Osmoregulation And Excretion
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Osmoregulation and Excretion
The urinary system
Osmoregulation
All animals face the same central problem of osmoregulation.
35.1
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.
Osmolarity
Osmolarity is defined as
35.1
Moles of solute (salt) per liter of solution (water) A value of 300 mosm/L
Excretion
35.1
The removal of nitrogenous waste (from the break down of amino acids primarily) Urea is the waste product in humans
Types of Waste Products Nucleic acids
Proteins Amino acids
Among the most important wastes are the nitrogenous breakdown products of proteins and nucleic acids
Nitrogenous bases
–NH2 Amino groups
Many reptiles Most aquatic Mammals, most (including animals, including amphibians, sharks, birds), insects, most bony fishes some bony fishes land snails O
NH3
35.2
Ammonia
O
C
NH2 NH2 Urea
O
HN C
C
H C N
C N N H H Uric acid
C O
Ammonia
Animals that excrete nitrogenous wastes as ammonia
35.2
Need access to lots of water Release it across the whole body surface or through the gills
Urea
The liver of mammals and most adult amphibians
Urea is carried to the kidneys, concentrated
35.2
Converts ammonia to less toxic urea
And 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
Uric acid is largely insoluble in water
35.2
And can be secreted as a paste with little water loss
The Excretory System
The Steps in Urine Production
35.3
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
Most excretory systems produce urine by refining a filtrate derived from body fluids
Capillary Filtrate
Excretory tubule
1 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.
2 Reabsorption. The transport epithelium reclaims valuable substances from the filtrate and returns them to the body fluids.
3 Secretion. Other substances, such as toxins and excess ions, are extracted from body fluids and added to the contents of the excretory tubule.
Urine
35.3
4 Excretion. The filtrate leaves the system and the body.
Structure and Function The mammalian excretory system centers on paired kidneys
35.4
Which are also the principal site of water balance and salt regulation
Anatomy
Each kidney
Is supplied with Posterior vena cava blood by a renal Renal artery and vein artery and Aorta drained by a Ureter renal vein
Kidney
Urinary bladder
Urethra (a) Excretory organs and major associated blood vessels
35.4
The mammalian kidney has two distinct regions
An outer renal cortex and an inner renal medulla Renal medulla Renal cortex
Renal pelvis
Ureter Section of kidney from a rat
35.4
(b) Kidney structure
The nephron is the functional unit of the vertebrate kidney
It consists of a single long tubule and a ball of capillaries called the glomerulus
JuxtaCortical medullary nephron nephron
Afferent arteriole from renal artery
Glomerulus Bowman’s capsule Proximal tubule
Renal cortex
Peritubular capillaries Collecting duct
To renal pelvis
20 µm Renal medulla
SEM Efferent arteriole from glomerulus
Loop of Henle
35.5
(c) Nephron
Distal tubule Collecting duct
Branch of renal vein Descending limb Ascending limb
(d) Filtrate and blood flow
Vasa recta
Filtration of the Blood
Filtration occurs as blood pressure
35.5
Forces fluid from the blood in the glomerulus into the lumen of Bowman’s capsule
Filtration of the Blood
Filtration of small molecules is nonselective
35.5
And 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
35.5
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
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
From Blood Filtrate to Urine: A Closer Look Proximal tubule
1
4
NaCl Nutrients HCO3− H2O K+
H+
Filtrate H2O Salts (NaCl and others) HCO3– H+ Urea Glucose; amino acids Some drugs Key Active transport Passive transport
35.6
Distal tubule
NaCl
H2O HCO3−
K+
NH3
H+
CORTEX 2
Descending limb of loop of Henle
3
Thick segment of ascending limb NaCl
OUTER MEDULLA
H2O NaCl 3
Thin segment 5 Collecting of ascending duct limb Urea NaCl
INNER MEDULLA
H2O
From Blood Filtrate to Urine: A Closer Look
Secretion and reabsorption in the proximal tubule
Substantially alter the volume and composition of filtrate
Reabsorption of water continues
35.6
As the filtrate moves into the descending limb of the loop of Henle
From Blood Filtrate to Urine: A Closer Look
As filtrate travels through the ascending limb of the loop of Henle
The distal tubule
Salt diffuses out of the permeable tubule into the interstitial fluid Plays a key role in regulating the K+ and NaCl concentration of body fluids
The collecting duct
35.6
Carries the filtrate through the medulla to the renal pelvis and reabsorbs NaCl
Water Conservation
The mammalian kidney
35.7
Can produce urine much more concentrated than body fluids, thus conserving water
Solute Gradients and Water Conservation
In a mammalian kidney, the cooperative action and precise arrangement of the loops of Henle and the collecting ducts
35.7
Are largely responsible for the osmotic gradient that concentrates the urine
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 300
Osmolarity of interstitial fluid (mosm/L)
300 100
300 100
CORTEX
H2O
Active transport Passive transport
H2O
OUTER MEDULLA
NaCl 400
H2O H2O
NaCl
200
NaCl
600
NaCl
H2O
NaCl
H2O
NaCl
300
300
400
400
600
600
H2O
H2O H2O
400
H2O H2O Urea
INNER MEDULLA
35.7
H2O
900
NaCl
700
900
H2O Urea H2O
1200
Urea 1200 1200
From Blood Filtrate to Urine: A Closer Look
The countercurrent multiplier system involving the loop of Henle
35.7
Maintains a high salt concentration in the interior of the kidney, which enables the kidney to form concentrated urine
From Blood Filtrate to Urine: A Closer Look
The collecting duct, permeable to water but not salt
35.7
Conducts the filtrate through the kidney’s osmolarity gradient, and more water exits the filtrate by osmosis
From Blood Filtrate to Urine: A Closer Look
Urea diffuses out of the collecting duct
As it traverses the inner medulla
Urea and NaCl
35.7
Form the osmotic gradient that enables the kidney to produce urine that is hyperosmotic to the blood
The urinary system
Osmoregulation
All animals face the same central problem of osmoregulation.
35.1
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.
Osmolarity
Osmolarity is defined as
35.1
Moles of solute (salt) per liter of solution (water) A value of 300 mosm/L
Excretion
35.1
The removal of nitrogenous waste (from the break down of amino acids primarily) Urea is the waste product in humans
Types of Waste Products Nucleic acids
Proteins Amino acids
Among the most important wastes are the nitrogenous breakdown products of proteins and nucleic acids
Nitrogenous bases
–NH2 Amino groups
Many reptiles Most aquatic Mammals, most (including animals, including amphibians, sharks, birds), insects, most bony fishes some bony fishes land snails O
NH3
35.2
Ammonia
O
C
NH2 NH2 Urea
O
HN C
C
H C N
C N N H H Uric acid
C O
Ammonia
Animals that excrete nitrogenous wastes as ammonia
35.2
Need access to lots of water Release it across the whole body surface or through the gills
Urea
The liver of mammals and most adult amphibians
Urea is carried to the kidneys, concentrated
35.2
Converts ammonia to less toxic urea
And 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
Uric acid is largely insoluble in water
35.2
And can be secreted as a paste with little water loss
The Excretory System
The Steps in Urine Production
35.3
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
Most excretory systems produce urine by refining a filtrate derived from body fluids
Capillary Filtrate
Excretory tubule
1 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.
2 Reabsorption. The transport epithelium reclaims valuable substances from the filtrate and returns them to the body fluids.
3 Secretion. Other substances, such as toxins and excess ions, are extracted from body fluids and added to the contents of the excretory tubule.
Urine
35.3
4 Excretion. The filtrate leaves the system and the body.
Structure and Function The mammalian excretory system centers on paired kidneys
35.4
Which are also the principal site of water balance and salt regulation
Anatomy
Each kidney
Is supplied with Posterior vena cava blood by a renal Renal artery and vein artery and Aorta drained by a Ureter renal vein
Kidney
Urinary bladder
Urethra (a) Excretory organs and major associated blood vessels
35.4
The mammalian kidney has two distinct regions
An outer renal cortex and an inner renal medulla Renal medulla Renal cortex
Renal pelvis
Ureter Section of kidney from a rat
35.4
(b) Kidney structure
The nephron is the functional unit of the vertebrate kidney
It consists of a single long tubule and a ball of capillaries called the glomerulus
JuxtaCortical medullary nephron nephron
Afferent arteriole from renal artery
Glomerulus Bowman’s capsule Proximal tubule
Renal cortex
Peritubular capillaries Collecting duct
To renal pelvis
20 µm Renal medulla
SEM Efferent arteriole from glomerulus
Loop of Henle
35.5
(c) Nephron
Distal tubule Collecting duct
Branch of renal vein Descending limb Ascending limb
(d) Filtrate and blood flow
Vasa recta
Filtration of the Blood
Filtration occurs as blood pressure
35.5
Forces fluid from the blood in the glomerulus into the lumen of Bowman’s capsule
Filtration of the Blood
Filtration of small molecules is nonselective
35.5
And 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
35.5
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
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
From Blood Filtrate to Urine: A Closer Look Proximal tubule
1
4
NaCl Nutrients HCO3− H2O K+
H+
Filtrate H2O Salts (NaCl and others) HCO3– H+ Urea Glucose; amino acids Some drugs Key Active transport Passive transport
35.6
Distal tubule
NaCl
H2O HCO3−
K+
NH3
H+
CORTEX 2
Descending limb of loop of Henle
3
Thick segment of ascending limb NaCl
OUTER MEDULLA
H2O NaCl 3
Thin segment 5 Collecting of ascending duct limb Urea NaCl
INNER MEDULLA
H2O
From Blood Filtrate to Urine: A Closer Look
Secretion and reabsorption in the proximal tubule
Substantially alter the volume and composition of filtrate
Reabsorption of water continues
35.6
As the filtrate moves into the descending limb of the loop of Henle
From Blood Filtrate to Urine: A Closer Look
As filtrate travels through the ascending limb of the loop of Henle
The distal tubule
Salt diffuses out of the permeable tubule into the interstitial fluid Plays a key role in regulating the K+ and NaCl concentration of body fluids
The collecting duct
35.6
Carries the filtrate through the medulla to the renal pelvis and reabsorbs NaCl
Water Conservation
The mammalian kidney
35.7
Can produce urine much more concentrated than body fluids, thus conserving water
Solute Gradients and Water Conservation
In a mammalian kidney, the cooperative action and precise arrangement of the loops of Henle and the collecting ducts
35.7
Are largely responsible for the osmotic gradient that concentrates the urine
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 300
Osmolarity of interstitial fluid (mosm/L)
300 100
300 100
CORTEX
H2O
Active transport Passive transport
H2O
OUTER MEDULLA
NaCl 400
H2O H2O
NaCl
200
NaCl
600
NaCl
H2O
NaCl
H2O
NaCl
300
300
400
400
600
600
H2O
H2O H2O
400
H2O H2O Urea
INNER MEDULLA
35.7
H2O
900
NaCl
700
900
H2O Urea H2O
1200
Urea 1200 1200
From Blood Filtrate to Urine: A Closer Look
The countercurrent multiplier system involving the loop of Henle
35.7
Maintains a high salt concentration in the interior of the kidney, which enables the kidney to form concentrated urine
From Blood Filtrate to Urine: A Closer Look
The collecting duct, permeable to water but not salt
35.7
Conducts the filtrate through the kidney’s osmolarity gradient, and more water exits the filtrate by osmosis
From Blood Filtrate to Urine: A Closer Look
Urea diffuses out of the collecting duct
As it traverses the inner medulla
Urea and NaCl
35.7
Form the osmotic gradient that enables the kidney to produce urine that is hyperosmotic to the blood
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