Unit 6 - Homeostasis

Question 1

What is homeostasis?

Answer 1

Involves physiological control systems that maintain the internal environment within restricted limits.

Question 2

In humans, what is the “optimum point” in terms of body temperature?

Answer 2

37 degrees

Question 3

In human control systems, which part of the brain is responsible for monitoring a number of optimum points?

Answer 3

Hypothalamus

Question 4

What is positive feedback; explain why positive feedback is normally dangerous.

Answer 4

Deviation from the normal values causes changes that result in even greater deviation from normal

Question 5

Suggest two beneficial examples of positive feedback.

Answer 5

1) Influx of sodium ions which increases permeability of the neurone membrane to sodium ions bringing a large and rapid response

2) childbirth

Question 6

Describe two ways in which endotherm bodies respond to hyperthermia.

Answer 6

1) increased sweating

2) lowering of body hair

Question 7

Explain why ectotherms need to spend time “warming up” but endotherms do not.

Answer 7

Ectotherms rely on external sources of heat to control body temperature. Endotherms generate heat metabolically to control body temperature

Question 8

State how endotherm control systems respond to hypothermia.

Answer 8

raising of hair to trap heat

Question 9

Define “negative feedback.”

Answer 9

When any deviation from the normal values are restoreed to their original level

Question 10

Describe how negative feedback eventually results in corrective measures being turned off in a human who has become too hot.

Answer 10

Once body temperature is restored to its originnal state

Question 11

What are hormones?

Answer 11

Chemical messengers produced by glands in the endocrine system that regulates various bodily functions

Question 12

Hormones are secreted through endocrine glands. What does the word endocrine mean?

Answer 12

Secretes substances into the blood

Question 13

Hormones act on target cells. What would the target cells be for the hormone insulin?

Answer 13

Liver cells

Question 14

Describe the exact mechanism by which adrenaline triggers the release of glucose as part of the fight or flight response. You must mention adenyl cyclase, cyclic AMP, and kinase enzyme.

Answer 14

Adrenaline attaches to receptor site of target cells. Then, fuses to the receptor site and in doing so activates adenyl cyclase inside the membrane. Adenyl cyclase converts ATP to cyclic AMP (second messenger) that activates kinase enzyme that converts glycogen into glucose.

Question 15

What exocrine function does the pancreas have?

Answer 15

Secretion of enzymes

Question 16

Describe the structure and the secretions of the Islets of Langerhans in the pancreas.

Answer 16

Alpha cells: manufacture and secrete glucagon

Beta cells: manufacture and secrete insulin

Question 17

Define
• Glycogenesis
• Glycogenolysis
• Gluconeogenesis

Answer 17

Glycogenesis: converting glucose into glycogen

Glycogenolysis: hydrolysis of glycogen to glucose

Gluconeogenesis: creating glucose from other molecules (e.g. amino acids, glycerol)

Question 18

Explain why high blood glucose is problematic for health.

Answer 18

Too high = lowers water potential of blood causing the cells to shrivel up and die

Question 19

Explain the effect of insulin on the cells of the body.

Answer 19

Triggers movement of glucose via facilitated diffusion into cells where it forms glycogen

Question 20

Explain the effects of glycogen; do not use the phrase “breaks down!”

Answer 20

Hydrolyses glycogen into glucose to help regulate blood glucose level

Question 21

Propose some reasons why a person’s blood glucose levels might temporarily spike.

Answer 21

Ingestion of food/drink containing carbohydrates

Question 22

Explain the difference between Type 1 and Type 2 diabetes.

Answer 22

Type I: unable to produce insulin

Type II: receptors on target cells lose their responsiveness to insulin

Question 23

Explain how Type 1 and Type 2 diabetes are controlled.

Answer 23

Type I: injections of insulin before and after a meal

Type II: regulating intake of carbohydates

Question 24

Describe the structure of the kidney; how many nephrons are there in each kidney?

Answer 24

Long tubules surrounded by capillaries

About 1 million

Question 25

What is the glomerulus?

Answer 25

Tiny ball-shaped composed of capillaries actively involved in the filtration of the blood to form urine

Question 26

Why is blood pressure very high in the glomerulus? (2 reasons)

Answer 26

Larger diameter of the afferent arteriole compared to the efferent arteriole

Question 27

In the Bowman’s capsule, what causes water to be forced out of the glomerulus and into the kidney tubule?

Answer 27

Hydrostatic pressure

Question 28

Describe the role of podocytes in the Bowman’s capsule.

Answer 28

Supports substances to squeeze between cells

Question 29

Which substances are filtered out into the Bowman’s capsule; describe also what remains in the bloodstream, and why it is not filtered out.

Answer 29

Glucose, amino acids, hormones, vitamins, water, uric acid, urea, creatinine, inorgsnic ions.

White blood cells, red blood cells, large plasma proteins, platelets, plasma.

Too large to be filtered out

Question 30

List the substances that are reabsorbed in the Proximal Convoluted Tubule (PCT).

Answer 30

Glucose, amino acids, vitamins, some ions, some urea

Question 31

Explain the process of co-transport in the PCT.

Answer 31

Sodium-potassium pump continuously pumps 3x sodium ions into the bloodstream from cells in PCT wall

Concentration gradient between filtrate + cells of PCT wall so sodium ion diffuses in and carries glucose or amino acid with it

Glucose returns to blood through glucose uniporter

Question 32

How is the process of co-transport in the PCT different to the process of co-transport that occurs in the villi of the small intestine?

Question 33

In the Loop of Henle, describe how a counter-current is set up.

Answer 33

Water potential gradient maintained down whole length of collecting duct so osmosis takes place continuously.

Due to filtrate in collecting duct with a lower water potential meets interstitial fluids with an even lower water potential

Question 34

In the descending limb of the Loop of Henle, why does solute concentration increase further down the loop?

Answer 34

Descending limb - permeable to water so moves out into the blood.

Sodium and Chlorine ions diffuse into descending limb

Question 35

How does water diffuse out of the descending loop into the interstitial space; and where does it go after this movement?

Answer 35

Descending limb is highly permeable to water so it moves out into the blood

Question 36

What is the link between Loop of Henle length, and reabsorption of water?

Answer 36

Longer length of the Loop of Henle, greater concentration of urine produced so more water is reabsorbed

Question 37

What is the role of the Distal Convoluted Tubule?

Answer 37

Controls pH of blood by selecting which ions to reabsorb - permeability of walls become altered by hormones in order to achieve this

Question 38

How does ADH affect the permeability of the collecting duct? Under what circumstances would ADH be released, and where is it released from?

Answer 38

Increases permeability of walls of collecting duct & DCT.

Dehydration

Released from pituitary gland

Question 39

How is urea important in the reabsorption of water, using ADH?

Answer 39

Increase osmolarity in the kidneys, further helping water reabsorption and forming concentrated urine

Question 40

Why should there be no glucose in the urine; what does glucose in the urine normally indicate?

Answer 40

All should be reabsorbed by PCT

Glucose in the urine indicates undiagnosed diabetes