Which of the following structures is primarily responsible for the filtration of blood in the human excretory system?
Ureter
Nephron
Glomerulus
Bladder
Correct Answer:C
Explanation
The correct option is C. Glomerulus.
Detailed Explanation:
Understanding the Excretory System:
The human excretory system is responsible for the removal of waste products from the body and the regulation of water and electrolyte balance. The kidneys are the primary organs involved in this process.
Role of the Nephron:
The nephron is the functional unit of the kidney, and each kidney contains about a million nephrons. Each nephron consists of several parts, including the glomerulus, Bowman's capsule, renal tubules, and collecting duct. While the nephron is crucial for the overall process of urine formation, it is not the specific structure that performs the initial filtration of blood.
Function of the Glomerulus:
The glomerulus is a network of tiny blood vessels (capillaries) located at the beginning of each nephron. It is surrounded by Bowman's capsule. The primary function of the glomerulus is to filter blood. When blood flows into the glomerulus, the high pressure forces water, ions, and small molecules (like glucose and urea) out of the blood and into Bowman's capsule, forming what is known as the glomerular filtrate. Larger molecules, such as proteins and blood cells, are typically too large to pass through the filtration barrier and remain in the bloodstream.
Why Other Options Are Incorrect:
A. Ureter: The ureter is a tube that carries urine from the kidney to the bladder. It does not play a role in the filtration of blood; rather, it is involved in the transport of urine after it has been formed.
B. Nephron: While the nephron is essential for urine formation, it is the glomerulus specifically that is responsible for the initial filtration of blood. The nephron includes the glomerulus but also encompasses other structures that process the filtrate into urine.
D. Bladder: The bladder is a storage organ for urine. It does not participate in the filtration of blood; its role is to store urine until it is excreted from the body.
Summary of Key Points:
The glomerulus is the primary structure responsible for filtering blood in the kidneys.
It allows water, ions, and small molecules to pass into Bowman's capsule while retaining larger molecules in the bloodstream.
The nephron is the functional unit of the kidney but includes multiple components, with the glomerulus being the specific site of filtration.
The ureter and bladder are involved in urine transport and storage, not filtration.
Revision Summary:
The glomerulus is the key structure for blood filtration in the kidneys.
It filters out waste and excess substances while retaining larger molecules.
The nephron includes the glomerulus but has additional roles in urine formation.
Ureters and bladders are involved in urine transport and storage, not filtration.