BIO 169 Urinary system + fluid, electrolytes, and acid-base imbalances

Explain the primary anatomic structures and physiologic conditions that affect tubular reabsorption and secretion.

-The barrier that a substance must cross is the simple epithelium of the tubule wall -substacnes can either pass between the epithelial cells of teh tubular wall by paracellular transport or move through teh epithelial cells by transcellular transport -during transcellular transport, a substance must cross two plasma membranes: The luminal membrane that is in contact with the tubular fluid and the basolateral membrane that rests on the basement membrane, the roder depends on if its being reabsored or secreted. -Different transport proteins are embedded within the two membranes. They control the movement of various substances using membrane transport processes that include simple or facilitated diffusion, osmosis, primary and secondary active transport, and vesicular transport -Peritubular capillaries have both low hydrostatic pressure (8 mm Hg), because of the loss of fluid during filtration at the glomerulus, and high colloid osmotic (oncotic) pressure (>30 mm Hg) exerted by protein, because most proteins remain in the blood during filtration. These two important properties facilitate reabsorption of substances from the filtrate within the renal tubule into the peritubular capillaries through bulk flow.

Name the three nitrogenous waste products, and describe the fate of each.

-Urea (3-9 mEq/L), produced from protein breakdown in the live, both secreted and reabsorbed, half is reabsorbed at PCT but secreted back at nephron loop by urea uniporters, 100% of filtered urea is present as it enters DCT.. 5-%is reabsorbed is CT's, and 50% is excreted. -Uric acid, produced from nucleic acid breakdown primarily in liver, both secreted and reabsorbed -Creatinine, produced from metabolism of creatine in muscle tissue, only secreted

Explain what is meant by the countercurrent multiplier that occurs within the nephron loop.

A positive feedback mechanism called the countercurrent multiplier involves the nephron loop and is partially responsible for establishing the salt concentration gradient within the interstitial fluid. Multiplies refers to the positive feedback loop that increases the concentration of salts (Na, Cl) within the IF. Juxtamedullary nephrons (long loops) are primarily involved.

Describe the effects of atrial natriuretic peptide (ANP) on the glomerular filtration rate (GFR).

ANP increases GFR to eliminate fluid from the blood, it is relased from the atrial cardiac muscle cells into the blood in response to stretch of the chambers, increased stretch occurs when there is either an increase in blood volume return or an increase in BP. ANP provides a means of increasing urine output to decrease blood volume and BP to normal.

Describe the stimulus for the release of atrial natriuretic peptide (ANP) and its three actions.

ANP is released in response to increased blood volume and BP, its net effect is to decrease BP.

Define acid-base disturbance and list the four primary types.

An acid-base disturbance occurs with either (a) abnormal changes in respiration, which alter blood concentration of CO, (which forms the weak acid HCO3) or (b) abnormal metabolic changes that alter blood HCO₂ = (a weak base). These changes in the formation of either the weak acid or the weak base can occur to such an extent that the buffering capacity of chemical buffering systems is exceeded (i.e., the chemical buffering systems are unable to either sufficiently absorb or release H‡ to prevent changes in blood pH). Consequently, there is a transient, or temporary, change in blood H‡ concentration, resulting in a change in blood pH beyond the normal range of 7.35 to 7.45. Four major types of acid-base disturbances are distinguished based on two criteria: whether the primary disturbance (which is the cause of the acid-base disturbance) is respiratory or metabolic in nature and whether the pH change is acidic or alkaline. The four categories are respiratory acidosis, respiratory alkalosis, metabolic acidosis, and metabolic alkalosis.

Describe the stimuli that cause release of aldosterone from the adrenal cortex.

Angiotensin II (produced with a decrease in BP) Increased K+ blood plasma levels

Describe the stimuli that cause the hypothalamus to trigger release of antidiuretic hormone (ADH) from the posterior pituitary.

Angiotensin II (produced with a decrease in BP) Low blood volume (detected by sensory input from baroreceptors in heart and vessels) Increased blood osmolarity (detected by chemoreceptors within hypothalamus)

Identify the four hormones that are involved in regulating fluid output, and describe the general effects of each.

Angiotensin II, ADH & Aldosterone: help decrease urine output. These three hormones function to maintain both blood volume and blood pressure. In contrast, ANP increases urine output to decrease both blood volume and blood pressure. The specific mechanisms employed by each of these hormones in regulating fluid output in the kidneys also function in regulating some electrolytes (e.g., Na+).

Trace the fluid from its formation at the renal corpuscle until it exits the body through the urethra.

Blood enters the glomerulus through the afferent arteriole and produces filtrate -> PCT -> nephron loop -> DCT -> collecting tubules -> collecting ducts -> papillary duct -> renal papilla -> minor calyx -> major calyx -> renal pelvis -> ureter -> urinary bladder -> urethra -> excreted

Describe the main location, functions, and means of regulation for each of the common electrolytes.

Chloride ions (CI¯) are a common anion that is normally associated with Na* (as NaCl). It is the most abundant anion in the ECF. Chloride ions are within the lumen of the stomach as hydrochloric acid, function in establishing inhibitory postsynaptic potentials (IPSPs) in dendrites and cell bodies of neurons, and participate in the chloride shift within erythrocytes for transport of carbon dioxide in the form of HCO3. Normal blood plasma Cl concentration is 96-106 mEq/L. Chloride is obtained in the diet, primarily from table salt and processed foods. Chloride is normally lost in the sweat, stomach secretions, feces and urine. The amount lost in urine is primarily dependent upon blood plasma Na*. Chloride levels are directly correlated with Na* levels. Calciqum ions (Ca²*) are the most abundant electrolyte in bone and teeth. Approximately 99% of all body Ca₂- (most commonly as calcium phosphate, Ca3[PO4]2) is stored within the extracellular matrix of these structures, causing them to harden. To prevent hardening or calcification of other tissue, Ca₂-is normally moved by Ca₂- pumps either out of cells or into the sarcoplasmic reticulum within muscle cells. This prevents Ca½- from binding to the abundant PO4 3- within cells. In addition to hardening of both bones and teeth, Ca½‡ is needed to initiate muscle contraction (see section 10.3c) and release neurotransmitters (see section 12.8d); it also serves as a second messenger (see section 17.5b) and participates in blood clotting.Normal blood plasma Ca2+ concentration is approximately 5 mEq/L. In blood plasma, Ca²+ can exist bound to protein such as albumin (about 35%), associated with anions such as PO4³- (about 15%), or in an ionized or unbound state (about 50%). Only the ionized form is physiologically active. Calcium is obtained in the diet from yogurt, milk, soy products, cheese, sardines, broccoli, and dark green leafy vegetables (e.g., kale, spinach). Calcium is lost from the body in urine, feces, and sweat. Phosphate is the most abundant anion in the ICF. Approximately 85% is stored in the extracellular matrix of bone and teeth as calcium phosphate, Ca3(PO4)2. Phosphate is a component of nucleotides of DNA and RNA and of phospholipid molecules within plasma membranes. It serves as an intracellular buffer against pH changes and is a common buffer in urine. Normal blood plasma concentration of PO43- ranges from 1.8 to 2.9 mEq/L. Most PO³- is ionized (about 90%) in blood plasma and the rest is bound to plasma proteins such as albumin. Phosphorus is obtained in the diet from milk, meat, and fish. In addition, many food additives (used to prevent spoilage) and most soft drinks contain PO4³-. 3- Phosphate is regulated by many of the same mechanisms as Ca²+; this is because, as just described, 99% of body calcium is stored in bone, with the majority stored as calcium phosphate. Magnesium ions (Mg²*) are primarily located within bone or within cells. After K+, Mg2+ is the most abundant cation in the ICF. Magnesium participates in over 300 enzymatic reactions, including ATP synthesis, protein synthesis, and enzymatic reactions involving carbohydrate metabolism. It also assists in the movement of Na* and K* across the plasma membrane by the Na+/K+ pump, and it is important in muscle relaxation. Normal blood plasma concentration of Mg2+ ranges from 1.4 to 2.1 mEq/L. Because most Mg2+ is located within cells, this represents only a small fraction of total body Mg2+. In blood plasma, Mg2+ is either in a free, ionized form or bound to protein. The ionized form is physiologically active. Magnesium is obtained in the diet from beans and peas, leafy green vegetables, and other sources and is lost from the body in sweat and urine. Magnesium blood plasma levels are regulated through the kidney.

Name and compare the two types of nephrons and the functional differences between them.

Cortical(85%) and Juxtamedullary (15%) Cortical nephrons have peritubular capillaries and a relatively short nephron loop that barely penetrate the medulla. Juxtamedullary nephrons have a vasa recta, their corpuscles lie adjacent to the corticomedullary junction and have relatively long nephron loops that extend deep into the medulla. They are important in establishing a salt concentration gradient within the interstitial space that lies outside the nephron loop, the collecting tubules, and collecting ducts-- thus allowing for the regulation of urine concentration by ADH.

Identify the substance that is normally produced within the body that may be measured to estimate the glomerular filtration rate.

Creatinine

Explain the autonomic innervation of the kidney.

Each kidney is innervated by both divisions of the ANS, sympathetic nerves extend from the T10-T12 segments of the spinal cord to the blood vessles of the kidney (including the afferent and efferent arteriole, and JG Apparatus) The general effect of sympathetic stimulation of the kidneys is to decrease urine production. Parasympathetic nerves to the kidney extend from the Vagus nerve (CN X) but the effects of the parasympathetic innervation are not known.

List the functions of the kidneys.

Essential processes occur when filtrate is converted into urine like the Elimination of metabolic wastes, Regulation of ion levels, Regulation of acid-base balance, and Regulation of blood pressure.

Describe how we may have conscious control over micturition.

Expulsion of urine is facilitated by the voluntary contraction of muscles in the abdominal wall and breathing muscles as part of the Valsalva maneuver. Upon emptying of the urinary bladder (all but about 10 mL), the detrusor muscle relaxes, and the neurons of the micturition reflex center are inactivated, while those of the storage reflex are activated. If an individual does not urinate at the time of the first micturition reflex, the detrusor muscle relaxes as a consequence of the stress- relaxation response of smooth muscle. The bladder continues to fill with urine, and the micturition reflex is initiated again after another 200-300 mL of urine is added. This cycle continues until there is between 500 mL and 600 mL. At this point, urination occurs without conscious control.

Differentiate among filtrate, tubular fluid, and urine, and list the urinary system structures that transport each of these fluids.

Filtrate is blood that is filtered, made of water and solutes that flowed through the glomerulus and into the capsular space. Tubular Fluid is filtrate (basically plasma - large solutes like proteins) that has entered through the PCT and into the the rest of the nephron. Urine is tubular fluid that has not changed after leaving the collecting ducts, and through the rest of the urinary system.

Define fluid balance.

Fluid balance exists when fluid intake is equal to fluid output, and a normal distribution of water and solutes is present in the two major fluid compartments. I.E fluids in vs fluids out

Compare and contrast the different types of fluid imbalances.

Fluid imbalances with constant osmolarity occur when isotonic fluid is lost or gained. Volume depletion occurs when isotonic fluid loss is greater than isotonic fluid gain. Examples of conditions that result in volume depletion include severe burns, chronic vomiting, diarrhea, or the hyposecretion of aldosterone (a hormone that stimulates both Na+ and water reabsorption in the kidney. Volume excess occurs when isotonic fluid gain is greater than isotonic fluid loss. This typically results when fluid intake is normal, but there is decreased fluid loss through the kidneys (e.g., from either renal failure or aldosterone hypersecretion). In both volume depletion and volume excess, there is no change in osmolarity. Consequently, there is no net movement of water between fluid compartments. Certain types of fluid imbalance involve fluid loss or gain that is notisotonic. Dehydration involves water loss that is greater than solute loss. Dehydration can result from insufficient water intake, profuse sweating,diabetes mellitus, hyposecretion of antidiuretic hormone (ADH—a hormone that stimulates water reabsorption in the kidney, intake of alcohol (which inhibits release of ADH), or overexposure to cold weather. In each case, the greater loss of water than the loss of solutes results in the blood plasma becoming hypertonic (relatively more concentrated). Consequently, water moves between fluid compartments with a net movement of water from the cells into the interstitial fluid and then into blood plasma. Hypotonic hydration, also called water intoxication or positive water balance, involves water gain (or retention) that is greater than solute gain (or retention). Hypotonic hydration can result from ADH hypersecretion, but it is generally caused by drinking a large amount of plain water following excessive sweating. An example is an amateur athlete who runs a marathon and drinks excessive amounts of plain water. Both Na‡ and water are lost during sweating, and drinking water replaces only the water but not the solutes. The blood plasma becomes hypotonic to the other fluid compartments. Fluid moves from blood plasma into the interstitial fluid, and then into the cells. Cells may become swollen with fluid. Fluid sequestration differs from the other fluid imbalances because total body fluid may be normal, but it is distributed abnormally. Fluid accumulates in a particular location, and it is not available for use elsewhere. Edema is an example of fluid sequestration in which there is excess interstitial fluid around cells. Edema is characterized by swelling. Anatomic or physiologic changes that can result in edema are depicted either an increased formation of interstitial fluid or a decreased removal. These altered levels of interstitial fluid are generally a result of abnormal changes in the cardiovascular system (e.g., faulty valves within the heart or blood vessels), blood composition (e.g., decreased plasma proteins), or changes to lymph vessels (e.g., removal or blockage of lymph vessels Other examples of fluid sequestration include hemorrhage (specifically, internal hemorrhage), ascites, pericardial effusion, and pleural effusion. Ascites is the accumulation of fluid within the peritoneal cavity. pericardial effusion is fluid within the pericardial cavity pleural effusion is the accumulation of fluid, sometimes up to several liters, in the pleural cavity as a consequence of lung infections

Explain how fluid moves between the major body fluid compartments.

Fluid movement between compartments occurs continuously in response to changes in relative osmolarity (concentration). This movement happens when the fluid concentration in one fluid compartment becomes either hypotonic or hypertonic with respect to another compartment; water immediately moves by osmosis between the two compartments until the water concentration is once again equal. water always moves by osmosis from the hypotonic solution to the hypertonic solution. This movement of water between the compartments is possible because the plasma membranes and the capillary wall are both permeable to water.

List examples of substances that are freely filtered, that are not filtered, and that are filtered in a limited way.

Freely filtered- small substances like water, glucose, amino acids, ions, urea, some hormones, water soluble vitamins, and ketones. These substances have the same concentration of ions, molecules, and waste in filtrate as in the plasma. Not Filtered- Formed elements like RBC's. WBC's, and platelets, and large proteins cannot pass through and are restricted from becoming part of filtrate. Limited filtration- Proteins of intermediate size are blocked from filtration because of size or negative charge that repels them from the membranes negative charge. Only limited amounts of these substances become part of filtrate.

Define glomerular filtration rate, the factors that influence it, and the factors that it influences.

GFR is an important variable influenced by NFP, it is defined as the rate at which the volume of filtrate is formed, usually as volume per 1 minute. The NFP directly influences the GFR, as NFP increase, GFR also increases, usually as the consequence of HPg. As NFP decreases, GFR decreases. Increase HPg increases NFP which increases GFR, amount of filtrate formed, solutes and water remaining in the tubular fluid, and substances in urine. A decrease would result in decreased filtrate reabsorption.

Compare and contrast the renal processes of filtration, reabsorption, and secretion.

Glomerular filtration passively separates some water and dissolved solutes from the blood plasma within the glomerulus. Water and solutes enter the capsular space of the renal corpuscle due to pressure differences across the filtration membrane. This separate fluid is called filtrate which is basically plasma without the large solutes like proteins. Tubular reabsorption occurs when components within the tubular fluid move by membrane transport processes (e.g. diffusion, osmosis, active transport) from the lumen of the renal tubules, collecting tubules and collecting ducts across their walls and return to the blood within the peritubular capillaries and vasa recta. Generally, all vital solutes and most water that were in the filtrate are reabsorbed, whereas excess solutes, some water, and waste products remain within the tubular fluid. Tubular secretion is the movement of solutes, usually by active transport, out of the blood within the peritubular capillaries and vasa recta into the tubular fluid. Materials are moved selectively into the tubules to be eliminated or excreted from the body. (Secretion results in excretion)

Explain the functions of both granular cells and cells of the macula densa.

Granular cells are modified smooth muscle cells of the afferent arteriole located near its entrance into the renal corpuscle. They have two functions (a) They contract when stimulated either by stretch or by the sympathetic division of the ANS and (b) they synthesize, store, and release the enzyme Renin which is required in the production of Angiotensin I, which is then converted by angiotensin-converting-enzyme (ACE) to angiotensin II. The Macula Densa is a group of modified epithelial cells in the wall of the DCT where it contacts the granular cells. The cells of the MD located only in the tubule wall adjacent to the granular cells of the afferent arteriole, and they are narrower and taller than other DCT cells. The MD cells detect changes in the NaCl concentration of tubular fluid within the lumen of the DCT. They signal granular cells in the afferent arteriole to release renin through paracrine stimulation.

Define glomerular hydrostatic pressure (HPg), and explain why it is higher than the pressure in other capillaries.

HPg is the blood pressure in the glomerulus, it is the driving force that "pushes" water and some dissolved solutes out of the blood within the glomerulus and into the capsular space of the renal corpuscle, this pressure promotes filtration. The HPg (60mmHg) is so high because it is required for filtration to occur, and because the afferent arteriole is larger than the efferent arteriole, forcing more blood in than it can let out, forcing filtration.

Describe how pH is regulated by intercalated cells.

Increased H+ typically occurs when eating a more acidic diet like animal protein and wheat. type A intercalated cells are actively engaged in secreting H (which is excreted in the urine) and synthesizing newly formed HCO3 - (which is reabsorbed into the blood). The result is a decrease in urine pH (i.e., urine is more acidic) and an increase in blood pH (i.e., blood is more alkaline). Decreased blood [H] is more typical of individuals consuming a more alkaline diet, such as is a diet high in fruits and vegetables and little or no animal protein. In this case, type B intercalated cells are active. The action of type B cells is the reverse of that of type A cells. Think of type B intercalated cells as "flipped" type A cells: Type B cells reabsorb H* (which lowers blood pH) and secrete HCO3 (which increases urine pH).

Explain why infants are more susceptible to respiratory acidosis.

Infants are more susceptible to respiratory acidosis because their smaller lungs and lower residual volume do not eliminate CO2 as effectively those of as adults. CO2 accumulates in the blood, with a subsequent increase in carbonic acid (H2CO3).

List both the sources of fluid intake and the categories of water loss.

Ingested water (or preformed water) includes the water absorbed from food and drink taken into the GI tract. On average, this is approximately 2300 milliliters (mL) of fluid intake per day. Metabolic water includes the water produced daily from aerobic cellular respiration and dehydration synthesis It is approximately 200 mL of fluid per day. Water loss can be described in two ways: as either sensible or insensible water loss and as either obligatory or facultative water loss. Sensible water loss is measurable, and it includes fluid lost through feces and urine. I In contrast, insensible water loss is not measurable. It includes both fluid lost in expired air and fluid lost from the skin through sweat and cutaneous transpiration. Obligatory water loss is a loss of water that always occurs, regardless of the state of hydration of the body. It includes water lost through breathing and through the skin (insensible water loss), as well as fluid lost in the feces and in the minimal amount of urine produced to eliminate wastes from the body, approximately 0.5 L (500 mL) per day. Facultative water loss is controlled water loss through regulation of the amount of urine expelled from the body. It is dependent upon the degree of hydration of the body and is hormonally regulated in the collecting tubules and collecting ducts in the nephrons of the kidney.

Describe what is meant by intrinsic and extrinsic controls, and list examples of each.

Intrinsic controls come from within the kindey, which consists of renal autoregulation that maintains GFR at normal levels Renal autoregulation is the intrinsic ability of the kidney to maintain constant BP and GFR despite changed in systemic arterial pressure. The two systems that function this are called Myogenic response and Tubuloglomerular feedback mechanism. Extrinsic which come from the external of the kidney involve both nervous system regulation, which decreases GFR, and hormonal regulation which increases GFR.

Describe how glomerular filtration rate is measured.

Inulin is injected which is neither reabsorbed nor secreted so the amt is equal to that that is filtered. Enough inulin is injected into a subject to achieve a blood plasma concentration of 1 mg/mL. Urine is collected and measured for volume and concentration of the inulin. Additionally, blood is drawn and the plasma concentration of inulin is measured at given time intervals. Glomerular filtration rate is determined by the following formula: GFR = UV/ P where U = concentration of inulin in urine, V = volume of urine produced per minute, and P = concentration of inulin in plasma. Normal adult GFR is 125 mL/min. A lower glomerular filtration rate indicates a decrease in kidney function, and thus it is more likely that nitrogenous wastes and other unwanted substances are accumulating in the blood.

Describe the location of the kidneys in the body.

It is retroperitoneal, floating ribs and adipose tissue help protect it. They are located on the posterior abdominal wall, lateral to the vertebral column. The right kidney is 2 centimeters lower than the left.

Identify the structures that compose the urinary system, and describe the general function of each.

Kidneys, Ureters, Urinary bladder, Urethra the primary function of the kidneys is to filter blood and convert filtrate into urine. the ureters connect the kidney to the urinary bladder, it transfers urine through peristalsis. The urinary bladder is a muscular organ that is a reservoir for urine and connected to the ureters and urethra. The urethra is a tube that connects the urinary bladder to the exterior or the body, the male urethra varies from the female urethra and is made of 3 sections instead of one.

Describe Respiratory compensation.

METABOLIC ACIDOSIS Metabolic acidosis involves decreased HCO3 (a base) caused by either excess formation of H* or excessive loss of HCO3 through diarrhea. Compensation by the respiratory system may occur by increasing the breathing rate. Consequently, higher than normal amounts of CO2 are expired and lower than normal levels of CO2 (volatile acid) remain in the blood. Note that arterial blood gas readings will show lower than normal readings for both (a) HCO3 because of the primary disturbance and (b) CO₂ (because of the respiratory compensation). The lower blood CO2 (which forms a weak acid) compensates for the lower HCO3¯ (a base). If compensation is complete, blood pH has been returned to normal. METABOLIC ALKALOSIS Metabolic alkalosis involves increased HCO3 (a base) caused by either loss of acid (typically from vomiting) or excessive ingestion of antacids (which contain a weak base. Compensation by the respiratory system may occur by decreasing the breathing rate. Consequently, lower than normal amounts of CO2 are expired and higher than normal levels of CO, (volatile acid) remain in the blood. Note that arterial blood gas readings will show higher than normal readings for both (a) HCO3 produced from the primary disturbance and (b) CO2 (from decreased respiration as part of respiratory compensation). The higher blood CO2 (a volatile acid) compensates for the higher HCO3- (a base). If compensation is complete, blood pH has been returned to normal.

Describe the phagocytic function of mesangial cells.

Mesangial cells are modified smooth muscle cells positioned between the capillary loops of the glomerulus. Their phagocytic function is that they engage in phagocytosis of unwanted substances that become trapped on the filtration membrane.

Define both metabolic acidosis and metabolic alkalosis, identify some of the causes of each type of acid-base disturbance, and explain how each occurs.

Metabolic acidosis involves a lower than normal blood pH caused by a decrease in blood HCO3− (a weak base). It is clinically recognized when: arterial blood levels of HCO3- fall below 22 mEq/L. The decrease in arterial blood levels of HCO - may be caused by one of the following • An accumulation of fixed acid, which develops from (a) increased production of metabolic acids (e.g., ketoacidosis from diabetes mellitus, lactic acidosis, acetic acidosis from excessive intake of alcohol; or (b) decreased elimination of acid due to renal dysfunction -An excessive loss of HCO3-, which develops from severe diarrhea (because HCO3- is normally lost in the feces and excessive amounts are lost with diarrhea) The abnormal increase in blood H levels (from increased production of metabolic acids or the kidneys failing to secrete H) binds with HCO3- and lowers blood HCO₂ levels (or there is excessive loss of HCO3- that occurs with diarrhea). The decrease in HCO3- (a weak base) is initially overcome by chemical buffers absorbing excess Hª. However, if the buffering capacity of chemical buffers is exceeded (i.e., reached their limit to absorb H‡, blood H levels increase and blood pH decreases below 7.35, resulting in acidosis. Metabolic alkalosis involves a higher than normal blood pH caused by an increase in blood HCO3—. It clinically recognized when arterial blood levels of HCO3 exceed 26 mEq/L. This increase in arterial blood levels of HCO3- may be caused by one of the following: • A loss of H that occurs (a) from vomiting or prolonged nasogastric suction (due to loss of acidic stomach secretions) or (b) through loss of acids by the kidneys with overuse of diuretics (medications that increase urine output) An increased input of base (e.g., from consuming large amounts of antacids, which contain a weak base) Let us consider how metabolic alkalosis (HCO3- levels above 26 mEq/L) occurs. The abnormal decrease in H‡ (from the loss of HCI from the stomach or by the kidney in response to certain diuretics) increases blood HCO3- levels (or excessive amounts of antacids are ingested). The increased loss of H or gain of weak base in antacids is initially overcome by chemical buffers releasing H‡. However, if the buffering capacity of chemical buffers is exceeded (i.e., reached their limit to release H‡), blood H levels decrease and blood pH increases above 7.45, resulting in alkalosis. Note tha prolonged vomiting is the most comon cause of MA.

Explain how metabolic acid-base disturbances differ from respiratory acid-base disturbances.

Metabolic disturbances result from any acid-base disturbance that does not involve the respiratory system (and changes in the volatile acid HCO3), but instead involve changes in fixed acid that alter blood concentrations of HCO3− (a weak base). These acid-base disturbances include metabolic acidosis and metabolic alkalosis.

Explain the relationship among minor calyces, major calyces, and renal pelvis.

Minor -> Major -> Pelvis There are typically 8-15 funnel shaped minor calyces that merge to form 2-3 major calyces that merge to form the renal pelvis, the renal pelvis merges at the medial edge of the kidney with the ureter.

Describe the difference between a nonelectrolyte and an electrolyte.

Molecules that do not dissociate (or come apart) in solution are called nonelectrolytes. Most of these substances are covalently bonded organic molecules (e.g., glucose). In contrast, an electrolyte is any substance that dissociates in solution to form cations and anions. The term electrolyte refers to the ability of these substances, when dissolved and dissociated in solution, to conduct an electric current. Electrolytes include salts, acids, bases, and some negatively charged proteins.

Explain the relationship between collecting tubules and collecting ducts.

Multiple nephrons drain into each collecting tubule, which then thousands of collecting tubules drain into collecting ducts. Both collecting tubules and collecting ducts project through the renal medulla toward the papilla, numerous collecting ducts then empty into a papillary duct within the papilla where it can drain into the minor then major calyces and then the renal pelvis.

Explain how to calculate the net filtration pressure.

NFP is calculated by: HPg - (OPg + HPc) = NFP 60 - (32 + 18) - 10mmHg

Explain the normal relationship between breathing rate and acid-base balance.

Normally, whether the body is at rest or engaging in exercise, the elimination of CO, from the lungs is equivalent to the CO₂ produced by body cells to maintain a normal blood CO₂ level. Cells typically produce about 200 mL/min of CO2 as a waste product during aerobic cellular respiration when the body is at rest. The resting breathing rate of 12-15 breaths per minute (eupnea) provides the means of eliminating this CO2.

Describe the reabsorption of water, and compare how it is regulated by the actions of aldosterone and antidiuretic hormone.

Of the 180L of water filtered daily, all except about 1.5L is reabsorbed, Approximately 65% of the water in the tubular fluid is reabsorbed in the proximal convoluted tubule. The aquaporins here are permanent components of the luminal membrane and are relatively constant in number. The movement of water out of the proximal convoluted tubule follows Na+ by osmosis, and it is referred to as obligatory water reabsorption. Obligatory water reabsorption occurs in the proximal convoluted tubule (PCT): about 65%. In the nephron loop, approximately 10% of the water is reabsorbed. The amount excreted in the urine is regulated in the collecting tubules (CTs) and collecting ducts (CDs) in response to binding of antidiuretic hormone (ADH). water reabsorption regulated by ADH near the end of the tubule is independent of Nat reabsorption, and as a result, solute concentration of the tubular fluid increases. Tubular reabsorption of water in response to ADH is referred to as facultative water reabsorption.

Name and describe two pressures that oppose HPg.

Osmotic colloid pressure (OPg) and Capsular Hydrostatic pressure (HPc). OPg (32mmHg) is the osmotic pressure exerted by the blood due to the unfiltered dissolved solutes it contains. The most important of these solutes are the plasma proteins (colloid), it opposes filtration because it tends to pull or draw fluids into the glomerulus. HPc (18mmHg) is the pressure due to the amount of. filtrate already within the capsular space. The presence of this filtrate impedes the movement of additional fluid from the blood into the capsular space, thus it also opposes filtration.

Describe the variables that influence K+ distribution.

Potassium is the principal cation within the intracellular fluid (ICF). (a) Normal blood plasma K concentration is 3.5-5.0 mEq/L. Potassium balance is dependent upon both total K and its distribution in the fluid compartments. Total K+ levels are a function of intake from the diet and loss through urine, feces, and sweat. (b) Potassium distribution is altered in response to changes in blood plasma levels of K, changes in H blood plasma concentration, and the presence of specific hormones (e.g., insulin). Insulin decreases blood plasma K* by stimulating the activity of Na*/K* pumps in cells, thus increasing the transport of K* from the ECF into the ICF (hyperkalemia is treated with insulin). The movement of H+ moves opposite to K+ so when H+ decreases, (pH increases) within the ECF(alkalosis) H+ moves into the ECF from the ICF to restablish acid-base balence, K+ moves from the ECF to the ICF(possibly resulting in hypokalemia).

Describe the process by which protein is transported out of the filtrate and into the blood.

Protein is transported from teh tubular fluid in the OCT back into the blood so as not to be excreted in the urine. We use the general term transported here (instead of reabsorbed) because the proteins actually undergo structural changes while being reabsorbed. Protein is moved across the luminal membrane by endocytosis (either pinocytosis or receptor-mediated endocytosis) Lysosomes in these tubule cells then digest the proteins into their amino acid building blocks. These amino acids are released by exocytosis across the basolateral membrane and then enter the blood. Very small proteins, such as angiotensin II, are degraded by peptidases within the luminal membrane and the amino acids are absorbed directly into the tubule cell. Thus, proteins are first degraded into amino acids, which are then absorbed into the blood.

Explain the contribution of urea cycling to the concentration gradient.

Recycled urea, in fact, makes up approximately one-half of the solutes of the interstitial fluid concentration gradient. Urea is removed from the tubular fluid in the collecting duct by urea uniporters: urea diffuses back into the tubular fluid in the thin segment of the ascending limb. Because both the thick segment of the ascending limb and the DCT are not permeable to urea, urea remains within the tubular fluid until it reaches the collecting duct, where it is removed from the tubular fluid. Thus, urea is "cycled" between the collecting duct and the ascending limb of the nephron loop. Some of this urea remains in the interstitial fluid, contributing to its concentration gradient.

List the series of blood vessels for the path of blood flow into and out of the kidney.

Renal artery -> Segmental artery -> Interlobar artery -> Arcuate artery -> Interlobular artery -> afferent arteriole -> Glomerulus -> Efferent arteriole -> Peritubular capillaries/vasa recta -> Interlobular vein -> Arcuate vein -> Interlobar vein -> Renal Vein

Describe renal compensation.

Renal compensation is the physiologic adjustments of the kidney to a primary disturbance and occurs by increased activity of either type A intercalated cells or type B intercalated cells. RESPIRATORY ACIDOSIS Remember that type A intercalated cells excrete H* (acid, which is then excreted in the urine) and synthesizes and reabsorbs HCO3(a weak base) into the blood. However, during renal compensation, this occurs to a greater degree than normal. Consequently, higher than normal levels of H* are excreted, and higher than normal amounts of HCO3 are synthesized and absorbed into the blood. Note that arterial blood gas readings will be higher than normal for both (a) CO2 (due to impaired respiratory function, which caused the primary disturbance) and (b) HCO3(as a result of renal compensation). The higher blood HCO3 (base) compensates for the higher CO2 (which forms the volatile acid H₂CO2). If compensation is complete, blood pH has been returned to normal. RESPIRATORY ALKALOSIS cells. Recall that type B intercalated cells excrete HCO3(a weak base, which is then excreted in the urine) and absorbs H* (acid) into the blood. However, during renal compensation, this occurs to a greater degree than normal. Consequently, higher than normal levels of HCO3 are excreted, and higher than normal amounts of H* are absorbed into the blood. Note that arterial blood gas readings will show lower than normal readings for both (a) CO2 (due to hyperventilation, which caused the primary disturbance) and (b) HCO3¯ (as a result of renal compensation). The lower blood HCO3 (base) compensates for the lower CO2 (which forms the volatile acid H2CO3). If compensation is complete, blood pH has been returned to normal.

Define respiratory acidosis, identify some of the causes of this type of acid-base disturbance, and explain how it occurs.

Respiratory acidosis involves a lower than normal blood pH caused by an increase in blood CO,. It is the most common acid-base disturbance and occurs when the elimination of CO, is less than the amount of CO₂ being produced by the body's cells; thus, CO, blood concentration increases. It is clinically recognized as occurring when the Pcoŋ in the arterial blood (Paco) becomes elevated above 45 mm Hg. Respiratory acidosis is a consequence of impaired respiratory function and can have many different causes, including: Hypoventilation, which is breathing that is too slow or too shallow as a result of (a) disorders of the nerves or muscles involved with breathing or (b) injury to the respiratory center that is perhaps caused by trauma, drug overdose, or poliovirus infection • Decreased airflow caused by (a) an object lodged in the respiratory tract (choking), (b) severe bronchitis, or (c) severe asthma Impaired pulmonary gas exchange due to (a) reduced respiratory membrane surface area (e.g., emphysema) or (b) thickened width of the respiratory membrane (e.g., pneumonia) An individual with impaired respiratory function expires less CO2. Consequently, more CO2 remains within the blood. The additional CO2 drives the carbonic anhydrase reaction (CO2 + H2O → H2CO3 → HCO3¯ + H) to the right, with the most significant change being decreased formation of H+. If the buffering capacity of chemical buffers is exceeded (i.e., reached their limit to absorb H*, and blood pH decreases below 7.35, acidosis results.

Define respiratory alkalosis, identify some of the causes of this type of acid-base disturbance, and explain how it occurs.

Respiratory alkalosis involves a higher than normal blood pH caused by a decrease in blood CO₂. The elimination of CO₂ is greater than the amount of CO₂ being produced by the body's cells; thus, CO, blood concentration decreases. It is clinically recognized as occurring when the Paco, decreases to levels below 35 mm Hg. Respiratory alkalosis occurs due to hyperventilation, which is when the breathing rate or depth is increased to eliminate greater amounts of CO₂ than are being produced by the body's cells. Causes include (a) severe anxiety; (b) hypoxia, which is insufficient oxygen delivery to body cells (e.g., as might occur when climbing to a high altitude where there is a decrease in the partial pressure of oxygen [Po2], in an individual with congestive heart failure, or as a result of severe anemia); and (c) aspirin overdose (a condition that stimulates the respiratory center). During hyperventilation, an Consequently, less CO2 remains within the blood. The decrease in CO₂ individual expires more CO₂ than is being produced by body cells. drives the carbonic anhydrase reaction (CO2 + H2O H2CO3 HCO3 + H*) to the left, with the most significant change being de- creased formation of H. If the buffering capacity of chemical buffers is exceeded (i.e., reached their limit to release H*; and blood pH increases above 7.45, alkalosis results.

Explain why Na+ is a critical electrolyte in the body.

Sodium ions (Na¹) are located almost exclusively within the ECF-in both the interstitial fluid (IF) and blood plasma. Approximately 99% of Na‡ within the body is in the ECF and only 1% in the ICF, a gradient that is maintained by Na+/K¯ pumps. Sodium is the principal cation within the ECF, composing 94% of the cations there. It typically dissociates from either sodium bicarbonate (NaHCO3) or sodium chloride (NaCl). Sodium functions in a number of physiologic processes. For example, sodium functions in depolarization of skeletal muscle, neurons, and cardiac muscle. Sodium also functions in establishing excitatory postsynaptic potentials (EPSPs) in dendrites and cell bodies of neurons and functions in cotransport in kidney tubules. Note that the gain and loss of water relative to the plasma directly influence both blood volume and blood pressure. Thus, retention of Na+ and water increases both blood volume and blood pressure, whereas the loss of Na± and water causes both a decrease in blood volume and blood pressure. For this reason, individuals with high blood pressure may be instructed by their physician to restrict their sodium intake. Although high blood pressure has many causes, and individuals retain Na+ to varying degrees, studies have shown that decreasing dietary intake of Na is effective in lowering blood pressure in some individuals. Sodium imbalance is one of the most common types of electrolyte imbalances. A Na imbalance occurs when the Na concentration is either above the normal levels, hypernatremia, or below normal levels, hyponatremia.

List the six major electrolytes found in body fluids, other than H+ and HCO3-.

Sodium, potassium, chloride, calcium, phosphate asnd magnesium

List substances for which reabsorption is regulated.

Some substances (e.g., nutrients) are recovered completely from the tubular fluid, whereas others (e.g., ions, water) are not completely reabsorbed, resulting in a variable and often small percentage of that substance being excreted into the urine. By varying the amount of a substance excreted, the nephron has a substantial role in regulating the blood level of that substance. A number of substances fall into the category of undergoing regulated reabsorption, including Na+, water, K+. HCO3-, and Ca2+.

Explain what is meant by specific gravity.

Specific gravity is the density (g/mL) of a substance compared to the density of water (1 g/mL). For example, if your urine were composed only of pure water, it would have a specific gravity of 1.000. The average specific gravity of urine is slightly higher, with levels ranging from 1.003 to 1.035 because solutes are normal components of urine. Urine levels vary due to time of day, amount of food and liquids consumed, and amount of exercise. Generally, if you are well hydrated, urine output increases and specific gravity values decrease. A specific gravity value below 1.010 indicates relative hydration, whereas a specific gravity value above 1.020 indicates relative dehydration.

List and explain the stimuli that regulate fluid intake.

Stimuli for activating the thirst center, which occur when fluid intake is less than fluid output, include the following: - Decreased blood volume and decreased blood pressure. When fluid intake is less than fluid output, blood volume decreases, with an accompanying decrease in blood pressure. Renin is released from the kidney in response to a lower blood pressure. Renin (and ACE enzyme) initiate the conversion of angiotensinogen to angiotensin II. An increase of 10-15% in the concentration of angiotensin II within the blood stimulates the thirst center. This mechanism is especially important when extreme volume depletion occurs-for example, when an individual is hemorrhaging. • Increased blood osmolarity. Blood osmolarity most commonly increases from insufficient water intake and dehydration. The increase in blood osmolarity directly stimulates sensory receptors in the thirst center within the hypothalamus and causes the hypothalamus to initiate nerve signals to the posterior pituitary to release antidiuretic hormone (ADH). ADH activates the thirst center. This stimulation of the thirst center occurs with as little as a 2-3% increase in ADH. . - Decreased salivary secretions. A separate mechanism not related to blood volume, blood pressure, and blood osmolarity can also stimulate the thirst center. This additional stimulus is a relatively dry mouth. The oral cavity mucous membranes are not as moist when less fluid is available and saliva production decreases. Sensory receptors in the mucous membranes of the mouth and throat relay sensory input to the thirst center. Stimuli that inhibit the thirst center: Increased blood volume and increased blood pressure. Blood volume and blood pressure increase with the addition of fluid. This rise in blood pressure inhibits the kidney from releasing renin, and the subsequent production of angiotensin II decreases. A decrease in angiotensin II results in a reduced stimulation of the thirst center. -Decreased blood osmolarity. Blood osmolarity decreases when additional fluid enters the blood. In response, the thirst center is no longer stimulated directly, and the hypothalamus decreases stimulation of ADH release from the posterior pituitary. -Increased salivary secretions. When body fluid level is high, salivary secretions increase, and the mucous membranes of the oral cavity and pharynx become moist. Sensory input to the thirst center decreases. -Distension of the stomach. Fluid entering the stomach causes it to stretch, and nerve signals are relayed to the hypothalamus to inhibit the thirst center. (Note that an empty stomach does not stimulate the thirst center; rather, only a stretched stomach wall will inhibit the thirst center.)

Explain the effects of sympathetic division stimulation on the glomerular filtration rate (GFR).

Sympathetic division stimulation is an extrinsic control, Decreasing GFR through SDS is part of the fight-or-flight response and decreases GFR through vasoconstriction of the afferent arteriole and decreased surface area of the filtration membrane. it also sends nerve signals to the kidneys during exercise or an emergency where both afferent and efferent arteriole vasoconstrict to reduce blood flow in the glomerulus and BPg and GFR decrease. Sympathetic stimulation also causes granular cells of the JG apparatus to release renin which produces angiotensin II, which stimulate mesangial cells to contract to decrease the GFR by decreasing the surface area of the filtration membrane.

Explain the ways in which the effects of atrial natriuretic peptide differ from the effects of angiotensin II, ADH, and aldosterone.

Systemic blood vessels. ANP dilates systemic blood vessels, resulting in decreased total peripheral resistance. Systemic blood pressure decreases as a result . Kidneys. ANP causes two separate actions on the kidneys: (a) vasodilation of the afferent arterioles in the kidneys and relaxation of mesangial cells; both increase the glomerular filtration rate, and (b) inhibits Na* and water reabsorption by nephron tubules, resulting in additional loss of Na* and water. Both of these changes increase fluid loss by increasing urine output. Blood volume and systemic blood pressure decrease. Atrial natriuretic peptide also inhibits the release of renin, the action of angiotensin II, and the release of ADH and aldosterone, thus preventing the actions of these hormones.

Describe the primary effects of angiotensin II following its formation.

Systemic blood vessels: Stimulates vasoconstriction of systemic blood vessels to increase total peripheral resistance, which increases systemic blood pressure Kidneys: Decreases urine output from the kidneys as a result of decreased glomerular filtration rate (GFR) in the nephrons by stimulating vasoconstriction of afferent arterioles and contraction of the mesangial cells within the glomerulus; this decreases urine output and helps to maintain systemic blood volume, and thus blood pressure Thirst center: Stimulates the thirst center in the hypothalamus; if fluid intake occurs, this increases blood volume, which increases systemic blood pressure Hypothalamus and adrenal cortex: Stimulates both the hypothalamus (to activate the posterior pituitary to release ADH) and the adrenal cortex to release aldosterone (both described shortly) It is synthesized either when blood pressure is low or the sympathetic division is activated. It causes an increase in peripheral resistance, a decrease in fluid output (which helps to maintain blood volume and blood pressure), and an increase in blood volume (if fluid intake occurs). Consequently, blood pressure increases. Increasing blood pressure is aided by the release of both ADH and aldosterone. As blood pressure returns to within normal homeostatic levels, both renin release and angiotensin II formation are decreased by negative feedback.

Identify and describe the two distinct regions of the kidney and the components of each.

The Cortex contains renal columns that project into the medulla, most nephrons reside in the cortex but also extend into the medulla. The Medulla contains renal pyramids, renal papillas, and meets with the cortex at the corticomedullary junction.

Identify the location and describe the structure of the juxtaglomerular apparatus.

The JG apparatus helps regulate filtrate formation and systemic blood pressure. The main components include Granular cells and Macula Densa cells.

Describe how the kidneys counteract increasing blood H+.

The additional H* must be eliminated (or the excessive loss of base replaced) to maintain acid-base balance. type A intercalated cells of the distal convoluted tubule and collecting tubules and ducts respond to increased blood H* concentration - Secrete H into the tubular fluid (which is then excreted in the urine) -Synthesize new HCO3-, which is then absorbed into the blood Thus, under conditions when blood H* concentration is increasing, kidneys help to maintain a normal blood pH by both eliminating excess H* (acid) into the urine and synthesizing and absorbing HCO3 (base) into the blood. Both processes help to increase blood pH to normal.

Identify the three different capillaries within the kidney and describe the function of each as the site of either the filtration of blood or the exchange of gases and nutrients.

The afferent arteriole supplies blood to the glomerulus where blood plasma is filtered and then exits through the efferent arteriole. Each efferent arteriole branches into a secondary capillary network, the peritubular capillaries or the vasa recta. Peritubular capillaries are associated with and intertwined around the PCT and DCT and primarily reside in the cortex. The vasa recta capillaries are straight and associated with the nephron loop and primarily reside in the medulla. The two capillary beds help the exchange of gases, nutrients, and wastes that occur between the tissues of the kidney and the blood.

Describe how the reabsorption of sodium, potassium, calcium, and phosphate occurs.

The amount of sodium (Na) reabsorbed from the tubular fluid can vary from 98% to 100%. Unlike glucose and other nutrients, Na+ is reabsorbed along the entire length of the nephron tubule, collecting tubules and collecting ducts, with the majority of the Na* (about 65%) reabsorbed in the proximal convoluted tubule. Approximately 25% is reabsorbed in the nephron loop, about 5% in the DCT, and a varying (and regulated) amount in the collecting tubule and collecting duct. In the proximal convoluted tubule, 60% to 80% of the K* in the tubular fluid is reabsorbed by paracellular transport. Approximately 10% to 20% of the K+ in tubular fluid is reabsorbed in the thick segment of the nephron loop ascending limb by both transcellular and paracellular transport. Calcium and phosphate are two substances generally considered together because 99% of the body's calcium is stored in bone, and the majority is stored as calcium phosphate. Approximately 60% of the Ca2+ in blood becomes part of the filtrate and then the tubular fluid. The remainder of the Ca2+ is bound to protein in the blood and is prevented from being filtered. In comparison, 90% to 95% of the PO4³- is filtered as blood passes through glomeruli.

Describe how the bicarbonate buffering system maintains acid-base balance in the ECF.

The bicarbonate buffering system in the blood is the most important buffering system in the ECF. Bicarbonate ion and carbonic acid are the key components of this buffering system. Bicarbonate (HCO3¯) serves as a weak base, whereas carbonic acid (H2CO3) acts as a weak acid. The chemical change to HCO3- and H2CO3 is shown here: Weak base (HCO3-) + Strong acid (H+) -> Weak acid (H2CO3) Weak acid (H2CO3) + Strong base (OH-) -> Weak base (HCO3-) + H2O In summary, the phosphate buffering system is important in buffering against pH changes within cells, whereas the bicarbonate buffering system buffers against pH changes in the blood. Proteins buffer in both cells (intracellular proteins) and within the blood plasma (plasma proteins, hemoglobin).

Explain the changes that occur in response to binding of aldosterone by kidney cells.

The binding of aldosterone to principal cells within the kidney increases the number of Na/K+ pumps and Na channels, so that more Na is reabsorbed from the tubular fluid back into the blood. Water follows the Na by osmosis, K+ is secreted from the blood into the tubular fluid to be excreted. the net effect of aldosterone is (a) reabsorption and retention of both Na* and water and (b) increased secretion and loss of K. The retention of Na* and water decreases urine output to help maintain blood volume and blood pressure. In comparison to ADH, aldosterone stimulates equal amounts of Na* and water reabsorption. Consequently, aldosterone does not change blood osmolarity, but instead blood osmolarity remains constant.

Compare and contrast the functions of the two types of specialized epithelial cells found within collecting tubules and ducts.

The collecting tubules cells are cuboidal-shaped but become very tall columnar cells in the collecting ducts near the papilla. The CT's and CD's contain two types of specialized epithelial cells called Principal Cells and Intercalated cells. Principal cells have cellular receptors to bind both Aldosterone (from the Adrenal Cortex) and ADH (From the posterior pituitary). Intercalated Cells (types A and B) are specialized epithelial cells that help regulate urine pH and blood pH. Type A cells eliminate acid (H+), and Type B cells eliminate base (HCO3-).

Describe the countercurrent exchange system that maintains the concentration gradient.

The descending limb of the nephron loop is permeable to water. It is also impermeable to the movement of salts out of the tubule. Water is moved from the tubular fluid into the interstitial fluid as a result, whereas salts are retained within the tubular fluid. (Note that solute concentration in the tubule increases from 300 mOsm to as much as 1200 mOsm as the tubular fluid moves through the tubule deeper into the nephron loop within the medulla—by the loss of water and retention of salt.) In contrast to the descending limb, the ascending limb is impermeable to water, and it actively pumps salt out of the tubular fluid into the interstitial fluid. As a result, water is retained in the tubular fluid, and salt is moved from the tubular fluid into the interstitial fluid. The solute concentration goes from 1200mOsm to 100mOsm going through the ascending limb.

Define micturition.

The expulsion of urine from the bladder is called micturition, urination, or voiding. Two reflexes are associated with the process of micturition: the storage reflex and the micturition reflex. These reflexes are regulated by the sympathetic and parasympathetic divisions of the autonomic nervous system, respectively.

Compare and contrast the female urethra and male urethra.

The female urethra has a single function: to transport urine from the urinary bladder to exterior of the body. The lumen of the female urethra is lined by transitional epithelium (near its junction with the bladder) and then by nonkeratinized stratified squamous epithelium along most of its length. The urethra is approximately 4 centimeters (about 1.6 inches) long, and it opens to the outside of the body at the external urethral orifice located in the perineum.. The male urethra has both urinary and reproductive functions because it serves as a passageway for both urine and semen (but not at the same time). It is approximately 19 centimeters long (7.5 inches) and is partitioned into three segments: the prostatic urethra, the membranous urethra, and the spongy urethra. The prostatic urethra is approx. 3.5 cm, and the most dilatable portion, it is surrounded by smooth muscle bundles and it is lined in transitional epithelium. The membranous erethra is the shortest and least dilatable portion, it is surrounded by skeletal muscle fibers and is made of stratified or pseudostratified columnar epithelium. The spongy urethra is the longest part at around 15cm and extends to the external urethral orifice, it is lined by pseudostraitified columnar and statified squamous epithelium a the distal end.

Identify and describe the three layers that make up the glomerular filtration membrane.

The filtration is porous, thin and negatively charged, made of three layers. 1) Endothelium of the Glomerulus, it is fenestrated and allows plasma and its dissolved substances to be filtered while restricting larger solutes (RBCs, WBCs, and platelets) 2)Basement membrane of glomerulus, its porous and made of glycoproteins and proteoglycan molecules, it restricts large plasma proteins like albumin. 3) Visceral layer of glomerular capsule, it is composed of podocytes which have footlike processes called pedicells and wrap around the glomerulus to support the capillary wall. The pedicels are separated by filtration slits that are covered by a membrane. The pedicels interlock with one another and restrict passage of small proteins.

Describe the two major body fluid compartments, and compare their chemical compositions.

The fluid in our body is partitioned into two fluid compartments: intracellular fluid and extracellular fluid. Intracellular fluid (ICF), is the fluid within our cells. Approximately two-thirds of the total body fluid is within our cells. (a) Fluid is contained within two major compartments: intracellular and extracellular fluid compartments. (b)Approximately two-thirds of the total body fluid is intracellular fluid (fluid within cells), and the other one-third is extracellular fluid (fluid outside of cells). Approximately two-thirds of the extracellular fluid is interstitial fluid (fluid around the cells), and one-third of the extracellular fluid is plasma within blood vessels K´ and Mg2+ cations, PO3 anion, and proteins are more common in the intracellular fluid than in the extracellular fluid. Na cation and CI and HCO3 anions are more prevalent in the extracellular fluid than in the intracellular fluid. The only significant difference between the interstitial fluid and blood plasma is the presence of protein within the blood plasma, with little or no protein in the interstitial fluid. most abundant ICF Cation: K+ most abundatant ICF Anion: Po43- most abundant ECF Cation: Na+ most abundatant ECF Anion: Cl-

Explain the general role of electrolytes in fluid balance.

The human body fluids contain common electrolytes. The common electrolytes include Na‡, K‡, CI-, Ca²±, PO4³-, and Mg²+ (as well as H‡ and HCO3−). Each electrolyte has unique functions in the body in addition to its general function of contributing to the exertion of osmotic pressure. To carry out these functions effectively, each electrolyte must be maintained within a normal concentration range in the blood plasma.

List the factors that influence the percentage of body fluid and explain its significance relative to fluid balance.

The human body typically contains between 45% and 75% fluid by weight, with an average of about 65%. Individuals who have a lower percentage of body fluid are more likely to experience a fluid imbalance. The specific percentage of body fluid depends upon two variables: the age of an individual and the ratio of adipose connective tissue to skeletal muscle tissue: • Age. Infants have the highest percentage of fluid, at approximately 75% fluid by weight. In contrast, elderly individuals have the lowest percentage of fluid at 45%. decreasing percentage of body fluid is seen with increasing age. • Ratio of adipose connective tissue to skeletal muscle tissue. The percentage of fluid in the body at each age depends upon the ratio of adipose connective tissue to skeletal muscle tissue, because of the difference in water content of these tissues. Adipose connective tissue is approximately 20% water, whereas skeletal muscle tissue is approximately 75% water. Lean adult females are, on average, typically composed of 55% body fluid, whereas lean adult males are, on average, typically composed of 60% body fluid. This difference reflects the relatively lower amounts of skeletal muscle and relatively higher amounts of adipose connective tissue in a lean adult female compared to a lean adult male.

List and describe the four tissue layers that surround and support the kidneys.

The kidney layers consist of the fibrous capsule, the PERInephric fat, the renal fascia and the PARAnephric fat. The fibrous capsule is adhered directly to the kidney, it is made of dense irregular connective tissue, maintains its shape, protects it from trauma and prevents infectious pathogens from penetrating it. The perinephric fat is external to the fibrous capsule and contains adipose connective tissue, it provides cushioning and stabilization. The renal fascia is external to the perinephric fat and is made of dense irregular connective tissue. it anchors the kidney to surrounding structures. The paranephric fat is the outermost layer surrounding the kidney, it is composed of adipose connective tissue and provides cushioning and stabilization for the kidney.

Compare and contrast the myogenic response and the tubuloglomerular feedback mechanism, which are involved in renal autoregulation.

The myogenic response involves contraction and relaxation of smooth muscle in response to changes in stretch, specifically in the response of the smooth muscle in the wall of the afferent arteriole in response to changes in stretch caused by an increase/decrease in systemic blood pressure. a decrease in Systemic BP reults in lower volumes of blood entering the afferent arteriole and reducing the stretch of the smooth muscle in the arteriole wall, the myogenic response is to relax and cause vasodilation and BPg and GFR remain normal. Likewise, it is the same if there is an increase, and vasocontriction occurs. However, if this isnt enough to maintain normal BPg, then BPg and NaCl concentration goes up, signaling the macula densa cells and initiating the tubuloglomerular feedback mechanism. The macula densa cells respond by releasing a signaling molecule that causes paracrine stimulation and bind to and stimulate contraction of smooth muscle cells, causing further vasoconstriction and decreased blood volume, also binding to mesangial cells which decrease the surface area of the filtration membrane and GFR and amount of filtrate return to normal. The TG feedback is like a backup mechanism to the myogenic response in response to increase systemic BP.

Explain the reactions of the phosphate buffering system within the ICF.

The phosphate buffering system is found within intracellular fluid (ICF). It is especially effective in buffering metabolic acid produced by cells because phosphate (PO43) is the most common anion within cells. The phosphate buffering system is also composed of both a weak base and a weak acid. Here hydrogen phosphate (HPO2-) is the weak base and dihydrogen phosphate (H₂PO¯) is the weak acid. The chemical change to HPO²¯ and H2PO¯ is shown here: Weak base (HPO42-) + Strong acid (H+) -> weak acid (H2PO4- ) Weak acid (H2PO4-) + Strong base (OH-) -> Weak base (HPO42-) + H2O As with the protein buffering system, the net result is either a strong acid buffered to produce a weak acid or a strong base buffered to produce a weak base.

Describe the components of the protein buffering system and where and how they help prevent pH changes.

The protein buffering system is a chemical buffering system composed of proteins within both cells and blood. It accounts for about three-quarters of the chemical buffering in body fluids. The amine group (-NH₂) of amino acids acts as a weak base to buffer acid, whereas the carboxylic acid (-COOH) of amino acids acts as a weak acid to buffer base. The chemical change to each group is shown here: Weak base (-NH2) + Strong acid (H+) -> weak acid (NH3+) Weak acid (-COOH) + Strong base (OH-) -> Weak base (COO-) + H2O With the addition of strong acid, shown in equation (1), the weak base (NH) of the protein buffering system binds the H‡ that was added to the solution. This weak base becomes a weak acid (NH₂‡) as a result. The net effect is the elimination of a strong acid (H´) and the production of a weak acid (NH3²). In comparison, the addition of strong base, as in equation (2), causes the weak acid (-COOH) of the protein buffering system to release H‡, and as it does so, it becomes a weak base (COO). The net effect is the removal of a strong base (OH-) and the production of a weak base (COO=). Proteins are components within both cells (cellular proteins) and blood (both plasma proteins and hemoglobin within erythrocytes), and their buffering systems help minimize pH changes throughout the body. The most notable exception is in the cerebrospinal fluid (CSF), where there are no proteins.

Compare and contrast the general concept of physiologic buffering systems and chemical buffering systems.

The regulatory processes of the kidney and respiratory system are calle Physiologic buffering systems.

Identify and describe a renal corpuscle and its components.

The renal corpuscle is the enlarged, bulb portion of a nephron and is made of two structures, the glomerulus and the glomerular capsule. The glomerulus is a thick tangle of capillary loops and blood enter the glomerulus through afferent and efferent arterioles. The Glomerular (Bowmans) capsule is made with two layers, the visceral and parietal layer. The visceral layer is permeable and directly overlies the glomerulus. The Parietal layer is the external layer and is impermeable, made out of simple squamous epithelium. Between the two layers is a capsular space that receives the filtrate that is modified into urine.

Define renal plasma clearance and its importance.

The renal plasma clearance test measures the volume of plasma that can be completely cleared of a substance in a given period of time—usually in 1 minute. We may infer from this test whether a substance is reabsorbed or secreted. Substances that are filtered and secreted have renal plasma clearance values higher than the GFR. This occurs because additional amounts of the substance are secreted into the tubular fluid and excreted in the urine.

Compare and contrast the storage reflex and the micturition reflex.

The storage of urine in the urinary bladder is controlled by both the autonomic and somatic nervous systems. During the filling of the urinary bladder, urine moves through the ureters from the kidneys. Varying nerve signals conducted by sympathetic axons cause smooth muscle cells of (a) the detrusor muscle of the urinary bladder wall to relax, which allows the bladder to accommodate the urine, and (b) the internal urethral sphincter to contract, so that urine is retained within the bladder. This process is referred to as the storage reflex. The skeletal muscle of the external urethral sphincter is also continuously stimulated by nerve signals along the pudendal nerve so it remains contracted. The process of micturition is also controlled by both the autonomic and somatic nervous systems in a toilet-trained individual, and it usually proceeds as follows. 1) When the volume of urine retained within the bladder reaches approximately 200 to 300 mL, the bladder becomes distended, and baroceptors in the bladder wall are activated. 2) These baroceptors send nerve signals through visceral sensory neurons to stimulate the micturition center within the pons. 3) The micturition center alters nerve signals propagated down the spinal cord and through the pelvic splanchnic nerves (which are parasympathetic nerves). 4) Parasympathetic stimulation causes the smooth muscle cells composing the detrusor muscle to contract and the internal urethral sphincter to relax. In infants, urination occurs at this point because they lack voluntary control of the external urethral sphincter. The sensation of having to urinate is relayted along sensory axons to the cerebral cortex.

Define transport maximum and renal threshold.

The transport maximum (Tm) is the maximum amount of a substancethat can be reabsorbed (or secreted) across the tubule epithelium in a given period of time (i.e., the substance's rate of movement). This maximum is dependent upon the number of the transport proteins in the epithelial cell membrane specific for the substance. For example, the T for glucose reabsorption by the glucose transport m proteins is approximately 375 milligrams per minute (mg/min). As long as the tubular fluid contains no more than this amount of glucose passing through a region of the renal tubule every minute, all of the glucose will be reabsorbed. If the tubular fluid contains more than this amount, then the transport proteins are saturated, and cannot move any additional substance. Thus, the excess glucose is excreted in the urine. In comparison, the renal threshold is the maximum plasma concentration of a substance that can be transported in the blood without the substance being excreted in the urine. Thus, renal threshold is the maximum plasma concentration value whereby the transport maximum is not exceeded. Consequently, the substance does not appear in the urine. For example, the renal threshold for glucose in blood plasma is 300 milligrams per deciliter (mg/dL). Above this concentration, the substance is so concentrated in the plasma, and thus in the tubular fluid following filtration, that the transport proteins are saturated. The T is m exceeded, and the substance remains within the tubular fluid and is excreted in the urine.

Identify and describe the location and structure of the three components of a renal tubule.

The tubule makes of the remaining of the nephron and is made of simple epithelium on a basement membrane. It consists of a PCT, nephron loop, and DCT. The PCT is the first section, and originates at at the corpuscle, it is made of simple cuboidal epithelium with tall, apical microvilli (to increase its surface area and its reabsorption capacity). The Nephron loop has an ascending and descending limb, the loop descends partially into the medulla. The thick segments of the of each limb are made of simple cuboidal epithelium, and the thin segments are made of simple squamous epithelium. The DCT starts at the end of the ascending limb of the nephron loop and is made of simple cuboidal epithelium. They have spare, short, apical microvilli.

Describe the structure and function of the ureters, urinary bladder, and urethra.

The ureters are about 25 cm long and is retroperitonealm they originate from the renal pelvis as it exits the hlium of the kidney and enter the base of the urinary bladder, it is composed of three tunics: A mucosa, which is formed by transitional epithelium and is distensible and imperable to urine; the middle muscularis, which is made of a inner longitudinal and outer circular layer of smooth muscle cells, which helps contract to propel urine through the ureters; and an Adventitia, the external layer and composed of collagen and elastic fibers within areolar connective tissue. The urinary bladder is an expandable, musclar organ that serves as a reservoir for urine, it is anteroinferior to the uterus in women, superior to the prostate and anterior to the rectum in males. It is a retroperitoneal organ. I contains a trigone formed by the two openings of the ureters and the urethral opening and functions as a funnel to direct urine. It is made of four tunics, the innermost mucosa, which is made of transitional epithelium and has rugae for greater distension; the submucosa, made with dense irregular connective tissue; the muscularis, which is made of 3 layers of smooth muscle called the detrusor muscle; and the adventitia, the outermost layer made of areolar connective tissue covering the bladder. The urethra transports urine to the exterior of the body, it has an internal and external urethral sphincter. The internal urethral sphincter is made of smooth muscle, is involuntary and ocntrolled by the ANS; the exterior urethral sphincter is made of skeletal muscle, voluntary, and controlled by the somatic nervous system (the frontal lobe).

Explain how the kidneys function in response to decreasing blood H+.

These increase alkaline (or basic) substances within the blood, and blood H* concentration decreases. Blood H* concentration may also decrease with abnormal loss of hydrochloric acid (HCl) as a result of vomiting. The additional base must be eliminated (or the excessive loss of acid replaced) to maintain acid-base balance. type B intercalated cells of the distal convoluted tubule and collecting tubules and ducts respond to decreased blood H* as follows: • Synthesize new HCO3 that is secreted into the tubular fluid (which is then excreted in the urine) . Absorb H into the blood Thus, under conditions when blood H+ concentration is decreasing, kidneys help to maintain a normal blood pH by both synthesizing and secreting HCO3 (base) that is excreted in urine and absorbing H (acid) into the blood. Both processes help to decrease blood pH to normal.

Explain the primary effects of antidiuretic hormone.

Thirst center. ADH stimulates the thirst center in the hypothalamus. If fluid intake occurs, blood volume and blood pressure increase, and blood osmolarity decreases. Kidneys. ADH increases water reabsorption in the kidneys. ADH binds to principal cells of the collecting tubules and ducts, stimulating these cells to increase the number of aquaporins in the tubular membrane. Additional water is reabsorbed through these aquaporins. This helps to maintain blood volume by decreasing fluid loss in urine. In addition, it is important to note that only water is reabsorbed (and not Na* or other solutes). Consequently, ADH increases water retention, which decreases blood osmolarity. Blood vessels. High doses of ADH (which occur, for example, with severe hemorrhage) cause vasoconstriction of systemic blood vessels, which increases peripheral resistance. This action is the reason that ADH is also referred to as vasopressin. Systemic blood pressure increases as a result.

Distinguish between the two categories of acids in the body and name the physiologic buffering system that regulates each category.

Two major categories of acid are present in the body: fixed acid and volatile acid. Fixed acid (also called nonvolatile acid or metabolic acid) is the wastes produced from metabolic processes (other than from carbon dioxide). Examples of fixed acids include lactic acid from glycolysis, phosphoric acid from nucleic acid metabolism, and ketoacids from metabolism of fat. Note that the term fixed acids was given to these types of acids because they are not produced from carbon dioxide, which is volatile and expired by the lungs. Rather, they are nonvolatile acids that are "fixed" in the body. Fixed acid is regulated by the Kidney (type A and B intercalated calls) through the absorption and elimination of HCO3- and H+ Volatile (to evaporate quickly) acid formed within the body is carbonic acid, which is produced when carbon dioxide combines with water, as shown: C02 + H20 <-> H2Co3 (carbonic acid) CO2 + H20 <-> H2CO3 <-> H+ + HCO3- The term volatile acid refers to the fact that carbonic acid is produced from a gas that is normally expired (or "evaporated"). Because CO₂ is readily converted to carbonic acid in the presence of carbonic anhydrase, CO₂ itself is often referred to as the volatile acid. Volatile acid is eliminated by the respiratory system, and the amount of CO2 expired is regulated by respiratory rate and depth.

List the various sources of fixed acid.

Typically, more acid is absorbed from the GI tract because most individuals, at least in the United States, consume a diet rich in animal protein and wheat. These various ingested items contribute H to the blood. Body cells also contribute acid as waste products from metabolic processes. These products include lactic acid, phosphoric acid, and ketoacids. An increase in blood H concentration may also result from the excessive loss of HCO = (a weak base) as a consequence of diarrhea. (Bicarbonate ion [HCO3=] is normally lost in the feces, but excess amounts can be lost when an individual has diarrhea

Explain the reabsorption of nutrients such as glucose.

all glucose should be reabsorbed in the PCT, failure to do so results in glucose in the urine (Glucosuria). Glucose reabsorption occurs in the proximal convoluted tubule. In a healthy individual, 100% of the glucose is reabsorbed. Glucose is transported (1) across the luminal membrane against its concentration gradient-this occurs by secondary active transport via Na*/glucose symporters-and (2) across the basolateral membrane down its concentration gradient by facilitated diffusion via glucose uniporters.

Explain angiotensin II formation.

angiotensinogen is an inactive hormone synthesized and released continuously from the liver. Its activation, which occurs within the blood, is initiated by the enzyme renin. Renin is released from the juxtaglomerular (JG) apparatus of the kidneys in response to either (a) low blood pressure (as detected by decreased stretch of baroreceptors within granular cells or by decreased NaCl detected by chemoreceptors within macula densa cells or (b) stimulation by the sympathetic division. The sequential action of renin and angiotensin-converting enzyme (ACE) (which is bound to the endothelial lining of blood vessels) causes the formation of angiotensin II.

List examples of other substances typically eliminated by kidneys.

certain drugs: antibiotics, aspirin, moprhine, chemotherapy drugs, saccharin, chemicals in marijuana other metabolic wastes: urobilin, and hormone metabolites. Some hormones: Human chorionic gonadotropin (used to detect pregnancy in tests), epinephrine and prostaglandins