Kidneys
1. Regulation of water, inorganic ion balance and
acid/base balance (homeostasis)
2. Removal of metabolic waste from blood, into the urine
3. Removal of foreign molecules
4. Gluconeogenesis
5. Production of hormones
-erythropoietin, renin, and vitamin D
Anatomy of kidney
*Bilateral, retroperitoneal
*Receive 20% of the cardiac output
Nephron
The function unit of the kidney. Each kidney has about a million nehprons; this is where blood filtration and subsequent modification of the filtrate occurs. The nephron empties into collecting ducts (minor calix?), which empty into the ureter.
Glomerulus
small network of capillaries encased in the upper end of a nephron; where the filtration of blood takes place
Bowman's capsule
cup-shaped strucutre of the nephron of a kidney which encloses the glomerulus and which filtration takes place.
Proximal convoluted tubule
first section of the renal tubule that the blood flows through; reabsorption of water, ions, and all organic nutrients
Distal convoluted tubule
Between the loop of Henle and the collecting duct; Selective reabsorption and secretion occur here, most notably to regulate reabsorption of water and sodium
Loop of henle
The loop of the nephron that dips downward into the renal medulla. The loop of Henle sets up a concentration gradient in the kidney such that from the cortex to the renal pelvis osmolarity increases. The descending limb of the loop of Henle is permeable t
Cortical collecting duct
*This part of the tubule reabsorbs sodium when aldosterone signaling is present, Potassium is secreted here in exchange for sodium
*A small increase in extracellular K will stimulate the pump and cause K secretion
Mesangial cells
*produce vasoactive substances that influence the GFR by regulating glomerular capillary blood flow.
*located among the glomerular capillaries and in the cleft between afferent and efferent arterioles
Juxtaglomerular cells
Smooth muscle cells in the wall of the arteriole; contains stretch receptors that detect pressure changes; maintains pressure to keep filtration rate constant
Podocytes
*A cell with branching tentacle-shaped extensions that constitutes the barrier through which blood is filtered in the glomerulus of the kidney.
*Located on the visceral/inner wall of the Bowmann's capsule. Contain long, branching processes that interdigit
Basic renal processes
1. Filtration
2.Reabsorption
3.Secretion
4.Excretion
Glomerular Filtration
the first step of urine production, water and most solutes in blood plasma move across the wall of glomerular capillaries into the glomerular capsule and then into the reanl tubule.
Tubular Secretion
Active movement of certain molecules from blood into the distal convoluted tubule of a nephron so that they are added to urine
Tubular reabsorption
Water, glucose, amino acids, and needed ions are transported out of the filtrate into the tubule cells and then enter the capillary blood.
Factors effecting GFR
1. Pressure in the glomerulus
*Favoring filtration- glomerular capillary blood pressure
*Opposing filtration- fluid pressure in bowmans capsule and osmotic force due to protein in plasma
*also regulated by constriction of the AA (decrease in GFR) and EA (
Filtration
� GFR - glomerular filtration rate
- This is a volume per time
- Usually expressed as ml/min: it's a rate
� Filtered load
- the mass of a substance that gets filtered over time
- eg. the filtered load of glucose is equal to GFR X plasma glucose
conce
Reabsorption
� Moving filtered substances back into the blood
� Reabsorption is more involved.
- Different substances are reabsorbed by various
mechanisms
- Some things are important to be reabsorbed
- Others are waste and you don't want them back
� The movement
Secondary active transport of numerous substances of secondary Na
the expenditure of energy takes place on the basolateral side- contransport molecule driving force from ATP energy and Na concentration- to make the intracellular concentration of Na low.
Renal Clearance
These pressures determine how much total urine is formed by the kidneys
over time (how many ml/min)
The rate of urine formation is known asthe Glomerular filtration rate or GFR.
GFR is an important measure of renal function. It can be measured by knowing
Clearance (renal)
� A volume per time
� units are ml/min
� It's a theoretical volume
- of the volume required to account for the mass of a substance removed from the
plasma.
C= U x V/ P
urine concentration times volume of urine divided by the palsma concentration
*ans
Inulin
This is freely filtered, not reabsorbed or secreted, we don't make it in our bodies and can be used to determine renal clearance.
*filtered inulin = excreted inulin
*clearance of inulin is equal to the GFR
Clearance of PAH
PAH= para amino hippuric acid
-dreely filtered
-not reabsorbed
-completely secreted
-it gets filtered. And what isnt filtered is secreted... all of it. So, with respect to the kidney and PAH, what goes into the kidney does NOT come out
*Clearance of PAH=
Micturation
discharge of urine form the bladder, occurs by combination of involuntary & voluntary muscle contractions, when volume exceeds 200-400mL, pressure increases & stretch receptors are innervated.
Micturation muscles
*Detrusor (parasympathetic- acetylcholine/ muscarinic)
*internal urethral sphincter (sympathetic- norepinephrine/ alpha)
*external urethral sphincter (somatic motor- acetlycholine/nicotinic)
How the final reabsorpiton is regulated
Aquaporins in the late distal convoluted tubules and in the cortical and medullary collecting ducts and mention about the effect of vasopressin (ADH) on their
synthesis.
Principle cells
(cortical collecting duct)
*Potassium is secreted here in exchange for sodium
*mediates the collecting duct's influence on Na and K balance via Na and K channels (aldosterone and vasopressin let the principle cells control the quantity of water that's rea
Loop diuretics
Inhibits sodium and chloride reabsorption - Site of action= directly on the ascending limb of the loop of Henle
countercurrent multiplier system
*hyperosmotic interstition
*this system maintains a high salt concentration in the interior of the kidney, which enables the kidney to form concentrated urine
*It can be very dilute when water is abundant
*Very concentrated when water is scarce or when wa
urea recyclying
helps maintain the large hyperosmotic gradient due to selective permeability of urea in given places
aldosterone
salt-retaining hormone" which promotes the retention of Na+ by the kidneys. na+ retention promotes water retention, which promotes a higher blood volume and pressure
Renin/ Angiotensin
Renin-catalyzes the formation of angiotensin and thus affects blood pressure
Angiotensin- any of several vasoconstrictor substances (trade name Hypertensin) that cause narrowing of blood vessels
Angiotensin converting enzyme
An enzyme in the renin-angiotensin aldosterone hormone cascade that converts angiotensin I to angiotensin II. Very powerful vasoconstrictor. Also acts on adrenal cortex to stimulate the adosterone that acts on cortical collecting ducts. Inhibitors of this
Responses to fluid loss
*subsequent sympathetic stimulation, or decreased NA+ presentation to the macula densa
Angiotensin II
� Is a direct vasoconstrictor
- Increases BP
� Stimulates aldosterone release
- Inc Na+ and water retention > Inc BP
� Stimulates vasopressin release
- Inc water retention > Inc BP
� Stimulates thirst
- Inc water intake > blood volume > BP
Atrial Natriuretic Peptide
A peptide hormone secreted by cardiac atrial cells in response to atrial distension (increased blood flow); causes increased renal sodium excretion and as such lowers blood pressure (antagonizing aldosterone).
Vasopressin
pituitary hormone that raises blood pressure and enables the kidneys to reabsorb water and therefore to secrete highly concentrated urine, decrease in plasma volume
Osmoreceptor
if there is an increase in solute concentration interstitially, it causes water to leave cell which affects firing rate- decreases vasopressin secretion
Potassium regulation
*A major stimulus to aldosterone release is an increase in plasma K levels
-aldoserone increases NA reabsorption and K secretion and exretion
*anything that increases the appearance of Na in the lumen of the cortical collecting ducts will increase Na reab
Ca and PO4 in the kidney
� Only 60 % of plasma Ca++ is filtered and 50% of the plasma PO4
� Much reabsorption occurs in the PCT
� Ca++ reabsorption in the DCT and CD is under the control of PTH (chapter 11)
� PTH inhibits PO4 reabsorption
- this increases free Ca++
� PTH also inc
Physiologic acid/base balance
*Increasing CO2 or decreasing HCO3 will increase [H+], and
that means more acidity and reduced pH.
*The opposite is true: Decreasing CO2 or increasing HCO3
- will lower [H+], and
that means less acidity and higher pH.
Common ways to change pH
*Diarrhea results in loss of HCO3 (bicarbonate)
*Vomiting results in loss of H
*Also common: acidosis from excessive protein breakdown, excessive lactic acid production, ketoacidosis etc.
*the lungs compensate for metabolic change in pH
*The kidneys compe