Homeostasis and

ExcretionChapter 44

Presentation by: Imani Phillips, Stephanie Riley, and Jamie Chavez

Osmoregulation and Excretion

• Osmoregulation: how animals regulate solute concentrations and balance the gain and loss of water

• Excretion: how animals get rid of the nitrogen-containing waste products of metabolism

Osmosis

• Osmolarity: total solute concentration expressed as molarity or moles of solute per liter of solution– Unit of measurement: milliosmoles per liter(mosm/L) where 1

mosm/L = a total solute concentration of 10-3 M– Osmolarity of human blood= 300 mosm/L while osmolarity of

seawater= 1000 mosm/L

• When tow solutions differ in osmolarity,– The one with greater concentration of solutes is hyperosmotic– The more dilute solution is hypoosmotic

• When two solutions separated by a selectively permeable membrane have the same osmolarity they are said to be isoosmotic

2 Basic Solutions to the Problem of Balancing Water Gain with

Water Loss• Osmoconformers:

– Available only to marine animals that mostly live in water that has a very stable composition

– Does not actively adjust its internal osmolarity

• Osmoregulators:– An animal that must control its internal osmolarity

because its body fluids are not isoosmotic with the outside environment

Energy Cost of Osmoregulation

• Depends on how different an animal’s osmolarity is from its environment, how easily water and solutes move across the animal’s surface, and how much work is required to pump solutes across the membrane

• Adaptations that reduce water loss is a key to survival on land

Transport Epithelia• Is a layer or layers of specialized epithelial

cells that regulate solute movements • Moves specific solutes in controlled amounts

in specific directions

Nitrogenous Wastes

• One of the most important waste products especially when it comes to its effect on osmoregulation are the nitrogenous breakdown products of proteins and nucleic acids

• The amount of nitrogenous waste produced is coupled to the energy budget because it strongly depends on how much and what kind of food the animal eats

Forms of Nitrogenous WastesAmmonia Urea Uric Acid

•ammonia excretion is most common to aquatic species•Very toxic•in many vertebrates, ammonia release occurs across the whole body surface

•Excreted by most terrestrial animals and many marine species•Low toxicity•Animals must expend energy to produce it from ammonia

•Excreted by insects, land snails, and many reptiles•Relatively nontoxic•Largely insoluble in water and can be excreted as semi-solid paste with very little water loss

Spoiler: Not all animals have kidneys!!

• Before we get to vertebrate kidneys, lets take a look on how other living organisms such as flatworms, earthworms and insects.

Prontonephridia: Flame Bulb Systems(page930)

Metanephridium• Metanephridia is a type of excretory tubule

in which there are internal openings that collect body fluids in a nephridiopore and continues to pass through the bladder.

• Each part of a worm has two metanephridium.

• Functions for osmolarity and excretion.• Metanephridium are responsible for the

worm’s ability to live in damp soil and balance water by producing dilute urine.

Malpighian tubule

• In insects and other terrestrial arthropods.• Functions in osmoregulation and secreting

nitrogenous wastes.• These tubules drain salt, water, and

nitrogenous into the digestive tract. • Water and solutes leave the digestive tract

through osmosis so the remaining waste is nearly dry.

• This allows them to live on land.

The Vertebrate Kidneys

• Absorb the beauty and majesty of these amazing organs. It’s the least you can do for these extraordinary organs.

• The main function of the kidneys are to filter blood.

ADH(antidiuretic hormone)

• This hormone is released from the posterior pituitary gland when the hypothalamus recognizes that the osmolarity of the blood exceeds 300 mosm/L.

• Alcohol inhibits ADH which causes dehydration.

Angiotensin II

• What is initially a protein, is turned into a peptide angiotensin II by an enzyme when blood pressure lowers in the afferent arteriole which supplies blood to the glomerulus.

• This peptide increases blood pressure, and the reabsorption of water and salt.

Aldosterone

• Angiotensin II causes this hormone to be excreted from the adrenal glands.

• Aldosterone increases blood pressure, and the reabsorption of water and salt in the distal tubules.

• It is a form of positive feedback.• ADH: Response to change in osmolarity.• Aldosterone: Osmolarity does not change, but

the blood volume and pressure.

Diabetes• Since the body cannot properly process

glucose without insulin or cells do not turn glucose into glycogen. There is more glucose present in the blood.

• The kidneys end up filtering the unprocessed glucose and it is excreted out the body in urine. This keeps the blood from reaching dangerous glucose levels.

• Can cause damage to the kidneys.

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ellness-medicine/save-your-kidneys-with-vitamin-b1• http://www.parade.com/health/2009/03/new-kidney-dange

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