CH. 12 - Excretion

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1. General

1. Elimination - removable of indigestible material

2. Excretion - removal of metabolic wastes, especially nitrogenous wastes produced by deamination of amino acids, like urea and ammonia

2. Excretion in Invertebrates

1. Malpighian tubules - minearl salts and uric acid accumulated here and transported to intestine for disposal

2. Nephridia - in annelids, two pairs in each segment that rid body of wastes

3. Spiracle - air openings in arthropod for gas exchange

4. Uric Acid - nitrogenous waste crystals formed by arthropods

3. Excretion in Human

1. Bowman's capsule - bulb within nephron for filtration

2. Collecting duct - section of tubule within nephron

3. Countercurrent-multiplier system - loop of Henle arranged so 99% of filtrate reaborbed

4. Distal convoluted tubule - tubule within nephron for water reaborption

5. Filtrate - fluid and small solutes entering nephron

6. Glomerulus - special capillary bed in the nephron

7. Hyperosmolar - medium in medulla of kidney is hyperosmolar with respect to filtrate

8. Kidney - consists of three regions, outer cortex, inner medulla, and renal pelvis

9. Loop of Henle - a section of tubule within nephron responsible for water reaborption

10. Nephron - consists of Bowman's capsule, glomerulus.  Reabsorbs nutrients and water

11. Peritubular capillary - surrounds nephron to facilitate reabsorption of nutrients

12. Proximal convoluted tubule - tubule within nephron responsible for nutrient reaborption

13. Renal pelvis - funnel-like region that opens into the ureter

14. Ureter - from each kidney empty into urinary bladder

15. Urethra - path of piss excretion

16. Urinary bladder - urine collects here until expelled via urethra

Excretion in Invertebrate

1. Excretion in Protozoans and Cnidarians

1. All cells in contact with external aqueous environment, thus wastes are simply diffused out of cell membrane

1. Passive excretion of ridding itself ammonia and carbon dioxide

2. Freshwater Protozoan

1. Paramecium

1. Must use specialized contractile vacuole for getting rid of excess water

1. Water constantly diffuses into cell due to hypotonic environment

2. To maintain the volume and pressure inside cell

2. Excretion in Annelids

1. Carbon Dioxide excretion occurs directly through moist skin

2. Nephridia

1. Two pairs in each body segment

2. Excrete water, minearl salts, and nitrogenous wastes in form of urea

3. Excretion in Arthropods

1. Carbon dioxide released from tissues into tube-like tracheae

1. Converges into air openings called spiracles

2. Uric acid

1. Nitrogenous wastes are excreted in form of solid crystals

2. Mineral salts and uric acid accumulated in the Malpighian tubules and then expelled via intestine with rest of the solid wastes of digestion

Excretion in Humans

1. General

1. Principal organs involved

1. Lungs, liver, skin, kidney

2. Lung

1. Carbon dioxide and water vapor from lung constantly exhaled

3. Skin

1. Sweat gland constantly excrete water and dissolved salt

2. Small quantity of urea also excreted

3. Regulates body temperature when water evaporates

4. Liver

1. Processes

1. nitrogenous wastes

2. Blood pigment wastes

3. Other chemicals for excretion

2. Produces urea here, but diffuse into blood for excretion in kidneys

3. Bile salts, and red blood pigments are excreted as bile and passes out with feces

2. The Kidney

1. Function

1. Regulate the concentration of salt and water in blood via formation and excretion of urine

2. Maintain the osmolarity of blood

3. Excrete numerous wastes products and toxic chemicals

4. Conserve glucose, salt, and water

5. Located behind stomach and liver

6. Composed of one million nephron units

2. Structure

1. Divided into three regions

1. Outer cortex

2. Inner medulla

3. Renal pelvis

2. Nephron

1. Consists of a bulb called Bowman's capsule

1. Embraces a special capillary bed called glomerulus

2. Leads into long coiled tubule that's divided into units

1. Proximal convoluted tubule

1. Have Na+/K+ pump

2. Loop of Henle

3. Distal convoluted tubule

4. Collecting duct

2. Positioned in a special way

1. loop of Henle runs through the medulla

2. Convoluted tubules and Bowman's capsule in the cortex

3. Surrounded by complex peritubular capillary network to facilitate reabsorption of amino acids, glucose, salts, and water

3. Urine pathway

1. Concentrated urine flows into the pelvis of the kidney

1. Flow s into the ureter

2. Ureters from each kidney empty into the urinary bladder

1. Urine collects until expelled through urethra

3. Urine formation

1. Filtration

1. Blood pressure would force 20% of blood plasma into the Bowman's capsule via the glomerulus

1. Fluid and small solutes entering the nephron are called filtrate

1. Filtrate is isotonic to blood plasma

2. Particles too large to filter remain in circulation

2. Passive process driven by the hydrostatic pressure of the blood

2. Secretion

1. Nephron secretes acids, bases, ions from interstitial fluids into the filtrate

1. Done by passive and active transport

3. Reabsorption

1. Essential substances like glucose, salts and amino acids are reabsorbed from filtrate and returned to blood

2. Occurs primarily in the proximal convoluted tubules

1. Active process

3. Result is the formation of concentrated urine

1. Hypertonic to blood

4. Nephron Function

1. Via selective permeability of its walls and maintenance of an osmolarity gradient, nephron reabsorbs nutrients, salts, and water from filtrate

2. Osmolarity Gradient

1. The selective permeability establishes an osmolarity gradient in the surrounding interstitial fluid

2. Tissue osmolarity increases from cortex to inner medulla

1. Solutes like urea and salt contribute to maintaining this gradient

3. Countercurrent-multiplier system

1. Anatomic arrangement of Loop of Henle within the kidney creates a situation where 99% of the filtrate are reabsorbed.

3. Concentration of Urine

1. In medulla of kidney, the concentration of medium is hyperosmolar with respect to the filtrate

1. Thus water flows out to the collecting tubules by osmosis

2. The reabsorption of water in this zone is regulated by ADH (vasopressin)

1. ADH increases the permeability of the collecting duct, thus more concentrated urine

2. ADH produced in hypothalamus and stored in posterior pituitary

Excretion in Plants

1. General

1. No specific excretory system in plants

Anything excess would be expelled by the plant through the stomates and lenticels