bio 225 exam 4 osmoregulation

enzymatic reactions, gas exchange, etc.

300 mOsM total, most of it is Na+ and Cl-, the rest are small amounts of K+, Ca2+, Mg2+, and (SO4)2-

1000 mOsM total, most of it is Na+ and Cl-, the rest are small amounts of K+, Ca2+, Mg2+, and (SO4)2-

< 5 mOsM total, most comes from Ca2+, (SO4)2-, Na+, and Cl-, with slightly smaller amounts of Mg2+ and K+

“tonic” refers to one solute, while “osmotic” refers to all solutes

concentration of solutes outside cell = concentration of solutes inside cell, net flow is 0

concentration of solutes outside cell > concentration of solutes inside cell, water leaves cell (shrinks)

concentration of solutes outside cell < concentration of solutes inside cell, water enters cell (swells)

they gain salts and lose water

they gain water and lose salts

they lose water

they can alter their osmotic/salt homeostasis

typically invertebrate aquatic animals that change their body’s osmolarity to be similar to their environment

typically vertebrate aquatic animals that maintain constant osmolarity regardless of the environment

typically invertebrate animals that exert little control over ion profile within their extracellular space

typically vertebrate animals that control ion profile within their extracellular space

it changes the Km (rate of reaction) within an organism, the most important ones being nitrogenous wastes or NaCl; too much can disrupt macromolecule function and kill

it has no effect on Km (rate of reaction) within an organism, examples being amino acids or methyl amine

it’s deleterious on its own but can be used in combination to counteract the deleterious effects of another; ex: urea + THAMO has no effect as they have inverse effects on Km

they can tolerate only a narrow range of salinity

they can tolerate a wide range of salinity

1. asymmetrical distribution of membrane transporters (solutes selectively transported)

2. cell interconnected to form impermeable sheets of tissue (little leakage in between)

3. high cell diversity within tissue

4. abundant mitochondria (large energy supply)

the basolateral side is always connected towards the blood, while the apical cell is opposite and sometimes has cilia

movement through the cell across membranes

movement between cells, can be leaky or tight epithelia

• Na+/K+ ATPase - with or against gradient

• ion channels (Na+, Cl-, K+) - with gradient, no energy

• electroneutral cotransporters - transfer ions with opposite charges to flow in same direction

• electroneutral exchangers - transfer ions with same charge to flow in opposite directions

they are always losing water and gaining salt, so they compensate by having extremely concentrated urine

they are always gaining water and losing salt, so they compensate by having extremely dilute urine

3. they will uptake salts and ions through their gills

mitochondria-rich chloride cells and pavement (mitochondria-rich or mitochondria-poor) cells; transport is carried out by mitochondria-rich cells

fish that can migrate between saltwater and freshwater

fish that live in freshwater and migrate to saltwater to spawn

fish that live in saltwater and migrate to freshwater to spawn

both lose water to their environment

skin and hydrophobic layers

amphibians

humans, amniotes (vertebrates that are exclusively land animals, unlike amphibians and fish)

arthropods (insects, crustaceans, etc.)

• top layer is epidermis, bottom layer is dermis, separated by basement membrane

• epidermis contains stratum corneum, corneocytes that maintain the stratum corneum, and keratinocytes that make keratin

• the dermis has blood vessels and nerves

1. dietary water (from pre-formed water in plants and animals)

2. metabolic water (generated from final steps of cellular respiration)

3. drinking

urine, evaporation, feces

nitrogenous wastes are toxic and need to be excreted

1. ammonia (ammonioteles)

2. uric acid (uricoteles)

3. urea (ureoteles)

aquatic animals, because ammonia is water-soluble

terrestrial animals like birds, reptiles, and insects, uric acid isn’t very dangerous but it doesn’t dissolve in water

all mammals, some larval bony fish, lungfish

• advantages: released by deamination of amino acids, requires little energy to produce (0-1 ATP)

• disadvantages: highly toxic (used as cleaners), requires lots of water to store and excrete

• advantages: few toxic effects, can be excreted in small volume of water

• disadvantages: expensive to produce (6 ATP)

• advantages: only slightly toxic, relatively energy inexpensive to produce (3 ATP)

• disadvantages: it’s a perturbing solute

production of hyperosmotic (concentrated) urine

1. ion balance

2. osmotic balance

3. blood pressure

4. pH balance

5. excretion of metabolic wastes and toxins

6. hormone production (renin-angiotensin system)

minor and major calyx

urine in the bladder is the final urine, urine in the renal pyramids is primary urine

renal cortex and renal medulla

functional units of the kidney

• has renal tubules lined with transport epithelium, various segments with specific transport functions

• has glomeruli (ball of capillaries), where nutrient and water transport occurs, which are surrounded by bowman’s capsule, where urine starts to be made

the proximal tubule in the renal cortex

proximal tubule → descending loop of Henle → ascending loop of Henle → distal tubule → collecting duct

1. filtration of blood formed at glomerulus

2. reabsorption, specific molecules in the filtrate removed

3. secretion, specific molecules added to filtrate

4. excretion of urine from the body

water and small solutes; NOT blood cells and large macromolecules

glomerular capillaries, podocytes with food processes form filtration structure

they control blood pressure and filtration within glomerulus

the amount of filtrate produced per minute

pressure in 3 forces

1. glomerular capillary hydrostatic pressure

2. bowman’s capsule hydrostatic pressure

3. oncotic pressure — osmotic pressure due to protein concentration in blood

1. mesangial control — altered permeability of glomerulus via diameter, controls flow

2. myogenic regulation — constriction/dilation of afferent arteriole

3. tubuloglomerular apparatus

   1. juxtaglomerular apparatus

      1. macula densa cells in distal tubule — control diameter of afferent arteriole

      2. juxtaglomerular cells in afferent arteriole

via active transport, primary urine is isosmotic to blood

Na+, Cl-, K+, Ca2+, (HCO3)-, H2O, glucose, amino acids, vitamins, urea, choline

H+, (NH4)+, toxins, drugs

they are permeable to water only, most water being reabsorbed here

very concentrated, because water is reabsorbed from the urine into the blood

they are impermeable to water and permeable to salts, Na+, Cl-, K+, Mg2+, Ca2+, and (NH4)+ reabsorbed here

very dilute, because salts are reabsorbed from the urine into the blood

the number of transporters

concentration of specific solute that will overwhelm reabsorptive capacity

it’s reabsorbed from the urine (in tubule) to the blood by secondary active transport

• many solutes reabsorbed by Na+ cotransport

• water reabsorbed by osmosis via aquaporins

• proximal tubule carries out secretion via active (secondary) transport

describe secretion

• similar to reabsorption but in reverse

• molecules removed from blood and transported to filtrate/primary urine

• K+, (NH4)+, H+, drugs, water-soluble vitamins all secreted

• requires transport proteins and energy

descending limb, water is reabsorbed, primary urine decreases in volume and gets more concentrated

ascending limb, ions are reabsorbed, primary urine becomes dilute

two liquids moving in opposite directions allow for diffusion to occur

in the loop of henle, blood and urine move in opposite directions, allowing diffusion of water and salt between the two

it increases ca2+ reabsorption

it increases k+ secretion

via the urethra

a spinal cord reflex arc that opens and closes sphincters, influenced by voluntary controls

avp controls aquaporin expression

• permeable (high avp): water reabsorbed from collecting duct, concentrated urine excreted

• impermeable (low avp): water not reabsorbed from collecting duct, dilute urine formed in ascending limb excreted

• steroid hormones like aldosterone, slow response

• peptide hormones like vasopressin, rapid response

• diuretics, stimulate excretion of water

• anti-diuretics, reduce excretion of water

vasopressin and the renin-angiotensin-aldosterone (RAA) pathway

1. vasopressin binds to G-protein receptors in the kidneys

2. ATP converts to cAMP via adenylate cyclase, and cAMP activates protein kinase A

3. PKA causes phosphorylation of preformed vesicles, fusing it with the cell membrane and inserting aquaporins

1. it enters the cell via diffusion

2. it binds to its receptor, acts as a transcription factor for transporter genes

3. new transporter proteins (Na+/K+ pumps) made in ER, exported to vesicles

4. vesicles containing Na+/K+ pumps are sent to the membrane

5. Na+ pumped into blood and water follows

when blood pressure or GFR is lower than normal

1. baroreceptors in JG cells release renin in response to low BP

2. sympathetic neurons in the cardiovascular control center of the medulla trigger renin secretion from JG cells in response to low BP

3. macula densa cells in distal tubule send paracrine signal to JG cells, stimulating renin release

• RAA starts in JG cells, which secrete enzyme renin

• renin converts angiotensinogen, made in liver, to angiotensin I

• angiotensin converting enzyme (ACE), made in lungs, converts angiotensin I to angiotensin II

• angiotensin II causes synthesis and release of aldosterone from adrenal cortex, ADH secretion, vasoconstriction, and increased sympathetic activity

a vasoconstrictor, it increases blood pressure; it stimulates Na+ and water reabsorption from urine and K+ excretion

it raises blood pressure by increasing blood volume

lungs; angiotensin I; angiotensin II

fluid retention

4. hyperhydration

1. aldosterone

1. a countercurrent multiplier

1. Na+