Finals Questions Flashcards
The majority of the epithelial cells and the most important functional cells of the thyroid
Follicular cells
is the most important enzyme in the synthetic pathway of thyroid hormones.
Thyroperoxidase
oxidizes iodide ion (I-) taken up by follicular cells into reactive iodine (I2) which binds to the tyrosine residues in thyroglobulin
Thyroperoxidase
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
This amino acid is an essential component of thyroid hormones, is incorporated within the molecular
structure of thyroglobulin.
Tyrosine
(Enumerate) The skeletal lesion of generalized fibrous osteodystrophy (osteitis fibrosa) is characterized by
- increased bone resorption
- decreased radiographic density
- incomplete fractures
In response to 1,25 dihydroxycholecalciferol, the absorptive cells of this organ synthesize and secrete a specific calcium-binding protein (CaBP)
intestine
(Enumerate) The more active metabolites of ergosterol synthesized by the liver and kidney
a) 25-hydroxyergosterol
b) 1,25-dihydroxyergosterol
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
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.
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
A high-affinity vitamin D-binding protein in the serum transports cholecalciferol from its site of synthesis in the skin to the
liver
this hormone is secreted continuously under conditions of normocalcemia
Calcitonin
is an important PTH-like factor that plays a central role in the pathogenesis of humoral hypercalcemia of malignancy
Parathyroid hormone-related protein (PTHrP)
Stimulation of _________ stimulates the
conversion of ATP to cAMP in target cells.
adenylyl cyclase
Overexpression of _________ leads to
osteopetrosis associated with decreased osteoclast formation and function
osteoprotegerin (OPG)
is a complex, multistep, process that involves the activation of multiple genes and the action of multiple hormones
Bone resorption
is the principal hormone involved in the minute-to-minute, fine regulation of
blood calcium in mammals.
Parathyroid hormone
(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
(Enumerate) The major inhibitors of PTH synthesis and secretion
1) increased serum levels of Ca2+
2) 1, 25-dihydroxyvitamin D
is the major intracellular anion existing in inorganic form
Phosphate
(Enumerate) inorganic form of phosphate
HPO4 and H2PO4
(Enumerate) organic form or compounds of phosphate
- phospholipids
- nucleic acids
- phosphoproteins
- ATP
(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
(Enumerate) two components of calcium absorption from the intestinal tract
- saturable or transcellular transport
- 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
- structural integrity of bones and teeth
- as a messenger or regulatory ion
(Enumerate) Two sources of Ca2+ in bone that can enter the circulation
- readily mobilizable calcium salts in the ECF
- 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:
- energy metabolism
- delivery of O2 to tissues
- muscle contraction
- 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
- acquiring, handling, and disposal of radioactive materials
- expensive radiation detection equipment
- limited availability of reagents for animal hormones
- 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
