Lesson 1: General Principles of Hormone and Hypothalamic-pituitary axis

What is the endocrine system?

A series of glands or isolated cells that produce chemical messengers called hormones.

How do hormones travel throughout the body?

Through the bloodstream to reach target cells

What are the chemical messengers of the nervous system?

neurotransmitters

What type of hormone is derived from cholesterol?

Steroid

What type of hormone is composed of several amino acids?

Peptides

What type of hormone is derived from a single amino acid?

Amine

What type of cells do the endocrine glands consist of?

Ductless glandular epithelial cells

Where do endocrine glands secrete hormones?

Directly into the bloodstream

What is a chemical messenger that is produced by endocrine glands or cells that is released into the bloodstream to regulate various physiological processes in the body?

Endocrine Hormones

What functions do hormones influence?

Metabolism, Growth, Reproduction, and Homeostasis

What are the two types of hormone signaling?

Autocrine signaling and Paracrine signaling

What type of hormone signaling is a cell secreting a hormone or signaling molecule that binds to receptors on its own surface?

Autocrine signaling

What type of signaling is a cell releasing hormone or signaling that affects nearby cells?

Paracrine signaling

What are the two ways that hormones can travel through the bloodstream?

Bound to a transporter protein or unbound (free)

What type of hormone travels freely in the blood?

Water-soluble hormones (peptides)

What type of hormone is often bound to a carrier protein in the blood?

Lipid-soluble hormones (steroids)

How long will a hormone travel through the bloodstream?

Until they bind to their target cells or they are broken down and deactivated

What are the cells that have a specific protein receptor design to bind with hormones?

Target cells

What are the two types of receptors?

Cell-surface receptors and intracellular receptors

What type of receptors are located on the plasma membrane of target cells?

Cell-surface receptors

What type of hormone do cell surface receptors bind to?

water soluble hormones

How do cell surface receptors work?

The binding of a hormone activates intracellular signaling pathaways via a second messenger such as cAMP or Ca+ ions

What type of receptors are located in the cytoplasm or nucleus of target cells?

Intracellular receptors

What type of hormone do intracellular receptors bind to?

Lipid soluble hormones

How do intracellular receptors work?

Once bound they often regulate gene expression, creating new proteins, that can change metabolic pathways

What are the three types of cellular responses to hormones?

Metabolic changes

Change in gene expression

Cell division or differentiation

What type of cellular response is the activation or inhibition of enzymes involved in a specific metabolic pathway?

Metabolic changes

What type of cellular response is the generation of specific transcription factors can modify the expression of specific genes?

Change in gene expression

What type of cellular response is caused by stimulating cell growth or division tissues can grow?

Cell division or differentiation

How long does the effect that hormones have normally have take?

minutes, hours, or even days

What type of hormone is usually transported in blood by carrier proteins?

Steroid hormones (lipid soluble)

Do steroid hormones have a longer or shorter half life?

Longer because the protein binding protects against quick degradation in the liver.

Why can steroid hormones enter through the phospholipid bilayer?

They are lipid-soluble

What type of hormone moves freely through the bloodstream?

Peptide/protein

Do peptide/protein hormones have a longer or shorter half life?

Shorter because they are easily degraded and excreted due to being free roaming

Why can peptide/protein travel freely through the blood?

They are water soluble and easily dissolve in plasma

What type of hormones are derived from only one amino acid, typically tyrosine and trytophan?

Amine Hormones

What hormone is the smallest?

The amine hormones

What type of receptor does the amine hormones use?

Cell-surface hormones

What is the exception to the cell surface receptor rule of the amine hormones?

Thyroid hormones since they have intracellular receptors

How can thyroid hormones have intracellular receptors if they are water-soluble?

They are so small that they can pass through the phospholipid bilayer

What type of hormones are a group of bioactive lipid compounds derived from arachidonic acid and other fatty acids?

Eicosanoids

What type of hormone are produced by the enzymatic action of cyclooxygenases (COX) and lipoxygenases (LOX)?

Eicosanoid hormones

Do Eicosanoids have cell-surface receptors or intracellular receptors?

Eicosands have cell-surface receptors

How does the synthesis of any type of hormone occur?

Appropriate stimulus to the endocrine gland

When the appropriate stimulus is applied to the endocrine gland what will initiate?

Transcription of genes that codify for hormone gene

Where is the active hormone stored in the cell?

In the vesicles

For the synthesis of steroid hormones what happens when the stimulus is applied to the endocrine gland?

The activation of a series of enzymes that will sequentially convert cholesterol into a precursors until the hormone is formed.

What is the first step involved in synthesis of steroid hormones?

Conversion of cholesterol to pregnenolone

Where does the conversion of pregnenolone take place in the cell?

In the mitochondria

Do steroid hormones need stored in the cell?

No because they are produced so quickly they don’t need to store them

Describe the mechanism of action of Peptide hormones?

1. Hormone binds to cell surface receptor

2. It activates or inhibits enzymes inside the cell

3. If activated a second messenger increase in the cytosol

4. Triggering a signaling cascade to activate or inhibit enzymes

5. The enzymes regulate key metabolic pathways

Describe the Mechanism of action of steroid hormones?

1. Hormones diffuse freely across the cell membrane

2. Binding to intracellular receptors

3. The hormone receptor complex binds to nuclear DNA

4. Alters gene transcription and protein synthesis

5. Resulting in enzymes that regulate metabolic pathways

What are the two configuration of a negative feedback loop in the endocrine system?

Hypothalamic-pituitary-endocrine axis feedback

Physiological response-driven configuration

What type of configuration of a feedback loop is a linear list showing the hypothalamus represents the first level, the pituitary the second level, and the endocrine gland the third.

Hypothalamic-pituitary-endocrine axis feedback

What type of configuration of a feedback loop is a circular diagram in which the secretion of hormones is stimulated or inhibited by a change in the level of a specific extracellular parameter.

Physiological response-driven configuration

What does the hypothalamic neuroendocrine neurons secrete?

Releasing hormones

What does the releasing hormones from the hypothalamic neuroendocrine neurons stimulate?

The pituitary gland

When stimulated what are the hormones called that are secreted by the pituitary gland?

Tropic hormone

Where is the tropic hormones released?

From the pituitary into the systemic circulation

What does the tropic hormones stimulate?

Peripheral endocrine glands

Hormones from what endocrine glands travel to the target organs?

Hormones from the peripheral endocrine gland

If there is to much hormone from the peripheral endocrine gland, how does it stop?

Negative feedback loop to the either the pituitary or the hypothalamus to stop producing their hormones.

What are metabolic pathways?

Chemical reactions in metabolism are organized into metabolic pathways

What are the two types metabolic pathways?

Catabolism

Anabolism

What is Catabolism?

Taking a large molecule such as a protein and transforming it into a smaller molecule such as an amino acid.

What is the result of catabolism?

Production of energy/heat

What are examples of mobilization of energy through catabolism?

Glycolysis

Proteolysis

Lipolysis

Glycogenolysis

What is Anabolism?

Taking small molecules and using energy to make large molecules such as storing fat and making new proteins.

What are examples of storage of energy through anabolism?

Glycogenesis

Lipogenesis

How is glucose important for the bodies metabolism?

ATP is the fuel of the body

Glucose is the preferred fuel for all tissues

What are the glucose dependent tissues?

CNS

RBCs

retina

renal medulla

fetus

lactation

How does the body maintain adequate concentration of blood glucose?

Eating, digesting, and absorbing glucose in the GI tract

Storing glucose in the form of glycogen in the liver and muscle

Releasing glucose from glycogen when needed

Synthesis of new glucose from precursors

What is glycogenesis?

Creation of glycogen from glucose

What is glycogenolysis?

The process in which glycogen is broken down into glucose-6-phosphate via an enzyme Glucose-6-Phosphates.

What is gluconeogenesis?

Creation of new glucose from precursors

What are the gluconeogenic precursors?

Amino acids

Glycerol

Lactate

Propionate in ruminates

Where does glycogenesis occur in the body?

Primarily in the liver and the muscle

How is glycogenesis stimulated?

Stimulated by high glucose concentrations and Insulin

Where does Glycogenolysis occur in the body?

in both the liver and the muscles.

In which cells does glycogenolysis use Glucose-6-phosphate to make glucose?

Liver cells

How is glycogenolysis stimulated during fasting?

low levels of glucose stimulate glucagon secretion and with the help of epinephrine and cortisol it stimulates glycogenoslysis.

What is lipogenesis?

The conversion of excess glucose and amino acids into free fatty acids (FFA) into fat tissue.

Where does lipogenesis occur in the body?

in the liver or mammary glands

Is the liver used for fat storage?

No

What does the liver do with the fat?

It repackages FFAs in the form of triglycerides as very low-density lipoproteins and secretes them into circulation

What is lipolysis?

Stored triglycerides in adipocytes are broken down by Hormone Sensitive Lipase into FFA and Glycerol.

How is HSL stimulated?

Glucagon, Epinephrine, and Cortisol

Describe the process of Beta oxidation and how it can cause ketoacidosis?

Excess FFA in the liver enter beta oxidation, resulting in more acetyl COA.

Accumulating acetyl CoA is condensed into Acetoacetic acid, acetone, and beta-hydroxybutyrate, which causes ketone bodies. In excess, ketone bodies can cause ketoacidosis.

What is the process by which the amino group is removed from the amino acid, forming a keto analogue and ammonia?

Deamination

What is it when an amino group transfers are catalyzed by intracellular enzymes referred to as aminotransferases: ALT and AST

Transamination

What is the livers role in deamination?

The livers role is to excrete the excess ammonia

How does excess ammonia from deamination harm the body?

Ammonia is highly toxic, particularly to the CNS, so it must be rapidly converted by the liver into urea.

Why is it important that ammonia is converted into urea?

Since Ammonia is toxic it is not safe for the kidneys to excrete, once its converted it will be safe.

In response to stimuli how does the hypothalamus coordinate the activities of various tissues and organs?

Through both the endocrine and ANS

How does the hypothalamus exert control over the endocrine system?

Through the pituitary

How does the hypothalamus communicate with the anterior pituitary?

Through the portal system that allows the releasing/inhibiting hormones to reach the pituitary

What are the releasing hormones produced by the hypothalamus?

TRH (Thyrotropin-releasing hormone)

CRH (Corticotropin-releasing hormone)

GHRH (Growth hormone-releasing hormone)

GnRH (Gonadotropin-releasing hormone)

PRH (Prolactin-releasing hormone)

What are the inhibiting hormones that are released from the hypothalamus?

GHIH (Growth hormone-inhibiting hormone) → Inhibits GHRH

Dopamine → Inhibits Prolactin

What tropic hormone is stimulated by TRH?

TSH (Thyroid-stimulating hormone)