The Kidneys

Question 1

WHERE ARE THE KIDNEYS LOCATED?

Answer 1

Just below the diaphragm

Question 2

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

Question 3

INTERNAL ANATOMY

Question 4

KIDNEY BLOOD SUPPLY

Question 5

WHERE DO THE KIDNEYS GET MOST OF THEIR BLOOD SUPPLY FROM?

Answer 5

Renal Artery

Question 6

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 _.

Answer 6

Filtering

Ureter

Question 7

FUNCTIONAL UNIT OF THE KIDNEYS: THE NEPHRON

Question 8

AT REST, WHAT PERCENTAGE OF CARDIAC OUTPUT GOES TO THE KIDNEYS?

Answer 8

20-25%

Question 9

STRUCTURAL FEATURES OF THE NEPHRON

Question 10

WHAT PARTS OF THE NEPHRON DOES THE CORTEX OF THE KIDNEY CONTAIN?

Answer 10

All of the Bowman’s Capsule, proximal and distil tubules

Question 11

WHAT PARTS OF THE NEPHRON DOES THE MEDULLA OF THE KIDNEY CONTAIN?

Answer 11

Loops of Henle

Collecting Ducts

Question 12

TUBULE STRUCTURE

Question 13

WHERE IN THE NEPHRON DOES BLOOD FILTRATION OCCUR?

Answer 13

Bowman’s capsule

Question 14

STRUCTURAL FEATURES OF THE RENAL CORPUSCLE

Question 15

WHAT ARE FENESTRATED CAPILLARIES?

Answer 15

Large gaps between endothelial cells (but not big enough for cells to pass through)

Question 16

WHAT IS THE BASAL LAMINA?

Answer 16

Thin layer of extracellular matrix, separates the endothelial cells from the podocytes

Question 17

WHAT ARE PODOCYTES?

Answer 17

Pedicels,narrow filtration slits, finest level of filtration

Question 18

THE CAPILLARY ENDOTHELIUM, BASEMENT MEMBRANE AND VISCERAL EPITHELIUM FORM A FILTRATION BARRIER

Question 19

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.

Answer 19

Pores

Question 20

WHAT IS THE GLOMERULER FILTRATE?

Answer 20

An ultrafiltrate of the plasma. It contains water and dissolved solutes, but no cells and, in health, only trace amounts of protein

Question 21

THE HYDROSTATIC PRESSURE OF THE GLOMERULER CAPILLARIES DRIVES FILTRATION

Question 22

WHAT IS GLOMERULER FILTRATION RATE (GFR)?

Answer 22

The volume of filtrate produced by the kidney’s per minute

Question 23

WHAT IS THE AVERAGE GFR IN A HEALTHY ADULT?

Answer 23

GFR is ≈125 mL/min (equivalent to 180 L/day)

This filtration fraction is ≈20% of total renal blood flow

Question 24

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 *

Answer 24

Capillaries

High

Question 25

WHAT ARE THE THREE REASONS WHY THE VOLUME OF THE GLOMERULER FILRATE IS LARGE?

Answer 25

* The surface area of the glomerular capillaries is large * The glomerular capillary endothelium is fenestrated * The glomerular capillary blood pressure is high

Question 26

**_CHANGES IN THE DIAMETER OF THE AFFERENT AND EFFERENT ARTERIOLES ALTER RENAL BLOOD FLOW AND GFB_**

Question 27

**_THE URINARY EXCRETION OF A SUBSTANCE DEPENDS ON ITS FILTRATION, REABSORPTION AND SECRETION_**

Question 28

WHAT THREE THINGS DOES THE URINARY EXCRETION OF A SUBSTANCE DEPEND ON?

Answer 28

Its filtration, reabsorption and secretion

Question 29

**_REGIONS OF THE NEPHRON WHERE FILTRATE IS MODIFIED_**

Question 30

WHAT PART OF THE NEPHRON ARE MOST FLUIDS AND SOLUTES (65%) REABSORBED?

Answer 30

Proximal convoluted tubule

Question 31

WHAT IS UROBILINOGEN?

Answer 31

A colourless by-product of bilirubin reduction

Question 32

**_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.

Answer 32

Reduction Vein

Question 33

**_THE SIX SUBDIVISIONS OF RENAL FUNCTION_** ## Footnote 1. Regulation of extracellular fluid volume and blood pressure 2. Regulation of blood Osmolarity (≈300mOsM) - the number of osmotically active particles per litre of fluid 3. Maintenance of _ balance (e.g., Na+, K+, Ca2+ & Cl-) - Na+ is the most important in respect of ‘1’ and ‘2’ 4. Homeostatic regulation of plasma pH (7.38 – 7.42) - secretion and/or reabsorption of H+ and HCO3- 5. Excretion of metabolic and other wastes - creatinine, urea, urobilinogen; hormones; drugs and xenobiotics 6. Production of \_ - synthesis of erythropoetin; production of 1,25-dihydroxyvitamin D3

Answer 33

Ion Hormone

Question 34

**_THE KIDNEY'S MAINTAIN FLUID AND ELECTROLYTE BALANCE IN ACCORDANCE WITH THE PRINCIPLE OF 'MASS BALANCE'_**

Question 35

WHAT IS THE PRIMARY FUNCTION OF THE KIDNEYS?

Answer 35

The maintenance (homeostasis) of fluid and electrolyte balance (the main function is NOT the removal of wastes)

Question 36

WHAT WOULD HAPPEN TO A CELL IF YOU PUT IT INTO A HYPOTONIC SOLUTION?

Answer 36

The cell would swell as water moves in (as there is a lower conc. of solute in the surrounding solution than in the cell)

Question 37

WHAT IS AN ISOTONIC SOLUTION?

Answer 37

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)

Question 38

WHAT IS A HYPERTONIC SOLUTION?

Answer 38

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.

Question 39

**_INGESTING FLUID_**

Question 40

**_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

Answer 40

Blood Water Reabsorbed Hypothalamus

Question 41

TO WORK OUT HOW MUCH SODIUM IS EXCRETED IN URINE, DO: sodium excreted = sodium filtered – sodium reabsorbed

Question 42

**_THE CONSEQUENCES OF ELECTROLYTE IMBALANCES_**

Question 43

**_THE KIDNEYS FULFIL THEIR HOMEOSTATIC FUNCTION BY REGULATING URINARY VOLUME, OSMOLARITY AND ACIDITY_** ## Footnote **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

Question 44

**_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

Question 46

**_MOVEMENT OF WATER AND SOLUTES IN THE NEPHRON_** ## Footnote **Remember:** The descending limb is permeable to water but the ascending limb isn't.

Question 47

WHAT IS THE CARBONIC ACID FORMULA?

Answer 47

H₂CO₃

Question 48

**_REABSORPTION OF Na⁺ AND HCO₃ AND SECRETION OF H⁺ IN THE PCT_**

Question 49

**_REABSORPTION OF GLUCOSE IN THE PCT_**

Question 50

**_PASSIVE REABSORPTION OF OTHER IONS AND WATER IN THE PCT_**

Question 51

**_MOVEMENT OH H20 IN THE LOOP OF HENLE: THE DESCENDING LOOP IS PERMEABLE AND THE ASCENDING LOOP IS IMPERMEABLE_** ## Footnote 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.

Answer 51

Water Solute Solutes Dilute

Question 52

**_REABSORPTION IN THE THICK SEGMENT OF THE ASCENDING LOOPS_**

Question 53

**_REABSORPTION IN THE DCT AND COLLECTING DUCT_**

Question 54

**_OVERVIEW OF TUBULE FUNCTIONS_** ## Footnote •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 \_.

Answer 54

Chloride Acid Salts Water

Question 55

**_THE HOMEOSTATIC REGULATION OF BLOOD PRESSURE AND BLOOD VOLUME IS INTEGRATED_**

Question 56

**_EXTRINSIC FACTORS AFFECTING TUBULAR REABSORPTION AND SECRETION_**

Question 57

**_THE RENIN-ANGIOTENSIN-ALDOSTERONE SYSTEM CO-ORDINATES THE RESPONSES OF THE CARDIOVASCULAR AND RENAL SYSTEMS TO DECREASES IN BLOOD PRESSURE/VOLUME._**

Question 58

WHAT CONDITIONS ARE ACE INHIBITORS LARGELY USED TO TREAT?

Answer 58

High BP Heart failure Diabetic nephropathy Type 2 diabetes

Question 59

WHAT DOES ALDOSTERONE DO?

Answer 59

Stimulates Na⁺ absorption

Question 60

CONSUMING ALCOHOL REDUCES ADH EFFECT. TRUE OR FALSE?

Answer 60

TRUE

Question 61

**_ADH RELEASE_**

Question 62

**_ANTI-DIURETIC HORMONE (VASOPRESSIN) REGULATES THE REABSORPTION OF WATER IN THE COLLECTING DUCT_**

Question 63

**_ADH REGULATES THE REVERSIBLE INSERTION OF WATER PORES IN THE APICAL MEMBRANE OF CELLS IN THE COLLECTING DUCT_**

Question 64

WHAT DOES ADH DO SPECIFICALLY?

Answer 64

Regulates the reversible insertion of water pores in the apical membrane of cells in the collecting duct

Question 65

WHAT DOES ATRIAL NATRIURETIC PEPTIDE (ANP) DO?

Answer 65

Decreases the reabsorption of Na⁺ and water in the DCT and CCD

Question 66

**_HOW DOES THE KIDNEY HANDLE DIFFERENT SUBSTANCES?_**

Question 67

**_RENAL CLEARANCE: HOW A SOLUTE IS HANDLED BY THE KIDNEYS_** ## Footnote 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):

Answer 67

Question 68

**_RENAL CLEARANCE: HOW A SOLUTE IS HANDLED BY THE KIDNEYS (2)_** ## Footnote 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.

Answer 68

Plasma Secreted

Question 69

**_RENAL CLEARANCE: INULIN AND GLUCOSE_**

Question 70

**_RENAL CLEARANCE: UREA AND PENICILLIN_**

Question 71

WHAT IS INULIN?

Answer 71

A plant polysaccharide that is freely filtered by the kidney, but is neither reabsorbed nor secreted.

Question 72

WHAT IS PARESTHESIA?

Answer 72

An abnormal condition where you feel a sensation of burning, numbness, tingling, itching or prickling

Question 73

**_THE MAINTENENCE ACID-BASE BALANCE DEPENDS ON THE RESPIRATORY AND RENAL SYSTEMS_**

Question 74

WHAT DOES ACID-BASE BALANCE DEPEND ON?

Answer 74

Respiratory and renal systems

Question 75

**_ACIDOSIS: pH IS TOO LOW_** THE KIDNEY'S WILL EXCRETE _ IONS AND REABSORB _ IONS

Answer 75

H⁺ HCO₃^-

Question 76

**_ALKALOSIS: pH IS TOO HIGH_** THE KIDNEY'S EXCRETE _ IONS AND HCO₃^- IONS REABSORB _ IONS.

Answer 76

K⁺ H⁺