Homeostasis and Blood Glucose Regulation

Study Notes

Homeostasis is the regulation of internal conditions to maintain a stable internal environment, crucial for optimal functioning of cells and enzymes
The pancreas monitors blood glucose levels and releases hormones to regulate it
High blood glucose levels: detected by the pancreas, insulin is released, promoting glucose uptake by cells and conversion to glycogen in the liver
Low blood glucose levels: detected by the pancreas, glucagon is released, promoting the breakdown of glycogen to glucose in the liver
Negative feedback ensures that blood glucose levels are kept within a narrow range

Thermoregulation is the maintenance of a stable internal body temperature
The hypothalamus acts as the body's thermostat
Response to heat:
- Sweating: sweat glands release sweat, which evaporates and cools the body
- Vasodilation: blood vessels widen, increasing blood flow to the skin, allowing more heat to be lost
Response to cold:
- Shivering: muscles contract rapidly, generating heat
- Vasoconstriction: blood vessels narrow, reducing blood flow to the skin, conserving heat
Behavioural responses:
- Seeking shade or drinking water in hot conditions
- Wearing more clothing or seeking warmth in cold conditions

The nervous system detects and responds to stimuli
Types of neurones:
- Sensory Neurones: carry impulses from receptors to the CNS
- Relay Neurones: connect sensory and motor neurones within the CNS
- Motor Neurones: carry impulses from the CNS to effectors
Pathway of a reflex arc:
- Stimulus → Receptor → Sensory Neurone → Relay Neurone → Motor Neurone → Effector → Response
Function of synapses:
- Synapses are gaps between neurones
- Neurotransmitters are released from one neurone and cross the synapse to the next neurone

The menstrual cycle is controlled by hormones to prepare the body for pregnancy
Role of FSH (Follicle-Stimulating Hormone):
- Produced by the pituitary gland
- Stimulates the maturation of eggs in the ovaries and production of oestrogen
Role of LH (Luteinizing Hormone):
- Produced by the pituitary gland
- Triggers ovulation and stimulates the production of progesterone
Role of Oestrogen:
- Produced by the ovaries
- Causes the lining of the uterus to thicken
- Inhibits FSH and stimulates LH production
Role of Progesterone:
- Produced by the corpus luteum
- Maintains the lining of the uterus
- Inhibits LH and FSH production to prevent the maturation of more eggs

Auxins are plant hormones that regulate growth by promoting cell elongation
Auxins are distributed unevenly in response to light, causing differential growth rates
Phototropism: growth of a plant towards light
Auxins accumulate on the shaded side of the plant, causing cells to elongate more on that side, bending the plant towards the light