BIOLOGY 12

Excretory System

Excretion - is defined as the elimination of all metabolic wastes from the body.

Our main organs of the excretory system which is responsible for cleaning and maintaining homeostasis in our blood- stream are your KIDNEYS.

The Urinary System

Structures

Comparison of blood between RENAL ARTERY and RENAL VEIN

RENAL ARTERY RENAL ARTERY

1. High concentration of O2 1. High concentration of CO2

2. Higher concentration of glucose and mineral salts

2. Lower concentration of glucose and mineral salts.

3. Higher concentration of nitrogenous wastes like (urea, uric acid and creatinine)

3. Lower concentration of nitrogenous wastes like (urea, uric acid and creatinine)

More excretory substances.

2. Bile: From breakdown of hemoglobin - produces belirubin.

3. CO2: excreted mainly at lungs with some HCO3

- at kidneys.

4. Salts: inorganic ions - removed or conserved depending upon body needs.

5. Water: water is moved all over - depends if it needs to be conserved or excreted.

WATER CO2

BILE

EXCESS SALTS

Excretory Substances from our KIDNEYS

1. Nitrogenous Wastes: from proteins and nucleic acids.

A. Ammonium salts: NH3 from amino acid deamination - very toxic!

B. Urea: converts NH3 to NH2 -C=O -NH2

Requires ATP - less toxic.C. Uric Acid: from deamination of

nucleic acids - requires more ATP - much less toxic.

D. Creatine: product of skeletal muscle activity

Summary of Exretory Organs

Organ of Excretion

Excretory Substances Source

1. SKIN Sweat (urea, salts, water )

Cellular respiration

2. LIVER Bile salts Breakdown of hemoglobin

3. LUNGS Carbon dioxide, water vapour

Cellular respiration

4. LARGE INTESTINES

Excess salts , water Digestion

5. KIDNEYS •Ammonia

•Urea

•Uric acid

•Creatinine

•Deamination of Amino acids •Breakdown of Ammonia •Breakdown of Nucleotides •Breakdown of Creatine in muscles

Functions of Excretory System:

Four MAIN roles of the KIDNEYS1. Removal of metabolic wastes2. Regulation of blood pH - excretion of

excess H+ or OH-.3. Regulation of osmotic balance in tissues

- by conserving or excreting water.4. Regulation of ionic balance of blood by

conserving or excreting ions - especially K, Na, Ca, Mg.

ANATOMY of the KIDNEY

NEPHRONS are the filtering units which separate the wastes from the nutrients.

NEPHRONS filtering units

Urine Production1. Glomerulus and Bowman’s Capsule• The glomerulus is a capillary bed off

the renal artery that is surrounded by the Bowman’s capsule.

• Pressure filtration occurs here where all blood plasma components except plasma proteins cross to the capsule.

• This occurs by simple diffusion and the force of blood pressure.

• Filtrate include lots of good stuff besides metabolic wastes.

Urine Production

2. Proximal Convoluted Tubules (PCT)• Selective reabsorption occurs here

where all the “good stuff” is reabsorbed back into the blood stream.

• Diffusion occurs first then active transport until all nutrients reabsorbed.

• What’s left is nitrogenous wastes, water, and salts (mainly Na+).

Urine Production3. Loop of Henle: goes from isotonic cortex

to very hypertonic medulla.• A. Descending Arm: Water diffuses out but

wall is impermeable to Na+

• As filtrate descends, more water is reabsorbed.

• By the bottom of the descending arm, filtrate is hypertonic.

• B. Ascending Arm: As filtrate moves up, Na+ is actively transported out making filtrate hypotonic - water diffuses out. As filtrate reaches top of L. of H. it is again isotonic or slightly hypotonic.

Urine Production

4. Distal Convoluted Tubules:• This area is under hormonal control

(seen later) that regulates water reabsorption.

• More water may be reabsorbed.• Tubular excretion also occurs here

as well as pH regulation.

Urine Production

5. Collecting Tubules• From the DCT, the isotonic filtrate

enters the collecting ducts which once again go through the hypertonic medulla.

• Water is again reabsorbed and the membrane is impermeable to Na+.

• Hormones also regulate here.

Summary of Urine Production Steps Parts of Nephron Involved Summary of Process

1. GLOMERULAR FILTRATION

Takes place between the glomerulus(capillaries) and the Glomerular capsule (Bowman’s capsule)

Blood pressure forces all small molecules out of bloodstream into the Glomerular capsule. All large (macronutrients remain in the blood) The substances which leave the blood make up the FILTRATE.

2. TUBULAR REABSORPTION

Takes place between the Proximal convoluted tubule and the blood stream (peritubular capillary network)

At this part of the nephron the nutrients which are valuble to the body are reabsorbed first by diffusion and then by active transport back into the blood stream. Nutrients which are absorbed are ( glucose, amino acids, and some salts like Na,Cl, and Ca )

3. TUBULAR SECRETION

Takes place between the Distal convoluted tubule and the bloodstream (peitubular capillary network)

This is where the pH of the blood is regulated. Excess H+ ions are excreted from the bloodstream back into the distal tubule while more HCO3- ions are absorbed to maintain pH of 7.4 in blood

Regulatory Function of the Kidneys

The tonicity of the urine will be less than the blood since there would be fewer solutes in comparison to the blood. Blood has about 75%water. Most of the water is absorbed in the LOOP of HENLE or the NEPHRON LOOP.

Urine Production

Control of Urine Concentration• The nature of urine is variable

depending upon our need to conserve or excrete water.

• This is regulated by hormones:1. Anti-diuretic hormone (ADH)• Produced by the hypothalamus and

stored in the pituitary.

Urine Production

• Released when osmoreceptors in the hypothalamus detect a decline in blood volume.

• ADH stimulates epithelia of DCT and Collecting Duct to increase permeability to water, thus allowing more water to be reabsorbed.

• Less ADH produces a dilute urine

NEGATIVE FEEDBACK LOOP

Urine Production

SALT NaCl is controlled by a hormone called Aldosterone

• Released from the adrenal cortex, it stimulates reabsorption of Na+ and therefore water in DCT.

• Used to conserve salts and control tissue water levels.

• Also results in excretion of K+

Urine Production

Control of Urine Production:• Osmoregulators in the

hypothalamus of the brain are sensitive to blood volumes.

• If blood volume declines (due to a lack of water), the hypothalamus signals the pituitary to release ADH to increase water absorption.

• Low ADH produces dilute urine.

Urine Production

• Aldosterone is also controlled by a negative feedback loop.

• If blood pressure declines, Renin is released from the kidneys.

• This triggers the release of aldosterone which increases the absorption of Na+ and water in the distal tubules - increasing blood volume.

Urine Production

• So what’s the difference?• ADH responds to thirst - normal

decrease in blood volume.• Aldosterone responds to traumatic

blood loss, as from injury, to restore blood volumes.

• This is controlled by negative feedback between adrenals and kidneys.

Diuretics Diuretics are chemicals that prevent the release of ADH from the posterior pituitary. By decreasing the levels of ADH in the blood the kidney nephrons water is prevented from being reabsorbed into the blood stream and therefore you have an increase in URINE OUTPUT along with diluted URINE.

Urine Production

Conclusion:• The excretory system is the chief

homeostatic regulator of the body.• For each metabolite, there are “set

points”.• If any substance rises beyond the set

point, it’s excreted, even if useful.• Therefore, excretory systems goal is

to maintain a constant level - not total elimination

BIOLOGY 12

Excretory System

Introduction

• One of the problems that all organisms have is the generation of metabolic wastes as the result of their biological activity.

• For mammals, and additional waste to be dealt with is heat, a residue from our much higher metabolism.

Thermoregulation

• As a homeotherm, we try to maintain our body temperature within a narrow, elevated range.

• Therefore, sometimes we need to conserve heat and other times we need to get rid of it.

• We have incredible abilities to thermoregulate.

Thermoregulation

• Heat is both generated within our bodies and exchanged with our external environment.

1. How we get rid of heat:A. Vasodialation. By dilating the

sphincters in surface capillaries, we increase the blood flow to the skin.

• Heat is lost by conduction to air.

Thermoregulation

B. Evaporative Cooling• Sweat glands in the

skin secrete sweat onto the surface of the skin.

• To evaporate, it draws heat from the skin and dilated capillaries - cooling.

• Various metabolic wastes are also excreted by sweat.

Thermoregulation2. Heat Conservation:• As homeotherms typically have a

body temperature above ambient, the more common problem is heat conservation.

A. Vasoconstriction: the surface capillary sphincters constrict reducing blood flow to surface - less heat lost.

Thermoregulation

• This can involve major redistribution of blood flow from periphery to interior during times of severe heat loss (hypothermia).

B. Goose bumps: erector muscles attached to hair follicles contract elevating hair (in other mammals this fluffs them up - insulating effect).

• Causes “Goosebumps” in us - increases metabolic rate - increases heat production.

Thermoregulation

C. Shivering: rapid, spasmic contractions of major muscles increases heat production.

• Due to release of thyroxinD. Insulation: subcutaneous fat

insulates.E. Countercurrent Exchange: primarily

in sea mammals - warm arteriole blood out lays right beside cool venule blood in - heat diffuses between and is conserved.

Thermoregulation• Most of these mechanisms are under

the control of the Hypothalamus of the brain which contains the bodies thermostat.

• Blood temperature in the carotid is monitored by thermoreceptors and appropriate adjustments are initiated.

Metabolic Excretion

• Metabolic excretion is the elimination of wastes associated with cell activity.

• Excretory organs:1. Skin – sweat2. Lungs - CO2, H2O and heat

3. Liver – bilirubin, ammonia, urea 4. Large Intestines: Excretion of heavy metals.5. Kidneys: major excretory organ of

nitrogenous wastes and excess water.

Metabolic ExcretionFunctions of Excretory System:Overall - homeostasis of bodies internal

environment.Specifically:1. Removal of metabolic wastes2. Regulation of blood pH - excretion of

excess H+ or OH-.3. Regulation of osmotic balance in tissues -

by conserving or excreting water.4. Regulation of ionic balance of blood by

conserving or excreting ions - especially K, Na, Ca, Mg.

Excretory Substances1. Nitrogenous Wastes: from proteins

and nucleic acids.A. Ammonium salts: NH3 from amino

acid deamination - very toxic!B. Urea: converts NH3 to NH2 -C=O -

NH2

• Requires ATP - less toxic.C. Uric Acid: from deamination of

nucleic acids - requires more ATP - much less toxic.

D. Creatine: product of skeletal muscle activity

More excretory substances.

2. Bile: From breakdown of hemoglobin - produces belirubin.

3. CO2: excreted mainly at lungs with some HCO3

- at kidneys.

4. Salts: inorganic ions - removed or conserved depending upon body needs.

5. Water: water is moved all over - depends if it needs to be conserved or excreted.

WATER CO2

BILE

EXCESS SALTS

The Urinary System

Structures

Summary of Exretory Organs

Organ of Excretion

Excretory Substances Source

1. SKIN Sweat (urea, salts, water )

Cellular respiration

2. LIVER Bile salts Breakdown of hemoglobin

3. LUNGS Carbon dioxide, water vapour

Cellular respiration

4. LARGE INTESTINES

Excess salts , water Digestion

5. KIDNEYS •Ammonia

•Urea

•Uric acid

•Creatinine

•Deamination of Amino acids •Breakdown of Ammonia •Breakdown of Nucleotides •Breakdown of Creatine in muscles

NEPHRONS filtering units

Urine Production1. Glomerulus and Bowman’s Capsule• The glomerulus is a capillary bed off

the renal artery that is surrounded by the Bowman’s capsule.

• Pressure filtration occurs here where all blood plasma components except plasma proteins cross to the capsule.

• This occurs by simple diffusion and the force of blood pressure.

• Filtrate include lots of good stuff besides metabolic wastes.

Urine Production

2. Proximal Convoluted Tubules (PCT)• Selective reabsorption occurs here

where all the “good stuff” is reabsorbed back into the blood stream.

• Diffusion occurs first then active transport until all nutrients reabsorbed.

• What’s left is nitrogenous wastes, water, and salts (mainly Na+).

Urine Production3. Loop of Henle: goes from isotonic cortex

to very hypertonic medulla.• A. Descending Arm: Water diffuses out but

wall is impermeable to Na+

• As filtrate descends, more water is reabsorbed.

• By the bottom of the descending arm, filtrate is hypertonic.

• B. Ascending Arm: As filtrate moves up, Na+ is actively transported out making filtrate hypotonic - water diffuses out. As filtrate reaches top of L. of H. it is again isotonic or slightly hypotonic.

Urine Production

4. Distal Convoluted Tubules:• This area is under hormonal control

(seen later) that regulates water reabsorption.

• More water may be reabsorbed.• Tubular excretion also occurs here

as well as pH regulation.

Urine Production

5. Collecting Tubules• From the DCT, the isotonic filtrate

enters the collecting ducts which once again go through the hypertonic medulla.

• Water is again reabsorbed and the membrane is impermeable to Na+.

• Hormones also regulate here.

Summary of Urine Production Steps Parts of Nephron Involved Summary of Process

1. GLOMERULAR FILTRATION

Takes place between the glomerulus(capillaries) and the Glomerular capsule (Bowman’s capsule)

Blood pressure forces all small molecules out of bloodstream into the Glomerular capsule. All large (macronutrients remain in the blood) The substances which leave the blood make up the FILTRATE.

2. TUBULAR REABSORPTION

Takes place between the Proximal convoluted tubule and the blood stream (peritubular capillary network)

At this part of the nephron the nutrients which are valuble to the body are reabsorbed first by diffusion and then by active transport back into the blood stream. Nutrients which are absorbed are ( glucose, amino acids, and some salts like Na,Cl, and Ca )

3. TUBULAR SECRETION

Takes place between the Distal convoluted tubule and the bloodstream (peitubular capillary network)

This is where the pH of the blood is regulated. Excess H+ ions are excreted from the bloodstream back into the distal tubule while more HCO3- ions are absorbed to maintain pH of 7.4 in blood

URINE PRODUCTION

Urine Production

Control of Urine Concentration• The nature of urine is variable

depending upon our need to conserve or excrete water.

• This is regulated by hormones:1. Anti-diuretic hormone (ADH)• Produced by the hypothalamus and

stored in the pituitary.

Urine Production

• Released when osmoreceptors in the hypothalamus detect a decline in blood volume.

• ADH stimulates epithelia of DCT and Collecting Duct to increase permeability to water, thus allowing more water to be reabsorbed.

• Less ADH produces a dilute urine

Urine Production

2. Aldosterone• Released from the adrenal cortex, it

stimulates reabsorption of Na+ and therefore water in DCT.

• Used to conserve salts and control tissue water levels.

• Also results in excretion of K+

Urine Production

Control of Urine Production:• Osmoregulators in the

hypothalamus of the brain are sensitive to blood volumes.

• If blood volume declines (due to a lack of water), the hypothalamus signals the pituitary to release ADH to increase water absorption.

• Low ADH produces dilute urine.

Urine Production

• Aldosterone is also controlled by a negative feedback loop.

• If blood pressure declines, Renin is released from the kidneys.

• This triggers the release of aldosterone which increases the absorption of Na+ and water in the distal tubules - increasing blood volume.

Urine Production

• So what’s the difference?• ADH responds to thirst - normal

decrease in blood volume.• Aldosterone responds to traumatic

blood loss, as from injury, to restore blood volumes.

• This is controlled by negative feedback between adrenals and kidneys.

Urine Production

Conclusion:• The excretory system is the chief

homeostatic regulator of the body.• For each metabolite, there are “set

points”.• If any substance rises beyond the set

point, it’s excreted, even if useful.• Therefore, excretory systems goal is

to maintain a constant level - not total elimination