response to starvation

Definition

Target type: biologicalprocess

Any process that results in a change in state or activity of a cell or an organism (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of a starvation stimulus, deprivation of nourishment. [GOC:go_curators]

Response to starvation is a complex and highly regulated process that involves a coordinated series of physiological and metabolic adaptations to ensure survival in the absence of sufficient nutrients. When an organism is starved, it experiences a decline in energy stores and nutrient availability, triggering a cascade of signaling pathways that aim to conserve energy, mobilize nutrient reserves, and maintain vital functions.

**1. Nutrient Sensing and Signaling Pathways:**

* **Insulin/IGF-1 signaling (IIS) pathway:** This pathway is downregulated during starvation, leading to a decrease in protein synthesis and an increase in autophagy.
* **mTOR pathway:** The mechanistic target of rapamycin (mTOR) pathway is inhibited during starvation, promoting autophagy and reducing protein synthesis.
* **AMPK pathway:** The AMP-activated protein kinase (AMPK) pathway is activated by an increase in AMP levels, which occurs during starvation. AMPK promotes catabolic processes like fatty acid oxidation and glucose uptake.
* **PPARα pathway:** Peroxisome proliferator-activated receptor alpha (PPARα) is activated by starvation, promoting the breakdown of fatty acids for energy production.

**2. Metabolic Adaptations:**

* **Glucose sparing:** The organism prioritizes the use of alternative energy sources, such as fatty acids and ketone bodies, to conserve glucose for vital organs like the brain.
* **Gluconeogenesis:** The liver increases the production of glucose from non-carbohydrate sources, such as amino acids and glycerol.
* **Ketogenesis:** The liver produces ketone bodies from fatty acids, providing an alternative energy source for the brain and other tissues.
* **Lipolysis:** Stored triglycerides in adipose tissue are broken down into fatty acids and glycerol, providing energy and substrates for gluconeogenesis.
* **Proteolysis:** Proteins are broken down into amino acids, which can be used as fuel or for gluconeogenesis.

**3. Cellular Adaptations:**

* **Autophagy:** This process involves the degradation of cellular components, including damaged organelles and proteins, providing building blocks for new molecules and energy.
* **Cell cycle arrest:** Starvation can trigger cell cycle arrest, preventing unnecessary cell division and conserving energy.
* **Increased lifespan:** In some organisms, starvation can extend lifespan by reducing oxidative stress and promoting cellular repair.

**4. Behavioral Changes:**

* **Increased food-seeking behavior:** Starvation drives organisms to actively search for food sources.
* **Reduced physical activity:** To conserve energy, organisms may become less active.

**5. Hormonal Changes:**

* **Increased glucagon and cortisol levels:** These hormones promote glucose production and protein breakdown.
* **Decreased insulin levels:** Insulin promotes glucose uptake and storage, which is reduced during starvation.

**6. Organ-Specific Adaptations:**

* **Brain:** The brain adapts to utilize ketone bodies as an energy source during prolonged starvation.
* **Muscle:** Muscle protein breakdown is increased to provide amino acids for gluconeogenesis.
* **Adipose tissue:** Fat stores are mobilized to provide fatty acids for energy.
* **Liver:** The liver plays a central role in regulating metabolism during starvation, producing glucose, ketone bodies, and amino acids.

The specific mechanisms and adaptations involved in response to starvation can vary depending on the organism, the duration of starvation, and the nutritional state of the individual. However, the overall goal is to ensure survival by conserving energy, mobilizing nutrient reserves, and maintaining vital functions until food becomes available again.'
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Proteins (13)

Compounds (324)