Histology — MCQs

Histology Indian Medical PG Practice Questions and MCQs

Question 421: Inorganic component of bone is:

A. 65% (Correct Answer)
B. 85%
C. 35%
D. 45%

Explanation: **65%** - The inorganic component of bone, primarily **hydroxyapatite crystals**, makes up approximately **60-70%** of the bone's dry weight [1]. - This high percentage of inorganic material is responsible for the bone's **hardness and compressive strength**. *85%* - This percentage is **too high** for the inorganic component, as it would leave insufficient room for organic material, making bones exceedingly brittle and prone to fracture. - While bone is very hard, reaching 85% inorganic content would significantly compromise its **flexibility and tensile strength**. *35%* - This percentage is **too low** for the inorganic component; such a composition would result in bones that are overly flexible and weak, unable to provide adequate structural support [1]. - Bones with only 35% inorganic material would lack the necessary **rigidity and resistance to deformation**. *45%* - While closer than 35%, 45% is still **below the typical range** for the inorganic component of bone. - Such a composition would still lead to **reduced bone density** and increased susceptibility to fractures compared to normal bone.

Question 422: The bone matrix has the following crystals -

A. Calcium pyrophosphate
B. Calcium hydroxyapatite (Correct Answer)
C. Calcium phosphate
D. Calcium sulphate

Explanation: ***Calcium hydroxyapatite*** - The primary mineral component of bone matrix is **calcium hydroxyapatite**, which gives bone its rigidity and strength [1]. - These crystals are formed from **calcium and phosphate ions** arranged in a specific crystalline structure within the collagen fibers [1]. *Calcium pyrophosphate* - **Calcium pyrophosphate dihydrate (CPPD)** crystals are associated with **pseudogout**, a condition causing joint inflammation, not the normal bone matrix [1]. - They are found in articular cartilage and synovial fluid, not as a structural component of healthy bone. *Calcium phosphate* - While hydroxyapatite is a form of **calcium phosphate**, simply "calcium phosphate" is too general and does not specify the exact crystalline structure found in bone [1]. - Many calcium phosphate compounds exist, but **hydroxyapatite** is the specific and most abundant one in bone [1]. *Calcium sulphate* - **Calcium sulfate** is not a naturally occurring mineral component of the bone matrix in vertebrates. - It is sometimes used in medical applications as a **bone graft substitute** or a drug delivery system, but not as an endogenous component.

Question 423: Which of the following layers of epidermis is known as "prickle layer"?

A. Stratum basale
B. Stratum granulosum
C. Stratum spinosum (Correct Answer)
D. Stratum corneum

Explanation: ***Stratum spinosum*** - This layer is called the **"prickle layer"** due to the presence of **desmosomes** which provide strong cell-to-cell adhesion, making the cells appear spiny or "prickly" under a microscope due to the shrinkage of cells during histological preparation. [1] - It consists of several layers of polyhedral cells, rich in **keratin filaments**, which contribute to the skin's strength and flexibility. *Stratum basale* - This is the **deepest layer** of the epidermis, responsible for continuous cell division and renewal of the epidermis. [1] - It contains **melanocytes** and **Merkel cells** in addition to keratinocytes, but its appearance is not prickly. [1] *Stratum granulosum* - This layer is characterized by the presence of **keratohyalin granules** and **lamellar granules**. [2] - Cells in this layer begin to flatten and their nuclei and organelles start to disintegrate as they move closer to the skin surface. *Stratum corneum* - This is the **outermost layer** of the epidermis, composed of flattened, dead keratinocytes called corneocytes, which form a protective barrier. [1] - It is known for its **tough, resistant nature** and ability to prevent water loss and protect against external damage.

Question 424: Stem cells in skin involved in skin homeostasis are present in the following areas except ______

A. Basal layer of interfollicular epidermis
B. Base of apocrine glands (Correct Answer)
C. Base of sebaceous glands
D. Bulge of Hair follicle

Explanation: ***Base of apocrine glands*** - **Apocrine glands** do not typically house multipotent stem cells responsible for skin homeostasis and regeneration in the same manner as other skin adnexal structures [1] - These glands are primarily involved in secreting a specific type of sweat and have **limited regenerative capacity** from intrinsic stem cells compared to other areas - Unlike other skin appendages, apocrine glands lack the well-characterized stem cell niches that contribute to continuous skin renewal *Basal layer of interfollicular epidermis* - The basal layer contains **keratinocyte stem cells** that are crucial for continuous replenishment of epidermal layers [1] - These stem cells ensure constant turnover and repair of the skin's outermost protective barrier [1] - This is a major site of stem cells involved in skin homeostasis *Base of sebaceous glands* - Contains stem cell populations that contribute to regeneration of sebaceous glands and can differentiate to contribute to epidermal repair, especially after injury - These stem cells maintain the integrity and function of sebaceous glands, which produce sebum - Plays an active role in skin homeostasis and wound healing *Bulge of hair follicle* - The **bulge region** is a well-established niche for multipotent **hair follicle stem cells (HFSCs)** [1] - These HFSCs are responsible for cyclical regeneration of the hair follicle and can contribute to repair of the interfollicular epidermis and sebaceous glands after injury [1] - One of the most important stem cell reservoirs in the skin

Question 425: Vitreous humor of eye contains collagen type:

A. Collagen I
B. Collagen IV
C. Collagen III
D. Collagen II (Correct Answer)

Explanation: ***Collagen II*** - Collagen II is the **predominant collagen type** found in hyaline cartilage and the **vitreous humor** of the eye, providing structural support. - In the vitreous, it forms fine fibrils that contribute to the gel-like consistency and **transparency** essential for vision. *Collagen I* - Collagen I is the most abundant collagen in the body, found in connective tissues such as **bone**, **skin**, **tendons**, and **ligaments**. - Its primary role is to provide **tensile strength** and structural integrity to these tissues. *Collagen IV* - Collagen IV is a major component of **basement membranes**, where it forms a mesh-like network providing structural support and **filtration barriers**. - It is found in the basal lamina of epithelia, kidneys, and blood vessels, but not primarily in the vitreous humor. *Collagen III* - Collagen III is typically found alongside type I collagen in **reticular fibers** in tissues like skin, blood vessels, and internal organs. - It contributes to the **elasticity** and resilience of connective tissues, but is not the main collagen of the vitreous.

Question 426: The connective tissue layer around each muscle fascicle is called:

A. Epimysium
B. Perimysium (Correct Answer)
C. Sarcolemma
D. Endomysium

Explanation: ***Perimysium*** - This **connective tissue sheath** surrounds a bundle of muscle fibers, known as a **fascicle**. - It contains **blood vessels** and **nerves** that supply the muscle fibers within the fascicle. *Epimysium* - This is the **outermost layer of connective tissue** that surrounds the entire skeletal muscle. - It blends with the **deep fascia** and helps to separate individual muscles from surrounding tissues. *Sarcolemma* - This refers to the **plasma membrane** of a muscle fiber (muscle cell). - It plays a crucial role in transmitting the **electrical impulses** that initiate muscle contraction. *Endomysium* - This delicate layer of connective tissue surrounds and **insulates each individual muscle fiber**. - It contains **capillaries** and **nerve fibers** that supply the individual muscle cells.

Question 427: Prefilaggrin is found in which layer of epidermis?

A. Stratum granulosum (Correct Answer)
B. Stratum basale
C. Stratum spinosum
D. Stratum corneum

Explanation: ***Stratum granulosum*** - **Prefilaggrin** is synthesized in the **stratum granulosum** as a large, insoluble protein that is stored in keratohyalin granules [1]. - It later undergoes proteolytic cleavage to form **filaggrin**, which is crucial for keratin filament aggregation and skin barrier function in the upper layers [1]. *Stratum basale* - This layer contains **basal cells** responsible for epidermal regeneration and is where keratinocyte proliferation occurs [1]. - It does not contain prefilaggrin, as this protein is synthesized in more differentiated keratinocytes. *Stratum spinosum* - This layer is characterized by abundant **desmosomes** (spinous processes) providing structural integrity. - While keratinization begins here, **prefilaggrin synthesis** primarily occurs in the stratum granulosum. *Stratum corneum* - This outermost layer consists of flattened, dead keratinocytes filled with **keratin** and **filaggrin**, a breakdown product of prefilaggrin [1]. - **Prefilaggrin itself is not found here**; it has already been processed into filaggrin by the time cells reach this layer.

Question 428: True about multipotential connective tissue cells is:

A. They have intermediate sensitivity to radiation (Correct Answer)
B. These are most radiosensitive
C. These are most radioresistant
D. None of the options

Explanation: They have intermediate sensitivity to radiation - Multipotential connective tissue cells, also known as mesenchymal stem cells, exhibit a moderate or intermediate sensitivity to radiation, meaning they are not the most sensitive nor the most resistant. [1] - This intermediate sensitivity allows them to survive some radiation exposure while still being affected by higher doses, playing a role in tissue repair after injury. [1, 3] *These are most radiosensitive* - The most radiosensitive cells are typically those with high rates of proliferation and undifferentiated status, such as lymphocytes and hematopoietic stem cells. - Multipotential connective tissue cells have a more moderate proliferation rate and differentiation capacity, placing them in an intermediate category for radiation sensitivity. *These are most radioresistant* - Highly differentiated cells with low mitotic activity, like mature neurons and skeletal muscle cells, are generally the most radioresistant. - Multipotential connective tissue cells retain the ability to divide and differentiate, making them more sensitive than truly radioresistant cells. *None of the options* - This option is incorrect because the statement about intermediate sensitivity accurately describes the radiation response of multipotential connective tissue cells.

Question 429: Barr body was first detected in:

A. Liver
B. Skin
C. Brain (Correct Answer)
D. Buccal mucosa

Explanation: ***Brain*** - The **Barr body** (sex chromatin) was first discovered by **Murray Barr and Ewart Bertram in 1949** in the **neurons of cats**. - This historical discovery was made while studying **nerve cells**, where they observed a distinct chromatin mass at the periphery of the nucleus in female cells. - The structure was later identified as the **inactive X chromosome** and named after its discoverer. *Buccal mucosa* - While buccal mucosa became the **most popular site for clinical sex chromatin testing** due to its **easy accessibility** and non-invasive collection method, it was **not** the site of original discovery. - Buccal smears became widely used for **routine screening** and sex determination, but this was **after** the initial discovery in neurons. *Skin* - Skin cells do contain Barr bodies in females, but they were neither the site of first detection nor commonly used for sex chromatin analysis. - Skin biopsies are **more invasive** than buccal swabs, making them less practical for routine testing. *Liver* - Liver cells are nucleated and can show Barr bodies, but they were not involved in the **historical first detection** of sex chromatin. - Liver tissue is **difficult to access** and not suitable for routine cytogenetic screening.

Question 430: Which of the following site doesn't contain brown adipose tissues?

A. Subcutaneous tissue
B. Around blood vessel
C. Scapula (Correct Answer)
D. Around adrenal cortex

Explanation: ***Scapula*** - While brown adipose tissue (BAT) is strategically located for **thermoregulation**, it is not typically found directly within the **scapular bone** itself. - BAT is primarily found in soft tissue depots around the shoulder girdle, but not as part of the bone structure. *Subcutaneous tissue* - **Brown adipose tissue** is present in the subcutaneous layers, particularly in neonates and to some extent in adults, where it contributes to **non-shivering thermogenesis**. - These subcutaneous depots are crucial for maintaining **body temperature** in colder environments. *Around blood vessel* - BAT is often found in close proximity to **large blood vessels**, such as in the neck and mediastinum. - This strategic location allows for efficient transfer of heat generated by BAT directly into the **circulatory system**, warming the blood. *Around adrenal cortex* - Significant deposits of **brown adipose tissue** are found in perirenal areas, including around the **adrenal glands**. - This location is important for **local heat production** and protection of vital organs.

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Histology — MCQs

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