Chapter 44 Osmoregulation and Excretion Overview A Balancing

Chapter 44: Osmoregulation and Excretion

Overview: A Balancing Act • Animals must maintain water and solute concentration within certain limits. – An extreme external environment can greatly impact the water to solute levels of an organism. • Osmoregulation: how animals regulate solute concentrations and balance the gain and loss of water.

Overview: A Balancing Act • Metabolism presents organism with problems of waste disposal. – The breakdown of nucleic acids and proteins have a very toxic product of ammonia. Many animals have adapted to meet these physiological challenges • Excretion: How animals dispose of nitrogencontaining waste products from metabolism.

Osmoregulation • Balances the uptake and loss of water and solutes.

Osmosis • Water enter and leaves cells through the process of osmosis. • The difference in osmolarity (total solute concentration expressed in moles) of two solutions determines where the water is moving.

Osmotic Challenges • The Osmotic challenges an animal faces depends on how it deals with its internal osmolarity. – Osmoconformer: An animal that does not need to actively adjust its internal osmolarity because they match the conditions of their environment. – Osmoregulator: An animal that does not share the same osmolarity with its environment and has the need to adjust its internal concentrations.

• Osmoregulation requires an expense of energy since active transport is used to manipulate solute concentration in an organisms cells.

Animal tolerance to change in osmolarity • Most animals are said to be either Euryhaline or Stanohaline • Euryhaline can live in environments of great fluctuation in solute concentration. • On the other hand, stanohaline cannot. • Both can be either osmoconformers or osmoregulators.

Osmoregulation adaptations in aquatic life • Marine Animals – These animals are broken up into Osmoregulators and Osmoconformers. – Most invertebrate marine animals are Osmoconformers – Some invertebrates and all vertebrates are Osmoregulators • Many vertebrates like the bony fish are hypoosmotic to salty sea water and take in solutes.

• Freshwater Animals – These osmoregulatory animals are hyperosmotic to their environment. – Their body fluids are much more concentrated then their freshwater habitat. – Freshwater Animals adapted to there environment by having a decrease in solute concentration from their salt-water relatives.

• Animal living in temporary waters – Some aquatic invertebrates like the tartigrade (water bear) can lose almost all of their body water and still survive. – Tatrigrades have grown the adaptation known as anhydrobiosis, which is living without water. – The Tatrigade can live with reduced water weight of 85%-2% for a decade.

Osmoregulation adaptation in terrestrial animals • Many land animals eat moist foods and use metabolic water (water produced from cellular respiration) to maintain water levels.

• Desert Animals have many adaptations and strategy to conserve water – Waxy cuticles – Live nocturnally to reduce evaporation and take advantage of the moist atmosphere – Use large amounts of metabolic water

Transport Epithelia • The composition of the cellular cytoplasm is usually managed by an internal body fluid that surrounds the cells. • Transport Epithelia are cells that control solute movement through our internal body fluids. – Solutes leaving or entering the body must pass through the selectively permeable membrane of the Transport Epithelia.

Animal’s nitrogenous wastes reflect phylogeny and habitat • The type and amount of an organism’s waste products has a lot to do with the animal’s water balance • The most common nitrogenous waste product is the extremely toxic ammonia (NH 3).

Forms of Nitrogenous Waste • Ammonia – Ammonia can only be tolerated at low levels and need a lot of water to dilute it. • This is why ammonia excretion is very common in aquatic life. – Invertebrates can have ammonia released throughout their whole body surface.

• Urea – A combination of CO 2 and ammonia that is formed in the liver. – 100, 000 times less toxic then ammonia – Disadvantage is that it takes sufficient energy to create Urea through the liver’s metabolic processes. – Mammals, sharks, bony fish, amphibians, sharks and turtles use Urea.

• Uric Acid – Used by Insects, land snails, reptiles, and birds – Relatively non-toxic – Insoluble and is efficient for animals with little water and/or a relatively dry environment. – However, Uric Acid is the most energy insufficient nitrogenous waste to produce.

Influence of Evolution and Environment on Nitrogenous Wastes • Uric Acid started to be naturally selected for because soluble nitrogenous wastes could dangerously accumulate in the embryo. • Environmental factors – Temperature: Higher the temperature, the less water is available to dilute the waste – Energy Available: How much and what kind of food an organism eats

Diverse Excretory systems are variations on a tubular theme • Excretory Systems: controls fluid movement between internal fluids and external environment. – Key to homeostasis – Disposes metabolic wastes and controls the composition of body fluids by adjusting the amount of solute lost. – http: //www. youtube. com/watch? v=chh. Na. Li 9 P 3 E

Excretory processes 1. Filtration: Water and solutes (the filtrate) are forced through a selectively permeable membrane of many capillaries into the excretory tubule. 2. Reabsorption: The transport epithelium finds valuable substances of the filtrate and sends them back to their bodily fluids. 3. Secretion: More toxins and excess ions were added to the substances in the excretory tubule. 4. Excretion: The filtrate exits the body.

Types of Excretory Systems • Protonephridia: Flame-Bulb Systems – A network of dead end tubules that do not have internal openings. – Water is provided from the Flame-Bulb and travels to the tubules. The water is released into the outside world through openings known as nephridiopores – Tubules release for diluted urine.

• Metanephridia – Internal openings that obtain body fluids – Metanephridia are found in most annelids. – Useful solutes are reabsorbed and nitrogenous wastes are excreted. – Also produce very diluted urine to balance the water influx.

• Malpighian Tubules – Insects and terrestrial anthropods – Nitrogenous wastes are removed from hemolymph. – The is a key adaptation to conserve water for terrestrial life through waste matter and feces

• Vertebrate Kidneys: – Thrive in both osmoregulation and excretion

Nephrons and associated blood vessels are the functional units of the mammalian kidney • A pair of mammal kidneys are responsible for water balance and salt regulation. • Renal artery: The blood vessel that brings blood to the kidney. – Renal vein drains the blood. • Urine travels from the two ureters in the kidney to a urinary bladder and through the urethra.

Structure and Function of the Nephron and Associated Structures Renal cortex and Renal Medulla are made of microscopic excretory tubules and their blood vessels.

• The nephron is the functional area of the kidney that includes one long tubule and a cluster of cappillaries known as the glomerulus.

• Filtration of the Blood – The filtration of small molecules is non-selective • Pathway of the Filtrate – The filtrate travels through three segments of the nephron • Proximal tubule, the loop of Henle, distal tubule, and finally the filtrate empties into the collecting duct. • Nephron and collecting duct lined by a transport epithelium that enables the filtrate to make urine.

• Blood Vessels Associated with the Nephrons – Afferent arteriole: a type of renal artery that subdivides into the capillaries of the glomerulus – All nephrons take blood from an afferent arteriole. – When capillaries leave the glomerulus and converge to form an efferent arteriole. This subdivides to create peritubular capillaries. – The tubules and capillaries do not exchange materials directly.

From Blood Filtrate to Urine 1. Proximal tubule- Secretion and reabsorbtion manipulate the volume and composition of the filtrate. – A majority of the water and Na. Cl from the original filtrate is reabsorbed 2. Reabsorbtion of water continues to occur. The filtrate shifts to the descending limb of the loop of Henle. 3. Salt diffuses out of the permeable tubule into the interstitial fluid. 4. Distal tubule: Regulates the balance in concentration of K+ and Na. Cl. 5. Collecting Duct: The Filtrate is finally carried through the medulla to the renal pelvis

The mammalian kidney’s ability to conserve water is a clear terrestial adaptation • Urine can be filled with a diluted solute because then the organism will not have too much water loss. • Conserving water successfully Is very advantageous for terrestrial organisms.

Solute Gradients and Water Conservation • Nephrons consume energy and produce a region of high osmolarity. • Filtrate flows from cortex to medulla and water leaves the tubule through osmosis The 1200 mos/ml enlarges the amount Na. Cl that is diffused out of the tubule

The Counter Current Multiplier System • This system deals with the loop of Henle • It keeps a high salt concentration in the kidney, so urine is tightly compact with solute.

Regulation of Kidney Function • Water in the kidney can be regulated by nervous and hormonal control • Antiuretic hormone: Increases water reabsorption which as a result, reduces urine volume. • Renin-angiotensin-aldosterone system (RAAS): This a complex feedback circuit that heavily contributes to an organisms homeostasis. • Atrial Natriuretic Factor-This has an opposing process of the RAAS.

• All three factors create a system of checks and balances that let the kidney properly control – Osmolarity – Salt concentration – Volume – Blood Pressure

Diverse adaptations of the vertebrate kidney • Different nephron structures can supply species with osmoregulation that match up with their environment.

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