Which of the following substances would pass through the filtration membrane to become part of the filtrate under normal circumstances? (Circle all that apply.)


a. Sodium ions
b. Albumin
c. Glucose
d. Erythrocytes
e. Leukocytes
f. Amino acids
g. Urea

Verified step by step guidance

1. Understand the structure of the filtration membrane in the kidneys, which consists of three layers: the fenestrated endothelium, the basement membrane, and the podocyte filtration slits.
2. Identify the size and charge of the substances listed: sodium ions, albumin, glucose, erythrocytes, leukocytes, amino acids, and urea.
3. Recall that the filtration membrane allows small molecules and ions to pass through while restricting larger molecules and cells.
4. Determine which substances are small enough to pass through the filtration membrane: typically, ions, small molecules like glucose, amino acids, and urea can pass, while larger proteins like albumin and cells like erythrocytes and leukocytes cannot.
5. Circle the substances that are small enough to pass through the filtration membrane under normal circumstances: sodium ions, glucose, amino acids, and urea.

Key Concepts

Filtration Membrane

The filtration membrane is a selective barrier in the kidneys, specifically in the glomerulus, that allows certain substances to pass into the filtrate while retaining larger molecules and cells. It consists of three layers: the fenestrated endothelium, the basement membrane, and the podocytes. This structure is crucial for maintaining the balance of fluids and electrolytes in the body.

Substance Size and Charge

The ability of a substance to pass through the filtration membrane is largely determined by its size and charge. Small molecules, such as sodium ions, glucose, and urea, can easily pass through, while larger molecules like albumin and cells (erythrocytes and leukocytes) are typically retained. This selective permeability is essential for proper kidney function and homeostasis.

Normal Filtrate Composition

Normal filtrate composition includes water, electrolytes, glucose, amino acids, and waste products like urea. Understanding what constitutes normal filtrate helps in identifying which substances can pass through the filtration membrane. Abnormal levels of certain substances in the filtrate can indicate underlying health issues, such as kidney damage or disease.