The lungs which are part of the lower respiratory tract begins at the trachea and branch into the bronchi and bronchioles and receives air breathed in through the conducting zone. The conducting zone ends at the terminal bronchioles which then divide into the respiratory bronchioles of the respiratory zone which further divide into alveolar ducts that give rise to the alveolar sacs that contain the alveoli, where the process of gas exchange occurs. Alveoli are also sparsely present on the walls of the respiratory bronchioles and also the alveolar ducts.
Each adult human kidney contains about one million nephrons. Nephrons are the urine-producing functional structures of the kidney, which span the cortex and medulla. The initial filtering portion of a nephron is the renal corpuscle, which is situated in the cortex, this is followed by a renal tubule that passes from the cortex deep into the medullary pyramids. Part of the renal cortex, a medullary ray is a collection of renal tubules that drain into a single collecting duct.
The comparison of Alveoli in the lungs and Nephrons in the kidneys are as follows.

Alveoli in the lungs
1.Alveoli in the lungs are the tiny air sacs that are located in the lungs that help in the rapid exchange of gases.
2.Situated in the respiratory system
3.Around four eighty million alveoli found in each lung
4.Sac-like structures
5.Facilitates gaseous exchange in lungs
6.Made up of simple squamous epithelium
7.Pulmonary arterioles supply blood to the alveoli
8.Blood is supplied to pulmonary veins by the alveoli

Nephrons in the kidney
1.Nephrons in the kidneys consist of glomerulus and tubules through which glomerular filtrate passes.
2.Belongs to the excretory system
3.One million nephrons found in kidneys
4.Tubular structures
5.Facilitates blood filtration in order to produce urine
6.Made up of simple cuboidal epithelium with microvilli
7.Afferent arterioles supply blood to the nephrons
8.Nephrons supply blood to renal veins

Alveoli in the lungs and nephrons in the kidneys both facilitate exchange across a barrier but serve different purposes. Alveoli facilitate gas exchange (oxygen and carbon dioxide) between the lungs and the blood. Nephrons filter blood and produce urine, removing waste products and excess substances.
Alveoli:
Structure:
Tiny, sac-like structures within the lungs, one cell thick, with a rich network of capillaries surrounding them.
Function:
Facilitate gas exchange. Oxygen from inhaled air diffuses into the blood through the thin alveolar walls and into the surrounding capillaries, while carbon dioxide from the blood diffuses out into the alveoli to be exhaled.
Key Features:
High surface area for efficient gas exchange, thin walls for easy diffusion.
Nephrons:
Structure:
Tubular structures within the kidneys, consisting of a glomerulus (a network of capillaries), Bowman’s capsule, and various tubules (proximal and distal convoluted tubules, loop of Henle, and collecting duct).
Function:
Filter blood to remove waste products (like urea, uric acid, and excess water), reabsorb essential substances (like glucose, amino acids, and water) back into the bloodstream, and produce urine.
Key Features:
Complex structure allowing for filtration, reabsorption, and secretion of substances.