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The kidney and osmoregulation

Topic 11
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3

Biology HL

Uric acid isn’t water soluble and therefore it can be stored within the egg as
the embryo develops

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Energy inexpensive and the animals don’t need to drink water so often

Anatomy of the kidney
➢ The function of the kidneys is to filter waste products from the blood
➢ The renal artery takes blood into each of the kidneys and the filtered blood goes
away from them by the renal vein
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The blood is filtered in the renal cortex and renal medulla

➢ Excess water and waste products make up the urine which is collected in an area
called renal pelvis and later it’s taken away to the bladder by the ureter
➢ The composition of blood plasma in the renal artery compared with the renal vein
is different, since the levels of water, salts and urea differ
Nephrons
➢ Each kidney is made up pf filtering units called nephrons
➢ Each nephron consists of:
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A glomerulus ⇒ a capillary bed which filters substances

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The Bowman’s capsule ⇒ a capsule that surrounds the glomerulus

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A tubule that extends from the Bowman’s capsule ⇒ includes the proximal
and distal convoluted tubule, loop of Henle and the collecting duct

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The peritubular capillary bed which surrounds the tubule mentioned above

Bowman’s capsule
➢ The afferent arteriole is a small branch of the renal artery that brings unfiltered
blood to the nephron and branches into the glomerulus
➢ The glomerulus has small slits in the walls called fenestrations which open when
the blood pressure increases
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The blood is provided by the efferent arteriole

➢ The efferent arteriole drains blood from the glomerulus and has smaller diameter
than the afferent arteriole
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That’s why the pressure increases when they join at the glomerulus

➢ Ultrafiltration describes the process by which various substances are filtered
through the glomerulus and its fenestrations under the unusually high blood
pressure in the capillary bed
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The fluid that is ultrafiltered passes through the basement membrane
2

The kidney and osmoregulation
■
○

Topic 11
...
3

Biology HL

➢ Alcohol consumption gives an abnormally low production of ADH and therefore
the urine contains more water
Differences
➢ What changes do the kidneys make to the blood?
➢ The blood in the renal vein compared with the renal artery will have:
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A lower concentration of urea

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A lower concentration of salt ions

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A lower concentration of water

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A nearly identical concentration of glucose

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A nearly identical concentration of protein

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Absolutely no change in blood cells

Water conservation
➢ Kidneys are highly diverse organs when you compare them in different species
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Frogs and toads have no loops of Henle and so they can’t absorb water

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Animals that live in desert regions have longer loops

➢ The banner-trail kangaroo rat lives in South-West USA
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They have a very long loop of Henle that produces a large hypertonic area for
water reabsorption in the medulla using ADH collective duct mechanism
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Almost all the water is recycled

Osmoregulation
➢ The total volume of water eliminated depends on many physiological factors:
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Perspiration rate

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Ventilation rate

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Volume of water ingested recently

➢ The body’s response mechanisms that attempt to maintain homeostatic levels of
water are called osmoregulation
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Homeostasis describes the body’s ability to maintain a stable internal
environment

➢ Animals can either be osmoregulators or osmoconformers
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Osmoregulators are animals whose internal tissues have a different
concentration of solute compared to the environment
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Must be actively maintained ⇒ energy expensive

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Most animals are osmoregulators
4

The kidney and osmoregulation
■

Topic 11
...
They actively transport ions out through the
gills and very concentrated urine

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Freshwater fish have hypertonic tissues in a hypotonic
environment
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3

Biology HL

Testing
➢ In a healthy individual should be no glucose in the urine
➢ Blood cells are too big to pass through the fenestrations, which means that finding
blood in the urine signals kidney malfunction, infection or bleeding in the renal
tubes
➢ Proteins are also too big to pass through the fenestrations and therefore should not
be found in the urine
➢ Most drugs are filtered by the kidneys and as they’re soluble in water, they end up
in the urine
De- and overhydration
➢ Dehydration
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Sleepiness

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Constipation

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Dry mouth and skin

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Dizziness and headache

➢ Overhydration
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Change in behaviour/confusion

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Blurred vision

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Muscle cramps

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Nausea and vomiting

6



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