Serous inflammation is characterized by the effusion of non-viscous serous fluid rich in proteins but lacking white blood cells or neutrophils. This fluid dilution noxious agents and is produced by mesothelial cells lining body cavities. Examples include skin blisters, inflammation of body cavities like the pericardium and peritoneum, rheumatoid arthritis, and acute rhinitis or the common cold. Serous pulmonary alveolitis involves the accumulation of exudate in the pulmonary alveoli due to inhaled particles or spores.

1. Serous inflammation: Is a type of acute inflammation which is
characterised by the copious effusion of non-viscous serous fluid,
commonly produced by mesothelial cells of serous membranes, but
may be derived from blood plasma. The exudation of this
inflammation is clear fluid with no WBCs or PMNs.
The serous fluid which is produced by these mesothelial membranes
is pink in color and defined as plasma derived from blood or a thin
clear watery fluid from secretions of mesothelial cells lining the
peritoneal, pleural and pericardial cavities (called effusion).
Biologic purpose of serous exudation: Immediate dilution of the
noxious agent at the site of inflammation.
Etiologic factors include:
1) Hypersensitive reactions.
2) Bacterial and viral tissue injury.
3) Physical and chemical tissue injury.
Morphology: According to tissue:
- Serosa: Erythema (Hyperemia) and inflammatory swelling from
effusion with large numbers of displaced serosal covering cells and
few macrophages in the exudate.
- Skin: Erythema and swelling that varies according to epidermal
involvement.
- Mucus membrane: Erythema and swelling lead to mucosal edema
with risk of stenosis.
- Parenchyma: Erythema and swelling are present with sparse
leukocytic infiltrate. This expands the organ capsule, which is tender
to palpation due to its sensory innervation. Here the exudate takes
the form of an edema.

2. Examples of this type of Inflammation:
1) Skin blisters.
2) Inflammation of body cavities: Serous pericarditis, Pleuritis
(Pleurisy), Peritonitis.
3) Rheumatoid arthritis (serous fluid in joints).
4) Seromucous Otitis.
5) Acute Rhinitis.
6) Serous Pulmonary alveolitis.
7) Organ inflammation such as serous hepatitis, nephritis (acute
interstitial nephritis), myocarditis and encephalitis.
8) Vesicular skin infections.
9) Sero-mucosal inflammations can lead to acute glottal and
laryngeal edema with risk of asphyxia.

3. 1) Skin Blisters:
The skin blisters result from a burn or viral infection and they
represent a large accumulation of serous fluid, either within or
immediately beneath the epidermis of the skin.
The picture shows an illustration of a skin blister filled with
serous fluid.
A blister is basically a patch of raised skin that is filled with fluid
called serum. This serum is excreted by tissues and blood vessels
that go through trauma, such as intense force or friction. The liquid
then collects between the gap of the epidermis and dermis. When
the area heals, the serum is reabsorbed back into the body. The
blister then crusts over and the scab peels off after a few days.
Blisters are usually itchy, painful. The area around them may feel
warm and swollen. Patients with blisters will definitely experience
discomfort to some extent.
Blisters are commonly found on the hands and the feet, but they
may also manifest on the other parts of your body, depending on
the cause.

4. (A) (B)
The previous are microscopic pictures of normal skin (A) and
a skin blister (B)
Causes:
1) Burns. 2) Rashes. 3) Chicken Pox. 4) Diabetes. 5)
Gangrene. 6) Various viral infections. 7) Pressure ulcer.
2) Seromucous inflammation: acute inflammation that occurs
exclusively on the mucus membranes of the respiratory and
gastrointestinal tracts and produces a watery exudate of serum
and mucus.
Examples of Seromucous inflammations:
A) Acute rhinitis common cold
B) Acute catarrhal bronchitis
C) Enteritis

5. Acute rhinitis / common cold: Viral serous catarrhal
inflammation of the nasal mucosa.
Causes:
1) Upper respiratory tract infection.
2) Flu.
3) Hay fever.
4) Bacterial infections.
5) Certain medication.
Pathogenesis and morphology: The disorder is caused by
droplet infection by rhinoviruses. The viruses penetrate the
epithelium of the upper respiratory tract, triggering inflammation
with hyperemia of the mucus membrane and serous exudation.
This leads to obstruction of the nasal passage creating optimum
conditions for proliferation of the virus. The cytopathic effect of the
viruses leads to epithelial necrosis which in turn releases viruses.
Inflammatory irritation of the mucous glands and goblet cell
hyperplasia (cause hypersecretion of mucus). Result in a runny
nose which is a sign of serous catarrhal inflammation. This triggers
the sneezing reflex. Sneezing releases both the pathogen and
exudate and completes the cycle of droplet infection by which the
virus spreads.
Gross Picture of Acute rhinitis

6. A microscopic picture of acute rhinitis
An Illustration of acute rhinitis

7. 3) Serous pulmonary alveolitis
Acute inflammation of the pulmonary alveoli resulting in necrosis
and hemorrhage into the lungs. It involves the occurrence of
exudate into the pulmonary alveoli.
It leads to toxic pulmonary edema with exudation into the
interstitium of the alveolar wall, causing expansion of the alveolar
wall and impaired diffusion.
Causes:
1) Inhaling chemical-laden dust particles in an industrial setting
2) Inhaling fungal, bacterial and other naturally occurring spores.
Microscopic pictures of a normal lung (C) and a lung tissue
with serous alveolitis (D)