Why are lipase that found in saliva and the stomach not very effective at digestion?

Lipases found in saliva and the stomach are not very effective at digestion primarily due to the following reasons:

1. Saliva:

- pH Sensitivity: The pH of saliva is typically around 6.8-7.4, which is slightly alkaline. Lipases generally have an optimal pH range for activity, and most salivary lipases are most active at a pH closer to neutral or slightly acidic. The alkaline pH of saliva can reduce the enzymatic activity of lipases.

- Limited Substrate Accessibility: Salivary lipase is present in low concentrations and does not effectively emulsify dietary fats. Fats in the diet are often present in large globules, and salivary lipase cannot efficiently access and break down these fats.

2. Stomach:

- Low pH: The stomach has a highly acidic environment, with a pH ranging from 1 to 2. Most lipases are not stable or active at such low pH levels. The acidic conditions in the stomach can denature and inactivate lipases, impairing their ability to digest fats.

- Presence of Proteases: The primary function of the stomach is to initiate protein digestion. The stomach secretes proteolytic enzymes such as pepsin, which break down proteins. Lipases require a neutral or slightly acidic pH for optimal activity, but the presence of these proteases and the acidic environment can hinder lipase activity.

- Limited Fat Emulsification: The stomach does not produce bile salts, which are essential for the emulsification of dietary fats. Bile salts help disperse fat into smaller droplets, increasing the surface area available for lipases to work on. Without proper emulsification, lipases have difficulty accessing and digesting fats.

Therefore, salivary and gastric lipases play a limited role in fat digestion compared to the pancreatic lipase that is secreted into the small intestine. Pancreatic lipase operates at a more suitable pH and is aided by bile salts, allowing for efficient digestion and absorption of dietary fats.