Endocrine I

Homeostasis

The conceptual framework for the study & understanding of physiology, describing the relative stability of the internal environment despite changes in the external environment.

Walter Cannon

The person who coined the term 'homeostasis'.

Key components of homeostatic control systems

Include a sensor that constantly monitors, an integrating center that coordinates, and a response system that changes.

Negative feedback loop

A mechanism in homeostasis where most systems operate to return a physiological variable to its normal range after a shift.

Major regulatory systems

Include the skin, cardiovascular, renal, digestive, respiratory, and musculo-skeletal systems.

Regulated factors in homeostasis

Factors such as water, electrolytes/pH, nitrogenous compounds, oxygen, carbon dioxide, temperature, and toxicants that are maintained.

Endocrine system

Maintains homeostasis largely through hormone regulation and the actions of various endocrine glands.

Endocrine dysfunctions

Include conditions like hyper-function (too much hormone), hypo-function (too little hormone), and resistance (too little effect).

Endocrine gland

A tissue that releases (secretes) substances into the blood stream, which then influence target cells.

Minkowski experiment

An experiment in 1889 involving surgically removing the pancreas from a dog, leading to diabetes symptoms which were preventable by implanting pancreatic pieces.

Banting & Best experiment

In 1921, identified an antidiabetic substance in pancreatic extracts that prevented symptoms of diabetes when injected.

Insulin

A peptide hormone produced by beta cells of the pancreas that promotes glucose absorption.

Main function of insulin

To promote the absorption of glucose from blood to skeletal muscle & fat tissue.

Chemical categories of hormones

Proteins & polypeptides, steroids (cholesterol derivatives), glycoproteins, and amines (catecholamines or thyroid).

Three levels of hormone effect

Autocrine, paracrine, and endocrine.

Peptide hormones secretion mode

Synthesized in advance, stored in secretory vesicles, released via exocytosis, dissolved in plasma for transport, with a short half-life.

Steroid hormones secretion mode

Synthesized on demand, not stored in vesicles, released via diffusion, bound to carrier proteins for transport, with a long half-life.

Thyroid hormones secretion mode

Synthesized in advance, stored in secretory vesicles, released via exocytosis, bound to carrier proteins for transport, with a long half-life.

Catecholamines secretion mode

Synthesized in advance, stored in secretory vesicles, released via exocytosis, dissolved in plasma for transport, with a short half-life.

Hormone binding to receptors

Shows high specificity for a particular hormone and a continuous turn-over of the receptor-hormone complex.

Receptors for most hormones

Located in the plasma membrane of target cells.

Receptors for steroid & thyroid hormones

Located inside the target cells.

Transmembrane receptors mechanism for peptide hormones

Bind extracellularly, activating cytoplasmic signaling pathways often involving phosphorylation & enzyme activation.

Adenylate cyclase pathway

A signaling pathway involving G-proteins, leading to the production of cAMP and a hormonal response.

Epinephrine example

An example of a hormone that uses the adenylate cyclase pathway by binding to the β–adrenergic receptor on liver cells.

Role of G protein-coupled receptors

Proteins that facilitate cell signaling networks, allowing cells to sense their environments.

Phospholipase C-Ca2+ pathway

Involves activation of PLC, leading to the release of Ca2+ from the endoplasmic reticulum and a hormonal response.

Alpha vs beta-adrenergic receptors

Alpha-adrenergic receptors activate phospholipase C, while beta-adrenergic receptors activate adenylate cyclase.

Steroid hormone receptors mechanism of action

Binding to cytoplasmic receptors, translocating to the nucleus, and acting as transcription factors to stimulate gene transcription.

Thyroid hormone receptors mechanism of action

Involves T4 being converted to T3, entering the nucleus, and binding to DNA to stimulate new mRNA and protein synthesis.