Urinary system Flashcards
renal hilus
the kidneys medial surface is concave and has a cleft called the renal hilus that leads into the renal sinus
the ureters, blood vessels, and nerves are in the sinus and enter the kidney at the hilus
on top of each kidney is an adrenal gland
Kidneys 3 protective tissue layers
outer renal capsule- inner layer of protective tissue, the renal capsule is a tough fibrous outer skin of the kidney that protects from injury and infection
adipose capsule -outside the renal capsule is a fatty layer that protects the kidney from trauma
renal fascia -outer layer is a dense fibrous connective tissue that keeps the kidney in place inside the abdominal cavity
three distinct regions of the kidney
cortex, medulla and pelvis
outer renal cortex
just inside the renal capsule, is a continuous outer region with several projections called (cortical columns) and extend between the medulla pyramids
within the cortex are glomerular capsule and the distal and proximal convoluted tubule sections of the nephrons along with the associated blood vessels
renal medulla
deeper within the kidney lies the renal medulla that is divided into sections called pyramids that point toward the center of the kidney
located in the medulla are the loop of Henle and the collecting duct sections of the nephrons and associated blood vessels
renal pelvis
the centermost section of the kidney near the renal hilus is the renal pelvis, which constitutes a funnel shaped tube that connects the ureter as it leaves the hilus
the extensions on the pelvis are called calyces
calyces
collect urine which drains continuously into the renal pelvis and subsequently into the ureter. The ureter transports urine to the bladder to be stored
segmental arteries
the renal arteries branch into five segmental arteries that divide further into lobar arteries, then further into interlobar arteries, which pass between the renal pyramids. The interlobar arteries diveide further into the arcuate ateries, whicb divide into the interlobular that feed the afferent arterioles.
interlobar arteries
divide into arcuate arteries which branch into several interlobular arteries that feed into afferent arteries that supply the glomeruli
efferent arterioles
After filtration occurs, the blood moves into efferent arterioles and either the peritubular or vasa recta capillaries and then drains into the interlobular veins which converge into arcurate veins, then interlobular veins, then to the renal vein, which exits the kidney
renal plexus
the kidney and nervous system interact via the renal plexus whose fibers follow the renal arteries to reach the kidney
input from the sympathetic nervous system adjusts the diameter of the Renal arteries, thereby regulating blood flow
ureters
urine is carried from the kidneys to the badder by thin muscular tubes called ureters that begin as a continuation of the renal pelvis and descend at the base of the bladder
ureterovesicle valves
are sphincters located where the ureters enter the bladder.
the downward flow of urine in addition to the ureterovesicle valve help to prevent urine from flowing back toward the kidney
Three layers of the ureters
inner lining made up of traditional epithelium continuous with the kidney lining
middle layer is two sheets of muscles-one longitudinal and the other circular
the outer adventitia layer is fibrous connective tissue
distention on the middle muscle layer by the urine as it enters the ureter causes it to contract and push the urine through the ureter
bladder
is a hollow, muscular, elastic pouch that receives and stores urine excreted by the kidneys before the urethra
in males, the base of the bladder lies in front of the rectum and just behind the pubic symphysis.
In females, the bladder sits below the uterus and in front of the vagina, so the maximum capacity of the bladder is lower in females than in males
transitional epithelium
the cells in transitional epithelium are specialized to stretch, allowing for the organ to increase its volume as it fills, while protecting and covering the underlying tissues.
As the bladder empties they recoil back to their original shape
three layers of the bladder
the outer adventitia is a fibrous connective tissue
the middle layer is a muscular layer known as detrusor muscle with inner and outer longitudinal layers and a middle circular layer
inner mucosal layer composed of transitional epithelium
urethral orifices
both ureters open into the bladder via the urethral orifices
the urethra begins as it opens at the base of the bladder
these three openings occupy the corners of the smooth triangular center region of the bladder called trigone
bladder anatomy
the bladder is very elastic, collapsing into a pyramidial shape when empty
As its filled with urine, the bladder swells and becomes pear shaped, rising in the abdominal cavity
the muscular wall stretches and thins, allowing the bladder to store larger amounts of urine without a significant rise of internal pressure
Rugae
folds in the bladder wall that also extend to help the capacity of the bladder internally.
A moderatley full bladder holds approximately 500 ml of urine
If necessary the bladder can hold 1000 ml, which is stored in the bladder until urination (miticulation) is convenient.
urethra
is a thin walled muscular tube that carries urine from the urinary bladder out of the body.
the mucosal lining of the urethra starts off as transitional cells as it exits the bladder, which become stratified columnar cells near the external urethral orifice
internal urethral sphincter
involuntary controlled internal urethral sphincter is located near the bladder and keeps the urethra closed to prevent urine from leaving the bladder
external urethral sphincter
composed of skeletal muscle, surrounds the urethra as it passes through the pelvic floor
male and female differences of the urethra
the length of the urethra differs in length.
the female urethra is shorter and only carries urine while the male urethra is about 5 times longer and carries both semen and urine from the body
since the female urethra is so short and the external opening is close to the anus, poor hygiene after defication can easily carry fecal bacteria into the urethra. Bacteria enter the urethra and travel up to the bladder causing a UTI
Three regions of the male urethra
prostatic urethra- which runs within the prostatic gland
membranous urethra- which runs within the urogenital diaphragm
spongy (penile) urethra- which runs within the penis and opens to the external urethral opening
nephrons
the basic and structural unit of a kidney is called a nephron of which there are about million present in each kidney
function of nephron
to control the concentration of water and soluble materials for filtering the blood, reabsorbing needed materials, and excreting the rest as urine
The nephron thereby eliminates wastes from the body, regulates blood volume, pH and pressure, and controls the levels of elecctrolytes
what are the two parts of the nephron
glomerular capsule (renal capsule) and the renal tubule
these two parts are connected through the tubule to the associated connecting ducts
glomerular capsule and renal tubule
renal corpuscle -filters blood
renal tubule - reabsorbs needed materials and the collecting ducts carry the remaining material away to be excreted as urine.
the three parts of the renal tubule
the proximal convoluted tubule (PCT)
the loop of henle
distal convoluted tube (DCT)
glomerulus
the renal corpuscle is composed of glomerulus, a network of tiny blood capillaries surrounded by the glomerular capsule (Bowman’s)
glomerular capsule
a double walled simple squamous epithelial cup
glomerulus capillaries of the renal corpuscle
the capillary pores are extremely porous
the capillary endothelium has fenestrations (pores) that allow certain substances to leave the capillaries
the glomerulus capillaries are the only capillaries in the body that lie between two arterioles (the afferent arteriole and the efferent arteriole) rather than between and artery and a vein
afferent arteriole and efferent arteriole
which is fed by the interlobular artery is much larger in diameter than the efferent artery - this difference in diameter causes an extremely high blood pressure in the glomerulus capillaries forcing water and solutes out the blood, thus making filtration possible
filtrate
water and solutes leave the glomerulus, enter the glomerular capsule, and subsequently flow into the renal tubule. Once water and solute leave the blood and enter the glomerular capsule is called filtrate
Cortical nephrons
Most of the kidneys nephrons are cortical nephrons (85%)
these are in the cortex region of the kidney except for a portion of the loop on Henle which extends into the medulla
juxtamedullary nephrons
the remaining nephrons that are not cortical nephrons, pass deeply into the medulla because of their location and their longer loops of henle
proximal convoluted tubule
first section of the renal tubule
is specialized to reabsorb water and many solutes from the glomerular filtrate into low pressure peritubular capillaries that surround the renal tubule as well as secrete unwanted substances
loop of henle
the second section of the renal tubule is the hairpin loop of henle
initially the loop of henle has the descending limb followed by the ascending
the descending limb allows water loss and the ascending limb allows salt loss (NaCl)
distal convoluted tubule
the last section of the Renal tubule
which allows for hormonally controlled reabsorption of water and solutes
mainly responsible for the secretion of unwanted substances
urine
the filtrate is considered urine once it reaches the renal pelvis
collecting ducts
urine passes from several tubules and then drains it the collecting ducts
many collecting ducts converge to form papillary ducts which drain into the calyces and subsequently into the renal pelvis and out the kidneys by way of the ureter
three types of capillary beds
glomerular capillaries, peritubular capillaries, and the vasa recta
glomerular capillaries
glomerulus - are highly coiled capillary beds formed from the afferent arteriole, leaving as the efferent capillaries
because of the porosity and high pressure in the glomerular capillaries, they are specialized for filtration as it forces fluid and solutes out of the blood and into the glomerulus (Bowman’s) capsule
about 99 percent of glomerular filtrate is reabsorbed through the renal tubule and returned to the blood in the peritubular capillary beds, which arise from the efferent tubules as they leave the glomerulus.
the peritubular capillaries
closely follow the renal tubules and drain into the interlobular vein
because of their porosity and low blood pressure- these are adapted for absorption reclaiming water and solutes from filtrate
vasa recta
third set of capillaries -which follow the loop of henle in the juxtamedullary nephrons of the medulla
micturition
urination also called micturition is the act of emptying the bladder
As urine accumulates the rugae flatten and the wall of the bladder thins and stretches allowing the bladder to store larger amounts of urine without significant rise is internal pressure
when does the urge to urinate start?
usually when urine has accumulated around 200 ml, causing distention of the bladder walls, which initiates the vicseral reflex arc
this causes the detrusor muscles to contract and the internal sphincter to relax, forcing stored urine through the internal sphincter into the upper part of the urethra.
a person can consciously resist their initial urge to urinate because the external urethra is voluntarily controlled
as the bladder continues to fill the urge becomes stronger
eventually if the amount of urine reached 100% of the bladders capacity, the voluntary sphincter opens and micturition happens involuntarily
incontinence
the inability to control micturition voluntarily
this is a normal condition in babies and later life with diagnosis such as end stage dementia
can also occur from emotional trauma, pregnancy, nervous system injuries such as stoke or spinal cord injury
urinary retention
the inability to expel stored urine
this is common condition after general anesthesia since the detrusor muscle is slow to regain muscular activity
male urinary retention can occur due to an overgrowth of the prostate gland which narrows the urethra, making micturition difficult
insertion of a rubber tube (catheter) tube in the urethra is necessary to allow urine to empty from the bladder
how many times do kidneys filter blood plasma a day?
The kidneys filter the entire blood plasma volume about 60 times a day and subsequently use 25% of the resting body energy to excrete waste from the body
filtrate quantities
47 gallons of glomerular filtrate containing water, essential ions, and nutrients are removed from the blood plasma daily
by the time filtrate enters the collecting ducts it contains about 0.5 gallons of urine, with the other 99% being returned to the blood
the filtrate loses most of its water, nutrients, and essential ions and contains mostly wastes
what are the three processes must occur for the body to filter all the blood and retain important elements
filtration -takes place in the glomerulus
reabsorption and secretion take place in the renal tubules so excretion can occur
glomerular filtration
filtration in the glomerulus takes place across a very porous membrane that lies between the capillaries and glomerular capsule
filtration at the glomerulus is mechanical and does not require energy
the filtration at the glomerulus depends on the opposing pressures exerted within the glomerular capsule and glomerulus capillary
all fluid pressures discussed are in units of mmHg
hydrostatic pressure (HP)
is the amount of pressure found inside the blood in the capillaries, driving fluid out of the capillaries
the hydrostatic pressure varies from person to person, depending on the blood pressure in the heart and
vessels
If blood pressure rises so does the hydrostatic pressure
colloid osmotic pressure (COP)
also called oncotic pressure is dependent on the amount of protein in the plasma
COP opposes Hydrostatic pressure (HP) by driving fluids back into the capillary beds, drawing water out of the filtrate
COP needs to remain in a normal range between 25-32 mmHg
damage occurs to the glomerulus if the COP goes outside of the normal range
capsular hydrostatic pressure
is the mechanical pressure exerted by the recoil of elasticity inside the glomerular arterioles
this pressure also opposes blood hydrostatic pressure (HP) and drives fluid back into the glomerular capillaries
net filtration pressure (NFP)
is the difference in pressures between outgoing and incoming forces at the glomerulus
the NFP is the pressure with which the filtrate enters the convoluted tubule
how do fluids and solutes move through the membranes?
fluids and solids (such as water, glucose, amino acids, and nitrogenous wastes) are forced out through the membrane by high hydrostatic pressure inside the glomerular capillary
the size of the fenestrations prevents passage of red blood cells and proteins from exiting the filter
total fluid loss inside the capillaries is prevented by the colliod osmotic pressure pressure of the glomerular blood.
the presence of proteins in the capillaries help to maintain the osmotic pressure of the glomerular blood
glomerular filtration rate (GFR)
is the amount of blood filtered by the glomerulus over time
the normal GFR is 120-125 ml/min or 180 L/day due to the huge surface area of the glomerular capillaries, the large degree of filtration membrane permeability, and the moderate net filtration pressure
the GRF is increased by an increase in arterial (and therefore glomerular) blood pressure in the kidneys
what decreases GFR?
The GRF is decreased by an increase glomerular osmotic pressure most often caused by dehydration
why is important to maintain a relatively constant GFR?
it is important for adequate reabsorption of water and other needed substances from the filtrate and filtration of waste
if flow is too rapid, needed substances can not be adequately reabsorbed.
If flow is too slow, nearly all the filtrate is reabsorbed, including most of the waste that should be excreted
three mechanisms that regulate renal flow and therefore regulate the GFR
renal autoregulation, nervous system control, and hormone control
renal autoregulation
Under normal circumstances the GFR is controlled by the kidney itself - this is called renal autoregulaition
the kidney determines its own rate of blood flow by controlling the diameter of the afferent and efferent arterioles
by means of the renal autoregulaiton, the kidney can maintain a constant GFR despite variations in the arterial blood pressure in the rest of the body
when is the renal autoregulations suspended
in times of emergency it becomes necessary to divert blood away from the kidneys to vital organs such as the heart, skeletal muscles, brain
during these times the renal autoregulatory system is suspended by higher nervous system controls.
when the nervous system takes over regulation the afferent arteriole diameter is narrowed by sympathetic nerve fibers
epinephrine
the release of epinephrine by the adrenal medulla (in the adrenal glands) causes a decrease in blood flow and decreases the GRF
constriction of the renal arteries is only to be used for a short time
if the nervous system continues to constrict blood flow to the kidney for long periods of time, kidney damage occurs because of the decreased blood supply to the cells and kidneys
renin angiotensin aldosterone system (RAA)
a hormone control mechanism also controls the renal flow and GRF
the RAA system responds when blood pressure drops too low
angiotensinogen
is a pre-enzyme produced by the liver and freely circulates in the blood
renin
when blood pressure drops too low, renin is released by the juxtaglomerular (JG) cells of the nephron
renin causes constriction of the afferent and efferent arterioles
in addition renin converts angiotensinogen to angiotensin I
angiotensin II
In the lungs angiotensin 1 is converted to angiotensin II which triggers the thirst mechanism in the hypothalamus to cause a person to feel thirsty
drinking water helps increase blood volume and therefore blood pressure
angiotensin II also acts to constrict the body’s blood vessels (vasoconstriction) to increase peripheral blood pressure
once angiotensin II reaches the adrenal cortex it causes the release of aldosterone
aldosterone
aldosterone causes the renal tubules in the nephron to reabsorb more sodium ions, increasing water retention
The RAA system helps reabsorption of more water and sodium from the filtrate
reabsorption
most of the contents of glomerular filtrate that enter the renal tubules get reabsorbed back into the blood by the peritubular capillaries.
the process of fluid and substances moving from the filtrate back to blood is called reabsorption
what would happen if reabsorption does not occur?
the entire plasma would be drained away as urine within an hour
tubular reabsorption process
the tubular reabsorption process occurs by the reabsorbed substances moving through the membrane barriers of the tubules to reach the peritubular capillary blood
reabsorption of water and ions are hormonally regulated and may be passive or active
diffusion is the passive process and active means that the pumps are ATP-driven, requiring energy expenditure
proximal convoluted tube (PCT)
the greatest amount of renal tubular reabsorption occurs in the cells of the PCT.
all glucose and amino acids are actively reabsorbed in the PCT in addition to most water and other ions
65 % Na+
65% water
90% bicarbonate
50% chloride
50% of potassium K+
along with most of the calcium
most of the phosphate
most of the magnesium
are reclaimed in the filtrate
Loop of henle reabsorption
the ascending and descending limb portions of the loop have different characteristics
Water can leave the descending limb but not the ascending limb
Na+ and K+ can leave the ascending limb but the not the descending limb
in the loop of henle another 25% Na +, 15% water, and 40% K+is reabsorbed by the peritubular capillaries to return the ions to the blood circulation
hormonal control that regulate the kidney
they regulate the kidneys ability to form dilute and concentrated urine via controls over channels placed in various places along the nephron
reabsorption after the PCT, and Loop of henle in the Distal convoluted tube
10% of Na+ and Cl-
20% of water
remain in the filtrate once it reaches the DCT
hormonally regulated reabsorption can reclaim nearly all the water and Na+ if necessary
abnormal blood pressure, low blood volume, low Na+ concentration or high K+ concentration in the extracellular fluid are all conditions that can be controlled through ion channels in placed in the DCT and the collecting ducts
secretion
certain substances present in the peritubular capillaries need to be removed through tubular secretion
secretion involves substances entering the filtrate from the surrounding fluid, allowing for the elimination of undesirable substances such as urea
the body also increases the concentration of filtrate and rids itself of extra K+, and drugs such as penicillin
secretion of bicarbonate (HCO3-) and H+controls blood pH
the composition of urine that is excreted
is a combined process of glomerular filtration, tubular filtration, and tubular secretion
homeostasis
urine concentration and volume is altered by the kidneys to maintain homeostasis, or equilibrium state of the total solute concentration of body fluids
the blood vessels (vasa recta and peritubular capillaries and the filtrate through the loop of henle accomplish this through countercurrent flow
countercurrent flow
is the movement of the fluids in the opposite directions through opposite channels
in the nephrons, filtrate flows in one direction through the renal tubules while blood in the adjacent blood vessels flow in the opposite direction
this helps the kidneys maintain an osmotic gradient from the renal cortex to medulla
osmatic gradient
refers to the concentration of solutes inside a solution measured in mOsm/L
isomotic
when the fluid outside and inside have the same have the same osmotic concentrations
urea
is a substance converted from ammonia to be excreted in urine
urea also contributes to high osmolarity of the deep medullary area
concentration of urea is high in the DCT and cortex regions of collecting ducts because the tubules in the cortex are impermeable to it
Medullary ducts are highly permeable to urea so it diffuses out of the ducts and into the medullary interstitial fluid
in the medulla it causes high osmolarity until its concentration inside and outside the ducts are equal
Antidiuretic Hormone (ADH)
a hormone produced by the hypothalamus and stored in the posterior pituitary.
It inhibits urine output
The release of ADH is tied to the degree of hydration, allowing the body to respond to dehydration
dehydration
many factors lead to dehydration, excessive water loss, such as vomiting, diarrhea, sweating
ADH and hemorrhage
it also responds to life threatening circumstances like hemorrhage (blood loss) - a severe hemorrhage causes large amount of blood loss and severe drop in blood pressure.
ADH responds by retaining up to 99% of water in filtrate. Kidneys excrete a small amount of concentrated urine
when ADH is released the osmolarity of the filtrate can be concentrated as much as 1200 mOsm/L
when no ADH is released dilute urine is excreted which can be as low as 65 mOsm/L
Aldosterone
a hormone secreted by the adrenal cortex under control of the RAA system
It acts to place several types of ion channels inside the cells of collecting ducts
Aldosterone and sodium-hydrogen ion pump
Aldosterone increases Na+ reabsorption through the excretion of H+ ions
sodium ions are pumped out of the filtrate and H+ ions are pumped inside for excretion
**because water follows salt, Na+ reabsorption also causes water reabsorption
Aldosterone and sodium-potassium pumps
this is to increase potassium secretion through the sodium-potassium pump
Na+ is pumped out of the filtrate and returned to the blood while potassium (K+) is excreted in urine
what is the overall goal of aldosterone?
To increase the blood volume and therefore the blood pressure when needed
aldosterone release can occur directly (without stimulation from RAA) in response to high K+ levels or low Na+ levels in the extracellular component
however normal triggers from the RAA system are from the CNS, decreased renal filtrate, decreased osmotic pressure, or decreased blood pressure
this aldersterone control system is slow acting, requiring hours to days to take effect
diuretic
are substances that act on the nephrons to increase urinary output
most diuretic drugs decrease Na+ reabsorption, therefore less water is being reabsorbed from the filtrate
types of diuretics
caffeine- is a diuretic that causes renal tubules to increase in diameter, increasing the amount of flow through the tubules
alcohol is another diuretic that inhibits the release of ADH
other diuretics act on different parts of the nephron to cause a greater flow of urine
when filtrate moves at a faster rate through the nephron, it allows for less time for ions to be removed from the filtrate
cardiovascular baroreceptors
also exert control over the nephron to regulate blood volume
these are found in the aortic arch and carotid sinus arteries under the control of the vagus and glossopharyngeal cranial nerves.
these are mechanoreceptors that detect stretch inside the vessels
the two nerves relay info to the medulla, which monitors blood volume to maintain blood pressure
urochrome
the yellow color of urine is caused by urochrom, the principle pigment in urine derived from the metabolic breakdown of hemoglobin
normal urine is pale to deep yellow and clear
Abnormal colors of urine
may result from drugs, food (such as beets or rhubarb), the presence of bile or blood in the urine
cloudiness in urine
due to the presence of pus and may indicate a UTI
pus is the presence of dead white blood cells indicating a recent or current infection in the urinary system
odor of urine
it is slightly aromatic but develops a stinging ammonia oder upon standing because of bacterial breakdown of the urea
asparagus and some drugs cause abnormal odors as do some diseases like diabetes, which imparts a fruity smell due to acetone formed
pH of urine
a normal range is 4.5-8
a diet high in citrus, vegetables, or dairy cause higher (basic pH).
a diet high in protein causes lower acidic pH
urine density
urine has a higher density than water (1.00) since it contains dissolved solutes with its normal density range between 1.003- 1.035 depending on whether it is dilute or concentrated
urine composition
urine contains 95% water, with about 5% solutes of varying amounts
urea is the most abundant solute at 2%
urea is a nitrogenous waste found in urine, which also include uric acid, creatine, and ammonia
other solutes include sodium, potassium, phosphate, sulfate calcium, magnesium, chloride, and bicarbonate ions
abnormal things in urine
abnormal substances in urine include glucose, blood proteins, red blood cells, hemoglobin, white blood cells, bile pigments
urine volume
on average 1.4 Liters for an adult a day
intercellular fluid and extracellular fluid
intercellular is the fluid inside the cell
extracellular is the fluid outside the cell
water is found in two main components -intercellular and extracellular
intercellular fluid accounts for 60 percent of fluid in the body ) -in a 150 pound adult male this is around 25 L
extracellular fluid accounts for 40 percent of fluid in the body (about 15 L in a 150 pound adult male)
two parts of extracellular fluid
plasma and interstitial fluid
plasma is the fluid portion of the blood that contains about 3 L (8% of total body water)
interstitial fluid is the fluid in the microscopic spaces between cells that contains about 12 L (32% of total water in the body)
acid-base pH
refers to the balance of concentration of Hydrogen ions (H+ in the blood)
pH scale
pH scale ranges from 1-14
a pH of 0 is the most acidic, 7 is neutral, and 14 is the most alkaline (basic)
higher concentration of H+ means more acidic - when strong acids dissolve in water they produce H+ ions making the solution more acidic and lowering pH
a lower concentration of H+ means the solution is more basic. when bases dissolve in water. OH- is produced, which combines with H+. the combo of OH- and H+ removes the H+ ions so they are no longer active becoming more alkaline (basic and raising pH)
enzymes
maintaining a constant pH is particularly important for enzymes, specialized proteins that control the rate of metabolic reactions
all proteins need a narrow range of pH in the fluid which they function.
normal pH is 7.35-7.45
alkalosis
if arterial blood pH rises above 7.45, the condition is called alkalosis because the pH is more alkaline than normal (basic)
acidosis
if the arterial blood pH drops below 7.35 this is called acidosis because it more acidic than normal
venous blood and interstitial fluid have lower (more acid) pH because of the acidic materials produced by cellular metabolism
cellular metabolism
chemical reactions inside the cell to maintain life is the principle method through which acids enter the human body.
the blood acidity (pH) is controlled by three main methods: chemical buffer systems, the brain stem respiratory center, and the renal system
anion
negatively charged ion
an example is bicarbonate ion (HCO3-)
cation
is a positively charged ion such as ammonium (NH4+)
Chemical acid base buffers
are composed of combinations of weak acid and its anion or a weak base and its cation
these pairs act to minimize pH changes since the one substance of the pair (weak acid anion or weak basic) reacts with free H+ in the acid to bind it.
this prevents the substance from lowering the pH
the other substance ( weak acid or weak base cation) reacts with the OH- to bind it, preventing a rise in pH
three main chemical buffers systems in the body
these are fast acting, generally responding in seconds
bicarbonate system acts as the main buffer for plasma fluids and interstitial fluids
phosphate system acts as one of the buffers in the urine and intercellular fluid
protein system acts as the main buffer on intercellular fluid
they act within seconds to minimize changes in pH by binding free H+ or free OH-
bicarbonate system
is composed of weak carbonic acid (H2CO3) and bicarbonate (HCO3-)
phospate system
is composed of the weak acid (H2PO4- ) and mono hydrogen phosphate (HPO4 2-)
protein system
provides three times the buffering capacity of all the systems combined due to substantial concentration of proteins in the cells
the protein buffer includes amino acids, hemoglobin, and plasma proteins
respiratory center
CO2 is removed from the blood and O2 is added to the blood under the control of the respiratory center
chemoreceptors
the respiratory center has chemoreceptors in the medulla (of the brainstem that monitor the level of CO2 in the blood
carbonic acid
CO2 reacts reversibly with water to form carbonic acid
carbonic acid dissociates when dissolved in water to form H+ and bicarbonate ions in a series of equilibrium reactions
bicarbonate is the form in which carbon dioxide is transported in the blood plasma
these reactions are carefully regulated by the respiratory center to maintain blood pH
respiratory rate control
the brainstem controls the respiratory rate to increase or decrease depending on the levels of CO2 and therefore pH detected in the blood
the normal range of CO2 is between 35-45 mm
hyperventilation
If blood pH begins to fall (becoming more acidic), the respiratory center is excited causing hyperventilation
this is an increase in respiratory rate, helping to remove additional CO2
within minutes increasing amounts of CO2 is removed, which pushes reaction 1 to the left
removing CO2 uses up H+ causes the pH to rise (become more alkaline and restores correct blood pH
reaction 1
CO2 + H2O <—> H2CO3 <–>H+ +HCO3-
hypoventilation
if blood pH begins to rise (become more alkaline), the respiratory center is depressed causing hypoventilation
during hypoventilation, the respiratory rate slows down, allowing more CO2 to accumulate
reaction 1 shifts to the right forming more H+ ions. The pH falls becoming more acidic and restores the correct blood pH
respiratory center malfunctions
these lead to pH imbalances called respiratory acidosis (due to CO2 retention) or respiratory alkalosis (due to CO2 or removal)
Weak acids
do not significantly contribute to the pH
H+ is tightly bound and cannot dissociate to become free H+
ex. carbonic acid
renal control mechanisms
only the kidneys can remove (rather than just bind) acids and bases from the body
the renal control is much slower acting compared to the respiratory system (1-3 mins), and chemical buffers (less than 1 min) taking hours or days to take effect
however the renal control has a larger impact on the pH level
this is a major system used to manage acid-base imbalances caused by daily metabolic processes or abnormal disease conditions
what is the major renal control mechanism
the major renal acid-base regulating process is by way of excreting or reabsorbing the bicarbonate ion
this acid-base balance by the renal mechanism depends on H+ ion secretion and the conversion of bicarbonate.
H+ secretion through the renal filtrate is in response to the pH of extracellular fluid
what allows for secretion and reabsorption
the renal peritubular capillaries are tiny blood vessels that travel alongside the nephrons allow for secretion and reabsorption between blood and the nephron
conservation of bicarbonate
another important pH regulating mechanism is the conservation of bicarbonate, the most important anion responsible for chemical buffering of the extracellular compartment
bicarbonate can be replenished in the plasma by reclaiming it from the renal filtrate
How does the blood react to alkalosis with bicarbonate?
during alkalosis, renal collecting duct intercalated cells can secrete bicarbonate while simultaneously recovering H+ to lower the pH of blood
respiratory or metabolic disorders
disorders are classified as respiratory or metabolic depending on whether they cause lower CO2 pressure (respiratory) or other cellular process in the body (metabolic)
acidosis
disorders of body’s acid base balance systems cause acidosis ( pH less then 7.35)
in severe acidosis, the blood pH drops below 7.0, and the CNS is markedly depressed causing coma and imminent death
alkalosis
blood pH more than 7.4
in severs alkalosis the blood pH rises above 7.8, and the CNS is markedly excited causing extreme nervousness, muscle contraction, convulsion, and death due to cessation of breathing
respiratory acidosis
is characterized by lower pH because of higher pressure of CO2 (PCO2 > 45mm)
respiratory acidosis is caused by shallow breathing or limited gas exchange
diseases such as cystic fibrosis, pneumonia, emphysema limit gas exchange increasing CO2 in the blood
respiratory alkalosis
is characterized by higher pH because of lower CO2 pressure (PCO2 <35mm)
this is almost always caused by hyperventilation (over breathing such as in the case of a panic attack
renal compensation
respiratory acidosis or respiratory alkalosis causes the renal system to attempt to correct the disorder
metabolic acidosis
is characterized by lower pH (with normal CO2 levels) because of lower HCO3- concentration (bicarbonate)
this is caused by a buildup of acidic metabolic products like acetic acid (from alcohol overdose), lactic acid (byproduct of muscular contractions when exercising), diabetic ketosis, or extreme diarrhea
metabolic alkalosis
is characterized by higher pH (with normal CO2 levels) because of higher HCO3- concentration.
this is caused by vomiting (loss of acidic stomach contents, intake of excess antacids, and constipation (which is caused by abnormal absorption of HCO3-)
the respiratory system works to correct metabolic alkalosis and metabolic acidosis with renal compensation
normal blood serum levels
normal pH - 7.35-7.45
normal PCO2 = 35-45 mm
normal HCO3- = 22-26 mEq/L
