Human Physiology T06 PDF 2024

HUMAN PHYSIOLOGY T06 HA201A | Dr. R.Gemarino, Dr. B. Gemarino, Dr. K. Acosta | PSU School of Medicine Year 1 | Batch 2028 09/03/2024...

HUMAN PHYSIOLOGY T06 HA201A | Dr. R.Gemarino, Dr. B. Gemarino, Dr. K. Acosta | PSU School of Medicine Year 1 | Batch 2028 09/03/2024 SKELETAL BLOCK Figure 1.1 The four parathyroid glands lie immediately behind the thyroid gland. Almost all of the parathyroid OUTLINE hormone (PTH) is synthesized and secreted by the chief cells. The function of the oxyphil cells is uncertain, but they I. Parathyroid Hormone may be modified or depleted chief cells that no longer A. Physiological Anatomy of The Parathyroid secrete PTH. Glands B. Chemistry of PTH PHYSIOLOGICAL ANATOMY OF THE C. Control Of Parathyroid Secretion by Calcium PARATHYROID GLANDS Ion Concentration Parathyroid Glands: Humans typically have four D. Summary of Effects of PTH parathyroid glands located behind the thyroid gland. ○ Location: One gland is behind each upper and II. Calcitonin lower pole of the thyroid. A. Increased Plasma Calcium Concentration ○ Size: Approximately 6 mm long, 3 mm wide, and Stimulates Calcitonin Secretion 2 mm thick. B. Calcitonin Decreases Plasma Calcium ○ Appearance: Dark brown fat-like tissue; difficult Concentration to distinguish during thyroid surgeries. C. Calcitonin Has a Weak Effect on Plasma Surgical Considerations: Calcium Concentration in Adult Humans ○ Challenge: Parathyroid glands can resemble thyroid lobules, leading to accidental removal III. Summary of Calcium Ion Concentration during thyroidectomy. ○ Implication: Before their importance was IV. Physiology of the Teeth understood, total/subtotal thyroidectomies often A. Function of the Different Parts of the Teeth resulted in unintended parathyroid gland removal. B. Dentition ○ Physiological Impact: C. Formation of the Teeth Removal of half the glands usually has no D. Eruption of Teeth major effects. E. Development of the Permanent Teeth Removal of three out of four glands causes F. Metabolic Factors Influence Development of transient hypoparathyroidism. the Teeth Remaining parathyroid tissue can G. Mineral Exchange in Teeth hypertrophy to compensate and maintain normal function. PARATHYROID HORMONE ○ Cell Types: PTH (Parathyroid Hormone) regulates extracellular Chief Cells: Predominantly found in the adult parathyroid gland; primarily responsible for calcium and phosphate concentrations. It controls intestinal reabsorption, renal excretion, and secreting PTH. exchange between extracellular fluid and bone of Oxyphil Cells: Present in small to moderate numbers in adults, absent in many animals these ions. Excess parathyroid activity causes rapid calcium and young humans. Function: Uncertain, but believed to be release from bones, leading to hypercalcemia in the extracellular fluid. modified or depleted chief cells that no Hypofunction of the parathyroid glands results in longer secrete hormones. hypocalcemia, which can lead to tetany. NICE TO KNOW: CHEMISTRY OF PARATHYROID HORMONE (PTH) PTH Synthesis ○ PTH is synthesized as a preprohormone on ribosomes, consisting of 110 amino acids. ○ The endoplasmic reticulum and Golgi apparatus process the preprohormone: Cleaved to a prohormone with 90 amino acids. Further processed into the active hormone with 84 amino acids. ○ The final hormone is packaged into secretory granules in the cytoplasm of parathyroid cells. Molecular Characteristics TRANSCRIBER/S: Asag, Maestro, Villaruel-Jagmis 1 HA201A Parathyroid Hormone, Calcitonin, Calcium Ion Concentration, Teeth TRANS #06 ○ The active PTH has a molecular weight of about resorption, not just the release of calcium 9500. phosphate salts from the bone. ○ Smaller fragments, including those with as few as 34 amino acids from the N-terminus, also exhibit RAPID PHASE OF CALCIUM AND PHOSPHATE full PTH activity. MOBILIZATION FROM BONE—OSTEOLYSIS Hormonal Activity of PTH Fragments ○ The whole 84-amino acid PTH is rapidly removed Immediate Effects of PTH Injection: by the kidneys within minutes. ○ Calcium Rise: Blood calcium levels begin to rise ○ Many PTH fragments are not removed as quickly within minutes of PTH injection and can persist for hours, contributing ○ Occurs long before the development of new significantly to hormonal activity. bone cells. Areas of Bone Affected: PTH EFFECTS ON EXTRACELLULAR FLUID ○ Osteocytes: Calcium is mobilized from the bone CALCIUM AND PHOSPHATE CONCENTRATIONS matrix near osteocytes within the bone. Characterization: mature bone cells that originate from osteoblasts. reside within the bone matrix in small spaces called lacunae. maintain the bone tissue and communicate with other bone cells ○ Osteoblasts: Calcium is also mobilized from areas near osteoblasts on the bone surface. Characterization: bone-forming cells responsible for synthesizing and secreting the bone Figure 1.2 Approximate changes in calcium and phosphate matrix, including collagen and other concentrations during the first 5 hours of parathyroid proteins. hormone infusion at a moderate rate. active in the early stages of bone development and repair. Once they Effect of PTH Infusion on Calcium and Phosphate become embedded in the matrix they ○ Calcium concentration begins to rise produce, they differentiate into immediately after PTH infusion and plateaus osteocytes. after about 4 hours. ○ Phosphate concentration decreases more rapidly, reaching a low level within 1-2 hours. Osteocytes: Maintain bone, regulate bone Mechanisms of Calcium Increase remodeling. ○ PTH increases calcium and phosphate Osteoblasts: Build bone, active in bone formation. absorption from bone. ○ PTH rapidly decreases calcium excretion by the kidneys, contributing to the rise in calcium levels. Osteocytic Membrane System: Mechanism of Phosphate Decrease ○ System Overview: Osteoblasts and osteocytes ○ PTH causes a strong increase in renal form a network of interconnected cells phosphate excretion, which overrides the throughout the bone and across bone surfaces, increased phosphate absorption from bone, except near osteoclasts. leading to a net decrease in phosphate ○ Structure: The system includes long processes concentration. that connect osteocytes with each other and with surface osteoblasts, creating the osteocytic PARATHYROID HORMONE MOBILIZES CALCIUM membrane system. AND PHOSPHATE FROM BONE ○ Function: This membrane system separates the bone from the extracellular fluid. Two Phases of Mobilization: Osteolysis Process: ○ Rapid Phase: ○ Bone Fluid: Located between the osteocytic Begins within minutes and continues to membrane and bone, containing a calcium ion increase over several hours. concentration one-third that of the extracellular Mechanism: Activation of existing bone fluid. cells, mainly osteocytes, promotes the ○ Osteocytic Pump: Pumps calcium ions from release of calcium and phosphate. bone fluid into the extracellular fluid, lowering ○ Slow Phase: bone fluid calcium concentration. Takes several days to weeks to fully ○ Osteolysis: When the pump is excessively develop. activated, calcium phosphate salts are released Mechanism: Proliferation of osteoclasts from bone without resorbing the fibrous and gel leads to increased osteoclastic bone matrix. ○ Calcium Re-deposition: If the pump is inactivated, calcium phosphate salts are HA201A TRANSCRIBER/S: Asag, Maestro, Villaruel-Jagmis 2 Parathyroid Hormone, Calcitonin, Calcium Ion Concentration, Teeth TRANS #06 redeposited into the bone matrix as bone fluid PTH DECREASES CALCIUM EXCRETION AND calcium concentration rises. INCREASES PHOSPHATE EXCRETION BY THE KIDNEYS Role of PTH: PTH on Phosphate Excretion ○ PTH Receptors: Both osteoblasts and ○ rapid increase in phosphate excretion by osteocytes have PTH receptors on their cell reducing proximal tubular reabsorption of membranes. phosphate ions in the kidneys. ○ Calcium Pump Activation: PTH strongly PTH Effect on Calcium Reabsorption activates the calcium pump, causing rapid ○ increases renal tubular reabsorption of calcium, removal of calcium phosphate salts from reducing calcium loss in the urine. amorphous bone crystals near the cells. This reabsorption mainly occurs in the thick ○ Mechanism: PTH increases calcium permeability ascending loop of Henle and distal tubules. on the bone fluid side of the osteocytic PTH Effect on Other Ions membrane, allowing calcium ions to diffuse into ○ increases reabsorption of magnesium and the cells. hydrogen ions. ○ Calcium Transfer: The calcium pump on the ○ decreases reabsorption of sodium, potassium, other side of the membrane then transfers and amino acids similar to its effect on calcium ions into the extracellular fluid. phosphate. Calcium Homeostasis SLOW PHASE OF BONE RESORPTION AND CALCIUM ○ Without PTH effect to enhance calcium PHOSPHATE RELEASE—ACTIVATION OF THE reabsorption in the kidneys, continual calcium OSTEOCLASTS. loss would lead to depletion of calcium in both extracellular fluid and bones. PTH Activation of Osteoclasts ○ PTH indirectly activates osteoclasts as they do PTH INCREASES INTESTINAL not have PTH receptors. ABSORPTION OF CALCIUM AND PHOSPHATE ○ Osteoblasts and osteocytes respond to PTH and send secondary signals to osteoclasts. Intestinal Absorption of Calcium and Phosphate ○ A key secondary signal is RANKL, which binds ○ PTH enhances calcium and phosphate to receptors on pre-osteoclast cells. absorption in the intestines. ○ RANKL transforms pre-osteoclasts into mature ○ This effect occurs by increasing the formation of osteoclasts, initiating bone resorption. 1,25-dihydroxycholecalciferol (active form of Two Stages of Osteoclastic Activation vitamin D) in the kidneys. 1. Immediate activation of already formed ○ 1,25-dihydroxycholecalciferol promotes osteoclasts. increased absorption of calcium and phosphate 2. Formation of new osteoclasts for sustained from the gastrointestinal tract. resorption. cAMP as a Second Messenger ○ Excess PTH for several days leads to a well- ○ A major portion of PTH's effects on target developed osteoclastic system. organs is mediated by the cyclic adenosine ○ Prolonged PTH stimulation continues to promote monophosphate (cAMP) second messenger osteoclast development for months. system. Effects of Prolonged PTH Exposure ○ Within minutes of PTH administration, cAMP ○ Osteoclastic bone resorption weakens bones levels increase in osteocytes, osteoclasts, and after prolonged excess PTH. other target cells. ○ Secondary stimulation of osteoblasts occurs to ○ cAMP is likely responsible for: counter the weakened bone state. Osteoclastic secretion of enzymes and acids ○ Long-term effect enhances both osteoblastic and for bone resorption. osteoclastic activity. Formation of 1,25-dihydroxycholecalciferol ○ However, bone resorption still exceeds bone in the kidneys. deposition with continuous PTH excess. Calcium Release and Bone Health ○ Bone contains much more calcium than CONTROL OF PARATHYROID SECRETION BY extracellular fluids (≈1000x). CALCIUM ION CONCENTRATION ○ Despite significant calcium release into fluids from PTH action, immediate bone effects are not Rapid PTH Secretion Response to Calcium Decline noticeable. ○ Even a slight decrease in extracellular calcium ○ Prolonged PTH excess over months or years ion concentration triggers an increase in PTH causes significant bone resorption, leading to secretion within minutes. the development of large cavities with ○ If the decrease persists, the parathyroid glands multinucleated osteoclasts. hypertrophy, sometimes up to fivefold. Examples of Parathyroid Hypertrophy ○ Rickets: Glands enlarge due to mildly depressed calcium levels. HA201A TRANSCRIBER/S: Asag, Maestro, Villaruel-Jagmis 3 Parathyroid Hormone, Calcitonin, Calcium Ion Concentration, Teeth TRANS #06 ○ Pregnancy: Glands enlarge despite minimal Acting / Released in response to decreased calcium ion reduction in the mother's extracellular calcium levels: extracellular fluid. Bone Resorption: PTH stimulates bone resorption, ○ Lactation: Enlarged glands due to calcium usage releasing calcium into the extracellular fluid. for milk production. Renal Effects: ○ Calcium Reabsorption: Increases calcium Inhibition of PTH Secretion with Increased Calcium reabsorption in the renal tubules, reducing ○ Excess calcium in the diet, increased vitamin D, calcium excretion. and bone resorption from disuse reduce ○ Phosphate Excretion: Decreases phosphate parathyroid gland activity and size. reabsorption, increasing phosphate excretion. Calcium-Sensing Mechanism Intestinal Absorption: PTH is essential for converting ○ The calcium-sensing receptor (CSR) in 25-hydroxycholecalciferol to 1,25- parathyroid cell membranes detects changes in dihydroxycholecalciferol, which enhances calcium extracellular calcium ion concentration. absorption in the intestines. ○ CSR is a G protein-coupled receptor that Regulate extracellular fluid calcium concentration. activates phospholipase C, increasing inositol 1,4,5-triphosphate and diacylglycerol, which CALCITONIN release intracellular calcium and inhibit PTH A peptide hormone secreted by the thyroid gland secretion. Tends to decrease plasma calcium concentration ○ Decreased extracellular calcium suppresses In general, has effects opposite to those of PTH these pathways, stimulating PTH release. The quantitative role of calcitonin in humans is far Feedback Control of Plasma Calcium Levels less than that of PTH in regulating calcium ion ○ Acute effect: Small drops in calcium can double concentration or triple plasma PTH levels within hours (shown Calcitonin is a 32–amino acid peptide with a molecular by a solid red curve). weight of about 3400. ○ Chronic effect: Over weeks, persistent small decreases in calcium concentration cause Parafollicular cells or C cells significant parathyroid hypertrophy, further ○ Where synthesis and secretion of calcitonin increasing PTH secretion (shown by a dashed occurs red line). ○ Lies in the interstitial fluid between the follicles of ○ This mechanism is crucial for long-term control the thyroid gland of plasma calcium concentration. ○ Constitute only about 0.1% of the human thyroid gland SUMMARY OF EFFECTS OF PTH Increased Plasma Calcium Concentration Stimulates Calcitonin Secretion The primary stimulus for calcitonin secretion is increased extracellular fluid calcium ion concentration. In contrast, PTH secretion is stimulated by decreased calcium concentration. An increase in plasma calcium concentration of about 10% causes an immediate two-fold or more increase in calcitonin secretion rate, which is shown by the blue line in Figure 80-13. ○ Happens in young animals, but much less so in older animals and humans Figure 1.3 Summary of effects of parathyroid hormone (PTH) on bone, the kidneys, and the intestine in response to decreased extracellular fluid calcium ion concentration. CaSR, Calcium-sensing receptor. HA201A TRANSCRIBER/S: Asag, Maestro, Villaruel-Jagmis 4  Parathyroid Hormone, Calcitonin, Calcium Ion Concentration, Teeth TRANS #06 only a small effect on plasma calcium ion concentration, even after the rate of absorption is slowed by calcitonin. o Children: The effect of calcitonin is This increase provides a second hormonal much greater because bone feedback mechanism for controlling plasma calcium remodeling occurs rapidly. ion concentration. Absorption and deposition = 5 ○ But one that is relatively weak and works in a way grams or more per day = 5 to opposite that of the PTH system. 10 times the total calcium in all the extracellular fluid. In some young animals, calcitonin decreases blood o Certain bone diseases such as calcium ion concentration rapidly, within minutes Paget’s disease, in which after injection of calcitonin, in at least two ways: osteoclastic activity is greatly accelerated, calcitonin has a much Immediate Effect of Prolonged Effect of more potent effect of reducing Calcitonin Calcitonin calcium absorption. o Decrease the o Decrease formation of absorptive activities new osteoclasts followed SUMMARY OF CONTROL OF CALCIUM ION of the osteoclasts by decreased numbers of CONCENTRATION and osteolytic effect osteoblasts, because Regulation of calcium ion concentration in the body of the osteocytic osteoclastic resorption of with the help of exchangeable salt and parathyroid membrane bone leads secondarily to hormone (PTH). throughout the bone. osteoblastic activity. Calcium is primarily found in the body as calcium phosphates and its levels are regulated in the body; the body has the ability to reabsorb it. o The balance shifts in Net result is reduced The first line of defense - buffering function of favor of calcium osteoclastic and deposition in the exchangeable calcium osteoblastic activity, and exchangeable bone ○ Exchangeable calcium salts primarily dicalcium little prolonged effect on calcium salts. phosphate (CaHPO4) in the bone, liver, and plasma calcium ion intestine concentration. Significant in young The effect on plasma animals due to the calcium is mainly a rapid interchange of transient one, lasting for absorbed and a few hours to a few deposited calcium. days at most. Calcitonin also has minor effects on calcium handling in the kidney tubules and the intestines. o Effects are opposite those of PTH o Appear to be of such little importance; seldom considered Calcitonin Has a Weak Effect on Plasma Calcium Concentration in Adult Humans Figure 2.1 Overview of calcium exchange between different The reason for the weak effect of calcitonin on tissue compartments in a person ingesting 1000 mg of plasma calcium is twofold. calcium per day. Note that most of the ingested calcium is 1. Any initial reduction of the calcium ion normally eliminated in the feces, although the kidneys have concentration caused by calcitonin leads the capacity to excrete large amounts by reducing tubular within hours to a powerful stimulation of PTH reabsorption of calcium. secretion, which almost overrides the calcitonin effect. ○ Example: If you have eaten food rich in calcium, o When the thyroid gland is removed, and if there is no calcium regulation, your and calcitonin is no longer secreted, calcium that were in the blood and the interstitial the long-term blood calcium ion fluid will acutely rise and hereby giving you concentration is not measurably hypercalcemia. altered, which again demonstrates Having hypercalcemia the overriding effect of the PTH shortens the QT interval system of control. forming of kidney stones ○ If we have calcium 0.6 to 1.5 grams of calcium per 2. Adult human: Daily rates of absorption and day. It is actually regulated whether it’s going to deposition of calcium are small and still have be reabsorbed or not absorbed by the parathyroid HA201A TRANSCRIBER/S: Asag, Maestro, Villaruel-Jagmis 5 Parathyroid Hormone, Calcitonin, Calcium Ion Concentration, Teeth TRANS #06 hormone. Once the calcium is reabsorbed in the o Allows even small particles of food to be blood, it will be checked by the level, whether it is caught and ground between the tooth high enough or low enough so that there is an surfaces. exchangeable calcium salt that can actually broken down in the bone to increase the calcium levels for the release into the interstitial fluid. If Function of the Different Parts of the Teeth Dentition there is increased calcium in the interstitial fluid Major functional parts: the enamel, dentin, or in the blood, the calcium is exchangeable in the cementum, and pulp form of exchangeable salt to be further deposited in the bone, liver and intestines. The second line of defense - hormonal control of calcium ion concentration ○ PTH and calcitonin ○ If there is a decrease in the calcium ion concentration, the rate of the PTH decreases. At the same time, there is also an acute increase of calcitonin which will be deposited to the bones. If parathyroid hormone decreases, consequently calcitonin decreases. ○ However, calcitonin is a weak regulator of calcium ion concentration compared to the PTH ○ Example: if the patient has a continued deficiency of calcium in the diet, the PTH can regulate the calcium absorption for the bone maintaining calcium ion levels. However, if there is chronic or long standing decrease in the calcium level in the blood, eventually the bone will become The tooth can also be divided into: demineralized because of the low calcium. Part of The Description Teeth Crown The portion that protrudes out from the gum into the mouth. Root The portion within the bony socket of the jaw. Neck Collar between the crown and the root where the tooth is surrounded by the gum. Enamel A layer that covers the outer surface of the tooth. o Formed before the eruption of the tooth by special epithelial cells called ameloblasts. Once the tooth has erupted, no more enamel is formed. o Composed of large and dense crystals of hydroxyapatite with adsorbed carbonate, magnesium, sodium, Figure 2.2 Bones and Calcium Regulation potassium, and other ions embedded in a fine meshwork of strong and almost insoluble protein fibers Crystalline structure of salts – PHYSIOLOGY OF THE TEETH makes the enamel extremely hard, much harder than the The teeth cut, grind, and mix the food that is eaten. dentin o To perform these functions, jaws have powerful Special protein fiber muscles capable of providing an occlusive force: meshwork – about 1% of the Between the front teeth - 50 to 100 pounds enamel mass, makes enamel Jaw teeth - 150 to 200 pounds. resistant to acids, enzymes, and other corrosive agents The upper and lower teeth are provided with projections and facets that interdigitate, so the upper Dentin Has a strong bony structure and set of teeth fits with the lower. compose the main body of the tooth ○ This fitting is called occlusion. HA201A TRANSCRIBER/S: Asag, Maestro, Villaruel-Jagmis 6 Parathyroid Hormone, Calcitonin, Calcium Ion Concentration, Teeth TRANS #06 Made up principally of Dentinal tubules – Important in hydroxyapatite crystals similar to the exchange of calcium, those in bone but much denser. phosphate, and other minerals o Crystals are embedded in a with the dentin. strong meshwork of collagen fibers Dentition Humans and most other mammals develop two sets Principal constituents of dentin are of teeth during a lifetime. much the same as those of bone. Deciduous teeth or Milk teeth – first set of teeth o Major difference is its histological o They number 20 in humans and erupt between organization because dentin does the seventh month and the second year of life, not contain any osteoblasts, and they last until the sixth to the 13th year. osteocytes, osteoclasts, or Permanent tooth – the second set of teeth that spaces for blood vessels or replaces the lost deciduous tooth. nerves. o An additional 8 to 12 molars appear posteriorly in the jaws, making the total number of permanent o It is deposited and nourished by a teeth 28 to 32. layer of cells called o Depending on whether the four wisdom teeth odontoblasts, which line its inner finally appear, which does not occur in everyone. surface along the wall of the pulp cavity. Formation of the Teeth Calcium salts in dentin – make it extremely resistant to compressional forces. Collagen fibers – make it tough and resistant to tensional forces that might result when the teeth are struck by solid objects. Cementum A bony substance secreted by cells of the periodontal membrane, which lines the tooth socket. Collagen fibers and the cementum hold the tooth in place. When the teeth are exposed to excessive strain, the layer of cementum becomes thicker and stronger. Increases in thickness and strength with age, causing the teeth to become more firmly seated in the jaws by adulthood and later. Pulp Fills the pulp cavity of each tooth. Invagination of the oral epithelium into the dental lamina, which is followed by the development of a Composed of connective tissue with tooth-producing organ is shown in Figure 80-16A. an abundant supply of nerve fibers, The epithelial cells above form ameloblasts - which blood vessels, and lymphatics. form the enamel on the outside of the tooth. Odontoblasts – cells lining the o The epithelial cells below invaginate upward into surface of the pulp cavity, which, the middle of the tooth to form the pulp cavity and during the formative years of the the odontoblasts that secrete dentin. tooth, lay down the dentin but at the Enamel – formed on the outside of the tooth same time encroach more and more Dentin – formed on the inside, giving rise to an early on the pulp cavity, making it smaller. tooth In later life, the dentin stops Eruption of the Teeth growing and the pulp cavity remains essentially constant in Early childhood - teeth begin to protrude outward size. from the bone through the oral epithelium into the The odontoblasts are still viable mouth and send projections into small dentinal tubules that penetrate all Cause of “eruption” - growth of the tooth root and the the way through the dentin. bone underneath the tooth progressively shoves the HA201A TRANSCRIBER/S: Asag, Maestro, Villaruel-Jagmis 7 Parathyroid Hormone, Calcitonin, Calcium Ion Concentration, Teeth TRANS #06 tooth forward (most likely explanation as it is o Dentin - does not have those characteristics unknown). o This difference undoubtedly explains the different rates of mineral exchange. Development of the Permanent Teeth o Continual mineral exchange occurs in the dentin and cementum of teeth. During embryonic life, a tooth-forming organ also o Enamel exhibits extremely slow mineral exchange, develops in the deeper dental lamina for each so it maintains most of its original mineral complement permanent tooth that will form after the deciduous teeth throughout life. are gone. o Tooth-producing organs - slowly form the permanent teeth throughout the first 6 to 20 years of life NICE TO KNOW o When each permanent tooth becomes fully formed, it, like the deciduous tooth, pushes Two most common dental abnormalities: outward through the bone. o Caries – erosion of the teeth o It erodes the root of the deciduous tooth and o Maloclussion – failure of the projections of the eventually causes it to loosen and fall out, and upper and lower teeth to interdigitate properly. soon, the permanent tooth erupts to take the place of the original one. Caries and the Role of Bacteria and Ingested Carbohydrates Metabolic Factors Influence Development of the Caries result from the action of bacteria on the Teeth teeth, the most common of which is Streptococcus The rate of development and the speed of eruption of mutans. teeth - can be accelerated by thyroid and growth The enamel of the tooth is the primary barrier to hormones. development of caries. Deposition of salts in the early-forming teeth - affected Because of the dependence of the caries bacteria on considerably by various factors of metabolism, such carbohydrates for their nutrition, it has frequently as: been taught that eating a diet high in carbohydrate o Availability of calcium and phosphate in the content will lead to excessive development of diet caries. o Amount of vitamin D present o However, it is not the quantity of carbohydrate o Rate of PTH secretion ingested but the frequency with which it is eaten When all these factors are normal, dentin and enamel that is important. will be correspondingly healthy. When they are deficient, calcification of the teeth Role of Fluorine in Preventing Caries also may be defective and the teeth will be abnormal Teeth formed in children who drink water that throughout life. contains small amounts of fluorine develop enamel that is more resistant to caries. Mineral Exchange in Teeth Small amounts of fluorine deposited in enamel make teeth about three times as resistant to caries as teeth without fluorine. The salts of teeth, like those of bone, are composed of hydroxyapatite with adsorbed carbonates and various Malocclusion cations bound together in a hard crystalline substance. Usually caused by a hereditary abnormality that o New salts – constantly being deposited causes the teeth of one jaw to grow to abnormal o Old salts – being absorbed from the teeth, as positions. occurs in bone. Cannot perform their normal grinding or cutting action adequately. o Deposition and absorption occur mainly in the The orthodontist can usually correct malocclusion dentin and cementum and to a limited extent in the by applying prolonged gentle pressure against the enamel. teeth with appropriate braces. ▪ In the enamel - these processes occur mostly by diffusional exchange of minerals with the saliva. REFERENCES ▪ Rate of absorption and deposition of minerals Hall, J. E., & Hall, M. E. (2020). Guyton and Hall In the cementum - equal to that in the Textbook of Medical Physiology E-book: Guyton and Hall surrounding bone of the jaw textbook of medical physiology E-book. Elsevier Health In the dentin - only one-third that of bone Sciences. ▪ Characteristics o Cementum - has characteristics almost identical to those of usual bone, including the presence of osteoblasts and osteoclasts HA201A TRANSCRIBER/S: Asag, Maestro, Villaruel-Jagmis 8