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functions of excretory system

regulation of blood pressure, blood osmolarity, acid-base balance, and removal of nitrogenous wastes


functional unit of the kidneys

nephron; each kidney has about 1,000,000


path of kidney excretion

nephrons empty into the renal pelvis, which narrows to form ureter which urine travels through to the bladder and from the bladder through urethra



kidney's outermost layer



sits within the cortex of the kidney


renal hilum

part of each kidney; it is a slit in the center of kidney's medial surface through which the renal artery, renal vein and ureter enter and exit


renal pelvis

widest part of the ureter which spans the entire width of the renal hilum


portal system

consists of two capillary beds in series through which blood must travel before returning to the heart


three portal systems in the body

hypophyseal portal system, hepatic portal system, and kidney portal system


path of blood in kidneys

renal artery - afferent arteriole - glomerulus - efferent arteriole - vasa recta - renal vein


Bowman's capsule

cuplike structure around the glomerulus which leads to a long tubule with many areas


Areas of long tubule that Bowman's capsule leads to

proximal convoluted tubule, descending and ascending limbs of the Loop of Henle, distal convoluted tubule and collecting duct


Bladder's muscular lining

detrusor muscle; parasympathetic activity causes it to contract


internal urethral sphincter

one of two sphincters urine must pass through to leave the body; consists of smooth muscle and is normally contracted


external urethral sphincter

one of two sphincters urine must pass through to leave the body; skeletal muscle under voluntary control


path of urine to exit body

Bowman's space - proximal convoluted tubule - descending limb of loop of Henle - ascending limb of loop of Henle - distal convoluted tubule - collecting duct - renal pelvis - ureter - bladder (stretch receptors signal nervous system bladder is full which causes parasympathetic neurons to fire and the detrusor muscle to contract; contraction causes internal sphincter to relax) - urethra


micturition reflex

contraction of the detrusor muscle when bladder needs to be emptied reflexively causes internal sphincter muscle to relax


three kidney function processes

filtration, secretion and reabsorption



20% of blood that passes through glomerulus is filtered as fluid into Bowman's space (called filtrate). This movement is governed by Starling forces.



nephrons secrete salts, acids, bases and urea directly into the tubule by either active or passive transport based on the needs of the body at the time. also mechanism for excreting wastes too large to pass through glomerular pores



certain substances such as glucose, amino acids, and vitamins are taken back up for use by kidneys


proximal convoluted tubule (PCT)

area where filtrate first enters; here amino acids, glucose, water-soluble vitamins and majority of salts are reabsorbed along with water; also site of secretion of a number of waster products, including hydrogen ions, potassium ions, ammonia and urea



connective tissue surrounding the nephron


descending limb of the Loop of Henle

dives into the medulla before turning around to become ascending limb of the loop of Henle; filtrate from proximal convoluted tubule enters here after proximal convoluted tubule; permeable only to water which causes water to be extracted into medulla that can be reabsorbed by the vasa recta


concurrent multiplier system

created by the vasa recta and nephron; the flow of filtrate through the loop of Henle is in the opposite direction from flow of blood through vasa recta so that the filtrate is constantly exposed to hypertonic blood which allows maximal reabsorption of water


Ascending limb of the loop of Henle

not permeable to water; only permeable to salts and salt is removed


diluting segment

area where loop of Henle (after ascending limb) becomes thicker because the cells lining it are thicker here, at the transition from inner to outer medulla. The cells contain lots of mitochondria allowing the reabsorption of sodium and chloride by active transport; only portion of the nephron that can produce urine more dilute than the blood


Distal convoluted tubule (DCT)

after loop of Henle; responds to aldosterone which promotes sodium reabsorption which will increase water volume; also site of waste product secretion


Collecting Duct

tube that follows distal convoluted tubule; responsible to aldosterone and antidiuretic hormone (ADH or vasopressin); ever increasing water reabsorption. the water then enters interstitium and goes to vasa recta where it reenters bloodstream; when well hydrated not much water absorbs here, when not aldosterone and ADH absorb a lot here; this is the last opportunity for reabsorption


Path of Aldosterone release

steroid hormone in decreased bp which also stimulates renin release from juxtaglomerular cells in kidneys; renin cleaves angiotensinogen (liver protein) to form angiotensin I which is then metabolized by angiotensin-converting enzyme in lungs to form angiotensin II which promotes release of this from the adrenal cortex.