Biology 20 Excretion General, Structure & Function, Four Steps to Urine Formation Hormones, Composition of Urine

Biology 20

Excretion

General, Structure & Function,

Four Steps to Urine Formation

Hormones, Composition of Urine

Introduction

• Humans are 70% water– 1/3 of this is in plasma

• Blood – carries nutrients, picks up waste• Wastes need to be removed• Composition of fluids need to be kept in

balance• Excretion: monitor, analyze, select, reject

EXCRETION• Excretion is the process of removing

metabolic wastes from the body.• During the metabolic processes of the

body, waste products are removed from the site of production by the blood.

• As these wastes accumulate, the kidney removes them from the blood and excretes them to the environment.

• The excretory product becomes urine.

Excretion

• Process of removing cellular waste

• Balance pH of blood• Maintain water balance• Happens in Kidney

FUNCTIONS OF THE EXCRETORY SYSTEM

• Functions:• To maintain homeostasis• Regulates and stabilise the internal environment

by controlling 4 groups of chemicals– Water: – Excretion of metabolic wastes: Elimination of

poisonous by-products of chemical reactions:– Osmoregulation fluid and salt regulation: regulation of

hydrogen, sodium, potassium, calcium, chloride ions:– Regulation of body fluid composition: Removal of

essential nutrients that dangerous in excess:

WASTE PRODUCTS• The principle metabolic wastes in most

animals are:oCarbon Dioxide – is excreted through the

respiratory surfacesoWater – excreted through respiratory

surfaces, skin as sweat as well as kidneysoNitrogenous Wastes – products of protein

and nucleic acid digestion

Waste Products

NITROGENOUS WASTES• Ammonia – The first metabolic product of

amino acid deamination – hydrolysis (protein digestion)o highly toxico cannot accumulate in bodyomust be converted into less toxic uric acid and

urea• Uric Acid – produced from ammonia

o not very soluble – can be excreted as a paste with little water loss

o non - toxic

Deamination & Urea

• Proteins – contain a nitrogen molecule– Amino acid – building blocks of protein

• Nitrogenous base

• Removal of N and H• Occurs in the liver• Byproduct – ammonia

– Toxic substance• Ammonia combines with CO2 to form urea• Urea –less toxic• Uric acid – waste product from the breakdown of

nucleic acids (DNA)

NITROGENOUS WASTES

• Urea – converted from ammonia

o less toxic than ammonia

o produced in the liver

o can be excreted in concentrated form

o requires more water to excrete than uric acid

Urinary System

1. Vena cava

2.Right Kidney

3. Ureter

4. Bladder

5. Urethra

6. Aorta

7. Left Kidney

8. Renal Vein

9. Renal Artery

Adrenal gland

Kidney

Ureters

Bladder

Urethra

Urinary System

• ORGAN: Function

• Kidney: site of blood filtration• Renal artery: brings blood to kidney• Renal vein: brings blood back to heart• Ureter: Brings waste TO bladder• Bladder: Temporary urine storage site• Urethra: Brings waste FROM bladder,

out of system

The Kidney

Collects waste

Joins kidney to ureter

Renal Pelvis

Inner area

Water reabsorption

Medulla

Outer layer

Where filtration occurs

Cortex

FunctionStructure

STRUCTURE AND FUNCTION OF KIDNEY

• Three distinct regions of the kidneyoCortex – outer regionoMedulla – just below cortexoPelvis – a hollow chamber within the medulla

• The cortex and medulla of each kidney are made up of a approximately one million nephrons

The Kidney


• NEPHRON – the structural and functional unit of the

kidney

Label the following diagramGlomerulus

Loop of Henle

Capillary bedCollecting duct

Distal tubule

Renal veinProximal tubule

Renal artery

Bowman’s Capsule

Ball of capillaries – site of filtrationGlomerulus

Leaves glomerulus, goes to veinEfferent Arteriole

Brings blood to glomerulus Afferent arteriole

FilterBowman’s Capsule

Collecting site for all nephrons – waste out to ureter

Renal pelvis

Empties waste into renal pelvisCollecting duct

Leads to collecting ductDistal Tubule

First tube in nephron. From BC. Reabsorption of Water

Proximal Tubule

FUNCTIONSTRUCTURE


• NEPHRON o the structural and functional unit of the

kidney

• BOWMAN’S CAPSULE o a double walled chamber – start of the

tubule.

The Nephron


• GLOMERULUS o network of capillaries within the Bowman’s

capsuleo high pressure (4x higher than in capillaries)

The Nephron

The Nephron


• PROXIMAL TUBULE– active transport of many valuable substances

back into blood network• glucose • amino acids• sodium

The Nephron


• PROXIMAL TUBULE

• What doesn’t get absorbed?

o urea

o other toxic substances

o some salt

omuch of the water


• LOOP OF HENLE

o the long hair-pin turn!!

The Nephron


• LOOP OF HENLE

o the long hair-pin turn!!

o some of the remaining water and salt will be

returned to the blood

o lies in the medulla which is relatively salty

(hypertonic)


• DISTAL TUBULE and COLLECTING DUCTS

The Nephron

The Nephron


• DISTAL TUBULE and COLLECTING DUCTSoMore water reabsorption

• This depends on the presence of certain hormones

• (ADH) Anti diuretic Hormone

oExact amounts of substances are reclaimed to the blood• very precise

Urine Formation

• Depends on three functions:– Filtration

• Movement from blood – Bowman’s capsule

– Reabsorption• Transfer of needed nutrient back INTO blood• Tubules

– Secretion• Movement of material from blood back into

nephron


1) FILTRATION – Occurs at the junction of the glomerulus and

the wall of the Bowman’s capsule– Each glomerulus receives blood from an

afferent arteriole and discharges its blood into an efferent arteriole (hypertonic).

– Fluid and dissolved materials (nutrients, wastes, ions) in the blood plasma pass from the glomerulus into Bowman’s capsule• due to a local increase in blood pressure within the

glomerulus


1) Filtration (con’t)

– this material is then called nephric filtrate

– blood cells, plasma proteins and platelets are

too large to pass through the wall of the

capillary and therefore remain within the

capillary.


2) REABSORPTION

– in the proximal tubule

– returns about 99% of filtrate to the blood

– efferent arteriole feeds second capillary network

that surrounds the tubule

– this network receives reabsorbed

substances• eventually leads to renal vein


2) REABSORPTION (con’t)• Water rushes into the blood because of

osmosis

Problem• Not enough water is returned this way.

Solution• Just actively transport water into the blood

right?

Wrong!!!

There is no way of ACTIVELY transporting water

So how can we transport more water into the blood?

Solution2) Reabsorption (con’t)

o active transport of solutes into the capillary

bed • glucose

• amino acids

• vitamins

• inorganic ions (Na+)

owater is passively reabsorbed from the

proximal tubule as these solutes are

actively removed from the filtrate


2) Reabsorption (con’t)• Reabsorption and the distal tubule.

– A more selective, precisely regulated reabsorption occurs in the distal tubules

– Additional quantities of salts and water may be reabsorbed

– The exact amount of each substance reclaimed occurs in the distal tubules.

– excess is excreted in urine• e.g. glucose and diabetes

Four Steps to Urine Formation3) SECRETION

– This is the last chance for anything to leave the blood and enter the urine

– Active transport– Occurs in the distal tubule and collecting

duct– Hydrogen ion secretion – helps regulate

blood pH• Distal tubule• Na+ moves into the blood and H+ moves into the

tubule filtrate– blood pH increases (ranges 7.3 - 7.4)– urine pH decreases (ranges 4.5 - 8.5)

Four Steps to Urine Formation– potassium secretion

• prevents accumulation of potassium that can

create neural and muscular problems

– some drugs are removed from the body by

secretion

– substances eliminated in this manner are • creatine – by product of protein metabolism

• potassium

• penicillin


4) Elimination• Pathway

o collecting ducto renal pelviso uretero urinary bladdero urethrao environment

What is in urine?• Excess sugars• Excess salts• Excess H+ ions• Urea and uric acid• Excess H2O

Control of Excretion Disorders and Treatments

HORMONES• ADH• The Antidiuretic hormone

– influences the RATE of water reabsorption into blood from collecting ducts

– released by the pituitary gland in the brain

• Osmoreceptors in brain stimulated by low blood volume and increased osmotic pressure– both of those means that there is not enough water in

the blood.– rate of ADH secretion is increased. ADH saves water.– More ADH = more H2O absorption = increased urine

concentration– Very yellow concentrated urine

• Most water reabsorbed in proximal tubule– permeable

• Rest of tubule permeable ONLY IF ADH is present– Ascending loop– Distal tubule

Aldosterone and Sodium

• Aldosterone – hormone– Produced in adrenal gland– Increased Na+ uptake in nephron– More water may also move out

• Osmosis (high to low)

• Blood pressure– Less fluid – lower blood pressure

– Angiotensin produced• Constricts blood vessels, increase blood pressure• Causes release of aldosterone

– Aldosterone acts on distal tubule and collecting duct• More sodium reabsorbed• Fluid level increase• BP increases

Kidney Disease

• Diabetes Insipidus– Problems with ADH production– No ADH, no H2O reabsorption– Huge urine output

• Up to 20 L/day

• Kidney Stones– Minerals forming solid crystals (Ca+, Na+)– Get lodged in pelvis or ureter– Can tear tissues as it moves out– OHMYGOODNESSMAKEITSTOPICANNOTSTAN

DTHEPAIN!!!!!!!!!!!!!!!!• Stone removal

– Surgery– Ultrasound– catheter

Kidney Stones

• Kidney Dialysis– Cleaning of blood– Treatment of kidney failure– Blood goes through a filter– Concentration gradients remove waste

Continuous Dialysis

• Kidney Donation– Human system built in twos– Extra kidney for backup– One kidney – can do all the work– With less than 20% kidney function, problems

occur• Requires kidney dialysis

– If problem gets really bad, might need a new one TRANSPLANT

Documents

Biology 20 Excretion General, Structure & Function, Four Steps to Urine Formation Hormones, Composition of Urine