Negative Feedback Mechanisms in Endocrine System: Blood Glucose, Calcium, Cortisol, Thyroid, Water Balance, and Reproductive Hormones

What is negative feedback?

A process where the body's response reverses the original change to maintain homeostasis.

What is the main purpose of negative feedback in the endocrine system?

To keep hormone levels and body conditions within a normal range.

What hormone is released when blood glucose is too high?

Insulin

What does insulin do?

It causes cells to take up glucose and promotes glucose storage, causing blood glucose to decrease.

What is the insulin negative-feedback loop?

↑ Blood glucose → ↑ insulin → glucose uptake/storage → ↓ blood glucose → ↓ insulin

What hormone is released when blood glucose is too low?

Glucagon

What does glucagon do?

It causes the liver to release glucose into the blood, causing blood glucose to increase.

What is the glucagon negative-feedback loop?

↓ Blood glucose → ↑ glucagon → liver releases glucose → ↑ blood glucose → ↓ glucagon

Why are insulin and glucagon called antagonistic hormones?

They have opposite effects: insulin lowers blood glucose, while glucagon raises it.

What hormone is released when blood calcium is too low?

Parathyroid hormone (PTH)

What does PTH do?

It increases blood calcium levels.

What is the PTH negative-feedback loop?

↓ Blood calcium → ↑ PTH → ↑ blood calcium → ↓ PTH

What hormone helps lower high blood calcium?

Calcitonin

What is the calcitonin negative-feedback loop?

↑ Blood calcium → ↑ calcitonin → ↓ blood calcium → ↓ calcitonin

Which two hormones have opposing effects on blood calcium?

PTH and calcitonin

Which gland produces cortisol?

The adrenal cortex.

What is the HPA axis?

Hypothalamus → Pituitary → Adrenal cortex

What hormone does the hypothalamus release to start the cortisol pathway?

CRH

What hormone does the anterior pituitary release in response to CRH?

ACTH

What does ACTH do?

It stimulates the adrenal cortex to release cortisol.

What is the cortisol pathway?

Hypothalamus → CRH → Pituitary → ACTH → Adrenal cortex → Cortisol

How does cortisol create negative feedback?

High cortisol levels inhibit the hypothalamus and pituitary, decreasing CRH and ACTH release.

What is the cortisol negative-feedback loop?

↑ Cortisol → ↓ CRH → ↓ ACTH → ↓ cortisol production

What hormone does the hypothalamus release to start the thyroid pathway?

TRH

What hormone does the pituitary release in response to TRH?

TSH

What does TSH do?

It stimulates the thyroid gland to produce T3 and T4.

What do T3 and T4 do?

They help regulate metabolism and other body processes.

What is the thyroid hormone pathway?

Hypothalamus → TRH → Pituitary → TSH → Thyroid → T3/T4

How do T3 and T4 provide negative feedback?

High T3/T4 levels reduce TRH and TSH release, which decreases thyroid stimulation.

What is the thyroid negative-feedback loop?

↑ T3/T4 → ↓ TRH + ↓ TSH → ↓ T3/T4 production

What happens to ADH when the body is dehydrated?

ADH increases.

What does ADH do?

It causes the kidneys to reabsorb more water, keeping water in the body.

What is the ADH negative-feedback loop?

↓ Body water → ↑ ADH → ↑ water reabsorption → ↑ body water → ↓ ADH

What is the basic reproductive hormone pathway?

Hypothalamus → GnRH → Pituitary → FSH/LH → Gonads → Sex hormones

How do sex hormones usually provide negative feedback?

Higher levels of sex hormones generally reduce GnRH, FSH, and LH, preventing hormone levels from continuously increasing.