Osmoregulation and Excretion

Chapter 44

Osmoregulation

A balancing act The physiological systems of animals

Operate in a fluid environment The relative concentrations of water

and solutes in this environment Must be maintained within fairly narrow limits

Osmoregulation & Excretion Osmoregulation

Regulates solute concentrations and balances the gain and loss of water

Is based largely on controlled movement of solutes

Excretion Gets rid of metabolic wastes Most important is the nitrogenous wastes

Ammonia Urea Uric Acid

Nitrogenous Wastes Ammonia generally produced by aquatic

animals, very toxic, Need access to lots of water,release it across the whole body surface or through the gills

Urea ammonia converted to less toxic urea by the liver of mammals and most adult amphibians Urea is carried to the kidneys,

concentrated ,excreted with a minimal loss of water

Uric Acid insects, land snails, and many reptiles, including birds excrete uric acid as their major nitrogenous waste Is insoluble in water and can be secreted as a

paste with little water loss

Excretory Systems

Regulate solute movement between internal fluids and the external environment

Produce urine by refining a filtrate derived from body fluids

Filtration. The excretory tubule collects a filtrate from the blood.Water and solutes are forced by blood pressure across the selectively permeable membranes of a cluster of capillaries and into the excretory tubule.

Reabsorption. The transport epithelium reclaims valuable substances from the filtrate and returns them to the body fluids.

Secretion. Other substances, such as toxins and excess ions, are extracted from body fluids and added to the contents of the excretory tubule.

Excretion. The filtrate leaves the system and the body.

Capillary

Excretorytubule

Filtrate

Urine

1

2

3

4

Tubular Theme of Excretory Systems

Key Functions Filtration, pressure-filtering of body

fluids producing a filtrate Reabsorption, reclaiming valuable

solutes from the filtrate Secretion, addition of toxins and

other solutes from the body fluids to the filtrate

Excretion, the filtrate leaves the system

Survey of Excretory Systems

The systems that perform basic excretory functions Vary widely among animal groups Are generally built on a complex

network of tubules

Nucleusof cap cell

Cilia

Interstitial fluidfilters throughmembrane wherecap cell and tubulecell interdigitate(interlock)

Tubule cell

Flamebulb

Nephridioporein body wall

Tubule

Protonephridia(tubules)

Protonephridia:Flame-Bulb Systems

Is a network of dead-end tubules lacking internal openings

The tubules branch throughout the body And the smallest

branches are capped by a cellular unit called a flame bulb

These tubules excrete a dilute fluid And function in

osmoregulationFigure 44.10

Metanephridia Each segment of

an earthworm a pair of open-ended metanephridia

Consist of tubules that collect coelomic fluid and produce dilute urine for excretion

Nephrostome Metanephridia

Nephridio-pore

Collectingtubule

Bladder

Capillarynetwork

Coelom

Digestive tract

Midgut(stomach)

Malpighiantubules

RectumIntestine

Hindgut

Salt, water, and nitrogenous

wastes

Feces and urineAnus

Malpighiantubule

Rectum

Reabsorption of H2O,ions, and valuableorganic molecules

HEMOLYMPH

Malpighian Tubules Insects and other

terrestrial arthropods Remove nitrogenous

wastes from hemolymph

Function in osmoregulation

Figure 44.12

Vertebrate Kidneys Kidneys, the excretory organs of

vertebrates Function in both excretion and

osmoregulation

Mammalian Excretory System Centers on paired

kidneys Each kidney

Is supplied with blood by a renal artery and drained by a renal vein

Urine exits each kidney Through a duct called

the ureter Both ureters

Drain into a common urinary bladder

Posterior vena cava

Renal artery and vein

Aorta

Ureter

Urinary bladder

Urethra

(a) Excretory organs and major associated blood vessels

Kidney

Mammalian Kidney The mammalian kidney has two

distinct regionsAn outer renal cortex and an inner renal

medulla

(b) Kidney structure

UreterSection of kidney from a rat

Renalmedulla

Renalcortex

Renalpelvis

Figure 44.13b

Both regions are packed with microscopic excretory tubules, nephrons, and their associated blood vessels.

Each nephron consists of a single long tubule and a ball of capillaries, called the glomerulus.

The blind end of the tubule forms a cup-shaped swelling, called Bowman’s capsule, that surrounds the glomerulus

Each human kidney packs about a million nephrons.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 44.21

Filtration of the Blood

Filtration occurs as blood pressure Forces fluid from the blood in the

glomerulus into the lumen of Bowman’s capsule

The filtrate in Bowman’s capsule is a mixture that mirrors the concentration of various solutes in the blood plasma

Pathway of the Filtrate

From Bowman’s capsule, the filtrate passes through three regions of the nephron The proximal tubule, the loop of

Henle, and the distal tubule Fluid from several nephrons

Flows into a collecting duct

Processes

FiltrationSecretionReabsorption

Proximal Tubule

Secretion and reabsorption changes vol & comp of filterate

controls of pH by H+ and bicarbonate

Glucose and amino acids reabsorbed

NaCl and water reabsorbed

Loop of Henle

Descending-permeable to water, reabsorption of water

Ascending-permeable to salt, no water

Distal Tubule

Regulates K= secretion into filtrate and NaCl reabsorption from filtrate

Regulation of Kidney Function Antidiuretic hormone (ADH)-made in

hypothalamus, released from pituitary, keeps water in Alcohol inhibits ADH

Renin released by kidneys activates Angiotensin II

Angiotensin IIhormone that causes arterioles to contract blood press. Goes up causes adrenal glands to release Aldosterone

Aldosteronekidney to reabs. Na+ water retention, blood volume and pressure go up