Renal structure + function Flashcards
renal refers to kidney
whata re the functions of the kidney?
Functions of kidney:
* maintains body fluids e.g. reabsorption of water
* maintains electrolyte balances
* eliminates waste
* regulates acid-base conditions
what percentage of cardiac output reaches the kidneys?
What percentage of cardiac output reaches the kidneys: 20%
what is the difference between juxtamedullary nephrons and cortical nephrons?
Juxtamedullary nephrons: have loops of Henle that extend deep into the medulla
Cortical nephrons= loop of Henle does not extend deep into medulla
what is the glomerulus
the network of capillaries that resides in the Bowman’s capsule that functions as a filtration unit of kidney. The glomerular function ensures that essential plasma proteins are retained in blood and the filtrate is passed on as urine
n.b. the glomerulus originates from the afferent arteriole {branch of the renal artery}
the efferent arteriole is the one EXITING the bowmans capsule;
(renal) afferent arteriole is more dilated than the efferent; allowing for what?
(renal) afferent arteriole is more dilated than the efferent; allowing for a larger blood pressure in the glomerulus at the kidneys compared to other organ sites
in between the glomerulus + bowman’s capsule there are [____]
in between the glomerulus + bowman’s capsule there are PODOCYTES which are additional layers of filtration= the podocytes make up the basement membrane;
Podocytes form the glomerular filtration barrier together with the opposing monolayers of fenestrated endothelium in the vascular space 12 and glomerular basement membrane (GBM) in between
which fenestrations{gaps} are smaller
*capillaries in glomerulus
*podocytes in glomerulus
Capillaries in glomerulus are fenestrated (have gaps); allows lil moelcules through ,however, the gaps in podocytes are much smaller (so 2 levels of filtration
what is the glomerular filtration rate + how do we use it for diagnosis of kindey disease
Glomerular filtration rate
eGFR: estimate GFR. A calculation used to estimate how well your kidneys are filtering certain agents.
eGFR based on serum creatinine, age, race, & sex
WARNING: Possible inaccurate estimates of GFR, especially in early stages of kidney disease
In adults, the normal eGFR number is usually more than 90 ml/min. eGFR declines with age, even in people without kidney disease
n.b. the lower the eGFR number= the greater the extent of kidney disease
Explain the mechanism of fluid and solute reabsorption in the proximal convoluted tubule, loop of Henle and distal nephron
-
Proximal Convoluted Tubule (PCT)
* Main Function: Reabsorbs about 60-70% of the glomerular filtrate.
* Mechanisms:- Sodium Transport: Sodium (Na+) ions are actively pumped out of the tubular fluid by Na+/K+ ATPase pump into the interstitial fluid + then into the peritubular capillaries, which drives most other reabsorption processes.
- Water Follows Sodium: Water reabsorption happens passively due to osmosis, following the sodium.
- Nutrient Reabsorption: Glucose, amino acids + bicarbonate are almost completely reabsorbed here via transport mechanisms linked with sodium.
-
Loop of Henle
* Descending Limb: Allows water to exit into the surrounding more concentrated tissue fluid, increasing the filtrate’s solute concentration. Primarily permeable to water but not to solutes. As the filtrate moves down this limb, water exits the tubule by osmosis into the hyperosmotic medullary interstitium, leading to an increase in the concentration of the tubular fluid.
* Ascending Limb: Actively pumps out sodium, potassium, and chloride, but is impermeable to water, which helps create a concentration gradient in the kidney’s medulla. This segment is impermeable to water but actively transports ions such as sodium, potassium, and chloride out of the tubule. The thick ascending limb, in particular, uses active transport mechanisms (via the Na-K-2Cl cotransporter) to create a hypo-osmotic tubular fluid and contribute to the osmotic gradient in the medulla. -
Distal Nephron (Distal Convoluted Tubule and Collecting Duct)
* Distal Convoluted Tubule (DCT): Continues to reabsorb sodium (controlled by aldosterone) but at a reduced rate compared to the PCT. This is mediated by sodium chloride cotransporters (NCCs)
* Collecting Duct:Adjusts water and sodium reabsorption based on the body’s needs, heavily influenced by ADH and aldosterone.- ADH: Increases water permeability, enhancing water reabsorption.
- Aldosterone: Boosts sodium reabsorption and potassium secretion.
Hormonal Regulation
* Aldosterone: Increases sodium reabsorption and potassium secretion in the distal nephron.
* Antidiuretic Hormone (ADH): Increases water reabsorption in the collecting duct, making the urine more concentrated.
These mechanisms are crucial for the kidneys’ role in maintaining fluid balance, electrolyte levels, and removing wastes from the body.
Describe acid-base homeostasis maintained by kidneys
The kidneys play a critical role in maintaining acid-base homeostasis in the body, which involves the regulation of the pH level of the blood. The normal pH range of blood is tightly regulated between 7.35 and 7.45. Here’s how the kidneys contribute to maintaining this balance:
- Bicarbonate Reabsorption
The kidneys reabsorb bicarbonate (HCO3-) from the urine. This is the primary method of acid-base regulation and occurs mostly in the proximal convoluted tubule (PCT).
For each bicarbonate ion reabsorbed, a hydrogen ion (H+) is secreted into the urine, preventing the blood from becoming too acidic. - Hydrogen Ion Secretion
The kidneys secrete H+ into the urine, which binds to urinary buffers like phosphate (as H2PO4-) and ammonia (to form NH4+), and is excreted.
This process takes place in the PCT, the distal convoluted tubule (DCT), and the collecting ducts. - Generation of New Bicarbonate
When there’s an excess of acid in the body, the kidneys can produce new bicarbonate ions, which are added to the blood. This helps to neutralize the excess acid.
The generation of new bicarbonate is linked with the secretion of H+ into the urine since the creation of one bicarbonate molecule is dependent on the excretion of one H+. - Excretion of Acidic or Basic Urine
Depending on the body’s requirements, the kidneys can adjust the acidity or alkalinity of the urine.
When the blood pH is too low (acidosis), the kidneys excrete more H+ ions, leading to acidic urine.
When the blood pH is too high (alkalosis), the kidneys excrete less H+ ions, leading to more basic urine.
Hormonal Influence
Aldosterone can affect acid-base balance by increasing sodium reabsorption (which is often accompanied by H+ secretion) in exchange for potassium in the collecting ducts.
Respiratory Compensation
Although primarily a function of the lungs, respiratory compensation can affect renal function. Changes in breathing rate can lead to increases or decreases in CO2 excretion, which can influence the amount of bicarbonate in the blood, since CO2 reacts with water to form carbonic acid, which can dissociate into H+ and bicarbonate ions.
In summary, the kidneys maintain acid-base homeostasis by regulating the reabsorption of bicarbonate, the secretion of hydrogen ions, and the generation of new bicarbonate. These processes collectively ensure that the body’s pH remains within a narrow and optimal range.
what is osmotic concentration? units its measured in?
Osmotic concentration = Measure of solute concentration, defined as number of osmoles of solute per litre
where is ADH (anti-diuretic hormone) made + stored
what is function of ADH
Antidiuretic hormone/ADH aka vasopressin is made by a part of the brain called the hypothalamus and is then stored + secreted into the blood by the posterior pituitary gland.
fun fact: Certain types of tumors {e.g. Macroadenomas can put pressure on the pituitary gland} may release high amounts of antidiuretic hormone, which can cause low levels of sodium in the blood and the body to retain water.
function of ADH:
When your body needs to conserve water, perhaps if you’re dehydrated or if you haven’t drunk enough fluids, ADH levels rise. The kidneys respond to this hormone by reabsorbing more water back into the blood. This makes your urine more concentrated and decreases the amount of urine produced, helping to prevent further water loss.
On the other hand, when you have plenty of water in your body, ADH levels fall, and the kidneys reabsorb less water. This results in the production of more dilute urine, allowing your body to get rid of excess water.
define diuresis
diuresis= an increase in the amount of urine made by the kidney and passed from the body
what part(s) of the nephron is found in the cortex of the kidney vs the medulla
The glomerulus and proximal + distal convoluted tubules of the nephron, as well as thick descending limb are located in the cortex of the kidney
while the collecting ducts +thin limb loop of henle are located in the pyramids of the kidney’s medulla
n.b. thick ascending limb of the loop of Henle travels through both cortex + medulla of kidney
