Respiratory System and Urine Formation: A Comprehensive Look

The Respiratory System: How Air Enters Your Body

Air entry is performed through the nostrils and reaches the nasal cavity, where it is warmed. The nasal wall is full of blood vessels. The nostrils open into the pharynx, an organ common to the respiratory and digestive tracts. The inferior pharynx communicates with the larynx, allowing air to enter the trachea.

In the larynx, a cartilaginous lamina, the epiglottis, closes to prevent food from entering the respiratory tract. The larynx, in addition to serving as an air passage, is also a vocal apparatus. Inside the larynx, the vocal cords vibrate as air passes over them, allowing us to produce sounds.

The trachea is lined with a mucous membrane rich in glands that trap dust particles. The walls are reinforced with C-shaped cartilage. The trachea divides into two bronchi, which also have cartilage and ciliated cells. These bronchi enter the lungs, branching into smaller bronchioles that terminate in pulmonary vesicles.

Urine Formation: A Three-Phase Process

Urine formation occurs in three phases:

1. Glomerular Filtration

This is the passage of blood from the capillaries of the glomerulus into Bowman's capsule. Blood cells and most proteins are not filtered. The filtrate has a similar composition to plasma, containing glucose, amino acids, vitamins, minerals, water, urea, uric acid, and creatinine. Approximately 125 ml of filtrate is produced.

2. Tubular Reabsorption

Most of the filtrate is reabsorbed along the tubules of the nephron through the network of capillaries that surround them. Reabsorption is performed by active transport and passive diffusion. In the proximal tubule, glucose, water, urea, vitamins, and amino acids are reabsorbed. In the loop of Henle, sodium, chlorine, and water are reabsorbed.

3. Tubular Secretion

A number of substances are secreted from the capillaries into the nephron tubules, including some drugs. The fluid produced passes into the collecting ducts, where water can be reabsorbed before it is transported to the bladder for storage.