Excretory Systems Ch. 44

Regulating Water Loss and Solute Concentrations

Ch. 44 & 45 - Digestion & Fluid Balance1. What organism is used by Dr. Carol Beuchat to illustrate

how fluid is regulated and the role played by the urinary tract in maintaining homeostasis? (1st segment)

2. How is a complete digestive system different from an incomplete one? What function does each segment (region) of the digestive system have?

3. Name two enzymes mentioned by Dr. Sokolowski that play a role in the digestive system. How is the diet of a dog different from a cat? What are the nutritional needs for a cat and dog? What is the name of the café mentioned in the video?

4. The final segment discusses the role the kidneys play in maintaining homeostasis. What kind of machine is the patient connected to? **Write the title for each segment and FIVE statements for each segment.

Introductory Questions #71) How is an osmoconformer different from an osmoregulator?2) Name a fish that is able to adjust to salt concentrations

ranging from freshwater to 2,000mosm/L (twice that of sea water).

3) How do marine fishes (hyperosmotic to the water) adjust and balance their water loss?

4) Name the three types of nitrogenous waste products that are released fish, mammals, and reptiles. Which one is most toxic? Which one is a semi-solid form? Which one is made by combining ammonia and carbon dioxide?

5) Name the key excretory structures found in Flatworms (Platyhelminthes), Earthworms (annelids), and Insects (Arthropodds).

6) Name the two distinct regions of the mammalian kidney. Name the three regions of nephron starting from the Bowman’s capsule.

• Nitrogen-containing wastes are toxic by-products of protein and nucleic acid breakdown– Ammonia is poisonous but soluble and easily

disposed of– Urea is less toxic and easy to store and excrete– Some land animals save water by excreting a

virtually dry waste

Animals must dispose of nitrogenous wastes

Water Balance and waste disposal

• Osmoregulation: – management of the body’s water content and solute

composition (hyper, iso, hypo tonic soln’s)• Nitrogenous wastes:

– breakdown products of proteins and nucleic acids; ammonia-very toxic

• Deamination– Ammonia: most aquatic animals, many fish– Urea: mammals, most amphibians, sharks, bony fish (in

liver; combo of NH3 and CO2)– Uric acid: birds, insects, many reptiles, land snails

Water Balance and waste disposal

Osmoregulators• Osmoconformer: no active adjustment of

internal osmolarity (marine animals); isoosmotic to environment

• Osmoregulator: adjust internal osmolarity (freshwater, marine, terrestrial)

• Freshwater fishes (hyperosmotic)- gains water, loses; excretes large amounts of urine salt vs. marine fishes (hypo-osmotic)- loses water, gains salt; drinks large amount of saltwater

Osmoregulators

Excretory Systems• Production of urine by 2 steps:

-Filtration (non-selective)

-Reabsorption (secretion of solutes)

• Protonephridia ~ flatworms (“flame-bulb” systems)• Metanephridia ~ annelids (ciliated funnel system)• Malpighian tubules ~ insects (tubes in digestive tract)• Kidneys ~ vertebrates

Excretory Systems

Kidney Functional Units

• Renal artery/vein: kidney blood flow

• Ureter: urine excretory duct

• Urinary bladder: urine storage

• Urethra: urine elimination tube

• Renal cortex (outer region)

• Renal medulla (inner region)

• Nephron: functional unit of kidney

• Cortical nephrons (cortex; 80%)

• Juxtamedullary nephrons (medulla; 20%)

Nephron Structure• Afferent arteriole: supplies blood to nephron from renal artery• Glomerulus: ball of capillaries• Efferent arteriole: blood from glomerulus• Bowman’s capsule: surrounds glomerulus

• Proximal tubule: secretion & reabsorption• Peritubular capillaries: from efferent arteriole; surround proximal &

distal tubules• Loop of Henle: water & salt balance

• Distal tubule: secretion & reabsorption• Collecting duct: carries filtrate to renal pelvis

Overview of Mammalian Nephron Function

Figure 25.11

Bowman’scapsule

Blood

Proximal tubule

NaClHCO3

–H2O Glucose and

amino acids

Somedrugsand poisons

NH3H+

CORTEX

MEDULLA

FiltrateH2OSalts (NaCl, etc.)

HCO3–

H+

Urea

Glucose

Amino acids

Some drugs

Reabsorption

Active transport

Passive transport

Secretion

(active transport)

Distal tubule

H2OHCO3

–NaCl

K+

H+

Collectingduct

NaCl

NaCl

Urea

H2ONaCl

H2O

Urine (to renal pelvis)

Loop ofHenle

The Human Kidney & Nephron

Kidney regulation: hormones• Antidiuretic hormone (ADH) ~ secretion

increases permeability of distal tubules and collecting ducts to water (H2O back to body); inhibited by alcohol and coffee

• Juxtaglomerular apparatus (JGA) ~ reduced salt intake--->enzyme renin initiates conversion of angiotension (plasma protein) to angiotension II (peptide); increase blood pressure and blood volume by constricting capillaries

• Angiotension II also stimulates adrenal glands to secrete aldosterone; acts on distal tubules to reabsorb more sodium, thereby increasing blood pressure (renin-angiotension-aldosterone system; RAAS)

• Atrial natriuretic factor (ANF) ~ walls of atria; inhibits release of renin, salt reabsorption, and aldosterone release

• Basking in the sun

• Sitting in the shade

• Bathing

• Burrowing or huddling

• Migrating

Behavior often affects body temperature

Figure 25.3

• Torpor is a state of reduced activity and lowered metabolic rate– Hibernation

in cold weather

– Estivation in warm weather

Reducing the metabolic rate saves energy

Figure 25.4

• Land animals gain water by drinking and eating

– They lose water and solutes by evaporation and waste disposal

– Their kidneys, behavior, and waterproof skin conserve water

• Water lost in thermoregulation can cause osmoregulatory problems– Drinking water

is the best way to prevent dehydration during exercise

Sweating can produce serious water loss

Figure 25.6

• Many small invertebrates can dehydrate and become dormant when their environment dries up

Some animals face seasonal dehydration

Figure 25.7

• Each nephron consists of a folded tubule and associated blood vessels– The nephrons

extract a filtrate from the blood

– They refine the filtrate into a much smaller amount of urine

Figure 25.9D

Bowman’s capsule

Arteriolefrom renalartery

Arteriolefrom glomerulus

Branch ofrenal vein

Glomerulus

Capillaries

Fromanothernephron

Collectingduct

1 Proximal tubule

2 Loop of Henlewith capillarynetwork

3 Distaltubule

D. DETAILED STRUCTURE OF A NEPHRON

• Filtration– Blood pressure forces water and many solutes

from the blood into the nephron

• Reabsorption– The nephron tubule reclaims valuable solutes

The key functions of the excretory system are filtration, reabsorption, secretion,

and excretion

• Secretion

– The nephron removes substances and adds them to the filtrate

• The product of all of the above processes is urine, which is excreted

Figure 25.10

Nephron tubuleFILTRATION

H2O, other small molecules

REABSORPTIONSECRETION

EXCRETION

Capillary

Urine

• The proximal tubule reabsorbs– nutrients– salts– water

• Antidiuretic hormone and other hormones regulate the amount of salt and water the kidneys excrete

From blood to filtrate to urine: A closer look

• Controlled secretion of H+ and reabsorption of bicarbonate ions help regulate blood pH

• Secretion also includes the active transport of drugs and poisons

• Reabsorption of salts and urea promote the osmotic reabsorption of water

• A dialysis machine compensates for kidney failure– It performs the function of the nephrons by

removing wastes from the blood and maintaining its solute concentration

Kidney dialysis can be a lifesaver

Line from arteryto apparatus

Pump

Line fromapparatusto vein

Fresh dialyzingsolution

Dialyzingsolution

Used dialyzingsolution (with urea and excess salts)

Tubing made of aselectively permeable

membrane

Figure 25.12

• It assists the kidneys by– making urea from ammonia– breaking down toxic chemicals

The liver is vital in homeostasis

• Blood from the intestines flows through the liver before distribution to the rest of the body – This allows the

liver to adjust the blood’s chemical content

Figure 25.13

Inferiorvena cava

Hepatic vein

Liver

Hepaticportal vessel

Intestines