--- title: "The Heart and the Blood" book: "Primary & Middle School Biology" subject: biology language: en chapter: 27 exercises: 11 source: https://one-course.com/books/biology/1/en/chapter/27-the-heart-and-the-blood --- # Chapter 27 — The Heart and the Blood Press two fingers — not the thumb — on the inside of your [wrist](https://one-course.com/books/biology/1/en/chapter/4-my-body#def-g1-my-body-joint), below the thumb’s base, and wait. There: a small, steady knock, again and again, about once a second. That knock is your [heart](#def-g4-heart-and-blood-heart) at work, felt from a distance. It has been beating since before you were born, and it is the engine of the body’s delivery service. ## 27.1 The blood, the body’s delivery service **Proposition 27.1 (What the blood carries).** The *blood* is a liquid that reaches every corner of the body, and it is the body’s carrier: - from the [small intestine](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#def-g4-journey-of-food-tract) , it collects the *[nutrients](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#def-g4-journey-of-food-digestion)* ( [Proposition 25.5](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) ); - from the [lungs](https://one-course.com/books/biology/1/en/chapter/26-breathing#def-g4-breathing-organs) , it collects *oxygen* ( [Proposition 26.5](https://one-course.com/books/biology/1/en/chapter/26-breathing#prop-g4-breathing-exchange) ); - it delivers both to every part of the body — [muscles](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-muscle) , brain, [bones](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-skeleton) , [skin](https://one-course.com/books/biology/1/en/chapter/5-the-five-senses#def-g1-the-five-senses-sense) ; - on the way back it carries off the wastes, delivering the carbon dioxide to the [lungs](https://one-course.com/books/biology/1/en/chapter/26-breathing#def-g4-breathing-organs) to be breathed out. **Proof.** *Admitted at this level.* ∎ **Example 27.2 (One delivery round).** Follow a drop of [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb): through the [lungs](https://one-course.com/books/biology/1/en/chapter/26-breathing#def-g4-breathing-organs) it turns bright red, loaded with oxygen; the [heart](#def-g4-heart-and-blood-heart) sends it out; in a running [leg](https://one-course.com/books/biology/1/en/chapter/4-my-body#def-g1-my-body-parts) [muscle](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-muscle) it hands over oxygen and [nutrients](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#def-g4-journey-of-food-digestion), takes on carbon dioxide, and darkens; back at the [heart](#def-g4-heart-and-blood-heart), it is sent to the [lungs](https://one-course.com/books/biology/1/en/chapter/26-breathing#def-g4-breathing-organs) to unload and reload — and out again. A full round takes well under a minute. **Definition 27.3 (Blood vessels).** [Blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) travels in tubes called [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) *vessels*: wide ones leaving and entering the [heart](#def-g4-heart-and-blood-heart), branching finer and finer — down to hair-thin vessels that thread between the body’s parts, where the deliveries are handed over. Laid end to end, one body’s vessels would stretch for tens of thousands of kilometres. **Remark 27.4 (Seeing the vessels).** Look at the underside of your [wrist](https://one-course.com/books/biology/1/en/chapter/4-my-body#def-g1-my-body-joint): bluish lines under the [skin](https://one-course.com/books/biology/1/en/chapter/5-the-five-senses#def-g1-the-five-senses-sense) — [blood vessels](#def-g4-heart-and-blood-vessels) on their way back to the [heart](#def-g4-heart-and-blood-heart). A scraped [knee](https://one-course.com/books/biology/1/en/chapter/4-my-body#def-g1-my-body-joint) shows the other end of the network: even the thinnest cut finds [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb), because the finest [vessels](#def-g4-heart-and-blood-vessels) are everywhere. ## 27.2 The heart, the pump **Definition 27.5 (The heart).** The *heart* is a hollow [muscle](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-muscle), about the size of its owner’s fist, in the middle of the chest behind the [rib](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-skeleton) cage. By squeezing — a *beat* — it drives the [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) through the [vessels](#def-g4-heart-and-blood-vessels). It has two sides: the right side pumps [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) to the *[lungs](https://one-course.com/books/biology/1/en/chapter/26-breathing#def-g4-breathing-organs)* to load oxygen; the left side pumps the oxygen-rich [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) to the *whole body*. ![The heart’s two sides: the right side sends blood to the lungs for oxygen; the left side sends the loaded blood around the body.](https://one-course.com/images/onecourse/chapters/biology-1/g4-heart-and-blood/fig-0d33dbb2add1.svg) *The [heart](#def-g4-heart-and-blood-heart)’s two sides: the right side sends [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) to the [lungs](https://one-course.com/books/biology/1/en/chapter/26-breathing#def-g4-breathing-organs) for oxygen; the left side sends the loaded [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) around the body.* **Proposition 27.6 (The pulse).** Each [beat](#def-g4-heart-and-blood-heart) drives a little wave of [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) along the [vessels](#def-g4-heart-and-blood-vessels); felt at the [wrist](https://one-course.com/books/biology/1/en/chapter/4-my-body#def-g1-my-body-joint) or the neck, that wave is the *pulse*. Counting the [pulse](#prop-g4-heart-and-blood-pulse) counts the [heartbeats](#def-g4-heart-and-blood-heart): about $80$ to $100$ a minute for a child at rest, $60$ to $80$ for an adult — and much more during effort. **Proof.** *Admitted at this level.* ∎ **Example 27.7 (The heart keeps up with the legs).** Running, your [leg](https://one-course.com/books/biology/1/en/chapter/4-my-body#def-g1-my-body-parts) [muscles](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-muscle) burn [nutrients](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#def-g4-journey-of-food-digestion) and oxygen fast; the deliveries must speed up. So the [heart](#def-g4-heart-and-blood-heart) [beats](#def-g4-heart-and-blood-heart) faster *and* harder — a child’s [pulse](#prop-g4-heart-and-blood-pulse) can pass $150$ in a sprint — while [breathing](https://one-course.com/books/biology/1/en/chapter/26-breathing#def-g4-breathing-movements) quickens to reload the [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) ([Example 26.6](https://one-course.com/books/biology/1/en/chapter/26-breathing#ex-g4-breathing-running)). [Heart](#def-g4-heart-and-blood-heart) and [lungs](https://one-course.com/books/biology/1/en/chapter/26-breathing#def-g4-breathing-organs) are two halves of one supply chain. **Method 27.8 (Taking a pulse).** 1. Turn a hand palm up; place two fingers of the other hand on the [wrist](https://one-course.com/books/biology/1/en/chapter/4-my-body#def-g1-my-body-joint) , just below the thumb’s base — never the thumb, which has a little [pulse](#prop-g4-heart-and-blood-pulse) of its own; 2. press gently until you feel the knocking; 3. count the knocks for one minute (a clock with seconds helps); 4. write the number down, with what the body was doing: resting, walking, after a sprint. ![After the run: two fingers on the wrist, counting the heart’s race from a distance.](https://one-course.com/images/onecourse/chapters/biology-1/g4-heart-and-blood/img-228b37d46537.jpg) *After the run: two fingers on the [wrist](https://one-course.com/books/biology/1/en/chapter/4-my-body#def-g1-my-body-joint), counting the [heart](#def-g4-heart-and-blood-heart)’s race from a distance.* **Remark 27.9 (A muscle that never rests — almost).** Between two [beats](#def-g4-heart-and-blood-heart) the [heart](#def-g4-heart-and-blood-heart) relaxes for a fraction of a second — that sliver is all the rest it ever takes. Day and night, about $100000$ [beats](#def-g4-heart-and-blood-heart) a day, for a whole life. Like every [muscle](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-muscle) ([Method 17.9](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#met-g3-bones-and-muscles-care)), it grows stronger with exercise: a trained [heart](#def-g4-heart-and-blood-heart) moves more [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) per [beat](#def-g4-heart-and-blood-heart), and so can [beat](#def-g4-heart-and-blood-heart) more calmly. ## 27.3 Exercises **Exercise 27.1 ★.** Name two things the [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) delivers, and where it collects each. **Solution of Exercise 27.1.** [Nutrients](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#def-g4-journey-of-food-digestion), collected at the [small intestine](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#def-g4-journey-of-food-tract); and oxygen, collected at the [lungs](https://one-course.com/books/biology/1/en/chapter/26-breathing#def-g4-breathing-organs). **Exercise 27.2 ★.** What waste gas does the [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) carry away, and where does it drop it off? **Solution of Exercise 27.2.** Carbon dioxide — dropped off at the [lungs](https://one-course.com/books/biology/1/en/chapter/26-breathing#def-g4-breathing-organs), where it is breathed out. **Exercise 27.3 ★.** What is the [heart](#def-g4-heart-and-blood-heart) made of, how big is it, and where does it sit? **Solution of Exercise 27.3.** It is a hollow [muscle](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-muscle), about the size of its owner’s fist, sitting in the middle of the chest behind the [rib](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-skeleton) cage. **Exercise 27.4 ★.** What does each side of the [heart](#def-g4-heart-and-blood-heart) do? **Solution of Exercise 27.4.** The right side pumps [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) to the [lungs](https://one-course.com/books/biology/1/en/chapter/26-breathing#def-g4-breathing-organs) to load oxygen; the left side pumps the oxygen-rich [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) out to the whole body. **Exercise 27.5 ★.** What is the [pulse](#prop-g4-heart-and-blood-pulse), and what does counting it tell you? **Solution of Exercise 27.5.** The little wave each [heartbeat](#def-g4-heart-and-blood-heart) drives along the [vessels](#def-g4-heart-and-blood-vessels), felt at [wrist](https://one-course.com/books/biology/1/en/chapter/4-my-body#def-g1-my-body-joint) or neck. Counting it counts the [heartbeats](#def-g4-heart-and-blood-heart) per minute. **Exercise 27.6 ★.** Why must the [pulse](#prop-g4-heart-and-blood-pulse) be taken with fingers and not the thumb? **Solution of Exercise 27.6.** The thumb has a noticeable little [pulse](#prop-g4-heart-and-blood-pulse) of its own, so you might count your thumb instead of the [wrist](https://one-course.com/books/biology/1/en/chapter/4-my-body#def-g1-my-body-joint) you are testing. **Exercise 27.7 ★.** Why does the [pulse](#prop-g4-heart-and-blood-pulse) race during a sprint? Tell the story from the [leg](https://one-course.com/books/biology/1/en/chapter/4-my-body#def-g1-my-body-parts) [muscles](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-muscle)’ point of view. **Solution of Exercise 27.7.** Sprinting [legs](https://one-course.com/books/biology/1/en/chapter/4-my-body#def-g1-my-body-parts) burn [nutrients](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#def-g4-journey-of-food-digestion) and oxygen fast and must have them replaced fast; the [heart](#def-g4-heart-and-blood-heart) speeds and strengthens its [beats](#def-g4-heart-and-blood-heart) so the [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) makes its delivery rounds more often. **Exercise 27.8 ★.** Try it: take your resting [pulse](#prop-g4-heart-and-blood-pulse) with [Method 27.8](#met-g4-heart-and-blood-pulse), do thirty seconds of star jumps, and take it again. Report both numbers. **Solution of Exercise 27.8.** Open answer. Typically about $80$–$100$ resting, $120$–$150$ after the star jumps — the supply chain at work. **Exercise 27.9 ★★.** In [Example 27.2](#ex-g4-heart-and-blood-round), the drop of [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) is bright red leaving the [lungs](https://one-course.com/books/biology/1/en/chapter/26-breathing#def-g4-breathing-organs) and darker leaving the [leg](https://one-course.com/books/biology/1/en/chapter/4-my-body#def-g1-my-body-parts) [muscle](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-muscle). What changed in it, each time? **Solution of Exercise 27.9.** Leaving the [lungs](https://one-course.com/books/biology/1/en/chapter/26-breathing#def-g4-breathing-organs) it had just loaded oxygen — bright red. In the [muscle](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-muscle) it handed the oxygen over and took on carbon dioxide — darker. Color follows cargo. **Exercise 27.10 ★★.** The [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) connects three organs of your grade: [small intestine](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#def-g4-journey-of-food-tract), [lungs](https://one-course.com/books/biology/1/en/chapter/26-breathing#def-g4-breathing-organs), [heart](#def-g4-heart-and-blood-heart). Draw or describe the network: what does each contribute to the delivery service? **Solution of Exercise 27.10.** The [small intestine](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#def-g4-journey-of-food-tract) puts [nutrients](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#def-g4-journey-of-food-digestion) into the [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb); the [lungs](https://one-course.com/books/biology/1/en/chapter/26-breathing#def-g4-breathing-organs) put in oxygen and take out carbon dioxide; the [heart](#def-g4-heart-and-blood-heart) is the pump that keeps the [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) moving between them and out to every consumer — [muscles](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-muscle), brain, [bones](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-skeleton), [skin](https://one-course.com/books/biology/1/en/chapter/5-the-five-senses#def-g1-the-five-senses-sense). **Exercise 27.11 ★★★.** A trained cyclist’s resting [pulse](#prop-g4-heart-and-blood-pulse) can be $50$; an untrained adult’s, $75$. Using [Remark 27.9](#rem-g4-heart-and-blood-rest), explain how *slower* can mean *stronger* — what must each of the cyclist’s [beats](#def-g4-heart-and-blood-heart) be doing? **Solution of Exercise 27.11.** The trained [heart](#def-g4-heart-and-blood-heart) is a stronger [muscle](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-muscle): each [beat](#def-g4-heart-and-blood-heart) moves more [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb). Delivering the same supply then needs fewer [beats](#def-g4-heart-and-blood-heart) per minute — so the cyclist’s calm $50$ does the work of the untrained $75$, with spare power held in reserve for effort.