Renal Anatomy, Physiology, and Urine Production Flashcards
Renal system
Maintain a stable internal environment for optimal cell and tissue metabolism by:
- Balancing solute and water transport
- Excreting metabolic waste products
- Conserving nutrients
- Regulating acids and bases
Additional renal functions
Endocrine functions (secrete hormones):
- Renin
- Erythropoietin
- 1,25-dihydroxy-vitamin D3
Gluconeogenesis (synthesize glucose from amino acids)
Urinary system
Formation of urine is achieved within the kidney through the process of (1) glomerular filtration, (2) tubular reabsorption, and (3) tubular secretion
Urinary bladder: stores urine received from the kidney by way of the ureters
Urine is removed from the body through the urethra
Kidney anatomy
The kidneys are paired, retroperitoneal organs located in the posterior region of the abdominal cavity, behind the peritoneum
Renal capsule: tight adhering capsule that surrounds each kidney
Cortex: outer layer of the kidney that contains glomeruli, most PCTs, and some segments of DCTs
Medulla: inner layer of the kidneys consisting of regions called pyramids
Apex (ends) of pyramids project into minor and major calyces (cup-shaped cavities) to form the renal pelvis
Nephron
Functional unit of kidney
Contains:
- Renal corpuscle (glomerulus, Bowman’s capsule, and mesangial cells)
- PCT
- Loop of Henle
- DCT
- Collecting duct
Glomerulus
Tuft of capillaries that loop into Bowman’s capsule; structurally supported by mesangial cells
Synthesizes NO (vasodilator) and endothelin-1 (vasoconstrictor) to regulate blood flow and GFR
Fenestrae: endothelial cells with pores that line the capillaries and allow filtration of fluid, plasma, solutes, and small proteins; prevent filtration of RBCs, WBCs, and platelets
JGA is formed by the afferent arteriole and portion of DCT; juxtaglomerular cells produce renin to regulate renal perfusion and GFR
Macula densa: specialized Na and Cl-sensing cells in between afferent and efferent arterioles (in a portion of the DCT)
Podocytes: cells that adhere to the capillaries of the GBM; gaps allow filtration
Renal blood flow
GFR: the filtration of the plasma per unit of time; directly related to renal perfusion
Controlled by:
- Autoregulation
- Neural regulation
- Hormonal regulation
Autoregulation
Maintain constant renal perfusion and GFR despite increasing/decreasing range of systolic BP
Mechanisms:
1.) Increasing/decreasing arteriole resistance (increased resistance with increased BP)
2.) Tubuloglomerular feedback:
Pathway:
1. Decreased arterial pressure
2. Decreased glomerular hydrostatic pressure and GFR
3. Macula dense sense lack of Na and Cl in DCT
4. JGA releases renin, and formation of angiotensin
5. Vasoconstriction and increased resistance
6. Increase glomerular hydrostatic pressure and GFR
Neural regulation
Afferent arterioles are innervated by SNS fibers
- Decreased arterial pressure
- Sensed by aortic baroreceptors
- Increase sympathetic output of epinephrine
- Afferent arteriole (renal) vasoconstriction
- Decreased GFR (initially)
- Increase sodium and water reabsorption
- Increases plasma blood volume, BP, and GFR
Hormonal regulation
- Decreased BP, ECF, renal perfusion, serum Na OR increased urine Na
- Renin (formed in the JGA) is released
- Stimulates angiotensinogen production (in liver)
- Renin and angiotensinogen form angiotensin I
- Angiotensin I is converted into angiotensin II (by ACE)
- Angiotensin II stimulates: (1) vasoconstriction of arterioles and (2) aldosterone secretion (from adrenal cortex)
- Aldosterone: (1) retains sodium and water in kidneys and (2) stimulates ADH secretion (and thirst)
- Increases ECF, BP, and GFR
Nephron function
Filters plasma at glomerulus for (1) excretion, and (2) reabsorption and (3) secretion along the tubules
Ultrafiltration: protein-free filtrate, that helps maintain body fluid volume, pH, and electrolyte balance
Functions:
- Tubular reabsorption: movement of fluid and ions from renal tubules to capillary
- Tubular secretion: movement from capillaries to renal tubules
- Excretion: elimination of a substance in the final urine
Function of nephron segments
PCT: active reabsorption of most ions (Na+, Ca2+, K+, Mg2+, Cl-, HCO3-, H2O, amino acids, glucose)
Loop of Henle (THIN descending): highly permeable to water (osmosis); no ions
Loop of Henle (THICK ascending): active reabsorption of ions (Na+, Ca2+, K+, Cl-)
DCT: active reabsorption of Na+, Ca2+, Cl-, HCO3-, H2O and secretion of K+, H+ NH4+
Collecting duct:
- Principle cells reabsorb Na+ and H2O, and secrete K+
- Intercalated cells reabsorb K+, and secrete H+
Concentration and Dilution of Urine
Occurs mainly in the Loop of Henle, DCT, and collecting ducts
Concentrated urine is produced by a concurrent mechanism in the Loop of Henle; the longer the loop, the more concentrated urine can become
Aldosterone stimulates the release of ADH (from the pituitary gland) which increases the permeability and reabsorption of water in the DCT and collecting ducts (concentrates urine)
Problems with renal failure
HTN (inability to regulate BP)
Edema (nephrotic syndrome)
Anemia (EPO deficiency)
Hypocalcemia, vitamin D deficiency, and hyperphosphatemia (1,25-dihydroxy vitamin D3 deficiency)
Hypoglycemia (impaired gluconeogenesis)
Accumulation of toxic metabolites (inability to excrete toxins)
Diuretics
Enhance urine flow; decrease renal sodium reabsorption, and as a result, decrease ECF
Types of diuretics:
1. Osmotic: act on PCT and the descending Loop to inhibit reabsorption of water and sodium
- Loop: act on ascending Loop and DCT to inhibit reabsorption of Na+, Ca2+, K+, and Cl-
- Thiazide: act on DCT to inhibit reabsorption of Na+ and Cl-; promotes Ca2+ reabsorption
- Potassium-sparing: act on end of DCT and collecting duct to promote reabsorption of K+
