Urinary System Flashcards
What are the 6 main functions of the kidney
Regulating ECF volume and blood pressure, regulating osmolarity, maintaining ion balance (Na+, K+, and Ca2+), regulating pH (H+ and HCO3-), excreting wastes, and producing hormones
What are metabolic wastes excreted by the kidneys
Creatinine (from skeletal muscles) and nitrogenous wastes like urea and uric acid (from protein breakdown)
What are xenobiotics
Foreign substances like drugs, environmental toxins, saccharin, and potassium benzoate
What is involved in production of hormones in the kidney
Renin (enzyme regulating hormones for Na+ balance and BP regulation) and erythropoietin (controls erythropoiesis/ the RBC production in bone marrow)
What are the key functions of the nephron
To filter blood by keeping water, sugars, vitamins, amino acids, and other vital substances while eliminating excess water, salts, minerals, urea, uric acid, creatinine, hormone waste, toxins, xenobiotics, etc.
What are the 4 steps that take place in a nephron
Filtration (Moving from blood to lumen), reabsorption (from lumen to blood), secretion (from blood to lumen), and excretion (from lumen to outside of body)
Describe filtration
First step in forming urine, takes place in a glomerulus (network of capillaries) surrounded by nephron (Bowman’s capsule), creates filtrate, leaving blood cells and most plasma proteins in capillary
What is filtrate
Filtered plasma (H2O and dissolved solutes) that is isosmotic with plasma
What is the filtration fraction
% of plasma that is filtered into Bowman’s capsule from capillary (~20%)
What would happen if you filtered and removed 100% of plasma from blood
Blood would turn into sludge of cells and proteins
What is the renal corpuscle
Glomerular capillaries surrounded by Bowman’s capsule
What drives filtration
Net filtration pressure (~10mmHg) = hydrostatic pressure - colloid osmotic pressure - capsule fluid pressure
What is hydrostatic pressure
Blood pressure (MAP) that pushes water and solutes out of capillaries
What is colloid osmotic pressure
Oncotic pressure due to plasma proteins that opposes hydrostatic pressure
What is capsule fluid pressure
Fluid within Bowman’s capsule that opposes more fluid movement in
What is bulk flow
Mass movement due to pressure gradient
What is glomerular filtration rate (GFR)
Volume of fluid filtered per unit time = Filtration pressure * Filtration coefficient, fairly constant over range of MAPs
What is autoregulation
Local kidney control process to maintain relatively constant GFR by regulating blood flow through renal arterioles (dilate, increases P(H), increases GFR, increases RBF)
What are the 2 autoregulation mechanisms
Myogenic response (Inherent ability of vascular smooth muscle to respond to pressure changes and alter blood flow) and tubuloglomerular feedback (paracrine signaling mechanism caused by changes in fluid flow through loop of Henle)
How does the Myogenic response react due to increased MAP (5 steps)
Stretch afferent arteriole smooth muscle opens stretch-sensitive ion channels, muscle cells depolarize opening voltage-gated Ca++ channels, vascular smooth muscle contracts, causing vasoconstriction that increases resistance to flow
What effect does vasoconstriction of the afferent arteriole have
Decrease RBF, decreased filtration pressure (because decreased hydrostatic pressure), and decreased GFR
Why is local control in the kidneys possible
Because of the twisted configuration of the nephron (ascending limb close to renal corpuscle)
Paracrine signaling occurs between the afferent arteriole and what cells to change arteriole diameter and influence GFR
Macula densa cells
What is the function of macula densa cells
To sense distal tubule flow and release paracrine that affect afferent arteriole diameter
What cells in the juxtaglomerular apparatus secrete renin
Granular cells
Describe the 4 steps of tubuloglomerular feedback response to increased GFR
Macula densa cells sense increased tubular flow rate (NaCl), release more ATP and adenosine, and decrease nitric oxide secretion, which binds to receptors on afferent arteriole smooth muscle to cause vasoconstriction
What does nitric oxide do
Cause vasodilation of afferent arteriole in the kidney
Reabsorption happens between the nephron and what kind of capillaries
Peritubular capillaries
Where does reabsorption occur in a nephron
Proximal tubule, the loop of Henle, distal tubule, and collecting duct
Where does most reabsorption of fluid reoccur
Proximal tubule
How is H2O reabsorbed
Passively via osmosis
Other than osmosis, what other kind of transport is involved in reabsorption
Passive and/or active transepithelial transport (depending on solute electrochemical gradient)
How is Na+ resorbed
Passive facilitated diffusion (uses NHE and ENaC) from filtrate into ICF, then secondary active transport (Na/K ATPase) from ICF to ECF
What is the main driving force for most renal reabsorption
Na+ (99% is reabsorbed)
What percent of Na+ is resorbed in the proximal tubule and what is its role (6 things)
67%, it plays role in reabsorbing glucose, amino acids,H20, Cl-, K+, and urea
What percent of Na+ is resorbed in the ascending loop of Henle and what is its role
25%, plays key role in ability to produce urine of varying concentrations
What percent of Na+ is resorbed in the distal and collecting tubules and what is its role
8%, role varies (based on hormonal control), but helps regulate ECF volume
How is glucose reabsorbed
Via secondary active transport (Na+-linked secondary active transport / “SGLT transporter) from lumen into ICF, then GLUT passive facilitated diffusion from ICF to ECF
Reabsorption of what molecules relies on Na+-linked secondary active transport
Glucose, amino acids, ions, etc.
What is renal threshold
Plasma concentration at which saturation of transporters occurs
What is transport maximum
The transport rate at saturation
How is glucose handled by a nephron
Filtration proportional to plasma concentration (can’t saturate), reabsorption also proportional until transport maximum is reached (~300mg/100mL plasma), and only exerted once renal threshold is reached
Is glucose ever secreted
No
What is glucosuria
Lots of glucose in the urine
Which is selective, filtration or secretion
Secretion (uses transporters)
Where does secretion occur
Proximal tubule, distal tubule, and collecting duct
What kind of transport is involved in secretion
Active transport
What 2 things is secretion important for
Homeostatic regulation (K+ and H+) in the collecting duct, and organic anion & cation elimination (hormones and xenobiotics) in proximal tubules
What is filtrate referred to after it leaves the collecting duct and why
Urine because composition can no longer be altered
Where does excretion occur
Collecting duct
What is renal handling
The amount of substance in urine = amount filtered - amount reabsorbed + amount secreted
What is clearance
Rate at which substance is cleared from the body by excretion (Excretion rate * Concentration)
What is clearance used for
To determine how a nephron handles a substance that’s filtered into it (drug clearance and non-invasive way to measure GFR)
What is another word for micturition
Urination
What is micturition
A simple spinal reflex, under conscious and unconscious control from higher brain centers
At rest, describe the sensory input to the bladder, internal sphincter, and external sphincter
External sphincter tonically active, internal sphincter passively active, bladder wall inactive
What happens when stretch receptors in the bladder wall activate
Parasympathetic neurons contract smooth muscle in the bladder wall (in waves) and relax the internal sphincter, urine forces the internal sphincter open, somatic neurons to external sphincter are inhibited and it relaxes
What hormone effects blood ECF volume
Vasopressin
What changes disturb fluid and electrolyte homeostasis
Blood (ECF) volume affects blood pressure and osmolarity affects tonicity and membrane potentials
What 3 hormone/systems effect osmolarity
Aldosterone, atrial natriuretic peptide, and renin-angiotensin system
What 3 systems/responses integrate fluid and electrolyte balance
Cardiovascular system, behavioral responses, and kidney responses
What does vasopressin do and where
It is an anti-diuretic hormone produced by the posterior pituitary that controls H2O reabsorption in the collecting duct and distal tubules
How do kidneys maintain homeostasis of H2O
They can conserve or excrete it but can’t replace it
What change does an increased secretion of vasopressin have on the distal nephron and collecting ducts
Increases the permeability of the collecting duct epithelium to water so that it is conserved rather than excreted (prevents reabsorption)
How does vasopressin change the epithelium’s permeability to water
By inserting aquaporins (water pores) through a cAMP secondary messenger pathway that results in exocytosis
What are the 3 stimuli to conserve fluid
Increased ECF osmolarity, decreased BP (baroreceptor stretch), and decreased blood volume (atrial stretch)
What effect does ingested salt (NaCl) have on blood osmolarity
It increases
What triggers thirst in the hypothalamus
Angiotensin II
What are the 2 responses to increased blood osmolarity
Increased vasopressin release and thirst to conserve and bring in more water (both will also increase ECF volume and blood pressure)
What is K+ important for and what is it controlled by
Maintaining membrane potentials, controlled by aldosterone
What is Na+ important for in electrolyte homeostasis and what controls it
Important for ECF volume and osmolarity, controlled by aldosterone, RAS pathway, and ANP
What does aldosterone do
Acts on principal (P) cells of the collecting duct to increase Na+ reabsorption and K+ secretion in distal nephron
What produces aldosterone
Adrenal cortex
What are the 3 stimuli for aldosterone
Increased K+ (hyperkalemia), decreased BP (via RAS pathway), and very high osmolarity inhibits it
What does the liver do in the RAS/RAAS pathway
Constantly produces angiotensinogen
How is ANG I made
Renin converts angiotensinogen to ANG I
How is ANG II made
ACE enzyme converts ANG I to ANG II
What are the 5 things ANG II acts on to raise blood pressure
Arterioles (vasoconstrict), cardiovascular control center in medulla oblongata (increases BP via CO and TPR), hypothalamus (triggers thirst and vasopressin), adrenal cortex (produces aldosterone), and proximal tubule (increases Na+ reabsorption)
What is atrial natriuretic peptide (ANP) and what does it do
Stretch of myocardial cells in atria indicates increased ECF and blood volume, has the opposite effect of RAAS pathway (decreases vasopressin, renin, and aldosterone secretion, decreases BP, decrease blood volume, and increases Na+ and H2O excretion)
What are 3 consequences of pH disturbances in the blood
Disruption of protein shape, disturbance of K+ levels, and effects on excitable tissues
What is a normal pH range for plasma
7.38-7.42 (<7.38 = acidosis, and >7.42 = alkalosis)
Do acidity or basicity have a greater input effect
Acids
How does the body reduce H+ to neutralize acids
Buffers, ventilaiton, and kidneys
What is the largest source of H+
CO2 (bicarbonate buffering reaction)
What is the first line of defense to neutralize acids
Buffer system = mixture of two compounds that can remove or produce free H+ as needed, fastest response but only removes H+ from solution, not body
What are 2 buffers within cells and plasma
Extracellular buffering: Bicarbonate (HCO3-)
Intracellular buffering: Proteins
What is the 2nd response to neutralize acids
Respiratory compensation (hyperventilate if acidosis, hypoventilate if alkalosis)
What is the most important site for renal pH regulation
Intercalated disks of distal nephron (secrete H+ and reabsorb HCO3- if acidosis, secrete HCO3- and reabsorb H+ if alkalosis)
What are the 2 characteristics of renal compensation for acidosis
Type A intercalated cells secrete H+ at apical membrane (H+/K+ exchanger often leads to hyperkalemia) and HCO3- is absorbed at the basolateral membrane
What are the characteristics of renal compensation for alkalosis
Type B intercalated cells reabsorb H+ at basolateral membrane (H+/K+ exchanger often leads to hypokalemia) and secretes HCO3- at apical membrane
