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Biology 102 > Lecture 12 - Excretory System > Flashcards

Lecture 12 - Excretory System Flashcards

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1
Q

Main ideas of excretory sysem

A
  1. Maintains volume, concentration and composition of extracellular fluids (interstitial fluid)
    - determines water balance of cells that those fluids bathe
    - thorough exchange between blood vessels and interstitial fluid –> blood volume and pressure
  2. Excretes waste
    - metabolic wastes of cell carried through bloodstream to kidneys
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2
Q

Cells and osmosis

A

Volume depends on osmosis

  • volume of cells depends on whether they take up water or lose it to extracellular fluids
  • depends on difference in solute concentration on the two sides of the membrane

osmolarity: moles of solute in liters of solvent

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3
Q

Osmotic Regulation Across a Membrane

A

WATER IN:
If solute concentration in cytoplasm is greater than that in extracellular fluid, water moves into cells
- swell and possibly burst
- HYPOTONIC conditions
- cell is HYPEROSMOTIC relative to extracellular fluid

WATER OUT:
If solute concentration in extracellular fluid is greater than that of cytoplasm, water moves out of cells
- Shrink
- HYPERTONIC conditions
- cell is HYPOOSMOTIC relative to extracellular fluid

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4
Q

Controlling Fluid Osmolarity and Composition

A
  1. OSMOLARITY: must maintain osmolarity of extracellular fluid within appropriate range for homeostasis
    - volume and salt concentration must be kept within certain limits
  2. SOLUTE COMPOSITION: must maintain appropriate solute composition
    - how much AND what
    - SAVE some substances, solutes valuable in short supply –> re-absorption (glucose)
    - ELIMINATE other substances, solutes in excess, toxic waste products –> secretion (urea, excess sodium)
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5
Q

Marine animals

A
  • hypoosmotic to sea water
  • gain water and salt from food and drinking salt water
  • excrete salt ions from gills
  • also excrete small amount of urine containing water and ions
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6
Q

Freshwater animals

A
  • constantly take in water by osmosis
  • gain some salts from food
  • lose salts by diffusion and maintain water balance by excreting large amounts of dilute urine
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7
Q

Terrestrial Animals

A

Adaptations to reduce water lost
- eating moist food and producing water metabolically through cellular resp

Can vary depending on diet
- special structures aid in proper osmotic balance with sepcific environment

Ex. Salt intake: herbivores must conserve salts, but birds that eat marine animals excrete excess sodium

Ex: water intake: desert animals urine is so concentrated it can form crystals

Flexible adaptation
ex vampire bat - blood meals, lots of water –> rapidly eliminate water to maximize consumption. But meals may be few and far between so then conserve body water with highly concentrated urine

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8
Q

Challenges faced by:

Marine animals

Freshwater animals

Terrestrial animals

A

Marine: salt concentration is too high

freshwater animals:

  • water is plentiful, but salt mus tbe conserved
  • must constantly bail out the excess water entering their body
  • produce copious amounts of very dilute urine

Terrestrial

  • msut conserve both salts and water
  • can vary depending on diet, specialized structures aid in proper osmotic balance

specificity - want to secrete some ions and maintain others

ALL need to get rid of ammonia waste

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9
Q

Excretion of Nitrogen

A
  • in addition to maintaining salt and water balance, animals must eliminate the waste products of metabolism

carb and fat metabolism:
- end products are H2O and CO2, easy to eliminate

protein and nucleic acid metabolism:

  • end products: H2O, CO2 and nitrogenous waste
  • NH3 is TOXIC
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10
Q

Three types of nitrogenous waste

A
  • ammonia
  • urea
  • uric acid

differ in toxicity and energy costs of producing them

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11
Q

Ammonia

A

NH3

  • highly toxic but diffuses rapidly in water
  • animals that excrete nitrogenous wastes as ammonia need to access lots of water
  • continuously excreted
  • lost from blood to environment by diffusion across gill membranes
  • for animsla that cannot continuously excrete ammonia, its buildup would be toxic so must convert it to urea or uric acid
  • fish
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12
Q

Urea

A
  • the liver of mammals and most adult amphibians converts ammonia to the less toxic urea
  • the circulatory system carries urea to the kidneys, where it is excreted
  • conversion of ammonia to urea is energetically expensive
  • large loss of water

*mammals

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13
Q

Uric Acid

A
  • relatively nontoxic and does not dissolve readily in water
  • it can be secreted as a semisolid paste with little water loss
  • uric acid is more energetically expensive to produce than urea

*insects, land snails, many reptiles and birds

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14
Q

Vertebrate Excretory organ and its functional unit

A

Kidney

Nephron

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15
Q

Processes of urine formation

A

most excretory systems produce urine by refining a filtrate derived from body fluids

  1. filtration
  2. reabsorption
  3. secretion
  4. excretion
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16
Q

Filtration

A

1.

  • at start of each nephron is a dense ball of capillaries called a glomerulus
  • highly permeable to water, ions, and small molecules
  • impermeable to large molecules
  • blood pressure drives the movement of water and small solutes out of the glomular capillaries and into the nephron
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17
Q

Friltration –> Bowman’s Capsule

A
  1. 5
    - glomerulus filters blood to produce a fluid (renal filtrate) that lacks cells and large molecules
    - filters fluid into bowman’s capsule (beginning of nephron, encolses glomerulus)
    - the filtrate produced in Bowman’s capsule contains salts, glucose, amino acids, vitamins, nitrogenous wastes and other small molecules
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18
Q

Reabsorption

A
    • In renal tube
    • all of the nephron past the Bowman’s capsule = renal tube, several sub divisions
    • converts renal filtrate into urine
    • capillaries run alongside renal tube

Reabsorption:

  • specific ions, nutrients, water, are reabsorbed out of renal filtrate and are returned to the blood
  • glucose, amino acids, most NaCl
19
Q

Secretion

A

3.

  • additional waste substance that the body needs to excrete are transported into the renal tubule
  • ex: drugs (penicillin), H+ ions
20
Q

Excretion

A
  • processed filtrate (urine) of the individual nephrons enters collecting ducts and is delivered to a common duct leaving the kidney
  • goes to bladder
21
Q

Organization of the kidney

A
  • two regions
  1. outer cortex
  2. inner medulla

nephron = major functional unit
~ 1 million nephrons per kidney
- nephron empties into ureter which leads to bladder

22
Q

Organization of nephrons within the kidney

A
  1. glomeruli and Bowman’s capsule
    - located in the outer laywe (cortex) of the kidney
  2. Proximal concoluted tube
    - also located in the cortex
  3. loop of henle
    - renal tubule straightens and descends into inner core of kidney (medulla)
    - makes a hairin tirn and ascends back to cortex
    - peritubular capillaries run into the medula in paralles
  4. distal convoluted tube
    - ascending limb of loop of henle becomes the distal convoluted tube when it reaches the cortex
  5. collecting duct
    - distal convoluted tubes of many nephrons join
    - descend back down through the medulla
    - join with other tubes to leave the kidney for the bladder
23
Q

Nephron uses movement of water and ions to concentrate urea

A
  • most of the water and solutes filtered by the glomerulus are re-absorbed and do not appear int he urine
  • 98% of the fluid filtered out of the glomerulus is returned ot the blood
  • concentration f urea
  • modulation of other solute concentrations
24
Q

Proximal Convoluted Tubule

A
  • proximal convoluted tube is responsible for most of the reabsorption of water and solutes
  • active transport of Na+ (Cl- follows), glucose, amino acids, and other valuable solutes –> nulk reabsorption of solutes
  • active transport of solutes causes water to follow osmotically (passive –> flows out through aquaporins)
  • reabsorbs ~75% of fluid that initially enters nephron
25
Q

Osmolarity of fluid in PCT

A
  • osmolarity is not changed
  • solute leaves but water follows in same proportion
  • fluid that enters the loop of henle has the same osmolarity as blood plasma, although its composition is different (removed vlauable solutes)
  • needs to make urine that is more concentrated than blood plasma (must now go through loop of henle and colelcting duct)
26
Q

How urea becomes predominant solute

A

Osmolarity in loop of henle

  • loop of henle increases osmolarity of the extracellular fluid as you move deeper into the medulla
  • different segments of the loop of henle have different properties

3 limbs:

  • thin descending
  • thin ascending
  • thick ascending
27
Q

Thin descending limb

A
  • permeable to water, but not to Na+ or Cl-
  • as descend deeper into medulla, higher salt concentration in interstitial fluid
  • outside is saltier than renal fluid
  • high osmolarity drives the water to flow our of renal tube
  • flows out through aquaporins
  • filtrate becomes increasingly concentrated
28
Q

Thin ascending limb

A
  • permeable to salt but not water
  • at base of loop of henle, salt concentration in interstitial fluid is maximal. water had flowed out of renal fluid to make it osmotically balanced
  • as fluid flows up, it is flowing into areas that have a lower salt concentration in interstitial fluid
  • outside is less salty than renal fluid
  • salf diffuses out of the renal tube into interstitial fluid passively

now:
- less water from thin descending, less salt from thin ascending, still urea

29
Q

Thick ascending

A
  • active transport of Na+ and Cl-
  • not permeable to water
  • as renal fluid continues to moce up ascending limb, active transport continues to pump salt out
  • gives the interstitial fluid of the medulla its high salt concentration

now:
less water from thin descending, even less salt from thin ascending, STILL urea

30
Q

Distal convoluted tube

A
  • continues to pump NaCl out
  • permeable to water
  • water follows the flow of salts out of the tubule
  • fine tuning the ionic composition of the urine
  • large numbers of active transporters for many different ions
  • adjusts amount reabsorbed based on physiological needs of the individual (ex by hormone regulation)
31
Q

Collecting Duct

A
  • when the renal fluid enters the collecting duct, the composition is very different from the start (proportion of water to solute is very similar, but makeup is very different)
  • major solute is now urea
  • as renal fluid flows down collecting duct, it is concentrated
  • descending into the increasingly high-salt interstitial fluid of the medulla
  • water flows out by osmosis (passive)
  • byt the bottom of the colelcting duct, urine is greatly concentrated with urea as its major solute
  • ability of a mammal to concentrate its urine is determined by the maximum concentration gradient it can establish in the renal medulla
32
Q

Recycling of urea

A
  • as water leaves the collecting duct, some urea also leaks out into the interstitial fluid of medulla
  • adds to osmotic potantial
  • urea diffuses back into loop of henle and is returned to collecting duct
33
Q

Summary of Reabsorption

A
  1. proximal converted tubule –> bulk of reabsorption of solutes by active transport
  2. loop of henle
    - Thin descending limb- removal of water, passive
    - thin ascending - removal of salt, passive
    - thin ascending - removal of salt, active
  3. distal convoluted tubule –> fine tuning ionic composition of solutes based on physiological needs
  4. collecting duct –> removal of water (passive), concentration of urine
34
Q

Renal failure

A
  • loss of kidney function results in retention of salts and water, leading to high blood pressure
  • retention of urea in blood
  • decreasing pH

Dialysis

  • patients blood flows through many small channels made of semipermeable membranes
  • dialysis solution flows on other side of membrane, through which molecules can diffuse
  • concentration of molecules that need to be conserved must be at the same concentration in blood and dialysis fluid
  • concentration of molecules that need to be removed from the blood are zero int eh dialysis fluid
35
Q

Hormones that regulate kidney function

A
  • antidiuretic hormone (ADH)
  • renin-antiotensis-aldosterone system (RAAS)
  • atrial natriuretic peptide (ANP)
36
Q

Blood osmolarity

A
  • the osmolarity of the urine is regulated by nervous and hormonal control
  • osmoreceptors in the hypothalamus monitor blood osmolarity
  • an increase in osmolarity triggers the release of (ADH) from the posterior pituitary (ex after profuse sweating)
  • ADH helps to conserve water by controlling water reabsorption
37
Q

ADH

A
  • triggers cells in the colelcting duct to insert aquaporins in their plasma membrane
  • increase permeability of these membranes to water
  • more water is reabsorbed from the collecting duct fluid into the interstitial space
  • higher the levels of AHD, greater the number of aquaporins
38
Q

ADH regulated by blood pressure

A
  • ADH also responds to signals about blood pressure
  • stretch receptors in wall of aorta and cartoid arteries are activated when blood pressure is high
  • -> inhibit release of ADH
  • -> less water reabsorbed, which decreases blood volume and thus lowers blood pressure
  • if blood pressure falls too low, no longer inhibit ADH release
  • -> more ADH –> more water reabsorption –> increased blood volume –> increased blood pressure
39
Q

dehydration and alcohol

A
  • alcohol inhibits ADH release
  • water is not reabsorbed
  • excessive urination and dehydration
40
Q

Blood pressure decrease and glomular filtration rate

A

(GFR)

  • blood must be supplied to the kidneys at adequate blood pressure in order for glomeruli to filter blood
  • drop in blood pressure near the glomerulul causes the release of renin
  • activates RAAS (renin-angiontensin-aldosterone system)
41
Q

RAAS

A
  • drop in blood pressure triggers release of renin
  • RENIN triggers formatino of angiotensis II (or simply angiotensin)
  • ANGIOTENSIS, raises blood pressure
  • constricts blod vessels at glomerulus
  • constricts peripheral blood vessels all over body
  • stimulates thirst to increase blood volume
  • stimulates adrenal gland to release ALDOSTERONE

ALDOSTERONE

  • stimulates sodium reabsorption form the kidney
  • therby making reabsorption of water more effective
  • thus increases blood volume and pressure
42
Q

Blood Pressure: increase

A
  • atrial natriuretic peptide (ANP) opposes the RAAS

- ANP is released in response to an increase in blood volume and pressure and inhibits the release of renin

43
Q

ANP acts during high blood pressure

A
  • when blood volume is high, heart muscle fibers are overly stretched
  • heart releases a hormone called atrial natriuretic peptide (ANP)
  • ANP decreases the reabsorption of sodium from the kidney
  • less water is absorbed
  • -> more to pass to urine
  • -> blood mlowered
  • -> blood pressure lowered

Biology 102 (15 decks)

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