i want 25 mutiple choice questions with their model answer below each question that covers different aspects of all of the following information : THE SKIN
➢ The skin is the outer covering of the body.
➢ Largest organ of the body which forms about 16%
of body weight.
Histological Structure:
1- The epidermis: (thin superficial layer)
- Formed of stratified squamous keratinized
epithelium.
- Ectodermal in origin.
2- The dermis: (thick deep layer)
- Formed of connective tissue.
- Mesodermal in origin.Types of the skin:
1- Thick skin: Found in the palms and soles.
2- Thin skin: It covers the rest of the body.
The Thick Skin
I- The epidermis: It consists of 4 types of cells:
A- Keratinocytes: (85 % of the cells).
- They are responsible for keratin formation.
- They form several layers, which are continuously
shed at the top layer and repaired by cell division of
deeper layers.
- They are arranged in 4 layers.1- Malpighian layer (stratum Malpighii):
a- Basal cell layer or stratum germinativum:
- Single layer of columnar cells resting on thick wavy
basement membrane.
- Have basal oval deeply stained nuclei with deep
basophilic cytoplasm.
b- Prickle cell layer or stratum spinosum:
- Formed of 4-8 layers of polyhedral cells.
- Have central rounded nuclei with less basophilic
cytoplasm than that of the basal layer.
- Cells appears connected by processes giving spinous
appearance.2- Granular layer or stratum granulosum or skin
barrier layer:
- Formed of 2-4 layers of flattened cells.
- Have central flat nuclei with basophilic granules in
their cytoplasm act as skin barrier.
3- Clear layer or stratum lucidum:
- It appears as a thin wavy acidophilic line formed of
dead non-nucleated flattened cells “ Scales”.
4- Horny layer or stratum corneum:
- It consists of several layers of acidophilic horny
scales called squames contains soft keratin with no
nuclei.B- Melanocytes:
- Found just under or in between the cells of the basal
layer of the epidermis and at the basal parts of the hair
follicles.
- They are branched cells with rounded central nuclei.
- Their cytoplasm contains granules containing
melanin pigment with abundant rER, Golgi
apparatus and mitochondria.
C- Langerhans cells:
- Found in the upper layer of the stratum spinosum.
- They are branched cells with deeply stained nuclei.
- They are considered as macrophage cells.D- Merkel’s cells:
- Found at the basal layer of the epidermis.
- Large cells with underlying sensory nerves and
considered as receptors for touch sensations.
II- The dermis:
A- The papillary layer: (the thinner superficial layer)
- It is called papillary because it forms dermal
papillae which fit into the concavities on the under
surface of the epithelium.
- It is formed of loose C.T.
- It is more cellular i.e. rich in all types of C.T cells.
- It is more vascular i.e. rich in blood capillaries.B- The reticular layer: (the thicker deep layer)
- It is called reticular because of its high content of
interlacing collagen fibers forming a network.
- It is formed of dense C.T.
- It is less cellular i.e. with few C.T cells.
- It is less vascular i.e. with few blood capillaries.The Thin Skin
• It differs from the thick skin in the following:
1- Site: whole body areas excepts palms, soles.
2- Epidermis:
a- Thickness: thinner.
b- Prickle cell layer: 2-4 layers.
c- Granular layer: thinner.
d- Clear layer: absent.
e- Horny layer: thinner.3- Dermis:
a- Dermal papillae: irregular, fewer and narrower.
b- Sweat glands: less numerous.
c- Hair follicles: present
d- Sebaceous glands: present
e- Arrector pili muscle: present