Biology Test 2 Osmoregulation

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iso-osmotic

Back 1

Has the same osmotic pressure or osmolality inside as it does outside

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hyperosmotic

Back 2

a liquid that has a higher osmotic pressure

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hypo-osmotic

Back 3

a cell or another membrane bound organelle that has a lower concentration of solutes inside than out of the cell, water moves out.

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Osmoconformers

Back 4

normally iso-osmotic:

composition of solutes is different from the outside

Osmoconformers are only found in the ocean.

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Osmoregulators

Back 5

Maintain an internal osmolarity that is different from from external environment

is energetically expensive metabolically expensive

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Osmoregulators

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ii. Almost all vertebrates, and all freshwater and terrestrial organisms are osmoregulators

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Aquatic Osmoregulators

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osmoregulators need to reduce permeability over much of the body, but can’t with some structures such as gills

iv. Water flows through permeable membranes toward areas of higher osmolarity

Fish loses water through gills due to osmoliss
Gain water from food and drinking seawater.
Excreats sat ions from gills and through urin

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Osmoconformers in the ocean

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b. Rely on chloride cells, which use the energy potential in gradients created by Na+/K+-ATPase to pump Cl- out of interstitial fluid into the environment. Na+ follows along its electrochemical gradient.

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Bony Fish

Back 9

Are osmoregulators, hypo-osmotic with seawater.
i. Lose water through osmosis from the gills
ii. Must actively excrete salt ions from the gills and kidneys to maintain osmolarity in the face of uptake (drinking) from a hyperosmotic medium.

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d. Sharks (cartilaginous fishes)

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are nearly iso-osmotic with sea water, but they maintain similar salt ion concentrations as other vertebrates, they make up the difference with urea and TMAO (two organic molecules that are metabolites).

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Maine Mamals

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No permeable resperatory serfaces exposed to water, no water loss due to omosis

ii. Must consume sea water (mainly in food), which is hyperosmotic to tissues – therefore need an efficient way to get rid of excess salts

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How marine Mammals get rid of excess salts

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Nasal Glands - active transport of salt ions from blood by epithelial cells

Efficient kidneys of marine mammals -

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Osmoregulation in Marine Fish

Back 13

Gains water and salt ions by drinking sea water and eating food

Osmotic water loss through gills and other body surfaces

excrets salt ions from gills

excrettes salts and small amounts of water in scanty urine from kidneys

medium is hyper osmotic

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Osmoregulation in freshwater fish

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Uptakes water and some ions from food

uptake of salt ions by gills

osmotic water gain through gills and other body surfaces

excretion of large amounts of water in dilute urine from the kidneys

medium is hypoosmotic

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Salmon and other anadromous fishes

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have two populations of chloride cells in their gills, with opposite polarities. These species can switch modes (i.e., direction of ion pumping) when moving from fresh to salt water and back.

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Maintaining osmolarity on land

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Water loss is a big challenge

prevented by coating body in an impermeable substance i.e. wax, dead cells

Water loss necessary during respiration, evaporative cooling and excrettion

Water obtained from food, drinking, and metabolsm.

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Specialized adaptions that allow organisms to survive in arid environments

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Behavior : noctornal

Concentrated urin: more water

Anhydrobiosis: metabolic state cover themselves in cist that maintains water

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Nitrogenous wastes

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Main waste product excreted

come from the breakdown of proteins and nucleic acids

Wastes include:
ammonia

urea

Uric Acid

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Ammonia

Back 19

Produced durring Deamination

as a waste product is energy-efficient because no energy is needed to convert it into a more tractable substance

very toxic, needs to be excreted in dilute solutions, and thus is not appropriate for terrestrial habitats

passes easily across membranes – it is used by aquatic organisms

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Uric Acid

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Non-soluble

excreted as a paste wasting little water

Used by birds, reptiles, insects

because uric acid does not dissolve in water it has devloped in egg laying orgnaisms

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Urea

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1. Used by mammals, amphibians (adult)

2. Much less toxic than ammonia, but still needs to be dissolved in water for excretion

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Other wastes need to be excreted

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b. Other wastes that need to be excreted include excess salts, toxins (after detoxification by liver).

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Excretory system basics

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Filtration

Reabsorbtion

secretion

excretion

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Filtration

Back 24

i. Blood filtered by size, using pressure (ultrafiltration) or pumping; reminiscent of ultrafiltration in capillaries

pressure or a pump drives serum of blood/hemolymph, containing solutes, through a filter (e.g., capillary walls). Filtrate is similar in composition to interstitial fluid.

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Reabsorbtion

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small molecules like sugars, amino acids, some ions)
ii. This material is in equilibrium with blood plasma, must be actively transported back into the blood by specialized cells
iii. Important in freshwater spp., where the production of dilute urine helps in osmoregulation (i.e., most solutes reabsorbed into the blood)

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Secretion

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a separate group of specialized cells uses active transport to secrete unwanted / toxic wastes into filtrate. Secretion of salts & urea also help produce a hypertonic urine (helpful in terrestrial and marin vertebrates).

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Excretion

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Once the filtrate has been modified by reabsorption and secretion, it can be stored and expelled from the body as urine

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Types of Excretory Systems

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Protonephiridia - flatworms, some annelids, some mollusks

Metanephridia - in annelids

Malpighian tubules - In insects

Kidneys - in vertebrates

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Protonnephridia

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i. Flame cells with cilia inside tubule pump interstitial fluid through filter

ii. Tubules reabsorb most of the solutes in filtrate

iii. Nitrogenous wastes diffuse through the skin (in fresh water forms) no concentrated urine

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Metannephridia

Back 30

There is a pair of metanephridia in each body segament

ii. Filtration occurs across blood vessel walls into coelom

Nephrostome pumps fluid from coelom using cilia

iv. Tubules reabsorb solutes, but retain nitrogenous wastes

v. A dilute urine is produced (earthworms need to get rid of excess water)

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Malpighian Tubules

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i. Blind tubes empty into gut.

ii. Active transport of solutes and wastes into tubule by epithelium. Water follows, driving fluid into gut.

iii. In rectum, solutes are actively transported out of gut and into hemolymph (water follows) producing nearly dry uric acid that is voided with feces.

iv. Excellent system for terrestrial existence; uses little water (but some energy).

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Kidneys

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composed of cortex medulla and pelvis

ii. Nephron is the functional unit (~1,000,000 nephrons per kidney).

iii. Hormonal control of osmoregulation in humans

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Structure of Nephron

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1. Glomerulus (ball of capillaries) and Bowman’s capsule is site of filtration

2. Long tube flows out of Bowman’s capsule; site of secretion & reabsorption

3. Secretion occurs mainly in proximal and distal tubules.

4. The loop of Henle and the collecting duct work together to control the osmolarity of the urine (this allows the production of hypertonic urine).

5. Mammals adapted to arid environments have a high proportion of very long loops of Henle (e.g., desert rodents, marine mammals).

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Kidney Filtration

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a. High blood pressure
b. High blood flow – 20% of cardiac output, or > 1 L / min
c. Blood flows through glomeruli 250 – 300 times a day.

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Tube leading out of bowmans capsule

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lined with a transport epithelium that varies in transport and permeability properties depending on location.

c. Empties into collecting duct shared by many nephrons; collecting ducts join to form the ureter at the pelvis of the kidney.
d. Capillaries form after glomerulus, and surround the proximal and distal tubules, extend along loop of Henle (= vasa recta).

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Distal and Proximal tubules

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a. Secretion of toxins occurs in proximal tubule.
b. Nutrients (sugar, amino acids, vitamins) are reabsorbed in proximal tubule
c. Salt balance and pH balance controlled by proximal and distal tubules, as well.

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Loop of Henel

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a. The key to increasing the osmolarity of urine above blood is the creation and maintenance of an osmolarity gradient from the cortex to the medulla.
b. The development of this gradient occurs in juxtamedullary nephrons (as opposed to cortical nephrons)
c. Filtrate from the proximal tubule is isotonic with plasma.
d. As filtrate descends the loop of Henle (permeable to water but not salt), water leaves by osmosis, because the osmolarity of the interstitial fluid increases deeper into the medulla of the kidney ([NaCl] increases)
e. As filtrate ascends back toward cortex (ascending loop impermeable to water, permeable to salt), urea enters and NaCl leaves to maintain osmotic balance.
f. Active transport of NaCl occurs in upper region of ascending limb, creating a filtrate hypoosmotic to the interstitial fluid.
g. As filtrate moves down the collecting duct, water leaves by osmosis, creating concentrated urine. Wall of collecting duct is permeable to urea, maintaining high osmolarity in medulla.

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Hormonal control of osmoregulation

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Antidiuretic hormon

Angeotensin- renin system

3. Atrial natriuretic factor (ANF)

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Antidiuretic Hormone

Back 39

Diuresis = production of dilute urine)
a. Produced in the hypothalamus in response to increased blood osmolarity (the body wants to hold on to the water it has)
b. Reduces water loss, by increasing permeability of distal tubules and collecting ducts thus allowing more reabsorption of water (= more concentrated urine)

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Angeotensin

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a. Renin is produced by the juxtaglomerular apparatus (JGA) (part of the afferent arteriole near distal tubule of the nephron)
b. Reacts to lower blood pressure
c. Renin cleaves pre-existing but inactive angiotensinogen (a globular protein produced in the liver and released into the blood) to angiotensin I, which is further cleaved to angiotensin II
d. Angiotensin II increases blood pressure by constricting arterioles, it also stimulates release of aldosterone
e. Aldosterone (from adrenal glands) causes increased Na+ reabsorption in distal tubule, increasing blood volume.
f. Different from ADH in that aldosterone responds to blood volume, not osmolarity,

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3. Atrial natriuretic factor

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a. ANF is a diuretic, it works in opposite direction to the above antidiuretic hormones
b. Produced in the walls of the atria in response to elevated blood pressure and blood volume.

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Atrial Natriuretic factor effects

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i. Inhibits NaCl reabsorption in the distal tubule, producing a more dilute urine
ii. Opens the afferent glomerular arteriole, but constricts the efferent arteriole, leading to a higher filtration rate an a larger volume of urine
iii. Inhibits renin secretion by the JGA