General Science MCQs – Page 44 (Q431-440)

The liver is generally considered the largest internal organ in the human body, typically weighing around 1.5 kilograms in an adult and performing hundreds of essential metabolic functions, including producing bile for fat digestion, filtering and detoxifying harmful substances from the blood, storing glycogen and certain vitamins, regulating blood glucose levels, and synthesizing important blood proteins. The liver possesses a remarkable capacity for regeneration, able to regrow to nearly its original size even after significant portions are surgically removed or damaged, a property that has made partial liver transplants from living donors a viable and increasingly common medical option.

The kidneys are the pair of organs in the human body primarily responsible for filtering blood and producing urine, continuously removing metabolic waste products, excess water, and excess salts and minerals from the bloodstream while carefully regulating the body's overall fluid balance, electrolyte levels, and blood pressure. Each kidney processes an enormous volume of blood daily, filtering it through millions of tiny functional units called nephrons, and the kidneys also play important roles in producing hormones that regulate red blood cell production and activate vitamin D, making them essential for far more than simple waste filtration alone.

A normal, healthy human body typically has two kidneys, bean-shaped organs located on either side of the spine toward the back of the abdominal cavity, each roughly the size of a fist, working together to filter blood and produce urine. Remarkably, a person can survive and function normally with only a single healthy kidney, which is why living kidney donation between family members or matched donors is a viable and relatively common medical practice, since the remaining kidney can compensate and handle the filtration workload previously shared between both original kidneys.

The nephron is the basic structural and functional filtering unit found within each kidney, with roughly one million nephrons present in a typical adult kidney, each consisting of a filtering component called the glomerulus and a long tubule that reabsorbs useful substances like water, glucose, and salts back into the bloodstream while allowing waste products to continue on and eventually form urine. This intricate, highly efficient filtering system allows kidneys to process the body's entire blood volume many times per day, precisely regulating what stays in the blood and what gets excreted as waste, maintaining the body's critical internal chemical balance.

Urea is the primary nitrogen-containing waste product filtered out of the blood and excreted by the kidneys, formed in the liver as a byproduct of breaking down excess amino acids and proteins, a process that converts toxic ammonia into the much less harmful, water-soluble urea for safer transport through the bloodstream and eventual elimination in urine. Measuring blood urea nitrogen, commonly abbreviated as BUN, is a standard clinical test used to assess kidney function, since elevated levels can indicate impaired kidney filtration ability, making urea an important biomarker in diagnosing and monitoring various kidney-related health conditions.

The urinary bladder is the organ in the human body mainly responsible for storing urine before it is expelled from the body, a muscular, expandable sac located in the pelvis that can typically hold several hundred milliliters of urine, stretching to accommodate increasing volume as urine continuously drains into it from the kidneys via the ureters. When the bladder becomes sufficiently full, stretch receptors in its wall signal the brain, triggering the urge to urinate, at which point voluntary relaxation of the urethral sphincter, along with bladder muscle contraction, allows urine to be expelled through the urethra.

The human central nervous system is primarily made up of the brain and the spinal cord, together serving as the body's main control and processing center, receiving sensory information from throughout the body, processing and interpreting that information, and coordinating appropriate motor responses sent back out to muscles and organs. The spinal cord runs through the protective bony vertebral column, serving as the primary communication pathway between the brain and the peripheral nervous system, which includes all the nerves extending throughout the rest of the body, and it is also capable of coordinating certain rapid, automatic reflex actions independently of direct brain involvement.

The cerebrum is generally considered the largest and most prominent part of the human brain, accounting for roughly 85 percent of total brain mass and divided into two hemispheres, each further subdivided into four lobes, frontal, parietal, temporal, and occipital, responsible respectively for functions including reasoning and movement, sensory processing, hearing and memory, and vision. The cerebrum's outer layer, the cerebral cortex, is highly folded to increase surface area within the confined space of the skull, and it is responsible for higher-order cognitive functions like conscious thought, language, decision-making, and voluntary movement control.

The cerebellum, located at the back of the brain beneath the larger cerebrum, primarily controls balance and coordination of movement, continuously receiving sensory feedback from muscles, joints, and the inner ear's balance organs to fine-tune motor commands, ensuring smooth, precise, and well-coordinated voluntary movements. Damage to the cerebellum typically results in noticeable difficulties with balance, coordination, and fine motor control, a condition called ataxia, causing unsteady, jerky movements. Despite comprising only about 10 percent of total brain volume, the cerebellum contains a disproportionately large number of the brain's total neurons, reflecting its complex, fine-tuned regulatory role.

The medulla oblongata, located at the base of the brainstem where the brain connects to the spinal cord, primarily regulates essential involuntary functions such as heartbeat, breathing rate, and blood pressure, continuously monitoring the body's internal chemical and physiological state and adjusting these vital functions automatically without any need for conscious thought or control. Because it controls such fundamental, life-sustaining processes, significant damage to the medulla oblongata is often immediately life-threatening, unlike damage to other brain regions that might impair specific functions like memory or movement while still leaving basic survival functions intact.