Question

Which of the following would most likely be filtered through the glomerulus into Bowman's capsule? A. Erythrocytes B. Monosaccharides C. Platelets D. Proteins

Short answer

B. Monosaccharides

Step-by-step solution

Understand the Function of the Glomerulus

The glomerulus is a network of capillaries in the kidneys that filters blood to form urine. It allows small molecules and waste products to pass through while retaining larger molecules and cells.

Identify the Molecule Sizes

A key factor in determining what gets filtered through the glomerulus is the size of the molecules. Erythrocytes (red blood cells) and platelets are too large to pass through. Proteins can range in size, but larger proteins are generally not filtered.

Determine Which Molecule Can Pass Through

Monosaccharides are small molecules (simple sugars) that easily pass through the filtration barrier of the glomerulus into Bowman's capsule.

Choose the Correct Answer

Based on the information, the molecule that would most likely be filtered through the glomerulus into Bowman's capsule is B. Monosaccharides.

Key concepts

Kidney Function

The kidneys play a crucial role in maintaining the body's overall health. They filter waste products and excess substances from the bloodstream, ensuring that the body's internal environment remains stable. Kidneys consist of many tiny units called nephrons, and each nephron has a glomerulus. The glomerulus filters blood and begins the process of urine formation. Key functions of the kidneys include:

• Regulating blood pressure
• Balancing fluid levels
• Excreting waste products
• Maintaining electrolyte balance

If the kidneys fail to function properly, it can lead to harmful accumulations in the blood, which affects overall health.

Molecular Size

Molecular size is a critical factor in glomerular filtration. The glomerulus acts as a sieve, filtering small molecules while preventing larger ones from passing through.

Small molecules like monosaccharides, electrolytes, and water can easily pass through the filtration barrier. However, large molecules such as erythrocytes (red blood cells), platelets, and most proteins are too large to be filtered. The filtrate that passes through generally includes small molecules and is free of large cells and proteins. This selective filtration ensures that important proteins and cells remain in the bloodstream while waste products are excreted.

Urine Formation

Urine formation occurs in three main steps: filtration, reabsorption, and secretion.

The process starts in the glomerulus with filtration. Here, blood pressure forces water and solutes through the glomerular filtration barrier into Bowman's capsule. The resulting filtrate contains waste products and small molecules.

During reabsorption, essential substances and water are reabsorbed into the bloodstream from the filtrate. This ensures that the body retains necessary nutrients and maintains fluid balance.

The final step, secretion, involves the active transport of additional waste substances into the filtrate. Together, these processes ensure that only waste products and excess substances are excreted while retaining vital nutrients and water.

Glomerular Filtration Barrier

The glomerular filtration barrier is a crucial structure in the nephron. It consists of three layers:

• Endothelial cells
• Basement membrane
• Podocytes

The endothelial cell layer contains fenestrations (small pores) that allow fluid passage but block large cells. The basement membrane acts as a physical and electrostatic barrier, filtering based on size and charge. Finally, the podocytes cover the basement membrane with slit diaphragms further restricting large molecules.

This barrier ensures selective filtration, allowing small molecules to pass while retaining crucial larger proteins and cells in the bloodstream. This selective filtration is key to maintaining homeostasis and proper kidney function.