The Endocrine System

Question 1

Define homeostasis and explain its importance

Answer 1

• Homeostasis is the tendency to maintain a balance or constant internal rate
• The reason why homeostasis is important is because it maintains certain conditions to ensure that the organisms can function. If organisms or cells cannot function normally, then the organism can get sick and die
• Homeostasis is not a steady state but happens at a dynamic equilibrium, failure for homeostasis leads to disease.

Question 2

Define ‘hormone’, name the chemical classes of hormones and identify the major endocrine glands and the hormones they produce

Answer 2

• Hormone are chemical signals secreted by the endocrine glands or tissues that travel in the bloodstream to cause an effect on other tissue
• Endocrine system- is the collection of glands that produce hormones that regulate metabolism, growth and development, tissue function, sexual function, reproduction, sleep, and mood, among other things.

• Chemical classes of hormones:

1. peptide/ polypeptide:
   • Largest group
   • Short chains of amino acids
   • All water soluble
   • E.g: insulin, glucagon, growth hormone
2. Amino acid derivatives (amines):
   • Synthesised from aromatic amino acids
   • Adrenal medulla hormones are water soluble
   • Thyroid hormones are lipid soluble
   • E.g: adrenaline, noradrenaline, thyroid hormones
3. Glycoproteins:
   • Large protein molecule
   • Often made of subunits
   • Has a carbohydrate side chain
   • All water soluble
   • E.g: luteinising hormone, follicle stimulating hormone
4. Steroids:
   • They all derived from cholesterol
   • steroidogenic tissues convert the cholesterol into different hormones
   • All lipid soluble
   • e.g: cortisol, testosterone

Major endocrine glands and hormones that they produce:
• Hypothalamus: luteinising hormone, prolactin releasing hormone
• Pituitary gland: growth hormone, follicle stimulating hormone
• Thyroid gland: thyroxine, calcitonin
• Parathyroid: parathormone (PTH)
• Adrenal gland: aldosterone, adrenaline, noradrenaline
• Pancreas: glucagon, insulin, somatostatin
• Pineal gland: melatonin
• Ovary: oestrogen and progesterone
• Testis: testosterone

Question 3

Understand the concepts of negative and positive feedback

Answer 3

• Negative feedback: response in a way to reverse the direction of change it usually form of feedback in psychological systems
• Positive feedback: response in a way to change the variable even more in the direction of change. Used when rapid changes are desperate e.g: blood clotting and ovulation
• Negative feedback regulation of secretion of hormones:

Question 4

Understand the relationship between the hypothalamus and pituitary gland (anterior & posterior)

Answer 4

• The hypothalamus and pituitary gland form a complex FUNCTIONAL UNIT that serves the major link between the endocrine and nervous systems.
• The processes that the hypothalamus and pituitary gland modulates are:
• Body growth
• Reproduction
• Milk secretion
• Lactation
• Adrenal gland function
• Thyroid gland function
• Water homeostatis
• Puberty

• The pituitary gland consists of:
1. Anterior pituitary gland
2. Posterior pituitary gland
They both have distinct embryological origins and distinct features

• Function of posterior pituitary gland:
See pic

• Function of anterior pituitary gland:
See pic

• The hormones produced by nerve cells in the hypothalamus act via two distinct neurocrine pathways
1. direct effect on distant target tissue via oxytocin and antidiuretic hormone from posterior pituitary
2. hormones secreted exclusively into hypophyseal portal system affect endocrine cells within the anterior pituitary

• What are the two hormones produced in the hypothalamus for release from posterior pituitary?
• OT - oxytocin
• ADH - antidiuretic hormone

Question 5

Describe how hormones are transported, how they act on cells and how hormone secretion is controlled

Answer 5

• some hormones travel in the blood in simple solution
• Most hormones must bind to proteins and it’s often specific proteins
• Water soluble hormones bind to cell surface receptors
• Lipid soluble hormones bind to intracellular receptors
• Liver has transport proteins
• bind to lipid soluble molecules and allows these molecules to travel through
• hormone attaches to transport protein is called bound hormone

Three ways that hormone secretion can be controlled:
2. Rate of production: synthesis and secretion (the most highly regulated aspect of hormonal control)
3. Rate of delivery: higher blood flow to a particular organ will deliver more hormone
4. Rate of degradation: hormones are then metabolised and excreted from the body

Question 6

Understand common conditions related to the endocrine system