Y3 Bio chapter 9 hormones + Hormones

🔹 Definitions (TIER 1 — easy marks, must be word-perfect)

Q: Define homeostasis.

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• Maintenance of a relatively constant internal environment within a narrow range, even when the external environment changes significantly

Q: Define negative feedback.

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1. Stimulus — any change

2. Receptor/Sensor — detects the change

3. Control centre — processes information, coordinates the response

4. Effector — carries out the corrective response

5. Response fed back to receptor → negative feedback (change is reversed, returns to normal)

• ⚠ Any essay on glucose/water potential/temperature regulation MUST be structured through these 5 stages in order — missing "control centre" or not explicitly closing the loop ("returns to normal") loses marks even if the biology is right.

🔹 Blood Glucose Regulation (TIER 1 — near-guaranteed essay)

Q: ESSAY — Explain how the body responds when blood glucose RISES.

• Stimulus: blood glucose rises above normal (e.g. after eating starch/sugar)

• Receptor: islets of Langerhans in the pancreas detect the rise

• Corrective mechanism: islets of Langerhans secretes more insulin → transported by blood to liver & muscles

• Effect: permeability of cell membrane to glucose increases; liver & muscles convert excess glucose → glycogen (glycogenesis) — stored in liver AND muscle

• Blood glucose concentration falls back to normal → insulin production falls — negative feedback to to the islets of Langerhans

Q: ESSAY — Explain how the body responds when blood glucose FALLS.

1. Stimulus: blood glucose falls below normal (e.g. starvation, vigorous exercise)

2. Receptor: islets of Langerhans in pancreas detect the fall

3. Corrective mechanism: islets of Langerhans secretes more glucagon → transported to liver

4. Effect: glucagon stimulates conversion of stored glycogen → glucose (glycogenolysis) in the liver only; glucose enters bloodstream

5. Blood glucose rises back to normal → glucagon secretion decreases

• ⚠ TRAP: insulin lowers glucose, glucagon raises it — commonly flipped under pressure. 🧠 "Insulin In (takes glucose IN to cells), Glucagon Gives (glucose back OUT)"

• ⚠ TRAP: insulin acts on liver AND muscle; glucagon acts on the liver only (muscle can't release glucose back into blood — no glucose-6-phosphatase). If a question asks specifically where glycogen is converted back to glucose, say liver, not "liver and muscles."

🔹 Osmoregulation & ADH (TIER 1 — same mechanism as covered in your Excretion set — compressed here since it's a repeat)

Q: ESSAY — Water potential falls / rises: quick recap.

• Falls (dehydration) → hypothalamus detects → posterior pituitary secretes MORE ADH → DCT and MAINLY collecting duct reabsorbs more water → urine more concentrated, less produced

• Rises (excess drinking) → hypothalamus detects → posterior pituitary secretes LESS ADH → DCT and MAINLY collecting duct reabsorbs less water → urine more dilute, more produced

• ⚠ Same keyword trap as before: use "water potential," never hypo/hypertonic. Full 5-stage negative feedback structure required for full marks.

• (See your Excretion/Kidney set for the full essay writeup — this is the identical mechanism, just introduced again here as the "general homeostasis" example.)

Q: Freshwater vs marine fish osmoregulation — worth learning?

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⚠ Flagging as likely extension/FYI content, not confirmed in your past papers. Gist only: marine fish live in a hypertonic environment (lose water, drink lots, produce little concentrated urine, actively excrete salt at gills); freshwater fish live in a hypotonic environment (gain water, produce lots of dilute urine, actively take up salt at gills). Don't sink heavy revision time here unless your teacher confirms it's examinable.

🔹 Skin Structure (TIER 3 — compressed; only the parts that feed into the thermoregulation essay matter)

Q: What structures in the dermis are relevant to temperature regulation?

• Arterioles (+ shunt vessels) → vasodilation/vasoconstriction controls blood flow to skin capillaries

• Sweat glands → produce sweat; evaporation removes latent heat (also excretes urea — minor excretion link)

• Hair erector muscles → contract/relax hair to trap or release an insulating air layer

• Adipose tissue (subcutaneous fat) → insulating layer, reduces heat loss

• Thermoreceptors (in dermis & epidermis) → detect temperature changes, send impulses to hypothalamus

• ⚠ Skip memorising the epidermis sublayers (cornified/granular/Malpighian) in depth unless a labelling question specifically asks — low essay value, mostly MCQ/diagram-label risk only

🔹 Thermoregulation (TIER 1 — the biggest essay in this chapter, long causal chain, high mark value)

Q: ESSAY — Explain how the body regulates temperature on a HOT day.

1. Stimulus: blood and skin temperatures rise

2. Receptor: temperature receptors detect the change → send nerve impulses to the hypothalamus

3. Hypothalamus is stimulated → sends nerve impulses to relevant body parts

4. Corrective mechanisms (list all — examiners award marks per mechanism):

   • Arterioles in skin dilate (vasodilation); shunt vessels constrict → more blood flows to skin capillaries → greater heat loss (by radiation/convection/conduction)

   • Sweat glands become more active → sweat production increases → more latent heat lost as sweat evaporates

   • Hair erector muscles relax → hair lies flat → no insulating air layer trapped

   • Decreased metabolic rate → reduces heat production

5. Blood temperature returns to normal — negative feedback

• ⚠ EXAM KEYWORD: always say "vasodilation of ARTERIOLES," not just "blood vessels widen" — examiners want the specific structure named.

Q: ESSAY — Explain how the body regulates temperature on a COLD day.

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• Stimulus: blood and skin temperatures fall

• Receptor: temperature receptors detect the change → send impulses to hypothalamus

• Hypothalamus stimulated → sends impulses to relevant body parts

• Corrective mechanisms:

  • Arterioles in skin constrict (vasoconstriction); shunt vessels dilate → less blood flows to skin capillaries → less heat loss

  • Sweat glands less active → sweat production decreases → less latent heat lost

  • Hair erector muscles contract → hair stands up → traps an insulating layer of air (air is a poor conductor → reduces heat loss to environment)

  • Shivering: a reflex — skeletal muscles contract rapidly in small movements → generates heat by expending energy — occurs when insufficient heat is produced

  • Increased metabolic rate → increases heat production

• Blood temperature returns to normal — negative feedback

Q: Define the 4 methods of heat loss (definitions sometimes asked directly).

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• Radiation — transfer of heat from a warm body to a cooler body/surroundings through air (your slides phrase this as "loss of heat down a concentration gradient" — reproduce that exact wording if it's how your mark scheme phrases it, even though technically it's a temperature gradient, not a concentration gradient)

• Convection — movement of air where warmer air is replaced by cooler air due to differences in air density; speeds up heat loss by radiation and evaporation

• Conduction — transfer of heat from a hot solid to a cooler solid in contact with each other

• Evaporation — change of phase from liquid to vapour; evaporation of sweat removes latent heat, producing a cooling effect

📗 CHAPTER 12: HORMONES (CO-ORDINATION & RESPONSE) — Essay-Focused Flashcard Set 🔹 Hormones — Definition & Glands (TIER 1 — definition is a guaranteed easy mark, word-perfect)

Q: Define a hormone.

• A chemical substance, produced by a gland, carried by the blood, which alters the activity of one or more specific target organs

• Produced in minute quantities by an endocrine gland

• Influences growth, development, and activity of an organism

Q: Distinguish endocrine glands from exocrine glands.

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• Endocrine glands (ductless) — secrete their products (hormones) directly into the blood, no duct

• Exocrine glands — secrete products into ducts which lead to the external environment (or a body cavity)

• Examples of exocrine glands: sweat glands, salivary glands, mammary glands, stomach, liver, pancreas

• ⚠ CLASSIC MCQ TRAP: the pancreas is BOTH — its islets of Langerhans (endocrine portion) secrete insulin/glucagon directly into blood, while its exocrine portion secretes digestive enzymes via the pancreatic duct into the small intestine. Don't call it purely one or the other.

Q: State the major endocrine glands and their hormones.

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• Pituitary gland — the "master gland"; secretes hormones that control other endocrine glands; also secretes ADH

• Hypothalamus — regulates secretion of pituitary hormones

• Thyroid gland — secretes thyroxine; controls rate of metabolism, influences physical development

• Adrenal gland (medulla) — secretes adrenaline; prepares body for 'fight or flight'

• Pancreas (islets of Langerhans) — secretes insulin and glucagon; regulates blood glucose

• Ovaries — oestrogen and progesterone; Testes — testosterone

Q: Describe the general pathway of hormone action.

1. Hormones produced by ductless (endocrine) glands

2. Enter the bloodstream, transported to other parts of the body

3. Reach target organs where they exert their effects

4. Hormones are eventually destroyed in the liver

• 🧠 The nervous system also controls endocrine glands, preventing excessive hormone production (a feedback-style check on hormone levels)

🔹 Insulin & Blood Glucose (TIER 1 — mechanism detail is new/essay-worthy beyond your Ch.11 cards)

Q: ESSAY — Explain the 3 specific ways insulin decreases blood glucose concentration.

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1. Makes cell membranes more permeable to glucose → increases the rate of glucose uptake by cells

2. Stimulates liver and muscle cells to convert glucose into glycogen for storage (glycogenesis)

3. Increases the oxidation of glucose during tissue respiration

• ⚠ Your Ch.11 set covered the negative feedback loop (stimulus→receptor→effect→normal); THIS card is the extra mechanistic detail of exactly how insulin lowers glucose — use both together for a full-marks answer.

Q: What happens if insulin is over-secreted?

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• Results in abnormally low blood glucose concentration → condition called shock

• Untreated: can progress to coma and death

🔹 Glucagon (TIER 1)

Q: ESSAY — Explain the 3 specific ways glucagon increases blood glucose concentration.

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• Main target organ of glucagon is the liver

1. Stimulates conversion of glycogen into glucose (glycogenolysis)

2. Stimulates conversion of fats and amino acids into glucose (gluconeogenesis)

3. Stimulates conversion of lactic acid into glucose

• ⚠ This third point (lactic acid → glucose) links directly to your Respiration chapter's oxygen debt/Cori cycle content — good cross-topic connection if a question combines exercise physiology with hormone regulation.

🔹 Diabetes Mellitus (TIER 1 — near-guaranteed structured question, both types)

Q: Define diabetes mellitus and explain the underlying mechanism.

• A condition where the body does not secrete enough insulin (or cells don't respond to it) to control blood glucose concentration

• Blood glucose reaches a level that exceeds the kidney's ability to reabsorb glucose (exceeds the renal threshold) → glucose excreted in urine

• Since muscle cells have no reserves of glycogen in this state, the body grows weak and continuously loses weight

• Body oxidises fats instead of glucose for energy → produces poisonous substances called ketones

• Ketonuria = abnormally large amounts of ketones excreted in urine

Q: State the signs of diabetes mellitus.

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1. Persistently high blood glucose concentration

2. Presence of glucose in urine, especially after a meal

3. Healing of wounds is slow and difficult

• (Also acceptable from general knowledge: frequent urination/polyuria, excessive thirst/polydipsia — but the 3 above are the ones explicitly listed in your slides)

Q: ESSAY — Distinguish Type 1 from Type 2 diabetes (onset, cause, treatment).

	Type 1	Type 2
Onset	Early in life — "juvenile"/early-onset	Later in life — "late-onset"
Cause	Islets of Langerhans unable to produce sufficient insulin	Target cells (e.g. muscle cells) do not respond well to insulin (insulin resistance) or insufficient production
Treatment	Injection of insulin into the body	Control of dietary intake, exercise, and lifestyle changes

• ⚠ EXAM KEYWORD: Type 1 = production problem; Type 2 = response/resistance problem (or insufficient production) — don't describe both as "not enough insulin produced," Type 2's defining feature per your syllabus is insulin resistance

• Risk factors for Type 2 (per your scheme of work): unhealthy diet, sedentary lifestyle

• Management of Type 2: dietary control, regular exercise, weight management, monitoring blood glucose

🔹 Adrenaline (TIER 1 — the nervous-then-hormonal pathway is a distinctive essay type, plus the effects list)

Q: ESSAY — Describe how a stressful stimulus leads to adrenaline secretion (full pathway).

1. Stimulus: fear, anger, anxiety, stress, etc.

2. Stimulus activates certain sensory neurones in the hypothalamus (receptor)

3. Nerve impulses are transmitted to the spinal cord

4. Nerve impulses leave the spinal cord and travel to the adrenal medulla

5. Adrenal medulla is stimulated → produces adrenaline

6. Adrenaline is carried in the blood to target organs throughout the body

7. Adrenaline brings about short-term responses that prepare the body for 'fight or flight'

• 🧠 This is a hybrid pathway — starts as a nervous response (electrical impulses, fast, to the adrenal medulla) and finishes as a hormonal response (adrenaline via blood, reaches multiple organs). A great answer to "explain how the two coordination systems can work together."

Q: ESSAY — State the effects of adrenaline secretion on the body. (classic "list the effects" question — worth memorising as a full set)

• Increases blood glucose levels — speeds up breakdown of glycogen to glucose in the liver and muscles

• Increases metabolic rate — more energy released

• Increases rate and depth of ventilation (breathing)

• Increases rate of heartbeat and causes a rise in blood pressure

• Constricts arterioles → channels more blood to the muscles

• Causes pupils to dilate → enhances vision

• Increases the rate of blood coagulation (clotting) — survival advantage if wounded

• Contracts hair erector muscles → causes 'goose pimples'

• ⚠ If asked to explain WHY each effect is adaptive, link it to preparing the body for physical exertion (fight or flight): more glucose/O₂ to muscles, faster reactions, reduced blood loss risk if injured, better vision to assess threat.

🔹 Comparing Hormonal and Nervous Systems (TIER 1 — comparison table is a recurring MCQ/short-answer format)

Q: ESSAY — Compare the nervous system and hormonal (endocrine) system.

	Nervous system	Hormonal system
Signal	Nerve impulses (electrical)	Hormones (chemical substances)
Transmission	By neurones	By the blood
Speed	Fast/quick response	Slow response
Duration	Short-lived	May be short-lived or long-lived
Voluntary?	May be voluntary or involuntary	Always involuntary
Scope	Usually localised (one part of body affected)	Affects more than one target organ (widespread)

Q: State one similarity between the two systems.

Both involve a stimulus and a target organ (effector), whereby a message is transmitted to the target organ that carries out a response