Question

How do the details of nephron anatomy help explain why you do not expect to find evidence of glucose or protein in a urine sample from someone whose kidneys are healthy?

Answer 1

A urinary protein test determines how much protein is found in the urine. Protein isn't found in large amounts in the urine of healthy people. If the kidneys aren't functioning properly or when high levels of such proteins are found in the bloodstream, protein may be excreted in the urine.

Complete answer:
Nephron is a convoluted tubule which is blind at one end and opens in another duct. Various types of epithelial tissues form different parts of the tubule. Blood vessels are closely associated with nephrons. Nephron is a structural and functional unit of the kidney: one kidney has up to one million nephrons in humans. The structural association of nephrons and blood vessels primarily helps in the filtration of blood to remove nitrogenous waste products.

Nephron selectively reabsorbs filtrate materials that are not to be excreted and these materials re-enter the circulation of the blood. Tubular nephron secretion is also present, which helps to maintain the pH of blood.

There are different parts of nephron:
Bowman Capsule
Proximal Convoluted Tubule (PCT)
Loop of Henle—Descending limb and Ascending limb
Distal Convoluted Tubule (DCT)

Bowman's capsule is a cup shaped with an inner visceral layer, closely associated with a capillary tuft (=glomerulus). This layer is made of special cells (with cytoplasmic processes) called PODOCYTES that surround the sifting capillaries. Filtration is carried out across the visceral membrane. The outer parietal layer of the capsule cup is made of squamous epithelium.

Except the descending limb of Henle, all other parts of the line are made of CUBOIDAL epithelium. In PCT, the cuboidal epithelium is bordered by a brush due to the presence of microvilli at the free ends of the cells to increase the surface area for reabsorption. Tubular secretion occurs mainly along the DCT.
The reabsorption of water from urine continues beyond its passage through nephrons in the collection of tubules.

Healthy nephrons do not allow blood proteins to appear in the filtrate, i.e. the pores in the capsular sieve are smaller in size than proteins. Glucose molecules (& amino acids, ions) are reabsorbed by PCT from the filtrate.

Note: The microalbumin test detects microalbumin, a protein type, in the urine. Protein is present in the urine when kidney damage occurs. Since damage to the blood vessels that occurs as a complication of diabetes can lead to problems with the kidneys, a microalbumin test is performed to check for damage to the kidneys over time.