Renal Chapter 1: Renal Functions, Anatomy, and Basic Processes

Question 1

Describe the kidney’s function in regards to regulation of water and electrolyte balance.

Answer 1

balance when inputs/outputs are matched. difference between input/output leads to increase/decrease in substance.

(drink water when thirsty but its also a part of foods…) kidneys respond by varying the output of water in urine.

Minerals (Na, K, Mg) components of foods, have more than enough in body.. kidneys excrete minerals at rate that matches input.

Question 2

Describe the kidney’s function in regards to excretion of metabolic waste.

Answer 2

bodies form end products of metabolic substances that have little purpose mostly and can be harmful at high concentrations:

urea (from protein) 
uric acid (from nucleic acids)
creatinine (from muscle creatine), the end products of hemoglobin breakdown, metabolites of various hormones

Question 3

Describe the function of the kidney in regards to excretion of bioactive substances that affect body function.

Answer 3

drugs and hormones in blood are removed in many ways, mostly in the liver, but a number are removed in parallel by renal process.

(physicians have to be mindful of how fast drugs are excreted in order to prescribe a dose that achieves the appropriate body levels)

Question 4

Describe the kidney’s regulation of blood pressure.

Answer 4

bp depends on blood volume, kidney’s maintenance of Na and water balance achieves regulation of blood volume.

Thus, through volume control, kidneys participate in bp control
-they also generate vasoactive substances that regulate smooth muscle in peripheral vasculature

Question 5

Describe the kidney’s regulation of RBC production.

Answer 5

kidney is major source of erythropoietin (a peptide hormone that is involved in control of RBC production by bone marrow) erythropoietin stimulates bone marrow to increase production of erythrocytes.
(liver also excretes some small amounts)

renal cells that secrete erythropoietin are a particular group of cells in the interstitum.

Question 6

What will stimulate the kidneys to secrete erythropoietin?

How does this relate to renal disease?

Answer 6

stimulus for secretion is a reduction in partial pressure of O2 in kidneys (anemia, arterial hypoxia, and inadequate renal blood flow) erythropoietin stimulates bone marrow to increase production of erythrocytes

one consequence of renal disease can be dimished erythropoietin secretion

Question 7

Describe the kidney’s regulation of vitamin D production.

Answer 7

In vivo vitamin D synthesis involves a series of biochemical transformations, the last of which occurs in the kidneys. The active form of vitamin D (1,25 dihydroxyvitamin D3) is actually made in the kidneys, and its rate of synthesis is regulated by hormones that control calcium and phosphate balance.

Question 8

Describe the kidney’s role in gluconeogenesis.

Answer 8

CNS always needs glucose.
Whenever the intake of carbs is stopped for much more than half a day our body begins to synthesize glucose (glucogenesis) from noncarb sources (amino acids from protein and glycerol from triglycerides) most occurs in liver but a substantial fraction occurs in kidneys (esp. during prolonged fast)

Question 9

What is the basic way that kidneys carry out its functions?

Answer 9

involves transporting water and solutes between blood flowing through the kidneys and the lumina of tubules (nephrons and ocllecting tubules)

Lumen of nephron is topologically outside the body and any substance in the lumen that is not transported back into the blood is eventually excreted in the urine

Question 10

Where are the kidneys? Describe their anatomic location.

Answer 10

lie outside the peritoneal cavity close to the posterior abdominal wall, 1 on each side of the vertebral column. Each is bean shaped. Rounded outer convex surface of each faces the side of the body. Indented surface (hilum) is medial.

Question 11

Describe the hilum of the kidney.

Answer 11

indented surface of the bean shaped structure. faces medially.

each hilum is penetrated by a renal artery, renal vein, nerves, and a ureter, which carries urine out of the kidney to the bladder

Question 12

Describe the ureter.

Answer 12

Ureter penetrates hilum of kidney.

each ureter is formed from funnel like structures called major calyces, which in turn are formed from minor calyces.

Question 13

What are papilla?

Answer 13

Minor calyces fit over underlying cone-shaped renal tissue called pyramids. Tip of each pyramid is called a papilla and projects into a minor calyx.

Question 14

What do the calyces do?

Answer 14

calyces act as collecting cups for urine formed by the renal tissue in the pyramids.

Question 15

How are pyramids arranged in the kidney? What do they form?

Answer 15

Pyramids are arranged radially around the hilum with the papillae pointing toward the hilum and the broad bases of the pyramids facing outside, top and bottom of the kidney.

Pyramids constitute the medulla of the kidney.

Question 16

What overlies the medullary tissue? What overlies that?

Answer 16

cortex, and covering the cortical tissue on the very external surface of the kidney is a thin, connective tissue capsule

Question 17

What do tubules and blood vessels form?

Answer 17

working structure of both the cortex and medulla is constructed almost entirely of tubules (nephrons and collecting tubules) and blood vessels (capillaries and capillary-like vessels).

They are arranged in parallel arrays or intertwined.

between tubules and blood vessels in interstitum

Question 18

Describe the interstitum.

Answer 18

Between the tubules and vessels is an interstitum.
contains fluid and scattered interstitial cells that synthesize an extracellular matrix of collagen, proteoglycans and glycoproteins
(comprises less than 10 percent of renal volume)

Question 19

Describe some structural differences between the cortex and the medulla.

Answer 19

cortex has a highly granular appearance (absent in medulla)

each medullary pyramid is divisible into an outer zone (adjacent to the cortex) and an inner zone, which includes the papilla

Question 20

Describe where urine formed by kidney goes.

Describe/draw kidney structure.

Answer 20

collects in renal pelvis, flows through ureter into bladder, then is eliminated in urethra

The outer portion
(cortex) contains all the glomeruli. The collecting ducts form a large portion of the inner kidney (medulla),
giving it a striped, pyramid-like
appearance, and these drain into the renal pelvis. The papilla is in the inner portion of the medulla.

p 14.

Question 21

Describe the nephron. How many/ what does it consist of?

Answer 21

1 million nephrons in each kidney
each nephron consists of a spherical filtering component, called the renal corpuscle and a tubule extending from the renal corpuscle

renal corpsule is responsible for the initial step in urine formation (a separation of protein-free filtrate from plasma)

Question 22

Draw the relationships of component parts of a long-looped nephron.

Answer 22

See printout/p 15 book

(Combination of glomerulus and Bowman’s capsule is the renal corpsule.

Question 23

What does the renal corpsule consist of?

Answer 23

the glomerulus, or glomerular capillaries, surrounded by a balloon like hollow capsule: Bowman’s capsule

Blood enters and leaves Bowman’s capsule through arterioles that penetrate the surface of the capsule at the vascular pole.

fluid filled space (urinary space or Bowman’s space) exists within the capsule.

Refer to figure 1-3 p 16

Question 24

Describe the layers in the filtration barrier in the renal corpsule.

Describe distinguishing characteristics of each layer.

Describe path of filtrate.
What is the functional significance?

Answer 24

3 layers:

• capillary endothelium of glomerular capillaries
• thick basement membrane
• single-celled layer of epithelial cells

first layer, endothelial cells of capillaries is perforated by many large fenestrae (“windows”) freely permeable to everything except RBC and platelets

middle layer- gel like meshwork of glycoproteins and proteoglycans

third layer - has podocytes (has pedicels or foot processes that embed in basement membrane… interdigitate wtih pedicels from adjacent podocytes

(filtrate, once through the endothelial cells and basement membrane, travels through the space in between pedicels to enter Bowman’s space)

this anatomic arrangement permits the filtration of large volumes of fluid from the capillaries into Bowman’s space but restricts filtration of large plasma proteins such as albumin.

Question 25

Describe the layers of tubule and how they are linked together.

Answer 25

single layer of epithelial cells resting on basement membrane

tight junctions between adjacent cells

Question 26

Draw a structure of connecting nephrons beginning with the renal corpsule (Bowman’s capsule and glomerulus).

Answer 26

The pathway taken by fluids flowing within a nephron always begins in the cortex (in Bowman’s capsule), descends into the medulla (descending limb of the loop of Henle), returns to the cortex (thick ascending limb of the loop of Henle), passes down into the medulla once more (medullary collecting tubule), and ends
up in a renal calyx. Each renal calyx is continuous with the ureter, which empties
into the urinary bladder, where urine is temporarily stored and from which it is intermittently eliminated. The urine is not altered after it enters a calyx. From this point on, the remainder of the urinary system serves only to maintain the fluid composition established by the kidney.

proximal convoluted tubule drains Bowman’s capsule
consists of coiled segment: proximal convoluted tubule, followed by a straight segment, the proximal straight tubule, which descends toward medulla

proximal straight tubule drains to descending thin limb of Henle’s loop.

ascending thin limb of Henle’s loop- beyond this, the epithelium thickens, then have thick ascending limb of Henle’s loop which rises back to cortex.

end of thick ascending is macula densa then have beginning of distal convoluted tubule. connecting tubule, cortical collecting tubule

Question 27

How does blood enter each kidney? (Cortex and medulla)

Where are these arteries never found?

Answer 27

enters through renal artery
(divides into interlobar, arcuate, and interlobular arteries)

afferent arterioles branch off interlobular and lead to glomerulus

(these arteries are found ONLY in cortex, never medulla)

20% plasma (no erythrocytes) entering glomerulus is filtered from glomerulus into Bowman’s capsule and 80% is left to flow on to the next vascular segment

medulla receives less blood… no glomeruli in medulla. efferent arterioles from juxamedullary glomeruli do not branch into peritubular capillaries but instead descend downward into the outer medulla where they divide into parallel vessels called vasa recta

Question 28

How are glomerulus capillaries different from most?

Answer 28

in most organs, capillaries recombine to form the beginning of venous system but the glomerular capillaries instead recombine to form another set of arterioles called efferent arterioles.

Thus, blood enters each glomerulus through a single afferent arteriole
and leaves via a single efferent arteriole at the vascular pole of Bowman’s capsule

Question 29

Describe the vasa recta.

Answer 29

Blood supply to medulla.

The beginnings of the descending vasa recta are like arterioles, with pericytes containing smooth muscle in their walls, but become more capillary like as they descend (see Figure 1–6). The ascending vasa recta have a fenestrated endothelium
like that found in the glomerular capillaries. Therefore, the vasa recta,
in addition to being conduits for blood, also participate in exchanging water and
solutes between plasma and interstitium

Question 30

What is a main distinction among superficial cortical nephrons, midcortical neprhons, juxtamedullary neprhons?

Describe the thick ascending limb- where is it?

Answer 30

superficial cortical -short loops
(hairpin turns before junction of cortex and medulla)

justamedullary -long loops, extend into inner medulla often to tip of papilla

midcortical can be short or long looped

the beginning of thick ascending limb marks border between outer and inner medulla- thick ascending limbs only found in cortex and outer medulla.

Question 31

What is filtration?

Answer 31

process by which water and solutes in the blood leave the vascular system through the filtration barrier and enter Bowman’s space (space that is topologically outside the body)

The filtrate contains substances X, Y, and Z in the same concentrations as the plasma (ie, each one is freely filtered).
The filtrate enters the proximal convoluted tubule and begins its flow through the rest of the tubule. Simultaneously, the remaining 80% of the plasma, with its substances X, Y, and Z in the same concentrations as they had when entering the
kidney, leaves the glomerular capillaries via the efferent arterioles and enters the
peritubular capillaries.

Question 32

What is secretion?

Answer 32

the process of moving substances into the tubular lumen from the cytosol of epithelial cells that form walls of the nephron

Question 33

What is re-absorption?

Answer 33

re-absorption is the process of moving substances from lumen across epithelial layer into the surrounding interstitum

In most cases, reabsorbed substances then move from the interstitium into surrounding
blood vessels, so that the term reabsorption implies a 2-step process of removal
from the lumen followed by movement into the blood.

Question 34

What is excretion?

Answer 34

exit of the substance from the body… substance present in the final urine

Question 35

What does synthesis and catabolism refer to?

Answer 35

means a substance is constructed from molecular precursors

catabolism means a substance is broken down into smaller component molecules.

Question 36

What does it mean for a substance to be “freely filtered”?

Answer 36

substances found in filtrate at same concentration as found in plasma (doesn’t mean all filtered)

many low-molecular weight components of blood are freely filtered. Na, K, Cl, bicarbonate, glucose, urea, amino acids, peptides like insulin and ADH found in freely filtered substances

glomerular filtration (fluid from glomerular capillaries into Bowman’s capsule) is very much like blood plasma but contains little protein… (large proteins like plasma and globulin can’t get through filtration barrier)

Question 37

What is the GFR? What can cause reductions?

Answer 37

volume of filtrate formed per unit time

young adult male GFR is 180L/ day

(fluid across other capillaries in body is approx 4L/day)

…aging and renal pathologies can cause reduction in GFR

GFR is 125mL/min

Question 38

Draw ex. of substance X being filtered and secreted but not reabsorbed. Substance Z is filtered but completely reabsorbed.

Answer 38

p. 28 Vander’s

screenshot or pic.

Question 39

Describe how products like urea and glucose and water, electrolytes might be reabsorbed.

Answer 39

re-absorption of waste products like urea is incomplete, so large fractions of their filtered amounts are excreted in urine

“useful” plasma components like water, electrolytes, and glucose vary from essentially complete reabsorption to complete so urine concentrations should be mostly undetectable

Question 40

Describe metabolism by tubules.

Answer 40

tubular cells may extract organic nutrients from glomerular filtrate or peritubular capillaries and metabolize them as dictated by cell’s own nutrient requirements

other metabolic functions are to alter composition of urine and plasma (synthesis of ammonium from glutamate and production of bicarbonate)

Question 41

Describe signals that regulate the kidney. From where do they originate?

Answer 41

signals arise from both neural and hormonal input.

neural signals originate in sympathetic celiac plexus. exert control over renal blood flow, glomerular filtration and release of vasoactive substances (renin-angiotensin system)

hormonal signals originate in adrenal gland, pituitary gland and heart… adrenal cortex secretes steroid hormones aldosterone and cortisol
adrenal medulla secrets catecholamines epi and NE
(all hormones, esp aldosterone, are regulators of Na and K excretion by kidney)

pituitary gland- vasopressin (ADH) …water excretion/Na excretion

heart secretes peptides too

Question 42

At what site does the greatest mass of excreted substances enter the nephron?

Answer 42

glomerulus

Question 43

Where would penicillin most likely be secreted?

Answer 43

proximal convoluted tubule

Question 44

As a whole, how much Na and Cl and water does the loop of Henle reabsorb? What are the consequences of these proportions?

Answer 44

reabsorbs 20% of filtered Na and Cl and 10% of filtered water

by reabsorbing relatively more salt than water, the luminal fluid becomes diluted relative to normal plasma and the surrounding interstitum.

During periods when the kidneys excrete dilute final urine, the role of the loop of Henle in diluting the luminal fluid is crucial

Question 45

What is the macula densa?

Answer 45

the end of the loop of Henle contains cells of the macula densa, which senses or assays the Na and Cl content of the lumen and generates signals that influence other aspects of renal function (specifically the renin-angiotensin system)

Question 46

What will happen with large amounts of ADH present? With little ADH present?

Answer 46

with large amounts of ADH present- most water remaining in the lumen is reabsorbed, leading to concentrated, low-volume urine

With little ADH present, most of the water passes on to final urine, producing dilute, high-volume urine.

Question 47

Is the following statement true or false? The difference between superficial and
juxtamedullary nephrons is that superficial nephrons have their glomeruli in the cortex whereas the glomeruli of juxtamedullary nephrons are in the medulla.

Answer 47

false

all glomeruli are in the cortex

Question 48

What percentage of the blood entering the kidney flows directly into the medulla
without passing through the cortex?

Answer 48

The correct answer is none. Most medullary blood is supplied by efferent
arterioles near the corticomedullary border. A small fraction may
be supplied from cortical radial arteries. All of these vessels are in the
cortex.

Question 49

Substance T is present in the urine. Does this prove that it entered the renal tubule
by filtration at the glomerulus?

Answer 49

The correct answer is no. It is possible that substance T was filtered, but substance T might also enter tubules by secretion into the tubules.

Question 50

Substance V is not normally present in the urine. Does this mean that it does not
enter the kidney at all (in the blood), or is neither filtered nor secreted?

Answer 50

All substances in the general circulation enter the kidneys via the renal arterial system and flow through the renal microvasculature. It is possible
that it was neither secreted nor filtered, accounting for its not being in the urine, but it is more likely that whatever substance V reaches the lumen via filtration or secretion is completely reabsorbed. Many substances fall into this category.

Question 51

A substance is filtered into Bowman’s space and excreted in the urine. How many
cell plasma membrane barriers must it cross in order to move from the blood to
outside the body?

Answer 51

Book: The answer is none. In glomerular filtration, the filtered substances pass around the endothelial cells (through fenestrations) and around
the podocytes. Topologically, Bowman’s space is continuous with the external environment; thus, a filtered substance can move from blood to the bladder and be excreted without crossing through any plasma membrane.

Webber: filtered substances pass not only through fenestrae (pores) but also across basement membrane which is thicker than those found in other capillaries. And the basement membrane constitutes part of the endothelial cells which must be traversed for substances to reach Bowman’s space

Question 52

A substance is freely filtered. Does this mean that it is all filtered?

Answer 52

The answer is no. Freely filtered means the substance is filtered in the same proportion that volume is filtered. If 20% of the volume is filtered,
then 20% of a freely filtered substance is filtered, meaning that 80% is not filtered and passes on to the efferent arterioles and peritubular
capillaries.

Question 53

If you immunologically labeled cells of the macula densa with label X, and labeled
cells of the thick ascending limb with label Y, would you find labels X and Y in the
cortex, medulla, or both?

Answer 53

You would find label X in the cortex. Cells of the macula densa are part of the juxtaglomerular apparatus, just next to the glomeruli that are all
in the cortex. You would find label Y in the cortex and outer medulla. Thick ascending limbs of all nephrons begin in the outer medulla and
continue back to the glomerulus from which that nephron arose.

Question 54

Given the generalizations about transport events in the medulla (secretion, reabsorption), can you say that blood flow into the medulla is in any way different in
volume from blood flow out of the medulla?

Answer 54

The answer is yes. Under all circumstances, there is net volume reabsorption
in the medulla. By mass balance, this requires that the reabsorbed volume leave the medulla. The only way out for reabsorbed substances is in the blood. Thus blood flow out is slightly greater than
blood flow in.

Question 55

Where do secreted substances come from?

Answer 55

may originate by synthesis within the epithelial cells or more often by crossing epithelial layer from surrounding interstitium