Homeostasis of body temperature and body fluid

Question 1

What is thermoregulation ?

Answer 1

The maintenance of constant core body temperature

Question 2

Why is thermoregulation important ?

Answer 2

Body temperatures outside the tolerance limit can:
Reduce the efficiency of enzymatic reactions
Alter the fluidity of cellular membranes

Question 3

what are the type of thermoreceptors ?

Answer 3

2 types of thermoreceptors:
cold receptors – detect temperatures lower than normal
heat receptors – detect temperatures higher than normal

Question 4

Describe peripheral thermoreceptors

Answer 4

In the skin

Provide info about external environment

Question 5

Describe central thermoreceptors

Answer 5

In the hypothalamus & internal organs

Provide info about core body temperature

Question 6

Whats the modulator in thermoregulation?

Answer 6

The hypothalamus interacts with organs throughout the body (effectors) to maintain the body’s core temperature via a negative feedback response

Question 7

Whats the effector in thermoregulation?

Answer 7

The skin is one of the effectors

in thermoregulation

Question 8

What are the physiological response to increase in core body temperature ?

Answer 8

1.Vasodilation
Autonomic nerves cause arterioles close to the skin surface dilate
Increase blood flow (carries heat) through the skin > greater heat loss to the surroundings via radiation & convection
2.Sweating
Sympathetic nerves stimulate the sweat glands to produce and release sweat to the skin surface
Evaporation of sweat from the skin cools the body – heat is removed from the skin when liquid sweat changes into vapour
Sweating is only effective in fairly dry environment
3.Lower metabolic rate
Metabolic rate decreases in the long term, so less heat energy is generated by the body
This is achieved by lower secretion of thyroxine

Question 9

What are the behavioural response to increase in core body temperature ?

Answer 9

Behavioural response
Reduce physical activity
Use of air conditioner or fan

Question 10

What are the physiological response to decrease in core body temperature ?

Answer 10

1.Vasoconstriction
The hypothalamus stimulates sympathetic nerves to constrict arterioles close to the skin surface

Reduce blood flow (which carries heat) through the skin > less heat loss to the surroundings via convection or radiation

2.Stimulation of adrenal medulla
The hypothalamus stimulates the adrenal medulla by sympathetic nerves
Results in the secretion of adrenaline and noradrenaline into the blood > increase cellular metabolism > increase generation of heat

3. Shivering
   The hypothalamus sends impulse to the parts of the brain that increase skeletal muscle tone
   Increase in muscle tone leads to rhythmic skeletal muscle tremors (shivering) which generate heat
4. Increase secretion of thyroxine
   The hypothalamus stimulates the anterior pituitary to secrete thyroid-stimulating hormone (TSH) which causes the thyroid gland to secrete thyroxine
   Thyroxine increases metabolic rate > increase heat production
   This response takes time to have an effect but is longer lasting

Question 11

What are the behavioural response to decrease in core body temperature ?

Answer 11

Behavioural response
Wear extra layer of clothing
Reduce the surface area of the body from which heat can be lost

Question 12

What is heat stroke/ hyperthermia?

Answer 12

Heat stroke/Hyperthermia
When the temperature and relative humidity are high, it is difficult for the body to lose heat by radiation or evaporation.
In this case body temperature rises and the regulatory mechanisms cease.
It can be very serious, or even fatal, if brain cells are affected.
Treatment consists of cooling the body as quickly as possible by immersing the patient in cold water.

Question 13

What is heat exhaustion ?

Answer 13

Heat exhaustion
Occurs more frequently than heat stroke
Result of extreme sweating and vasodilation to lose heat
The loss of water in sweating reduces the volume of blood plasma and the vasodilation reduces resistance to blood flow.
Blood pressure is thus reduced and output of blood from the heart decreases.
The person may, therefore, collapse.
Unlike heat stroke, the body temperature is almost normal.

Question 14

What is Hypothermia ?

Answer 14

Hypothermia
If a person’s core temperature falls below 33°C, the metabolic rate is so low that heat production is unable to replace the heat lost and body temperature continues to fall.
Death can occur at core temperatures below 32°C, but people have been known to survive even lower temperatures.

Question 15

What is osmoregulation?

Answer 15

Regulation of solute concentrations and water balance

Question 16

What is the fluid inside the cells ?

Answer 16

the intracellular fluid or cytosol

Question 17

What is the fluid outside the cells ?

Answer 17

The fluid outside the cells is the extracellular fluid, including: 
Interstitial fluid (intercellular or tissue fluid) – fills the spaces between cells
Plasma (intravascular fluid) -  fluid portion of the blood

Question 18

Where is kidney located?

Answer 18

Located on either side of the vertebral column, near the posterior body wall

Question 19

Describe kidney

Answer 19

Appear reddish-brown, with the size of your fist & shaped like a kidney bean

Question 20

What connect the kidney yo the aorta and inferior vena cava?

Answer 20

A renal artery & a renal vein connect each kidney to the aorta & inferior vena cava respectively

Question 21

What is nephron ?

Answer 21

Each kidney contains about 1.2 million microscopic units called nephrons.

Question 22

What is the function of nephron ?

Answer 22

The nephron is the functional unit of the kidney – the structure that carry out the kidney’s role in excretion and water regulation

Question 23

What is filtration ?

Answer 23

High blood pressure forces water and small dissolve molecules out of the blood and into the capsule

Question 24

What is reabsorption ?

Answer 24

Movement of substances (water and other useful molecules) from the tubules into the peritubular capillaries

Question 25

Explain reabsorption of water

Answer 25

Reabsorption of water at the proximal tubule and the loop of Henle occurs passively via osmosis
From high concentration to areas of low concentration
Reabsorption of water at the distal tubules & collecting duct is subjected to hormonal control

Question 26

What is secretion?

Answer 26

Movement of waste substances from peritubular capillaries to kidney tubules

Question 27

Core body temperature rises

How? Absorption of heat from environment by radiation? By internal conditions (e.g. high cellular resp)?

Answer 27

1. Central thermoreceptors in the hypothalamus detect the increase in core body temperature.
2. Nerve impulses travel to the hypothalamus where message from receptors is processed. New nerve impulses sent out to effectors.
3. Sympathetic nerve impulses sent to sweat glands to stimulate the increase production and secretion of sweat onto the skin surface. This increases heat loss through the evaporation of sweat from the surface of the skin, by convection of air.
4. Autonomic nerve impulses sent to signal arterioles beneath the skin to dilate (peripheral vasodilation). This increases the diameter of arterioles, thus allowing more blood flow (carrying heat) through skin, hence increases heat loss to surroundings by convection and radiation.
5. Hypothalamus release less of TSH-RH into the anterior pituitary gland which decreases the TSH secreted into the bloodstream. This ultimately reduces the amount of thyroxine hormone secreted into the bloodstream by the thyroid gland. The fall in thyroxine levels reduces metabolic rate and reduce heat production in the body.
   * under long term heat stress
6. Such physiological changes reduce the core body temperature back to set points.

Question 28

Core body temperature falls

How? Loss of heat to environment from body by radiation? By internal conditions (e.g. low cellular resp)?

Answer 28

1. Central thermoreceptors in the hypothalamus detect the fall in core body temperature.
2. Nerve impulses travel to the hypothalamus where message from receptors is processed. New nerve impulses sent out to effectors.
3. Hypothalamus sends out impulses through the somatic nerve to the cerebellum to increase skeletal muscle tone (rapid contraction and relaxation) thus increases cellular respiration and heat production in the body. AKA shivering of skeletal muscles.
4. Sympathetic nerve impulses are sent to signal arterioles beneath the skin to constrict (peripheral vasoconstriction). This decreases the diameter of arterioles, thus allowing less blood flow (carrying heat) through skin, hence decreases heat loss to surroundings by convection and radiation.
5. Hypothalamus stimulates the adrenal medulla by sympathetic nerves to increase the secretion of adrenaline and noradrenaline into the bloodstream, to increase cellular metabolism thus increase heat production in the body.
6. Increased thyroxine secretion- hypothalamus stimulates ATG to secrete TSH which causes thyroid gland to increase secretion of thyroxine thus increase metabolic rate and heat production.
7. Such physiological changes increase the core body temperature back to set points.

Question 29

Osmotic pressure of the blood is raised

How? Loss too much water from plasma (e.g. sweating) / increased amount of solutes in blood

Answer 29

1. Osmoreceptors in the hypothalamus detect the rise in blood osmotic pressure.
2. Hypothalamus sends nerve impulses to the posterior pituitary gland to increase the release of ADH into the bloodstream.
3. ADH travels to the nephron and increase the permeability of the DCT and CD wall to water as more aquaporins formed at the cell surface.
4. Increased water reabsorption from the filtrate into the peritubular capillaries, by osmosis down the water potential gradient created by the high concentration of ions in the renal medulla
5. Blood osmotic pressure decreases. Urine volume decreases, urine concentration increases.

Question 30

Osmotic pressure of the blood falls

How? Drank too much water/ loss too much solutes from blood.

Answer 30

1. Osmoreceptors in the hypothalamus detect the fall in blood osmotic pressure.
2. Hypothalamus sends nerve impulses to the posterior pituitary gland to decrease the release of ADH into the bloodstream.
3. Less ADH travels to the nephron, so the permeability of the DCT and CD wall to water decreases as less aquaporins form at the cell surface.
4. Reduced water reabsorption from the filtrate into the peritubular capillaries by osmosis down the water potential gradient.
5. Blood osmotic pressure rises. Urine volume increases, urine concentration decreases.

Question 31

OSMOREGULATION (conscious control)

Answer 31

1. Blood osmotic pressure increases
2. Osmoreceptors in the thirst centre of the hypothalamus detect the rise in blood osmotic pressure
3. Stimulation of thirst centre makes the person feel thirsty/ mouth feels dry. This conscious feeling of thirst stimulates the person to drink water. Nerve impulses will be sent from the cerebral cortex (motor area) to skeletal muscles to initiate skeletal muscle movement.
4. When fluid is consumed, and absorbed into the bloodstream in the alimentary canal, blood osmotic pressure is decreased