The kidney and osmoregulation PDF

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Summary

IB Biology HL
Topic 11.3
nitrogenous waste, evolutionary history, anatomy of the kidney, nephrons, Bowman's capsule, reabsorption, loop of Henle, ADH, water conservation, osmoregulation, kidney failure, haemodialysis...

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The kidney and osmoregulation

Topic 11.3

Biology HL

Nitrogenous waste ➢ Reactions within body cells are collectively referred to as metabolism ➢ The bloodstream supplies the substances needed for metabolism and removes molecular waste from the tissues ➢ The body breaks down proteins to amino acids to make new proteins and the amino acids that aren’t immediately used will be deaminated meaning that the amine group (-NH2) will become a waste product and the rest will be used for energy ○

The waste products that result from deamination of amino acids are called

nitrogenous waste and contain ≥ 1 N atoms ➢ Dierent animals have dierent ways of getting rid of nitrogenous waste, as the amine group can be turned to into one of the following 3 molecules ○

Ammonia ⇒ fish

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Urea ⇒ mammals

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Uric acid ⇒ birds ■

Insoluble in water, can be stored inside the eggs of birds and reptiles

➢ These are filtered out of the bloodstream by the kidneys ➢ Insects get rid of nitrogenous waste and other waste products by the use of

malpighian tubes which have a proximal end and a distal end ○

Compounds transported in the blood empty at the distal end and the wanted compounds are reabsorbed in the tubes while the rest is emptied to the proximal end and turn into faeces

Evolutionary history ➢ Animals can’t evolve an entirely new physiology ○

If a species has an ancestor that primarily used 1 of the 3 nitrogenous waste types, it will use the same

➢ Fish use ammonia, because they have unlimited water which they use to dilute and flush out the toxic substance ⇒ energy inexpensive ➢ Mammals produce and excrete urea ○

They can cope with a certain level of urea in their tissues since it is toxic in high concentration

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It’s kept under control by the kidneys and it’s stored in the urinary bladder

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Since water isn’t available to the same extent as to fish, urea needs less water for dilution and elimination

➢ Birds and reptiles produce uric acid because ammonia can’t be stored in their self-contained eggs 1

The kidney and osmoregulation

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Topic 11.3

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 ○

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 dierent, since the levels of water, salts and urea dier

Nephrons ➢ Each kidney is made up pf filtering units called nephrons ➢ Each nephron consists of: ○

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 aerent 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 ○

The blood is provided by the eerent arteriole

➢ The eerent arteriole drains blood from the glomerulus and has smaller diameter than the aerent arteriole ○

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 ○

The fluid that is ultrafiltered passes through the basement membrane 2

The kidney and osmoregulation

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Topic 11.3

Biology HL

Large molecules stay in the blood

The filtrate enters the proximal convoluted tubule and the ultrafiltered blood exits the capsule in the eerent arteriole

Reabsorption ➢ The filtrate contains valuable substances like water, salts and glucose, which are reabsorbed into the bloodstream ➢ Much of the reabsorption takes place in the proximal convoluted tubule and then the substances enter the bloodstream via the peritubular capillary bed ➢ The wall of the proximal convoluted tubule is one cell thick and the inside has

microvilli, which increase the surface area for reabsorption ○

The interior of the tubule is called lumen

➢ Most salt ions and all glucose are reabsorbed by active transport ➢ Water moves by osmosis from a hypotonic region to a hypertonic

Loop of Henle ➢ Much of the water remains in the filtrate after this has left the proximal convoluted tubule and it enters the loop of Henle ○

The descending part and the loop are permeable to water but not to salt ions

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The ascending portion is impermeable to water but permeable to salt ions ■

More ions will leave the filtrate leading to the medulla becoming hypertonic and the filtrate hypotonic

ADH ➢ The filtrate enters a collecting duct which extends into the hypertonic medulla ○

Some more water is reabsorbed as the filtrate is extremely hypotonic

➢ The permeability of a collecting duct depends on the presence/absence of the

antidiuretic hormone (ADH) ➢ ADH is secreted from the posterior lobe of the pituitary gland and circulates in the bloodstream ➢ If ADH is present, the collecting duct becomes permeable to water which moves by osmosis into the medulla and from there it enters the peritubular capillary bed and returns into the bloodstream ➢ If it’s absent, the collective duct becomes impermeable to water staying in the duct making the urine more diluted

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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

Dierences ➢ What changes do the kidneys make to the blood? ➢ The blood in the renal vein compared with the renal artery will have: ○

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 dierent species ○

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 ○

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 ■

Almost all the water is recycled

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

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 ○

Homeostasis describes the body’s ability to maintain a stable internal environment

➢ Animals can either be osmoregulators or osmoconformers ○

Osmoregulators are animals whose internal tissues have a dierent concentration of solute compared to the environment ■

Must be actively maintained ⇒ energy expensive

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Most animals are osmoregulators 4

The kidney and osmoregulation

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Topic 11.3

Biology HL

Examples ●

Saltwater fish have hypotonic tissues in a hypertonic environment. 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. They actively transport ions in through the gills and very diluted urine

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Osmoconformers have internal tissues that have the same concentration of solute as their environment ■

Iso-osmotic to the water of their surroundings

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No mechanisms to take in or to eliminate water, water moves in and out freely

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Can only live in very specific environments

Kidney failure ➢ Due to diseases or injury the kidneys might fail ○

Possible to survive with only one kidney

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If both fail, the person needs an organ transplant ■

The receiver and donor must have matching blood and tissue types

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The receiver has to take immune-suppressing drugs for the rest of their life

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While waiting for a donor, the patient must go through haemodialysis every 1-3 days

Haemodialysis ➢ A patient’s blood is pumped into a device that contains a large surface area of the dialysis membrane ➢ On one side of the membrane is their blood and on the other a solution similar to their blood without urea ( dialysate) ➢ Urea diuses through the membrane leaving the blood and entering the dialysate ➢ The balance of water and some ions can also be regulated

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The kidney and osmoregulation

Topic 11.3

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 ○

Sleepiness

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Constipation

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Dry mouth and skin

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Dizziness and headache

➢ Overhydration ○

Change in behaviour/confusion

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Blurred vision

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Muscle cramps

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Nausea and vomiting

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