Bio - Excretion and Kidneys

define excretion

the process of removing waste products of metabolic processes

define osmoregulation

a form of homeostasis where the concentrations of hemolymph or blood is kept within a particular homeostatic range

define hemolymph

the circulating fluid in arthropods

What are included in arthropods?

insects, crustaceans, and arachnids

what does it mean if an animal is an osmoregulator?

animals that maintain a constant internal solute

what does it mean if an animal is an osmoconformer?

animals whose internal solute concentration tends to be the same as the concentration of solutes in the environment

what does the liver do in terms of excretion?

transforms toxins such as alcohol, drugs, heavy metals, and products of protein metabolism into soluble compounds that can be eliminated by the kidneys

what is the function of the urinary system?

remove waste, balances blood pH, and maintains water balance

what three waste products are excreted by the kidney and what is their origin of waste

• ammonia: deamination of amino acids by liver

• urea: deamination of amino acids by liver and ammonia combined with CO₂

• uric acid: products of the breakdowns of nucleic acids, such as DNA

which waste product is excreted by the lungs and what is its origin of waste

carbon dioxide: waste products of cellular respiration

what two waste products are excreted by the liver and what are their origins of waste

• bile pigments: breakdown of red blood cell pigment, hemoglobin

• lactic acid: products of anaerobic respiration

which product is excreted by the large intestine and what is its origin of waste

solid waste: by product of digestible and indigestible materials

label the kidney!

what is the function of proteins in the diet

• maintain tissues

• promote cell growth

• direct cell processes

what are excess proteins often converted into and how does this result in nitrogenous bases as a waste product? what is this process called and what other waste product does it produce?

• often converted into carbs which are broken down for ATP

• since carbs do NOT have nitrogenous bases, they need to be removed

• called deamination

• produces ammonia

what is the nephron and what is its function?

• functional unit of the kidney

• where urine is formed

give the pathway of blood through the kidneys

renal artery —> afferent arteriole —> glomerulus —> efferent arteriole —> peritubular capillaries —> renal vein

give the pathway of urine through the kidney starting at the glomerulus

glomerulus —> Bowman’s capsule —> proximal tubule —> loop of Henle —> distal tubule —> collecting ducts —> renal pelvis —> ureter

what are the three steps of the formation of urine?

• filtration

• reabsorption

• secretion

what is filtration in the formation of urine and how does it work?

• fluids move from blood to Bowman’s capsule

• ultrafiltration: volume forced out of the glomerulus is 100x greater than in other tissues

  • filtration occurs because of pressure difference pushing blood into the Bowman’s capsule through the fenestrations of the glomerulus

what three things are NOT filtered into the Bowman’s capsule?

• red blood cells

• plasma proteins

• platelets

what is reabsorption in the formation of urine and how does it work?

• transfer of essential solutes and water from nephron back to the blood

• both active and passive transport are used

• occurs until homeostatic threshold is reached and the excess material is excreted in urine

what is secretion in the formation of urine?

movement of materials from paratubular capillaries into nephron at location other than Bowman’s capsule

what things are secreted into the nephron from the paratubular capillaries?

• nitrogen-containing wastes

• excess H⁺ ions

• minerals

• drugs and poisons

in what form do aquatic animals secrete their waste and why?

• directly as ammonia

• easily diluted in their environment

what is the feature of echinoderms and what are three examples?

• show radial symmetry

• sea urchins, star fish, sea cucumbers

what is the feature of coelenterates and what are two examples

• tube or cup-shaped body and single opening with tentacles

• jelly fish, coral

in what form do insects excrete waste and how?

• the form of uric acid

• have tubes that branch off large intestine called the Malpighian tubes

what happens in the glomerulus and bowman’s capsule? how does it work?

• site of filtration

• glomerulus is fenestrated: small slits that open when pressure is increased

• high pressure in glomerulus forces fluids into the Bowman’s capsule

  • blood pressure is high because the afferent arteriole is wider than the efferent

• only molecules small enough to fit through the fenestrations will move to the Bowman’s capsule

what is filtrate and what three things must it pass through?

filtrate: fluid that enters the Bowman’s Capsule

must pass through:

• glomerular walls

• basement membrane

• podocytes

define the basement membrane and podocytes?

• basement membrane:

  • covers and supports walls of the glomerulus

  • made of glycoproteins

  • prevents plasma proteins from being filtered out

• podocytes:

  • cells that form the inner wall of the Bowman’s capsule

  • wrap around the capillaries

what happens in the proximal tubule? how does it work?

• site of most reabsorption of useful materials via active and passive transport

• epithelial cells lining proximal tubule have:

  • lots of mitochondria (for active transport)

  • brush border of microvilli into lumen (increase surface area)

• almost all of the filtrate is reabsorbed into the blood

• exterior side has smaller surface area so as to minimize movement of salt and water back into the tubule

what is reabsorbed into paratubular capillaries? what is secreted into the nephron?

reabsorbed

• 80% of water

• glucose and amino acids

• vitamins

• hormones (small ones)

• sodium and other mineral ions

secreted

• H⁺ and NH₃ to manage pH

• drugs and poisons that didn’t pass through Bowman’s capsule

what is moved by active transport? what is moved by passive transport? (in proximal tubule)

active transport:

• Na/K pump: pumps Na⁺ out into interstitial fluid and K⁺ into tubule lumen

passive transport:

• Na⁺: moves into tubule lumen (b/c of Na/K pump creating concentration gradient)

• Cl^-: follows Na⁺ (electrochemical gradient)

• glucose: CO^- transported into interstitial fluid (because of Na⁺ movement)

• water: osmotic force b/c of Na⁺ movement causes reabsorption into interstitial fluid

what happens in the loop of henle?

• creates gradient of solute concentration in the medulla that is essential for H₂O reabsorption

what happens in the descending limb of the loop of Henle?

only water is reabsorbed, therefore sodium chloride concentration increases inside nephron

what happens in the ascending limb of the loop of Henle and what are the two parts?

• thin segment:

  • passive transport of NaCl into interstitial fluid (because of concentration gradient)

  • inner medulla

• thick segment:

  • active transport of NaCl into interstitial fluid (against concentration gradient)

  • outer medulla

what is the countercurrent multiplier system?

• countercurrent: because flow of fluid in the descending and ascending limb are in opposite directions

• multiplier: a steeper osmotic gradient is produced

• osmotic gradient is produced because of “u” shape

• NaCl leaves nephron in ascending limb to make solute concentration in interstitial fluid high, moving water out of the descending limb

what happens in the distal tubule and how does it work?

• selective reabsorption of nutrients to maintain homeostasis in blood

• regulates K⁺ and NaCl of body fluids by varying amount secreted/reabsorbed

• note: less mitochondria and microvilli here compared to proximal tubule / not as much transfer of nutrients occurs

how is pH and blood solute concentration regulated in the distal tubule?

• pH: regulated by secretion of H⁺ ions and reabsorption of HCO₃^- ions

• blood solute concentration:

  • if low, little water will be reabsorbed

  • if hight, ADH will be released by pituitary gland and water reabsorption is increased in distal tubule

what happens in the collecting duct? what happens in what areas?

• carries filtrate to renal pelvis

• water reabsorption continues

• outer medulla: NaCl reabsorbed in interstitial fluid

• inner medulla: small amount of urea diffuses into interstitial fluid due to high concentration in fil

what six things are left in the nephron to make up urine?

• sodium chloride (NaCl)

• water

• urea

• liver metabolites

• uric acid

• minerals

what happens in the renal pelvis?

collecting ducts merge to the ureter which takes urine to the bladder

Draw the nephron

Annotate the nephron

what does diabetes mellitus cause?

• excess sugar in the nephrons because inadequate secretion of insulin

• excess sugar provides osmotic pressure which leads to more water secreted and excreted in the urine

• as a result, release large volume of urine

what is diabetes insipidus and what does it cause?

• destruction of ADH producing cells (regulate water reabsorption) or inability of the distal tubules to respond to ADH

• as a result, water is not reabsorbed and too much water is lost through urination

what is Bright's Disease (nephritis) and what is it caused by? what does it effect?

• inflammation of the nephrons

• can be caused by toxins which destroy blood vessels in the glomerulus

• affects the permeability and allows larger molecules such as proteins to pass into the nephron

  • since proteins do not often pass through, there is no mechanism for reabsorption

  • results in excess water in nephron and increased urine output

what are kidney stones caused by and where are they lodged? why are they so painful?

• caused by precipitation of mineral solutes from the blood

• stones become lodged in the renal pelvis or may move into the ureter

• as it moves through the ureter, the jagged edges can tear the delicate tissues and pain

what three ways can kidney stones be removed?

• surgery

• shock-wave lithotripsy

  • shock waves break apart stones into small fragments that can be passed

• medication to widen urinary tract

what is dehydration and what can cause it? what is a sign of dehydration?

• when more water leaves the body than enters

• can be a result of exercise, insufficient water intake, diarrhea, water loss during overheating

• sign: darker, more concentration urine with stronger odour due to increased solute concentration

what is over hydration? what can cause it? what does it result in?

• when there is over consumption of water, diluting blood solutes

• may result from excessive water consumption after exercise without replacing lost electolytes

• results in swelling of body cells resulting in headaches and disruption of nerve function

two treatments of kidney failure

• dialysis

• transplant

what is dialysis?

• exchange of substances across a semipermeable membrane

what hormone is responsible for osmoregulation? what does it do?

ADH - antidiuretic hormone

• increases water reabsorption in the kidney

outline the steps of the negative feedback loop for osmoregulation when blood osmotic pressure is high (water is low)?

1) osmoreceptors in hypothalamus detect change in osmotic pressure

2) cells of hypothalamus shrink (bc water leaves cells and moves into blood) and a nerve message is sent to the pituitary gland to release ADH

3) water reabsorption is increased in distal tubules and collecting duct

4) water reabsorption prevents the osmotic pressure of body fluids from increasing any further, preventing dehydration

Osmoreceptors also cause you to get thirsty and drink water which lowers the osmotic pressure back to homeostasis

• once returned to homeostasis, water moves from plasma to hypothalamus cells which swell and stops ADH release

what hormone is responsible for maintaining homeostatic blood pressure and blood volume in the kidneys? what does it do?

aldosterone

• maintains homeostatic blood pressure (raises it when low)

• increases sodium concentration in blood by increasing sodium reabsorption in the distal tubule and collecting ducts

• water follows concentration gradient, increasing volume of blood plasma and therefore blood pressure

outline the steps of the negative feedback loop for when blood pressure and blood volume is low?

1) specialized cells within the apparatus release renin (enzyme)

2) renin converts angiotensinogen into angiotensin

3) angiotensin does the two following things:

• stimulates release of aldosterone which acts on nephrons to increase sodium absorption and therefore water absorption

• causes constriction of blood vessels

what is the low blood pressure detector called?

juxtaglomerular apparatus