AP BIO/MEMIS

The Excretory System

Why excretion & osmoregulation?

Animal Cells can’t survive a net water gain/loss

Need to get rid of nitrogenous waste (poison)

Intracellular Waste

What waste products? what do we digest our food into…

carbohydrates = CHO CO2 + H2O

lipids = CHO CO2 + H2O

proteins = CHON CO2 + H2O + N

nucleic acids = CHOPN CO2 + H2O + P + N

|

| ||H

HN C–OH

O

R

H–C–

Nitrogenous waste disposal

Ammonia (NH3) very toxic

carcinogenic very soluble

easily crosses membranes must dilute it & get rid of it… fast!

How you get rid of nitrogenous wastes depends on who you are (evolutionary relationship) where you live (habitat)

aquatic terrestrial terrestrial egg layer

Nitrogen waste

Aquatic organisms can afford to lose water Ammonia: most toxic

Terrestrial need to conserve

water Urea: less toxic

Terrestrial egglayers

need to conserve water need to protect

embryo in egg uric acid: least toxic

OsmoregulationWater balance

freshwaterhypotonicwater flows into cells & salt loss

saltwaterhypertonicwater loss from cells

landdry environmentneed to conserve watermay also need to conserve salt

Why do all land animals have to conserve water? always lose water (breathing &

waste) may lose life while searching for

water

hypertonic

hypotonic

Freshwater animalsWater removal & nitrogen waste disposal• remove surplus water

use surplus water to dilute ammonia & excrete it

need to excrete a lot of water so dilute ammonia & excrete it as very dilute urine

also diffuse ammonia continuously through gills or through any moist membrane

• overcome loss of salts reabsorb in kidneys or active transport across

gills

Land animals• Nitrogen waste disposal on land

need to conserve water must process ammonia so less toxic

urea = larger molecule = less soluble = less toxic- 2NH2 + CO2 = urea- produced in liver

kidney filter solutes out of blood reabsorb H2O (+ any useful solutes) excrete waste

- urine = urea, salts, excess sugar & H2O - urine is very concentrated- concentrated NH3 would be too toxic

Ureacosts energyto synthesize,but it’s worth it!

mammals

Egg-laying land animals

• Nitrogen waste disposal in eggo no place to get rid of waste in eggo need even less soluble molecule

- uric acid = BIGGER = less soluble = less toxic

- birds, reptiles, insects

Various Excretory Mechanisms – for osmoregulation and removal of wastes

Contractile Vacuolesparamecium & amoebasvacuole fills with water, merges with plasma membrane and releases water to environment

Flame Cells

In Platyhelminthes, ie, planaria

Spread out along branched tube system

Body fluids filtered across flame cells

Cilia move fluids through system

Wastes excreted from tube system through pores

Flame Cells

Nephridia

Occur in pairs in each section of annelids

Consist of nephrostome (ciliated opening), collecting tubule and excretory pore

Body fluids selectively filtered as they pass through tube, materials to be retained, secreted back to body fluids, concentrated wastes excreted through tube at far end

Nephridia

Malphigian Tubules

Tubes attached to midsection of digestive tract

Collect body fluids from hemolymph

Fluids, containing both wastes and materials to be retained pass to midgut

Pass to hindgut, materials to be retained pass back through walls of digestive tract, wastes excreted through anus

Malphigian

Vertebrate kidney

Millions of individual filtering tubes called nephrons

Produce urine that passes through ureter to bladder for temp storage, excreted through urethra

Transformation of Blood Filtrate to Urine

1. In the proximal tubule, secretion and reabsorption changes the volume and composition of the filtrate. The pH of body fluids is controlled, and bicarbonate is absorbed, as are NaCl and water.

2. In the descending loop of Henle, reabsorption of water continues.

3. In the ascending loop of Henle, the filtrate loses salt without giving up water and becomes more dilute.

Transformation of Blood Filtrate to Urine

4. In the distal tubule, K+ , NaCl levels are regulated, as is filtrate pH.

5. The collecting duct carries the filtrate through the medulla to the renal pelvis, and the filtrate becomes more concentrated by the movement of salt.

Urea

Urea 2NH2 + CO2 = urea combined in liver Requires energy to produceCarried to kidneys bycirculatory system

NH

H

N

H

H

C O

Mammalian System- filtration body fluids (blood) collected water & soluble material removed

- reabsorption reabsorb needed substances back to blood

- secretion pump out unwanted substances to urine

- excretion remove excess substances &toxins from body

Nephron: Filtration

Filtered outH2O glucose salts / ions urea

Not filtered out cells proteins

Nephron: Re-absorption

Proximal tubulereabsorbed NaCl active transport Na+Cl- follows by diffusionH2O glucoseHCO3-(bicarbonate - buffer for blood pH)

Nephron: Re-absorption

Loop of Henle descending limb

many aquaporins in cell membranes high permeability

to H2O low permeability

to salt reabsorbed

H2O

Nephron: Re-absorption

Loop of Henle - ascending limb

low permeability to H2O

- Cl- pump - Na+ follows by

diffusion reabsorbed

salts maintains osmotic gradient

Nephron: Re-absorption

Distal tubule reabsorbed

saltsH2O HCO3-

(bicarbonate)

Nephron: Reabsorption & Excretion

Collecting duct reabsorbed

H2Oexcretion

urea passed through to bladder

Osmotic control in nephron

How is all this re-absorption achieved?

tight osmotic control to reduce the energy cost of excretion

as much as possible, use diffusion instead of active transport

Summary

Not filtered out (remain in blood) cells ◆ proteins Reabsorbed: active transport Na+ ◆ amino acids Cl- ◆ glucose Reabsorbed: diffusionNa+ ◆ Cl- Reabsorbed: osmosis H2O Excretedurea ◆ H2O any excess solutes

Maintaining Water Balance

High Solutes

In brain

ADH

Maintaining Water Balance

High blood osmolarity level-too many solutes in blood

- dehydration, salty foods - release ADH (anti-diuretic hormone)

from pituitary (in brain)- increases permeability of collecting duct &reabsorption of water in kidneys- increase water absorption back into blood- decrease urination- also stimulates thirst = drink more

Low solutes

renin activatesangiotensinogen

angiotensin triggersaldosterone

aldosteroneincreases absorptionof NaCl & H2O in kidney

Maintaining Water Balance

Low blood osmolarity level or low blood pressure- JGA releases renin in kidney- renin converts angiotensinogen to angiotensin

- angiotensin causes arterioles to constrict- increase blood pressure- angiotensin triggers release of aldosterone from adrenal gland- increases reabsorption of NaCl & H2O in kidneys- puts more water & salts back in blood