CH 5 HOMEOSTASIS: GLUCOSE & BODY TEMP

Question 1

define homeostasis

Answer 1

the maintenance of a relatively constant internal environment despite fluctuations in the external environment

Question 2

which aspects of the body need to be regulated in order for the body to function at its best?

Answer 2

• core body temp
• pH & conc. of dissolved substances in the body fluids
• conc. of glucose in the blood
• conc. of o2 and co2 in the blood and other body fluids
• blood pressure
• conc. of metabolic wastes

Question 3

define feedback system

Answer 3

a circular situation in which the body responds to change, or a stimulus, with the response altering the original stimulus and thus providing feedback

Question 4

differentiate between positive and negative feedback and give examples for each

Answer 4

negative feedback: feedback that decreases or eliminates the stimulus
- e.g. absorption of glucose during exercise, putting on a jumper when you are cold
positive feedback: feedback that reinforces the stimulus [no role in homeostasis]
- e.g. oxytocin released in response to baby pushing on cervix (causing more contractions), fever

Question 5

define dynamic equilibrium

Answer 5

fluctuation around a set point

Question 6

define tolerance limits

Answer 6

the upper and lower limits between which the levels fluctuate

Question 7

identify the common features of a feedback system

Answer 7

• stimulus is the change in the environment
• receptor detects the change
• modulator is the control centre responsible for processing and sending information
• effector carries out a response
• feedback is achieved because the original stimulus has been altered by the response

Question 8

what is the worded equation for cellular respiration?

Answer 8

glucose + oxygen&raquo_space;> carbon dioxide + water + energy

Question 9

define glycogen

Answer 9

a polysaccharide made up of thousands of glucose molecules bonded together in branching chains; functions as a store of glucose molecules in the liver and muscle cells.

glycogen is a short term supply of energy and usually lasts about 6 hours. if more energy is required, glucose is derived from fat storage.

Question 10

what is the role of the liver for blood glucose levels?

Answer 10

able to convert glucose into glycogen for storage, or glycogen to glucose for release into the blood

Question 11

how do carbohydrates extracted from food reach the liver?

Answer 11

glucose is absorbed into the blood capillaries in the villi of the small intestine. the hepatic portal vein transports nutrients from the small intestine, large intestine, pancreas, spleen and stomach to the liver.

Question 12

after it is delivered to the liver by the hepatic portal vein, glucose may…

Answer 12

• be removed from the blood by the liver to provide energy for liver functioning
• be removed by the liver and/or muscles and converted into glycogen for storage
• continue to circulate in the blood, available for body cells to absorb and use as a source of energy
• be converted into fat for long term storage if it is in excess of that required to maintain both normal blood sugar and tissue glycogen levels

Question 13

how is blood glucose level decreased

Answer 13

insulin stimulates glycogenesis; process whereby glucose molecules are chemically combined in long chains to form glycogen molecules.

Question 14

how is blood glucose level increased?

Answer 14

glucagon stimulates glycogenolysis; the process of converting glycogen back to glucose

Question 15

what is the role of the pancreas for blood glucose levels?

Answer 15

contains clusters of hormone-secreting cells; islets of Langerhans. the cells in the islets are of two types;

• alpha cells that secrete glucagon
• beta cells that secrete insulin

Question 16

how does insulin cause a decrease in blood glucose levels?

Answer 16

• accelerating the transport of glucose from the blood into the body cells, especially those of skeletal muscles
• accelerating the conversion of glucose into glycogen in the liver and skeletal muscles (glycogenesis)
• stimulating the conversion of glucose into protein (protein synthesis)
• stimulating the conversion of glucose into fat (lipids) in adipose tissue, or fat storage tissue (lipogenesis)

Question 17

describe the feedback system of HIGH blood glucose levels

Answer 17

when blood glucose level rises above normal, chemoreceptors in the beta cells of the islets of Langerhans stimulate those cells to secrete insulin [neg. feedback]. when BCL decreases, cells no longer stimulated, production reduced

Question 18

how does glucagon cause an increase in blood glucose levels?

Answer 18

• stimulating glycogenolysis
• stimulating gluconeogenesis [production of new sugar molecules from fats (lipids) and amino acids, in the liver] involving lipogenesis (lipid breakdown)
• having a mild stimulating effect of protein breakdown

glucose formed is released into the blood

Question 19

describe the feedback system of LOW blood glucose levels

Answer 19

when blood glucose level falls below normal, chemoreceptors in the alpha cells of the islets of Langerhans stimulate those cells to secrete glucagon [neg. feedback]. when BCL increases, cells no longer stimulated, production reduced

Question 20

how do the adrenal glands play a role in blood glucose regulation?

Answer 20

• one above each kidney
• outer = cortex, inner = medulla
• secretion of glucocorticoids by the cortex, stimulated by ATCH from anterior pituitary
• secretion/synthesis of epinephrine and norepinephrine by the medulla

Question 21

what is the function of the glucocorticoids for blood glucose levels?

Answer 21

• regulate carbohydrate metabolism by ensuring enough energy is provided to body cells.
  
  • • in doing so, they stimulate the conversion of glycogen to glucose during glycogenolysis
• increase rate at which amino acids are removed from cells, mainly muscle cells, and transported to the liver
  
  • • some of said AAs may be converted into glucose by liver during gluconeogenesis if glycogen and fat levels are low
• promote metabolism of fatty acids from adipose tissue, allowing muscle cells to shift from using glucose to fatty acids for much of their metabolic energy

Question 22

what are the effects of synthesis of epinephrine and norepinephrine?

Answer 22

• adrenaline in particular elevates BCL through glucogenolysis and therefore counteracts effects of insulin
• synthesis stimulates production of lactic acid from glycogen in muscle cells, which can be used by liver to manufacture glucose

Question 23

what are the normal levels of blood glucose and body temperature?

Answer 23

BCL: 4-6 millimoles/L or 90mg/100mL
BT: 36.8ºC usually, 37ºC for cellular reactions, death at 45º (usually higher temp than surroundings)

Question 24

identify 2 means of heat input

Answer 24

• heat from body processes, e.g. metabolism, respiration of liver and muscle cells
• heat gained from surroundings by conduction and radiation

Question 25

identify 2 means of heat output

Answer 25

• radiation, conduction, convection to surroundings

- evaporation of water from skin and lungs; warm air breathed out; warm urine and faeces

Question 26

how might the body produce heat?

Answer 26

metabolic rate: rate at which energy is released by the breakdown of food, affected by exercise, stress and body temp

• muscular activity can increase metabolic rate up to 40 times, large quantities of heat released
• release of noradrenaline from sympathetic increases metabolic rate in times of stress
• for each 1ºC rise in body temp, the rate of biochemical reactions increased by about 10% (this explains fever conditions)

Question 27

identify all the types of thermo receptors

Answer 27

• peripheral thermoreceptors: skin and mucous membranes detect temp change in external environment
• central thermoreceptors: hypothalamus detects temp change in internal environment

these can be categorised into two types;
- cold receptors: stimulated by temps lower than normal
- heat receptors: stimulated by temperatures higher than normal
when stimulated, the hypothalamus stimulates the correct response

Question 28

identify the 4 means of heat transfer

Answer 28

• conduction: direct contact between particles
• convection: movement of liquid or gas
• radiation: infrared radiation being emitted by objects
• evaporation: liquid forming gas, which absorbs heat energy

Question 29

what do blood vessels have to do with thermoregulation?

Answer 29

• vasodilation: diameter of BVs increased, more blood is transported to the capillaries in the skin and the rate of heat loss increases
• vasoconstriction: diameter of BVs reduced, less blood is transported to the capillaries in the skin and the rate of heat loss decreases

Question 30

define sweating

Answer 30

• the active secretion of fluid by the sweat glands and the periodic contraction of cells surrounding the ducts to pump the sweat to the skin surface
• production and transport of sweat stimulated by sympathetic nerves
• water containing dissolved substances; mostly sodium chloride, some urea, lactic acid & potassium ions