Integration of body systems

Fast **electrical impulses** carried along **neurons**.

Slower **chemical hormones** carried in the **blood**.

A **chemical messenger** released by an endocrine gland into the **blood**; it travels to **target cells** and changes how they behave.

An organ that makes and releases a **hormone** directly into the **blood** (e.g. pancreas, adrenal gland, thyroid, testis).

A cell with the **matching receptor** for a hormone — only target cells respond to that hormone.

**Nervous** = fast and short-lived; **endocrine** = slower and longer-lasting.

The **hypothalamus** signals the **pituitary gland**, which controls other endocrine glands — so the nervous system can drive the endocrine system.

**Neurons (nerves)** of the nervous system, often via the **hypothalamus and pituitary**.

It **lowers blood glucose** (body cells take up glucose). Insulin is released by the **pancreas**.

It **raises heart rate** (and breathing rate) for 'fight-or-flight'. It is released by the **adrenal gland**.

It **drives male sexual development** (e.g. sperm production, body changes at puberty). It is released by the **testis**.

A control loop where the **response opposes the change**, returning a level to its **set point** and keeping the body stable.

The **nervous** system handles **quick** reactions; the **endocrine** system handles **sustained** changes. Together they cover both.

The heartbeat **starts within the heart muscle itself** (at the SA node), not from a signal sent by the brain.

The **sinoatrial (SA) node** — a patch of special muscle in the **wall of the right atrium**. It is the heart's natural **pacemaker** and starts every beat.

The structure that **sets the rhythm** of the heartbeat. In a healthy heart this is the **SA node**.

The **atrioventricular (AV) node** **delays** the impulse between the atria and ventricles, so the **atria empty before the ventricles contract**.

**SA node fires → atria contract → AV node delays → ventricles contract.**

So the **atria can finish emptying** their blood into the ventricles **before** the ventricles contract — keeping the beat coordinated.

**Intercalated discs** containing **gap junctions**, which let the impulse pass **directly from cell to cell**.

Nerves from the brain's **medulla** reach the SA node — one **speeds it up**, one **slows it down**.

**Adrenaline** — it reaches the SA node and **speeds it up**. It always raises heart rate.

**Adrenaline** — it speeds up the SA node and never slows it down.

An implanted device that sends **regular electrical impulses** to keep a normal rhythm when the **SA node is faulty**.

The **ventricles are relaxing / recovering** (repolarising) after contracting.

The **breakdown of large food molecules** into small, soluble ones that can be absorbed.

The movement of the **small, soluble products of digestion** out of the gut and into the **blood** (or lymph).

**Waves of muscle contraction** in the gut wall that **push food along** the digestive tract.

**Involuntary smooth muscle** — it is **not** under conscious control.

The **autonomic nervous system** — the nerves in the gut wall (the **enteric nervous system**).

**Hydrochloric acid (HCl)** — giving a very **low pH** (about 1.5–2).

(1) It **kills most ingested bacteria**; (2) it gives the enzyme **pepsin** its **optimum (acidic) pH**.

It **denatures** (unfolds) proteins and provides the acidic pH that lets **pepsin** (a protease) break them into shorter chains.

**Proton-pump inhibitors** (antacids neutralise acid that is already there).

**Amylase** (starch), **protease** (protein) and **lipase** (fat).

Starch → **glucose**; protein → **amino acids**; triglyceride (fat) → **fatty acids and glycerol**.

**Villi** (large surface area), a **thin (one-cell) wall** (short diffusion distance), and a **rich blood supply** (steep concentration gradient).

To **reabsorb water** (and mineral ions) and form faeces — it does no enzyme digestion.

**Glucose is small** enough to cross the partially permeable membrane; **starch is too large** — it must be digested first. This models absorption in the gut.

It processes the nutrient-rich blood from the gut, adjusting, storing and removing nutrients to keep the blood's composition **steady**.

A **liver cell** — the cell type that carries out the liver's chemical jobs, including regulating blood nutrients.

A **storage carbohydrate** (a polymer of glucose) made by the liver when blood glucose is high and broken down when it is low.

It **takes up glucose and stores it as glycogen** (triggered by insulin), so blood glucose falls back to normal.

It **breaks glycogen back into glucose** and releases it (triggered by glucagon), so blood glucose rises back to normal.

**Insulin** → store as glycogen (high glucose); **glucagon** → release glucose from glycogen (low glucose).

Because the liver's response always **opposes** the change — a rise triggers storage, a fall triggers release — returning glucose toward its set point.

The liver removes it from the blood and releases it into **bile**; the cholesterol is then lost from the body in the **faeces**.

Removing excess **cholesterol** (into bile), **detoxifying** substances like alcohol, and breaking down old **red blood cells**.

A yellow **pigment** produced when the liver breaks down old **red blood cells**; it is passed into bile.

Bilirubin **is not cleared** by a damaged liver, so it **builds up** in the blood and colours the skin and the whites of the eyes **yellow**.

Alcohol is **detoxified by hepatocytes**; an excess **damages and scars** them, so the liver regulates glucose, cholesterol and other substances less effectively.

**Carbon dioxide (CO₂)** — not oxygen. A rise in CO₂ is the main signal that speeds up breathing.

The **number of breaths taken per minute** (together with how deep each breath is).

A **sensor that detects a chemical change** — here, a rise in blood CO₂ (and the fall in pH it causes).

In the **medulla** of the brain and in the walls of the **aorta and carotid arteries**.

The **medulla** (in the brainstem) — it sends nerve impulses to the breathing muscles to set the ventilation rate.

The **diaphragm and intercostal muscles** — they make breathing faster and deeper.

Ventilation rate **increases** — chemoreceptors detect the rise and the medulla speeds up breathing to exhale the extra CO₂.

Faster, deeper breathing **exhales more CO₂**, so blood CO₂ (and pH) fall back to the normal level.

The response (faster breathing, which removes CO₂) **opposes** the change (rising CO₂), returning CO₂ to its set point.

Chemoreceptors are stimulated **less**, the medulla **slows breathing down**, so less CO₂ is exhaled and CO₂ rises back to normal.

It **lowers** blood pH (makes the blood more acidic), because dissolved CO₂ forms acid.

As CO₂ **increases**, ventilation rate **increases** — a positive correlation.

A nutrient the body **cannot make** for itself, so it **must come from the diet** (e.g. vitamin C, vitamin D).

A diet containing **all the nutrient groups in the correct proportions** to meet the body's needs.

Poor health from a diet with **too little, too much, or the wrong balance** of nutrients (under- OR over-nutrition).

It is needed to make strong **collagen** for skin, gums and blood-vessel walls.

**Scurvy** — weak connective tissue, bleeding gums and slow wound healing.

It is needed to **absorb calcium** from food into the blood.

Less calcium is absorbed → too little calcium for bone → bones are **not hardened properly** → soft, deformed bones (**rickets**).

Saturated fat → raises **cholesterol** → **plaques** in arteries (atherosclerosis) → coronary arteries **narrow** → less **oxygen** to heart muscle → **CHD / heart attack**.

The build-up of **fatty plaques** in artery walls, which **narrows** the arteries.

It raises blood pressure (**hypertension**) and is linked to **type-2 diabetes** and **coronary heart disease**.

It is **high in fat, salt and energy** but low in vitamins, minerals and fibre — contributing to obesity and high blood pressure.

**Under-nutrition** (too little → deficiency diseases) and **over-nutrition** (too much → obesity, CHD).