Hormones and the Endocrine System

Page
7

This is an example of positive feedback, where the stimulus leads to an even greater response

Antidiuretic hormone (ADH) enhances water reabsorption in the kidneys

Slide 46

A simple neurohormone pathway

Suckling

Pathway

Stimulus

Hypothalamus/ posterior pituitary

Positive feedback

Example

Sensory neuron

Neurosecretory cell

Blood vessel

Posterior pituitary secretes oxytocin ( )

Target cells

Response

Smooth muscle in breasts

Milk release

+

Slide 47

Anterior Pituitary Hormones

Hormone production in the anterior pituitary is controlled by releasing and inhibiting hormones from the hypothalamus

For example, the production of thyrotropin releasing hormone (TRH) in the hypothalamus stimulates secretion of the thyroid stimulating hormone (TSH) from the anterior pituitary

Slide 48

Production and release of anterior pituitary hormones

Hypothalamic releasing and inhibiting hormones

Neurosecretory cells of the hypothalamus

HORMONE

TARGET

Posterior pituitary

Portal vessels

Endocrine cells of the anterior pituitary

Pituitary hormones

Tropic effects only: FSH LH TSH ACTH

Nontropic effects only: Prolactin MSH

Nontropic and tropic effects: GH

Testes or ovaries

Thyroid

FSH and LH

TSH

Adrenal cortex

Mammary glands

ACTH

Prolactin

MSH

GH

Melanocytes

Liver, bones, other tissues

Slide 49

Hormone Cascade Pathways

A hormone can stimulate the release of a series of other hormones, the last of which activates a nonendocrine target cell; this is called a hormone cascade pathway.

The release of thyroid hormone results from a hormone cascade pathway involving the hypothalamus, anterior pituitary, and thyroid gland.

Hormone cascade pathways are usually regulated by negative feedback.

Slide 50

Cold

Pathway

Stimulus

Blood vessel

Example

Sensory neuron

Hypothalamus secretes thyrotropin-releasing hormone (TRH )

Neurosecretory cell

A hormone

casade

pathway

Slide 51

Cold

Pathway

Stimulus

Hypothalamus secretes thyrotropin-releasing hormone (TRH )

Example

Sensory neuron

Neurosecretory cell

Blood vessel

+

Anterior pituitary secretes

thyroid-stimulating

hormone (TSH

or thyrotropin )

A hormone

casade

pathway

Slide 52