Control of peristalsis in the digestive system by the central nervous system and enteric nervous system
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Question
What is digestion?
Answer
The **breakdown of large food molecules** into small, soluble ones that can be absorbed.
Question
What is absorption (in the gut)?
Answer
The movement of the **small, soluble products of digestion** out of the gut and into the **blood** (or lymph).
Question
What is peristalsis?
Answer
**Waves of muscle contraction** in the gut wall that **push food along** the digestive tract.
Question
What type of muscle produces peristalsis, and is it conscious?
Answer
**Involuntary smooth muscle** — it is **not** under conscious control.
Question
What controls peristalsis?
Answer
The **autonomic nervous system** — the nerves in the gut wall (the **enteric nervous system**).
Question
Which acid does the stomach secrete, and what is its pH?
Answer
**Hydrochloric acid (HCl)** — giving a very **low pH** (about 1.5–2).
Question
Give two reasons the stomach keeps a low pH.
Answer
(1) It **kills most ingested bacteria**; (2) it gives the enzyme **pepsin** its **optimum (acidic) pH**.
Question
How does stomach acid help digest protein?
Answer
It **denatures** (unfolds) proteins and provides the acidic pH that lets **pepsin** (a protease) break them into shorter chains.
Question
Name a class of drugs that lowers stomach acid secretion.
Answer
**Proton-pump inhibitors** (antacids neutralise acid that is already there).
Question
Name three enzymes secreted by the exocrine pancreas.
Answer
**Amylase** (starch), **protease** (protein) and **lipase** (fat).
Question
Match each food to its absorbable products.
Answer
Starch → **glucose**; protein → **amino acids**; triglyceride (fat) → **fatty acids and glycerol**.
Question
List three adaptations of the small intestine for absorption.
Answer
**Villi** (large surface area), a **thin (one-cell) wall** (short diffusion distance), and a **rich blood supply** (steep concentration gradient).
Question
What is the main role of the large intestine?
Answer
To **reabsorb water** (and mineral ions) and form faeces — it does no enzyme digestion.
Question
In a dialysis-tubing model, why does glucose pass through the membrane but starch does not?
Answer
**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.
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Integration of body systems
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