Question

When tracing the path of blood, the blood vessel that follows the renal artery is the a. peritubular capillary. d. renal vein. b. efferent arteriole. e. glomerulus. c. afferent arteriole.

Short answer

The blood vessel that follows the renal artery in the path of blood flow through the kidneys is the afferent arteriole. So, the correct answer is c. Afferent arteriole.

Step-by-step solution

Understand the renal blood vessels' path

The path of blood through the renal blood vessels is as follows: 1. Renal artery 2. Segmental artery 3. Interlobar artery 4. Arcuate artery 5. Interlobular artery 6. Afferent arteriole 7. Glomerulus 8. Efferent arteriole 9. Peritubular capillary / Vasa recta 10. Interlobular vein 11. Arcuate vein 12. Interlobar vein 13. Renal vein

Identify the blood vessel after the renal artery

In the path of blood flow mentioned in Step 1, the blood vessel that follows the renal artery is the segmental artery. However, since the segmental artery is not one of the options provided in the exercise, we need to consider the blood vessel directly after the renal artery amongst the given options. Among the given options, the first blood vessel in the path after the renal artery is the afferent arteriole. Therefore, the correct answer is: c. Afferent arteriole.

Key concepts

Afferent Arteriole

The afferent arteriole plays a crucial role in the function of the kidneys. It is the blood vessel responsible for bringing blood into the glomerulus, the small filtering unit within the kidney. The word 'afferent' itself signals the direction of flow, indicating arteries that carry blood towards an organ.

In the context of the renal circulation, the afferent arteriole arises from the interlobular arteries, which branch off from the larger arcuate arteries. These, in turn, branch from the interlobar arteries that stemmed from the segmental arteries. Each kidney contains around a million nephrons, and for each one, there is an afferent arteriole supplying blood to it.

This tiny vessel has the critical job of regulating blood pressure within the glomerulus by constricting or dilating. These changes in diameter affect the rate of blood flow into the glomerulus, which directly influences the glomerular filtration rate (GFR) - a measure of how well your kidneys are cleaning your blood. If there is a need to increase the GFR, the afferent arteriole dilates; conversely, if there is a need to decrease the GFR, it constricts.

Renal Circulation

Renal circulation refers to the path that blood takes through the kidneys. It's a dynamic process that ensures waste removal, balance of electrolytes, and regulation of blood pressure. The journey of blood through the renal circulation is complex and finely controlled.

After blood enters the kidney through the renal artery, it branches into segmental arteries and progressively into smaller arteries until the afferent arterioles. From the afferent arterioles, blood reaches the glomeruli. After filtration occurs in the glomerulus, the now waste-depleted, yet nutrient- and ion-rich blood exits via the efferent arterioles. It then enters the peritubular capillaries or vasa recta, which surround the nephron tubules, allowing for the exchange of substances between the blood and the urinary filtrate.

• The direction of blood flow is highly regulated through the actions of various hormones and signaling molecules to meet the metabolic demands of the body.
• Renal circulation is integral in maintaining a stable internal environment, facilitating the removal of toxins, reabsorption of vital substances, and secretion of waste.

Finally, the cleansed blood exits the kidney through the renal vein, completing its circulation through this vital organ.

Glomerulus

The glomerulus is the tiny, yet mightily important, structure within the kidney's nephron where blood filtration begins. A network of capillaries, it functions much like a sieve, allowing certain small molecules to pass through while retaining larger molecules like proteins.

Blood enters the glomerulus under pressure through the afferent arteriole, and this pressure facilitates the filtration process. The membrane of the glomerulus acts as a barrier that determines what gets filtered and what stays in the blood. The key substances that pass through into the Bowman's capsule (the encasing structure) are water, ions, and small molecules, which then form the primary urine.

Mechanism of Filtration

The glomerulus has a three-layered filtration barrier consisting of:

• The endothelium of the glomerular capillaries with pores.
• A basement membrane that filters based on the charge and size of molecules.
• Epithelial cells (podocytes) with foot processes that provide an additional layer of filtration.

The efficiency of the glomerulus is paramount to overall kidney function and health. Diseases or damage affecting the glomerulus can lead to conditions such as glomerulonephritis, which can greatly impact the body's ability to cleanse the blood properly.