The Kidneys Flashcards
WHERE ARE THE KIDNEYS LOCATED?
Just below the diaphragm
KIDNEYS: ANATOMICAL LOCATION
Partially protected by ribs
- Adrenal glands – endocrine function
- Vascular supply – renal artery/vein
- Hilum – attachment point of vasculature
- Filtration and modification of fluids
- Urinary tract – transportation/storage of urine
- Renal fascia – connective tissue anchor
- Adipose capsule – support and shock
- Renal capsule – connective tissue protective wrap
INTERNAL ANATOMY
KIDNEY BLOOD SUPPLY
WHERE DO THE KIDNEYS GET MOST OF THEIR BLOOD SUPPLY FROM?
Renal Artery
The kidneys have lobes; these lobes have pyramids that feed into the papilla, which allows the _ of blood to occur. The filtered product then moves into the pyramids, then to the papilla and then eventually into the _.
Filtering
Ureter
FUNCTIONAL UNIT OF THE KIDNEYS: THE NEPHRON
AT REST, WHAT PERCENTAGE OF CARDIAC OUTPUT GOES TO THE KIDNEYS?
20-25%
STRUCTURAL FEATURES OF THE NEPHRON
WHAT PARTS OF THE NEPHRON DOES THE CORTEX OF THE KIDNEY CONTAIN?
All of the Bowman’s Capsule, proximal and distil tubules
WHAT PARTS OF THE NEPHRON DOES THE MEDULLA OF THE KIDNEY CONTAIN?
Loops of Henle
Collecting Ducts
TUBULE STRUCTURE
WHERE IN THE NEPHRON DOES BLOOD FILTRATION OCCUR?
Bowman’s capsule
STRUCTURAL FEATURES OF THE RENAL CORPUSCLE
WHAT ARE FENESTRATED CAPILLARIES?
Large gaps between endothelial cells (but not big enough for cells to pass through)
WHAT IS THE BASAL LAMINA?
Thin layer of extracellular matrix, separates the endothelial cells from the podocytes
WHAT ARE PODOCYTES?
Pedicels,narrow filtration slits, finest level of filtration
THE CAPILLARY ENDOTHELIUM, BASEMENT MEMBRANE AND VISCERAL EPITHELIUM FORM A FILTRATION BARRIER
THE THREE FILTRATION BARRIERS
Very large surface area for filtration to occur
Size of _ determines the level of filtration and the compostition of filtrate.
Water and electrolytes, glucose, very small proteins and amino acids to be filtered. Waste products, urea, ammonium
Large cells in healthy kidney cannot pass through.
Filtration fraction – 20%, amount of substance that is filtered from plasma into capsule.
Pores
WHAT IS THE GLOMERULER FILTRATE?
An ultrafiltrate of the plasma. It contains water and dissolved solutes, but no cells and, in health, only trace amounts of protein
THE HYDROSTATIC PRESSURE OF THE GLOMERULER CAPILLARIES DRIVES FILTRATION
WHAT IS GLOMERULER FILTRATION RATE (GFR)?
The volume of filtrate produced by the kidney’s per minute
WHAT IS THE AVERAGE GFR IN A HEALTHY ADULT?
GFR is ≈125 mL/min (equivalent to 180 L/day)
This filtration fraction is ≈20% of total renal blood flow
GLOMERULER FILTRATION RATE: THE VOLUME OF FILRATE PRODUCED BY THE KIDNEYS PER MINUTE
In an healthy adult, and over a wide range of blood pressures,
GFR is ≈125 mL/min (equivalent to 180 L/day)
This filtration fraction is ≈20% of total renal blood flow
Despite a net filtration pressure of only 10 mmHg, the volume of filtrate is large for three reasons:
- the surface area of the glomerular _ is large
- the glomerular capillary endothelium is fenestrated
- the glomerular capillary blood pressure is _
* 99% of the filtered volume is reabsorbed *
Capillaries
High
WHAT ARE THE THREE REASONS WHY THE VOLUME OF THE GLOMERULER FILRATE IS LARGE?
- The surface area of the glomerular capillaries is large
- The glomerular capillary endothelium is fenestrated
- The glomerular capillary blood pressure is high
CHANGES IN THE DIAMETER OF THE AFFERENT AND EFFERENT ARTERIOLES ALTER RENAL BLOOD FLOW AND GFB
THE URINARY EXCRETION OF A SUBSTANCE DEPENDS ON ITS FILTRATION, REABSORPTION AND SECRETION
WHAT THREE THINGS DOES THE URINARY EXCRETION OF A SUBSTANCE DEPEND ON?
Its filtration, reabsorption and secretion
REGIONS OF THE NEPHRON WHERE FILTRATE IS MODIFIED
WHAT PART OF THE NEPHRON ARE MOST FLUIDS AND SOLUTES (65%) REABSORBED?
Proximal convoluted tubule
WHAT IS UROBILINOGEN?
A colourless by-product of bilirubin reduction
UROBILINOGEN
A colorless by-product of bilirubin _. It is formed in the intestines by bacterial action on bilirubin. About half of the urobilinogen formed is reabsorbed and taken up via the portal _ to the liver, enters circulation and is excreted by the kidney.
Reduction
Vein
THE SIX SUBDIVISIONS OF RENAL FUNCTION
- Regulation of extracellular fluid volume and blood pressure
- Regulation of blood Osmolarity (≈300mOsM)
- the number of osmotically active particles per litre of fluid - Maintenance of _ balance (e.g., Na+, K+, Ca2+ & Cl-)
- Na+ is the most important in respect of ‘1’ and ‘2’ - Homeostatic regulation of plasma pH (7.38 – 7.42)
- secretion and/or reabsorption of H+ and HCO3- - Excretion of metabolic and other wastes
- creatinine, urea, urobilinogen; hormones; drugs and xenobiotics - Production of _
- synthesis of erythropoetin; production of 1,25-dihydroxyvitamin D3
Ion
Hormone
THE KIDNEY’S MAINTAIN FLUID AND ELECTROLYTE BALANCE IN ACCORDANCE WITH THE PRINCIPLE OF ‘MASS BALANCE’
WHAT IS THE PRIMARY FUNCTION OF THE KIDNEYS?
The maintenance (homeostasis) of fluid and electrolyte balance (the main function is NOT the removal of wastes)
WHAT WOULD HAPPEN TO A CELL IF YOU PUT IT INTO A HYPOTONIC SOLUTION?
The cell would swell as water moves in (as there is a lower conc. of solute in the surrounding solution than in the cell)
WHAT IS AN ISOTONIC SOLUTION?
A solution that won’t cause a change in cell size when the cell is placed into it (as the conc. of water in the solution is the same as the conc. of water in the cell)
WHAT IS A HYPERTONIC SOLUTION?
A solution that has a higher conc. of solutes than inside the cell= water moves out of the cell and into the solution surrounding it.
INGESTING FLUID
REGULATION OF FLUID BALANCE
Involves sensing osmolarity, pressure and volume of _.
- Kidneys are the site of salt regulation.
- Salt (Na+) regulation is important in regulating blood volume, as it controls the movement of _ across the plasma membranes. Water will follow the movement of sodium if that membrane is permeable to water.
- Sodium regulation relies on balance between sodium being filtered and _.
- Body detects changes in sodium (salt) concentration indirectly as changes in blood volume, and therefore detects this with the baroreceptors and osmoreceptors in the _.
- Regulation of blood volume also regulates total body sodium.
- Low sodium = low blood volume, high sodium = high blood volume
Blood
Water
Reabsorbed
Hypothalamus
TO WORK OUT HOW MUCH SODIUM IS EXCRETED IN URINE, DO: sodium excreted = sodium filtered – sodium reabsorbed
THE CONSEQUENCES OF ELECTROLYTE IMBALANCES
THE KIDNEYS FULFIL THEIR HOMEOSTATIC FUNCTION BY REGULATING URINARY VOLUME, OSMOLARITY AND ACIDITY
KEY FACTORS:
- the cortico-medullary osmotic gradient
- regional differences in the permeability of the nephron and collecting duct
- regional differences in the selective reabsorption* and secretion of solutes in the nephron and collecting duct
- the arrangement and proximity of the peritubular capillaries and vasa recta
TUBULAR TRANSPORT
•Two membrane surfaces
–Basolateral membrane (adjacent to interstitial fluid)
–Luminal/apical membrane (adjacent to tubular fluid)
- From tubular filtrate into tubular cell along concentration gradient
- Require facilitated or carrier systems to cross basolateral membrane
MOVEMENT OF WATER AND SOLUTES IN THE NEPHRON
Remember: The descending limb is permeable to water but the ascending limb isn’t.
WHAT IS THE CARBONIC ACID FORMULA?
H2CO3
REABSORPTION OF Na+ AND HCO3 AND SECRETION OF H+ IN THE PCT
REABSORPTION OF GLUCOSE IN THE PCT
PASSIVE REABSORPTION OF OTHER IONS AND WATER IN THE PCT
MOVEMENT OH H20 IN THE LOOP OF HENLE: THE DESCENDING LOOP IS PERMEABLE AND THE ASCENDING LOOP IS IMPERMEABLE
The wall of the thin segment of the descending limb of the loop of Henle is permeable to _ and, to a lesser extent, to solutes. The interstitial fluid in the medulla of the kidney and the blood in the vasa recta have a high _ concentration. Water therefore moves by osmosis from the tubule into the interstitial fluid and into the vasa recta. An additional 15% of the filtrate volume is reabsorbed. To a lesser extent, solutes diffuse from the vasa recta and interstitial fluid into the tubule.
The thin segment of the ascending limb of the loop of Henle is not permeable to water but is permeable to _. The solutes diffuse out of the tubule and into the more _ interstitial fluid as the ascending limb projects toward the cortex. The solutes diffuse into the descending vasa recta.
Water
Solute
Solutes
Dilute
REABSORPTION IN THE THICK SEGMENT OF THE ASCENDING LOOPS
REABSORPTION IN THE DCT AND COLLECTING DUCT
OVERVIEW OF TUBULE FUNCTIONS
•Proximal tubule:
–70% Na removed by active transport,
–_ ions and water follow passively
–secretion of _, absorption of bicarbonate
•Descending loop Henle:
–water permeable, not _.
–osmotic loss of water concentrates salts in lumen
•Ascending, loop Henle:
–thin segment; salt permeable, not water
–salts diffuse out of lumen
–thick segment; active Na+ and Cl- & K+ cotransport
•Distal Tubule:
–active Na+ and Cl- co transport
–permeable to _.
Chloride
Acid
Salts
Water
THE HOMEOSTATIC REGULATION OF BLOOD PRESSURE AND BLOOD VOLUME IS INTEGRATED
EXTRINSIC FACTORS AFFECTING TUBULAR REABSORPTION AND SECRETION
THE RENIN-ANGIOTENSIN-ALDOSTERONE SYSTEM CO-ORDINATES THE RESPONSES OF THE CARDIOVASCULAR AND RENAL SYSTEMS TO DECREASES IN BLOOD PRESSURE/VOLUME.
WHAT CONDITIONS ARE ACE INHIBITORS LARGELY USED TO TREAT?
High BP
Heart failure
Diabetic nephropathy
Type 2 diabetes
WHAT DOES ALDOSTERONE DO?
Stimulates Na+ absorption
CONSUMING ALCOHOL REDUCES ADH EFFECT.
TRUE OR FALSE?
TRUE
ADH RELEASE
ANTI-DIURETIC HORMONE (VASOPRESSIN) REGULATES THE REABSORPTION OF WATER IN THE COLLECTING DUCT
ADH REGULATES THE REVERSIBLE INSERTION OF WATER PORES IN THE APICAL MEMBRANE OF CELLS IN THE COLLECTING DUCT
WHAT DOES ADH DO SPECIFICALLY?
Regulates the reversible insertion of water pores in the apical membrane of cells in the collecting duct
WHAT DOES ATRIAL NATRIURETIC PEPTIDE (ANP) DO?
Decreases the reabsorption of Na+ and water in the DCT and CCD
HOW DOES THE KIDNEY HANDLE DIFFERENT SUBSTANCES?
RENAL CLEARANCE: HOW A SOLUTE IS HANDLED BY THE KIDNEYS
The excretion rate (E) of a substance into the urine provides no mechanistic insights into how the kidney handled that substance. This is because, as can be seen from the figure, E depends on i) the filtration rate of the substance (F) and whether it is resorbed (R), secreted (S) or both.
The renal handling of a substance and GFR are often of clinical and regulatory interest.
Clearance of a solute (e.g. a drug) is the rate at which that solute disappears from the body by excretion or metabolism (TURN OVER):
RENAL CLEARANCE: HOW A SOLUTE IS HANDLED BY THE KIDNEYS (2)
For any solute that is cleared only by excretion, clearance is expressed as the volume of _ passing through the kidneys that has been totally cleared of that solute in a given time.
Inulin (a plant polysaccharide) has the interesting property in that it is freely filtered by the kidney, but is neither reabsorbed or _. Essentially, all the inulin filtered in kidney is recovered in the urine and hence we can state the following:
GFR= Inulin clearance
In the hypothetical examples that follow, we follow the renal excretion of 4 molecules of inulin, glucose, urea and penicillin, all present in the plasma at 4 molecules per 100 mL, over a 1 minute period. For simplicity, 100% of the filtered volume is assumed to be reabsorbed and GFR to be 100 mL of plasma filtered per min.
Plasma
Secreted
RENAL CLEARANCE: INULIN AND GLUCOSE
RENAL CLEARANCE: UREA AND PENICILLIN
WHAT IS INULIN?
A plant polysaccharide that is freely filtered by the kidney, but is neither reabsorbed nor secreted.
WHAT IS PARESTHESIA?
An abnormal condition where you feel a sensation of burning, numbness, tingling, itching or prickling
THE MAINTENENCE ACID-BASE BALANCE DEPENDS ON THE RESPIRATORY AND RENAL SYSTEMS
WHAT DOES ACID-BASE BALANCE DEPEND ON?
Respiratory and renal systems
ACIDOSIS: pH IS TOO LOW
THE KIDNEY’S WILL EXCRETE _ IONS AND REABSORB _ IONS
H+
HCO3-
ALKALOSIS: pH IS TOO HIGH
THE KIDNEY’S EXCRETE _ IONS AND HCO3- IONS REABSORB _ IONS.
K+
H+
