Excretory System

p. 941-950

Invertebrates Ex. Earthworm, insects

Nephridia: excretory organ of worms (annelids)

• Fluids enter the nephridia, become more concentrated as it passes through the collecting tubules, concentrated waste exits out the excretory pore p. 943 Figure 44.19

Malpighian tubules: excretory organ insects (arthropods)

• Empties digestive tract, removes nitrogenous waste from blood (hemolymph) and functions in osmoregulation (water balance) p. 943 Figure 44.20

 

Human Excretory

Kidney: filters blood for wastes

• Just above waist, toward rear of body cavity
• Produces urine
• p. 944 Figure 44.21

Nephrons: each kidney made up of millions of nephrons

• The functional unit of the kidney

Kidney

 

Regions of nephrons

Nephron

Nephron Overview

p. 946 Figure 44.22

 

The nephron begins with the

1. Bowman’s Capsule

• blood enters via the renal arteries to a ball of capillaries called the GLOMERULUS, which filters blood
• blood pressure forces water, urea, salts and other solutes from the blood in the glomerulus into the lumen (lining) of the Bowman’s capsule. The fluid in the lumen is called FILTRATE

2. The filtrate then passes to the Convoluted Tubule

• The convoluted tubule is a winding tube that begins with proximal convoluted tubule (at the Bowman’s capsule) and ends with the distal convoluted tubule (where the tube connects with the collecting duct). The middle portion of the convoluted tube is called the Loop of Henle (hairpin shaped portion of the duct)

The proximal convoluted tubule

• Reabsorption of amino acids, glucose, and salts
• Reabsorption of NaCl is key
• Reabsorption in the proximal tubule helps maintain a pH in body fluids by controlling secretion of H+ ions and by reabsorbing 90% of the important buffer, HCO₃^-, bicarbonate
• Drugs and poisons processed in liver are secreted into the filtrate by the epithelium
• Proximal means toward the point of origin

Loop of Henle

• Water absorption

Distal Convoluted tubule

• Site of selective and absorption…regulates K+ and NaCl concentrations

Collecting ducts; there are a number of collecting ducts that merge into the renal pelvis

• The renal pelvis takes concentrated Urine to the ureters then into the bladder, then urethra

Sphincter muscles near the junction of the urethra and the bladder control urination

 

How urine is made:

 (The 3 processes of operation of the nephron)

3 steps

Filtration

Reabsorption

Secretion

 

Filtration:

• Small substances, i.e., Ions, water, salts, vitamins, nitrogen wastes glucose and amino acids pass thru capillary into the Bowman’s capsule…remember the substances that pass into the capsule are now called Filtrate. From the Bowman’s capsule the filtrate moves into the convoluted tubules. Larger substances (red blood cells, proteins) remain in the capillaries

 

• Secretion: as filtrate passes through the tubules additional material from the surrounding capillaries are selectively secreted into the convoluted tubule…active and passive transport

Reabsorption: as filtrate moves down the Loop of Henle, water will passively be removed creating a highly concentrated filtrate.

 

Hormones of the Kidney

Regulate the concentration of water and salt in the kidneys

Vasopressin: aka antidiuretic hormone (ADH) Reabsorbs water from collecting ducts Controls volume of urine Retain water when dehydrated by concentrating urine Urine contains large amounts of water when fluid intake is high

Aldosterone

Absorbs salt at distal convoluted tubule (mainly Na+) The breakdown of amino acids and nucleic acids produce ammonia (NH3), or any nitrogenous waste Aquatic animals excrete ammonia into the surrounding water Mammals convert ammonia to urea in the liver Birds, insects and many reptiles convert urea to uric acid…precipitates and forms a solid. This allows for considerable water conversation

• Kidney Stones: formation of crystals of calcium, Mg or uric acid salts…form sharp crystals

Skin: largest organ; helps body to rid waste, mainly excess Salt

Skin

• Contains 2.5 million sweat glands that secrete water and ions
• Maintains body temperature

Epidermis

• Covered by a layer of dead cells called Stratum Corneum (cells that form a barrier against invading microorganisms)

Dermis

• Contains sweat glands, blood vessels, nerves and SebacEOUS GLANDS (produce oil)
• Subcutaneous: mostly Fat