Excretory systems

1. Excretory systems The excretory system is crucial to homeostasis because they dispose of metabolic wastes and control of body fluid composition by adjusting the rates of loss of particular solutes. Funto Adebo and Erin Ford

2. Production of Urine • Most all systems produce urine by a two step process • Body fluid is collected (blood, coelomic fluid, or hemolymph) • Composition of the fluid is adjusted by selective re-absorption or secretion of solutes. • The fluid is filtrated through selectively permeable membranes of transport epithelia. Filtrate- the fluid retained

3. Types of Excretory Systems • Excretory systems are diverse and vary from species to species, but are all variations of a tubular theme. Protonephriduim- type of excretory system in flatworms. Composed of a network of dead end tubules that lack internal openings. Function mainly in osmoregulation. Metanephridium- type of tubular excretory system that has internal openings and collects body fluids. Found in most annelids. It has both excretory and osmoregulation functions. Malpighian Tubules- organs that remove nitrogenous wastes and also function in osmoregulation. Present in insects and other arthropods. Vertebrate Kidneys - function in both osmoregulation and excretion. Built of tubules.

4. The Kidney • Mammals have a pair of kidneys supplied with blood by a renal artery and renal vein. • Urine exits each kidney through a duct called the ureter. Both ureters drain into a common urinary bladder. • Urine is expelled from the bladder through a tube called the urethra. • Sphincter muscles near the junction of the urethra and the bladder control urination.

5. Structure and Function of Kidneys • Have two distinct regions • Outer renal cortex • Inner renal medulla • The nephron, the functional unit of vertebrate kidney consists of a single long tubule and a ball of capillaries called the glomerulus. • Surrounding the glomerulus is the Bowman’s capsule, which is the cup shaped swelling at the end of the tubule.

6. Filtration of Blood • Blood pressure forces fluid from the blood in the glomerulus into the lumen of Bowman’s capsule • Porous capillaries are permeable to water and small solutes but not to blood cells or large molecules like plasma proteins. • Filtration of small molecules is nonselective, therefore the filtrate in Bowman’s capsule contains salts, glucose, and vitamins, nitrogenous wastes, and other small molecules.

7. Pathway of the Filtrate • Filtrate passes through the proximal tubule, the loop of Henle, and the distal tubule which empties into a collecting duct. • The loop of henle is a hairpin turn with a descending limb and an ascending limb.

8. Important factors to the regulation of the osmolarty of urine include ADH, RAAS, and ANF. ADH (antidiuretic hormone)-important in regulating water balance. RAAS (renin-angiotensin)- part of a complex feedback circuit that functions in homeostasis ANF (atrial natriuretic factor)- a peptide that opposes RAAS; balancing the two

9. An Overview • The mammalian kidneys ability to conserve water is a key terrestrial adaptation. • The collecting duct carries the filtrate through the kidneys osmolarity gradient, then more water exits by osmosis. • Urea containing salt diffuses out of the tubule and forms the osmotic gradient that enables the kidney to produce urine that is hyperosmotic to the blood. • Osmolarity of urine is regulated by the nervous system and hormonal control of water and salt reabsorption in the kidneys.

10. Diverse adaptations of the vertebrate kidney have evolved in different habitats. • The form and function of nephrons in the various vertebrate classes are related primary to the requirements for osmoregulation in the animal’s habitat. • Interacting regulatory systems maintain homeostasis