biology 20 excretion general, structure & function, four steps to urine formation hormones,...
TRANSCRIPT
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
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
1. Vena cava
2.Right Kidney
3. Ureter
4. Bladder
5. Urethra
6. Aorta
7. Left Kidney
8. Renal Vein
9. Renal Artery
• 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
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
STRUCTURE AND FUNCTION OF KIDNEY
• NEPHRON o the structural and functional unit of the
kidney
• BOWMAN’S CAPSULE o a double walled chamber – start of the
tubule.
STRUCTURE AND FUNCTION OF KIDNEY
• GLOMERULUS o network of capillaries within the Bowman’s
capsuleo high pressure (4x higher than in capillaries)
STRUCTURE AND FUNCTION OF KIDNEY
• PROXIMAL TUBULE– active transport of many valuable substances
back into blood network• glucose • amino acids• sodium
STRUCTURE AND FUNCTION OF KIDNEY
• PROXIMAL TUBULE
• What doesn’t get absorbed?
o urea
o other toxic substances
o some salt
omuch of the water
STRUCTURE AND FUNCTION OF KIDNEY
• 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)
STRUCTURE AND FUNCTION OF KIDNEY
• 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
Four Steps to Urine Formation
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
Four Steps to Urine Formation
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.
Four Steps to Urine Formation
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
Four Steps to Urine Formation
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
Four Steps to Urine Formation
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
Four Steps to Urine Formation
4) Elimination• Pathway
o collecting ducto renal pelviso uretero urinary bladdero urethrao environment
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 Dialysis– Cleaning of blood– Treatment of kidney failure– Blood goes through a filter– Concentration gradients remove waste