Lecture Final: Chapter 22

Question 1

Importance of Animal Body Fluids

Answer 1

Usually more than half of the animal’s body weight

Constitute immediate environment for cells and molecules in body

Particular inorganic ions dissolved in body fluids and their concentrations are important for:

• • Influencing the crucial 3D molecular conformation of enzymes and other proteins
• • Maintaining correct electrical gradients across cell membranes; important for nerve and muscle function

Water is important:

• • Matrix in which ions are dissolved
• • Affects volumes of cells and tissues → passive movement = osmosis

Question 2

THREE FLUID COMPARTMENTS

Answer 2

1. Intracellular: ⅔ of the body fluid will be inside the cell ⇒ ICF
2. Interstitial: fluid btwn cells BUT not in blood plasma; usually connective tissue → ¾ of the remaining ⅓ found here ⇒ ECF
3. Blood (and lymph) plasma: remaining ¼ of the ⅓ lmao ⇒ ECF

All three are isosmotic → no net flow of water within these compartments but differ in ion composition.

• • Intracellular has High [K+], low [Na+]
• • Interstitial and Blood with low [K+], high [Na+]

There is fluid movement btwn these compartments via aquaporins

• • Water specific file that allows single file facilitated diffusione
• • Some allow glycerol to move through
• • osmotic exchange btwn interstitial into intracellular via facilitated diffusion

Question 3

Solute concentrations and Osmosis

Answer 3

1. Water flux btwn cellular compartments driven by osmotic differences
   - - Hyperosmotic: higher solute concentration; lower free H2O concentration
   - - Hypoosmotic: lower solute concentration; higher free H2O concentration
   - - Net water flow will be from hypoosmotic to hyperosmotic across a selectively permeable membrane
2. Solutes lower the number of “free” H2O molecules → hydration spheres are formed when the dipoles of H2O are attracted to the ions of solutes (“shield the ion”)
   - - Hyperosmotic solution thus has fewer free H2O molecules
   - - Osmosis will move from more free H2O to less free H2O
3. Osmolarity: number of moles of solute per liter of solution → dependent on the number of dissociated particles
   - - Unit of measurement is Osm (Osmoles) = 6.022 x1023 osmotically effective dissolved entities
   - - Seawater = 1000 mOsm / L
   - - Human blood = 300 mOsm / L

Question 4

Regulators and Conformers, revisited
+ three types of regulation (1sub2)
+ stenohaline and euryhaline
+ mussels / barnacles / hagfish

Answer 4

Regulators: blood Osm pressure maintained on own, somewhat independent of environment
Conformers: blood Osm pressure reflects that of the environment

THREE TYPES

1. Osmotic regulation: maintenance of constant or nearly constant osmotic pressure of blood plasma
   - - Contrast to conformity: blood Osm pressure always equals the osmotic pressure of the environment
   - - Many marine invertebrates have body fluids isosmotic with environment (equal flux of water in and out of the organism) BUT most vertebrate are osmoregulators (expensive but more steady state, good for migrators)
2. Ionic regulation
3. Volume regulation

Stenohaline (animals): cannot tolerate substantial changes in external osmolarity (most animals, ie freshwater fish will die in the ocean)
Euryhaline (animals): actually can tolerate a wide range of osmolarities

Mussels, barnacles → anadromous (born in freshwater streams but mature in saltwater ocean; will return to mate)
Hagfish is the only modern chordate that can trace a continuous marine ancestry → only chordate with isosmotic blood (conformer!)

Question 5

Osmoregulation

• Freshwater
• Marine Teleost

Answer 5

Assume Osm pressure in this environment is 0.

FRESHWATER teleost osmotic blood pressure = 250 to 350 mOsm

• • Maintain hyperosmotic blood → bulk flow into the fish mainly through the gills
• • Problem: too much water in their body
• • Solution: excrete large volumes of urine that is hypoosmotic to blood (therefore, urine has less Osm than plasma ;; U / P <1)
• • Gill sites of ion uptake, in addition to extracting O2 from water

MARINE TELEOST: freshwater ancestor but now saltwater fish

• • Marine teleost osmotic blood pressure = 300 to 500 mOsm
• • Maintain hypoosmotic blood → bulk flow out of the fish!
• • Problem: water loss
• • Solution: drink seawater to counteract osmotic to prevent water loss → small volume of urine excreted is isosmotic to blood (U/P = 1)
• • Gills excrete monovalent ions; divalent ions excreted by kidneys

Note: only birds and mammals can excrete urine that is hyperosmotic to blood (bc it has toxins in it or smthg)

Question 6

Forms of Nitrogenous Waste

Answer 6

1. Excess amino acids are never stored → DE-AMINATE instead by forming ammonia (ion is very toxic!)
2. Metabolism of nucleotides also generates ammonia (with its ion; usually in fish)
3. Amines are converted into UREA (mammals) in the liver at a cost of 3-4 ATP per urea molecule formed → UREA is 10x less toxic (when compared to ammonium ion)
   Amines converted into URIC ACID (birds) at a cost of 9-10 ATP per uric acid molecule → can be voided from the body without losing any water

Question 7

Excretory Organs (4)
\+ functions (5)

Answer 7

Kidney: Bowman’s capsule > glomerulus > PCT > loop of henle > DCT > collecting duct
Ureter: from kidney to urinary
Urinary bladder: storage until excretion
Urethra: exit from the body

1. Control solute concentrations and balance water gain and loss
2. Excrete metabolic wastes and toxins
3. Maintain pH of blood (recover HCO3- and excrete H+)
4. Stimulate RBC production in red marrow by secreting erythropoietin (hormone)
5. Activate vitamin D into calcitriol (promotes Ca2+ absorption from small intestine)

Question 8

What happens in a nephron? (5)

Answer 8

1. Filtration in Bowman’s capsule via glomerulus
   - - One of the most porous capillaries in the body bc fenestrated
2. Reabsorption in proximal tubule (cortex) of glucose / amino acids through secondary active transport BUT ALSO sodium (with accompanying water) via aquaporins (water will follow because changes in osmolarity) – no change in osmotic pressure of filtrate
3. Reabsorption of water (to produce hyperosmotic urine) involves Loop of Henle and Vasa Recta (medulla)
   - - Juxtaposed descending and ascending limbs of the loop of henle generate an osmotic gradient in medullary interstitial fluid by acting as a COUNTERCURRENT MULTIPLIER (building of osmotic gradient to reabsorb water) – remove water when descending, NaCl when ascending
   - - Vasa recta = juxtaposed capillary vessels act as a COUNTER CURRENT EXCHANGER (maintains the gradient) to maintain osmotic gradient in interstitial fluid
4. Secretion in distal convoluted tubule (cortex) via active transport to secrete H+ / K+ / NH4+ and reabsorb Ca2+ / Na+ / HCO3-
5. Secretion in collecting duct (medulla) to adjust urine volume and composition, specifically of ADH to increase aquaporins for H2O reabsorption
   - - Urea reabsorbed to contribute to the medullary interstitial osmotic gradient

Question 9

Filtration of blood (from glomerular capillaries) into Bowman’s capsule (2)
+ Filtration membrane (3)

Answer 9

Urine formation begins when blood pressure forces cell-free and protein-free plasma out of glomerular capillaries into bowman’s capsule
– Diameter of efferent arteriole < afferent = high hydrostatic pressure that drives filtration

HP = hydrostatic pressure → NFP (net filtration pressure) = HP(gc) - (HPCS + Opgc)
where HP(glomerulus capsule) = +55 mmHg = outward pressure
and HP (capsular space) - 15 mm Hg = inward pressure
and Op(gc) = +30 mmHg = pull of proteins 
-- Therefore, NFP = +10 mmHG, which is sufficient to force plasma out
** Osmotic pressure remains constant

1. Fenestrated endothelium (capillary wall) excludes blood cells as they are too large
2. Negatively charged basement membrane repels plasma proteins, which are mostly negatively charged
3. Podocyte foot processes are the body’s last chance to capture macromolecules → reabsorption and secretion

Question 10

Loop of Henle + Vasa Recta, revisited

Answer 10

LOOP OF HENLE! Counter current multiplier that creates the gradient

1. Isosmotic filtrate enters into the DESCENDING limb (interstitial fluid is isosmotic as well, therefore no gradient)
2. Active transport of NaCl out of ASCENDING limb, causes a single effect that generates a 200 mOsm difference → triggers diffusion of H2O out of the descending limbs
   - - Single effect: Na pumped out of ascending, causing the osmolarity change everywhere
3. Filtrate moves through loop and process repeats over and over, continuing filtrate and interstitial fluid (multiplier)

== End result: large increase in end to end osmotic gradient in LoH
– Allows for increasingly more concentrated gradients between the loops that are formed → this gradient is the key to the creation of a hyperosmotic urine in birds and mammals

VASA RECTA! Counter current exchanger that maintains the medullary osmotic gradient

1. loses H2O (gains Na+) in descending limb
2. gains H2O (loses Na+) in the ascending limb
   * * Osmotic pressure in ascending and descending limbs of vasa recta are equal BUT ascending has greater volume bc includes return of plasma (lost from the descending limb) and H2O reabsorbed (from the nephron loop and collecting duct)

Question 11

Antidiuretic Hormone, revisited

• overhydration
• dehydration

Answer 11

released in response to low bloodmolarity (sensed by osmoreceptors in hypothalamus)

Overhydration: little to no ADH because of decreased osmolarity of extracellular fluids → less aquaporins in collecting duct → less H2O reabsorbed from the collecting duct → large volume of dilute urine

Dehydration: maximal ADH because of increased osmolarity of extracellular fluids → more aquaporins in collecting duct → more H2O reabsorbed from the collecting duct → small volume of concentrated urine

Question 12

Regulation of blood volume and blood pressure by RAAS system

• pathway
• active form

Answer 12

caused by low blood pressure sensed by juxtaglomerular apparatus (ie major blood loss)

Pathway: release of renin, which splits the protein angiotensin, producing angiotensin 1 (inactive), which is acted on by the angiotensinogen converting enzyme (ACE) to yield angiotensinogen 2 (active)

Angiotensinogen 2: causes vasoconstriction; also stimulates secretion of water-retaining (antidiuretic) hormone vasopressin from pituitary gland, which will trigger thirst and reduce urine – will also trigger release of norepinephrine, aldosterone, and adrenaline from adrenal gland