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