Freshwater animals show adaptations that reduce water uptake and conserve solutes
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Freshwater animals show adaptations that reduce water uptake and conserve solutes Desert and marine animals face desiccating environments that can quickly deplete body water Osmoregulation regulates solute concentrations and balances the gain and loss of water

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Freshwater animals show adaptations that reduce water uptake and conserve solutes

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Freshwater animals show adaptations that reduce water uptake and conserve solutes

  • Freshwater animals show adaptations that reduce water uptake and conserve solutes

  • Desert and marine animals face desiccating environments that can quickly deplete body water

  • Osmoregulation regulates solute concentrations and balances the gain and loss of water

  • Excretion gets rid of metabolic wastes


Osmoregulation balances the uptake and loss of water and solutes

Osmoregulation balances the uptake and loss of water and solutes

  • Osmoregulation is based largely on controlled movement of solutes between internal fluids and the external environment

  • Osmoregulators expend energy to control water uptake and loss in a hyperosmotic or hypoosmotic environment


Freshwater animals show adaptations that reduce water uptake and conserve solutes

Gain of water and

salt ions from food

and by drinking

seawater

Osmotic water loss

through gills and other parts

of body surface

Excretion of salt ions

and small amounts

of water in scanty

urine from kidneys

Excretion of

salt ions

from gills

Osmoregulation in a saltwater fish


Freshwater animals show adaptations that reduce water uptake and conserve solutes

Osmotic water gain

through gills and other parts

of body surface

Uptake of

water and some

ions in food

Uptake of

salt ions

by gills

Excretion of

large amounts of

water in dilute

urine from kidneys

Osmoregulation in a freshwater fish


Transport epithelia

Transport Epithelia

  • Transport epithelia are specialized cells that regulate solute movement

  • They are essential components of osmotic regulation and metabolic waste disposal

  • They are arranged in complex tubular networks

  • An example is in salt glands of marine birds, which remove excess sodium chloride from the blood


Freshwater animals show adaptations that reduce water uptake and conserve solutes

Nasal salt gland

Nostril

with salt

secretions


Freshwater animals show adaptations that reduce water uptake and conserve solutes

Lumen of

secretory tubule

Vein

Capillary

Artery

Secretory

tubule

NaCl

Transport

epithelium

Direction

of salt

movement

Blood

flow

Secretory cell

of transport

epithelium

Central

duct


Freshwater animals show adaptations that reduce water uptake and conserve solutes

Nucleic acids

Proteins

Amino acids

Nitrogenous bases

—NH2

Amino groups

Most aquatic animals, including most bony fishes

Mammals, most amphibians, sharks, some bony fishes

Many reptiles (including birds), insects, land snails

Ammonia

Urea

Uric acid


Ammonia

Ammonia

  • Animals that excrete nitrogenous wastes as ammonia need lots of water

  • They release ammonia across the whole body surface or through gills


Freshwater animals show adaptations that reduce water uptake and conserve solutes

Urea

  • The liver of mammals and most adult amphibians converts ammonia to less toxic urea

  • The circulatory system carries urea to the kidneys, where it is excreted


Uric acid

Uric Acid

  • Insects, land snails, and many reptiles, including birds, mainly excrete uric acid

  • Uric acid is largely insoluble in water and can be secreted as a paste with little water loss


Excretory processes

Excretory Processes

  • Most excretory systems produce urine by refining a filtrate derived from body fluids

  • Key functions of most excretory systems:

    • Filtration: pressure-filtering of body fluids

    • Reabsorption: reclaiming valuable solutes

    • Secretion: adding toxins and other solutes from the body fluids to the filtrate

    • Excretion: removing the filtrate from the system


Freshwater animals show adaptations that reduce water uptake and conserve solutes

Capillary

Filtration

Excretory

tubule

Filtrate

Reabsorption

Secretion

Urine

Excretion


Protonephridia flame bulb systems

Protonephridia: Flame-Bulb Systems

  • A protonephridium is a network of dead-end tubules lacking internal openings

  • The smallest branches of the network are capped by a cellular unit called a flame bulb

  • These tubules excrete a dilute fluid and function in osmoregulation


Freshwater animals show adaptations that reduce water uptake and conserve solutes

Nucleus

of cap cell

Cilia

Interstitial fluid

filters through

membrane where

cap cell and tubule

cell interdigitate

(interlock)

Tubule cell

Flame

bulb

Protonephridia

(tubules)

Tubule

Nephridiopore

in body wall


Metanephridia

Metanephridia

  • Each segment of an earthworm has a pair of open-ended metanephridia

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


Freshwater animals show adaptations that reduce water uptake and conserve solutes

Coelom

Capillary

network

Bladder

Collecting

tubule

Nephridio-

pore

Nephrostome

Metanephridium


Malpighian tubules

Malpighian Tubules

  • In insects and other terrestrial arthropods, Malpighian tubules remove nitrogenous wastes from hemolymph and function in osmoregulation

  • Insects produce a relatively dry waste matter, an important adaptation to terrestrial life


Freshwater animals show adaptations that reduce water uptake and conserve solutes

Digestive tract

Rectum

Hindgut

Intestine

Midgut

(stomach)

Malpighian

tubules

Anus

Feces and urine

Salt, water, and

nitrogenous

wastes

Malpighian

tubule

Rectum

Reabsorption of H2O,

ions, and valuable

organic molecules

HEMOLYMPH


Nephrons and associated blood vessels are the functional unit of the mammalian kidney

Nephrons and associated blood vessels are the functional unit of the mammalian kidney

  • Kidneys, the excretory organs of vertebrates, function in both excretion and osmoregulation

  • The mammalian excretory system centers on paired kidneys, which are also the principal site of water balance and salt regulation

  • 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


Freshwater animals show adaptations that reduce water uptake and conserve solutes

Posterior vena cava

Renal artery and vein

Kidney

Renal

medulla

Aorta

Renal

cortex

Ureter

Renal

pelvis

Urinary bladder

Urethra

Ureter

Excretory organs and

major associated blood

vessels

Section of kidney from a rat

Kidney structure

Juxta-

medullary

nephron

Cortical

nephron

Afferent

arteriole

from renal

artery

Glomerulus

Bowman’s capsule

Proximal tubule

Peritubular capillaries

Renal

cortex

Collecting

duct

SEM

20 µm

Efferent

arteriole from

glomerulus

Renal

medulla

Distal

tubule

To

renal

pelvis

Collecting

duct

Branch of

renal vein

Descending

limb

Loop

of

Henle

Nephron

Ascending

limb

Vasa

recta

Filtrate and blood flow


Structure and function of the nephron and associated structures

Structure and Function of the Nephron and Associated Structures

  • The mammalian kidney has two distinct regions: an outer renal cortex and an inner renal medulla

  • The nephron, the functional unit of the vertebrate kidney, consists of a single long tubule and a ball of capillaries called the glomerulus


Filtration of the blood

Filtration of the Blood

  • Filtration occurs as blood pressure forces fluid from the blood in the glomerulus into the lumen of Bowman’s capsule

  • Filtration of small molecules is nonselective

  • The filtrate in Bowman’s capsule mirrors the concentration of solutes in blood plasma


Pathway of the filtrate

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


Blood vessels associated with the nephrons

Blood Vessels Associated with the Nephrons

  • Each nephron is supplied with blood by an afferent arteriole, a branch of the renal artery that divides into the capillaries

  • The capillaries converge as they leave the glomerulus, forming an efferent arteriole

  • The vessels divide again, forming the peritubular capillaries, which surround the proximal and distal tubules


From blood filtrate to urine a closer look

From Blood Filtrate to Urine: A Closer Look

  • Filtrate becomes urine as it flows through the mammalian nephron and collecting duct

  • Secretion and reabsorption in the proximal tubule greatly alter the filtrate’s volume and composition

  • Reabsorption of water continues as filtrate moves into the descending limb of the loop of Henle


Freshwater animals show adaptations that reduce water uptake and conserve solutes

  • In the ascending limb of the loop of Henle, salt diffuses from the permeable tubule into the interstitial fluid

  • The distal tubule regulates the K+ and NaCl concentrations of body fluids

  • The collecting duct carries filtrate through the medulla to the renal pelvis and reabsorbs NaCl

  • The mammalian kidney conserves water by producing urine that is much more concentrated than body fluids


Freshwater animals show adaptations that reduce water uptake and conserve solutes

Proximal tubule

Distal tubule

Nutrients

NaCl

H2O

HCO3–

K+

HCO3–

H2O

NaCl

H+

H+

NH3

K+

CORTEX

Descending limb

of loop of

Henle

Thick segment

of ascending

limb

Filtrate

H2O

Salts (NaCl and others)

HCO3–

H+

Urea

Glucose; amino acids

Some drugs

NaCl

H2O

OUTER

MEDULLA

NaCl

Thin segment

of ascending

limb

Collecting

duct

Key

Urea

NaCl

Active transport

Passive transport

H2O

INNER

MEDULLA


Solute gradients and water conservation

Solute Gradients and Water Conservation

  • The cooperative action and precise arrangement of the loops of Henle and collecting ducts are largely responsible for the osmotic gradient that concentrates the urine

  • NaCl and urea contribute to the osmolarity of the interstitial fluid, which causes reabsorption of water in the kidney and concentrates the urine


Freshwater animals show adaptations that reduce water uptake and conserve solutes

Osmolarity of

interstitial

fluid

(mosm/L)

300

300

100

300

100

300

300

H2O

NaCl

H2O

CORTEX

Active

transport

200

400

400

400

H2O

NaCl

H2O

Passive

transport

NaCl

H2O

H2O

OUTER

MEDULLA

H2O

NaCl

H2O

400

600

600

600

H2O

NaCl

H2O

Urea

H2O

NaCl

H2O

700

900

900

Urea

H2O

H2O

NaCl

INNER

MEDULLA

Urea

1200

1200

1200


Freshwater animals show adaptations that reduce water uptake and conserve solutes

  • The countercurrent multiplier system involving the loop of Henle maintains a high salt concentration in the kidney

  • This enables the kidney to form concentrated urine


Freshwater animals show adaptations that reduce water uptake and conserve solutes

  • The collecting duct conducts filtrate through the osmolarity gradient, and more water exits the filtrate by osmosis

  • Urea diffuses out of the collecting duct as it traverses the inner medulla

  • Urea and NaCl form the osmotic gradient that enables the kidney to produce urine that is hyperosmotic to the blood


Regulation of kidney function

Regulation of Kidney Function

  • The osmolarity of the urine is regulated by nervous and hormonal control of water and salt reabsorption in the kidneys

  • Antidiuretic hormone (ADH) increases water reabsorption in the distal tubules and collecting ducts of the kidney


Freshwater animals show adaptations that reduce water uptake and conserve solutes

Osmoreceptors

in hypothalamus

Thirst

Hypothalamus

Drinking reduces

blood osmolarity

to set point

ADH

Increased

permeability

Pituitary

gland

Distal

tubule

H2O reab-

sorption helps

prevent further

osmolarity

increase

STIMULUS

The release of ADH is

triggered when osmo-

receptor cells in the

hypothalamus detect an

increase in the osmolarity

of the blood

Collecting duct

Homeostasis:

Blood osmolarity


Freshwater animals show adaptations that reduce water uptake and conserve solutes

  • The renin-angiotensin-aldosterone system (RAAS) is part of a complex feedback circuit that functions in homeostasis


Freshwater animals show adaptations that reduce water uptake and conserve solutes

Homeostasis:

Blood pressure,

volume

Increased Na+

and H2O reab-

sorption in

distal tubules

STIMULUS:

The juxtaglomerular

apparatus (JGA) responds

to low blood volume or

blood pressure (such as

due to dehydration or

loss of blood)

Aldosterone

Arteriole

constriction

Adrenal gland

Angiotensin II

Distal

tubule

Angiotensinogen

JGA

Renin

production

Renin


Animations and videos

Animations and Videos

  • Water Uptake

  • The Human Kidney

  • Bozeman – Osmoregulation

  • The Mammalian Kidney

  • Chapter Quiz Questions – 1

  • Chapter Quiz Questions – 2


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