Question

Describe the structure and functional properties of: i) the (renal) filtration membrane, and ii) the respiratory membrane. Indicate what forces are involved in driving exchange at these locations, describe and quantify these forces, and describe what is exchanged. Finally, explain clearly Goodpasture Syndrome and how/why it compromises normal function of these two important “membranes”.

Answer 1

RENAL FILTERING MEMBRANE

• A nephron is the anatomical and structural unit of kidney
• Nephron consists of 1)renal corpuscle (2) the renal tubules
• The renal tubule starts as ablind end called Bowman's capsule
• BOWMAN'S CAPSULE
• It haves 2 layers 1)visceral and 2) parietal layer
• In between these 2 layers lies the glomerular space or BOwman's space
• 
• FILTERING MEMBRANE
• blood of the glomerular capillaries is filtered and ultrafilterate collects within the Bowman's space
• The filtering membrane (GBM,glomerular basement membrane) consists of ;
• the capillary endothelium of the glomerular capillary + epithelium of the visceral layer of the Bowman's capsule +the basement membrane present in between these two layers
• This filtering membrane is sufficiently thin so that filteration is possible.
• This thinness facilitates the filtration.This thinness is because of;

1. the endothelial cells of the capillary are very flat and thin.They also contain pores whose sizes are between 50-100nm
2. The epithelium of the visceral layer of the Bowman's capsule are highly specialised and are called podocytes.The main cell body stands on the basement membrane by the help of several pods.

• The individual pods have several foot process called pedicels.The space between pedicels are called slit pores.This arrangement ensures that the filterate does not have to cross the main cell body of the podocytes so that in effect the filtering membrane becomes extremely thin.

RESPIRATORY MEMBRANE

• Respiration is the process by which oxygen is taken in and carbondioxide is given out.
• Functional anatomy:
• Respiratory tract is the anatomical structure through which air moves in and out
• It consists of nose,pharynx,larynx,trachea,bronchi and lungs.
• RESPIRATORY UNIT :
• Lung parenchyma is formed by respiratory unit that forms the terminal portion of respiratory tract.
• RESPIRATORY UNIT is defined as the structural and functional unit of lung
• Exchange of gases occurs only in this part of the respiratory tract.
• The respiratory unit starts from the respiratory bronchioles
• each respiratory bronchiole divides into alveolare ducts
• Each alveolar duct enters an enlarged structure called the alveoli sac
• the space inside the alveolar sac is calles antrum
• Alveoli sac consists of cluster of alveoli
• Few alveoli are present in the wall of alveolar duct also
• It includes :

1. Respiratory bronchioles
2. Alveolar ducts
3. Alveolar sacs
4. Antrum
5. Alveoli

• RESPIRATORY MEMBRANE
• It is a membraneous structure through which the exchange of gases occurs
• The respiratory membrane seperates air in the alveoli from blood in capillary
• It is formed by the alveolar membrane and capillary membrane
• Respiratory membrane has a surface area of 70sq.meters and thickness of 0.5microns
• Layers of respiratory membrane
• 
• From Alveolar portion

1. Monomolecular layer of surfactant,which spreads over the surface of the fluid lining of alveoli
2. A thin layer of fluid that lines the alveoli
3. The alveolar epithelial layer,which is composed of thin epithelial cells resting on the basement membrane

In between alveolar and capillary portion

4.An interstitial space

From capillary portion

5.Basement membrane of capillary

6.capillary endothelial cells.

GOODPASTURE SYNDROME

• It is a combination of necrotising haemorrhagic interstitial pneumonitis and rapidly progressive glomerulonephritis
• aetiology
• The condition result from immunologic damage produced by anti-basement membrane antibodies formed against antigens common to the glomerular and pulmonary basement membranes(typeII hypersensitivity reaction)
• the trigger is viral infection,exposure to hydrocarbons, and smoking.
• MORPHOLOGIC FEATURES :
• Grossly,the lungs are heavy with red -brown areas of consolidation
• Microscopically :
• In acute stage ,focal areas of haemorrhages in the alveoli and focal necrosis in the alveoli walls
• In more chronic cases, interstitial fibrosis and filling of alveoli with haemosiderin laden microphages
• CLINICAL FEATURES
• common in 2nd and 3rd decades of life with prepondence in males.
• Pulmonary manifestation generally precede the renal disease.
• most cases present with haemoptysis accompanied with dyspnoea,fatigue,weakness,and anaemia
• Renal manifestations are haematuria,proteinuria,uraemia and progressive renal failure.
• SEROLOGICAL examination : High titers of Anti-GBM antibody ,the levels of which correlate with severity of illness.