Excretion Flashcards
excretion
refers to the removal of metabolic wastes produced in the body. it is distinguished from elimination. most of the bodies activities produce waste that needs to be removed
Elimination
removal of indigestible material
All metabolic processes lead to
the production of mineral salts which must be excreted by the kidneys
Excretions in protozoans and cnidarians
all cells are in contact with the external aqueous environment. Water soluble wastes like ammonia and carbon dioxide exit by simple diffusion. This type of excretion is passive.
vacuole
some fresh water protozoa possess a contractile vacuole, an organelle specialized for water excretion by active transport. excess water continually diffuses into the cell is collected and pumped out to maintain volume and pressure.
excretion in annelids
in earthworms the carbon dioxide excretes through the moist skin.
also two pairs of nephridia in each body segment excrete water and mineral salts and nitrogenous wastes in the form of urea
excretion in arthropods
in insects CO2 is released from the tissues into adjacent tube like tracheae which are continuous with the external air through openings called spiracles.
nitrogenous waste from arthropods
excreted in the form of solid uric acids crystals. the use of solid waste is an adaption for the conservation of water. Mineral salts and uric acid accumulate in Malphigian tubes and are transported to the intestine to be expelled with the solid wastes of digestion.
principal organs of excretion in the human
lungs, liver, skin and kidneys.
lungs
release carbon dioxide and water vapor diffuse from the blood into the alveoli and are continually exhaled.
skin
excretes water and dissolved salts (and a small quantity of urea). perspiration also serves to regulate body temperature since the evaporation of seat produces cooling
liver
processes nitrogenous wastes, blood pigment wastes and other chemicals for excretion.
-urea is produced by the deamination of amino acids in the liver and diffuses to the blood for ultimate excretion in the kidneys.
The kidneys
regulate concentration of salt and water in the blood through the formation and excretion of urine.
-bean shaped and are located behind the stomach and liver. each kidney is composed of approximately 1 million nephrons
kidney structure
divided into three regions: the outer cortex the inner medulla and the renal pelvis. The nephron is positioned such that the loop of Henle runs through the medulla, while the convoluted tubules and Bowman’s capsule are in the cortex.
nephron
functional unit of the kidney consist of a bulb called the Bowman’s Capsule, which embraces a special capillary bed called a glomerulus.
- Bowman’s leads to a long coiled tube that is divided into distinct sections, proximal convoluted tubule, the loop of Henle and the distal convoluted tubule and the collecting duct.
- most of the neprhon is surrounded by a complex peritubular capillary network to facilitate re-absorption of amino acids, glucose, salts and water.
path of concentrated urine
concentrated urine in the collecting tubules flows into the pelvis of the kidney, a funnel like region that opens into the ureter,
the ureters from each kidney empty into the urinary bladder, where urine collects until expelled via the urethra.
three process that lead to urine formation
filtration, secretion and reabsorption
filtration
blood pressure forces 20% of blood plasma entering the glomerulus through capillary walls into the surrounding Bowman’s capsule.
the fluid and small solutes entering the nephron are called filtrates.
-a passive process driven by the hydrostatic pressure of the blood.
secretion
the nephron secretes potentially harmful substances such as acids, bases and ions like potassium and phosphate from the interstitial fluid into the filtrate by both passive and active transport. materials are secreted from the peritubular capillaries into the nephron tubule.
reabsorption
essential substances (glucose, salts and amino acids) and water are reabsorbed from the filtrate and returned to the blood. -occurs primarily in the proximal convoluted tubule and is an active process. this results in the formation of concentrated urine (hypertonic to blood)
nephron function
through the maintenance of an osmolarity gradient, the nephron reabsorbs nutrients, salts and water from the filtrate and returns them to the body, thus maintaining the bloodstream’s solute concentration.
osmolarity gradient
the selective permiability of the tubules establishes an osmolarity gradient in the surrounding interstitial fluid. by exiting and then re-entering at different segments of the nephron, solutes create an osmolarity gradient with tissue osmolarity increasing from cortex to inner medulla
contercurrent-multiplier systems
the osmolarity of urine is established by the collecting tubule by this system. the anatomic arrangement of the loop of Henle within the kidney permits the establishment of a concentration gradient that permits the reabsorption of 99 percent of the filtrate in the collecting tubules.
-leading to concentration of urine and conservation of as much water as possible
concentration of urine
the countercurrent system causes the medulla of the kidney to be hyperosmolar with the respect to the dilute filtrate flowing in the collecting tubule. as the filtrate flows into the collecting tubules passes through the medulla of the kidney and its path the water flows out of the collecting tubules by osmosis
regulation of permeability of the collecting tubules
to water is accomplished by the hormone ADH. ADH increases the permeability of the collecting duct to water, allowing more water to be absorbed and concentrated urine to be formed to increase blood osmolarity.
Excretion in plants
there is no specific excretory system in plants. Plants are able to use many “waste” products and are utilized as precursors in the synthesis of complex molecules.
-any excess carbon dioxide as well as waste oxygen and water vapor leave the plant by diffusion through the stomates and lenticles- this is known as transpiration.
stomates
pores in leaves
lenticles
pores in stems
