Endocrine Part 5 Flashcards
Which of the following best describes the function of parathyroid hormone (PTH)?
A. Increases plasma calcium and increases plasma phosphate
B. Decreases plasma calcium and increases bone resorption
C. Increases plasma calcium and decreases plasma phosphate
D. Decreases plasma calcium and promotes vitamin D synthesis
. Increases plasma calcium and decreases plasma phosphate
Rationale: Slide 3 explicitly states that PTH increases calcium and decreases phosphate levels in plasma. This is a key hormonal mechanism in calcium-phosphate homeostasis.
Which hormone is NOT directly involved in calcium and phosphate balance?
A. PTH
B. Calcitonin
C. Insulin
D. Active Vitamin D
C. Insulin
Rationale: The “3-source, 3-hormone, 3-target” model on Slide 7 lists PTH, calcitonin, and active Vitamin D as the key hormones regulating calcium and phosphate. While insulin influences bone formation (Slide 20), it is not primarily responsible for calcium/phosphate balance.
which is true about calcium distribution?
bone, other tissue, free calcium 500mg
Why is bone resorption an important physiological mechanism in calcium homeostasis?
A. It strengthens bones by replacing old calcium with new dietary calcium
B. It allows rapid correction of low plasma calcium by releasing stored calcium
C. It increases phosphate excretion via the kidneys to maintain acid-base balance
D. It promotes calcium deposition in bones during times of high serum calcium
It allows rapid correction of low plasma calcium by releasing stored calcium
answer is not D because high calcium levels already means there is lots of calcium in the bones
Rationale: As shown on Slide 10, osteoclast-mediated bone resorption releases calcium into the plasma, making it a crucial mechanism for quickly restoring plasma calcium levels when they drop. This process is especially triggered by PTH under hypocalcemic conditions (see also Slide 3 and Slide 14).
comepare and contrast the importance of calcium and phosphate:
calcium:
- for bone structure
- blood coagulation
- intracellular messaging
- excitatability regulation
phosphate
- structural role
- metabolism
- buffer
a hormone released by the kidney that targets the GI tract to absorb calcium from diet
a. PTH
b. 1,25 vitamin D
c. calcitonin
1,25 vitamine D 9active vitamin D)
a hormone secreted by the thyroid clands that target the kidneys directly and the bones and GIT inferectly
a. PTH
b. 1,25 vitamin D
c. calcitonin
calcitonin
parathyroid glands secrete a hormone that targets bone kidneys and GIT indierectly
a. PTH
b. 1,25 vitamin D
c. calcitonin
PTH
a. PTH
b. 1,25 vitamin D
c. calcitonin
Slide 20 clarifies that chronic elevation of PTH promotes bone resorption, largely through osteoclast stimulation (also discussed on Slide 10).
compare and contrast osteoclasts, osteoblasts and osteocytes
osteoblasts: bone builders, add ca+ to bone
osteoclasts: bone reabsorption, have ruffled boarders that increase surface area
- remove calcium from bone
osteocytes: cyctoplasmic extensions used for communication
what is the sequence of bone remodelling?
- osteoclasts attatched to bone and secrete H+ and enzymes to dissolve calcium phosphate in the bones, which dissolve bone
- osteoblasts attatch to site and add calcium to bone
- formation of osteoids (secretions of osteoblasts)
- osteoids differentiate into osteocytes
What is the role of calcitriol (active Vitamin D) in calcium homeostasis?
A. Enhances renal calcium excretion
B. Inhibits intestinal calcium absorption
C. Increases calcium absorption in the GI tract
D. Reduces bone mineralization in children
Increases calcium absorption in the GI tract
Rationale: Slide 16 details that Vitamin D upregulates Epithelial calcium channel (ECaC), Calbindin, and Basolateral calcium pump, all of which increase intestinal calcium absorption.
Which of the following best explains why parathyroid hormone (PTH) secretion is not under the control of the hypothalamus or anterior pituitary?
A. PTH is regulated by thyroid-stimulating hormone instead of hypothalamic input
B. The parathyroid gland lacks receptors for hypothalamic-releasing hormones
C. PTH secretion is directly regulated by plasma calcium levels, not by trophic hormones
D. PTH is stored in the posterior pituitary and released by neuroendocrine signals
PTH secretion is directly regulated by plasma calcium levels, not by trophic hormones
note that PTH is activated by low calcium levels in the blood
does PTH stimulate the bone, GI, and kidney directly or indirectly?
stimulates bone directly
stimulates kidney and GI tract INDIRECTLY
(activity of 1alpha hydroxylase (to activate vitamin D) )
Which of the following proteins is regulated by active Vitamin D to facilitate calcium absorption in the intestine?
A. Na⁺/K⁺ ATPase, Calmodulin, and ClC-5
B. Epithelial Calcium Channel (ECaC), Calbindin, and Basolateral Calcium Pump
C. Voltage-Gated Calcium Channel, Paraferrin, and Carbonic Anhydrase
D. PTH receptor, Aquaporin-2, and Sodium-Phosphate Cotransporter
from the apical to the basolateral side of the duodenal cell:
Epithelial Calcium Channel (ECaC), Calbindin, and Basolateral Calcium Pump
*purpose of traansfer to the luminal to basolateral side
which of the following explains what happens to 1,25(OH)2D3?
a. binds to a surface receptor, causes a signalling cascade in the cell
b. binds to a intracellular receptor in the plasma, causes transcription and transplation
binds to a intracellular receptor in the plasma, causes transcription and transplation
vitamine D is a cholesterol
which is true for the three calcium regulating hormones?
a. PTH, calcitonin and activ vitamine d are all peptide hormones
b. they all decrease blood phosphate
c. they all act on bones
d. they are all secreted by calcium blood levels
c is the only correct statement
a-PTH AND CALCITONIN are peptide hormones
b-active vitamine d only increases blood phosphate
d-only PTH and calcium are secreted based on blood calcium levels, vitamine d is onlt secreted due to PTH
match the following disorders for too much PTH, too little PTH, and too little active vitamin D?
i) rickets
ii) osteomalacia
iii) bones stones and groans
iv) tetany
rickets-too little vit d in children
osteomalacia-too little vitamine d in adults
bones stones and groans- too much PTH
tetany- too little PTH
list the hormones favouring bone formation and the hormones favouring bone remodelling/breakdown
favour bone formation (IGETIC)
- Insulin
- growth hormone
- estrogen
- testosterone
- insuline (GF1)
- calcitonin
What are the key characteristics of rickets as seen in children?
A. Excessive bone mineralization and increased bone density
B. Failure of bone matrix mineralization, leading to soft and deformed bones
C. Increased calcium deposition in joints and ligaments
D. Hyperphosphatemia causing brittle and fragile bones
Failure of bone matrix mineralization, leading to soft and deformed bones
Which of the following best describes the physiological basis of tetany due to hypocalcemia?
A. Reduced excitability of neurons due to calcium blockade of sodium channels
B. Increased nerve and muscle excitability due to opening of sodium channels
C. Muscle relaxation caused by lack of ATP in skeletal muscle fibers
D. Hyperpolarization of neurons, making action potentials less likely
(memorize)
Increased nerve and muscle excitability due to opening of sodium channels
