Chapter 9 muscles and muscle tissue

Chapter 26
Urinary System

functions of the urinary system
1. regulation of blood volume and blood pressure 2. regulates plasma concentrations of ions calcium - site of calcitriol synthesis (vit D) 3. controls blood pH (acid base balance) controls acid and bicarbonate loss from blood 5. detoxifies poisons and drugs (along with liver) general kidney anatomy
each kidney contains over one million nephron parts of the nephron
each nephron is composed of a blood supply called the renal corpuscle and a long tube called the renal tubule I) renal corpuscle
is the blood supply of the nephron called the glomerulus and the tissue that surrounds the 1. glomerulus
the afferent
arteriole and is drained by the
efferent arteriole
efferent goes on to produce
the peritubular capillaries
filtrate
thus has lots of good stuff the body needs back over 90% of filtrate is reabsorbed in the peritubular capillary beds which surround the nephron tube 2. mesangila cells
mesangila cell function
1. are resident macrophages that remove materials that exits the cap but can not enter the renal tube 2. provide some physical support for cap. 3. contain actomyosin and can contract or relax changing cap diameter and may regulate filtration rate 3. Bowman’s or glomerular capsule
has two layers (like a fist pushed into a 1. visceral layer
made of podocytes that are
podocytes form foot processes
(pedicels) on the glomerulus which
form filtration slits or slit pores so
that filtrate can exit the capillaries
the filtration slit, the fenestrated
endothelium, and the lamina densa
between the two make up the
filtration membrane which
determines what can leave the
capillary and enter the capsule as a
filtrate
filtration membrane is affected
during glomerulonephritis or
inflammation of the glomeruli
2. parietal layer
contains the filtrate passing from the glomerulus capsular space
fluid pressure will build here and force the filtrate down the renal tubule the Bowman’s capsule has a vascular pole
or end where the capillaries enter and a tubular pole or end where the renal tubule
proximal
convoluted
functions:
reabsorbs
reabsorption is by active and passive mechanisms epithelium also secretes substances
functions:
convoluted
function
collecting duct
papillary
minor calyx
major calyx
renal pelvis
collecting system adjusts the finial composistion of the filtrate controlling the final osmotic concentration and volume of urine
juxtaglomerular
apparatus
located where the distal tubule lies against the afferent and efferent 1. juxtaglomerular cells
specialized smooth muscle cells located in the wall of the afferent arteriole functions: the release of renin
JG cells function as a blood pressure receptor which
releases renin when pressure drops
JG cells also are innervated by the sympathetic
nervous system which triggers the release of renin
JG cells also releases erythropoietin in response to
low pressure and low O2
functions
chemoreceptors
sensitive to changes in the solute levels (sodium) of the filtrate in the distal convoluted tubule a decline in osmolarity of fluid in DCT triggers renin release tubule to slow (more time to absorb sodium, and potassium) 1. cortical nephron- 85% are located almost entirely in
2. juxtamedullary nephrons- are located near the cortex
loop of Henle plunges deeply into the medulla have a longer loop then the cortical nephrons important in producing a concentrated urine
Urine formation

kidneys filter entire blood volume 60 times per day are 1% of body weight but consume 20-25% of oxygen at rest the object is to regulate the volume and composition of the blood to maintain of particular importance is the clearance of three organic waste products urea: 21 grams/day from the breakdown of amino acids (actually
is converted from ammonia)
creatinine: 1.8 grams/day from the breakdown of creatinine
phosphate by the skeletal muscle
uric acid: 480 mg/day formed from the breakdown of RNA and
DNA
urine formation involve three processes
1. glomerular filtration
2. tubular reabsorption
the removal of water and solutes from the filtrate 3. secretion
transport of solutes from the peritubular fluid across the tubular epithelium and into the filtrate
1) glomerular filtration
is a passive process in which fluids and solutes are forced across the wall of the glomerulus by hydrostatic pressure filtration membrane: the filtration slit, the fenestrated endothelium, and
the lamina densa between the two
it is the barrier that the filtrate crosses passing from the glomerulus to the Bowman’s capsule determines what can leave the capillary and enter the capsule as a filtrate lamina densa blocks all but the smallest plasma proteins filtration slits block small plasma proteins only allowing ions nutrients and water to cross glomerular filtration rate (GFR)
total amount of filtrate formed per minute by the kidneys 10% of the fluid delivered to the kidneys leaves the blood rate is 180 (50 gal) liters per day or 70 times the blood volume everyday average adult will reabsorb 99% of the filtrate volume GFR is controlled by the same forces that control filtration/reabsorption at capillary beds (balance between hydrostatic pressures and osmotic pressures) Hydrostatic pressures
Bp of 50 subtract capsular hydrostatic pressure of 15 = Osmotic pressures
Cap osmotic of 25 subtract capsular hydrostatic pressure of 0 = 25 mmHg (in) Filtration pressure = 35(out) – 25 (in ) or 10mmHg(out)
two factors that result in glomerular filtration being high 1. filtration membrane is 1000 times more permeable (fenestrated) 2. glomerular blood pressure is higher then at a cap bed (50 due to small diameter of the efferent arteriole GFR must be carefully controlled
If filtrate flow is to fast, can’t reabsorb sufficient solutes and water (loss of nutrients and blood volume) If too slow, blood levels of wastes increase and results in reabsorption of wastes that should be eliminated
regulating
the normal way to adjust GFR is to change the blood pressure at the glomerulus autoregulation
is the ability of the kidneys to maintain a relatively stable GFR in spite of changes in arterial blood pressure maintains glomerular blood pressure and thus
1. changing the diameter of the afferent arteriole 2. changing the diameter of the efferent arteriole The changes in diameter are the result of the effect that stretch has on smooth muscle contractions in the wall of the vessel increase in glomerular blood pressure
1. afferent arteriole wall is stretched by pressure decline in glomerular blood pressure results in

hormonal
regulation
angiotensin
works to increased systemic blood volume and blood pressure and the restoration of normal GFR 1. renin from the juxtaglomerular cells is released by a drop in glomerular blood pressure due to fall in renal blood pressure due to renal artery blockage 3. sympathetic activity to the JG apparatus effects of renin -AII
a) peripheral capillary beds
direct fast effect on
b) at nephron
AII constricts efferent arterioles
Direct fast effect of GFR
Triggers the release of aldosterone stimulates reabsorption of Na and water by DCT and collecting system indirect and slow
effect on GFR
Indirect and slow
effect on GFR

increase blood volume and blood pressure indirect and slow
atrial natriuretic peptide
main role is to lower blood volume and pressure released by stretch on the atrial wall by high BP ANP triggers dilation of afferent arteriole and This will increase GFR so produce more urine and thus lower blood volume and blood pressure ANP blocks the affects of ADH so lose water and sodium sympathetic regulation of GFR
most nerve fibers are sympathetic fibers are activated during high levels of sympathetic activity especially by acute drastic fall in blood pressure will override all other forms of GFR regulation effects on GFR
decreases GFR and slows the production of moderate sympathetic activity, like during prolonged strenuous exercise, alters the pattern of blood flow and the kidney see less flow. If autoregulation and hormonal regulation can’t oppose this change renal damage may occur due to hypoxia conversion of the filtrate to urine involves the recovery of useful substances by tubular reabsorption and the disposal (tubular secretion) of undesirable solutes that did not leave the blood stream during filtration 2) tubular reabsorption
Typically almost 99% of the filtrate volume and salts content, and almost 100% of the glucose and amino acids will be reabsorbed by the renal tubule This material is returned to the peritubular capillaries by diffusion movement into the peritubular capillaries is easy to do 2. very low blood pressure due to narrow efferent arteriole 3. slow flow rate Tubular reabsorption of PCT
1. sodium (65%)
is 140 mEq/L in filtrate only 12 in tubule cell once inside the cell it is pumped out the other side by the sodium/potassium ATP-ase sodium is also reabsorbed by cotransport with other nutrients 2. glucose (100%)
is a transcellular route (through the cells) once inside the cell it diffuses out the secondary active transport
no ATP directly used must use ATP to maintain the sodium gradient 3. amino acids (100%)
are more concentrated inside the cell so will both amino acids and sugars require a transport
protein which are limited in number thus there is a
transport maximum
if filtrate moves too fast (high GFR) or
levels of sugars or amino acids are too high
the transporters will become saturated and
the nutrients will pass out in the urine
diabetes mellitus = sugar in the
urine
4. reabsorption of water(65%)

as nutrients and ions reabsorbed the filtrate 5. reabsorption of other cations ions
concentrated so move in by diffusion
called solvent drag
solvent drag also used to reabsorb lipid-soluble materials and vitamins 6. Chloride and other anions
negative chloride tends to follow positive 7. nitrogenous wastes
kidneys remove less then half of the urea in uric acid is 100% reabsorbed but secreted Tubular reabsorption of loop of Henle
Primary function is to enable the collecting duct to concentrate the urine by conserving water reabsorb half the remaining water and two-thirds remember: the two parallel segments of the loop are separated only by peritubular fluid and have different permeability characteristics 1. filtrate concentration entering the loop is 300 2. concentration increases to 1200 at the bottom of 3. concentration drops from 1200 to 100 as the remember the surrounding tissue will have similar 1. sodium, potassium and chloride are pumped out of the
thick ascending limb by a sodium, potassium, 2 chloride
cotransporter
the concentration of salts within the loop goes from the pumping of Na, K, Cl results in a concentrated salt fluid in the tissues around the descending limb with the bottom being most concentrated 1200 mosm 2. the thin descending limb is permeable to water but not
salts so water flows out of the thin descending limb
attracted to the salt pumped out by the thick ascending limb
this increases the concentration of the salts in the filtrate as you move alone the thick ascending limb toward the bottom 300 to 1200 mosm at the bottom makes it easier to pump out Na,K and Cl in the ascending limb the vasa recta, with is a part of the peritubular capillary bed, parallels the loop so that the salt gradient is established in the vasa recta so not to disturb the salt gradient and yet it picks up the excess water and salts countercurrent
multiplication
countercurrent

multiplication
effect
the fluid entered the loop at 300 mosm. Only half of this volume will enter the DCT and it will be at 100mosm due to the reabsorption of NaCl and K by the ascending limb. This solution will also have high concentrations of urea and other wastes that were not transported out Tubular reabsorption and secretion of distal convoluted
filtrate is only 15-20% of original volume electrolyte and waste concentration are no longer similar to selective reabsorption along the DCT makes adjustmenst in the composition and volume of the filtate reabsorption
1. sodium reabsorption
Sodium is actively transported out of filtrate in exchange from potassium more sodium gained then potassium lost so this sodium transport is selectively
controlled based on the bodies needs by the
hormone aldosterone
1. trigger the production and insertion of a sodium channel in the basal membrane 2. stimulate the synthesis and activity of the sodium-potassium ATPase thus aldosterone triggers sodium reabsorption but also potassium loss so can cause hypokalemia
atrial natriuretic factor
inhibits the effects of aldosterone (don’t forget ADH too) on sodium and water reabsorption in DCT 2. also site of calcium reabsorption
1. stimulate the production of a calcium channel 2. stimulate the production and activity of a calcium pump (Ca-H ATPase) Tubular reabsorption of collecting system
sodium- in cortical region aldosterone-sensitive
water reabsorption occurs if ADH is present
filtrate has a osmolarity of 100 as it enters the collection system ANF effects
The distal portion of the collecting system is permeable to urea which is concentrated by the movement of water out of the collecting system Now urea will travel down its contrition gradient and collects here the bottom of the loop 2) tubular secretion
movement of substances from the peritubular capillaries into the tubule most occurs in the distal convoluted tube potassium
hydrogen ion
occurs when blood and filtrate pH is low this diffuses into kidney cells which have carbonic anhydrase the bicar will enter the blood and buffer pH
ammonium
when blood pH drops DCT and PCT will be stimulated to deaminate amino acids producing NH3 (ammonia) the ammonia will bind to H from the break the bicarb will enter the blood to buffer pH

Source: http://mtweb.mtsu.edu/biolap/Lecture_Materials/Stewart_Lecture_Notes/renal(23).pdf