Which of the following plasma proteins is responsible for colloid osmotic pressure?

a. Decrease in sodium reabsorption: This would lead to further lowering of blood pressure, which is not a compensatory response.

b. Dilation of the afferent arteriole: This typically increases glomerular filtration rate but is not a primary response to decreased blood pressure.

c. Constriction of the efferent arteriole: This response helps to increase glomerular pressure but is secondary to other mechanisms.

d. Release of renin: Renin is released by the kidneys in response to low blood pressure, initiating the renin-angiotensin-aldosterone system (RAAS) to increase blood pressure by conserving sodium and water and constricting blood vessels.

a. Secretes fluid to reduce friction between layers: This is correct. The pleural membranes secrete pleural fluid, which reduces friction between the visceral and parietal layers during breathing.

b. Secretes a substance that reduces surface tension of alveoli: This describes the function of surfactant, which is secreted by alveolar cells, not pleural membranes.

c. Secretes a substance to keep epithelial cells wet: This is a general description that doesn't specifically apply to pleural membranes.

d. Secretes fluid involved in protection from infections: While pleural fluid may have some protective roles, its primary function is to reduce friction, not directly to protect from infections.