responses to ionic environments (part two)

8/3/2019 Responses to Ionic Environments (Part Two)

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Responses to Ionic Environments (Part Two)

Sample Exam Questions

Freeze avoidance is a strategy used by ectotherms in freezing environments.

This involves:

a. The generation of proteins that promote ice-crystal in cells.

b. The generation of proteins that enables the supercooling of

tissue fluids.

c. Changes in metabolism leading to the reduced osmolarity of

extracellular fluids.

d. The increased generation of metabolic heat.

Following consumption of a highly salty meal, which of the following wouldbe a likely consequence in a human?

a. Increased glomerular filtration

b. Increased secretion of aldosterone

c. Decreased secretion of aldosterone

d. Formation of a hypo-osmotic urine

Readings

y Pages 774-778

y Pages 848-850

y Chapter 51

Ionic and Osmotic Balance

Mammals

y Preventing dehydration

y Regulating kidney function

y Extreme regulation in the kangaroo rat

y Humans are regulators

o Water loss happens when water is evaporated via the lungs,

mouth, and nose, sweating excretion via the urine and feces



o Solution to water loss

Kidneys do a lot of waste reabsorption

Our lungs are internalized to prevent water loss and

utilize a countercurrent mechanism to retain respiratory

water vapour.

Plants

y Xerophytes

o Plants that have adapted to cope with dry desert conditions

are called xerophytes. Many do not have leaves, which would

lose water through evaporation in the heat. Instead they may

have defensive spines. Some xerophytes have shallow roots

that absorb water quickly after rain. Others have very long

taproots that extract water from deep in the ground.

y Halophytes

o Plants that have adapted to live in salty environments are

called halophytes. Salt draws water out of the roots of most

plants, slowly drying them out. Some halophytes have ways

to get rid of excess salt. Others need a salty environment in

order to survive. Halophytes are able to grow in salt marshes,

shallow coastal waters, dry salt pans, and on sand dunes.

Terrestrial Vertebrates

Problem

y Made of water

Consequence

y Loss of water to air by«

o Evaporation via the lungs, mouth, and nose

o Sweating

o Excretion via the urine and feces

Solution

y Modify kidney to reabsorb water ± only mammals and birds produce

urine more concentrated than the blood



y Internalize lungs to prevent water loss. Utilize a counter-current

mechanism to retain respiratory water vapour

Human Osmoregulation

Problem

y How do you maintain constant osmolarity of the blood despite wide

variations in«

o Water intake

o Salt intake

Consequence

y Dehydration or excessive water retention

Solution

y Modify volume and concentration of ions in the urine



The Kidneys

y Filter blood (about 200 liters/day)

y Selectively reabsorb both water and solutes

y Eliminates ions and nitrogenous wastes

y http://www.sumanasinc.com/webcontent/animations/content/kidne

y.html

y http://www.biologymad.com/resources/kidney.swf



Compound Reabsorption (%)

Water 99.4

Na 99.4

Glucose 100



Urea 53

Hormones and Reabsorption

y Aldosterone ± reabsorption of sodium

o Affects mineral concentrations from the adrenal glands,

excrete potassium, promotes water retention



o http://www.youtube.com/watch?v=bg0kuu46KCM

y Antidiuretic hormone (vasopressin) ± reabsorption of water

o Concentrates urine, raises blood pressure

o Twin sister to oxytocin, made in the hypothalamus stored in

posterior pituitaryo http://www.youtube.com/watch?v=KINOArtDeWg

What is the difference in urine output after drinking

y A liter of water?

y A liter of water and half a bag of salted chips?

y When a person is dehydrated, the hypothalamus is activated

causing the posterior pituitary secretes large amounts of ADH

y Urine output is affected by ingesting salty chips. You have to deal

with the extra salt until it is excreted.

y The ADH will cause the kidney collecting ducts to insert water

pores. If ADH is high, this makes concentrated urine and conserves

water.

y When a person is dehydrated or consumes a large amount of salt,

the blood osmotic pressure rises

o Osmoreceptors in the hypothalamus fire, causing the

posterior pituitary to secrete large amounts of ADH

o The ADH will cause the kidney collecting ducts to insert water

pores

o If ADH is high, the kidney makes concentrated urine and

conserves water

o The dehydration will also make the person thirsty and

drinking will restore the water volume.



Osmoregulation in the Kangaroo Rat



Problems

y Has to maintain ionic balance in«

o Hot, dry environment

o High metabolic rate

Consequence

y Survival

o It is so good at conserving

water that it does not drink

Solutions

y No evaporative cooling ± nocturnal

y Nasal counter-current exchange for retaining respiratory moisture

y Efficient kidney producing a hyperosmotic urine (20x more

concentrated)

rectal absorption of water from feces

y Gains water from oxidative processes

Kangaroo Rat Characteristics



y Animal remains in cool burrow during daytime

y Respiratory moisture condensed in nasal passages

y Metabolic water derived from dry seeds

y Free water in seeds

y Uring concentrated by countercurrent exchange in extra-long loopof Henle

y Feces dehydrated prior to defecation

Xerophytes

y Heavy cuticle to limit evaporative loss

y Succulent form to store water

y Epidermal hairsy Regulate the opening of the stomata

y Drop leaves and wilting

y Deep tap roots or extensive fibrous roots

Halophytes

Problems



y Saline conditions reduce the water potential and uptake of water to

plants

o Toxic effects of specific ions on enzyme function and

respiration

o Growth inhibition

Solutions

y Salt regulators:

o Exclude salt uptake

o Excrete salt ± salt glands in leaves

y Salt accumulators:

o Put salt in vacuoles

o Succulents ± take on extra water (and salt)

responses to ionic environments (part two)

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