homeostasis

Question 1

define hormone

Answer 1

chemical substance secreted in minute amounts by glands, carried by the blood, which alters the activity of one or more specific target organs, and is eventually broken down by liver

Question 2

what biomolecules can make up hormones?

Answer 2

either protein or steroid (lipid)

Question 3

contrast endocrine and excocrine glands

Answer 3

Endocrine: ductless glands that produce hormones and secrete them directly into bloodstream, which the blood carries to target organ or tissue

Exocrine: glands with ducts that produce a secretion that is carried by the duct

Question 4

state at least 1 example of endocrine and exocrine gland

Answer 4

endocrine
* hypothalamus
* testes
* pancreas (islets of Langerhans)

exocrine
* salivary
* sweat

both
* pancreas (pancreatic juice through pancreatic duct)

Question 5

define homeostasis

Answer 5

maintenance of a constant internal environment

Question 6

explain why homeostasis is important

Answer 6

cells function well only within a narrow range of conditions, so large changes can result in cells not functioning efficiently, or even dying, and homeostasis ensures a stable internal environment in organism with minimal unavoidable disturbances,

thus allowing the organism to function more efficiently, as cells are maintained in an internal environment with optimal conditions, as well as with a degree of independence from the external environment, as the organism is not adversely affected by changes in external environment

Question 7

state how the internal environment differs at cellular and tissue level

Answer 7

cellular level
cytoplasm constituents are controlled by
* cell surface membrane (rates at which molecules are exchanged are controlled by diffusion and osmotic gradients, and active transport mechanisms
* enzyme activity, controlled by the rate of protein synthesis

tissue level
tissue fluid formed when higher blood pressure at the arterial ends of capillaries force blood plasma out of the capillaries, with features that need to be kept constant:
* temperature
* pH
* concentration of respiratory gases
* concentration of essential molecules
* concentration of ions
* concentration of toxic substances

Question 8

define reference point

Answer 8

the optimal level in a homeostatic control system

Question 9

describe the components of a control system and how it achieves negative feedback

Answer 9

1- Stimulus
any change or deviation from normal condition

2- Receptor
detects the stimulus from reference point, and relays the information to control centre

3- Control centre
compares information with reference point, and sends an appropriate signal to the effector if there is deviation

4- Effector
carries out the appropriate response based on signal received from control centre to counteract the initial deviation which results in an effect that is picked up by receptor, which relays information to the control centre and returns the system to normal, optimal conditions, after comparison against reference point

this process is negative feedback

Question 10

define negative feedback

Answer 10

mechanism that counteract changes in internal environment and restore it to the reference point

Question 11

explain why blood glucose level regulation is important

Answer 11

glucose is the ideal substrate for cellular respiration, preferred fuel molecule for both cardiac and skeletal muscles, and the only metabolic fuel molecule used by the brain.
a drastic decrease in blood glucose level could lead to fainting, convulsions, coma and finally death

Question 12

where is insulin and glucagon produced

Answer 12

insulin: beta cells of the islets of Langerhans in the pancreas

glucagon: alpha cells of the islets of Langerhans in the pancreas

Question 13

explain how concentration of glucose in blood is maintained (explain together)

Answer 13

blood glucose concentration is monitored constantly by islets of Langerhans in the pancreas

an increase or decrease in blood glucose levels causes the beta cells or alpha cells respectively of islets of Langerhans in the pancreas to produce insulin or glucagon respectively
which are transmitted via the bloodstream to all parts of the body

insulin travel to liver and muscles cells, causing the following responses
* increase permeability of cell membranes to glucose, thus increasing uptake of glucose from blood by cells
* increase rate of cellular respiration and hence rate of oxidation of glucose in cells
* stimulate liver and muscle cells to increase rate of glycogenesis to convert excess glucose to glycogen for storage

glucagon travels to the liver cells, causing the following responses
* stimulate conversion of stores glycogen back to glucose
* conversion of non-carbohydrate sources such as pyruvate, amino acids, and glycerol to glucose

the decrease or increase in blood glucose concentrations back to reference point is detected by beta cells or alpha cells in islets of Langerhans respectively which decreases the secretion of insulin or glucagon respectively

the circulating insuling or glucagon is then broken down in the liver and excreted by the kidneys

Question 14

contrast type 1 and type 2 diabetes mellitus.

Answer 14

Type 1: pancreas fails to produce enough functional insulin
Type 2: body cells no longer respond / are desensitised to insulin produced by pancreas

Question 15

state signs and symptoms of diabetes, and treatment

Answer 15

signs and symptoms
* increase in blood glucose
* glucose found in urine
* excessive thirst and urination
* tiredness
* loss of weight

treatment
* insulin injection (only for Type 1)
* controlled diet and exercose
* taking medicine

Question 16

explain why temperature regulation is important

Answer 16

enzymes in the body can only work within a certain range of temperatures, and changes in the body temperature may result in enzyme inactivation or even denaturation

Question 17

state which body organ produces the most heat

Answer 17

liver

Question 18

explain how body temperature is maintained

Answer 18

body temperature is monitored constantly by thermoreceptors in the skin and hypothalamus

an increase or decrease in temperature of external environment is detected by thermoreceptors in the skin which sends nerve impulses to the hypothalamus

an increase / decrease in blood temperature is also directly detected by thermoreceptors in the hypothalamus when warm / cool blood flows thorugh it

the hypothalamus in brain sends out nerve impulses to relevant body parts, where corrective processes occur to restore the temperature back to normal

when body tempeartures needs to be raised:
* arterioles in skin dilate while shunt vessels constrict, to allow more blood to flow through blood capillaries under skin surface. thus, more heat is lost through skin by radiation, convection and conduction
* sweat glands become more active, so there is increased production of sweat, and as more sweat evaporates from surface of skin, more latent heat of vaporisation is removed from the body
* the metabolic rate of body slows down thus less heat is produced within the body
these processes decrease blood temperature to reference point

when body temperature needs to be lowered:
* arterioles in skin constrict while shunt vessels dilate, to allow less blood to flow through blood capillaries under skin surface. thus, more less is lost through skin by radiation, convection and conduction
* sweat glands become less active, so there is decreased production of sweat, and as less sweat evaporates from surface of skin, less latent heat of vaporisation is removed from the body
* the metabolic rate of body increases thus more heat is produced within the body
* sometimes, ‘shivering’ also occurs when above reactions are insufficient to prevent drop in body temperature, and this spasmodic contraction of muscles increases heat production
these processes increase blood temperature to reference point

this decrease or increase in blood temperature back to reference point is detected by thermoreceptors, which stops the homeostatic action

processes are vice versa

Question 19

where is ADH produced

Answer 19

hypothalamus in the brain (and is released by the pituitary gland)

Question 20

explain why blood plasma water potential regulation is important

Answer 20

if blood plasma is too dilute, water molecules enter the cells by osmosis, so the cells swell and burst
if blood plasma is too concentrated, water molecules move out of the cells by osmosis, so the cells become dehydrated, shrink, and are thus unable to carry out metabolic functions

Question 21

explain how blood plasma water potential is maintained

Answer 21

blood plasma water potential is monitored constantly by osmoreceptors in the hypothalamus

an increase or decrease in water potential of blood plasma above or below reference point is detected by osmosreceptors in the hypothalamus in the brain, which stimulates the pituitary gland

if blood plasma water potential needs to be decreased
* pituitary gland RELEASES less ADH into the bloodstream, causing the walls of distal convoluted tubule and collecting duct to be less permeable to water
* kidney tubules reabsorb less water back into blood capillaries
* more urine is produced
* urine is more dilute
these actions decrease blood plasma water potential back to reference point

if blood plasma water potential needs to be increased
* pituitary gland RELEASES more ADH into bloodstream, causing the walls of distal convoluted tubule and collecting duct to be more permeable to water
* kidney tubules reabsorb more water back into blood capillaries
* less urine is produced
* urine is more concentrated
these actions increase blood plasma water potential back to reference point

this decrease or increase in blood plasma water potential back to reference point is detected by the osmoreceptors, which causes secretion of ADH to return to norm