sigmoidi

Sigmoidi is the plural form of sigmoide, used to describe several S-shaped structures or concepts in anatomy and mathematics. The term derives from Latin sigmoideus, indicating an S-shaped form.

In anatomy, the most commonly referenced sigmoidi are the sigmoid colon and the sigmoid sinuses. The sigmoid colon is an S-shaped portion of the large intestine that connects the descending colon to the rectum. It is typically about 40 centimeters long in adults and located in the left lower abdomen. Its main role is to store fecal material before defecation. Conditions affecting the sigmoid colon include diverticulosis, diverticulitis, sigmoid volvulus, and colorectal cancer. The sigmoid sinuses are dural venous sinuses with an S-shaped course along the posterior cranial fossa, draining blood from the brain to the internal jugular vein via the jugular foramen. They can be involved in thrombosis or injury, and such events may present with headache or focal neurologic symptoms.

Sigmoid arteries are arterial branches that supply the sigmoid colon; they are usually derived from the inferior mesenteric artery and may appear as several arteries along the distal colon. In mathematics, the sigmoid function describes an S-shaped curve that maps real numbers to the interval between 0 and 1. The standard form is f(x) = 1/(1 + e^-x); its derivative is f'(x) = f(x)(1 - f(x)). This function is widely used as an activation function in neural networks and to model probabilities, reflecting its characteristic gradual, saturating growth.