Chapter 07: Homeostasis Of Body Temperature And Body Fluid

Question 1

• What is metabolic rate?
• How does stress increase metabolic rate?
• Why must heat loss equal heat gain?
• What are the 2 types of thermoreceptors and in what parts of the body are they located?
• What happens when cold and heat receptors are stimulated?
• What are the 4 ways heat can be lost from the body?
• What is sweating?
• What does sweat consist of?
• Explain how sweat is a mechanism of cooling.
• Explain how the physiological response of vasoconstriction acts to prevent falling body temp.

Answer 1

• The rate at which energy is released by the breakdown of food.
• Stress increases stimulation of sympathetic nerves that release noradrenaline to increase cell metabolic activity.
• To maintain a constant body temp.
• Peripheral thermoreceptors: In skin and mucous membranes. Central thermoreceptors: In hypothalamus.
• When cold receptors are stimulated, the hypothalamus initiates heat conservation and production mechanisms. When heat receptors are stimulated, the hypothalamus decreases heat production and increase heat loss mechanisms.
• Conduction, convection, radiation and evaporation.
• Sweat gland secretions to help heat loss through evaporation.
• Dissolved substances such as sodium chloride, urea, lactic acid and potassium ions.
• Heat is removed from the body when sweat evaporates.
• Vasoconstriction decreases warm blood flow to the skin thus decreasing the transfer of heat from the internal organs to the skin.

Question 2

• Explain how stimulation of the adrenal medulla assists in preventing falling body temp.
• How does shivering prevent body temp falling?
• How does increased thyroxine production prevent body temp falling?
• How does behaviour prevent body temp falling.
• Where are all the places in the body where heat is lost?
• Describe the role of the skin in regulating body temp.
• When temperatures reach 37°, how is heat lost differ?
• In summer, metabolic rate can decrease, how is this effective, how does it occur?

Answer 2

• Adrenaline and noradrenaline increases metabolic rate increasing heat production.
• Muscles contract and relax rapidly, increasing metabolic rate, releasing heat, increasing body temp.
• Increases metabolic rate, increasing heat and body temp but is slower to have an effect but is longer lasting.
• Being consciously aware of cold conditions we can behave in a way that reduces heat loss, eg putting on a jumper.
• Skin, gases breathed out from the lungs, faeces and urine.
• Skin regulates constriction/dilation of blood vessels to control blood flow. More blood flowing near the skin’s surface, more heat is lost by convection and radiation and also controls amount of sweat secreted.
• Heat no longer lost though vasodilation as outside temp is higher. Instead only evaporation of sweat works.
• Less heat produced and occurs by reduction of thyroxine secretion.

Question 3

• Explain the difference between heat stroke and heat exhaustion.
• Explain the effects of hypothermia.
• Where is water stored in the body?
• Where is fluid lost in the body?
• What is the renal vein?
• What is the nephron?
• What is the Urethra?
• What is the renal artery?
• List in order the path travelled by a RBC through the kidneys.
• List in order the structures that materials filtered from the blood will flow through in the nephron.

Answer 3

• Heat exhaustion: extreme sweating and vasodilation reducing blood volume and which may cause the person to collapse but body temp remains normal. Heat stroke: heat loss mechanisms are inadequate rising body temp.
• Metabolic rate so slow that heat production is unable to replace heat lost and temp continues to fall.
• Intracellular fluids (cytosol), extracellular fluid (blood plasma) and intercellular fluid (fluid between cells).
• Kidneys, skin, surface of lungs, and alimentary canal.
• Blood vessel that takes blood away from the kidney.
• Functional units of kidney responsible for excretion and water regulation.
• The tube that empties the bladder to the outside.
• A blood vessel that takes blood to the kidney
• Afferent arteriole, glomerulus, efferent arteriole, peritubular capillary network and venule.
• Bowmans capsule, proximal convoluted, loop of Henle, distal convoluted tubule and collecting duct.

Question 4

• Explain how the lungs are involved in excretion.
• Explain how sweat glands are involved in excretion.
• Explain how the alimentary canal is involved in excretion.
• What are the kidneys?
• Why is the kidneys the only method of regulating composition of body fluids?
• What is the ureter?
• What is the bladder?
• Where is 99% of the water entering the kidneys reabsorbed?
• What substance is not normally found in the ureter but found in both renal vein and renal artery.
• What substance would you find in renal vein and ureter but much less in renal vein?

Answer 4

• They excrete CO2 and H2O produced by body cells during cellular respiration.
• Sweat consists of salt, urea and lactic acid which are all metabolic byproducts.
• Excretes bile pigments from bile.
• A pair of excretory organs responsible for maintaining concentration of substances in the body fluids and excreting waste products eg urea
• Water loss from the skin, lungs and alimentary canal cannot be regulated whereas the kidneys can regulate body fluids.
• Tube leaving kidney that drains urine into the urinary bladder.
• A muscular bag that holds the urine until it’s passed out the body.
• Entire length of kidney tubule walls. Reabsorption at proximal convoluted tubule and loop of Henle is by osmosis, whereas reabsorption at the distal convoluted tubule and collecting duct is active reabsorption (through aldosterone and antidiuretic hormone.
• Glucose
• Urea

Question 5

• Explain how a nephron functions in 5 steps.
• Explain how the aldosterone plays a part in the regulation of water output.
• How does increased aldosterone increase blood pressure?

Answer 5

1. Blood enters glomerulus under high pressure.
2. Filtration: high BP forces water and dissolved molecules (filtrate) into glomerulus capsule. Large molecules and blood cells are retained in blood.
3. Reabsorption: filtrate passes through proximal convoluted tubule and loop of Henle. Water and useful substances here are reabsorbed by osmosis into peri tubular capillaries, whereas at the distal convoluted tubule and collecting duct is active reabsorption.
4. Active secretion: Non-useful materials are secreted into peri-tubular capillaries.
5. Urine: Remaining water and substances form urine carried by collecting ducts to the ureter and then to bladder.
   - Secreted by adrenal cortex, acts on kidney tubules to increase the sodium reabsorption and potassium excretion in forming urine. As the blood sodium concentration increases, water from kidney tubules diffuses back into the blood through osmosis.
   - Increases water reabsorption, increases blood volume, increasing BP.

Question 6

• Explain the steady state mechanism of ADH controlling water balance.
• Describe the steady state mechanism responsible for thirst
• What is water intoxication?
• What is water dehydration?
• What is physiology?

Answer 6

S: Increased blood osmotic pressure.
R: Osmoreceptors in hypothalamus stimulated.
M: Posterior lobe stimulated, releasing ADH.
E: Increased water permeability of distal convoluted tubules and collecting ducts.
R: Increased water reabsorbed into blood plasma.
F: Blood osmotic pressure decreased.
S: High blood osmotic pressure.
R: Osmoreceptors stimulated
M: Hypothalamus informs cerebral cortex and a conscious feeling of thirst occurs.
E: Skeletal muscles responds
R: Drink a glass of water.
F: Decreased blood osmotic pressure.
-Drinking too much water and not replacing amount of salt intake.
-Excessive loss of water and salts from body, when the body loses more fluid than it takes in.
-How the body functions internally

Question 7

• Why should new born babies be dried and wrapped up?
• What is the effects of glucagon?
• Is the blood glucose level high or low very early in the morning before breakfast and why?
• What’s the difference between plasma and lymph?
• What 3 homeostatic mechanisms are used in an effort to restore the correct amount of water in the blood?
• What are diuretics?
• Even if we do not drink very much we still produce some urine. Where does the water come from?
• What is urea? Where is it produced? Why do we have to excrete it?
• What is filtration?
• What are 3 reasons why the filtration from the glomerulus to the bowman’s capsule occurs.

Answer 7

• New born babies are wet and have no temp control so need to be dried to reduce the effects of evaporation and wrapped to keep them warm and prevent heat loss.
• Stimulates breakdown of glycogen to glucose (gluconeogenesis).
• High because stored glycogen is released is released over night.
• Plasma is the liquid portion of blood found in blood vessels. Lymph is liquid found in lymph vessels and doesn’t contain RBC or platelets.
• Thirst reflex, increased secretion of ADH and aldosterone.
• Substances that increase urine production. Eg caffeine and alcohol.
• From food and metabolic by products.
• Is a waste product produced in the liver if it isn’t removed it can become toxic.
• Separation of materials in blood to be eliminated from the body, occurs in nephron.
  1. Glomerular capillaries are very long increasing surface area.
  2. Membranes which substances pass are very thin and porous.
  3. High BP in glomerulus as Afferent arteriole has a large diameter than the efferent arteriole.

Question 8

• What is selective reabsorption?
• Where does ultrafiltration, selective reabsorption and active secretion occur in the nephron?
• What are the 2 effects of active secretion?

Answer 8

• Movement of substances by active and passive processes from filtrate in nephron back into blood.
• Bowman’s capsule; entire length not involving glomerulus and collecting duct; proximal and distal convoluted tubule.
• Remove unwanted substances and maintain blood pH.