EXCRETORY SYSTEM

Presented by

Daw Ei Ei khing

Assistant Lecturer

Zoology Department

Objective

1. Define the term excretion and describe how this process helps maintain homeostasis

2. Name the major metabolic wastes and the processes by which they are formed

3. Describe type of vertebrate kidney.

4. Explain the parts of urinary system and the process of urine formation.

As an organism carries out its life processes

- waste products built up in the body fluids

Life processes

• Respiration

• Feeding

• Sensitivity

• Movement

• Reproduction

• Growth

• Excretion

Waste product (metabolic waste)

the products of metabolic activity

- after oxygen and nutrients have

been supplied to a cell

- If these metabolic wastes were not from the body,

removed

the organism would die.

- Therefore, organism must be able metabolic waste

to remove &

other excess

substances

(e.g- salt, water)

Excretion

- The process by which these metabolic waste &

excess substances are removed from the

organism.

- also removes excess heat from the body,

keep the temperature of the body constant.

(Thermoregulation) ( e.g - sweating )

The average human body temperature

37°C , 98.2°F

Thermoregulation • Sweat glands in the skin secrete

sweat onto the surface of the skin

• To evaporate

• Sweat draws heat from the skin and dilated capillaries

• Various metabolic wastes are also excreted by sweat

Organs of excretion In humans & other complex animals,

Organs of excretion are – lungs, kidneys, liver & skin

Skin

excretes water and other salts in the sweat

Liver

excrete bile pigments

and cholestrol

Lungs excrete carbon dioxide

and water

Kidneys

excrete urea

and water

These organs work with circulatory , nervous &

endocrine systems

to keep or maintain

the body’s internal environment constant

(homeostasis)

Homeostasis – the process involved in maintaining the internal condition of an organism so that normal metabolic activity continues even though the external environment condition vary , Temperature regulation (thermoregulation) and osmoregulation are examples of homeostatic control.

Osmoregulation

Water content of the blood LOW

Brain produces More ADH

Too much salt or sweating

High volume of water reabsorbed by kidney

Urine output LOW

(small volume of Concentrated urine)

Water content of the blood normal

Too much water drunk

Water content of the blood HIGH

Brain produces Less ADH

Low volume of water reabsorbed by kidney

Urine output HIGH

(large volume of dilute urine)

Major Metabolic Wastes Most important metabolic wastes are

- Carbondioxide formed during cellular

respiration

- Water glucose + oxygen water +

carbondioxide + energy

- Certain nitrogen compounds formed by

( ammonia, urea & uric acid ) break down of

amino acid

- Mineral salts build up during

( sodium chloride & metabolism

potassium sulfate)

Major Metabolic Wastes

Excretory organs Metabolic wastes

1.Lungs Carbondioxide,Water (Cellular respiration)

2. Skin Water, Salts (Perspiration)

3. Liver Nitrogen Compounds (Ammonia,Urea,Uric acid)

4.Kidney Mineral salts(Sodium chloride and Potassium sulfate) and water (Urination)

Formation of urea

- All of these wastes poisonous

in high concentration

Elimination or Defecation

- The removal from the digestive tract of

unabsorbed and undigested food, in the form of

feces.

- These materials have never entered the body

cells,

- are not metabolic wastes(non-metabolic wastes)

Liver Function (Detoxification & Inactivation)

- Liver - removes harmful substances

( bacteria, certain drugs & hormones )

from the blood.

- changed harmful substances into inactive

or less poisonous forms

- Thus, liver purifies the blood.

detoxifies

- Inactive substances returned blood stream

formed in the liver to

excreted from the body

by kidneys

Formation of urea

Formation of urea

- Amino acids are the break down

products of proteins.

- Excess amino acids cannot be in the body

stored

are in the liver

broken down

- Parts of are into other substances

amino acids changed

- Amino acids by deamination amino group (NH2)

is changed into

Ammonia (NH3)

- The remainder of the amino acid molecule

is changed into ;

- pyruvic acid (used as an energy source in

cellular respiration)

- glycogen or fat ( storage )

Amino acids Structure

- The ammonia produced is very poisonous

from amino group

- In liver,

ammonia + carbondioxide enzyme-catalyzed urea

reaction

- ammonia is changed urea

into (less harmful substance)

by a series of enzyme-catalyzed reactions

- Urea from liver diffuse into blood stream.

- Bloodstream carries urea to kidneys.

- Kidneys filter urea from blood

- Urea is finally from the body

excreted in the urine

The urinary system

- Kidneys

- Ureters

- Urinary bladder

- Urethra

The urinary system

- Kidneys ( organs that produce urine )

- Ureters ( tubes, urine passes from kidneys

through which to the urinary bladder)

- Urinary bladder ( sac which stored urine )

- Urethra ( the stored urine travels from the

bladder to the outside of the body through which

during urination )

Urine Formation

- Urine is made

- in the nephrons

Glomerulus Bowman’s capsule

Proximal tubule

Loop of Henle

Distal tubule

Collecting duct

Peritubular capillaries

1 2 3

Duct

- in two stages

( filtration & reabsorption)

- During the first stage ( Filtration stage )

- useful substances ( glucose, salt, vitamin )

- wastes ( urea )

are removed from the blood.

Glomerulus

Bowman’s capsule

(Filtrate useful substances & wastes from the blood)

- During the second stage ( reabsorption stage )

- some of the useful substances

re-enter the blood

to be used by the body. Proximal tubule

Distal tubule

Collecting

duct Loop of Henle

Peritubular capillaries

Filtration

- Filtration take in the glomeruli &

place Bowman’s capsules

- The blood is under pressure

(enters a glomerulus)

Bowman’s capsule

Glomerulus

Blood Under pressure

- The pressure forces the filtrate

(water, urea, glucose,

amino acids & various salts )

through thin walls of glomerulus

into Bowman’s capsule.

- Blood cells & are too large to pass through

blood proteins the walls of the glomerulus.

remain in the blood

- The filtrate is like blood plasma

(enters Bowman’s capsule) (does not contain

protein)

- If all of the filtrate that is formed were excreted,

the body would lose - too much water

- important nutrients &

- salts dissolved in the water.

Reabsorption

- After the filtrate has left Bowman’s capsule,

- Reabsorption occurs in the renal tubule

( uriniferous tubule )

reduces the volume of filtrate

returns various important

substances

(nutrients, water, salt)

to the blood.

- As the filtrate passes through the renal tubules of

the nephrons,

- about 99% of water, are into the blood

glucose, amino acid reabsorbed by the

& many salt capillaries that

surround the

tubules

(peritubular capillaries)

In mammals,

- Reabsorption of water is an important means

from the renal tubule of water

conservation

- Since most of the water is reabsorbed,

the substances left in the filtrate are highly

concentrated.

- Water is reabsorbed by osmosis.

Osmosis - Water molecules pass from weak

solution to strong solution through

semipermeable membrane.

- Glucose, amino acid & salts are by active

absorbed transport.

- ATP (the energy source is by many

for active transport) supplied mitochondria

found in the

cells of the

renal tubule.

- The tubules are lined with microvilli

greatly the absorptive surface

increase area

- Large area allows the reabsorption of huge

amounts of water and

other substances.

• Reabsorption by region: PCT

–65% sodium ions and water

–100% glucose, lactate, amino acids, vitamin

–90% bicarbonate ions

–50% chloride ions

–55% potassium ions

– calcium, phosphate, and magnesium ion (hormonally controlled)

Loop of Henle

25% sodium ions

10% water

35% chloride

30% potassium

DCT (NOTE: not all that remains in DCT will be reabsorbed - review ADH, Aldosterone, and ANP)

10% sodium ions

10% chloride ions

25 % water

After reabsorption

- The fluid remaining is urine

in the tubules

- Urine is made water, urea & various salts

up of

- Urine flows into the collecting ducts

(from the tubules)

- Urine passes out to the bladder

(from the kidneys) through ureters

- Urine is to the outside

(from bladder) emptied through the urethra

Types of Vertebrate Kidney

Types of vertebrate kidney

- A basic structural pattern of

vertebrate kidneys (nephroi)

consists of –

(1) glomeruli, incorporated

in renal corpuscles

(malpighian)

(2) tubules, surrounded

by peritubular capillaries

(uriniferous tubules)

(3) a pair of longitudinal ducts

from fish to man

Variation of structure of kidney:

- number & arrangement of glomeruli

- relative length of tubules

In present-day vertebrates,

The uriniferous tubules – develop anterio-posteriorly

in two or three stages

in succession

These stages are

- pronephros (anterior kidney)

- mesonephros (mid kidney) &

- metanephros (hind kidney)

have evolved from archinephros(primitive kidney)

Types of vertebrate kidney

Types of kidney

1.Archinephros Embryo of cyclostomes

2. Pronephros Adult cyclostomes( lamprey , hagfish ) Embryo of anamniotes ( frog, fish)

3. Mesonephros Adult Frog , Fish Embryo of amniotes

4.Metanephros Reptiles , Aves , Mammmals ( Amniotes )

Pronephros

Pronephros

Pronephric duct

Segmental nephron

PRONEPHROS (ANTERIOR KIDNEY)

- develop in anterior most part of

the nephrotome)

- each pronephros consists of

only 1-13 uriniferous tubules

- one pair of uriniferous tubules

in each segment

•

Near each tubule is

- a glomerulus but Bowman’s capsule &

peritoneal funnel are lacking

- are called external glomeruli

The uriniferous tubules of pronepros

open into

pronephric duct

runs to enter

backward

the embryonic cloaca

•

A pair pronephroi become

functional in

- some cyclostomes

- embryos of all anamniote ( animals that have no

amnion in embryo life )

degenerate during development in

- other vertebrates

•

MESONEPHROS ( MIDKIDNEY)

- develop from part of nephrotome

lies behind the pronephros

At first,

- consists of paired

segmental uriniferous tubules

•

Mesonephros

Each uriniferous tubules with

- a peritoneal funnel opening

- a glomerulus enclosed in a Bowman’s capsule

Mesonephric uriniferous tubules

join

existing pronephric duct

called

mesonephric duct

( Wolffian duct )

Later,

undergo

mesonephric tubules hundreds of tubules

budding

So that their segmental arrangement is lost.

Later tubules have no peritoneal funnels.

•

Mesonephroi form

- adult functional kidneys in some fishes &

amphibians.

- kidneys of embryos of amniotes ( animals that

have amnion in embryo life ), but degenerate in

adult.

Metanephros

Metanephros

• The first embryonic hint of a metanephros is the formation the metanephric duct that appear as a ureteric diverticulum arising at the base of the preexisting mesonephric duct.

The ureteric diverticulum grows dorsally into the posterior region of the nephric ridge.

-Here it enlarges and stimulates the growth of metanephric tubules that come to make up the metanephric kidney .

The metanephros - becomes the adult kidney of amniotes and

the metanephric duct is called the ureter.