Phagocytosis, or 'cell eating', is a type of endocytosis where the cell membrane engulfs large solid particles, such as bacteria or cellular debris, forming a vesicle called a phagosome. This phagosome then fuses with a lysosome for digestion. It is primarily performed by specialized cells like macrophages and neutrophils.
Explanation:
The juxtaglomerular apparatus (JGA) is a specialized structure where the distal convoluted tubule (DCT) comes into contact with the afferent arteriole. It consists of juxtaglomerular cells (modified smooth muscle cells in the afferent arteriole that secrete renin), macula densa cells (modified DCT cells that sense NaCl concentration), and extraglomerular mesangial cells. It plays a crucial role in regulating blood pressure and glomerular filtration rate via the renin-angiotensin-aldosterone system.
Explanation:
The pulmonary artery (trunk) exits the right ventricle and carries deoxygenated blood to the lungs for oxygenation. The pulmonary veins return oxygenated blood from the lungs to the left atrium. The aorta distributes oxygenated blood to the body, and the vena cava returns deoxygenated blood to the heart.
Explanation:
Emil Fischer proposed the lock-and-key model in 1894, suggesting that the enzyme's active site is exactly complementary to the substrate, like a key fits a lock. Koshland later proposed the induced fit model, which is more widely accepted. Michaelis and Menten developed enzyme kinetics equations.
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