Renal Physiology Flashcards
Two primary functions of the kidneys include:
● To rid the body of waste
● To control the volume and composition of body fluids
Kidneys are primarily responsible for eliminating these waste products of metabolism:
○ Urea (from the metabolism of amino acids)
○ Creatinine (from muscle creatine)
○ Uric acid (from nucleic acids, purines)
○ End products of hemoglobin breakdown (e.g., bilirubin)
○ Metabolites of various hormones
○ Most toxins and other foreign substances (pesticides,
drugs, food additives, etc.) are also eliminated
Electrolytes:
sodium, chloride,
potassium, calcium, hydrogen,
magnesium, and phosphate
By regulating ______, the kidneys work with
the lungs to regulate the pH of
blood
the concentration of bicarbonate and hydrogen ions in the blood
Kidneys are responsible for up to _____% of gluconeogenesis during fasting
40
_____ – deep to the cortex,
houses the loop of Henle and
collecting ducts
Medulla
_____ - sit at the end of
renal pyramids and collect formed urine
Calyces (minor/major)
T/F the kidney Cannot regenerate new nephrons
T
The renal corpuscle is composed of two parts:
● Glomerulus - ball of capillaries
○ Afferent arterioles - bring blood into
glomerulus for filtration
○ Efferent arterioles - the remaining blood
exits via these arterioles
○ The arterioles are lined with smooth
muscle - controlled by the sympathetic
nervous system
● Bowman’s capsule
The ____ is where water and
solutes are exchanged (formation of urine)
renal tubule
Glomerular filtrate route (follow the urine):
● Bowman’s capsule
● Renal tubules
○ Proximal convoluted tubule
○ Loop of Henle
■ Descending limb
■ Ascending limb
○ Distal convoluted tubule
○ Collecting duct
The juxtaglomerular complex/apparatus helps regulate:
● Blood pressure
● Glomerular Filtration Rate (GFR)
● Located between Distal Convoluted Tubule (DCT) and afferent arteriole
Three kinds of cells of the juxtaglomerular complex:
○ Macula Densa Cells (DCT): Sense decrease Na+ and Cl-
○ Mesangial Cells: Help with signaling between densa/juxta cells
○ Juxtaglomerular Cells (AKA “Granular Cells”)
■ Sense decrease in BP
■ Secrete Renin
Renal circulation has two capillary beds:
- Glomerular capillaries
● High hydrostatic pressure → causes rapid
fluid filtration - Peritubular capillaries
● Lower hydrostatic pressure → permits rapid
fluid reabsorption
Surround renal tubules and allow
reabsorption and secretion
between blood and tubules
Peritubular capillaries
Specialized peritubular capillaries
that surround the Loop of Henle
Vasa Recta
Renal blood flow in the small vessels:
Efferent arterioles → Peritubular capillaries + Vasa Recta → Veins
The glomerular capillary membrane is a
_____ charged membrane that has three layers that allows for filtration (due to fenestrations)
negatively
GFR = ______
the volume (mL) of fluid that filters into the Bowman’s capsules per unit of
time (min)
In an average, healthy adult, GFR =
125 mL/min (180 L/day)
Kidney disease = _____ GFR
decreased
Items freely filtered by kidneys: ____
Na, K, Cl, bicarb, glucose, urea, amino acids (not large proteins like albumin), insulin, and ADH
GFR can be increased or decreased depending on various factors:
● Glomerular hydrostatic pressure (GHP)
● Glomerular oncotic pressure (GOP)
● Bowman’s capsule hydrostatic pressure (BHP)
● Capillary permeability
● Resistance of Afferent or Efferent arterioles
Three things that can↑↓ Glomerular hydrostatic
pressure:
○ ↑or ↓ blood pressure
○ Afferent arteriole resistance
○ Efferent arteriole resistance
Primary method of physiologic GFR regulation
Glomerular Hydrostatic Pressure (GHP)
Increasing GHP increases ____
GFR
Oncotic pressure =
osmotic pressure exerted by proteins (AKA – Colloid osmotic pressure)
What are starling forces?
Hydrostatic and oncotic pressure gradients
that govern passive exchange of water
between interstitium and capillary walls
Net Filtration Pressure (NFP) = ____
sum of hydrostatic and osmotic forces across the glomerular capillaries
Bowman’s Capsule Hydrostatic Pressure (BHP)
The pressure inside Bowman’s capsule is approximately 18 mmHg
Capillary Permeability
● ↑ capillary membrane permeability =
↑ GFR
● ↓ capillary membrane permeability =
↓ GFR
Vasoconstriction that ↑ afferent resistance will
↓ Glomerular Hydrostatic Pressure = ____
↓ GFR
Vasoconstriction that ↑ efferent resistance will ↑
Glomerular Hydrostatic Pressure = ____
↑ GFR
Mean Arterial Pressure (MAP) –____
Average blood pressure (not glomerular
hydrostatic pressure) between systole and diastole
When MAP falls below 80 mmHg it _____
triggers baroreceptor reflexes
that increase sympathetic activity
● This response causes contraction of smooth muscle and affects
both the afferent and efferent arterioles
● This will increase MAP and decrease GFR which will decrease urine
output and conserve fluid
______ – movement of filtered solutes/H2O from tubules back into capillaries
Tubular Reabsorption
_____ “second pass” – molecules move from
plasma of the peritubular capillary bed back into the renal tubule filtrate
Tubular Secretion
Reabsorption is a two-step process occurring via
____ transport
passive or active
Reabsorption is a two-step process:
- H2O and dissolved substances from tubule →
cell/interstitium - From the cells/interstitium, H2O and solutes → capillary walls → blood stream
_____ – Transports through the interstitium
via concentration gradients
Passive Transport
Reabsorption – Na+
Reabsorption of Na+
(PCT)
● Active transport – Na+ /K+ Pump
● Co-transport with a.a, glucose, Cl–
● Countertransport with H+
Reabsorption of K+ (PCT)
● Active transport – Na+ /K+ Pump
● Potassium channels
Reabsorption of H2O
● 70% in the PCT
● 20% DCT
● 10% CD
Reabsorption of Ca++
● 99% of filtered Calcium is reabsorbed
○ 70% in the PCT
○ 25% loop of Henle
○ 5% DCT
Water can cross the plasma membranes via _____
aquaporins (water channels)
Tubular Secretion
Occurs in the same way reabsorption does,
but in REVERSE
● Passive secretion
● Active transport
Secretion of K+
● Na+ /K+ Pump
○ DCT and CD
Secretion of Ca++
● DCT (very limited, <1%)
Anatomy of Excretion
● Calyx
○ Minor
○ Major
● Renal pelvis
● Ureter – autonomic nervous system, peristaltic action
● Bladder – Detrusor muscle, surrounded by fibrous connective tissue
● Urethra
Control of urination is achieved via
● Autonomic control (involuntary)
○ Internal urethral sphincter
● Somatic control (voluntary)
○ External urethral sphincter
ADH – Antidiuretic Hormone/“Vasopressin”
● Secreted from posterior pituitary
○ Stimulates aquaporin placement
■ Aquaporin ↑↑ H2O permeability
■ Conserves H2O by reducing its loss through excretion
Conserves H2O by reducing its loss through excretion
ADH
Hypothalamus measures osmolality and release of ADH:
● If osmolality ↑↑→ ADH released → ↑ H2O
reabsorption = ↓ H2O excretion (less urine)
● If osmolality ↓↓ → no ADH → ↓↓ H2O
reabsorption = ↑ H2O excretion (more urine)
Aldosterone
● Steroid hormone
○ Released from adrenal cortex
○ Works in the distal tubule
Principle regulator
● Reabsorption of Na+ (increase serum Na+)
● Secretion of potassium (decrease serum K+)
Principle regulator for reabsorption of Na+ and Secretion of potassium
Aldosterone
Renin
● Enzyme
○ Released from juxtaglomerular cells
○ Converts Angiotensinogen to Angiotensin I
○ Stimulates release of aldosterone and cortisol
● Eventually increases Angiotensin II
○ Increases thirst
○ Increase Na+ in body and release K+
Stimulates release of aldosterone and cortisol
Renin
Angiotensin Converting Enzyme (ACE)
● Enzyme
○ Secreted by the lungs and kidneys
○ Converts Angiotensin I into Angiotensin II
● Indirectly causes increased blood pressure via
○ Vasoconstriction of systemic arterioles
○ Adrenal cortex to release aldosterone
○ Posterior pituitary to release ADH
○ Hypothalamus induces thirst = ↑ fluid intake
Atrial Natriuretic Peptide
● Peptide Hormone
● Primary roles
○ Decreases blood pressure
○ Electrolyte homeostasis
Parathyroid Hormone (PTH)
● Hormone
○ Produced from the parathyroid glands
○ Triggered by ↓ plasma Ca++
● Primary role to increase serum Ca++ levels
○ Increase absorption of Ca++ in the GI tract
■ Via calcitriol
○ Increase reabsorption of Ca++ in the kidneys
■ Loop of Henle and DCT
○ Increase resorption of Ca++ in the bone
Primary role to increase serum Ca++ levels
PTH
Calcitriol
○ Active form of Vitamin D3
(1,25-dihydroxycholecalciferol)
○ Produced in the proximal tubule
○ Increases GI absorption of Ca++
Increases GI absorption of Ca++
Calcitriol
Calcitonin
○ Released from the thyroid gland in response
to elevated Ca++ levels
○ Role to decrease serum Ca++
■ Decrease calcium reabsorption in the kidney
■ Inhibits osteoclast activity in the bones
Role to decrease serum Ca++
Calcitonin
