Test 5: Renal Flashcards
What are the (7) functions of the Kidneys?
Lecture & 1211-1214
Formation of urine by:
1. Excretion of metabolic waste products: Urea, creatinine, bilirubin, drugs and hormone metabolites
2. Regulation of water and electrolyte balance
3. regulation of arterial blood pressure: RAAS
4. Regulation of acid/base balance: excretion of H+ & reabsorption of bicarb
5. erythrocyte production (erythropoietin)
6. Production of Calcitriol (1,25 dihydroxy vitamin)
7. Gluconeogenesis
Structural components of the Kidney
lecture & 1211-1212
- cortex: outer layer
- Medulla: inner part of the kidney and consists of regions called pyramids
—–Pyramids: organized tissue in the medulla that communicates with the renal pelvis - Minor and major calyx: chambers receiving urine from the collecting ducts and form the entry into the renal pelvis
- Nephron: functional unit. consists of: renal corpuscle, proximal tubule, loop of Henle, distal tubule, and collecting duct. (can not be regenerated)
Glomerulus
-definition
-structure
-function
1212
-A tuft of fenestrated capillaries that loop into the Bowman’s space, like a “fist pushed into bread dough”
INITIAL FILTRATION SITE OF NEPHRON
-Glomerular filtration membrane
——1. inner capillary endothelium (fenestrae)
——2. middle basement membrane (collagen and proteoglycan)
——3. outer layer of capillary or visceral epithelium (podocytes/filtration slits/slit membranes)
-membrane allows all components of the blood to be filtered with the exception of blood cells and plasma proteins with a high molecular weight. Filtrate passes through the three layers of the glomerular membrane and forms the primary urine.
WATER FREELY PERMEATES
NEED A VIDEO, THIS IS SO CONVOLUTED WHEN EXPLAINED LIKE THIS
What are the types of nephron (3)?
-prevalence
-approximate location
1212
-Cortical: 85% of all nephrons, originate close to the surface of the cortex or in the midcortex and extend into the medulla
-Midcortical: have short or long loops
-Juxtamedullary: 12% of nephrons lie near, and have long loops that extend deep into the medulla and are important for the concentration of urine.
——specialized vasculature surrounding their peritubular capillaries called VASA RECTA that absorb fluid determining the urine concentration
What are the (7) major blood vessels of the kidney?
1215-1216
- Renal arteries: off the abdominal aorta
- Interlobar arteries: subdivisions that travel down renal columns and between pyramids to form afferent glomerular arteries
- Arcuate arteries: branches of interlobar arteries at the cortical medullary junction.
- Glomerular capillaries: 4-8 vessels arranged in a fist like structure. arise from afferent arteriole and empty into efferent arteriole MAJOR RESISTANCE VESSELS FOR THE REGULATION OF INTRARENAL BLOOD FLOW
- Peritubular capillaries: surround convoluted portions of the proximal and distal tubules and the loop of Henle. Adapted for cortical and juxtamedullary nephrons.
- Vasa Recta: network of capillaries that forms looks and closely follows the loops of Henle; ONLY BLOOD SUPPLY TO THE MEDULLA/ IMPORTANT FOR THE FORMATION OF CONCENTRATED URINE.
- Renal veins: follow the arterial path in reverse direction and have same names as corresponding arteries, then dump into the inferior vena cava.
What is glomerular filtration rate (GFR)?
How is it controlled?
1217
-The filtration of the plasma per unit of time, which is directly related to the perfusion pressure of the glomerular capillaries.
-neuronal and hormonal regulation
What is Tubular Reabsorption?
1219
-the movement of fluids and solutes from the tubular lumen into the peritubular capillary plasma
-as filtrate progresses through the renal tubules a selective process of reabsorption occurs.
-essential nutrients (glucose and amino acids), electrolytes, and water are actively and passively transported back into the bloodstream.
What is glomerular filtration?
1219 & AO
-First step in urine formation
-Driven by hydrostatic pressure, water and small solutes are forced from the blood across the glomerular filtration barrier into the bowman’s capsule forming INITIAL FILTRATE
-Filtrate is similar to blood plasma but lacks proteins and cellular components
What keeps large proteins from ending up in urine?
1219
Molecule size compated to small size of filtration slits in glomerular epithelium
Negative charge of the filtration membrane repels the negative charge of the macromolecules like protein.
–though positively charged macromolecules can permeate more easily than negative or neutral charged particles.
What is tubular secretion?
1219
-the transfer of substances from the plasma of the peritubular capillary to the tubular lumen.
-simultaneously, unwanted substances are actively transported from the blood into the filtrate. Including metabolic waste, H+, drugs/toxins etc.
-secretion shapes the final composition of the filtrate preparing it for its role as urine
What is the function of the glomerular membranes endothelium?
1213
-REGULATE vasomotor tone: Synthesize nitric oxide (dilation) and endothelin-1(constriction) to help regulate glomerular blood flow
-FACILITATE homeostasis: fluid electrolyte balance
-CONTROL trafficking of leukocytes into the glomerulus
What is the function of the glomerular basement membrane?
What is it made of?
1213-1214 & AO
-structural integrity/scaffolding for both the endothelium and the podocyte layer
-Size and charge based barrier (keep protein, allow water and small solutes to pass)
-Collagen and proteoglycan
What is the function of potocytes?
1213-1214 & AO
-Final filtration barrier
-prevents albumin leakage into filtrate
-maintains and repairs the glomerular membrane
What are the (4) ways to increase GFR?
1217-1218, 1220 & AO
- increase glomerular hydrostatic pressure
—–Increased vascular volume or MAP, dilation of afferent arterioles allowing more blood in, or constricting of efferent arterioles slowing the outflow and increasing pressure - Increased Bowman’s capsule hydrostatic pressure
—–obstruction of urinary tract (stones or BPH) initially increase pressure (though sustained obstruction decreases GFR long term) - Decrease glomerular capillary colloid osmotic pressure
—–increased intake of protein or temporary conditions (hyperglycemia) increase oncotic pressure gradient, affecting fluid dynamics across the membrane. - Hormones and Autacoids
—–angiotensin II constricts EFFERENT arterioles
—–nitric oxide, prostaglandins, bradykinin dilate AFFERENT arterioles
What are the (2) ways to decrease GFR?
1220-1221 & AO
- Change blood flow
—–Sympathetic nervous system
———Norepi: constriction of BOTH afferent and efferent arterioles reducing overall renal blood flow
———Epi: constricts AFFERENT arterioles decreasing flow INTO the glomeruli - Hormone
—–Endothelin: vasoconstricts afferent arterioles
Proximal tubule
What is it?
Reabsorption?
Secretion?
Controlled by?
1214 & Lecture & AO
longest and most metabolically active segment, VERY WATER PERMEABLE
Reabsorbs 65-70% of filtrate to reclaim:
-Na, Cl, K, Phos, bicarb, glucose and amino acids
Secretes: H+, organic acids and bases (bile salts, uric acid and catecholamines)
Control: Angiotensin II (increased H2O & Na), parathyroid hormone DECREASES Phos reabsorption
Thin DESCENDING loop of Henle
Reabsorption?
Secretion?
Controlled by?
Lecture & AO & 1214
HIGHLY water permeable, creates highly concentrated filtrate (water leaves)
Reabsorption: small amounts of Na
Secretion: None
Control: None
Thin ASCENDING loop of Henle
Reabsorption?
Secretion?
Controlled by?
Lecture & AO & 1214
Permeable to IONS NOT WATER
actively transports Na and Cl creating a hyperosmolar environment
Reabsorption: None
Secretion: None
Control: None
Thick ASCENDING loop of Henle
Reabsorption?
Secretion?
Controlled by?
Lecture & AO & 1214
IMPERMIABLE TO WATER AND UREA
REABSORPTION: Na, Cl, K, Ca, Mg, and bicarb
SECRETION: H+
Control:
-Angiotensin II increases Na absorption and secretion of H+
-Parathyroid hormone increases reabsorption of Ca
NOT PHOS
Collecting Tubules
Reabsorption?
Secretion?
Controlled by?
Lecture & AO & 1214-1215
Final conduit of nephron, receive concentrated urine from multiple distal tubules. Hormones influence last modifications before it is delivered to renal pelvis for excretion
Reabsorption: Na, Cl, Ca and bicarb, possibly H2O
Secretion: K, H+ and Urea
Control:
-Aldosterone increases NaCl Reabsorption and K secretion
-Vasopressin increases H2O reabsorption
-ANP decreases Na reabsorption
Medullary Collecting ducts
Reabsorption?
Secretion?
Controlled by?
Lecture & AO
segment that traverses the hyperosmolar medulla allowing further water reabsorption under the influence of ADH
Reabsorption: Urea and H2O (if ADH)
Secretion: Na, K, H+ and bicarb
Control: ADH increases H2O reabsorption
Creatinine Clearance (CrCl)
Lecture & AO & 1226
Provides a good clinical measure of GFR as it only over estimates GFR by a small amount because the renal tubules secreta a small amount of creatinine themselves (book)
Overestimates actual kidney function (lecture & AO)
NOTES:
GFR (mL/min)= (Urine creatinine x volume of urine)/(Plasma creatinine)
REQUIRES A SINGLE BLOOD TEST AND A 24 HOUR URINE SAMPLE