Which of the following is an example of the adhesive property of water?

Diffusion down a concentration gradient

Reasoning:

The primary mechanism by which carbon dioxide (CO₂) moves from the blood into the alveoli of the lungs is diffusion. This occurs because of a concentration gradient between the blood (where CO₂ levels are higher) and the alveolar air (where CO₂ levels are lower).

This Is Correct because:

• Diffusion is a passive process that does not require energy.
• CO₂ moves from areas of high partial pressure in the blood to areas of low partial pressure in the alveolar air.
• This process occurs across the thin respiratory membrane in the alveoli.

Supporting Mechanisms of CO₂ Movement:

• Carbonic Anhydrase Role:
  Inside red blood cells, carbon dioxide (CO₂) combines with water to form bicarbonate ions (HCO₃⁻), aiding CO₂ transport in the bloodstream. In the lungs, this reaction is reversed—bicarbonate converts back to CO₂, which then diffuses into the alveoli for exhalation.
• Partial Pressure Gradient:
  • In venous blood (PvCO₂): ~45 mmHg
  • In alveolar air (PACO₂): ~40 mmHg
    This 5 mmHg difference creates the necessary gradient for CO₂ to move from the blood into the alveoli via diffusion.

Why the Other Options Are Incorrect:

• 2. Active transport using energy: CO₂ transport across the alveolar membrane does not involve active transport or ATP.
• 3. Conversion to carbon monoxide: CO₂ is never converted to carbon monoxide (CO); CO is a toxic gas and not part of normal respiratory physiology.
• 4. Passive transport using carrier proteins: While CO₂ can bind to hemoglobin in the blood, its movement into the alveoli happens by simple diffusion, not via carrier proteins.

Clinical Significance:

• Hypercapnia: An abnormal buildup of CO₂ in the blood, often due to impaired gas exchange as seen in conditions like emphysema.
• Hypoventilation: Reduced breathing efficiency (e.g., from opioid overdose) leads to CO₂ retention, potentially causing respiratory acidosis.

Atoms are made up of protons, neutrons, and electrons:

• Protons and neutrons are located in the nucleus and have similar masses (~1 atomic mass unit each).
• Electrons are much smaller in mass (about 1/1836 the mass of a proton) and orbit the nucleus.

Since protons and neutrons are both relatively heavy compared to electrons, they account for almost all of the atom's mass. Therefore, neutrons do contribute significantly to atomic mass—just like protons.

Why the Other Options Are Incorrect:

1. The mass of each electron is the same as the mass of each proton.

• Incorrect.
• Electrons are much lighter than protons (about 1/1836 the mass of a proton).

3. Isotopes of an element differ in the number of protons in the nucleus.

• Incorrect.
• Isotopes have the same number of protons (same element) but different numbers of neutrons.
• Example: Carbon-12 vs. Carbon-14 — both have 6 protons, but different neutron counts.

4. The amount of charge on a proton is greater than the amount of charge on an electron.

• Incorrect.
• A proton has a +1 charge, and an electron has a -1 charge.
• Their charges are equal in magnitude but opposite in sign.

Pancreas

Reasoning:

The pancreas plays a crucial role in digestion by releasing digestive enzymes and sodium bicarbonate (NaHCO₃) into the duodenum (the first section of the small intestine). Sodium bicarbonate helps neutralize the acidic chyme that enters the small intestine from the stomach.

1. Function of Sodium Bicarbonate:
   • The chyme from the stomach is highly acidic due to gastric hydrochloric acid (HCl).
   • The pancreas releases sodium bicarbonate to buffer this acid, raising the pH and creating a more alkaline environment ideal for enzyme activity in the small intestine.
2. Role of the Pancreas:
   • Part of both the endocrine and exocrine systems.
   • Exocrine function includes secreting:
     • Digestive enzymes (lipase, amylase, proteases).
     • Sodium bicarbonate via the pancreatic duct into the duodenum.

Why the Other Options Are Incorrect:

• 1. Liver:
  • Produces bile, which helps emulsify fats but does not release sodium bicarbonate.
• 2. Appendix:
  • A small, vestigial organ with no known role in digestion or pH regulation.
• 3. Gallbladder:
  • Stores and concentrates bile made by the liver, but does not produce sodium bicarbonate.

Mechanism of pH Regulation in the Small Intestine:

• Stomach Acid (HCl):
  The chyme entering the small intestine from the stomach is highly acidic due to hydrochloric acid.
• Pancreatic Bicarbonate (NaHCO₃):
  The pancreas secretes sodium bicarbonate, which neutralizes the acid through the following reaction:

NaHCO₃+HCl→NaCl+H₂CO₃

• Carbonic Acid (H₂CO₃):
  This intermediate breaks down into carbon dioxide (CO₂) and water (H₂O):

H₂CO₃→CO₂+H₂O

The CO₂ is exhaled via the lungs, and the water remains in the intestinal tract, helping to protect the intestinal lining from acid damage.

Clinical Relevance:

• Pancreatic Insufficiency:
  A decrease in bicarbonate and enzyme secretion (e.g., in chronic pancreatitis) can result in acidic intestinal contents and nutrient malabsorption.
• Cystic Fibrosis:
  Thick mucus obstructs pancreatic ducts, impairing bicarbonate delivery and enzyme flow into the small intestine, leading to digestive complications.

Flagella

Reasoning:

The basal body is a cellular structure that acts as the organizing center for the growth of flagella and cilia. It is structurally similar to a centriole and anchors the flagellum to the cell, providing the foundation from which the flagellum extends.

The basal body is a microtubule-based structure that functions as the foundation and organizing center for two key cellular appendages:

• Flagella: Long, whip-like structures used for movement (e.g., sperm tails).
• Cilia: Short, hair-like projections that move substances across cell surfaces or serve sensory roles (e.g., respiratory tract cilia).

Structure and Function

• Structure: Composed of nine triplet microtubules arranged in a cylindrical pattern—similar to centrioles.
• Functions:
  • Serves as a template for building the axoneme (core) of flagella and cilia.
  • Anchors these structures to the cell membrane via transition fibers.
  • Helps regulate movement patterns, such as the synchronized beating of cilia.

Why the Other Choices Are Incorrect

• 1. Nucleus: The nucleus contains DNA and is not involved in microtubule organization or flagellar function.
• 2. Ribosome: Ribosomes produce proteins and are made of RNA and protein, not microtubules.
• 3. Mitochondria: Mitochondria generate energy for the cell but are not connected to basal body formation or function.

Clinical Significance

• Primary Ciliary Dyskinesia: A genetic disorder caused by defective basal bodies or cilia, leading to impaired mucus clearance and chronic respiratory issues.
• Infertility: Faulty sperm flagella, often due to basal body dysfunction, can result in reduced motility and infertility.

Epithelial layer gets thinner.

Reasoning

As air travels from the trachea into smaller airways like the primary bronchi, secondary bronchi, tertiary bronchi, and eventually into the bronchioles, there are notable structural and functional changes in the airway walls to accommodate efficient air conduction and gas exchange. Among these changes, one key transition is the progressive thinning of the epithelial lining.

Explanation

1. Epithelial Layer Gets Thinner:
   • The airway epithelium begins as pseudostratified ciliated columnar epithelium in the trachea and primary bronchi. As the airways branch into smaller bronchi and then bronchioles, this epithelium gradually transitions to simple columnar, then to simple cuboidal epithelium in the terminal bronchioles. This thinning of the epithelial layer reduces airway resistance and facilitates easier gas exchange in the lower airways.
2. Cilia Become Less Plentiful:
   • Contrary to option 2, the number of cilia actually decreases as the airway branches. Ciliated cells are most abundant in the larger airways (trachea and bronchi) where they help move mucus upward. In the bronchioles, fewer ciliated cells are present.
3. Tube Diameter Decreases:
   • The diameter of the airways decreases, not increases, as you move from primary bronchi to bronchioles. The large bronchi have a wide lumen, but as the airways branch, they become narrower and more numerous, increasing total cross-sectional area.
4. Cartilage Rings Become Smaller and Disappear:
   • In larger airways (like the trachea and primary bronchi), cartilage rings provide structural support. As the airways get smaller, these rings become irregular plates and eventually disappear entirely in the bronchioles, which rely on smooth muscle instead.

Swelling of the neck

Reasoning:

Endemic goiter is a condition resulting from iodine deficiency, which impairs the synthesis of thyroid hormones (T₃ and T₄). When the body senses low thyroid hormone levels, the pituitary gland secretes more thyroid-stimulating hormone (TSH) to compensate. This constant stimulation leads to hypertrophy (enlargement) of the thyroid gland, causing a visible swelling in the neck known as a goiter.

1. Cause of Endemic Goiter:
   • Iodine is essential for the production of thyroid hormones.
   • In iodine-deficient regions (often inland or mountainous), low iodine intake leads to reduced T₃ and T₄ levels.
   • The pituitary increases TSH secretion, stimulating thyroid growth in an attempt to normalize hormone levels.
2. Physical Symptom:
   • The thyroid gland enlarges, resulting in a swelling at the base of the neck, which may be clearly visible and even interfere with swallowing or breathing in severe cases.
3. Why the Other Options Are Incorrect
   • 1. Enlarged hands and feet:
     This symptom is characteristic of acromegaly, a condition caused by excessive growth hormone, not related to iodine deficiency or thyroid enlargement.
   • 2. Increased bone fractures:
     Frequently associated with osteoporosis or hyperparathyroidism, both of which affect calcium metabolism — not conditions linked to iodine deficiency.
   • 3. Rounded face (moon face):
     Typically seen in Cushing’s syndrome, which results from prolonged exposure to high cortisol levels. This is unrelated to thyroid or iodine disorders.
4. Additional Symptoms of Iodine Deficiency

• Hypothyroidism Symptoms:
  • Fatigue
  • Weight gain
  • Cold intolerance
  • Dry skin
• Severe Iodine Deficiency Outcomes:
  • Cretinism (in children): Delayed growth and cognitive impairment.
  • Myxedema (in adults): Puffiness of the skin, slowed metabolism, and mental sluggishness.

Proteases (also called peptidases or proteinases) are enzymes that digest or break down proteins by hydrolyzing the peptide bonds between amino acids. Since enzymes themselves are proteins, proteases can digest enzymes just like any other protein substrate.

Explanation:

What Proteases Do:

• Target proteins, including enzymes.
• Break peptide bonds.
• Convert large proteins into smaller peptides or amino acids.
• Examples: Pepsin, trypsin, chymotrypsin.

So if you put any protein — even another enzyme — in the presence of active proteases, it will get digested.

Why the Other Options Are Incorrect:

• A. Endonucleases: These cut nucleic acids (DNA or RNA) at specific internal sites. They don’t affect proteins or enzymes.
• B. Lipases: These digest lipids/fats, not proteins or enzymes.
• C. Kinases: These are enzymes that add phosphate groups to other molecules (phosphorylation). They do not digest anything.

Clinical Relevance of Proteases

Proteases in the Human Body:

• Stomach:
  • Pepsin breaks down proteins in an acidic environment (low pH).
• Pancreas & Small Intestine:
  • Trypsin and chymotrypsin function in the alkaline environment of the small intestine to continue protein digestion.
• Lysosomes (inside cells):
  • Cathepsins help break down and recycle intracellular proteins.

Medical Applications of Proteases:

• Enzyme Supplements:
  • Patients with pancreatic insufficiency (e.g., cystic fibrosis, chronic pancreatitis) may need digestive enzyme therapy.
• Protease Inhibitors in Antiviral Therapy:
  • Drugs like ritonavir are used to block viral proteases (e.g., in HIV), stopping viral replication.

Nursing Considerations:

• Monitor for Signs of Malabsorption:
  • Watch for steatorrhea (fatty stools), weight loss, and nutrient deficiencies in patients with enzyme deficiencies.
• Patient Education:
  • Teach patients to take pancreatic enzyme replacements with meals to improve digestion and nutrient absorption.

Fun Fact:

• Bacterial Proteases in Wound Care:
  • Enzymes like collagenase (from bacteria) are used in wound debridement to remove dead tissue and promote healing.

A stem cell maturing to become a muscle cell that can contract.

Reasoning:

Cell differentiation is the biological process by which a less specialized cell (like a stem cell) becomes a more specialized cell type with a specific structure and function, such as a muscle cell, nerve cell, or blood cell.

1. What Is Cell Differentiation?
   • In multicellular organisms, stem cells give rise to different cell types during development or tissue repair.
   • Differentiation involves gene expression changes that lead to specialized structures and functions.
2. Why Option C Is Correct:
   • A stem cell becoming a muscle cell is a classic example of differentiation.
   • This transformation enables the cell to contract, a function unique to muscle cells.
3. Why Other Options Are Incorrect:
   • 1. Muscle cell producing more ATP is an example of cellular metabolism, not differentiation.
   • 2. A pancreatic cell releasing hormones reflects normal cell function, not a change in cell type.
   • 3. A mutation in a stomach cell is a genetic change, possibly harmful, but it is not differentiation.

Key Examples of Differentiation:

1. Embryonic Development:
   During early development, pluripotent stem cells (from the embryo) have the ability to become any cell type in the body. As development progresses, these stem cells differentiate into specialized cells such as:
   • Neurons: Specialized for transmitting electrical signals in the brain and nervous system.
   • Blood cells: Including red blood cells (which carry oxygen) and white blood cells (which fight infection).
   • Cardiomyocytes: Heart muscle cells that contract to pump blood.
2. Adult Tissues (Somatic Differentiation):
   In fully developed organisms, certain tissues still contain multipotent stem cells that can replenish specific cell types. A key example:
   • Hematopoietic Stem Cells (HSCs): Found in bone marrow, these stem cells differentiate into various blood cells, including:
     • Red blood cells (erythrocytes): Carry oxygen.
     • White blood cells (leukocytes): Defend against pathogens.
     • Platelets (thrombocytes): Help in blood clotting.

Mucosa, submucosa, muscularis, serosa

Reasoning
The gastrointestinal (GI) tract is structured in four main layers that are arranged from the innermost (facing the lumen) to the outermost part of the wall. Understanding this organization is crucial to comprehending how digestion and absorption occur.

Here’s the correct order of layers:

1. Mucosa (Innermost layer)

• Function: Secretes mucus, digestive enzymes, and hormones; absorbs nutrients; protects against pathogens.
• Structure: Includes the epithelium, lamina propria, and muscularis mucosae.

2. Submucosa

• Function: Provides support with connective tissue, blood vessels, lymphatics, and nerves (submucosal plexus).
• It allows the mucosa to move flexibly during peristalsis and digestion.

3. Muscularis (Muscularis externa)

• Function: Responsible for segmentation and peristalsis (movement of food through the GI tract).
• Structure: Typically consists of two layers of smooth muscle – inner circular and outer longitudinal.

4. Serosa (Outermost layer)

• Function: Reduces friction between digestive organs and surrounding structures.
• Structure: A protective outer layer made of connective tissue and a simple squamous epithelium. In areas not exposed to the peritoneal cavity, it may be called adventitia.

Milliliters

Reasoning:

Milliliters (mL) are the appropriate unit for measuring volume in the metric system, especially for fluids like blood.

Here's why:

• Milliliters (mL) measure liquid volume, which makes them ideal for medical samples such as blood, urine, or intravenous fluids.
  • For example, a typical blood sample drawn for lab analysis is often between 2 mL and 10 mL.
  • The milliliter is equivalent to 1/1000 of a liter.

Other Units Explained:

• Centimeters (cm):
  • A unit of length, not volume. It measures distance or size in one dimension.
• Milligrams (mg):
  • A unit of mass or weight, not volume. It is used to measure the weight of a substance, not how much space it occupies.
• Millimeters (mm):

Another unit of length, used to measure small distances (e.g., the diameter of a blood vessel), not volume.