Week 4 Renal

Question 1

Where are the kidneys located?

Answer 1

Kidneys are in the posterior region of the abdominal cavity, behind the peritoneum. They lie on either side of the vertebral column, with upper and lower poles extending from 12th Thoracic vertebra to 3rd lumbar vertebra.

Question 2

Define cortex of kidney

Answer 2

Outer layer of kidney, contains all the glomeruli, most of proximal tubules and some of the segments of the distal convoluted tubule

Question 3

Define Medulla

Answer 3

Inner part of the kidney consisting of regions called pyramids

Question 4

Define pyramids of kidney

Answer 4

Extend into the renal pelves and contain loops of Henle and collecting ducts

Question 5

What are the renal columns

Answer 5

extension of the cortex, extend between the pyramids to the renal pelvis

Question 6

What are the renal calyces

Answer 6

=chambers receiving urine from collecting ducts and form entry of renal pelvis (extension of upper ureter)

Question 7

What is the structural unit of the kidney, and what is it composed of

Answer 7

Structure unit of the kidney is the lobe. Each love is composed of a pyramid and overlying cortex, with 14-18 lobes in each kidney

Question 8

What is the functional unit of the kidney? Describe

Answer 8

Nephron is a tubular structure with: 1. Renal Corpuscle 2. Proximal convoluted tubule 3. Loop of Henle 4. Distal convoluted tubule 5. Collecting duct=all help with formation of urine

Question 9

What are the 3 kinds of nephrons

Answer 9

(1) superficial cortical nephrons (85% of all nephrons), which extend partially into the medulla; (2) midcortical nephrons with short or long loops; and (3) juxtamedullary nephrons (about 12% of nephrons), which lie close to and extend deep into the medulla and are important for the concentration of urine

Question 10

What is the glomerulus

Answer 10

The glomerulus is a tuft of capillaries that loop into the Bowman capsule (Bowman space), like fingers pushed into bread dough.

Question 11

What do mesangial cells do

Answer 11

Mesangial cells (shaped like smooth muscle cells) secrete the mesangial matrix (a type of connective tissue) and lie between and support the capillaries. Mesangial cells also have phagocytic abilities=release inflammatory cytokines + can contract to regulate glomerular capillary blood flow

Question 12

What does the renal corpuscle consist of (3 components)

Answer 12

Combo of glomerulus, the Bowman capsule, and mesangial cells (GBM)

Question 13

Describe the 3 layers of the glomerular filtration membrane

Answer 13

The glomerular filtration membrane filters blood components through its 3 layers:

(1) an inner capillary endothelium (cells in continuous contact with the basement membrane + has pores)

(2) a middle basement membrane (glycoproteins + mucopolysaccharides)

(3) an outer layer of capillary epithelium (Podocytes from which pedicles (foot projections) stick to basement membrane)

Filtration slits=pedicles interlock with podocytes

Endothelium, basement membrane + podocytes covered with protein molecules with anionic (negative) charges=help with filtration of anionic proteins and prevention of proteinuria

The membrane separates blood of glomerular capillaries + fluid of Bowman space. Filters everything EXCEPT blood, plasma proteins

Question 14

What blood source is the glomerulus supplied be? Where does blood drain?

Answer 14

Glomerulus: is supplied by the afferent arteriole and drained by the efferent arteriole.

Question 15

What hormone do juxtaglomerular cells release

Answer 15

renin

Question 16

Where are juxtaglomerular cells located

Answer 16

around the afferent arteriole where it enters the glomerulus

Question 17

What is the macula densa? Where is it located?

Answer 17

Macula Densa: (sodium-sensing cells) located Between the afferent+ efferent arterioles on the distal convoluted tubule

Question 18

What does the juxtaglomerular apparatus consist of? What is are its 3 functions?

Answer 18

Juxtaglomerular Apparatus=Juxta cells + Macula Densa

Function: 1. Control renal blood flow (RBF) 2. glomerular filtration 3. Renin secretion occurs here

Question 19

Describe the proximal convoluted tubule

Answer 19

Proximal convoluted tubule: Consists of 1 layer of cuboidal epithelial cells+surface layer or microvilli=increases reabsorptive surface area **only surface with microvilli in nephron

Joins the Loop of Henle which extends into Medulla

Question 20

Describe the loop of Henle

Answer 20

Loop of Henle: Cells of thick segment are cuboidal=transport solutes, no H2O—thin segment is thin squamous cells, no transport

Question 21

Describe the distal convoluted tubule

Answer 21

The distal convoluted tubule: has straight and convoluted segments. It extends from the macula densa to the collecting duct

Principal cells: reabsorb sodium, secrete potassium

intercalated cells: secrete hydrogen, reabsorb potassium + bicarbonate.

Adjusts acid-base balance by excreting acid into the urine and forming new bicarb ions

Question 22

Describe the collecting ducts

Answer 22

Collecting duct: a large tubule that descends down the cortex, through the renal pyramids of the inner and outer medullae, draining urine into the minor calyx

Question 23

What is GFR

Answer 23

Glomerular filtration rate (GFR) – is the measurement of plasma filtration per unit of time.

Question 24

How is GFR regulated?

Answer 24

GFR is autoregulated via the perfusion pressures (capillary hydrostatic pressure, oncotic pressure, hydrostatic pressure of Bowmans space) of the glomerular capillaries.

Question 25

What substance cannot pass through the glomerular capilleries into Bowmans capsule?

Answer 25

The glomerular capillaries do not allow RBCs and plasma proteins to pass into the Bowmans capsule, because the glomerular filtration barrier consists of 3 layers that eliminate loss of RBC and prevent proteinuria. This then only leaves a small amount of filtrate (a combination of substances: water, solutes like Na+) to circulate in the tubules, approx. 125ml.

Question 26

What hormones affect blood flow to the kidney?

Answer 26

Adrenaline and Angiotensin II increase arterioles (afferent and efferent) resistance which in turn decrease renal blood flow and decreases GFR. These hormones are stimulated in order to raise BP and stimulate reabsorption. Atriopeptin (ANP) (secreted via Atria) and Brain Natriuretic Peptide (BNP) (secreted via ventricles) decreases arterioles resistance which in turn increase renal blow flow and increases GFR. These peptides are stimulated in order to help lower BP and excrete substances.

Question 27

What is Autoregulation of Renal Blood Flow

Answer 27

-local mechanism with kidney – will keep renal blood flow and GFR constant over a range of systemic blood pressures (80mmHg – 200mmHg)

Question 28

What is the myogenic mechanism?

Answer 28

Myogenic mechanism – smooth muscle cells contract when stretched because of high volumes/pressures of blood. Once cells are stretched, the afferent and efferent arterioles contract.

Question 29

What is the Tubuloglomerular Mechanism

Answer 29

Tubuloglomerular Mechanism – involves distal convoluted tubule and glomerulus. The macula densa cells – chemoreceptors - sense when GFR is up or down based on quantity of Na+ or Cl- ions floating thru tubules. -If increase in BP = Increase renal blood flow = increase GFR therefore more fluid and more dissolved ions reach macula densa which in response will release adenosine causing the afferent arteriole to constrict, decreasing GFR.

Question 30

What is the vasa recta

Answer 30

Vasa Recta – network of capillaries that is the only blood supply to the medulla (contributes to formation of concentrated urine). The capillaries form loops and closely follows the loop of Henle.

Question 31

Describe the process of urine formation

Answer 31

Glomerular Filtration: Movement of fluid and solutes across the glomerular capillary membrane into the bowman space - Water, electrolytes (sodium, chloride, and potassium), and organic molecules (creatinine, urea, glucose) are filtered at the glomerulus. - Protein free Tubular reabsorption: Movement of fluids and solutes from the tubular lumen to the peritubular capillary plasma reabsorption of h20 by osmosis- occurs when ADH is present Reabsorption of sodium by active transport. More sodium is conserved when aldosterone is secreted Glucose by active transport Tubular Secretion: Transfer of substances from the plasma of the peritubular capillary to the tubular lumen - Secretion of ammonia, hydrogen, and potassium by active transport.

Question 32

What factors determine GFR

Answer 32

Factors determining GFR are related to the pressures that favour or oppose filtration. Obstruction of outflow (ex. Strictures, stones, tumours) can cause an increase in hydrostatic pressure at bowman space and a decrease in GFR Low levels of plasma protein in the blood can results in a decrease in capillary oncotic pressure resulting in an increase in GFR Excessive loss of protein-free-fluid from vomiting diarrhea or use of diuretics can increase capillary oncotic pressure and decrease GFR

Question 33

Where does urine concentration primarily occur

Answer 33

Urine concentration/dilution occurs primarily in the loop of Henle, distal convoluted tubules and collecting ducts

Question 34

What determines final urine composition

Answer 34

Final urine composition is determined by the distal convoluted tubules and collecting duct according to what the body needs

Question 35

What is the countercurrent exchange system

Answer 35

The production of concentrated urine involves a countercurrent exchange system in which fluid flows in opposite directions through the parallel tubes of the loop of Henle

Question 36

What is substance is transported out of the ascending limb of Henle to the descending limb of vasa recta/ interstitium

Answer 36

NaCl

Question 37

As urine flows _________________ in the collecting tubule, it encounters higher and higher concentrations of solutes in the interstitium. Hence it goes on losing water due to osmosis. This is how urine is concentrated.

Answer 37

downwards

Question 38

Define tubular reasbsorption

Answer 38

Tubular reabsorption is the movement of fluids and solutes from the tubular lumen to the peritubular capillary plasma.

Question 39

Define tubular secretion

Answer 39

Tubular secretion is the transfer of substances from the plasma of the peritubular capillary to the tubular lumen...for eventual excretion.

Question 40

Define excretion

Answer 40

Excretion is the elimination of a substance in the final urine

Question 41

Where is the primary site of sodium reabsorption

Answer 41

Proximal Convoluted tubule: Primary site of sodium reabsorption.

Question 42

What happens to drug elimination if renal tubules are damaged

Answer 42

Damage to the renal tubules results in retention and accumulation of metabolites and causes toxic effects.

Question 43

What moves into the tubule in exchange for sodium ions?

Answer 43

Hydrogen ions move into the tubule in exchange for sodium ions

Question 44

How is bicarb transported out of the tubule into the peritubular capillery?

Answer 44

Basically, hydrogen and sodium are positive ions that are required for the transport of bicarb from the tubule back into the peritubular capillary. In more detail: Hydrogen ions move into the tubule in exchange for sodium ions. These ions then combine with bicarbonate (HCO3) to form carbonic acid H2CO3 which can break down into Carbon dioxide and water to allow it to be absorbed from the tubular space into the tubular cell. Here it forms bicarbonate and hydrogen ions again but this time sodium ions join the bicarbonate ions as a sodium bicarbonate buffer (NaHCO3) to move it into the peritubular capillary. The reabsorption of the hydrogen ions as water means that there is not a large shift in pH in either the blood or the urine.

Question 45

What mechanism is responsible for urine concentration? What does it rely on?

Answer 45

The Countercurrent exchange system is responsible for urine concentration and relies on a concentration gradient that causes the exchange of fluid.

Question 46

T/F The concentration gradient in the kidney increased from the cortex to the medulla

Answer 46

T: The concentration gradient increases from the cortex to the tip of the medulla as you move down the descending limb of the loop of henle.

Question 47

What part of the loop of henle is permeable to water?

Answer 47

descending

Question 48

Where is water rebabsorbed from the tubular system? why?

Answer 48

As fluid in the tubular system descends in the medulla, the concentration gradient increases causing water to be reabsorbed from the tubular system. This occurs in the descending limb of the loop of henle because this area is only permeable to water (some passive transport of sodium and chloride is allowed, but not active transport).

Question 49

What is transported in the ascending loop of Henle, and how

Answer 49

NaCl, active transport

Question 50

Is the ascending loop of Henle permeable to water?

Answer 50

No

Question 51

Describe the journey of tubular fluid throughout the whole loop of Henle. What does the end product look like?

Answer 51

As fluid in the tubular system descends in the medulla, the concentration gradient increases causing water to be reabsorbed from the tubular system. This occurs in the descending limb of the loop of henle because this area is only permeable to water (some passive transport of sodium and chloride is allowed, but not active transport). The result is that by the time the fluid reaches the bottom of the loop of henle where the concentration gradient is greatest, the fluid within the tubule is very concentrated because mostly sodium and chloride have remained in the tubule while water has been reabsorbed into the medullary interstitium. As the fluid in the tubule rounds the corner and ascends the ascending limb of the loop of henle, the surrounding interstitium has a less and less concentration gradient. Active transport of sodium and chloride out of the tubule into the medullary interstitium occurs. However, water is not able to diffuse in this location. This results in relative dilution of the fluid in the tubule (but not an increase in volume!) In theory, the fluid within the tubular system has the same concentration at the top of the medulla, so where it enters from the proximal convoluted tubule and where it exits in the distal convoluted tubule. However, the volume has decreased because reabsorption of water and sodium chloride have occurred.

Question 52

What happens to sodium and potassium in the DCT under the influence of aldosterone?

Answer 52

Sodium is readily reabsorbed here under the regulation of aldosterone. Potassium is actively secreted here under the regulation of aldosterone and potassium concentration in body fluids.

Question 53

What is the site of acid base balance? (what part of kidney)

Answer 53

DCt

Question 54

How is acid eliminated in urine?

Answer 54

Hydrogen ions are secreted in the distal convoluted tubule to combine with ammonium and phosphate buffers to eliminate acid in the urin

Question 55

What is the normal ph of urine

Answer 55

4.6 and 8

Question 56

Why do we want acidic urine

Answer 56

protects against bacteria

Question 57

What hormone is responsible for reabsorption of water before final excretion of urine? Where does this occur?

Answer 57

ADH in the collecting duct

Question 58

Describe tubuloglomerual feedback (an autoregulation mechanism of the kidney)

Answer 58

Macula densa cells in the distal convoluted tubule sense changes in glomerular filtration rate (GFR) and the amount of filtered sodium. When the GFR and sodium concentration increase, this stimulates vasoconstriction in the afferent arteriole to decrease the GFR. The opposite is also true. This is called tubuloglomerular feedback which is an autoregulation mechanism in the kidneys. The result is the avoidance of large fluctuations of water and salt in the body.

Question 59

What are the 3 major endocrine functions of the kidney

Answer 59

Vitamin D activation, EPO, renin

Question 60

Describe the process of vit D activation by kidney

Answer 60

Vitamin D Activation (Hydroxylation) Vitamin D is necessary for the absorption of calcium and phosphate by the small intestine Activation is stimulated by Parathyroid Hormone A decrease in plasma calcium level stimulates the secretion of parathyroid hormone Parathyroid Hormone stimulates the following sequence of events to restore calcium levels: Calcium mobilization from Bone Synthesis of 1,25-dihydroxy-Vitamin D3 Absorption of calcium from the intestine Increased Renal calcium reabsorption Decreased Renal Phosphate reabsorption Decreased Phosphate levels stimulate 1,25-dihydroxy-vitamin D3 formation and increased levels inhibit its formation This results in compensatory changes in the phosphate absorption from bone and intestine

Question 61

Describe the process of EPO production by the kidney

Answer 61

Stimulates Erythropoiesis in the blood marrow in response to hypoxia Peritubular Fibroblasts, in the juxtamedullary cortex, sense decreased oxygen levels and produce EPO

Question 62

How does renal disease impact EPO production

Answer 62

Chronic Kidney Disease can cause these cells to be non-functional and lack of EPO can cause anemia

Question 63

What is urodilatin?

Answer 63

Is a natriuretic peptide It is produced by cells in the distal convoluted tubule and collecting duct It increases renal blood flow causing diuresis Causes vasodilation, increased sodium and water excretion, and decreased blood pressure It is an antagonist to the Renin-Angiotensin-Aldosterone System

Question 64

Define hydrostatic pressure

Answer 64

Hydrostatic pressure = mechanical force of water pushing against cellular membranes Force that PUSHES water

Question 65

Describe colloid osmotic pressure

Answer 65

Colloid osmotic pressure = aka oncotic pressure; a form of osmotic pressure exerted by proteins, notably albumin, in a blood vessel's plasma (blood/liquid) that usually tends to pull water into the circulatory system Force that PULLS water

Question 66

Describe tubuloglomerular feedback

Answer 66

Macula densa cells in the distal convoluted tubule are sensitive to flow rates and sodium concentration If low flow rates or low sodium in DCT, macula densa cells signal for relaxation of the afferent arterioles (=more flow) If high flow rates or high sodium in DCT, macula densa cells signal for construction of the afferent arterioles (=less flow)

Question 67

Describe the myogenic mechanism

Answer 67

Myogenic mechanism in afferent arterioles When BP increases, the smooth muscle around afferent arterioles are stretched and respond by contracting. This reduces incoming blood volume to protect the glomerulus from high BP damage When BP is lower, the smooth muscle is relaxed to lower resistance and therefore increase flow to the glomerulus (maintaining normal GFR)

Question 68

What do the macula densa cells do if low sodium is sensed in DCT?

Answer 68

relaxation of aff arterioles- more flow

Question 69

BP is low. How does the myogenic mechanism help maintain normal GFR?

Answer 69

smooth muscle relaxes, therefore increased blood flow to glomerulus to maintain gfr

Question 70

What happens to blood flow to kidneys when sympathetic nervous system (SNS) is stimulated?

Answer 70

Increases in sympathetic stimulation cause vasoconstriction of afferent arterioles and decreased blood flow through the kidneys

Question 71

How does Angiotensin II decreased GFR rate? Why would it do this?

Answer 71

Angiotensin II decreases GFR rates through vasoconstriction. This decreases flow rates allows more time for water and sodium reabsorption in the nephrons

Question 72

What is a trigger for the juxtaglomerular cells to secrete renin?

Answer 72

When circulating blood volume/pressure is reduced or sodium levels are low, the kidney juxtaglomerular cells release renin

Question 73

How is Angiotensin II made?

Answer 73

renin stimulates formation of angiotensin I, which then is converted to angiotensin II by the ACE enzyme (angiotensin-converting-enzyme)

Question 74

What does Angiotensin II do?

Answer 74

Angiotensin II stimulates release of aldosterone and ADH, and causes vasoconstriction

Question 75

What is aldosterone?

Answer 75

mineralcorticoid

Question 76

Where is aldosterone secreted from

Answer 76

adrenal cortex

Question 77

What does aldoesterone do

Answer 77

Aldosterone causes renal sodium and water reabsorption

Question 78

Blood volume and sodium levels are very high in the body. What peptides do you expect to be releases?

Answer 78

natriuretic peptides (anp, bnp)

Question 79

What do ANP and BNP cause?

Answer 79

Cause vasodilation and increased sodium and water excretion

Question 80

Where do ANP and BNP come from

Answer 80

ventricles

Question 81

What is ADH? Where is it secreted from?

Answer 81

Antidiuretic Hormone, posterior pituitary gland

Question 82

Describe the process of ADH secretion and what is causes

Answer 82

Hypothalamic osmoreceptors detect when plasma osmolality increases or when circulating blood volume/BP decreases. In response to this the brain sends thirst signals and also the posterior pituitary gland releases ADH Thirst signals stimulate drinking ADH increases water reabsorption in the distal tubules and collecting ducts

Question 83

What is normal K+ range in the serum

Answer 83

3.5-5 mmol/L

Question 84

Is K+ filtered by the kidney?

Answer 84

ya

Question 85

Where does 90% of K+ reabsorption occur in the kidney?

Answer 85

proximal tubule

Question 86

Describe the NaK pump

Answer 86

Sodium-Potassium adenosine-triphosphatase active transport system (Na+- K+ATPase Pump) maintains the concentration differences and moves K+ from ICF to ECF with the help of ATP (ATP open the channels)

Question 87

What promotes K+ shift INTO cells

Answer 87

Insulin, epinephrine, and Alkalosis promote K+ shift into cells

Question 88

What promotes K+ shift OUT of cells

Answer 88

Exercises, cell lysis, hyperosmolality and acidosis promote K+ shift out of the cells

Question 89

What part of the nephron determines amount of K+ excretion?

Answer 89

distal tubule

Question 90

What factors influence K+ concentration and excretion

Answer 90

Increase in plasma K+ (e.g. through increased dietary intake) causes K+ excretion in urine Rate of filtrate flow also affects K+ concentration, high flow (e.g due to diuretics) causes K+ excretion into urine Changes in PH: - Acidosis: K+ shifts to ECF. Decreased K+ levels in ICF result in decreased secretion of K+ by the tubule (contributing to Hyperkalemia) - Alkalosis: K+ shifts into ICF, tubular also increase K+ secretion (contributing to Hypokalemia) Aldosterone: increase reabsorption of Na and H2O and therefore increased K+ secretion. More K+ gets excreted in urine also increases K+ secretion through sweat glands increases the amount of Na+ and K+ pumps available (= increased movement of K and Na in and out of cells)

Question 91

Increase in plasma K+ causes K+ ____________ (excretion/ reabsorption)

Answer 91

excreteion

Question 92

High rate of filtration (i.e., caused by diuretics) causes K+ ____________ (excretion/ reabsorption)

Answer 92

excretion

Question 93

How does acidosis contribute to hyperkalemia?

Answer 93

- Acidosis: K+ shifts to ECF. Decreased K+ levels in ICF result in decreased secretion of K+ by the tubule (contributing to Hyperkalemia)

Question 94

How does alkalosis contribute to hypokalemia?

Answer 94

- Alkalosis: K+ shifts into ICF, tubular also increase K+ secretion (contributing to Hypokalemia)

Question 95

Does aldosterone cause K+ reabsorption or excretion?

Answer 95

increase reabsorption of Na and H2O and therefore increased K+ secretion. More K+ gets excreted in urine also increases K+ secretion through sweat glands increases the amount of Na+ and K+ pumps available (= increased movement of K and Na in and out of cells)

Question 96

Describe symptoms of hypokalemia

Answer 96

Lethargy, fatigue, confusion Nausea & vomiting Decreased bowel sounds; distention; ileus; constipation Thirst; inability to concentrate urine Weakness Flaccid paralysis Respiratory arrest Bladder distention

Question 97

Describe symptoms of hyperkalemia

Answer 97

Restlessness/Irritability/Anxiety Nausea & vomiting GI cramps; Diarrhea Tingling; numbness Early: hyperactive muscles Late: weakness & flaccid paralysis Muscle weakness (difficult to walk) Loss of muscle tone Paralysis

Question 98

Describe ECG changes in hypokalemia

Answer 98

Flattened T wave Prolonged QT interval ST depression Peaked P wave U waves present

Question 99

What dysrhythmias do you see in hypokalemia

Answer 99

Dysrhythmia Sinus bradycardia Atrioventricular block Paroxysmal atrial tachycardia.

Question 100

Describe ECG changes in hyperkalemia

Answer 100

Peaked T wave Shortened QT interval ST depression Absent P wave Widened QRS complex Prolonged PR interval

Question 101

What dysrhythmias would you expect with hyperkalemia

Answer 101

Dysrhythmia Bradycardia Delayed conduction rhythms Ventricular fibrillation Cardiac arrest

Question 102

A renal patient presents with restlessness, diarrhea, tingling, and hyperactive muscles. Their EC shows peaked T waves. What electrolyte disturbance are they likely experiencing?

Answer 102

hyperkalemia

Question 103

A patient has been vomiting for 4 days with poor po intake. They are lethargic and fatigued. Their ECG shoes U waves and a flattened t wave. What electrolyte abnormality are they likely experiencing?

Answer 103

hypokalemia