Urinary System & Fluid Balance - Exam 3 Flashcards
What are the basic parts of a nephron?
- Renal Corpuscle- contains the glomerular capsule and glomerulus
- Proximal Convoluted Tubule- S-shaped tube located closest to the glomerulus
- Nephron Loop / Loop of Henle - includes the ascending and descending limbs
- Distal Convoluted Tubule - S-shaped tube located furthest from the glomerulus
- Collecting Duct- trunk-like tube
What are the two different classes of nephrons?
Cortical nephron
Juxtamedullary nephron
What are the characteristics of cortical nephrons?
- account for 85% of nephrons in the kidney
- located entirely in the cortex
- short nephron loop
- glomerulus further from cortex-medulla junction
What are the characteristics of juxtamedullary nephrons?
- originate close to the cortex-medulla junction
- important in kidney’s ability to produce concentrated urine
- long nephron loops
- glomerulus closer to cortex-medulla junction
What components make up the filtration membrane?
fenestrated capillaries
basement membrane
podocytes
What is glomerular filtration rate (GFR)?
volume of filtrate formed each minute
What factors influence GFR?
- hydrostatic pressure in glomerulus
- hydrostatic pressure in capsule
- colloid osmotic pressure
If there is a fall in blood pressure, what can be done to increase GFR?
- Myogenic Mech. - smooth muscle dilates to increase blood flow, increases GFR
- Tubuglomerular Mech. - macula densa cells detect low levels of NaCl due to longer filtration time, which causes vasodilation to allow for more blood flow and increased GFR
- Neural Controls - norepinephrine is released which causes vasoconstriction, which increases peripheral resistance and brings BP back up
- RAAS - granular cells release renin and catalyzes the formation of angiotensin II. This increases aldosterone secretion which increases blood volume, and causes vasoconstriction
Where does most reabsorption occur in the nephron?
proximal convoluted tubule
What provides the energy and means for reabsorbing almost every other substance, including water?
reabsorption of sodium by primary active transport
How does the initial active transport of sodium influence the reabsorption of other substances (water, glucose, amino acids etc.)
- via secondary active transport
- apical carrier moves sodium down it’s concentration gradient as it cotransports another solute
What is tubular secretion?
excretion of unwanted substances that were reabsorbed
Why is tubular secretion important?
- disposes of substances that are tightly bound to plasma proteins (drugs, metabolites)
- eliminate undesirable substances or end products (urea, uric acid)
- ridding body of excess potassium
- controls blood pH
What are the renal functions?
- excretion of wastes, H2O, drugs, excess electrolytes/macros
- endocrine function - hormone release
- regulation- solute, water, blood pH
What are the three major renal processes?
- glomerular filtration
- tubular reabsorption
- tubular secretion
Glomerular filtration is a passive process driven primarily by what?
gradients
Glomerular capillaries are subject to high what?
blood pressure
How is net filtration pressure (NFP) measured?
outward pressures - inward pressures
What are the factors that maintain blood pressure?
cardiac output
peripheral resistance
blood volume
GFR must be relatively constant to do what?
maintain kidney function
What is the consequence of having a GFR that is too high or too low?
too high = lose too much
too low = too much absorption time
What triggers renin release?
- reduced stretch of granular cells AKA low BP
2. direct and indirect stimulation of granular cells
What are the direct and indirect stimulators of granular cells?
Direct - SNS triggers renal sympathetic nerves to active Beta-adrenergic receptors that cause granular cells to release renin
Indirect - low blood pressure causes vasoconstriction and slow filtrate movement, decreasing sodium concentration. Macula densa cells sense low sodium concentration and signal release of renin by releasing less ATP and/or prostoglandin PGE2
What are the effects of angiotensin II (Ang II) on systemic blood pressure?
- increasing peripheral resistance
2. increasing blood volume
Ang II increases peripheral resistance by doing what?
vasoconstriction
Ang II causes an increase in blood volume, which results in what?
-release of aldosterone, which increases sodium retention
release of ADH from posterior pituitary, which increases water retention
What is blood volume?
determined by the amount of water and sodium digested, excreted by kidneys in urine, and lost through GI tract, lungs and skin
Ang II can affect GFR by doing what?
constriction of efferent arterioles, which increases glomerular hydrostatic pressure, which increases GFR
When does tubular reabsorption occur?
as soon as filtrate enters the proximal convoluted tubule
What are the two routes of tubular reabsorption?
transcellular
paracellular
What is transcellular reabsorption?
across/through the cell
What is paracellular reabsorption?
alongside the cell
What transport types does tubular reabsorption utilize?
active and passive transport
What are the two phases of sodium reabsorption?
- primary active transport
2. secondary active transport
The secondary active transport of sodium aids in what?
reabsorption of nutrients, water, and ions
How does the movement of sodium aid in moving water and negatively charged ions?
movement of sodium establishes a strong osmotic gradient, and water moves via osmosis into peritubular capillaries. Aquaporins aid this process, and aid in obligatory water reabsorption
How does the movement of water help drive the reabsorption of solutes from the filtrate?
as water leaves the tubules, concentration of solutes increases and if able to, they follow their concentration gradients as well
How do the kidneys influence osmolality?
kidney functions to keep osmolality constant by regulating urine concentration
Why is regulating osmolality important?
prevents cells (especially in brain) from shrinking or swelling from osmotic movement of water
What are the three key players of osmolality?
long nephron loops
vasa recta
collecting ducts
What is the long nephron loops orientation in the osmotic gradient?
create the gradient
countercurrent multipliers
What is the vasa recta’s orientation in the osmotic gradient?
preserve the gradient
countercurrent exchangers
What is the collecting duct’s orientation in the osmotic gradient?
use gradient to adjust osmolality
What are the mechanisms that cause an increase in osmolality (and gradient) in the medulla?
- dehydration
- increase in osmolality
- causes ADH release from posterior pituitary
- increases number of aquaporins in collecting duct
- causes increase in water absorption
- creates small volume of concentrated urine
What influence does ADH have on the kidney and urine concentration?
- Overhydration
- ADH production decreases and osmolality falls - Dehydration
- ADH production increases and osmolality increases
What influence does aldosterone have on the kidney and urine concentration?
If aldosterone is present during overhydration, it can further dilute the urine
The three key players and how they affect the gradients of the kidney team together to form what?
medullary osmotic gradient
What structure does the urine travel through after expulsion from the kidney?
ureters — bladder — urethra
What is the chemical composition of urine?
95% water, 5% solutes
What are the normal solutes present in urine in decreasing concentration?
Urea Sodium Potassium PO4(3-) SO4(2-) creatinine uric acid calcium magnesium HCO3(-)
What is urine used for?
to test for pathologies
What does the process of micturition (urination) involve?
- contraction of detrusor muscle (smooth muscle)
- opening of internal urethral sphincter (smooth muscle)
- opening of external urethral sphincter (skeletal muscle)
How does the brain receive urination signals?
signals of fullness from bladder are sent to pons and higher brain centers
What happens to cells if they are surrounded by a hypertonic solution?
cells shrink as water moves to area of lower concentration
What happens to cells if they are surrounded by a hypotonic solution?
cells swell as water moves to area of lower concentration (the cell)
What are the major locations of sodium?
blood plasma
interstitial fluid
What are the major locations of potassium?
intracellular fluid
What are the major locations of calcium?
blood plasma
interstitial fluid
What are the major locations of chloride?
blood plasma
interstitial fluid
What are the major locations of bicarbonate ions?
blood plasma
interstitial fluid
What are the major locations of proteins?
blood plasma
intracellular fluid
How is metabolism a source of water?
water is a by-product of oxidation of carbs and fatty acids
water released from break down of glycogen
What is the hormonal response to a rise in osmolality?
stimulate secretion of ADH
increases water absorption and concentrated urine
What is the hormonal response to a decrease in osmolality?
suppresses ADH release
decreases water absorption and produces less concentrated urine
What are the resulting effects of hypotonic hydration on osmolality and cells?
hyponatremia (low ECF sodium concentration)
- promotes net osmosis into cells
- causes cells to swell and decreases osmolality
What are the general causes of edema?
increased fluid out
decreased fluid returning to blood
blocked removal of excess interstitial fluid
How is estrogen linked to fluid retention during a female’s menstrual cycle?
estrogen is like aldosterone, increasing the amount of NaCl reabsorbed. Water follows NaCl, causing increased fluid retention
How can hyperkalemia lead to sudden cardiac death ? (think action potentials)
increased extracellular potassium reduces myocardial excitability
suppressed impulse generation by SA node, resulting in eventual cardiac death
What gland and hormone regulates calcium levels in the blood?
parathyroid hormone released by parathyroid glands
How much of your body weight is composed of intracellular fluid?
40% of body weight
How much of your body weight is composed of interstitial fluid?
80% of ECF
ECF makes up 20% of body weight
How much of your body weight is composed of plasma?
20% of ECF
Water is the universal what?
solvent
Solutes are classified as what?
nonelectrolytes and electrolytes
Electrolytes dissociate into what?
ions
Nonelectrolytes are what kind of chemical compound?
mostly organic
no charged particle created
Osmotic and hydrostatic pressure regulates what?
continuous exchange and mixing of fluids
Change in solute concentration = change in what?
water flow
Osmolality is maintained at what level?
280-300 mOsm
What is obligatory water losses?
insensible water loss from lungs, skin, feces, urine
What is dehyration?
ECF water loss due to hemorrhaging severe burns prolonged vomiting diarrhea profuse sweating water deprivation
What can dehydration lead to?
weight loss fever mental confusion hypovolemic shock loss of electrolytes
Why can dehydration lead to a dry/”cotton” mouth?
loss of water in saliva and mucosa
decreased saliva production
Can water kill you?
Yes, drinking too much water can cause cells to swell, and could later cause cerebral edema
What is the treatment option for hypotonic hydration?
administration of IV hypertonic saline to reverse osmotic gradient
What are electrolytes?
salts
acids
bases
some proteins
Salts are involved in what?
fluid movement
provide minerals for excitability
secretory activity
How do salts enter and leave the body?
enter - foods, fluids, small amounts during metabolic activities
loss- perspiration, feces, urine, vomit
99% of the body’s calcium is found where?
bone
The calcium in ECF is important for what?
blood clotting
cell membrane permeability
secretory activities
neuromuscular excitability
How does PTH promote an increase in calcium?
- Bone - PTH activates osteoclasts which causes release of calcium into blood
- Kidneys - PTH increases calcium reabsorption and decreases phosphate reabsorpion
- Small Intestine - PTH enhances intestinal absorption of calcium
How does progesterone alter sodium?
decreases sodium reabsorption (blocks aldosterone)
What is the normal pH values for arterial blood, venous blood and interstitial fluid, and ICF?
arterial blood - 7.4
venous blood and IF- 7.35
ICF - 7.0
What is alkalosis/alkalemia?
arterial pH greater than 7.45
What is acidosis/acidemia?
arterial pH less than 7.35
Most hydrogen is produced by metabolism via what?
- lactic acid from anaerobic respiration of glucose
- fatty acids and ketone bodies
- conversion of CO2 to HCO3
What is a system of one or more compounds that act to resist pH changes when strong acid or base is added?
chemical buffer systems
What are the types of chemical buffer systems and which one is the most important?
bicarbonate, phosphate, and protein buffer systems
Bicarbonate buffer system is most important
