Let’s explore the fascinating world of the human body with our guide on secretion vs excretion. Uncover the intricate processes of how living organisms manage internal substances, and discover the key differences between secretion and excretion.

LOCATION:

• Secretion typically occurs in specialized cells or glands equipped with the machinery to synthesize and release specific substances, such as salivary glands, digestive glands, etc.
• Excretion primarily occurs in organs and structures specifically designed for waste removal, such as the kidneys, lungs, skin, and intestines.

 READ MORE: ”Hormones vs Neurotransmitters: Battle Of The Signals”

 NATURE OF SUBSTANCE:

• The substances secreted in Secretion are usually complex molecules such as enzymes, hormones, mucus, saliva, and digestive juices.
• The substances excreted in the process of Excretion are typically waste products resulting from metabolic processes, excess substances, or toxic materials that need to be eliminated from the body, including tears, sweat, urine, and faeces.

FUNCTION:

• Secretion serves various purposes, including maintaining homeostasis, facilitating digestion, lubrication, communication between cells, and regulating body functions.
• Excretion plays a crucial role in maintaining homeostasis by removing substances that could be harmful if accumulated, regulating electrolyte balance, and controlling the body’s fluid composition.

PROCESS:

• In Secretion, the substances are synthesized within the secretory cells, often in response to specific stimuli, and then transported to the cell membrane or distinct storage compartments. They are released through exocytosis (vesicles fusing with the cell membrane) or diffusion.
• In Excretion, waste substances are collected and filtered by excretory organs. They are then processed and eliminated from the body via various routes, such as urine through the kidneys, carbon dioxide through the lungs, excess water and electrolytes through sweat, and undigested food through the intestines.

VARIOUS TYPES:

                                                  SECRETION

• Endocrine Secretion:

This involves the release of hormones directly into the bloodstream by endocrine glands. Hormones travel throughout the body to regulate various physiological processes and maintain homeostasis.

• Exocrine Secretion:

Exocrine glands release substances through ducts that lead to body surfaces or cavities. Examples include sweat, salivary, and digestive glands like the pancreas.

• Holocrine Secretion:

In this type of secretion, entire cells filled with secretory products disintegrate and release their contents. The skin’s Sebaceous (oil) glands are an example of holocrine secretion.

• Merocrine (Eccrine) Secretion:

This is the most common type of exocrine secretion, where cells release their products via exocytosis without losing cellular material. Examples include sweat glands and certain salivary glands.

• Apocrine Secretion:

This type of secretion involves the release of cytoplasm and secretory products from the apical portion of the cell. Apocrine sweat glands are an example.

                                                   EXCRETION

• Renal Excretion:

The kidneys filter waste products and excess substances from the blood to form urine, which is then excreted from the body.

• Pulmonary Excretion:

The lungs help remove carbon dioxide from the body during exhalation, a waste product of cellular respiration.

• Gastrointestinal Excretion:

The digestive system eliminates waste products through defecation. Undigested food, fibre, and other indigestible substances are excreted as faeces.

• Skin Excretion:

 The skin excretes small amounts of waste products, such as water, salts, and urea, through sweat glands. Sweating also helps regulate body temperature.

• Liver Excretion:

The liver is involved in excretion by producing bile, which contains waste products like bilirubin. Bile is then released into the intestines and eventually eliminated from the body through faeces.

• Biliary Excretion:

This involves the excretion of waste products and certain substances from the liver into the bile, which is then eliminated through the digestive tract.

ROLE IN THE BODY:

• The substance of Secretion contributes to the metabolism of the body.

• Excretion mainly contributes to the elimination of the body’s wastes.

EXAMPLE:

• Salivary glands secrete saliva-containing enzymes for digestion and endocrine glands like the pituitary gland. The thyroid gland secretes hormones into the bloodstream, and mucous cells secrete mucus to lubricate surfaces.
• Kidneys excrete waste products like urea and excess ions through urine, lungs excrete carbon dioxide during respiration, and skin excretes sweat containing metabolic waste products.

PATHWAYS FOR THE PROCESS OF SECRETION:

• LYSOSOMAL PATHWAY: 

These organelles play an essential role in the biological secretion process. Many categorized cell types, like blood stem cells and pigment cells, specifically use the lysosome secretory pathway. Lysosomes, (secretory vesicles) fuse with the membrane of the cells to discharge their contents. However, the fusion process requires numerous different types of proteins.

• TRANSPORT THROUGH MEMBRANE: 

In some instances, cytoplasm proteins migrate through the cell membrane by transporter proteins. The products are not packed in vesicles in these cases; they are bound to specific proteins and transported through the cell membrane.

• POROSOMES AND GOLGI PATHWAY: 

The products to be secreted are initially manufactured in the endoplasmic reticulum and then transported into the vesicles known as transport vesicles made up of lipid bilayer. These products are then recast in the Golgi apparatus before being packaged into a specialized secretory vesicle.

PATHWAYS FOR THE PROCESS OF EXCRETION:

• RENAL PATHWAY: 

The kidneys are responsible for removing metabolic wastes and foreign particles from the body and monitoring the water volume and the concentration of various ions within the body. Renal arteries are responsible for the blood supply to the kidneys. Glomerular filtration removes waste compounds from the blood and enters the nephron. Later Tubule reabsorption process is used to bring combinations within the filtrate into the blood.

•  HEPATIC PATHWAY: 

The liver is a significant organ of excretion. It is responsible for the breakdown of many substances, including toxins. The liver is an effective site for compound metabolism. The purpose of metabolism is to form metabolites that are more water soluble and polarized so they can easily be eliminated from the kidneys. It usually involves Phase 1 reaction facilitated by Cytochrome P450 enzymes, along with Phase 2 reaction involving the conjugation of the modified compounds from Phase I reactions with various endogenous molecules, such as glucuronic acid, sulfate, amino acids (like glycine and taurine), and glutathione. After it reaches the digestive system and is eliminated from the body.

The respiratory system is also an essential pathway of excretion by eliminating carbon dioxide (CO2) and small amounts of other volatile waste products through exhalation. During cellular respiration, carbon dioxide is produced from the cells of the whole body, which diffuses into the blood and reaches the lungs. Through the alveoli, it becomes expelled from the body. By expelling carbon dioxide from the blood, the lungs help maintain acid-base homeostasis.

 

CONCLUSION:

In every human being, there is a formation of waste products which are no longer needed by the body, and if they remain in the body results in toxification. These waste products are formed due to metabolic and catabolic reactions. Both secretion and excretion are essential for the body as secretion is responsible for maintaining various body functions by secreting hormones and enzymes. In contrast, excretion is necessary for eliminating waste products of the body.