Osmoregulation and Excretion
Transcript of Osmoregulation and Excretion
Osmoregulation and Excretion
The urinary system
Osmoregulation
All animals face the same central problem of osmoregulation. Over time, the rates of water uptake and
loss must balance. Animal cells—which lack cell walls—swell
and burst if there is a continuous net uptake of water, or shrivel and die if there is a substantial net loss of water.
35.1
Osmolarity
Osmolarity is defined as Moles of solute (salt) per liter of solution
(water) A value of 300 mosm/L
35.1
Excretion
The removal of nitrogenous waste (from the break down of amino acids primarily)
Urea is the waste product in humans
35.1
Proteins Nucleic acids
Amino acids Nitrogenous bases
–NH2
Amino groups
Most aquaticanimals, includingmost bony fishes
Mammals, mostamphibians, sharks,some bony fishes
Many reptiles(includingbirds), insects,land snails
Ammonia Urea Uric acid
NH3 NH2
NH2O C
C
CN
CO N
H H
C ONC
HN
OH
Types of Waste Products
Among the most important wastes are the nitrogenous breakdown products of proteins and nucleic acids
35.2
Ammonia
Animals that excrete nitrogenous wastes as ammonia Need access to lots of water Release it across the whole body surface
or through the gills
35.2
Urea
The liver of mammals and most adult amphibians Converts ammonia to less toxic urea
Urea is carried to the kidneys, concentrated And excreted with a minimal loss of water
35.2
Uric Acid Insects, land snails, and many reptiles,
including birds Excrete uric acid as their major nitrogenous
waste Uric acid is largely insoluble in water
And can be secreted as a paste with little water loss
35.2
The Excretory System
The Steps in Urine Production 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
35.3
Most excretory systems 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
Filtra
teU
rine
1
2
3
4
35.3
Structure and Function
The mammalian excretory system centers on paired kidneys Which are also the principal site of water
balance and salt regulation
35.4
Anatomy
Each kidney Is supplied with
blood by a renal artery and drained by a renal vein
Posterior vena cava
Renal artery and vein
Aorta
Ureter
Urinary bladder
Urethra
(a) Excretory organs and major associated blood vessels
Kidney
35.4
(b) Kidney structure
UreterSection of kidney from a rat
Renalmedulla
Renalcortex
Renalpelvis
The mammalian kidney has two distinct regions
An outer renal cortex and an inner renal medulla
35.4
The nephron is the functional unit of the vertebrate kidney It consists of a single long tubule and a ball
of capillaries called the glomerulusJuxta-medullarynephron
Corticalnephron
Collectingduct
To renalpelvis
Renalcortex
Renalmedulla
20 µm
Afferentarteriolefrom renalartery
Glomerulus
Bowman’s capsule
Proximal tubule
Peritubularcapillaries
SEM
Efferentarteriole fromglomerulus
Branch ofrenal vein
DescendinglimbAscendinglimb
Loopof
Henle
Distal tubule
Collectingduct
(c) Nephron
Vasarecta(d) Filtrate and
blood flow35.5
Filtration of the Blood
Filtration occurs as blood pressure Forces fluid from the blood in the
glomerulus into the lumen of Bowman’s capsule
35.5
Filtration of the Blood
Filtration of small molecules is nonselective And the filtrate in Bowman’s capsule is a
mixture that mirrors the concentration of various solutes in the blood plasma
35.5
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
35.5
Blood Vessels Associated with the Nephrons
Each nephron is supplied with blood by an afferent arteriole a branch of the renal artery that subdivides into the capillaries
The capillaries converge as they leave the glomerulus forming an efferent arteriole
The vessels subdivide again forming the peritubular capillaries, which surround the proximal and distal tubules
35.5
Proximal tubule
Filtrate
H2OSalts (NaCl and others)HCO3
–
H+
UreaGlucose; amino acidsSome drugs
KeyActive transport
Passive transport
CORTEX
OUTERMEDULLA
INNERMEDULLA
Descending limbof loop ofHenle
Thick segmentof ascendinglimb
Thin segmentof ascendinglimb
Collectingduct
NaCl
NaCl
NaCl
Distal tubuleNaCl Nutrients
Urea
H2O
NaClH2O
H2OHCO3 K+
H+ NH3
HCO3
K+ H+
H2O
1 4
32
3 5
From Blood Filtrate to Urine: A Closer Look
35.6
Secretion and reabsorption in the proximal tubule Substantially alter the volume and composition
of filtrate Reabsorption of water continues
As the filtrate moves into the descending limb of the loop of Henle
35.6
From Blood Filtrate to Urine: A Closer Look
As filtrate travels through the ascending limb of the loop of Henle Salt diffuses out of the permeable tubule into the
interstitial fluid The distal tubule
Plays a key role in regulating the K+ and NaCl concentration of body fluids
The collecting duct Carries the filtrate through the medulla to the renal
pelvis and reabsorbs NaCl
35.6
From Blood Filtrate to Urine: A Closer Look
Water Conservation
The mammalian kidney Can produce urine much more
concentrated than body fluids, thus conserving water
35.7
Solute Gradients and Water Conservation
In a mammalian kidney, the cooperative action and precise arrangement of the loops of Henle and the collecting ducts Are largely responsible for the osmotic
gradient that concentrates the urine
35.7
Two solutes, NaCl and urea, contribute to the osmolarity of the interstitial fluid which causes the reabsorption of water in the kidney and concentrates the urine
H2O
H2O
H2O
H2O
H2O
H2O
H2O
NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
300
300 100
400
600
900
1200
700
400
200
100
ActivetransportPassivetransport
OUTERMEDULLA
INNERMEDULLA
CORTEX
H2O
Urea
H2OUrea
H2O
Urea
H2O
H2O
H2O
H2O
1200
1200
900
600
400
300
600
400
300
Osmolarity of interstitial
fluid(mosm/L)
300
35.7
The countercurrent multiplier system involving the loop of Henle Maintains a high salt concentration in the
interior of the kidney, which enables the kidney to form concentrated urine
35.7
From Blood Filtrate to Urine: A Closer Look
The collecting duct, permeable to water but not salt Conducts the filtrate through the kidney’s
osmolarity gradient, and more water exits the filtrate by osmosis
35.7
From Blood Filtrate to Urine: A Closer Look
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
35.7
From Blood Filtrate to Urine: A Closer Look