Endocrinology 1
ENDOCRINOLOGY
Communication
Neurons
Chemicals
Autocrine-via ICF
Paracrine-via ECF
Exocrine-via ducts
Endocrine-via blood stream
BASIC STRUCTURE
AMINES: Derivatives Amino Acids: tyrosine: T3 T4.Adrenal Med. H
PEPTIDES: Majority of Hormones
STEROIDS: Derived from cholesterol
adrenal cortex
gonadal
placental
Organs
Hormones
Transport in blood
Water soluble
Peptides and catecholamines, water soluble: free transport in Plasma
Lipid soluble
Thyroid hormones, Steroids----transported by binding to proteins
(free hormone + Binding protein
Hormone/Protein complex)
Mechanism of action
Target cell----Receptor-----LOCK KEY phenomenon
Water soluble ----Receptor on the plasma membrane
Lipid soluble ----Receptor in the interior ofthe cell
CONCEPT OF SECOND MESSENGER----Signal transduction mechanism
Mechanism of Action of Hormones
CONTROL OF SECRETION
Variation in Secretion
Short burst
Fluctuating level
Cyclical with a 24hr variation
Controlled by 4 main types of input into endocrine
Changes in Plasma mineral concentration
Changes in concentration of organic nutrients
Neuronal control via neurotransmitters
Another Hormone acting on the endocrine cells
Hypothalamus
Anatomy
Functions:
Synthesis of two hormones from
Para ventricular
and Supr aoptic nuclei
Control of Anterior pituitary
Pituitary Gland
Anterior Pituitary: adeno hypophysis
Posterior Pituitary: neuro hypophysis:
ADH (vasopressin)
Oxytocin
Formed in the Hypothalamus (for Posterior)
Move down the neuronal connection for storage in the posterior hypophysis. The hormones are transported by NEUROHYPOPHYSINS-protein
Oxytocin
Type: Peptide
Effects:
Uterine Contraction --end of pregnancy
Milk ejection or “let-down” reflex
Uterine contraction
Stimulus for secretion:
Afferent impulses from cervix in late pregnancy
Increased receptors in pregnancy as a result of Uterine distension and estrogen
Oxytocin
Let-down reflex ( Milk already secreted into lumen of alveoli but cant be sucked out unles it is ejected into the ducts)
Stimulus: Sucking of the nipple
Milk Let down reflux
BABY SUCKS
STIMULATION OF NIPPLE MECHANOCEPTORS
afferent impulses to hypothalamus
Inc SECRETION OF OXYTOCIN FROM POST PIT
CONTRACTION OF MYOEPITHELIUM
MILK EJECTION
Let Down Reflex
ANTI DIURETIC HORMONE (ADH)- Arginine vasopressin
Type: Peptide
Action: Water and Electrolyte balance
Stimulus and control of secretion
Baroreceptor control-- (atrial volume receptors) Reduced ECF--diarrhoea, haemorrhage
Osmoreceptor control-- located in hypothalamus
Higher centre control-- Stress, trauma, pain, anxiety, fear: increase ADH
Drugs alcohol inhibits ADH,
ADH
Hypo-States: (Diabetes Insipidus)
Failure of Supra-optico-hypophysial system to secrete ADH due to manufacturing defect
Non responsive receptors in Kidney (Nephrogenic Diabetes insipidus)
Features
polyuria
low SG urine
dehydration
thirst
ADH
Hyper state: (SIADH Secretion)
Features:
Low volume concentrated urine
Increase SG of urine
Mild retention of water
Reduced [Na+] (hyponatremia) due to excess water and not decreased NA+
Hypo-osmolality
HORMONAL CONTROL: ROLE OF HYPOTHALAMUS
Regulate functions of Ant Pituitary:
By secreting inhibiting and secreting factors or factors that control trophic hormones.
These are passed down the: Hypothalamo-pituitary portal system (do not enter the systemic circulation)
Pituitary Hormones
Releasing and Inhibiting factors (hormones)
Gonadotropin RH
Growth Hormone RH
Growth Hormone IH (Somatostatin)
Thyrotrophin RH
Prolactin RH
Prolactin IH
Corticotropin RH
Hypothalamus Control of the Ant Pituitary
Control of Secretions
Neural:
Stimulation and inhibition from CNS by specific neural pathways
neurotransmitters involved therefore can be controlled by drugs
Hormonal:
Feedback mechanisms:
Negative Feedback
Positive feedback
(Short loop, Long loop, Intermediate loop)
,
Feedback
Negative and positive feedback loops
ANTERIOR PITUITARY
Produces mainly trophic hormones: Hormones that stimulates the production and secretion of other hormones
DEFECTS IN SECRETION
Hypo-secretion:
1o: due to organ itself
2o: lack of trophic hormone
Hyper-secretion:
1o: due to organ itself
2o: excess trophic hormone
Hypothalamus-Ant Pituitary
Growth Hormone
Type: peptide
Effect: Stimulates postnatal somatic growth and development (Hypertrophy and hyperplasia of all body tissues)
Metabolic effects: (directed at promoting growth)
END