Ch 44 Osmoregulation and Excretion

Title: Oct 12­3:37 PM (1 of 39)

Water Balance and Waste Disposalosmoregulation ­ managing water content and solute composition

­based on movements of solutes­excretion of metabolic wastes­regulates bathing fluid of cells

­in excretory organs ­ maintain water balance and dispose of wastes

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Excretion ­ process that rids the body of nitrogenous metabolites and other waste products

What organic compounds produce nitogenous wastes?

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How do organisms balance water gain and loss?

osmoconformer­ being isoosmotic to surroundings­will not gain or lose water­live in water with consistant osmolarity

osmoregulator­an animal that must control its internal osmoregularity

in hypoosmotic ­ gets rid of waterin hyperosmotic ­ gains water

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stenohaline ­ animals that cannot tolerate large changes in external osmolarity

euryhaline ­ animals that can tolerate large changesex. salmon

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Osmolarity ­ solute concentration expressed as molarity

isoosmotic ­ if two solutions separated by a selectively permeable membrane have the same osmolarity

When two solutions differ in osmolarity, the one with the greater solute concentration is hyperosmotic and the one with the lower solute concentration is the hypoosmotic.

Water flows from hypoosmotic to hyperosmotic.

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hypoosmotic to seawater, loses water by osmosis, gains salt by diffusion

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constantly gains water and loses salt

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anhydrobiosis­adaptations for animals that live in water temporarily

Hydrated ­ 85% water Dehydrated ­ 2% water

tardigrades ­ water bears

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Land animals have body coverings that prevent dehydration

­keratinized skin

lose water from skin, urine, feces, respiration

have to rehydrate regularly

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­transport epithelium helps regulate solute movements

­move solutes in specific directions­form a barrier at tissue environment

boundary­in animals arranged in tubes with high

surface areaex. Salt glands in marine birds

remove excess sodium chloride from blood

Title: Oct 12­3:47 PM (11 of 39)

So why can't humans drink salt water like a seagull can?

­ bird gets rid of extra salt through a salt gland

­if humans drink salt water, they need a greater amount of water to excrete the salt load using their kidneys

therefore: become dehydrated

Title: Oct 12­3:56 PM (12 of 39)

Metabolic wastes­dissolved in water (except carbon dioxide)­nitrogenous wastes (breakdown products of proteins and nucleic acids)

ammonia­toxic molecule­common in aquatic species­diffuse easily­in invertebrates ­ diffuses through body­fish­ lost as ammonium ions form gills­can be excreted directly or as urea­must be very dilute in land animals or toxic

Title: Oct 12­3:48 PM (13 of 39)

Urea

­used for land animals (mammals, most adult amphibians, marine fish, turtles

­produced by liver that combines ammonia with carbon dioxide, then carried to excretory system by blood­low toxicity (100,000 x less than ammonia)­reduces need for water for excretion­disadvantage­ must expend energy to make form ammonia

Title: Oct 12­3:49 PM (14 of 39)

Uric Acid

­land snails, insects, birds and many reptiles­nontoxic­insoluble in water, excreted as semisolid paste­advantage if little water is around, but takes lots of energy to produce­uric acid is favored for egg layers because it can be stored within the egg without harming the embryo

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Diversity of excretory systems

regulate solute movement between internal fluids and the external environment

the filtrate produced by the system is from body fluids

Based on four processes:• filtration• reabsorption• secretion• excretion

Title: Oct 12­3:49 PM (17 of 39)

Filtration

Reabsorption

Secretion

Excretion

Capillary

Filtration ­ collects filtrate from blood; water/ solutes forced by blood pressure across selectively permeable membrane

Reabsorption ­ transport epithelium reclaims valuable substances from filtrate ­ puts back in body

Secretion ­ toxins and ions are extracted from body fluids and added to excretory tube

Excretion ­ fitrate (urine) leaves system and body

Title: Oct 12­4:06 PM (18 of 39)

Excretory systems in other organisms

Protonephridia ­ network of dead­end tubules connected to external openings• flame bulb is the cap end• excrete dilute fluid ­ nitrogenous waste (Ex parasitic flatworms); involved in osmoregulation (other flatworms• found in flatworms (phylum Platyhelminthes), rotifers, mollusc larvae and lancelets

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Title: Oct 12­5:47 PM (20 of 39)

• Metanephridia­ consist of tubules that collect coelomic fluid and produce dilute urine for excretion

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Malpighian Tubules ­ remove nitrogenous from hemolymph and used in osmoregulation

­in insects and other terrestrial arthropods

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Kidneys ­ excretory organ for vertebrates

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Cross Section of Kidney

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only mammals and some birds have loops of Henle

In human ­ 85% of nephrons have short loops of Henle and are in renal cortex

­ 15% are juxtamedullary nephrons ­ have loops of Henle that go deep into the renal medulla

­ 1,600L of blood flows through pair of kidneys/day­ but only 1.5L leaves body as urine

Title: Oct 12­6:08 PM (26 of 39)

How is blood filtered?

1. blood pressure forces fluid from blood into glomerulus­contains salts, glucose, amino acids, vitamins, nitrogenous wastes, water and other small molecules

2. From Bowman's Capsule ­ passes through three regions of nephron

• proximal tubule• loop of Henle• diatal tubule

Title: Oct 12­6:13 PM (27 of 39)

In the proximal tubule:

­get reabsorption of ions, water and nutrients

­molecules are transported actively and passively

­some toxic materials are secreted into the filtrate

­fitrate volume decreases

Title: Oct 12­6:18 PM (28 of 39)

In Loop of Henle:

Descending part­reabsorption of water contiues through aquaporins

­movement driven by high osmolarity of interstitial fluid (hyperosmotic to filtrate)

­filtrate becomes more concentrated

Title: Oct 12­6:20 PM (29 of 39)

Loop of Henle continued:

Ascending part

­salt, not water diffuses from tubule to interstitial fluid

­filtrate gets more dilute

Title: Oct 12­6:23 PM (30 of 39)

Distal Tubule:­regulates potassium and NaCl concentrations

­ion movement controls pH level

Collecting duct:

­filtrate goes from medulla to renal pelvis

­water, salt and some urea is lost

­filtrate gets more concentrated

Title: Oct 12­6:25 PM (31 of 39)

Filtering process

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Osmolarity of interstitial fluid depends on NaCl and urea

as filtrate flows in collecting duct past interstitial fluid of increasing osmolarity, more water moves out = concentrated urine

Title: Oct 12­6:31 PM (33 of 39)

How do hormones regulate the blood osmolarity?

Antidiuretic hormone (ADH)

­increases water reabsorption in the distal tubule and collecting ducts

­an increase in osmolarity triggers release of ADH ­ helps conserve water

Title: Oct 12­6:39 PM (34 of 39)

ADH allows aquaporins to be inserted into the membrane lining the lumen.

Aquaporin channels allow water to be reabsorbed from the collecting duct and put back into the body

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• Mutation in ADH production causes severe dehydration and results in diabetes insipidus

• Alcohol is a diuretic as it inhibits the release of ADH

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How is blood pressure regulated by the kidneys?

Renin­Angiotensin­Aldosterone System (RAAS)

1. Renin is released by the kidney when blood pressure drops2. Renin cleaves angiotensinogen (plasma protein) into

angiotensin II (functions as a hormone)3.Angiotensin II increases the blood pressure by constricting

capillaries; also signals adrenal glands to release aldosterone 4. Aldosterone acts on nephrons' distal tubules ­ makes them

reabsorb sodium and water ­ which increases blood volume and pressure

Title: Oct 12­6:49 PM (37 of 39)

So what if you have high blood pressure?

­ drugs that block angiotensin II are used to treat hypertension

­inhibit angiotensin converting enzyme (ACE) which catalyzes the 2nd step on production of angiotensin II

Title: Oct 12­6:58 PM (38 of 39)

So..... ADH and RAAS are partners in homeostasis

• ADH and RAAS both increase water reabsorption, but only RAAS will respond to a decrease in blood volume

• Another hormone, atrial natriuretic peptide (ANP), opposes the RAAS

• ANP is released in response to an increase in blood volume and pressure and inhibits the release of renin

Title: Oct 12­7:03 PM (39 of 39)