Hormones and Endocrine System Overview

Hormones and Endocrine System

• The endocrine system and nervous system work together to coordinate and complement responses to changes in the environment.
• Hormones are chemical messengers that circulate in the bloodstream, regulating energy use, metabolism, and growth.
• Hormones maintain homeostasis.
• They are secreted into the bloodstream by ductless endocrine glands, reaching all parts of the body via bloodstream, and affecting target cells.
• A small amount of hormones produces a significant effect.
• Hormones have different receptors in different cells.
• This leads to different responses within different cells and tissues (e.g. vasoconstriction versus vasodilation).
• Two major communication systems: nervous & endocrine.
• Endocrine effects are slower than nervous system effects, but their effects are more widespread and last longer.

Types of Hormones

• Three main types of hormones exist:
  • Proteins (water-soluble): Examples include insulin and glucagon.
  • Amines (either water or lipid soluble): Synthesized from amino acids (usually tyrosine). Example is adrenaline.
  • Steroids (lipid soluble): Examples include cortisol, estrogen, and progesterone.

Lipid-Soluble Hormones

• Pass through the target cell membrane.
• Bind to an intracellular receptor.
• The hormone-receptor complex binds to DNA, which turns specific genes on or off.
• This leads to the synthesis of new proteins.

Water-Soluble Hormones

• Bind to receptors on the cell membrane target cell.
• Receptor protein activates a signal-transduction pathway.
• A series of relay molecules transmit the signal.
• A cellular response occurs.

Adrenaline and Glucose Release

• Adrenaline (epinephrine) stimulates release of glucose.
• This is controlled via the G protein-coupled receptor.
• Adenylyl cyclase is activated, leading to cAMP production and activation of protein kinases.
• In turn, glycogen synthesis is inhibited, and glycogen breakdown is promoted, ultimately releasing glucose.

Control of Glucose

• Insulin and glucagon are antagonistic hormones.
• Negative feedback mechanisms control glucose levels in the blood.
• Glucose levels in blood trigger the release of insulin and glucagon in the pancreas.
• The pancreas comprises alpha and beta cells.
  • Alpha cells produce glucagon.
  • Beta cells produce insulin.
• Elevated blood glucose triggers insulin release, promoting blood glucose uptake in the blood.
• Decreased blood glucose triggers glucagon release, promoting glucose release into the blood.

Steroid Hormones and Gene Expression

• Steroid hormones regulate gene expression.
• Receptors are located in the cytosol.
• Hormone-receptor complex, conformational change, nuclear translocation activates gene transcription and production of proteins.

Mechanisms Controlling Hormone Release

• Specific metabolites in the blood (e.g., glucose).
• Other hormones in the blood (e.g., TSH, thyroid-stimulating hormone).
• Stimulation of neurons (using the autonomic nervous system) e.g. adrenaline.

Pituitary Gland and Hypothalamus

• The pituitary gland has anterior and posterior parts.
• The anterior pituitary releases hormones that regulate many processes in the body.
• The hypothalamus controls the release of anterior pituitary hormones.
  • Special network blood vessels connect the hypothalamus and anterior pituitary.
  • Hypothalamus produces stimulatory/inhibitory hormones.
• The hypothalamus synthesizes and secretes ADH & oxytocin into the posterior pituitary for release into bloodstream via vesicles.

Posterior Pituitary

• Hormones made in the hypothalamus are stored and transported in vesicles in the posterior pituitary.
• These hormones are released into the bloodstream.
• Positive feedback involved (e.g., suckling during breastfeeding).

The Anterior Pituitary

• Special network blood vessels carry hormones from the hypothalamus (releasing hormones) to the anterior pituitary for hormone secretion.
• Hormones produced or regulated in anterior pituitary include TSH, ACTH, FSH, LH, GH, Prolactin, Endorphins.

The Thyroid

• The thyroid gland secretes thyroid hormone (T3 and T4).
• Regulates heart rate, muscle tone, bioenergetics (energy in cells), digestive and reproductive function.

Control of Thyroxine Secretion

• Negative feedback mechanisms regulate the release of thyroxine (T3 and T4).
• If the body is cold, the hypothalamus secretes TRH.
• The anterior pituitary gland in turn releases TSH, triggering the thyroid gland to release T3 and T4.
• Increased levels of T3 and T4 have a negative effect on the hypothalamus and anterior pituitary, reducing TSH and TRH release back to original levels.

Hypothyroidism and Goitre

• Insufficient thyroid hormone production can cause hypothyroidism.
• Insufficient iodine for the synthesis of thyroid hormones can result in enlarged thyroid gland (goitre).
• Leads to weight gain, lethargy, and cold intolerance.

Hyperthyroidism

• Constant production and release of thyroid hormones result in hyperthyroidism.
• Characterized by weight loss, tremors, sweating, hyperactivity and Graves' ophthalmology.

Summary

• Two communication systems: nervous & endocrine; endocrine releases are slower, more widespread, and longer lasting.
• Main hormone types: steroid and non-steroid, with different modes of action (e.g. lipid versus water soluble).
• Hormone levels controlled by negative feedback.
• The hypothalamus controls pituitary secretions using nervous and hormonal control.

Classification of Diabetes

• Type 1 diabetes: an autoimmune attack, managed with insulin (genetic risk).
• Type 2 diabetes: metabolic disorder, managed via treatment and lifestyle (lifestyle and genetic risk).
• Gestational diabetes: special case of type 2 diabetes, temporary during pregnancy.

Diabetes Burden

• Diabetes is a severe worldwide healthcare issue.
• Prevalence varies by region.
• Millions undiagnosed.
• Diabetic complications place significant financial and health burdens on healthcare systems.

Metabolic Syndrome

• Cluster of disorders, increasing risk of type 2 diabetes and cardiovascular disease.
• Includes obesity, insulin resistance, and hyperglycaemia.

Cardiovascular Disease Research

• Researchers study high blood pressure and other blood vessel issues using systems biology approaches.
• VSMC (vascular smooth muscle cells) are focus, especially how they interact with myeloid cells.

SysVasc Consortium

• A project (2014-2017) involving translational systems biology, identifying targets for disease treatment.

Type 2 Diabetes

• A complex multifactorial disease with multiple symptoms, risk factors and organs involved.

T2D Metabolic Context

• T2D is increasingly recognised as a component of the metabolic syndrome, linked to increased adipose tissue, insulin resistance and hyperglycaemia.

Insulin Sensitivity of Skeletal Muscle

• Insulin signals initiate intracellular signalling pathways resulting in glucose uptake and glycogen synthesis in skeletal muscles.

Link between Diabetes, Obesity and Cancer

• The Lancet Diabetes and Endocrinology (2018) study shows a link among diabetes, obesity and increased cancer incidence.

Explore the basics of the endocrine system and its interplay with the nervous system. This quiz covers types of hormones, their functions, and how they regulate bodily processes. Test your knowledge on the essential roles hormones play in maintaining homeostasis and communication within the body.