B5: The human body - staying alive

How do substances get into

out of and around our bodies?,Substances move into and out of cells via diffusion, osmosis, and active transport. The cardiac system (heart and blood vessels) transports gases, nutrients, hormones, and waste to and from cells.

How does the heart function?

Deoxygenated blood enters the right atrium via the vena cava, moves to the right ventricle, then to the lungs via the pulmonary artery. Oxygenated blood returns via pulmonary vein to the left atrium, moves to the left ventricle, and exits through the aorta to the body. Valves prevent backflow.

What are the types of blood vessels and their functions?

Arteries: thick muscle and elastic layers for high pressure; Veins: thin walls, valves to prevent backflow; Capillaries: thin walls, large surface area for exchange.

How are substances transported in the blood?

Oxygen binds to haemoglobin in capillaries at the alveoli, nutrients diffuse into capillaries in the small intestine (villi). Waste products like urea are transported to kidneys for excretion.

How are exchange surfaces adapted?

They have short diffusion distances, large surface area, large concentration gradients, and are moist to allow efficient diffusion.

How does the nervous system help us respond to changes?

It sends electrical impulses along neurones, coordinating movement and homeostasis. It consists of CNS (brain and spinal cord) and PNS (motor and sensory neurones).

What are the types of neurones?

Sensory: receptor → CNS; Relay: CNS → CNS; Motor: CNS → effector.

What is a synapse?

A gap between two neurones where neurotransmitters pass the impulse. Ensures unidirectional flow.

How are nerve cells adapted?

Long axons, myelin sheath for insulation, dendrites to receive impulses, neurotransmitters for communication, receptors for stimuli detection.

What is a reflex?

An involuntary, rapid response to a stimulus via the reflex arc: receptor → sensory neurone → relay neurone → motor neurone → effector.

What are the main brain structures?

Cerebral cortex: thought, processing; Brain stem: connects brain & spinal cord, controls involuntary actions; Cerebellum: coordination.

How do hormones control responses in the human body?

Hormones are secreted by glands into blood to target organs. Responses are often regulated by negative feedback.

What is thyroxine?

Thyroxine regulates metabolism, growth, and development. Its release is controlled by negative feedback.

What is adrenaline?

Released by adrenal glands during stress, increasing heart rate, widening pupils, and converting glycogen to glucose for energy.

Why is maintaining a constant internal environment important?

Homeostasis maintains optimum conditions for cells using negative feedback with hormones, nerves, receptors, and effectors.

How is body temperature regulated?

By the hypothalamus using thermoreceptors. Responses include shivering, vasoconstriction, hair erection (cold) or sweating and vasodilation (hot).

How is water balance regulated?

Kidneys filter water and urea; ADH hormone controls water reabsorption. Too much water causes cells to swell; too little causes shrinkage.

How do hormones control human reproduction?

FSH: egg development & oestrogen production; LH: triggers ovulation & progesterone; Progesterone: maintains uterus lining; Oestrogen: repairs uterus lining, triggers LH.

How can the menstrual cycle be controlled artificially?

Hormonal contraceptives (oestrogen & progesterone) inhibit ovulation; fertility treatments stimulate ovulation or control timing.

How is blood sugar level regulated?

Insulin decreases blood glucose; glucagon increases it. Both work antagonistically to maintain homeostasis.

What is diabetes?

Type 1: no insulin produced, treated with insulin injections & diet. Type 2: insulin resistance or low production, managed with diet & exercise.

What are the structure and functions of the eye?

Cornea: refracts light; Iris: controls light entering; Pupil: allows light in; Lens: focuses image; Retina: photoreceptors (rods & cones).

How does the eye focus?

Ciliary muscles and suspensory ligaments change lens shape. Near objects: lens thicker; distant objects: lens thinner.

What is the pupil reflex?

Pupil dilates in low light, constricts in bright light to protect retina.

What are common eye defects?

Short-sightedness: lens too thick/eyeball too long, distant objects blurry; Long-sightedness: lens less elastic/eyeball short, near objects blurry; Cataracts: cloudy lens, treated surgically.

What is neurone damage?

Differentiated neurones cannot divide; damage leads to diseases like Alzheimer's. Stem cells may replace damaged neurones in the future, but ethical concerns exist.