Osmoregulation and excretion

Goal

1. To understand how the kidneys allow osmoregulation and excretion of wastes

Outline

Introduction

osmoregulation: an example of homeostasis

osmoregulation & excretion: both take place in kidney

Osmoregulation

in marine environments

osmoconformers: blood has same osmolarity as environment

osmoregulation:

fish: blood more dilute than environment -- drink seawater, excrete salts

sharks: blood more concentrated than environment -- don't drink seawater, excrete dilute urine

 

in freshwater environments

all osmoregulate

fish: don't drink, eat food with solutes, actively transport salts in via gills, excrete dilute urine

in terrestrial environments

water inputs: food, drink, metabolism

outputs: evaporation, feces, urine, etc.

need to conserve water, but need to excrete nitrogenous wastes

ammonia (most aquatic orgs) -- highly toxic, must get rid of right away at low conc.

urea (mammals, adult amphibians, sharks) -- less toxic, can concentrate

uric acid (birds, insects, some reptiles) -- very low solubility (water efficient), requires lots of energy to make

Osmoregulation and excretion in humans

our kidneys must: osmoregulate, excrete urea and conserve water

structure

click here to see the structure of the human kidney

function

3 processes:

filtration: removal of substances from blood, creating a filtrate

water, salts, glucose, vitamins, urea, etc.

secretion: addition of substances from blood to filtrate

poisons, drugs

pH balance

reabsorption: putting some stuff in the filtrate back into the blood

water, salts, glucose, vitamins, etc.

the process:

glomerulus: filtration

distal and proximal tubules: secretion and reabsorption

loop of Henle and collecting duct: water conservation

control of osmoregulation

ADH: responds to changes in blood osmolarity -- responds by altering urine osmolarity/volume

 

Vocabulary

click here to go to osmoregulation vocabulary