Living Control Mechanisms Dr Kate Earp MBChB MRCP Specialty Registrar Chemical Pathology & Metabolic Medicine kate.earp@sth.nhs.uk 15/10/2015 Contents Aims & objectives Homeostasis Cell communication Introduction to endocrine system Endocrine glands Feedback loops Types of hormone Examples of endocrine disease 1
Aims Consider the nature of homeostasis Describe how cells message each other Describe how signals can be amplified Describe a simple feedback loop Give an overview of the endocrine system Consider the difference between peptide and steroid hormones Consider some examples of abnormal signalling loops (ie. Endocrine diseases) Diseases caused by failure of endocrine communication Thyroid disease Diabetes Acromegaly Cushing s 2
Homeostasis Definition; maintenance of a constant internal environment Examples Temperature Blood pressure ph Glucose Oxygen concentration Energy production & demand 3
Control Systems Homeostasis Cells must communicate with each other to achieve homeostasis Major communication systems Endocrine Nervous Immune 4
Methods of Cell Communication Cell Signal Cell receives the signal. In biology this is done through a receptor. Types of Signals Hormones Signals Electrical Ions 5
Types of Communication Autocrine Paracrine Endocrine Autocrine Cell Cells talking to themselves. 6
Paracrine Cell Cells talking to neighbouring cells a short distance away. Signal diffuses across gap between cells Inactivated locally, so doesn t enter the blood stream Cell Paracrine Example Acetylcholine at neuromuscular junctions Nerve ending Acetylcholine Neuromuscular junction Muscle 7
Endocrine Endocrine Cell Cells talking to other cells elsewhere in the body. Blood Hormone Target Cell Endocrine Organs Hypothalamus Pituitary Thyroid Parathyroid Adrenals Pancreas Ovaries Testes 8
Hypothalamus & Pituitary Endocrine System Hypothalamus 6 main hormones Anterior Pituitary 6 main hormones Endocrine Gland Target Tissue 9
Hypothalamic Hormones Gonadotrophin-releasing hormone (GnRH) Growth hormone-releasing hormone (GHRH) Somatostatin (SS) Thyrotropin-releasing hormone (TRH) Corticotropin-releasing hormone (CRH) Dopamine (DA) Anterior Pituitary Hormones Folicle stimulating hormone (FSH) Lutenising hormone (LH) Growth hormone (GH) Thyroid stimulating hormone (TSH) Prolactin Arendocorticotrophic hormone (ACTH) Gonadotrophic hormones 10
Posterior Pituitary Hormones Oxytocin Anti-diuretic hormone (ADH), also known as vasopressin Signal Amplification Positive feedback loop Cell A Cell A Cell B Cell B 11
Negative Feedback Loop Anterior Pituitary Example; Pituitary-thyroid axis TSH Θ Thyroid Thyroxine Target Cell Negative Feedback Loop Hypothalamus Θ TRH Anterior Pituitary TSH Θ Thyroid Thyroxine Target Cell 12
Hormone Definition: Molecule that act as a chemical messenger Classified according to structure; Peptide Steroid Amino-acid derivatives How peptide hormones work Peptide & amino acid hormones produce a quick reaction in the body Adrenaline 13
Peptide Hormones - TSH Pituitary cell Thyroid cell Hormone premade and stored in cell ready to be released when needed. Hormone dissolved in blood. Receptor on cell membrane. Chemical reaction produces quick response from cell. (Signal transduction cascade) Peptide Hormones Made of amino acids Vary in size from few amino acids to small proteins Some have carbohydrate side chains (glycoproteins) Hydrophillic (like water) 14
Amino Acid Hormones Synthesised from tyrosine OH CH 2 CH(NH 2 )COOH Examples; adrenaline and thyroid hormones (thyroxine & triiodothyronine) Other Peptide Hormone Examples Insulin Growth hormone 15
How steroid hormones work Steroid hormones produce a slow response Testosterone Steroid Hormones - Testosterone Testes Testosterone made by cell and diffuses out once made Transported in blood bound to transport protein as can t dissolve in water Receptor is in the target cell Slow response as directly affects DNA 16
Steroid Hormones All made from cholesterol Different enzymes modify molecule to produce a variety of hormones Can t dissolve in water Can dissolve in lipids Steroid Hormone Examples Testosterone Oestrogen Cortisol 17
Problems with feedback - primary hypothyrodism Anterior Pituitary TSH Θ Thyroid Thyroxine Target Cell Primary means the problem is with the endocrine gland eg. the thyroid Hypo = under active Problems with feedback - primary hyperthyroidism Anterior Pituitary Hyper = over active TSH Θ Thyroid Thyroxine Target Cell 18
Problems with feedback secondary hypothyroidism Anterior Pituitary TSH Θ Thyroid Thyroxine Target Cell Secondary means the initial problem is with the anterior pituitary (or the hypothalamus) Summary Homeostasis (maintenance of the internal environment) is essential Hormones allow cell-cell communication Feedback loops maintain steady state Type of hormone determines how it works Hypothalamus-pituitary-endocrine gland axis major part of endocrine system Disease states & treatment can be predicted with knowledge of feedback loops 19