Question

Assertion: Urinary bladder can considerably expand to accommodate urine. Reason: It is lined by stretchable transitional epithelium.

Short answer

Yes, the assertion and the reason are co-related. The urinary bladder can considerably expand to accommodate urine because it is lined by stretchable transitional epithelium.

Step-by-step solution

Understand the Assertion

The urinary bladder is a hollow muscular organ that stores urine from the kidneys before disposal by urination. When it fills up, it can considerably expand to accommodate more urine.

Understand the Reason

The urinary bladder is lined with transitional epithelium which is a type of tissue consisting of multiple layers of epithelial cells which can contract and expand. This makes it possible for organs, such as the urinary bladder, to stretch and expand.

Connect the Assertion and the Reason

The ability of urinary bladder to expand and accommodate urine is due to the stretchable transitional epithelium with which it is lined. When urine is produced and sent from the kidneys to the bladder, the bladder expands thanks to the transitional epithelium.

Key concepts

Urinary Bladder Function

The urinary bladder plays a crucial role in the human excretory system. It operates as a storage container for urine, which is produced by the kidneys as they filter waste products from the blood. As urine accumulates in the bladder, the organ can expand significantly.

This expansion is essential to its function, as the bladder must hold varying amounts of urine until it is convenient for excretion. The act of urination involves the coordination of the muscular bladder wall and the sphincters. The sphincters relax to allow urine to flow out of the bladder through the urethra, while the bladder wall contracts to push the urine out. Efficient bladder function is not only necessary for the excretion process but also aids in maintaining internal balance and preventing infections.

Epithelial Tissue Types

Epithelial tissues are lining cells that cover internal organs and external surfaces, including the skin. They serve various functions, such as protection, secretion, absorption, and filtration. There are several types of epithelial tissue, and they are classified based on the shape of the cells and the number of layers they form.

The most common types include:

• Squamous epithelium – made of flat cells and found in areas where passive diffusion occurs, eg. the lining of the lungs.
• Cuboidal epithelium – composed of cube-shaped cells, often found in glandular tissues.
• Columnar epithelium – taller cells, which may have surface specializations like cilia and microvilli, commonly lining the digestive tract.

An exceptional type is the transitional epithelium, the focus of our discussion, which lines the bladder and related passageways. It is unique for its ability to stretch and maintain a barrier during the stress of filling and emptying.

Urine Storage and Excretion

Urine storage and excretion is a continuous process and one of the body's key methods for removing waste and maintaining homeostasis. After formation in the kidneys, urine travels down the ureters to the bladder.

The bladder's capacity for urine storage is a balance between urine production and the frequency of urination. Transitional epithelium plays a pivotal role in this process, as it allows for considerable expansion of the bladder. This means that the bladder doesn't need to empty as urine arrives from the kidneys – a feature crucial for daily function and social convenience.

When the bladder reaches its storage limit, nerve signals trigger the urge to urinate, leading to the active phase of excretion. A conscious control mechanism allows individuals to decide when to empty the bladder, underscoring not only the biological but also the social importance of this sophisticated system.