Week 18: Endocrine System I

Comprehensive practice flashcards covering the structured lecture on the Endocrine System, including hormone types, mechanisms of action, and glandular functions.

What are the three primary long-term processes regulated by the endocrine system?

Growth, development, and reproduction.

What are the three chemical types of hormones classified by structure?

1. Amino acid derivatives, 2. Peptide hormones, and 3. Lipid derivatives.

Which two amino acids are the precursors for amino acid derivative hormones?

Tyrosine and tryptophan.

Give examples of hormones derived from tyrosine.

Thyroid hormones such as Thyroxine ($T_4$), and catecholamines such as Epinephrine ($E$), Norepinephrine ($NE$), and Dopamine.

Which hormone is a derivative of tryptophan and which gland secretes it?

Melatonin, which is secreted by the pineal gland.

What characterizes peptide hormones?

They consist of chains of amino acids and represent the largest class of hormones.

What are the two classes of lipid-based hormones?

Steroid hormones (structurally similar to cholesterol) and eicosanoids (derivatives of arachidonic acid).

Where are the two primary locations for hormone receptors in a target cell?

On the cell membrane and inside the cell (cytoplasm or nucleus).

Which types of hormones bind to receptors on the cell membrane?

Non-lipid soluble hormones, including catecholamines (epinephrine and norepinephrine), all peptide hormones, and eicosanoids.

What is the role of $cAMP$ in hormonal action via cell membrane receptors?

It acts as a second messenger that activates kinase enzymes to alter enzyme activity or open ion channels.

Which enzyme converts ATP to $cAMP$ when a G protein is activated?

Adenylate cyclase.

Which enzyme is responsible for the breakdown of $cAMP$ in the cytoplasm?

Phosphodiesterase ($PDE$).

Which types of hormones bind to intracellular receptors?

Steroid hormones and thyroid hormones.

What is the mechanism of action for steroid hormones once they bind to their receptor?

The hormone-receptor complex binds to DNA to trigger gene activation, transcription ($mRNA$ production), and translation (protein synthesis).

How long do free hormones typically remain functional in circulation?

Less than $1$ hour.

Why do thyroid and steroid hormones remain in circulation much longer than free hormones?

Because more than $99\%$ of them are attached to special transport proteins, creating a substantial reserve of bound hormones.

List the hormones produced by the anterior lobe of the pituitary gland.

Adrenocorticotropic hormone ($ACTH$), Thyroid-stimulating hormone ($TSH$), Growth hormone ($GH$), Prolactin ($PRL$), Follicle-stimulating hormone ($FSH$), Luteinizing hormone ($LH$), and Melanocyte-stimulating hormone ($MSH$).

Which two hormones are released (but not produced) by the posterior lobe of the pituitary gland?

Antidiuretic hormone ($ADH$) and Oxytocin ($OXT$).

What is the function of the hypophyseal portal system?

It delivers regulatory hormones from the hypothalamus directly to the anterior lobe of the pituitary gland.

How does the hypothalamus provide direct control over the adrenal gland?

Through neural control (sympathetic output) to the adrenal medullae to stimulate the secretion of catecholamines.

What are the direct effects of Growth Hormone ($GH$) on tissues?

It stimulates cell division in epithelial and connective tissue, triglyceride breakdown in adipocytes, and glycogen breakdown in the liver.

What substance does Growth Hormone ($GH$) trigger the liver to release?

Somatomedins, such as Insulin-like Growth Factors ($IGFs$), which stimulate tissue growth and protein synthesis.

What are the primary hormones secreted by the adrenal cortex?

Cortisol, corticosterone, aldosterone, and androgens.

Commonly, how is endocrine secretion regulated to maintain homeostasis?

Via negative feedback mechanisms.

What are the risks of anabolic steroid use in females?

Facial hair, male pattern baldness, and cessation of menstrual cycles.