PHS 204 Endocrinology

Question 1

What is endocrinology?

Answer 1

The study of the endocrine system and the diagnosis and treatment of disorders

Question 2

Difference between the Endocrine and Nervous system

Answer 2

Nervous system
1. Fast acting and short lived
2. Makes use of chemical and electrical signals
3. Releases neurotransmitters
4. Effect is localized

Endocrine System
1. Slow acting and long lasting
2. Makes use of chemical messengers
3. Releases hormones
4. Effect is widespread

Question 3

Definition Characteristics of endocrine glands

Answer 3

Endocrine glands are a group of cells organized into a ductless gland (no tubes) that secrete molecular messengers (hormones) directly into
the bloodstream.

They are ductless glands
Secrete hormones
Secrete hormones directly into bloodstream
Their effect is intracellular

Question 4

Characteristics of exocrine glands

Answer 4

Glands of the digestive system
Ducted glands
Secrete hormones into tubes/ducts
Extra cellular effects

Question 5

What are hormones?

Answer 5

Chemical messengers released and produced by endocrine glands into the blood stream, this influences the function of cells at another location in the body, bind to target cells and elicit its actions.

Question 6

All the physiological activities of the body are regulated by two major systems

Answer 6

Nervous system
Endocrine system

Question 7

What is cell-to-cell signaling / intracellular communication?

Answer 7

Cell­-to-­cell signalling refers to the transfer of information from one cell to another. The cells of the body communicate with each other through some chemical substances called chemical messengers.

Question 8

Classification of chemical messengers

Answer 8

1. Endocrine messengers
2. Paracrine messengers
3. Autocrine messengers
4. Neurocrine messengers.

Question 9

Endocrine hormone

Answer 9

transported by the blood to the target organs or tissues (site of action).
secreted into blood and bind to receptor sites on distant cells to exert its biological actions
Examples are epinephrin and insulin.

Question 10

Paracrine hormone

Answer 10

Binds to receptors of neighbouring or adjacent cells
Paracrine: Released by cells that exert biological effect on other cell types in close proximity (neighboring cell)
- E.g. Somatostatin (inhibits insulin secretion)
Examples are prostaglandins and histamine

Question 11

Autocrine hormones

Answer 11

Bind to the receptors of the same cell that they’re released aka intracellular chemical mediators.
Examples are leukotrienes.

Question 12

Intracrine hormone

Answer 12

It exacts its biological function intracellularly
E.g. parathyroid hormone-related peptides in malignant cells and some of the effects of androgen-derived estrogen

Question 13

Types of hormones

Answer 13

Peptide hormones
Amino acid derivatives
Steroid hormones

Question 14

What are neurotransmitters?

Answer 14

Neurotransmitters are released by axon terminals of neurons into the synaptic junctions and act locally to control nerve cell functions.

Question 15

Cytokines

Answer 15

Cytokines are peptides secreted by cells into the extracellular fluid and can function as autocrines, paracrines, or endocrine hormones. Examples of cytokines include the interleukins and other lymphokines that are secreted by helper cells and act on other cells of the immune system

Question 16

What are peptide hormones?

Answer 16

Proteins and polypeptides, including hormones secreted by the anterior and posterior pituitary gland, the pancreas (insulin and glucagon), the parathyroid gland (parathyroid hormone), and many others

Question 17

What is the endocrine system and its primary fucntion?

Answer 17

The endocrine system includes the endocrine glands and their hormones

The primary function of the endocrine system is to coordinate and integrate cellular activities within the whole body in order to maintain homeostasis

Question 18

Function of the endocrine system

Answer 18

Helps coordinate functions between cells
Critical for maintaining homeostasis

Regulates
growth and development
metabolism and water balance
stress responses

Controls uterine contractions
Controls milk production
Regulates ions (calcium, sodium, potassium)
Regulates heart rate and blood pressure
Monitors blood glucose levels
Aids the immune system
Reproductive functions

Question 19

Difference between endocrine and exocrine glands

Answer 19

Exocrine glands
 release secretions to tissue by ducts
 Extracellular effects (food digestion)
 Liver - Bile released into the gallbladder, then through a duct into the small intestine
The pancreas - releases pancreatic juice into the small intestine via a duct

Endocrine glands
ductless
 release hormones directly into the blood (Intracellular effects)
Blood transports hormones throughout the body
Each hormone acts on only a certain kind of tissue called its target tissue
other organs not usually considered endocrine glands
e.g., brain and heart, releasing important substance

Question 20

Binding sites of peptides, steroids and amino acid derivative

Answer 20

 Proteins (peptides): Bind to receptors on the cell surface

 Steroids: They cross the cell membrane because they are lipid soluble and bind to intracellular receptors.

 Amino acid derivatives (amines): Bind to receptors on the cell surface with the exception of the thyroid hormone that is transported into the cell and binds to its nuclear receptor

Question 21

What is the half-life and metabolic clearance rate of a hormone?

Answer 21

The half-life of a hormone is the time it takes to reduce the plasma hormone concentration by one-half, and is used as an indicator of the rate of hormone elimination.

The metabolic clearance rate of a hormone is the volume of plasma cleared of a hormone per minute.

Question 22

Half-life of amines, peptide and steroid hormones

Answer 22

 Amines have the shortest half life (2 - 3 minutes)
 Polypeptides have 4 - 40 minutes half-life
 Proteins and steroids have 4 – 170 minutes and
 Thyroid hormones have 0.75 – 6.7 days

Question 23

Chracteristics of protein hormones

Answer 23

 Constitute the majority of the hormone
 Have between 3 to 200 amino acid residues
 Synthesized as preprohormones in the ribosomes
 Undergo post-translational processing to prohormones in the endoplasmic reticulum
 Prohormones are packaged in secretory vesicles in the Golgi apparatus
 Released from the cell by exocytosis in response to ca2+ influx similar to how neurotransmitters are released.
 Examples include Insulin, Glucagon, Adrenocorticotropic hormone and Growth hormone.

Question 24

Chracteristics of glycoprotein hormones

Answer 24

 Have carbohydrate moieties
 The carbohydrate moieties play a crucial role in determining the biological activities and circulating clearance rates of glycoprotein hormones.
 Examples include; Gonadotropic hormone, Thyroid stimulating hormone, Human chorionic gonadotropin hormone, Luteinizing hormone and follicle-stimulating hormone

Question 25

Characteristics of steroid hormones

Answer 25

 Derived from cholesterol
 Synthesized in the adrenal cortex, gonads and placenta
 Lipid soluble
 Cross the plasma membrane to intracellular cytosolic or nuclear receptors
 Receptors for steroid hormones are found in the cell’s cytoplasm or in its nucleus
 Vitamin D and its metabolites are equally considered steroid hormones

Question 26

Characteristics of amino acid hormones

Answer 26

 Amino acid derivatives hormones:
 Synthesized from the amino acid tyrosine
 Examples include: Catecholamines, norepinephrine, epinephrine, dopamine and thyroid hormones

Question 27

Characteristics of non-steroid hormones

Answer 27

React with specific receptors outside the cell
This triggers an enzyme reaction which leads to the formation of a second messenger (cAMP).
cAMP can produce specific intracellular
functions:
Activates cell enzymes
Change in membrane permeability
Promote protein synthesis
Change in cell metabolism
Stimulation of cell secretions

Question 28

Process of the generation of intercellular messengers

Answer 28

1.In this case, the binding of hormone (first messenger) to its receptor causes the generation of intracellular signalling molecules (second messengers)

2. Second messengers amplify the hormonal signal within the target cell. A common means that second messengers use to bring about changes in cellular activity is through the stimulation of kinases; the enzymes that phosphorylate target proteins
3. The process of second messenger generation usually begins when the hormone receptor complex associates with intracellular heterotrimeric G proteins.
4. G-proteins have three subunits: α, β, and γ. Interaction with the hormone receptor complex causes the Gα subunit to dissociate from the βγ subunit.
5. The Gα subunit can interact with one of several effector proteins to regulate second messenger production.
6. The G protein family is large, and different G proteins activate different second messenger pathways, including the
   ubiquitous cyclic adenosine monophosphate (cAMP) pathway and the diacylglycerol (DAG) and the inositol 1,4,5triphosphate (IP3 ) pathways

Question 29

Describe the hypothalamus

Answer 29

 A structure of the diencephalon of the brain; ventral to the thalamus
 Located just over optic chiasm and pituitary stalk (infundibulum)
 Shaped like a flattened funnel, forms floor and walls of third ventricle
 Regulates primitive functions from water balance, sex drive, . . .
 Regulate many functions carried out by pituitary gland
 Has both neural and endocrine functions, producing and secreting many
hormones.
 It is anatomically and functionally related to the pituitary gland

Question 30

Functions of the hypothalamus

Answer 30

Controls many endocrine glands:
regulates the endocrine system through it’s direct connection to the pituitary gland

 The hypothalamus controls basic functions such as:
 Body temperature, blood pressure, growth and development, reproduction, electrolyte balance and water regulation.

 It accomplishes this by producing both releasing and inhibiting hormones that influence the anterior pituitary gland.

 Produces ADH and Oxytocin which are transported to the posterior pituitary where they will ultimately be released.

Question 31

Describe the pituitary gland

Answer 31

 The pituitary gland (or hypophysis), is a bean-sized organ suspended from it by a stem called the infundibulum (or pituitary stalk).
 It is situated below the hypothalamus in a depression of the sphenoid the bone at the base of the skull called the sella turcica
 The pituitary stalk contains nerve fibres and blood vessels.
It consists of two lobes that arise from distinct parts of embryonic tissue:

The posterior pituitary (neurohypophysis) is neural tissue, whereas
The anterior pituitary (also known as the adenohypophysis) is glandular tissue that develops from the primitive digestive tract.

Question 32

What hormones are secreted by the anterior pituitary gland?

Answer 32

Follicle-stimulating hormone (FSH)
Growth hormone (GH)
Luteinizing hormone (LH)
Thyroid-stimulating hormone
Prolactin
Adenocorticotropic hormone

Question 33

What hormones are secreted by the posterior pituitary gland (but produced by the hypothalamus)?

Answer 33

Antidiuretic hormone (ADH, or vasopressin). Oxytocin

Question 34

Modes of control of the HYPOTHALAMO-PITUITARY LINK

Answer 34

 Direct neural connection between the hypothalamus and posterior pituitary via the hypothalamo-hypophyseal tract
 Hormonal regulation via a dedicated portal vascular system linking the hypothalamus to the anterior pituitary.

Question 35

Importance of the hypothalamo pituitary link

Answer 35

 The hypothalamus-pituitary unit is the most dominant portion of the entire endocrine system.
 The output of the hypothalamus-pituitary unit regulates the function of the thyroid, adrenal and reproductive glands and also controls somatic growth, lactation, milk secretion and water metabolism.

Question 36

Describe the parathyroid gland

Answer 36

Function is to control metabolism of calcium
Necessary for normal nerve and muscle function, blood clotting, healthy bones and teeth
Located in back of thyroid gland (in neck)
Hormone released is parathyroid hormone (PTH)
Undersecretion of parathormone results in nerve disorders, brittle bones and clotting problems

Question 37

Discuss the parathyroid hormone and it’s importance

Answer 37

Parathyroid hormone (PTH) and vitamin D are the principal hormones that regulate Ca 2+ and phosphate homeostasis.
 The homeostasis of Ca2+ and phosphate is linked because these hormones are both present in hydroxtapatite crystals which form the major mineral components in bone.
Other functions include:
muscle contraction, exocytosis, intracellular signaling and nerve conduction.
 Phosphate is also required by all cells e.g. phosphate transfer reactions are the basis of cellular energy metabolism (ATP and ADP) and of the control of cellular function via phosphorylation and dephosphorylation reactions.

Question 38

Discuss calcium-phosphate balance

Answer 38

The maintenance of normal plasma Ca2+ and phosphate concentrations requir es a balance between inputs to the circulation and outputs from the circulation.

Ca2+ and phosphate enter the circulation from the gastrointestinal system and from the resorption of bone. The processes of renal excretion and bone formation remove Ca2+ and phosphate from plasma.

Bone is being continuously remodeled by the simultaneous formation of bone by osteoblasts and its resorption by osteoclasts. Depending on the balance between osteoblast and osteoclast activity, bone re modeling may either add ca2+ and phosphate to plasma or it may remove these ions.

After the completion of bone growth, daily rates of bone formation and resorptio n should be equal

Question 39

Characteristics of hormones

Answer 39

Chemical messengers
Secreted by endocrine glands or tissues into blood
Travel everywhere blood goes
Affect only target cells, cells with receptors and
induces a characteristic response
May affect very distant organs or cells

Question 40

Activation of a receptor by hormone binding changes the target cell in what manner and how?

Answer 40

 In most cases, activation of a receptor by hormone binding changes the target cell activity either through the generation of intracellular second messengers or via changes in gene transcription and translation

Question 41

What affects a hormone’s response?

Answer 41

 Hormones’ response is affected by the number of available receptors
 Downregulation or upregulation of the receptor number determines the sensitivity of a target cell to a hormone.

Question 42

Discuss intracellular signalling

Answer 42

 This applies to the peptide hormones and catecholamines (water-soluble hormones)
 In this case, the binding of hormone (first messenger) to its receptor (G-protein coupled receptor) causes the generation of intracellular signalling molecules (second messengers)
 Second messengers amplify the hormonal signal within the target cell. A common means that second messengers use to bring about changes in
cellular activity is through the stimulation of kinases; the enzymes that phosphorylate target proteins
 The process of second messenger generation usually begins when the hormone receptor complex associates with intracellular heterotrimeric G proteins.

Question 43

Define gene transcription and translation in steroids

Answer 43

 This is carried out by the steroids and thyroid hormones.
 The effects of steroids and thyroid hormones occur slowly when compared with the effects of peptide hormones. The effects of the classic steroid hormones are slow because they occur due to changes in gene transcription and translation.
(Some fast steroid responses have recently been identified and may be attributed to surface membrane receptors.)
 Most steroid hormone receptors are present in the cytoplasm and are accessed when steroids diffuse through lipid membranes to enter target cells

Question 44

Hormones can be removed from plasma by which processes?

Answer 44

 Metabolism or binding in the tissues.
 Hepatic excretion.
 Renal excretion

Question 45

Describe the transport of soluble and insoluble hormones

Answer 45

Insoluble
 Only free hormone molecules can diffuse out of capillaries and bind to their receptors on the target cell.
 The binding of a hormone to plasma proteins reduces the amount of free concentration available in the blood.
 For instance, steroids and thyroid hormones are poorly soluble in water and must bind to plasma proteins in order to be carried in the plasma.
 About 90% of the total hormone concentration is protein bound.
 The protein-bound hormone fraction remains in the plasma and is inactive, giving it a long half-life because the protein acts as a reservoir of the hormone.

Soluble
 Water-soluble hormones such as peptides and catecholamines dissolve readily in the blood plasma and are able to freely diffuse from the plasma
to their sites of action.
 Water soluble hormones that are exclusively protein bound tend to have a faster onset of action and act for shorter periods of time (catecholamines) than hormones with a high fraction bound to carrier proteins in plasma (thyroids)

Question 46

What are G proteins?

Answer 46

G-proteins can be heterotrimeric or monomeric
heterotrimeric have three subunits: α, β, and γ. Interaction with the hormone-receptor complex causes the Gα subunit to dissociate from the βγ subunit.
 The Gα subunit can interact with one of several effector proteins to regulate second messenger production.
 The G protein family is large, and different G proteins activate different second messenger pathways, including the ubiquitous cyclic adenosine monophosphate (cAMP) pathway and the diacylglycerol (DAG) and the inositol 1,4,5triphosphate (IP3) pathways.

Question 47

Explain the process of gene transcription and translation in steroids

Answer 47

 Once a steroid receptor binds to its hormone, it enters the nucleus to interact with DNA.
 An activated steroid receptor partners with another steroid receptor to form a receptor dimer as it binds to DNA.
 Binding to DNA occurs at a specific sequence of DNA known as a steroid response element, which is located at the 5 regions of a gene, upstream from the starting point for gene transcription.
 The nucleotide sequences of steroid response elements are highly conserved and recognized by several steroid receptors.
 The specificity of steroid response in a given target
cell is mainly determined by the type of steroid receptor present in the cell.
 Thyroid hormone receptors are widely expressed among the body tissues and function in the same manner as steroid receptors.

Question 48

Describe the POSTERIOR PITUITARY GLAND AND ITS RELATION TO THE HYPOTHALAMUS

Answer 48

The posterior pituitary gland,
 Composed mainly of glial-like cells called pituicytes.
 The pituicytes do not secrete hormones;
 Act simply as a supporting structure for large numbers of terminal nerve fibers and terminal nerve endings from nerve tracts that originate in the
supraoptic (ADH) and paraventricular (oxytocin) nuclei of the hypothalamus
 These tracts pass to the neurohypophysis through the pituitary stalk (hypophysial stalk).
 The nerve endings are bulbous knobs that contain many secretory granules. These endings lie on the surfaces of capillaries, where they secrete two posterior pituitary hormones: (1) antidiuretic hormone (ADH), also called vasopressin, and (2) oxytocin.

 The posterior lobe is composed of axonal terminals of the hypothalamic
magnocellular neurons surrounded by astrocytes (AKA pituicytes).

The magnocellular neurons from supraoptic nuclei synthesize vasopressin majorly
While the one from paraventricular nuclei synthesize oxytocin primarily.
Though each of these nuclei can synthesize about one sixth as much of its primary hormone.
 Nerve fibres from the paraventricular and supraoptic nuclei pass directly to the posterior pituitary, secrete their hormones and transport them to the axonal terminals in the posterior pituitary where they are secreted into the general circulation

Question 49

Describe the regulation of the posterior pituitary gland

Answer 49

REGULATION OF POSTERIOR PITUITARY
 Posterior lobe control - neuroendocrine reflexes
hormone release in response to nervous system signals suckling infant stimulates nerve endings  hypothalamus posterior lobe  oxytocin  milk ejection

hormone release in response to higher brain centers
milk ejection reflex can be triggered by a baby’s cry

Question 50

Describe the ANTERIOR PITUITARY- HYPOTHALAMIC RELATIONSHIP

Answer 50

 The anterior pituitary has no direct neural connection with the hypothalamus.
 The gland receives blood through the hypophysial portal circulation, which carries the hypothalamic hormones to the specialized adenohypophysial cells.
 Hypothalamic stimulatory and inhibitory factors, together with feedback signals derived from target organs converge with the auto- and paracrine factors, to induce transcriptional regulation, translation, and secretion of the pituitary hormones.
 Collectively, these regulatory mechanisms manage an accurate and dynamic gland homeostasic process.

Question 51

What are the CELLS OF THE ADENOHYPOPHYSIS (anterior pituitary gland)?

Answer 51

FLAT PEG

 FSH and LH-producing GONADOTROPHS,
 Prolactin (PRL)-producing LACTOTROPHS,
 GH-producing SOMATOTROPHS,
 TSH-producing THYROTROPHS, and
 ACTH( adrenocorticotropic hormone)-producing CORTICOTROPHS.
 This lobe also contains the non-hormone-producing folliculostellate cells, which are glia-like cells, and endothelial cells that line the capillaries.
 The anterior lobe central nervous system (CNS) neurotransmitters act as releasing and inhibitory hormones delivered through the portal vessels

Question 52

The magnitude of a response to a hormone depends on what?

Answer 52

how many receptors are occupied at the target cell, which in turn depends on the free hormone concentration in the extracellular fluid.

Question 53

The plasma free hormone concentration is affected by what?

Answer 53

 The rate of hormone secretion.
 The rate of hormone elimination.
 The extent of hormone binding to plasma proteins.

Question 54

At which level does negative feedback work?

Answer 54

Negative feedback can operate at the level of the primary gland, the anterior pituitary, or hypothalamus.

Question 55

Describe the negative feedback mechanism

Answer 55

Act like a thermostat in a home
As the temperature cools, the thermostat detects the change and triggers the furnace to turn on and warm the house
Once the temperature reaches its thermostat setting, the furnace turns off
Example: Body sugar increases after a meal, so the pancreas secretes insulin, which tells the body’s cells to take in glucose. Once blood sugar levels reach normal, the pancreas stops making insulin.
Often used to maintain homeostasis

Question 56

What is the antogonisticeffect of hormones?

Answer 56

Each hormone does the opposite of the other.
For example, if the blood pressure drops too low, the pituitary releases antidiuretic hormone (ADH), which causes the kidneys to reabsorb more water. If the blood pressure increases too much, then the heart will
release atrial natriuretic peptide (ANP), which will cause the kidneys to reabsorb less water.

Question 57

What is a Positive Feedback mechanism?

Answer 57

 Positive Feedback: change in a factor triggers a physiological response that AMPLIFIES an initial change
 PF mechanisms control events that can be out of control and do not require continuous adjustment
 Rarely used to maintain homeostasis
 In a few cases, the rate of hormone secretion may be controlled by positive feedback, in which the effects of the hormone result in further hormone secretion. For example, the surge in the plasma luteinizing hormone concentration, which occurs just prior to ovulation, is due to positive feedback stimulation by estrogen

Oxytocin stimulates and enhances labor contractions
As labor continues, more oxytocin is produced
Intensifies contractions until the baby is outside birth canal Oxytocin production stops and labor contractions stop

Question 58

Types of endocrine disorders

Answer 58

Endocrine disorders can be classified as primary, secondary, or tertiary.
Primary disorder is an excess or deficiency of secretion by the target gland
Secondary disorder is an excess or deficiency of secretion by the pituitary gland.
Tertiary disorder is an excess or deficiency of secretion by the hypothalamus

Question 59

Forms in which calcium and phosphate exist in plasma

Answer 59

Ca2+ exists in three forms in plasma, in approximately the following proportions:
 45% exists as free ionized Ca2+ . The plasma concentration of free ionized Ca2+ is tightly regulated in the 1.0–1.3 mmol/L (4.0–5.2 mg/dL).
 45% is bound to plasma proteins, particularly albumin.
 10% is complexed with low molecular weight anions such as citrate and oxalate
 Phosphate occurs in two major forms in plasma, alkaline phosphate and acid phosphate
 80% exists as alkaline phosphate (HPO4 2−) at a normal plasma PH of 7.4.2)
20% exists as acid phosphate (H2PO4 − ).
 The plasma [phosphate] is less strictly regulated than Ca2+, and is within the range of 0.8–1.5 mmol/L (2.5–4.5 mg/dL)

Question 60

The direct effects of PTH

Answer 60

The direct effects of PTH are:
1. Stimulation of bone resorption, which adds both Ca2+ and phosphate to p
lasma. The rate of resorption of the organic bone matrix can be assessed by measuring urinary excretion of hydroxyproline.

2. Decrease in renal Ca2+ excretion in response to PTH stimulation of Ca2+ reabsorption in the thick ascending limb and distal tubule of the nephron.

3.Increase in renal phosphate excretion, due to the inhibition of phosphate reabsorption in the proximal renal tubule.

Question 61

Action of PTH and synthesis of PTH

Answer 61

PTH exerts dominant control of Ca2+ and phosphate homeostasis. Normally, there are four small parathyroid glands, with two on the back of each lobe of the thyroid gland.
 Chief cells are responsible for production of the peptide hormone PTH, which is formed from the cleavage of preproPTH. Like most peptide hormones, PTH is water soluble and circulates free in plasma
 PTH is broken down by cleavage into smaller peptide fragments in the liver and by hydrolysis of the active
Nterminal fragment in the kidney. PTH has a short halflife, of approximately 5 minutes.
 PTH increases the free plasma Ca 2+ concentration and decreases the plasma phosphate concentration.

Question 62

Describe the control of the secretion of the parathyroid hormone

Answer 62

The rate of PTH secretion is regulated by the following three factors :
1. Plasma free [Ca2+]: A decrease in the plasma [Ca 2+] is the most potent stimulus for PTH secretion. Chief cells sense plasma Ca2+ concentration through the expression of the extracellular ca2+ sensing receptor (CaSR). The CaSR is a G-protein-coupled receptor linked to IP3/DAG intracellular signaling pathway.
2. Plasma [phosphate]: A prolonged increase in phosphate concentration stimulates PTH secretion.
3. Vitamin D: PTH stimulates vitamin D synthesis, which exerts negative feed back inhibition on PTH secretion

Question 63

RELATIONSHIP BETWEEN PTH, CA AND PHOSPHATE ION

Answer 63

The plasma concentration of both hormones increases
because hypocalcemia stimulates PTH secretion, which in turn stimulates the production of 1,25(OH)2D3
To return the plasma Ca2+ concentration to normal,
Bone resorption (destruction of bone tissue that causes bone loss) and intestinal Ca2+ absorption increase and urinary Ca2+ excretion decreases.
Bone resorption due to increased PTH
concentration produces an unwanted phosphate input into the plasma; increased 1,25(OH)2D3 causes further addition of phosphate to plasma through increased intestinal absorption.
An increase in plasma phosphate concentration is prevented because PTH strongly increases urinary phosphate excretion.

Question 64

What is HYPOCALCEMIA?

Answer 64

Hypocalcemia causes instability of membrane potentials, neuronal hyperexcitability, and muscle tetanus.
Hypocalcemic tetany can be assessed clinically by attempting to elicit either Chvostek’s sign or Trousseau’s sign

Question 65

RESPONSE OF PTH TO HYPERCALCEMIA

Answer 65

RESPONSE OF PTH TO HYPERCALCEMIA
To counter hypercalcemia, there is a decrease in PTH and vitamin D activity, shifting the balance of bone remodeling toward bone formation. Urinary
Ca2+ excretion increases and intestinal Ca2+ absorption decreases, restoring normal plasma free [Ca2+].

Question 66

What is calcitonin?

Answer 66

Calcitonin is a peptide hormone produced by the thyroid C cells in response to hypercalcemia.
In animals, studies have shown that calcitonin
decreases bone resorption through inhibition of osteoclasts and that it increases urinary Ca2+ excretion to counter hypercalcemia.
However, in humans, calcitonin has weak effects of Ca2+ homeostasis, and neither the absence nor the excess of calcitonin causes defects in Ca2+ or phosphate homeostasis.

Question 67

Symptoms of hypercalcemia

Answer 67

The phrase “bones, stones, moans, groans, and psychiatric overtones” indicates potential signs and symptoms of hypercalcemia:
Bones: Bone pain.
Stones: Kidney stones.
Moans: Abdominal pains associated with constipation or pancreatitis.
Groans: General malaise and weakness.
Psychiatric overtones: Depression, delirium, and coma.

Question 68

The active form of vitamin D is

Answer 68

1,25(OH)2D3 Calciferol

Question 69

Forms of vitamin D in the body

Answer 69

Vitamin D is present in the body as vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol).

Question 70

What is cholecalciferol

Answer 70

Cholecalciferol can be synthesized from 7dehydrocholesterol in the skin when it is exposed to an adequate amount of ultraviolet light
Cholecalciferol is a fat soluble vitamin that must be dissolved in bile acid micelles to be absorbed in the small intestine.
Hydroxylation of cholecalciferol at the 25th position occurs in the liver and is not regulated.
Activation of vitamin D is completed by 1hydroxylation in the kidney and is stimulated by PTH and, to a lesser degree, by low plasma phosphate concentration