Endocrine

Question 1

What is the structure of the Endocrine System

Answer 1

• Derived from neural ectoderm
  
  • Strong association with vascular and neural tissue
• Organs include:
  
  • Pituitary gland
  • Thyroid gland
  • Parathyroid gland
  • Adrenal gland
  • Gonads
  • Endocrine pancreas
  • Cemoreceptor organs
  • Pineal gland
  • Adipose tissue

Question 2

What is the function of the Endocrine System

Answer 2

Maintain homeostasis

Question 3

How does the endocrine system maintain homeostasis?

Answer 3

• Hormone are the mediators of homeostasis
  
  • Polypptides
  • Steroids
  • Catecholamines and iodothyronines
• Feedback systems regulate most hormone concentrations
  
  • Hypothalamus → pituitary → Target tissue axis
• Some Hormonesrespond to plasma concentrations of vrious products or nervous stimuli
  
  • Thyroid C-cells, Parathyroid Cheif cells, adrenal medulla

Question 4

What are the different types of dysfunction of the Endocrine System?

Answer 4

• Increaed function
• Decreased function

Question 5

What are the types of increased function of the Endocrine System?

Answer 5

• Primary hyperfunction
  
  • increasd hormone secretion by an abnormal gland
• Secondary hyperfunction
  
  • Increased hormone secretion by a normal endocrine gland that is excessively stimulated

Question 6

What are the types of decreased function of the Endocrine System?

Answer 6

• Primary hypofunction
  
  • decreased hormone secretion by an abnormal glad
• Seconday hypofunction
  
  • Decreased hormone secretion by a normal endocrine gland that is inadequately stimulated

Question 7

What is the pattern of disease seen in the endocrine system?

Answer 7

• Metabolic processes are altered with any enocrine abnormality
• Neoplasia is the most common pathology pattern
• Cell adaptation is fairly common; atrophy, hyperplasia
• Immunopathology (autoimmunity) is relatively common as a pattern of endocrine disease
• Developmental, cell injury, vascular disturbanes and inflammation are less common patterns associated with endocrine disease

Question 8

What are the causes of disease in the Endocrine System?

Answer 8

• Genetic alterations are important as predisposing factors for neoplasia, immunopathologic and developmental endocrine diseases
• Nutritional factors can have significant impact on hormone-regulated homeostasis
• Infectious, chemical and physical insults are less common causes of endocrine disease

Question 9

What is the structure of the pituitary gland?

Answer 9

• Anterior lobe (adenohypophysis)
• Posterior lobe (Neurohypophysis)

Question 10

What are the parts of the Adenohypophysis and what hormones do they produce?

Answer 10

• “Anterior Lobe”
• Pars dstalis
  
  • acidophils (somatotrophs and Gonadotrophs)
    
    • GH and LTH
  • Basophils (Gonadotrophs and Thyrotrophs)
    
    • LH, FSH, and TH
  • Chromophobes (Corticotrophs and melaotrophs)
    
    • ATCH and MSH
• Pars intermedia
  
  • Melnotrophs
• Pars Tuberalis

Question 11

What is the structure of the Neurohypophysis?

Answer 11

• “Posterior Lobe”
• Hypothalamic neurosecretory neurons
  
  • Paraventricular and supraoptic nuclei
    
    • ADH and Oxytocin
• Infundibular stalk
• Pars nervosa

Question 12

What are the functions of the hormones from the Adenohypophysis

Answer 12

• Growth Hormone (somatotrophin)
  
  • regulates growth and metabolism
• Luteotropic Hormone
  
  • Stimulates progesterone secretion
• Luteinizing Hormone
  
  • Stimulates estrogen secretion
• Follicle Stimulating Hormone
  
  • Stimulates ovarian follicle growth and spermatogenesis
• Thyroid Stimulating Hormone (Thyrotrophinc, TSH)
  
  • Stimulats thyroid hormone secretion
• Adrenocorticotrophic Hormone
  
  • Stimulates glucocorticoid secretion
• Melanocyte Stimulating Hormone
  
  • stimulates melanocytes

Question 13

What are the functions of the hormones from the Neurohypophysis?

Answer 13

• Antidiuretic Hormone
  
  • Regulates water exretion
• Oxytocin
  
  • Stimulates smooth muscle contraction

Question 14

What are the types of dysfunction of the Pituitary gland?

Answer 14

• Increased Hormone Activity
• Decreased Hormone Activity

Question 15

What can cause increased hormone activity of the pituitary gland?

Answer 15

• Functional neoplasia
• Increased stimulation by hypothalamus
• Hormone-like substances

Question 16

What can cause decreased hormone activity of the pituitary gland?

Answer 16

• Destructive lesions
• Non-responsive target cells

Question 17

What are the pathology patterns seen in the pituitary gland?

Answer 17

• Neoplasia
  
  • functional or non-functional
• Cell adaptaion
  
  • Hyperplasia and atrophy
• Developmental anomalies
  
  • Aplasia, hypoplasia or cysts
• Immunopathology
  
  • Autoimmunity (lymphoplasmacytic hypophysitis)
• Inflammation
  
  • Uncommon
• Metabolic
  
  • All hormonal dysfunctions will result in metabolic alterations

Question 18

What causes pathology of the pituitary gland?

Answer 18

• Genetic injury
  
  • inherited or acquired
• Infectious agents
  
  • Uncommon
• Nutritional
• Chemical

Question 19

What is Chromophobe Adenoma in dogs?

Answer 19

• Functional Adenoma
• Neoplastic Chromophobes are unregulated and produce large amounts of ACTH
• Excessive ACTH causes diffuse adrenocortical hyperplasia
  
  • “Hyperadrenocorticism” “Cushing’s Disease”
• Approximately 80-90% of cases of canine hyperadrenocorticism are due to pituitary neoplasia
• Most Common Pituitary tumor of dogs
  
  • Increased frequency in Boston Terriers, Beagles, Boxers, Dachshunds, and Miniature Poodles
• May arise from hyperplastic nodules that mutate to become clonal
• Microadenoma
  
  • More likely to be functional and produce excess ACTH
• Macroadenoma
  
  • Less likely to be functional and act as space-occupying mass
    
    • Hypopituitarism or hypothalamic compression

Question 20

What is Pars intermedia adenoma?

Answer 20

• Pars intermedia is the second most common location for chromophobe adenoma in dogs
  
  • Can be functional or compressive, just like those from the pars distalis
    
    • Compressive = hypopituitarism or diabetes insipidus due to pressure on the hypothalamus or destruction of the neurohypophysis
• Pars intermedia dysfunction is the most common endocrine abnormality of horses
  
  • most common in older horses
  • Possibly due to age-related oxidative injury of dopaminergic neurons

Question 21

What is pituitary pars intermedia dysfunction in horses?

Answer 21

• Decreased dopamine production results in increased activity of melanotrophs
  
  • Melanotrophs produce proopiomelanocortin (POMC)
  • POMC > ACTH > a-MSH + B-endorphin + corticotrophin-like intermediate peptide
• Signs include increased hair growth (hypertrichosis/hirsutism), increased adipose tissue deposition, weight loss
• Lesions range from diffuse hyperplasia to micro/macro adenoma
• Hirsutism may be due to increased POMC activity or hypothalamic compression
  
  • Compression can interfere with thermoregulation and appetite centers
• Melanotrophs are regulated by dopaminergic neurons and not the hypothalamic-pituitary-adrenal axis
  
  • Adrenal glands are usually normal

Question 22

What is somatotroph adenoma?

Answer 22

• Arise from somatotrophs (Acidophils)
  
  • Uncommon, mainly cats, dogs, sheep
  • Functional adenoma (increased growth hormone) in cats
    
    • Increased production of insulin-like growth factor 1 by the liver
      
      • Growth of soft tissue and bone (acromegaly, mainly facial bones)
      • Insulin-resistant diabetes mellitus (Type 2)
  • Non-functional adenoma can cause panhypopituitarism and hypothalamic compression
• Basophil Adenoma
  
  • Rare

Question 23

What are Pituitary Cysts?

Answer 23

• Mainly in brachycephalic dogs
• Abnomal development in or around the pituitary gland
  
  • Craniopharyngeal duct cyst
  • Pharyngeal hypophyseal cyst
  • Oropharyngeal ectoderm cyst
• Can compress and damage surrounding structures

Question 24

What are the types of pituitary cysts?

Answer 24

• Craniopharyngeal duct cysts
  
  • Diabetes insipidus, pituitary hypofunction
• Pharyngeal hypophyseal cysts
  
  • Respiratory distress
• Oropharyngeal ectoderm cysts
  
  • Panhypopituitarism
  • Juvenile hypopituitarism in GS

Question 25

What is Pituitary dwarfism?

Answer 25

• Failure of Rathkes pouch ectoderm to differentiate into the adenohypophysis
• Autosomal recessive in GS
  
  • Also occurs in Spitz, Toy Pinschers, and Karelian bear dogs
  • Generally normal until 2 months of age
• Manifestations due to decreased growth hormone
  
  • Decreased insulin-like growth factor 1
  • Decreased growth (retain infantile characteristics)
  • Retention of puppy hair progressing to alopecia

Question 26

What is Craniopharyngioma?

Answer 26

• Neoplastic remnants of Rathkes pouch oropharyngeal ectoderm
  
  • Occurs in Young dogs, Rare
  • Hypothalamic destruction and decreased hypothalamic trophic hormones

Question 27

What is a non-functional adenoma?

Answer 27

• Dogs, cats, and others
• These can arise from any cell, but often of chromophobe origin
• Hypopituitarism with endocrine gland atrophy and hypofunction

Question 28

What causes Pituitary Gland Inflammation?

Answer 28

• Pituitary Abscesses
  
  • Most common in Cattle
    
    • Secondary to nasal septal infections
  • Acts as a space occupying lesion
    
    • Blindness, depression, drooling, tongue prolapse
      
      • Can mimic rabies

Question 29

What are the Neurohypophysis diseases?

Answer 29

• Pituitary Diabetes Insipidus
  
  • Destruction of the neurohypophysis or supraoptic nuclei of the hypothalamus
    
    • Decreased ADH production or release
      
      • PU/PD, Dilute urine
    • Decreased Oxytocin
• Nephrogenic diabetes insipidus
  
  • Primary renal disease, ADH is normal

Question 30

What is the structure of the Adrenal Gland?

Answer 30

• Cortex (mesoderm origin)
  
  • Zona glomerulosa
    
    • Mineralocorticoids
  • Zona fasciculata
    
    • Glucocorticoids
  • Zona reticularis
    
    • Sex steroids
• Medulla (Neural crest origin)
  
  • Catecholamines

Question 31

What are the functions of Adrenal Gland?

Answer 31

• Mineralocorticoids
  
  • Aldosterone:
    
    • Regulates blood pressure
    • Promotes sodium retention and potassium excretion by renal tubules
      
      • Increases intracellular fluid volume and regulates extracellular fluid volume
• Glucocorticoids
  
  • Cortisol and corticosterones
    
    • Gluconeogenesis, protein and fat catablism, suppressive for inflammation and immunity
• Sex Steroids
  
  • Progesterone, estrogen and androgens
• Catecholamines
  
  • Epinephrine and norepinephrine

Question 32

What regulates the functions of the Adrenal Gland?

Answer 32

• Pituitary hormones
  
  • ACTH
• Renin-angiotensin system
  
  • Renin (released from juxtaglomerular cell in response to low blood pressure) cleaves angiotensinogen
  • Angiotensin I and II contracts vascular smooth muscle and stimulates aldosterone secretion
• Neural Controls
  
  • Catecholamine secretion

Question 33

How can the Adrenal Gland dysfunction?

Answer 33

• Hyperfunction (Hyperadrenocorticism)
• Hypofunction (hypoadrenocorticism)

Question 34

What is Hyperadrenocorticism?

Answer 34

• Primary or secondary adrenal involvement
• Polyuria, polydipsia, increased appetite, weakness, alopecia, increased infection
• “Cushing’s Disease”

Question 35

What is Hypoadrenocorticism?

Answer 35

• Primary or secondary adrenal involvement
• Anorexia, weight loss, GI disturbances, dehydration
• “Addison’s Disease”

Question 36

What are the pathology patterns that affect the Adrenal Gland?

Answer 36

• Metabolic
  
  • Adrenal dysfunction will result in metabolic alterations
• Neoplasia
  
  • Functional or non-functional
• Cell alteration and injury
  
  • Secondary hyperplasia is common secondary to pituitary disease
  • Secondary atrophy due to hypopituitarism
• Developmental anomalies
  
  • Aplasia, hypoplasia or cysts
• Immunopathology
  
  • Autoimmunity

Question 37

What causes pathology of the Adrenal Gland?

Answer 37

• Genetic predisposition
  
  • pituitary neoplasia causing adrenal hyperplasia
• Chemical
  
  • Exogenous administration of glucocorticosteroids

Question 38

What is adrenal cortical neoplasia?

Answer 38

• Adrenal cortical adenoma or carcinoma
  
  • Most arise from the zona fasciculata
    
    • Less commonly the zona glomerulosa in cats (hyperaldoteronism) or zona reticularis in ferrets (hyperestrogenism)
  • Adenomas are more common than carcinoma
    
    • old dogs mainly affected, also seen in old cattle
• Can be multiple or single, unilateral or bilateral
  
  • Contralateral adrenal gland atrophy occurs with functional unilateral neoplasms

Question 39

What is functional adrenal cortical neoplasia?

Answer 39

• Result in hyperadrenocorticism
  
  • PU/PD
  • Increased appetite
  • Muscle atrophy and weakness
  • Alopecia (Endocrine dermatopathy)
  • Increased incidence of infections

Question 40

What is Hyperadrenocrticism?

Answer 40

• Clinical syndrome characterized by increased cortisol/glucocorticosteroids
  
  • Cushings disease
• Most often due to ACTH-secreting pituitary adenoma
  
  • less often due to adrenal cortical adenoma or carcinoma
• Lesions associated with hyperadrenocorticism
  
  • Hepatic lipidosis and glycogenosis
  • Epidermal and adnexal atrophy
  • Systemic mineralization
    
    • Skin, lung, muscle, stomach
  • Lymphoid tissue depletion

Question 41

What are the Functions of glucocorticosteroids?

Answer 41

• Gluconeogenesis
• Lipogeness
• Protein Catabolic
• Anti-inflammatory
• Immunosuppression
• Inhibition of fibroplasia

Question 42

What is Diffuse Adrenal Cortical Hyperplasia?

Answer 42

• Diffuse adrenal cortical hyperplasia
  
  • Common in dogs
  • Occurs secondary to functional chromophobe adenoma of the pituitary gland
    
    • Excessive and unregulated secretion of ACTH
  • Hyperadrenocorticism is the result
    
    • Signs and lesions are the same as those of hyperadrenocorticism caused by primary adrenal neoplasia

Question 43

What is Adrenal Cortical nodular hyperplasia?

Answer 43

• Common age-related change in dogs, cats and horses
• Some of these are functional
  
  • Increased ACTH from pituitary hyperplasia or neoplasia
• Some are non-functional and of minimal to no clinical significance

Question 44

What are the types of Adrenal Medullary neoplasia?

Answer 44

• Phenochromocytoma
  
  • Arise in chromaffin cells of the medulla
  • Most common in dogs and cattle
• Ganglioneuroma and neuroblastoma
  
  • Uncommon
  • Neuroectoderm origin

Question 45

What is Pheochromocytoma?

Answer 45

• Most are non-functional
  
  • Functional neoplasia results in systemic hypertension due to norepinephrine secretion
• They can be benign or malignant
  
  • Malignant neoplasms often invade the great vessels
    
    • Approximately 50% metastasize in dogs

Question 46

What is Adrenal Hypoplasia or agenesis?

Answer 46

• Rare condition of dogs
• Total agenesis is fatal
• Hypoplasia results in variable degrees of hypoadrenocorticism

Question 47

What is Diffuse (Iatrogenic) adrenal cortical atrophy?

Answer 47

• Most common in dogs on long-term glucocorticosteroids therapy
• Exogenous glucocorticosteroids result in inhibition of adrenal cortical function and subsequent atrophy

Question 48

What is Idiopathic Adrenal Cortical Atrophy?

Answer 48

• Uncommon conditions of dogs and cats
• Immune-mediated damage and atrophy of the adrenal cortex
  
  • May also result from destruction (chronic inflammation) or non-functional neoplasia of the pituitary gland
    
    • Signs usually occur only after 90% of the cortex is destroyed or atrophied
• Results in hypoadrenocorticism
  
  • Anorexia and weight loss
  • Diarrhea and dehydration

Question 49

What Causes Adrenal Gland Destruction?

Answer 49

• A wide variety of processes periodically affect the adrenal gland
  
  • This is mainly due to the rich vascular network a the cortico-medullary junction
• Ex:
  
  • Thrombosis due to DIC
  • Adrenalitis due to infectious emboli
  • Metastatic neoplasia
    
    • 15-30% of metastatic lesion may occur here
      
      • Melanotic neoplasia, hemangiosarcoma, Lymphosarcoma

Question 50

What is Hypoadrenocorticism?

Answer 50

• Clinical syndrome characterized by decreased adrenocortical hormones
  
  • Addison’s Disease
• Mainly affects the zona glomerulosa
  
  • immune-mediated most common in Portuguese water dogs, Bearded Collie, Standard poodle
  • Hypoaldosteronism
    
    • Hyponatremia and hyperkalemia
    • Decreased cortisol is also present

Question 51

What is the Structure of the Thyroid Gland?

Answer 51

• Two lobes with a narrow isthmus
• Thyroid Epithelial cells
  
  • Arranged in follicles
  • Produce thyroid hormones
• Thyroid C-cells
  
  • Small aggregates of cells between follicles
  • Produce calcitonin

Question 52

What is the Function of the Thyroid Gland?

Answer 52

• Thyroid hormones (Triiodothyronine; T₃ and Tetraiodothyronine; T₄)
  
  • increased metabolism (protein synth, glycolysis, gluconeogenesis, lipolysis
  • Stimulate heart and neural function
• Calcitonin
  
  • Regulation of serum calcium concentration
    
    • Inhibition of osteoclasts and bone resorption and synergistic with parathormone to decrease renal phosphorus absorption
• Regulation of adrenal function
  
  • Hypothalamic releasing factors
  • Pituitary hormones
    
    • TSH

Question 53

how can the Thyroid gland Dysfunction?

Answer 53

• Hyperfunction (hyperthyroidism)
• Hypofunction (hypothyroidism)

Question 54

What is Hyperthyroidism?

Answer 54

• Usually primary thyroid involvement
• Polyphagia, weight loss, weak, tachycardia
• Most common in cats

Question 55

What is Hypothyroidism?

Answer 55

• Usually primary thyroid involvement
• Inactivity, alopecia, lethargy, weight gain, obesity
• Most common in dogs

Question 56

What are the Patterns Pathogenesis of The Thyroid Gland follow?

Answer 56

• Metabolic
  
  • Thyroid dysfunction will result in metabolic alterations
• Neoplasia
  
  • Usually functional, sometimes non-functional
• Cell alteration and injury
  
  • Hyperplasia and atrophy are common
• Immunopathology
  
  • Autoimmune destruction of the thyroid
• Developmental
  
  • Ectopic thyroid tissue

Question 57

What causes pathogenesis of the Thyroid Gland?

Answer 57

• Genetic predisposition
  
  • Thyroid neoplasia, hyperplasia or autoimmunity
• Nutritional
  
  • Deficiency of iodine, tyrosine or other thyroglobulin components
• Chemical
  
  • Goitrogenic compounds
    
    • Thiouracil, sulfonamides, cyanogenic plants

Question 58

What are the types of Thyroid Gland Neoplasia?

Answer 58

• Thyroid follicular adenoma and carcinoma
  
  • Most common in old cats (usually adenoma)
    
    • These are often functional resulting in hyperthyroidism
    • There can be nodules in one or both lobes
    • Distinction between hyperplasia is sometimes difficult
  • Less Common in dogs (usually carcinoma)
    
    • These are often large, invasive, and metastatic to regional lymph nodes

Question 59

What is Thyroid Follicular Nodular Hyperplasia?

Answer 59

• Most common as an age-related change in horses, dogs, and cats
• Most are non-functional and of minimal significance
  
  • In cats, some of these may progress to adenoma

Question 60

What is Hyperthyroidism?

Answer 60

• Functional neoplasms result in hyperthyroidism (increased basal metabolic rate)
  
  • Polyphagia with weight loss
  • Hyperactivity and nervousness
  • Weakness and heat intolerance
  • Tachycardia
• May be due to mutation in the gene coding for the TSH receptor
  
  • This is different than Graves disease in humans since there are no auto-antibodies to the TSH receptor in cats

Question 61

What is Parafollicular (C-cell) neoplasia?

Answer 61

• Most common in old bulls and horses
  
  • Often malignant in bulls, but incidental in horses
• Bulls
  
  • These may arise due to long-term ingestion of high calcium rations
    
    • High calcium rations also induce hyperplasia initially
  • Pituitary or adrenal medulla neoplasia may occur concurrently
• Some can be functional
  
  • Hypercalcitoninism
    
    • Vertebral osteophytes and osteosclerosis

Question 62

What is Goiter?

Answer 62

• Inhibition of thyroid hormone formation
  
  • Nutritional deficiency of iodine or tyrosine
  • Goitrogenic compound ingestion
    
    • Cruciferous plants (Brassica sp.)
    • Drugs (phenobarbital, rifampin, among others)
• Thyroid hyperplasia is the lesion
  
  • Cause varies
• Results in hypothyroidism in postnatal animals
  
  • Stillbirth is most common when affected in utero
  • Neonates can also have signs of hypothyroidism
    
    • Myxedema

Question 63

What are the types of Goiter?

Answer 63

• Diffuse:
  
  • Excessive TSH stimulus due to decreased thyroid hormones
    
    • Iodine deficiency is a common cause
• Multinodular
  
  • Independent of TSH (autonomous)
  • Mainly in old cats
• Dyshormonogenic
  
  • Defective synthesis with normal iodine levels
    
    • Due to genetic defect in thyroglobulin synthesis or thyroid peroxidase
  • Autosomal recessive in sheep and goats

Question 64

What is Idiopathic follicular atrophy?

Answer 64

• Most common in dogs
• There is primary degeneration and atrophy of the thyroid gland
• Results in hypothyroidism
  
  • Accounts for approximately 50% of the cases of canine hypothyroidism

Question 65

What is Lymphocytic thyroiditsi?

Answer 65

• Type of Thyroid Gland atrophy
• Most common in dogs
• Autoimmune destruction of the thyroid gland
  
  • There is fibrosis, atrophy, and lymphocytic infiltration of the gland
• Results in hypothyroidism
  
  • Accounts for approximately 50% of these cases in dogs
• Similar to Hashimoto’s thyroiditis
  
  • Auto-antibodies to thyroglobulin

Question 66

What is Hypothyroidism?

Answer 66

• Clinical syndrome characterized by decreased T3/T4
• Signs include:
  
  • Weight gain and inactivity
  • Alopecia (Endocrine dermatopathy)
  • Reproductive abnormalities
  • Hypercholesterolemia
• Systemic Lesion associated with disease - The cause of ~50% of the cases of hypothyroidism in dogs
  
  • Hyperkeratosis and adnexal atrophy of the skin
  • Myxedema (facial edema)
  • Atherosclerosis
  • Hepatic lipidosis

Question 67

What is the structure of Parathyroid Gland?

Answer 67

• Chief cells
  
  • Comprise most of the gland
  • Produce parathormone
• Oxyphil Cells
  
  • Modified Chief cells

Question 68

What is the function of the Parathyroid Gland

Answer 68

• Control nd maintenance of serum Calcium levels
  
  • Parathyroid hormone (Parathormone)
    
    • Released in response to low serum calcium
    • Stimulates GI absorption and resorption of Ca²⁺ from bone, increased renal retention of Ca²⁺ and inhibits phosphorus reabsorption
  • Calcitonin (From Thyroid C-Cells)
    
    • Released in response to high serum calcium
    • Decreases GI absorption and resorption from bone, decreased renal retention
  • Vitamin D (From skin or diet)
    
    • Conversion to calcitriol in the kidney
    • Synergistic with parathormone

Question 69

What is Hyperparathyroidism?

Answer 69

• Primary or secondary parathyroid involvement
  
  • Usually secondary (primary renal or nutritional)
• Increased lameness and fractures, facial bone enlargement and weakening (fibrous osteodystrophy)

Question 70

What is Hypoparathyroidism?

Answer 70

• Usually primary parathyroid involvement
• Variable signs, including anorexia, weakness, or tetany or convulsions

Question 71

What is the Pattern of pathogenesis of the Parathyroid gland?

Answer 71

• Metabolic
  
  • Parathyroid dysfunction will result in abnormal calcium metabolism
  • Metabolic problems frequently causes parathyroid abnormalities
• Cell alteration and injury
  
  • Hyperplasia is common secondary to renal or nutritional disease
  • Idiopathic hyperplasia
• Development
  
  • Cyst formation; variable significance
• Immunopathology
  
  • Autoimmunity
• Neoplasia
  
  • Parathyroid involvement
  • Non-parathyroid neoplasm producing parathormone-like substances

Question 72

What are the causes of pathology in the parathyroid gland?

Answer 72

• Nutritional
  
  • Deficiency or imbalance of calcium and phosphorus
• Chemical
  
  • Plants with Vitamin-D-Like activity
• Genetic Predisposition
  
  • Parathyroid neoplasia or autoimmunity

Question 73

What is Hyperparathyroidism?

Answer 73

• A clinical syndrome characterized by excessive activity of parathormone
• Features:
  
  • Hypercalcemia due to enhanced intestinal absorption and bone calcium mobilization
  • Fibrous osteodystrophy
    
    • Bone weakness and factures
    • Thickened facial bones
  • Gastrointestinal disturbances
  • Muscle weakness

Question 74

What is Nutritional Secondary Hyperparathyroidism?

Answer 74

• Diets high in phosphorus and low in calcium
  
  • Grain with low quality roughage - Bran disease
• Persistent hypocalcemia results in parathyroid hyperplasia and increased PTH secretion
• Clinical and pathological features are those on hyperparathyroidism

Question 75

What is Renal Secondary hyperparathyroidism?

Answer 75

• Dogs with chronic renal failure
• Renal retention of phosphorus and loss of calcium
  
  • Decreased renal conversion of calcifediol to calcitriol also contributes to hypocalcemia
• Persistent hypocalcemia results in parathyroid hyperplasia and increased PTH secretion
  
  • In long-standing cases, hyperplasia becomes autonomous (no longer responsive to Ca2+ levels
    
    • Tertiary parathyroid hyperplasia
• Clinical and pathological features are those of hyperthyroidism and renal failure
  
  • Fibrous osteodystrophy
  • Uremia and PU/PD

Question 76

What is Pseudohyperparathyroidism?

Answer 76

• Mainly dogs and sometimes cats
• Persistent hypercalcemia without increased PTH
• Hypercalcemia is due to production of parathormone hormone-related peptide (PHRP), osteolytic factors, Cytokines (TNF), among other substances by certain neoplasms
  
  • Adenocarcinoma of anal sac apocrine glands
  • Lymphosarcoma (canine)
  • Plasma cell tumors (multiple myeloma)
• Unregulated hypercalcemia due to PTH-like activity
  
  • Neuromuscular and cardiovascular dysfunction
  • Soft tissue mineralization
• Parathyroid gland atrophy

Question 77

What is Calcinogenic plant toxicity?

Answer 77

• Grazing animals in areas with appropriate plants
  
  • Plants with Vit D activity
    
    • Cestrum diurnum
• Hypercalcemia is the result
  
  • Increased bone density
  • Soft tissue mineralization

Question 78

What are parathyroid cysts?

Answer 78

• Relatively common in dogs
• Originate from embryonic duct between thyroid and parathyroid glands or other embryonic structures
  
  • Kursteiners usts
• Minimal significance unless they are large and space-occupying

Question 79

What is lymphocytic parathyroiditis?

Answer 79

• A type of parathyroid atrophy
• Uncommon in adult dogs
  
  • increased incidence in miniature schnauzers
• Most likely autoimmune origin
  
  • Lymphoid infiltrate, chief cell atrophy, fibrosis
• Results in hypoparathyroidism
  
  • Increased neuromuscular excitability
  • Decreased bone reabsorption

Question 80

What is Hypoparathyroidism?

Answer 80

• A clinical syndrome characterized by decreased activity or response to parathormone
• Features:
  
  • Hypocalcemia
    
    • Decrease bone resorption of Ca2+
    • Increased phosphorus retention by tubules
  • Altered neuromuscular excitability
    
    • Weakness, ataxia, tremors, tetany
    • Paresis

Question 81

What is Parturient paresis / Puerperal tetany?

Answer 81

• Mainly in cattle and dogs
  
  • Cattle - parturient paresis “milk fever”
  • Dogs - puerperal tetany “eclampsia”
• Profound hypocalcemia
• Disease often due to acute need during parturition or lactation

Question 82

How does Parturient paresis occur?

Answer 82

• PTH is produced, but there are reduced osteoclasts due to high Ca2+ ration
• Mechanisms:
  
  • High threshold potential at neuromuscular junctions
  • Concurrent hypermagnesemia
    
    • Magnesium acts as a calcium channel antagonist
  • increased levels of VFA
    
    • Inhibitory at neuromuscular synapses

Question 83

How does Puerperal tetany occur?

Answer 83

• Typically occurs at the peak of lactation
  
  • 2-3 weeks after whelping
  • More frequent in small breed dogs
• Mechanisms
  
  • Not due to inadequate PTH
  • Low threshold potential at neuromuscular junction
    
    • Na+ channels are activated with very little increase in membrane potential
      
      • Low Ca2+ in extracellular fluid lowers the threshold potential for activation of NA channels
    • Repetitive firing of motor nerve fibers occurs

Question 84

What is the structure of the Endocrine Pancreas?

Answer 84

• Alpha Cells
  
  • Comprise 5-30% of the islet cell population
  • Glucagon is the major product
• Beta Cells
  
  • 60-80% of the islet cell population
  • Insulin is the major product

Question 85

What is the function of the Endocrine Pancreas?

Answer 85

• Control of glucose metabolism
  
  • Glucagon:
    
    • Increases blood glucose concentration
    • increased glycogenolysis (liver and other tissues)
    • Enhances hepatic gluconeogenesis and FA oxidation (lipolysis)
  • Insulin:
    
    • Decreases blood glucose concentration
    • Enhances glucose entry into cells and hepatic glycogen storage
      
      • Mainly hepatocytes, skeletal muscle, adipocytes
    • Increased glycogenesis and glucose oxidation, Increased lipogenesis

Question 86

What results in Pancreas Dysfunction?

Answer 86

• Hyperfunction (Hyperinsulinism)
  
  • Primary islet cell neoplasia
  • Neurological signs and weakness
• Hypofunction (Diabetes mellitus)
  
  • Beta cell destruction and deficiency
  • Emaciation, PU/PD, Dehydration, various organ and tissue abnormalities

Question 87

What patterns of Pathogenesis occur in the Pancreas?

Answer 87

• Metabolic:
  
  • Endocrine pancreas dysfunction will result in abnormal carbohydrate metabolism
  • Metabolic problems (Amyloidosis) may cause islet cell abnormalities
• Cell alteration and injury
  
  • Acute pancreatic necrosis of dogs will damage islets
• Developmental:
  
  • Rare
  • Hypoplasia
• Immunopathology
  
  • Autoimmunity

Question 88

What causes pathogenesis of the pancreas?

Answer 88

• Nutritional
  
  • Carb and fat excess or imbalance in the ration
• Genetic predisposition
  
  • Neoplasia or autoimmunity

Question 89

What is Diabetes Mellitus?

Answer 89

• Most common in dogs, sometimes in cats
  
  • Often middle-age to older female dogs
  • more common in smaller breeds
• The problem is inadequate insulin activity
  
  • Type I (insulin-dependent) form is due to decreased insulin secretion
  • Type II (non-insulin-dependent) form is due to inadequate insulin release or target cell response
    
    • more common in cats

Question 90

What conditions can cause reduced insulin activity?

Answer 90

• Islet cell hypoplasia
• Destruction of Pancreatic islets
  
  • acute pancreatic necrosis in dogs (chronic relapsing pancreatitis)
    
    • less often immune-mediated destruction
  • Islet amyloidosis in cats
• Failure of insulin release from islet cells
• Failure of tissues to respond to insulin
  
  • Antagonism between insulin and other hormones
    
    • Hyperadrenocorticism promotes hyperglycemia and insulin resistance
    • Growth hormone stimulates increased secretion of insulin-like growth factor

Question 91

How does Diabetes Mellitus occur in cats?

Answer 91

• More often type II
• Predisposing factors:
  
  • Hyperadrenocorticism, excess GH activity, Obesity
• Islet amyloidosis
  
  • Co-secretion of Islet amyloid Polypeptide (IAPP; amylin) with insulin
  • Amylin fibrils can cause B-cell death due to misfolding protein response
• Insulin resistance
  
  • Decreased uptake of glucose by insulin-sensitive cells
    
    • Predominately hepatocytes, skeletal muscle, adipocytes

Question 92

What are the clinical features of Diabetes Mellitus?

Answer 92

• Emaciation
• PU/PD
• Increased infections
• Hyperglycemia
• Glycosuria
• Ketoacidosis and ketonuria

Question 93

What are the pathological features of Diabetes mellitus?

Answer 93

• Hepatic lipidosis/glycogenosis
• Glomerulosclerosis and glycogen nephrosis
• Microangiopathy
  
  • Glomerulopathy retinopathy and gangrene
• Cataracts (shift to sorbitol pathway)
• Vascular lesions and necrosis are not as prominent as in humans
• Other lesion associated with any predisposing factors
  
  • Adrenal cortical hyperplasia or pituitary adenoma

Question 94

What are Islet Cell Tumors?

Answer 94

• Rare, mainly dogs
• Insulinoma is the most common type
  
  • a wide variety of hormones can be associated with functional islet cell neoplasia
  • May also see amyloidosis due to concurrent secretion of IAPP
• Neoplastic Bet cells produce excess insulin
  
  • Hyperinsulinemia resulting in hypoglycemia
• Neurological disease