Hormone Classification lec 2

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Questions and Answers

What is a characteristic of receptor-enzymes?

They act via a G protein and intracellular second messenger.

They have intrinsic enzymatic activity. (correct)

They are only found on the cell surface.

They are only activated by steroids.

What happens to the receptor-hormone complex after activation?

It is released back into the bloodstream.

It stays on the cell surface permanently.

It is broken down immediately.

It is endocytosed into the cell and then recycled or broken down. (correct)

What is the function of kinases in peptide signaling?

To phosphorylate and inactivate the receptor (correct)

To produce a second messenger

To break down the hormone

To activate the receptor

Which of the following is NOT a class of hormones?

Lipids Signup and view all the answers

What is a characteristic of peptide hormones?

They are water-soluble. Signup and view all the answers

What type of receptors do peptide hormones bind to?

Receptor-enzymes Signup and view all the answers

What is the effect of altering sensitivity to other chemical messengers on the synthesis of cellular receptors?

Increased synthesis of cellular receptors for progesterone Signup and view all the answers

What is the solubility of peptide hormones?

Water-soluble Signup and view all the answers

What is the primary function of the signal peptide in peptide hormone synthesis?

To cleave off the N-terminal of prohormone Signup and view all the answers

What is the typical half-life of peptide hormones?

Several minutes Signup and view all the answers

What is the primary mechanism of peptide hormone secretion?

Exocytosis Signup and view all the answers

What is the primary effect of peptide hormone binding to receptors in the target cell's membrane?

Modification of existing proteins Signup and view all the answers

What is the characteristic of glycoprotein hormones?

Protein + carbohydrate Signup and view all the answers

What is the typical amino acid sequence of peptide hormones?

Approximately 3-40 amino acids Signup and view all the answers

What is the mechanism of secretion of steroid hormones in response to pulsatile signals from pituitary hormones?

Secreted in pulses (bursts) Signup and view all the answers

Why do steroid hormones circulate in blood bound to carrier proteins?

To protect them from degradation Signup and view all the answers

What is the average half-life of steroid hormones?

Several hours Signup and view all the answers

How do steroid hormones enter cells according to the conventional model?

Simple diffusion across plasma membranes Signup and view all the answers

What is the effect of steroid hormones on gene transcription?

Affect gene transcription Signup and view all the answers

Where are steroid hormone receptors typically located?

Cell nucleus or cytoplasm Signup and view all the answers

What is the function of co-activator proteins in steroid hormone action?

Enhance transcriptional effects Signup and view all the answers

What is the 'Free Hormone Hypothesis'?

Only unbound hormone molecules can enter target cells Signup and view all the answers

Where is the hormone from neurosecretory cells stored?

Posterior pituitary Signup and view all the answers

What is the function of Vasopressin (AVP) in the kidney?

Increase water retention Signup and view all the answers

What is the effect of Oxytocin on the uterus?

Trigger smooth muscle contractions Signup and view all the answers

What is released in response to an increase in blood osmolarity?

Vasopressin Signup and view all the answers

What is the effect of Oxytocin on milk letdown?

Trigger smooth muscle contractions Signup and view all the answers

What is the effect of Vasopressin within the brain?

Increase aggression and social bonding Signup and view all the answers

What is a characteristic that catecholamines, such as norepinephrine, epinephrine, and dopamine, have in common?

They are water-soluble. Signup and view all the answers

Which of the following hormones is lipid-soluble?

Thyroid hormones Signup and view all the answers

What is the function of the hypothalamus in the endocrine system?

To integrate information from many parts of the brain and regulate endocrine control Signup and view all the answers

What is the posterior pituitary also known as?

Neurohypophysis Signup and view all the answers

Which nuclei of the hypothalamus are involved in the synthesis of hormones stored in the posterior pituitary?

Paraventricular nucleus and supraoptic nucleus Signup and view all the answers

What is the function of the posterior pituitary?

To store and secrete hormones Signup and view all the answers

Which hormone is synthesized in the paraventricular nucleus and stored in the posterior pituitary?

Vasopressin Signup and view all the answers

What is the connection between the hypothalamus and the pituitary gland?

Pituitary stalk Signup and view all the answers

Study Notes

Alteration of Sensitivity to Other Chemical Messengers

Estradiol (E) increases the synthesis of cellular receptors for progesterone and some neurotransmitters.

Classes of Hormones

A. Peptides: Water-soluble
B. Steroids: Lipid-soluble
C. Amines:
- 1. Catecholamines: Water-soluble (NE, EPI, dopamine)
- 1. Indoleamines (Serotonin, melatonin)
- 1. Thyroid hormones: Lipid-soluble (Triiodothyronine, tetraiodothyronine)

Peptide Hormones

Structure:
- Includes most hormones
- Amino acid sequence can vary among species
- Peptide hormones: ~3-40 amino acids
- Polypeptide/protein hormones: ~50-200 amino acids
- Glycoproteins: protein + carbohydrate
Synthesis & Storage:
- Water-soluble
- Synthesized as preprohormone
- Signal peptide is cleaved off N-terminal → prohormone
- Enzymatic processing of prohormone → ≥1 hormone
- Hormone (or prohormone + enzyme) is stored in secretory vesicle & eventually expelled from the cell
Secretion, Transport, & Metabolism:
- Released in bursts by exocytosis
- Dissolve in plasma
- Bind to receptors in a target cell’s membrane
- Rapidly degraded (by peptidases) or excreted
- Half-life is around several minutes (short-lived)
Receptors:
- Embedded in plasma membrane of target cell
- Binding of hormone leads to changes inside cell
- Modify existing proteins (e.g., membrane channels, metabolic enzymes, transport proteins) → rapid response
- May affect synthesis of new proteins → slow response
- Two major types of receptor complexes:
  1. Receptor-enzymes
  2. G protein-coupled receptors (GPCRs)

Peptide Hormone Receptors

1. Receptor-enzymes:
- Have intrinsic enzymatic activity
- Binding of hormone activates enzyme on cytoplasmic side → series of reactions within cell
1. G protein-coupled receptors (GPCRs):
- Act via a G protein and intracellular second messenger (e.g., cAMP)

Activation and Termination of Peptide Signaling

1. Receptor is activated by ligand; hormone has its effect on the cell
1. Receptor is phosphorylated by kinases (inactivation, desensitization)
1. Hormone-receptor complex is endocytosed (internalized) into cell
1. Receptor is recycled or broken down

Steroid Hormones

Transport:
- Not soluble in plasma; circulate in blood bound to carrier proteins/binding proteins (CPs)
- Thought to be inactive while bound to CPs
- Free Hormone Hypothesis: Only unbound (free) hormone molecules can enter target cells
Metabolism:
- Carrier proteins protect steroids from degradation
- Inactivated in liver
- Half-life is about several hours (comparatively long-lived hormones)
Entry into Cells:
- Conventional Model: simple diffusion across plasma membranes
- New Hypothesis: facilitated diffusion via transporters
“Classical” Actions:
- Bind to receptors in target cell cytoplasm or nucleus
- Affect gene transcription (slow response)
- Co-activator proteins may be necessary for transcriptional effects

The Hypothalamus & the Pituitary

Hypothalamus:
- At base of brain; comprises many distinct nuclei
- Integrates info from many parts of brain
- Important in behavioral drives, emotions, biological rhythms, homeostasis, & endocrine control
Pituitary Gland(s):
- Connected to hypothalamus by pituitary stalk (infundibulum)
- Anterior and posterior pituitary are developmentally, anatomically, and functionally distinct organs

Posterior Pituitary (neurohypophysis/pars nervosa)

Develops as an outgrowth of the brain
Made of brain tissue (neural)
Contains axon terminals of neurosecretory cells originating in two nuclei of hypothalamus:
- Paraventricular nucleus (PVN)
- Supraoptic nucleus (SON)
Stores and secretes two peptide hormones synthesized in PVN and SON:
- Vasopressin (AVP), or antidiuretic hormone (ADH)
- Oxytocin (OT)

Posterior Pituitary: Hormones Secreted

1. Vasopressin (AVP) = Antidiuretic Hormone (ADH):
- Acts on kidney to increase water retention (decrease diuresis)
- Acts on blood vessels to increase vasoconstriction
- Released in response to increase blood osmolarity, decrease blood volume, or decrease blood pressure
- Also released within brain to increase aggression, paternal behavior, and social bonding
1. Oxytocin (OT):
- Acts on uterus to trigger smooth muscle contractions which induce/progress labor
- Acts on breasts to trigger smooth muscle contractions and induce milk letdown
- Also released within brain to increase social bonding, trust, empathy, and maternal behavior

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Description

Learn about the different classes of hormones, including peptides, steroids, and amines, and how they interact with chemical messengers and receptors.