excretion

EXCRETION & OSMOREGULATION

OVERVIEW

A) DEFINITIONS & IMPORTANCE OF EXCRETION AND OSMOREGULATION

B) OSMOREGULATION IN A TERRESTRIAL INSECT

C) OSMOREGULATION IN BONY FISH (TELEOSTS)

D) THE HUMAN KIDNEY

Definitions

Excretion – the elimination of waste metabolic substances

from the body which if permitted to accumulate would prevent the maintenance of a steady state

CO2

urea

Definitions

Egestion - the elimination of waste substances,

mainly undigested food, which have never been involved in the metabolic activities of cells

Definitions

Secretion :- the process involved in producing and

releasing a substance which is useful, from the cell e.g. digestive juiceshormonessweatmilk

Definitions

Osmoregulation : the maintenance of constant osmotic conditions

in the body the control of the gain and loss of:

water solutes

Importance of excretion and osmoregulation

1) Removal of unwanted by-products of metabolic pathwaysis important to prevent unbalancing

chemical equilibria of reactionse.g. A + B → C + D- constant synthesis of C requires constant

removal of D


2) Removal of toxic wastes e.g. urea, ammonia

Ammonia

Protein in


3) Regulation of ionic concentration of body fluids e.g. Na+, Ca2+

An albatross possesses nasal salt glands that can

secrete excess salt through ducts and out of

the nostrils.


4) Regulation of water content of body fluids

5) Regulation of the pH of the body fluids

Excretory organs control the:VolumeConcentrationComposition

of the extracellular fluid

Animals in different environments have different excretory functions:

Terrestrial animals must conserve:

Freshwater animals have to: conserve salts excrete excess water

salts + water

Source of the total amount of excreted nitrogen

5%

A variety of animals also excrete small quantities of:

creatine creatinine

95%

Ammonia: is the immediate nitrogenous waste of

deamination

amino acidNH3

ammonia

PROTEINS

Amino acids

NUCLEIC ACIDS

Ammonia Urea Uric acid

Most aquatic animals

Nitrogenous bases

Amino groups

Birds, reptiles, insects

Mammals, most amphibians, sharks,

marine bony fish

Ammonia:Explain why ammonia cannot

be stored in the body.Highly toxic

Large volumes of water are needed for ammonia to be excreted. Why?

To make it less toxic.

Urea is less toxic & soluble than ammonia

Urea is about 100,000 times less toxic than ammonia.

Urea forms during the

Ornithine Cycle

Bird droppings = faeces + nitrogenous waste

Car covered in bird droppings.

Why is uric acid an ideal excretory product for terrestrial organisms

(e.g. insects, reptiles & birds) which produce shelled eggs?

Uric acid can be stored in cells without producing toxic or harmful osmoregulatory effects.

Uric acid is stored in the allantois.

Uric acid: is largely insoluble

in water can be excreted as

a paste with little water loss

Energy required for production:

Amount of water required for excretion:

Toxicity of waste :

Ammonia Urea Uric acidNone Moderate High

High Moderate Low

High Low Low

Correlation with habitatAmmonia: Freshwater

Uric acid: Terrestrial

Urea: Marine/Terrestrial

Question: DEC, 1987

The earthworm, although terrestrial, excretes mainly ammonia. How does this affect the

worm’s habitat preferences?

Must inhabit moist environments.

Question: DEC, 1987

Marine turtles have the ability to excrete all three nitrogenous waste products, yet they excrete mainly

ammonia. What are the advantages and disadvantages of excreting ammonia?

Advantages: no energy is needed to produce ammoniaDisadvantages: animal loses a lot of water to eliminate ammonia, risking dehydration

Percentage of waste nitrogen excreted as:Ammonia Urea Uric acid

51 12 6

AMMONIATadpoles excrete:

UREAFrogs excrete:

Question: [MAY, 2010]

1. What are nitrogenous wastes? Name a biochemical process that produces nitrogenous waste. (2)Nitrogenous wastes are substances produced as a result of metabolism that are not required by the body and contain nitrogen. Deamination / break down of nucleic acids.

2. Name ONE organism that excretes nitrogenous wastes as urea and

ONE organism that excretes nitrogenous wastes as ammonia: (2)Urea: mammal / marine bony fish / frogAmmonia: protozoans / Amoeba / freshwater bony fish / tadpole

OVERVIEW



C) OSMOREGULATION IN BONY FISH (TELEOSTS)D) THE HUMAN KIDNEY

How are insects adapted to avoid water loss?

1. An almost impermeable waxy layer covering the exoskeleton

2. Spiracles are the only openings to the body for gaseous exchange

SpiracleSpiracle

3. Valve-like structures and hairs in spiracles reduce water loss

Fully open ant spiracle. A nearly closed grasshopper spiracle; the black areas are the valves.

4. The excretory product is semi-solid

insect droppings

5. CLEIDOIC EGGS: the embryo develops inside the egg with a relatively impermeable shell that prevents water loss

Malpighian Tubules in insects:

Function: excrete uric acid

Location: - lie in the abdomen- open into the

hindgut at its junction with the midgut

Malpighian Tubules are:

blind-ending tubules of the hindgut of insects

Tubules vary in :

Shape:long & slender orshort and compact

Number: a pair - several hundred

Figure 44.12

Upper segment:Absorbs fluid from blood

Lower segment:Cells have microvilli

Rectal glands:Reabsorb water

Haemolymph

What is eliminated?

Faeces & uric acid

OVERVIEW




D) THE HUMAN KIDNEY

Fish are osmoregulators:control concentration of body fluidsuse energy to regulate

Osmoconformereg. marine

invertebratesosmoregulator

Hypertonic solution

Hypotonic solution

Isotonic solution

osmoregulator

Bony Fish can be:

FRESHWATER Eliminate

ammonia

MARINE Eliminate urea

&Trimethylamine oxide

Trimethylamine oxide = fish odour

Why is the nitrogenous waste product different in the two groups of fish?

FRESHWATER fish afford to lose

water

MARINE fish cannot afford

to lose water

Gills are permeable to:

1. Water2. Ions

Freshwater Bony Fish:

Hypertonic body fluids

Not salty

Gills of freshwater bony fish:


GAIN water

But this disturbs body fluid concentration!!

LOSE salts

gills



Water flows by osmosis through the gill surfaces

Water must be removed otherwise fish is no longer hypertonic.

How?



The fish discharges copious quantities of very dilute urine, few salts lost

Nitrogenous waste: Ammonia

No drinking

Kidneys of freshwater bony fish:

contain many large Malpighian bodies, with large glomeruli

high rate of filtration produces a large volume of glomerular filtrate

How does the fish remain hypertonic?

GAINS salts:

Selective reabsorption in kidney


Selective uptake of Cl- at gills

In food

Marine Fish:

Hypotonic body fluids

SALTY

Marine Fish:


Loss of water by osmosis

Compensatory mechanisms to

avoid dehydration MUST be present

At gills:

Gain of ions by diffusion

Marine Fish DRINK sea water. WHY?


To replace water lost

But this means SALTS are gained too. What happens to salts?

Excess ions are:

Nitrogenous waste:Urea + Trimethylamine oxide


actively secreted by special excretory cells in the gills

Some marine bony fish:

have NO glomeruli at all, and so do not filter their blood

urine is isotonic with the body fluids

Question: [SEP, 2010]

Fish do not need to convert ammonia into urea. Suggest ONE reason for this. (1)Freshwater bony fish eliminate ammonia by adding large quantities of water to make it less toxic. As they can afford to lose a lot of water, they eliminate their nitrogenous waste in the form of ammonia rather than urea.

OVERVIEW




D) THE HUMAN KIDNEY

The kidneys contribute to homeostasis

Let us see how:

Functions of the Human Kidney:

1. Removal of metabolic waste products

2. Regulation of the water content

3. Regulation of the pH of body fluids

4. Regulation of the chemical composition of body fluids by removal of substances which are in excess of immediate requirements

Position and structure of kidneys

External structure of a Pig Kidney

Kidneys are surrounded by a fibrous capsule:

LS through human kidney

medulla

cortex

LS through human kidney

the apex of each pyramid

papilla

The renal artery branches inside kidney

Renal artery

Ureter

Renal vein

Each capillary supplies blood to hundreds of thousands of tiny filtration units called nephrons

Let’s have a look at a nephron!!!

Two types of nephron:

Juxtamedullary nephron

Cortical nephron

Juxta = close to

CORTEX

MEDULLA

Loop of Henle

Collecting duct

Nephron is the basic structural & functional unit of the kidney

Deal with the control of blood volume under

normal conditions of water

availability

Increase water retention when

water is in short supply

Cortical nephron Juxtamedullary nephron

Nephron Structure

vasa recta

Slow blood flow: important to produce a

concentrated urine

The nephron1.5 million per kidney

collectingduct

Bowman’scapsule

distaltubule

loop ofHenle

proximaltubule

The nephronblood supply

peritubularcapillaries

VasaRecta

glomerulus

branch of renalartery

afferent arterioles

efferent arterioles

branch of renalvein

The glomerular capillariesdrain into efferent arteriolesnot venules.‘Portal System’

Three key process in urine formation:

Ultrafiltration

Ultrafiltration

• takes place in the renal capsule• is filtration under pressure• pressure comes from blood pressure

(hydrostatic pressure)

http://en.wikipedia.org/wiki/File:Gray1130.svg

Glomerular Filtrate (GF): is the filtered fluid

chemical composition is similar to blood plasma, containing:-

GlucoseAmino acidsVitaminsIonsNitrogenous wasteSome hormones Water

Glomerular filtrate


Key Words!!

Nephron:structure in the kidney that acts as a microscopic filtration unit

Glomerulus:dense mass of very fine blood capillaries at the nephron that act as a filter

Key Words!!

Bowman’s capsule:cup-shaped part of the nephron that holds a glomerulus and collects the products of filtration from it

Glomerular filtrate:liquid removed from the blood by filtration in the kidney

Explain why proteins & RBC are not found in urine. Too large to be filtered.

But can blood ever be detected in urine?

YES. But, this shows that something is

wrong .

Ultrafiltration takes place through three layers:

1) Endothelium of the blood capillary

2) Basement membrane of the blood capillaries

3) Epithelium of the renal capsule


Cells lining the Bowman’s capsule:

Podocyte

Squamous epithelium

Podocytes are highly

modified for filtration


Podocytes:

each podocyte has many foot-like extensions projecting from its surface

the projections interlink with extensions from neighbouring cells

they fit together loosely, leaving slits called SLIT PORES or FILTRATION SLITS

The basement membrane is the main filtration barrier

What is the ‘endothelial fenestration’?


Some types of capillaries have ‘fenestrations’

Fenestrated capillary has holes to facilitate filtrationContinuous capillary

Filtrate passes through the

basement membrane & not across cells

Basementmembrane

Fenestrated capillaries

(capillaries with windows)(capillaries with windows)Permeableto substances< 100 nm

endothelial cell

fenestration

nucleus

Filtration Barrier

mesangial cells

podocyte

slit pore

glucoseamino acids

(basement membrane)

podocyte slit pore

Na+

--

-

-

-

---

--

-

-

-

-

-

-

--

--

- -

-

-

--

--

-

Limited permeability to molecules between

7000 > mwt > 70000 Da4 nm > diameter > 8 nm

Freely permeable tosmall moleculesmwt < 7000 Da

diameter < 4 nm

Not permeable to large moleculesmwt > 70000 Dadiameter > 8 nm

Water Permeablealbumin60000 Da

completelyexcluded…

because of –ve charge

endothelial cellfenestration

Bowman’s Capsule

Bowman’sSpace

Proximal [email protected]

Factors affecting the glomerular filtration rate (GFR)

The filtration pressure forcing fluid out of the glomerulus depends on the:

1. hydrostatic pressure of the blood

2. pressure of the glomerular filtrate

The net filtration pressure =

1.3 kPa

8 kPa2.7 kPa

4 kPa

The kidneys act to maintain the GFR

kidneys have AUTOREGULATORY mechanisms to maintain their:blood supply blood pressure

regardless of what is happening elsewhere in the

body

Three ways to increase the filtration rate:

1. Raising blood pressure Efferent arteriole

2. Dilating the afferent arterioles (to decrease the resistance to the flow of blood into the glomerulus)

3. Constricting the efferent arterioles

Afferent arteriole

Filtration pressure

GFR maintained

Afferent arteriole narrow

LOW pressure HIGH pressure

Efferent arteriole

wide

Dilating the afferent arterioles & Constricting the efferent arterioles

BUT when arterial pressure falls too low, however, the kidney fails to produce urine

Arterial pressure 8 kPa

Plasma osmotic pressure 4 kPa

Glomerular capsule pressure 2.7 kPa6.7 kPa

Function of the nephron is to :

further waste substances may be added to the tubules by active secretion from the blood capillaries

selectively reabsorb substances useful to the body

Where does the glomerular filtrate go to after being formed?

Selective reabsorption in the proximal convoluted tubule

In humans:Glomerular filtrate production: 125 cm3 min-1

Urine production: 1 cm3 min-1

24 cm3

100 cm3

Urine 1 cm3

125 cm3

The Proximal Convoluted Tubule longest (14 mm) and widest (60 m) part of the

nephron

carries filtrate from Bowman’s capsule to loop of Henle CORTEX

MEDULLA

Proximal Convoluted Tubule is composed of:

a single layer of cuboidal epithelial cells with extensive microvilli forming a ‘brush border’ on the inside surface of the tubule

Figure 44.9

Proximal Convoluted Tubule is adapted for reabsorption in three ways:

1. large surface area due to:

Figure 44.9

Microvilli

Basal channels

BLOOD FILTRATE

Tight junction

Epithelial cell

Proximal Convoluted Tubule is adapted for reabsorption:

Figure 44.9

2. numerous mitochondria (M)

Proximal Convoluted Tubule is adapted for reabsorption:

Figure 44.9

3.closeness of blood capillaries

blood capillaryGlomerular filtrate

MicrovilliCuboidal epithelium

Over 80% of filtrate is reabsorbed in the proximal tubule

• all the glucose, amino acids, vitamins, hormones • about 80% of the NaCl and water

Figure 44.9

Fig. 16 Selective reabsorption of sodium in the proximal convoluted tubule

Figure 44.9

1

Selective reabsorption of glucose in the proximal convoluted tubule

Figure 44.9

Secondary Active

Transport

Na+

glucose Na+

ATPADP

Blood

Urine

Proximal tubule epithelial cell

[email protected]

Question: MAY, 2012

Briefly describe the following processes in the context of urine formation in humans. a) Ultrafiltration. (2)Filtration of blood occurs under high pressure. Small molecules which can cross the glomerular lining, end up as glomerular filtrate inside the Bowman’s capsule.

b) Selective reabsorption of glucose. (3) Occurs in the proximal convoluted tubule. All glucose is reabsorbed in a normal person but appears in urine in a diabetic one. Secondary active transport is involved in the reabsorption of glucose. A symport binds sodium ions and glucose to transport them from the lumen of the proximal convoluted tubule into the epithelial cells.

THE LOOP OF HENLE

Function: to conserve water

the concentration of urine produced is directly related to the:length of the loop of Henlethickness of the medulla

relative to the cortex

The longer the loop of Henle, the more concentrated the urine that can be produced

BEAVER(abundant water)

RABBIT(moderate water)

SAND RAT(scarce water)


Use your knowledge of biology to describe the selective advantage of the following adaptation.Desert rats have a long loop of Henle. (5)The loop of Henle acts as a counter-current multiplier. Fluid moves in opposite directions in the descending and ascending limbs. The ascending limb is permeable to salts which contribute towards a concentrated medulla. As water moves down the descending limb, it moves out into the vasa recta.Desert rats need to conserve water. Thus having a long loop of Henle enables them to extract as much water as possible out of the glomerular filtrate as there is more time for reabsorption.


The table below gives the thickness of the medulla in relation to the rest of the kidney in a number of mammals. The maximum urine concentration for each mammal is also given. The data suggest that maximum urine concentration increases with relative thickness of the medulla.

Mammal Relative thickness of medulla

Maximum urine concentration in arbitrary units

Beaver 1.0 52Human 2.6 140Kangaroo rat

7.8 550

Species X 9.8 940

a) Why is such a relation between urine concentration and the relative thickness of the medulla observed?

(1)The thicker the medulla, the higher the urine concentration produced due to more chance for water reabsorption.



Beaver 1.0 52Human 2.6 140Kangaroo rat 7.8 550

Species X 9.8 940

b) What habitat is species X likely to inhabit? (1)

Desert / dry habitat



Beaver 1.0 52Human 2.6 140Kangaroo rat 7.8 550

Species X 9.8 940

Birds & Mammals are the only vertebrates:

which can produce a urine which is more concentrated than the blood[hypertonic]

with loops of Henle

Loop of Henle

Three distinct regions in the loop of Henle

Thin ascending limb

Descending limb

Thick ascending limb

Thin walls

Thick walls

Permeability of the loop of Henle to water:

Highly permeable

Descending limb

Almost totally

impermeable to water Thin ascending

limb


Permeability of the loop of Henle to Na+ & Cl-

ions:

Not very permeable

Descending limb

Thin ascending limb


Permeable

Active secretion

What happens to the concentration of the fluid in the ascending limb as it reaches the

distal convoluted tubule?

The fluid becomes very dilute

Distil convoluted tubule

Reason:IONS are lost

WHY it is vital for ions to move out of the tubule?

ions

To create an Osmotic Gradient From Cortex to Medulla

PelvisMedulla

Cortex

The outer layer of the kidney is isotonic with the blood: ~300 milliosmoles/liter

The innermost layer (medulla) is very hypertonic: ~1200 milliosmoles/liter

Osmolarity is :

a measure of solute concentration

the osmolarity of a solution is the number of moles of active solutes per litre of solvent

osmole [Osm or osmol][For your information only]

The concentration gradient allows:

Water to move out by osmosis from

descending loop of Henle

Osmotic gradient is produced by a:

a countercurrent mechanism located in the loop of Henle

What is a ‘countercurrent mechanism’?

Countercurrents exist when :fluids flow in opposite directions in

parallel and adjacent tubes

Fig. 18 Three Countercurrents:

1. the two limbs of the Henle's loop



2. the two limbs of the vasa recta



2. the two limbs of the vasa recta

3. the descending limb of Henle with the ascending limb of the vasa recta; the ascending limb of Henle and the descending vasa recta

The loop of Henle as a countercurrent multiplier

countercurrent refers to the direction of urine flow in the descending versus the ascending limbs of the loop

multiplier refers to the ability of this system to create a concentration gradient in the renal medulla

CortexWater leaves - ion concentration in filtrate increases

Filtrate reaches maximum concentration

Chloride ions out (sodium follows) -ion concentration in filtrate decreases

Medulla

To ureter

Collecting duct •Several nephrons empty into one collecting duct.

•The collecting duct passes through the progressively more concentrated medulla, losing water by osmosis. This water is reabsorbed by the capillaries.

•This water is conserved, and a highly concentrated urine is produced.

Water reabsorbed into vasa recta, urine becomes more concentrated

Cortex

Medulla

Question: [SEP, 2009]

Briefly describe the role of each of the following in osmoregulation in humans:

i) The descending limb of the Loop of Henle; (2)

Is permeable to water. Functions towards water conservation.

ii) The ascending limb of the Loop of Henle; (2)Is relatively impermeable to water but permeable to salts. The tissue fluid inside the medulla becomes concentrated as salts move out of the ascending limb. This causes water to be drawn out of the descending limb.

Question: MAY, 2012

The diagram below shows the simplified structure of a human nephron. the loop of Henle

Substance Quantity passing through P

Quantity passing through Q

% reabsorbed

Water 180 dm3 1.5 dm3 99.17%Glucose 180 g 0 g 100%Urea 53 g 25 g 52.8%

The table below represents the quantities of water, glucose and urea passing through P and Q over a period of time, while the last column shows the percentage reabsorption during the same period of time.

Question: MAY, 2012

a) Relate the role of structure R to the filtrate composition as it passes through Q. (5)Structure Q is permeable to water. Water is reabsorbed by the vasa recta as fluid passes through Q. This is possible because the ascending limb creates the ideal concentration gradient within the medulla by losing ions. The thin ascending limb of Structure R is permeable to ions but impermeable to water. The thick ascending limb of Structure R allows ions to move actively out of it and is also impermeable to water. Loss of ions from the whole ascending limb, creates an ever increasing salt concentration on moving deeper into the medulla.

Question: MAY, 2012

Substance Quantity passing through P

Quantity passing through Q

% reabsorbed

Water 180 dm3 1.5 dm3 99.17%Glucose 180 g 0 g 100%Urea 53 g 25 g 52.8%

b) Explain the biological significance of the percentage reabsorption of water and urea. (3)Most of the water is reabsorbed to avoid dehydration.Only half of the urea is reabsorbed so that it contributes to the concentration of solutes in the medulla. A high solute concentration is needed to ensure reabsorption of water from the loop of Henle.

Vasa recta as countercurrent exchangers

• the countercurrent exchange of salt occurs in the vasa recta

1. Blood flowing into the medulla in the descending limb picks up salt from the hypertonic medulla

2. As the surrounding medullary fluid becomes more salty toward the papilla, more salt is picked up by the descending vasa recta limb

Vasa recta as countercurrent exchangers

3. But as the blood heads back up to the cortex in the ascending limb of the vasa recta, the interstitial fluid becomes less and less salty

4. This causes the gradient to reverse and salt diffuses back out of the vasa recta into the medulla

What is the importance of the vasa recta as an exchanger of salts?

1. to help conserve salt 2. keep the medulla hypertonic

OSMOREGULATION, ADH & URINE FORMATION

In this topic we mention TWO hormones that affect the kidneys:

Urine

ADH(antidiuretic

hormone)

Posterior pituitary

Adrenal cortex

Aldosterone

ADH brings about the precise control of solute potential in TWO ways:

1. increasing the permeability of the distal convoluted tubule and collecting duct to water

2. increasing the permeability of the collecting duct to urea

1. Urea moves into medulla

2. Medulla becomes concentrated

3. Water moves out of descending limb

ADH is released when osmoreceptors:

detect a low level of water in blood

kidney

Water Salts

Fig. 21 The effect of ADH on the permeability of the distal convoluted tubule and collecting duct to water

Blood too concentratedADH level high

Blood too diluteADH level low

Dilute urine

Urine concentrated

Water Salts

Fig. 20 Aquaporins

H2O

H2O

H2O

Release of ADH from the posterior pituitary is inhibited by drinking

alcohol & caffeine.

How would this affect urination?

Increases

ADH

Failure to release sufficient ADH leads to a condition: DIABETES INSIPIDUS large quantities of dilute urine are produced

Water level regulation by negative feedback control

Water content of the blood normal

Water content of the blood HIGH

Water content of the blood LOW

Too much water drunk

Too much salt or sweating

Brain producesMore ADH

Urine output LOW

Brain produces Less ADH

Urine output HIGH

High volume of waterreabsorbed by kidney

Low volume of waterreabsorbed by kidney

(small volume of Concentrated urine)

(large volume of dilute urine)

ALDOSTERONE:maintains a steady level of Na in

plasma influences water reabsorption is secreted by the adrenal cortex

Control of Blood Sodium Level:Aldosterone is a:Steroid hormone

A decrease in blood Na leads to a decrease in blood volume. WHY?

Because less water enters the blood by osmosis.

Less water = reduction in blood pressure

The decrease in pressure & volume: stimulates a group of secretory cells,

the juxtaglomerular complex situated between the:

distal convoluted and afferent arteriole

juxtaglomerular complex releases an enzyme called

RENIN

What is the function of renin?angiotensinogen angiotensin

Angiotensin releases aldosterone from the adrenal cortex

Aldosterone: travels in the blood to the distal

convoluted tubule stimulates the Na+/K+ pumps in the cells of

the tubule

Angiotensinogen [a plamsa protein] produced in the liver

Renin

Aldosterone causes:

2. K+ to move into lumen & ends in urine

1. Na+ ions to be pumped from distil tubule into the blood capillaries

TS distil tubule K+

Na+

RESULT OF more Na+ in blood is….

Na+ in blood = more negative water potential & so more water is reabsorbed

Decrease in Na+

Results in a low blood volume & pressure (as less water enters by osmosis)

Activates angiotensinogen to become ANGIOTENSIN

RENIN is released

ALDOSTERONE is released

Causes Na/K pump in distal tubule to take up Na+ into the blood

Water enters the blood


1. The human kidney, in association with various hormones, plays a central role in the regulation of the chemical and physical characteristics of blood.

a) List THREE ways through which the human kidney may affect the

chemical composition of blood. (3)1) Through aldosterone, the kidney determines the amount of

sodium and potassium in the blood.

2) Through ADH, the kidney plays a role in the amount of water in the blood.

3) The kidney helps to keep the blood pH constant by secreting H+ or OH-.

b) Complete the table below by filling in the empty spaces with the appropriate answers: (3)

Hormone Site of production

Effect

Antidiuretichormone

Adrenal cortex

Stimulates excretion of potassium ions and reabsorption of sodium ions in the nephron

b) Complete the table below by filling in the empty spaces with the appropriate answers: (3)

Hormone Site of production

Effect

Antidiuretichormone

Hypothalamus

Stimulates distal convoluted tubule and collecting duct to reabsorb water

AldosteroneAdrenal cortex

Stimulates excretion of potassium ions and reabsorption of sodium ions in the nephron


c) Briefly describe how vasoconstriction and vasodilation of blood vessels may affect blood pressure. (4)When blood vessels dilate, the blood pressure is lowered as there is less resistance to blood flow. When blood vessels constrict, the blood pressure becomes higher as cross-sectional area decreases.

Control of Blood pH

Control of Blood pH

pH of blood is maintained at a constant value of 7.4

pH of urine varies: 4.5 - 8.2

Abrupt changes in blood pH:

are prevented by:Plasma proteinsPhosphate Hydrogen carbonate

buffers

Longer-term adjustments in the ion balance of the blood :

are made in the distal convoluted tubule

If the pH falls below 7.4:distal tubule cells secrete H+ into the urine

If the pH rises:Distal tubule cells secrete OH- & HCO3

- into the urine

H+

HCO3-

OH-

Essay Titles

1. Give an overview of the role of the mammalian kidney in excretion and osmoregulation.

[SEP, 2000] 2. Evaluate the role of the human kidney in excretion

and osmoregulation. [SEP, 2002] 3. The mammalian kidney is a homeostatic organ.

Discuss. [SEP, 2004]

Essay Titles

4. Describe the role of countercurrent flows in biological systems [MAY, 2007]

Gills in bony fish – blood & seawater flow Thermoregulation – blood flow in artery & vein in a

limb Excretion – loop of Henle; vasa recta Pregnant female - blood of embryo & uterus

Just a reminder, before we end:

Recall role of the hormone

Erythropoietin :

Made by:Kidneys

Released when:Oxygen levels in blood are low

Causes:RBC formation

Figure 11-61 of 7

Bone marrow

Stemcells

Erythroblasts

Reticulocytes

Increasedmitotic rate

Acceleratedmaturation

Release oferythropoietin

(EPO)

Tissueoxygenlevels

decline

Tissueoxygenlevelsrise

Improvedoxygencontentof blood

Increased numbersof circulating RBCs

Negative Feedback Control

Manneken Piss [Brussels, Belgium]

excretion

Documents

ammonia ammonia protein

ammonia disadvantages

habitat ammonia

excretion osmoregulation

definitions osmoregulation

terrestrial urea

definitions excretion

freshwater uric acid