📚 Question Bank

Umbilical arteries carry deoxygenated blood from the heart to the placenta during the fetal period.

Arteries carry oxygenated blood away from the heart, with the exception of the pulmonary and umbilical arteries that carry deoxygenated blood.

Muscular arterioles contribute to the major part of peripheral resistance to blood flow.

The smallest arteries of the muscular type are called arterioles. They have a tunica media that is relatively thicker than the tunica adventitia. Arterioles cause the largest drop in blood pressure before the blood flows into the tissue capillary beds. They are densely innervated by sympathetic fibres. The contraction of arterioles is mainly regulated by local vasoactive and metabolic factors, but central mechanisms also play a role.

The following image shows a micrograph of a muscular arteriole:

All the other arteries except the posterior cerebral artery are end arteries.

Arteries whose terminal branches do not anastomose with branches from neighbouring arteries are called end arteries or terminal arteries. They can be of two types:

• Anatomic end arteries (or true end arteries) - do not have anastomoses. e.g., central artery of retina, internal auditory artery (labyrinthine artery of the internal ear).
• Functional end arteries - have anastomoses but they are insufficient to provide adequate blood supply when the main vessel is occluded. e.g., segmental arteries supplying the kidney.

Dry skin is not expected to see due to sympathetic stimulation.

The sympathetic nervous system (SNS) arises from the lateral horn of T1 to L2 segments of the spinal cord (thoracolumbar outflow). Sympathetic stimulation causes the following effects:

• Sweating due to secretomotor supply to sweat glands - Sudomotor
• Erection of hair due to contraction the arrector pili muscle - Pilomotor
• Raised blood pressure due to vasoconstriction - Vasomotor
• Dilated pupils
• Dry mouth
• Tachycardia

Common examples of sympathomimetic drugs include phenylephrine, albuterol, cocaine and amphetamines.

The linear fibrous band formed by interdigitation of the tendinous or aponeurotic ends of the muscles is known as raphe.

Unlike most ligaments, the raphe are stretchable. Examples of raphe include:

• linea alba
• pterygomandibular raphe
• mylohyoid raphe
• median pharyngeal raphe
• anococcygeal raphe

The structure marked X in the image is the interosseous membrane which is a modified form of deep fascia. It is present in the forearm and leg.

The interosseous membrane helps in:

• Maintaining optimum distance between bones
• Increasing surface area for attachment of muscles
• Transmission of weight from one bone to another

The following image shows the graphical illustration of interosseous membrane of the Leg:

The statement 'ligaments are devoid of nerve supply' is false.

Ligaments have a rich nerve supply. This helps them function as sense organs and participate

in reflex mechanisms important for monitoring the position and movements of the joint. Intrinsic ligaments surround the joint, whereas extrinsic ligaments are away and independent of the joint.

The majority of ligaments are made up of collagen fibres predominantly. These are inelastic and not stretchable. Ligamentum flavum and ligaments of auditory ossicles are exceptions, as

they predominantly have elastin fibres that make them elastic and stretchable.

The non-fibrous element of the extracellular matrix in the connective tissue is formed by the ground substance.

Connective tissue consists of cells and extracellular matrix:

• The cells include fibroblasts, macrophages, plasma cells, mast cells, fat cells, and pigment
• cells.
• The extracellular matrix contains fibrous and non-fibrous elements.
• The fibrous element has three types of fibres - collagen, elastin and reticulin
• The non-fibrous element is formed by the ground substance

The white opaque crescent present in the proximal part of the nail is known as the lunula. Parts of the nail:

• Root - It is the proximal hidden part, buried into the nail groove and is overlapped by the nail fold of the skin.
• Free border - It is the distal part of the nail that is free from the skin.
• Body - It is the exposed part of the nail that is adherent to the underlying skin.

Apocrine sweat glands produce secretions that undergo bacterial decomposition to generate odour.

Sweat glands are classified as follows:

• Eccrine sweat glands - The majority of sweat glands in the body are eccrine and open via rounded pores to the skin surface.
• Apocrine sweat glands - They are present in the axillae, perianal area, areolae, periumbilical skin, and genitalia.

The muscle responsible for goosebumps (image) is the arrector pili muscle which is a smooth muscle supplied by the sympathetic nerves. It connects the dermal sheath of the hair follicles to the papillary layer of the dermis.

Contraction of these muscles makes the hair more vertical (piloerection), elevates the epidermis around the hair (goosebump), and dimples the skin surface where the muscle is inserted.

The image given below shows the arrector pili muscle attached to the hair follicles:

Meissner corpuscles are present in the dermal papillae (upper dermis).

They are primarily present in the dermal papillae of all parts of the hand and foot, the lips, the anterior aspect of the forearm, palpebral conjunctiva and mucous membrane of the apical part of the tongue. They are highly concentrated in the finger pads.

Meissner’s corpuscles are rapidly adapting mechanoreceptors that are sensitive to shape and textural changes during exploratory and discriminatory touch. Their high sensitivity provides the neurological basis for sensing the Braille text.

The Merkel cells act as touch receptors. They are present in the basal layer of the epidermis and outer root sheath of some big hair follicles and their functions are as follows:

• Act as slowly adapting mechanoreceptors in the skin that convey touch sensation.
• Detects the directional deformation of the epidermis and hair movement.
• Sense sustained pressure and edges of applied objects on the skin.

The given clinical scenario of an itchy, asymmetrical pigmented lesion on the face with

an irregular border(image) that rapidly grew in size, points towards a diagnosis of malignant melanoma arising from the melanocytes. These cells are present in the stratum basale layer of the epidermis.

Melanocytes are derived from neural crest cells. They produce melanin which is packed into organelles called melanosomes and transferred via finger-like processes called dendrites to the keratinocytes.

The number of melanocytes does not affect the colour of human skin.

The racial differences in skin colour is determined by:

• Melanocyte morphology and activity.
• Number and size of melanosomes in melanocytes.
• The number of melanosomes individually dispersed within keratinocytes.

Melanin pigmentation is influenced by constitutive (genetically determined) and facultative factors (reversible changes due to environmental factors like UV-rays, chemicals, and hormones).

Non-nucleated cells are present in the stratum corneum layer of the epidermis. The cells are devoid of both a nucleus and membranous organelles.

The cells in this layer contain densely arranged keratin filaments within the cytoplasmic matrix providing a barrier function that prevents the entry of microbes from the environment and leakage of fluids from the body.

The correct order of the given layers from deep to superficial is stratum basale, stratum spinosum, stratum granulosum, stratum corneum.

Most of the body is covered by thin skin that has 4 layers as follows (superficial to deep):

• stratum corneum
• stratum granulosum
• stratum spinosum
• stratum basale

Some parts of the body such as the palms, soles and flexor surfaces of digits have thick skin

(glabrous skin) with 5 layers as follows (superficial to deep):

• stratum corneum
• stratum lucidum
• stratum granulosum
• stratum spinosum
• stratum basale

Mnemonic for skin layers (superficial to deep): Come Let's Get Some Beer (Corneum, Lucidum, Granulosum, Spinosum, and Basale).

The following image shows an illustration of layers of epidermis:

There are 8 pairs of spinal nerves in the cervical region.

The cerebrospinal nervous system includes 12 pairs of cranial nerves and 31 pairs of spinal nerves. The 31 pairs of spinal nerves are distributed as follows:

• Cervical nerves - 8 pairs
• Thoracic nerves-12 pairs
• Lumbar nerves-5 pairs
• Sacral nerves-5 pairs
• Coccygeal nerves-1 pair

Sinusoids are absent in parotid glands.

Sinusoids are large, irregular, vascular spaces with true discontinuities in their walls. This allows close contact between blood and parenchyma of the surrounding organ.

Sinusoids are present in:

• Liver
• Spleen
• Bone
• Suprarenal glands
• Adenohypophysis
• Parathyroid glands
• Carotid body

Compared to their corresponding arteries, the veins have a much lesser muscular and elastic content. This explains the venous pressures being lower than the arterial pressures.

The following image shows a graphical illustration of the structure of the vessels (a amp; b) and a micrograph of the cross-sections(c):

Comparison of arteries and v eins

Arteries

Carry oxygenated blood away from the heart except for pul monary artery

Thick-walled,highly muscular except arteries of cranium a nd vertebral column

Narrow lumen Valves absent

High-pressure flow Reddish in colour

Veins

Carry deoxygenated blood to wards the heart except for pu lmonary veins

Thin-walled

Wide lumen

Valves present to maintain u nidirectional blood flow

Low-pressure flow Bluish in colour

The thoracic and right lymphatic ducts are vessels of the lymphatic system which is referred to as the drainage system of coarse type.

The lymphatic system helps remove larger particles such as proteins and particulate matter from the tissue fluid. Therefore, they are considered as the drainage system of coarse type.

The venous system is considered as the drainage system of fine type.

The lymph nodes have both afferent and efferent lymphatics.

• The afferent lymphatics enter the lymph node at different parts of its periphery.
• The efferent lymphatics exit at the hilum.

The following image shows a schematic representation of a lymph node:

The tonsils, thymus, and the spleen have no afferent lymphatics.

The right upper limb is drained by the right lymphatic duct, not the thoracic duct.

The filtered lymph passes through larger lymphatics and eventually collect into two large trunks, the thoracic duct and right lymphatic duct, which in turn drain into the brachiocephalic veins.

• Thoracic duct - drains both lower limbs, left upper limb, abdomen, left halves of thorax, and left side of the head and neck regions (areas shaded green in the image).
• Right lymphatic duct - drains right upper limb, and right halves of thorax, and right side of the head and neck regions (areas shaded blue in the image).

Injury to the thoracic duct is a rare complication of traumatic chest tube insertion.

Lymph capillaries are wider than blood capillaries.

Lymph capillaries begin blindly (tips are closed) in the tissue spaces and form intricate networks. The endothelial wall is thin and is permeable to substances of much greater molecular size. They have relatively lower pressure than blood capillaries.

Lymph capillaries

Colourless, difficult to observ e

Blind (closed at the tip)

Wider than blood capillaries

Wall consist of thin endotheli um and poorly developed bas ement membrane

Contain colourless lymph Have relatively low pressure

Absorb tissue fluid from inter cellular spaces

Blood capillaries Reddish, easy to observe

Joined to arterioles at one en d and to venules at another e nd

Narrower than lymph capilla ries

Wall consist of normal endot helium and basement membr ane

Contain red blood

Have relatively high pressure

Add tissue fluid to intercellul ar spaces

Microglial cells do not originate from the ectoderm but are derived from the mesoderm. Microglia are possibly derived from the circulating monocytes which migrate into the CNS during the late fetal and early postnatal life.

Neuroglial cells found in the parenchyma of the brain and spinal cord are broadly classified as follows:

• Macroglia cells of ectodermal origin (neuroectoderm) including the astrocytes, oligodendrocytes, and glioblasts.
• Microglia cells of mesodermal origin.