Intestino vs. tripa
While both words refer to the same internal organ, the choice between intestino and tripa depends entirely on formality and context. Intestino is the standard biological term, whereas tripa is colloquially used for food, slang, or idioms.
Intestino
B1This is the formal, anatomical, and medical term for the intestine. You should use intestino when speaking to a doctor, discussing biology, or talking about health and digestion in a polite or serious way.
O médico disse que o meu intestino delgado está saudável.
(The doctor said that my small intestine is healthy.)
Uma dieta rica em fibras ajuda o funcionamento do intestino.
(A diet rich in fiber helps the intestine function.)
A infecção começou no intestino grosso.
(The infection started in the large intestine.)
Nós estudamos a anatomia do intestino na aula de ciências.
(We studied the anatomy of the intestine in science class.)
Ela toma probióticos para regular o intestino.
(She takes probiotics to regulate her intestine.)
Tripa
B2This is an informal, popular word often translated as gut or tripe. Tripa is used when referring to animal intestines in cooking (like sausage casings), in slang to refer to a person's belly, or in colorful idioms. It can sound vulgar if used in a formal medical context.
Para fazer linguiça caseira, você precisa limpar bem a tripa.
(To make homemade sausage, you need to clean the intestine casing well.)
Ele teve que fazer das tripas coração para terminar o projeto a tempo.
(He had to bend over backward to finish the project on time.)
Estou com tanta fome que minhas tripas estão roncando.
(I am so hungry that my guts are growling.)
No norte de Portugal, o prato tripas à moda do Porto é muito famoso.
(In northern Portugal, the dish tripe Porto-style is very famous.)
O peixeiro removeu as tripas do peixe antes de vender.
(The fishmonger removed the fish guts before selling it.)
Summary
Use intestino for all medical, biological, or polite conversations regarding the body. Use tripa when talking about culinary ingredients (tripe/casings), slang for guts, or idiomatic expressions like fazer das tripas coração (to making a huge effort).