Endocrine System Notes

Endocrine & Reproductive Systems Introduction to endocrine glands and hormones Endocrine system A collection of endocrine glands releasing hormones A control system acting in partnership with the nervous system to control other systems Homeostasis, growth and maturation, reproduction and adaptation to stress Features Tissue capable of releasing hormones directly into the blood May have other non-endocrine functions Supplied by a rich capillary network Therefore no ducts Widely distributed about the body 10 major 8 minor Hormones Chemical signals released into blood in response to a specific stimulus and delivered via circulation to other cells to cause a specific response There are subclasses based on production and transport (a) Neurotransmitter (b) Autocrine (act directly back on cell) & paracrine (act on adjacent cells (c) Neurohormone (produced by nerve cells eg hypothalamus) (d) Endocrine hormone Differences Hormone signals are more diffuse Hormone signals are slower Hormones exert longer lasting and sometimes permanent effects Amplitude of the effect Concentration of the hormone Duration of the exposure Number of receptors Affinity of the hormone for its receptors Major endocrine glands 1. 2. 3. 4. 5. 6. 7. 8. Pineal gland Pituitary gland Thyroid Thymus Adrenal Pancreas Ovary Testes Features of Hormones Stable Well defined structure that is unique Variable structure by small substitutions or changes in the molecule Classes Peptides <50 AA / Proteins <200 AA eg oxytocin Amides eg adrenalin Steroids derived from cholesterol eg progesterone Prostaglandins eg PGE2 Receptors Seven-transmembrane, G-protein coupled receptors Most common family 4 extracellular domains, 7 transmembrane domains and 4 cytoplasmic domains They operate by activating membrane enzymes eg adenylate cyclase leading to cAMP production or phospholipase C leading to generation of IP3 and DAG Intracellular receptors For steroid hormones Hormone can easily cross the membrane Receptors are mainly located in the nucleus Once occupied, the receptor binds to a hormone response element found on DNA, upstream of the promoter region of the target gene Steroid control genes involved in cell growth, differentiation and synthesis of specific functional proteins Organisation of the Hypothalamus & Pituitary The hypothalamo-pituitary axis is the interface between the CNS and the endocrine system It controls the homeostatic function for reproduction, energy balance, water balance, growth, stress, immune function, thermoregulation & sleep Hypothalamus Part of the diencephalon on either side of the 3rd ventricle below the thalamus Small - 4g Anterior - lamina terminalis Posterior - mamillary bodies Below - median eminence In the midline, caudal to the optic chiasm, lies a small elevated area, the tuber cinereum from which the apex of the infundibulum emerges, which is attached to the pituitary gland Hypothalamic neurosecretory cell Release peptides which are stored in axon terminals Output is controlled by the rate of peptide synthesis and the frequency of APs Neural information is transduced to hormonal information Embryological Development 32 days - floor of the diencephalon grows down to form the infundibulum and the ectoderm grows upwards 

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