Describe the location of the kidneys.
The bean shaped kidneys lie in a retroperitoneal position between the dorsal body wall and the parietal peritoneum. Some protection from lower part of the rib cage. Extending from T12 to L3. Right kidney is crowded by the liver and lies slightly lower than the left.
What is meant by retroperitoneal?
is the anatomical space in the abdominal cavity behind (retro) the peritoneum. Organs are retroperitoneal if they have peritoneum on their anterior side only. Structures that are not suspended by mesentery in the abdominal cavity and that lie between the parietal peritoneum and abdominal wall are classified as retroperitoneal.
Name the blood vessels which lead up to the glomerulus. What is an afferent vessel? What is an efferent vessel?
Segmental Artery, Interlobar Artery, Arcuate Artery, Cortical Radiate Artery, Afferent Arteriole, Efferent Arteriole,
Afferent: carries blood from Cortical Radiate Artery into glomerulus. Afferent is larger than Efferent.
Efferent: Feeds into either the peritubular capillaries or the vasa recta.
This arrangement maintains the higher pressure in the glomerulus needed for filtration.
What is the vasa recta?
Long, straight efferent arterioles of juxtamedullary nephrons. Important role in forming concentrated urine.
Where does the blood go after it leaves the efferent arteriole?
The efferent arterioles either 1) carry blood to capillaries in the medulla (Vasa recta) or 2) form anastomotic capillaries in the cortex (peritubular plexus).
Efferent arterioles of glomeruli in the outer cortex form the peritubular plexus which surrounds proximal and distal tubules.
Efferent arterioles of glomeruli in the deeper cortex contribute to the adjacent peritubular plexus and also form the vasa recta which accompany the loop of Henle into the medulla.
Where is the renal fascia?
Outer layer of dense fibrous connective tissue that anchors the kidney and adrenal glands to surrounding structures.
Where are the peritubular capillaries?
They arise from the high resistant efferent arterioles they only experience low pressure. They cling closely to adjacent renal tubules and empty into nearby venules. Absorb substances from several adjacent nephrons.
Are made up of parallel bundles of urine collecting tubules
are inward extensions of cortical tissue
Most superficial, is light colored and has a granular appearance.
Deep to the cortex is the darker, reddish-brown medulla which exhibits cone shaped tissue masses called renal pyramids.
Major Calyces and Minor Calyces
Major calyces collect urine draining from papillae, empty urine into the pelvis
Each major calyce subdivides to form several minor calyces, cup shaped areas that enclose the papillae.
flat, funnel-shaped tube; is continuous with ureter leaving the hilum. Branching extensions of the pelvis form two or three major calyces.
collects urine from the pyramids and conveys it into the ureter for passage to the urinary bladder.
What type of cells line Bowman’s capsule? The Bladder?
the visceral layer of the glomerular capsule or bowman's capsule is made up of specialized cells called podocytes. The parietal layer is simple squamous epithelium.
Transitional Epithelium tissue lines the bladder, ureters and urethra
What is the renal corpuscle made of?
glomerulus, bowman's capsule
Why do the renal pyramids look striated?
They have parallel bundles of ducts carrying urine from the nephrons.
What do the juxtamedullary nephrons do that cortical nephrons don’t do?
Cortical nephrons account for 85% of the nephrons. For the most part they are located entirely in the cortex.
Juxtamedullary play an important role in the concentration of urine. They have long nephron loops that deeply invade the medulla and their ascending limbs have both thin and thick segments.
Describe the structure of a nephron and its collecting duct. What are principal cells and intercalated cells?
Each collecting duct contains two cell types: principal cells (maintain the body's water and Na+) and intercalated cells which are cuboidal with abundant microvilli. There are two types of intercalated (type a and type b) each play a role in maintaining acid-base balance.
How much blood is pumped by the heart everyday?
How much of this goes to the kidneys?
Every day the heart pumps 2,000 gallons of blood through blood vessels to carry critical oxygen and nutrients to all parts of the body and remove waste products.
The kidneys process about 180L/day (47 gallons) of blood derived fluid daily. Of this amount typically less than 1% leaves the body as urine. The rest returns to circulation.
What is and what is not found in the filtrate?
molecules smaller than 3nm in diameter, such as water, glucose, amino acids and nitrogenous wastes pass freely from blood into glomerular capsule. Filtrate includes everything found in blood plasma except proteins. Larger molecules greater than 5 nm like proteins pass with difficulty keeping them in the capillaries which maintains the colloid osmotic pressure.
What mechanisms control glomerular filtration? Describe the tubuloglomerular feedback system.
1.) Net filtration pressure, the hydrostatic pressure which is controlled by the diameter of the afferent and efferent arterioles.
2.) Total surface area available for filtration, Glomerular mesangial cells surrounding these capillaries can fine-tuen GFR by contracting to adjust the total surface area.
3.) Filtration membrane permeability,
is one of several mechanisms the kidney uses to regulate glomerular filtration rate (GFR). It involves the concept of purinergic signaling, in which an increased distal tubular sodium chloride concentration causes a basolateral release of ATP from the macula densa cells. This initiates a cascade of events that ultimately brings GFR to an appropriate level
Intrinsic controls (2 types of auto regulation)
1.) Myogenic: responds to changes in pressure in the renal blood vessels. Rising systemic blood pressure stretches vascular smooth muscle in the arteriolar walls causing afferent arterioles to constrict.
2.) Flow-dependent tubuloglomerular feedback: senses changes in the juxtaglomerular apparatus. Respond to filtrate NaCl concentration. When GFR increases, there is not enough time for reabsorption so NaCl is high. The high levels of NaCl signals release of vasoconstriction chemicals which cause afferent arterioles to constrict and flow to decrease to allow more time for reabsorption of NaCl.
Extrinsic controls under stress (maintain systematic blood pressure)
Sympathetic nervous system controls. When blood pressure falls, no epinephrine is released by adrenal medulla causing vascular smooth muscle to constrict increasing peripheral resistance and brining pressure back up to normal.
Renin-agiotensin-aldosterone mechanism. Low blood pressure causes granular cells of the juxta to release renin. Renin acts on angiotensinogen to release angiotensin 1... angio 1 is converted to angio 2. Angio 2 causes mean arterial pressure to rise and stimulates the adrenal cortex to release aldosterone. As a result, both systemic and glomerular hydrostatic pressure rise.
Every day 180 liters of fluid is filtered by the kidney. Account for this fluid, i.e., how much of it goes where?
1.5 Liter is excreted. 178.5 reabsorbed. 99.2% is reabsorbed.
What are podocytes?
(or visceral epithelial cells) are cells in the Bowman's capsule in the kidneys that wrap around the capillaries of the glomerulus.
Who said "Superficially, it might be said that the function of the kidney is to make urine; but in a more considered view one can say that the kidneys make the stuff of philosophy itself."
How are salts and water reabsorbed by the proximal convoluted tubule?
85% of NaCl and water and all of glucose and amino acids in the filtrate are reabsorbed in the PCT.
Sodium reabsorption is almost always active. Na+ enters the tubule cells at the luminal membrane and then is actively transported out of the tubules by Na+-K+ ATPase pump. From there it moves to peritubular capillaries due to low hydrostatic pressure and high osmotic pressure of the blood. Na+ reabsorption provides the energy and the means for reabsorbing most other solutes.
Prostaglandins (PGE2 and PGI1)
vasodilators produced in response to sympathetic stimulation and angiotensin 2
Are thought to prevent renal damage when peripheral resistance is increased.
vasodilator produced by the vascular endothelium
vasoconstrictor of renal vasculature
a powerful vasoconstrictor secreted by tubule cells
Proximal Convoulated Tubule (PCT) Mechanisms for Reabsorption of:
1.) Sodium Ions
2.) virtually all nutrients
3.) Cl-, K+, Mg2+, Ca2+, and HCO3-
5,) Lipid-soluble solutes
1.) Primary Active Transport
2.) Secondary Active Transport
3.) Passive paracellular diffusion driven by electrochemical gradient
5.) Passive diffusion driven by concentration gradient
6.) Primarily passive paracellular diffusion
What is Tm?
Transport maximum. There is a max for nearly every substance that is reabsorbed using a transport protein in the membrane. The Tm reflects the number of transport proteins available to ferry a particular substance. When transporters are saturated that is all bound to the substance they transport. Excess is excreted in the urine.
What is the function of the Henle's Loop?
The principal function of the loop of Henle appears to be the recovery of water and sodium chloride from the urine. Loop of Henle reabsorbs water, Na+, Cl-, K+ in the descending limb and Ca2+. Mg2+ , and Na+ in ascending limb.
The rule for what is that is leaves the descending limb of the nephron loop but NOT ascending limb. However, virtually NO solute reabsorption happens in descending limb but solutes are reabsorbed both actively and passively in ascending limb.
Countercurrent Mechanism: Descending and ascending limb
Descending limb: water permeable and salt impermeable
Ascending limb: salt permeable and water impermeable.
What range of urine concentrations are normally observed? How is urine concentrated?
Can plunge as low as 50 mOsm and may rise as high as 1200 mOsm when we are dehydrated and the posterior pituitary releases large amounts of ADH when this happens only 1/2 liter of highly concentrated urine is excreted.
What is the structural and functional unit of the kidneys?
Two components of the renal corpuscle?
Glomerulus and Bowman's Capsule
The endothelium of the glomerular capillaries is fenestrated which makes these capillaries exceptionally porous. The property allows large amounts of solute-rich, protein-free fluid to pass from blood into glomerular capsule
Name the two layers of the glomerular capsule:
parietal layer and visceral layer
What cells make up the parietal layer?
simple squamous epithelium
What cells make up the visceral layer?
Describe the renal tubule
the proximal convoluted tubule leaves the glomerular capsule drops into the nephron loop (descending loop, ascending loop) to the distal convoluted tubule before emptying into a collecting duct.
The walls of PCT are made up of?
Cuboidal epithelial cells.
Act as mechanoreceptors that sense the blood pressure in the afferent arterioles.
Are chemoreceptors that monitor the NaCl content of the filtrate entering the distal convoluted tubule.
Urine formation and the adjustment of blood composition involve three things:
1.) Glomerular Filtration: produces a cell and protein free filtrate
2.) Tubular Reabsorption: moving substances from filtrate back into the blood
3.) Tubular Secretion: moving substances from blood to filtrate
3 layers of the filtration membrane?
1.) Fenestrated endothelium
2.) Basement membrane
3.) Foot processes of podocytes
Sympathetic nervous system control of GFR
When blood pressure falls, norepinephrine released by sympathetic nerve fibers and epinephrine released by adrenal medulla causes vascular smooth muscle to constrict, increasing peripheral resistance and brining blood pressure back up toward normal.
Renin-angiotensin-aldosterone mechanism of GFR
Body's main mechanism for increasing blood pressure. Without adequate blood pressure GF is not possible.
Low blood pressure causes the granular cells of the juxta to release renin. Renin causes secretion of angiotensin 2 which increases secretion of aldosterone which leads to increase in Na+ reabsorption which increases blood volume and therefore blood pressure.
OR Angio 2 increases peripheral resistance (vasoconstriction) which increases blood pressure.
inhibits urine output. ADH makes the principal cells of the collecting ducts more permeable to water causing aquaporins to be inserted into their apical membranes.
Role is to increase blood volume and therefore blood pressure. As a result, little or no Na+ leaves the body in urine. Fine-tune reabsorption of the remaining Na+. Decreased blood volume or blood pressure or high K+ concentration can cause the adrenal cortex to release aldosterone into the blood.
ANP (atrial natriuretic peptide)
In contrast to aldosterone (conserves Na+) ANP reduces blood Na+ to decrease blood volume and therefore blood pressure.
PTH (parathyroid hormone)
Acting primarily at the DCT. PTH increases the reabsorption of Ca2+
Tubular secretion is important for?
1.) Disposing of substances such as drugs
2.) Eliminating undesirable substances or end products (urea and uric acid)
3.) Ridding the body of excess of K+
4.) Controlling blood pH