Difference Between Alveoli and Nephron

Main Difference – Alveoli vs Nephron

Alveoli and nephron serve as both structural and functional units in two distinct systems. Alveoli can be found in the lungs while nephron is found in the kidney. The main difference between alveoli and nephron is that alveoli occur in the respiratory system whereas nephron occurs in the excretory system. The main function of alveoli is to provide sites for the gas exchange through the respiratory membrane in a process known as external respiration. Nephron serves as the basic filtration unit that produces urine from the blood. The wall of both alveoli and nephron is one-cell thick and surrounded by an extensive network of blood capillaries.

Key Areas Covered

1. What are Alveoli
– Definition, Structure, Function
2. What is a Nephron
– Definition, Structure, Function
3. What are the Similarities Between Alveoli and Nephron
– Outline of Common Features
4. What is the Difference Between Alveoli and Nephron
– Comparison of Key Differences

Key Terms: Alveoli, Blood Capillaries, Filtration, Gas Exchange, Kidney, Lungs, Nephron

What are Alveoli

Alveoli (singular: alveolus) refer to the many tiny air sacs of the lungs that allow the rapid exchange of respiratory gases. The alveoli found in the respiratory system of mammals are also called pulmonary alveoli. They are located at the end of the respiratory passageways in the lung. The diameter of the sac is 0.2-0.5 mm. Alveoli look like a bunch of grapes. The total average surface area of alveoli is around 75 m³. The respiratory membrane of the alveoli is made up of a simple squamous epithelium. The structure of alveoli is shown in figure 1.

Figure 1: Alveoli

The main function of alveoli is to facilitate the exchange of respiratory gases. Deoxygenated blood reaches the lungs through the pulmonary artery from the right ventricle of the heart. At the alveoli, this blood uptakes oxygen from the alveoli and releases carbon dioxide into the alveoli. The formed oxygenated blood returns to the left atrium of the heart through pulmonary veins.

What is a Nephron

A nephron is the functional unit of the kidney that consists of the glomerulus and the associated tubules through which the glomerular filtrate passes before emerging as urine. The structure of a nephron can be divided into two parts: renal corpuscle and renal tubule. Renal corpuscle is the first part of the nephron and it is composed of the glomerulus and Bowman’s capsule. The blood is filtered through the renal corpuscle. Renal tubule is composed of proximal convoluted tubule (PCT), loop of Henle, and Distal convoluted tubule (DCT). The functions of the renal tubule are reabsorption, secretion, and excretion. The structure of the nephron is shown in figure 2.

Figure 2: Nephron

Based on the function, two types of nephrons can be identified: cortical nephron and juxtamedullary nephron. Cortical nephrons are the usual types of nephrons in the kidney while juxtamedullary nephron is involved in concentrating urine.

Similarities Between Alveoli and Nephron

Alveoli and nephron are structural and functional units of two distinct systems.
Both alveoli and nephrons can be found in large number inside the corresponding organ.
Both alveoli and nephron are involved in a kind of exchange function in the body.
Both alveoli and nephron are made up of simple epithelium that is one cell thick.
Both alveoli and nephron are surrounded by an extensive network of blood capillaries.

Definition

Alveoli: Alveoli refers to the many tiny air sacs of the lungs that allow the rapid exchange of respiratory gases.

Nephron: Nephron refers to the functional unit of the kidney that consists of the glomerulus and the associated tubules through which the glomerular filtrate passes before emerging as urine.

Location

Alveoli: Alveoli can be found in the lungs.

Nephron: Nephron is found in the kidney.

Number

Alveoli: There are about 480 million alveoli in each lung.

Nephron: There are about 0.8 to 1.5 million nephrons in each kidney of an adult.

Type of System

Alveoli: Alveoli belong to the respiratory system.

Nephron: Nephron belongs to the excretory system.

Structure

Alveoli: Alveoli are sac-like structures.

Nephron: Nephron is a tubular structure.

Function

Alveoli: Alveoli facilitates the respiratory gas exchange.

Nephron: Nephron filters blood to produce urine.

Type of Epithelium

Alveoli: Alveoli are made up of simple squamous epithelium.

Nephron: Nephron is made up of simple cuboidal epithelium with a few microvilli.

Type of Blood Capillaries

Alveoli: Alveoli are surrounded by blood capillaries that link pulmonary arterioles to pulmonary veins.

Nephron: Glomerules and peritubular capillaries are the two types of blood capillaries that surround a nephron.

Vessels that Supply Blood

Alveoli: Pulmonary arterioles supply blood to alveoli.

Nephron: Afferent arterioles supply blood to a nephron.

Vessels that Collect Blood

Alveoli: Pulmonary venules collect blood from alveoli.

Nephron: Renal vein collects blood from a nephron.

Conclusion

Alveoli and nephron serve as structural and functional units of respiratory and excretory systems, respectively. Alveoli are sac-like structures while nephrons are tubular. Both alveoli and nephrons can be found in large numbers in the lungs and the kidney, respectively. They are surrounded by an extensive network of blood capillaries. Alveoli facilitate the gas exchange while nephrons filter blood to produce urine. The main difference between alveoli and nephron is their structure and function.

Reference:

1. “2309 The Respiratory Zone” By OpenStax College – Anatomy & Physiology, Connexions Web site, Jun 19, 2013 (CC BY 3.0) via Commons Wikimedia
2. “2611 Blood Flow in the Nephron” By OpenStax College – Anatomy & Physiology, Connexions Web site, Jun 19, 2013 (CC BY 3.0) via Commons Wikimedia

Image Courtesy:

1. “Alveoli.” Kenhub, Available here.
2. Leslie Samuel “NEPHRON: THE FUNCTIONING UNIT OF THE KIDNEY.” INTERACTIVE BIOLOGY, Available here.