Made up of the urinary system (bladder, urethra), kidneys, liver and uses the circulatory system to rid the body of wastes

Water and solute balance

Human urinary system

Starts at the liver◦ Liver breaks down amino acids (proteins) from

blood by removing an amino group (-NH2) called deamination

◦ This NH2 forms ammonia (NH3) – VERY TOXIC!

◦ So what happen is 2–NH3 molecules + CO2 to form urea – less toxic to body

◦ Uric acid is also produced, but from the breakdown of nucleic acids

Liver also helps to transform injected toxins (heavy metals and alcohol) into less toxic forms within the body

Removal of wastes Balancing blood pH **Maintenance of water balance**

Human kidney

**must maintain water balance◦ 1% water loss = thirst◦ 5% water loss = collapse and dehydration◦ 10% water loss= death

Need to intake 2L per day because we lose ~2L through perspiration, exhalation, urination

3 main regions Renal Cortex

◦ Outer layer of kidneys

Renal medulla◦ Inner layer of

kidney under cortex Renal pelvis

◦ Where ureter connects to the kidney

Renal artery◦ Carries blood from

aorta to kidneys Renal vein

◦ Drains blood from the kidney

◦ Returns solutes and water reabsorbed by kidneys to bloodstream

Filtration unit found in the kidneys

Filters and absorbs substances

Produces urine Millions of nephrons

make up each kidney Is partially in renal

cortex and partially in renal medulla

Efferent arteriole◦ Carries blood from

glomerulus and joins renal vein

Afferent arteriole◦ Carries blood from

renal artery to glomerulus

1.Glomerulus◦ Network of capillaries◦ Impermeable to RBC and

proteins (stay in blood)◦ Allows water, ions and urea

to pass through capillary walls

◦ Filtrate heads into Bowman’s capsule.

◦ Blood enters through the afferent arteriole and leaves glomerulus through the efferent arteriole

filt

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Structure of the glomerulus

2.Bowman’s capsule (C)◦ Surrounds the

glomerulus◦ Receives Na+, Cl-, H+,

glucose, amino acids and urea from glomerulus

3.Proximal tubule (Reabsorption)

◦ Joins Bowman’s capsule to loop of Henle

◦ Lined with many mitochondria that are used to make ATP for active transport

Proximal tubule (Reabsorption)

◦ Glucose and Na+ are actively transported back into bloodstream

◦ Water follows due to osmosis◦ Cl- follows the positive ion

4.Loop of Henle (descending) [M]◦ Plunges into medulla region (very

salty environment)◦ This part of the loop is permeable to

water, so water flows out back into capillaries H20 leaving the loop causes the Na+

concentration inside the loop to reach maximum concentration

◦ Loop at this point is impermeable to solutes

5.Loop of Henle (ascending) [M]◦ Loop is now impermeable to water

and permeable to solute◦ Na+ is actively transport from

loop to nearby blood vessels Cl- passively flows out as well

◦ Allows the medulla to remain salty◦ Is dependent upon the need for

salt (if body has lots, less is reabsorbed into bloodstream

6.Distal Tubule (re-absorption & secretion) [C]◦ K+ and H+ ions from

bloodstream are actively transported here

◦ Drugs taken are also reabsorbed from bloodstream here

◦ Continues to actively transport out Na+ and osmosis of water to bloodstream

Movement of wastes from blood to nephron◦ K+ H+ ions, drugs like penicillin

7.Collecting duct [M](water reabsorption)

◦ Reclaims water back to bloodstream from filtrate to reduce water loss

◦ Based on water levels: If a person is dehydrated, the permeability of duct increases so more water may return to the bloodstream.

At this point, the filtrate is called “urine” [1% of original filtrate]

Inside the nephron

Urine formation

The kidney also functions to balance pH When the pH of blood lowers (due to

excess H+ ions) HCO3- (bicarbonate) can react with it to maintain pH levels

Excess H+ ions are excreted in urine

• Osmotic pressure –The amount of pressure exerted on water to travel out of the blood vessel

• The greater the osmotic pressure the more water is reabsorbed back into the bloodstream from the distal tubule and the collecting duct

• Osmoreceptors (hypothalamus) detect the difference in osmotic pressure to signal the release of the hormone ADH

•ADH causes less urine to be produced by making the upper part of distal tubule and collecting duct permeable to water.

•Produced in Hypothalamus gland and stored in the Pituatary gland

A hormone that increases the reabsorption of Na+ in the distal tubule and the collecting duct.◦ This increases the osmotic gradient and more

water is reeabsorbed.

Urinary Tract Infection – is painful urination due to bacteria from bowels to enter urethra◦ More common in females due to their anatomy

If untreated may cause kidney infections

Kidney Stones – the formation of calcium crystallization in the urinary system◦ Can be urinated out or may require surgery

Diabetes Mellitus – when the body does not release enough insulin to reduce glucose levels in the blood; will excrete large amounts of urine due to a lack of water reabsorption in the kidney

Diabetes Insipidus – defect in the ADH that does not allow for as much water reabsorption.◦ These people produce large amounts of urine.

Nephritis ◦ A range of diseases that cause the inflammation

of the nephron. E.g. – toxins from invading microbes can cause the

glomerulus to become more permaeble to large molecules like proteins. Since proteins can not be reabsorbed they change the

osmotic gradient and more water leaves the body as urine.

Can lead to kidney damage or complete failure.

Dialysis is the exchange of materials across a semi-permeable membrane◦ Hemodialysis – machine is connected to a vein

and is cleaned of wastes (acts like a kidney); is external of the body

◦ Peritoneal dialysis – a catheter is placed in abdominal cavity where dialysate is pumped through, drained and replaced every 6 hours.

Kidney dialysis

85% success rate today

Preferred form of treatment

Although dialysis is good, nothing can replace the workings of a real kidney

The main disadvantage as with any organ transplant…◦ Immune system sees the new kidney as a foreign

invader and acts against it.◦ Often patients are given immunosuppressant drugs to

help with this issue.

Xenotransplants!!!!! Page 391

Islet cell transplants◦ Quirks and Quarks Islet cell transplant