HLTAP301A ANATOMY & PHYSIOLOGY
PART 1 – BODY MEMBRANES
There are two types of membranes in the body which are responsible for lining cavities,
protecting organs and covering surfaces – epithelial membranes and connective
membranes. We will only look at the three types of epithelial membranes in this lecture.
Epithelial membranes are actually simple organs that contain an epithelial sheet (of
cells) and an underlying layer of connective tissue.
They include cutaneous
membranes, mucous membranes and serous membranes.
The cutaneous membrane is your skin – we will examine this in more detail later in the
lecture.
The mucous membranes line all body cavities which are open to the exterior
environment, for example the lining of the mouth. Remember that the term mucosa
refers to the location of the membrane and not it’s make-up or it’s product which may
actually be mucus. The secretions of these membranes are slightly acidic, which is a
protective mechanism of the body.
The serous membranes line body cavities that are internal and always occur in pairs –
the parietal layer which folds in on itself to form the visceral layer. For example the
parietal peritoneum lines the walls of the abdominal cavity and the visceral peritoneum
lines the organs within this cavity. These serous pairs are separated by a thin clear
serous fluid which is secreted by both membranes. This fluid allows the organs to slide
against the cavity wall and each other without friction. Remember visceral covers the
organ, and parietal covers the cavity.
PART TWO – THE INTEGUMENTARY SYSTEM
The skin, along with its accessory structures such as hair, nails and glands form what is
called the Integumentary System.
The skin is often referred to as the integument, which simply means ‘covering’. It keeps
fluid and molecules in the body and keeps water out. It protects from damage
(mechanical, chemical, thermal, UV radiation and bacteria), insulates and cushions
deep body organs and the uppermost layer is full of keratin that prevents water loss
from body surface. Other functions include regulation of heat loss, excretion of wastes
and it synthesizes Vitamin D. Finally sensory receptors in the skin provide information
about environment (including touch, temperature and pain).
The skin is composed of two kinds of tissue – the Epidermis and the Dermis.
The Epidermis (or outer layer) is comprised of layers of epithelium (stratified epithelium)
and it is avascular, which means without blood supply. This is technically not quite
correct, as the bottom layer does actually get blood supply from the next layer of the
skin, the dermis. There are up to five layers in the epidermis (four on most parts and
five on the palms of the hands and soles of the feet). The lowest layer (stratum basale
= think basement) contains melanocytes, cells that make the pigment melanin, which
gives the skin it’s colour. If someone has lots of melanin in their skin, their skin will tend
to be darker. This layer also contains merkel cells, which are associated with sensory
nerve endings – this is why when you get a paper cut, it hurts (nerve impulses) but does
not bleed (avascular)
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The dermis is located under the epidermis and consists of dense connective tissue, It is
highly vascular (lots of blood supply) and consists of two major regions – the papillary
layer and the reticular layer.
The upper region of the dermis is the papillary layer and it is comprised of fingerlike
projections called the dermal papillae. Some of these contain capillaries which provide
oxygen and nutrients to the epidermis. Others have pain receptors (free nerve endings)
and touch receptors (which are called Meissner’s corpuscles). The papillae on the
palms of the hands and soles of the feet are arranged in swirly ridges that are designed
to improve our gripping ability. Films of sweat on the ridges on the fingertips leave
fingerprints, which are unique to all individuals – even identical twins have different
fingerprints.
The reticular layer accounts for 80% of the dermis, and is comprised mostly of dense
connective tissue with many structures including blood vessels, sweat and oil glands.
The hypodermis or subcutaneous layer is deeper than the dermis and is not considered
to be part of skin. It is composed of adipose (or fatty) tissue which anchors the skin to
underlying organs, acts as a shock absorber and insulates deeper structures.
There are three pigments which contribute to skin colour. Melanin is located in
epidermis and can be either yellow, reddish brown or black. Carotene, which is found in
the stratum corneum of the epidermis and subcutaneous tissue, can give the skin an
orange- yellow hue. Finally the amount of oxygen bound to haemoglobin contributes to
the skin if it is a flushed rosy colour.
Certain skin colours can indicates homeostatic imbalances. For example, if the skin has
a bluish tone, this may be an indication of cyanosis (low blood O2 levels). Redness may
be caused by fever, hypertension (high blood pressure), inflammation or an allergic
reaction. Pallor (pale skin) may be due to emotional stress, anaemia, low BP or
impaired blood flow. Jaundice (which is a yellow tinge to the skin) can be a sign of a
liver disorder or excess bile pigments absorbed into blood. Bruises (black and blue)
occur when blood that has escaped from circulation clots in tissue spaces.
Appendages of the Skin
The cutaneous glands are exocrine glands that release their secretions directly onto the
skin surface via ducts and there are two different types – sebaceous glands and sweat
glands.
Sebaceous (oil) glands – found all over skin except on palms of hands and soles of feet.
They produce sebum – mixture of oil and fragmented cells, and their ducts empty into a
hair follicle. They are very active during adolescence – a whitehead is a block
sebaceous gland and seborrhea (cradle cap) is usually a result of overactivity of the
sebaceous glands.
Sweat glands - produce sweat and there are two types of these glands – apocrine and
eccrine. Eccrine sweat glands are found almost all over body and the sweat they
produce is comprised of mostly water, some salts and traces of metabolic wastes.
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The apocrine glands are confined to the axillary and genital areas. Their secretions
contain fatty acids and proteins as well as sweat and it may be milky or yellowish in
colour. It is usually odourless but when bacteria that live on the skins surface uses it’s
proteins for nutrients, an unpleasant odour may be produced.
There are millions of hairs all over our body, but apart from some minimal protection,
such as the eyelashes shielding our eyes and nose hairs keeping foreign particles out of
the respiratory tract, it does not have a great deal of usefulness.
The arector pili muscle connects to each hair follicle and when you are cold or
frightened, these muscles contract, pulling the hair upright and causing ‘goose bumps’.
The anatomical implication of this is that in animals this activity adds a layer of
insulating air to the fur, but for humans it is not particularly useful.
Homeostatic Imbalances of the Skin
Infections and allergies:
Athelete’s foot is an itchy red, peeling condition between toes that results from a fungus
infection
Boils and carbuncles are inflammations of the hair follicles and sebacous glands any
may be common on the neck. Carbuncles are composite boils that can be caused by a
bacterial infection.
Contact Dermatitis is the itching, redness and swelling of skin that can lead to blisters.
It may be caused by exposure to chemicals.
Cold Sores are small fluid filled blisters that are caused by herpes simplex infection.
Impetigo are raised, pink, water-filled lesions, common around mouth and nose and
common in school children and are usually caused by a staphylococcus infection.
Psoriasis is chronic condition, characterised by reddened lesions. It may be hereditary,
however, attacks can be caused by trauma, infection, hormonal changes and stress
Skin cancer
Most skin cancers are benign and do not metastasize to
However, in the case of melanoma, they can be malignant.
cancers is unknown but we do know that one risk factor
radiation. The three main types of skin cancers are Squamous Cell Carcinomas and Malignant Melanomas.
other part of the body.
The cause of most skins
is over exposure to UV
Basal Cell Carcinomas;
Basal cell carcinomas are the most common and least malignant of skin cancers. They
invade the dermis and sub cutaneous tissue but are usually slow growing and can
easily be removed surgically.
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The squamous cell carcinoma is a lesion that appears as a scaly, reddened small
rounded elevation that gradually forms a shallow ulcer with a firm, raised border. Often
seen on scalp, ears, upper hands and lower lip, they can grows rapidly and metastasize
to adjacent lymph nodes if not removed
Malignant melanoma is a cancer of melanocytes that can begin wherever there is
pigment. They first appear as a spreading brown to black patch and metastasize rapidly
to surrounding lymph and blood vessels. Early detection is a must as the survival
chances only are only 50%.
The Cancer Foundation suggest applying the ABCD rule to recognise melanomas.
A
B
C
D
Asymmetry : the two sides of pigmented spot or mole do not match
Border irregularity: the borders of the lesion are not smooth but exhibit
indentations.
Colour: pigmented spot contains areas of different colours (blacks, browns, tans,
and sometimes blue or red)
Diameter: the spot is larger than 6mm (the size of a pencil eraser)
Some organisations now also suggest E – elevation, if the spot is above skin level, that
is another warning sign.
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