The humerus is the long bone in the upper arm that connects the shoulder to the elbow. It is distinct from other bones found in the forearm or leg.

The heart functions as the pump of the circulatory system by contracting rhythmically to move blood. It is essential for transporting oxygen and nutrients to tissues.

The cerebellum plays a key role in balance and coordination by integrating sensory information and motor commands. It ensures smooth and precise movements.

Red blood cells transport oxygen from the lungs to the tissues using hemoglobin. Their design maximizes oxygen-carrying capacity, which is critical for cellular respiration.

Muscle tissue contracts and relaxes to produce movement. It is uniquely structured for generating force, distinct from other tissue types.

The term 'anterior' refers to the front of the body. It is commonly used to describe the relative position of anatomical structures in relation to one another.

Pivot joints enable rotational movement around a single axis. They are essential for actions like turning the head.

Myosin interacts with actin filaments to generate force through a cross-bridge cycling mechanism. This process, driven by ATP, is crucial for muscle contraction.

The nephron is the kidney's basic functional unit responsible for filtering blood, reabsorbing needed substances, and excreting waste. It ensures the maintenance of fluid and electrolyte balance.

The small intestine has a highly specialized structure with villi and microvilli, increasing its surface area for nutrient absorption. Its design optimizes the uptake of digested nutrients.

The myelin sheath insulates axons, which increases the speed and efficiency of nerve impulse conduction. This insulation is key to rapid communication within the nervous system.

Thyroxine is crucial for regulating the body's metabolism and energy production. Its balance is essential for maintaining overall metabolic homeostasis.

The aorta is the main artery that transports oxygenated blood from the heart to the rest of the body. Its large caliber supports the high-pressure output from the heart.

Homeostasis refers to the process by which organisms maintain a stable internal environment. This stability is critical for optimal physiological function despite external changes.

The skull encases and protects the brain from physical damage. Its rigid structure is essential for shielding the delicate neural tissue from trauma.

Osmosis is the passive movement of water across a selectively permeable membrane due to solute concentration differences. It does not require energy and is fundamental to many physiological processes.

After the ventricles contract (systole), they begin to relax in a phase known as ventricular diastole. This relaxation allows the chambers to refill with blood for the next cycle.

The central nervous system originates mainly from the ectoderm, which forms the neural tube during embryonic development. This layer is fundamental in establishing the basic framework of the brain and spinal cord.

The sliding filament theory describes how myosin heads attach to actin filaments and pull them inward, resulting in muscle contraction. This process, powered by the hydrolysis of ATP, is essential for muscle function.

The counter-current multiplier mechanism in the loop of Henle establishes a concentration gradient in the medulla of the kidney. This gradient is crucial for water reabsorption and the production of concentrated urine.