PATHOLOGY - Endocrine System Flashcards
What is endocrine signalling?
Endocrine signalling is the synthesis and secretion of signalling molecules (hormones) by endocrine cells into the bloodstream to act on target cells at distant body sites
What is endocrine hypofunction?
Endocrine hypofunction refers to a decreased or underactive function of an endocrine gland, resulting in reduced hormone production
What are the three possible mechanisms of primary endocrine hypofunction?
Failure of endocrine gland development
Destruction of secretory cells
Biochemical defect in the synthetic pathways
What is the main mechanism of secondary endocrine hypofunction?
The main mechanism of secondary endocrine hypofunction involves damage to the endocrine tissue, which leads to a decrease in trophic hormone secretion. This decrease in trophic hormones then affects the target organ’s hormone production
What is endocrine hyperfunction?
Endocrine hyperfunction refers to an increased or overactive function of an endocrine gland, resulting in excessive hormone production
What is the main mechanism of primary endocrine hyperfunction?
The main mechanism of primary endocrine hyperfunction involves abnormal cells within the endocrine glands producing excessive hormones
Usually functional/non-functional neoplasia and hyperplasia
What is the main mechanism of secondary endocrine hyperfunction?
The main mechanism of secondary endocrine hyperfunction involves abnormal cells within endocrine glands producing excessive trophic hormones. This excess of trophic hormones then causes excessive hormone production by the target organ
What are the consequences of anterior pituitary hypofunction?
Anterior pituitary hypofunction will result in decreased follicle stimulating hormone (FSH), luteinising hormone (LH), thyroid-stimulating hormone (TSH), growth hormone (GH) and adrenocorticotropic hormone (ACTH). Reduced FSH and LH will result in sub-fertility and infertility, reduced TSH will result in hair coat, metabolism and growth abnormalities, reduced GH will result in metabolism and growth abnormalities and reduced ACTH will result in reduced cortisol production by the adrenal glands, leading to delayed parturition and altered metabolism and growth
What are the six possible causes of primary anterior pituitary hypofunction?
Aplasia
Hypoplasia
Abscesses
Granulomas
Cystic Rathke’s pouch
Neoplasia
What is the possible cause of secondary anterior pituitary hypofunction?
Hypothalamic malfunction
Give an example of a disease caused by anterior pituitary hypofunction?
Pituitary dwarfism
What are the five main clinical signs of pituitary dwarfism?
Decreased growth rate
Abnormal hair growth (retain puppy coat followed by bilateral, symmetrical alopecia and hyperpigmentation)
Hypoplasia of gonads and genitalia
Permanent deciduous dentition
Delayed epiphyseal growth plate closure
Which breed of dog is suscepible to pituitary dwarfism?
German Shepherd
Why are German Shepherds susceptible to pituitary dwarfism?
German Shepherds have an autosomal recessive inherited disorder resulting in cystic Rathke’s pouch causing primary anterioir pituitary hypofunction resulting in pituitary dwarfism
What is the clincial term for posterior pituitary hypofunction?
Diabetes insipidus
What is central diabetes insipidus?
Central diabetes insipidus is caused by hypofunction of the posterior pituitary gland, resulting in reduced antidiuretic hormone (ADH) secretion. Antidiuretic hormone (ADH) is responsible for increasing the permeability of the collecting ducts in the nephrons of the kidney to increase the reabsorption of water and allow for the concentration of urine. Where there is antidiuretic hormone (ADH) deficiency, it will lead to large volumes of dilute urine, hypernatraemia and dehydration
What is nephrogenic diabetes insipidus?
Nephrogenic diabetes insipidus is a condition where the kidneys are unable to respond to antidiuretic hormone (ADH)
How does diabetes insipidus cause hypernatraemia?
Diabetes insipidus causes excessive urination and dehydration which can lead to hypernatraemia as the body is losing more water relative to sodium, causing an imbalance
What are the three clinical signs of central and nephrogenic diabetes insipidus?
Polyuria
Polydipsia
Low urine specific gravity (USG)
Which two tumours most commonly cause primary pituitary hyperfunction?
Adenoma
Adenocarcinoma
What is the most common cause of primary pituitary hyperfunction in dogs?
Adenoma in the anterior pituitary gland (pars distalis)
What is the most common cause of primary pituitary hyperfunction in horses?
Adenoma in the pars intermedia
What are the consequences of anterior pituitary hyperfunction?
Anterior pituitary hyperfunction leads to excessive adrenocorticotropic hormone (ACTH) production which will stimulate excessive cortisol production in the adrenal glands, causing cushing’s disease. Excessive cortisol causes polyuria, alopecia, immune supression which makes the animal more susceptible to secondary infection, increases protein catabolsim causing muscle wasting, increased appetite and increased glycogen metabolism in the liver causing vacuolar hepatopathy
Describe what vacuolar hepatopathy looks like on a histological slide
There will be the presence of both vacuoles and hepatocytes, the vacuoles will appear as small, clear spaces within the hepatocytes
What are the six clinical signs of anterior pituitary hyperfunction leading to cushing’s disease?
Pot-belly
Alopecia
Polyuria
Polyphagia
Calcinosis cutis
Muscle wastage
What type of control is exerted on the pars intermedia in a normal, healthy horse?
In healthy, normal horses the pars intermedia is under dopaminergic control from the hypothalamus
How does the dopaminergic control of the pars intermedia differ in autumn in normal, healthy horses?
In the autumn, most healthy horses have a decrease in dopaminergic control of the pars intermedia which allows for increased growth of the hair coat and increased fat deposition
What is equine pars intermedia dysfunction (PPID)?
Equine pars intermedia dysfunction (PPID) is when there is decreased dopaminergic control exerted on the pars intermedia all year round. Without this inhibition, melanotrophs of the pars intermedia synthesise excessive hormone, including ACTH, MSH and β-endorphins in combination with hyperplasia and the development of micro- and macro-adenomas. This can cause compression of the hypothalamus which can contribute to clinical signs
Which age group of horses are commonly affected by equine pituitary pars intermedia dysfunction (PPID)?
Older horses (15 years and older)
What are the ten clinical signs of equine pituitary pars intermedia dysfunction (PPID)?
Polyphagia
Polyuria
Polydipsia
Hyperglycaemia
Insulin resistance
Laminitis
Generalised hyperhidrosis (excessive sweating)
Somnolence
Hypertrichosis (abnormal hair growth)
Abnormal fat deposition
What is equine metabolic syndrome (EMS)?
Equine metabolic syndrome (EMS) is a condition characterised by abnormal fat deposits particularly around the neck and tail head and insulin resistance, both of which predisposing the affected individual to laminitis
What causes equine metabolic syndrome (EMS)?
Equine metabolic syndrome (EMS) is caused by the excessive production of adipokine hormones by adipose tissue, resulting in increased cortisol production. This abnormal hormone production disrupts the body’s normal response to insulin, resulting in hyperglycaemia and insulin resistance
Which age group of horses are commonly affected by equine metabolic syndrome (EMS)?
Young horses
Which three factors should you consider to differentiate equine pituitary pars intermedia dysfunction (PPID) and equine metabolic syndrome (EMS)?
Age of onset
Additional clinical signs associated with equine pituitary pars intermedia dysfunction (PPID)
Positive diagnostic test for equine pituitary pars intermedia dysfunction (PPID)
(T/F) Horses can have both equine pituitary pars intermedia dysfunction (PPID) and equine metabolic syndrome (EMS) at the same time
TRUE.
What are the two other names used to describe adrenal cortical hypofunction?
Hypoadrenocorticism
Addison’s disease
With adrenal cortical hypofunction which three hormones will have decreased secretion?
Aldosterone
Cortisol
Androgens
What are the consequences of decreased aldosterone production due to adrenal cortical hypofunction?
Decreased aldosterone production will increase renal potassium retention and renal sodium excretion causing hyperkalaemia and hyponatraemia resulting in polyuria and polydipsia
What are the consequences of decreased cortisol production due to adrenal cortical hypofunction?
Decreased cortisol production will lead to a lack of appropriate immune response resulting in poor wound healing, increased susceptibility to secondary infection and cause the individual to lack a stress leukogram. Furthermore, decreased cortisol production causes vomiting, diarrhoea, weakness and a poor body condition score
What are the consequences of decreased androgen production due to adrenal cortical hypofunction?
Decreased androgen production causes sub-fertility
What are the four main causes of adrenal cortical hypofunction?
Idiopathic
Atrophy
Damage to the adrenal cortex
Secondary to anterior pituitary hypofunction
Which two breeds of dog are genetically predisposed to adrenal cortical hypofunction?
Bearded collies
Portugese Water dogs
What is adrenocortical haemorrhage (Waterhouse-Friderichsen syndrome)?
Adrenocortical haemorrage (Waterhouse-Friderichsen syndrome) is a diffuse, bilateral haemorrhage of the adrenal cortex seen at end-stage overwhelming sepsis
Which species is seen to develop adrenocortical haemorrhage (Waterhouse-Friderichsen syndrome)?
Horses
(T/F) Adrenal medulla hypofunction is very common
FALSE. Adrenal medulla hypofunction is actually very rare
What are the two other names used to describe adrenal cortical hyperfunction?
Hyperadrenocorticism
Cushing’s disease
What is the main cause of adrenal cortical hyperfunction?
Functional neoplasia
Give two examples of tumours most likely to cause adrenal cortical hyperfunction
Adenoma
Adenocarcinoma
Which hormone is secreted in excess by functional tumours of the adrenal cortex?
Cortisol
What are the consequences of adrenal cortical hyperfunction caused by functional neoplasia?
For adrenal cortical hyperfunction, functional neoplasms of the adrenal cortex secrete excessive cortisol, causing cushing’s disease. Excessive cortisol causes polyuria, alopecia, immune supression which makes the animal more susceptible to secondary infection, increases protein catabolsim causing muscle wasting, increased appetite and increased glycogen metabolism in the liver causing vacuolar hepatopathy
Why does the unaffected adrenal gland undergo atrophy in unilateral adrenal cortical hyperfunction?
For healthy adrenal glands, when blood cortisol levels are high, the anterior pituitary gland will release less adrenocorticotropic hormone (ACTH) which will reduce stimulation of the adrenal glands and thus decrease cortisol production. However, in adrenal cortical hyperfunction, the affected adrenal gland with functional neoplasia will override normal negative feedback mechanisms and continue producing cortisol. However, the unaffected adrenal gland will respond to this negative feedback and stop producing cortisol, causing atrophy of the unaffected adrenal gland
What are the three forms of cushing’s disease?
Pituitary dependent cushing’s disease
Adrenal dependent cushing’s disease
Iatrogenic cushing’s disease
Which form of cushing’s disease is most common in small breed dogs?
Pituitary dependent cushing’s disease
Which form of cushing’s disease is most common in female, large breed dogs?
Adrenal dependent cushing’s disease
What causes iatrogenic cushing’s disease?
Iatrogenic cushing’s disease is caused by prolonged use of exogenous corticosteroid treatment
What is the main cause of adrenal medulla hyperfunction?
Functional neoplasia of the adrenal medulla
Give an example of a tumour most likely to cause adrenal medulla hyperfunction
Pheochromocytoma
Which hormones are secreted in excess by functional tumours of the adrenal medulla?
Catecholamines (adrenaline and noradrenaline)
What are the three clinical signs of adrenal medulla hyperfunction?
Tachycardia
Oedema
Cardiac hypertrophy
Describe the normal endocrine pathway that results in hormone production by the thyroid gland
The hypothalamus secretes thyrotrophin releasing hormone (TRH) which acts on the anterior pituitary gland to stimulate the secretion of thyroid stimulating hormone (TSH) which will act on the thyroid gland to stimulate T3 and T4 hormone secretion
What is the other name used to describe thyroid hypofunction?
Hypothyroidism
Which species is thyroid hypofunction most commonly seen in?
Dogs
What are the consequences of thyroid hypofunction?
Thyroid hypofunction results in decreased T3 and T4 production which will cause a decreased meabolic rate and increased cholesterol
What are the two possible causes of primary thyroid hypofunction?
Idiopathic follicular atrophy
Lymphocytic thyroiditis
What is the main cause of secondary thyroid hypofunction?
Anterioir pituitary disease or dysfunction resulting in decreased production of thyroid stimulating hormone (TSH) and thus decreased stimulation of the thyroid to produce T3 and T4
What are the three metabolic associated clinical signs of thyroid hypofunction?
Lethargy
Weight gain
Exercise intolerance
What are the four dermatological associated clinical signs of thyroid hypofunction?
Hair thinning
Decreased coat quality
Hyperpigmentation
Pyoderma
How can thyroid hypofunction contribute to the development of atherosclerosis?
Thyroid hypofunction causes elevated levels of cholesterol leading to hyperlipidaemia and an accumulation of lipid in the blood vessels leading to atherosclerosis
What is goitre?
Goitre is thyromegaly (enlargement of the thyroid gland)
What are the three main causes of goitre?
Iodine deficiency
Iodine toxicity
Goitrogens
How does iodine deficiency cause goitre?
T3 and T4 production by the thyroid gland requires iodine, however, if there is an iodine deficiency there will be insufficient T3 and T4 production. If there is decreased T3 and T4 production, the anterior pituitary gland will release more thyroid-stimulating hormone (TSH) to stimulate more thyroid hormone production, causing the thyroid to enlarge due to this increased stimulation
(T/F) Pregnant animals with an iodine deficiency can cause goitre in their offspring
TRUE.
What are the three characteristic signs of goitre in newborn animals?
Stillborn/weakness
Thyromegaly
Hairless
What are goitrogens?
Goitrogens are compounds containing thiocyanate which competes with iodine for absorption by the thyroid gland, leading to insufficient iodine for T3 and T4 hormone production resulting in goitre
Which family of plants contain goitrogens?
Brassica family (kale etc.)
Which two drugs contain goitrogens?
Phenobarbital
Rifampin
What is the other name used to describe thyroid hyperfunction?
Hyperthyroidism
Which species is thyroid hyperfunction most commonly seen in?
Cats
What are the consequences of thyroid hyperfunction?
Thyroid hyperfunction results in increased T3 and T4 production which will increase metabolic rate resulting in cardiac hypertrophy and even sudden death
What are the two possible causes of primary thyroid hyperfunction?
Thyroid hyperplasia
Functional neoplasia of the thyroid
Give two examples of tumours most likely to cause thyroid hyperfunction
Adenoma
Adenocarcinoma
What is the main cause of secondary thyroid hyperfunction?
Anterioir pituitary disease or dysfunction resulting in increased production of thyroid stimulating hormone (TSH) and thus increased stimulation of the thyroid to produce T3 and T4
Describe the role of the parathyroid gland in calcium homeostasis
In response to hypocalcaemia, the parathyroid gland secretes parathyroid hormone (PTH) which increases renal calcium reapsorption, stimulates calcitriol release from the kidneys to stimulate increased calcium absorption in the small intestine, and stimulates osteoclasts to mobilise calcium stores within bone
What is the other name used to describe parathyroid hypofunction?
Hypoparathyroidism
Which procedure can cause parathyroid hypofunction, a condition which is typically very rare?
Parathyroid hypofunction is usually only seen following accidental removal of the parathyroid glands during a thyroidectomy
What is the other name used to describe parathyroid hyperfunction?
Hyperparathyroidism
What are the consequenses of parathyroid hyperfunction?
Parathryroid hyperfunction would cause excess parathyroid hormone (PTH) secretion causing increased renal calcium reapsorption, increased calcitriol release from the kidneys to stimulate increased calcium absorption in the small intestine, and increased osteoclasts stimulation to mobilise calcium stores within bone, resulting in hypercalcaemia
What is the most common cause of primary parathyroid hyperfunction?
Functional neoplasia of the parathyroid
What are the two possible causes of secondary parathyroid hyperfunction?
Chronic renal disease
Dietary imbalance
How can chronic renal disease cause secondary parathyroid hyperfunction?
Chronic renal disease causes a decrease in glomeruler filtration rate (GFR). This impaired kidney function will affect the balance of calcium and phosphorus in the body resulting in low blood calcium and high blood phosphorus levels, causing hypocalcaemia, stimulating the parathyroid to produce excess parathyroid hormone (PTH) resulting in parathyroid hyperfunction
How can parathyroid hyperfunction cause fibrous osteodystrophy?
Parathyroid hyperfunction causes excessive stimulation of osteoclasts which will mobilise excessive calcium in the bones which can lead to the replacement of bone by fibro-osseus tissue, known as fibrous osteodystrophy
What is pseudohyperparathyroidism?
Pseudohyperparathyroidism is caused by tumours of non-endocrine origin which produce parathyroid hormone related peptide (PTHrP) which will act as parathyroid hormone (PTH)
Give three examples of non-endocrine tumours which can cause pseudohyperparathyroidism
Lymphoma
Multiple myeloma
Anal sac adenocarcinoma
What is the clinical term for pancreatic hypofunction?
Diabetes mellitus
What are the consequences of pancreatic hypofunction?
Pancreatic hypofunction causes decreased insulin secretion resulting in hyperglycaemia and reduced glucose bioavailability as insulin would usually facilitate glucose transport from the bloodstream into cells.
What are the five clinical signs of pancreatic hypofunction?
Weakness
Glucosuria
Polyuria
Polydipsia
Cataracts
How does pancreatic hypofunction cause cataracts?
Pancreatic hypofunction causes increased glucose metabolism by the sorbitol pathway resulting in an accumulation of sugar alcohol in the eye lens causing cataracts
What is the most common cause of pancreatic hypofunction?
Damage to islets of langerhans
What are the four most common causes of damage to the islets of Langerhans causing pancreatic hypofunction?
Amyloidosis
Immune-mediated destruction
Vacuolar degeneration
Secondary to pancreatitis
What is the most common cause of damage to the islets of Langerhans causing pancreatic hypofunction in cats?
Amyloidosis
What is the most common cause of damage to the islets of Langerhans causing pancreatic hypofunction in dogs?
Immune-mediated destruction
What are the consequences of pancreatic hyperfunction?
Pancreatic hyperfunction causes increased insulin secretion resulting in hypoglycaemia and reduced glucose bioavailability as excessive insulin production will lead to increased uptake and utilisation of glucose by cells
What are the clinical signs of pancreatic hyperfunction?
Neurological signs
Hypertension (due to the excess secretion of catecholamines from the adrenal medulla in response to the hypoglycaemia)
What are the two most common causes of pancreatic hyperfunction?
Pancreatic hyperplasia
Functional neoplasia of the islets of Langerhans
What is the term used to describe functional tumours of the β-cells within the islets of Langerhans?
Insulinomas
