Chapter 6 Endocrine system biol 1720

Stimulus

A factor that triggers a change in a specific activity within the body.

Response

The change in activity triggered by a stimulus.

Endocrine system

A system that uses hormones (signaling molecules) released into the bloodstream to coordinate physiological responses.

Nervous system

Uses neurons to transmit electrical signals to specific locations in the body.

Endocrine glands

Groups of cells that secrete hormones into the circulatory system.

Exocrine glands

Secrete substances through ducts (e.g., sweat glands, salivary glands).

Hormones

Signaling molecules that regulate physiological processes and maintain homeostasis.

Target cells

Cells with receptors for a specific hormone; only these cells respond to the hormone.

Receptor

A protein that binds to a specific hormone in a lock-and-key mechanism, triggering a cellular response.

Water-soluble hormones

Secreted by exocytosis, travel freely in the bloodstream, and bind to cell-surface receptors.

Lipid-soluble hormones

Diffuse across cell membranes, travel in the bloodstream bound to transport proteins, and diffuse through the membrane of target cells to bind to cytoplasmic or nuclear receptors.

Hypothalamus

Controls most neuroendocrine signaling in mammals; often triggers the pituitary gland.

Posterior pituitary

Stores and secretes hormones produced by the hypothalamus (e.g., ADH, oxytocin).

Anterior pituitary

Synthesizes and secretes its own hormones.

Neurosecretory cells

Hypothalamic cells that produce neurohormones.

Neurohormones

Hormones released by neurosecretory cells (e.g., ADH, oxytocin).

ADH (Antidiuretic Hormone)

Targets kidney tubules to regulate water reabsorption.

Oxytocin

Targets mammary glands (stimulates milk release) and uterine muscles (stimulates contractions during labor).

Thyroid gland

Secretes hormones that control the basal metabolic rate and regulate calcium (Ca²⁺) levels.

Adrenal glands

Secrete glucocorticoids (e.g., cortisol) for stress response and epinephrine for "fight-or-flight" response.

Gonads

Sex hormones

Pineal gland

Secretes melatonin to regulate sleep-wake cycles.

Parathyroid glands

Secrete parathyroid hormone (PTH) to regulate calcium and phosphate levels.

Pituitary gland

The "master gland" that controls other endocrine glands by secreting hormones like growth hormone (GH), prolactin, ACTH, TSH, FSH, and LH.

Feedback loops

Built-in control systems that regulate hormone levels and maintain homeostasis.

Negative feedback

response to a signaling pathway reduces the stimulus for its activation

Positive feedback

response reinforces a stimulus to increase the response

TRH (Thyroid-Releasing Hormone)

Secreted by the hypothalamus in response to low thyroid hormone levels; stimulates the anterior pituitary.

TSH (Thyroid-Stimulating Hormone)

Secreted by the anterior pituitary in response to TRH; stimulates the thyroid gland.

Thyroid hormone

Secreted by the thyroid gland in response to TSH; increases metabolic rate.

Endocrine regualtion

1. Release of acidic stomach contents into duodenum stimulates endocrine cells there to secrete hormone secretin

2. Secretin targets pancreatic cells and causes them to raise the pH in the duodenum

Another example of endocrine regulation

1. Suckling stimulates neurons in nipples to send signal to hypothalamus

2. Hypothalamus causes release of oxytocin from posterior pituitary

3. Oxytocin stimulates further milk release

Hormone cascade

release of other hormones

Epinephrine

secreted by adrenal glands and can:
Raise blood glucose, Increase air flow into the lungs,Decrease blood flow to the digestive system

What is the normal blood sugar

70–110 mg glucose/100 mL blood; the target range for healthy blood sugar regulation.

Type 1 diabetes

Autoimmune disorder, immune system destroys the pancreatic beta cells 

Type 2 diabetes

1. Failure of target cells to respond normally to insulin. Heredity is a factor; excess body weight and lack of exercise increase risk

Glucose homeostasis

1. Blood glucose level increases( such as after eating)
   
   
   2. Secreation of insulin by beta cells of pancreas
   
   3. Beta cells→Cells in the pancreas that secrete insulin in response to high blood glucose levels.
   
   
   4. Insulin→Hormone secreted by beta cells of the pancreas when blood glucose levels rise (e.g., after eating); promotes transport of glucose into body cells and storage of glucose as glycogen in the liver and muscles.

5. Transport of glucose into body cells and storage of glucose into glycogen

6. blood glucose levels falls
   
   7. normal blood glucose (70-110 mg glucose/ 100 ml blood)

8. Blood glucose level decreases (such as after fasting)

9. secreation of glucagon by alpha cells of the pancreas

10. Glucagon→Hormone secreted by alpha cells of the pancreas when blood glucose levels decrease (e.g., after fasting); stimulates the breakdown of glycogen and release of glucose into the blood.

    
    11. Breakdown of glycogen and release of glucose into blood.

12. Blood glucose levels rises
    
    13. goes back to normal blood glucose (70-110 mg glucose/ 100 ml blood)
    

Neurosecretory cells of the hypothalamus

Specialized cells in the hypothalamus that produce neurohormones.

Neurohormones

Hormones produced by neurosecretory cells and transported via axons to the posterior pituitary.

Axons

Nerve fibers that transport neurohormones from the hypothalamus to the posterior pituitary.

Posterior pituitary

Stores and secretes neurohormones (ADH and oxytocin) produced by the hypothalamus.

ADH (Antidiuretic Hormone)

Neurohormone secreted by the posterior pituitary; targets kidney tubules to regulate water reabsorption.

Oxytocin

Neurohormone secreted by the posterior pituitary; targets mammary glands (stimulates milk release) and uterine muscles (stimulates contractions during labor).

Kidney tubules

Target of ADH; site of water reabsorption to maintain fluid balance.

Mammary glands

Target of oxytocin; stimulated to release milk.

Uterine muscles

Target of oxytocin; stimulated to contract during labor.

Hypothalamic releasing and inhibiting hormones

Hormones secreted by the hypothalamus that regulate the anterior pituitary via the portal vessels.

Portal vessels

Blood vessels that connect the hypothalamus to the anterior pituitary, carrying releasing and inhibiting hormones.

Endocrine cells of the anterior pituitary

Cells that produce and secrete anterior pituitary hormones in response to hypothalamic signals.

Anterior pituitary hormones

Hormones synthesized and secreted by the anterior pituitary (e.g., FSH, LH, TSH, ACTH, Prolactin, MSH, GH).

FSH (Follicle-Stimulating Hormone)

Anterior pituitary hormone; targets testes or ovaries; tropic effects only.

LH (Luteinizing Hormone)

Anterior pituitary hormone; targets testes or ovaries; tropic effects only.

TSH (Thyroid-Stimulating Hormone)

Anterior pituitary hormone; targets the thyroid gland; tropic effects only.

ACTH (Adrenocorticotropic Hormone)

Anterior pituitary hormone; targets the adrenal cortex; tropic effects only.

Prolactin

Anterior pituitary hormone; targets mammary glands; nontropic effects only.

MSH (Melanocyte-Stimulating Hormone)

Anterior pituitary hormone; targets melanocytes; nontropic effects only.

GH (Growth Hormone)

Anterior pituitary hormone; targets liver, bones, and other tissues; has both tropic and nontropic effects.

Testes or ovaries

Target organs for FSH and LH; regulate reproductive function.

Thyroid gland

Target organ for TSH; regulates metabolism and growth.

Adrenal cortex

Target organ for ACTH; regulates stress response and cortisol secretion.

Mammary glands

Target for prolactin; stimulates milk production.

Melanocytes

Target for MSH; stimulates melanin production in skin cells.

Liver, bones, other tissues

Targets for GH; promotes growth and metabolism.

Tropic effects only

Hormones that stimulate other endocrine glands to secrete their hormones (e.g., FSH, LH, TSH, ACTH).

Nontropic effects only

Hormones that directly affect non-endocrine target tissues (e.g., Prolactin, MSH).

Tropic and nontropic effects

Hormones with both direct and indirect actions (e.g., GH stimulates liver to produce IGF-1 and directly affects tissues).