Coordination and Control MCQs with Answers
Which of the following defines nervous coordination?
Coordination through chemical messengers.
Coordination through electric signals.
Regulation of body temperature only.
The study of the structure of the nervous system.
How do receptors function as transducers?
By generating heat energy from chemical signals.
By converting nerve impulses into light energy.
By converting one form of energy into another form.
By transmitting electrical signals without any conversion.
Which of the following is an example of a receptor acting as a transducer?
Muscles contracting in response to a nerve impulse.
Rod and cone cells in the retina.
Glands secreting hormones into the bloodstream.
The brain processing sensory information.
What are muscles and glands primarily identified as in the context of nervous transmission?
Receptors.
Sensory neurons.
Effectors.
Interneurons.
What are the basic structural and functional units of the nervous system?
Glial cells.
Neurotransmitters.
Neurons.
Synapses.
Which of the following is NOT one of the three basic components of all neurons?
Cell body.
Dendrites.
Axon.
Myelin sheath.
What is the primary function of dendrites?
To conduct action potentials away from the cell body.
To receive stimuli and conduct impulses to the cell body.
To synthesize proteins for the neuron.
To form the myelin sheath.
What structures are responsible for conducting action potentials from the neuron cell body to the presynaptic terminals?
Dendrites.
Cell bodies.
Axons.
Synaptic vesicles.
What is the fatty substance that acts as an insulator around axons?
Neuroglia.
Nissl's granules.
Myelin sheath.
Cytoplasm.
What is the non-myelinated part of an axon between two Schwann cells called?
Synaptic cleft.
Presynaptic terminal.
Node of Ranvier.
Cell body.
Which type of neuron conducts impulses towards the central nervous system from receptors?
Motor neurons.
Interneurons.
Sensory neurons.
Associative neurons.
Where do interneurons primarily occur?
Entirely within the Peripheral Nervous System.
Entirely within the Central Nervous System.
Between receptors and sensory neurons.
Between motor neurons and effectors.
Which statement accurately describes motor neurons?
They receive stimuli from receptors.
They occur entirely within the CNS.
They conduct impulses away from the CNS to effectors.
Their cell body is typically outside the CNS.
Which factor contributes to a faster velocity of nerve impulse transmission?
Smaller axon diameter.
Presence of a myelin sheath.
Longer axon length.
Absence of Schwann cells.
What is saltatory conduction?
The continuous flow of nerve impulses along an unmyelinated axon.
The jumping of nerve impulse from one node of Ranvier to another.
The transmission of impulses across a synaptic cleft.
The slow movement of ions across the axon membrane.
How does the diameter of a neuron fiber affect the velocity of nerve impulse?
Thicker neuron fibers conduct slower impulses.
Thicker neuron fibers conduct faster impulses.
Diameter has no effect on impulse velocity.
Only myelination affects impulse velocity, not diameter.
What is the cytoplasm of a neuron cell body characterized by?
Absence of organelles.
Presence of Nissl's granules.
High concentration of fatty acids.
Lack of a nucleus.
What type of neurons have three or more processes, typically several dendrites and one axon?
Unipolar neurons.
Bipolar neurons.
Multipolar neurons.
Pseudounipolar neurons.
What is the role of Schwann cells in the peripheral nervous system?
To act as receptors for stimuli.
To conduct impulses between interneurons.
To nourish neurons.
To synthesize neurotransmitters.
A voluntary response controlled by the brain.
An involuntary response to a stimulus.
A slow, conscious response to an external change.
A learned behavior pattern.
In a typical reflex arc, what is the role of the interneuron?
To receive stimuli from the external environment.
To transmit impulses from the motor neuron to the effector.
To act as a link between sensory and motor neurons.
To conduct impulses directly from receptors to effectors.
What happens if the sensory neuron in a reflex arc is damaged?
The effector will still respond normally.
The stimulus cannot be received and transmitted to the CNS.
Only the motor response will be affected, not sensory perception.
The interneuron will take over the function of the sensory neuron.
Which component of a reflex arc carries impulses away from the central nervous system to the muscles or glands?
Receptor.
Sensory neuron.
Interneuron.
Motor neuron.
The withdrawal reflex, where a hand is pulled away from a hot object, involves which type of neurons?
Only sensory neurons.
Only motor neurons.
Sensory, inter, and motor neurons.
Only interneurons.
Where is the cell body of a sensory neuron typically located in a reflex arc?
Within the spinal cord (CNS).
In the effector organ (e.g., muscle).
In the PNS.
In the brain.
Which of the following is an effector in a reflex arc?
Skin.
Spinal cord.
Gland.
Dorsal root ganglion.
A knee-jerk reflex is an example of what type of reflex arc?
A complex reflex involving the brain.
A polysynaptic reflex.
A monosynaptic reflex.
A conditioned reflex.
What is the correct sequence of components in a reflex arc?
Effector → Motor neuron → Interneuron → Sensory neuron → Receptor.
Receptor → Sensory neuron → Interneuron → Motor neuron → Effector.
Sensory neuron → Receptor → Interneuron → Motor neuron → Effector.
Receptor → Motor neuron → Interneuron → Sensory neuron → Effector.
What is a nerve impulse defined as?
A purely chemical signal.
A mechanical vibration within the neuron.
An electrochemical change.
A static electrical charge on the neuron membrane.
What is the state of a neuron membrane when it is at its resting potential?
Depolarized.
Repolarized.
Hyperpolarized.
Polarized.
Which of the following ions has a higher concentration inside the neuron cell during the resting membrane potential?
Sodium ions (Na+).
Potassium ions (K+).
Chloride ions (Cl-).
Calcium ions (Ca2+).
What is the primary role of the Sodium-Potassium (Na+/K+) pump in maintaining the resting membrane potential?
To allow Na+ and K+ to freely diffuse across the membrane.
To actively transport 3 Na+ ions out and 2 K+ ions into the cell.
To equally exchange Na+ and K+ ions across the membrane.
To only pump K+ ions out of the cell.
What contributes to the negative charge inside the neuron during resting potential, in addition to the Na+/K+ pump?
High concentration of positive ions.
Leakage of Na+ ions into the cell.
Presence of negative ions in the cell.
Active transport of positive ions into the cell.
What is the immediate event that occurs when a stimulus reaches the threshold level, leading to an action potential?
K+ channels open, and K+ rushes out.
Na+ channels open, and Na+ rushes in.
Cl- channels open, and Cl- rushes in.
The Na+/K+ pump stops working.
What is the term for the rapid influx of sodium ions that causes the inside of the neuron membrane to become positive?
Repolarization.
Hyperpolarization.
Depolarization.
Resting potential.
During the repolarization phase of an action potential, which ion movement is primarily responsible for restoring the negative charge inside the cell?
Influx of Na+ ions.
Efflux of K+ ions.
Influx of Cl- ions.
Efflux of Ca2+ ions.
What is hyperpolarization?
A state where the membrane potential is less negative than the resting potential.
A brief period when the membrane potential becomes more negative than the resting potential.
The initial depolarization phase of an action potential.
The point at which the membrane potential reaches zero.
What is the minimum strength of a stimulus required to generate an action potential?
Sub-threshold stimulus.
Suprathreshold stimulus.
Threshold stimulus.
Refractory stimulus.
If a stimulus is applied that is too weak to cause a significant change in membrane potential, it is referred to as a:
Threshold stimulus.
Suprathreshold stimulus.
Sub-threshold stimulus.
Weak-threshold stimulus.
What is the refractory period of a neuron?
The time during which the neuron is constantly firing impulses.
The time during which a neuron cannot generate another action potential.
The time it takes for an impulse to travel across a synapse.
The duration of the resting membrane potential.
In which type of neuron fiber does saltatory conduction occur, leading to faster impulse transmission?
Non-myelinated fibers.
Myelinated fibers.
Dendrites.
Cell bodies.
How does the diameter of an axon influence the velocity of nerve impulse conduction?
Larger diameter axons conduct impulses slower.
Smaller diameter axons conduct impulses faster.
Larger diameter axons conduct impulses faster.
Axon diameter has no impact on conduction velocity.
The "All-or-None Law" applies to:
The strength of a neurotransmitter.
The magnitude of the resting membrane potential.
The generation of an action potential.
The number of dendrites on a neuron.
Which ion channels are crucial for the repolarization phase of an action potential?
Voltage-gated Na+ channels.
Voltage-gated K+ channels.
Ligand-gated Na+ channels.
Mechanically-gated ion channels.
During which phase of an action potential is the membrane most permeable to sodium ions?
Resting potential.
Repolarization.
Depolarization.
Hyperpolarization.
The initial segment of the axon where action potentials are typically generated is called the:
Dendrite.
Synaptic knob.
Axon hillock.
Cell body.
What maintains the resting membrane potential of a neuron?
The passive diffusion of ions only.
The active transport of ions by the Na+/K+ pump and the selective permeability of the membrane to K+ ions.
The continuous influx of Na+ ions.
The complete impermeability of the membrane to all ions.
What is the specialized junction where a nerve impulse is transmitted from one neuron to another, or from a neuron to an effector cell?
Node of Ranvier.
Axon hillock.
Synapse.
Dendrite.
Which part of a synapse is located at the end of the presynaptic axon and contains synaptic vesicles?
Synaptic cleft.
Postsynaptic membrane.
Synaptic knob.
Dendrite.
What is the narrow gap between the presynaptic and postsynaptic neurons called?
Axon hillock.
Node of Ranvier.
Synaptic cleft.
Myelin sheath.
What are the chemical messengers stored in synaptic vesicles and released into the synaptic cleft?
Hormones.
Enzymes.
Neurotransmitters.
Ions.
What is the essential role of Calcium (Ca2+) ions in synaptic transmission?
To depolarize the postsynaptic membrane directly.
To activate enzymes that break down neurotransmitters.
To trigger exocytosis of synaptic vesicles.
To repolarize the presynaptic membrane.
Upon release, what do neurotransmitters bind to on the postsynaptic membrane?
Voltage-gated ion channels.
Receptor proteins.
Sodium-Potassium pumps.
Myelin sheath.
Which type of neurotransmitter increases the likelihood of an action potential in the postsynaptic neuron?
Inhibitory neurotransmitter.
Excitatory neurotransmitter.
Modulatory neurotransmitter.
Regulatory neurotransmitter.
Which type of neurotransmitter decreases the likelihood of an action potential in the postsynaptic neuron?
Inhibitory neurotransmitter.
Excitatory neurotransmitter.
Modulatory neurotransmitter.
Facilitatory neurotransmitter.
The process of neurotransmitter removal from the synaptic cleft is crucial for:
Ensuring prolonged postsynaptic excitation.
Allowing for precise and rapid control of synaptic transmission.
Preventing the presynaptic neuron from firing.
Increasing the sensitivity of postsynaptic receptors.
What is the direct effect of a neurotransmitter binding to its receptor on the postsynaptic membrane?
It causes the release of more neurotransmitters from the presynaptic terminal.
It triggers the production of new action potentials in the presynaptic neuron.
It opens or closes ion channels.
It directly synthesizes ATP for the postsynaptic neuron.
The human nervous system is broadly divided into which two main parts?
Somatic and Autonomic Nervous System.
Sympathetic and Parasympathetic Nervous System.
Central and Peripheral Nervous System.
Brain and Spinal Cord.
Which part of the nervous system serves as the coordinating center and lies in the midline of the body?
Peripheral Nervous System (PNS).
Autonomic Nervous System.
Central Nervous System (CNS).
Somatic Nervous System.
What is the primary function of the Peripheral Nervous System (PNS)?
To process and integrate sensory information.
To transmit information.
To control reflex activities only.
To generate thoughts and emotions.
Which division of the human nervous system controls voluntary movements?
Autonomic Nervous System.
Sympathetic Division.
Somatic Nervous System.
Parasympathetic Division.
The "Fight or Flight" response is primarily mediated by which division of the Autonomic Nervous System?
Somatic Nervous System.
Central Nervous System.
Sympathetic Division.
Parasympathetic Division.
Which division of the Autonomic Nervous System is primarily associated with "Rest and Digest" functions?
Sympathetic Division.
Somatic Nervous System.
Peripheral Nervous System.
Parasympathetic Division.
What are the two main components of the Central Nervous System (CNS)?
Sensory neurons and motor neurons.
Brain and Spinal cord.
Somatic and Autonomic systems.
Cranial nerves and spinal nerves.
The brain is responsible for all of the following EXCEPT:
Receiving and processing sensory information.
Initiating responses.
Directly controlling reflex activities without spinal cord involvement.
Storing memories and generating thoughts.
What is the primary function of the spinal cord?
Generating complex thoughts.
Conducting signals to and from the brain.
Producing hormones.
Filtering blood.
Which of the following best describes the function of cranial and spinal nerves?
They are part of the Central Nervous System.
They primarily process sensory information.
They connect the CNS to the rest of the body.
They only control involuntary responses.
Which of the following is categorized as a narcotic drug affecting the nervous system?
Caffeine.
Heroine.
Nicotine.
Alcohol.
Which of the following is a common withdrawal symptom associated with alcohol addiction?
Increased appetite.
Enhanced coordination.
Convulsions.
Improved sleep.
Drug addiction is primarily characterized by:
Occasional use of drugs for recreational purposes.
A psychological and physiological dependence on a drug.
The ability to easily stop drug use at any time.
Taking drugs only under medical supervision.
An individual's ability to resist the effects of a drug.
The reduced effect of a drug over time.
The immediate adverse reaction to a drug.
The complete elimination of a drug from the body.
Cannabis is classified as:
A stimulant.
A depressant.
A hallucinogen.
A narcotic.
Which of the following is a vascular disorder of the nervous system?
Meningitis.
Brain tumor.
Stroke.
Alzheimer's disease.
Which infectious disorder of the nervous system involves inflammation of the brain membranes?
Stroke.
Alzheimer's disease.
Meningitis.
Headache.
Which diagnostic test uses magnetic fields and radio waves to create detailed images of the brain and spinal cord?
Which neurodegenerative disorder is characterized by progressive memory loss and cognitive decline, primarily affecting older adults?
Brain tumor.
Meningitis.
Alzheimer's disease.
Headache.
An Electroencephalogram (EEG) is primarily used to:
Visualize brain tumors.
Detect and record the electrical activity of the brain.
Identify structural abnormalities in the spinal cord.
Measure blood flow to the brain.
What is the primary role of hormones in the body?
To produce electrical signals for rapid communication.
To act as chemical messengers that regulate various bodily functions.
To provide structural support to tissues.
To transport oxygen throughout the bloodstream.
How does the endocrine system primarily coordinate body cells?
Through direct nerve innervation of all cells.
By secreting hormones into the bloodstream.
By generating electrical impulses.
Through mechanical force.
Which type of gland secretes its products directly into the bloodstream?
Exocrine gland.
Digestive gland.
Salivary gland.
Endocrine gland.
Which type of gland secretes its products into ducts?
Endocrine gland.
Pituitary gland.
Exocrine gland.
Thyroid gland.
Which of the following is an example of an exocrine gland?
Thyroid gland.
Pancreas.
Salivary gland.
Adrenal gland.
Which of the following hormone types is derived from cholesterol and is lipid-soluble?
Protein hormones.
Peptide hormones.
Steroid hormones.
Catecholamines.
Which chemical nature characterizes hormones like insulin and growth hormone?
Steroid.
Amine.
Protein.
Fatty acid derivative.
Which of the following hormones typically utilizes a "second messenger system" to exert its effects on target cells?
Testosterone.
Cortisol.
Insulin.
Estrogen.
How do steroid hormones typically exert their action on target cells?
By binding to receptors on the cell surface and activating a second messenger.
By directly activating genes within the cell nucleus.
By modifying existing proteins in the cytoplasm.
By breaking down ATP to release energy.
Epinephrine are derived from which type of molecule?
Lipids.
Proteins.
Amino acids.
Carbohydrates.
Which hormone characteristic allows it to easily pass through the cell membrane to reach intracellular receptors?
Water solubility.
Large molecular size.
Lipid solubility.
Charged nature.
Cyclic AMP (cAMP) often acts as a second messenger for which type of hormone?
Steroid hormones.
Thyroid hormones.
Peptide hormones.
Hormones that bind to nuclear receptors.
When a protein hormone binds to its receptor on the cell membrane, what is the immediate effect inside the cell?
Direct gene activation.
Synthesis of new proteins.
Enzyme Activation.
Breakdown of the cell membrane.
Which of the following is an example of an amino acid derivative hormone?
Aldosterone.
Growth hormone.
Thyroxine.
Oxytocin.
What is the primary advantage of the second messenger system for water-soluble hormones?
It allows direct interaction with DNA.
It permits the hormone to enter the nucleus without a carrier.
It amplifies the original signal.
It converts the hormone into a steroid.
Which part of the brain is considered the "master control center" for the endocrine system?
Pituitary gland.
Thyroid gland.
Hypothalamus.
Adrenal gland.
The hypothalamus produces releasing and inhibiting factors that primarily control the secretions of which gland?
Thyroid gland.
Posterior pituitary gland.
Anterior pituitary gland.
Adrenal medulla.
Which two hormones are produced by the hypothalamus but stored and released by the posterior pituitary gland?
Growth Hormone and Prolactin.
ADH and Oxytocin.
TSH and ACTH.
Insulin and Glucagon.
What is the primary function of ADH (Antidiuretic Hormone)?
To stimulate growth.
To promote water reabsorption in the kidneys.
To stimulate milk production.
To regulate metabolism.
Which hormone, produced by the hypothalamus and released by the posterior pituitary, plays a key role in uterine contractions during childbirth and milk ejection?
Prolactin.
Oxytocin.
Follicle-Stimulating Hormone (FSH).
Luteinizing Hormone (LH).
Where is the pituitary gland primarily located?
In the neck, anterior to the trachea.
At the base of the brain.
On top of the kidneys.
In the pancreas.
How many lobes does the pituitary gland typically have?
Which lobe of the pituitary gland is often referred to as the "master gland"?
Posterior lobe.
Median lobe.
Anterior lobe.
All lobes contribute equally.
Which hormone secreted by the anterior pituitary stimulates overall body growth, especially bone and muscle?
TSH (Thyroid Stimulating Hormone).
ACTH (Adrenocorticotropic Hormone).
STH (Somatotropic Hormone).
Prolactin.
What is the condition caused by the oversecretion of Growth Hormone (GH) in adults?
Dwarfism.
Gigantism.
Acromegaly.
Cretinism.
Undersecretion of STH (Somatotropic Hormone) in children can lead to which condition?
Gigantism.
Acromegaly.
Dwarfism.
Graves' disease.
Which anterior pituitary hormone stimulates the thyroid gland to produce and secrete its hormones?
Which two gonadotropic hormones are secreted by the anterior pituitary?
ADH and Oxytocin.
Insulin and Glucagon.
FSH and LH.
Prolactin and MSH.
What is the primary function of Prolactin secreted by the anterior pituitary?
To stimulate adrenal cortex.
To stimulate milk production.
To regulate water balance.
To control metabolic rate.
Which hormone is secreted by the median lobe of the pituitary gland?
Which of the following hormones is released from the posterior pituitary but is actually produced in the hypothalamus?
Growth Hormone.
TSH.
ADH.
Prolactin.
Diabetes insipidus is a disorder caused by the undersecretion of which hormone?
Insulin.
Oxytocin.
ADH.
Thyroxine.
What is the primary function of Oxytocin?
To stimulate growth.
To regulate blood glucose levels.
To stimulate uterine contractions.
To control stress response.
If a person has abnormally low levels of ADH, what would be a likely symptom?
Decreased urine production.
Increased water retention.
Increased urine output.
Low blood pressure.
What is the general term for the hormones secreted by the anterior pituitary that influence the activity of other endocrine glands?
Neurotransmitters.
Tropic hormones.
Local hormones.
Steroid hormones.
Where is the thyroid gland located?
At the base of the brain.
In the neck, anterior to the trachea.
On top of the kidneys.
Posterior to the stomach.
Which two hormones, containing iodine, are primarily responsible for regulating the body's metabolic rate?
Calcitonin and PTH.
Thyroxine and Triiodothyronine.
Insulin and Glucagon.
Epinephrine and Norepinephrine.
What is the primary function of Calcitonin, secreted by the thyroid gland?
To increase blood calcium levels.
To decrease blood calcium levels.
To regulate metabolic rate.
To stimulate growth.
Graves' disease is a condition characterized by hyperthyroidism. Which of the following symptoms is commonly associated with it?
Weight gain and sluggishness.
Intolerance to cold and constipation.
Weight loss and increased metabolic rate.
Decreased heart rate and lethargy.
Cretinism, a condition characterized by stunted physical and mental growth in children, is caused by:
Hyperthyroidism.
Hypothyroidism.
Oversecretion of growth hormone.
Lack of ADH.
Where are the parathyroid glands typically located?
On the anterior surface of the thyroid gland.
Embedded in the posterior surface of the thyroid gland.
On top of the adrenal glands.
Within the pancreas.
What is the main hormone secreted by the parathyroid glands?
Calcitonin.
Thyroxine.
PTH.
ACTH.
What is the primary function of Parathyroid Hormone?
To lower blood glucose levels.
To decrease blood calcium levels.
To increase blood calcium levels.
To stimulate metabolism.
The endocrine functions of the pancreas are carried out by specialized clusters of cells called:
Acini.
Pancreatic ducts.
Islets of Langerhans.
Gastric pits.
Which hormone is secreted by the beta cells of the Islets of Langerhans?
Glucagon.
Insulin.
Somatostatin.
Pancreatic polypeptide.
Which hormone raises blood glucose levels?
Insulin.
Glucagon.
Somatostatin.
Amylin.
When blood glucose levels are high, which hormone is released to bring them back to normal?
Glucagon.
Adrenaline.
Insulin.
Cortisol.
What type of feedback mechanism controls the secretion of both insulin and glucagon to maintain blood glucose homeostasis?
Positive feedback.
Negative feedback.
Neural feedback.
Hormonal feedback.
Which two main subdivisions make up the adrenal gland?
Anterior and Posterior.
Cortex and Medulla.
Alpha and Beta.
Inner and Outer.
Which part of the adrenal gland secretes catecholamines like Epinephrine (Adrenaline) and Norepinephrine (Noradrenaline)?
Adrenal cortex.
Adrenal medulla.
Zona glomerulosa.
Zona fasciculata.
Which hormone, secreted by the adrenal cortex, is a glucocorticoid?
Aldosterone.
Epinephrine.
Cortisol.
Norepinephrine.
Which mineralocorticoid hormone, secreted by the adrenal cortex, is crucial for regulating sodium and potassium balance and blood pressure?
Cortisol.
Adrenaline.
Aldosterone.
Androgen.
Androgens, which are male sex hormones, are also produced in small amounts by which part of the adrenal gland?
Adrenal medulla.
Adrenal cortex.
Pituitary gland.
Pancreas.
What is the primary male sex hormone produced by the testes?
Estrogen.
Progesterone.
Testosterone.
Inhibin.
Which hormone secreted by the ovaries is primarily responsible for the development of female secondary sex characteristics and the regulation of the menstrual cycle?
Testosterone.
Estrogens.
Progesterone.
Inhibin.
Which ovarian hormone is mainly secreted by the corpus luteum after ovulation and is crucial for preparing and maintaining the uterus for pregnancy?
Estrogen.
Testosterone.
Progesterone.
FSH.
What is the primary function of Inhibin, produced by both testes and ovaries?
To stimulate FSH secretion.
To stimulate LH secretion.
To inhibit FSH secretion from the pituitary.
To stimulate estrogen production.
Undersecretion of progesterone during the menstrual cycle may lead to:
Development of fibroids.
Increased chance of pregnancy.
Early menstruation.
Male sterility.
Which hormone is primarily secreted by the Pineal Gland and helps regulate circadian rhythm?
Thyroxin.
Melatonin.
Thymosin.
Renin.
The Thymus gland secretes hormones called Thymosins, which are vital for the development and maturation of which type of immune cell?
B lymphocytes.
T lymphocytes.
Macrophages.
Plasma cells.
The heart produces hormones known as Natriuretic Peptides. What is their primary role?
To increase heart rate.
To lower blood pressure.
To stimulate red blood cell production.
To increase water reabsorption in kidneys.
Which hormone is produced by the kidneys and stimulates the production of red blood cells in the bone marrow?
Renin.
Erythropoietin.
Calcitriol.
Aldosterone.
Which active form of Vitamin D is produced by the kidneys and is essential for calcium absorption in the intestine?
Calcitonin.
Calcitriol.
Parathyroid Hormone.
Vitamin D2.
Adipose tissue (fat tissue) secretes a hormone that plays a role in regulating appetite and metabolism. What is this hormone called?
Ghrelin.
Leptin.
Insulin.
Gastrin.
The digestive tract produces numerous hormones that regulate digestion and absorption. Which of the following is an example of a hormone produced by the stomach that stimulates gastric acid secretion?
Secretin.
Cholecystokinin (CCK).
Gastrin.
Somatostatin.
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