opened book quiz exam 4

Calcium-sensing receptors on the parathyroid glands and some other tissues monitor blood calcium concentrations. When a drop in serum calcium concentration occurs, the parathyroid gland releases

PTH into the blood. This will increase serum calcium concentrations via actions in the kidneys and the bones.

Describe the mechanism for paracellular absorption of calcium.

Paracellular absorption of calcium occurs by diffusion where no carriers or energy are needed. It occurs throughout the small intestine, predominantly in the jejunum and ileum and is concentration dependent. This kind of absorption occurs between cells and is affected by tight junctions that are controlled by occludins and claudins and appear to exhibit properties similar to ion channels. This type of absorption occurs when high calcium concentrations are present in the lumen, creating a gradient of calcium concentrations between the lumen and the basolateral side of the enterocyte. Permeability is increased through the junctions by a series of reactions and calcium absorption is facilitated.

Calcium is the most abundant divalent cation in the body.

True

Meats and grains are poor sources of calcium.

True

In the bones, PTH attaches to receptors on

osteoblasts. These cells can differentiate into osteoclasts that degrade bone. They promote the release of calcium from the bones into the blood, which brings about an increase in serum calcium levels.

Malnourished individuals being refed who exhibit the "refeeding syndrome" may have low serum concentrations of __

phosphorus

c. ​forms part of the linear backbone of DNA

phosphorus

c. ​osteomalacia, neuromuscular, cardiac, and hematologic manifestations

phosphorus

The active form of vitamin D in the body is _

calcitriol

b. ​required for blood clotting

calcium

The calcitriol that was produced acts in the small intestine to increase

calcium absorption by interacting with nuclear vitamin D receptors to induce transcription of the gene that codes for calbindin D9k. This substance binds protein to allow for transport of calcium through the cytosol. In addition, calcitriol enhances calcium absorption at the brush border of the enterocytes by increasing TRPV6 channels and, at the basolateral membrane, by increasing calcium ATP-ase pumps.

Because bone is composed mainly of

calcium and phosphorus, a deficiency will have serious effects. Rickets occurs in infants and children due to inadequate mineralization of the bone matrix and growth plate cartilage.

By what mechanism is vitamin C thought to protect bone health?

contributing to the integrity of bone collagen

Alkalosis (elevated pH of the blood), critical illnesses, and alcoholism are all associated with

hypophosphatemia

Genetic disorders associated with hypophosphatemia include X-linked hypophosphatemia and hypophosphatemic rickets. Both conditions are caused by defects

in phosphorus reabsorption in the kidneys and lead to excess phosphorus in the urine.

d. ​absorption inhibited by excessive calcium

iron

Calcium supplements inhibit the absorption of

iron, especially nonheme iron, likely by causing the ferroportin protein to disengage from the basolateral membrane, diminishing iron absorption. Because this lower iron absorption has been shown to be temporary, an adaptation likely occurs that does not affect the iron status of the body.

a. ​forms a complex with ATP for use in glycolysis

magnesium

a. ​neuromuscular hyperexcitability, and CNS effects

magnesium

Although phosphorus deficiency is

rare, it is seen in premature infants because they have a higher need for it and human milk has a low level of the mineral. In addition, malnourished individuals who are being fed through a tube or intravenously must receive additional phosphorus or they will develop a deficiency.

In the kidneys, the hormone stimulates transcription of 1-hydroxylase yielding synthesis of calcitriol from 25-OH vitamin D. This leads to increased

renal absorption of filtered calcium by interacting with nuclear vitamin D receptors to induce transcription of the gene that codes for calbindin D28k.

n adults, a condition called osteomalacia develops associated with

soft bones due to failure of the bone matrix to mineralize.

f a phosphorus deficiency is severe, the individual will

suffer from reduced oxygen transport and delivery, reduced cardiac output, arrhythmias (irregular heartbeats), respiratory failure, damage to heart and skeletal muscles and neurological problems.

About 99% of the body's calcium is found in

​bones and teeth

Calcitriol can stimulate the absorption of calcium from the intestines by enhancing synthesis of ____and related proteins.

​calbindin

Rickets is caused by a deficiency in

​calcium

The most abundant divalent cation in the body is

​calcium

b. ​rickets, osteoporosis, tetany

​calcium

Food sources of calcium include

​canned sardines

During which period of the life cycle does peak bone mass occur?

​early adulthood

Which mineral, when combined with unabsorbed dietary fat, forms soaps that cannot be absorbed and are excreted in the feces?

​magnesium

hich mineral participates in all aspects of energy metabolism including glycolysis, beta-oxidation, and the TCA cycle?

​magnesium

Paracellular absorption of calcium

​occurs by diffusion mainly in the jejunum and ileum

Which cells are considered the bone-building cells?

​osteoblasts

The condition associated with decreased bone strength accompanied by the deterioration of the microarchitecture of bone tissue and low mineral density is _

​osteoporosis

A dietary mineral that is an important component of DNA and RNA is ____.

​phosphate

Which mineral is LEAST likely to be deficient in anyone's diet?

​phosphorus

By what mechanism is vitamin K thought to protect bone health?

​used for the formation of Gla protein in bone

is secreted in response to low plasma calcium concentrations and acts on the kidney to increase synthesis of ____, which promotes renal reabsorption of calcium

. ​Parathyroid hormone; calcitriol

Magnesium is absorbed in the small intestine through diffusion and __

. ​carrier-mediated active transport

Calcitriol enhances calcium reabsorption in the kidneys.

False Calcitriol enhances the reabsorption of phosphorous in the kidneys.

Calcium absorption occurs in the large intestine.

False Calcium absorption takes place in the small intestine by active transport and diffusion.

Ingestion of calcium, magnesium, and aluminum, along with phosphorus, will enhance its absorption.

False Ingestion of these minerals along with phosphorus will form insoluble complexes with the phosphorus and impair its absorption.​

Thyroid hormone increases serum calcium concentrations.

False Parathyroid hormone (PTH) increases serum calcium concentrations.​

regardless of age, the level of calcium absorption is the same.

False nfants, children, adolescents, and women during lactation and pregnancy exhibit a greater calcium absorption level than other age groups.​