Bio 161: Anatomy and Physiology Final Exam

Correct Answer:

C. Tunica media

Explanation

The tunica media is the middle layer of a blood vessel and is primarily composed of smooth muscle. It plays the most important role in controlling vessel diameter. When smooth muscle contracts, vasoconstriction occurs, narrowing the lumen and increasing resistance. When smooth muscle relaxes, vasodilation occurs, widening the lumen and decreasing resistance. This regulation is critical for maintaining blood pressure and controlling blood flow.

Why Other Options Are Wrong

A. Tunica interna

The tunica interna, or intima, is the innermost layer made of endothelium. It provides a smooth lining for blood flow and helps prevent platelet adhesion, but it does not regulate vessel diameter.

B. Tunica externa

The tunica externa, or adventitia, is the outer connective tissue layer that provides support and anchors the vessel to surrounding structures. It does not actively control vessel constriction or dilation.

D. Endothelium

The endothelium is the single layer of cells lining the lumen, part of the tunica interna. While important for preventing clotting and controlling permeability, it does not play a role in adjusting vessel diameter.

Correct Answer:

B. Vitamin D production

Explanation

The skin contributes to Vitamin D production when exposed to ultraviolet (UV) radiation from sunlight. This stimulates the conversion of a cholesterol derivative into Vitamin D precursors, which are further processed in the liver and kidneys into calcitriol, the active form of Vitamin D. Calcitriol is essential for calcium absorption in the intestines, enabling proper calcium uptake into bones for strength and density. Without this process, bones can become weak or brittle, leading to conditions such as rickets or osteoporosis.

Why Other Options Are Wrong

A. Thermoregulation

Thermoregulation refers to maintaining body temperature through mechanisms like sweating, vasodilation, or vasoconstriction. While important, it does not involve Vitamin D synthesis or calcium absorption into bones.

C. Excretion

Excretion refers to the removal of metabolic waste products such as salts, urea, and ammonia via sweat. This is a function of the skin but is unrelated to calcium uptake or Vitamin D synthesis.

D. Sensory reception

Sensory reception is the skin’s ability to detect stimuli such as touch, pressure, pain, and temperature via sensory receptors. While critical for protection and interaction with the environment, it does not influence calcium absorption or Vitamin D production.

Correct Answers:

A. Digestive tract; B. Blood vessels; C. Respiratory passages; D. Surface of organs; E. Hollow, tubular organs

Explanation of Each Correct Answer

A. Digestive tract

Epithelial tissue lines the digestive tract, such as the stomach and intestines, where it controls absorption of nutrients and secretion of digestive fluids.

B. Blood vessels

The inner lining of blood vessels is composed of simple squamous epithelium, also called endothelium, which allows smooth blood flow and exchange of substances.

C. Respiratory passages

Epithelial tissue lines the respiratory tract, including the trachea and bronchi. It often has cilia and mucus-secreting cells to trap and remove particles.

D. Surface of organs

Epithelial tissue covers the outer surfaces of many organs, serving as a protective barrier and interface between the organ and its environment.

E. Hollow, tubular organs

Epithelial tissue lines hollow organs such as the bladder, intestines, and uterus, regulating absorption, secretion, and protection.

Why Other Options Are Wrong

F. Skeletal muscles

Skeletal muscles are composed of muscle tissue, not epithelial tissue. Their role is contraction and movement, not lining or covering surfaces.

Correct Answer:

B. Serous membrane

Explanation

The serous membrane, or serosa, lines sealed internal body cavities such as the thoracic and abdominal cavities and also covers organs within them, like the lungs and intestines. It is composed of a simple squamous epithelial layer (mesothelium) resting on a thin layer of areolar connective tissue. Serous membranes secrete serous fluid, which reduces friction between moving organs and the cavity walls. This structure provides both protection and lubrication, essential for organ function.

Why Other Options Are Wrong

A. Mucous membrane

Mucous membranes line body cavities that open to the outside, such as the digestive and respiratory tracts. They secrete mucus for protection and lubrication but are not the same as serous membranes, which line internal sealed cavities.

C. Cutaneous membrane

The cutaneous membrane is the skin, which covers the body surface. It is composed of epidermis (epithelial tissue) and dermis (connective tissue). While protective, it does not line internal cavities or cover organs like the serous membrane.

D. Synovial membrane

Synovial membranes line the cavities of freely movable joints. They are made of connective tissue and secrete synovial fluid to reduce friction in joints. Unlike serous membranes, they do not include an epithelial component and do not line body cavities or organs.

Correct Answer:

B. Carrier protein

Explanation

Carrier proteins can mediate active transport, which moves molecules up their concentration gradient from low concentration to high concentration. This process requires ATP or another energy source, since it goes against the natural flow of diffusion. A common example is the sodium-potassium pump, which actively exchanges sodium and potassium ions to maintain proper electrochemical gradients in cells. Carrier proteins are essential for maintaining cellular homeostasis.

Why Other Options Are Wrong

A. Channel protein

Channel proteins allow ions or water to move across membranes, but this occurs through facilitated diffusion down a concentration gradient. They provide a hydrophilic passage without requiring ATP. Therefore, they cannot move substances up a concentration gradient.

C. Receptor protein

Receptor proteins are specialized for signaling and communication. They bind specific ligands, such as hormones or neurotransmitters, to trigger a cellular response. They do not function in moving molecules across a membrane and cannot provide the active transport role performed by carrier proteins.

D. Structural protein

Structural proteins help maintain the shape, stability, and framework of the cell membrane or cytoskeleton. They provide support but do not participate in transport processes. As such, they cannot move molecules across the membrane or influence concentration gradients.

Correct Answer:

B. Excretion

Explanation

Excretion refers to the elimination of metabolic waste products from the body. The skin assists this process through sweat glands, which release substances such as urea, salts, and ammonia in sweat. While the kidneys are the primary excretory organs, the integumentary system plays a supportive role in waste removal and maintaining homeostasis. This process highlights how the skin contributes to both waste elimination and thermoregulation.

Why Other Options Are Wrong

A. Secretion

Secretion is the release of substances like mucus, hormones, or enzymes that serve a functional role in the body. While glands in the skin also secrete substances such as sebum for lubrication, this is different from the removal of waste, which is excretion.

C. Filtration

Filtration refers to the process of separating substances based on size or charge, such as in the kidneys’ glomeruli. It is not a function of the skin and does not describe the elimination of waste through sweat glands.

D. Absorption

Absorption refers to the uptake of substances into the body, such as nutrients through the intestines or certain medications through the skin. This is the opposite of excretion, which involves releasing substances from the body rather than taking them in.

Correct Answer:

B. Elastic (conducting) arteries

Explanation

Elastic (conducting) arteries, such as the aorta and pulmonary arteries, play a critical role in maintaining continuous blood flow. During systole, they expand to absorb the surge of blood. During diastole, their elastic walls recoil, pushing blood forward and smoothing the jerky, pulsatile discharge from the heart. This property ensures steady flow through smaller arteries and capillaries, reducing stress on the circulatory system.

Why Other Options Are Wrong

A. Muscular (distributing) arteries

Muscular arteries contain more smooth muscle than elastic fibers. They regulate blood flow to specific organs but cannot recoil strongly to smooth pulsatile flow like elastic arteries.

C. Arterioles

Arterioles are resistance vessels that regulate blood pressure and control entry into capillaries through vasoconstriction and vasodilation. They do not have the elastic properties to recoil during diastole.

D. Capillaries

Capillaries are exchange vessels that allow diffusion of gases, nutrients, and waste products. Their thin walls are ideal for exchange but lack elastic fibers to expand or recoil with pressure changes.

Correct Answer:

C. Hemoglobin is a protein in red blood cells made of four subunits that binds oxygen.

Explanation

Hemoglobin (Hb) is the oxygen-carrying protein found in red blood cells. It is composed of four subunits, each containing a heme group with an iron atom that binds oxygen. This allows hemoglobin to transport oxygen from the lungs to tissues and carry carbon dioxide back to the lungs for exhalation. Its structure and binding properties make it essential for cellular respiration and energy production.

Why Other Options Are Wrong

A. Hemoglobin is a carbohydrate in red blood cells that stores glucose for energy.

This is incorrect because hemoglobin is a protein, not a carbohydrate. RBCs rely on glycolysis for energy, but hemoglobin’s role is oxygen transport, not glucose storage.

B. Hemoglobin is a lipid in red blood cells that regulates membrane fluidity.

Lipids like cholesterol affect membrane fluidity, but hemoglobin is not a lipid. Its primary role is oxygen transport, not membrane structure.

D. Hemoglobin is a nucleic acid in red blood cells that carries genetic information.

Nucleic acids like DNA and RNA carry genetic information, but red blood cells lack nuclei. Hemoglobin is a protein, not a nucleic acid.

Correct Answer:

A. Adipose tissue stores fat as white blobs, and areolar tissue contains many fibers for support.

Explanation

Adipose tissue is specialized for fat storage and appears as large white blobs under the microscope because lipids take up most of the cell’s volume, pushing the nucleus to the side. Its primary functions include insulation, cushioning, and energy storage. Areolar tissue, in contrast, contains a loose arrangement of fibers (collagen, elastic, and reticular) that provide support, elasticity, and cushioning. Areolar tissue fills spaces around organs and underlies epithelial tissue, making it the most widely distributed connective tissue in the body.

Why Other Options Are Wrong

B. Areolar tissue stores fat as white blobs, and adipose tissue contains many fibers for support.

This is the reverse of the correct answer. Areolar tissue is fiber-rich, while adipose tissue is specialized for fat storage. Confusing the two would misrepresent their structural and functional roles.

C. Both adipose and areolar tissues primarily contain fibers with little fat storage.

This is incorrect because adipose tissue’s defining feature is fat storage, not fibers. Areolar tissue contains fibers, but adipose does not rely on them for its primary function.

D. Both adipose and areolar tissues primarily store fat and do not contain fibers.

This is incorrect because areolar tissue is fiber-rich and not primarily a fat-storing tissue. Only adipose tissue is specialized for fat storage.