Urinary System
I
II
Functions
A
Excretion - by kidneys
1)
removal of metabolic wastes, toxins, excess ions, and water
(a)
also performed by skin, liver, and lungs
B
Regulation
1)
of body fluids and electrolytes
2)
blood pressure
3)
RBC production
C
Transportation and storage of urine
1)
ureters, bladder, and urethra
Kidney Structure
A
External structure - 3 layers
1)
renal fascia - thin layer of fibrous C.T., fastens kid. to surrounding struct.
2)
adipose capsule - layer of fat, cushions kid.
3)
renal capsule - thin layer of fibrous C.T., prevents entrance of infections
B
Internal structure
1)
renal cortex - borders convex side of kid, granular appearance
(a)
renal columns - portions of cortex tissue that extend inward btwn
pyramids
2)
renal medulla - deep to cortex, contain 8 - 10 renal pyramids, cone shaped
striated structure containing microscopic tubules
3)
renal sinus - cavity on concave side of kidn.
(a)
renal pelvis - a membrane lined cavity w/ funnel shaped extensions called
calyces that collect urine, merges w/ ureters
(b)
hilum - concave margin of each kid. where renal artery, vein, ureters, and
nerves join kid.
III
Blood Supply
A
Renal arteries branch off abdominal aorta to each kid., carry 1/4 of cardiac output per
min
B
R.A. branches into 5 lobular arteries, enter renal sinus
1)
branch into interlobular arteries which extend btwn pyramids
2)
branch into arcuate arteries which extend btwn cortex and medulla
(a)
also branch into afferent arterioles that carry blood to nephrons
C
Blood is drained by veins w/ similar names into renal vein which empties into infer. vena
cava
IV
Nephron Structure
1M nephrons make up functional tissue of kidney
each nephron has a filtering body (renal corpuscle) and urine collecting and concentrating tube (renal
tubule)
A
Renal Corpuscle
1)
located in cortex
2)
Bowman's capsule - bowl like strctr that encircles a capillary network called
the glomerulus, collects filtrate that is forced out of capillaries
3)
fenestrae - large pores in endothelial walls of capillaries, leaky caps.
4)
podocytes - modified simple squamous epith., forms inner wall of Bowman's
capsule
(a)
branches in cell mem. form filtration slits w/ branches of adjacent cells
5)
filtration mem. - glomerulus wall, basement mem., and podocytes, filtrate must
cross to enter cavity of Bowman's capsule
B
Renal Tubule
1)
proximal convoluted tubule (PCT) - coiled tube connecting Bow. cap and
descending limb of Loop of Henle, lined by simple squamous, lot of mitochondria for
reabsorption and secretion
2)
Loop of Henle- portion of R.T. that descends into medulla, makes U turn and
ascends back to cortex
3)
distal convoluted tubule (DCT) - links loop of H. and collecting tube
C
Blood flow thru the Nephron
1)
afferent arteriole >> glomerulus capillary >> efferent arteriole
(a)
afferent larger diameter that efferent, blood backs up, increases pressure
in glom., forces fluid and solutes out of blood into Bow cap.
2)
peritubular capillaries - after efferent arteriole, porous, low pressure, surround
renal tubule, empties into venous system
D
Juxtaglomerular Apparatus
1)
located where DCT contacts afferent arteriole, made of specialized cells of each
(a)
granular juxtaglomerular cells in afferent arteriole are specialized smooth
muscle cells for mechanoreception, control blood pressure
(b)
macula densa cells in DCT are chemoreceptors that monitor [Na] and [Cl]
in urine
2)
regulates rate of urine formation and blood pressure
V
Urine Formation
1200 ml of blood filtered/min
10% pushed into renal tubules as filtrate; 995 returned to blood
1% leaves body as concentrated urine, 1-2 liters/day
A
Filtration
1)
movement of blood plasma across filtration me.
(a)
blood cells, platlets, and proteins can't cross
(b)
glucose, amino acids, urea, K, Cl and plasma enter Bowman's capsule
2)
net filtration pressure (NFP) determines quantity of filtrate
(a)
more pressure >>more urine, less pressure >>
(b)
controlled by
(i)
blood pressure +
(ii)
osmotic pressure of proteins still in glomerulus (iii)
capsular pressure of H2O in Bowman's capsuleB
Tubular Reabsorption
1)
process of reclaiming needed materials and returning them to the blood stream,
results in [urine]
2)
substances move in one direction, from tubule into peritubular capillaries
(a)
move by: active transport (Na, AA), diffusion (ions), and osmosis
(b)
cross three layers
3)
PCT - main site of H2O and solute reabsorption, 65%
(a)
permeability to H2O and ions controlled by hormones
4)
Loop of Henle
(a)
C
descending limb -H2O reabsorbed, less solutes >>concentrated filtrate
(b)
ascending limb - less H2O reabsorbed, glucose and ions actively
transported >>dilute filtrate
(c)
DCT - all but 1% of filtrate has been reabsorbed
Secretion
VI
VII
1)
movement of substances from the peritubular cap. into the
renal tubule by diffusion, active transport, or facilitated diffusion
2)
includes ions that may become toxic (H+, K+0), drugs,
ammonia, urea, and uric acid
3)
blood pH monitored and controlled by CO2/H2CO3 buffer
system
Urea and Uric Acid Excretion
A
Both are nitrogen-containing waste products
1)
urea results from protein metabolism >> ammonia ,
converted by liver to urea, 50% of urea in filtrate is excreted in urine
2)
uric acid result of nucleic acid metabolism, 10% removed in
urine
Regulation of Urine Concentration and Volume
A
Kidneys work to maintain constant blood composition and volume
1)
affected by food and water intake, activity level, disease
2)
controlled by hormones and nervous input
Renin
juxtaglomerular cells
causes Angioitension I to be
converted to Angiotension II
which stimulates adrenals to
release Aldosterone, causes
afferent arteriole to constrict
net affect: Increase BP
>>more filtrate
Aldosterone
Adrenal gland
increase active transport of
Na and Cl back into blood,
H2O follows, net affect:
reduced volume of urine,
increase BP
Antidiuretic Hormone
ADH
Posterior Pituitary
increase H2O reabsorption in
DCT and collecting ducts, net
affect: concentrated urine,
increase in BP
Atrial Natriuretic Factor
Right Atrium of Heart
reduces ability of kid. to
reabsorb solutes and H2O, net
affect: large volume of urine,
decrease in blood volume and
BP
Sympathetic impulses during
f,f,f
Hypothalamus
vasoconstriction of afferent
arteriole, reduces flow to
glomeruli, net affect:
decrease in filtrate and urine
formation