Urine Formation

Question 1

Glomerular filtrate is the fluid that is filtered through the glomerular membrane into the Bowman’s capsule.

Answer 1

Glomerular Filtration

Question 2

Reabsorption plays a major role than the secretion in the formation of urine. More than 90% of the water in the glomerular filtrate is reabsorbed as it passes through the tubules.

Answer 2

Tubular Reabsorption

Question 3

Tubular secretion is the transport of solute from the peritubular capillaries to the tubular fluid.

Answer 3

Tubular Secretion

Question 4

The volume of blood delivered to the kidneys per unit time.

Answer 4

Renal Blood Flow (RBF)

Question 5

Glomerular filtration rate (GFR) is the quantity of GF formed each minute in all the nephrons of both the kidneys/kg body weight.

Answer 5

Glomerular Filtration Rate (GFR)

Question 6

Filtration fraction is the percentage of the renal plasma flow that becomes Glomerular Filtrate.

Answer 6

Filtration Fraction

Question 7

According to this theory, the increase in BP would expand an artery and it would respond by contracting. In this way, RBF would be decreased and glomerular HP reduced. The reduced glomerular HP reduces GFR.

Answer 7

Myogenic Theory

Question 8

Juxtaglomerular apparatus (JGA) contains renin (a proteolytic enzyme). Renin is released when there is Reduced GFR, Reduced glomerular pressure, and Increased sympathetic stimulation of kidneys.

Answer 8

JG Theory

Question 9

A counter current system of tubules or vessels exists where the inflow of fluid runs parallel to, counter to, and in close proximity to the outflow for some distance.

Answer 9

Countercurrent Mechanism

Question 10

Micturition is the process in which the urinary bladder empties when it becomes filled with urine.

Answer 10

Micturition

Question 11

Functions of the Kidney

Answer 11

• Excretion of metabolic waste products and foreign chemicals (e.g., urea, creatinine, uric acid).
• Regulation of water and electrolyte balance.
• Regulation of arterial pressure.
• Regulation of acid-base balance.
• Regulation of RBC production.
• Regulation of 1,25 Dihydroxy Vitamin D3 production.
• Gluconeogenesis (synthesis of glucose during fasting).
• Formation and concentration of urine.

Question 12

Layers of the Glomerular Capillary Membrane

Answer 12

• Endothelium of the capillary (perforated by fenestrae).
• Basement membrane (meshwork of collagen and proteoglycan fibrillae).
• Podocytes (finger-like projections forming slit pores).

Question 13

Factors Affecting GFR

Answer 13

• Glomerular Hydrostatic Pressure.
• Plasma Colloidal Osmotic Pressure.
• Bowman’s Capsular Pressure.

Question 14

Effects of Afferent and Efferent Arteriolar Constriction on GFR

Answer 14

• Afferent arteriolar constriction: Decreases blood flow, lowers glomerular pressure, decreases GFR.
• Efferent arteriolar constriction: Initially increases glomerular pressure and GFR but prolonged constriction leads to stagnation, increased plasma COP, and reduced GFR.

Question 15

Steps in the Countercurrent Mechanism

Answer 15

• Countercurrent Multiplier (Loop of Henle):
  1. Active transport of NaCl from the ascending limb.
  2. Water exits descending limb due to osmotic gradient.
  3. Tubular fluid becomes progressively concentrated in descending limb and diluted in ascending limb.
• Countercurrent Exchanger (Vasa Recta):
  1. Water exits descending vasa recta and enters ascending vasa recta.
  2. NaCl enters descending vasa recta and exits ascending vasa recta.
  3. Prevents washout of medullary osmolarity.

Question 16

Hormones Involved in Kidney Function

Answer 16

• Antidiuretic Hormone (ADH): Increases water reabsorption in the collecting ducts.
• Aldosterone: Increases sodium reabsorption in distal tubules.
• Renin-Angiotensin System: Regulates blood pressure and sodium balance.
• Parathyroid Hormone (PTH): Regulates calcium and phosphate excretion.
• Atrial Natriuretic Peptide (ANP): Inhibits sodium reabsorption and reduces blood pressure.

Question 17

Formation of Urine in the Nephron

Answer 17

• Glomerular Filtration: Plasma is filtered through the glomerular capillaries into Bowman’s capsule.
• Tubular Reabsorption: Water and essential solutes are reabsorbed back into the blood.
• Tubular Secretion: Additional waste products are secreted into the tubule for excretion.

Question 18

Glomerular Filtration Dynamics

Answer 18

• Glomerular filtration depends on three pressures:
  
  1. Glomerular Hydrostatic Pressure (forces fluid out).
  2. Plasma Colloid Osmotic Pressure (opposes filtration).
  3. Bowman’s Capsular Pressure (opposes filtration).

Question 19

Tubular Reabsorption and Secretion

Answer 19

• Reabsorption mainly occurs in the proximal tubule and Loop of Henle.
• Secretion of hydrogen ions, potassium, and organic acids occurs in the distal tubule.

Question 20

Renin-Angiotensin System and Blood Pressure Regulation

Answer 20

• Low blood pressure → JG cells release renin → converts angiotensinogen to angiotensin I → converted to angiotensin II by ACE → vasoconstriction & aldosterone release → increases BP and sodium retention.

Question 21

Countercurrent Multiplication in the Loop of Henle

Answer 21

• Creates a concentration gradient that allows for urine concentration.
• Descending limb allows water loss; ascending limb actively pumps out NaCl.

Question 22

Effects of ADH on Urine Concentration

Answer 22

• High ADH → more water reabsorbed → concentrated urine.
• Low ADH → less water reabsorbed → dilute urine.

Question 23

Autoregulation of Renal Blood Flow

Answer 23

• Myogenic Mechanism: Increased BP → afferent arterioles constrict →
  maintains stable GFR.
• Tubuloglomerular Feedback: Macula densa senses NaCl levels and adjusts afferent arteriole diameter.

Question 24

Process of Micturition

Answer 24

• Bladder fills → stretch receptors activated → parasympathetic signals trigger detrusor muscle contraction → sphincter relaxes → urine expelled.