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

The correct answer is A, B, and C

Concept:

• Transcranial Magnetic Stimulation (TMS) is a non-invasive method used in neuroscience and clinical applications to modulate brain activity using magnetic fields.
• It involves the generation of a magnetic field through an electromagnetic coil placed near the scalp. This field induces an electric current in the underlying brain tissue, which can alter neuronal activity.
• TMS is widely used in research to investigate brain functions and in clinical settings for treating conditions such as depression.

Explanation:

Statement (A): The magnetic field generated in TMS induces an electrical field in the underlying brain area.

• This is a correct statement because the principle of electromagnetic induction is the foundation of TMS. The rapidly changing magnetic field creates an electric field, which can influence neuronal activity in the brain.

Statement (B): The electrical field in the brain alters the membrane potential of neurons, causing them to depolarize synchronously, which may change the probability of firing.

• This is also correct. The induced electric field can alter the resting membrane potential of neurons, leading to depolarization or hyperpolarization. This modulation can increase or decrease the likelihood of neuronal firing.

Statement (C): In cognitive neuroscience research, TMS can be used to induce a ‘virtual lesion’ in a selected region of the cerebral cortex.

• This is correct. TMS can transiently disrupt the normal functioning of a specific brain region, simulating the effects of a lesion. This allows researchers to study the role of that region in cognitive or motor tasks without causing permanent damage.

Statement (D): TMS is safe and non-invasive, but the neuronal activity of the stimulated area is disrupted for a long period.

• This statement is incorrect. While TMS is safe and non-invasive, the effects on neuronal activity are typically short-lived and not long-lasting unless repetitive TMS (rTMS) is used over multiple sessions for therapeutic purposes.

The correct answer is A and C

Concept:

• The androgen receptor (AR) plays a critical role in the development and progression of prostate diseases, including benign prostatic hyperplasia (BPH) and prostate cancer.
• AR is a nuclear receptor that binds to androgens (male hormones like testosterone and dihydrotestosterone) to regulate gene expression. It consists of three key functional domains:
  • N-terminal domain (NTD): Responsible for transcriptional activity.
  • Nuclear localization signal (NLS) domain: Facilitates movement of AR into the cell nucleus.
  • Ligand-binding domain (LBD): Binds to androgens and mediates conformational changes in the receptor.
• In the context of prostate disease, targeting specific AR domains can help inhibit the receptor's activity and alleviate symptoms of an enlarged prostate.

Explanation:

​A. Drugs should target the N-terminal domain of the AR.

• The N-terminal domain (NTD) is essential for the transactivation function of the AR. Targeting this domain can effectively inhibit AR activity because it contains activation function-1 (AF-1) which is crucial for AR-mediated transcription. Therapeutics targeting this region could impact the AR's ability to stimulate the transcription of genes involved in prostate growth.

B. Drugs should not target the NLS domain of the AR.

• Targeting the Nuclear Localization Signal (NLS) domain could prevent AR from entering the nucleus, effectively inhibiting its function.
• Some AR-targeting therapies work by blocking nuclear translocation, so avoiding the NLS domain is not necessary..

C. The drug should bind to the ligand-binding domain of the AR.

• The ligand-binding domain (LBD) is where androgens such as testosterone and dihydrotestosterone (DHT) bind. Drugs that target this domain can effectively block androgen binding, diminishing the AR's ability to activate androgen-responsive genes that contribute to prostate enlargement. Most current anti-androgens already use this mechanism.

D. The drug should activate CYP17A1 to facilitate conversion of pregnenolone to DHEA.

• CYP17A1 (17α-hydroxylase/17,20-lyase) is an enzyme involved in steroidogenesis
• Activating CYP17A1 increases the production of dehydroepiandrosterone (DHEA), which is a precursor to testosterone and other androgens.
• This could potentially be counterproductive, since promoting androgen synthesis may worsen prostate growth, contrary to the goal of the treatment.

The correct answer is A and D

Concept:

Osmotic diuresis refers to an increase in urine output caused by the presence of certain substances (such as mannitol) in the renal tubule that prevent water from being reabsorbed. Mannitol, an osmotic agent, is filtered at the glomerulus but not reabsorbed in the renal tubules. This leads to alterations in water and solute reabsorption across different segments of the nephron, thereby increasing urine production.

• Mannitol creates an osmotic gradient in the tubules, reducing water reabsorption.
• It affects the medullary concentration gradient, which is critical for water reabsorption in the collecting ducts.
• Osmotic diuresis leads to changes in both water and electrolyte handling in different parts of the nephron.

Explanation:

A. In the proximal tubule, water reabsorption falls due to the presence of mannitol in tubular fluid, and the concentration of Na+ is decreased in this fluid: This statement is correct. Mannitol in the proximal tubule increases the osmolarity of the tubular fluid, which reduces the reabsorption of water. As a result, the concentration of Na+ in the tubular fluid decreases because water reabsorption is not proportional to solute reabsorption.

B. In the descending loop of Henle, reabsorption of water is increased as medullary hypertonicity is decreased in osmotic diuresis: This statement is incorrect. In osmotic diuresis, the medullary hypertonicity is reduced due to the dilution of the interstitial fluid. This reduction in hypertonicity decreases the driving force for water reabsorption in the descending loop of Henle.

C. In the thin ascending loop of Henle, reabsorption of Na+ is increased as the concentration gradient for Na+ is decreased: This statement is incorrect. Sodium reabsorption in the thin ascending loop of Henle is passive and depends on the concentration gradient. In osmotic diuresis, the concentration gradient for sodium is reduced, which decreases sodium reabsorption in this segment.

D. In the collecting duct, reabsorption of water is less because of a decrease in the osmotic gradient along the medullary pyramid in osmotic diuresis: This statement is correct. Osmotic diuresis decreases the medullary interstitial osmotic gradient, which reduces the reabsorption of water in the collecting ducts, even in the presence of antidiuretic hormone (ADH).

Explanation:

• The muscle spindle is a sensory receptor located within skeletal muscle that senses changes in muscle length and the rate of these changes. It plays a key role in proprioception and the stretch reflex, which helps maintain muscle tone and posture.
• Muscle spindles contain specialized intrafusal muscle fibers, sensory neurons, and motor neurons. These components work together to detect and respond to muscle stretch.

Statement A: Incorrect.

• The intrafusal fibers in muscle spindles have non-contractile centers and contractile polar ends, not the other way around as mentioned in the statement.
• The contractile ends are innervated by gamma motor neurons, which adjust the sensitivity of the spindle to stretch.

Statement B: Correct.

• The intrafusal fibers do not contribute significantly to the overall contractile force of the muscle. Instead, their primary role is to detect changes in muscle length.
• They are specialized for sensory function and are distinct from the extrafusal fibers, which are responsible for generating force during muscle contraction.

Statement C: Correct.

• The primary sensory endings of the muscle spindle are formed by group Ia afferent fibers, which are highly sensitive to changes in muscle length and the rate of length change.
• The group Ia fibers wrap around the central, non-contractile region of the intrafusal fibers and transmit information about muscle stretch to the central nervous system.

Statement D: Incorrect.

• The axons of alpha motor neurons (a-motor neurons) do not directly innervate the muscle spindles. Instead, they innervate extrafusal muscle fibers to produce contraction.
• It is the gamma motor neurons that innervate the intrafusal fibers in muscle spindles, adjusting their tension and sensitivity to stretch.

The correct answer is C and D only

Explanation:

• The pulse is the pressure wave that travels through the arteries as a result of blood being ejected into the aorta during systole (the contraction phase of the heart).
• The characteristics of the pulse are affected by factors such as arterial stiffness, stroke volume, and blood pressure.

Statement A:The rate of travel of the pulse wave is lower than the velocity of blood flow in arteries.

• This statement is incorrect because pulse wave velocity (PWV) is actually much faster than blood flow velocity. The pulse wave moves through the arterial walls (elastic recoil) at speeds of 5-15 m/s, whereas blood flow velocity is much slower (~0.2-0.5 m/s in arteries).

Statement B: "The pulse wave moves more slowly with advancing age as the arteries become more rigid."

• This statement is incorrect. With advancing age, arteries lose their elasticity and become more rigid due to arteriosclerosis. As a result, the pulse wave velocity (PWV) actually increases, not decreases, with age.

Statement C: "The pulse wave is strong when the stroke volume is large as in exercise."

• This statement is correct because a larger stroke volume (as seen in exercise) leads to a higher systolic pressure, resulting in a stronger pulse wave.

Statement D: "The strength of the pulse depends on the magnitude of pulse pressure and not on the mean arterial pressure" 

• This statement is correct because pulse strength is primarily determined by pulse pressure (systolic - diastolic pressure), not by mean arterial pressure (MAP).

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.