A&P II Unit 5

Describe the function of the most prevalent electrolytes found in body fluids.

1) Na+ --> most abundant extracellular cation; critical for electrophysiological processes 2) K+ --> most abundant intracellular cation; critical for the functioning of neurons & the 3 muscle cells 3) Ca2+ --> main component of osseous tissue, stimulate muscle contractions, participate in intracellular signaling, blood clotting, & neuronal synaptic transmission 4) PO4 3- --> also make up inorganic portion of bone, an integral part of the structure of ATP 5) Cl- --> important osmotic particle, involved in production of HCl by the stomach & secretion of bicarbonate by erythrocytes 6) Mg2+ --> activate many enzymes, magnesium salts are important parts of bone tissue

Describe how the renin-angiotensin-aldosterone system, antidiuretic hormone, and atrial natriuretic peptide each work to regulate reabsorption and secretion.

1) aldosterone = increases cells' permeability to Na+ & increases the number of Na+/K+ channels leading to the reabsorption of Na+ from filtrate & secretion of K+ into filtrate; also causes secretion of H+ into filtrate 2) antidiuretic hormone = causes insertion of aquaporins in membranes of cells, causing water reabsorption 3) atrial natriuretic peptide = triggers urinary excretion of Na+, & can inhibit aldosterone & ADH

Describe the buffer systems that help to keep the pH of the body's fluids stable.

1) chemical buffer systems = system that resists changes in pH of the body's fluids, & consists of a weak acid & its conjugate base a) carbonic acid-bicarbonate buffer b) phosphate buffer c) protein buffer 2) physiological buffer systems = actions taken by the respiratory & urinary systems to excrete H+ &/or retain H2CO3 in order to maintain homeostasis of the pH of the body's fluids

Describe the physical and chemical properties of a urine sample.

1) color = colored yellow by the pigment urochrome, which is a byproduct of the breakdown of hemoglobin; more concentrated --> less water --> darker color 2) translucency = should be able to see light through urine; cloudy urine means infection or proteinuria 3) odor = should have a mild odor 4) pH = should be ~6.0, but can range from 4.5-8.0 5) specific gravity = compares amount of solutes in solution to amount in deionized water (1.0); ranges from 1.001 (very dilute urine) to 1.035 (very concentrated urine)

Describe the three major processes in urine formation.

1) glomerular filtration = process by which blood is filtered in the glomeruli of the kidneys 2) tubular reabsorption = process by which water & solutes are reclaimed from the filtrate in the renal tubules & collecting system, & returned to the blood 3) tubular secretion = the process by which solutes are removed from the blood & placed into the filtrate in the renal tubules for excretion from the body

Name the two capillary beds through which blood must pass in the kidney.

1) glomerulus 2) peritubular capillaries

Provide specific examples to demonstrate how the cardiovascular, endocrine, and urinary systems respond to maintain homeostasis of fluid volume, electrolyte concentration, and pH in the body.

CV --> vasoconstriction or vasodilation of blood vessels, induces hypo- or hyperventilation endocrine --> secretion of Ang II, ADH, & aldosterone urinary --> reabsorption & secretion of water & ions

Explain how calcium ion regulation is related to phosphate ions.

calcium & phosphate are both present in hydroxyapatite crystals of bones, & thus, the inorganic portion of bone cannot be present w/o both ions; are regulated by the same hormones (PTH & calcitriol)

Compare and contrast cortical and juxtamedullary nephrons.

cortical nephrons = have short nephron loops; confined to the renal cortex or extend only into the superficial renal medulla; ~80% of nephrons juxtamedullary nephrons = have long nephron loops; dip deeply into the renal medulla; play a role in the production of concentrated urine

Describe the hormonal regulation of electrolyte levels in the plasma.

angiotensin II & aldosterone increase Na+ retention ANP decreases Na+ reabsorption insulin, aldosterone, & epinephrine stimulate uptake of K+ by cells aldosterone also causes K+ secretion in the distal tubule & collecting system only parathyroid hormone triggers osteoclast activity to release Ca2+ from bone tissue & decreases PO4 2- reabsorption vitamin D3 (calcitriol) stimulates Ca2+ & PO4 2- absorption by the small intestine

Compare and contrast the relative concentrations of major electrolytes in intracellular and extracellular fluids.

extracellular fluid --> high amounts of Na+, Cl-, Ca2+, & bicarbonate intracellular fluid --> high amounts of protein, K+, Mg2+, SO4^2-, & HPO4^2-

Distinguish between filtrate, tubular fluid, and urine.

filtrate = fluid resulting from glomerular filtration tubular fluid = the fluid in the tubules of the kidney urine = liquid produced by the kidneys consisting of water, electrolytes, & metabolic wastes

Describe a nephron and explain why it is considered the basic using of filtration.

functional unit of the kidney where blood is filtered & the resulting filtrate is modified (urine)

Describe the relationship of PCO2 and bicarbonate ions to blood pH.

increased PCO2 causes the pH of the blood to become more acidic because the ratio of PCO2 to H2CO3 decreases decreased PCO2 causes the pH of the blood to become more basic because the ratio of PCO2 to H2CO3 increases

Name the veins through which blood leaves the kidney in sequence from smallest to largest.

interlobular (cortical radiate) vein --> arcuate vein --> interlobar vein --> renal vein

List and describe the organs of the urinary system, and their location in the body.

kidneys = paired retroperitoneal organs that filter the blood to remove wastes & maintain fluid, electrolyte, & acid-base homeostasis urinary tract = composed of the 2 ureters, urinary bladder, & the urethra that transport, store, & eliminate urine

List specific conditions that cause the kidneys to produce dilute versus concentrated urine.

low solute concentration --> dilute high solute concentration --> concentrated more water --> dilute less water --> concentrated low ADH secretion --> dilute high ADH secretion --> concentrated

Explain the regulation of urine concentration and volume.

mainly determined by the amount of water present in urine, which is regulated by facultative water reabsorption

Compare and contrast the male and female urinary tracts.

males --> bladder located anterior to the rectum; urethra is ~20 cm & consists of 3 regions: prostatic urethra --> membranous urethra --> spongy urethra; passage for both urine & semen females --> bladder located anterior to the vagina & inferior to the uterus; urethra is shorter & serves exclusively as a passage for urine

Describe the micturition reflex.

micturition is the process of voiding urine from the urinary bladder through the urethra; activated by the micturition reflex that is under control of the PSNS & thus is involuntary 1) urine fills the bladder & stretches its walls 2) stretch receptors send a signal via afferent sensory fibers to the sacral portion of the spinal cord 3) PSNS efferent fibers stimulate the detrusor muscle to contract & the internal sphincter to relax, causing micturition

Explain how the myogenic and tubuloglomerular feedback mechanisms affect the GFR.

myogenic mechanism = an autoregulatory mechanism in blood vessels by which the degree of stretch of the vessel wall triggers a reflex that maintains blood flow to a tissue; vasoconstricts the afferent arteriole & thus decreases GFR tubuloglomerular feedback = a negative feedback loop that controls pressure in the glomerulus; GFR increases --> filtrate volume increases --> increased Na+ & Cl- absorption --> ATP released into interstitial fluid --> ATP converted to adenosine --> vasoconstriction of afferent --> GFR decreases

Explain the role of the countercurrent mechanism in the concentration of urine.

occurs in the juxtamedullary nephrons that establishes a concentration gradient in the medullary interstitial fluid in order to produce concentrated urine 1) countercurrent multiplier system in the thick ascending limb of nephron loops of juxtamedullary neurons establishes the medullary interstitial gradient by pumping NaCl into the interstitial fluid 2) the recycling of urea in the medullary collecting ducts causes continued solute reabsorption, adds to the gradient 3) a countercurrent exchanger in the vasa recta allows perfusion of the inner medulla while maintaining the medullary interstitial gradient

Explain how osmotic pressure is generated, and compare and contrast the roles that hydrostatic and osmotic pressures play in the movement of water between fluid compartments.

osmotic pressure = the force that would need to be applied to a solution to stop water from moving into it by osmosis; OP gradients cause water to move by osmosis toward a solution with higher OP & more solute hydrostatic pressure = the pressure that a fluid exerts on the wall of its container/on cells; HP gradients cause water to move from an area of higher HP to an area of lower HP under normal conditions HP = OP --> no gradient

Describe how and where water, organic compounds, and ions are reabsorbed in the nephron by both passive and active processes.

paracellular route = substances like small ions & water pass between adjacent tubular cells through leaky tight junctions (passive) transcellular route = substance like glucose & amino acids move through tubular cells (mostly passive) facilitated diffusion = carrier protein transports substances w/ concentration gradient primary & secondary active transport = uses ATP & a carrier protein pump to transport substances against their concentration gradient

Name the arteries that supply the kidney, in sequence from largest to smallest.

renal artery --> segmental artery --> interlobar artery --> arcuate artery --> interlobular (cortical radiate) artery

Discuss the concept of compensation to correct respiratory and metabolic acidosis and alkalosis.

respiratory compensation = adjustment of the respiratory rate to compensate for an increase or decrease in the pH of the body's fluids renal compensation = adjustment of the secretion or retention of H+ and/or HCO3- to compensate for an increase or decrease in the pH of the body's fluids *respiratory & metabolic acidosis* --> hyperventilation to remove CO2, retention of HCO3- by kidneys, excretion of H+ by kidneys *respiratory & metabolic alkalosis* --> slow respiratory rate, excretion of HCO3- & retention of H+ by kidneys

Explain how filtration, reabsorption, and secretion determine the rate of excretion of any solute.

substances secreted by renal tubules have a renal clearance greater than their GFR, while substances that are reabsorbed have a renal clearance less than their GFR

Define the glomerular filtration rate (GFR) and its average value.

the amount of filtrate produced in the glomeruli of both kidneys in 1 minute; ~125 ml/min

Relate the anatomy and histology of the bladder to its function.

the bladder sits on the floor of the pelvic cavity & is suspended by a fold of parietal peritoneum; when its empty, its flat/collapsed, but becomes pear-shaped when distended in order to hold urine; does not expand full capacity in females due to position of the uterus; the detrusor muscle & internal urethral sphincter are muscles that help expel urine from the bladder and though the urethra

Explain why the differential permeability of specific sections of the renal tubule is necessary to produce concentrated urine.

thin descending limb is permeable to water but not solutes --> more concentrated filtrate thick ascending limb is permeable to solutes but not water --> less concentrated filtrate early distal tubule is also more permeable to solute than water --> less concentrated filtrate late distal tubule & collecting duct begin facultative water reabsorption so the concentration of the filtrate depends on how much water is reabsorbed more water absorbed --> concentrated urine less water absorbed water --> dilute urine

Describe the fluid compartments, and explain how each contributes to the total body water.

total body water = the total amount of water in the intracellular & extracellular compartments of the body 1) intracellular compartment = the fluid compartment located w/in cells that contains cytosol of intracellular fluid; consists of trillions of microscopic compartments inside cells; cytosol accounts for ~60% of the body's fluids 2) extracellular compartment = the fluid compartment located outside cells that contains ECF; consists of plasma (8%) & interstitial fluid (32%)

Describe the routes of water gain and loss from the body.

*water loses:* (total = 2.5 L) 1) kidneys (urine) = 1500 mL 2) feces = 100 mL 3) skin = 600 mL 4) lungs = 300 mL *water gains:* (total = 2.5 L) 1) liquids = 1500 mL 2) food = 750 mL 3) catabolism = 250 mL

Describe the mechanisms that regulate water intake and output, and explain how dehydration and overhydration develop.

1) obligatory water loss = the amount of urine that must be produced daily irrespective of fluid intake to excrete wastes & other solutes 2) thirst mechanism = drives water intake from liquids & is controlled by the hypothalamus 3) dehydration = a condition characterized by a decreased volume & increased osmolarity; caused by profuse sweating, prolonged diarrhea/vomiting, certain endocrine conditions, & overusing diuretics; water loss decreases the plasma volume, & increases its solute concentration & osmotic pressure 4) overhydration = a condition characterized by an increased volume & decreased osmolarity; results in electrolyte imbalances due to dilution of the ECF

Identify the location(s) in the nephron where tubular secretion occurs.

1) proximal tubule = a significant amount of secretion occurs here: H+ ions, nitrogenous waste products, drugs 2) distal tubule = aldosterone causes secretion of K+ & H+ into filtrate 3) collecting duct = secrete H+ ions into filtrate

Describe the six functions of the kidneys.

1) removal of metabolic wastes 2) maintenance of fluid & electrolyte balance 3) maintenance of acid-base balance 4) maintenance of blood pressure 5) regulation of erythropoiesis 6) perform other metabolic functions

Trace the path of filtrate through the nephron and collecting system.

1) renal corpuscle = filters blood; consists of glomerulus & Bowman's capsule 2) proximal tubule = 1st segment of the renal tubule in which water, electrolytes, & organic nutrients are reabsorbed 3) nephron loop = 2nd segment of the renal tubule in which water & electrolytes are reabsorbed; consists of a descending & ascending limb 4) distal tubule = final segment of the renal tubule in which filtrate modification is controlled by hormones to fine-tine fluid, electrolyte, & acid-base balance 5) collecting system = series of tubules that receive filtrate from the distal tubules; responsible for fine-tuning fluid, electrolyte, & acid-base balance

Describe the major structures and subdivisions of the kidneys at both a macro and microscopic levels.

1) renal cortex = outer region of the kidneys that consists of blood vessels & most components of a kidney's nephrons 2) renal medulla = middle region of the kidneys that consists of renal pyramids & renal columns 3) renal pelvis = the inner region of the kidneys that receives urine drained from the major & minor calyces

Describe the role of each of the following in the control of the GFR:

1) reninangiotension-aldosterone system = results in the formation of angiotensin II, which raises BP & preserves blood flow to the kidneys/raises GFR 2) atrial natriuretic peptide = lowers blood volume & BP by diluting afferent & constricting efferent arterioles of the glomeruli, which increases glomerular hydrostatic pressure & thus increases GFR 3) SNS activity = releases norepinephrine, which causes vasoconstriction of afferent arterioles & elevates BP, & maintains GFR

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

1) ureters = muscular tubes that transport urine from the kidneys to the urinary bladder; composed of a superficial fibrous CT layer called the adventitia, a middle layer of smooth muscle called the muscularis, & the innermost mucosa composed of epithelium 2) urinary bladder = the hollow organ of the urinary tract that stores urine & contracts to expel it from the body; holds ~700-800 mL of urine; consists of a superficial adventitia, middle detrusor muscle, & innermost mucosa 3) urethra = terminal portion of the urinary tract through which urine is expelled from the urinary bladder to the outside of the body; consists of outer adventitia, middle muscularis, & inner mucosa; begins at internal urethral orifice in urinary bladder & ends at the external urethral orifice

Trace the pathway of urine from papillary duct to urethra.

collecting duct --> papillary duct --> minor calyx --> major calyx --> renal pelvis --> ureter --> urinary bladder --> urethra

Explain the role of the nephron loop in the concentration of urine.

helps establish the medullary osmotic gradient 1) NaCl is actively transported from filtrate in the thick ascending limb into the interstitial fluid, raising its NaCl concentration --> increases osmolarity 2) the NaCl pumped into the interstitial fluid draws water out of the filtrate in the thin descending limb into the interstitial fluid through osmosis 3) due to the continuing loss of water, the NaCl concentration of the filtrate increases as it approaches the bottom of the loop 4) the high NaCl concentration of the filtrate that reaches the thick ascending limb allows the NaCl reabsorption to continue

Explain how the hydrostatic and colloid osmotic pressures combine to yield the net filtration pressure in the glomerulus.

hydrostatic pressure = blood pressure --> pushes water out of capillary & into interstitial space colloid osmotic pressure = pressure created by proteins --> pulls water into capillaries by osmosis hydrostatic + colloid osmotic pressures work together in a capillary bed to determine the net filtration pressure --> direction of water movement hydrostatic > COP --> water out of capillary COP > hydrostatic --> water into capillary

Explain the mechanisms by which the kidneys secrete or retain hydrogen and bicarbonate ions, and describe how these processes affect blood pH.

the kidneys are able to excrete fixed acids that the respiratory system cannot, like lactic acid, ketones, phosphoric acid, uric acid, & ammonium the kidneys control blood pH by reabsorbing HCO3- & secreting H+ in a coupled secondary active transport process in which H+ bind to HCO3- to form H2CO3 in the filtrate; carbonic anhydrase then catalyzes the conversion of H2CO3 to CO2 & water which enter the kidney tubule cells; in the cells, H2CO3 is formed again & then dissociates into H+ & HCO3- again; HCO3- leaves the cell & enters the blood, & the H+ is recycled H+ secretion is mediated by the intercalated cells of the late distal tubule that use primary active transport pumps to pump H+ into the filtrate

Describe the external structure of the kidney, including its locations, support structures, and coverings.

the kidneys are protected by 3 layers of connective tissue 1) renal fascia = most superficial layer; dense irregular collagenous CT; anchors each kidney to the peritoneum & to the fascia covering the muscles of the posterior abdominal wall 2) adipose capsule = middle layer, thickest layer; consists of adipose tissue that wedges each kidney in place & shields it from physical shock 3) renal capsule = deepest layer; extremely thin layer of dense irregular collagenous CT that covers the exterior of each kidney like plastic wrap; protects kidney from infection & physical trauma

Describe the role of the respiratory system in regulating blood pH, and predict how hypo- and hyperventilation will affect blood pH.

the lungs control the amount of CO2 in the blood, & thus (indirectly) control the levels of H+ & H2CO3 in the blood too; under normal conditions, the amount of CO2 expired by the lungs matches the CO2 produced by metabolic reactions; during exercise, more CO2 is generated by metabolic reactions so respiration also increases to match hypoventilation --> increased PCO2 & decreased PO2 --> decreased pH (acidic) hyperventilation --> increased CO2 expired --> decreased blood PCO2 --> increased pH (basic)

Describe the structure of the filtration membrane.

the membrane in the renal corpuscle that filtrate passes through; consists of fenestrated glomerular endothelial cells, basal lamina, & podocytes, through which blood is filtered to produce filtrate in the kidneys

Explain the factors that determine the pH of blood, and describe how it is maintained within its normal range.

the pH of bodily fluids must remain between 7.35 & 7.45 metabolic acids like H2CO3, HCO3-, lactic acid, & uric acid will decrease pH; dietary acids like amino acids (protein), citric acid; dietary bases like bicarbonate

Explain how renal clearance rate can be used to measure the GFR.

the rate at which the kidneys remove a solute/substance from the body/blood; used to estimate the GFR using creatine or inulin; creatine excretion is used to estimate GFR by comparing the amount of creatine excreted in the urine to the plasma concentration of creatine; inulin is a complex carbohydrate that is filtered by the glomerulus but is neither reabsorbed or secreted, so GFR can be measured by injecting inulin into the blood & comparing its excretion in the urine to its plasma concentration

Describe voluntary control of micturition.

the second half of micturition is under voluntary control following step 3 of the reflex 4) interneurons in the spinal cord communicate "full bladder" signal to the micturition center in the pons 5) if micturition is appropriate, the cerebral cortex facilitates this process by allowing the external urethral sphincter to relax & urine is voided *if micturition is not appropriate, the detrusor muscle relaxes & external urethral sphincter remains closed, & the urge to urinate dissipates for about an hour

Explain the role of the vasa recta in the concentration of urine.

vasa recta = capillary beds that surround the nephron loops of juxtamedullary nephrons; its flow is opposite to that of the nephron loop, which allows it to act as a countercurrent exchanger that can supply blood to the renal medulla cells while maintaining the medullary osmotic gradient 1) the blood in the descending vasa recta loses water & gains NaCl from the medullary interstitial fluid 2) the blood in the ascending vasa recta "exchanges" water for NaCl, preserving the medullary osmotic gradient

Name specific factors that will increase or decrease the GFR.

vasoconstriction of afferent --> decreases GFR vasoconstriction of efferent --> increases GFR vasodilation of afferent --> increases GFR vasodilation of efferent --> decreases GFR