Question

In humans, the excretory system coexist of (a) Pair of kidneys (b) Pair of ureters (c) A urinary bladder and a urethra (d) All of these

Short answer

The correct answer is (d) All of these. These parts - pair of kidneys, pair of ureters, urinary bladder and urethra, all make up the human excretory system and are essential in the process of urine formation and its removal from the body.

Step-by-step solution

Understanding the options

(a) A pair of kidneys: These are major organs in the excretory system that filter the blood and remove waste in the form of urine. \n (b) A pair of ureters: These are tubes that carry urine from the kidneys to the urinary bladder. \n (c) A urinary bladder and urethra: The urinary bladder stores urine until it is excreted out of the body through the urethra.

Connecting the options

It can be seen that all these components, kidneys, ureters, urinary bladder and urethra, work together in urine production and excretion, which is the main function of the excretory system. Thus, they are all parts of the human excretory system.

Arriving at the answer

Since all these components form the human excretory system, the correct answer would be (d) All of these.

Key concepts

Kidneys

Kidneys are vital organs in the human excretory system. They are bean-shaped and located on either side of the spine beneath the rib cage. Their primary role is to filter blood and remove waste products that are generated from various bodily processes.
After filtering, these waste products are converted into urine, which contains urea, excess salts, and water. Kidneys also help in maintaining electrolyte balance and regulating blood pressure by managing fluid levels.
The filtering unit of the kidney is called a nephron. Each kidney contains about a million nephrons which work tirelessly day and night to ensure our body's waste is efficiently eliminated.

• Regulate water and salt balance
• Produce urine
• Help in blood pressure regulation

Ureters

Ureters are thin, muscular tubes that play a crucial role in transporting urine from the kidneys to the urinary bladder. Each kidney has its own ureter, making a pair that functions in synchrony.
The walls of ureters are lined with smooth muscles, which undergo peristaltic contractions to effectively push the urine downwards. This process is essential as it ensures the urine is continuously moved in one direction, preventing any potential backflow.
Ureters enter the bladder at an angle which helps in creating a natural valve that prevents urine from backing up into the kidneys. This prevents infections and other complications.

• Connect kidneys to bladder
• Transport urine through peristalsis
• Prevent urine backflow to kidneys

Urinary Bladder and Urethra

The urinary bladder is a hollow, muscular organ that temporarily stores urine until it is ready to be expelled from the body. It is flexible and can expand to hold varying volumes of urine.
Normally, a healthy adult bladder can hold about 400-600 milliliters of urine. The bladder has a lining of stretchy tissue and a smooth muscle layer that facilitates its expansion and contraction.
The urethra is the final component of the excretory system, serving as the passage through which urine exits the body. The length of the urethra varies between sexes, being longer in males than in females.

• Stores urine until excretion
• Bladder expands and contracts
• Urethra channels urine out of the body