Ch: regulating the internal enviornment

Animal life is challenged under changing environmental conditions-_________________compensate for changing conditions and maintain the internal environment within the relatively narrow limits that calls can tolerate

homeostatic control systems- glomeruli in a kidney

osmoregulation

the regulation of water and ion balance

Excretion

helps maintain the body’s water and ion balance while ridding the body of metabolic wastes

Thermoregulation

is the control of body temperature 

Osmosis

water molecules diffuse across a selectively permeable membrane from a region of higher water concentration (low solute concentration) to a region of lower water concentration (higher solute concentration)

Osmolarity

• total solute concentration of a solution is measured in osmoles- the number of solute molecules and ions (in moles) per liter of solution 

What is the osmolarity of body fluids in humans and other mammals about

300 mOsm/L

Hyperosmotic 

• the solution with higher osmolarity is ____to the other solution

• concentrated salt solution

• water leaves the cell so the cell shrinks

Isotonic

• if the solutions on either side of a membrane have the same osmolarity, they are_____

• normal salt concentration 

• no net movement

Hypoosmotic

• the solution with lower osmolarity is ______to the other solution 

• distilled water

• water enters the cell so cell swells or bursts

For metabolic stability, animals must keep their cellular fluids and ECFs

isoosmotic

Osmoconformers

• the osmolarity of cellular and extracellular solutions matches that of the environment

Osmoregulators

• use control mechanisms to keep the osmolarity of cellular and extracellular fluid the same, but at levels that may differ from the osmolarity of the surroundings

What structures carry out osmoregulation and excretion in animals?

Microscopic tubules formed from a transport epithelium that regulate water, ions, and waste.

How are these tubules positioned in the body?

the tubules are immersed in body fluids at the proximal end and open to the body exterior at the distal end

How do the tubules move substances in and out?

transport proteins move specific molecules and ions into and out of the tubule by either active or passive transport, depending on the substance and its concentration gradient

Four steps in tubule function

1. Filtration

2. Tubular reabsorption

3. Tubular secretion

4. Excretion 

Filtration

• The process by which blood pressure forces water and small solutes (like ions, glucose, and urea) out of the glomerulus into Bowman’s capsule, forming filtrate.

• Location: Glomerulus (renal corpuscle).

• Purpose: To separate waste and small molecules from blood.

Tubular Reabsorption

• Definition: The process of returning useful substances (like water, glucose, and ions) from the filtrate back into the blood.

• Location: Along the renal tubule, mainly in the proximal convoluted tubule.

• Purpose: To conserve valuable nutrients and maintain fluid balance.

Secretion

is a selective process in which specific small molecules and ions are transported from the ECF and blood into the tubules

Excretion

fluid (urine) containing waste materials is released into the environment from the distal end of the tubule- solid or semisolid form 

: What is metabolic water, and how is it used in the body?

Metabolic water is the water produced during the metabolism of ingested food. It’s used in chemical reactions and physiological processes such as waste excretion.

: What happens to the nitrogenous products from the breakdown of proteins, amino acids, and nucleic acids?

They are excreted as ammonia, urea, uric acid, or a combination of these substances.

What determines which nitrogenous waste molecule an animal produces?

The type depends on a balance between toxicity, water conservation, and energy requirements.

Ammonia

• NH₃ results from biochemical reaction removing amino groups from amino acids during protein breakdown

• soluble in water, but highly toxic- it must be either excreted or converted can be excreted only in dilute conditions

• Examples: teleost, larval amphibians, aquatic invertebrates

  • excrete this straight into the surrounding water 

  • This works because:

    • Ammonia is very soluble in water.

    • They can diffuse it easily across gills or body surfaces.

    • The constant water flow dilutes the ammonia quickly, preventing toxicity. 

Urea

• made by all mammals, mostly amphibians, some reptiles, some marine fishes, and some terrestrial invertebrates combine ammonia with HCO3 relatively nontoxic substance

• requires more energy than forming ammonia, excreting urea instead of ammonia requires minimal water.

Uric acid

• formed by terrestrial invertebrates, reptiles, and birds

• nontoxic and insoluble - it participates in water and excreted as a paste 

• more energy than urea to generate but allows four times nitrogen

• excretion conserves about 99% of the water required to excrete the same amount of nitrogen as ammonia

Most marine invertebrates are __________

osmoconformers – the osmolarity of their intracellular and extracellular fluids and the surrounding seawater is the same, about 1,000 mOsm/L

All freshwater invertebrates are _________

osmoregulators – they must expend energy to excrete excess water to keep their internal fluids hyperosmotic to their surroundings

Fresh water invertebrates also _______salt ions from the water, through skin or gills, into their bodies

actively transport

Invertebrate osmoregulators use three types of tubules for carrying out excretion: 

• Protonephridia, the simplest form of excretory tubule, found in flatworms and larval mollusks

• Metanephridia, found in annelids and most adult mollusks

• Malpighian tubules, found in insects and other arthropods

Protonephridia

the simplest form of excretory tubule, found in flatworms and larval mollusks

Metanephridia

found in annelids and most adult mollusks

Malpighian tubules

found in insects and other arthropods

Protonephridia

• found in flatworms

• proximal branches of the tubule network and with a flame cell containing cilia that move fluid through the tubule

• when hemolymph passes through ____, some molecules and ions are reabsorbed, and nitrogenous wastes are secreted into the tubules

• urine is released through pores at the distal ends of the tubules where they reach the body surface

Metanephridia

• in the earthworm

• urine from the distal end of the tubule collects in a saclike storage organ, the bladder

• hemolymph enters through openings at proximal ends of metanephridia in each segment

• urine is released from the bladder through pore opening to exterior

• reabsorption and secretion occur in a convoluted section of the tubule (green) which is surrounded by a capillary network

Malpighian tubules

• have a closed proximal end immersed in hemolymph

• distal ends empty into the gut 

• tubules secrete K+ into the lumen of the proximal segment, which draws in Cl- from the hemolymph

• water follows the KCl

• uric acid is secreted into the tubule

• when fluid reaches the hindgut K+ and Cl- are reabsorbed, followed by water

• uric acid precipitates as crystals released with feces

Osmoregulation and excretion in mammals

• specialized excretory tubules (nephrons) located in the kidney carry out excretion

The ________carries blood into the kidney

renal artery

The filtered blood leaves the kidney by the

renal vein

reabsorb important molecules and ions from the filtrate

peritubular capillaries

Urine is processed in

• collecting ducts then drain through the 

  • renal pelvis

  • ureter

  • urinary bladder

  • urethra

The mammalian kidney is divided into an outer ________and a central________

renal cortex; renal medulla

• nephrons extend between the two regions

• each kidney can obtain up to a million nephrons

Nephrons have ____major regions and are closely associated with a collecting duct

• four

Renal corpuscle (Bowman’s capsule)

filters blood, forming a '“pre urine” or filtrate consisting of ions, nutrients, wastes, and water

• ultrafiltration

Proximal convoluted tubule (PCT)

epithelial cells reabsorb nutrients, vitamins, valuable ions, and water

• selective reabsorbtion

Loop of Henle

establishes a strong osmotic gradient in the tissues outside of the loop, and osmolarity increases as the loop descends

• osmoregulation (salt gradient)

Distal convoluted tubule (DCT)

ions and water are reabsorbing

• selective reabsorption

collecting duct

• water retention

Renal corpuscle

• composed of glomerulus and Bowman’s capsule 

• glomerular filtration occurs in the Bowman’s capsule which cups around a ball of arterial capillaries (the glomerulus)

Glomerular capillaries

have pores that make them more permeable to water and solutes than other capillaries 

Blood pressure drives fluid containing solutes through the pores of the capillaries into _________blood cells and plasma proteins are retained in the capillaries

Bowman’s corpuscle

The diameter of the afferent arteriole -delivering blood to the glomerulus is _______than that of the efferent arteriole- maintaining a high level of glomerular capillary pressure

larger

Proximal tubule is for what region function

reabsorption

Things moving out of the tubule (→ back into the body / reabsorbed):

Substance	How it moves	Why it moves
Na⁺ (sodium)	Active transport (Na⁺/K⁺ pumps)	Needed for fluid and ion balance; creates a gradient for other substances to follow
Cl⁻ (chloride)	Follows Na⁺ passively (voltage gradient)	Balances charge
Glucose, amino acids, nutrients	Active transport (specific proteins)	Body needs them for energy and growth
Water (H₂O)	Osmosis through aquaporins	Follows solutes to balance concentration

Movement of vessels

• All of these go from the tubule → interstitial fluid → peritubular capillaries → back into the bloodstream.

Things moving into the tubule (→ to be excreted):

Substance	How it moves	Why it moves
H⁺ (hydrogen ions)	Active transport	Helps control blood pH (removes excess acid)
Detoxified waste products (from liver)	Passive diffusion	Gets rid of toxins or drugs

Region 3

Descending loop of hele

Descending loop of henle

• Filtrate leaving the proximal convoluted tubule enters the descending segment of the loop of Henle, where water is reabsorbed

This segment descends through regions of increasingly___________ in the interstitial fluid of the medulla – water moves out of the tubule through aquaporins

increasingly higher solute concentrations so water moves out of the tubule through aquaporins

What happens to the osmolarity of the filtrate as it moves down the descending loop of Henle?

The osmolarity of the filtrate gradually increases, reaching a peak of about 1,200 mOsm/L at the bottom of the loop because water leaves and solutes stay behind.

Difference between ascending and descending loop of henly

• The descending loop of Henle is permeable to water but not to salts, so water leaves the filtrate, making it more concentrated as it moves down.

• The ascending loop of Henle is impermeable to water but actively transports salts out, so salts leave and the filtrate becomes more dilute as it moves up.

👉 In short:
Descending = water out, Ascending = salts out

The scending segment

has membrane proteins that transport salt ions, but no aquaporins-water is trapped, while salt ions move out of the tubule

• the reabsorption of salt ions helps establish the concentration gradient of the medulla – high near the renal pelvis and low near the renal cortex

• At the top of the ascending loop, filtrate osmolarity has dropped to about 150 mOsm/L

Descending limb is highly

permeable to water but impermeable to solutes

Ascending limb is nearly

impermeable to water but highly permeable to Na+ and Cl-

Thin ascending limb

passive transport

Thick ascending limb

active transport

Distal convoluted tubule what it does

• secretion and reabsorption 

Substances moving out of the DCT (→ reabsorbed back into the body)

additional water is recovered by osmosis from the fluid in the distal convoluted tubule in response to hormones triggered by changes in the body’s salt concentrations 

• Na+ and Cl- ions are reabsorbed- urea and other nitrogenous wastes remain the same

Substances moving into the DCT (→ secreted into the filtrate)

varying amounts of K+ and H+ ions are secreted into the fluid,

Fluid urine entering the collecting ducts

• by the time the fluid (urine) enters the collecting ducts, it is isosmotic with blood plasms ( about 300mOsm/L) but very different in composition 

Collecting ducts

• these are permeable to water but not salt ions

• as they descend from the medulla of the kidney, they encounter an increasing solute concentration

• water moves out osmotically

• passive urea transporters near the bottom of the medulla contribute to the concentration gradient of the solutes in the medulla 

Three features interact to conserve nutrients and water, balance salts, and concentrate wastes for excretion:

1. The loop of Henle, which descends through the medulla and returns again to the cortex

2. Differences in permeability along the nephron, established by specific membrane transport proteins in each region

3. A concentration gradient of molecules and ions in the interstitial fluid of the kidney, which increases from the renal cortex to the deepest levels of the renal medulla

What do the three kidney control systems monitor?

They link kidney function to blood pressure, osmolarity/pH of body fluids, and water balance, ensuring homeostasis.

How does the kidney maintain constant glomerular filtration despite small blood pressure changes?

Through autoregulation — an internal kidney system that adjusts arteriole diameter to keep filtration stable.

What role do hormonal controls play in kidney function?

Hormones compensate for salt or water loss and adjust water reabsorption in the kidneys to maintain proper fluid and electrolyte balance.

If blood pressure rises:

• More blood enters the glomerulus → filtration rate would go up if unregulated.

• Kidney sensors (receptors) detect this.

• Response:

  • Afferent arteriole constricts → less blood flows into glomerulus.

  • Efferent arteriole dilates → blood leaves faster.

• ✅ Result: Filtration rate goes back down to normal.

If blood pressure drops:

• Less blood enters glomerulus → filtration rate would fall.

• Kidney sensors detect this.

• Response:

  • Afferent arteriole dilates → more blood flows in.

  • Efferent arteriole constricts → blood stays longer.

• ✅ Result: Filtration rate rises back to normal.

Specialized tubule cells in the ___________monitor salt level of the fluid in the tubule

juxtaglomerular apparatus

If salt level rises

• ______________

  • The macula densa cells release paracrine signals (local hormones) that act on the afferent arteriole.

  • Response: afferent arteriole constricts → less blood enters the glomerulus.

  • ✅ Result: filtration rate decreases, preventing too much salt from being lost in urine.

If salt it too low

• ____________

  • The opposite happens: afferent arteriole dilates, increasing filtration to allow more salt excretion.

What RAAS Does

hormonal system involved in regulating Na+ balance

Analogy for RAAS

Blood pressure drops → renin calls the team → angiotensin II constricts roads (vessels) and tells the reservoirs (kidneys) to keep water and salt → system restores pressure.

The RAAS system responds when

• reduced sodium delivery to the distal convoluted tubule detected by macula densa cell. (excessive sodium is excreted)

• Reduced perfusion pressure in the kidney detected by baroreceptors in the afferent arteriole (BP drop and/or blood volume drop)

• Sympathetic stimulation of the JGA via B1, adrenoreceptors 

How does Angiotensin II affect water absorption and blood pressure?

Angiotensin II stimulates ADH secretion, which increases water reabsorption in the kidneys, helping to raise blood pressure.

• elevated blood pressure has the opposite effect on the RAAS

Elevated blood pressure also stimulates cells in the heart to release _____________that inhibits renin release, dilatates afferent arterioles to the glomeruli, and inhibits aldosterone release

atrial natriuretic factor (ANF)

• that inhibits renin release

• dilates afferent arterioles to the glomeruli, and inhibits aldosterone release

• inhibits aldosterone release

What does the ADH system regulate in the body?

ADH regulates osmolarity and water balance by increasing water reabsorption in the kidneys without changing salt excretion.

How do the hypothalamus and osmoreceptors control ADH?

: ADH-secreting neurons in the hypothalamus sense osmolarity; when osmolarity rises, they increase ADH secretion.

How does ADH increase water reabsorption in the kidneys?

ADH acts on distal convoluted tubules and collecting ducts by inserting more aquaporins into epithelial membranes, allowing more water to move back into the blood.

How do marine teleosts replace water lost by osmosis?

Marine teleosts continually lose water to their environment by osmosis and must replace it by continual drinking.

How are ions and nitrogenous wastes handled in marine teleosts?

Excess Cl– is eliminated by chloride cells in the gills, which actively transport it into the surrounding seawater – Na+ and K+ are actively transported to maintain electrical neutrality. Ca2+ and Mg2+ are removed in isoosmotic urine. Nitrogenous wastes are released from the gills as ammonia – kidneys play little role in nitrogenous waste removal.

Sharks and Rays

• maintain osmolarity of their body fluids close to that of seawater by retaining high levels of urea and trimethylamine oxide (TMAO) in body fluids Sharks and rays maintain osmolarity of their body fluids close to that of seawater by retaining high levels of urea and trimethylamine oxide (TMAO) in body fluids

• Isoosmolarity keeps them from losing water to the surrounding sea by osmosis, and they do not have to drink seawater continually to maintain their water balance

• Excess salts ingested with food are excreted in the kidney and by a rectal salt gland located near the anal opening

Freshwater fishes and amphibians

• are hyperosmotic to the surrounding water (water moves osmotically into their tissues)

• they rarely drink, and excrete large volumes of dilute urine to get rid of excess water

• salt ions lost urine are replaced by salt in foods and by active transport of Na+ and K+ into the body by gills (in fishes) or across the skin (in amphibians)

Terrestrial amphibians

• must conserve both water and salt, which is obtained primarily in foods

• kidneys secrete slat into urine, causing water to enter urine by osmosis- salt is reclaimed in the bladder by active transport and returned to body fluids

• also have behavioral adaptation that help minimize water loss, such as seeking shaded, moist environments and remaining inactive during the day.  

Reptiles and birds

• conserve water by secreting nitrogenous wastes in the form of uric acid crystals

• epithelial cells of the cloaca absorb water from feces and urine before wastes are excreted

• these that live in or around seawater take in large quantities of salt with their food and rarely drink fresh water

• secrete excess salt through salt glands in the head, which remove salts from the blood by active transport 

Adaptations that conserve water

• Water-conserving activities of the kidneys, length of loop of Henle

• Location of the lungs deep inside the body reduces water loss by evaporation during breathing

• A body covering of keratinized skin almost eliminates water loss by evaporation

Water-conserving adaptations reach their greatest efficiency in _________ such as the kangaroo rat – 90% of its daily water supply is generated from oxidative reactions in its cells

desert rodents

Temperature regulation (thermoregulation)

• is based on negative feedback pathways in which temperature receptors (thermoreceptors) detect changes from a set point

• signals from receptors trigger phsiological and behavioral responses that return the temperature to the set point

• All responses triggered by negative feedback mechanisms involve adjustments in rate of heat generating oxidative reactions within the body-couples with adjustments in rate of heat gain or loss at the body surface

Within a range of tolerable temperatures, an animal’s ____________varies greatly

organismal performance (biochemical, psychological, and whole body processes)

Heat exchange

• All animals gain or lose heat by a combination of conduction, convection, radiation, and evaporation

• To maintain constant body temperature, the heat gained and lost through these pathways must balance