What is the Difference Between Endocrine and Paracrine

The key difference between endocrine and paracrine is that endocrine signals use the circulatory system to transport ligands through the blood to distant cells while paracrine signaling acts on neighboring cells.

Cells usually communicate through chemical signals. These chemical signals are typically proteins secreted from a cell and released to the extracellular space. From there, they transmit to neighboring cells. The messages or signals carried by a ligand run through a chain of chemical messengers inside a cell. Cell to cell signaling usually involves transmitting signals from a sending cell to a receiving cell. There are four basic categories of chemical signaling and they are paracrine signaling, endocrine signaling, autocrine signaling, and signaling by direct contact.

CONTENTS

1. Overview and Key Difference
2. What is Endocrine 
3. What is Paracrine
4. Similarities – Endocrine and Paracrine
5. Endocrine vs Paracrine in Tabular Form
6. Summary – Endocrine vs Paracrine

What is Endocrine?

An endocrine system is composed of many glands that release hormones. These hormones are released directly into the blood circulatory system and regulate distant target organs. When cells transmit signals over long distances, they often use the circulatory system. This long-distance signaling is known as endocrine signaling. The hypothalamus is the neural control center for endocrine functions. The main endocrine glands of humans include the pituitary gland, pineal gland, thyroid gland, and adrenal glands. Glands signal each other in an axis, and it is known as the hypothalamic-pituitary-adrenal axis. There are several other organs such as bones, kidneys, liver, heart, and gonads, which have secondary endocrine functions.

A special feature of endocrine glands is the absence of ducts. They are vascular and possess intracellular vacuoles to store hormones. The endocrine system operates through feedback loops. Most important feedback is mediated via the hypothalamus and pituitary. The hypothalamus and anterior pituitary play an important role in cell signaling since they are a part of hypothalamic-pituitary-adrenal axis. The endocrine system regulates almost all biological processes in the body from conception to old age. This also involves the development of the brain and nervous system, metabolism, blood sugar levels, and growth and function of the reproductive system.

What is Paracrine?

Paracrine signaling acts locally between cells that are close to each other. These signals move by diffusion through the extracellular matrix. They exhibit quick responses but last only for a short period of time. To keep the signals localized, paracrine ligands are degraded by enzymes or removed by neighboring cells. Removal of signals reestablishes a concentration gradient for signals, allowing them to diffuse faster through the intracellular space. Transfer of signals across a synapse between nerve cells is an example of paracrine signals.

Different organs in the body utilize similar paracrine factors that are categorized into four families based on their structure. They are fibroblast growth factor (FGF) family, Hedgehog family, Wnt family, and TGF-β superfamily. The binding of a certain paracrine factor to its respective receptor initiates specific signals with different responses. The FGF family has a range of functions; however, their major function is to stimulate proliferation and differentiation. Hedgehog family is involved in inducing cell types and creating tissue boundaries, and patterning in bilateral organisms. Wnt family includes a large number of cysteine-rich glycoproteins. They activate signal transduction cascades. TGF-β superfamily regulates the development of an embryo to an adult organism via cell growth, differentiation, apoptosis, and homeostasis.

What are the Similarities Between Endocrine and Paracrine?

• Endocrine and paracrine are types of cell signaling.
• Both contain proteins.
• They transmit signals through ligands.

What is the Difference Between Endocrine and Paracrine?

Endocrine signals use the circulatory system to transport ligands through the blood to distant cells, while paracrine signaling acts on neighboring cells. Thus, this is the key difference between endocrine and paracrine. Hormones in endocrine signaling usually are diluted and are present in lower concentration when acting on target cells, while in paracrine signaling, the concentration of ligands is very high. Moreover, the response in endocrine signaling is quick, while paracrine signaling shows a slower response.

The below infographic presents the differences between endocrine and paracrine in tabular form for side by side comparison.

Summary – Endocrine vs Paracrine

Cells usually communicate through chemical signals. Endocrine and paracrine are two types of chemical signaling. Endocrine signals use the circulatory system to transport ligands through the blood to distant cells. On the other hand, paracrine signaling acts on neighboring cells. An endocrine system is composed of many glands, which release hormones. These hormones are released directly into the blood circulatory system and regulate distant target organs. This process is known as endocrine signaling. Paracrine signals move by diffusion through the extracellular matrix. Endocrine signals produce a slower response, but they have a long-lasting effect, while paracrine signals usually respond quickly but last only for a shorter period of time. So, this summarizes the difference between endocrine and paracrine.

Reference:

1. “Introduction to Cell Signaling.” Khan Academy.
2. “Paracrine Signalling.” An Overview | ScienceDirect Topics.

Image Courtesy:

1. “1801 The Endocrine System” By OpenStax College – Anatomy & Physiology, Connexions Web site, Jun 19, 2013. (CC BY 3.0) via Commons Wikimedia
2. “Figure 09 01 01” By CNX OpenStax – (CC BY 4.0) via Commons Wikimedia