Regulation of Body Fluids

Regulation of Body Fluids

• Osmoregulation and excretion maintain water and ion balance.
• Osmoregulation balances water and ion levels.
• Excretion eliminates metabolic wastes.

The Internal Environment

• Water makes up 60% of the body composition.
• Intracellular fluid equates to 2/3 of total body water.
• Extracellular fluid surrounds cells as an internal environment.
• Extracellular fluid includes fluid outside cells like blood plasma, transcellular fluid, and interstitial fluid.
• Interstitial fluid between blood vessels and cells makes about 11 liters of extracellular fluid and 26% of total body water.
• Blood plasma is the yellowish liquid part of the blood or intravascular fluid.
• Blood plasma is about half the total volume of blood, or 3 liters of the extracellular fluid in the body.
• Transcellular fluid include fluids that don't flow or have biological functions, like water in eyes.

Osmolarity

• Osmolarity expresses dissolved solutes in the extracellular fluid.
• Osmolarity is measured in milliosmoles per liter of solution (mOsm/L).
• Water flows from higher to lower osmolarity across a semi-permeable membrane through osmosis.

Types of Animals

• Osmoconformers allow their body fluids osmolarity to equal the environment's osmolarity, also called isosmotic condition.
• Most marine invertebrates are osmoconformers who need less energy for osmoregulation.
• Osmoregulators keep their osmolarity different from the environment.
• Osmoregulators discharge water in hypotonic conditions or take it in water in hypertonic conditions.

Nitrogenous Wastes

• Ammonia comes from aquatic invertebrates and larval amphibians.
• It is soluble in water, highly toxic and is released in dilute amounts.
• Urea comes from most amphibians, reptiles, mammals.
• It takes energy when combining ammonia with a bicarbonate ion (HCO3-), but is less toxic and needs less water to excrete.
• Uric acid comes from birds, insects, and some reptiles.
• It is non-toxic however needs more energy to create and cannot dissolve in water.

Excretion in Simple Organisms

• Cell membranes let waste exit in unicellular organisms.
• Protists like Paramecium get rid of excess water and wastes through a contractile vacuole in the cytoplasm.

Invertebrate Excretory Systems

• Flatworms, like Dugesia, that live in hypotonic areas have protonephridia.
• Protonephridia, a network of tubules, ends in a flame cell where water enters and is filtered.
• Wastes go out the external nephridiopore.
• Annelids and mollusks usually have metanephridia.
• Metanephridia refers to a tubular network with a funnel-shaped nephrostome that collects body fluids.
• Wastes sit as urine in the bladder and later excreted by a nephridiopore.
• Malpighian tubules in terrestrial arthropods don't filter water.
• Malpighian tubules secrete uric acid, sodium(Na+) and potassium(K+) ions so fluids osmotically flow from hemolymph to the hindgut to allow for absorption.
• Urine and feces are excreted at the anus.

The Mammalian Excretory System

• The mammalian system is made up of two kidneys with a ureter.
• Kidneys lead to a urinary bladder for urine storage which is expelled through the urethra.
• Bean-shaped kidneys contain an outer coat of connective tissue, or the renal capsule.
• The kidney is then followed by the cortex or middle layer, and inner medulla which contain blood vessels and nephrons.
• Each kidney has about 1.3 million nephrons, its functional unit, that is 80 km long if connected.
• The nephron's function is to filter blood; about 1,600 L of blood pass through each day.

Components of the Nephron

• Filtration by the nephron begins in the glomerulus, a ball of capillaries.
• The glomerulus is enclosed by an enfolded Bowman's capsule.
• High blood pressure forces filtrate out of the capillaries, getting collected by the Bowman's capsule.
• Larger solutes, proteins, and cells can't pass the capillary walls, but some nutrients and ions mix in the glomerular filtrate.
• The filtrate passes by the Bowman's capsule into the renal tubules.
• Renal tubules filter and reabsorb ions.
• The proximal tubule have surfaces which lead into regions such as the loop of Henle, distal tubule, and collecting duct.
• Useful materials like salts, water, amino acids, and glucose go into the peritubular capillaries next to the renal tubules and glomerulus during tubular reabsorption.

Regulation of the Kidney

• Blood pressure impacts blood volume flow.
• Blood volume flow affects the rate of filtration which the receptors in the juxtaglomerular apparatus regulates.
• Vasopressin, or antidiuretic hormone (ADH), is secreted by the hypothalamus if the body is dehydrated.
• Vasopressin is meant to make renal tubules more permeable and save water.
• Kidneys release renin if pressure receptors sense low extracellular fluid, which helps with the production of aldosterone for sodium reabsorption.
• High concentrations of solutes in the extracellular fluid stimulate the hypothalamus thirst center, leading to saliva restriction and stimulation of thirst.
• Kidneys help balance acid-base by eliminating excess H+ ions or reabsorb HCO3 ions to the blood if concentration of hydrogen ions, or pH, increases /decreases.