🧠 Endocrine System & Hormones

Endocrine System

A chemical communication network that uses hormones to regulate physiological processes.

What is the primary function of hormones?

To act as chemical messengers affecting physiology and behavior at distant sites.

Endocrine Signaling

Hormones travel via blood to distant targets.

Paracrine Signaling

Signals act on neighboring cells.

Autocrine Signaling

Signals act on the same cell that released them.

Synaptic Signaling

Neurons release neurotransmitters directly to a target cell.

Neuroendocrine Signaling

Neurons release hormones into the bloodstream.

Tropic Hormones

Hormones that stimulate other glands to release hormones.

Non-tropic Hormones

Hormones that act directly on target tissues.

Releasing Hormones

Hormones that stimulate the anterior pituitary to release other hormones.

Release-inhibiting Hormones

Hormones that block the release of other hormones.

Peptide/Protein Hormones

Water-soluble hormones that act on cell surface receptors and are fast-acting.

Steroid Hormones

Lipid-soluble hormones that cross membranes and act on nuclear receptors, slower but longer-lasting.

Amine Hormones

Hormones derived from amino acids, with varying properties.

Hypothalamus

The master controller of the endocrine system, sending releasing hormones.

Pituitary Gland

The gland that releases tropic and direct hormones, often referred to as the master gland.

Thyroid Gland

The gland that regulates metabolism.

Adrenal Glands

Glands that are responsible for the stress response, producing cortisol and adrenaline.

Pancreas

An endocrine gland that regulates blood sugar levels through insulin and glucagon.

Gonads

The reproductive glands (ovaries in females, testes in males) that produce sex hormones.

Negative Feedback

A regulatory mechanism that reduces hormone output in response to a stimulus.

Positive Feedback

A mechanism that amplifies a response, such as oxytocin during childbirth.

Castrated Rats vs. Intact Rats

Castrated rats have no gonadal hormones, leading to high levels of LH and FSH due to lack of negative feedback.

ELISA

A biochemical assay used to detect and quantify antigens or antibodies.

Steps of a Sandwich ELISA

1. Capture antibody binds antigen; 2. Add sample; 3. Add detection antibody; 4. Add enzyme-linked secondary antibody; 5. Add substrate for color change.

What does a high signal in a positive control during ELISA indicate?

It indicates that reagents are functioning properly.

False Positives in ELISA

Results caused by non-specific binding or cross-reactivity with similar antigens.

False Negatives in ELISA

Results caused by low antigen/antibody levels or expired/inactive reagents.

Antigens

Molecules recognized as foreign that can trigger an immune response.

Antibodies

Y-shaped immune proteins produced by B cells that bind specifically to antigens.

How does CoV-19 spread easily?

High viral shedding before symptoms, aerosol transmission, and a high mutation rate in spike proteins.

Color Change in ELISA

Indicates the presence of the target antigen or antibody.

Why is feedback regulation essential in the endocrine system?

To prevent overproduction and maintain internal balance.

Action Potential Phases

1. Resting Potential; 2. Depolarization; 3. Repolarization; 4. Hyperpolarization; 5. Return to Resting.

Ion flow during depolarization of an action potential

Na⁺ channels open, allowing Na⁺ influx and making the membrane more positive.

Role of the enzyme in ELISA

Converts substrate to a colored product for detection.

How do steroid hormones differ from peptide hormones?

Steroid hormones are lipid-soluble and act on nuclear receptors, while peptide hormones are water-soluble and act on cell surface receptors.

What is the role of the adrenal glands in the endocrine system?

They manage the body's stress response and acute responses.