Excretory System An organism’s way of breaking down nitrogenous wastes When proteins are broken down, they form ammonia Birds and reptiles convert ammonia to uric acid and mammals convert it to urea Malpighian tubules are found in arthropods Nephridia are found in earthworms Flame cells are found in flatworms

Human Excretory System Kidney regulate excretion Kidneys are made up of nephrons Areas of the nephron Renal cortex Bowman’s capsule Proximal convoluted tubule Collecting duct Renal Medulla Loop of Henle Distal convoluted tubule

Cortical nephron Fibrous capsule Renal cortex Collecting duct Renal medulla Renal cortex Proximal convoluted tubule Renal pelvis Glomerulus Ureter Juxtamedullary nephron Distal convoluted tubule Loop of Henle Renal medulla (a) Figure 15.3a

Flow of blood through a nephron Blood enters at the Bowman’s capsule The renal artery leads to the kidney and branches into arterioles then into a ball of capillaries called the glomerulus Blood is filtered and plasma passes from the capillaries into the Bowman’s capsule – it is now called a filtrate

Path of the filtrate Passes through the B. capsule, through the proximal convoluted tubule, then the loop of Henle, then the distal tubule, and finally the collecting duct. As it travels, it is modified to form urine. Then the urine travels through ureters to the bladder, to the urethra

Cortical radiate artery Proximal convoluted tubule (PCT) Peritubular capillaries Glomerular capillaries Distal convoluted tubule (DCT) Glomerular (Bowman’s) capsule Efferent arteriole Afferent arteriole Cells of the juxtaglomerular apparatus Cortical radiate artery Arcuate artery Arcuate vein Cortical radiate vein Collecting duct Loop of Henle (b) Figure 15.3b

How urine is made Filtration – small substances such as ions, water, nutrients, salts pass from the glomerulus to the Bowman’s capsule, proteins and blood cells are too big Reabsorption – as the filtrate moves through the proximal convoluted tubule, the small substances are re-absorbed by the blood in the peritubular capillaries (what remains is urine) Secretion – as the filtrate moves through the remaining tubules, H ions, K ions, ammonium ions are secreted from the capillaries into the tubule

Proximal tubule Distal tubule Glomerular capsule HCO3– Glucose and amino acids NaCl NaCl H2O Blood Some drugs and poisons H+ K+ and some drugs Collecting duct Filtrate Cortex H2O Salts (NaCl, etc.) HCO3– (bicarbonate) H+ Urea Glucose; amino acids Some drugs Medulla H2O Loop of Henle NaCl NaCl H2O Reabsorption K+ Active transport Passive transport Urea Secretion (active transport) NaCl H2O Urine (to renal pelvis) Figure 15.5

Hepatic veins (cut) Inferior vena cava Renal artery Adrenal gland Renal hilum Aorta Renal vein Kidney Iliac crest Ureter Rectum (cut) Uterus (part of female reproductive system) Urinary bladder Urethra (a) Figure 15.1a

Hormones of the Kidney Regulation occurs primarily by hormones Antidiuretic hormone (ADH) - vasopressin Prevents excessive water loss in urine Causes more water re-absorption from the collecting duct If you are dehydrated, ADH will work to re-absorb the water and urine will be concentrated If your fluid intake is high, ADH will be low, the body won’t re-absorb most of the water and your urine will be dilute

Hormones cont. Aldosterone Regulates sodium ion content of the distal convoluted tubule Sodium is the electrolyte most responsible for osmotic water flows Aldosterone promotes reabsorption of sodium ions Remember, water follows salt!

Skin Epidermis, dermis, subcutaneous layers Sweat glands are found in the dermis Stratum corneum is in the epidermis and forms are barrier against invading microorganisms

Cutaneous vascular plexus Hair shaft Dermal papillae Epidermis Papillary layer Pore Appendages of skin • Eccrine sweat gland • Arrector pili muscle Dermis Reticular layer • Sebaceous (oil) gland • Hair follicle • Hair root Hypodermis (superficial fascia) Cutaneous vascular plexus Nervous structures • Sensory nerve fiber • Lamellar corpuscle Adipose tissue • Hair follicle receptor (root hair plexus) Figure 4.3

Excretory Bingo Ammonia Uric acid Urea Malpighian tubules Nephridia Nephron Renal cortex Renal medulla Bowman’s capsule Loop of Henle Renal artery Glomerulus Filtrate Ureters Bladder Urethra Filtration Reabsorption Secretion ADH (vasopressin) Aldosterone Epidermis Dermis Subcutaneous layer