Biol 226 (A&P II) Exam #5 Renal Physiology Review

Kidneys

This organ functions to (1) regulate the composition and volume of body fluids, (2) excrete and remove metabolic waste products, (3) produce erythropoietin to regulate erythropoiesis, (4) regulate and maintain MAP by controlling fluid volume of blood, and (5) regulate calcium absorption with the use of parathyroid hormone and activation of vitamin D.

Urine

This is the product of the kidneys functioning to regulate the composition and volume of body fluids, but the function of kidneys is not to form this

Cortex

This is the surrounding outside region of the kidneys that contains renal corpuscles

Medulla

This is the region towards the center of the kidneys that contains the renal pyramids and collecting ducts

Arcuate arteries and veins

(1)These blood vessels run right along the border of the renal cortex and the renal medulla. (2) These branch off and form the cortical radiate arteries and veins

Renal corpuscle

(1) This is the site where substances leave the blood vessels and enter into a series of tubules which leads to production of urine. (2) This is made up of the glomerulus and the glomerular capsule

Glomerulus

This is a mass of capillaries where substances filter out of the blood coming from the afferent arterioles. These filtered substances then enter the glomerular capsule

Afferent arteriole

This vessel delivers blood supply to the glomerulus

Efferent arteriole

This vessel delivers blood filtered in the glomerulus to the peritubular capillaries. This is the pathway for blood exiting the glomerulus

Glomerular capillaries

These structures are present in the glomerulus of the renal corpuscle where filtration takes place

Glomerular capsule

This structure (1) surrounds the glomerular capillaries and (2) is a tubular structure that captures the filtrate leaving the glomerulus where it enters the tubule system. (3) This is the beginning of the tubule structures

Proximal convoluted tubule

This is the first portion of the tubule system closest to the renal corpuscle

Nephron loop

This structure is made up of the descending and ascending limbs that go from the cortex into the medulla where there is a 180° turn, eventually ending up back in the cortex

Distal convoluted tubule

This is the twisted portion of the tubule system further away from the capsule that dumps into a collecting duct

Collecting duct

This structure (1) has many distal convoluted tubules that feed into it, (2) it connects to minor and major calyces which lead to ureters, and (3) it collects components of the urine produced by the nephrons which will eventually end up in the urinary bladder

Peritubular capillaries

(1) These vessels surround the kidney tubules and allow secretion and reabsorption in certain areas. (2) This is the second capillary system of the kidneys after the glomerulus

Vasa recta

These are a series of blood vessels that surround the nephron loop and deal with reabsorption

Renal artery

This blood vessel is the main source of blood for the kidneys and branches into interlobar arteries

Interlobar arteries

These arteries divide the medulla of the kidney into sections and eventually branch into arcuate arteries

Cortical radiate arteries

These blood vessels branch off of arcuate arteries and eventually form the afferent arterioles that supply the glomerulus with blood

Cortical nephrons

These nephrons (1) make up 80% of the total nephrons, (2) are located high up in the cortex, and (3) have relatively short nephron loops

Juxtamedullary nephrons

These nephrons (1) make up 20% of all nephrons in humans, (2) they are located in the cortex close to the border between the cortex and medulla, and (3) they have very long nephron loops

Glomerular filtration

(1) This is the first step in urine formation that is a passive process and is selective by size only. (2) The only place this takes place is in the glomerulus. (3) The substances resulting from this exit the glomerulus and enter the capsule which is part of the tubule system

Tubular reabsorption

(1) This can be an active or passive process that transfers substances from the tubules into the blood. Substances present in the filtrate that enter the tubule system can be returned to the bloodstream. (2) This takes place between the tubules (proximal convoluted, distal convoluted, and nephron loop) and the peritubular capillaries or the vasa recta

Tubular secretion

(1) This is an active process requiring ATP that removes substances from the bloodstream and allows them to enter the tubules. (2) This only takes place between the distal and proximal convoluted tubules and the peritubular capillaries. (3) Components in the blood that entered the glomerulus but could not be filtered exit through the efferent arteriole and are then transferred from the bloodstream into the tubules

Urine

Substances from glomerular filtration - substances recovered from tubular reabsorption + substances lost through tubular secretion = product of __________

Glomerular capillary hydrostatic pressure

(1) This is the hydrostatic pressure of blood inside the glomerulus that is the main force driving the movement of substances by filtration through the glomerular capillary wall. (2) A large amount of this creates a high outward pressure

Glomerular capillary osmotic pressure

(1) This is created by the osmotic pressure of proteins in the blood opposing the filtration of blood. (2) This produces a significant inward pressure, but since the glomerulus only allows substances to filter outward into the capsule, no substances filter back into the glomerular capillaries

Capsular hydrostatic pressure

(1) This is the fluid pressure from what has already filtered into the capsule that helps determine what else can be filtered since swelling is not possible. (2) This is normally kept low because the ureters carry out peristalsis, pulling filtrate away from the capsule and through the tubules, eventually reaching the collecting duct. (3) This opposes filtration of substances out of the glomerulus due to the fluid pressure of filtrate already in the capsule providing inward pressure

Net filtration pressure outwards from the glomerulus

High glomerular capillary hydrostatic pressure creates outward pressure in the glomerulus. There is significant inward pressure from glomerular capillary osmotic pressure as well as some inward pressure from capsular hydrostatic pressure. The result of this is net filtration pressure (Inwards / Outwards) from the glomerulus into the capsule

Glomerular filtration rate

(1) This is the rate at which volumes of blood are filtered by the glomeruli. (2) It is directly proportional to net filtration pressure, and (3) glomerular hydrostatic pressure is normally the most important factor in determining net filtration pressure and this

Glomerular hydrostatic pressure

This pressure is normally the most important factor that determines net filtration pressure and glomerular filtration rate

Autoregulation

(1) This is how glomerular filtration rate is controlled by the autonomic nervous system with some hormones assisting. (2) The arterioles entering and exiting the glomerulus have smooth muscle surrounding them, so glomerular filtration rate can be adjusted by constricting or relaxing either end of the afferent or efferent arteriole. (3) The autonomic nervous system controls muscular contraction of blood vessels, and the sympathetic division control blood vessel diameter and the removal of the sympathetic influence relaxes the vessels

Afferent arteriole

This is because substances filter in the capsule, so more volume enters the glomerulus through the afferent arteriole than what exits through the efferent arteriole

Between the afferent arteriole and the efferent arteriole, this one has a wider diameter

Increases GFR

The only force favoring filtration is glomerular hydrostatic pressure, so the more blood that enters the glomerulus or that is restricted from leaving the glomerulus (Increases / Decreases ) glomerular filtration rate as glomerular hydrostatic pressure increases

Decrease GFR

If less blood enters the glomerulus or blood exits the glomerulus faster, glomerular hydrostatic pressure is reduced and glomerular filtration rate (Increases / Decreases)

Renin-angiotensin-aldosterone system

(1) This method for controlling glomerular filtration rate is stimulated by low pressure and is designed to raise pressure. (2) Low blood pressure is detected by juxtaglomerular cells or macula dense cells, triggering the secretion of the enzyme renin from the juxtaglomerular cells. Renin converts inactive angiotensinogen into angiotensin I. Angiotensin converting enzyme converts angiotensin I into angiotensin II, and angiotensin II increases blood pressure. The increase in blood pressure is continued in the glomerulus where glomerular filtration rate is increased as glomerular hydrostatic pressure increases

Juxtaglomerular cells

(1) These cells are located next to the glomerulus and have baroreceptors that monitor pressure in the afferent arteriole for blood entering the glomerulus. (2) These cells secrete renin if there is low blood pressure entering the glomerulus or if there is a decreased concentration of ions detected by macula dense cells. Renin is secreted by these cells in response to less filtrate

Macula densa cells

(1) These are a set of cells located on the distal convoluted tubule that are part of the juxtaglomerular apparatus when paired with juxtaglomerular cells. (2) These cells have chemoreceptors on the distal convoluted tubule that pick up the concentrations of ions in the filtrate. This is stimulated by low amounts of filtrate and signaled by low ion concentrations

Juxtaglomerular apparatus

(1) This is made up of the juxtaglomerular cells and the macula densa cells. (2) The baroreceptors and chemoreceptors of these both respond to low pressure resulting from low filtrate. The stimuli picked up from this then causes juxtaglomerular cells to secrete renin. (3) The baroreceptors pick up pressure of the blood in the afferent arteriole and communicate with juxtaglomerular cells - chemoreceptors on the distal convoluted tubule pick up concentration of ions in the filtrate and communicate with macula densa cells

Renin

This is an enzyme coming form juxtaglomerular cells that converts inactive angiotensinogen into angiotensin I

Angiotensin converting enzyme (ACE)

This enzyme converts angiotensin I into angiotensin II

Angiotensin II

This hormone causes (1) vasoconstriction, (2) increased aldosterone secretion, (3) increased ADH secretion, and (4) increased thirst. All things that raise blood pressure. Everything completed by this hormone is done to raise blood pressure, correcting the initial stimulus from low blood pressure that lead to secretion of renin

Angiotensin II

Vasoconstriction (raises pressure), increased aldosterone secretion (maintenance of sodium and water follows, so an increase in volume and pressure), increased ADH secretion (retain volume), and increased thirst (increase volume) are all caused by this hormone. This hormone acts to raise blood pressure

Low filtration pressure

(High / Low) filtration pressure in the kidneys leads to a decreased amount of filtrate, causing renin secretion. Renin activates inactive angiotensinogen into angiotensin I. Angiotensin I is converted to angiotensin II by ACE, and angiotensin II has several functions that raise blood pressure. The increase in blood pressure is continued in the glomerulus where glomerular filtration rate is increased as glomerular hydrostatic pressure increases

Mean arterial pressure (MAP)

The renin-angiotensin system is stimulated by low blood pressure resulting in low filtrate. The system then responds by producing angiotensin II which has several functions that raise blood pressure - This system detects effects from low blood pressure and acts to increase blood pressure. As blood pressure increases, the change plays a role in determining and maintaining __________ __________ __________

Atrial natriuretic peptide (ANP) and ventricular natriuretic peptide (BNP)

(1) These two peptides are stimulated to be released by high blood pressure, leading to the loss of sodium which is then followed by a loss of water due to osmosis, resulting in increased urinary output. This results in a decrease in volume which decreases pressure. (2) These inhibit the renin-angiotensin system and help control mean arterial pressure by lowering pressure

Atrial natriuretic peptide (ANP)

This is secreted by the atria of the heart in response to an increase in blood volume

Ventricular natriuretic peptide (BNP)

This is secreted by the ventricles of the heart in response to an increase in blood pressure

Inhibition of the renin-angiotensin aldosterone system in order to decrease pressure - decrease blood pressure

This decrease in blood pressure helps determine and maintain MAP

What is the main function of atrial natriuretic peptide (ANP) and ventricular natriuretic peptide (BNP)? This is stimulated by high blood pressure and volume being detected

Tubular reabsorption

(1) Since filtration in the glomerulus is selective by size only, some substances that filter and enter the tubule system are needed by the body, so THIS PROCESS is completed primarily through active transport and some passive transport so that these substances can re-enter the bloodstream at the peritubular capillaries or vasa recta. (2) This occurs when substances go form the tubule system into the bloodstream

Primarily active transport

(1) This is the main method for substances to re-enter the bloodstream through tubular reabsorption. (2) Glucose, amino acids, urea, uric acid, and sodium re-enter the bloodstream by this methods

Some passive movement couples active transport

Diffusion of chlorine and osmosis of water are both passive processes

(1) This is the less abundant method for substances to re-enter the bloodstream through tubular reabsorption. (2) Chlorine ions reabsorb by diffusion, following the sodium ions that were actively transported. Water then follows the ion concentrations by osmosis, which is always a passive process

Proximal convoluted tubule

(1) A majority of reabsorption occurs in this structure of the tubule system. (2) A majority (70%) of ion reabsorption occurs here as filtered sodium is reabsorbed by active transport, causing bicarbonate and chlorine ions to reabsorb by diffusion due to their charge differences. (3) A majority (70%) of water reabsorption occurs here by osmosis as the water obligatorily follows the ions that formed the osmotic gradient. (4) All glucose is reabsorbed here through active transport (unless transport maximum is reached). (5) All amino acids are reabsorbed here through active transport (unless transport maximum is reached)

Size

What has just been filtered in the glomerulus is reabsorbed in the proximal convoluted tubule because filtration is not selective besides anything but ___________. We then have to regain substances lost through filtration

They are true waste products, but they need to be reabsorbed to retain water volume. If you were to lose all of these waste products, water would follow and be lost due to osmosis

Why do we have to complete active transport of some urea and uric acid?

Transport maximum

If something has to be reabsorbed by active transport, it needs to have a carrier of some sort. In the body, there are a finite number of carriers, so if all of the carriers are saturated, one reaches a maximum rate at which something can be reabsorbed. This describes what factor that, when achieved, prevents the body from reabsorbing any more of the same substance?

Renal plasma threshold

(1) This is the amount of a substance in the plasma traveling through the kidneys that's level means all the carriers are operating at maximum capacity (saturated). This is the most of the substance that can be reabsorbed, and when this is exceeded, you cannot reabsorb all that was filtered, so some ends up in the urine and is removed. (2) This describes the level of a substance's concentration in the plasma when, if high enough, it exceeds the ability of the kidneys to reabsorb it

Renal plasma threshold

When the amount of sugar present in a diabetic's plasma is beyond this level, sugar cannot be reabsorbed, so it is removed from the body in the urine

Osmotic diuresis

(1) This occurs when glucose ends up in the urine and takes a certain amount of water with it that was not able to be reabsorbed into the bloodstream. (2) This is why people with poorly controlled diabetes may have a large urinary output and are often thirsty. Glucose present in the urine draws water out, and the water is lost through urination and does not enter back into the bloodstream

Transport maximum

This is one of the three methods for establishing a maximum capacity of something that can be reabsorbed in the kidneys. If this maximum amount is surpassed, reabsorption will not occur

Renal plasma threshold

This is one of the three methods for establishing a maximum capacity of something that can be reabsorbed in the kidneys. If this maximum amount is surpassed, the substance will be removed from the body in the urine

Osmotic diuresis

This is one of the three methods for establishing a maximum capacity of something that can be reabsorbed in the kidneys. If this maximum amount is surpassed, it will pull water with it as it is removed from the body.

Tubular secretion

(1) This is an active process that allows substances that were too large for filtration in the glomerulus to be removed from the body through urination. The substances exited the glomerulus through the efferent arteriole, entering the peritubular capillaries where this takes place. (2) This allows the quantity of substances excreted in urine to be greater than the quantity filtered. (3) This process is limited to the proximal and distal convoluted tubules where substances go from the bloodstream into the tubules

Penicillin

Aldosterone and this substance are actively secreted. This is too large to filter, so the quantity filtered is 0, but this is actively transported from the blood into the tubules, so if there is any amount excreted in the urine, it is greater than the quantity filtered (which was 0 because the substance was too large)

Aldosterone

(1) This substance is removed from the bloodstream by tubular secretion and (2) is responsible for the reabsorption of sodium and the secretion of potassium. (3) This substance is triggered by high extracellular potassium, but it is too large to filter and must be secreted

Aldosterone

(1) Plasma is a type of extracellular fluid, and extracellular fluid is supposed to be high in sodium and low in potassium, so we are constantly making sure that extracellular fluid is high in sodium and we are eliminating potassium. Potassium should be high inside of cells, so high extracellular potassium triggers the release of this hormone, getting rid of potassium to maintain appropriate charge differences. (2) This is responsible for the reabsorption of sodium and the secretion of potassium

Tubular secretion

(1) Due to this process, the substances that were not able to filter but need to be removed from the body are removed from the peritubular capillaries into the proximal and distal convoluted tubules. (2) This active process allows the excreted amount of a substance to exceed the amount that filtered

Countercurrent

This mechanism describes how the flow in the nephron loop goes in opposite directions within the ascending and descending limbs

Ascending limb of the nephron loop

(1) This limb of the nephron loop is permeable to ions and/or actively transports ions like sodium out (chlorine ions follow). (2) This side is impermeable to water, so as sodium is transported out of this limb, water cannot follow, and the contents become more dilute

Descending limb of the nephron loop

(1) This limb of the nephron loop is not permeable to ions, but it is permeable to water. (2) Water is drawn out of this limb as it moves towards sodium that was removed from the opposite limb. (3) This limb concentrates the ions in the countercurrent mechanism

The turnaround point of the nephron loop

The turning point in the nephron loop has the highest concentration anywhere in the tubule system because the descending limb is permeable to water. This thens sets the concentration possible in the collecting duct

As we go down the descending limb of the nephron loop, contents get more concentrated as we lose water. Once we reach this point, the contents are the most concentrated. As we go up the ascending limb, the ions leave and water remains, making the contents more dilute. What is this point where the ions are the most concentrated?

Vasa recta

The different permeabilities of the ascending and descending limbs of the nephron loop allow all of the sodium and chloride ions that exit as well as the water that was removed to enter the bloodstream through these blood vessels

Collecting duct

This segment of the tubule system has flow going in the same direction as the descending limb of the nephron loop, so the ion gradient produced by the descending limb is matched by this structure.

As water leaves the descending limb of the nephron loop, it allows one to set an upper limit of how concentrated the urine can be. Whatever the concentration is in the nephron loop at the turnaround point, this upper limit for the concentration is matched by the collecting duct

What allows the concentration of urine?

~97-99%

Since the proximal convoluted tubule and all of the nephron loop reabsorbs more water and salt, by the time we end up in the distal convoluted tubule and collecting duct, what percentage of the original filtrate has been reabsorbed?

Countercurrent multiplier

(1) This concept for the nephron loop states that as the length of the nephron loop increases, the ability to concentrate urine greatly increases. (2) This says a higher concentration of urine is possible with a longer nephron loop. The longer the nephron loop, the more magnified the vasa recta concentration of salt becomes, and the greater the ability of the kidneys to concentrate urine

Countercurrent exchanger

Vasa recta are blood vessels found around the nephron loop that accentuate the saltiness of the area. Salts that come out of the nephron loop enter these blood vessels, and there is a magnification process that increases the saltiness of the vasa recta, helping to increase the amount of water drawn out of the descending limb of the nephron loop. This describes what mechanism of the nephron loop?

Antidiuretic hormone (ADH)

(1) This hormone binds to the distal convoluted tubule and the collecting duct, allowing them to become permeable to water (they normally are impermeable to water). (2) The salt that is transported out of the ascending limb of the nephron loop could draw water out of the distal convoluted tubule and collecting duct only when this hormone is secreted. (3) This determines the final concentration of urine because it controls how much water comes out of the distal convoluted tubule and the collecting duct - this allows us to concentrate urine

- Low levels of ADH cause the distal convoluted tubule and collecting duct to remain relatively impermeable to water. This causes you to not produce very concentrated urine. Low levels of ADH occur when someone is well hydrated

- If the body needs to conserve water, higher levels of ADH are secreted which open up aquaporins on the distal convoluted tubule and collecting duct, allowing loss of water from the urine as it is reabsorbed. This results in more concentrated urine

Explain ADH levels and corresponding urine concentrations

Urea

This is a waste product from protein metabolism

Uric acid

This is a waste product from nucleic acid metabolism

Nitrogenous nonprotein products

Proteins and nucleic acids contain nitrogen, so urea and uric acid are __________ __________ __________ and area way for the body to remove nitrogen

Urea and uric acid

These are two true waste products of metabolism that should be eliminated from the body through urination, but they are reabsorbed in certain quantities to prevent osmotic diuresis

The kidneys function to maintain the composition and volume of body fluids and also get rid of waste products and remove them from the body. If all of the urea and uric acid were removed from eh body, we would lose large amounts of water. We expend ATP to reabsorb a waste product so that we do not lose too much water. The loss of water being prevented is called osmotic diuresis (our bodies can tolerate a certain amount of waste products, and they are included in the composition of body fluid)

Why does our body reabsorb 80% of urea by diffusion and 100% of uric acid actively (the excreted quantity is entirely secreted)?

Urine

(1) This has a composition similar to plasma, but the quantities of substances are different. (2) This is 95% water, (3) it contains non-protein nitrogenous wastes like urea, uric acid, and creatinine, (4) it contains trace amino acids, and (5) it contains various electrolytes

Urine

(1) This is a way of monitoring the composition and volume of body fluids, so we get rid os the number of electrolytes needed to maintain our plasma concentration of electrolytes. (2) This is mostly electrolytes because our body tries to maintain the right composition of salts

Glomerular filtrate

(1) This substance is very similar to blood plasma, but it does not contain proteins since they are too large to filter. (2) This contains glucose, amino acids, urea and uric acid, creatinine, and various ions

Glucose

This substance does not normally end up in the urine unless it is a severely diabetic person. Most of this is reabsorbed back into the body

Creatinine

This is another true waste product besides urea and uric acid that must be removed from the body through urination

Sodium

Most of this ion that is filtered is reabsorbed because it is needed outside the cells

Potassium

This ion is concentrated in the urine because very little amounts of it that filter are reabsorbed

Renal clearance

This is the rate at which a chemical is removed from the plasma

Renal clearance test

This is a way to measure the efficiency of the kidneys in removing a substance from the bloodstream

Inulin clearance test

(1) This type of renal clearance test uses a product from plants that is not reabsorbed or secreted since it is not naturally present in the body and there are no mechanisms to do so. (2) The substance is administered to a patient through an IV to see how long it takes to be removed from the body. (3) A known quantity is administered, and urine is collected and evaluated to determine when all of the substance passed through the kidneys, was filtered, and was collected in the urine

Creatinine clearance test

Creatinine is a waste product that is produced at a dependable rate, so it is used in this test

(1) This type of renal clearance test uses a substance that is naturally produced by the body but is not reabsorbed or secreted. (2) This is measured to test renal clearance if you do not want to administer something through an IV injection to the patient. (3) This is completed by measuring the presence of the substance in the plasma and then collect urine samples for 24 hours. You then measure the amounts of the substance produced in the urine compared to the amount in the bloodstream

Para-aminohippuric acid (PAH) test

PAH is removed form the plasma faster than inulin

(1) This is a type of renal clearance test that uses a substance that is not reabsorbed, but it is secreted. As a result, 100% of this is removed from the plasma. (2) The substance is administered to a patient since the substance is not naturally present in the body. (3) This differs from inulin and creatinine clearance tests because it is secreted, so the test is much faster because the substance is freely filtered, none is reabsorbed, but we can add to the filtered quantity through secretion.

Ureters

(1) These structures transport urine via peristalsis by pulling it away from the kidneys and collecting ducts. (2) These are continuous with all of the tubules and the glomerular capsule, so peristalsis completed by them pulls filtrate away from the glomerulus, through the tubules, and eventually to the urinary bladder. (3) The constant pulling of filtrate out of the capsule by these structures allows capsular hydrostatic pressure to remain relatively low

Urinary bladder

(1) This is the storage place for urine so that it can be eliminated by choice. (2) This is lined with transitional epithelium cells.

Transitional epithelium

(1) The urinary bladder, ureters, and urethra are all lined. with this type of tissue. (2) This is multi-layered and the cells are able to change shape . An example of this is when the bladder empties, the lining of the organ is relaxed and the cells are more of a rounded shape. If the bladder is full, the walls of the organ would be stretched, so the cells lining the inside wall are stretched and have a squamous-like appearance