CHAPTER 25Control of the Internal

Environment

internal homeostatic mechanisms

Thermoregulation maintains the body temperature within a tolerable range

Osmoregulation controls the gain and loss of water and dissolved solutes

Excretion is the disposal of metabolic wastes

Excretion

Function: Maintain homeostasis

*Nitrogenous wastes:

1. ammonia (most toxic)

2. urea

3.uric acid (least toxic)

Metabolic activity

Wastes

Respiration CO2 + Water

Dehydration Synthesis

Water

Certain metabolic processes

Mineral salts

Protein metabolism

Nitrogenous wastes *

Human Excretion

Must remove cellular metabolic wastes because at high concentration they are toxic.

Organs of excretion:1. Lungs:

a. Carbon dioxide and water from aerobic cellular respiration diffuse from blood into lungs. Excreted when you exhale2. Skin:

a. sweat glands- water, salts, & some urea diffuse from the blood into sweat glands & are subsequently excreted as perspiration

b. major function of skin is to excrete excess heat (help maintain body temperature)

Human Excretion

Organs of excretion:

3. Liver:

a. breakdown of red blood cells excreted in bile

b. detoxification of blood (removal of harmful substances)

c. urea formation -> nitrogenous wastes are made of ammonia & carbon dioxide

~ Urea is formed by process called deamination

Human Excretion

Organs of excretion:4. Kidney: main excretory organ & main organ of urinary system

a. located just above waist behind stomach

b. main function~ filter blood to expel wastes , regulate salt & water balance & maintain blood pH

c. urine formationThus kidneys play a major role in

maintaining homeostasis

Urinary sytem

Urine pathway:

Kidney->Ureter->Urinary bladder->Urethra

Ureters: Tubes that carry urine from kidneys to urinary bladder

Urinary bladder: smooth muscle bag that stores urine

Urethra: urine passes out of the body through this tube

Kidney

Ureter

Bladder

Urethra

Closer look at Kidney

3 parts

1. cortex-outer portion

2. medulla-middle layer

3. renal pelvis- inner area

Renalmedulla

Renalcortex

Renal pelvis

Ureter

Nephrons

Microscopic functional unit of kidney (approx. 1million per kidney)

Each nephron consists of a folded tubule and associated blood vessels extract a filtrate from the

blood refine the filtrate into a

much smaller amount of urine

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

and excretionFiltration

Blood pressure forces water and many solutes from the blood (glomerulus) into the nephron (Bowman's capsule) filtrate

ReabsorptionThe nephron tubule

reclaims valuable solutes

Glomerulus

Bowman’s capsule

Loop of Henlewith capillarynetwork

Proximal tubule

Distaltubule

Collectingduct

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

and excretionSecretion

The nephron removes substances and adds them to the filtrate

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

FILTRATION REABSORPTIONSECRETION EXCRETION

H2O, other small molecules

Nephron tubule

Capillary

Urine

From blood to filtrate to urine: A closer look

The proximal tubule reabsorbsnutrientssaltswater

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

~ How do caffeine and ethyl alcohol effect urine output?

Diuretic chemicals that inhibit antidiuretic hormone

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

Kidney malfunction

Kidney disease:various conditions in which kidneys are unable to function effectively in excreting nitrogenous wastesmay lead to

Dialysis( artificial kidney)

Kidney transplant