OBJECTIVE QUESTIONS

1. Bilirubin is produced by
   (d) Liver
2. Which of the following is not an enzyme?
   (c) Somatotropin
3. What is the fundamental unit of contraction?
   (c) Myofibrils
4. What is the main division of the nervous system that includes the brain and spinal cord?
   (d) Central nervous system
5. Which respiratory pigment is found in most molluscs and arthropods?
   (b) Haemocyanin

SUBJECTIVE QUESTIONS

Answer any two questions

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(i) Write the function of the Liver.

The liver is a vital organ in the human body, playing a crucial role in various metabolic processes, detoxification, and homeostasis. Here are its main functions:

1. Metabolism:

• Carbohydrate Metabolism:
  The liver regulates blood glucose levels by converting excess glucose into glycogen (glycogenesis) for storage. When blood sugar levels are low, it converts glycogen back into glucose (glycogenolysis) and releases it into the bloodstream. It also plays a role in gluconeogenesis, the formation of glucose from non-carbohydrate sources.
• Lipid Metabolism:
  The liver synthesizes cholesterol and lipoproteins, which are essential for transporting fats in the bloodstream. It also helps in the breakdown of fats for energy and the production of ketone bodies during fasting.
• Protein Metabolism:
  The liver is responsible for the synthesis of plasma proteins, including albumin (which maintains osmotic pressure) and clotting factors (which are crucial for blood coagulation). It also converts ammonia (a byproduct of protein metabolism) into urea for excretion.

2. Detoxification:

The liver detoxifies various metabolites and drugs. It breaks down and eliminates toxins, such as alcohol, drugs, and metabolic waste products, through chemical processes that render them less harmful and easier to excrete. This is accomplished through phase I and phase II detoxification pathways involving enzymatic reactions.

3. Synthesis of Bile:

The liver produces bile, a digestive fluid that aids in the emulsification and absorption of fats in the small intestine. Bile salts, derived from cholesterol, play a crucial role in fat digestion.

4. Storage:

The liver serves as a storage site for several essential nutrients and substances, including:

• Vitamins: Fat-soluble vitamins (A, D, E, K) and some water-soluble vitamins (B12) are stored in the liver.
• Minerals: It stores minerals like iron and copper, which are important for various biochemical processes.
• Glycogen: The liver stores glycogen, which can be converted back to glucose as needed.

5. Regulation of Hormones:

The liver plays a role in regulating hormone levels by metabolizing and inactivating hormones such as insulin and glucagon. This regulation is crucial for maintaining metabolic homeostasis.

6. Immune Function:

The liver contains specialized immune cells known as Kupffer cells, which are part of the mononuclear phagocyte system. These cells help in filtering blood and removing pathogens, dead cells, and debris.

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(ii) Explain briefly the structure & function of the stomach.

The stomach is a hollow organ located between the esophagus and the small intestine, primarily involved in the digestion of food. Its structure and function can be summarized as follows:

Structure of the Stomach:

• Anatomy:
  The stomach is a muscular sac with four main regions:
• Cardia: The area where the esophagus connects to the stomach. It contains the lower esophageal sphincter, which prevents the backflow of stomach contents.
• Fundus: The upper portion of the stomach, which stores undigested food and gases released during digestion.
• Body (Corpus): The largest part of the stomach, where most digestion occurs.
• Pylorus: The lower section that connects to the small intestine. It has the pyloric sphincter, which regulates the passage of chyme (partially digested food) into the duodenum.
• Layers of the Stomach Wall:
  The stomach wall is made up of four layers:

1. Mucosa: The innermost layer that contains gastric glands producing gastric juices (HCl and enzymes). It is lined with specialized epithelial cells that secrete mucus to protect the stomach lining from acid.
2. Submucosa: A connective tissue layer containing blood vessels, nerves, and lymphatics.
3. Muscularis: Composed of three layers of smooth muscle (longitudinal, circular, and oblique), allowing for churning and mixing of food.
4. Serosa: The outermost protective layer that reduces friction between the stomach and surrounding organs.

Function of the Stomach:

• Digestion:
  The stomach mechanically and chemically digests food. The muscular contractions (peristalsis) mix food with gastric juices, breaking it down into a semi-liquid form called chyme.
• Secretion of Gastric Juices:
  Gastric glands in the stomach secrete:
• Hydrochloric Acid (HCl): Lowers the pH of the stomach, creating an acidic environment that activates pepsinogen into pepsin (an enzyme that digests proteins) and kills bacteria.
• Pepsin: The main enzyme responsible for protein digestion. It breaks down proteins into smaller peptides.
• Mucus: Secreted by goblet cells to protect the stomach lining from the acidic environment and mechanical damage.
• Absorption:
  While most absorption occurs in the small intestine, the stomach can absorb certain substances, including alcohol and some medications.
• Regulation of Gastric Emptying:
  The pyloric sphincter regulates the release of chyme into the small intestine, ensuring that food is adequately processed before entering the next stage of digestion.

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(iii) Discuss the categories of reflex action.

Reflex actions are involuntary and automatic responses to stimuli. They are essential for maintaining homeostasis and protecting the body from harm. Reflex actions can be categorized based on various criteria, including the number of synapses involved and the type of response. Here are the main categories:

1. Based on the Number of Synapses:

• Monosynaptic Reflexes:
  These reflexes involve a direct connection between the sensory neuron and the motor neuron, with only one synapse in the reflex arc.
• Example: The knee-jerk reflex (patellar reflex), where tapping the patellar tendon stretches the quadriceps muscle, triggering a response from the spinal cord that contracts the muscle.
• Polysynaptic Reflexes:
  These reflexes involve one or more interneurons between the sensory and motor neurons, resulting in multiple synapses.
• Example: The withdrawal reflex, such as pulling your hand away from a hot surface. This reflex involves several interneurons and can include more than one muscle group.

2. Based on the Response Type:

• Somatic Reflexes:
  These reflexes involve the skeletal muscles and are responsible for voluntary movements and responses.
• Example: The flexor reflex, where a painful stimulus causes the flexor muscles to contract, pulling a limb away.
• Autonomic Reflexes (Visceral Reflexes):
  These reflexes involve the autonomic nervous system and control involuntary functions, such as heart rate, digestion, and blood pressure.
• Example: The baroreceptor reflex, which helps regulate blood pressure by adjusting heart rate and blood vessel diameter in response to changes in blood pressure.

3. Based on the Location of the Reflex Arc:

• Spinal Reflexes:
  Reflex actions that occur in the spinal cord without involving the brain.
• Example: The crossed extensor reflex, which stabilizes the body when a withdrawal reflex occurs.
• Cranial Reflexes:
  Reflex actions that occur in the brain, involving cranial nerves.
• Example: The pupillary light reflex, where the pupils constrict in response to light, involves processing in the brain.

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(iv) Discuss the respiratory volumes and capacities.

Respiratory volumes and capacities are essential for understanding pulmonary function and assessing respiratory health. They represent different measurements of air movement in the lungs during various phases of breathing. Here are the key components:

1. Respiratory Volumes:

• Tidal Volume (TV):
  The amount of air inhaled or exhaled during a normal breath, averaging about 500 mL in adults. This volume is crucial for regular gas exchange during quiet breathing.
• Inspiratory Reserve Volume (IRV):
  The maximum amount of air that can be inhaled after a normal tidal inhalation. It typically averages around 3000 mL in adults, allowing for deep breaths during exertion.
• Expiratory Reserve Volume (ERV):
  The maximum amount of air that can be forcibly exhaled after a normal tidal expiration, averaging about 1200 mL. This volume aids in clearing excess air and carbon dioxide from the lungs.
• Residual Volume (RV):
  The amount of air remaining in the lungs after a maximal exhalation. It averages about 1200 mL and prevents lung collapse by keeping the alveoli partially inflated.

2. Respiratory Capacities:

Respiratory capacities are combinations of various volumes:

• Total Lung Capacity (TLC):
  TLC = Tidal Volume (TV) + Inspiratory Reserve Volume (IRV) + Expiratory Reserve Volume (ERV) + Residual Volume (RV)
  Approximate Value: 6000 mL
• Vital Capacity (VC):
  VC = Tidal Volume (TV) + Inspiratory Reserve Volume (IRV) + Expiratory Reserve Volume (ERV)
• Approximate Value: 4800 mL
• Inspiratory Capacity (IC):
  IC = Tidal Volume (TV) + Inspiratory Reserve Volume (IRV)
  Approximate Value: 3500 mL
• Functional Residual Capacity (FRC):
  FRC = Expiratory Reserve Volume (ERV) + Residual Volume (RV)
  Approximate Value: 2400 mL

3. Clinical Importance:

Understanding these respiratory volumes and capacities is crucial for diagnosing and managing respiratory conditions such as asthma, chronic obstructive pulmonary disease (COPD), and restrictive lung diseases. Changes in these measurements can indicate issues with lung function, airway obstruction, or chest wall mechanics.

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