Feedback Loops

homeostasis

regulation that keeps an internal condition constant regardless of external environment

The primary control center of homeostasis is the

hypothalamus, since it links with pituitary gland to control homeostasis of numerous physiological states

How does the hypothalamus function in homeostasis?

it acts like a thermostat signaling hormonal and autonomic nervous system responses when internal conditions deviate from the set point

How does the hypothalamus regulate temperature?

it detects changes in temperature and triggers appropriate responses to maintain balance

What is a negative feedback loop?

system that helps return a variable to its normal range or a steady-state set point when internal conditions are disrupted

What happens in a negative feedback loop?

Signal is "inverted" to reverse the change, preventing excessive responses.

Biological examples of negative feedback loops

thermoregulation and blood glucose regulation

How does thermoregulation work?

if body temperature is too high, mechanisms activate to cool the body

How does the body regulate high blood sugar in a negative feedback loop?

insulin lowers glucose (from beta cells) by increasing uptake

How does the body regulate low blood sugar in a negative feedback loop ?

glucagon raise glucose (from alpha cells) by stimulating the breakdown of stored glycogen

What is a positive feedback loop?

Loop that amplifies a physiological response instead of reversing it

What happens if a positive feedback loop does not stop?

It can be pathological unless an external signal breaks the loop

• External signal breaker = circuit breaker

Biological example of positive feedback loops

childbirth, blood clotting, and lactation

How does positive feedback work in childbirth?

the baby’s head presses on the cervix, signaling the release of oxytocin, which causes stronger contractions, repeating until birth

How does blood clotting work as a positive feedback loop?

Platelets release signals to attract more platelets, continuing until a clot forms

How does lactation work as a positive feedback loop?

Baby suckling triggers oxytocin release, stimulating more milk release, continuing until baby stops feeding

What are the three ways endocrine glands can be stimulated to secrete hormones?

• Humoral stimuli

• Neural stimuli

• Hormonal stimuli

Humoral stimuli

caused by altered blood levels of certain critical ions/nutrients

Neural stimulus

caused by neural input

Hormonal stimulus

caused by another hormone (e.g tropic hormone)

tropic hormone

hormone that acts indirectly by stimulating other endocrine glands to release hormones

Example of tropic hormone

TSH signals the thyroid to release T3 and T4

non-tropic hormone

hormone that acts directly by stimulating a response in a non-endocrine gland

example of a non-tropic hormone

insulin acts on cells to promote glucose uptake

Pituitary gland

major endocrine gland that works under the control of the hypothalamus

What are the two lobes of the pituitary gland?

anterior and posterior

What is the function of the posterior pituitary?

stores and secretes hormones that are made in the hypothalamus

• made up of neural tissue

• not a true endocrine gland

What is the function of the anterior pituitary?

Makes and releases its own hormones

• Made of glandular endocrine tissue

• True endocrine gland

Hormones released by the posterior pituitary

• oxytocin

• antidiuretic hormone (ADH)

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Hormones released by the anterior pituitary:

• adrenocorticotropic hormone (ACTH)

• thyroid-stimulating hormone (TSH)

• follicle-stimulating hormone (FSH)

• growth hormone (GH)

• luteinizing hormone (LH)

• prolactin (PRL)

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Example Tropic Hormones

• Thyroid-stimulating hormone (TSH)

• Adrenocorticotropic hormone (ACTH)

• Follicle-stimulating hormone (FSH)

• Lutienzing Hormone (LH)

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Examples Non-tropic hormones

• Antidiuertetic Hormone (ADH)

• Prolactin (PRL)

• Oxytocin

• growth hormone (GH)

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Growth hormone (GH) has both

tropic and non-tropic effects