:
i. Linear chromosomes in their nuclei,
with different species having different
numbers of chromosomes.
ii. DNA in organelles (e.g., mitochondria)
that is usually a circular molecule.
NTONI WILBER-skin and genetics
24. Expression of Gene
• Gene expression is the process by which a
gene produces its product (protein)
• Production of proteins requires two steps
1. Transcription
2. Translation
NTONI WILBER-skin and genetics
25. Gene expression cont’d
• Transcription involves an enzyme (RNA
polymerase) making an RNA copy of part of
one DNA strand.
• There are four main classes of RNA
1.Messenger RNAs – mRNA
2.Transfer RNAs - tRNA
3.Ribosomal RNAs - rRNA
4.Small nuclear RNAs - snRNA
NTONI WILBER-skin and genetics
28. CELL DIVISION
• Cell division is the process by which a cell
reproduces itself.
• There are two types of cell division
1. Mitosis
2. Meiosis
NTONI WILBER-skin and genetics
29. MITOSIS ( I Pee and MATe)
• One cell with the diploid number of
chromosomes divides into two identical cells,
each with the diploid number of
chromosomes.
• This necessary for the growth of the
organism and for repair of tissues
NTONI WILBER-skin and genetics
30. Interphase
• Chromosomes are in the nucleus,
• Chromosomes are less tightly compacted-lose.
• Chromatids joined in pairs as sister chromatids
• A pair of centrosomes in one pole of the cell,
each with a pair of centrioles.
• Chromosomes (DNA) replicate to double the
chromatin number/Replication of chromatin
occurs.
• Cell preparing for division. Centrioles scattered.
NTONI WILBER-skin and genetics
32. Prophase
• Nuclear membrane begins to dissolve into small
vesicles.
• Chromatids condense and become visible
• Formation of the mitotic spindle.
• The nucleolus disappears.
• Has migration of the two daughter centrioles and their
asters toward the poles of the cell.
NTONI WILBER-skin and genetics
34. Early metaphase
• The spindle fibers
interact with the sister
chromatids.
• Sister chromatid pairs
are “captured” and
firmly attached to the
spindle fibres.
NTONI WILBER-skin and genetics
35. Metaphase
• The pairs of sister chromatids
align themselves along the
equator
• Each pair of sister chromatids
is attached to both spindle
poles by spindle fibres.
36. Anaphase
• The centromeres holding the two sister chromatids
break and let free the chromatids
• The sister chromatids of each pair are separated
• Each chromatid, now becomes an individual
chromosome linked to only one of the two poles.
• There are now two sets of chromosomes moving
to either of the poles.
• This involves a shortening of the kinetochore
microtubules
NTONI WILBER-skin and genetics
38. Telophase
• The chromosomes have reached their
respective poles and decondense.
• The nuclear membrane reforms to produce
two separate nuclei with the same diploid
number of chromosomes.
• The nucleolus also reappear in either
nucleus.
NTONI WILBER-skin and genetics
39. Cytokinesis
• Formation of cleavage furrow in the cell
membrane to segregate the two nuclei into
separate daughter cells.
• Also segregation of cell organelles into the
two daughter cells.
NTONI WILBER-skin and genetics
41. MEIOSIS
• In meiosis, one cell with the diploid number
of chromosomes divides twice to form four
cells, each with the haploid number (half the
usual number) of chromosomes
• Meiosis results in the formation of gametes,
which are egg and sperm cells.
• Read about meiosis
NTONI WILBER-skin and genetics
