System Physiology Animal MCQ Quiz - Objective Question with Answer for System Physiology Animal - Download Free PDF

The correct answer is Only C

Explanation:

• Calcitropic hormones, such as calcitriol (active vitamin D), parathyroid hormone (PTH), and calcitonin, play a key role in maintaining calcium homeostasis in the body. These hormones regulate calcium levels in the blood by influencing calcium absorption, bone remodeling, and renal calcium reabsorption or excretion.
• Calcium homeostasis is crucial for various physiological processes, including bone health, muscle contraction, nerve signaling, and blood clotting.
  • Option A:  Calcium-binding proteins (CaBP) enhance the movement of calcium from the intestinal brush border into the cytoplasm of enterocytes. This process is essential for intestinal calcium absorption, which is regulated by calcitriol. Therefore, this statement is correct.
  • Option B: Calcitonin acts on receptors present in osteoclasts, where it increases cyclic AMP (cAMP) production. This action inhibits osteoclast activity, reducing bone resorption and contributing to calcium homeostasis. Hence, this statement is also correct.
  • Option C: Parathyroid hormone (PTH) does not work independently to mobilize bone mineral. Instead, it often works in concert with vitamin D (calcitriol) to regulate calcium homeostasis. PTH stimulates the production of calcitriol in the kidneys, which enhances calcium absorption in the intestines and works synergistically to maintain calcium levels. Therefore, this statement is incorrect.
  • Option D: Calcitriol, the active form of vitamin D, is the major calcitropic hormone responsible for regulating intestinal calcium absorption. It increases the synthesis of calcium-binding proteins (CaBP) in enterocytes, thereby facilitating calcium uptake from the diet. This statement is correct.

The correct answer is B and C

Concept:

• Angiotensin-converting enzyme (ACE) plays a critical role in the renin-angiotensin-aldosterone system (RAAS), which regulates blood pressure and fluid balance.
• ACE converts angiotensin I into angiotensin II. Angiotensin II is a potent vasoconstrictor and stimulates the release of aldosterone, leading to sodium and water retention in the kidneys.
• ACE inhibitors block the formation of angiotensin II, thereby causing vasodilation (relaxation of smooth muscle in arteries) and reducing aldosterone secretion, which decreases sodium and water retention.
• In cases of severe blood loss (hypovolemia), RAAS activation is crucial for maintaining blood pressure and ensuring adequate blood volume. Using ACE inhibitors in such cases can be harmful.

Explanation:

• ACE inhibitors relax smooth muscles in the arteries: ACE inhibitors prevent the formation of angiotensin II, which is responsible for vasoconstriction. This leads to vasodilation, lowering blood pressure. In a person with severe blood loss, vasodilation can further reduce blood pressure, which is dangerous in hypovolemic conditions.
• ACE inhibitors reduce aldosterone secretion and prevent water retention: ACE inhibitors block the production of angiotensin II, which stimulates aldosterone secretion. Aldosterone helps retain sodium and water in the kidneys, increasing blood volume. In cases of severe blood loss, preventing aldosterone secretion can worsen hypovolemia and decrease blood pressure further.

Incorrect Options:

• Option A (ACE inhibitors increase renal tubular K+ excretion): This is incorrect. ACE inhibitors do not directly increase renal tubular potassium (K+) excretion; rather, they can cause potassium retention by reducing aldosterone levels. Lower aldosterone levels reduce sodium reabsorption and potassium excretion in the kidneys, leading to hyperkalemia instead of increased K+ excretion.
• Option D (ACE inhibitors decrease renal tubular NaCl and water excretion): This is incorrect. ACE inhibitors actually increase renal tubular NaCl and water excretion by reducing aldosterone secretion. Aldosterone promotes sodium and water reabsorption in the kidneys, so blocking its secretion has the opposite effect.

The correct answer is A and C

Explanation:

• The nerve action potential is a rapid electrical signal that travels along the axon of a neuron. It consists of different phases: depolarization, repolarization (descending phase), and hyperpolarization.
• The descending phase of the action potential, also known as repolarization, is critical for restoring the resting membrane potential after the neuron has been depolarized.
• Repolarization is driven by changes in the activity of voltage-gated ion channels, specifically potassium (K⁺) and sodium (Na⁺) channels.

Delayed opening of voltage-gated K⁺ ion channels (Option A):

• During the descending phase of the action potential, voltage-gated K⁺ channels open with a delay following depolarization.
• These channels allow K⁺ ions to move out of the neuron, making the inside of the cell more negative and contributing to the repolarization of the membrane.
• This is a key mechanism responsible for the descending phase.

Closing of voltage-gated Na⁺ ion channels (Option C):

• During the descending phase, voltage-gated Na⁺ channels, which were previously open during depolarization, close (inactivate).
• This prevents further influx of Na⁺ ions, halting the depolarization process and allowing repolarization to occur.
• The inactivation of Na⁺ channels is essential for the descending phase of the action potential.

Incorrect Options:

Rapid opening of voltage-gated Na⁺ ion channels (Option B):

• This is associated with the depolarization phase of the action potential, not the descending phase.
• During depolarization, the rapid opening of these channels allows Na⁺ ions to enter the neuron, making the inside of the cell more positive.

Leaky K⁺ ion channels (Option D):

• Leaky K⁺ channels contribute to maintaining the resting membrane potential, not the action potential phases.
• These channels are always open and allow a small amount of K⁺ to move across the membrane, maintaining the resting potential.

The correct answer is C and D

Explanation:

• The thyroid gland produces thyroid hormones, primarily thyroxine (T4) and triiodothyronine (T3), which are critical for regulating metabolism, growth, and development.
• The biosynthesis of thyroid hormones involves several steps, including the uptake of iodide (I^-), its transport into the colloid, iodination of tyrosine residues on thyroglobulin, and coupling reactions to form T3 and T4.
• Key transporters and enzymes, such as the Na+/I- symporter (NIS), pendrin, thyroid peroxidase (TPO), and thyroglobulin, play vital roles in this process.

Statement C: "Pendrin, a Cl^-/I^- exchanger, helps I^- entry into the colloid" is correct.

• Pendrin, a Cl^-/I^- exchanger located on the apical membrane of thyroid follicular cells, facilitates the transport of iodide (I^-) from the cytoplasm into the colloid of the thyroid follicle.
• This step is essential for the subsequent iodination of tyrosine residues on thyroglobulin.

Statement D: "Iodination of tyrosine residue takes place first on the 3rd position in the thyroglobulin protein" is correct.

• In the colloid, iodide is oxidized by thyroid peroxidase (TPO) and incorporated into the tyrosine residues of thyroglobulin.
• The iodination occurs at the 3rd position of the tyrosine ring, forming monoiodotyrosine (MIT). A subsequent iodination at the 5th position leads to the formation of diiodotyrosine (DIT).

Other Options:

Statement A: "An antiporter transports two Na⁺ ions and one I^- ion across the thyroid follicular cells" is incorrect.

• The Na⁺/I^- symporter (NIS) is not an antiporter. It is a symporter that transports two Na⁺ ions and one I^- ion into the thyroid follicular cells from the bloodstream.
• This process is driven by the sodium gradient established by the Na⁺/K⁺ ATPase pump, not through antiport mechanisms.

Statement B: "Pendrin, a Cl^-/I^- symporter, helps I^- entry into the colloid" is incorrect.

• Pendrin is not a Cl^-/I^- symporter. It is a Cl^-/I^- exchanger, meaning it facilitates the exchange of chloride (Cl^-) and iodide (I^-) ions across the apical membrane.

The correct answer is A and C only

Concept:

• The tumour microenvironment (TME) refers to the non-cancerous cells, molecules, and blood vessels that surround and support tumour growth and progression. These components play a critical role in cancer development, progression, and metastasis.
• The interaction between tumour cells and the TME significantly influences the metastatic process, which is the spread of cancer cells from the primary tumour to distant sites in the body.
• Key elements of the TME include hypoxia, tumour-associated macrophages (TAMs), cancer-associated fibroblasts (CAFs), and extracellular matrix (ECM) components, among others. 

Explanation:

Statement A: Hypoxia in primary tumours can induce the expression of VEGF (vascular endothelial growth factor) and matrix metalloproteinases (MMPs) to promote metastasis.

• This statement is correct.
• Hypoxia, or low oxygen levels in the tumour microenvironment, is a common feature of rapidly growing tumours. It triggers the activation of hypoxia-inducible factors (HIFs), which in turn upregulate VEGF and MMPs.
• VEGF promotes angiogenesis, which is the formation of new blood vessels, providing pathways for tumour cells to disseminate. MMPs degrade the extracellular matrix, facilitating tumour cell invasion and migration.

Statement B: Tumour-associated macrophages (TAMs) always inhibit metastasis through immune surveillance.

• This statement is incorrect.
• While some macrophages can promote immune surveillance and anti-tumour activity, TAMs in the tumour microenvironment are typically polarized to an M2-like phenotype, which supports tumour growth and metastasis.
• M2-like TAMs secrete factors that promote angiogenesis, suppress immune responses, and enhance tumour cell invasion, rather than inhibiting metastasis.

Statement C: Cancer-associated fibroblasts (CAFs) provide structural support and secrete factors that promote metastasis.

• This statement is correct.
• CAFs are a major component of the tumour stroma and contribute to tumour progression by remodeling the extracellular matrix, enhancing tumour cell invasion, and secreting pro-metastatic factors such as growth factors, cytokines, and chemokines.
• They also contribute to creating a supportive niche for tumour growth and metastasis.

Statement D: The acidic pH of the tumour microenvironment impedes cancer cell migration.

• This statement is incorrect.
• The acidic pH of the tumour microenvironment, caused by increased glycolysis and lactate production (Warburg effect), actually promotes tumour progression and metastasis.
• Acidic conditions enhance the activity of proteases like MMPs, which degrade the extracellular matrix, and support cancer cell motility and invasion.

The correct answer is B and C.

Explanation:

Thermoregulatory mechanisms are essential for maintaining body temperature within a narrow optimal range despite varying external conditions. Let's evaluate each statement about thermoregulation to determine their correctness.

A. Human voluntary activity is decreased in cold: Incorrect

• In cold environments, humans may reduce voluntary activity to conserve energy and minimize exposure to the cold. Movements and activities that generate heat might be reduced as part of an adaptive response to maintain core body temperature. However, sometimes shivering, an involuntary activity, increases which contributes to heat production.
• Voluntary activity might not decrease uniformly because shivering can be considered an involuntary response to generate heat.

B. There is a cutaneous vasodilation by heat: Correct

• When the body is exposed to heat, cutaneous (skin) blood vessels dilate (vasodilation) to increase blood flow to the skin. This helps release excess heat from the body through radiation, convection, and evaporation, thereby cooling the body.

C. There is an increased secretion of epinephrine and nor-epinephrine in cold: Correct

• In cold environments, the body increases the secretion of epinephrine and norepinephrine (catecholamines) which stimulate metabolic processes, increasing heat production. These hormones aid in thermogenesis by promoting glycogenolysis and lipolysis, which generate heat.

D. There is a decreased heat production in cold: Incorrect

• When exposed to cold, the body typically increases heat production through mechanisms such as shivering (which generates heat through muscle activity) and non-shivering thermogenesis (increased metabolic activity mediated by hormones like epinephrine and norepinephrine).

Conclusion: Combining the evaluations, the statements that are correct regarding thermoregulatory mechanisms are: B and C

The correct answer is 32.

Explanation:

Calcitonin is a polypeptide hormone produced by the C-cells (also known as parafollicular cells) of the thyroid gland. It plays a crucial role in regulating calcium levels in the blood by lowering them when they are elevated.

The primary structure of calcitonin in humans consists of 32 amino acids. This sequence includes several important functional residues that contribute to its biological activity, including its ability to inhibit osteoclast activity and reduce bone resorption, leading to a decrease in blood calcium levels.

Thus, calcitonin is composed of 32 amino acids, making 32 the correct answer.

The correct answer is Option 3 i.e.Their half-life is 20-24 days.

Key Points

• Blood is the connective tissue that is composed of an extracellular matrix called blood plasma.
• It consists of two main components: plasma and blood cells. 
• Following are different types of blood cells.

1. RBC: 
   • They are circular and biconcave-shaped cells. 
   • It has a diameter of about 7-8μ 
   • The total number of RBCs in females is about 4.8 million RBCs per microliter of blood and about 5.4 million RBCs per microliter of blood in males.
   • It contains a red respiratory pigment called hemoglobin. 
   • The life span of RBCs is about 120 days.
2. WBC:
   • Eosinophils - It is granulocyte, that contains larger granules in the cytoplasm, these granules contain histamine. It has a diameter of about 10-15μ. The nucleus is bilobed. 
   • Basophils - It is granulocytes, that contain smaller granules in larger number. It has a diameter of about 8-10μ. It has an S-shaped nucleus. 
   • Neutrophils - It is granulocytes, that contain the finest granules in the cytoplasm. It is about 10-12μ in diameter. It has a multilobed nucleus. 
   • Lymphocytes - It is the smallest WBCs. It has a diameter of about 8-12μ. It has large, spherical and surrounded by a thin layer of cytoplasm. It has a lifespan of about 24 hours in lymph and about 00 days in the bloodstream.
   • Monocytes - It is the largest WBCs. It has about 15-22μ diameter. It has a kidney-shaped nucleus that is surrounded by abundant cytoplasm. It has a lifespan of about 3 days. 
3. Platelets:
   • They are small and non-nucleated. It has a diameter of about 2-4μ.
   • They are formed by the fragmentation of large cells called megakaryocytes of bone marrow. 
   • Their life span is about 12 days in the bloodstream.

Explanation:

• Hemopoietic stem cells also differentiate into platelets. 
• Platelets' main function is to prevent blood loss from damaged blood vessels by the formation of platelet plugs. 
• Platelets have a short life span, normally it is just 5-9 days. 

Hence, the correct answer is Option 3.

The correct answer is Option 3 i.e. Opening of Na+ channels in the outer segment of photoreceptors

Concept:

• Vertebrate rod and cone photoreceptors use graded, hyperpolarizing responses to indicate the rate of photons absorbed. 
•  In darkness the photoreceptor's membrane potential is around -40 mV, significantly more depolarized than that of most neurons.
• When light reduces the level of cGMP, thus closing cGMP-gated channels, the inward current that flows through these channels is reduced and the cell becomes hyperpolarized.

Explanation:

• In darkness the cytoplasmic concentration of cGMP is high, thus maintaining the cGMP-gated channels in an open state and allowing a steady inward current, called the dark current. 

• In complete darkness, a photoreceptor has two dominant currents.
• While an outward K⁺ current travels through non-gated K⁺-selective channels and is restricted to the inner segment of the photoreceptor, while an inward current travels through cGMP-gated channels, which are restricted to the photoreceptor's outer segment.
• The K⁺ channels' outward current tends to hyperpolarize the photoreceptor in the direction of the K+ equilibrium potential (around -70 mV).
• The photoreceptor is often depolarized by the inward current.
• The inner segment of the photoreceptor possesses a high density of Na⁺-K⁺ pumps, which pump out Na⁺ and pump in K⁺, allowing the photoreceptor to maintain stable intracellular concentrations of Na⁺ and K⁺ in the face of these massive fluxes.

​
Explanation:

Option 1: Closing of Na+ channels in the outer segment of photoreceptors.

• Consider the explanation above thus this option is not true, as in darkness cGMP is generated which causes opening of Na⁺ channels ​​

• Consider the explanation above thus this option is not true

• Consider the explanation above thus this option is true,  in darkness cGMP is generated which causes the opening of Na⁺ channels.                     

The correct answer is Option 2 i.e. A - iii; B - iv; C - ii; D - i

Concept:

• Hormones are organic substances that are produced in small amounts by particular tissues, secreted in the blood and control the metabolic and biological activities of the target tissue or organs.
• Hormones are also called chemical messengers.
• In some cases, the endocrine gland can produce more than one hormone.
• One physiological effect can be regulated by more than one hormone.  For example, glucose concentration in the blood is regulated by insulin as well as glucagon hormone. 
• According to their chemical nature, hormones are classified as follows:

1. Steroid hormone - 
   • They are mainly derived from cholesterol.
   • It includes two classes corticosteroids and sex steroids.
   • It includes glucocorticoids and mineralocorticoids, androgens, etc. 
2. Amine hormones - 
   • They are made of amines and they are derivatives of amino acid tyrosine. 
   • They are secreted by the adrenal medulla and thyroid.
   • Before being released into the bloodstream they are stored in the respective organs.
   • Some of these hormones are polar while others are protein bound.
3. Peptide hormone - 
   • They are hormones which contain peptide chains.
   • They are unable to pass the plasma membrane due to their hydrophilic and lipophobic property. 
   • Oxytocin, vasopressin, insulin, etc are examples of peptide hormones.
4. Glycoprotein hormone - 
   • They are glycoproteins in nature where protein is conjugated with carbohydrate group
   • Examples, are FSH, LH, TSH, etc.
5. Eicasanoid hormones - 
   • They are fatty acid derivatives of arachidonic acid. 
   • They include prostaglandins, thromboxane, etc.

Explanation:

• Cortisol is a steroid hormone that is produced by two adrenal glands located on the top of each kidney. It plays an important role in stress response. 
• Adrenaline is also known as flight or fight hormone, it helps our body to deal with emergency situations. it acts on various organs to its effect include, increases in heart rate, dilation of pupils, increased in blood pressure, etc. 
• Melatonin hormone is produced in response to darkness, it helps to maintain the circadian rhythms or internal clock of the body. Nocturnal secretion of melatonin is important for initiating and maintaining sleep. 
• Dopamine is an amine hormone and also a neurotransmitter. It plays an important role in many various body functions, including movement, memory, motivation, etc.

Corrected table:

Hence, the correct answer is Option 2.

The correct answer is Option 3 i.e.Oxidized iodine

Concept:

• The "organification of tyrosine residues in thyroglobulin" refers to a crucial step in the biosynthesis of thyroid hormones, which is an important physiological process for maintaining metabolism and growth in humans.
• Thyroglobulin is a glycoprotein that serves as the precursor for the production of the thyroid hormones triiodothyronine (T3) and thyroxine (T4).
• This protein is synthesized by the follicular cells within the thyroid gland and stored within its structures awaiting iodination and further processing.
• The process begins with the active uptake of iodide by the thyroid cells.
• This iodide is then oxidized to iodine, typically in the presence of an enzyme known as thyroid peroxidase.
• Thyroglobulin has several tyrosine residues within its structure, which provide a site for the attachment of iodine.
• This process is known as "organification" and it results in the formation of monoiodotyrosine (MIT) and diiodotyrosine (DIT) residues on thyroglobulin.
• When the need for thyroid hormones arises, the MIT and DIT residues combine to form T3 (formed by one DIT and one MIT) and T4 (formed by two DIT residues), which are then released into the blood.
• This iodination and subsequent combination of iodinated tyrosine residues is critical for thyroid hormone production.
• Importantly, it is the "oxidized iodine" that participates in the organification process, iodinating the tyrosine residues on thyroglobulin

Explanation

Iodide ions (I^-) are transported into the thyroid gland and subsequently oxidized to form iodine (I₂), which is then able to iodinate tyrosine residues on thyroglobulin for the synthesis of thyroid hormones. Thus, it is the oxidized form of iodine that participates directly in the organification process.

The correct answer is A and D.

Explanation: 

P₅₀ is the partial pressure of oxygen at which hemoglobin is 50% saturated with oxygen. An increase in P₅₀ means hemoglobin has a lower affinity for oxygen, which facilitates oxygen unloading to tissues like active muscles during exercise. Several physiological factors influence P₅₀, such as temperature, pH (Bohr effect), CO₂ levels, and 2,3-DPG levels.

Statement A: "P₅₀ is increased during exercise as the temperature rises in active muscles."

• True. During exercise, active muscles produce heat, raising the temperature. Increased temperature shifts the oxygen-hemoglobin dissociation curve to the right, increasing P₅₀. This helps release more oxygen to the tissues.

Statement B: "During exercise, metabolites accumulate in the active muscles resulting in higher pH that increases P₅₀."

• False. During exercise, lactic acid and CO₂ accumulate, leading to a decrease in pH (i.e., muscles become more acidic, not alkaline). Lower pH reduces hemoglobin's affinity for oxygen (Bohr effect), increasing P₅₀. Thus, it's not a higher pH but a lower pH that increases P₅₀ during exercise.

Statement C: "P₅₀ is increased during exercise as CO₂ is decreased in active muscles."

• False. During exercise, CO₂ levels increase due to increased metabolic activity in muscles. Higher CO₂ levels lead to increased P₅₀ by promoting oxygen unloading (Bohr effect). A decrease in CO₂ would actually decrease P₅₀ (increase oxygen affinity), so this statement is incorrect.

Statement D: "An increase in 2,3-DPG has been reported in non-trained persons within 60 min of exercise resulting in higher P₅₀."

• True. 2,3-DPG (2,3-diphosphoglycerate) is a byproduct of glycolysis that binds to hemoglobin and decreases its affinity for oxygen, increasing P_50. During prolonged or intense exercise, especially in untrained individuals, 2,3-DPG levels can rise, aiding in oxygen release to tissues.​

The correct answer is 'A' is a ligand secreted from the brain and 'B' is a receptor in ovaries.

Explanation:

Key Observations from the Experiment

1. Overexpression of 'A' in the brain causes ovary degradation: This suggests that protein 'A' has an effect that originates in the brain but impacts the ovaries. The degradation implies a negative influence on ovary development.
2. Overexpression of a secretion-incompetent allele of 'A' does not cause ovary degradation: This indicates that protein 'A' must be secreted from the brain to affect the ovaries.
3. Downregulation of protein 'B' in the ovaries, along with overexpression of 'A' in the brain, prevents ovary degradation: This suggests that protein 'B' is required in the ovaries for the degradation effect to occur. In other words, 'B' might be acting in concert with 'A' to cause ovary degradation.
4. Physical interaction of 'A' and 'B' in ovary lysates: This means that when both proteins are present in the ovaries, they physically interact, implying a direct or indirect functional relationship.

Evaluation of the Inferences:

1. The protein 'A' cell autonomously influences ovary development while 'B' is secreted to influence brain function:  This is inconsistent with the observations. 'A' needs to be secreted from the brain to affect the ovaries, and there's no indication from the experiments that 'B' influences brain function.
2. A' is a ligand secreted from the brain and 'B' is a receptor in ovaries: This matches the observation that 'A' needs to be secreted from the brain to have an effect. The prevention of ovary degradation by downregulating 'B' suggests 'B' might be responding to 'A', fitting the ligand-receptor model. The physical interaction in the ovary lysates also supports this inference.
3. A' is a neurotransmitter secreted from the brain and 'B' is a signal transducer in the ovaries:This is incorrect because Neurotransmitters typically function at synapses between neurons or between neurons and other cell types, generally having a very short-range action due to the small synaptic gap.
   • Neurotransmitters are not usually described as having long-distance effects on organs (like the ovaries) because they primarily mediate communication between adjacent or closely situated cells within the nervous system.
4. A' is a receptor secreted from the ovaries and 'B' is a ligand in the ovary cell membrane:  This contradicts the requirement for 'A' to be secreted from the brain and the described interaction within the ovaries.

Conclusion: Based on the described evidence the correct answer is  'A' is a ligand secreted from the brain and 'B' is a receptor in ovaries.

The correct answer is a - iii, b - iv, c - i, d - ii

Explanation:

Types of Mammalian Nerve Fibers and Their Conduction Velocities:
1. Aa (Alpha) fibers:

• These are large-diameter, myelinated fibers. They are the fastest conducting fibers.
• Conduction Velocity: Typically in the range of 70-120 m/s.

2. B fibers:

• These are smaller diameter, myelinated fibers than Aa fibers. They belong primarily to the autonomic nervous system.
• Conduction Velocity: Generally in the range of 3-15 m/s.

3. Aδ (Delta) fibers:

• These medium-diameter, myelinated fibers are responsible for transmitting quick, sharp pain sensations.
• Conduction Velocity: Usually between 12-30 m/s.

4. Aβ (Beta) fibers:

•  These are medium to large-diameter, myelinated fibers involved in touch and pressure sensation.
• Conduction Velocity: Typically in the range of 30-70 m/s.

Therefore,

• Aa fibers should match with iii (70-120 m/s), as they are the fastest conducting fibers.
• B fibers should match with iv (3-15 m/s), which fits their slower conduction compared to other myelinated fibers.
• Aδ fibers should match with i (12-30 m/s), corresponding to their moderate conduction speed.
• Aβ fibers should match with ii (30-70 m/s), as they have a faster conduction velocity than Aδ fibers but slower than Aa fibers.