Medical PG Online Test Series 123 – Physiology

• Primary hyperaldosteronism is characterised by absence of peripheral oedema, metabolic alkalosis and marked fall in plasma potassium levels.
• There is rise in plasma sodium, but decrease in sodium content of sweat, saliva and GI secretions.

Ref: Textbook of Physiology, A K Jain, 3rd edition, Volume 2, page 743.

• Parathormone increases bone resorption while calcitonin inhibits it.
• Calcitonin reduces calcium and phosphate absorption from GIT and inhibits the renal formation of 1-25 DHCC.

Ref: Textbook of Physiology, A K Jain, 3rd edition, Volume 2, page 719.

• Somatomedin increases glucose oxidation in fat.
• Activity of somatomedin is reduced by protein deficiency and glucocorticoids.
• It has insulin like effect on tissues and causes lipolysis and increased glucose and amino acid transport by muscle.

Ref: Textbook of Physiology, A K Jain, 3rd edition, Volume 2, page 670.

• Juxtamedullary nephrons comprise 14-15% nephrons in the kidney.
• They have large sized glomeruli which are situated at the junction of the cortex and medulla of the kidney.
• The rate of filtration is high.
• They have long loops of Henle which penetrate into the medulla.
• Their Henle loops manifest vascular supply in the form of vasa recta.
• Both descending and ascending limbs of loop of Henle contain thin segments. (In cortical nephrons, descending limb contains a thin segment whereas the ascending limb contains a thick segment.)

Ref: Textbook of Physiology, A K Jain, 3rd edition, Volume 2, page 520.

• Hensen’s cells are supporting cells of organ of Corti which lie outside the outer hair cells.
• Reticular lamina is a tough membrane which is supported by rods of Corti.
• Tectorial membrane is a thin, gelatinous, elastic structure made of glycoprotein.
• Efferent cholinergic fibers arise from ipsilateral and contralateral superior olivary nucleus.

Ref: Textbook of Physiology, A K Jain, 3rd edition, Volume 2, page 1103.

Eukaryotic flagellum showing the 9+2 arrangement of microtubules. Dynein arms (blue) are visible.

• Axonemal dynein oscillates and is responsible for the beating of flagella and cilia.
• Cytoplasmic dynein moves particles to the ‘minus‘ end of microtubule.
• Kinesin moves particles towards ‘plus‘ end of microtubule.
• Myosin II binds to actin and produce motion by bending their neck region.

Ref: Review of Medical Physiology, William F Ganong, 22nd edition, p14.
Image credits: Author: Smartse. Licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license. http://en.wikipedia.org/wiki/File:Eukaryotic_flagellum.svg

Sarcomere

• Each successive pair of cross bridges of myosin filaments is axially displaced from the previous pair by 120 degrees.
• The backbone of the actin filament is the double stranded F-actin protein molecule.
• Each strand of the double F-actin helix is composed of polymerised G-actin molecules.
• The strong affinity of troponin for calcium ions initiates the contraction process.

Ref: Textbook of Medical Physiology, Guyton and Hall, 11th edition, page 76.
Image credits: Richfield, David. “Medical gallery of David Richfield 2014” ( https://en.wikiversity.org/wiki/Medical_gallery_of_David_Richfield_2014 ). Wikiversity Journal of Medicine 1 (2). DOI:10.15347/wjm/2014.009. ISSN 2001-8762.

• As sodium intake is increased, sodium output initially lags slightly behind the intake.
• This time delay causes small increase in cumulative sodium balance.
• This leads to slight increase in extracellular fluid volume.
• This increase in extracellular fluid volume triggers various mechanisms in the body to increase sodium excretion.

• On intake of large quantities of salt and water, signals from the stretch receptors of the right atrium and the pulmonary blood vessels go to the brain stem.
• This will inhibit sympathetic nerve activity to the kidney.
• This in turn leads to decrease in tubular sodium reabsorption.
• This mechanism is most important in the first few hours after large increase in salt and water intake.

Ref: Textbook of Medical Physiology, Guyton and Hall, 11th edition, page 380.

• Inhibin is secreted by the sertoli cells in males and by the granulosa cells in females.
• It inhibits the secretion of Gonadotrophin Releasing Hormone.
• It is a glycoprotein with molecular weight between 10,000 and 30,000.
• It has potent inhibitory feedback effect on the anterior pituitary gland which in turn provides negative feedback mechanism for the control of spermatogenesis.

Ref: Textbook of Medical Physiology, Guyton and Hall, 11th edition, page 1007.

• When light energy is absorbed by rhodopsin, photoactivation of electrons in the retinal portion of rhodopsin leads to the change of cis form of retinal into the all trans form.
• The first stage in the reformation of rhodopsin is to reconvert the all trans retinal into 11 cis retinal.
• This process is catalysed by the enzyme – retinal isomerase.

Ref: Textbook of Medical Physiology, Guyton and Hall, 11th edition, page 629.