Homeostasis and Excretion

• Homeostasis - stable internal environment maintained.

• Done in three ways.• 1Thermoregulation - maintenance of

specific body temperature.• 2Excretion - get rid of wastes.• 3Osmoregulation - maintenance of

water and solute balance.

http://www.umanitoba.ca/faculties/afs/soil_science/MSSS/links/Images/cartoons/osmoregulation.jpg

• Warm-blooded animals (endotherms) – regulators; regulate internal body temperature (mammals).

• Conformers - cold-blooded animals (ectotherms); do not have constant internal temperature (lizards) - compensate for temperature through behavior (sit in sun if cold).

• Skin of humans protects body from microbial invasion and from environmental stresses (wind).

• Melanocytes produce melanin - protects body from UV light.

• Skin receives stimuli (pressure, temperature) - excretes water and salts from body.

http://www.loc.gov/rr/scitech/mysteries/images/hair-melanin.jpg

• Mammals sweat or pant to release heat.

• Sweat glands secrete mixture of water, dissolved salts, and urea via sweat pores.

• As sweat evaporates - skin cooled by absorption of heat that occurs during evaporation.

http://www.homestead.com/doctorderm/files/SkinStructure.gif

• Sweating involuntary reaction.• Panting also cools through

evaporative heat loss.

http://www.kateconnick.com/postcards/bcpant.jpg

• Warm up - mammal can increase metabolic rate, insulate itself from environment.

• Animals in cold environments have large size, round shapes that reduce surface area presented to cold.

• Fat in hypodermis insulates body.

• Hair or fur traps, retains warm air at body’s surface.

• Hormones (epinephrine) can increase metabolic rate - increase heat production.

• Thyroid hormone can increase long-term metabolic rate to increase metabolic heat in cold environment.

• Muscles generate heat by contracting rapidly (shivering).

http://www.dpcweb.com/images/medicalconditions/thyroid/thyroid%20comp.jpg

• Vasoconstriction (constriction of blood vessels) conserves heat in dermis - moves blood away from cooling atmosphere.

• Dilation (vasodilation) of blood vessels releases heat.

http://www.venomsupplies.com/exoticconference/vasodilitation.jpg

• Most mammals have layer of fur which traps and conserves heat.

• Some - torpor (decrease in metabolic rate) in winter to conserve energy.

http://www.canr.uconn.edu/paine/afrecol/images/kara303.jpg

• Heart rate, metabolism, respiration rate decrease.

• Hibernation - intense torpor during which animal remains dormant over period of weeks or months with body temperature maintained below normal.

http://whyfiles.org/187hibernate/images/squirrel_ball_big.gif

• Body temperature in mammals is controlled by hypothalamus - tries to adjust core body temperature to set point.

• Uses mechanisms to maintain temperature (dilation, constriction of blood vessels, shivering, sweating)

http://www.worsleyschool.net/science/files/hormones/hypothalamus.gif

• Temperature of hypothalamus determines body temperature.

• Fevers - response to infection - alters set-point to higher level than normal to try and slow replication of microorganism that infected individual.

Excretion• Cells require water and specific

concentrations of salts.• Most organisms have salt

concentration equal ocean.• Cells must regulate salt

concentration in order for bodies to function.

• Cells produce nitrogenous waste - must be removed.

http://www.theevidence.org.uk/library/science3_3.jpg

• Excretory system responsible for balance of water and salt and removal of nitrogenous wastes.

• Invertebrate excretion differs from vertebrate.

• Simple organisms (sponges) - cells in direct contact with external aqueous environment (water).

http://www.cartage.org.lb/en/themes/Sciences/Zoology/Biologicaldiverstity/AnimalsI/sponge_2.gif

• Wastes that are water-soluble (carbon dioxide, ammonia) can exit through simple diffusion of cell membrane.

• Some protozoa (paramecium) - contractile vacuole that excretes water via active transport.

• Excess water collected, pumped out of cell.

http://protist.i.hosei.ac.jp/pdb/Images/Ciliophora/Dileptus/gabonensis.jpg

• Allows cell to maintain volume and pressure.

• Flatworms (planaria) live in freshwater - tubules that end in specialized excretory flame cells.

• Cilia projecting from flame cells drive water out of excretory pores - remove excess water from body.

• Annelids (earthworms) 2 pairs of nephridia in each body segment -excrete water, mineral salts, nitrogenous wastes.

• Arthropods excrete nitrogenous wastes in solid uric acid crystals - allows arthropods to conserve water.

• Minerals, uric acid accumulate in Malphigian tubules - transported to intestine to be expelled with solid waste.

• Ammonia highly toxic in significant levels in tissues, animals convert it to urea or uric acid - excrete it from body.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 44.13

• Birds excrete uric acid - semiliquid material.

• Vertebrates - different system for excretion.

• Primary organ – kidney - forms urine that passes to urinary bladder through ureter.

http://www.bostwicklaboratories.com/patientservices/Hematuria%20Images/Image%209B.jpg

Uric acid crystal

• From bladder, urine passes to exterior of body via urethra.

• Kidney filters blood - remove harmful metabolic waste (urea) while retaining cells, proteins, salts, glucose, other essential factors in blood.

• Also regulate volume, salt content of extracellular fluids, like blood.

http://galileo.phys.virginia.edu/classes/304/kidney.gif

• Kidneys filter blood, secrete material into filtrate, reabsorb material from filtrate to form urine.

• Excess amino acids present, or during period of starvation, body will break down amino acids from proteins, use them for energy (via Krebs cycle).

• Nitrogen removed from amino acid, released to ammonia - toxic.

• Humans - liver converts ammonia to urea - less toxic than ammonia - kidneys remove urea from bloodstream.

http://www.biologymad.com/Kidneys/liver1.gif

• Fish in salty environments have to deal with difference in salt concentration externally, internally.

• Prevent water loss - fish swallow water, actively transport salt ions from gills or kidneys.

• End up producing less urine to save water.

• Cartilaginous fish (sharks) accumulate urea in tissues to very high levels - same osmotic potential as seawater.

• Keep salt levels same as external environment - prevents water loss.

http://138.192.68.68/bio/Courses/biochem2/AminoAcids/AminoAcidResources/UreaCycle.gif

• Amphibians, fresh water fish more salt in extracellular fluids than environment - tendency of water to flow into body (instead of out).

• Secrete large amounts of very dilute urine to remove excess water from bodies.

• Terrestrial animals - loss of water through evaporation of body fluids to environment.

• Reptiles, birds deal - excretion of uric acid as solid - do not lose water in urine.

• Mammals - ability to conserve water by making water more concentrated than extracellular fluids.

http://mcdb.colorado.edu/courses/3280/images/kidney/nephron.gif

The kidney

• Basic unit of kidney that performs functions - small tubelike structure –nephron - filters blood, modifies filtrate to produce urine.

• Blood filtered enters nephron in ball-shaped cluster of capillaries - glomerulus.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

• Pressure of blood in glomerulus squeezes liquid part of blood through filtering structure.

• Blood cells - too large to pass through; most proteins retained in blood because of size and charge.

• Other smaller molecules (salts, amino acids, glucose, water, urea) pass easily into filtrate.

http://www.biotech.um.edu.mt/home_pages/chris/Renal/Renalhtml/glomerulus.jpg

• Filtrate leaves blood, enters structure around glomerulus - Bowman’s capsule.

• Starting end of nephron.• From Bowman’s capsule filtrate

moves down nephron tubule, becoming increasingly modified.

http://w3.ouhsc.edu/histology/Glass%20slides/35_08.jpg

• Passes through proximal convoluted tubule, loop of Henle, distal tubule, collecting ducts.

• Proximal convoluted tubule, active transport pumps glucose, amino acids, sodium, proteins out of filtrate.

• Water follows through osmosis, concentrating urine, reducing volume of filtrate.

http://library.thinkquest.org/22016/excretion/neph2.gif

• Reabsorbed materials reenter blood in capillaries that surround nephron.

• Conserves necessary materials that may be wasted in urine; concentrates urinary filtrate to conserve water.

• From proximal tubule, filtrate passes to loop of Henle.

http://www.ivy-rose.co.uk/Topics/Urinary/Loop_of_Henle_cIvyRose.jpg

• Glomerulus and Bowman’s capsule both located in outer region of kidney (cortex), loop of Henle dips into inner kidney region (medulla).

• Medulla has high concentration of sodium. (extracellular)

http://www.uic.edu/classes/bios/bios100/lecturesf04am/kidney01a.jpg

• As filtrate passes down loop of Henle, water drawn out of filtrate due to osmosis, passing from low ion concentration in filtrate to high ion concentration of extracellular fluid in medulla.

• When filtrate passes back up loop of Henle, sodium is pumped out into medulla.

http://www.ivy-rose.co.uk/Topics/Urinary/Kidney_cIvyRose.jpg

• Help further reduce volume of urinary filtrate by drawing water along with sodium; helps to preserve high concentration of sodium in medulla.

• After passing through distal tubule, filtrate must pass through collecting duct before passing out to ureter and urinary bladder.

http://www.nexavar.com/img/kidney_nephron.gif

• Collecting duct passes back down through high ion concentration in medulla.

• To make concentrated or dilute urine, vasopressin (antidiuretic hormone or ADH) regulates how permeable walls of collecting duct are.

• Determines how much salt actually secreted, how much is retained.

• Person needs water - secrete vasopressin, excrete more concentrated urine.

• Secreted by posterior pituitary gland when stretch sensors in arteries detect drop in blood pressure.

• Vasopressin acts on walls of collecting ducts - make them more permeable to water.

http://www.rcsed.ac.uk/journal/svol3_2/009.gif

• Fluid of medulla very concentrated with ions - water will flow out of collecting ducts if walls of collecting duct are water permeable and allow osmosis.

• Saves water, creates concentrated urine.

• No vasopressin present - walls of collecting ducts do not permit osmosis, urine will remain dilute.

http://www.uic.edu/classes/bios/bios100/lecturesf04am/adh02a.jpg

• Regulates urine - aldosterone (steroid)• Secreted in response to low

extracellular sodium - distal tubule increases resorption of sodium from urinary filtrate.

• Water removed from filtrate by osmosis, reducing urine volume, increasing volume of extracellular fluids - increases blood pressure.

http://www.colorado.edu/kines/Class/IPHY3430-200/image/angiotensin.jpg

• Secretion of aldosterone helps to conserve water loss.