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