APPP 04 and 07: Kidney Flashcards
What is total body fluid distributed between?
- extracellular fluid – divided into interstitial fluid and blood plasma
- intracellular fluid
What are some of the functions of the kidney? (3)
- to rid the body of waste materials that are either ingested (drugs, pesticides, food additives) or produced by metabolism (urea from metabolism of proteins, creatinine from muscle metabolism, uric acid from nucleic acid metabolism)
- regulate blood pressure (renin-angiotensin-aldosterone system), controlling reabsorption of water (ADH/vasopressin), and maintaining intravascular volume
- control the volume and composition (concentration of various ions) of the body fluids
What is the size of the extracellular compartment largely determined by and why?
body’s total content of dissolved sodium
- Na+ is the predominant ion of the ECF is therefore available in quantities sufficient to influence the osmotic distribution or redistribution of large amounts of water
- movements of Na+ between the extracellular and intracellular compartments are controlled by transport mechanisms
What do diuretics do?
inhibit the tubular reabsorption of Na+ ions
What role do the kidneys play in the body?
- blood filtration and reabsorption – keep levels of electrolytes stable, such as Na+, K+, and phosphate
- excretion of endogenous and exogenous compounds – prevent buildup of wastes and extra fluid in the body
- endocrine functions – ie. blood pressure regulation
Where are the kidneys located?
lie on the posterior wall of the abdomen
How do they kidneys clear waste?
kidneys control the volume/composition of body fluids, therefore it clears waste by excretion into urine and returning essentials back into the blood
How much do the kidneys filter?
125 ml/min (180 L/day)
- but make only 1 ml/min urine
How much of the cardiac output do the kidneys receive?
20% of the cardiac output – from a pair of renal arteries arising from the abdominal aorta
What do renal arteries become?
afferent arterioles
What is each kidney made up of?
about 1 million nephrons (filtering units) that are each capable of forming urine
What are the 2 major components of nephrons?
- glomerulus – glomerular capillaries surrounded by Bowman’s capsule
- long tubule – proximal tubule, loop of Henle, distal tube, and collecting tubule
What happens in the glomerulus?
large amounts of fluid are filtered from the blood
- glomerular capillaries are supplied with blood by the afferent arteriole while blood leaves via the efferent arteriole
What are the two capillary beds of the renal circulation?
- glomerular – afferent arteriole ends in the capillaries of the glomerulus where high pressure causes filtration
- peritubular – efferent arteriole ends in the peritubular capillary network where low pressure permits absorption
What happens in the long tubule?
filtered fluid is converted into urine
The rate at which different substances are excreted in the urine represent the sum of what 3 renal processes?
urinary excretion rate = filtration rate - reabsorption rate + secretion rate
- glomerular filtration
- reabsorption of substances from the renal tubules into the blood
- secretion of substances from the blood into the renal tubules
Describe the one of the ways that urine formation occurs.
- blood enters from afferent arteriole
- filtration from the glomerular capillaries into Bowman’s capsule of a large amount of fluid (180 L/day virtually free of protein) occurs: glomerular hydrostatic pressure (55 mmHg) - osmotic pressure (30 mmHg) + capsular hydrostatic pressure (15 mmHg) = net outward pressure (10 mmHg)
How do glomerular capillary membranes differ from other capillaries?
has 3 (instead of the usual 2) major layers
What are the 3 layers of glomerular capillary membranes?
- endothelium
- basement membrane
- epithelial cells
What is the endothelium?
perforated by thousands of small holes called fenestrae
What is the basement membrane?
main filtration barrier – meshwork of collagen and proteoglycans
What are epithelial cells?
podocytes – have long ‘foot-like’ processes that wrap around the capillaries, leaving gaps called slit-pores
What do the 3 layers of glomerular capillary membranes make up?
the filtration barrier
- the primary restriction point for plasma proteins appears to be the basement membrane
What can glomerular filtration rate (GFR) be regulated by?
constriction or dilation of afferent artrioles
What is the other way that urine formation occurs?
as filtered fluid leaves Bowman’s capsule and passes through tubules, it is modified by reabsorption of water and specific solutes back into the blood (active and passive transport depending on substance and site) or by secretion of other substances from the peritubular capillaries into the tubule
- 125 ml/min is the amount of fluid which leaves the glomerular capillaries to go into the glomerular space (GFR) but only 1 ml/min is excreted in urine
- blood exits through the efferent arteriole
Is tubular reabsorption or tubular secretion more important the formation of urine?
in general, tubular reabsorption is quantitatively more important than tubular secretion
What is the difference between glomerular filtration and tubular reabsorption?
- glomerular filtration is relatively non-selective – all solute in the plasma are filtered except the plasma proteins
- tubular reabsorption is highly selective
What are some substances that are reabsorbed from the tubules?
some substances like glucose and amino acids are almost completely reabsorbed from tubules so that the urinary excretion rate is essentially zero
What are some substances that are poorly reabsorbed from the tubules?
certain waste products like urea and creatinine are poorly reabsorbed from the tubules and excreted in relatively large amounts
What are some substances that are secreted into the tubular fluid for removal?
- K+
- H+
- urea
- some drugs like thiazides
What is essential for precise control of the composition of body fluids?
kidneys can regulate the excretion of solutes by controlling the rate at which they reabsorb different substances
Where does urine go once it is formed?
propelled down the ureter to the bladder where it is stored, and eventually excreted via the urethra
Renin-Angiotension-Aldosterone System
What is renin?
a protease produced and secreted by the juxtaglomerular cells (JGC)
Renin-Angiotension-Aldosterone System
What are juxtaglomerular cells (JGC)?
specialized set of smooth muscle cells that line the afferent and efferent arterioles
Renin-Angiotension-Aldosterone System
What are the 3 mechanisms that control JGC release of renin?
- a direct pressure sensing mechanism within the afferent arteriole – decreased blood pressure increases renin release
- sympathetic innervation of the JGC promotes renin release via beta1-adrenoceptor signaling – stimulation of beta1 receptors increases renin release
- specialized cells within the distal tubule called macula densa that is especially sensitive to electrolyte concentration (especially NaCl) – decreased luminal NaCl delivery increases JGC renin release