Urinary System Ch. 35

Urinary systems Helps maintain homeostasis – Maintains water balance Either blood or interstitial fluid is filtered, removing water and small dissolved molecules Nutrients are selectively reabsorbed from the filtrate Excess water, excess nutrients, and dissolved wastes are excreted from the body

Invertebrate excretory systems Protonephridia Malipighian tubules Nephridia

Protonephridia Consists of tubules that carry fluid and wastes to an excretory pore that empties to outside Hollow cells containing flame cells (beating cilia) produce a current that draws water and dissolved wastes into the tubules and directs it out through the excretory pores Freshwater flatworms – Large amounts of water diffuse into body – Have 2 protonephridia that branch throughout the body – They collect excess water and some wastes that are emptied through excretory pores – Most cellular wastes diffuse through the body walls

Protonephridia

Malpighian tubules Insects excretory systems consist of Malpighian tubules Small tubules that extend outward from the intestine and end within the blood of the hemocoel Wastes and salts move from surrounding blood into tubules by diffusion and by active transport Water enters by osmosis Important salts are secreted back in the blood in the intestine and rectum by active transport

Malpighian tubules

Nephridia Earthworms, mollusks, other invertebrates Earthworm – Body cavity filled with fluid that surrounds internal organs – Fluid collects wastes and nutrients from blood and tissues – Fluid moves into a nephrostome which is a funnel shaped structure – Fluid continues through a narrow, twisted tubule surrounded by capillaries – Re-absorption of nutrients and other salts by capillaries – Wastes and water left behind – Resulting urine excreted through a nephridiopore, an opening in the body wall

Nephridia

Vertebrate urinary system Filters wastes out of blood Retains nutrients and adequate water Kidneys filter blood – Dissolved molecules and water filtered out – Reabsorb water and nutrients back into blood – Leave behind toxic substances, cellular wastes, excess vitamins, salts, hormones, and water – Additional wastes transported into remaining fluid becoming urine – Channels and stores urine until it is excreted

Vertebrate urinary system Regulates levels of blood ions Regulates water content of blood Maintains proper blood pH Retains important nutrients in blood (i.e. glucose and amino acids) Secretes hormones (i.e. erythropoietin) Eliminates cellular waste products like urea

Elimination of cellular wastes Nitrogenous wastes, a bi-product of cellular metabolism, are eliminated Derived from amino acids Some amino acids used directly in protein synthesis Others have amino group (-NH2) removed rest of molecule used as a source of energy or in making other molecules Amino groups released as ammonia Terrestrial vertebrates – ammonia travels to liver where it is converted to urea, travels back to kidneys, excreted as urine Birds – uric acid

Human urinary system Renal artery Kidney Renal vein Ureter Urinary bladder Urethra

Human urinary system

Urinary system

Human kidney Renal cortex – Outer layer Renal medulla – Inner layer – Important in producing concentrated urine Renal pelvis – Deep to cortex and medulla – Collects urine and funnels it into ureters Nephrons – Microscopic filters that line the outer layer (cortex) – Functional unit of kidney – Where blood is filtered and urine formed

Human kidney

Kidneys Regulate water content in blood Release hormones that help regulate blood pressure and oxygen levels Monitors and regulates substances in the blood