Finals Questions Flashcards by Danica Mae Araza

The majority of the epithelial cells and the most important functional cells of the thyroid

Follicular cells

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is the most important enzyme in the synthetic pathway of thyroid hormones.

Thyroperoxidase

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oxidizes iodide ion (I-) taken up by follicular cells into reactive iodine (I2) which binds to the tyrosine residues in thyroglobulin

Thyroperoxidase

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also functions as a “coupling” enzyme to combine monoiodotyrosine (MIT) and
diiodotyrosine (DIT) to form triiodothyronine (T3) or 2 molecules of DIT to form tetraiodothyronine
(T4) or thyroxine

Thyroperoxidase

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This amino acid is an essential component of thyroid hormones, is incorporated within the molecular
structure of thyroglobulin.

Tyrosine

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(Enumerate) The skeletal lesion of generalized fibrous osteodystrophy (osteitis fibrosa) is characterized by

increased bone resorption
decreased radiographic density
incomplete fractures

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In response to 1,25 dihydroxycholecalciferol, the absorptive cells of this organ synthesize and secrete a specific calcium-binding protein (CaBP)

intestine

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(Enumerate) The more active metabolites of ergosterol synthesized by the liver and kidney

a) 25-hydroxyergosterol
b) 1,25-dihydroxyergosterol

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The first step in the metabolic activation of vitamin D is the conversion of cholecalciferol to 25-dihydroxycholecalciferol (25-OH-CC) in what organ?

liver

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The first step in the metabolic activation of vitamin D is the conversion of cholecalciferol to 25-
dihydroxycholecalciferol (25-OH-CC) in the liver under the enzymatic control of a hepatic microsomal
enzyme referred to as?

calciferol-25-hydroxylase.

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High circulating levels of 25-OH-CC serve as a reservoir of vitamin D for the synthesis of the active forms of vitamin D by what organ?

kidney

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A high-affinity vitamin D-binding protein in the serum transports cholecalciferol from its site of synthesis in the skin to the

liver

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this hormone is secreted continuously under conditions of normocalcemia

Calcitonin

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is an important PTH-like factor that plays a central role in the pathogenesis of humoral hypercalcemia of malignancy

Parathyroid hormone-related protein (PTHrP)

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Stimulation of _________ stimulates the
conversion of ATP to cAMP in target cells.

adenylyl cyclase

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Overexpression of _________ leads to
osteopetrosis associated with decreased osteoclast formation and function

osteoprotegerin (OPG)

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is a complex, multistep, process that involves the activation of multiple genes and the action of multiple hormones

Bone resorption

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is the principal hormone involved in the minute-to-minute, fine regulation of
blood calcium in mammals.

Parathyroid hormone

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(Enumerate) The most important biologic effects of PTH are to:

elevate the blood concentration of calcium.
decrease the blood concentration of phosphorus.
increase the urinary excretion of phosphorus by a decreased rate
of tubular reabsorption.
increase the tubular reabsorption of calcium.
increase the rate of skeletal remodeling and the net rate of bone
reabsorption.
increase the number of osteoclasts on bone surfaces and the rate
of osteolysis.
increase the urinary excretion of hydroxyproline.
activate adenylate cyclase in target cells.
accelerate the formation of 1,25-dihydroxycholecalciferol or 1,25-
dihydroxyvitamin D

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(Enumerate) The major inhibitors of PTH synthesis and secretion

1) increased serum levels of Ca2+
2) 1, 25-dihydroxyvitamin D

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is the major intracellular anion existing in inorganic form

Phosphate

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(Enumerate) inorganic form of phosphate

HPO4 and H2PO4

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(Enumerate) organic form or compounds of phosphate

phospholipids
nucleic acids
phosphoproteins
ATP

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(Enumerate) Factors which increase intestinal calcium absorption, directly or indirectly, due to stimulation of 1,25-dihydroxyvitamin D synthesis,

parathyroid hormone
growth hormone
testosterone
estrogen
furosemide

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(Enumerate) two components of calcium absorption from the intestinal tract

1. saturable or transcellular transport 2. non-saturable or intercellular (paracellular) transport

The principal stimulator of calcium reabsorption in the distal convoluted tubules

parathyroid hormone

(Enumerate) Reabsorption of calcium in the distal convoluted tubule is an active transcellular process requiring the presence of calcium channels in the luminal cell membrane, intracellular calcium-binding proteins, such as

1) calbindins, 2) Ca2+ - ATPase 3) Na+ / Ca2+ exchanger

About 70% of filtered calcium is reabsorbed in the ___________ by diffusion and convection with water uptake between the epithelial cells

proximal convoluted tubules

also absorbs about 20% of the filtered calcium.

ascending loop of Henle

reabsorbs approximately 10% of the filtered calcium

distal convoluted tubule

(Enumerate) Functions of Calcium

1. structural integrity of bones and teeth 2. as a messenger or regulatory ion

(Enumerate) Two sources of Ca2+ in bone that can enter the circulation

1. readily mobilizable calcium salts in the ECF 2. hydroxyapatite crystals that require digestion by osteoclasts before Ca2+ can be released from bone

(Enumerate) Phosphate plays an integral role in metabolic processes such as:

1. energy metabolism 2. delivery of O2 to tissues 3. muscle contraction 4. skeletal integrity

major organ for the degradation of PTH

kidney

25-hydroxycholecalciferol is synthesized in what organ?

liver

25-hydroxycholecalciferol synthesized in the liver and is metabolized in the _________ to 1,25-dihydroxycholecalciferol or 1,25-(OH)2- CC

kidney

The 25-hydroxycholecalciferol synthesized in the liver is metabolized in the kidney to ____________.

1,25-dihydroxycholecalciferol (1,25-(OH)2- CC)

The assembly of thyroid hormones within the follicular lumen is made possible by a unique protein which is synthesized by follicular cells.

thyroglobulin

is a peptide hormone of the mammalian thyroid that has been shown to be secreted by C-cells.

Calcitonin

The biosynthesis of thyroid hormones is also unique among endocrine glands because the final assembly of hormones occurs extracellularly within the follicular lumen.

Essay: Hypothalamic-pituitary-thyroid axis

The hypothalamic-pituitary-thyroid axis regulates thyroid hormone levels. Thyrotropin-releasing hormone (TRH) from the hypothalamus stimulates the pituitary to release thyroid-stimulating hormone (TSH), which promotes the secretion of T4 and T3 from the thyroid gland. T4 is converted to the more active T3 in the pituitary by monodeiodinase. T3 and T4 regulate TSH secretion through negative feedback at the pituitary and hypothalamus. Additionally, somatostatin and dopamine inhibit TSH release, while thyroid hormone stimulates somatostatin secretion, providing further negative feedback.

__________ and thyroid function should be viewed as an integrated system composed of metabolic subsystem for uptake and transport of iodide, iodine incorporation into the hormones of the thyroid gland (e.g., T4 and T3), and factors which regulate the overall function of the thyroid gland.

Iodine Metabolism

the ratio of T4 to T3 in thyroglobulin

3.6:1

the ratio of the daily production rates, based on plasma concentration and turnover of the two hormones

2:1

About 40% of the extrathyroidal T4 in the dog is in the plasma.

clinical term for a non-neoplastic and non-inflammatory enlargement of the thyroid gland which develops in mammals, birds, and sub-mammalian vertebrates

Hyperplasia of Thyroid Follicular Cells (‘Goiter’)

The removal of the caudal one-fourth of either lobe of the thyroid for histologic examination is a simple surgical procedure that is without significant risk, even if the dog is hypothyroid

Thyroid Biopsy

In terrestrial vertebrates, both of these hormones are important regulators of total body calcium

parathyroid glands kidneys

are the major regulators of the phosphate concentration in the serum

kidneys

basic type of secretory cell which secrete and release parathyroid hormone

chief cells

Low levels of intra- and extracellular calcium speed up the rate of secretion and shorten the resting phase; conversely, high intra- and extracellular levels of calcium suppress the rate of PTH secretion and lengthens the resting phase of the secretory cycle.

The concentration of blood phosphate has no direct regulatory influence on the synthesis and secretion of PTH

This receptor is a membrane-bound protein on osteoblasts that serves as a common mediator for osteoclastic bone resorption.

RANK ligand or RANKL

is a novel member of the TNF receptor superfamily that is produced by cells of the osteoblast lineage and is a negative regulator of bone resorption

Osteoprotegerin (decoy receptor)

The site of action of PTH on the tubular reabsorption of phosphate has been localized to the __________ of the nephron

proximal convoluted tubule

The other important effect of PTH on this organ is the regulation of the conversion of 25-hydroxycholecalciferol to 1, 25-dihydroxycholecalciferol and other metabolites of vitamin D

kidney

Calcitonin is a polypeptide hormone composed of how many amino acid residues?

32 amino acid

The actions of PTH and CT on bone resorption are antagonistic but they synergize to decrease the renal tubular reabsorption of phosphorus

Hypophosphatemia develops from a direct action of calcitonin on increasing the rate of movement of phosphate out of plasma into soft tissue and bone

Osteoclasts have receptors for calcitonin, however the action of calcitonin is not dependent on vitamin D. Calcitonin acts in vitamin D-deficient animals and after the administration of large doses of vitamin D.

The vitamin D family includes

1) vitamin D3 (cholecalciferol) 2) vitamin D2 (ergocalciferol or irradiated ergosterol) 3) 1,25-dihydroxycholecalciferol (calcitriol; 1,25-dihydroxyvitamin D)

A high-affinity vitamin D-binding protein in the serum transports cholecalciferol from its site of synthesis in the skin to the liver. In response to prolonged exposure to sunlight, previtamin D3 is converted to lumisterol and tachysterol. Because the vitamin D-binding protein has no affinity for lumisterol and minimal affinity for tachysterol, the translocation of these photoisomers into the circulation is negligible and they are sloughed with the natural turnover of the skin.

The first step in the metabolic activation of vitamin D is the conversion of cholecalciferol to __________ in the liver under the enzymatic control of a hepatic microsomal enzyme referred to as ____________.

25-dihydroxycholecalciferol (25-OH-CC) calciferol-25-hydroxylase

will also result in rickets because of the failure to maintain an adequate ion product of serum calcium and phosphorus at the zones of mineralization in bone

Phosphorus deficiency

cholecalciferol also known as what vit.?

Vit. D3

The active metabolites of this vitamin also act on bone.

cholecalciferol (vitamin D₃)

__________ of chief cells are usually single and result in considerable enlargement of the parathyroid gland

Adenomas

give examples of hypocalcemic syndromes of major economic and veterinary significance

Parturient hypocalcemia in dairy cows Puerperal tetany of bitches

is a metabolic disease of high-producing dairy cows characterized by the development of severe hypocalcemia and hypophosphatemia resulting from the mineralization of fetal bones and the initiation of lactation, and is associated with paresis near the time of parturition

Parturient hypocalcemia

resulting from hypocalcemia is frequently encountered in the small, hyperexcitable breeds of dogs. The clinical course is rapid and the bitch may proceed from premonitory signs including restlessness, panting, and nervousness to ataxia, trembling, and muscular tetany (Fig. 4-76), and result in convulsive seizures within 8 to 12 hours

Puerperal tetany

inactive form of T3

reverse T3 (rT3)

is a type of in vitro competitive protein-binding assay in which radioactively labeled and non-radiolabeled ligand, e.g., hormone, compete for a limited number of binding sites on a binding protein

radioimmunoassay

(Enumerate) Radioimmunoassays have several advantages over other quantitative procedures for hormones:

(a) small sample volumes are needed; (b) one can assay many samples at a time (c) little if any sample preparation is required

can provide excellent specificity, accuracy, sensitivity, and precision

Radioimmunoassays

(Enumerate) few disadvantages of Radioimmunoassays

1. acquiring, handling, and disposal of radioactive materials 2. expensive radiation detection equipment 3. limited availability of reagents for animal hormones 4. limited shelf life of reagents

Majority of the renal phosphate reabsorption occurs in the _______ of the kidney with small amounts reabsorbed from _________ of the nephron.

proximal convoluted tubules distal elements

Finals Questions Flashcards

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