CHAPTER 25 Control 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 RespirationCO2 + 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 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)

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 formation Thus 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 Renal medulla Renal cortex 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 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 Glomerulus Bowman’s capsule Loop of Henle with capillary network Proximal tubule Distal tubule Collect ing duct

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 FILTRATION REABSORPTION SECRETION EXCRETION H2O, other small molecules Nephron tubule Capillary Urine

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

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 wastes may lead to Dialysis( artificial kidney) Kidney transplant