Ch 10 Part 1

Question 1

Excretion

Answer 1

Disposal of Waste. Generally refers to the Kidneys - although the liver, large intestine, and skin are involved.

Question 2

Liver

Answer 2

Deals with large hydrophobic waste products that the kidney cannot attend. Releases waste into bile.

Synthesizes urea which is a carrier of excess nitrogen (from protein breakdown). Important because free ammonia is toxic.

Question 3

Colon

Answer 3

ie. The large intestine.

Reabsorbs water and ions. Does not typically excrete, rather recycles components of waste.

Although can excrete excess ions if necessary using active transport.

Question 4

Skin

Answer 4

Produces sweat which releases water, ions, and urea.

Although excretion of waste is only a secondary role of sweating.

Question 5

Kidneys

Answer 5

Excretion of hydrophilic waste. Ex. Urea, sodium, bicarbonate, water.

Maintain constant solute concentration and pH.

Maintain constant fluid volume.

Important to think of the kidney as a regulator of optimal levels, not simply a passive reservoir for waste excretion.

Question 6

Kidney processes (General)

Answer 6

3 Step Process:
FILTRATION - pressurized blood flows over a filter leaving cells and proteins in blood, while removing water and small molecules into RENAL TUBE. Water and molecules become known as FILTRATE –> urine.

SELECTIVE REABSORPTION - recycle useful products like glucose, water, and aa.

SECRETION - Addition of substances to the filtrate, which can increase the rate at which substances are eliminated from the blood (osmosis mediated)

Ends with - CONCENTRATION and DILUTION - decision to produce dilute or concentrated urine. Anything in renal tube is excreted.

Question 7

Artery and Veins supplying Kidney

Answer 7

Inferior Vena Cava and Abdominal Aorta.

See pg. 369 for details.

Question 8

Blood in the kindey

Answer 8

Enters via the renal artery and purified blood leaves via the renal vein.

Question 9

Urine leaving Kidneys

Answer 9

Leaves via a URETER that empties into the urinary bladder

Question 10

Urinary Sphincters

Answer 10

Internal Sphincter - made of smooth involuntary muscle. Relaxes when the bladder is full.

External Sphincter - made of skeletal voluntary muscle. Person decides when to urinate.

Question 11

Regions of the Kidney

Answer 11

Cortex - outer region

Medulla - inner region

Medullary Pyramids - Pyramid striations in the medulla as a result of collecting ducts. Urine empties from collecting ducts and leaves at the tip of a pyramid known as PAPILLAE.

Calyx (Calyces) - a space in which urine empties

RENAL PELVIS - formed by convergence of Calyces

Pg. 370

Question 12

Functional Unit of a Kidney

Answer 12

Nephron

Question 13

Nephron Components

Answer 13

Two components:

Bowmans Capsule - a rounded region surrounding capillaries, where filtration takes place.

Renal tube - a coiled structure, that receives filtrate from capillaries and empties into collecting duct.

Question 14

Blood vessels surrounding the Nephron

Answer 14

Arterial blood is carried toward the capillaries of capsule for filtration.

Blood vessels also surround the tubule to carry filtered blood and reabsorbed substances away from tubule.

Question 15

Kidney Filtration

Answer 15

Renal artery flows into afferent arteriole which branches into the GLOMERULUS (ball of capillaries).

Blood then flows in efferent arteriole. Constriction here results in high pressure in the glomerulus causing blood plasma (fluid) to leak out of capillaries.

Fluid flows through the GLOMERULAR BASEMENT MEMBRANE before entering BOWMAN’s CAPSULE.

Lume of Bowman capsule is continuous with rest of tubule/renal tube.

Question 16

Kidney Selective Reabsorption

Answer 16

Filtrate molecules that can be recycled are taken from the filtrate, often by active transport, and carried by PERITUBULAR CAPILLARIES –> venules –> renal vein.

Most selective reabsorption occurs near the PROXIMAL CONVOLUTED TUBULE (PCT), which is closest to Bowman’s Capsule. Absorbs selectively - as much as it can, but only of specific things.

A lot of water absorption occurs here, up to 70% of filtrate is reabsorbed. Overall urine is really dictated by small fluxes more distally in the nephron.

Note: 5% of our blood that is circulating is passing through glomerulus, so majority needs to be reabsorbed.

Question 17

How much glucose is typically reabsorbed by the PCT?

Answer 17

Roughly 100%

Question 18

Kidney Secretion

Answer 18

Movement of substances into filtrate (typically by active transport).

A back up method to the glomerulus that ensures elimination of specific things. Primary method to excrete drugs and toxins.

Occurs along the entire tubule, but majority in the DCT and collecting duct.

Question 19

Kidney Concentration and Dilution

Answer 19

Distal Nephron (DCT + collecting duct) - location of urine adjustment for volume and osmolarity.

Controlled by ADH and aldosterone.

Question 20

Function of ADH in Kidney

Answer 20

Also known as Vasopressin.

During dehydration, blood fluid levels are low with high solute concentration. NEED to create SMALL AMOUNTS OF CONCENTRATED URINE. These conditions released ADH which prevent DIURESIS (water loss in the urine) by increasing water reabsorption in Distal Nephron by making it permeable to water.

If well hydrated, no ADH secreted.

Note that the Distal Nephron is normally impermeable to water - the first tissue I am aware of that is impermeable to water!

Question 21

Aldosterone in Kidney

Answer 21

Released in response to low blood pressure, by adrenal cortex.

Increases reabsorption of Na+ by distal nephron.

Increases plasma osmolarity. Increases thirst and water retention –> raises BP.

Aldosterone release can also be stimulated by low blood osmolarity, low blood volume, angiotensin II.

Note that ADH and Aldosterone both increase BP and work together.

Aldosterone is released first, increases blood osmolarity, causing release of ADH.

Question 22

Where are Bowman’s capsule and PCT located in the broader kidney?

Answer 22

Renal cortex

Question 23

More detailed structures of nephron

Answer 23

PCT empties into the LOOP of HENLE (which dips down into renal medulla); the part that dips down into medulla is the DESCENDING LIMB OF THE LOOP OF HENLE (thin, squamous epithelial tissue), while the part that returns out to the cortex is the ASCENDING LIMB (thick cuboidal epithelial cells - more active).

Loop of Henle becomes the DCT, DCT empties into collecting duct.

Question 24

Ion active transport

Answer 24

For Cl-; Na+; K+ - Occurs in the ascending limb of the loop of Henle, but there is also passive return of K+.

In the Collecting duct there is secretion of potassium and hydrogen ions as well as reabsorbtion of Na in response to Aldosterone (DCT and cortical region of collecting duct)

pg. 375

Question 25

Countercurrent Multiplier

Answer 25

The Loop of Henle.

Descending and Ascending loops have different permeabilities and flow in different directions.

Descending is permeable to water, but not ions. Water flows out of PCT into high-osmolarity medullary interstitium (tissue).
Consequence is filtrate is concentrated.

Ascending loses ions passively into medulla interstitium. Active Transport here too so medulla becomes very salty! Draws water out whenever conducting duct is permeable ie. in presence of ADH.

Question 26

Glomular Filtration Rate

Answer 26

GFR, depends entirely on blood pressure.

Kidneys therefore require a built in mechanism to regulate BP.

Question 27

Juxtaglomerular apparatus

Answer 27

A specialized contact point between the afferent arteriole and the distal tubule.

At this point, cells in the arteriole are referred to as JUXTAGLOMERULAR (JG) CELLS and cells on the tubule are referred to as MACULA DENSA.

Question 28

Juxtaglomerular cells

Answer 28

Barometer receptors. Monitor BP.

If BP is low, release renin.

Question 29

Renin

Answer 29

Release of renin causes the conversion of angiotensinogen to…

angiotensinogen I –> angiotensinogen II by angiotensin-converting enzyme (ACE)

Question 30

Angiotensinogen II

Answer 30

A powerful vasoconstrictor (systemically), causing an immediate increase in BP.

It also stimulates the release of aldosterone, which raise the BP.

Question 31

Macula Densa cells

Answer 31

Chemoreceptors. Monitor filtrate osmolarity in the distal tube.

If filtrate osmolarity decreases suggests a decrease in filtration rate. MD cells will stimulate JG Cells to release renin.

MD cells can also directly stimulate dilation of afferent arteriole which will increase blood flow (and it says BP too/filtration rate) through glomerulus.

Figure 7 - great image

Question 32

pH regulation by the kidneys

Answer 32

Essential for pH regulation.

If pH is too high, kidney excretes HCO3- into urine; if pH is too low it excretes H+ into urine.

The enzyme Carbonic anhydrase is involved, which is found in epithelial cells around the nephron (except the flat squamous cells of the thin part of the loop of Henle)

Catalyzes CO2 –> H2CO3

In general, HCO3- is reabsorbed and H+ is released.

Question 33

Renal pH adjustment time scale

Answer 33

Very slow - over days.

Much more effective method is respiration.

Question 34

Hormones affecting the Kidney

Answer 34

All are peptides, except for aldosterone (steroid).

Aldosterone (adrenal cortex)

ADH (posterior pituitary)

Calcitonin

Parathyroid hormone

Erythropoietin (produced by the kidney)

Question 35

Calcitonin

Answer 35

Released from C cells.

C cells are in the thyroid gland. Calcitonin is released when Ca2+ is too high, results in removed from the blood via…

1) deposition in bone
2) reduced absorption by gut
3) excretion in urine

Question 36

Parathyroid hormone

Answer 36

Released from parathyroid, also known as Parathromone. PTH.

There are four parathyroid glands located in the thyroid gland.

Effect is the opposite of Calcitonin.

Question 37

Erythropoietin

Answer 37

Produced in kidneys.

Causes increased synthesis of red blood cells.

Released when blood oxygen count falls.