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Flashcards in Excretion Deck (11):

What is homeostasis?

"Homeostasis is the ability of an organism to maintain a constant internal environment"

Necessary for organisms to survive efficiently in environments that are changing all the time

Organisms need to control their internal environment to allow metabolism

Examples of homeostasis:
- maintaining body temperature of 37 degrees = controlled by skin
- maintaining ph of blood and tissue fluid close to 7= controlled by kidneys
- preventing accumulation of waste in body= controlled by kidneys,skin and lungs
- maintaing correct concentration of oxygen = controlled by breathing system
- maintaining correct glucose concentration= controlled by endocrine system


What is temperature regulation in humans?

Temperature affects the rate of enzyme action

To control rate of enzyme reactions it is important to control body temperature

" Ectotherms are animals that gain or loose heat from their environment"

"Endotherms are animals that generate their own heat from metabolic reactions"

Endotherms are warm blooded


What are the parts of the skin?

The outer epidermis
- outer cornified layer full of keratin
- inner epidermis contains a granular layer, where keratin is formed
- The malphigan layer contains cells dividing by mitosis to replace those lost in cornified layer. Produces melanin
Which absorb uv rays that may cause cancer

The dermis contains sweat glands, nerve endings, sebaceous glands and blood glands

The innermost layer of adipose tissue is full of fat rich cells


What is temperature regulation by the skin

In cold conditions skin retains heat as follows...
- erector muscles contract. This causes the hairs to stand up and trap layer of warm air close to skin. "Piloerection"
- blood vessels contract, meaning less heat is lost to the outside. "Vascoconstriction"

I warm conditions....
- sweat is produced. As it evaporates it removes heat from the body. It is necessary to replace this loss of salt and water by drinking fluids especially when we perspire

- Blood vessels in the skin enlarge "vascodilation". Results in more blood flowing close to the surface to losses heat


What is excretion?

"Excretion Is the removal of all metabolic waste from the body"

Excretion in plants:

Equivilant to "loss of waste"

Plants loose oxygen and water vapour though stomata in the leaves and lenticels in the stem

They loose carbon dioxide through lenticels at night

Excretion and homeostasis:

- it removes excess water, salts and wastes from body
- acts to regulate osmosis

Organs of excretion....

- The skin ( excretes salts and water as sweat)
- The lungs (excrete co2 and water)
- The kidneys ( excrete water, salts and urea)


What is urea?

Proteins are digested into amino acids

Excess amino acids may become poisonous. To prevent this happening they are taken to our liver where they are broken down "deaminated" to form urea

Urea is a nitrogen containing salt. Carried out of our liver in our bloodstream


What are the parts of the urinary system?

The " renal arteries" carry blood that is high in waste products *salts, urea, and water* from aorta to kidney

The kidneys carry out 3 functions -

-They *filter* waste products from the blood, cortex
- They *reabsorb* useful materials from the filtrate, cortex and medulla
- They *secrete* some substances from the blood into the filtrate

The "renal viens" carry purified blood from kidneys back to vena cava for circulation around body

Urine is formed in the kidney

The bladder stores urine

The urethra carries urine out of the body


What are nephrons?

Neurons are structures in the kidney that make urine

A nephrons is a coiled tube about 3 cm long, which is open at one end.

Located mainly in the cortex

However the loop of Henle projects down into the medulla while collecting ducts enter pelvis


How is urine formed in the nephron?

Blood I renal arteries is high in wastes

The renal arteries forms many smaller arterioles

Each renal arteriole forms a number of afferent arterioles. Each of these arterioles enters the bowman capsule

Each afferent arterioles subdivides into a network of capillaries called a "glomerous "

Blood pressure in glomerous is higher than normal.....

- The blood in arteriole is under high pressure
- The incoming afferent arteriole is wide
- Outgoing arteriole is narrower " size difference increases pressure"

The high pressure causes filtration. This form is called ultra filtration

Larger substances *proteins, glucose, amino acids, vitamins, minerals* do not enter bowmans capsule

In the proximal convoluted tube

- water reabsorbed via osmosis
- glucose, amino acids, vitamins and minerals reabsorbed by diffusion and active transport

"Active transport is the movement of Molocules using energy against a concentration gradient "


How is urine formed in the nephrons or 2?

In the decending limb of Henle , water is reabsorbed by osmosis

In the ascending limb of the loop of Henle, salts salts are reabsorbed into medulla of the kidney by diffusion and active transport

In the distal convoluted tube

- water is reabsorbed by osmosis
- some salts are reabsorbed by diffusion and active transport
- secretion of salts and hydrogen ions from blood into tubule helps control the on of the blood

In the collecting duct, water is reabsorbed by osmosis ( due to high salt concentration in medulla), the liquid leaving the collecting ducts is urine


What controls the volume of urine?

A hormone called ADH controls the volume of water reabsorbed in the collecting ducts

ADH is produced in the hypothalamus and then passes into the pituitary gland

Low water content in plasma...

- If we don't drink enough or consume too much salt the water level in the blood plasma US too low

- in this case we release ADH. This causes the collecting ducts to become more permeable to water

- Extra water is reabsorbed into blood. The plasma gains water and becomes less salty

- The volume of urine produced is lower

Normal water content in plasma.....

- When Walter content in the plasma returns to normal, ADH is no longer released

- The collecting ducts stop reabsorbing water so the plasma does not become more diluted

- Volume of urine produced increases