UNIT O:EXCRETORY SYSTEM

Chapter 25

STANDARDS

CORE:

I can explain the overall function of the urinary system

I can outline the major organs and their function in the urinary system

I can explain how urine production contributes to homeostasis

NO ADVANCED!

EXCRETORY SYSTEM

AKA: the urinary system (how you make pee!)

HANK: https://www.youtube.com/watch?v=WtrYotjYvtU

TWO FUNCTIONS OF THE EXCRETORY SYSTEM:

Osmoregulation: the control of the gain and loss of water and dissolved solutes

Excretion: the disposal of metabolic wastes

OSMOREGULATION

Compared to our aquatic relatives, land animals need to be very aware of our water intake/output

Land animals

Gain water by drinking and eating

Lose water by evaporation and waste disposal

Their kidneys, behavioral adaptations, and waterproof skin help to conserve water (VERY important!)

CONNECTION

25.5 Do we need to drink eight glasses of water each day? Water lost in thermoregulation can cause osmoregulatory problems

Is it true you can “drown” from drinking too much water??

YES!! BUT…its very very rare – you’d need to drink many many litres of water in a very short amount of time.

Its called HYPONATREMIA: too much water in our blood, dilutes the salts/solutes to the point where the blood becomes hypotonic to the body’s cell causing them to swell (NOT good – especially in the brain!!) can be fatal!!

Thirst is usually an adequate guide to water intake – usually by the time you’re thirsty you are already dehydrated!

Figure 25.5

25.6 Animals must dispose of nitrogenous wastes Nitrogenous wastes are the toxic byproducts from the breakdown of

protein

Ammonia is poisonous but soluble and is easily disposed of by animals

Urea is less toxic and easier to store

Some land animals save water by excreting uric acid - virtually dry waste

Urea and uric acid take energy to produce Proteins Nucleic acids

Amino acids Nitrogenous bases

— NH2

Amino groups

Most aquatic animals,

including most fishes

Mammals, amphibians,

sharks, some bony

fishes

Birds and many other

reptiles, insects, land

snails

NH3 O CNH2

NH2

O

CC

CO

OC

C

NH

NH

HN

HN

Uric acidUreaAmmonia

Figure 25.6

25.7 The liver has 6 functions:

1) Produces urea from ammonia

2) Detoxification: converts alcohol fats (which are stored in the liver leads to a fatty liver – NOT good!)

3) Produces bile: emulsifier of fats, stored in the gall bladder

4) Produces blood plasma proteins and lipoproteins (EX. Albumin- regulating osmotic pressure; fibrinogen/prothrombin – clotting)

5) Adjusts the blood sugar level: glucose glycogen based on pancreatic hormones (insulin & glucagon)

6) Removes dead red blood cells from the blood, send the hemoglobin to the bone marrow and the rest is converted into bile

The liver has a strategic location in the body between the intestines and the heart

25.8 Alcohol consumption can damage the liver Liver function can be impaired by excessive alcohol consumption (converts

alcohol fats creating a fatty liver) or hepatitis (inflammation of parts of liver can lead to liver chirrosis: parts or all of liver stop working)

Liver

Intestines

Kidneys

Hepatic

Portal

vein

Figure 25.7

25.9 The excretory system plays several major roles in homeostasis The excretory system expels wastes and regulates water and ion balance

Nephrons, the functional units of the kidneys extract a filtrate from the blood and refine it to urine

Urine leaves the kidneys via ureters is stored in the urinary bladder, and is expelled through the urethra

Anatomy of the human excretory system

Aorta

Inferior

vena cava

Renal artery and vein

Ureter

Urinary bladder

Urethra

A The excretory system

Kidney

Renal cortex

Renal medulla

Renal pelvis

Ureter

B The kidney

Bowman’s

capsule

C Orientation of a nephron within the kidney

Renal artery

Renal vein

Nephron

tubule

Collecting

duct

To

renal

pelvis

Renal cortex

Renal medulla

Glomerulus1 Proximal tubule

3 Distal

tubule

Capillaries

From

another

nephron

Collecting

duct

Bowman’s capsule

Arteriole

from renal

artery

Arteriole

from

glomerulus

Branch of

renal vein

2 Loop of

Henle with

capillary

network

D Detailed structure of a nephronFigure 25.9A–D

25.10 Overview: The key processes of the excretory system are filtration, reabsorption, secretion, and excretion In filtration blood pressure forces water and many small solutes into the

nephron (occurs in Bowmen’s Capsule in the glomerulus)

In reabsorption valuable solutes are reclaimed from the filtrate (occurs through the rest of the nephron: in the PCT, LoH, DCT & CD)

In secretion excess H+

and toxins are added to the filtrate (occurs in PCT & DCT)

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

H2O, other small molecules Urine

ExcretionSecretionReabsorptionFiltration

CapillaryInterstitial fluid

Nephron tubule

25.11 From blood to filtrate to urine: A closer look Nutrients, salt, and water are reabsorbed from the proximal and distal

tubules

Blood pH is regulated by the secretion of H+ and reabsorption of HCO3–

There is a network of blood capillaries (vasa recta) that are located over the Loop of Henle which reabsorb many nutrients and salts

High NaCl concentration in the medulla promotes reabsorption of water in the Loop of Henle

LOOP OF HENLE DETAILS Descending loop is only permeable to water (osmosis)

Ascending loop in only permeable to salt (actively pumped)

Best to think of it backwards with ascending first (pump out salt) and then descending (water follows passively by osmosis)

Overview: reabsorption and secretion in a nephron

Blood

Bowman’s

capsule

Proximal tubule Distal tubule

NaCI –HCO3

Nutrients H2O

Some

drugs

and poisons

+H

Cortex

NaCI –HCO3

H2O

+H+ K

Collecting

duct

Loop of

HenleNaCI

NaCI

NaCI

Urea

H2O

H2O

Urine (to renal pelvis)

Medulla

Filtrate composition

H2O

NaCI

HCO3

H

Urea

Glucose

Amino acids

Some drugs

+–

Reabsorption

Secretion

Figure 25.11

Collecting Duct: reabsorbs water under hormonal control; regulates how concentrated the urine in response to blood osmolarity

HORMONE:

Antidiuretic hormone (ADH): regulates the amount of water the kidneys excrete by controlling the # of aquaporins in the collecting duct

ADH production is inhibited by alcohol consumption

CONNECTION

25.12 Kidney dialysis can be a lifesaver Compensating for kidney failure

A dialysis machine removes wastes from the blood and maintains its solute concentration

Line from artery

to apparatus

Dialyzing

solution

Fresh dialyzing

solutionUsed dialyzing solution

(with urea and excess ions)

Tubing made

of a

selectively

permeable

membrane

Pump

Line from

apparatus

to vein

Figure 25.12