The Excretory System Flashcards
excretion
the disposal of waste products
liver
responsible for excreting many wastes by chemically modifying them and releasing them into bile, deals with hydrophobic or large waste products that can’t be filtered out by the kidney, synthesizes urea and releases it into the bloodstream
heme is broken down into ______ in the _______
bilirubin; liver
urea
carrier of excess nitrogen resulting from protein breakdown, excreted in the urine
large intestine (colon)
reabsorbs water and ions from feces, processes wastes already destined for excretion, capable of excreting excess ions into the feces using active transport
skin
produces sweat , which contains water, ions, and urea, controlled by temperature and level of sympathetic nervous system activity
excretory and homeostatic roles of the kidneys
1) responsible for excretion of hydrophilic wastes (urea, sodium, bicarbonate, water)
2) maintains homeostasis by constant solute concentration and constant pH
3) maintains homeostasis by constant fluid volume (important for blood pressure and cardiac output)
homeostasis
constancy of physiological variables
what are the 3 processes the kidneys perform?
1) filtration (passage of pressurized blood over a filter where cells and proteins remain in the blood but water and small molecules are squeezed into the renal tubule which then becomes the filtrate (will eventually be made into urine)
2) selective reabsorption (take back useful items - glucose, water, amino acids, while leaving wastes and some water in the tubule)
3) secretion (addition of substances to the filtrate, increasing the rate at which substances are eliminated from the blood)
4) urine concentration and dilution (involves/determined by the selective reabsorption of water)
renal artery
carries blood to the kidney, a direct branch of the lower portion of the abdominal aorta
renal vein
leaves the kidney and carries purified blood back to the circulatory system, empties into the inferior vena cava
ureter
carries urine from the kidney to the urinary bladder
urinary bladder
muscular organ that stretches as it fills with urine, sends signal to the brain when full
what are the two sphincters that control release of urine from the bladder?
internal sphincter (smooth/involuntary muscle) and external sphincter (skeletal/voluntary muscle)
cortex
outer region of the kidney
medulla
inner region of the kidney
medullary pyramids
pyramid-shaped striations within the medulla, striations due to the presence of many collecting ducts
collectin ducts
where urine empties and leaves the medulla at the tip of the pyramid (papilla)
calyx
space in which each papilla, tip of pyramid, empties
renal pelvis
where calyces eventually converge, a large space where urine collects and ultimately empties into the ureter
nephron
the functional unit of the nephron, consists of:
1) capsule (rounded region surrounding the capillaries where filtration takes place)
2) renal tubule (coiled tube that receives filtrate from the capillaries in the capsule at one end and empties into a collecting duct at the other end and dumps urine into the renal pelvis.)
afferent arteriole carries blood towards the kidneys and forms a ball of capillaries known as the:
glomerulus, from there the blood flows into the efferent arteriole
the efferent arteriole constricts and causes…
high pressure in the glomerulus, which causes fluid to leak out of the glomerular capillaries and pass through a filter (glomerular basement membrane) and enter Bowman’s capsule
what structures does the filtration steps involve?
afferent arteriole, glomerulus (and glomerular basement membrane), efferent arteriole, Bowman’s capsule
some substances are extracted from the tubule via active transport and picked up by:
peritubular capillaries which train into venules that lead to the renal vein
most selective reabsorption occurs at:
the proximal convoluted tubule (PCT), some also occurs at the distal convoluted tubule (DCT) but is more regulated in this area (usually by hormones)
all solute movement in the proximal convoluted tubule is accompanied by:
water movement, i.e. a lot of water reabsorption
what structures are involved in selective reabsorption?
renal tubule (proximal convoluted tubule, distal convoluted tubule), peritubular capillaries
secretion occurs mostly:
in the distal convoluted tubule and the collecting duct (but also occurs all along the tubule) *impermeable to water
concentration and dilution adjusts urine volume and osmolarity and occurs in:
the distal nephron, the most distant part of the renal tubule which includes the distal convoluted tubule and the collecting duct, it is controlled by ADH and aldosterone
antidiuretic hormone, ADH, vasopressin
released by posterior pituitary when blood volume low and blood osmolarity high, increases water reabsorption in the distal nephron by making the distal nephron (especially the collecting duct) permeable to water so that water flows out of the filtrate into the tissue of the kidney (due to high osmolarity of kidney medulla) where it is picked up by peritubular capillaries
if there is a lot of water and plasma volume is high, will ADH by released?
no, because a large volume of dilute urine is necessary so that collecting duct remains impermeable to water and water in filtrate remains in the tubule and is lost in the urine (diuresed)
aldosterone
released by the adrenal cortex when the blood pressure is low, causes increased reabsorption of sodium by the distal nephron resulting in increased plasma osmolarity which leads to increased thirst and water retention which raises the blood pressure
if blood pressure is high, will aldosterone be released?
no, as a result, sodium will be lost, plasma osmolarity and eventually blood pressure will fall
aside from blood pressure, what else can trigger release of aldosterone?
low blood osmolarity, low blood volume, and angiotensin II
where is Bowman’s capsule and proximal convoluted tubule located?
in the renal cortex (the outer layer of the kidney)
the proximal convoluted tubule empties into:
the loop of Henle (the next part of the nephron) which dips down into the renal medulla
descending limb of the loop of Henle
thin walled, where water exits the tubule causing the filtrate to become more concentrated)
ascending limb of the loop of Henle
thin (composed of squamous/flat epithelial cells) and thick (cuboidal epithelial cells, perform active transport) ascneding limb
the loop of Henle eventually becomes:
the distal convoluted tubule which dumps into collecting duct which merges into renal calyces
proximal convoluted tubule roles
reabsorption of most filtered water and ions, reabsorption of glucose and amino acids by secondary active transport-sodium cotransporters, secretion of drugs, toxins and some ions
distal convoluted tubule roles
reabsorption of water and urea in response to ADH, sodium reabsorption in response to aldosterone, secretion of drugs, toxin and some ions
thick ascending limb of loop of Henle roles
active transport of sodium, potassium, and chlorine ions out of filtrate with subsequent passive return of potassium to filtrate, causing:
1) dilution of tubular fluid
2) increased osmolarity of medulla
collecting duct secretes:
potassium and hydrogen ions
the loop of Henle is a:
countercurrent multiplier: the ascending and descending limbs have different permeabilities that makes the medullar very salty and facilitates water reabsorption from the collecting duct (whenever the collecting duct is permeable to water; in the presence of ADH)
vasa recta
branches of efferent arterioles that surround the descending portion of the loop of Henle, forms a loop that helps to maintain the high concentration of salt in the medulla
role of vasa recta
carries off water that leaves the descending limb of the loop of Henle and returns it to the bloodstream, blood in the vasa recta moves in the opposite direction of the filtrate in the nephron, thus performs countercurrent exchange
glomerular filtration rate (GFR) depends on:
pressure
systemic and local (glomerular) blood pressure is regulated by:
built in mechanisms in the kidney
juxtaglomerular apparatus (JGA)
specialized contact point between the afferent arteriole and the distal tubule
juxtaglomerular (JG) cells
cells in the afferent arteriole at the juxtaglomerular apparatus, baroreceptors that monitor systemic blood pressure
macula densa
cells in the distal tubule at the juxtaglomerular apparatus, chemoreceptors that monitor filtrate osmolarity in the distal tubule)
what do JG cells secrete when there is a decrease in blood pressure?
renin (an enzyme) which catalyzes the conversion of angiotensinogen into angiotensin I, which is further converted to angiotensin II by angiotensin-converting enzyme, angiotensin II is a vasoconstrictor that immediately raises the blood pressure and stimulates the release of aldosterone which helps raise the blood pressure by increasing sodium and water retention
angiotensinogen
a plasma protein made by the liver, that is converted into angiotensin I by renin
angiotensin-converting enzyme
in the lungs, converts angiotensin I to angiotensin II (vasoconstrictor and stimulates release of aldosterone)
what do macula densa cells do when filtrate osmolarity decreases (decreased filtration rate)?
macula densa stimulates JG cells to release renin and also causes a direct dilation of the afferent arteriole to increase blood flow to (and thus blood pressure and filtration rate) in the glomerulus
high filtration rate is associated with:
high filtrate osmolarity, high blood pressure in the glomerulus
how does the kidney regulate pH
if the plasma pH is too high, bicarbonate is excreted in the urine; when the plasma pH is too low, hydrogen ions are excreted
carbonic anhydrase
catalyzes the conversion of carbon dioxide into carbonic acid, which can then dissociate into bicarbonate plus a proton (this reaction needs to occur before the kidney as reabsorb or secrete bicarbonate or protons as needed)
generally, how are the amounts of bicarbonate and protons adjusted to maintain pH?
generally, protons are secreted and bicarbonate is reabsorbed, amounts are adjusted to adjust pH
renal pH adjustments are slow, what other system allows for more rapid maintenance of pH?
regulation by the lung
what hormone does the kidney make?
erythropoietin (EPO), which causes increased synthesis of red blood cells in the bone marrow, it is released when blood oxygen content falls
aldosterone
released by adrenal cortex, causes sodium reabsorption and potassium secretion by increasing the synthesis of basolateral Na/K ATPases in the distal nephron, results in increased serum sodium, increased blood volume (through the action of ADH), and thus increased blood pressure
aldosterone raises blood osmolarity which release of:
ADH which helps to raise blood pressure (increased water reabsorption and thus increased plasma volume)
ADH
released by posterior pituitary when plasma volume/blood pressure is low or plasma osmolarity is too high, causes water reabsorption by causing epithelial cells of the distal nephron to become permeable to water, which allows water to flow out of the filtrate into the medullary interstitium. vasa recta returns water to the bloodstream which results in more concentrated urine and more diluted blood.
calcitonin
released by C cells located in the thyroid gland when serum calcium is too high. causes calcium to be removed from the blood by deposition in bone, reduced absorption by the gut, and excretion in urine
parathyroid hormone
released by the parathyroid glands embedded in the thyroid gland, functions opposite to calcitonin to raise serum calcium levels
