Homeostasis

Question 1

Define homeostasis

Answer 1

• the maintenance of a constant internal environment

- process which ensures that composition of body fluids kept within narrow limits

Question 2

Define internal environment

Answer 2

• refers to conditions within body of organism
• humans: blood and tissue fluids
• stable internal environment, allow organism to be independent from changes in external environment/surroundings

Question 3

Why does body temp need to be kept constant?

Answer 3

• environmental conditions in surroundings constantly changing
• enzymes in body can only work in specific range of temp
• change in body temp may lead to enzyme inactivation or denaturation
• high fever thus fatal

Question 4

Why must tissue fluid be kept at constant pH and wp?

Answer 4

• drastic change in pH, affect enzyme reactions in cells, harm body
• drastic change in wp may cause cells to swell, burst; shrivel, affect reactions
• composition of tissue fluid need to kept within very narrow limits to ensure constant pH and wp

Question 5

Homeostasis involves negative feedback

Answer 5

• in homeostatic control, body reacts to bring abt opposite effect to changes detected
• if system/body disturbed, disturbance sets in motion a sequence of event that tends to restore a system to original state (negative feedback process)

Question 6

Receptors/sense organs

Answer 6

-organs/structures in body that detect changes in body condition

Question 7

Negative feedback process

Answer 7

1. norm/set pt to be maintained
2. stimulus: change in internal environment e.g. condition rises/decreases below normal
3. receptor: detect stimulus, send signal to control centre
4. corrective mechanism: bring abt reverse effect of stimulus
5. feedback to stimulus once set pt reached, corrective mechanism stops

Question 8

Examples of homeostasis in humans

Answer 8

1. regulating body temp
2. regulating blood glucose conc
3. regulating wp

Question 9

Regulation of blood glucose conc

Answer 9

• glucose needed for cellular respiration, provide energy for vital activities
• blood normally contains 70-90 mg of glucose per 100cm3 of blood

Question 10

when blood glucose lvl rises above normal lvl

Answer 10

1. normal set pt
2. stimulus: blood glucose lvl rises above normal
3. receptor: islets of langerhans in pancreas stimulated (control centre)
4. corrective mechanism: islets of Langerhans secrete insulin into bloodstream, blood transport insulin to liver and muscles
   - insulin increases permeability of cell surface membrane to glucose, glucose absorbed more quickly
   - insulin causes liver and muscles to convert excess glucose to glycogen
   - glycogen stored in liver and muscles
5. blood glucose conc decreases, provides negative feedback to receptor to reduce insulin production

Question 11

when blood glucose lvl falls below normal

Answer 11

1. normal set pt
2. stimulus: blood glucose falls below normal
3. receptor: islets of Langerhans in the pancreas stimulated
4. corrective mechanism: islets of Langerhans secrete glucagon into bloodstream, blood transports glucagon to liver and muscles
   - glucagon causes conversion of stored glycogen back to glucose
   - from liver, glucose enters bloodstream
5. negative feedback: blood glucose conc increases, provides feedback to receptor to decrease glucagon production

Question 12

regulating blood water potential

Answer 12

1. normal set pt
2. stimulus: wp of blood increases/decreases (large intake of water/loss of water thru sweating)
3. receptor: hypothalamus in brain stimulated
4. corrective mechanism:
   - less/more ADH (anitdiuretic hormone) released by pituitary gland into bloodstream
   - less/more ADH transported to kidneys
   - cells in wall of collecting ducts become less/more permeable to water
   - less/more water absorbed into bloodstream
   - more/less water excreted, more concentrated/dilute

Question 13

Role of skin

Answer 13

• forms protective covering over body surface

- regulates temp and excretion

Question 14

Structure of skin: Blood vessels (capillaries and arterioles) in dermis layer

Answer 14

• blood vessels are present in dermis layer
• constriction and dilation of arterioles caused by contraction of muscles in arteriole walls
• constriction and dilation of arterioles help to regulate body temp
• vasodilation vs vasoconstriction

Question 15

Vasodilation

Answer 15

• dilation of arterioles
• more blood sent to blood capillaries in skin
• e.g. blushing/flushed after vigorous activities
• due to numerous blood vessels in skin dilating

Question 16

Vasoconstriction

Answer 16

• constriction of arterioles in skin
• reduces amt of blood flowing thru capillaries in skin
• become pale

Question 17

Structure of skin: Hair follicle

Answer 17

• though embedded in dermis, produced by epidermis
• Malpighian layer of epidermis sinks into dermis, form hollow tube called hair follicle
• each hair grows inside the hair follicle

Question 18

Structure of skin: Hair papilla

Answer 18

• a mass of tissue found at the base of the hair follicle
• contains blood capillaries and nerves
• covered with epidermal cells that constantly divide, pushing new cells outwards
• cells that are pushed outwards gradually die, harden to form hair

Question 19

Structure of skin: Hair erector muscles

Answer 19

• attached to hair follicles

- contracts, cause hair to stand on their ends, skin around hair raised, producing goose bumps

Question 20

Structure of skin: Sweat glands

Answer 20

• a coiled tube formed by a downgrowth of epidermis
• forms tight knot in dermis, surrounded by many blood capillaries
• secreted sweat flows thru sweat duct to a sweat pore that opens at skin surface
• secreted sweat mainly contains water, dissolved salts (sodium chloride), small amts of urea
• considered an excretory organ as is contains small amts of metabolic waste products eg urea
• sweat is secreted continuously, amt of sweat produced varies on the external and internal environmental conditions
• small quantity of sweat, evaporates almost immediately
• large quantity of sweat, droplets on skin/running streaks
• sweat is a mean by which skin regulates body temp

Question 21

Structure of skin: Sensory receptors

Answer 21

• detects changes in environment (stimuli)
• eg nerve endings in the skin are sensory receptors
• enable us to sense pain, pressure, temp changes in external environment
• receptors that detect temp changes are called thermoreceptors (e.g. nerve endings)

Question 22

Subcutaneous fat

Answer 22

• beneath dermis are several layers of adipose cells (adipose tissue)
• fat is stored there
• fat in these cells also act as an insulating layer, reduce heat loss

Question 23

How does our body produce and gain heat?

Answer 23

• heat is produced within body as a result of metabolic activities e.g. cellular respiration
• high lvls of cellular respiration takes plc in muscle and liver, large amt of heat released in these organs
• heat is distributed to rest of body via bloodstream
• heat also gained thru vigourous muscular exercise, consumption of hot food, being in warm environments
• excess heat thus needs to be removed from body, prevent overheating

Question 24

How does our body lose heat

Answer 24

• lost thru skin by radiation, convection and to a limited extent, conduction
• by evaporation of water in sweat from surface of skin
• in faeces or urine
• exhaled air

Question 25

Shunt vessels

Answer 25

- certain parts of skin contain shunt vessels - shunt vessels connect skin arterioles with skin venules - control amt of blood flowing thru skin capillaries - affect heat loss thru skin

Question 26

Shunt vessels constrict

Answer 26

- skin arteriole dilates, shunt vessel constrict, increase blood flow to skin surface - more heat carried to skin surface, greater heat loss

Question 27

Shunt vessels dilate

Answer 27

- skin arteriole constricts, shunt vessels dilate, less blood flow to skin surface - less heat carried to skin surface, less heat loss

Question 28

Hypothalamus

Answer 28

- located in brain - monitors and regulates body temp - receives info abt temp changes from thermoreceptors in skin(detect temp from environment), and thermoreceptors in hypothalamus (detect temp of blood)

Question 29

WHat happens when body temp begins to rise

Answer 29

- e.g. vigorous body activities, large amt of heat is produced, - heat produced accumulates in body, rise in body temp - change detected by hypothalamus, sends nerve impulses to relevant body parts

Question 30

Homeostatic processes that decreases body temp

Answer 30

- dilation of arterioles in skin, constriction of shunt vessels allow more blood to flow thru blood capillaries in skin - more heat lost thru skin by radiation, convection and conduction - sweat glands become more active, increased production of sweat - more water in sweat evaporates from surface in skin, more latent heat of vaporization is lost from body (efficient means of losing heat) - decreased metabolic rate, reduces amt of heat released within body

Question 31

Why these homeostatic processes occur to decrease body temp

Answer 31

- body absorbs heat when surrounding temp is higher than body temp - rise in external temp is detected by temp receptors, receptors immediately send nerve impulses to hypothalamus - absorbed heat mainly lost by evaporation of sweat from body - extra heat accumulated in body is removed so body temp maintained in normal range

Question 32

what happens when human body temp begins to fall

Answer 32

- on cold day, rate of heat loss increases, esp at skin surface - drop in temp stimulates temp receptors in skin, rapidly send nerve impulses to hypothalamus - drop in temp ls also detected by hypothalamus - hypothalamus send nerve impulses to relevant body parts to enable homeostatic processes

Question 33

Homeostatic processes that increase body temp

Answer 33

- constriction of skin arterioles, dilation of shunt vessels, less blood flows thru blood capillaries in skin - reduces heat lost by convection, radiation and conduction - sweat glands less active, decreased production of sweat - less water in sweat evaporates from surface of skin, less latent heat of vaporization lost from body - increased metabolic rate, increase amt of heat released within body - if all the above doesn't work, shivering occurs - shivering is the reflex contraction of body muscles, spasmodic contraction of skeletal muscles increases amt of heat released within body, help raise body temp to rise to normal