Chapter 15: Homeostasis

Question 1

What is the role of the loop of Henle?

Answer 1

1. Cause decrease in water potential –> establish water potential gradient down medulla.
2. Ascending limb actively transports/pumps Cl- and Na+ ions out into medulla tissue fluid against conc. gradient.
3. Walls of descending limb permeable to water.
4. Water removed from descending limb.
5. Water potential of tissues surrounding collecting duct lower than fluid inside it.
6. Water removed from filtrate/urine in collecting duct.

Question 2

How is ADH dealt with as a protein?

Answer 2

1. Dealt with as a protein in the liver.
2. Hydrolysis –> broken down by protease.
3. Deamination –> amine group removed to form NH3.
4. Ornithine cycle –> formation of urea.
5. Amino acids –> used in metabolic pathways.

Question 3

How is ADH/urea dealt with as a small molecule?

Answer 3

1. In kidneys.
2. Ultrafiltered from blood –> moves into nephron.
3. Small molecule.
4. Urea/ADH not all reabsorbed + is present in urine.
5. Excreted.

Question 4

Define homeostasis.

Answer 4

• Maintaining a dynamic equilibrium with small fluctuations within a narrow range of conditions.

Question 5

Why are both receptors and effectors important in homeostasis?

Answer 5

• Sensory receptors = detect changes in internal + external environment/stimuli.
• Effectors = react to motor stimulus –> bring about change to restore original conditions –> negative feedback.

Question 6

How does an organism gain heat?

Answer 6

• Waste heat from cell respiration.

- Conduction, radiation + convection from surroundings.

Question 7

How does an organism lose heat?

Answer 7

• Evaporation of water.

- Conduction, radiation + convection to surroundings.

Question 8

What are ectotherms?

Answer 8

• Cold blooded organisms that rely on their surroundings to provide warmth.
• Core body temp. heavily dependent on surroundings.

Question 9

How do ectotherms increase core body temp?

Answer 9

• Bask in the sun –> expose larger s.a. to absorb more radiation/heat.
• Orientate body towards sun.
• Conduction –> press body against warm ground.
• Extend areas of body –> increase s.a. available to absorb heat.
• Exothermic metabolic reactions –> contract muscles, increase vibration to increase cellular respiration to warm muscles.
• Darker colours –> absorb more radiation.
• Increased heart rate.

Question 10

How do ectotherms decrease core body temp?

Answer 10

• Shelter from sun by seeking shade.
• Reduce movement –> lower metabolic activity.
• Orientate body away from sun.
• Press body against cool ground –> conduction to surroundings.
• Hide in burrows –> reduce s.a. exposed to sun to reduce heat absorption.
• Decreased heart rate.
• Convection –> stand up on high ground –> lose heat by convection currents in the air around it.
• Evaporation –> wallow in mud –> lose heat by evaporation of water from the surface of the skin.

Question 11

What are endotherms?

Answer 11

• Warm blooded organisms that rely on metabolic processes to maintain stable body temp.
• Minimise s.a. to vol ratio.

Question 12

How do endotherms increase core body temp?

Answer 12

• Sweat glands secrete less sweat onto skin –> less heat lost by evaporation of water.
• Erector pili muscles in skin –> contract + pull hairs or feathers of animal erect –> trap insulating layer of air –> reduce heat loss from skin by convection.
• Do not pant –> reduced evaporation of water from lungs, tongue + other moist surfaces.
• Spontaneous contraction of skeletal muscles (shivering) –> more heat produced as muscle cells respire.
• Arterioles constrict (vasoconstriction) –> narrow arterioles –> reduce blood flowing to capillaries near skin surface –> less heat radiated from skin.
• Increased rate of metabolism –> increased respiration releases more heat into the bloodstream.

Question 13

How do endotherms decrease core body temp?

Answer 13

• Sweat glands secrete more sweat onto skin surface (spreads out across skin surface)–> more heat lost by evaporation of water –> cool blood below skin surface.
• Erector pili muscles in skin –> relax + lie flat–> do not trap insulating layer of air –> increase heat loss by convection –> large s.a. to vol ratio.
• No spontaneous contraction of muscles.
• Vasodilation –> widen arterioles –> increase blood flowing to capillaries near skin surface –> more heat radiated from skin.
• Increased panting –> increased evaporation of water from tongue, lungs + other moist surfaces using heat.
• Reduced metabolic activity in liver cells –> less heat generated from exergonic reactions.

Question 14

Outline vasoconstriction + vasodilation in regulation of core body temp.

Answer 14

Vasodilation –> lower body temp:

• Arterioles dilate –> widen.
• Arteriovenous shunt vessels –> constrict.
• Blood forced into capillaries near surface of skin.
• Skin flushes + cools due to increased radiation.
• Skin pressed against cool surface –> loses heat by conduction.

Vasoconstriction –> raise body temp:

• Arterioles constrict –> narrow.
• Arteriovenous shunt vessels dilate.
• Reduce blood flowing into capillaries near skin surface.
• Skin appears pale –> less heat lost by radiation.

Question 15

Role of heat gain centre?

Answer 15

• Activated when temp of blood flowing through hypothalamus decreases.
• Sends impulse through autonomic nervous system to effectors in skin + muscle.
• Triggers response –> raises core body temp:
• Vasoconstriction, erector pili muscles contract + raised up (erect), panting, sweating, increased metabolic activity.

Question 16

Role of heat loss centre?

Answer 16

• Activated when temp of blood flowing through hypothalamus increases.
• Sends impulses through autonomic motor neurones to effectors in skin + muscle.
• Triggers response –> lowers core body temp:
• Vasodilation, erector pili muscles lie flat + relax, sweating, decreased metabolic activity, reduced panting.

Question 17

Define excretion.

Answer 17

• Removal of metabolic waste products from body.

Question 18

Define egestion.

Answer 18

• Removal of undigested material from an organism.

Question 19

Describe the rich blood supply in the liver.

Answer 19

Oxygenated blood:

• Supplied to the hepatocytes by the hepatic artery.
• Removed + returned to heart by the hepatic vein.
• Provides O2 for aerobic respiration.
• blood –> aorta –> hepatic artery –> liver.

Deoxygenated blood:

• Supplied by hepatic portal vein –> from intestines to liver.
• Contains products of digestion.
• Hepatic portal –> capillaries at both.

Question 20

Structure of liver.

Answer 20

Hepatocytes:

• Large nuclei, Golgi, lots of mitochondria –> divide + replicate.

Sinusoids –> surrounded by hepatocytes:

• Where blood from hepatic portal vein + hepatic artery are mixed.
• Empty into intra-lobular vessel.
• Increase O2 content of hepatic portal vein.
• Short diffusion distance between hepatocytes + sinusoids.
• Kupffer cells –> macrophages of the liver –> ingest foreign particles + protect against disease.

Canaliculi:

• Spaces where hepatocytes secrete bile from breakdown of blood.
• Bile drains into bile ductules which take it to the gall bladder.

Question 21

Explain carbohydrate metabolism in the liver.

Answer 21

When BGC too high:

• Beta islet cells produce insulin.
• Stimulate hepatocyte cells to convert glucose into glycogen.
• Glycogenesis.

When BGC too low:

• Alpha islet cells produce glucagon.
• Stimulate hepatocytes to convert glycogen into glucose.
• Glycogenolysis + gluconeogenesis.

Question 22

Explain deamination of amino acids in the liver.

Answer 22

• Transamination = conversion of one amino acid into another.
• Deamination = removal of amino acid group to form ammonia.

Ornithine cycle:

• Ammonia converted to urea.
• Urea –> less soluble + toxic than ammonia –> passed back into blood in kidneys.
• Kidneys filter out urea from the blood + store it as urine in the bladder.

Question 23

Describe the steps of the Ornithine cycle.

Answer 23

1. Deamination –> ammonia formed.
2. CO2 added to ornithine + ammonia –> water + citrulline formed

3 NH3 added to citrulline –> forms water + arginine.

4. Water added to arginine –> urea + ornithine formed.

Question 24

Outline detoxification in the liver.

Answer 24

• H2O2 broken down by catalase into water + O2.
• Alcohol dehydrogenase breaks down ethanol into ethanal which is then converted to ethanoate –> used to build up fatty acids or used in respiration.