CHAPTER 25 Control of the Internal Environment

1. CHAPTER 25Control of the Internal Environment

2. 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

3. Excretion • Function: Maintain homeostasis • *Nitrogenous wastes: 1. ammonia (most toxic) 2. urea 3.uric acid (least toxic)

4. 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 exhale 2. 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)

5. 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

6. 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 formation Thus kidneys play a major role in maintaining homeostasis

7. 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

8. Closer look at Kidney • 3 parts 1. cortex-outer portion 2. medulla-middle layer 3. renal pelvis- inner area Renalmedulla Renal pelvis Ureter Renalcortex

9. Nephrons • Microscopic functionalunit 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

10. Overview: The key functions of the excretory system are filtration, reabsorption, secretion, and excretion • Filtration • Blood pressure forces water and many solutes from the blood (glomerulus) into the nephron (Bowman's capsule) filtrate Reabsorption • The nephron tubule reclaims valuable solutes Bowman’s capsule Proximal tubule Glomerulus Distaltubule Loop of Henlewith capillary network Collectingduct

11. Overview: The key functions of the excretory system are filtration, reabsorption, secretion, and excretion • Secretion • The nephron removes substances and adds them to the filtrate • The product of all of the above processes is urine, which is excreted Nephron tubule FILTRATION REABSORPTION EXCRETION SECRETION H2O, other small molecules Urine Capillary

12. From blood to filtrate to urine: A closer look • The proximal tubule reabsorbs • nutrients • salts • water • 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

13. 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

14. Kidney malfunction • Kidney disease: various conditions in which kidneys are unable to function effectively in excreting nitrogenous wastes may lead to Dialysis( artificial kidney) Kidney transplant