৪৮তম বিশেষ বিসিএস [স্বাস্থ্য] ⎯ মডেল টেস্ট [Archived]

Karyotype of Classic Down Syndrome:

Foot drop is associated with paralysis of the ankle dorsiflexors (anterior compartment of the leg). 

The superficial peroneal nerve supplies the lateral compartment of the leg (peroneus longus and brevis) which causes eversion of foot. Injury to the superficial peroneal nerve does not cause foot drop. 

Injury to the sciatic nerve, CPN and DPN will result in paralysis of the ankle dorsiflexors causing foot drop.

Tributaries: 

The coupling of two molecules of diiodotyrosine (DIT) results in the formation of thyroxine (T4). The coupling of DIT to monoiodotyrosine (MIT) produces triiodothyronine (T3).

Closure of the aortic and pulmonic valves creates the second heart sound. The closure of these valves corresponds to the end of ventricular ejection and the beginning of ventricular relaxation.

H+–K+ transport occurs via H+,K+-adenosine triphosphatase (ATPase) in the luminal membrane of gastric parietal cells, a primary active transport process that is energized directly by ATP. Na+–glucose and Na+–alanine transport are examples of cotransport (symport) that are secondary active transport processes and do not use ATP directly. Glucose uptake into muscle cells occurs via facilitated diffusion. Na+–Ca2+ exchange is an example of countertransport (antiport) and is a secondary active transport process.

Monosaccharides (glucose, galactose, and fructose) are the absorbable forms of carbohydrates. Glucose and galactose are absorbed by Na+-dependent cotransport; fructose is absorbed by facilitated diffusion. Dipeptides and water-soluble vitamins are absorbed by cotransport in the duodenum, and bile acids are absorbed by Na+-dependent cotransport in the ileum (which recycles them to the liver). Cholesterol is absorbed from micelles by simple diffusion across the intestinal cell membrane

Glucose has the lowest renal clearance of the substances listed, because at normal blood concentrations, it is filtered and completely reabsorbed. Na+ is also extensively reabsorbed, and only a fraction of the filtered Na+ is
excreted. K+ is reabsorbed, but also secreted. Creatinine, once filtered, is not reabsorbed at all. Para-aminohippuric acid (PAH) is filtered and secreted; therefore, it has the highest renal clearance of the substances listed.

Residual volume is the volume present in the lungs after maximal expiration, or expiration of the vital capacity (VC). Therefore, residual volume is not included in the tidal volume (TV), VC, inspiratory reserve volume (IRV), or
inspiratory capacity (IC). The functional residual capacity (FRC) is the volume remaining in the lungs after expiration of a normal TV and, therefore, includes the residual volume.

Somatostatin is secreted by the hypothalamus and inhibits the secretion of growth hormone by the anterior pituitary. Notably, much of the feedback inhibition of growth hormone secretion occurs by stimulating the secretion of somatostatin (an inhibitory hormone). Both growth hormone and somatomedins stimulate the secretion of somatostatin by the hypothalamus.

Both the pulmonary and coronary circulations are regulated by PO2. However, the critical difference is that hypoxia causes vasodilation in the coronary circulation and vasoconstriction in the pulmonary circulation. The cerebral and muscle circulations are regulated primarily by local metabolites, and the skin circulation is regulated primarily by sympathetic innervation (for temperature regulation).

Saliva has a high [HCO3−] because the cells lining the salivary ducts secrete HCO3 −. Because the ductal cells are relatively impermeable towater and because they reabsorb more solute (Na+ and Cl−) than they secrete (K+ and HCO3 −), the saliva is rendered hypotonic. Vagal stimulation increases saliva production, so vagotomy (or atropine) inhibits it and produces dry mouth.

When adrenergic α1 receptors on the vascular smooth muscle are activated, they cause vasoconstriction and increased total peripheral resistance (TPR)

Types of sensory transducers

a. Mechanoreceptors
■ Pacinian corpuscles
■ Joint receptors
■ Stretch receptors in muscle
■ Hair cells in auditory and vestibular systems
■ Baroreceptors in carotid sinus

b. Photoreceptors
■ Rods and cones of the retina

c. Chemoreceptors
■ Olfactory receptors
■ Taste receptors
■ Osmoreceptors
■ Carotid body O2 receptors

d. Extremes of temperature and pain
■ Nociceptors

B. Somatosensory system

■ includes the sensations of touch, movement, temperature, and pain.
1. Pathways in the somatosensory system

a. Dorsal column system
■ processes sensations of fine touch, pressure, two-point discrimination, vibration, and
proprioception.
■ consists primarily of group II fibers.
■ Course: primary afferent neurons have cell bodies in the dorsal root. Their axons ascend ipsilaterally to the nucleus gracilis and nucleus cuneatus of the medulla. From the medulla, the second-order neurons cross the midline and ascend to the
contralateral thalamus, where they synapse on third-order neurons. Third-order neurons ascend to the somatosensory cortex, where they synapse on fourth order neurons.

b. Anterolateral system
■ processes sensations of temperature, pain, and light touch.
■ consists primarily of group III and IV fibers, which enter the spinal cord and terminate in the dorsal horn.
■ Course: second-order neurons cross the midline to the anterolateral quadrant of the spinal cord and ascend to the contralateral thalamus, where they synapse on thirdorder neurons. Third-order neurons ascend to the somatosensory cortex, where
they synapse on fourth-order neurons

3. Optic pathways and lesions (Figure 2-4)

■ Axons of the ganglion cells form the optic nerve and optic tract, ending in the lateral
geniculate body of the thalamus.

■ The fibers from each nasal hemiretina cross at the optic chiasm, whereas the fibers from
each temporal hemiretina remain ipsilateral. Therefore, fibers from the left nasal
hemiretina and fibers from the right temporal hemiretina form the right optic tract and
synapse on the right lateral geniculate body.

■ Fibers from the lateral geniculate body form the geniculocalcarine tract and pass to the
occipital lobe of the cortex.
a. Cutting the optic nerve causes blindness in the ipsilateral eye.
b. Cutting the optic chiasm causes heteronymous bitemporal hemianopia.
c. Cutting the optic tract causes homonymous contralateral hemianopia.
d. Cutting the geniculocalcarine tract causes homonymous hemianopia with macular sparing.

Surfactant

■ lines the alveoli.
■ reduces surface tension by disrupting the intermolecular forces between liquid molecules. This reduction in surface tension prevents small alveoli from collapsing and increases compliance.
■ is synthesized by type II alveolar cells and consists primarily of the phospholipid dipalmitoyl phosphatidylcholine (DPPC).
■ In the fetus, surfactant synthesis is variable. Surfactant may be present as early as gestational week 24 and is almost always present by gestational week 35.
■ Generally, a lecithin:sphingomyelin ratio greater than 2:1 in amniotic fluid reflects mature levels of surfactant.
■ Neonatal respiratory distress syndrome can occur in premature infants because of the lack of surfactant. The infant exhibits atelectasis (lungs collapse), difficulty reinflating
the lungs (as a result of decreased compliance), and hypoxemia (as a result of decreased V/Q).
In the absence of surfactant, the small alveoli have a tendency to collapse (atelectasis).

Semi essential = histidine and arginine.

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