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Characteristics of the Nephron

functional unit of the kidney
each kidney has one million nephrons
some nephrons are held in reserve


What are the two types of nephrons?

corticol- excretory, regulation functions
juxamedullary- concentration, dilution of urine


Describe the characteristics of the glomerulus

filtering point for the blood
3 layers - endothelium, basement membrane, epithelium


what is the bowman's capsule?

holding area for filtrate


proximal tubule

about 80% filtrate returned by reabsorption


loop of henle

filtrate (urine) becomes concentrated,
ascending limb: chloride removed, sodium dragged


distal tubule

reabsorption sodium
secretion of potassium, hydrogen ions, uric acid


What is the hilum?

where the blood vessels and ureters enter and exit the kidneys


What are the four primary roles of the kidney?

filtration - glomerulus
reabsorption - tubules
secretion - tubules
excretion - ureters


Describe the permeability of the loop of henle

the descending loop is only permeable to water, whereas the ascending loop is only permeable to solutes


Describe how the basement membrane helps with filtration

it is negatively charged which helps filter by repelling positively charged proteins and RBCs


What is meant by renal selective reabsorption?

selective reabsorption of sodium, amino acids, and glucose are secreted by the filtrate back into the blood. All glucose is reabsorbed in a healthy state


What is the difference between afferent and efferent arterioles?

afferent - supply blood to each glomerulus
efferent - forms peritubular capillaries, reabsorbs water and solutes as required


How much of the cardiac output is used by the renal system in a resting state?

20-25% or cardiac output


Describe the juxtaglomerular apparatus

glomerular blood pressure regulation accomplished by mechanoreceptors and chemoreceptors
regulates GFR by adjusting diameter and resistance of afferent and efferent renal arteries to act as a valve to maintain a constant MAP


How do the kidneys attempt to maintain adequate perfusion pressure over a wide range of blood pressure?

in hypotension, afferent arteriole dilates and efferent constricts. The opposite happens in hypertension


How does the kidney help to maintain homeostasis?

elimination and clearance of metabolic wastes, water soluble drugs
fluid balance through urine formation, and water excretion
electrolyte balance
acid-base balance


What are the characteristics of the GFR?

rate at which filtrate is formed
in health 180L/24 hours (125ml/min), all but 1.5 is returned to the patient
dependent on blood flow but stable over a wide range of blood pressures
status of Glomerular filtration system is assessed by measuring GFR


What are the determinants of GFR?

blood flow
net filtration pressure (NFP)


What are the three forces of net filtration pressure?

glomerular hydrostatic pressure (60mmHg)
bowman's capsule hydrostatic pressure (18mmHg)
glomerular colloid osmotic pressure (10mmHg)


Do you know which element is most commonly used to measure the adequacy of glomerular filtration rate?

creatinine - end product of protein metabolism that is always excreted in the urine in health


What are the characteristics of ADH?

antidiuretic hormone
secreted by posterior pituitary
negative feedback loops regulate ADH secretion


Give an example of how antidiuretic hormone works

dehydration - increased serum osmos
osmo receptors in the hypothalamus sensitive to serum osmolality
ADH increases permeability of collecting tubules to water for reabsorption


Describe the characteristics of renin

hormone secreted by juxtaglomerular cells
secreted by JGA when GFR falls
renin converts angiotensinogen (released by liver) to angiotensin I
Angiotensin I converted to Angiotensin II by Angiotensin convertin enzyme (found in lungs)
Angiotensin II
potent vasoconstrictor
stimulates secretion of aldosterone


Describe the characteristics of aldosterone

hormone secreted by the adrenal cortex
helps to maintain normal sodium composition
it helps conserve water because:
angiotensin II triggers secretion of aldosterone
promotes sodium reabsorption (distal tubules) and renal water reabsorption
kidneys reabsorb water and sodium
result? increased BP and decreased serum osmolalilty


Why assess the renal system?

-critical illness or injury may result in transitory or permanent renal issues
-patient may present with some degree of pre-existing disease/renal impairment
-critical care interventions/treatment may post threat to renal function
-75% patients experience renal impairment in icu


What is oliguria?

low urinary output
less than 400ml/24 hours


What is polyuria?

excessive or abnormally large passage of urine


What is anuria?

absence of urinary output (<50mL/24 hours)


What is azotemia?

high levels of nitrogen containing compounds in the blood