Chapter 32

Osmoregulation and Excretion

Kidney Vocalafferent arteriolealdosteroneammoniaantidiuretic hormone (ADH)Bowman’s capsule collecting ductcortical nephronscountercurrent multiplier systemdistal tubuleefferent arterioleexcretionfiltratefiltrationglomerulusjuxtamedullary nephronsloop of Henlenephronosmoconformerosmolarityosmoregulationosmoregulatorproximal tubule

renal arteryrenal cortexrenal medullarenal pelvisrenal veinsecretionselective reabsorptionultrafiltrationureaureterurethrauric acidurinary bladder

Overview/Background• Osmolarity vs Tonicity• both compare solute concentrations separated by a

membrane• osmolarity includes total solutes; both permeable and

impermeable• tonicity just includes permeable solutes• ex: a solution can be both hyperosmotic and isotonic

• Osmoregulation• Regulate solute concentrations• balance the gain and loss of water• controlled movement of solutes

• Excretion• Gets rid of metabolic wastes

THE INTERNAL ENVIRONMENT

WATER GAIN (milliliters)

WATER LOSS (milliliters)

by ingesting solids by ingesting liquids

by metabolism

in urine in feces

by evaporation

6.0 0.0

54.0 60.0

850 1,400

350 2,600

13.5 2.6

43.9 60.0

1,500 200 900

2,600

KANGAROO RAT HUMAN

Homeostasis - maintaining internal conditions, i.e. water concentration, temperature, pH, glucose level.

Proteins Nucleic acids

Amino acids Nitrogenous bases

–NH2 Amino groups

Most aquatic animals, including most bony fishes

Mammals, most amphibians, sharks, some bony fishes

Many reptiles (including

birds), insects, land snails

Ammonia Urea Uric acid

NH3NH2

NH2

O C

C

CN

CO

N

H H

C O

NC

HN

O

H

Nitrogenous Wastes

• Where do they come from?• products of proteins and

nucleic acids• What’s wrong with them?• toxic on their own

• Insects use:• Malphigian tubules

Nitrogenous waste type correlated with evolutionary history and habitat

Mammals: Functional Unit of the Excretory System• Nephrons and associated blood vessels• Mammals: paired kidneys• water balance and salt regulation

• Each kidney supplied by:• renal artery

• Drained by:• renal vein

Mammals: Functional Unit of the Excretory SystemBlood in the renal vein (i.e. after the kidney) will have:

▪ Less urea ▪ Less water and solutes / ions ▪ Less glucose and oxygen ▪ More carbon dioxide

Filtration of the Blood• Blood pressure forces fluid from the blood in the glomerulus

--> Bowman’s capsule• Nonselective filtration (=“ultrafiltration”)• The filtrate mirrors the concentration of various solutes in

the blood plasma

From Blood Filtrate to Urine: A Closer Look

s

sg

From Blood Filtrate to Urine: A Closer Look

• Role o/t descending limb of the Loop of Henle:• Reabsorption of

water• the longer the loop,

the more water is reabsorbed

• Countercurrent system:• maintains high salt

concentration in kidney interior

From Blood Filtrate to Urine: A Closer Look

• Role o/t ascending limb of the loop of Henle:• Salt diffuses out of the

permeable tubule into the interstitial fluid

• not permeable to water• The distal tubule• regulates K+ and NaCl

From Blood Filtrate to Urine: A Closer Look

• Role o/t collecting duct• Carries the filtrate through

the medulla to the renal pelvis

• permeable to water• not permeable to salt• permeable to urea

• helps maintain countercurrent gradient

REGULATION OF KIDNEY

FUNCTION

• Osmolarity of the urine is regulated by • nervous and hormonal control

• water and salt reabsorption in the kidneys

• Antidiuretic hormone (ADH)• Increases water reabsorption

• in the distal tubules and• collecting ducts of the

kidney