5.3 Homeostasis

Question 1

What is homeostasis ?

Answer 1

The body maintaining a dynamic equilibrium , with small fluctuations over a narrow range of conditions.

Question 2

What are some factors affected by homeostasis ?

Answer 2

Blood pH, blood glucose concentration levels, urea concentration, temperature, water content.

Question 3

What are 2 factors that are vital for homeostasis ?

Answer 3

Receptor and effectors as they detect and respond to change.

Question 4

What is a negative feedback system ?

Answer 4

When a small change in one direction is detected by sensory receptors, effectors work to reverse the change. They work to reverse the initial stimulus.

Question 5

What occurs in a negative feedback system when a increase is directed ?

Answer 5

An increase is detected, causing a reduction in levels to return back to ideal conditions.

Question 6

What occurs in a negative feedback system when a decrease is directed ?

Answer 6

A decrease is detected, causing an increase in levels to return back to ideal conditions.

Question 7

What is a positive feedback system ?

Answer 7

A change in conditions caused a reinforcement of the change.
Eg, blood clotting, contractions, depolarisation.

Question 8

What is thermoregulation ?

Answer 8

Maintenance of a relatively constant core body temperature to maintain optimum enzyme activity.

Question 9

What are ectotherms ?

Answer 9

Most animals are ectotherms and they use their surroundings to warm up their body temperature.

Question 10

What are endotherms ?

Answer 10

Mammals and birds are endotherms. They rely on metabolic processes to warm up.

Question 11

What are behavioural responses ?

Answer 11

Changing behaviour to control temperature of the body to warm up or cool down.

Question 12

What are physiological responses ?

Answer 12

Body features that help to warm up or cool down the body. Eg, dark fur.

Question 13

Why don’t ectotherms thermoregulate ?

Answer 13

They have a high heat capacity of water and many live in water.

Question 14

Why do ectotherms require less food ?

Answer 14

They require les food due to requiring less energy to regulate temperature.

Question 15

What are endotherms ?

Answer 15

They can regulate their body temperature within a very narrow range in a wide variety of external conditions.

Question 16

How is thermoregulation regulated in endotherms ?

Answer 16

Endotherms use their internal exothermic metabolic activities to keep them warm.

Question 17

How do endotherms cool down ?

Answer 17

Vasodilation occurs near surface if skin causing the arterioles to dilate. This forces blood through capillaries near the surface of the skin and heat is lost through evaporation of sweat from skin surface.

Question 18

How do endotherms warm up ?

Answer 18

Arterioles constrict so little blood flows near surface of the skin. Sweating is decreased reducing evaporation of radiation. Shivering also occurs due to involuntary contracting of muscles. Hairs also stand up trapping air under muscles causing it to warm up.

Question 19

How is the heat loss centre activated ?

Answer 19

Activated when blood flowing through hypothalamus increases.

Question 20

How is heat gain centre activated ?

Answer 20

Activated when temperature of blood flowing through hypothalamus decreases.

Question 21

What are the main metabolic waste products excreted in animals ?

Answer 21

Carbon dioxide, bile pigments and nitrogenous waste products, such as urea.

Question 22

How is oxygenated blood supplied to the liver ?

Answer 22

Supplied by hepatic artery from the aorta.

Question 23

What is the hepatic portal vein ?

Answer 23

Carries blood loaded with products of digestion straight from intestines to liver and this is the starting point for many metabolic activities.

Question 24

What are cells in the liver called ?

Answer 24

Hepatocytes have large nuclei, a prominent Golgi and lots of mitochondria, indicating they are metabolically active.

Question 25

What are the spaces called that are surrounded by hepatocytes ?

Answer 25

Sinusoids mixes blood from hepatic artery and hepatic portal vein. Mixing increases they oxygen content of the blood from hepatic portal vein.

Question 26

What cells do sinusoids contain ?

Answer 26

Kupffer cells which act as the resident macrophages of the liver, ingesting foreign particles and helping to protect against disease.

Question 27

What happens when the hepatocytes secrete bile ?

Answer 27

They secrete bile from the breakdown of blood into spaces called canaliculi and from these the bile drains into the bile ducts which take it into the gall bladder.

Question 28

What happens when blood glucose levels rise ?

Answer 28

Insulin levels rise and stimulate hepatocytes to convert glucose glucose into glycogen.

Question 29

What happens when blood glucose levels drop ?

Answer 29

Hepatocytes convert glycogen back to glucose under influence of hormone glucagon.

Question 30

What is deamination ?

Answer 30

This is the removal of an amine group from a molecule. Removing the amino group and converting it into ammonia which is toxic to urea.

Question 31

What is the ornithine cycle ?

Answer 31

Set of enzyme controlled reactions. Ammonia is added as well as CO2 forming citrulline and water. Ammonia is added to citrulline to form arginine and water. Finally, water is added to arginine forming ornithine and urea. Then the cycle repeats.

Question 32

What carries blood to kidneys ?

Answer 32

The renal artery carries blood to the kidneys from the abdominal aorta.

Question 33

What enzyme do hepatocytes contain ?

Answer 33

Contains catalase that breaks down hydrogen peroxide into oxygen and water.

Question 34

What are kidneys made up of ?

Answer 34

Made up of millions of nephrons that act as filtering units for urea to be excreted.

Question 35

What are the three main areas of the kidney ?

Answer 35

Cortex, medulla and the pelvis.

Question 36

What is the Bowmans Capsule ?

Answer 36

Cup shaped structure that contains the glomerulus and capillaries. This is where ultrafiltration takes place.

Question 37

What is the proximal convoluted tubule ?

Answer 37

The first coiled region of the tubule after the Bowmans capsule, found in the cortex of the kidney. This is where many of the substances needed by the body are reabsorbed by the blood.

Question 38

What is the Loop of Henle ?

Answer 38

This is a long loop of tubule that creates a region with a high solute concentration in the tissue fluid deep in the kidney medulla. Descending loop is permeable to water and ascending loop is permeable to ions.

Question 39

What is the distal convoluted tubule ?

Answer 39

The second twisted tubule where fine tuning of water takes place. The permeability of water varies in response to ADH.

Question 40

What is the collecting duct ?

Answer 40

This is where the urine passes down through the medulla to the pelvis. More fine-tuning occurs. Walls are also sensitive to ADH.

Question 41

What occurs during ultrafiltration ?

Answer 41

Glomerulus is supplied with blood via afferent arteriole and leaves through the efferent arteriole, causing pressure in capillaries. This forces blood out of capillaries and fluid passes through a basement membrane.

Question 42

How do podocytes help ultrafiltration ?

Answer 42

Found in wall of Bowmans capsule that act as an additional filter. They have extensions called pedicels that wrap around capillaries (like a claw clip), causing filtration.

Question 43

How does reabsorption occur ?

Answer 43

In proximal convoluted tubule, all glucose, amino acids and vitamins are reabsorbed back into blood via active transport.

Question 44

How does loop of Henle make more concentrated urea ?

Answer 44

Descending limb is permeable to water so water leaves down the concentration gradient during osmosis. Ascending limb is where ions are actively pumped out of tubule and is impermeable to water.