Chapter 44Controlling the Internal Environment

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Brief Overview to Body Temperature Regulation

Each animal species has an optimal temperature range Thermoregulation: the maintenance of

body temperature within a range that enables cells to function efficiently

Animals exchange heat with their environment and need some way to replenish it This creates the difference between

warm-blooded (endothermic) and cold-blooded (ectothermic) animals

Ectotherms Ectotherms are any

animal whose body temperature is a result of their surroundings

This is common in marine animals, retiles and amphibians in particular Breeding Ball, Cobra

Mating, or Meerkats

Endotherms An endotherm is an

organism that derives its internal temperature from its own metabolism

Humans are endothermic and maintain a relatively constant internal body temperature

Being endothermic solved many of the problems associated with living on land

Homeostasis By definition, homeostasis is the

property of a system (open or closed) that regulates its internal environment so that it maintains a stable, constant condition

Nerve cells that control thermoregulation and homeostasis are concentrated in the hypothalamusThe hypothalamus is a part of the brain

responsible for linking the nervous system to other systems like the endocrine system

Water Balance and Waste Disposal

Our body has to maintain a balance between water uptake and water loss

Because of our active aerobic metabolism, there are many by-products that can be toxic if accumulated

To keep balance, our body must move solutes between body fluid and environment

Water Balance When getting rid of

metabolic wastes, solutes must pass through transport epithelium This is the layer(s)

of epithelial cells that regulate solute movement

Most epithelial tissue is arranged in tubular networks These are very

important to the urinary system

Waste Disposal

The most toxic of all by-products are nitrogen-containing wastes (from breakdown of protein and nucleic acids)

Most are form of ammonia Ammonia: excreted by marine animals Urea: mammals excrete this; 10,000

times less toxic than ammonia Uric acid: excreted by land snails, birds,

and reptiles

Osmosis Def: the movement of

water across a selectively permeable membrane

Humans are osmoregulators: we must adjust internal solute concentration to match outside environment

FYI- humans will die if they lose 12% of their body water

Excretory Systems These systems (namely the urinary) are vital

to homeostasis because dispose of metabolic waste

Urine is produced through two processes: filtration of body fluids & refinement of aqueous solution from filtration Filtration: blood is exposed to filtering device of

selectively permeable membrane Water and small solutes in excretory system

because of force of blood pressure; proteins and other large molecules too big to fit through membrane

Urine Production Reabsorpion is one of

two mechanisms using active transport Selective transport of

water and valuable solutes (glucose, salts, amino acids) from filtrate back into body fluids

Filtration is nonselective-small molecules essestial to body are returned to fluids

Secretion is another mechanism Involves adding of

solutes (salt and toxins) from the body to the filtrate

Once added to the filtrate, the solutes will pass with the urine out of the body

Kidneys & The Urinary System Kidneys are involved in

excretion and osmoregulation (maintenance of solute concentration)

Bean-shaped organs (10 cm long)

Blood enters kidneys through renal artery and leaves through renal vein FYI- kidneys 1% of body

weight, but receive 20% of blood pumped with EACH heartbeat

The Kidneys & Urinary SystemFrom the kidneys, the urine flows to

ureters which connect to the urinary bladder leaves body through urethra

There are two regions of the kidney: outer renal cortex and inner renal medulla Both filled with nephrons: functional unit

of the kidneys Contains ball of capillaries (glomerulus)

covered by Bowman’s capsule

FiltrationFiltration occurs when blood pressure

forces water, urea, salts, and solutes from the blood in the glomerulus into the Bowman’s capsuleCapillaries called podocytes act as

filter-permeable to water and small solutes but not large molecules

If molecule is small enough to fit through the capillary wall, it will be filtered because filtration is nonselective

Nephrons and Components From the Bowman’s

capsule, the filtrate goes through 3 regions of nephron: Proximal tubule Loop of Henle (had

descending limb and ascending limb)

Distal tubule Distal tubule empties

into collecting duct (filtrate from nephrons)

Nephron The nephron and

collecting duct are lined with transport epithelium to process filtrate 1100-2000 L of

blood pass through kidneys/day, nephrons process 180 L of filtrate and create 1.5 L of urine

Rest is absorbed into blood as mostly water

Secretion and Reabsorption Secretion involves

both passive and active transport

The controlled secretion of hydrogen ions from the interstitial fluid is responsible for maintaining pH Proximal and distal

tubules involved in secretion

Nearly all sugars, vitamins, and other organic nutrients are reabsorbed along with a large amount of water Proximal and distal

tubules and loop of Henle contribute to reabsorption

Selective reabsorption and secretion control concentrations of salt in body fluids

Flow From Filtrate to Urine Step 1: proximal tubule

Maintains pH of body by controlling secretion of hydrogen ions

Secretes ammonia and absorbs 90% of bicarbonate buffer

Any drug/poison in liver is absorbed here

Glucose, amino acids, K+, and NaCl are reabsorbed

Water follows the movement of salt to interstitial fluid

Step 2: descending limb of loop of Henle Permeable to water,

not to salt/solutes Water leaves loop

because it is hypotonic to the interstitial fluid around it

NaCl concentration increases

Steps to Urine Formation Step 3: ascending limb

of loop of Henle Permeable to salt, not

water Two regions: thin

segment (loop tip) and thick segment (leads to distal tubule)

NaCl diffuses out in thin segment

NaCl actively trasported out of thick segment

Step 4: distal tubule Both secretion and

reabsorption happen here

Monitors amount of K+ secreted into filtrate and amount of NaCl reabsorbed from filtrate

Controls pH regulation

Urine Formation

Step 5: collecting duct Carries the filtrate to renal pelvis and

medulla, actively absorbs NaCl Permeable to water, not salt-loses more

and more water to osmosis High concentration of urea diffuses out of

ductThese five steps are parts of each

nephron, which are the components of the kidneys

Conserving Water by Kidney Action

NaCl and urea are responsible for the osmotic gradient Each step in filtration in

the nephron is meant to maintain conservation of water

Proximal tubule (1): large amount of water and salt are reabsorbed-volume of filtrate decreases; molarity is still equal to blood

Water ConservationDescending limb of the loop of Henle

(2): water leaves tubule by osmosis and NaCl concentration increases Salt concentration peaks at elbow of loop

of HenleAscending loop of Henle (3): salt

concentration decreases because it is permeable to salt, not water Two limbs combined maintain osmotic

balance and can affect each other’s chemical changes

Water Conservation

The filtrate is hypotonic when it reaches the distal tubule NaCl concentration lowered in ascending

limbFrom the cortex to medulla, the filtrate

loses water by osmosis- concentration of urea increases Urine is isotonic in relation to interstitial

fluid but hypertonic to blood and rest of body