Glucagon, Somatostatin, Cortisol and melatonin

Glucagon

A hormone released by alpha cells of the pancreas to raise blood glucose levels when they are too low.

• main function is to rause glucose levels, the opposite of insulin.

Glycogenolysis

The breakdown of glycogen into glucose in the liver, stimulated by glucagon.

What are the main effects of glucagon on the liver and adipose tissue?

It stimulates glycogen breakdown (glycogenolysis) and the creation of glucose (gluconeogenesis), pulling in amino acids from the blood to help make glucose.

• in adipose tissue, glucgon promotes lipolysis (breakdown of fats) releasing fatty acids into the blood for energy use

When is glucagon released?

During hypoglycemia (low blood sugar), after a high-protein meal, and after intense exercise—even if blood glucose is normal.

Insulin effects

somatostatin

Somatostatin is secreted by delta cells in the islets of Langerhans. Its release is stimulated by increased levels of blood glucose, amino acids, fatty acids, and gastrointestinal hormones released after eating.

• Within the islets, somatostatin inhibits the release of both insulin and glucagon, helping regulate the balance between the two hormones.

How does somatostatin affect digestion?

Somatostatin slows the movement of the stomach, duodenum, and gall bladder, and decreases secretion and absorption in the digestive tract, prolonging the availability of nutrients.

How is somatostatin related to growth hormone regulation?

Somatostatin is also known as growth hormone inhibitory hormone (GHIH) which is produced in the hypothalamus and suppresses the release of growth hormone from the anterior pituitary.

Cortisol

A glucocorticoid hormone that increases gluconeogenesis, raises blood glucose levels, and slightly reduces glucose use by body cells.

How does cortisol increase gluconeogenesis at the cellular level?

Cortisol enters liver cell nuclei, activates DNA transcription to produce mRNA, which leads to the creation of enzymes needed for gluconeogenesis.

How does cortisol affect glucose usage by other body cells and blood glucose levels?

Cortisol slightly decreases how much glucose most cells use (the exact reason is unknown). Together with its effect of increasing glucose production, this leads to higher blood sugar levels, which can cause adrenal diabetes when cortisol is abnormally high.

How does cortisol affect protein levels in most body cells (excluding the liver)?

Cortisol lowers protein levels by breaking down existing proteins and slowing new protein production. It reduces amino acid uptake and decreases RNA production in muscle and immune cells.

• Cortisol decreases protein by limiting amino acid entry and RNA production, causing muscle weakness and reduced immune function when cortisol is high.

• Cortisol causes protein breakdown in non-liver cells, releasing amino acids into blood, which the liver then uses for protein synthesis and gluconeogenesis.

How does cortisol affect protein levels in the liver?

Cortisol increases protein levels in the liver by helping more amino acids enter liver cells, leading to increased production of plasma proteins.

CONSENSUS:

• Liver cells: Cortisol increases protein levels. It does this by helping more amino acids enter liver cells, so the liver can make more plasma proteins and enzymes (including those for gluconeogenesis).

• Non-liver cells (like muscle and immune cells): Cortisol decreases protein levels by both breaking down existing proteins and reducing new protein synthesis. This happens because cortisol lowers amino acid uptake and reduces RNA production in these cells.

How does cortisol affect fatty acids in the blood?

Cortisol helps release fatty acids from fat tissue, increasing free fatty acids in the blood for energy use. Cortisol reduces glucose uptake, so the body breaks down fat for energy instead.

What role does d α-glycerophosphate play in fat cells, and how does cortisol affect it?

d α-glycerophosphate is needed to form and maintain triglycerides in fat cells; cortisol reduces its availability, causing fat cells to release fatty acids.

Why do people with excess cortisol still have fat deposits in areas like chest and head?

Cortisol may increase appetite, causing extra eating that leads to fat buildup in some areas faster than fat is broken down.

Release of cortisol in stress

• All types of stress like trauma, anxiety, infection, temperature extremes will cause the release of cortisol. 

• Cortisol makes glucose, amino acids and free fatty acids available as sources of energy - but its specific role in stress is unknown. 

anti-inflammatory effects of cortisol

It works by blocking the early stages of inflammation and if it has already began, it will cause rapid resolution of the inflammation and increase the speed of healing. 

1. The anti-inflammatory effects are due to the following effects:

2. Stabilizes lysosomes – Cortisol keeps the membranes of lysosomes (tiny enzyme-containing structures in cells) intact, preventing them from releasing proteolytic enzymes that cause inflammation when cells are damaged.

3. Reduces capillary leakiness – It makes capillaries (tiny blood vessels) less leaky, preventing plasma from escaping into surrounding tissues. This leakiness is usually caused by enzymes or histamine.

4. Limits white blood cell activity – Cortisol reduces the movement of white blood cells into the inflamed area and decreases how much phagocytosis (engulfing of damaged cells) occurs.

5. Suppresses the immune response – Cortisol lowers the number of T lymphocytes (T cells) and antibodies in the inflamed area, which reduces the tissue damage caused by the immune response.

6. Lowers fever – It reduces the release of interleukin-1 from white blood cells, which helps lower body temperature and, in turn, reduces vasodilation (widening of blood vessels), easing inflammation.

• it doesnt correct the basic disease, and in some cases inhibting inflammaion is dangoruous.

• it is usually combined with antibitoics to treat respiratory infections

Cortisol’s effects on allergy

Cortisol blocks bad inflammation in allergies, preventing anaphylaxis and stopping histamine release from mast cells in asthma, without affecting the initial antigen-antibody reaction.

What hormones regulate cortisol release?

Cortisol release is mainly controlled by ACTH from the anterior pituitary, which is stimulated by CRF and ADH from the hypothalamus.

• ACTH activates adenyl cyclase in adrenal cortex cells, producing cAMP that triggers cortisol synthesis. Cortisol then inhibits CRF and ACTH release via negative feedback to regulate its own levels.

Melatonin

Melatonin is secreted by the pineal gland and regulates the sleep-wake cycle, with secretion inhibited by light.

• Melatonin influences the pituitary-gonad axis to time fertility in seasonal breeders (stimulates in short day breeders, inhibits in long day breeders). In humans, excess melatonin can delay puberty onset.