Chapter 42 | Circulation and Gas Exchange

Circulation

Transport of materials/substances that will be transported in & out of the body and throughout the body

Circulation of materials through

• Direct diffusion

• Gastrovascular cavity

• Circulatory system with specialized structures

Heart

A pump that moves materials throughout the entire body

Vessels

Tubes that materials are transported through

Interstitial fluid

Fluid that surrounds cells and are in spaces found between cells

Circulatory fluid

Fluid that circulates and transports materials throughout the body

Materials transported through the blood

• O2 as intake & CO2 as out take

• Wastes to be eliminated

• Nutrients

• Signaling molecules

• Immune cells & molecules

Open circulatory system

Found in arthropods: A circulatory system in which fluid called hemolymph bathes the tissues and organs directly and there is no distinction between the circulating fluid and the interstitial fluid. A tubular heart pumps the hemolymph through large vessels to the rest of the cells found in the coelom, eventually returning to the heart

Closed circulatory system

All vertebrates and some invertebrates: A circulatory system in which blood is confined to vessels and is kept separate from the interstitial fluid. The heart pumps fluid to vessels that infiltrate the organs and deliver materials to all cells, eventually returning to the heart

Cardiovascular system

The circulatory system found in vertebrae (majority of Chordata phylum)

Arteries

Vessels that move away from the heart. Has thick smooth muscle layers that undergo peristaltic contractions

Capillaries

Connect the arteries, and form capillary beds consisting of several tubes that infiltrate the organs

Veins

Vessels moving blood toward the heart

• Has a very thin smooth muscle layer with no significant contractions

• Contains valves to prevent backflow

• Surrounding skeletal muscles help move blood

Single circulation

• Occurs in all fish

• Blood flows in a single loop:

  • Heart - 2 chambers; atria & ventricle

  • Blood moves from the heart through arteries to the capillary beds, then back through veins to the heart

• No separation between oxygen-rich and oxygen-poor blood

Double circulation

• Occurs in amphibians, reptiles, birds, and mammals

• Two separate circulatory circuits

  • Pulmocutaneous/Pulmonary Circuit: Carries blood to the lungs (or lungs and skin in amphibians) for oxygenation

  • Systemic Circuit: Delivers oxygenated blood to the rest of the body

• Blood passes through the heart twice: once for oxygenation and once for distribution throughout the body

Pulmocutaneous circulation

• Occurs in amphibians (e.g., frogs, salamanders, some reptiles)

• Heart: 3 chambers (2 atria, 1 ventricle)

• Blood flow:

  • Veins bring oxygen-poor blood to the right atrium

  • Blood moves from the right atrium to the ventricle (no separation between oxygen-rich and oxygen-poor blood)

  • Blood is pumped to the lungs and skin for gas exchange and oxygenation

• Oxygenated blood returns to the left atrium, moves to the ventricle, and is pumped into the systemic circuit to supply the rest of the body with oxygen

Pulmonary circulation

• Occurs in mammals

• Heart: 4 chambers (2 atria, 2 ventricles)

• Blood flow:

  • Right atrium → right ventricle → pulmonary circuit → lungs → left atrium → left ventricle → arteries → systemic circuit

Order of blood flow through the 4 chambers of the heart

Vena cava → Right atrium —(AV / tricuspid valve)→ Right ventricle —(Semilunar valve)→ pulmonary artery → Lungs → Pulmonary veins → Left atrium —(AV / bicuspid valve)→ Left ventricle —(Semilunar / aortic valve)→ Aorta → Systemic circuit

Chambers of the heart

• Right Atrium: Receives deoxygenated blood from the body

• Right Ventricle: Pumps deoxygenated blood to the lungs for oxygenation

• Left Atrium: Receives oxygenated blood from the lungs

• Left Ventricle: Pumps oxygenated blood to the body

Cardiac cycle

1. Heart fills with blood:

   • Atrial + ventricular diastole

2. Blood from the atria flows into the ventricles:

   • Atrial systole

   • Ventricular diastole

   • Semilunar valve closed, AV valve open

3. Blood flows to pulmonary or systemic circuit:

   • Ventricular systole

   • Atrial diastole

   • Semilunar valves open, AV valves closed

Heartbeat

Relaxation (diastole) and contraction (systole) of the heart

Control of heartbeat

Sinoatrial (SA) node sends electrical signal that causes the atria to contract first. The signal relays through ventricles to cause them to contract

Sinoatrial node

The heart's natural pacemaker, generating electrical signals that trigger heart contractions. It causes atrial contraction and sends signals to the ventricles, influencing heart rate. Is autorhythmic but is highly influenced by the nervous and endocrine system

Atrioventricular node

A region where electrical impulses are delayed for ~0.1s before spreading to both ventricles and causing them to contract

Cardiac output

The volume of blood pumped per minute by each ventricle of the heart (mL / min). Obtained by multiplying stroke volume by heart rate

Blood volume

Total about of blood found in the circulatory system

Stroke volume

Specific amount of blood that leaves the ventricles per heartbeat (mL / beat)

Heart rate

beats / min

Insufficient cardiac output

Heart failure

Blood pressure

Measures how much pressure it takes to push Hg through a tube. Is measured in the arm

• During systole, maximum pressure is on the artery (systolic pressure)

• During diastole (diastolic pressure)

Is high in arteries and low in veins

Arteries & Veins

Made of 3 layers of cells:

• Interior layer of epithelial cells, the endothelium

• Smooth muscle surrounding the endothelium

• Connective tissue surrounding smooth muscle to hold cells together

Path of blood flow through vessels

Heart → arteries → arterioles → capillaries → venules → veins → heart