Excretion and Osmoregulation

• Excretion is different from osmoregulation

Osmoregulation

• Osmoregulation is maintaining internal balance between water and dissolved materials
• Osmoregulation is Maintaining water and ion balance in cells and tissues

Excretion

• Excretion is removing waste products of osmoregulatory processes
• Excretion involves removing metabolic waste

Metabolic Waste

• Metabolic waste comes from internal biochemical processes
• Metabolic waste is absorbed by cells
• Metabolic waste is a byproduct of cellular processes
• Metabolic wastes must be expelled so they do not intervene with homeostasis

Feces

• Feces is undigested material not absorbed by cells
• Feces originates from the digestive system
• Feces is at the macromolecule level and does not reach the cellular level, unlike metabolic waste
• Feces might carry small amounts of metabolic waste
• Excretory systems are needed for biochemical processes and their waste products

Cellular respiration

• Cellular respiration produces CO2 and requires energy in the form of ATP

Protein metabolism

• Protein metabolism produces ammonia, which is then converted to urea
• Protein is converted into amino acids
• Cells absorb amino acids and release ammonia as a byproduct, which then turns into urea and then urine

Nucleic Acid Metabolism

• Nucleic acid metabolism produces purines, which are then converted to uric acid
• Nucleic acid comes from food containing DNA and RNA
• Nucleic acid is converted to purines and then uric acid when digested

Muscle Activity

• Muscle activity converts creatine phosphate into creatinine
• Muscle activity in muscle creates phosphate

Red blood cell breakdown

• Breakdown causes Bilirubin (bile pigment)
• RBCs can only survive for 20 days
• Waste products are toxic and must be urgently released through urine, sweat, breath, or bile

Main Excretory Products

• Nitrogenous wastes include ammonia, urea, and uric acid
• Carbon dioxide is a product of respiration
• Excess salt & water comes from osmoregulation
• Urine contains water, which can be used for survival in dire situations

Nitrogenous Wastes

• Including ammonia, urea, and uric acid

Ammonia

• Ammonia is the most toxic nitrogenous waste product
• Aquatic animals mostly use ammonia as it's highly soluble in water
• For ammonia production Energy>water conservation
• Water is used to conserve energy when producing ammonia

Urea

• Urea is less toxic than ammonia
• Mammals & amphibians mostly use urea
• Urea balances energy & water needs
• Urea requires energy to produce and is soluble in water

Uric Acid

• Uric Acid has the least toxicity
• Species that live in small and/or dry environments mostly use uric acid
• For uric acid Water conservation>energy
• Uric acid prioritizes water conservation by using a lot of energy
• Uric acid requires the most energy and is highly water conserving
• Uric acid is excreted as a solid that has crystallized
• Fishes excrete ammonia because they live in an environment where it can be easily diluted and flushed away
• Camels excrete urea because they consider a large amount of energy and conserve water in the desert
• Birds excrete uric acid due to the need for highly efficient conservation of water, as they are small species
• Lizards excrete uric acid because they are small and need more water
• Reptiles excrete uric acid as a paste because they live desert, where water conservation is critical

Excretory System

• Regulates solute (ions, salt, etc.) between internal fluids and the external environment
• The body balances the solutes and water before releasing fluids

Strategies to Excrete Materials

• Organisms use different strategies to excrete materials

Protists

• Unicellular eukaryotic organisms
• Release substances through the contractile vacuole, which contracts and evicts substances

Invertebrates

• Worms: 2 types, Flatworms and Earthworms

Flatworms

• Flatworms excrete through protonephridia

Protonephridia

• Protonephridia are dead-end tubules with one opening and exit
• Tubules excrete a dilute fluid and function in osmoregulation

Flame bulb

• Interstitial fluid
• Flame bulb filters needed materials
• Filtrate goes through the tubules
• Excretion of filtrate

Earthworms

• Earthworms are segmented worms

Metanephridia

• Metanephridia are open-ended tubules
• Metanephridia collect coelomic fluid and produce dilute urine for excretion
• Reabsorption of water occurs
• Longer tubes are present
• Metanephridia function in excretion and osmoregulation
• Capillaries try to claim the solutes with an external opening

Vertebrates

• Including insects and mammals

Insects

• Insects use malpighian tubules

Malpighian tubules

• Malpighian tubules are found in cockroaches, bathed in hemolymph
• Malpighian tubules take water and salt from hemolymph, transporting it to the rectum and released through the anus
• Pee, poop, and metabolic waste are released simultaneously in insects

Mammals

• Mammals use kidneys

Kidneys

• Kidneys filter blood and metabolic waste
• The excretory organs of vertebrates function in both excretion and osmoregulation
• The renal artery filters and passes through the ureter, releasing filtrate in the urethra
• The vertebrate excretory system also includes ducts and other structures that carry urine from the tubules out of the kidney and out of the body

Stages of Excretion

• Filtration involves filtering body fluids
• Reabsorption involves reclaiming valuable solutes in capillaries
• Secretion involves adding harmful substances to the filtrate
• Excretion involves removing the filtrate from the body

Excretory Processes

• Filtration
  • Solutes are filtered from the blood into the excretory tubule

Excretory Tubule

• Collects filtrate and will process it into urine
• Capillaries must be porous to allow solutes to pass through

Filtrate

• Filtrate includes substances filtered from the blood

Reabsorption

• Some filtered components are still needed by the body like Vitamins, water, glucose
• These components need to be recovered from the tubule
• Reabsorption recovers useful substances from the filtrate in the excretory tubule
• Reabsorption transports important substances back into the blood
• Facilitated by transport epithelium through active transport
• Transport molecules from excretory tubule into the blood vessel

Secretion

• Some unnecessary substances are too large to be filtered but still need to be excreted
• Selective secretion activates, and toxic substances and waste products from the blood are added to the filtrate by active transport

Excretion

• Filtrate is composed of waste, solutes, and some water
• Filtrate will now be released from the body as urine: the process of Excretion or Micturition (urinating)

Kidneys

• There are two main regions of the kidneys
  • The Upper renal cortex
  • The Lower renal medulla
• The renal artery is where unfiltered blood enters
• The renal vein is where filtered blood leaves, travelling back to the heart
• The renal pelvis collects processed filtrate from the kidney and transports it to the ureters for excretion

Nephron

• The nephron is the functional unit of filtration in the kidney
• Blood is filtered and filtrates are formed in the nephron and becomes urine
• Each kidney has millions of nephrons, tiny filtering units
• Nephrons are organized for stepwise processing of blood filtrate

Cortical Nephrons

• Cortical Nephrons are the shorter nephrons that only reach a short distance into the medulla
• 85% of nephrons are cortical

Juxtamedullary Nephrons

• Juxtamedullary Nephrons are the longer-limb nephrons that extend deep into the medulla

Renal cortex

• Renal Artery
  • Brings blood into the Bowman's capsule and splits into a ball of arterioles
  • Becomes a ball of glomerulus

Glomerulus

• Encapsulates many capillaries
• Capillaries are Porous; small molecules are pushed into Bowman's capsule

Bowman's capsule

• The blood becomes filtrate, which contains salts, glucose, amino acids, vitamins, nitrogenous wastes, and other small molecules

Reabsorption in the proximal tubule

• 90% of filtrate from Bowman's capsule goes back into the bloodstream in the proximal tubule

Proximal tubule

• Reabsorption of ions, water, and nutrients occurs
• H2O and nutrients (glucose, amino acid) are absorbed and diffused, returning into the blood vessels in the proximal tubule
• As the filtrate passes through the proximal tubule, materials to be excreted become concentrated
• Some toxic materials are actively secreted into the filtrate
• The proximal tubule is nearer to the glomerulus
• The proximal tubule is connected to the Bowman's capsule and the loop of Henle

Nephron loop/Loop of Henle

• Harpin-like tubes
• The loop dips down into the medulla
• Loop creates a concentration gradient

Renal Medulla

• Naturally Salty
• Descending Limb
  • Going down, becomes saltier due to medulla
  • Reabsorption of water continues through channels formed by aquaporin proteins
  • Movement is driven by the high osmolarity of the interstitial fluid, which is hyperosmotic to the filtrate
  • Hyperosmotic- A solution that exerts higher thrust or pushes through a membrane
  • The filtrate becomes increasingly concentrated
  • A salty environment attracts water, which then enters back into the bloodstream through osmosis

Ascending limb

• Ascending limb of the Nephron loop.
  • Water can't leave anymore in the ascending limb
  • NaCl is pumped out (the salt) where it actively transported
  • Ascending limb becomes impermeable to water
  • The filtrate becomes increasingly dilute

Distal tubule

• The distal tubule regulates the K and NaCl concentrations of body fluids
• Controlled movement of ions (H and HCO3-) contributes to pH regulation
• Distal Tubule secretes blood, removal of unnecessary materials

Collecting duct

• When Dehydrated: reabsorb in the bloodstream as much water as we can when the brain releases ADH
• When Hydrated: no absorption of water, brain stops releasing ADH and urination occurs
• Urine is hyperosmotic to body fluids in the collecting duct

Afferent arteriole

• The afferent arteriole is a branch of the renal artery that supplies blood to each nephron

Efferent arteriole

• Blood, once filtered in the glomerulus, flows through efferent arteriole
• Efferent arteriole carries off reabsorbed materials and supply blood for secretion
• Efferent arteriole then branches into peritubular capillaries
• Secretion occurs

Peritubular capillaries

• Secrete certain mineral ions and excess water into the tubule
• Tangled with the proximal and distal tubule

Vasa recta

• Vasa recta reabsorbs nutrients, water, and oxygen
• Vasa recta is formed when branches of peritubular capillaries extend downward the renal medulla
• Collecting duct leads to the the urethra and then anus for excretion

Solute Gradients & Water Conservation

• The mammalian kidney can conserve water through terrestrial adaptation
• Hyperosmotic urine can only be produced by spending considerable energy to transport solutes against concentration gradients
• The primary solutes affecting osmolarity are NaCl and urea

Concentrating Urine in the Mammalian Kidney

• In the proximal tubule, filtrate volume decreases as water and salt are reabsorbed, but osmolarity remains the same
• As the filtrate flows towards the descending limb of the loop of Henle, solutes become more concentrated as Water leaves the tubule by osmosis
• NaCl diffusing from the ascending limb maintains a high osmolarity in the interstitial fluid of the renal medulla

Osmolarity

• Osmolarity is the total concentration of all solutes in the solution
• Energy is spent to actively transport NaCl from the filtrate in the upper part of the ascending limb
• The countercurrent multiplier system involving the loop of Henle maintains a high salt concentration in the kidney
• This system the vasa recta supplies kidney with nutrients without interfering with the osmolarity gradient
• In the collecting duct, water is extracted by osmosis from the filtrate as it passes from the cortex to the medulla and encounters interstitial fluid of increasing osmolarity
• Urine produced is isoosmotic to the interstitial fluid of the inner medulla but hyperosmotic to blood and interstitial fluids elsewhere in the body
• Isoosmotic - same osmolarity to another substance
• Hypoosmotic - lower osmolarity compared to a substance, lesser concentration of solute
• Hyperosmotic - Higher osmolarity compared to a substance

Adaptations of the Vertebrate Kidney to Diverse Environments

• Variations in nephron structure and function equip the kidneys of different vertebrates for osmoregulation in various habitats

Mammals

• The juxtamedullary nephron is key to water conservation in terrestrial animals
• Mammals in dry environments have long loops of Henle, while those in freshwater have relatively short loops

Kidney Function in the Vampire Bat

• The South American vampire bat, which feeds at night on the blood of large birds and mammals, illustrates the versatility of the mammalian kidney
• The vampire bat can alternate rapidly between producing large amounts of dilute urine and small amounts of very hyperosmotic urine

Birds and Other Reptiles

• Birds have shorter loops of Henle than mammals and conserve water by excreting uric acid instead of urea
• Other reptiles have only cortical nephrons but reabsorb water from wastes in the cloaca
• Reptiles also excrete nitrogenous waste as uric acid

Freshwater Fishes and Amphibians

• Freshwater fishes conserve salt in their distal tubules and excrete large volumes of very dilute urine
• Kidney function in amphibians is similar to freshwater fishes
• Amphibians conserve water on land by reabsorbing water from the urinary bladder

Marine Bony Fishes

• Marine bony fishes are hypoosmotic compared with their environment
• Marine bony fishes kidneys have small glomeruli, and some lack glomeruli entirely
• Filtration rates are low, and very little urine is excreted
• Ion Movement and Gradients

Fishes - Osmoregulation

• Ion gradients drive the secretion of salt (NaCl), a process essential to avoid dehydration

Frogs - Information Processing

• In neurons, the opening and closing of channels selective for sodium or other ions underlie the transmission of information as nerve impulses

Plants - Gas Exchange

• Ion gradients provide the basis for the opening of plant stomata by surrounding guard cells

Bacterium Flagellum

• locomotion A gradient of H+ ions powers the bacterial flagellum

Hormonal control of the kidneys

• Major hormones keep individuals from losing too much water, becoming too salty, and having dangerous blood pressure levels

ADH antidiuretic hormones

• ADH stops the individual from peeing
• The water keeper hormone
• Produced by the hypothalamus in the brain
• Signaled by the brain when blood is too concentrated or when the individual are dehydrated
• "Overworked hormone"
• Acts on the collecting duct and makes it permeable to water
• Urine becomes very concentrated and yellow
• Causes the kidneys to release less water, decreasing the amount of urine produced

Aldosterone

• The salt saver
• Produced by adrenal glands (above kidneys)
• Acts when blood pressure is too low, so are salt levels
• Reabsorbs salt/sodium
• Water follows the sodium due to osmosis
• Potassium gets secreted into the urine
• Urine becomes less salty
• Urine volume decreases

ANP atrial natriuretic peptide

• ANP is produced from the heart
• functions as a pressure reducer
• Acts on of the distal convoluted tubule and collecting duct to blocks sodium reabsorption
• Water and sodium stay in urine
• Produced by the heart when blood pressure is too high
• Water goes to urine to regulate blood pressure
• Urine becomes more diluted

Qualitative Analysis of Urine

• Normal values are Pale yellow, clear, and have a slight smell, and mostly water, urea, and salts
• Abnormal urine has a Sweet smell, indicating possible diabetes
• Cloudy color, indicating a possible infection
• Dark color, indicating dehydration