Rucete ✏ Campbell Biology In a Nutshell
Unit 7 ANIMAL FORM AND FUNCTION — Concept 42.3 Patterns of Blood Pressure and Flow Reflect the Structure and Arrangement of Blood Vessels
1. Blood Vessel Structure and Function
- All blood vessels are lined with endothelium, a smooth layer reducing resistance
- Capillaries allow gas and nutrient exchange through thin walls
- Arteries have thick, elastic walls to handle high pressure
- Veins have thinner walls and valves to prevent backflow
2. Blood Pressure Dynamics
- Arteries expand during systole and recoil during diastole to maintain flow
- Blood pressure is highest in arteries and decreases across capillaries and veins
- Flow slows in capillaries due to large cross-sectional area
- Pulses felt in arteries reflect pressure changes during the heartbeat
3. Regulation of Blood Flow
- Vasoconstriction raises pressure; vasodilation lowers it
- Nitric oxide promotes dilation; endothelin promotes constriction
- Flow adjusts dynamically via cardiac output and vessel diameter during activity
4. Effects of Gravity and Muscle Activity
- Gravity affects flow, especially in upright animals
- Valves and skeletal muscle contractions aid venous return
- Cooldowns post-exercise help maintain steady circulation
5. Capillary Exchange
- Capillary beds open or close depending on tissue needs
- Precapillary sphincters control entry into beds
- Exchange involves diffusion, vesicle transport, and pressure gradients
6. Lymphatic System
- Excess interstitial fluid is returned to circulation via the lymphatic system
- Lymph moves through vessels by valves and muscle contractions
- Lymph nodes filter lymph and support immune function
- Blockage of lymph flow can lead to swelling (e.g., elephantiasis)
7. Blood Composition
- Plasma (55%) contains water, ions, proteins, nutrients, and waste
- Red blood cells carry oxygen; white blood cells defend; platelets aid clotting
- Plasma proteins help with pH balance and immunity
In a Nutshell
The circulatory system’s structure determines how pressure and flow are regulated. Arteries, veins, and capillaries adapt to their roles, while the lymphatic system recovers excess fluid and supports immunity. Blood composition and vessel function ensure that oxygen, nutrients, and waste are exchanged efficiently across the body.