Bio C6 - excretion

What is the role of the hypothalamus?

-To regulate physiological processes:

• Temperature

• Hunger & thirst

• Water balance & osmo regulation

• Hormones

What is excretion?

-The removal of substances that once formed part of the body of the organism

What is egestion?

The removal of undigested food from the gut

The nature of wastes:

-The breakdown of carbohydrates, lipids & proteins

-Waste products include CO2, water & nitrogenous wastes

-CO2 —> produced by cellular respiration

-H20 —> produced by cellular respiration & other metabolic processes

-Nitrogenous wastes —> produced by breakdown of proteins

Nitrogenous wastes:

-Ammonia —> small, highly toxic, highly soluble, diffuses easily across membranes

-Urea —> requires energy to produce, low toxicity, highly soluble, excreted in solution

-Uric acid —> requires 2x as much energy to produce than urea, insoluble, excreted as a solid

*ALL of these are produced from the breakdown of proteins in animals

What are the proportions of ammonia, urea or uric acid excreted in different groups of animals related to?

-The availability of water in the animal’s environment

-The toxicity of the nitrogenous waste

-The energy cost in producing the waste

-The species’ pattern of development

Examples of excretory mechanisms in animals:

-Salt-secreting cells in fish gills

-Salt glands in birds & reptiles

-Liver in vertebrates —> breaks down old RBCs

-Lungs excrete CO2 from breakdown of carbs or lipids

-Malpighian tubules —> in insects, and conserve water by excreting uric acid

What do our kidneys do?

-Clean our blood by removing the wastes and adjusting salt & water concentrations & produce urine by sending these wastes to the kidneys to be excreted as the urine

What is in urine?

-Water

-Urea (nitrogenous wastes)

-Salts

Anatomy of the kidney:

-Cortex —> filters large particles from the blood (e.g white blood cells)

-Pelvis —> collects urine

-Medulla —> where water, salt & urea are removed from blood

-Renal artery —> brings blood to the kidney

-Renal vein —> takes blood away from the kidney

-Ureter —> takes urine from the kidney to the bladder

How does a kidney function?

•Filtration occurs across the glomerulus into the Bowman's capsule.

•The high pressure of blood in the glomerular blood vessels forces fluid through the walls of glomerular capillaries and into the Bowman's capsule

•Only small molecules and water can pass through the wall membranes

•blood cells and large blood proteins remain behind in the glomerular capillaries.

•This primary filtrate has the same composition as blood plasma, without large proteins.

What does a nephron do?

-Carriers out filtering & reabsorption

How does each part of a nephron function?

•Water is reabsorbed from the urine passively, via osmosis.

•The loop of Henle produced concentrated urine

•A large amount of sodium chloride pumped out of the loop of Henle is retained in the medullary region of the kidney, producing a very high salt concentration.

•The osmotic concentration within the kidney increases dramatically from the outer cortex to the medulla.

•Urine passes down the collecting tubules towards the ureter, it passes through this region of high salt concentration.

•Because the collecting tubule is permeable to water, but not to salt, water passes from the collecting tubule back into the kidney and into blood vessels.

•As a result, the urine becomes concentrated.

•Antidiuretic hormone (ADH) from the pituitary gland increases the permeability of the collecting tubule to water, increasing reabsorption of water and causing urine to become concentrated.

What is secretion?

-Secretion is the active removal (excretion) of particular substances by the cells of the tubule wall.

What does a high ADH level cause?

-It causes the body to produce less urine