Hormones are a group of diverse biomolecules that are carried by the circulation and interacts with specific cells and receptors to produce a precise response.Each hormone is under the stimulation and inhibitory factors that acts to produce exquisite control of biological processes.
A common and diagnostically useful characteristics of hormones is Rhythmicity. Hormones are secreted on a periodic cycle referred to as Circadian hormone secretion.This occurs every 24 hours in addition to these cyclic secretions,there are also instances of pulsatile release of hormones triggered by events.
These events may be neurological,environmental or biochemical in nature and can often be initiated by the clinician under careful controlled conditions to elucidate the underlying pathology often the observation that the natural rhythm of secretion has been lost is enough to direct the diagnosis.Also,there are instances of ectopic hormones production.
This usually occurs when hormonal production takes place at a site where it is not normally produced.These tissues are normally neoplastic and can produce hormones that can be biologically and structurally identical to be a variant of a normal hormone.Clinical endocrinology addresses the various clinical disorder that arise from circulating hormone concentration,regulatory system failure,extraneous sources,molecular variants and receptor abnormalities.
Hormones and their clinical significance
It is release from the anterior pituitary and is the most abundant of anterior pituitary hormones.It is release in a pulsatile manner and is under direct control of growth hormone releasing hormone(GHRH) which stimulate its secretion and somatostatin which inhibit its secretion.
Clinical significance of Growth Hormone
- Clinical disorders due to growth hormones secretion are giantisms and acromegaly.This pathological condition are associated with a particular age group.Giantisms is found in children while adults are acromegalics.
- Growth hormone deficiency only leads to stunted growth,but other conditions such as malnutrition,genetic predisposition and systemic illness should be checked before confirmation of a growth hormone deficiency
It is secreted from the anterior pituitary.It’s secretion is stimulated by thyrotropin release hormone.in addition to this,prolactin secretion can be stimulated by suckling.Prolactin could as well be secreted from the hypothalamus but in a small amount.
Clinical significance of Prolactin
- Hyperprolactinemia is diagnostic tool for several clinical condition such as adenoma especially pituitary neoplasms,natural state of pregnancy and lactation
Follicle stimulating Hormone (FSH) and Luteinizing hormone (LH)
These hormones are released from the gonadotrophs located in the anterior pituitary in response to the stimulatory effect of gonadotropin releasing hormone (GnRH).GnRH secreted in a pulsatile fashion and seems to be sensitive to the circulating level of oestrogen in females and testosterone in males.
Clinical significance of FSH and LH
- These hormones are important in the diagnosis of pituitary insufficiency and gonadal insufficiency which can leads to amenorrhoea
Antidiuretic hormone (ADH)
Also called vasopressin,this is produced in the hypothalamus and stored in the posterior pituitary for subsequent secretion.The stimuli for ADH secretion are blood volume and osmolality.ADH secretion is also altered by osmotic changes in extracellular volume.Nausea,pain and many drugs such as narcotics are also potent non-osmotic
Clinical significance of Antidiuretic hormone
- Diabetes insipidus defects in ADH secretion or renal tubular action result in chronic polyuria,polydipsia and polyphagia.
- Central diabetes insipidus can result from variety of hypothalamic causes,trauma,neoplasma and infections disorder.
- Nephrogenic disease can occur as a result of renal disorders such as polycystic renal diseases and urinary tract obstruction
The two thyroid hormones are tetraiodothyronine (T4) and triiodothyronine (T3).These hormones are produced by the thyroid gland under the stimulation of thyrotropin stimulating hormone.Circulating T4 and T3 are bound to variety of thyroid transport proteins.Only about 0.03% of T4 and 0.3% of T3 are free and hence biological active.It is the excess or deficiency of the free thyronine fractions that determine hyper and hypothyroidism.
Clinical significance of Thyroid Hormones
Hyperthyroidism can arise from multiple etiologies.The most common etiology being
- Graves disease or diffuse toxic goiter.Other aetiologies of hyperthyroidism include
multinodular thyroid disorders,inflammatory disorders of the thyroid gland.
- Excess exogenous thyroid administration and rarely thyroid stimulating hormone production from a pituitary adenoma
Hypothyroidism which could be used to check
- Failure of pituitary hypothalamic thyroid stimulating hormone response to decrease circulating thyroids levels.This could be as a result of a disorder or disease of the pituitary gland
Adrenal Cortex hormones
The adrenal cortex is responsible for the synthesis and secretion of glucocorticoids and this is regulated by pituitary adrenocorticotropin (ACTH).Approximately 10% of circulating cortisol is free and therefore biologically active.The secretion of aldosterone is controlled principally the renin-angiotensin system such as interstitial nephritis
Adrenal hypertension result from primary adrenal mineralocorticoids excess and can be caused either from mineralocorticoid secreting solitary adrenal adenomas or from bilateral adrenal adenomatous hyperplasia
It is produced by the B-cells of the islets of langerhans in the pancreas.It’s function to regulate blood sugar level.
Clinical significance of insuline
- Diabetes mellitus type 1 which is the most common endocrine disorder of the pancrease.It result from absolute deficiency or lack of insulin
- Type 2 is caused by insulin insufficiency
- Hypoglycaemia which when sustained could lead to coma is caused by hyperinsulinemia
It is secreted by cells in the stomach.Tumours of these cells result to zollinger-ellison syndrome which is characterized by recurrent duodenal and peptic ulcer disease
Clinical significance of Gastrin
- Cushing syndrome : This is a clinical disorder that result from sustained cortisol excess.Symptoms include central weight gain,weakness,menstrual irregularity.The most common cause of cushing syndrome is adrenal hyperplasia.other include tumors of adrenal gland
- Addison’s disease : It result from either primary adrenocortical failure or pituitary ACTH deficiency.The disorder can present as both acute and chronic syndrome.
The most common etiology of chronic adrenal insufficiency is autoimmune adrenalitis.
Other etiologies include granulomatous disorders such as Tuberculosis sarcoidosis,adrenoleukodystrophy and metastatic adrenal involvement.
Secondary adrenal insufficiency arises from destructive or infiltrative disorders of hypothalamic-pituitary axis or functional suppression by exogenous glucocorticoids administration
- Mineralocorticoid deficiency is common in patients with diabetes mellitus and underlying kidney disease
It is secreted by the alpha cells of the islets of langerhans in the pancreas.
Clinical significance of Glucagon
Neoplasms of these cells result to hyperglycemia,weight loss and a characteristic migrating necrotizing dermatitis skin rash
Adrenal Medulla Hormones
The adrenal hormones that is epinephrine and norepinephrine are secreted by the chromaffin cells in the adrenal medulla.
Clinical significance of Adrenal Medulla Hormones
Clinically,these hormones are used as markers of pheochromocytomas which are tumours arising from adrenal medulla.
It is characterized by hypertension which may be labile or sustained,anxiety,heachache,tremor and weight loss.This is marked by an excess of adrenal medulla hormones
Parathyroid Hormones (Parathormone)
It is secreted by the parathyroid gland.This hormone is released when there is low level of plasma calcium.In stimulation of hypercalcemia,calcitonin ir released which helps in bringing down high calcium level to normal by inhibiting calcium absorption from the small intestines and kidneys.
The biosynthesis of testosterone occurs in the leydig cells of the testes under the primary influence of luteinizing hormones.
FSH binds to its specific receptors on the sertoli cells of the testes and by a mechanism similar to Luteinizing hormone induce androgen binding protein and inhibin
Testosterone increases secondary sexual characteristics in males
- It thickens the walls of the uterus in preparation for implantation
- It helps in maintaining bone mass and that is why low levels can leads to loss of bone mass leading to the development of osteoporosis
- It increases secondary sexual characteristics in female
Functions of Some hormones
- Prolactin stimulates the mammary gland to secrete milk during lactation
- Oestrogen stimulate thickening of the uterine walls in preparation for implantation
- Growth hormone stimulate bone growth and development at the epiphyseal plate
- Luteinizing hormone induces ovulation
- Follicle stimulating hormone enhances development of graafian follicles
- Luteinizing hormone stimulates the leydig cells of the testes to secrete or produce testosterone