Renal Physiology Quiz

Study Notes

Regulates water and inorganic ion balance in the body.
Excretes metabolic waste products to maintain homeostasis.
Eliminates foreign chemicals through urine production.
Secretes hormones such as:
- Erythropoietin: Stimulates red blood cell production.
- Renin: Secreted by juxtaglomerular cells to regulate angiotensin formation.
- 1,25-dihydroxyvitamin D3: Affects calcium balance.

Composed of three main structures: renal cortex, renal medulla, and renal pelvis.
Functional unit is the nephron, with approximately 1 million per kidney.
Each nephron consists of:
- Renal corpuscle (glomerulus and Bowman’s capsule).
- Renal tubule (proximal convoluted tubule, loop of Henle, distal convoluted tubule).

Cortical nephrons:
- Make up ~85% of all nephrons.
- Located primarily in the cortex.
Juxtamedullary nephrons:
- Found closer to the medulla.
- Characterized by longer loops of Henle that extend deep into renal pyramids.

Location:
- Cortical: Outer cortex.
- Juxtamedullary: Inner cortex near medulla.
Glomerulus Size:
- Cortical: Smaller.
- Juxtamedullary: Larger.
Loop of Henle Length:
- Cortical: Short.
- Juxtamedullary: Longer.
Efferent Arteriole:
- Cortical: Forms peritubular capillary.
- Juxtamedullary: Forms vasa recta.
Sympathetic Nerve Innervation:
- Cortical: Rich.
- Juxtamedullary: Poor.
Renin Concentration:
- Cortical: High.
- Juxtamedullary: Almost none.
Functions:
- Cortical: Reabsorption and secretion.
- Juxtamedullary: Concentration and dilution of urine.

Comprises macula densa, juxtaglomerular cells (JGC), and mesangial cells.
Macula densa detects Na+, K+, and Cl- in tubular fluid, signaling changes.
JGC, located in afferent arterioles, secretes renin to manage blood pressure and filtration.

Renal blood flow is significant: 1200 ml/min, constituting 1/5 - 1/4 of cardiac output.
Blood distribution: Cortex receives ~94%, outer medulla 5-6%, and inner medulla 1-2%.
Daily urine volume varies, reflecting fluid and electrolyte loss.

Urine travels from the ureters to the bladder via smooth muscle contractions.
Micturition Process:
- Bladder fills until pressure exceeds 400-500 ml.
- Initiated by the micturition reflex, which empties the bladder.
Bladder capacity ranges: 250-400 ml.
Stretching of bladder walls activates the spinal reflex for urination, involving:
- Parasympathetic stimulation, leading to bladder contraction.
- Opening of the internal and external sphincters.