Endocrine System

ENDOCRINE SYSTEM

Is a biochemical communication network through which several small glands control a broad range of vital body activities.

The endocrine glands secrete chemical messengers called hormones, which circulate in the blood and may affect a single target organ or the entire body.

The endocrine glands are:

• Pituitary gland
• Thyroid gland
• Parathyroid gland
• Adrenal gland
• Pancreas
• Ovaries
• Testes
• Pituitary gland
• It hangs from the hypothalamus and is enclosed by the sphenoid bone.

It is divided into posterior pituitary gland and anterior pituitary gland.

Posterior pituitary gland.

The two hormones of the posterior pituitary gland are produced by the hypothalamus and stored in the posterior pituitary gland until needed These hormones are anti-diuretic hormone (vasopressin) and oxytocin and both are peptides.

Antidiuretic hormone increases the reabsorption of water by kidney tubules, which decreases the amount of urine formed.

The water is reabsorbed into the blood, so as urinary output is decreased, blood volume is increased, which helps maintain normal blood pressure Oxytocin stimulates contraction of the uterus at the end of pregnancy and stimulates release of milk from the mammary glands.

Anterior pituitary gland

The hormones produced are regulated by releasing hormone from the hypothalamus.

The hormones produced are growth hormones (somatotropin), thyroid stimulating hormone, adrenocorticotropic hormone, prolactin, follicle stimulating hormone and luteinizing hormone.

Growth hormones promote growth as increases amino acids transport and protein synthesis.

Thyroid stimulating hormone stimulates the normal growth of the thyroid and the secretion of thyroxine (T4) and triiodothyronine (T3).

Adrenocorticotropic hormone (ACTH) stimulates the secretion of cortisol and other hormones by the adrenal cortex.

Secretion of ACTH is increased by corticotropin-releasing hormone (CRH) from the hypothalamus.

Prolactin is responsible for lactation. More precisely, prolactin initiates and maintains milk production by the mammary glands.

Follicle stimulating hormone stimulates the growth of ovarian follicles; that is, it initiates egg development in cycles of approximately28 days.

Luteinizing hormone is responsible for ovulation, the release of a mature ovum from an ovarian follicle.

Thyroid gland

The thyroid gland is located on the front and sides of the trachea just below the larynx The structural units of the thyroid gland are thyroid follicles, which produce thyroxine (T4) and triiodothyronine(T3) and iodine is necessary foe production of these hormones Thyroxine and T3

Thyroxine (T4) and T3 have the same functions: regulation of energy production and protein synthesis, which contribute to growth of the body and to normal body functioning throughout life.

Thyroxine and T3 increase cell respiration of all food types (carbohydrates, fats, and excess amino acids) and thereby increase energy and heat production.

Calcitonin

Decreases the reabsorption of calcium and phosphate from the bones to the blood, thereby lowering blood levels of these minerals.

This function of calcitonin helps maintain normal blood levels of calcium and phosphate and also helps maintain a stable, strong bone matrix Parathyroid gland

• They produce a hormone called parathyroid hormone.

Parathyroid hormone is an antagonist of calcitonin It increases the reabsorption of calcium and phosphate from bones to the blood, thereby raising their blood levels. And also increase their absorption from the intestine.

Pancreas

It is located in the upper left quadrant of the abdominal cavity, extending from the curve of the duodenum to the spleen.

It is also an exocrine gland.

The pancreatic hormones are produced by the cells called islet of Langerhans and the hormones are insulin and glucagon.

Endocrine System

Glucagon stimulates the liver to change glycogen to glucose (this process is called glycogen lysis, which literally means “glycogen breakdown”) and to increase the use of fats and excess amino acids for energy production.

The overall effect of glucagon, therefore, is to raise the blood glucose level and to make all types of food available for energy production and is stimulated by hypoglycaemia.

Insulin increases the transport of glucose from the blood into cells by increasing the permeability of cell membranes to glucose.

A deficiency of insulin or in its functioning is called diabetes mellitus.

Adrenal glands

The two adrenal glands are located one on top of each kidney.

Each adrenal gland consists of two parts: an inner adrenal medulla and an outer adrenal cortex.

The cells of the adrenal medulla secrete epinephrine and norepinephrine, which collectively are called catecholamine sand are sympathomimetic.

Epinephrine (Adrenalin) and norepinephrine (noradrenalin) are both secreted in stress situations and help prepare the body for “fight or flight.”

Endocrine System

The adrenal cortex secretes three types of steroid hormones: mineralocorticoids, glucocorticoids and sex hormones (oestrogens and androgens).

Aldosterone is a mineralocorticoid and increases the reabsorption of sodium and the excretion of potassium by the kidney tubules hence maintains normal blood volume and blood pressure.

Cortisol is a glucocorticoid and increases the use of fats and excess amino acids (gluconeogenesis) for energy and decreases the use of glucose It conserves glucose for use in brain.

Cortisol also has anti-inflammatory effect as they block the effects of histamine

Ovaries

The ovaries are located in the pelvic cavity, one on each side of the uterus.

The hormones produced by the ovaries are the steroids estrogen and progesterone, and the protein inhibin.

Estrogen promotes the maturation of the ovum in the ovarian follicle and stimulates the growth of blood vessels in the endometrium (lining) of the uterus in preparation for a possible fertilized egg Also estrogen is responsible for the development of female secondary characteristics Progesterone promotes the storage of glycogen and the further growth of blood vessels in the endometrium, which thus becomes a potential placenta.

Inhibin helps decrease the secretion of follicle stimulating hormone.

Testes

• The testes are located in the scrotum, a sac of skin between the upper thighs
• Two hormones, testosterone and inhibin, are secreted by the testes.
• Testosterone promotes maturation of sperm in the seminiferous tubules of the testes

Testosterone is also responsible for development of male secondary characteristics The function of inhibin is to decrease the secretion of FSH by the anterior pituitary gland The interaction of inhibin, testosterone, and the anterior pituitary hormones maintains spermatogenesis at a constant rate.

Hormones may be

• proteins (growth hormone),
• steroids (cortisone),
• peptides (antidiuretic hormone [ADH]),
• amino acids (thyroxine), or

amines (epinephrine).

The general functions of the endocrine system include:

• The growth and repair of tissues
• The utilization of food to produce energy
• Responses to stress
• The maintenance of the proper levels and pH of body fluids

The continuance of the human species all depend on hormones.

Common Endocrine disorders

Hyperparathyroidism

Excessive secretion of parathormone leads to a generalized disorder of calcium, phosphate, and bone metabolism that results in elevated serum values of calcium and phosphate Primary hyperparathyroidism may be caused by Parathyroid adenoma (80%) or

• Parathyroid carcinoma (2%) or by

generalized parathyroid hyperplasia (18%) of all glands.

Endocrine System

Secondary HPT is due to parathyroid hyperplasia in response to persistent hypocalcaemia (low blood calcium) and is seen in rickets, osteomalacia and chronic renal failure.

Tertiary HPT applies to cases of secondary HPT which gives rise to autonomous HPT (i.e. HPT exists irrespective of the initial low blood calcium)

Radiographic features;

• 1.General osteopenia

2.Bones erosion

Subperiosteal erosion (particularly along the radial aspect of phalanges and tufts of the fingers in the hand) Subchondral resorption (erosions of the distal clavicle, pubic symphysis and SI joints) 3.Rogger Jersey Spine

• 4.Brown Tumors
• 5.Salt & Pepper Sign in Skull

6.Superior & Inferior Rib Notching

Findings of secondary and tertiary hyperparathyroidism includes;

1.Elevation of serum calcium and decreased excretion of calcium in the urine may result in nephrocalcinosis and urinary tract stones.

2.Increased incidences of pancreatic calculi and pancreatitis, peptic ulcer, and gallstones have also been reported in patients with hyperparathyroidism.

Subperiosteal resorption

Erosions of the terminal tufts of the fingers

Endocrine System

Hyperparathyroidism. Lateral projection of the lumbar spine demonstrates osteosclerosis of the superior and inferior margins of the vertebral bodies (“rugger-jersey” spine) Hyperparathyroidism. Characteristic salt and-pepper skull.

Rugger Jersey Spine

Brown tumor

Hyperparathyroidism. Brown tumors have produced multiple lytic lesions about the knee.

Radiographic features;

Are often associated with osteosclerosis of renal osteodystrophy Renal osteodystrophy is the term applied to the bone changes associated with chronic renal failure. (include secondary HPT, osteomalacia and osteosclerosis).Soft tissue calcifications and the osteomalacia of vitamin D deficiency

Pituitary gland and hormones

Hyperpituitarism

An excess of growth hormone

Produced by a tumor or generalized hyperplasia of the anterior lobe of the pituitary gland.

• If occurs before enchondral bone growth has ceased results in gigantism;

If occurs after bone growth has stopped produces acromegaly

Generalized overgrowth of all the body tissues is the underlying abnormality in acromegaly.

• Long bones can no longer grow because the epiphyses are closed,
• The bones of the hands, feet, and face enlarge,

There is excessive growth of soft tissues.

Proliferation of cartilage may cause joint space widening, especially of the metacarpophalangeal and hip joints.

Radiographic features;

• Skull : -Calvarial thickening, enlarged sinuses and an enlarged sella turcica
• Prognathic jaw
• Terminal phalangeal tufts become hypertrophied
• Spade phalanx sign
• Joint spaces may be minimally enlarged
• Premature osteoarthritis can set in the advanced stages of acromegaly

Heel pad thickness may be increased (more than 25 mm)

Thickened calvarium with pituitary enlargement

Enlarged sella with double flooring , thickened skull vault , pneumosinus dilatans and prognathism

Acromegaly. Lateral skull projection demonstrating a thickened frontal bone with characteristic frontal bossing

Pituitary adenoma causing acromegaly. Ballooning of the sella turcica with downward displacement of the floor is demonstrated.

Endocrine System

Acromegaly. Posterior scalloping (arrows) associated with enlargement of vertebral bodies (especially in anteroposterior dimension).

Endocrine System

Widening of the terminal tufts (between long arrows) , bases of the distal phalanges , thickening of the digit soft tissues (between arrowheads) and widening of the metacarpophalangeal joints (between short arrows)

Increased heel pad thickness (more than 25 mm)

Pituitary microadenoma

Pituitary macroadenoma

Hypopituitarism

The pituitary gland controls the level of secretion of gonadal, thyroid hormones and the production of growth hormone.

Decreased function of the pituitary gland causes generalized disturbances in bone growth and maturation.

In children leads to a type of dwarfism as a result of failure of bones to grow normally in length or width.

Results in a person who is small in stature and sexually immature, but mentally normal.

Endocrine System

Arrested growth of the skeleton in childhood causes dwarfism, relatively large skull which may be believed to result from hydrocephaly.

Hypopituitarism occurring after adolescence results in hypofunction of the thyroid gland, adrenal glands, and gonads but usually causes few radiologic findings MRI is the preferred imaging modality because it is sensitive and can directly image the sellar and parasellar regions in multiple planes.

The use of contrast enhancement may help define a microadenoma or detect sarcoidosis in an older patient with Addison’s disease

Hypothyroidism

• It is due to insufficient production of thyroxine.
• In children (cretinism) there is delayed skeletal maturation and growth retardation.

The epiphyses, particularly the proximal femur, appear irregular and fragmented

AP of the pelvis in a child with hypothyroidism (cretinism).

There is irregular fragmentation of the proximal femoral epiphyses mimicking a congenital epiphyseal dysplasia. Note the severe constipation which is another feature of this condition.

Metabolic bone disease

Vitamin related bone disease

• Ricket’s
• Osteomalacia
• Scurvy

Hyperistaminosis

Rickets and osteomalacia

Are the same condition, occurring in children and adults respectively.

There is lack of mineralization of normal osteoid caused by vitamin D deficiency which may be due to;

• dietary deficiency

gastrointestinal malabsorption

liver disease

• anticonvulsant therapy (Eg. Phenytoin Phenobarbital)
• renal osteodystrophy (combination of osteomalacia and secondary hyperparathyroidism)

lack of sunlight (ultraviolet light)

Osteomalacia

Is bone softening due to insufficient mineralization of the osteoid secondary to any process that results in vitamin D deficiency or defects in calcium and phosphate metabolism:

• High remodeling rate: excessive osteoid formation with normal/little mineralization

Low remodeling rate: normal osteoid production with diminished mineralization Patients with osteomalacia may be asymptomatic or present with bone pain/tenderness and/or muscular weakness.

Radiographic appearance

Multiple pseudofractures/Looser zones are seen involving superior and inferior pubic rami bilaterally, and in the femoral neck of an adult Osteopenic changes involving bony pelvis and proximal femurs.

Coarsened trabeculae

Rickets

Refers to osteomalacia in the pediatric population that occurs prior to fusion of the growth plate Etiology

Vitamin D deficiency causes failure of mineralization of bone and cartilage (in adults this is termed osteomalacia)

Causes of Vitamin D deficiency include :

• 1.GI tract : -Nutritional deficiency (common) -Absorption abnormalities
• 2.Skin disease
• 3.Liver disease
• 4.Renal :
• Renal tubular acidosis

Renal failure (loss of calcium)

Radiographic Features

• Growth plate abnormalities (especially long bones) :
• A widened growth plate is due to rickets until proved otherwise
• Cupping of metaphysis

Disorganized (frayed) metaphysis

Radiographic Features cont….

• 2-Bowing deformities of bones
• 3-Delayed closing of fontanelles
• 4-Softening of cranial vault (craniotabes)

5-Rachitic rosary : expansion of the anterior rib ends at the costochondral junctions

Bowing of the legs caused by loading

Scurvy

Deficiency of vitamin C (ascorbic acid) impairs the ability of connective tissue to produce collagen.

Never occurs before 6 months of age because maternal stores are transmitted to fetus

Disorders of the Growth hormone:

Dwarfism

Hypo secretion of GH results in pituitary dwarfism, in which the person mayattain a final height of only 3 to 4 feet but will have normal body proportions.

Growth hormone can now be produced using genetic engineering and may be used to stimulate growth in children with this disorder

Giantism (Gigantism)

• Is the hyper secretion of growth hormone

The long bones grow excessively and the person may attain a height of 8 feet.

In adults, the hyper secretion of growth hormone due to pituitary tumour can result to acromegaly, a condition where by the long bones cannot grow due to closure of epiphyseal discs.

Disorders of the thyroxine

• Goitre

It is caused by dietary deficiency of iodine In an attempt to produce more thyroxine, the thyroid cells become enlarged, and hence the thyroid gland enlarges and becomes visible on the front of the neck.

Cretinism

It is a condition of hypo secretion of thyroxine in new born,It retards both physical and mental development.

• Myxedema
• It is a condition of hypo secretion of thyroxine in adults
• This decreases metabolic rate and hence general body weakness
• Grave’s disease

This is autoimmune disease which result to hypersecretion of thyroxine hormone

Diabetes Mellitus

There are two types of diabetes mellitus:

Type 1 is called insulin-dependent diabetes and its onset is usually in childhood (juvenile onset).

Is characterized by destruction of the beta cells of the islets of Langerhans and a complete lack of insulin

Type 2 is called non–insulin-dependent diabetes, and its onset is usually later in life (maturity onset).

Insulin is produced but cannot exert its effects on cells because of a loss of insulin receptors on cell membranes.

Risk factors include a family history of diabetes and being overweight. Control may not require insulin, but rather medications that enable insulin to react with the remaining membrane receptors.

Disorders of the adrenal cortex

• Addison’s disease
• It is a result of hypo secretion of the adrenal cortical hormones.

Atrophy of the adrenal cortex decreases both cortisol and aldosterone secretion.

Deficiency of cortisol is characterized by hypoglycaemia, decreased gluconeogenesis, and depletion of glycogen in the liver.

Consequences are muscle weakness and the inability to resist physiological stress.

Aldosterone deficiency leads to retention of potassium and excretion of sodium and water in urine. The result is severe dehydration, low blood volume, and low blood pressure.

Cushing’s syndrome

It is a result of hypersecretion of the adrenal cortex, primarily cortisol.

The cause may be a pituitary tumour that increases ACTH secretion or a tumour of the adrenal cortex itself.

Excessive cortisol promotes fat deposition in the trunk of the body, while the extremities remain thin. The skin becomes thin and fragile, and healing after injury is slow.